JP4581338B2 - Aqueous pigment dispersion and ink composition for ink jet recording - Google Patents

Description

【００５９】
表1から明らかなように、本発明の水性顔料分散液は、分散性に優れ、高温度での長期間放置でも粒径の増大が少なく、60℃条件下7日間の放置後の粒径の変化率が10%以下であり、また、同様に本発明の水性顔料分散液は粘度上昇が少なく、60℃条件下7日間の放置後の粘度の変化率が5%以下であり、且つ本発明の水性顔料分散液を用いて調製したインクジェット記録用インクはインクジェット記録適性に問題が認められないと同時に、普通紙上に記録を行った際に高い画像濃度が得られることが分かる。
これに対して、本発明の範囲外の水性顔料分散液では、60℃条件下7日間の放置後の粒径の変化率が10%を超えたり、60℃条件下7日間の放置後の粘度の変化率が5%を超えたりするか、あるいは本発明範囲外の水性顔料分散液を用いて調製したインクジェット記録用インクでは、インクジェット記録適性に問題が認められるか、または普通紙上に記録を行った際に画像濃度の低下が認められ、何らかの問題が存在する。
【００６０】
【発明の効果】
以上のように、本発明の水性顔料分散液は、保存安定性に優れ、これを用いてなるインクジェット記録用インクは、ノズル先端において、インクの乾燥による目詰まりが発生せず吐出安定性が良好であり、長期保存安定性が良好であり、普通紙上で高い画像濃度を得ることができるという特徴を有する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an aqueous pigment dispersion using a quinacridone pigment and an ink composition for ink jet recording using the pigment dispersion.
[0002]
[Prior art]
Water-based inks have excellent characteristics such as oil-based inks that have no or no toxicity such as fire hazard and mutagenicity, and as inks for inkjet recording other than industrial use, Water-based ink using water as a main solvent has become the mainstream of ink jet recording.
[0003]
The characteristics required for ink used in ink jet recording include: (1) a uniform image with high resolution and high density without bleeding on the recording medium, and (2) clogging due to ink drying at the nozzle tip. (3) Good drying properties of the ink on the recording medium, (4) Good image fastness, (5) Long-term storage stability The property is good.
[0004]
Conventionally, as a water-based ink for ink jet recording, a dye has been used as a colorant because it has high dissolution stability, has low nozzle clogging, has good color development, and enables high-quality printing. The dye has a problem that the image has poor water resistance and light resistance.
[0005]
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-based dispersant has been studied, but it is difficult to stably disperse the pigment over a long period of time, and the pigment has excellent long-term storage stability. Dispersed water-based ink jet recording inks are desired.
Conventionally, it has been difficult to ensure long-term storage stability of a magenta pigment-dispersed aqueous inkjet recording ink.
[0006]
In view of such a situation, the applicant of the present invention has previously described a quinacridone pigment, a phthalimidomethylated quinacridone compound or further a quinacridone sulfonic acid compound, and an anionic group-containing organic polymer having a glass transition point of −20 to 60 ° C. An aqueous pigment dispersion containing a molecular compound has been proposed (see, for example, Patent Document 1).
This aqueous pigment dispersion is excellent in dispersibility and dispersion stability, has a small increase in particle size even when left at high temperature for a long period of time, has a small increase in viscosity, and can be maintained in a low viscosity range, and has excellent printability.
[0007]
On the other hand, ink for inkjet recording is prepared by adding various additives such as a humectant, a penetrating agent, a viscosity adjusting agent, a pH adjusting agent, an antifungal agent to an aqueous pigment dispersion having a high colorant concentration, Long-term storage stability is required as in the case of the aqueous pigment dispersion.
Furthermore, ink for inkjet recording needs to obtain a uniform image with high resolution and high density without blurring when recording on a recording medium, and in particular has a dedicated receiving layer as a recording medium. In other words, it is important that no blurring occurs when so-called plain paper is used and the resolution of the image does not deteriorate.
For this reason, when plain paper is used as the recording medium, a method of increasing the color material concentration in the ink may be employed as a method for obtaining a high image density.
[0008]
[Patent Document 1]
JP 2000-191974 A
[0009]
[Problems to be solved by the invention]
However, when the color material concentration in the ink is increased, the storage stability as the ink tends to be lowered, and the increase in the measured particle diameter and the increase in the viscosity become remarkable. This is presumed to be due to an increase in the collision probability of the color material particles due to an increase in the color material concentration in the ink.
Therefore, it has been desired to provide an ink that has excellent storage stability and can obtain a higher image density, and an aqueous pigment dispersion that can produce such an ink.
Therefore, the present invention is excellent in dispersibility and dispersion stability, has a small increase in particle size even when left at high temperature for a long time, has excellent storage stability with little increase in viscosity, and has a high concentration when recorded on plain paper. It is an object of the present invention to provide an ink composition for ink-jet recording capable of obtaining a clear image, and an aqueous pigment dispersion capable of producing such an ink composition.
[0010]
[Means for Solving the Problems]
As a result of intensive studies on this problem, the present inventors have obtained a combination of (a) a quinacridone pigment, (b) a quinacridone compound having a substituent containing a phthalimide skeleton, and (c) a styrene acrylic resin having a specific configuration. The present inventors have found that the above problems can be achieved, and have reached the present invention.
[0011]
That is, the object of the present invention is at least (a) a quinacridone pigment, (b) a quinacridone compound having a substituent containing a phthalimide skeleton, and at least styrene, acrylic acid, methacrylic acid as a constituent monomer, and a constituent monomer composition ratio. The ratio of the styrene monomer component to the total monomer component is 60% by mass or more, and 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 component, and The resin has a weight average molecular weight of 7,500 to 30,000 in an aqueous pigment dispersion comprising (c) a styrene acrylic resin, (d) an alkali metal hydroxide, (e) a wetting agent, and (f) water. An object of the present invention is to provide an ink composition for ink-jet recording using a pigment dispersion.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
As the (a) quinacridone pigment used in the present invention, any known and commonly used pigments can be used. Specific examples include dimethylquinacridone pigments such as CI Pigment Red 122, CI Pigment Red 202, and Red 209. Examples thereof include dichloroquinacridone pigments, unsubstituted quinacridones such as CI Pigment Violet 19, and mixtures or solid solutions of at least two pigments selected from these pigments. The pigment may be a dry pigment in the form of powder, granule or block, or a wet cake or slurry.
Of the quinacridone pigments, CI Pigment Red 122 is preferably used.
[0013]
The (b) quinacridone compound having a substituent containing a phthalimide skeleton used in the present invention is a quinacridone compound having a substituent, and the phthalimide skeleton is included in a part of the structure of the substituent. Specific examples thereof include phthalimidomethylated quinacridone compounds, and phthalimidated methyl-3,10-dichloroquinacridone is particularly preferred.
This (b) quinacridone compound having a substituent containing a phthalimide skeleton is preferably used as a dispersion aid for improving the dispersion stability of the (a) quinacridone pigment in the aqueous pigment dispersion of the present invention.
[0014]
(b) The average number of phthalimide skeletons per molecule in a quinacridone compound having a substituent containing a phthalimide skeleton is preferably about 1 to 2, and more preferably about 1 to 1.5. If the number of skeletons is too small, the effect of the combined use of the (b) quinacridone compound having a substituent containing a phthalimide skeleton is hardly expressed, and if the number of skeletons is too large, the characteristics as a recording liquid, such as bleeding, are exhibited. There is a possibility of lowering.
[0015]
This (b) quinacridone compound having a substituent containing a phthalimide skeleton, for example, when this is a phthalimidomethylated quinacridone compound, contains unsubstituted quinacridone, dimethylquinacridone, dichloroquinacridone, etc. and phthalimide and formaldehyde or paraformaldehyde. It can be synthesized by reacting in sulfuric acid.
In the present invention, (b) the quinacridone compound having a substituent containing a phthalimide skeleton is not included in the (a) quinacridone pigment.
[0016]
In the present invention, the ratio of the (b) quinacridone compound having a substituent containing a phthalimide skeleton in the total of (a) a quinacridone pigment and (b) a quinacridone compound having a substituent containing a phthalimide skeleton, The content is preferably 1 to 20% by mass, and more preferably 2 to 15% by mass.
When the proportion of the quinacridone compound having a substituent containing the (b) phthalimide skeleton is less than 1% by mass, the combined use effect is hardly exhibited, and when it exceeds 20% by mass, the dispersion and the ink composition for inkjet recording are used. The storage stability of is extremely reduced.
[0017]
The (c) styrene acrylic resin used in the present invention comprises at least styrene, acrylic acid, and methacrylic acid as its constituent monomer, and in the resin constituent monomer composition ratio, the ratio of the styrene monomer component to the total monomer components is 60% by mass. 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, and the weight average molecular weight of the resin is in the range of 7,500 to 30,000. .
Here, the weight average molecular weight is a value measured by a GPC (gel / permeation / chromatography) method.
[0018]
In the constituent monomer composition of the (c) styrene acrylic resin, the amount of the styrene monomer component is 60% by mass or more, preferably 90% by mass or less, based on the total monomer components. If the amount of styrene monomer component is less than 60% by mass, the affinity of (c) styrene acrylic resin to (a) quinacridone pigment will be insufficient, and the dispersion stability tends 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. If the amount of styrene component is more than 90% by mass, the solubility of the (c) styrene acrylic resin in the aqueous medium tends to decrease, and the dispersibility and dispersion stability of the pigment in the aqueous pigment dispersion tend to decrease. There is a tendency that the printing stability when applied to the ink for printing is lowered.
[0019]
(c) The styrene acrylic resin comprises at least styrene, acrylic acid, and methacrylic acid as its constituent monomers, but by using acrylic acid and methacrylic acid together, the copolymerization during resin synthesis is improved, There is an effect that the uniformity of the resin is improved.
[0020]
(c) The styrene acrylic resin may contain less than 5% by mass of a component polymerizable 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; mono (meth) acrylic acid esters of polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, bisphenol A; dimethyl maleate And maleic acid dialkyl esters such as diethyl maleate. One or more of these monomers can be added as monomer components.
[0021]
The weight average molecular weight of the (c) styrene acrylic resin used in the present invention 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) the initial dispersion of the quinacridone pigment can be easily reduced in particle size, but the long-term storage stability of the dispersion tends to deteriorate, and precipitation due to aggregation of the pigment, etc. May occur.
(c) When the weight average molecular weight of the styrene acrylic resin exceeds 30,000, the viscosity of the ink for ink jet recording prepared from the aqueous pigment dispersion using the styrene acrylic resin tends to increase, and the ejection stability of the ink tends to become unstable. It is in.
[0022]
The (c) styrene acrylic resin used in the present invention may be a random copolymer or 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. (c) The styrene acrylic resin may be a mixture of the graft copolymer and the random copolymer.
[0023]
In the aqueous pigment dispersion of the present invention, the content of (c) styrene acrylic resin is 100 parts by mass in total of (a) quinacridone pigment and (b) quinacridone compound having a substituent containing a phthalimide skeleton. It is preferably 10 to 50 parts by mass, and more preferably 10 to 40 parts by mass. (c) When the content of the styrene acrylic resin 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 reduced. When the amount exceeds 50 parts by mass, the viscosity of the ink for ink jet recording tends to be too high.
[0024]
Examples of the (d) alkali metal hydroxide used in the present invention include sodium hydroxide, potassium hydroxide, lithium hydroxide and the like, and potassium hydroxide is particularly preferable. The amount of (d) alkali metal hydroxide added is in the range of 80 to 120% as the neutralization rate based on the acid value of (c) styrene acrylic resin.
[0025]
As the (e) wetting agent used in the present invention, known and commonly used 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.
[0026]
The content of the (e) 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.
[0027]
As a method for preparing the aqueous pigment dispersion of the present invention, the following method can be employed.
(1) An aqueous medium comprising (c) styrene acrylic resin, (d) alkali metal hydroxide, (e) wetting agent and (f) water contains (a) quinacridone pigment, (b) phthalimide skeleton A method of preparing an aqueous pigment dispersion by adding a quinacridone compound having a substituent and then dispersing (a) the quinacridone pigment in the aqueous medium using a stirring / dispersing device.
(2) (a) a quinacridone pigment, (b) a quinacridone compound having a substituent containing a phthalimide skeleton, and (c) a styrene acrylic resin are kneaded using a kneader such as a two-roll, mixer, etc. A method in which the kneaded product thus obtained is added to an aqueous medium containing (f) water, (d) alkali metal hydroxide, and (e) a wetting agent, and an aqueous pigment dispersion is prepared using a stirring / dispersing device.
(3) (a) a quinacridone pigment and (b) a phthalimide skeleton in a solution obtained by dissolving (c) a styrene acrylic resin in an organic solvent compatible with water such as methyl ethyl ketone and tetrahydrofuran. After adding the quinacridone compound having a substituent containing, (a) the quinacridone pigment is dispersed in the organic solution using a stirring / dispersing device, and then (d) an aqueous medium containing an alkali metal hydroxide is used. A method of preparing an aqueous pigment dispersion by distilling off the organic solvent after phase inversion emulsification.
[0028]
Examples of the agitation / dispersing 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.
[0029]
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 remove coarse particles by centrifugation or filtration after ink preparation.
(ii) For the purpose of preventing the ink from drying, the (e) wetting agent exemplified above can be added in the same manner. The content of (e) a wetting agent in the ink for the purpose of preventing drying is preferably 3 to 50% by mass.
[0030]
(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.
[0031]
(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.
[0032]
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.
[0033]
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 alkylol amide, 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 Preferred are alkylolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymer.
[0034]
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.
[0035]
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.
[0036]
(v) Preservatives, viscosity modifiers, pH adjusters, chelating agents, plasticizers, antioxidants, ultraviolet absorbers, and the like can be added as necessary.
[0037]
The amount of the (a) quinacridone 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 quinacridone 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) quinacridone pigment in the ink composition for ink jet recording prepared from the aqueous pigment dispersion of the present invention ensures the necessity of obtaining a sufficient image density and the dispersion stability of the pigment in the ink. Therefore, the content is preferably 2 to 10% by mass.
[0038]
【Example】
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%”.
[0039]
<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 mixture was allowed to cool and methyl ethyl ketone was added to obtain a solution of a styrene acrylic resin (A-1) having an anionic group with a solid concentration of 50%. This styrene acrylic resin (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.
[0040]
<Synthesis Example 2>
A styrene acrylic resin having an anionic group with an acid value of 148 mgKOH / g, a glass transition point of 107 ° C. (calculated value), and a weight average molecular weight of 11,000 (A--) except that the polymerization catalyst was changed to 5 parts. A solution containing 50% of 2) as a solid content concentration was obtained.
[0041]
<Synthesis Example 3>
Similar to Synthesis Example 1 except that 25 parts of styrene, 10 parts of acrylic acid, 13 parts of methacrylic acid, 52 parts of methyl methacrylate and 6 parts of polymerization catalyst were used, acid value 139 mg KOH / g, glass transition point 110 ° C. (calculated value) ), A solution containing 50% of a styrene acrylic resin (A-3) having an anionic group having a weight average molecular weight of 12,000 as a solid content concentration was obtained.
[0042]
<Synthesis Example 4>
73 parts of styrene, 10 parts of acrylic acid, 13 parts of methacrylic acid, 4 parts of styrene copolymer macromonomer having a methacryloyl group at one end (manufactured by Toagosei Co., Ltd./“AS-6S ”) as a solid content and a polymerization catalyst 5 The graft type styrene acrylic resin (A-4) having an anionic group having an acid value of 139 mgKOH / g, a glass transition point of 107 ° C. (calculated value), and a weight average molecular weight of 10,500, except that it is Was obtained as a solid content concentration.
[0043]
<Synthesis Example 5>
Similar to Synthesis Example 1 except that 50 parts of styrene, 10 parts of acrylic acid, 13 parts of methacrylic acid, 27 parts of butyl acrylate and 4 parts of polymerization catalyst were used, acid value 154 mg KOH / g, glass transition point 45 ° C (calculated value) ), A solution containing 50% of a styrene acrylic resin (A-5) having an anionic group having a weight average molecular weight of 12,000 as a solid content concentration was obtained.
[0044]
<Synthesis Example 6>
Except for 10 parts of acrylic acid, 13 parts of methacrylic acid, 50 parts of methyl methacrylate, 27 parts of butyl acrylate, and 10 parts of polymerization catalyst, the acid value was 138 mgKOH / g, the glass transition point was 46 ° C. ( Calculated value), a solution containing 50% of a styrene acrylic resin (A-6) having an anionic group having a weight average molecular weight of 12,000 as a solid content concentration was obtained.
[0045]
<Example 1>
<Preparation of aqueous pigment dispersion C-1>
While stirring 100 g of methyl ethyl ketone solution containing 50% of the styrene acrylic resin (A-1) obtained in Synthesis Example 1 as a solid content concentration, this solution was mixed with 125 ml of commercially available 1N KOH aqueous solution and 75 ml of ion-exchanged water. The solution was added to neutralize the styrene acrylic resin (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 resin (A-1) having a solid content 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 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-1) having a pigment concentration of 14.5%.
Styrene acrylic resin aqueous solution (B-1) 7.5 parts
CI Pigment Red 122 (Brand name Fastgen Super Magenta RTS "Dainippon Ink Chemical Co., Ltd.") 9.5 parts
Phthalimidomethylated 3,10-dichloroquinacridone (average number of phthalimidomethyl groups per molecule 1.4) 0.5 parts
Diethylene glycol 20 parts
20 parts of ion exchange water
Zirconia beads (1.25mm diameter) 400 parts
[0046]
<Example 2>
<Preparation of aqueous pigment dispersion C-2>
Example except that a mixture of 132 ml of 1N KOH aqueous solution and 68 ml of ion-exchanged water was added to 100 g of methyl ethyl ketone solution containing 50% of the styrene acrylic resin (A-2) obtained in Synthesis Example 2 as a solid content concentration In the same manner as in Example 1, an aqueous solution (B-2) containing a styrene acrylic resin (A-2) having a solid content concentration of 20% was obtained.
Next, a dispersion treatment was carried out in the same manner as in Example 1 except that (B-2) was used as the aqueous resin solution, to obtain an aqueous pigment dispersion (C-2) having a pigment concentration of 14.5%.
[0047]
<Example 3>
<Preparation of aqueous pigment dispersion C-3>
Using the aqueous solution (B-2) containing the styrene acrylic resin (A-2) obtained in Example 2, the following composition was charged and subjected to dispersion treatment in the same manner as in Example 1 to obtain a pigment having a pigment concentration of 14.5% An aqueous dispersion (C-3) was obtained.
Styrene acrylic resin aqueous solution (B-2) 15.0 parts
CI Pigment Red 122 (Brand name Fastgen Super Magenta RTS "Dainippon Ink Chemical Co., Ltd.") 9.5 parts
Phthalimidomethylated 3,10-dichloroquinacridone (average number of phthalimidomethyl groups per molecule 1.4) 0.5 parts
Diethylene glycol 20 parts
Ion exchange water 12.5 parts
Zirconia beads (1.25mm diameter) 400 parts
[0048]
<Example 4>
<Preparation of aqueous pigment dispersion C-4>
Using the aqueous solution (B-2) containing the styrene acrylic resin (A-2) obtained in Example 2, the following composition was charged and subjected to dispersion treatment in the same manner as in Example 1 to obtain a pigment having a pigment concentration of 14.5% An aqueous dispersion (C-4) was obtained.
Styrene acrylic resin aqueous solution (B-2) 7.5 parts
CI Pigment Red 122 (Brand name Fastgen Super Magenta RTS "Dainippon Ink Chemical Co., Ltd.") 9.25 parts
Phthalimidomethylated-3,10-dichloroquinacridone (average number of phthalimidomethyl groups per molecule 1.4) 0.75 parts
Diethylene glycol 20 parts
20 parts of ion exchange water
Zirconia beads (1.25mm diameter) 400 parts
[0049]
<Example 5>
<Preparation of aqueous pigment dispersion C-5>
Example except that a mixture of 124 ml of 1N KOH aqueous solution and 76 ml of ion-exchanged water was added to 100 g of methyl ethyl ketone solution containing 50% of the styrene acrylic resin (A-4) obtained in Synthesis Example 4 as a solid content concentration In the same manner as in Example 1, an aqueous solution (B-4) containing a styrene acrylic resin (A-4) having a solid content concentration of 20% was obtained.
Next, a dispersion treatment was performed in the same manner as in Example 1 except that (B-4) was used as the aqueous resin solution, to obtain an aqueous pigment dispersion (C-5) having a pigment concentration of 14.5%.
[0050]
<Comparative Example 1>
<Preparation of aqueous pigment dispersion C-6>
Example 1 except that a mixture of 137 ml of 1N KOH aqueous solution and 63 ml of ion-exchanged water was added to 100 g of methyl ethyl ketone solution containing 50% of the styrene acrylic resin (A-5) obtained in Synthesis Example 5 as a solid concentration. In the same manner as above, an aqueous solution (B-5) containing a styrene acrylic resin (A-5) having a solid concentration of 20% was obtained.
Next, a dispersion treatment was performed in the same manner as in Example 1 except that (B-5) was used as the aqueous resin solution, to obtain an aqueous pigment dispersion (C-6) having a pigment concentration of 14.5%.
[0051]
<Comparative example 2>
<Preparation of aqueous pigment dispersion C-7>
Example except that a mixture of 123 ml of 1N KOH aqueous solution and 63 ml of ion-exchanged water was added to 100 g of methyl ethyl ketone solution containing 50% of the styrene acrylic resin (A-6) obtained in Synthesis Example 6 as a solid content concentration In the same manner as in Example 1, an aqueous solution (B-6) containing a styrene acrylic resin (A-6) having a solid content concentration of 20% was obtained.
Next, a dispersion treatment was performed in the same manner as in Example 1 except that (B-6) was used as the aqueous resin solution, to obtain an aqueous pigment dispersion (C-7) having a pigment concentration of 14.5%.
[0052]
<Comparative Example 3>
<Preparation of aqueous pigment dispersion C-8>
Using the aqueous solution (B-1) containing the styrene acrylic resin (A-1) obtained in Example 1, the dispersion treatment was performed in the same manner as in Example 1 except that the composition having the following composition was used. An aqueous pigment dispersion (C-8) having a concentration of 14.5% was obtained.
Styrene acrylic resin aqueous solution (B-1) 7.5 parts
CI Pigment Red 122 (Brand name Fastgen Super Magenta RTS "Dainippon Ink Chemical Co., Ltd.") 10.0 parts
Diethylene glycol 20 parts
20 parts of ion exchange water
Zirconia beads (1.25mm diameter) 400 parts
[0053]
<Comparative example 4>
<Preparation of aqueous pigment dispersion C-9>
Example except that 100 g of methyl ethyl ketone solution containing 50% of the styrene acrylic resin (A-3) obtained in Synthesis Example 3 as a solid content concentration and a mixed solution of 124 ml of 1N KOH aqueous solution and 76 ml of ion-exchanged water were used. In the same manner as in Example 1, an aqueous solution (B-3) containing a styrene acrylic resin (A-3) having a solid content concentration of 20% was obtained.
Next, a dispersion treatment was performed in the same manner as in Example 1 except that (B-3) was used as the resin aqueous solution, to obtain an aqueous pigment dispersion (C-9) having a pigment concentration of 14.5%.
[0054]
<Stability evaluation>
The aqueous pigment dispersions obtained in each Example and Comparative Example were allowed to stand for 1 week under a temperature condition of 60 ° C., and the particle size before and after standing, the viscosity, and the state of occurrence of aggregates after standing were examined. The particle size before and after, the rate of change in 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).
[0055]
<Evaluation of ink suitability for inkjet recording (1)>
Using the aqueous pigment dispersions obtained in the respective Examples and Comparative Examples, inks for inkjet recording were prepared by the following formulation.
Aqueous pigment dispersion 27.6 parts
Diethylene glycol 2.0 parts
Sannics GP-600 (manufactured by Sanyo Kasei) 5.0 parts
Glycerol 3.0 parts
Ion exchange water 62.4 parts
The prepared ink was filtered using a membrane filter with a pore size of 5 μm, and then mounted on an inkjet printer `` NOVA Jet PRO36 '' (manufactured by ENCAD) to evaluate inkjet recording suitability, i.e., 80 A0 size paper. 100% image density was continuously printed in the% area range, and the ink ejection characteristics before and after printing 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.
[0056]
<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 hp DeskJet 957C (manufactured by Hewlett-Packard) is used as the recording medium, plain paper `` Xerox 4024 '' (Xerox 100% image density was recorded, and the density of the obtained image was measured by “Spectroscan” (GretagMacbeth).
Recording aptitude (2) Image density evaluation criteria: If the measured value is 0.95 or more, it can be judged that there is no problem in practical use.
[0057]
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 a pigment concentration of 4%.
The evaluation results are shown in Table 1.
[0058]
[Table 1]

[0059]
As is clear from Table 1, the aqueous pigment dispersion of the present invention is excellent in dispersibility, has little increase in particle size even when left for a long time at high temperature, and has a particle size after standing for 7 days at 60 ° C. The rate of change is 10% or less. Similarly, the aqueous pigment dispersion of the present invention has a small increase in viscosity, the rate of change in viscosity after standing at 60 ° C. for 7 days is 5% or less, and the present invention It can be seen that the ink for ink jet recording prepared using this aqueous pigment dispersion has no problem in ink jet recording suitability, and at the same time, a high image density can be obtained when recording on plain paper.
On the other hand, in the aqueous pigment dispersion outside the scope of the present invention, the change rate of the particle size after standing for 7 days under 60 ° C. exceeds 10%, or the viscosity after standing for 7 days under 60 ° C. Ink jet recording ink prepared using an aqueous pigment dispersion not exceeding the scope of the present invention has a problem in ink jet recording suitability or is recorded on plain paper. In this case, a decrease in image density is recognized and there is a problem.
[0060]
【The invention's effect】
As described above, the aqueous pigment dispersion of the present invention has excellent storage stability, and the ink for ink jet recording using the ink does not cause clogging due to drying of the ink at the nozzle tip and has good ejection stability. The long-term storage stability is good, and a high image density can be obtained on plain paper.

Claims (6)

At least (a) a quinacridone pigment, (b) a quinacridone compound having a substituent containing a phthalimide skeleton, (c) a styrene acrylic resin, (d) an alkali metal hydroxide, (e) a wetting agent, (f) water In the aqueous pigment dispersion for inkjet ink, the (b) quinacridone compound having a substituent containing a phthalimide skeleton is a phthalimidomethylated quinacridone compound, the (a) the quinacridone pigment, and the phthalimidomethylated compound The proportion of the phthalimidomethylated quinacridone compound in the total with the quinacridone compound is 1 to 20% by mass, and the (c) styrene acrylic resin comprises at least styrene, acrylic acid and methacrylic acid as its constituent monomers. , All monomer components of styrene monomer component And the sum of the styrene monomer component, acrylic acid monomer component, and methacrylic acid monomer component is 95% by mass or more based on the total monomer components, and the weight average molecular weight of the resin is 7,500. range der of 30,000 is, further (a) to the total amount 100 parts by weight of a quinacridone pigment and phthalimidomethylated quinacridone compound, the content of (c) styrene-acrylic resin is 10 to 50 parts by weight aqueous pigment dispersion characterized by Rukoto Oh. The aqueous pigment dispersion according to claim 1, wherein the phthalimidomethylated quinacridone compound is phthalimidated methyl-3,10-dichloroquinacridone. The (a) quinacridone pigment is C.I. I. The aqueous pigment dispersion according to claim 1 or 2, which is CI Pigment Red 122. The aqueous pigment dispersion according to any one of claims 1 to 3 , wherein a neutralization rate of the (c) styrene acrylic resin with the (d) alkali metal hydroxide is in a range of 80 to 120%. Jet recording ink composition comprising an aqueous pigment dispersion according to any one of claims 1 to 4. Thermal inkjet recording ink composition obtained by using the aqueous pigment dispersion according to any one of claims 1 to 4.