JP6627782B2 - Ink set and image forming method - Google Patents

Description

  The present invention relates to an ink set and an image forming method.

  The ink jet recording method is used in various printing fields because an image can be formed easily and inexpensively. As one of the inkjet inks, an ink containing a photopolymerizable compound that is cured by being irradiated with an actinic ray (hereinafter, also simply referred to as “actinic ray-curable ink”) is known. The actinic ray curable ink has been attracting attention in recent years because it can form an image having high adhesion even on a recording medium having low water absorption.

  The actinic ray curable ink can contain a pigment as a coloring material. At this time, the color gamut of an image to be formed can be expanded by discharging ink so that a plurality of pigments having different colors land on the recording medium. For example, in Patent Document 1, Pantone Red 032 (“Pantone” is a registered trademark of the company) published in various color sample books provided by Pantone by using an ink containing a red pigment and an orange pigment. It is described that a similar color can be exhibited. On the other hand, C.I. I. Pigment Violet (hereinafter, also simply referred to as “Pigment Violet”) 19 and C.I. I. Pigment Red (hereinafter, also simply referred to as “Pigment Red”) 202. The ink containing a magenta pigment containing a solid solution with 202 (hereinafter, also simply referred to as “magenta ink”) is formed more than the conventional red ink. It is known that the color gamut of an image can be expanded. Pigment Violet 19 and Pigment Red 202 are both pigments having a quinacridone skeleton.

  In addition, in the inkjet recording method, a suitable ink combination is selected from yellow ink, magenta ink, cyan ink, and black ink according to a color to be formed, and the selected ink is overprinted to form a full-color ink. An image can be formed. At this time, in order to further expand the color gamut of the formed image, the image may be formed by further combining the orange ink.

  Patent Literature 2 discloses an orange ink containing a gelling agent, which can be used in combination with another color to expand the color gamut of an image to be formed to a range of orange. According to Patent Literature 2, an image having a color tone close to orange described in Pantone Color Sample Book is formed by preparing an ink so as to obtain an image having a desired reflectance (gloss). Has been described. Patent Document 2 discloses C.I. as an orange pigment. I. An orange ink containing Pigment Orange (hereinafter, also simply referred to as "Pigment Orange") 36 is described.

  When the actinic ray-curable ink contains a pigment, the storage stability of the ink can be enhanced by increasing the affinity between the photopolymerizable compound and the pigment. From this viewpoint, a technique is known in which the affinity between the photopolymerizable compound and the pigment is improved by treating the surface of the pigment with alumina. Alumina can be applied to the surface of the pigment particles, for example, by the methods described in Patent Documents 3 and 4.

  Further, when the actinic ray-curable ink contains a pigment, it is known that when the ink further contains a dispersant, the dispersibility of the pigment is increased, and the storage stability of the ink is increased. For example, Patent Document 5 describes that the actinic radiation-curable ink contains a dispersant and a dispersing synergist in a larger weight ratio than a pigment, and thus has high dispersion stability. At this time, by subjecting the pigment particles to a surface treatment to impart an acidic adsorptive functional group such as sulfonic acid, the affinity between the dispersant and the pigment can be increased, and the storage stability of the ink can be increased.

  When the actinic radiation-curable ink contains a gelling agent, when the ink lands on the recording medium and cools, the ink is gelled by crystallization of the gelling agent, so that the pinning properties of the ink are increased and the dots of adjacent dots are increased. It is difficult for coalescence to occur. Further, since the viscosity of the ink containing the gelling agent increases even at a low temperature, the rubbing property of the formed image at room temperature can be improved. For example, in Patent Literature 6, by adding an oil gelling agent to an ink-jet ink containing a pigment and a photopolymerizable compound, solidification of ink droplets landed on a recording medium is completed in a short time to prevent identical dots. In. In Patent Literature 7, an image having good fastness is formed by adding a gelling agent that gels at a low temperature to a radiation-curable ink containing a pigment or a dye.

U.S. Pat. No. 8,868,062 JP 2014-118570 A JP-B-59-34737 JP 2002-121411 A U.S. Pat. No. 8,197,584 Japanese Patent No. 4556414 JP 2006-193745 A

  When an image is formed using an inkjet ink containing a plurality of different pigments as described in Patent Literature 1, the pigments are separated during storage due to a difference in the specific gravity of the pigments, and a clear image is obtained instead. May not be obtained. In order to prevent the image from becoming unclear due to the separation of the pigment, it is preferable that a plurality of actinic ray-curable inks exhibiting different colors are landed at the same position on the recording medium, and the actinic rays are cured in a short time after landing. These plural actinic ray curable inks can be used as an ink set. At this time, the color gamut of the formed image is further expanded by including the actinic ray-curable ink containing the solid solution in the ink set.

  Here, in the actinic ray-curable ink containing the gelling agent and the pigment, the degree of crystallization of the gelling agent may change depending on the surface treatment state of the pigment. For example, in an actinic ray curable ink containing a gelling agent and a pigment surface-treated only with sulfonic acid, the interaction between the pigment surface and the gelling agent inhibits the crystallization of the gelling agent, and the Pinning properties are likely to deteriorate. If the pinning property of the ink is low, the ink is likely to spread and spread, so that the glossiness of the image surface is higher than originally intended, and there is a possibility that a difference in gloss from the ink containing other pigments may occur. In addition, the gelling agent that has not crystallized precipitates on the surface of the ink over time after curing, which may cause blooming. According to the findings of the present inventors, these problems of gloss difference tend to occur particularly when a magenta pigment containing a solid solution surface-treated with sulfonic acid is used.

  On the other hand, by reducing the amount of the gelling agent, it is possible to prevent the association between the alumina and the gelling agent, but on the other hand, since the amount of the gelling agent is small, the pinning property does not increase, and the droplet diameter upon landing spreads This causes dot coalescence.

  Also, depending on the composition of the ink, the image formed by the orange ink containing Pigment Orange 36 or other orange pigments does not have a color close to orange described in Pantone's color sample book, or the image formed by the other color ink. The glossiness may differ from the formed image. Therefore, there is still a demand for an ink having a color tone close to orange described in the Pantone color sample book and capable of forming an image having gloss closer to an image formed by another color ink.

  In view of the above problems, the present invention provides an image having a color region that is difficult to form with only four YMCK inks, such as Pantone Red 032 and Pantone Orange 021 described in Pantone Color Sample Book. It is an object of the present invention to provide an ink set including magenta ink and orange ink that can form and expand a color gamut of a red to orange region in an L * a * b * color space. Another object of the present invention is to provide an ink set including a magenta ink and an orange ink so that the magenta ink and the orange ink can form an image having gloss close to that of an image formed by another color ink. Another object is to provide an ink set containing magenta ink and orange ink having sufficient pinning properties and storage stability, and to provide an image forming method using such an ink set.

The present invention relates to the following ink sets.
[1] An ink set including a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator, and including a plurality of types of inks that are cured by irradiation with actinic light, wherein the plurality of types of inks include a magenta ink and a magenta ink. An orange ink, wherein the pigment contained in the magenta ink is surface-treated with alumina and sulfonic acid; I. Pigment Violet 19 and C.I. I. Pigment Red 202, wherein the amount of the alumina in the magenta pigment is 1500 mass ppm or more and 7500 mass ppm or less, and the content of the gelling agent in each ink is 1 mass%. An ink set characterized by being at least 5% by mass.
[2] The C.I. I. Pigment Violet 19 and C.I. I. Pigment Red 202 has a mass ratio of 60/40 or more and 70/30 or less.
[3] The ink set according to [1] or [2], wherein the amount of the alumina with respect to the magenta pigment is from 5,000 ppm to 7,500 ppm by mass.
[4] An ink set including a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator, and including a plurality of types of inks that are cured by irradiation with actinic light, wherein the plurality of types of inks are magenta ink and An orange ink, wherein the orange ink further contains a sulfonated derivative of an insoluble azo pigment in an amount of 2.0% by mass or more and 15.0% by mass or less based on the mass of the pigment contained in the ink. The contained pigment has a cyclic structure, and includes an orange pigment having a basic site in the cyclic structure, the photopolymerizable compound contained in the orange ink, the total mass of the photopolymerizable compound 30% by mass or more of a photopolymerizable compound having a total of 6 or more ethylene oxide groups or propylene oxide groups with respect to each ink. Kicking the content of the gelling agent is equal to or less than 1.5 mass% to 3.0 mass%, the ink set.
[5] The photopolymerizable compound having six or more ethylene oxide groups or propylene oxide groups in total has two or more segments having three or more ethylene oxide groups or propylene oxide groups in a molecule. The ink set according to [4], wherein
[6] The ink set according to any one of [1] to [5], further including a yellow ink, a cyan ink, and a black ink.
[7] An ink set including a pigment, a gelling agent, a photopolymerizable compound, and a photopolymerization initiator, and including a plurality of types of inks which are cured by irradiation with actinic rays, wherein the plurality of types of inks are magenta ink and An orange ink, wherein the pigment contained in the magenta ink is surface-treated with alumina and sulfonic acid; I. Pigment Violet 19 and C.I. I. Pigment Red 202, wherein the amount of the alumina in the magenta pigment is 1500 mass ppm or more and 7500 mass ppm or less, and the amount of the orange ink is 2 to the mass of the pigment contained in the ink. The orange ink further contains a sulfonated derivative of an insoluble azo pigment in an amount of from 0.0% by mass to 15.0% by mass, wherein the pigment contained in the orange ink has a cyclic structure, and a basic moiety is contained in the cyclic structure. The orange ink contains an orange pigment, and the photopolymerizable compound contained in the orange ink has at least 30% by mass, based on the total mass of the photopolymerizable compound, of at least 6 ethylene oxide groups or propylene oxide groups. And the content of the gelling agent in each ink is 1.0% by mass or less. And characterized in that 5.0 wt% or less, the ink set.
[8] The orange ink is C.I. I. Pigment Orange 36, C.I. I. Pigment Orange 64 and C.I. I. Pigment Orange 71, the ink set according to any one of [1] to [7], comprising at least one pigment selected from the group consisting of Pigment Orange 71.

Further, the present invention relates to the following image forming method.
[9] A step of ejecting the magenta ink and the orange ink contained in the ink set according to any one of [1] to [8] from nozzles of an inkjet head to land on a recording medium; Irradiating the orange ink with actinic rays to cure the magenta ink and the orange ink.

  According to the present invention, there is provided a magenta ink containing a pigment containing a solid solution of Pigment Violet 19 / Pigment Red 202 and a gelling agent, which is surface-treated with alumina and sulfonic acid, and has good storage stability and pinning properties. And an image forming method using such an ink set.

1. Ink set The ink set according to the present invention is an ink set containing a plurality of types of inks containing a pigment, a photopolymerizable compound, a gelling agent, and a photopolymerization initiator, and cured by irradiation with actinic rays. The seed ink is an ink set that includes a magenta ink and an orange ink.

  The ink set means a combination of two or more inks that are configured to be installed in an ink jet recording apparatus so that an image can be formed. Examples of the ink set include an ink cartridge in which a plurality of inks are individually stored in a plurality of ink cartridges, or an ink cartridge in which a plurality of ink storage units are integrally formed and each of the ink storage units stores a different ink. Is included.

1-1. Magenta ink Magenta ink is an ink that contains a pigment, a photopolymerizable compound, a gelling agent, and a photopolymerization initiator, and is cured by irradiation with actinic light. Only one kind of magenta ink may be contained in the ink set, or two or more kinds of magenta inks having different compositions may be contained in the ink set.

1-1-1. Pigment The pigment contained in the magenta ink may be any pigment that allows the cured ink that has landed on the recording medium to exhibit a magenta color. From the viewpoint of increasing the affinity between the photopolymerizable compound or dispersant and the pigment and increasing the storage stability of the ink, the pigment is formed by converting a magenta pigment containing a solid solution of Pigment Violet 19 and Pigment Red 202 into alumina and sulfone. It is preferable to include those obtained by surface treatment with an acid (hereinafter, the magenta pigment is referred to as “magenta pigment-A”, the magenta ink containing magenta pigment-A is also referred to as “magenta ink-A”, Is also referred to as “magenta ink-B.” The simply referred to as “magenta ink” conceptually means a magenta ink that includes both. The amount of the alumina in the magenta pigment-A is preferably from 1500 ppm to 7500 ppm by mass. The magenta pigment contained in the magenta ink is preferably magenta pigment-A. However, when the color gamut is expanded by another ink such as an orange ink as described below, the magenta pigment is included in the magenta ink. It is not necessary that the pigment be magenta pigment-A. Further, the pigment contained in the magenta ink may include only one kind, or may include two or more kinds.

  The magenta pigment-A can extend the color gamut of an image formed by landing and curing the magenta ink included in the ink set of the present invention on a recording medium, as compared with a normal magenta pigment. Therefore, for example, by forming an image only with the magenta pigment, it becomes possible to obtain a color closer to the magenta color described in Japan color 2011, which is a color sample, and also to use an ink containing magenta ink-A and an orange ink. By forming an image as a set, it is possible to output a color closer to Pantone Red 032.

  The content of the pigment may be within a range that can sufficiently develop magenta color in the obtained image and that the viscosity of the ink can be ejected from the inkjet head, for example, 0.1 to magenta ink. It is preferably from 20% by mass to 20% by mass, and more preferably from 0.4% by mass to 10% by mass from the above viewpoint.

  Commercially available examples of magenta pigments containing the solid solution include CINQUASIA Magenta L4540, CINQUASIA Magenta D4500J and CINQUASIA Red K4330, manufactured by BASF (“CINQUASIA” is a registered trademark of the company), E7B, manufactured by Clariant.

  From the viewpoint of further expanding the color gamut of an image to be formed, and particularly forming an image with a color gamut closer to Pantone Red 032 by combining with the orange ink, the mass ratio of Pigment Violet 19 to Pigment Red 202 in the pigment. It is preferable that (mass of Pigment Violet 19) / (mass of Pigment Red 202) be 60/40 or more and 70/30 or less.

  Examples of the magenta pigment containing the solid solution satisfying the mass ratio include CINQUASIA Magenta D4500J, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 60/40) and 228-2120, manufactured by Sun Chemical (Pigment 19). / Pigment Red 202 ratio: 70/30).

  The surface treatment of the magenta pigment can be performed by a known method. The surface treatment with alumina can be performed by, for example, a method described in Patent Document 2 or Patent Document 3, or a method in which alumina is suspended in a dispersion liquid in which a pigment is dispersed, and the pH of the suspension is adjusted. The amount of alumina to be applied can be adjusted to a desired amount by changing the amount of alumina added in each method. The surface treatment with sulfonic acid can be performed, for example, by a method in which a sulfonating agent is added to a slurry-like pigment dispersion, and the two are reacted at a high temperature. The applied amount of the sulfonic acid can be adjusted to a desired amount by adjusting the amount of the sulfonating agent to be added.

  The amount of alumina in the magenta pigment-A is 1500 ppm or more and 7500 ppm or less based on 1 g of the pigment. When the amount of alumina is 1500 ppm or more, the affinity of the pigment for the photopolymerizable compound and the dispersant is increased, and the pigment can be stably stored. In addition, by setting the amount of alumina applied to 7500 ppm or less, insufficient crystallization of the gelling agent due to association between the alumina and the gelling agent can be prevented, and the occurrence of gloss due to excessive leveling can be suppressed. From the viewpoint of further increasing the affinity between the photopolymerizable compound and the pigment and further improving the storage stability of the magenta ink, the amount of alumina to be applied is preferably 5000 ppm or more and 7500 ppm or less per 1 g of the pigment.

  The amount of the sulfonic acid in the magenta pigment-A may be any range as long as the storage stability of the ink is sufficient, and may be, for example, 1000 ppm to 1500 ppm based on 1 g of the pigment.

  The amounts of alumina and sulfonic acid in the pigment can be calculated from the amounts of the Al element and the S element in the pigment obtained by measurement with, for example, an inductively coupled plasma emission spectrometer (ICP-AES) or the like. When the pigment is dispersed in the ink, a value calculated from the amounts of Al and S elements in the ink may be used as the amounts of alumina and sulfonic acid in the pigment.

1-1-2. Gelling agent The gelling agent can temporarily fix (pin) ink droplets that have landed on a recording medium in a gel state. When the ink is pinned in a gel state, the spread of the ink is suppressed and the adjacent dots are hardly identical, so that a higher-definition image can be formed. In addition, when the ink is in a gel state, the entry of oxygen in the environment into the ink droplets is suppressed, and the hardening is hardly inhibited by oxygen, so that a high-definition image can be formed at a higher speed. As the gelling agent, only one kind may be contained in the ink constituting the ink set of the present invention, or two or more kinds may be contained.

  The content of the gelling agent is 1% by mass or more and 5% by mass or less based on the total mass of the ink. By setting the content of the gelling agent to 1% by mass or more, the pinning property of the ink containing the magenta pigment surface-treated with alumina can be sufficiently enhanced, and a higher definition image can be formed. Further, by setting the content of the gelling agent to 1.5% by mass or more, sedimentation of the pigment due to liquefaction of the ink during storage of the ink is less likely to occur, and the storage stability of the ink can be further improved. By setting the content of the gelling agent to 5% by mass or less, the gelling agent hardly precipitates on the surface of the formed image, and the gloss of the image can be made closer to the gloss of the image by another ink, and The ink ejection property from the inkjet head can be further improved. From the above viewpoint, the content of the gelling agent in the magenta ink is more preferably from 1.5% by mass to 3% by mass.

  From the following viewpoints, the gelling agent preferably crystallizes in the ink at a temperature equal to or lower than the gelation temperature of the ink. The gelation temperature refers to a temperature at which the viscosity of the ink suddenly changes when the gelling agent undergoes a phase transition from a sol to a gel when the sol or liquid ink is cooled by heating. Specifically, the sol or liquid ink is cooled while measuring the viscosity with a viscoelasticity measuring device (for example, MCR300, manufactured by Physica), and the temperature at which the viscosity sharply rises is measured. It can be a gelling temperature.

  When the gelling agent crystallizes in the ink, a structure in which the photopolymerizable compound is included in the three-dimensional space formed by the gelling agent crystallized in a plate shape may be formed. , Hereinafter referred to as “card house structure”). When the card house structure is formed, the liquid photopolymerizable compound is held in the space, so that the ink droplets are less likely to wet and spread, and the pinning property of the ink is further improved. When the ink pinning property increases, ink droplets that have landed on the recording medium are less likely to coalesce, and a higher definition image can be formed.

  In order to form a card house structure, the photopolymerizable compound dissolved in the ink and the gelling agent are preferably compatible. On the other hand, if the photopolymerizable compound and the gelling agent dissolved in the ink are phase-separated, it may be difficult to form a card house structure.

Examples of gelling agents suitable for forming a card house structure by crystallization include:
Ketone waxes including dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone;
Behenyl behenate, icosyl icosanoate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, mycilyl citrate, stearyl stearate, oleyl palmitate, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol Ester waxes comprising fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters;
Petroleum-based waxes, including paraffin wax, microcrystalline wax and petrolactam;
Vegetable waxes including candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax and jojoba ester;
Animal waxes, including beeswax, lanolin and whale wax;
Mineral waxes including montan wax and hydrogenated wax;
Hydrogenated castor oil;
Modified waxes including hydrogenated castor oil derivatives, montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, 12-hydroxystearic acid derivatives and polyethylene wax derivatives;
Higher alcohols, including stearyl alcohol and behenyl alcohol;
Hydroxystearic acid, including 12-hydroxystearic acid;
Fatty acid amides, including lauric amide, stearic amide, behenic amide, oleic amide, erucic amide, ricinoleic amide and 12-hydroxystearic amide;
N-substituted fatty acid amides, including N-stearyl stearamide and N-oleyl palmitamide;
Special fatty acid amides including N, N'-ethylenebisstearylamide, N, N'-ethylenebis-12-hydroxystearylamide and N, N'-xylylenebisstearylamide;
Higher amines, including dodecylamine, tetradecylamine and octadecylamine;
Esters of sucrose fatty acids, including sucrose stearic acid and sucrose palmitic acid;
Synthetic waxes including polyethylene waxes and α-olefin maleic anhydride copolymer waxes;
Includes dimer acids, as well as dimer diols.

  Commercially available examples of fatty acid amides include the Nikka Amide series, manufactured by Nippon Kasei Co., Ltd. (“Nikka Amide” is a registered trademark of the company), the ITOWAX series, manufactured by Ito Oil, and the FATTYAMID series, manufactured by Kao Corporation.

  Commercially available examples of fatty acid ester compounds include the EMALLEX series, Nippon Emulsion's Riquemar Series and Poem Series, and Riken Vitamin's (both "Riquemar" and "Poem" are registered trademarks of the same company).

  Commercially available examples of esters of sucrose fatty acids include the Ryoto Sugar Ester Series, manufactured by Mitsubishi Chemical Foods, Inc. ("Ryoto" is a registered trademark of the company).

  Commercial examples of synthetic waxes include the UNILIN series, manufactured by Baker-Petrolite ("UNILIN" is a registered trademark of the company).

  Commercial examples of dimer diols include the PRIPOR series, manufactured by CRODA ("PRIPOR" is a registered trademark of the company).

  Among these gelling agents, ketone waxes, ester waxes, higher fatty acids, higher alcohols and fatty acid amides are preferable from the viewpoint of further improving pinning properties, and from the above viewpoint, ketones represented by the following general formula (G1) Waxes and ester waxes represented by the following general formula (G2) are more preferred. The ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may contain only one kind or two or more kinds in the magenta ink. Is also good. Further, the ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may contain only one or both of them in the magenta ink. It may be.

General formula (G1): R1-CO-R2
In General Formula (G1), R1 and R2 are each a linear or branched hydrocarbon group having 1 to 24 carbon atoms. However, one of R1 and R2 contains a straight-chain alkyl structure having 12 or more carbon atoms, and preferably both contain a straight-chain alkyl structure having 12 or more carbon atoms. From the viewpoint of easily taking a crystal structure and improving the pinning property of the ink, R1 and R2 are both linear hydrocarbon groups having 1 to 24 carbon atoms, and more preferably, both have a carbon number of 1 to 24. It is a linear hydrocarbon group having a number of 8 or more and 22 or less.

General formula (G2): R3-COO-R4
In General Formula (G2), R3 and R4 each are a linear or branched hydrocarbon group having 1 to 24 carbon atoms. However, one of R3 and R4 contains a straight-chain alkyl structure having 12 or more carbon atoms, and preferably both contain a straight-chain alkyl structure having 12 or more carbon atoms. From the viewpoint of easily obtaining a crystal structure and improving the pinning property of the ink, R3 and R4 are both linear hydrocarbon groups having 1 to 24 carbon atoms, and more preferably, both have a carbon number of 1 to 24. It is a linear hydrocarbon group having a number of 8 or more and 22 or less.

  The ketone wax represented by the general formula (G1) or the ester wax represented by the general formula (G2) containing a straight-chain alkyl structure having 12 or more carbon atoms increases the crystallinity of the gelling agent, and In the card house structure, a sufficient space is generated. Therefore, the photopolymerizable compound is easily included in the space sufficiently, and the pinning property of the ink is further improved. Further, when the number of carbon atoms of the linear or branched hydrocarbon group is 24 or less, the melting point of the gelling agent does not excessively increase, so that it is not necessary to heat the ink excessively when ejecting the ink. .

  Examples of the ketone wax represented by the general formula (G1) include dilignoceryl ketone (carbon number: 23 to 24), dibehenyl ketone (carbon number: 21 to 22), and distearyl ketone (carbon number: 17). -18), dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number: 15-16), dimyristyl ketone (carbon number: 13-14), dilauryl ketone (carbon number: 11) -12), lauryl myristyl ketone (carbon number: 11-14), lauryl palmityl ketone (11-16), myristyl palmityl ketone (13-16), myristyl stearyl ketone (13-18), myristyl behenyl ketone (13 -22), palmityl stearyl ketone (15-18), valmicil behenyl ketone (15-22) and stearyl behenyl ketone 17-22) are included. The number of carbons in the parentheses indicates the number of carbons of each of the two hydrocarbon groups separated by the carbonyl group.

  Commercial examples of the ketone wax represented by the general formula (G1) include 18-Pentriacontanon, manufactured by Alfa Aeser, Hentriacontan-16-on, manufactured by Alfa Aeser, and Kaowax T1, manufactured by Kao Corporation.

  Examples of the fatty acid or ester wax represented by the general formula (G2) include behenyl behenate (carbon number: 21-22), icosyl icosanoate (carbon number: 19-20), and stearyl stearate (carbon number: 17-20). -18), palmityl stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18) ), Myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyl dodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18) , Stearyl erucate (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), behenyl oleate (carbon number: 21-18) 18-22) and linoleic acid arachidyl (carbon number: 17-20) are included. The number of carbons in the parentheses indicates the number of carbons of each of the two hydrocarbon groups separated by the ester group.

  Commercially available examples of the ester wax represented by the general formula (G2) include Unistar M-2222SL and Sperm Acet, manufactured by NOF Corporation (“UNISTAR” is a registered trademark of the company), Exepar SS and Exepal MY-M, Kao Corporation (“Exepearl” is a registered trademark of the company), EMALEX CC-18 and EMALEX CC-10, manufactured by Nippon Emulsion Co., Ltd. (“EMALEX” is a registered trademark of the company), and AMLEPS PC; (Registered trademark of the company). Since these commercially available products are often a mixture of two or more kinds, they may be separated and purified as necessary to be contained in the ink.

1-1-3. Photopolymerizable compound The photopolymerizable compound is crosslinked or polymerized by irradiation with actinic light, and cures the ink. Examples of actinic rays include ultraviolet rays, electron beams, α-rays, γ-rays, and X-rays. The actinic ray is preferably an ultraviolet ray or an electron beam from the viewpoint of safety and that the polymerization and cross-linking can be generated even with a lower energy amount. The magenta ink may contain only one kind of the photopolymerizable compound or two or more kinds thereof.

  The content of the photopolymerizable compound may be any range as long as the effects of the present invention can be obtained. For example, the content can be 1% by mass or more and 97% by mass or less based on the total mass of the magenta ink. From the above viewpoint, the content of the photopolymerizable compound is preferably 30% by mass or more and 95% by mass or less based on the total mass of the magenta ink.

  The photopolymerizable compound includes a radical polymerizable compound and a cationic polymerizable compound. The photopolymerizable compound is preferably a radical polymerizable compound from the viewpoint that polymerization and cross-linking are easily generated and various compounds can be selected according to an image to be formed.

  The radical polymerizable compound is a compound having a radically polymerizable ethylenically unsaturated bond. The radical polymerizable compound may be any of a monomer, a polymerizable oligomer, a prepolymer, and a mixture thereof. The magenta ink may contain only one kind of the radical polymerizable compound or two or more kinds thereof.

  Examples of the compound having a radically polymerizable ethylenically unsaturated bond include unsaturated carboxylic acids and salts thereof, unsaturated carboxylic ester compounds, unsaturated carboxylic urethane compounds, unsaturated carboxylic amide compounds and anhydrides, Examples include acrylonitrile, styrene, unsaturated polyester, unsaturated polyether, unsaturated polyamide, and unsaturated urethane. Examples of unsaturated carboxylic acids include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, and the like.

  Among them, the radical polymerizable compound is preferably an unsaturated carboxylic acid ester compound, and more preferably (meth) acrylate. In the present invention, “(meth) acrylate” means acrylate or methacrylate, “(meth) acryloyl group” means acryloyl group or methacryloyl group, and “(meth) acryl” means acrylic Or methacrylic.

  Examples of the monomer (meth) acrylate include a monofunctional (meth) acrylate, a difunctional (meth) acrylate, and a trifunctional or higher (meth) acrylate.

  Examples of the monofunctional (meth) acrylate include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomyristyl (meth) acrylate, and isostearyl. (Meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) ) Acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (Meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl (meth) acrylate Is included.

  Examples of the bifunctional (meth) acrylate include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, and polypropylene glycol di (meth) acrylate. (Meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, Dimethylol-tricyclodecane di (meth) acrylate, PO adduct of bisphenol A di (meth) acrylate, neopentyl glycol di (meth) acrylate hydroxypivalate, polytetramethylene glycol di (meth) acrylate ) Acrylate, polyethylene glycol diacrylate and tripropylene glycol diacrylate.

  Examples of tri- or more functional (meth) acrylates include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and ditrimethylolpropane. Includes tetra (meth) acrylate, glycerin propoxy tri (meth) acrylate and pentaerythritol ethoxy tetra (meth) acrylate.

  Examples of (meth) acrylates that are polymerizable oligomers or prepolymers include epoxy (meth) acrylate oligomers, aliphatic urethane (meth) acrylate oligomers, aromatic urethane (meth) acrylate oligomers, polyester (meth) acrylate oligomers and polyester (meth) acrylate oligomers. And chain (meth) acrylic oligomers.

  The photopolymerizable compound preferably contains an ethylene oxide-modified (meth) acrylate. Ethylene oxide modified (meth) acrylate has higher photosensitivity. Further, ethylene oxide-modified (meth) acrylate is easily included in the card house structure when the ink gels at a low temperature, and is more easily compatible with other ink components even at a high temperature. Furthermore, since ethylene oxide-modified (meth) acrylate hardly shrinks on curing, curling of printed matter during image formation is less likely to occur.

  Commercial examples of ethylene oxide modified (meth) acrylates include CD561, SR454, SR499 and SR494, manufactured by Sartomer, and NK Ester A-400, NK Ester A-600, NK Ester 9G, NK Ester 14G, NK Ester DOD -N, NK ester A-DCP and NK ester DCP, manufactured by Shin-Nakamura Chemical Co., Ltd. are included.

  Examples of the cationic polymerizable compound include an epoxy compound, a vinyl ether compound, and an oxetane compound. The magenta ink may contain only one kind of the cationic polymerizable compound, or two or more kinds thereof.

  Examples of epoxy compounds include aromatic epoxides, cycloaliphatic epoxides, and aliphatic epoxides. From the viewpoint of further improving curability, aromatic epoxides and alicyclic epoxides are preferred.

  Examples of the aromatic epoxide include a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the above polyhydric phenol or its alkylene oxide adduct include bisphenol A or its alkylene oxide adduct. Examples of the alkylene oxide in the alkylene oxide adduct include ethylene oxide and propylene oxide.

  Examples of the alicyclic epoxide include a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or peracid. Examples of the above cycloalkane include cyclohexene and cyclopentene.

  Examples of the aliphatic epoxide include a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or its alkylene oxide adduct with epichlorohydrin. Examples of the aliphatic polyhydric alcohol or its alkylene oxide adduct include alkylene glycols including ethylene glycol, propylene glycol and 1,6-hexanediol, and alkylene oxide adducts thereof. Examples of the alkylene oxide in the alkylene oxide adduct include ethylene oxide and propylene oxide.

  Examples of the vinyl ether compound include a monofunctional vinyl ether compound and a bifunctional or higher vinyl ether compound. Among these, a bifunctional or higher functional vinyl ether compound is preferable from the viewpoint of further improving the curability of the ink or improving the adhesion between the recording medium and the image.

  Examples of monofunctional vinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexane dimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, Includes isopropenyl ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether and octadecyl vinyl ether.

  Examples of the bifunctional or higher vinyl ether compound include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, and cyclohexane dimethanol. Includes divinyl ether and trimethylolpropane trivinyl ether. Among these vinyl ether compounds, di- or trivinyl ether compounds are preferable in consideration of curability and adhesion.

  Examples of the oxetane compound include the oxetane compounds described in JP-A-2001-220526, JP-A-2001-310937, and JP-A-2005-255821.

1-1-4. When the photopolymerizable compound is a compound having a radically polymerizable functional group, the photopolymerizable initiator is a photoradical initiator, and the photopolymerizable compound has a cationically polymerizable functional group. When it is a compound having a photoacid generator. The magenta ink may contain only one kind of the photopolymerization initiator or two or more kinds thereof. The photopolymerization initiator may be a combination of both a photoradical initiator and a photoacid generator.

  The photo radical initiator includes a cleavage type radical initiator and a hydrogen abstraction type radical initiator.

  Examples of the cleavage type radical initiator include an acetophenone-based initiator, a benzoin-based initiator, an acylphosphine oxide-based initiator, benzyl and methylphenylglyoxyester.

  Examples of acetophenone-based initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 1- (4-isopropylphenyl) -2-hydroxy-2-. Methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4-thiomethylphenyl) Includes propan-1-one and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone.

  Examples of benzoin-based initiators include benzoin, benzoin methyl ether and benzoin isopropyl ether.

  Examples of the acylphosphine oxide-based initiator include 2,4,6-trimethylbenzoindiphenylphosphine oxide.

  Examples of the hydrogen abstraction type radical initiator include a benzophenone-based initiator, a thioxanthone-based initiator, an aminobenzophenone-based initiator, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, and 9,10- Includes phenanthrenequinone and camphorquinone.

  Examples of benzophenone-based initiators include benzophenone, methyl-4-phenylbenzophenone o-benzoylbenzoate, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenylsulfide, acrylated benzophenone , 3,3 ', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone and 3,3'-dimethyl-4-methoxybenzophenone.

  Examples of the thioxanthone-based initiator include 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone.

  Examples of aminobenzophenone-based initiators include Michler's ketone and 4,4'-diethylaminobenzophenone.

  Examples of the photoacid generator include compounds described in “Organic Materials for Imaging”, edited by the Society of Organic Electronics Materials, published by Bunshin Publishing (1993), pp. 187-192.

  The content of the photopolymerization initiator may be any range as long as the ink can be sufficiently cured, and for example, may be 0.01% by mass or more and 10% by mass or less based on the total mass of the magenta ink.

1-1-5. Other Components The magenta ink may further include other components including a dispersant, a photopolymerization initiator auxiliary agent, and a polymerization inhibitor as long as the effects of the present invention can be obtained. These components may be contained alone in the magenta ink, or may be contained in two or more kinds.

  The dispersant is a compound having an affinity for both the pigment and the photopolymerizable compound described below. The dispersant is dispersed in the photopolymerizable compound while being adsorbed on the pigment, whereby the dispersibility of the pigment can be increased.

  The content and type of the dispersant may be within a range that can further enhance the dispersibility of the pigment. The magenta ink may contain only one kind of dispersant or two or more kinds of dispersants.

  The content of the dispersant can be, for example, 20% by mass or more and 70% by mass or less based on the total mass of the pigment. By setting the content of the dispersant to 20% by mass or more based on the total mass of the pigment, the dispersant coats the pigment surface, so that aggregation of the pigments during storage of the ink can be made more difficult to occur. . By setting the content of the dispersant to 70% by mass or less based on the total mass of the pigment, the association between the dispersant and the gelling agent is less likely to occur, and the ink that has landed on the recording medium is more sufficiently gelled. It can be pinned. From the above viewpoint, the content of the dispersant is preferably from 30% by mass to 60% by mass, more preferably from 35% by mass to 50% by mass, based on the total mass of the pigment.

  Examples of dispersants include hydroxyl group-containing carboxylic esters, salts of long-chain polyaminoamides and high-molecular acid esters, salts of high-molecular polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, and high-molecular unsaturated acid esters. , High molecular weight copolymer, modified polyurethane, modified polyacrylate, polyetherester type anionic surfactant, naphthalenesulfonic acid formalin condensate, aromatic sulfonic acid formalin condensate, polyoxyethylene alkyl phosphate, polyoxyethylene Nonyl phenyl ether, and stearylamine acetate.

  The dispersant is preferably a block copolymer having a comb-shaped block structure, from the viewpoint of suppressing aggregation between the pigments due to steric hindrance caused by the extended side chains and improving the dispersibility of the pigment. The block copolymer having a comb-shaped block structure refers to a copolymer in which another type of polymer is graft-polymerized as a side chain with respect to each structural unit derived from a monomer constituting a linear main chain.

  Examples of commercially available block copolymers having a comb-shaped block structure include BYK-2164, BYK-168, BYK N-22024, BYK JET-9150 and BYK JET-9151, manufactured by BYK Chemie ("BYK" is a registered trademark of BYK). Trademarks), EFKA 7701, EFKA 4310, EFKA 4320 and EFKA 4401, manufactured by BASF, SOLSPERSE 24000GR and SOLSPERSE 39000, manufactured by Lubrizol (“SOLSPERSE” is a registered trademark of the company), and manufactured by AJISPER PB821 and AJISPER PB Fine Tech, ("Ajispar" is a registered trademark of Ajinomoto Co., Inc.).

  Examples of photopolymerization initiator assistants include tertiary amine compounds including aromatic tertiary amine compounds. Examples of the aromatic tertiary amine compound include N, N-dimethylaniline, N, N-diethylaniline, N, N-dimethyl-p-toluidine, N, N-dimethylamino-p-benzoic acid ethyl ester, Includes N, N-dimethylamino-p-benzoic acid isoamylethyl ester, N, N-dihydroxyethylaniline, triethylamine and N, N-dimethylhexylamine.

  Examples of the polymerization inhibitor include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone , Nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperon, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N- (3-oxyanilino- 1,3-dimethylbutylidene) aniline oxide, dibutyl cresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime and cyclohexanone oxy It is included.

1-1-6. Physical Properties From the viewpoint of further improving the ejection property from the inkjet head, the viscosity of the magenta ink at 80 ° C. is preferably from 3 mPa · s to 20 mPa · s. In addition, from the viewpoint of sufficiently gelling the ink when the ink has landed and cooled to room temperature, the viscosity of the magenta ink at 25 ° C. is preferably 1000 mPa · s or more.

  The gelation temperature of the magenta ink is preferably 40 ° C. or more and 70 ° C. or less. When the gelling temperature of the ink is 40 ° C. or higher, the ink quickly gels after landing on the recording medium, so that the pinning property is further improved. When the gelling temperature of the ink is 70 ° C. or lower, the ink is less likely to gel when the magenta ink is ejected from an inkjet head whose ink temperature is usually about 80 ° C., so that the ink can be ejected more stably.

  The viscosities at 80 ° C., the viscosities at 25 ° C., and the gelation temperature of the magenta ink and the orange ink described below can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. In the present invention, these viscosity and gelation temperature are values obtained by the following method. The magenta ink was heated to 100 ° C., and a shear rate of 11.7 (1/1) was measured while measuring the viscosity using a stress control type rheometer Physica MCR301 (cone plate diameter: 75 mm, cone angle: 1.0 °) manufactured by Anton Paar. s) The ink is cooled to 20 ° C. under the condition of a temperature decreasing rate of 0.1 ° C./s to obtain a temperature change curve of viscosity. The viscosities at 80 ° C. and 25 ° C. are determined by reading the viscosities at 80 ° C. and 25 ° C. in a temperature change curve of the viscosity. The gelation temperature is determined as a temperature at which the viscosity becomes 200 mPa · s in a temperature change curve of the viscosity.

  From the viewpoint of further improving the ejection property from the inkjet head, the average particle diameter of the pigment particles contained in the magenta ink is 0.08 μm or more and 0.5 μm or less, and the maximum particle diameter is 0.3 μm or more and 10 μm or less. preferable. The average particle diameter of the pigment particles in the present invention means a value obtained by a dynamic light scattering method using Datasizer Nano ZSP, manufactured by Malvern. In addition, since the ink containing the coloring material has a high density and does not transmit light with this measuring device, the measurement is performed after diluting the ink by 200 times. The measurement temperature is normal temperature (25 ° C.).

1-2. Orange ink Orange ink is an ink that contains a pigment, a photopolymerizable compound, a gelling agent, and a photopolymerization initiator, and is cured by irradiation with actinic rays. Only one kind of orange ink may be contained in the ink set, or two or more kinds of orange inks having different compositions may be contained in the ink set.

1-2-1. Pigment The pigment contained in the orange ink may be any pigment that allows the cured ink that has landed on the recording medium to exhibit an orange color. Examples of such pigments include Pigment Orange 16, Pigment Orange 34, Pigment Orange 36, Pigment Orange 38, Pigment Orange 43, Pigment Orange 64, and Pigment Orange 71.

  In addition, from the viewpoint that it is possible to reduce the interaction between the orange pigment and the gelling agent and make it difficult to accumulate the gelling agent on the pigment surface by the combination with other materials, the pigment contained in the orange ink is A pigment having a basic site in a non-aromatic cyclic structure (hereinafter, also simply referred to as "basic orange pigment"), and a sulfonated derivative of an insoluble azo pigment (hereinafter, also simply referred to as "azo derivative"). ) Is preferably used. Hereinafter, the orange pigment is referred to as "orange pigment-C", and the ink containing the orange pigment-C is referred to as "orange ink-C", and the other orange inks are referred to as "orange ink-D". When simply referred to as “orange ink”, it means conceptually an orange ink that includes both. Generally, a gelling agent, particularly a crystalline gelling agent, crystallizes in an ink due to electronic interaction between a high-polarity site and a low-polarity site in a gelling agent with a change in temperature. It is known to increase viscosity and pin the ink. However, the present inventors have found that depending on the composition of the ink, the pinning performance of the ink may be reduced or destabilized, and this may be caused by gelation with other components in the ink such as pigments. It is presumed that the amount of the gelling agent used for pinning due to the crystallization of the gelling agent is reduced or destabilized due to the electronic interaction of the agent. Therefore, by combining a pigment having a basic site with a polymerizable compound having a high polarity, such as orange pigment-C, the pigment and the polymerizable compound preferentially interact electronically, and the gelling agent has another property. It is presumed that it will be in a "free" state where it does not interact with the compound. Thereby, the sol-gel phase transition temperature of the ink can be stabilized, and the content of the gelling agent can be minimized. By reducing the content of the gelling agent, the orange ink-C can suppress an excessive increase in gloss of the formed image. Furthermore, the combination of the orange ink-C and the polymerizable compound having a high polarity improves the dispersion stability of the pigment, so that the storage stability of the pigment is good, and excessive accumulation of the pigments even during image formation. It can be considered that the image can be suppressed and an image of a desired color gamut can be easily formed. For the above reasons, the orange ink of the ink set of the present invention is preferably orange ink-C containing orange pigment-C, but the color gamut can be expanded by another ink such as magenta ink as described above. In this case, the pigment contained in the orange ink does not need to be orange pigment-C, but from the viewpoint of image formation having a good color gamut, the ink set of the present invention comprises at least the magenta pigment-A It is more preferable that the ink set includes a magenta ink-A containing an organic pigment and an orange ink-C containing an orange pigment-C. Further, only one kind of pigment may be contained in the orange ink, or two or more kinds of pigments may be contained.

  At least one of the cyclic structures of the basic orange pigment is a non-aromatic cyclic structure having a basic site. Examples of such a cyclic structure include an alicyclic structure in which the cyclic structure is composed of only carbon and hydrogen, a heterocyclic structure in which the cyclic structure contains carbon and other atoms, and a plurality of the cyclic structures each having one atom. And a structure in which a basic site is included in a part of a partial structure selected from spiro ring structures sharing the same structure, or a structure in which a part of the structure is substituted with a basic site. The cyclic structure may contain a double bond as long as it has no aromaticity.

  A basic site refers to a site that can have a positive charge. Examples of the basic moiety include an amino group including a secondary amino group, a tertiary amino group and a quaternary ammonium group, and a nitrogen-containing heterocyclic group having a pyrrolidine or piperidine skeleton. The basic site is preferably a secondary amino group or a tertiary amino group from the viewpoint of preventing the ink from deteriorating due to reaction with components in the ink containing the photopolymerizable compound.

  From the viewpoint of sufficiently associating the azo derivative described below with the basic orange pigment and further suppressing the occurrence of excessive gloss, the basic orange pigment preferably has two or more basic sites in the molecule, and preferably has three or more basic sites. It is more preferable to have the above.

  The content of the basic orange pigment may be within a range that can sufficiently develop the color of orange in the obtained image and that can cause the viscosity of the ink to be ejected from the inkjet head. From the above viewpoint, for example, the content of the pigment is preferably from 0.1% by mass to 20% by mass, and more preferably from 0.4% by mass to 10% by mass with respect to the orange ink-C. Is more preferred.

  Examples of the basic orange pigment include Pigment Orange 36 having a structure represented by the following (Formula 1), Pigment Orange 64 having a structure represented by the following (Formula 2), and a structure represented by the following Formula (3). Pigment Orange 71 having the following formula: Pigment Orange 36 and Pigment Orange 71 have two basic sites in the molecule, and Pigment Orange 64 has four basic sites in the molecule.

1-2-2. Azo Derivatives An azo derivative is a sulfonated derivative of an insoluble azo pigment. Since the azo derivative has a highly polar portion derived from sulfonic acid, it can be well associated with a basic orange pigment also having a highly polar portion. Therefore, when the ink contains an azo derivative and a basic orange pigment, it is possible to suppress the relative decrease of the gelling agent molecules in the ink due to the gelling agent accumulating on the surface of the basic orange pigment. it can. Therefore, according to the ink containing the azo derivative and the basic orange pigment, it is possible to form an image having a color tone close to orange described in the Pantone color sample book without excessively high gloss. it is conceivable that.

  In addition, since the insoluble azo lake derivative has a large number of functional groups in the water-soluble position, it has a high affinity for the photopolymerizable compound, and forms more associations with the photopolymerizable compound than with the pigment. Easy to form. In addition, the derivative of the quinacridone pigment is inactive because the surface of the pigment is covered with thick π electrons, and is less likely to form an association with the basic group of the basic orange pigment. On the other hand, the sulfonated derivative of the azo pigment often forms an association with the basic orange pigment, so that it is considered that the accumulation of the gelling agent on the surface of the basic orange pigment can be more effectively prevented.

  The content of the azo derivative is 2% by mass or more and 15% by mass or less based on the mass of the pigment contained in the ink. When the content of the azo derivative with respect to the mass of the pigment is 2% by mass or more, the basic orange pigment and the azo derivative can be well associated with each other, and it is considered that the gloss is not excessively increased. When the content of the azo derivative is 15% by mass or less based on the mass of the pigment, a change in gloss due to deposition of the azo derivative on the image surface can be suppressed. From the above viewpoint, the content of the azo derivative is preferably 5% by mass or more and 13% by mass or less with respect to the mass of the pigment contained in the ink, and is 7% by mass or more with respect to the mass of the pigment contained in the ink. More preferably, it is 12% by mass or less.

  Examples of azo derivatives include solsperse 22000, manufactured by Lubrizol (“solsperse” is a registered trademark of the company) and BYK synagist 2105, manufactured by BYK Chemie (“BYK” is a registered trademark of the company).

  1-2-3. Photopolymerizable compound

  The photopolymerizable compound contained in the orange ink can be the same compound as the magenta ink.

  The orange ink-C preferably contains a highly polar photopolymerizable compound described below. The orange ink-C may further include a photopolymerizable compound having a lower polarity than the highly polar photopolymerizable compound (hereinafter, also simply referred to as a “low-polarity photopolymerizable compound”).

  The content of the photopolymerizable compound in which the high-polarity photopolymerizable compound and the low-polarity photopolymerizable compound are combined in the orange ink-C may be within a range in which the ink irradiated with the actinic ray is sufficiently cured. , From 1% by mass to 97% by mass with respect to the total mass of the orange ink-C. From the above viewpoint, the content of the photopolymerizable compound is preferably 30% by mass or more and 95% by mass or less based on the total mass of the orange ink-C.

1-2-3-1. Photopolymerizable Compound The highly polar photopolymerizable compound is a photopolymerizable compound having six or more ethylene oxide groups (hereinafter, also simply referred to as “EO groups”) or propylene oxide groups (hereinafter, also simply referred to as “PO groups”). Compound. The orange ink may contain only one kind of the highly polar photopolymerizable compound, or two or more kinds thereof.

  Six or more EO groups and PO groups may be present as one connected segment, or may be present as being divided into two or more segments. However, from the viewpoint of further increasing the dispersibility of the azo derivative and further reducing the accumulation of the gelling agent on the pigment surface, when the EO group and the PO group are present in two or more segments, three or more It is preferable that there are two or more segments having an EO group or a PO group in the molecule.

  The highly polar photopolymerizable compound has six or more polar EO or PO groups and has a high affinity for a basic orange pigment having the same polarity. It is considered that the dispersibility of the pigment having the following can be enhanced. Similarly, since the high-polarity photopolymerizable compound has a high affinity for the azo derivative containing a polar part, it is considered that the dispersibility of the pigment having the azo derivative can be enhanced. Therefore, it is considered that the high-polarity photopolymerizable compound makes it easier for the azo derivative to be present near the surface of the basic orange pigment, and as a result, can reduce the electronic interaction between the pigment and the gelling agent in the ink. Can be By reducing the interaction between the pigment and the gelling agent, the sol-gel phase transition, which is the original function of the gelling agent, can proceed without being affected by other compounds in the ink. It is considered that glossiness can be improved by functioning of phase transition even with a small amount of gelling agent.

  Further, according to the findings of the present inventors, the high-polarity photopolymerizable compound has a high ability to disperse the pigment even at a temperature of 60 ° C. or higher, which is the temperature at which the orange ink is emitted from the inkjet head. It is considered that nozzle shortage due to precipitation can be suppressed.

  From the viewpoint of sufficiently exhibiting the above effects, the content of the highly polar photopolymerizable compound is 30% by mass or more based on the total mass of the photopolymerizable compound. From the viewpoint that the gelling agent having a non-polar portion hardly precipitates during image formation and the gloss of the image surface hardly occurs, the content of the highly polar photopolymerizable compound is determined by the total mass of the photopolymerizable compound. The amount is preferably 30% by mass or more and 80% by mass or less, more preferably 50% by mass or more and 70% by mass or less.

  Examples of commercially available products of the highly polar photopolymerizable compound include the products shown in Table 1. In Table 1, “the number of EO groups or PO groups” indicates the number of EO groups or PO groups contained in one molecule of the product represented by the brand. In Table 1, "New Frontier" is a registered trademark of Daiichi Kogyo Seiyaku Co., Ltd., and "Fancryl" is a registered trademark of Hitachi Chemical Co., Ltd.

1-2-3-2. Photopolymerizable compound The low-polarity photopolymerizable compound is a photopolymerizable compound in which the total number of EO groups and PO groups is less than six.

  Examples of the low-polarity photopolymerizable compound that is a (meth) acrylate include a monofunctional (meth) acrylate, a difunctional (meth) acrylate, and a trifunctional or higher (meth) acrylate.

  Examples of the monofunctional (meth) acrylate include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomyristyl (meth) acrylate, and isostearyl. (Meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) ) Acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (Meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl (meth) acrylate Is included.

  Examples of the bifunctional (meth) acrylate include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, and polypropylene glycol di (meth) acrylate. (Meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, Dimethylol-tricyclodecane di (meth) acrylate, PO adduct of bisphenol A di (meth) acrylate, neopentyl glycol di (meth) acrylate hydroxypivalate, polytetramethylene glycol di (meth) acrylate ) Acrylate, polyethylene glycol diacrylate and tripropylene glycol diacrylate.

  Examples of tri- or more functional (meth) acrylates include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and ditrimethylolpropane. Includes tetra (meth) acrylate, glycerin propoxy tri (meth) acrylate and pentaerythritol ethoxy tetra (meth) acrylate.

  From the viewpoint that the phase separation between the photopolymerizable compound and the gelling agent during image formation is less likely to occur and gloss is less likely to be generated on the image surface, the low-polarity photopolymerizable compound is an EO group, a PO group, or the like. It preferably has a polar structure.

  Examples of the low-polarity photopolymerizable compound having a polar structure include the products shown in Table 2. In Table 2, "the number of EO groups or PO groups" indicates the number of EO groups or PO groups contained in one molecule of the product represented by the brand. In Table 1, "Aronix" is a registered trademark of Toagosei Co., Ltd., and "Miramar" is a registered trademark of Bigen Specialty Chemical Co., Ltd.

1-2-4. Other Components The dispersant, the gelling agent, and the photopolymerization initiator contained in the orange ink can be the same compounds as in the magenta ink. From the viewpoint of increasing the affinity between inks and forming a higher definition image, the orange ink contains the same compound as the magenta ink as a photopolymerizable compound, a dispersant, a gelling agent, and a photopolymerization initiator. Is preferred. Note that the amount of the gelling agent contained in the orange ink can be 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. By setting the content of the gelling agent to 1.0% by mass or more, the pinning properties of the ink can be sufficiently increased, a higher-definition image can be formed, and the spread of the ink can be reduced. The gloss of the image can be made closer to the gloss of the image by another ink. Further, by increasing the pinning property of the ink, particularly when an image is formed on a water-absorbing substrate, it is possible to make it difficult to cause insufficient color development due to the ink entering the inside of the substrate, and to achieve a desired color gamut. An image can be easily formed. When the content of the gelling agent is 10.0% by mass or less, the gelling agent hardly precipitates on the surface of the formed image, and the gloss of the image can be made closer to the gloss of the image by another ink. In addition, the ejection property of ink from the inkjet head can be further improved. From the above viewpoint, the content of the gelling agent in the orange ink is preferably from 1.0% by mass to 5.0% by mass, and more preferably from 2.5% by mass to 5.0% by mass. Is more preferable, and it is still more preferable that it is 2.5 to 4.0 mass%.

  From the viewpoint of further improving the ejection property from the inkjet head and increasing the miscibility with the magenta ink after landing, the viscosity of the orange ink at 80 ° C. is preferably 8.0 mPa · s or more and 9.5 mPa · s or less. preferable. From the above viewpoint, the viscosity of the orange ink at 80 ° C. is more preferably 8.5 mPa · s or more and 9.0 mPa · s or less.

  From the viewpoint of further improving the ejection property from the inkjet head, the average particle diameter of the pigment particles contained in the orange ink is preferably 0.13 μm or more and 0.22 μm or less. From the above viewpoint, the average particle diameter of the pigment particles contained in the orange ink is preferably from 0.14 μm to 0.16 μm.

  Other physical properties of the orange ink are preferably in the same range as the above-described magenta ink for the same reason as the magenta ink.

1-3. Combination of magenta ink and orange ink The ink set of the present invention contains at least magenta ink-A or orange ink-C. That is, the color gamut of a good color gamut, particularly a red color gamut such as Pantone Red 032, may be achieved by the magenta ink-A or the orange ink-C, and the ink set of the present invention uses the magenta ink-A. When the ink set includes the orange ink-C or the orange ink-D, when the ink set of the present invention includes the orange ink-C, the magenta ink may be any of the magenta ink-A and the magenta ink-B. . In addition, from the viewpoint of forming an image having good pinning properties and good gloss, the ink set of the present invention is more preferably an ink set containing magenta ink-A and orange ink-C.

1-4. Other Inks An ink set contains a pigment, a photopolymerizable compound, a dispersant, a gelling agent, and a photopolymerization initiator other than the magenta ink or the orange ink, and is cured by irradiation with actinic rays (hereinafter, simply referred to as an ink set). (Also referred to as "other inks"). For example, when the ink set further includes a yellow ink, a cyan ink, and a black ink, a full-color image can be formed.

  The pigment contained in the yellow ink may be any pigment that allows the ink that has landed on the recording medium and cured to exhibit a yellow color. Examples of such pigments include C.I. I. Pigment Yellow (hereinafter, also simply referred to as "Pigment Yellow") 1, Pigment Yellow 3, Pigment Yellow 13, Pigment Yellow 13 and Pigment Yellow 14, Pigment Yellow 14, Pigment Yellow 17 and Pigment Yellow 17 55, Pigment Yellow 74, Pigment Yellow 81, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 94, Pigment Yellow 95, Pigment Yellow 97, Pigment Yellow 97 108, Pigment Yellow 109, Pigment Yellow 110, Pigment Yellow 137, Pigment Yellow 138, Pigment Yellow 139, Pigment Yellow 153, Pigment Yellow 154, Pigment Yellow 155, Pigment Yellow 157, Pigment Yellow 166, Pigment Yellow 167, Pigment Yellow 168, Pigment Yellow 180, Pigment Yellow 185, and Pigment Yellow 193. Only one of these pigments may be contained in the yellow ink, or two or more thereof may be contained.

  The pigment contained in the cyan ink may be any pigment that allows the ink that has landed on the recording medium and cured to exhibit a cyan color. Examples of such pigments include C.I. I. Pigment Blue (hereinafter, also simply referred to as "Pigment Blue") 1, Pigment Blue 15, Pigment Blue 15: 1, Pigment Blue 15: 2, Pigment Blue 15: 3, Pigment: Peugement: 15, Pigment: Peugement: 15, Pigment: Peugement: Peugement: 15, Pentage: Peugement: Peugement: Peugement: 15, Pentage: 15, Pentage: 15, Pentage: 15, Pentage: 15, Pentage: 15, Pentage: 15, Pentage: 15, Pentage: 15, Pentent: 15 Pigment Blue 16, Pigment Blue 17-1, Pigment Blue 22, Pigment Blue 27, Pigment Blue 28, Pigment Blue 29, Pigment Blue 29 and Pigment Blue 60 are included. One of these pigments may be contained in the cyan ink, or two or more thereof may be contained.

  The pigment contained in the black ink may be any pigment that allows the cured ink that has landed on the recording medium to exhibit a black color. Examples of such pigments include C.I. I. Pigment Black (hereinafter also simply referred to as “Pigment Black”) 7 (carbon black), Pigment Black 28 and Pigment Black 26. Only one of these pigments may be contained in the black ink, or two or more thereof may be contained.

  The photopolymerizable compound, dispersant, gelling agent, and photopolymerization initiator contained in the other ink can be the same compounds as the above magenta ink. From the viewpoint of increasing the affinity between inks and forming a higher-definition image, other inks use the same compound as the magenta ink as a photopolymerizable compound, a dispersant, a gelling agent, and a photopolymerization initiator. It is preferred to contain. From the viewpoint of forming a higher-definition image, bringing the gloss of the image closer to the gloss of the image with another ink, and further enhancing the ink ejection property from the inkjet head, the content of the gelling agent in the other ink is And 1.5% by mass or more and 3.0% by mass or less based on the total mass of the ink. From the above viewpoint, the content of the gelling agent in the other ink is preferably 2.0% by mass or more and 2.5% by mass or less.

1-5. Preparation of Ink The above-mentioned magenta ink, orange ink and other inks are obtained by mixing the above-mentioned pigment, dispersant, gelling agent, photopolymerizable compound and photopolymerization initiator, and optional components with heating. Can be obtained by It is preferable to filter the obtained mixed solution with a predetermined filter. At this time, a pigment dispersion in which the pigment and the dispersant are dispersed in a solvent may be prepared in advance, and the remaining components may be added and mixed while heating.

  The pigment and the dispersant can be dispersed by, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, and paint shaker.

2. Image Forming Method The image forming method of the present invention is a known method in which magenta ink and orange ink are ejected from an inkjet head, landed on a recording medium, and cured, except that the magenta ink and orange ink included in the above-described ink set are used. Can be performed in the same manner as in the image forming method.

  For example, in the image forming method of the present invention, a first step of ejecting the magenta ink and the orange ink included in the ink set from the nozzles of the inkjet head to land on a recording medium, and the landed magenta ink and orange ink A second step of irradiating the magenta ink and the orange ink by irradiating the magenta ink and the orange ink.

2-1. First Step In the first step, droplets of magenta ink and orange ink are ejected from an inkjet head and land on a recording medium at a position corresponding to an image to be formed. For example, both the orange ink and the magenta ink are landed at a position where an intermediate color between orange and magenta is formed. Either the orange ink or the magenta ink may be ejected first.

  The discharge method from the inkjet head may be any of an on-demand method and a continuous method. On-demand inkjet heads are electro-mechanical conversion methods such as single-cavity type, double-cavity type, bender type, piston type, shared mode type and shared wall type, as well as thermal inkjet type and bubble jet (bubble jet type). Any of an electric-thermal conversion method such as a registered trademark of Canon Inc.) may be used.

  By discharging the ink droplets from the inkjet head in a heated state, the discharge stability can be improved. The temperature of the ink at the time of ejection is preferably 35 ° C. or more and 100 ° C. or less, and more preferably 35 ° C. or more and 80 ° C. or less in order to further enhance ejection stability. In particular, it is preferable to perform ejection at an ink temperature at which the viscosity of the ink is 7 mPa · s or more and 15 mPa · s or less, more preferably 8 mPa · s or more and 13 mPa · s or less.

  The sol-gel phase transition type ink has a temperature at which the ink is filled into the discharge recording head when the ink is filled with the ink (gelation temperature + 10) ° C. to increase the ejectability of the ink from the discharge recording head. It is preferable to set the gelling temperature to +30) ° C. If the temperature of the ink in the ejection recording head is lower than (gelling temperature + 10) ° C., the ink gels in the ejection recording head or on the nozzle surface, and the ink ejection property is likely to be reduced. On the other hand, if the temperature of the ink in the ejection recording head exceeds (gelation temperature + 30) ° C., the temperature of the ink becomes too high, so that the ink components may deteriorate.

  The method of heating the ink to a predetermined temperature is not particularly limited. For example, at least one of an ink tank constituting a head carriage, an ink supply system such as a supply pipe and a front chamber ink tank immediately before the head, a pipe with a filter, a piezo head, and the like may be replaced by a panel heater, a ribbon heater, warm water, or the like. Either of them can be heated to a predetermined temperature.

  The amount of ink droplets when ejected is preferably 2 pL or more and 20 pL or less from the viewpoint of recording speed and image quality.

2-2. Second Step In the second step, the magenta ink and the orange ink landed in the second step are irradiated with an active energy ray to form an image obtained by curing these inks. The active energy ray is preferably irradiated for 0.001 second or more and 1.0 second or less after ink landing, and in order to form a high-definition image, 0.001 second or more and 0.5 second or less. It is more preferable that the irradiation is performed in between.

  The active energy ray for irradiating the ink can be selected from, for example, electron beam, ultraviolet ray, α-ray, γ-ray, and X-ray. Ultraviolet rays can be emitted by, for example, 395 nm, a water-cooled LED, manufactured by Phoseon Technology. By using the LED as the light source, it is possible to suppress the occurrence of poor curing of the ink due to the melting of the ink by the radiant heat of the light source.

The LED light source is installed such that the peak illuminance on the image surface of ultraviolet light having a wavelength of 370 nm or more and 410 nm or less is 0.5 W / cm ² or more and 10 W / cm ² or less, and 1 W / cm ² or more and 5 W / cm ² or less. It is more preferable to set it up. From the viewpoint of suppressing the irradiation of the ink with the radiant heat, the amount of light irradiated on the image is preferably less than 350 mJ / cm ² .

  Further, the irradiation of the active energy ray is divided into two stages. First, after the ink lands, the ink is temporarily cured by irradiating the active energy ray by the above-described method for 0.001 seconds or more and 2.0 seconds or less. After printing, the ink may be further hardened by irradiating it with an active energy ray. By dividing the irradiation of the active energy ray into two stages, the contraction of the recording material, which occurs during the curing of the ink, is less likely to occur.

  In the image forming method of the present invention, curling and wrinkling of the recording medium are performed by setting the total ink film thickness after curing by irradiating the ink landed on the recording medium with active energy rays to be 2 μm or more and 20 μm or less. Generation and a change in the texture of the recording medium can be prevented more efficiently. The “total ink film thickness” refers to the sum of the film thicknesses of all the inks applied or printed on the recording medium, or the film thickness measured at a plurality of points where ejection is expected to have a large amount of ink landing. Mean value.

[recoding media]
The recording medium used in the image forming method of the present invention may form an image with the ink set. For example, polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene Non-absorbable recording media (plastic base) composed of plastics such as copolymers, polyethylene terephthalate and polybutadiene terephthalate, non-absorbable inorganic recording media such as metals and glass, and absorbent papers (for example, , Coated printing paper and coated printing paper B).

  Hereinafter, the present invention will be described in more detail with reference to Examples, but these descriptions should not be construed as limiting the scope of the present invention.

[Example 1]
1-1. Magenta ink 1-1-1. Surface Treatment of Magenta Pigment The following untreated magenta pigment, which is a solid solution of Pigment Violet 19 and Pigment Red 202 (hereinafter, also referred to as “magenta pigment before treatment”), was surface-treated with alumina and sulfonic acid.

[Magenta pigment before treatment]
CINQUASIA Magenta L4540, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 50/50)
CINQUASIA Magenta D4500J, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 60/40)
228-2120, manufactured by Sun chemical (Pigment Violet 19 / Pigment Red 202 ratio: 70/30)
Cinquasia Red K4330, manufactured by BASF (Pigment Violet 19 / Pigment Red 202 ratio: 80/20)

1.0 kg of the untreated magenta pigment (L4540, manufactured by BASF) was added to water, and the pH was adjusted to 10 by adding an aqueous solution of sodium hydroxide to a stirred and dispersed aqueous solution. To this aqueous solution, an aqueous solution of sodium aluminate (manufactured by Wako Pure Chemical Industries, Ltd.) was added in an amount of 0.5 part in terms of aluminum hydroxide (Al (OH) ₃ ) with respect to 100 parts of the pigment, followed by stirring and mixing. Thereafter, the pH was adjusted to 6 by adding an aqueous acetic acid solution with further stirring. Immediately after the pH reached 6, the aqueous solution was filtered, and the obtained solid was washed with water and dried to obtain alumina-treated magenta pigment powder. 5000 ppm of alumina was added to the magenta pigment powder based on the amount of Al element contained in the pigment powder, as measured by ICP-AES (ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer (apparatus name), manufactured by SII Nano Technology Co., Ltd.)). Was calculated.

  The alumina-treated magenta pigment prepared above was dispersed in a solvent, 2-pyrrolidone. The dispersion is transferred to a container that can be degassed in a vacuum, and heated to 100 to 120 ° C. while reducing the pressure to 50 Torr (6.67 Pa) or less with an aspirator. C. was controlled. To this dispersion, sulfur trioxide (sulfuric anhydride, manufactured by Nippon Soda Co., Ltd.) as a sulfonating agent was added in an amount of 0.15 part with respect to 100 parts of the magenta pigment, and the mixture was stirred for 2 to 3 hours. The surface-treated magenta pigment obtained by filtration was washed several times with excess 2-pyrrolidone, poured into water, and then filtered to obtain magenta pigment 1 for ink. From the amount of S element contained in the powder of the magenta pigment 1 for ink measured by ICP-AES (inductively coupled plasma emission spectroscopy (device name), manufactured by SII Nano Technology Co., Ltd.), 1500 ppm of sulfonic acid was converted to magenta for ink. It was calculated that pigment 1 was provided.

  The same procedure was performed except that the magenta pigment before the treatment was changed according to Table 3 and that the amount of sodium aluminate was changed so that the amount of alumina applied to the magenta pigment powder was as shown in Table 3. Thus, magenta pigments 2 to 10 and 13 for ink to which different amounts of alumina were provided and also sulfonic acid were prepared. On the other hand, the magenta pigment for ink 11 was subjected to surface treatment with alumina, but was not subjected to surface treatment with sulfonic acid.

  The magenta pigment 12 for ink was not subjected to surface treatment with alumina and sulfonic acid. When the powder of the magenta pigment 12 for ink was measured by ICP-AES, only the Al element (usually about 1 to 15 ppm) and the S element (usually about 20 to 30 ppm) originally contained in the pigment were determined.

  Table 3 shows the physical properties of the untreated magenta pigments used for the ink magenta pigments 1 to 12 and the ink magenta pigments 1 to 13.

1-1-2. Preparation of Magenta Pigment Dispersion The magenta pigment for ink 1, the photopolymerizable compound, the dispersant, and the polymerization inhibitor were put in a 200 ml polybin, and 120 g of zirconia beads having a diameter of 0.5 mmφ were further put therein, and the lid was closed. Was dispersed in a vibration mill (Red Devil 4500L, manufactured by Nishimura Seisakusho) for 4 hours. After the dispersion, the beads were separated and the dispersion was taken out to obtain a magenta pigment dispersion 1a.
Magenta pigment for ink 1: 9.0 g
Photopolymerizable compound: 32.7 g of tripropylene glycol diacrylate
Dispersant: BYK Jet-9151, 3.2 g, manufactured by Big Chemie
Polymerization inhibitor: Irgastab UV-10, manufactured by BASF (“Irgastab” is a registered trademark of the company) 0.1 g

  Magenta pigment dispersions 2a to 13a were prepared by the same procedure except that magenta pigment 1 for ink was changed to magenta pigments 2 to 13 for ink.

1-1-3. Preparation of Magenta Ink The following photopolymerizable compound, surfactant, photopolymerization initiator and gelling agent were added to the magenta pigment dispersion 1 heated to 60 ° C., and then a WAC filter (0.3 μm accuracy), Pall Corporation Then, magenta ink 1a was prepared.
Magenta pigment dispersion 1a: 20.0 g
Photopolymerizable compound: 6.2 g of polyethylene glycol 600 diacrylate
Photopolymerizable compound: 6.2 g of 3PO-modified trimethylolpropane triacrylate
Surfactant: TSF-4452, manufactured by Shin-Etsu Chemical Co., Ltd. 0.3 g
Photopolymerization initiator: Irgacure 819, manufactured by BASF (“Irgacure” is a registered trademark of the company) 0.3 g
Photopolymerization initiator: DAROCUR TPO, manufactured by BASF ("DAROCUR" is a registered trademark of the company) 0.3 g
Gelling agent: Kaowax T-1, manufactured by Kao Corporation

  Magenta inks 2a to 13a were prepared in the same manner as magenta ink 1 except that magenta pigment dispersion 1a was changed to magenta pigment dispersions 2a to 13a.

  In addition, with respect to the magenta inks 1a to 13a, inks were prepared where necessary so that the content of the gelling agent in the ink was 0.5% by mass to 6.0% by mass of the total mass of the ink.

1-2. Orange inks Orange inks 1a to 6a were prepared in the same manner as magenta ink 1a, except that magenta pigment 1 for ink was changed to orange pigments 1 to 6 below.

[Orange pigment]
Orange pigment 1: Pigment Orange 36
Orange pigment 2: Pigment Orange 71
Orange pigment 3: Pigment Orange 64
Orange pigment 4: Pigment Orange 16
Orange pigment 5: Pigment Orange 34
Orange pigment 6: Pigment Orange 38

1-2-1. Preparation of Orange Pigment Dispersion Orange pigment 1, a photopolymerizable compound, a dispersant and a polymerization inhibitor are placed in a 200 ml polybin, and 120 g of zirconia beads having a diameter of 0.5 mmφ are further placed therein, and then a lid is closed. The dispersion was carried out for 5 hours using a vibration mill (Red Devil 4500L, manufactured by Nishimura Seisakusho). After the dispersion, the beads were separated and the dispersion was taken out to obtain an orange pigment dispersion 1.
Orange pigment 1: 8.5 g
Pigment derivative: 0.5 g Solsperse 22000 (Sulfonated Pigment Yellow 12)
Photopolymerizable compound: 32.7 g of tripropylene glycol diacrylate
Dispersant: BYK Jet-9151, 3.2 g, manufactured by Big Chemie
Polymerization inhibitor: Irgastab UV-10, manufactured by BASF (“Irgastab” is a registered trademark of the company) 0.1 g

  Orange pigment dispersions 2a to 6a were prepared by the same procedure except that orange pigment 1 was changed to orange pigments 2 to 6.

1-2-2. Preparation of Orange Ink The following photopolymerizable compound, surfactant, photopolymerization initiator and gelling agent were added to the orange pigment dispersion 1a heated to 60 ° C., and then a WAC filter (0.3 μm accuracy), Pall Corporation The mixture was filtered to prepare orange ink 1a.
Orange pigment dispersion 1a: 5.0 g
Photopolymerizable compound: polyethylene glycol 600 diacrylate 10.5 g
Photopolymerizable compound: 4.5 g of 3PO-modified trimethylolpropane triacrylate
Surfactant: TSF-4452, manufactured by Shin-Etsu Chemical Co., Ltd. 0.3 g
Photopolymerization initiator: Irgacure 819, manufactured by BASF (“Irgacure” is a registered trademark of the company) 0.3 g
Photopolymerization initiator: DAROCUR TPO, manufactured by BASF ("DAROCUR" is a registered trademark of the company) 0.3 g
Gelling agent: Kaowax T-1, manufactured by Kao Corporation

  Orange inks 2a to 6a were prepared in the same manner as the orange ink 1a, except that the orange pigment dispersion 1a was changed to orange pigment dispersions 2 to 6.

  With respect to the orange inks 1a to 6a, inks were prepared where necessary so that the content of the gelling agent in the ink was 0.5% by mass to 6.0% by mass based on the total mass of the ink.

1-3. Preparation of Yellow Ink, Cyan Ink and Black Ink Similar to Orange Ink 1 except that Orange Pigment 1 was changed to PY185 (Yellow Pigment), Pigment Blue 15: 4 (Cyan Pigment) and Pigment Black 7 (Black Pigment) , A cyan ink and a black ink, respectively.

  For each of the yellow ink, the cyan ink and the black ink, inks were prepared in which the content of the gelling agent in the ink was 0.5% by mass to 6.0% by mass of the total mass of the ink.

1-4. Ink set As a combination of magenta ink and orange ink described in Tables 4 to 5, and so that all the inks included in the ink set contain the gelling agent in the amount described in Tables 4 to 5, Ink sets 1-1 to 1-36 were obtained by combining magenta ink, orange ink, yellow ink, cyan ink, and black ink.

  Tables 4 and 5 show combinations of the magenta ink and the orange ink included in each ink set, and the amounts of the gelling agents contained in the inks included in the ink sets.

1-5. Evaluation Method and Evaluation Results The storage stability and pinning properties of each ink set, and the difference in gloss and color gamut between an image by each ink set and another image were evaluated according to the following criteria.

1-5-1. Storage stability For pigment particles contained in the magenta ink and the orange ink included in the ink sets 1-1 to 1-36, the average particle diameter in each ink diluted 200-fold with polyethylene glycol diacrylate (PEGDA) was measured using a data sizer. It was measured by the dynamic light scattering method using Nano ZSP, manufactured by Malvern. Each actinic ray-curable ink was collected in a heat-resistant tube and stored in a high-temperature bath at 50 ° C. for 6 weeks. The average particle size of the pigment particles were measured in the same manner in each of the ink after storage, the difference between the average particle size after storage for the average particle diameter before storage _{(P A) (P B)} (P A -P B) Was calculated.
A The difference between the average particle diameters of both the magenta ink and the orange ink is less than 7 nm. B The difference between the average particle diameters of the magenta ink and the orange ink is 7 nm or more and less than 15 nm. C The average particle of either the magenta ink or the orange ink. D Difference in diameter is 15 nm or more D Difference in average particle diameter of both magenta ink and orange ink is 15 nm or more

1-5-2. Pinning Ink sets 1-1 to 1-36 were introduced into an ink jet head HA512 type (manufactured by Konica Minolta), and natural images (published by the Japan Standards Association) under the conditions of a print width of 100 mm x 100 mm and a resolution of 720 x 720 dpi High-definition color digital standard image data “Fruit Basket”) was landed on a printing substrate at 50 ° C., and printing was performed using five color inks of YMCKO. As a printing substrate, an OK top coat (printing paper) was used. Using an LED lamp as a UV irradiation light source, the printed ink was irradiated with ultraviolet light at an energy of 250 mJ to cure the ink.

The above-mentioned images obtained with the respective actinic radiation-curable inks were observed with a microscope (× 200), and the average value of the diameters of 100 droplets randomly selected was determined.
A Average value is less than 45 μm and variation in droplet diameter is 10 μm or less B Average value is less than 45 μm C Average value is 45 μm or more and 50 μm or less D Average value is more than 50 μm E Average value is more than 50 μm Large, variation in droplet diameter is 10 μm or less

1-5-3. Gloss Difference By using each ink set, a magenta ink and an orange ink were heated to 50 ° C., and a 60 ° C. reflection gloss value of a solid image formed at a printing rate of 100% was measured with a digital handy gloss meter (Gloss Checker IG- 331, manufactured by Horiba, Ltd.). The difference between the reflection gloss value (40) determined as a preferable value from the viewpoint of enhancing the aesthetic appearance of the image and the reflection gloss value of the magenta and orange solid images included in each of the actinic ray curable ink sets was examined.
A The absolute value of the difference between the reflection gloss value of both magenta and orange magenta inks and the above reflection gloss value (40) is less than 3.0 B The reflection gloss value of either magenta or orange magenta ink and the above reflection gloss The absolute value of the difference between the reflection gloss value of the magenta ink of any of magenta and orange and the reflection gloss value (40) of which the absolute value of the difference from the value (40) is 3.0 or more and less than 5.0 is 5 D is greater than or equal to D. The absolute value of the difference between the reflective gloss value of the magenta ink of either magenta or orange and the reflective gloss value (40) is greater than or equal to 5.0.

1-5-4. Color gamut difference The images described in 1-5-2 using the ink sets of Pantone Red 032 and Pantone Orange 211, respectively, were measured using a portable integrating sphere spectrophotometer Ci6x, manufactured by X-lite, and a * and b * were measured. Value obtained. The square root of the value obtained by adding the square of the difference of each a * value and the square of the difference of each b * value is calculated, and the color gamut difference between the image by each ink set and the standard sample is calculated. And
A The color gamut difference of both Pantone Red 032 and Pantone Orange 021 is less than 1.0 B The color gamut difference of either Pantone Red 032 or Pantone Orange 021 is 1.0 or more and 2.0 or less C Pantone Red 032 and The color gamut difference of either Pantone Orange 021 is larger than 2.0 D The color gamut difference of both Pantone Red 032 and Pantone Orange 021 is larger than 2.0

1-5-5. Results The results are shown in Tables 6 to 8.

  The amount of alumina in the magenta pigment for ink is 1500 ppm or more and 7500 ppm or less by mass relative to the magenta pigment, and the ink set containing the magenta ink surface-treated with sulfonic acid has high storage stability, gloss difference and color. An image with a small area difference was formed. In addition, when the content of the gelling agent in each ink included in the ink set was 1% by mass or more and 5% by mass or less with respect to the mass of the ink, the pinning properties of the ink could be improved.

  When the ratio of Pigment Violet 19 and Pigment Red 202 contained in the magenta pigment was within the range of 60/40 or more and 70/30 or less, the color gamut difference with Pantone Red 032 became smaller. Further, when an ink set containing magenta ink-A and orange ink-C is used, an image close to the colors of Pantone Red 032 and Pantone Orange 21 can be formed, and red to orange in the L * a * b * color space can be formed. The color gamut that can be expressed as an ink set of the area could be expanded.

[Example 2]
2-1. Preparation of Ink An ink was prepared using one of the orange pigments shown in Table 9, one of the pigment derivatives shown in Table 10, two of the photopolymerizable compounds shown below, a gelling agent, and other materials. Was prepared.

  2-1-1. Pigment

  2-1-2. Pigment derivative

2-1-3. Photopolymerizable compound [Highly polar photopolymerizable compound]
PEG400DA: polyethylene glycol 400 diacrylate (A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., number of ethylene oxide groups: 9)
FA-137M: EO-modified trimethylolpropane trimethacrylate (FA-137M, manufactured by Hitachi Chemical Co., Ltd., number of ethylene oxide groups: 21)
[Low-polarity photopolymerizable compound]
BPP-4: PO-modified bisphenol A diacrylate (New Frontier BPP-4, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., number of propylene oxide groups: about 4)
TPGDA: Tripropylene glycol diacrylate (Aronix M220, Toagosei Co., Ltd.)

2-1-4. Gelling agent T1: Kaowax T-1, manufactured by Kao Corporation

2-1-5. Other materials [Polymerization inhibitor]
UV10: Irgastab UV-10, manufactured by BASF (“Irgastab” is a registered trademark of the company)
ITX: ITX, manufactured by BASF 819: Irgacure 819, manufactured by BASF (“Irgacure” is a registered trademark of the company)
TPO: DAROCUR TPO, manufactured by BASF (DAROCUR is a registered trademark of BASF)
[Dispersant]
BYK Jet-9151, manufactured by Big Chemie

2-1-6. Preparation of Orange Ink The following components were prepared in a total amount of 100 parts by mass, placed in a 250 ml pot together with 120 g of zirconia beads having a diameter of 0.5 mmφ, and the lid was closed. For 5 hours. After the dispersion, the beads were separated and the dispersion was taken out to obtain an orange pigment dispersion 1b.
Orange pigment: Pigment Orange 36 18.0 parts by mass Polymerization inhibitor: UV10 0.1 parts by mass Dispersant: 9151 6.0 parts by mass Pigment derivative: 1S-1 0.18 parts by mass Photopolymerizable compound: BPP-4 balance

Thereafter, while heating the dispersion to 60 ° C., the following gelling agent and photopolymerization initiator were added so as to have the following ratios, and the weight ratio of the high-polarity photopolymerizable compound to the low-polarity photopolymerizable compound was adjusted. Was 30:70. This orange ink was used as the orange ink of the ink set 2-1.
Pigment dispersion: Orange pigment dispersion 12.0 parts by mass Photopolymerizable compound: FA-137M 24.3 parts by mass Photopolymerizable compound: BPP-4 56.7 parts by mass Surfactant: TSF-4452 0.3 mass Parts Gelling agent: T-1 3.0 parts by mass Photopolymerization initiator: ITX 1.0 parts by mass Photopolymerization initiator: 819 2.0 parts by mass Photopolymerization initiator: TPO 2.0 parts by mass Orange pigment, light Except for changing the type and ratio of the polymerizable compound, and the type and amount of the gelling agent or the pigment derivative to the combinations or numerical values described in Tables 11 to 13, the same as in the orange ink 1b, An ink was prepared. These orange inks were used as the orange inks of the ink sets 2-2 to 2-42.

2-1-7. Preparation of Magenta Ink The following components were prepared in a total amount of 100 g, placed in a 250 ml pot together with 120 g of zirconia beads having a diameter of 0.5 mmφ, the lid was closed, and a vibrating mill (Red Devil 4500 L, manufactured by Nishimura Seisakusho) was used. Time dispersed. After the dispersion, the beads were separated and the dispersion was taken out to obtain a magenta pigment dispersion.
Magenta pigment: 18.0 parts by mass of magenta pigment 13 Polymerization inhibitor: 0.1 part by mass of UV10 Dispersant: 6.0 parts by mass of 9151 Pigment derivative: 0.18 parts by mass of 1S-1 Photopolymerizable compound: BPP-4 Remainder

Thereafter, while heating the dispersion to 60 ° C., the following gelling agent and photopolymerization initiator were added so as to have the following ratios, and the weight ratio of the high-polarity photopolymerizable compound to the low-polarity photopolymerizable compound was adjusted. Was 30:70 to prepare a magenta ink 1b. This magenta ink was used as the magenta ink of the ink set 2-1.
Pigment dispersion: Magenta pigment dispersion 12.0 parts by mass Photopolymerizable compound: FA-137M 24.3 parts by mass Photopolymerizable compound: BPP-4 56.7 parts by mass Surfactant: TSF-4452 0.3 parts by mass Part Gelling agent: T-1 3.0 parts by mass Photopolymerization initiator: ITX 1.0 part by mass Photopolymerization initiator: 819 2.0 parts by mass Photopolymerization initiator: TPO 2.0 parts by mass Hereinafter, similarly A magenta ink was prepared in the same manner except that the type and ratio of the photopolymerizable compound and the content of the gelling agent were the same as those of the orange ink having the same number, except for the type of the magenta pigment and the pigment derivative. These magenta inks were used as magenta inks of ink sets 2-2 to 2-42.

2-1-8. Preparation of Yellow Ink, Cyan Ink and Black Ink The pigment in the orange ink 1 was changed to Pigment YELLOW 185 (yellow pigment), Pigment Blue 15: 4 (cyan pigment) and Pigment Black 7 (black pigment), and contained a pigment derivative. Except that the ink was not used, the yellow ink 1b, the cyan ink 1b, and the black were used in the same manner as the orange ink under the same conditions as the orange ink of the same number, with the same type and ratio of the photopolymerizable compound and the content of the gelling agent. Ink 1b was prepared respectively. Ink sets 2-1 to 2-42 were obtained by combining the yellow ink 1b, the cyan ink 1b, and the black ink 1b with the orange ink and the magenta ink having the pigments shown in Tables 11 to 13.

  Tables 11 to 13 show the type of orange pigment, the type and content of the photopolymerizable compound, the ratio of the highly polar photopolymerizable compound, the content of the gelling agent, and the type and content of the pigment derivative in each ink. Indicates the amount. In Tables 11 to 13, the numerical values described in the columns of “high-polarity photopolymerizable compound” and “low-polarity photopolymerizable compound” indicate the amount of each photopolymerizable compound with respect to the mass of the entire photopolymerizable compound ( %), And the numerical value described in the column of “Ratio of Highly Polar Photopolymerizable Compound” is the amount (% by mass) of the highly polar photopolymerizable compound with respect to the total weight of the photopolymerizable compound. Further, in Tables 11 to 13, the numerical values described in the column of “gelling agent content” are the amount (% by mass) of the gelling agent with respect to the total mass of each ink, and the “content” of the pigment derivative. Are the amounts (% by mass) of the pigment derivative with respect to the mass of the pigment contained in each ink.

2-2. Evaluation Method and Evaluation Results The storage stability and pinning properties of each ink set, and the gloss difference and color gamut difference between an image by each ink set and another image were evaluated based on the same criteria as in Example 1. .

2-3. Results The results are shown in Tables 14 to 16.

  An image formed using an ink containing a basic orange pigment and an azo derivative and having a mass ratio of the highly polar photopolymerizable compound to the monomer composition of 30% by mass or more has a color tone from the Pantone color gamut. The deviation and the deviation from the gloss value of the other color ink were small, and the dot diameter was also in a desired range.

  On the other hand, an image formed using an ink containing an orange pigment having no basic site in the cyclic structure had a large deviation in color tone from the Pantone color gamut and a large deviation from the gloss value of the other color ink. This is considered to be because the orange pigment and the azo derivative could not be sufficiently associated with each other, and the accumulation of the gelling agent in the orange pigment could not be sufficiently prevented.

  In addition, an image formed using an ink having a content of the highly polar photopolymerizable compound of less than 30% by mass had a large color tone shift from the Pantone color gamut. This is considered to be because the basic orange pigment and the azo derivative could not be sufficiently associated with each other, and the accumulation of the gelling agent in the basic orange pigment could not be sufficiently prevented by the azo derivative.

  In the image formed using the ink having a gelling agent content of 1.0% by mass or more, the deviation from the gloss value of the other color ink was small, and the dot diameter was within a desired range. This is considered to be because the ink was sufficiently pinned by the gelling agent. Further, the ink set provided with both the magenta ink-A and the orange ink-C according to the present invention has good storage stability, excellent pinning properties, a small difference in gloss, and an L * a * b * color space. An ink set having good color reproducibility in the color gamut of the red to orange region could be provided.

  The ink set of the present invention can be used to form an image having a wider variety of color tones and a glossiness equivalent to that of a conventional image.

  This application claims priority based on Japanese Patent Application No. 2015-021455 filed on February 5, 2015 and Japanese Patent Application No. 2015-049543 filed on March 12, 2015, The contents of the claims and the description of the application are incorporated herein by reference.

Claims (9)

An ink set containing a pigment, a gelling agent, a photopolymerizable compound and a photopolymerization initiator, and including a plurality of types of inks that are cured by irradiation with actinic light,
The plurality of types of ink includes magenta ink and orange ink,
The pigment contained in the magenta ink was C.I. I. Pigment Violet 19 and C.I. I. A magenta pigment including a solid solution with C.I. Pigment Red 202,
The amount of the alumina in the magenta pigment is 1500 mass ppm or more and 7500 mass ppm or less,
The ink set, wherein the content of the gelling agent in each ink is 1% by mass or more and 5% by mass or less.   The C.I. I. Pigment Violet 19 and C.I. I. The ink set according to claim 1, wherein the mass ratio with Pigment Red 202 is 60/40 or more and 70/30 or less.   3. The ink set according to claim 1, wherein an amount of the alumina with respect to the magenta pigment is 5,000 ppm to 7,500 ppm by mass. 4. An ink set containing a pigment, a gelling agent, a photopolymerizable compound and a photopolymerization initiator, and including a plurality of types of inks that are cured by irradiation with actinic light,
The plurality of types of ink includes magenta ink and orange ink,
The orange ink further contains a sulfonated derivative of an insoluble azo pigment in an amount of 2.0% by mass or more and 15.0% by mass or less based on the mass of the pigment contained in the ink.
The pigment contained in the orange ink has a cyclic structure, and includes an orange pigment having a basic site in the cyclic structure,
The photopolymerizable compound contained in the orange ink contains a photopolymerizable compound having at least 30% by mass based on the total mass of the photopolymerizable compound and having a total of 6 or more ethylene oxide groups or propylene oxide groups. ,
The ink set, wherein the content of the gelling agent in each ink is 1.5% by mass or more and 3.0% by mass or less.   The photopolymerizable compound having 6 or more ethylene oxide groups or propylene oxide groups in total has two or more segments having 3 or more ethylene oxide groups or propylene oxide groups in a molecule, The ink set according to claim 4.   The ink set according to claim 1, further comprising a yellow ink, a cyan ink, and a black ink. An ink set containing a pigment, a gelling agent, a photopolymerizable compound and a photopolymerization initiator, and including a plurality of types of inks that are cured by irradiation with actinic light,
The plurality of types of ink includes magenta ink and orange ink,
The pigment contained in the magenta ink was C.I. I. Pigment Violet 19 and C.I. I. A magenta pigment including a solid solution with C.I. Pigment Red 202,
The amount of the alumina in the magenta pigment is 1500 mass ppm or more and 7500 mass ppm or less,
The orange ink further contains a sulfonated derivative of an insoluble azo pigment in an amount of 2.0% by mass or more and 15.0% by mass or less based on the mass of the pigment contained in the ink.
The pigment contained in the orange ink has a cyclic structure, and includes an orange pigment having a basic site in the cyclic structure,
The photopolymerizable compound contained in the orange ink contains a photopolymerizable compound having at least 30% by mass based on the total mass of the photopolymerizable compound and having a total of 6 or more ethylene oxide groups or propylene oxide groups. ,
The ink set, wherein the content of the gelling agent in each ink is 1.0% by mass or more and 5.0% by mass or less.   The orange ink is C.I. I. Pigment Orange 36, C.I. I. Pigment Orange 64 and C.I. I. The ink set according to any one of claims 1 to 7, further comprising at least one pigment selected from the group consisting of Pigment Orange 71.   A step of ejecting the magenta ink and the orange ink included in the ink set according to any one of claims 1 to 8 from a nozzle of an inkjet head to land on a recording medium, and applying the magenta ink and the orange ink that have landed. Irradiating actinic light to cure the magenta ink and the orange ink.