JP2015183161A - Aqueous pigment dispersion for inkjet ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous pigment dispersion that has a low viscosity as an aqueous pigment dispersion, that exhibits excellent ejection stability (re-dispersibility) when prepared into an inkjet ink, as well as has a small median diameter in terms of cumulative volumes and excellent storage stability, and that exhibits excellent image density and image glossiness when printed as an inkjet ink on a printing sheet.SOLUTION: An aqueous pigment dispersion for an inkjet ink is provided, which comprises at least water, a water-soluble polymer as a pigment dispersion resin, a basic compound, a water-soluble organic solvent, and a pigment. The water-soluble polymer comprises, as constituent monomers, benzyl methacrylate, acrylic acid and polyethylene glycol (meth)acrylate, and contains no styrene. The water-soluble polymer contains, with respect to the amount of all monomers constituting the polymer, 50 to 68 mass% of the benzyl methacrylate, 10 to 16 mass% of the acrylic acid, and 40 mass% or less of the polyethylene glycol (meth)acrylate.

Description

  The present invention relates to an aqueous pigment dispersion for inkjet ink.

  The ink jet recording system is a recording system in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle and attaching them to a recording member. This method is widely spread because it is easy to make full color and is inexpensive, and has many advantages such as the ability to use plain paper as a recording member and non-contact with the object to be printed. Among them, from the viewpoint of weather resistance and water resistance of printed matter, those using pigment-based ink as a colorant have become mainstream.

  The pigment has the property of being insoluble in water as a basic property. Therefore, the aqueous pigment dispersion using the same and the aqueous pigment ink are dispersed and stabilized by using a surfactant or a dispersion resin in order to keep the dispersion state of the pigment in the dispersion and the ink stable. .

  In order to stabilize dispersion by pigment adsorption, for example, Patent Document 1 attempts to improve the water resistance of an ink image by increasing the dispersibility with a water-dispersed polymer of a hydrophobic group and styrene. Patent Document 2 leads to the development of an ink having excellent dispersion and storage stability, and high printing density and gloss. However, since all of these documents have poor water solubility, ink ejection stability (redispersibility) is achieved. There is a problem that it decreases.

  On the other hand, Patent Document 3 attempts to improve water solubility by increasing the acid value. However, due to its high water solubility, the dispersibility decreases due to resin detachment from the pigment surface, and the ratio of free resin. Therefore, there is a problem that the viscosity of the dispersion and the ink is increased and the storage stability is deteriorated.

JP-A-8-231906 JP 2006-342294 A Japanese Patent Laid-Open No. 11-228891

  The problems of the present invention are that the aqueous pigment dispersion has a low viscosity and excellent ejection stability (redispersibility) when used as an inkjet ink, and has a small volume median diameter, excellent storage stability, and an inkjet ink. Another object of the present invention is to provide an aqueous pigment dispersion excellent in image density and image gloss when printed on printing paper.

  As a result of intensive studies to solve the above problems, the present inventors have reached the present invention.

  That is, the present invention comprises at least water, a water-soluble polymer as a pigment dispersion resin, a basic compound, a water-soluble organic solvent, and a pigment, and the water-soluble polymer contains benzyl methacrylate, acrylic acid and polyethylene as constituent monomers. Containing glycol (meth) acrylic acid ester, not containing styrene, benzyl methacrylate 50-68% by mass, acrylic acid 10-16% by mass, polyethylene glycol (meth), based on the total amount of monomers constituting the water-soluble polymer The present invention relates to an aqueous pigment dispersion for inkjet inks, characterized in that the acrylic ester is 40% by mass or less.

  The present invention also relates to the aqueous pigment dispersion for inkjet ink, wherein the water-soluble polymer has an acid value of 120 mgKOH / g or more and a weight average molecular weight (Mw) of 10,000 to 40,000.

The present invention also relates to the aqueous pigment dispersion for inkjet ink, wherein the polyethylene glycol (meth) acrylic acid ester is a polyethylene glycol (meth) acrylic acid ester represented by the following general formula (1).

Formula _{(1) CH 2 = C (} -R1) -COO (CH 2 -CH 2 -O) n-R2

[Wherein, R 1 and R 2 each independently represent H or CH ₃ , and n represents an integer of 1 to 23. ]

  The present invention also relates to the aqueous pigment dispersion for inkjet ink, wherein the water-soluble polymer is a water-soluble polymer obtained by polymerizing an azo ester compound not containing a nitrile group as a polymerization initiator.

  The present invention also relates to the aqueous pigment dispersion for inkjet ink, wherein the water-soluble polymer is a water-soluble polymer obtained by adding a basic compound and water to a reaction mixture after polymerizing monomers.

  Further, the present invention comprises 15 to 25% by mass of pigment and 5.0 to 6.0% by mass of a water-soluble polymer with respect to the total amount of the aqueous pigment dispersion for inkjet ink, and measured at 25 ° C. using a BL type viscometer. The water-based pigment dispersion for inkjet inks has a viscosity at 18 mPa · s or less.

  The present invention also relates to the aqueous pigment dispersion for inkjet ink, wherein the median diameter (D50) of the cumulative volume measured by a laser dynamic light scattering method is 150 nm or less.

  Since the water-based pigment dispersion of the present invention does not contain styrene, fixing the resin structure is eliminated, and since polyethylene glycol (meth) acrylate is used, water-soluble and dispersion stability due to steric repulsion are achieved. Since it is imparted, it has excellent effects on viscosity reduction, storage stability, image density of printed matter when used as an inkjet ink, image gloss, and ejection stability (redispersibility).

  In the following, the present invention and an inkjet ink comprising the aqueous pigment dispersion for inkjet inks (hereinafter sometimes simply referred to as an aqueous ink composition, an ink composition, a pigment ink, and an ink) will be described with reference to preferred embodiments. explain. In this specification, “aqueous pigment dispersion for inkjet ink” is “aqueous pigment dispersion”, “pigment dispersion”, “dispersion”, “water-soluble polymer” is “polymer”, “pigment dispersion resin” And “dispersion resin” may be abbreviated. Further, “(meth) acryl” means “acryl” and / or “methacryl”, and “(meth) acrylate” means “acrylate” and / or “methacrylate”, respectively.

<Aqueous pigment dispersion for inkjet ink>
First, the aqueous pigment dispersion for inkjet ink of the present invention and the material constituting it will be described.

<Water-soluble polymer>
First, the water-soluble polymer used in the present invention will be described.
The water-soluble polymer used in the present invention contains benzyl methacrylate, acrylic acid and polyethylene glycol (meth) acrylic acid ester as constituent monomers, does not contain styrene, and is based on the total monomer amount constituting the water-soluble polymer. It consists of 50 to 68% by mass of benzyl methacrylate, 10 to 16% by mass of acrylic acid, and 40% by mass or less of polyethylene glycol (meth) acrylate.

  The first constituent monomer is benzyl methacrylate. This is the hydrophobic part of the water-soluble polymer and acts as an adsorption site for the pigment. Since the distance from the polymer main chain is longer than that of styrene, the fixation of the three-dimensional structure due to the π-π interaction between the aromatic rings in the resin and between the resins can be eliminated, and the viscosity of the pigment dispersion is reduced. Contribute.

  The second constituent monomer is acrylic acid. This acts as an ionic hydrophilic site in the water-soluble polymer. It induces electrostatic repulsion between the pigment dispersions and contributes to the dispersion stability of the pigment dispersion.

  The third constituent monomer is polyethylene glycol (meth) acrylic acid ester. This is a nonionic hydrophilic portion in the water-soluble polymer and contributes to the dispersion stability of the pigment dispersion. Specific examples include polyethylene glycol mono (meth) acrylate and methoxypolyethylene glycol mono (meth) acrylate. Examples of available commercial products include NK Ester M-90G, M-230G, AM-90G, AM-130G, manufactured by NOF Corporation, Shin-Nakamura Chemical Co., Ltd., trade names: BLEMMER AE-90, AE-200, AE-400, AME-400, PE-90, PE-200, PE-350, PME-100, PME-200, PME-400, PME-1000 and the like can be preferably used. In the general formula (1) n = 1 to 23 is preferable, and n = 9 to 23 is more preferable.

  As a preferable embodiment of the polyethylene glycol (meth) acrylate, a polyethylene glycol (meth) acrylate represented by the general formula (1) can be given.

(Other monomers constituting water-soluble polymer)
Optional other monomers constituting the water-soluble polymer include hydroxyl group-containing acrylates. Specific examples include hydroxypropyl (meth) acrylates such as 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate. ) Acrylate is an embodiment of other monomers constituting the water-soluble polymer.

(Composition ratio of monomers constituting water-soluble polymer)
The composition ratio of benzyl methacrylate, which is the first constituent monomer of the water-soluble polymer used in the present invention, is in the range of 50 to 68% by mass and 60 to 68% by mass with respect to all monomers constituting the water-soluble polymer. It is preferable that it is the range of these.

  The composition ratio of acrylic acid of the second constituent monomer is 10 to 16% by mass and preferably in the range of 14 to 16% by mass with respect to all monomers constituting the water-soluble polymer.

  The composition ratio of the polyethylene glycol (meth) acrylic acid ester as the third constituent monomer is preferably 40% by mass or less, more preferably 15 to 25% by mass, based on all monomers constituting the water-soluble polymer. preferable. Moreover, when 2-hydroxyethyl (meth) acrylate is contained as a monomer which comprises a water-soluble polymer, it is more preferable to contain 5-10 mass% of 2-hydroxyethyl (meth) acrylate.

(Acid value of dispersed resin)
The acid value of the dispersion resin is preferably 120 mgKOH / g or more, and more preferably in the range of 120 to 230 mgKOH / g.

(Weight average molecular weight of water-soluble polymer)
The weight average molecular weight of the water-soluble polymer is preferably in the range of 10,000 to 40,000, and preferably in the range of 25,000 to 40,000.

(Method for producing water-soluble polymer)
The water-soluble polymer is obtained by a polymerization reaction in a solvent known in the industry. In order to dissolve the water-soluble polymer in the aqueous medium, a polymerization reaction is finally performed using an aqueous pigment dispersion or a water-soluble organic solvent contained in the inkjet ink. Thereafter, water and a basic compound are added to neutralize to make it aqueous, but the water-soluble organic medium is not removed, and the premixing and dispersion treatment described below is performed as it is.

  The water-soluble polymer is preferably contained in the aqueous pigment dispersion in an amount of 3.8 to 8.6% by mass or less, and more preferably 5 to 6% by mass.

<Water>
Next, water used in the present invention will be described.
The water suitable for forming the aqueous pigment dispersion of the present invention is preferably ion-exchanged water (deionized water), not general water containing various ions. The water content is in the range of 10% by mass to 90% by mass, more preferably 30% by mass to 80% by mass, based on the total mass of the aqueous pigment dispersion.

<Basic compound>
Next, the basic compound used in the present invention will be described.
Basic compounds include metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, organic waters such as ammonia water, dimethylaminoethanol, diethanolamine, and triethanolamine, and mixtures of these. Can be used.
The basic compound is used to stabilize the dispersion of the pigment particles in the aqueous pigment dispersion by neutralizing the carboxyl group in (meth) acrylic acid, which is a constituent monomer of the water-soluble polymer. The aqueous pigment dispersion is preferably adjusted to be neutral or alkaline. However, if the alkalinity is too strong, it may cause corrosion of various members used in the ink jet recording apparatus. Therefore, the pH is preferably in the range of 7 to 10.

<Water-soluble organic solvent>
Next, the water-soluble organic solvent used in the present invention will be described.
Examples of the water-soluble organic solvent include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, and n-pentanol. Alkyl alcohols, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol mono Propyl ether, triethylene glycol monopro Oxyethylene or oxypropylene addition polymers such as ether, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, ethylene glycol, propylene glycol, trimethylene glycol, trieryrene glycol, butylene glycol, 1,2 Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms, such as hexanediol, 1,2,6-hexanetriol, hexylene glycol, glycerin, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1, Examples include 3-dimethyl-2-imidazolidinone.
The water-soluble organic solvent may be an aqueous organic solvent finally contained in the pigment dispersion or inkjet ink, but it should be highly soluble in the water-soluble polymer, preferably propylene glycol or triethylene glycol. Examples thereof include monomethyl ether and 2-pyrrolidone.

  The content of the aqueous organic solvent in the aqueous pigment dispersion is in the range of 3% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 15% by mass or less of the total mass of the aqueous pigment dispersion. It is a range.

<Pigment>
Next, the pigment used in the present invention will be described.
In the present invention, the following pigments can be used. First, examples of the black pigment that can be used in the present invention include carbon black produced by a furnace method and a channel method. For example, these carbon blacks have a primary particle diameter of 11 to 40 nm, a specific surface area by BET method of 50 to 400 m ² / g, a volatile content of 0.5 to 10% by mass, a pH value of 2 to 10 and the like. Those having characteristics are preferred.

  Examples of cyan pigments that can be used in the present invention include C.I. I. Pigment Blue 1, 2, 3, 15: 3, 15: 4, 15: 6, 16, 22, C.I. I. Vat Blue 4, 6 etc. are mentioned. Examples of magenta pigments include C.I. I. Pigment Red 5, 7, 12, 31, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, quinacridone solid solution, 147, 150, 269, C.I. I. Pigment Violet 19 etc. are mentioned. Examples of yellow pigments include C.I. I. Pigment Yellow 1, 2, 3, 13, 16, 74, 83, 109, 128, 155 and the like. In addition, pigments of colors other than those described above can also be used, and in that case, any pigment may be used alone in each color aqueous pigment dispersion, or two or more pigments may be mixed. Of course, the present invention is not limited to these. In addition to the above, newly manufactured pigments such as self-dispersing pigments can also be used.

  The pigment is preferably in the range of 10 to 30% by mass, more preferably 15 to 25% by mass in the aqueous pigment dispersion.

<Inkjet ink>
As a method for producing an inkjet ink, first, a pigment is added to an aqueous medium in which water is at least mixed with a water-soluble polymer solubilized with a basic compound, and after mixing and stirring, a dispersion means described later is used. The desired pigment dispersion is obtained by carrying out a dispersion treatment and performing a centrifugal separation treatment if necessary. Next, a water-soluble organic solvent or an appropriately selected additive component as listed above is added to the pigment dispersion as necessary, and the mixture is stirred and filtered as necessary to obtain an inkjet ink. . However, the manufacturing method of an inkjet ink is not limited to this.
The ink-jet ink contains the aqueous pigment dispersion of the present invention, and further contains water or a water-soluble organic solvent so that the pigment content is 3 to 4% by mass.

  In the ink jet ink production method, a pigment dispersion obtained by carrying out a dispersion treatment is used for the preparation of the ink jet ink, but it is effective to perform premixing before the dispersion treatment carried out during the preparation of the pigment dispersion. Is. That is, premixing may be performed by adding a pigment to an aqueous medium in which at least a water-soluble polymer and water are mixed. Such a premixing operation is preferable because it improves wettability of the pigment surface and promotes adsorption of the dispersant onto the pigment surface.

  The disperser used in the pigment dispersion treatment may be any disperser that is generally used, and examples thereof include a ball mill, a roll mill, a sand mill, a bead mill, and a nanomizer. Among these, a bead mill is preferably used. Examples of such include a super mill, a sand grinder, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all are trade names).

  Further, in the pigment premixing and dispersion treatment, the water-soluble polymer may be dissolved only in water or may be dissolved in a mixed solvent of an aqueous organic solvent and water. In particular, in the dispersion treatment, as described above, when the water-soluble polymer is dissolved or dispersed in the mixed solvent of the aqueous organic solvent and water used as the synthesis solvent for the water-soluble polymer, the dispersion process is more stable during the dispersion treatment process. You may be able to get a body.

  Since the inkjet ink is used for inkjet recording, it is preferable to use a pigment having an optimum particle size distribution. That is, in order to enable the ink-jet ink containing the pigment particles to be suitably used in the ink-jet recording method, it is preferable to use a pigment having an optimum particle size distribution in view of demands such as nozzle clogging resistance. Examples of a method for obtaining a pigment having a desired particle size distribution include the following methods. Reduce the size of the grinding media of the disperser as mentioned above, increase the filling rate of the grinding media, increase the processing time, classify with a filter or centrifuge after grinding, etc. There are methods such as a combination of these methods.

<Other additives>
The ink-jet ink can be used in combination with a natural resin such as rosin, shellac, starch, or a synthetic resin that is not the water-soluble polymer as described above. In this case, the natural resin or the synthetic resin can be contained so as not to exceed the amount of the dispersion resin described above.

  In addition to the above components, the ink-jet ink may be appropriately added with additives such as surfactants, antifoaming agents, preservatives, etc., in order to obtain an ink-jet ink having desired physical properties as required. Can do. Examples of the amount of these additives added are 0.05% by mass or more and 10% by mass or less, and preferably 0.2% by mass or more and 5% by mass or less with respect to the total mass of the ink.

  Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto. In Examples and Comparative Examples, “part” and “%” mean “part by mass” and “% by mass”, respectively, unless otherwise specified.

Moreover, in the following examples, the weight average molecular weight is 2 gels permeation chromatography (GPC) “HLC-8320GPC” manufactured by Tosoh Corporation, and two “TSK-GELAM” manufactured by Tosoh Corporation are used as separation column fillers. This is a value in terms of polystyrene measured by using one “TSK-GELA-2500” connected in series and N, N-dimethylformamide containing 30 mM LiBr and 30 mM H ₃ PO ₄ in the mobile phase.

  First, the manufacture example of the water-soluble polymer used for the Example and the comparative example is shown.

<Production of water-soluble polymer>
(Production Example 1) Production of water-soluble polymer 1 A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 312.3 parts of propylene glycol and replaced with nitrogen gas. The inside of the reaction vessel is heated to 110 ° C., 51.3 parts of acrylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 223.7 parts of benzyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 2-hydroxy as a hydroxyl group-containing (meth) acrylic acid ester Ethyl acrylate (manufactured by Kishida Chemical Co., Ltd., hereinafter referred to as 2-HEA) 25 parts, polyethylene glycol (meth) acrylic acid ester M-90G (manufactured by Shin-Nakamura Chemical Co., Ltd., general formula (1) R1 = CH ₃ , R2 = CH ₃ , corresponding to n = 9) and 33.3 parts, and a mixture of 5 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator of an azoester compound having no nitrile group, was taken over 2 hours. The copolymerization reaction was carried out dropwise. After completion of the dropwise addition, the internal temperature was further maintained at 110 ° C., and 1 and 2 hours later, V-601 was added one by one and the reaction was continued. The reaction was further continued at 110 ° C. for 1 hour, and then the solution was cooled to 25 ° C. A portion of this was taken and dried by heating at 180 ° C. for 20 minutes, and the nonvolatile content in the solution was measured. A 10% potassium hydroxide (purity 85%: manufactured by Wako Pure Chemical Industries, Ltd.) aqueous solution is added to the cooled reaction solution so that the solution pH becomes 8.5, and the non-volatile content of the dispersion resin 1 becomes 20%. Water was added. As a result, a solution of water-soluble polymer 1 having a nonvolatile content of 20% was obtained. The weight average molecular weight of the water-soluble polymer 1 was 35,500, and the acid value was 120 mgKOH / g.

(Production Examples 2 to 16)
Except having changed into the monomer and polymerization initiator which are respectively shown in Table 1, operation similar to manufacture example 1 was performed and the water-soluble polymers 2-16 were manufactured. The acid value and weight average molecular weight of the obtained water-soluble polymer are shown together in Table 1. In Table 1, “AIBN” represents azobisisobutyronitrile, and “%” represents mass% of each constituent monomer with respect to the total amount of monomers constituting the water-soluble polymer. However, for Production Example 5, the first addition amount of V-601 was changed to 33.3 parts, and for Production Example 6, the first addition amount of V-601 was changed to 3.3 parts. Manufactured in the same manner as in Production Example 1.

Example 1 Production of Black Aqueous Pigment Dispersion 55.3 parts of the water-soluble polymer solution obtained in Production Example 1 was charged into a glass bottle, and 300.2 parts of water and 10% aqueous potassium hydroxide solution were added therein. It added so that pH might be 8.75, the resin was melt | dissolved using the ultrasonic cleaner (the Yamato Kagaku company make, 2510J-DTH), and the aqueous medium was obtained. Subsequently, Surfinol 104E (antifoaming agent, manufactured by Air Products Japan) 1.0 part, Proxel GXL (preservative, manufactured by Avisia) 1.0 part, carbon black as a pigment (# 850, manufactured by Mitsubishi Chemical Corporation) After adding 114.3 parts and pre-dispersing with a spatula, 937.5 parts of zirconia beads having a diameter of 1.0 mm were charged as dispersion media, and main dispersion was performed with a paint shaker to obtain a black aqueous pigment dispersion 1 It was. At this time, the ratio of the non-volatile content of the pigment and the water-soluble polymer 1 is pigment / dispersion resin (non-volatile content) = 8/2 (mass ratio).

(Examples 2-11, Comparative Examples 1-6)
Except having changed the water-soluble polymer 1 into the water-soluble polymers 2 to 17 shown in Table 2, respectively, the same operation as in Example 1 was performed, and the black aqueous pigment dispersions 2 to 11 and the comparative black aqueous pigment dispersions 1 to 1 were performed. 6 was produced.

(Examples 12-22, Comparative Examples 7-12)
Except having changed into the water-soluble polymer and pigment shown in Table 3, respectively, operation similar to Example 1 was performed and the cyan aqueous pigment dispersions 1-11 and the comparative cyan aqueous pigment dispersions 1-6 were manufactured. In Table 3, Pigment Blue 15: 3 was Lionol Blue FG-7351 (Toyo Color Co., Ltd.).

(Examples 23 to 33, Comparative Examples 13 to 18)
Magenta aqueous pigment dispersions 1 to 11 and comparative magenta aqueous pigment dispersions 1 to 6 were produced in the same manner as in Example 1 except that the water-soluble polymer and the pigment shown in Table 4 were respectively changed. In Table 4, Pigment Red 122 was Lionogen Magenta ID120 (Toyo Color Co., Ltd.).

(Examples 34 to 44, Comparative Examples 19 to 24)
A yellow aqueous pigment dispersions 1 to 11 and comparative yellow aqueous pigment dispersions 1 to 6 were produced in the same manner as in Example 1 except that the water-soluble polymer and the pigment shown in Table 5 were respectively changed. In Table 5, Pigment Yellow 74 was Lionogen Yellow 0380 (manufactured by Toyocolor Co., Ltd.).

(Measurement of viscosity of aqueous pigment dispersion)
The aqueous pigment dispersion prepared above was diluted by adding water to prepare a sample having 20% pigment and 5.7% water-soluble polymer (nonvolatile content) based on the total amount of the aqueous pigment dispersion. The viscosity of this sample was measured using a BL type viscometer (manufactured by Nihon Riken Kikai Co., Ltd.) under the conditions of 25 ° C. and a rotational speed of 60 rpm.

(Median diameter of the cumulative volume of aqueous pigment dispersion)
The prepared aqueous pigment dispersion was diluted by adding water so that the loading index value of the laser dynamic light scattering method (manufactured by Nikkiso Co., Ltd., UPA150EX) was within the range of 0.8 to 1.2. The median diameter (D50) of the cumulative volume at ° C was measured.

(Storage stability of aqueous pigment dispersion)
The prepared aqueous pigment dispersion was stored in a thermostat at 60 ° C. for 1 week. The respective viscosities before and after storage at 60 ° C. for 1 week were measured, and the change rate (%) of the viscosity after storage with respect to the storage before storage was calculated to be the storage stability. The closer the value of change rate is to 0 (zero), the better the storage stability.

The above results are shown in Tables 6-9.
It can be seen that each of the polymers used in the examples has a median diameter of a cumulative volume smaller than that of the polymer used in the comparative example, and an aqueous pigment dispersion having good storage stability is obtained. A polymer that does not contain styrene as a constituent monomer has a flexible structure, and is considered to be due to efficient pigment adsorption. In addition, a polymer having a small weight average molecular weight is inferior in pigment adsorbing ability, whereas a polymer having a large weight average molecular weight is likely to be entangled with a long polymer chain. . In addition, the polymer used in the comparative example is considered to have poor storage stability because it is inferior in dispersion stabilizing effect due to charge repulsion after neutralization, steric hindrance and the like.

(Example 45) Production of black inkjet ink Black aqueous pigment dispersion 1 was mixed with 3.8 parts, 2.5 parts of glycerin, 2.5 parts of ethylene glycol, 1.0 part of ethanol, and 15.2 parts of water, A black inkjet ink 1 was produced.

(Examples 46-55, Comparative Examples 25-30)
A black inkjet ink was prepared by performing the same operation as in Example 45 except that the black aqueous pigment dispersion 1 was changed to black aqueous pigment dispersions 2 to 11 and comparative black aqueous pigment dispersions 1 to 6 shown in Table 10, respectively. 2-11, comparative black inkjet inks 1-6 were produced.

(Examples 56 to 66, Comparative Examples 31 to 36) Manufacture of cyan inkjet inks The same operations as in Example 45 were performed except that the aqueous pigment dispersions shown in Table 11 were respectively changed, and cyan inkjet inks 1 to 11, Comparative cyan inkjet inks 1-6 were prepared.

Example 67 Production of Magenta Inkjet Ink Magenta aqueous pigment dispersion 1 was mixed with 5.0 parts, 2.5 parts glycerin, 2.5 parts ethylene glycol, 1.0 part ethanol, and 14.0 parts water. Magenta inkjet ink 1 was produced.

(Examples 68 to 77, Comparative Examples 37 to 42)
Except that the magenta aqueous pigment dispersion 1 was changed to the magenta aqueous pigment dispersions 2 to 11 and comparative magenta aqueous pigment dispersions 1 to 6 shown in the table, the same operation as in Example 67 was performed, and the magenta inkjet ink 2 11. Comparative magenta inkjet inks 1-6 were produced.

(Example 57) Manufacture of yellow inkjet ink Except having changed to the water-based pigment dispersion shown in Table 13, respectively, operation similar to Example 67 was performed, and yellow inkjet ink 1-11 and comparative yellow inkjet ink 1-6 were changed. Manufactured.

(Redispersibility of inkjet ink)
Spectral spectra were measured for a solution obtained by diluting the prepared ink-jet ink with water 2000 times on a mass basis, and measurement wavelengths corresponding to the colors of each ink (black: 550 nm, cyan: 617 nm, magenta: 534 nm, yellow: 430 nm). ) Was defined as A.
Separately, a part of the ink-jet ink is collected in a test tube, dried and solidified at 120 ° C., and then the same amount of water volatilized by drying is added to the solidified product. The spectrum was measured, and the absorbance at the measurement wavelength corresponding to the color of each ink was defined as B.
The respective absorbances obtained above were calculated according to the following formula, and used as the redispersibility of the inkjet ink. This redispersibility is an evaluation that serves as an index of the ejection stability of an inkjet nozzle during inkjet printing. That is, in inkjet printing, since inkjet ink is intermittently ejected from the inkjet nozzle, the inkjet ink is dried and re-dispersed (re-dissolved) at the nozzle tip. Therefore, poor re-dispersibility results in ejection failure. For this reason, evaluation by this method was performed as an index of ejection stability. A larger numerical value indicates better redispersibility.

Redispersibility = B / A x 100 (%)

When this value is 85% or more, A (very good), 70-84.9% as B (good, no practical problem), and less than 70% as C (defective, practical problem).

(Image density of printed matter)
The prepared ink-jet ink is coated on glossy paper (Canon Gold paper) using an automatic bar coater (RK PRINTCOAT INSTRUMENTS, K CONTROL COATER) and bar (manufactured, wet film thickness 12 μm), dried, and printed for testing. Got.
In order to evaluate the image density of the printed matter, an OD value was measured using a reflection densitometer (D19C, manufactured by GRETAGMACBETH). The larger the value, the better.
In black and cyan ink-jet inks, this value is 3.0 or higher for A (very good), 2.5 to 2.9 for B (good, practically no hindrance), and less than 2.5 for C (poor, practical) There was a hindrance).
In magenta and yellow ink-jet inks, this value is 2.0 or higher as A (very good), 1.5 to 1.9 as B (good, no practical problem), and less than 1.5 as C (bad, practical) There was a hindrance).

(Image gloss of printed matter)
Using the gloss meter (Nippon Denshoku Kogyo Co., Ltd., VG2000), the gloss at an angle of 60 ° of Japan Collaborative Standard (JIS) Z8741 was measured. The larger the value, the better.
In black inkjet ink, this value is 90.00 or higher as A (very good), 70.00 to 89.99 as B (good, no practical problem), and less than 70.00 as C (defective, practical problem) ).
In cyan and magenta ink-jet inks, this value is 70.00 or higher as A (very good), 60.00 to 69.99 as B (good, no practical problem), and less than 60.00 as C (defective, practical) There was a hindrance).
For yellow inkjet inks, this value is 55.00 or higher for A (very good), 45.00 to 54.99 for B (good, no practical problems), and less than 45.00 for C (poor, practical problems) ).

The evaluation criteria for the above results are shown in Tables 14 to 16, and the results are summarized in Tables 17 to 20.
All of the ink-jet inks described in the examples are excellent in redispersibility, image density, and image gloss, and it can be seen that the polymer used in the examples does not contain styrene. This is considered to promote the flexible structure of the polymer and improve the pigment adsorptivity and hydrophilicity.
It can be seen that the polymer used in the comparative example contains styrene and the ratio of benzyl methacrylate is smaller than that of the example. From this, contrary to the discussion of the examples, it is considered that the dispersibility is low and the image density and the image gloss are inferior. Moreover, it is thought that it is low in water solubility and inferior in redispersibility.
Moreover, it turns out that the polymer used for a comparative example has the ratio of the hydrophilic group of acrylic acid and polyethyleneglycol (meth) acrylic acid ester small compared with the thing of an Example. From this, it is thought that water solubility became low and it led to the fall of redispersibility.
Ink-jet ink using a high acid value polymer with a high acrylic acid ratio was inferior in image density and image gloss. Since this increases the solubility in water, it is considered that the proportion of the free resin in which the pigment adsorbing group does not function is increased and the dispersibility is lowered.

Claims (7)

  At least water, a water-soluble polymer as a pigment dispersion resin, a basic compound, a water-soluble organic solvent, and a pigment, wherein the water-soluble polymer includes benzyl methacrylate, acrylic acid and polyethylene glycol (meth) acrylic acid as constituent monomers Ester is included, styrene is not included, and benzyl methacrylate is 50 to 68% by mass, acrylic acid is 10 to 16% by mass, polyethylene glycol (meth) acrylic acid ester is 40% by mass with respect to the total amount of monomers constituting the water-soluble polymer. An aqueous pigment dispersion for inkjet inks, characterized by:   The aqueous pigment dispersion for inkjet ink according to claim 1, wherein the water-soluble polymer has an acid value of 120 mgKOH / g or more and a weight average molecular weight (Mw) of 10,000 to 40,000. The aqueous pigment dispersion for inkjet ink according to claim 1 or 2, wherein the polyethylene glycol (meth) acrylic acid ester is a polyethylene glycol (meth) acrylic acid ester represented by the following general formula (1).

Formula _{(1) CH 2 = C (} -R1) -COO (CH 2 -CH 2 -O) n-R2

[Wherein, R 1 and R 2 each independently represent H or CH ₃ , and n represents an integer of 1 to 23. ]   The aqueous pigment dispersion for inkjet ink according to any one of claims 1 to 3, wherein the water-soluble polymer is a water-soluble polymer obtained by polymerizing an azo ester compound not containing a nitrile group as a polymerization initiator.   The water-based pigment for inkjet ink according to any one of claims 1 to 4, wherein the water-soluble polymer is a water-soluble polymer obtained by polymerizing a monomer and then adding a basic compound and water to the reaction mixture. Dispersion.   Containing 15 to 25% by mass of pigment and 5.0 to 6.0% by mass of water-soluble polymer with respect to the total amount of the aqueous pigment dispersion for inkjet ink, the viscosity at 25 ° C. measured by a BL type viscometer is 18 mPa · The aqueous pigment dispersion for inkjet ink according to any one of claims 1 to 5, which is s or less.   The aqueous pigment dispersion for inkjet ink according to any one of claims 1 to 6, wherein a median diameter (D50) of cumulative volume measured by a laser dynamic light scattering method is 150 nm or less.