Dispersion liquid, ink composition for ink-jet recording, and dispersion resin

Abstract

To provide a dispersion and the like that enable a solidified color material from being easily re-dispersed and can prevent the clogging and can achieve enhanced ejection stability.SOLUTION: A dispersion contains water, a color material, and a dispersing resin that disperses the color material, the dispersing resin having a structural unit A containing a hydrophobic monomer, a structural unit B containing a hydrophilic acrylic acid monomer, and a structural unit C containing a sulfonic acid group-containing acrylamide monomer, where the dispersing resin has a weight average molecular weight of from 5000 to 100000 and a content of the structural unit A is 60 mol% or more with respect to a total amount of the dispersing resin.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a dispersion liquid, an ink composition for ink-jet recording, and a dispersion resin. [Background technology]

[0002] Inkjet recording methods are capable of recording high-definition images with a relatively simple device, and have been rapidly developed in various fields. In the process, various studies have been conducted on obtaining high-quality images while suppressing mist contamination of the recording head. For example, Patent Document 1 discloses a pigment inkjet recording ink in which pigment particles are dispersed in a styrene-acrylic resin. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-002096 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, ink compositions containing conventional dispersants such as the styrene-acrylic resin described in Patent Document 1 have the problem that once the ink is dried and the colorant is solidified, it is difficult to redisperse the ink, which can easily cause problems during ejection. [Means for solving the problem]

[0005] The present invention relates to a dispersion liquid comprising water, a colorant, and a dispersion resin for dispersing the colorant, the dispersion resin comprising a structural unit A containing a hydrophobic monomer, a structural unit B containing a hydrophilic acrylic acid monomer, and a structural unit C containing an acrylamide monomer having a sulfonic acid group, the weight-average molecular weight of the dispersion resin being 5,000 to 100,000, and the content of the structural unit A being 60 mol % or more relative to the total amount of the dispersion resin.

[0006] The present invention also provides an ink composition for ink jet recording, comprising the above dispersion, a surfactant, and a water-soluble organic solvent.

[0007] Furthermore, the present invention relates to a dispersion resin having a structural unit A containing a hydrophobic monomer, a structural unit B containing a hydrophilic acrylic acid monomer, and a structural unit C containing an acrylamide monomer having a sulfonic acid group, the weight average molecular weight of the dispersion resin being 5,000 to 100,000, and the content of the structural unit A being 60 mol% or more relative to the total amount of the dispersion resin. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Below, we will explain in detail the embodiment of the present invention (hereinafter referred to as the "present embodiment"). However, the present invention is not limited to this embodiment, and various modifications are possible without departing from the gist of the present invention.

[0009] 1.Dispersion liquid The dispersion liquid of the present embodiment contains water, a colorant, and a dispersion resin that disperses the colorant. The dispersion resin has a structural unit A containing a hydrophobic monomer, a structural unit B containing a hydrophilic acrylic acid monomer, and a structural unit C containing an acrylamide monomer having a sulfonic acid group, and the weight average molecular weight of the dispersion resin is 5,000 to 100,000. The content of the structural unit A is 60 mol% or more relative to the total amount of the dispersion resin.

[0010] A dispersion liquid or ink composition using a conventional dispersion resin has a problem that once the colorant solidifies, it is difficult to redisperse it. In contrast, in the present embodiment, by using a dispersion resin having the above-mentioned configuration, it is possible to easily redisperse the solidified colorant, and even when stored at high temperatures, there is little change in the particle size of the colorant particles or in the viscosity of the dispersion liquid, which makes it possible to prevent clogging and further improve the ejection stability of the ink composition for inkjet recording using the dispersion liquid. Each component will be described in detail below.

[0011] 1.1.Dispersion resin The dispersion resin of this embodiment is a copolymer having a structural unit A containing a hydrophobic monomer, a structural unit B containing a hydrophilic acrylic acid monomer, and a structural unit C containing an acrylamide monomer having a sulfonic acid group. In this embodiment, the term "monomer" refers to a monomer having a polymerizable unsaturated bond before polymerization, and the term "structural unit" refers to a repeating unit that constitutes a part of the dispersion resin after polymerization. In this embodiment, "hydrophobic" refers to a property of being incompatible with water at 25°C, and "hydrophilic" refers to a property of being compatible with water at 25°C.

[0012] The dispersion resin may be a random copolymer or a block copolymer. Examples of the block copolymer include a triblock copolymer having a block A composed of a structural unit A, a block B composed of a structural unit B, and a block C composed of a structural unit C, as well as a diblock copolymer having a block A composed of a structural unit A and a random block B / C composed of a structural unit B and a structural unit C. By using such a dispersion resin, the redispersibility after solidification is improved, and even when stored at high temperatures, the particle size and viscosity change tend to be smaller.

[0013] The content of the dispersion resin is preferably 2.5 to 10% by mass, more preferably 3.5 to 9.0% by mass, and even more preferably 4.5 to 8.0% by mass, based on the total amount of the dispersion liquid. By having the content of the dispersion resin within the above range, redispersibility after solidification is improved, and even when stored at high temperatures, changes in particle size and viscosity tend to be smaller.

[0014] The content of the dispersion resin is preferably 10 to 80 parts by mass, more preferably 15 to 70 parts by mass, and even more preferably 25 to 60 parts by mass, relative to 100 parts by mass of the colorant. By having the content of the dispersion resin within the above range, redispersibility after solidification is improved, and even when stored at high temperatures, there is a tendency for the particle size and viscosity to change less.

[0015] 1.1.1. Building Block A The structural unit A is a structural unit containing a hydrophobic monomer, and partially imparts hydrophobicity to the dispersed resin. Although not particularly limited, the structural unit A may be oriented on the surface of the colorant by hydrophobic interaction or the like, and may contribute to the adsorption of the dispersed resin to the colorant.

[0016] The hydrophobic monomer constituting the structural unit A is not particularly limited, and examples thereof include vinyl monomers having an aromatic group such as styrene, methylstyrene, and other styrene derivatives; and acrylic acid ester monomers having a hydrocarbon group such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and benzyl (meth)acrylate. Among these, styrene, methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate are more preferred. By using such a hydrophobic monomer, the adsorption of the dispersion resin to the coloring material is improved, the redispersibility after solidification is improved, and even when stored at high temperatures, the particle size and viscosity change tend to be smaller. The hydrophobic monomer may be used alone or in combination of two or more types. In this embodiment, "(meth)acrylate" includes acrylate and methacrylate.

[0017] The content of the structural unit A is 60 mol% or more, preferably 61 to 80 mol%, and more preferably 61 to 70 mol% based on the total amount of the dispersion resin. When the content of the structural unit A is 60 mol% or more, the adsorption of the dispersion resin to the coloring material is further improved. In addition, when the content of the hydrophobic structural unit A is 60 mol% or more, the hydrophilicity of the dispersion resin itself is usually reduced, but the dispersion resin of this embodiment can ensure the water solubility of the dispersion resin due to the contribution of other structural units, particularly the structural unit C. This further improves the adsorption of the dispersion resin to the coloring material, further improves the redispersibility after solidification, and tends to reduce the change in particle size and viscosity even when stored at high temperatures.

[0018] 1.1.2. Building block B The structural unit B is a structural unit containing a hydrophilic acrylic acid monomer, and partially imparts hydrophilicity to the dispersion resin. Although not particularly limited, the structural unit B is oriented on the side opposite to the surface of the colorant, and can contribute to improving dispersibility.

[0019] The hydrophilic acrylic acid monomer constituting the structural unit B is not particularly limited, and examples thereof include (meth)acrylic acid; acrylic acid ester monomers having a polyalkylene glycol group, such as ethylene glycol (meth)acrylate, diethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate; and other acrylic acid ester monomers, such as 2-hydroxyethyl (meth)acrylate. Among these, (meth)acrylic acid and acrylic acid ester monomers having a polyalkylene glycol group are preferred. The hydrophilic acrylic acid monomers may be used alone or in combination of two or more. In this embodiment, "(meth)acrylic acid" includes acrylic acid and methacrylic acid.

[0020] The content of the structural unit B is preferably 3 to 25 mol%, preferably 5 to 20 mol%, and more preferably 7 to 16 mol% relative to the total amount of the dispersion resin. By having the content of the structural unit B within the above range, the hydrophilicity of the dispersion resin is improved, redispersibility after solidification is improved, and changes in particle size and viscosity tend to be smaller even when stored at high temperatures.

[0021] 1.1.3. Building Block C The structural unit C is a structural unit containing an acrylamide monomer having a sulfonic acid group, and partially imparts hydrophilicity to the dispersion resin. Although not particularly limited, the structural unit C is oriented on the side opposite to the surface of the colorant, and can contribute to improving dispersibility.

[0022] The acrylamide monomer having a sulfonic acid group constituting the structural unit C is not particularly limited, and may be, for example, a compound represented by the following formula (1). Among these, 2-acrylamido-2-methylpropanesulfonic acid is more preferable. By using such an acrylamide monomer, the hydrophilicity of the dispersion resin is improved, the redispersibility after solidification is improved, and even when stored at high temperatures, the particle size and viscosity tend to change less. The acrylamide monomer may be used alone or in combination of two or more kinds. CH=CONH-R-SO3H (1) (In the formula, R represents a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms.)

[0023] The sulfonic acid group in the acrylamide monomer may form a salt, and the salt is not particularly limited, but examples thereof include alkali metal salts such as potassium, alkaline earth metal salts such as calcium and magnesium, ammonium salts, and alkylamine salts.

[0024] The content of the structural unit C is preferably 10 to 40 mol%, more preferably 10 to 35 mol%, and even more preferably 15 to 32 mol% based on the total amount of the dispersion resin. By having the content of the structural unit C within the above range, the hydrophilicity of the dispersion resin is improved, the redispersibility after solidification is improved, and even when stored at high temperatures, the particle size and viscosity tend to change less. In particular, by having the structural unit C, the redispersibility after solidification is improved.

[0025] 1.1.4. Weight average molecular weight and molecular weight distribution The weight average molecular weight of the dispersion resin is 5000 to 100000, preferably 5000 to 80000, more preferably 7000 to 60000, and further preferably 7000 to 30000. When the weight average molecular weight of the dispersion resin is within the above range, redispersibility after solidification is improved, and even when stored at high temperatures, changes in particle size and viscosity tend to be smaller.

[0026] The molecular weight distribution (Mw / Mn) of the dispersion resin is preferably 1.05 to 2.00, more preferably 1.05 to 1.80, even more preferably 1.05 to 1.60, and particularly preferably 1.05 to 1.40. By having the molecular weight distribution of the dispersion resin within the above range, the molecular size becomes more uniform, and redispersibility after solidification is improved, and changes in particle size and viscosity tend to be smaller. Such a relatively narrow molecular weight distribution can be achieved by living radical polymerization, which will be described later.

[0027] The weight average molecular weight and the molecular weight distribution can be measured by a known method, such as a chromatography method, and more specifically, by the method described in the Examples.

[0028] 1.1.5. Manufacturing method The dispersion resin of the present embodiment can be obtained by sequentially copolymerizing the hydrophobic monomer and the acrylamide monomer. The polymerization reaction is not particularly limited, but for example, radical polymerization, particularly living radical polymerization, can be used.

[0029] 1.2.Water The water content is preferably 60 to 90% by mass, more preferably 65 to 90% by mass, and further preferably 75 to 90% by mass, based on the total amount of the dispersion.

[0030] 1.3.Colorants The coloring material is not particularly limited, and examples thereof include disperse dyes and pigments. The coloring material may be used alone or in combination of two or more kinds.

[0031] The disperse dye is not particularly limited, and known disperse dyes such as CI Disperse Yellow, CI Disperse Orange, CI Disperse Blue, CI Disperse Violet, and CI Disperse Black can be used.

[0032] The inorganic pigment is not particularly limited, but examples thereof include carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, iron oxide, and titanium oxide.

[0033] Examples of organic pigments include, but are not limited to, quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments, and azo pigments.

[0034] The content of the coloring material is preferably 7.5 to 30% by mass, more preferably 8.0 to 20% by mass, and further preferably 8.5 to 15% by mass, based on the total amount of the dispersion.

[0035] 1.4.pH adjusters The dispersion liquid may further contain a pH adjuster. The pH adjuster is not particularly limited, but examples thereof include inorganic acids (e.g., sulfuric acid, hydrochloric acid, nitric acid, etc.), inorganic bases (e.g., lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, etc.), organic bases (triethanolamine, diethanolamine, monoethanolamine, tripropanolamine), organic acids (e.g., adipic acid, citric acid, succinic acid, etc.), etc. The pH adjuster may be used alone or in combination of two or more.

[0036] 2. Ink composition for ink-jet recording The ink composition for inkjet recording of this embodiment (also simply referred to as "ink composition") contains the above-mentioned dispersion liquid, a surfactant, and a water-soluble organic solvent, and may contain other components as necessary. Note that "for inkjet recording" means that the composition is used by an inkjet method in which ink droplets are ejected from the nozzles of an inkjet head.

[0037] 2.1.Dispersion liquid The dispersion liquid is as described above. The content of the dispersion resin added to the ink composition together with the dispersion liquid is preferably 0.1 to 3.0% by mass, more preferably 0.3 to 2.0% by mass, and even more preferably 0.5 to 1.5% by mass, based on the total amount of the ink composition. By having the content of the dispersion resin within the above range, redispersibility after solidification is improved, and even when stored at high temperatures, changes in particle size and viscosity tend to be smaller.

[0038] The content of the colorant added to the ink composition together with the dispersion liquid is preferably 1.0 to 7.0% by mass, more preferably 1.5 to 6.0% by mass, and even more preferably 2.5 to 4.5% by mass, based on the total amount of the ink composition. By having the content of the colorant within the above range, redispersibility after solidification is improved, and even when stored at high temperatures, changes in particle size and viscosity tend to be smaller.

[0039] In the ink composition, the content of the dispersion resin is preferably 10 to 80 parts by mass, more preferably 15 to 70 parts by mass, and even more preferably 25 to 60 parts by mass, relative to 100 parts by mass of the colorant. By having the content of the dispersion resin within the above range, redispersibility after solidification is improved, and even when stored at high temperatures, changes in particle size and viscosity tend to be smaller.

[0040] 2.2.Surfactants The surfactant is not particularly limited, but examples thereof include acetylene glycol surfactants, fluorine-based surfactants, and silicone-based surfactants.

[0041] The acetylene glycol surfactant is not particularly limited, but for example, one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol are preferred.

[0042] The fluorine-based surfactant is not particularly limited, but examples thereof include perfluoroalkyl sulfonate, perfluoroalkyl carboxylate, perfluoroalkyl phosphate, perfluoroalkyl ethylene oxide adduct, perfluoroalkyl betaine, and perfluoroalkyl amine oxide compound.

[0043] Examples of silicone surfactants include polysiloxane compounds and polyether-modified organosiloxanes.

[0044] The content of the surfactant is preferably 0.1 to 3.0% by mass, and more preferably 0.1 to 1.0% by mass, relative to the total amount of the ink composition.

[0045] 2.3. Water-soluble organic solvents The water-soluble organic solvent is not particularly limited, and examples thereof include glycerin; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and propylene glycol monomethyl ether. Examples of the water-soluble organic solvent include glycol monoethers such as ethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and triethylene glycol monomethyl ether; nitrogen-containing solvents such as 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone; and alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, 2-butanol, tert-butanol, iso-butanol, n-pentanol, 2-pentanol, 3-pentanol, and tert-pentanol. Among these, glycols are preferred, and diethylene glycol and 1,2-hexanediol are more preferred. The water-soluble organic solvent may be used alone or in combination of two or more.

[0046] The content of the water-soluble organic solvent is preferably 5.0 to 30% by mass, and more preferably 10 to 20% by mass, based on the total amount of the ink composition. When the content of the water-soluble organic solvent is within the above range, redispersibility after solidification is improved, and even when stored at high temperatures, changes in particle size and viscosity tend to be smaller.

[0047] 2.4.Water The water content is preferably 60 to 90% by mass, and more preferably 70 to 85% by mass, based on the total amount of the ink composition. When the water content is within the above range, redispersibility after solidification is improved, and changes in particle size and viscosity tend to be smaller even when stored at high temperatures.

[0048] 2.5. pH Adjusters The ink composition may further contain a pH adjuster. The pH adjuster is not particularly limited, but may be any of those exemplified in the dispersion liquid. The pH adjuster in the ink composition may be one that is mixed originating from the dispersion liquid, or may be one that is added separately when preparing the ink composition.

[0049] The content of the pH adjuster is preferably 0.1 to 2.0% by mass, and more preferably 0.5 to 1.5% by mass, relative to the total amount of the ink composition.

[0050] 2.6.Other resins The ink composition may further contain other resins other than the dispersion resin. The other resins are not particularly limited, but may include, for example, anionic resins, cationic resins, or nonionic resins. By including such resins, the colorant can be fixed to the recording medium.

[0051] The cationic resin is not particularly limited, but examples thereof include starch derivatives such as cationic starch, cationic urethane resins, cationic olefin resins, and cationic allylamine resins.

[0052] Examples of anionic resins include carboxymethyl cellulose salts, cellulose derivatives such as viscose, alginates, gum arabic, gum tragacanth, and lignin sulfonates. Examples of natural resins include:

[0053] The nonionic resin is not particularly limited, but examples thereof include acrylic resins, styrene-acrylic resins, urethane resins, ester resins, olefin resins, and vinyl acetate resins.

[0054] The content of the other resin is preferably 0.1 to 2.0 mass %, and more preferably 0.5 to 1.5 mass %, relative to the total amount of the ink composition. EXAMPLES

[0055] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0056] 1. Synthesis of copolymer 1.1. Manufacturing Example 1 Into a sidearm flask equipped with a stirrer and a Dimroth condenser, 16 parts by mass of styrene, 16 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, 5 parts by mass of acrylic acid, 2 parts by mass of 2-{[(carboxymethyl)sulfanylthiocarbonyl]sulfanyl}propanoic acid (CSPA), and 1 part by mass of azobisisobutyronitrile were placed and dissolved in 60 parts by mass of N,N-dimethylformamide.

[0057] After nitrogen bubbling was performed on the solution in the flask for 20 minutes, the solution was heated to 75°C under a nitrogen atmosphere and polymerized for 6 hours. After the reaction was completed, the reactant was diluted with tetrahydrofuran and dropped into hexane to precipitate a yellow solid. The precipitated solid was collected by centrifugation and vacuum dried at 50°C for 10 hours to obtain Dispersion Resin 1. The weight average molecular weight of the obtained dispersion resin was 8200. All of the reagents used above were manufactured by Tokyo Chemical Industry Co., Ltd.

[0058] 1.2. Manufacturing Examples 2 to 5 Dispersion resins 2 to 5 were synthesized in the same manner as in Production Example 1, except that the type and amount of the monomer used was changed so as to obtain the dispersion resins shown in Table 1 below. Note that PME400 used in Production Examples 3 to 4 is methoxypolyethylene glycol methacrylate (manufactured by NOF Corporation).

[0059] 1.3. Weight average molecular weight and molecular weight distribution The weight average molecular weight of each of the dispersed resins and each of the polymers A obtained as described above, and the molecular weight distribution (Mw / Mn) of each of the dispersed resins were measured by a chromatography method under the following conditions. (Measurement conditions) Device name: HLC8320GPC (Tosoh) Guard column: Super AW-L Column: Super AW3000 Column temperature: 25℃ Eluent Dimethylacetamide: Flow rate: 0.6 mL / min Detector RI:

[0060] [Table 1] *ATBS: 2-acrylamido-2-methylpropanesulfonic acid

[0061] 2. Preparation of Varnish Solution In a 1 L eggplant flask equipped with a stirrer and a Dimroth condenser, 15 parts by mass of the copolymer and 70 parts by mass of pure water were added, heated to 80°C, and stirred. Triethanolamine was added to the mixture until the pH reached 7.6, and pure water was further added to make the total amount 100 parts by mass. The mixture was then cooled to 25°C to obtain a varnish solution containing 15% by mass of the copolymer.

[0062] 3. Preparation of Dispersion 50 parts by mass of the varnish liquid, 15 parts by mass of DISPERSE YELLOW 232, and 35 parts by mass of pure water were mixed and ground in a bead mill for 1 hour to obtain a dispersion containing 6% by mass of the copolymer and 12% by mass of the colorant.

[0063] 4. Preparation of Ink Composition Each ink composition was obtained by mixing the dispersion liquid and other components so as to obtain the composition shown in Table 2. Table 2 also shows the composition of the ink water used in the redispersibility test described later.

[0064] 5. Evaluation 5.1. Redispersibility The ink composition prepared as described above was dropped onto a glass slide and dried to solidify. The glass slide was then immersed in a sample bottle containing ink water, and the behavior of redispersion of the solid matter was visually confirmed. Note that the operation was performed with care not to stir the ink water. Note that the ink water in Table 2 above does not contain coloring material and dispersion resin. The evaluation criteria for redispersibility are shown below. (Evaluation Criteria) A: The solid matter disappeared and redispersed. B: Some solid matter remained, but redispersion was observed. C: Solid matter remained and no redispersion was observed.

[0065] 5.2. Changes in particle size distribution The ink composition prepared as above was placed in a sample bottle and left at 60°C for 5 days. The volume-based cumulative 50% particle size (D50) of the ink composition before and after leaving it was measured by dynamic light scattering to confirm the change in cumulative 50% particle size before and after leaving it. A Microtrac UPA150 (trade name, manufactured by Microtrac Inc.) was used as the measuring device. The change in particle size distribution was determined based on the obtained measurement results. (Evaluation Criteria) A: The cumulative 50% increase in particle size was less than 10%. B: The cumulative 50% increase in particle size was 10% or more and less than 30%. C: The cumulative 50% increase in particle size was 30% or more.

[0066] 5.3. Viscosity Change The ink composition prepared as above was placed in a sample bottle and left to stand for 5 days at 60° C. After standing, the viscosity at a shear rate of 10 (1 / s) at 20° C. was measured using a digital viscometer VM-100 manufactured by Yamaichi Electronics Co., Ltd. The evaluation criteria are as follows: (Evaluation Criteria) A: The viscosity after standing was 4 mPa·s or more and less than 6 mPa·s. B: The viscosity after standing was 6 mPa·s or more and less than 10 Pa·s. C: The viscosity after standing was 10 mPa·s or more.

[0067] [Table 2] Carboxymethylcellulose sodium salt: Fujifilm Wako Pure Chemical Industries, Ltd. BYK-348: Silicone surfactant, manufactured by BYK-Chemie

[0068] As described above, the ink compositions of the examples using the dispersion liquid of the present invention have excellent redispersibility, show little change in particle size distribution and viscosity before and after thermal storage, and are also excellent in ejection stability, compared to the comparative examples.

Claims

1. The ink contains water, a colorant, and a dispersion resin that disperses the colorant, the dispersion resin has a structural unit A made of a hydrophobic monomer, a structural unit B made of a (meth)acrylic acid monomer or a (meth)acrylic acid ester monomer having hydrophilicity and compatible with water at 25°C, and a structural unit C made of an acrylamide monomer having a sulfonic acid group, The weight average molecular weight of the dispersion resin is 5,000 to 100,000; The content of the structural unit A is 61 to 70 mol% based on the total amount of the dispersion resin, The content of the structural unit C is 15 to 32 mol% based on the total amount of the dispersion resin. dispersion liquid.

2. The weight average molecular weight of the dispersion resin is 7,000 to 60,000. The dispersion of claim 1.

3. The hydrophobic monomer includes a vinyl monomer having an aromatic group and an acrylic ester monomer having a hydrocarbon group.

3. The dispersion according to claim 1 or 2.

4. The hydrophilic (meth)acrylic acid monomer or (meth)acrylic acid ester monomer includes (meth)acrylic acid and an acrylic acid ester monomer having a polyalkylene glycol group. The dispersion according to any one of claims 1 to 3.

5. the acrylamide monomer comprises 2-acrylamido-2-methylpropanesulfonic acid; The dispersion according to any one of claims 1 to 4.

6. The content of the structural unit B is 7 to 16 mol% based on the total amount of the dispersion resin. The dispersion according to any one of claims 1 to 5.

7. The content of the coloring material is 7.5 to 30% by mass based on the total amount of the dispersion liquid. The dispersion according to any one of claims 1 to 6.

8. The content of the dispersion resin is 2.5 to 10% by mass based on the total amount of the dispersion liquid. The dispersion according to any one of claims 1 to 7.

9. The dispersion liquid according to any one of claims 1 to 8, a surfactant, and a water-soluble organic solvent; Including, An ink composition for ink-jet recording.

10. A dispersion resin comprising: a structural unit A made of a hydrophobic monomer; a structural unit B made of a (meth)acrylic acid monomer or a (meth)acrylic acid ester monomer having hydrophilicity and compatible with water at 25°C; and a structural unit C made of an acrylamide monomer having a sulfonic acid group, The weight average molecular weight of the dispersion resin is 5,000 to 100,000; The content of the structural unit A is 61 to 70 mol% based on the total amount of the dispersion resin, The content of the structural unit C is 15 to 32 mol% based on the total amount of the dispersion resin. Dispersion resin that disperses color materials.

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