JP4815791B2 - Aqueous pigment dispersion and ink composition for ink jet recording - Google Patents

Description

  The present invention relates to an aqueous pigment dispersion using a red-orange pigment and an ink composition for ink jet recording using the pigment dispersion.

Water-based inks can reduce toxicity such as fire hazard and mutagenicity like oil-based inks, and are therefore mainstream in inkjet recording applications other than industrial applications.
As such a water-based ink, a dye has been used as a colorant because it has high stability, has low nozzle clogging, and has good color development and enables high-quality printing. There was a problem that it was inferior in water resistance and light resistance.

In order to solve this problem, conversion from dyes to pigments has been actively pursued. Although pigment ink can be expected to have excellent water resistance and light resistance, nozzle clogging due to aggregation and sedimentation of the pigment is a problem. Therefore, a method of dispersing a pigment in an aqueous medium using a polymer dispersant has been studied.
In particular, in recent years, color reproduction of printed images using inks with colors such as orange, red, green, and violet in addition to the four colors of black, cyan, magenta, and yellow that have been used for multicolor printing in the past. Attempts have been made to improve the properties, and there is a demand for pigment inks for ink-jet recording having good chroma and gloss while satisfying dispersion stability and ejection properties for many colors.

Conventionally, it has been difficult to ensure long-term storage stability, ejection stability, high saturation, and high gloss using a red-orange pigment-dispersed aqueous inkjet recording ink. In particular, the red-orange pigment dispersion system has difficulty in developing gloss, and for example, a pigment dispersion-based aqueous inkjet recording ink using Pigment Orange 16 has been studied (see Patent Document 1). However, with regard to saturation, the excellent properties inherent to pigments are likely to appear, but with regard to the gloss that is affected by the dispersion stability of the pigment during drying, the resin as a dispersant for each pigment is optimized to achieve high dispersion stability. It needs to be realized. However, such examination has not been made, and sufficient gloss is not yet obtained.
JP 2002-363455 A

In order to obtain high gloss of printed matter, it is necessary to reduce the particle size of the pigment and the stability in the liquid, but that is not enough, and in the drying process, aggregation is suppressed as much as possible and it is extremely stable. It is necessary to disperse the pigment, and such characteristics must be exhibited without impairing high saturation, ejection stability, and long-term storage stability.
An object of the present invention is to provide a red-orange aqueous pigment dispersion that exhibits high chroma and high gloss while having ejection stability and long-term storage stability.

The present applicant, in view of such a situation, as a result of intensive studies, found that a pigment dispersion containing a red-orange pigment having a specific structure and a resin having a specific configuration as a component can achieve the above-described problems, The present invention has been reached.
That is, the present invention is an aqueous pigment dispersion containing (a) a red-orange pigment, (b) a styrene-acrylic acid copolymer, (c) an alkali metal hydroxide, and (d) a wetting agent, (B) The styrene-acrylic acid copolymer has a styrene monomer unit of 60% by mass or more based on the total monomer components, an acid value of 50 to 300, and a weight average molecular weight of 7500 to 40,000. ) The pigment is an aqueous pigment dispersion characterized by being Pigment Orange 16 having a volume average particle size of 80 nm or less.

  The aqueous pigment dispersion of the present invention has a high chroma due to the use of Pigment Orange 16 by using a combination of the above-mentioned specific monomer composition, acid value, and styrene-acrylic acid copolymer having a molecular weight and Pigment Orange 16. And excellent discharge stability and good long-term storage stability due to the combination of the resin and the pigment. In addition, Pigment Orange 16 used in the present invention has a very stable dispersibility in which the particle size is fine and when used in combination with the resin, the initial particle size is maintained even during the drying process and aggregation is suppressed. As a result, it exhibits excellent gloss.

The pigment (a) used in the present invention is CI Pigment Orange 16, and the average particle size obtained by observation with an electron microscope is 80 nm or less. When the particle diameter exceeds 80 nm, the gloss of the printed material becomes insufficient.
The (b) styrene-acrylic acid copolymer used in the present invention contains at least styrene and at least one of acrylic acid and methacrylic acid as constituent monomers, and preferably contains all of styrene, acrylic acid and methacrylic acid. In the resin component monomer composition ratio, the ratio of the styrene monomer component to the total monomer components is 60% by mass or more, and preferably 90% by mass or less. In particular, the sum of the styrene monomer component, the acrylic acid monomer component, and the methacrylic acid monomer component is preferably 95% by mass or more based on the total monomer components.
If the amount of styrene monomer component is less than 60% by mass, the affinity of (b) styrene acrylic acid copolymer to (a) pigment will be insufficient, and dispersion stability will tend to decrease, and the resulting ink jet The plain paper recording characteristics using the recording ink composition tend to deteriorate, the image recording density tends to decrease, and the water resistance characteristics also tend to decrease. When the amount of the styrene component is more than 90% by mass, the solubility of the (b) styrene acrylic acid copolymer in the aqueous medium decreases, and the dispersibility and dispersion stability of the pigment in the aqueous pigment dispersion tend to decrease. Printing stability when applied to ink for ink jet recording tends to decrease.

The acid value of (b) styrene acrylic acid copolymer used in the aqueous pigment acid separation liquid of the present invention is 50 to 300. When the acid value is less than 50, the hydrophilicity becomes small and the dispersion stability of the pigment tends to be lowered. On the other hand, when the acid value is greater than 300, the aggregation of the pigment tends to occur, and the water resistance of the printed matter using the ink composition tends to decrease. The acid value is preferably from 60 to 250, more preferably from 70 to 200.
(b) Styrene acrylic acid copolymer is preferably used in combination with acrylic acid and methacrylic acid as constituent monomers, because the random copolymerization during resin synthesis is improved and the solubility of the resin is improved.

  (b) The styrene acrylic acid copolymer may contain less than 5% by mass of a component that can be polymerized with these monomers other than styrene, acrylic acid, and methacrylic acid. Examples of such monomers include styrene derivatives such as α-methylstyrene and vinyltoluene; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (Meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-methylbutyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, 3-methylbutyl (meth) acrylate, 1,3-dimethyl (Meth) acrylic acid such as butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, and nonyl (meth) acrylate Esters; 2-ethoxyethyl acrylate, 3-ethoxypropyl acrylate 2-ethoxybutyl acrylate, 3-ethoxybutyl acrylate, dimethylaminoethyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, ethyl-α- (hydroxymethyl) ) Acrylates, (meth) acrylate derivatives such as methyl-α- (hydroxymethyl) acrylate; aryl (meth) acrylates such as phenyl (meth) acrylate, benzyl (meth) acrylate, phenylethyl (meth) acrylate Esters and (meth) acrylic acid aralkyl esters; diethylene glycol, triethylene glycol, polyethylene glycol, glycerol, polyhydric alcohols such as bisphenol A, mono (meth) acrylic esters of polyphenols; Mention may be made, for example, of dialkyl maleates and dialkyl maleates such as diethyl maleate. One or more of these monomers can be added as monomer components.

The weight average molecular weight of the (b) styrene acrylic acid copolymer used in the present invention is in the range of 75,00 to 40,000. The weight average molecular weight is preferably in the range of 7,500 to 30,000, more preferably in the range of 10,000 to 25,000. When the weight average molecular weight is less than 7,500, (a) it is easy to reduce the initial dispersion size of the pigment, but the long-term storage stability of the dispersion tends to deteriorate, and precipitation due to aggregation of the pigment occurs. There is a case.
(b) When the weight average molecular weight of the styrene acrylic acid copolymer exceeds 40,000, the viscosity of the ink for ink jet recording prepared from the aqueous pigment dispersion using the styrene acrylic acid copolymer increases, and the ejection stability of the ink is impaired. It tends to be.

  The (b) styrene acrylic acid copolymer used in the present invention may be any of a random copolymer, a block copolymer, and a graft copolymer. As the graft copolymer, a copolymer of polystyrene or a nonionic monomer copolymerizable with styrene and styrene is used as a trunk or branch, and a copolymer of acrylic acid, methacrylic acid and other monomers including styrene is branched. Or the graft copolymer used as a trunk can be shown as the example. (b) The styrene acrylic acid copolymer may be a mixture of the above-mentioned copolymer and a random copolymer.

  In the aqueous pigment dispersion of the present invention, the content of (b) styrene acrylic acid copolymer is preferably 10 to 50 parts by mass, and 20 to 40 parts by mass with respect to 100 parts by mass of (a) pigment. Is more preferable. (b) When the content of the styrene acrylic acid copolymer is less than 10 parts by mass, the dispersion stability of the aqueous pigment dispersion decreases, and when the aqueous pigment dispersion is used for an inkjet recording ink, the friction resistance is increased. When the amount exceeds 50 parts by mass, the viscosity of the ink for inkjet recording tends to be too high.

Examples of the alkali metal hydroxide (c) used in the present invention include sodium hydroxide, potassium hydroxide, lithium hydroxide and the like, and potassium hydroxide is particularly preferable. The amount of (c) alkali metal hydroxide added is in the range of 80 to 120% as the neutralization rate based on the acid value of (b) styrene acrylic acid copolymer.
Setting the neutralization rate to 80% or more improves the dispersion rate in the aqueous medium and the dispersion stability. It is preferable from the viewpoint of storage stability. Also, from the viewpoint of preventing gelation during long-term storage, it is preferable that the printed matter prepared from the ink composition has a water resistance of 120% or less.

As the (d) wetting agent used in the present invention, known and conventional ones can be used. For example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1 , 3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, trimethylolpropane, pentaerythritol and other polyols, 2 -Pyrrolidone, N-methyl-2-pyrrolidone, lactams such as ε-caprolactam, 1,3-dimethylimidazolidine and the like.

The content of the (d) wetting agent in the aqueous pigment dispersion of the present invention is preferably 3 to 50% by mass, and more preferably 5 to 40% by mass. If it is less than this lower limit, the drying prevention effect tends to be insufficient, and if it exceeds the above upper limit, the dispersion stability of the dispersion tends to decrease.

As a method for preparing the aqueous pigment dispersion of the present invention, the following method can be employed.
(1) (b) Styrene acrylic acid copolymer, (c) Alkali metal hydroxide, (d) Wet agent and water are added to an aqueous medium, and after (a) pigment is added, a stirring / dispersing device is used. (A) A method of preparing an aqueous pigment dispersion by dispersing a pigment in the aqueous medium.
(2) (a) Pigment, (b) Styrene acrylic acid copolymer, and if necessary, kneading the organic solvent using a kneader such as a two-roll, Henschel mixer, planetary mill, etc. A method of preparing an aqueous pigment dispersion using a stirring / dispersing device by adding the product to an aqueous medium containing water and (c) an alkali metal hydroxide and (d) a wetting agent.
(3) To the solution obtained by dissolving (b) styrene acrylic acid copolymer in water-compatible organic solvent such as methyl ethyl ketone, tetrahydrofuran, etc., (a) after adding the pigment, stirring and A dispersion apparatus is used to produce a mixture in which (a) the pigment is dispersed in an organic solvent, and then the mixture is phase-inverted and emulsified using (c) an aqueous medium containing an alkali metal hydroxide, and then A method of preparing an aqueous pigment dispersion by distilling off the organic solvent.

  Examples of the agitation / dispersion device include an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a roll mill, a sand mill, a sand grinder, a dyno mill, a disperse mat, an SC mill, and a nanomizer. May be used alone, or two or more kinds of devices may be used in combination.

The ink composition for inkjet recording of the present invention can be prepared by a conventional method using the aqueous pigment dispersion.
When an ink composition for ink jet recording is prepared using the aqueous pigment dispersion of the present invention, the following treatments (i) to (v) and additives can be used depending on the purpose of improvement and adjustment.
(i) Since coarse particles cause nozzle clogging and other image characteristics to deteriorate, it is preferable to carry out a process of removing coarse particles by centrifugal separation or filtration after ink preparation.
(ii) For the purpose of preventing ink drying, the (d) wetting agent exemplified above can be added in the same manner. The content of (d) a wetting agent in the ink for the purpose of preventing drying is preferably 3 to 50% by mass.

(iii) A penetrant can be added for the purpose of improving the permeability to the recording medium and adjusting the dot diameter on the recording medium.
Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.
The penetrant content in the ink is preferably 0.01 to 10% by mass.

(iv) A surfactant can be added to adjust ink characteristics such as surface tension. The surfactant that can be added for this purpose is not particularly limited, and examples include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Of these, anionic surfactants and nonionic surfactants are preferred.

  Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, higher alcohol ether. Sulfate salts and sulfonates of the above, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. Specific examples include dodecylbenzene sulfonate, isopropyl naphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, dibutylphenylphenol disulfate. , And the like salts.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkyl alkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, Polyethylene glycol polypropylene glycol block copolymer, etc. Among them, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid Preference is given to alkylolamide, acetylene glycol, oxyethylene adducts of acetylene glycol and polyethylene glycol polypropylene glycol block copolymers.

  Other surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Biosurfactants such as spicrispolic acid, rhamnolipid, lysolecithin and the like can also be used.

These surfactants can be used alone or in combination of two or more.
In consideration of the dissolution stability of the surfactant, the HLB is preferably in the range of 7-20.
When a surfactant is added, the addition amount is preferably in the range of 0.001 to 1% by mass, more preferably in the range of 0.001 to 0.5% by mass, and in the range of 0.01 to 0.2% by mass with respect to the total mass of the ink. More preferably it is. When the addition amount of the surfactant is less than 0.001% by mass, the effect of the addition of the surfactant tends not to be obtained, and when it exceeds 1% by mass, problems such as blurring of the image are likely to occur.

(v) A preservative, a viscosity adjuster, a pH adjuster, a chelating agent, a plasticizer, an antioxidant, an ultraviolet absorber and the like can be added as necessary.

The amount of (a) pigment in the aqueous pigment dispersion of the present invention is preferably 5 to 25% by mass, and more preferably 5 to 20% by mass. (a) When the amount of the pigment is less than 5% by mass, the ink for inkjet recording prepared from the aqueous pigment dispersion of the present invention is insufficiently colored, and a sufficient image density tends not to be obtained. On the other hand, when the amount is more than 25% by mass, the dispersion stability of the pigment tends to decrease in the aqueous pigment dispersion.
The amount of the (a) pigment in the ink composition for ink jet recording prepared from the aqueous pigment dispersion of the present invention is necessary to obtain a sufficient image density and to ensure the dispersion stability of the pigment in the ink. Further, the content is preferably 2 to 10% by mass.

Hereinafter, the present invention will be described in more detail with reference to examples.
In the following synthesis examples, examples and comparative examples, “parts” and “%” represent “parts by mass” and “mass%”.

<Synthesis Example 1>
100 parts of methyl ethyl ketone was charged into a reaction vessel having a stirrer, a dropping device, and a reflux device, and the inside of the reaction vessel was purged with nitrogen while stirring. The reactor was heated to a methyl ethyl ketone reflux state while maintaining a nitrogen atmosphere, and then 77 parts of styrene, 10 parts of acrylic acid, 13 parts of methacrylic acid and a polymerization catalyst (made by Wako Pure Chemical Industries, Ltd./“V- 59 ") 8 parts of the mixture was added dropwise over 2 hours. In the middle of dropping, the temperature of the reaction system was kept at 80 ° C.
After completion of the dropwise addition, the reaction was continued for another 20 hours at the same temperature. In the course of the reaction, a polymerization catalyst was added as appropriate while confirming the consumption of the raw materials. After completion of the reaction, the reaction mixture was allowed to cool and methyl ethyl ketone was added to obtain a solution of a styrene-acrylic acid copolymer (A-1) having an anionic group with a solid concentration of 50%. This styrene-acrylic acid copolymer (A-1) had an acid value of 140 mgKOH / g, a glass transition point of 107 ° C. (calculated value), and a weight average molecular weight of 7,300.
The weight average molecular weight in the present invention is a value measured by a GPC (gel / permeation / chromatography) method.

In accordance with the production method of Synthesis Example 1, the following styrene acrylic acid copolymer was synthesized by adjusting the monomer type, the monomer blending amount, and the reaction conditions.
<Synthesis Example 2>
Styrene / acrylic acid copolymer having a monomer composition ratio of styrene / acrylic acid / methacrylic acid = 77/10/13 (mass ratio), a weight average molecular weight of 20000, an acid value of 151 mgKOH / g, and a glass transition point of 107 ° C. A-2).

<Synthesis Example 3>
Styrene / acrylic acid copolymer having a monomer composition ratio of styrene / acrylic acid / methacrylic acid = 77/10/13 (mass ratio), a weight average molecular weight of 5000, an acid value of 150 mgKOH / g, and a glass transition point of 107 ° C. A-3).

<Synthesis Example 4>
Styrene / acrylic acid copolymer having a monomer composition ratio of styrene / acrylic acid / methacrylic acid = 77/10/13 (mass ratio), a weight average molecular weight of 45,000, an acid value of 153 mgKOH / g, and a glass transition point of 107 ° C. A-4).

<Synthesis Example 5>
Styrene having a monomer composition ratio of styrene / methyl methacrylate / acrylic acid / methacrylic acid = 50/27/10/13 (mass ratio), a weight average molecular weight of 12,000, an acid value of 149 mgKOH / g, and a glass transition point of 107 ° C. Acrylic acid copolymer (A-5).

< Reference Example 1>
<Preparation of aqueous pigment dispersion>
While stirring 100 g of a methyl ethyl ketone solution containing 50% of the styrene-acrylic acid copolymer (A-1) obtained in Synthesis Example 1 as a solid content concentration, 125 ml of a commercially available 1N KOH aqueous solution and 75 ml of ion-exchanged water were added to this solution. Was added to neutralize the styrene-acrylic acid copolymer (A-1). After distilling off methyl ethyl ketone under reduced pressure, ion exchange water was added to obtain an aqueous solution (B-1) containing a styrene-acrylic acid copolymer (A-1) having a solid concentration of 20%.
Next, a container having a capacity of 250 ml was charged with the following composition, and then dispersed using a paint conditioner for 4 hours. After completion of the dispersion treatment, 11.5 parts of ion exchange water was further added, and then the zirconia beads were separated by filtration to obtain an aqueous pigment dispersion having a pigment concentration of 14.5%.
Styrene-acrylic acid copolymer aqueous solution (B-1) 15 parts
CI Pigment Orange 16 (trade name Symler Fast Orange V "Dainippon Ink Chemical Co., Ltd.") 10 parts Diethylene glycol 20 parts Ion-exchanged water 20 parts Zirconia beads (1.25 mm diameter) 400 parts

<Example 2>
Instead of the acrylic acid copolymer (A-1), a styrene - - styrene of Reference Example 1 except for using the acrylic acid copolymer (A-3) in the same manner as in Reference Example 1, an aqueous pigment dispersion Obtained.

<Comparative Example 1>
<Preparation of aqueous pigment dispersion>
A container having a capacity of 250 ml was charged with the following composition, and then dispersed for 4 hours using a paint conditioner. After the completion of the dispersion treatment, 11.5 parts of ion exchange water was further added, and then the zirconia beads were separated by filtration to obtain an aqueous pigment dispersion (C-2) having a pigment concentration of 14.5%.
John Crill 61 3 parts
CI Pigment Orange 16 (trade name Symler Fast Orange V "Dainippon Ink Chemical Co., Ltd.") 10 parts Diethylene glycol 20 parts Ion-exchanged water 32 parts Zirconia beads (1.25 mm diameter) 400 parts

<Comparative example 2>
In Reference Example 1, 10 parts of CI Pigment Orange 16 (trade name: Symuler Fast Orange V “Dainippon Ink Chemical Co., Ltd.”, average particle size = 60 nm) was added to CI Pigment Orange 36 (trade name: Symuler Fast Orange 4183H “ “Dainippon Ink Chemical Co., Ltd.”, average particle size = 100 nm) An aqueous pigment dispersion having a pigment concentration of 14.5% was obtained in the same manner as in Reference Example 1 except that 10 parts were used.

<Comparative Example 3>
In Reference Example 1, 10 parts of CI Pigment Orange 16 (trade name: Symuler Fast Orange V “Dainippon Ink Chemical Co., Ltd.”, average particle size = 60 nm) was added to CI Pigment Orange 43 (trade name: PV Fast Orange “Clariant”). “Obtained from Japan Co., Ltd.”, average particle diameter = 150 nm) An aqueous pigment dispersion having a pigment concentration of 14.5% was obtained in the same manner as in Reference Example 1 except that 10 parts were used.

<Comparative example 4>
In Reference Example 1, 10 parts of CI Pigment Orange 16 (trade name Symuler Fast Orange V “Dainippon Ink Chemical Co., Ltd.”, average particle size = 60 nm) were added to CI Pigment Red 242 (trade name Hostaperm Scarlet 4RF Clariant Obtained from Japan Co., Ltd. ”, average particle diameter = 140 nm) Except for the change to 10 parts, an aqueous pigment dispersion having a pigment concentration of 14.5% was obtained in the same manner as in Reference Example 1.

<Comparative Example 5>
In Reference Example 1, 10 parts of CI Pigment Orange 16 (trade name Symuler Fast Orange V “Dainippon Ink Chemical Co., Ltd.”, average particle size = 60 nm) was added to CI Pigment Red 177 (trade name Fastogen Super Red ATY- 01 “Dainippon Ink Chemical Co., Ltd.”, average particle size = 40 nm) An aqueous pigment dispersion having a pigment concentration of 14.5% was obtained in the same manner as in Reference Example 1, except that 10 parts were used.

<Comparative Example 6>
In the same manner as in Reference Example 1 except that the styrene-acrylic acid copolymer (A-2) was used instead of the styrene-acrylic acid copolymer (A-1) in Reference Example 1, an aqueous pigment dispersion was prepared. Obtained.

<Comparative Example 7>
Instead of the acrylic acid copolymer (A-1), a styrene - - styrene of Reference Example 1 except for using the acrylic acid copolymer (A-4) in the same manner as in Reference Example 1, an aqueous pigment dispersion Obtained.

<Comparative Example 8>
Instead of the acrylic acid copolymer (A-1), a styrene - - styrene of Reference Example 1 except for using the acrylic acid copolymer (A-5) in the same manner as in Reference Example 1, an aqueous pigment dispersion Obtained.

<Evaluation of ink suitability for inkjet recording (1)>
Using the aqueous pigment dispersion obtained in each of the examples and comparative examples, an ink for ink jet recording was prepared by the following composition.
Aqueous pigment dispersion 5.52 parts
2-pyrrolidinone 1.60 parts Triethylene glycol monobutyl ether 1.60 parts Surfinol 440 (Nisshin Chemical Industry Co., Ltd.) 0.10 parts Glycerin 0.60 parts Ion-exchanged water 10.58 parts After the prepared ink was filtered using a membrane filter with a pore size of 5 μm, Installed in the NOVA Jet PRO36 inkjet printer (manufactured by ENCAD) to evaluate inkjet recording suitability, that is, continuously print 100% image density on the 80% area range of A0 size paper, before and after printing Ink ejection characteristics were evaluated

.
Evaluation criteria for record aptitude (1):
○: No ejection failure was observed.
Δ: Abnormal ink discharge direction was observed after continuous printing, but no uneven printing density was observed.
X: After continuous printing, uneven printing density was observed, and an extreme decrease in printing density was observed.

<Evaluation of ink suitability for inkjet recording (2)>
Evaluation of ink suitability for ink jet recording (1) The ink prepared in the black cartridge position of the ink jet printer EM-930C (manufactured by EPSON) is used as a recording medium using Premiun Glossy Photo Paper (manufactured by Xerox) A 100% image density was recorded, and the saturation of the obtained image was measured by “SpectroScan” (Gretag Macbeth). In addition, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, and 100% image density are recorded, and the gloss of each obtained image is set to “micro-TRI-gloss”. (By BYK-Gardner) was measured at an angle of 20 °.

  Note that both the recording suitability (1) and the recording suitability (2) are the evaluation results when the image density was measured under the condition of the pigment concentration of 2%. The evaluation results are shown in Table 1 and FIG. The gloss values in Table 1 are values at an image density of 95%.

<Stability evaluation>
Ink prepared for inkjet recording ink suitability (1), the ink was allowed to stand for 4 weeks at a temperature of 70 ° C., and the particle size before and after the standing, the viscosity, and the state of occurrence of aggregates after standing were examined. The particle size before and after standing, the rate of change of viscosity, and the presence or absence of aggregates were evaluated as stability indicators. The results are shown in Table 1 below. The particle diameter was measured using “Microtrac UPA150” (manufactured by Leeds & Northrup), and the volume average particle diameter was measured as the particle diameter of the aqueous dispersion. The viscosity was measured at 25 ° C. using an E-type viscometer (TVE-20L, manufactured by Tokimec). The results are shown in Table 1.

  The aqueous pigment dispersion of the present invention comprises Pigment Orange 16, a styrene monomer having 60% by mass or more of a styrene monomer unit, an acid value of 50 to 300, and a weight average molecular weight of 7500 to 40,000 based on all monomer components. By combining the acrylic acid copolymer, the storage stability is excellent, and the ink for ink jet recording using the same is excellent in ejection stability and long-term storage stability, and gives high chroma and extremely high gloss. Those using pigments other than CI Pigment Orange 16 had insufficient storage stability, and in particular, the gloss did not reach that of Orange 16. Even when CI Pigment Orange 16 was used, when a styrene acrylic acid copolymer other than the above was used, the long-term storage stability and gloss were similarly insufficient. It is clear from FIG. 1 that the ink composition for ink jet recording comprising the aqueous pigment dispersion of the present invention forms a printed image with good gloss.

It is a figure showing the result of having measured the glossiness of the image produced by changing image density using the ink composition for inkjet recording which has the aqueous dispersion obtained in Reference Example 1 and Comparative Examples 1-5 as a main component. is there.

Claims (4)

(B) After adding the red-orange pigment to an aqueous medium composed of a styrene-acrylic acid copolymer, (c) an alkali metal hydroxide, (d) a wetting agent and water, a stirrer or a dispersing device is used. And (a) a method for producing an aqueous pigment dispersion in which a red-orange pigment is dispersed in the aqueous medium , wherein the (b) styrene-acrylic acid copolymer is 60% by mass or more based on the total monomer components. It contains a styrenic monomer component , an acrylic acid monomer component, and a methacrylic acid monomer component, and further has an acid value of 50 to 300 and a weight average molecular weight of 7500 to 40,000. A method for producing an aqueous pigment dispersion, which is Pigment Orange 16 having a diameter of 80 nm or less.   The method for producing an aqueous pigment dispersion according to claim 1, wherein the sum of the styrene monomer component, the acrylic acid monomer component, and the methacrylic acid monomer component is 95% by mass or more based on the total monomer components. 3. The aqueous pigment dispersion according to claim 1, wherein the addition amount of the (c) alkali metal hydroxide is a neutralization rate of 80 to 120% with respect to the (b) styrene-acrylic acid copolymer . Manufacturing method . Ink composition for ink jet recording obtained by using as a main component an aqueous pigment dispersion produced by the production method of the aqueous pigment dispersion according to any one of claims 1-3.

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