JP6406089B2 - Aqueous pigment dispersion for inkjet ink - Google Patents

Description

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

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

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

  However, pigment-based ink-jet inks have an upper limit on the amount of surfactant or dispersion resin added to ensure ejection stability (redispersibility), so that the coating film peels off when the recording surface is rubbed after printing. There was a problem that the so-called scratch resistance was poor.

  For example, Patent Document 1 attempts to improve scratch resistance by using a water-insoluble polymer in which the ratio of hydrophobic groups, styrene and benzyl methacrylate is increased. There is a problem that the property (redispersibility) decreases.

  On the other hand, in Patent Document 2, water solubility is improved by increasing the acid value. However, since the anion portion of the resin used is excessive, the film cannot be completely formed after coating, and the pigment is completely removed. Since it cannot be coated, the scratch resistance is considered to be poor. In addition, because of its high water solubility, the dispersibility decreases due to resin detachment from the pigment surface, and the proportion of free resin increases, so the viscosity of the dispersion and ink increases, and the storage stability deteriorates. There is a problem.

JP 2014-139298 A Japanese Patent Laid-Open No. 11-228891

  The problem of the present invention is that the water-based pigment dispersion for inkjet ink has a small volume median diameter, excellent ejection stability (redispersibility) when used as inkjet ink, excellent storage stability, and printing on printing paper It is an object to provide an aqueous pigment dispersion for ink-jet inks which has excellent scratch resistance.

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

  That is, the present invention is an aqueous pigment dispersion for inkjet inks comprising at least water, a water-soluble polymer as a pigment dispersion resin, a basic compound, a water-soluble organic solvent, and a pigment, and the aqueous pigment dispersion for inkjet inks The body has a solid content of water-soluble polymer / (solid content of water-soluble polymer + pigment) of 25 to 35%, and a median diameter (D50) of cumulative volume measured by a laser dynamic light scattering method is 120 nm or less, The water-soluble polymer contains styrene, benzyl (meth) acrylate, (meth) acrylic acid and polyethylene glycol (meth) acrylic acid ester as constituent monomers, and the total amount of monomers constituting the water-soluble polymer is (meth ) Acrylic acid 18-28% by mass, Styrene 25-30% by mass, benzyl (meth) ac Aqueous pigment dispersion for inkjet ink, characterized in that the rate is 25 to 30% by mass, polyethylene glycol (meth) acrylic acid ester is 21 to 26% by mass, and the weight average molecular weight (Mw) is 30,000 to 50,000 About.

  The present invention also relates to the aqueous pigment dispersion for inkjet ink, wherein the water-soluble polymer has an acid value of 120 to 180 mgKOH / g.

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

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

[Wherein, R 1 and R 2 each independently represent H or CH ₃ , and n represents an integer of 9 to 23. ]

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

  The water-based pigment dispersion for inkjet ink of the present invention uses a water-soluble polymer composed of (meth) acrylic acid, styrene, benzyl (meth) acrylate, and polyethylene glycol (meth) acrylic acid ester. The adsorptivity is enhanced, and an excellent effect is exhibited in ejection stability (redispersibility) and storage stability when an inkjet ink is obtained.

  Further, by using a water-soluble polymer having a D50 of an aqueous pigment dispersion for inkjet ink of 120 nm or less and a weight average molecular weight of 30,000 to 50,000, the scratch resistance and storage stability of the inkjet ink can be improved. Gives an excellent effect.

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

<Aqueous pigment dispersion for inkjet ink>
First, the aqueous pigment dispersion for inkjet ink of the present invention and the material constituting it will be described.
An aqueous pigment dispersion for inkjet ink is a liquid in which a pigment is dispersed in a liquid medium mainly composed of water, and the constituent materials are water, a water-soluble polymer, a basic compound, a water-soluble organic solvent and a pigment. is there.

<Water-soluble polymer>
First, the water-soluble polymer used in the present invention will be described.
The water-soluble polymer used in the present invention contains (meth) acrylic acid, styrene, benzyl (meth) acrylate, and polyethylene glycol (meth) acrylic acid ester as constituent monomers, and the total amount of monomers constituting the water-soluble polymer. On the other hand, it is composed of 18 to 28% (meth) acrylic acid, 25 to 30% styrene, 25 to 30% by mass benzyl methacrylate, and 21 to 26% by mass or less of polyethylene glycol (meth) acrylate.

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

  The second constituent monomer is styrene. This is the hydrophobic part of the water-soluble polymer and acts as an adsorption site for the pigment.

  The third constituent monomer is benzyl (meth) acrylate. This is the hydrophobic part of the water-soluble polymer, and acts as an adsorption site for the pigment as in styrene. In addition, since the distance from the polymer main chain is longer than that of styrene, the fixation of the three-dimensional structure due to the π-π interaction between the aromatic rings in the resin and between the resins can be eliminated. Contributes to reducing body viscosity.

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

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

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

(Composition ratio of monomers constituting water-soluble polymer)
The composition ratio of (meth) acrylic acid which is the first constituent monomer of the water-soluble polymer used in the present invention is 18 to 28% by mass with respect to all monomers constituting the water-soluble polymer, and 20 to 25% by mass. % Is preferable.

  The composition ratio of styrene of the second constituent monomer is in the range of 25 to 30% by mass and preferably in the range of 26 to 28% by mass with respect to all monomers constituting the water-soluble polymer.

  The composition ratio of benzyl (meth) acrylate as the third constituent monomer is in the range of 25 to 30% by mass and preferably in the range of 26 to 28% by mass with respect to all monomers constituting the water-soluble polymer. .

  The composition ratio of polyethylene glycol (meth) acrylic acid ester as the fourth constituent monomer is 21 to 26% by mass or less and preferably 23 to 26% by mass with respect to all monomers constituting the water-soluble polymer.

(Acid value of water-soluble polymer)
The acid value of the water-soluble polymer is preferably 120 to 180 mgKOH / g, and more preferably 140 to 160 mgKOH / g.

(Weight average molecular weight of water-soluble polymer)
The weight average molecular weight of the water-soluble polymer is in the range of 30,000 to 50,000, preferably in the range of 35,000 to 45,000.

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

  The water-soluble polymer is preferably contained in an amount of 5.5 to 10.5% by mass or less, and more preferably 6.0 to 9.0% by mass in the aqueous pigment dispersion for inkjet ink.

<Water>
Next, water used in the present invention will be described.
The water suitable for forming the aqueous pigment dispersion for inkjet ink of the present invention is preferably ion-exchanged water (deionized water), not general water containing various ions. The water content is in the range of 10% by mass to 90% by mass, more preferably 50% by mass to 65% by mass, based on the total mass of the aqueous pigment dispersion.

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

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

  The content of the aqueous organic solvent in the aqueous pigment dispersion for inkjet ink is in the range of 3% by mass to 30% by mass, more preferably 3% by mass or more, based on the total mass of the aqueous pigment dispersion for inkjet ink. 15 mass% or less.

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

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

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

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

The water-soluble polymer solid content / (water-soluble polymer solid content + pigment) of the aqueous pigment dispersion for inkjet ink is preferably in the range of 25 to 35% by mass.
If the amount is less than 25% by mass, the amount of the water-soluble polymer formed on the glossy paper after coating is small, resulting in poor scratch resistance. If the amount is more than 35% by mass, the scratch resistance is good, but the dispersion is not good. It is considered that the storage stability becomes poor because the amount of resin in the resin increases, the viscosity increases, and the dispersion does not proceed easily.

The median diameter (D50) of the cumulative volume of the aqueous pigment dispersion for inkjet ink is preferably 120 nm or less.
When it is larger than 120 nm, when the ink-jet ink is applied to glossy paper, dried, and rubbed with a finger, the particle size is large, so the collision with the finger increases and the scratch resistance is considered to be poor.

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

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

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

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

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

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

  As the antifoaming agent, an acetylene glycol surfactant and / or an acetylene alcohol surfactant is preferable. Examples of the acetylene glycol surfactant and / or acetylene alcohol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl- Selected from alkylene oxide adducts of 5-decyn-4,7-diol, 2,4-dimethyl-5-decyn-4-ol and alkylene oxide adducts of 2,4-dimethyl-5-decyn-4-ol 1 or more types are preferable. These are available as Air Products (UK) Olfin 104 series, Olfin E1010 and other E series, Nissin Chemical's Surfynol 465, Surfynol 61, and the like.

  Although it does not specifically limit as antiseptic | preservative, Sodium dehydroacetate, dichlorophen, sorbic acid, sodium benzoate, p-hydroxybenzoic acid ester, 1, 2- Benzisothiazoline-3-one (product name: Proxel GXL) (Abyssia)) is used.

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

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

  In the following examples, the acid value was measured using a Hiranuma automatic titrator COM-1700 (manufactured by Hiranuma Sangyo Co., Ltd.). Moreover, the measuring method was based on JIS K-0070.

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

<Production of water-soluble polymer>
(Production Example 1) Production of water-soluble polymer 1 A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 144.7 parts of propylene glycol and replaced with nitrogen gas. The inside of the reaction vessel is heated to 110 ° C., and 31.3 parts of methacrylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 43.3 parts of styrene (manufactured by Chuo Kasei Co., Ltd.), 43.3 parts of benzyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd.) , 41.7 parts of M-230G (manufactured by Shin-Nakamura Chemical Co., Ltd., equivalent to R1 = CH ₃ , R2 = CH ₃ , n = 23 in the general formula (1)) as a polyethylene glycol (meth) acrylic ester, and nitrile A mixture of 6.3 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator of an azoester compound having no group was dropped over 2 hours to carry out a copolymerization reaction. After completion of the dropwise addition, the internal temperature was further maintained at 110 ° C., and after 1 and 2 hours, 1.0 part of V-601 was added and the reaction was continued. The reaction was further continued at 110 ° C. for 1 hour, and then the solution was cooled to 25 ° C. A portion of this was taken and dried by heating at 180 ° C. for 40 minutes, and the solid content of the water-soluble polymer in the solution was measured. A 10% potassium hydroxide (purity 85%: manufactured by Wako Pure Chemical Industries, Ltd.) aqueous solution was added to the cooled reaction solution so that the solution pH was 8.5, and the solid content of the water-soluble polymer of dispersion resin 1 was 20%. Water was added to a percentage. As a result, a water-soluble polymer 1 solution having a solid content of 20% was obtained. The weight average molecular weight of the water-soluble polymer 1 was 35,500, and the acid value was 150 mgKOH / g.

(Production Examples 2-9)
Except having changed into the monomer and polymerization initiator which are respectively shown in Table 1, operation similar to manufacture example 1 was performed and the water-soluble polymers 2-9 were manufactured. The acid value and weight average molecular weight of the obtained water-soluble polymer are shown together in Table 1. In Table 1, “%” represents mass% of each constituent monomer with respect to the total amount of monomers constituting the water-soluble polymer. However, for Production Example 5, the first addition amount of V-601 is 3.3 parts, for Production Example 8, the first addition amount of V-601 is 21.7 parts, and for Production Example 9. Was produced in the same manner as in Production Example 1 except that the first addition amount of V-601 was changed to 1.6 parts.

Example 1 Production of Black Aqueous Pigment Dispersion 214.3 parts of the water-soluble polymer solution obtained in Production Example 1 was charged into a glass bottle, and 21.9 parts of water and 10% aqueous potassium hydroxide solution were added therein. It added so that pH might be 8.75, the resin was melt | dissolved using the ultrasonic cleaner (the Yamato Kagaku company make, 2510J-DTH), and the aqueous medium was obtained. Subsequently, Surfinol 104E (antifoaming agent, manufactured by Air Products Japan) 1.0 part, Proxel GXL (preservative, manufactured by Abyssia) 1.0 part, carbon black as a pigment (MONARCH800, manufactured by CABOT) 100. After adding 0 part and pre-dispersing with a spatula, 112.5 parts of zirconia beads having a diameter of 0.8 mm are charged as dispersion media, and until the median diameter (D50) of the cumulative volume reaches 120 nm or less with a paint shaker Dispersion was performed to obtain a black aqueous pigment dispersion 1. At this time, the ratio of the non-volatile content of the pigment and the water-soluble polymer 1 is pigment / water-soluble polymer (non-volatile content) = 7/3 (mass ratio).

(Examples 2-11, Comparative Examples 1-6)
The water-soluble polymer 1 was changed to the water-soluble polymers 2 to 9 shown in Table 2 except that the ratio of pigment / water-soluble polymer (non-volatile content) and the median diameter (D50) of the cumulative volume of the aqueous pigment dispersion were changed. The same operations as in Example 1 were performed to produce black aqueous pigment dispersions 2 to 5 and comparative black aqueous pigment dispersions 1 to 7. In Table 2, the pigment / water-soluble polymer (nonvolatile content) represents a mass ratio.

(Examples 6 to 10, Comparative Examples 8 to 14)
The same as Example 1 except that the water-soluble polymer and pigment shown in Table 3, the ratio of pigment / water-soluble polymer (non-volatile content), and the median diameter (D50) of the cumulative volume of the aqueous pigment dispersion were changed. Operation was performed to produce cyan aqueous pigment dispersions 1 to 5 and comparative cyan aqueous pigment dispersions 1 to 7. In Table 3, Pigment Blue 15: 3 was Lionol Blue FG-7351 (Toyo Color Co., Ltd.). In Table 3, the pigment / water-soluble polymer (nonvolatile content) represents a mass ratio.

(Example 11)
60.0 parts of the water-soluble polymer solution obtained in Production Example 1 was charged into a glass bottle, and 317.5 parts of water and 10% aqueous potassium hydroxide solution were added to the solution so that the solution pH was 8.75. The resin was dissolved using a sonic cleaner (2510J-DTH, manufactured by Yamato Kagaku Co., Ltd.) to obtain an aqueous medium. Subsequently, 1.0 part of Surfinol 104E (antifoaming agent, manufactured by Air Products Japan), 1.0 part of Proxel GXL (preservative, manufactured by Abyssia), Pigment Red 122 (PR 122B, Koyu) as a pigment After adding 75.0 parts) and pre-dispersing with a spatula, 112.5 parts of zirconia beads having a diameter of 0.8 mm were charged as dispersion media, and the median diameter (D50) of the cumulative volume was measured with a paint shaker. Dispersion was performed until the thickness became 120 nm or less to obtain a magenta aqueous pigment dispersion 1. At this time, the ratio of the non-volatile content of the pigment and the water-soluble polymer 1 is pigment / water-soluble polymer (solid content) = 7/3 (mass ratio).

<Solid content of water-soluble polymer>
After producing the water-soluble polymer, a part thereof was taken and dried by heating at 180 ° C. for 40 minutes, and the non-volatile content was used as the solid content of the water-soluble polymer.
The “solid content of water-soluble polymer / (solid content of water-soluble polymer + pigment)” according to claim 1 is the mass of the solid content of the water-soluble polymer contained in the aqueous pigment dispersion for inkjet ink, and the pigment. The ratio of the mass of the solid content of the water-soluble polymer in the mass of.

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

(Examples 12-15, Comparative Examples 15-21)
The water-soluble polymer 1 was changed to the water-soluble polymers 2 to 9 shown in Table 4 except that the pigment / water-soluble polymer (nonvolatile content) ratio and the median diameter (D50) of the cumulative volume of the aqueous pigment dispersion were changed. The same operations as in Example 1 were performed to produce magenta aqueous pigment dispersions 1 to 5 and comparative magenta aqueous pigment dispersions 1 to 7. In Table 4, the pigment / water-soluble polymer (nonvolatile content) represents a mass ratio.

(Examples 16 to 20, Comparative Examples 22 to 28)
The same operation as in Example 1 except that the water-soluble polymer and the ratio of pigment to pigment / water-soluble polymer (nonvolatile content) shown in Table 5 and the median diameter (D50) of the cumulative volume of the aqueous pigment dispersion were changed. The yellow aqueous pigment dispersions 1 to 5 and the comparative yellow aqueous pigment dispersions 1 to 6 were produced. In Table 5, Fast Yellow 7416 (manufactured by Sanyo Dye) was used as Pigment Yellow 74. In Table 5, the pigment / water-soluble polymer (nonvolatile content) represents a mass ratio.

(Example 21) Production of black inkjet ink 77.3 parts of black aqueous pigment dispersion 1, 294.2 parts of water, 75.0 parts of glycerin, 25.0 parts of triethylene glycol monobutyl ether, 2-pyrrolidone 25.0 parts, Surfynol 465 2.5 parts, and Proxel GXL 1.0 part were mixed, and the black inkjet ink 1 was manufactured.

(Examples 22 to 25, Comparative Examples 29 to 35)
A black inkjet ink was prepared by performing the same operation as in Example 21 except that the black aqueous pigment dispersion 1 was changed to black aqueous pigment dispersions 2 to 5 and comparative black aqueous pigment dispersions 1 to 7 shown in Table 6, respectively. 2 to 5 and comparative black inkjet inks 1 to 7 were produced.

(Examples 26-30, Comparative Examples 36-42) Manufacture of cyan inkjet inks The same operations as in Example 21 were performed except that the aqueous pigment dispersions shown in Table 7 were respectively changed, and cyan inkjet inks 1-5, Comparative cyan inkjet inks 1-7 were prepared.

(Example 31) Production of magenta inkjet ink 132.7 parts of magenta aqueous pigment dispersion 1, 238.8 parts of water, 75.0 parts of glycerin, 25.0 parts of triethylene glycol monobutyl ether, and 2-pyrrolidone Magenta inkjet ink 1 was produced by mixing 25.0 parts, 2.5 parts of Surfinol 465, and 1.0 part of Proxel GXL.

(Examples 32-35, Comparative Examples 43-49)
Except that the magenta aqueous pigment dispersion 1 was changed to the magenta aqueous pigment dispersions 2 to 5 and the comparative magenta aqueous pigment dispersions 1 to 7 shown in Table 8, the same operation as in Example 31 was performed, and the magenta inkjet ink 2 -5, comparative magenta inkjet inks 1-7 were produced.

(Example 36) Manufacture of yellow ink-jet ink Except for changing to the aqueous pigment dispersions shown in Table 9, the same operations as in Example 36 were performed, and yellow ink-jet inks 1 to 5 and comparative yellow ink-jet inks 1 to 7 were obtained. Manufactured.

(Redispersibility of inkjet ink)
Spectral spectra were measured for a solution obtained by diluting the prepared ink-jet ink with water 2000 times on a mass basis, and measurement wavelengths corresponding to the colors of each ink (black: 550 nm, cyan: 617 nm, magenta: 534 nm, yellow: 430 nm). ) Was defined as A.
Separately, a part of the ink-jet ink is collected in a test tube, dried and solidified at 140 ° C., the same amount of water volatilized by drying is added to the solidified product, dispersed in an ultrasonic washing machine, and similarly spectrally analyzed. The spectrum was measured, and the absorbance at the measurement wavelength corresponding to the color of each ink was defined as B.
The respective absorbances obtained above were calculated according to the following formula, and used as the redispersibility of the inkjet ink. This redispersibility is an evaluation that serves as an index of the ejection stability of an inkjet nozzle during inkjet printing. That is, in inkjet printing, since inkjet ink is intermittently ejected from the inkjet nozzle, the inkjet ink is dried and re-dispersed (re-dissolved) at the nozzle tip. Therefore, poor re-dispersibility results in ejection failure. For this reason, evaluation by this method was performed as an index of ejection stability. A larger numerical value indicates better redispersibility.

Redispersibility = B / A x 100 (%)

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

(Abrasion resistance of printed matter)
The prepared ink-jet ink was coated on glossy paper (Canon Gold paper) using an automatic bar coater (RK PRINTCOAT INSTRUMENTS, K CONTROL COATER) and a bar (manufactured by the company, wet film thickness 12 μm), dried, and printed for testing. Got.
The printed surface of the obtained test printed material was rubbed with a finger, and the presence or absence of peeling of the printed surface was visually observed and evaluated according to the following criteria.
A (very good) when the printed surface is not peeled, B (good, practically no hindrance) when the printed surface is partially peeled when rubbed strongly, and C (bad) when the printed surface is peeled off , There was a problem in practical use).

(Storage stability of inkjet ink)
The produced aqueous pigment dispersion was stored in a thermostat at 60 ° C. for 1 week. The respective viscosities before and after storage at 60 ° C. for 1 week were measured. The viscosity was measured using an E-type viscometer (TVE-25L, manufactured by Toki Sangyo Co., Ltd.) under the conditions of 25 ° C. and a rotation speed of 100 rpm.
The change rate (%) of the viscosity after storage relative to the storage before storage was calculated and used as storage stability. The closer the value of change rate is to 0 (zero), the better the storage stability.
If this value is ± 10.0% or less, A (very good), 10.2 to 20.0% is B (good, no practical problem), 20.1% or more is C (bad, practical problem) It was.

The evaluation criteria for the above results are shown in Tables 10 to 12, and the results are summarized in Tables 13 to 15.
The ink-jet inks described in the examples are all excellent in redispersibility, scratch resistance, and storage stability, and the water-soluble polymer used has an acid value of 120 to 180 mgKOH / g, a weight average molecular weight (Mw) of 30, 000 to 50,000, the solid content of the water-soluble polymer of the aqueous pigment dispersion used / (solid content of the water-soluble polymer + pigment) is 25 to 35%, and the median diameter of the total volume of the aqueous pigment dispersion is 120 nm or less. Yes, it is in the range having water-solubility optimum for redissolving after heating and drying of the ink-jet ink, good scratch resistance after applying and drying on glossy paper, and good storage stability.
When the acid value is in the range of 120 to 180 mgKOH / g, the ratio of the hydrophilic group in the water-soluble polymer composition is appropriate, and the redispersibility when used as an inkjet ink is good, and the inkjet ink is applied to glossy paper. In this case, the acidic component on the glossy paper surface can sufficiently react with the anion portion of the water-soluble polymer, and the water-soluble polymer can be completely formed, so that the scratch resistance is good.
When the Mw of the water-soluble polymer to be used is larger than 50,000, the adsorption point to the pigment increases and the pigment can be adsorbed so as to cover the pigment. Although the storage stability is improved, since the molecular chain becomes long, the water-soluble polymers tend to be entangled with each other and the solubility becomes low, so that the redispersibility is considered to be poor.
When the Mw of the water-soluble polymer to be used is smaller than 30,000, it is considered that the storage stability becomes poor because the adsorption point to the pigment is small and the opportunity to come into contact with the pigments and the solvent increases.
If the solid content of the water-soluble polymer in the aqueous pigment dispersion used / (solid content of the water-soluble polymer + pigment) is less than 25%, the amount of the water-soluble polymer formed on the glossy paper after coating is small, so Scratch resistance is poor, and if it is larger than 35%, the scratch resistance is good, but the amount of resin during dispersion increases, so the viscosity increases and the dispersion does not proceed easily, so that the storage stability is improved. It seems to be defective.
If the median diameter of the cumulative volume of the aqueous pigment dispersion for inkjet ink exceeds 120 nm, when the inkjet ink is applied to glossy paper, dried, and then rubbed with a finger, the particle diameter is large, resulting in collision with the finger. It is considered that the scratch resistance becomes poor.

Claims (4)

  An aqueous pigment dispersion for inkjet ink comprising at least water, a water-soluble polymer as a pigment dispersion resin, a basic compound, a water-soluble organic solvent, and a pigment, wherein the aqueous pigment dispersion for inkjet ink is a water-soluble polymer Mass ratio of solid content / (solid content of water-soluble polymer + pigment) is 25 to 35% by mass, and the median diameter (D50) of cumulative volume measured by the laser dynamic light scattering method is 120 nm or less, The polymer contains styrene, benzyl (meth) acrylate, (meth) acrylic acid, and polyethylene glycol (meth) acrylic acid ester as constituent monomers, and (meth) acrylic with respect to the total monomer amount constituting the water-soluble polymer. 18-28% by mass of acid, 25-30% by mass of styrene, benzyl (meth) acrylate 5 to 30 mass%, polyethylene glycol (meth) acrylate 21 to 26% by weight and the weight average molecular weight (Mw) of the ink-jet ink aqueous pigment dispersion, which is a 30,000 to 50,000.   The aqueous pigment dispersion for inkjet ink according to claim 1, wherein the water-soluble polymer has an acid value of 120 to 180 mgKOH / g. The aqueous pigment dispersion for inkjet ink according to claim 1 or 2, wherein the polyethylene glycol (meth) acrylic acid ester is a polyethylene glycol (meth) acrylic acid ester represented by the following general formula (1).

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

[Wherein, R 1 and R 2 each independently represent H or CH ₃ , and n represents an integer of 9 to 23. ]   The water-based pigment for inkjet ink according to any one of claims 1 to 3, wherein the water-soluble polymer is a water-soluble polymer obtained by polymerizing a monomer and then adding a basic compound and water to the reaction mixture. Dispersion.