JP2002121446A - Ink composition - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A water-based ink for inkjet recording,
Provided is an aqueous ink composition having excellent continuous ejection stability and good print image characteristics on a recording medium. An ink comprising an aqueous dispersion of colored resin particles coated with pigment particles by a film-forming resin contains 0.01 to 4% by mass of an alkylene oxide adduct of pentaerythritol, and preferably further contains acetylene. An ink composition containing a surfactant having a specific structure having a bond, and most preferably further containing a propylene oxide adduct of a lower alcohol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based ink for ink-jet recording, and more particularly to a water-based ink composition having excellent continuous ejection stability and good permeability to a recording medium.

[0002]

2. Description of the Related Art An ink jet recording ink excellent in dispersion stability, ejection stability and print quality is disclosed in JP-A-8-1.
JP 83920 proposes a recording aqueous ink containing colored resin particles comprising a microencapsulated colorant.

[0003]

However, when high-speed printing is performed with an ink jet printer using an ink comprising an aqueous dispersion of colored resin particles, the wettability of the surface of the colored resin particles or the inside of the resin film with an aqueous medium is high. Is insufficient, ink ejection becomes unstable due to the generation of air bubbles with insufficiently wet colored resin particles as nuclei, or the head material and ink in the print head are insufficiently wet,
Similarly, there has been a problem that ejection becomes unstable due to the effect of bubbles at the interface between the head material and the ink. In order to solve this problem, it is necessary to improve the wetting of the colored resin particles with the aqueous medium and the wetting between the ink and the head material. Furthermore, wetting of the ink and the recording medium is further improved by imparting ink permeability to the recording medium to improve the quick drying property of the recording medium, or to increase the dot diameter to improve the print quality. It needed to be improved.

[0004] On the other hand, various surfactants known to solve the above-mentioned problems, when used in large amounts, dissolve the resin coating the colored resin particles, destroy microcapsules, and cause non-ejection of ink. And the quality of printed images is degraded.

An object of the present invention is to provide a water-based ink for ink-jet recording, which has excellent continuous ejection stability and good print image characteristics on a recording medium.

[0006]

In order to solve the above-mentioned problems, the present invention provides a method of forming a pigment particle by using a film-forming resin, more preferably a film-forming resin having an acid group at least partially neutralized with a base. The present invention provides an ink composition containing a surfactant having an alkylene oxide adduct of pentaerythritol in an amount of 0.01 to 4% by mass in an ink comprising an aqueous dispersion of colored resin particles coated with a resin.

The alkylene oxide adduct of pentaerythritol of the present invention penetrates into the surface of the colored resin particles in the ink or the resin coating layer, and significantly enhances the affinity with the aqueous medium. Demonstrates the function of greatly improving wetting. As a result, the generation of air bubbles in the ink during high-speed printing is suppressed, extremely stable ejection is obtained, the ink droplets ejected and the recording medium are wet well, the dot diameter is widened with quick drying, and the printing quality is improved. It is possible to provide excellent printed matter.

The alkylene oxide adduct of pentaerythritol to be added to the ink composition of the present invention is obtained by adding an alkylene oxide to pentaerythritol by a known and publicly known means. The alkylene group of the alkylene oxide is derived from an ethylene group or a propylene group. And the average number of added moles is preferably from 1 to 12 moles. Examples of the alkylene oxide adduct of pentaerythritol include the compounds listed in the following table.

Compound No. Compound A-1 Ethylene oxide 4 mol adduct of pentaerythritol Compound A-2 Ethylene oxide 6 mol adduct of pentaerythritol Compound A-3 Ethylene oxide 8 mol adduct of pentaerythritol Compound A-4 Pentaerythritol Adduct of 4 mol of ethylene oxide and 2 mol of propylene oxide

If the content of the pentaerythritol alkylene oxide adduct is too small, the effect of addition is small. If the content is too large, the film-forming resin coating the colored resin particles of the present invention is dissolved to break capsules. In addition, non-discharge of ink and clogging of nozzles are liable to occur, and the resin coverage of the pigment is reduced, and the vividness of the printed matter is reduced. Therefore, in the ink of the present invention, the content of the pentaerythritol alkylene oxide adduct needs to be 0.01 to 4% by mass.

A surfactant having an acetylene bond can be used in combination with the ink composition of the present invention. The surfactant having an acetylene bond promotes the penetration of the colored resin particles of the alkylene oxide adduct of pentaerythritol into the resin coating layer, and significantly enhances the affinity with the aqueous medium over the alkylene oxide adduct of pentaerythritol alone. Accordingly, a function of greatly improving the wetting between the ink and the print head is exhibited. As a result, the generation of air bubbles in the ink during high-speed printing is suppressed, extremely stable ejection is obtained, the ink droplets ejected and the recording medium are wet well, the dot diameter is widened with quick drying, and the printing quality is improved. It is possible to provide excellent printed matter.

The surfactant having an acetylene bond of the present invention includes, for example, a compound represented by the following general formula (1):

[0013]

Embedded image (1) (wherein, R ¹ , R ² , R ³ and R ⁴ each independently represent an alkyl group having 1 to 5 carbon atoms, an alkoxyl group, an alkylene group, a phenyl group and a phenyl group having a substituent. And the sum of n and m is in the range of 0 to 6.)
The compound represented by these is mentioned.

Specific examples of the compound represented by the general formula (1) include the compounds listed in the following table. However, the value of m + n is represented by the average number of moles added. Further, i in the table represents iso.

[0015]

[Table 1]

In the ink composition of the present invention, a propylene oxide adduct of a lower alcohol may be used in combination. By using a propylene oxide adduct of a lower alcohol in combination, it is possible to improve the stability of ink ejection and the permeability of the ink to a recording medium.

The propylene oxide adduct of a lower alcohol which can be used in combination with the ink composition of the present invention is represented by the following general formula (2):

[0018]

Embedded image (2) (wherein, R represents an alkyl group having 1 to 6 carbon atoms,
n represents an integer of 1 to 20. ).

Specific examples of the compound represented by the general formula (2) include the compounds listed in the following table. However, the value of n is represented by the average number of moles added.

[0020]

[Table 2]

The content of the surfactant having an acetylene bond in the ink is preferably in the range of 0.01 to 2% by weight,
The range of 0.05 to 1.0% by weight is particularly preferred. Furthermore, the content of the lower alcohol propylene oxide adduct in the ink when the lower alcohol propylene oxide adduct is used in combination is 0.01 to 20.0% by weight.
Is preferable, and the range of 0.5 to 10.0% by weight is particularly preferable.

The surface tension of the ink obtained varies greatly depending on the content of an alkylene oxide adduct of pentaerythritol, a surfactant having an acetylene bond, and a propylene oxide adduct of a lower alcohol, but the surface tension is 28.0 to 40. By adjusting the amount to be within the range of 0.0 mN / m, an ink having excellent ejection stability can be obtained, and the quality of printed matter due to an increase in permeability to a recording medium can be improved.

The pigment used in the ink of the present invention is not particularly limited, and examples thereof include inorganic pigments such as carbon black, titanium black, titanium white, zinc sulfide, and red iron oxide; phthalocyanine pigments, monoazo pigments, and disazo pigments. Organic pigments such as azo pigments, phthalocyanine pigments and quinacridone pigments.

As the film-forming resin used in the ink of the present invention, any known and commonly used water-soluble film-forming resin can be used. More preferably, it has self-water dispersibility. Any conventional resin obtained by modifying a water-insoluble film-forming resin to have self-water dispersibility can be used. Therefore, the resin has an acid value of 50 to 280 (resin 1).
g of KOH required to neutralize g). Such a film-forming resin is not particularly limited, and examples thereof include an acrylic resin, a maleic resin, and a polyester resin.

Among them, generally, styrene- (meth)
Acrylic resins are preferred, for example, substituted styrenes such as styrene or α-methylstyrene, acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and methacrylic acid. At least one monomer unit selected from methacrylic acid esters such as acid methyl ester, methacrylic acid ethyl ester, methacrylic acid butyl ester, and 2-ethylhexyl methacrylate; and at least one monomer selected from acrylic acid and methacrylic acid And a unit. At least a part of these copolymers may be covalently crosslinked or ionically crosslinked by a polyvalent metal.

When a film-forming resin having an acid value is used as a self-water-dispersible resin, it is necessary that at least a part of the acid groups be neutralized with a base. The base, that is, the alkaline neutralizing agent, can be added to such an extent that the obtained self-water dispersible resin does not dissolve in water.

Examples of the base include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide and lithium hydroxide; basic substances such as ammonia, triethylamine and morpholine; triethanolamine, diethanolamine and N-methyldiethanolamine. And alcohol amines such as

The neutralization rate with a base is not necessarily limited, but it is preferable to neutralize 40 mol% or more of the acid value of the film-forming resin having an acid value. Neutralization rate of 4
When the content is 0 mol% or more, the obtained colored resin particles are fine particles and have excellent dispersion stability, and thus are preferable.

The proportion of the colored resin particles in the ink of the present invention is preferably such that it becomes 0.5 to 20% by weight in the aqueous ink finally obtained.
Those having an average particle size of less than 1 μm on the order of submicrons are preferred. This can be obtained by known and conventional means.

The method for producing the colored resin particles of the present invention is not particularly limited, but a more preferable method using a film-forming resin having an acid group at least partially neutralized with a base is as follows. This is a method including the following steps (1) to (3).

(1) A resin coloring step in which at least a pigment is dispersed or dissolved in a resin having an acid value to obtain a solid coloring compound.

(2) At least water, an organic solvent capable of dissolving the resin, a base, and the solid coloring compound obtained in the resin coloring step are mixed, and a colorant suspension in which at least a part of the resin is dissolved by dispersion. A suspension step for obtaining a liquid.

(3) A reprecipitation step of depositing a dissolved resin on the surface of the pigment in the colorant suspension obtained in the suspension step.

The resin coloring step (1) is a step in which at least a pigment is dispersed or dissolved in a resin having an acid group, preferably a carboxyl group, to obtain a solid coloring compound. In this step, for example, using a known kneading device such as a roll, kneader, or bead mill, the pigment is uniformly dissolved or dispersed in the resin in a solution or a heated and melted state, and finally the solid kneading is performed. It can be carried out by taking it out as a product (solid colored compound).

In the suspension step (2), at least
This is a step of mixing water, an organic solvent for dissolving the resin, a base, and the solid coloring compound obtained in the resin coloring step, and obtaining a colorant suspension in which at least a part of the resin is dissolved by dispersion. The solid coloring compound obtained in the resin coloring step (1) is added to water, an organic solvent dissolving the resin, and a mixed solvent containing a base as a dispersion medium, and the mixture is stirred so as to be uniformly dispersed. From the surface of the solid colored compound, the resin containing the pigment is dissolved or self-emulsified with the help of an organic solvent and a base, and in each case, a colorant suspension in which at least a part of the resin is dissolved Is obtained.

As a stirring method for obtaining a suspension, any known and commonly used method can be employed. For example, in addition to a conventional uniaxial propeller-type stirring blade, a stirring blade having a shape suitable for the purpose or a stirring blade may be used. It can be easily suspended using a container.

In obtaining a suspension, there is no or relatively small shearing force, simple mixing and stirring alone, or if the pigment is relatively easily agglomerated, in addition to this, and then under high shearing force The dispersion may be further stabilized. As a dispersing machine in this case, a high-pressure homogenizer, a beadless dispersing machine known under the trade name of a microfluidizer or a nanomizer is preferably used because reaggregation of the pigment is small.

The reprecipitation step (3) is a step of depositing a dissolved resin on the surface of the pigment in the colorant suspension obtained in the suspension step. In the present invention, "re-precipitation" does not mean that the pigment or the coloring agent in which the dissolved resin is adsorbed on the surface of the pigment is separated and settled from the liquid medium of the suspension. Therefore, what is obtained in this step is not a mere mixture in which the solid component and the liquid component are clearly separated, and the coloring agent in which the dissolved resin is adsorbed on the pigment surface is stable in the liquid medium of the suspension. This is an aqueous dispersion of colored resin particles dispersed in water.

The deposition of the dissolved resin on the surface of the pigment in the colorant suspension in the suspension step (2) can be performed, for example, by adding the resin to the colorant suspension in which the resin is dissolved at least partially. On the other hand, it can be easily carried out by a method in which water or an aqueous medium functioning as a poor solvent is added, and / or a method in which an organic solvent is removed from a colorant suspension.

By removing the co-existing organic solvent from the aqueous dispersion of colored resin particles thus obtained, a stable aqueous dispersion of pigmented resin particles contained by the resin can be obtained.

In the above-mentioned production method, an organic solvent that dissolves a resin having a carboxyl group is used, and this functions as a good solvent for the resin.
Such an organic solvent can be appropriately selected for the resin, for example, a ketone solvent such as acetone, dimethyl ketone, and methyl ethyl ketone; an alcohol solvent such as methanol, ethanol, and isopropyl alcohol; chloroform, methylene chloride Chloride solvents such as benzene; aromatic solvents such as benzene and toluene; ester solvents such as ethyl acetate; glycol ether solvents such as ethylene glycol monomethyl ether and ethylene glycol dimethyl ether; amides.

When the resin is styrene, substituted styrene,
In the case of a copolymer of a composition containing at least one monomer selected from the group consisting of (meth) acrylic esters and (meth) acrylic acid, a ketone-based solvent such as methyl ethyl ketone is mainly used, and isopropyl is used as a co-solvent. At least one combination selected from alcohol solvents such as alcohols is preferable.

Since the above aqueous medium is mainly used as jet ink, in order to avoid nozzle clogging,
Water of a grade equal to or higher than ion-exchanged water is preferred. The aqueous medium in the present invention refers to a liquid medium containing water as a main component.

In such an aqueous medium, a water-soluble organic solvent for preventing drying as an ink for ink jet recording is preferably used in combination as a drying inhibitor. As such an anti-drying agent, an agent having an effect of preventing drying of the ink at the ejection nozzle of the ink jet is used, and an agent having a boiling point higher than that of water is usually used.

The anti-drying agent is not particularly limited, and any conventionally known anti-drying agent can be used without any particular limitation. Examples of such anti-drying agents include polyhydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol, and glycerin; pyrrolidones such as N-methyl-2-pyrrolidone and 2-pyrrolidone; amides; dimethyl sulfoxide; And imidazolidinone.

The water-based ink composition of the present invention may optionally contain additives such as a water-soluble resin, a pH adjuster, a preservative, and a chelating agent.

The water-based ink composition of the present invention can be used as it is, but is preferably filtered so as not to contain coarse particles of 1 μm or more, more preferably to not contain coarse particles exceeding 0.5 μm. Filtration is preferably performed mainly using colored resin fine particles on the order of submicrons.

[0048]

The present invention will be described below in more detail with reference to examples and comparative examples. In the following examples, “parts” means “parts by mass” unless otherwise specified.

<Preparation Example 1> (Preparation Example of Colored Resin Particle Aqueous Dispersion) 20 parts of carbon black and a styrene-acrylic acid-methacrylic acid resin (styrene / acrylic acid / methacrylic acid = 77/10/13; molecular weight: 50,000) An acid value of 160 and a glass transition temperature of 107 ° C.) A kneaded product obtained by kneading 20 parts with a two-roll mill is composed of 210 parts of water, 35 parts of glycerin, 8 parts of triethanolamine, 90 parts of methyl ethyl ketone and 40 parts of isopropyl alcohol. The mixture was stirred in a mixed solution at room temperature for 3 hours to obtain a colorant suspension.

While stirring the resulting suspension, a mixture of 30 parts of glycerin and 210 parts of water was dropped at a rate of 5 ml / min to obtain an aqueous dispersion of black colored resin particles. Methyl ethyl ketone, isopropyl alcohol and a part of water were distilled off from the obtained aqueous dispersion using a rotary evaporator to obtain an aqueous dispersion of black colored resin particles (1) having a pigment content of 14% by weight.

<Preparation Example 2> (Preparation Example of Aqueous Dispersion of Colored Resin Particles) Cyan coloration was carried out in the same manner as in Preparation Example 1, except that a copper phthalocyanine pigment was used instead of carbon black. An aqueous resin particle dispersion (2) was obtained.

(Example 1) 30.0 parts of the aqueous dispersion of colored resin particles (1) obtained in Preparation Example 1 was mixed with 13.2 parts of glycerin,
1.0 part of 4-mol pentaerythritol ethylene oxide adduct (compound A-1), 0.1 part of surfactant having acetylene bond (compound B-4), 7.0 parts of propylene glycol propyl ether (compound C-1) Parts and 48.7 parts of ion-exchanged water, and then mixed to obtain an aqueous ink for inkjet recording.

The colored resin particles (microcapsules) in the obtained aqueous ink have an average particle size of 89.1 nm, have no aggregates, exhibit stable dispersibility over a long period of time, have a viscosity of 3.30 mPa · s, Surface tension 33.8mN /
m having physical properties of m.

Solid printing using a piezo-type ink jet printer (MJ8000C manufactured by Seiko Epson) was very stable, and continuous printing of 15 m or more on roll paper of 420 mm width was possible without nozzle clogging. Also,
When solid printing was performed on plain paper (PPC paper) using the obtained ink, a uniform and less uneven printed image was obtained.

Comparative Example 1 In Example 1, compound A
-1, A water-based ink for ink-jet recording was prepared in the same manner as in Example 1 except that Compound B-4 was not used and the amount of ion-exchanged water was 49.8 parts.

The colored resin particles in the obtained aqueous ink had an average particle diameter of 89.0 nm, had no aggregates, exhibited stable dispersion over a long period of time, had a viscosity of 3.26 mPa · s, and a surface tension of 35.0 mN / m. Met.

Solid printing using a piezo ink jet printer (MJ8000C manufactured by Seiko Epson)
Some of the nozzles did not discharge when printing continuously for 30 cm on roll paper having a width of 420 mm due to unstableness. Further, when solid printing was performed on plain paper (PPC paper) using the obtained ink, a usable print image was barely obtained although it was slightly uneven and uneven.

(Comparative Example 2) In Example 1, compound A
A water-based ink for ink-jet recording was prepared in the same manner as in Example 1 except that the amount of -1 was increased by 5 parts and the amount of ion-exchanged water was decreased by 5 parts.

The colored resin particles in the obtained aqueous ink have an average particle diameter of 100.0 nm, have no aggregates, exhibit stable dispersion for a long period of time, have a viscosity of 3.26 mPa · s, and a surface tension of 32.0 mN / m. Met.

Solid printing using a piezo ink jet printer (MJ8000C manufactured by Seiko Epson)
Immediately after continuous printing on roll paper having a width of 420 mm, the nozzle was slightly unstable, causing some nozzles to fail to discharge, and the nozzles were often clogged. Further, when solid printing was performed on plain paper (PPC paper) using the obtained ink, a good printed image with uniform and less unevenness was obtained.

[0061]

[Table 3]

◎ indicates excellent, は indicates good, Δ indicates acceptable, and × indicates unacceptable. (Evaluation items must all be △ or more)

Example 2 25.0 parts of the aqueous dispersion of colored resin particles (2) obtained in Preparation Example 2 were mixed with 24.2 parts of glycerin,
1.0 part of a pentaerythritol ethylene oxide 6 mol adduct (compound A-2), 0.1 part of a surfactant having an acetylene bond (compound B-3), 4 parts of propylene glycol propyl ether (compound C-1), After adding to an aqueous solution consisting of 1 part of propylene glycol butyl ether (compound C-2) and 44.7 parts of ion-exchanged water, they were mixed to obtain an aqueous ink for inkjet recording.

The colored resin particles (microcapsules) in the obtained aqueous ink had an average particle size of 147.7 nm, had no aggregates, exhibited stable dispersibility over a long period of time, had a viscosity of 3.58 mPa · s, Surface tension 31.1mN /
m having physical properties of m.

Solid printing using a piezo-type ink jet printer (MJ8000C manufactured by Seiko Epson Corporation) was extremely stable, and continuous printing of 15 m or more on a roll paper of 420 mm width was possible without nozzle clogging. Also,
When solid printing was performed on plain paper (PPC paper) using the obtained ink, a good printed image with uniform and less unevenness was obtained.

(Comparative Example 3) In Example 2, compound A
-2, a water-based ink for ink-jet recording was prepared in the same manner as in Example 2, except that Compound B-3 was not used and that the amount of ion-exchanged water was 45.7 parts.

The colored resin particles in the obtained aqueous ink had an average particle diameter of 145.8 nm, had no aggregates, exhibited stable dispersion over a long period of time, had a viscosity of 3.34 mPa · s and a surface tension of 32.8 mN / m. Met.

Solid printing using a piezo type ink jet printer (MJ8000C manufactured by Seiko Epson) is as follows.
Some of the nozzles did not discharge when continuous printing was performed for 30 cm on a roll paper of 420 mm width, which was somewhat unstable, but there was no nozzle clogging. Further, when solid printing was performed on plain paper (PPC paper) using the obtained ink, a usable print image was barely obtained although it was slightly uneven and uneven.

(Comparative Example 4) In Example 2, compound A
A water-based ink for ink-jet recording was prepared in the same manner as in Example 2 except that the amount of -2 was increased by 7 parts and the amount of ion-exchanged water was reduced by 7 parts.

The colored resin particles in the obtained aqueous ink had an average particle size of 150.5 nm, had no aggregates, exhibited stable dispersion for a long period of time, had a viscosity of 4.00 mPa · s, and a surface tension of 30.8 mN / m. Met.

Solid printing using a piezo-type ink jet printer (MJ8000C manufactured by Seiko Epson) was somewhat unstable, and some nozzles failed to discharge immediately after continuous printing on 420 mm wide roll paper, and the nozzles were often clogged. . When solid printing was performed on plain paper (PPC paper) using the obtained ink, a non-uniform and less uneven printed image was obtained.

[0072]

[Table 4]

◎ indicates excellent, は indicates good, Δ indicates acceptable, and × indicates unacceptable. (Evaluation items must all be △ or more)

From the results shown in Tables 4 and 5, it can be seen that the aqueous ink composition according to the present invention can provide a high-quality printed image and has excellent ejection stability.

[0075]

The ink composition of the present invention, when used for an ink jet printer, has excellent ejection stability and can provide a high quality printed image.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 FC01 FC02 2H086 BA55 BA59 BA60 4J039 AD03 AD09 AD10 AD14 AE06 BA04 BA13 BC12 BC13 BC39 BC40 BC60 BE01 BE12 BE22 CA06 DA01 DA02 EA44 EA46 EA47 GA24

Claims (6)

[Claims] 1. An ink comprising an aqueous dispersion of colored resin particles coated with pigment particles by a film-forming resin, comprising 0.01 to 4% by mass of an alkylene oxide adduct of pentaerythritol. Ink composition. 2. The ink composition according to claim 1, wherein the film-forming resin is a film-forming resin having an acid group at least partially neutralized with a base. 3. The ink composition according to claim 1, wherein the alkylene oxide adduct of pentaerythritol is a 2 to 12 mol adduct of ethylene oxide or propylene oxide. 4. A compound represented by the following general formula (1): (1) (wherein, R ¹ , R ² , R ³ and R ⁴ each independently represent an alkyl group having 1 to 5 carbon atoms, an alkoxyl group, an alkylene group, a phenyl group and a phenyl group having a substituent. And the sum of n and m is in the range of 0 to 6.)
The ink composition according to claim 1, further comprising a surfactant having an acetylene bond represented by the following formula: 5. The ink composition according to claim 1, further comprising a propylene oxide adduct of a lower alcohol. 6. The ink has a surface tension of 28.0 to 40.0.
The ink composition according to any one of claims 1 to 5, wherein the ink composition is in a range of mN / m.