(METH)acrylic copolymer, (meth)acrylic copolymer composition, and ink

Abstract

The present invention relates to a (meth)acrylic copolymer which is excellent in solubility in alkaline water, storage stability of ink, and hiding property in film printing; a (meth)acrylic copolymer composition containing the (meth)acrylic copolymer; and an ink containing the (meth)acrylic copolymer composition. The (meth)acrylic copolymer of the present invention has a structural unit derived from an alkyl (meth)acrylate having 1 to 8 carbon atoms in the alkyl group, a structural unit derived from a vinyl compound containing an acid group, and a chemical structure derived from a thiol having a functionality of three or more; the (meth)acrylic copolymer composition of the present invention contains the (meth)acrylic copolymer, water, and an alkaline compound; and the ink of the present invention contains the (meth)acrylic copolymer composition.

Description

Technical Field

[0001] This invention relates to a (meth)acrylic acid copolymer, a (meth)acrylic acid copolymer composition, and an ink.

[0002] This application claims priority based on Japanese Patent Application No. 2020-192003, filed with the Japan Patent Office on November 18, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] Water-based inks (also known as solvent-based inks) differ from solvent-based inks in that they reduce the amount of volatile organic compounds (VOCs), thus reducing fire hazards and mutagenic toxicity. Therefore, water-based inks are widely used in applications such as gravure printing. Among them, (meth)acrylic polymers and (meth)acrylic copolymers containing structural units derived from (meth)acrylic alkyl esters, structural units derived from (meth)acrylic acid, are widely used in water-based ink applications due to their high transparency and good pigment development.

[0004] In addition to good solubility in alkaline water, (meth)acrylic polymers and (meth)acrylic copolymers used in water-based inks are required to have a low total VOC content during dissolution, good storage stability, and good opacity during film printing.

[0005] Patent Document 1 describes a method in which a coating resin that can be diluted with water is produced by condensing a polycarboxylic acid resin and a polyol resin, which are produced by polymerization using a polyfunctional thiol solution, in a solvent different from the polymerization solvent, and then neutralizing them with an amine at 95°C and dispersing them in deionized water.

[0006] Patent document 2 describes a method for introducing hydrophobic and hydrophilic sites into a multifunctional thiol prepared in solution to obtain an aqueous pigment dispersion with high preservation stability.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 04-304277

[0010] Patent Document 2: International Publication No. 2019 / 065604 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, the method described in Patent Document 1 requires repeated solvent evaporation processes. Furthermore, amine neutralization is required to melt the resin during resin condensation and at a high temperature of approximately 95°C, resulting in low resin solubility in alkaline water. Additionally, there are problems such as the large total energy required to obtain the aqueous dispersion, and the solvents used in the polymerization and condensation processes remaining in the final composition.

[0013] In the method of Patent Document 2, the hydrophobic and hydrophilic components are introduced separately through a multi-stage polymerization process, resulting in a long polymerization process and low productivity. Furthermore, the (meth)acrylic acid copolymer obtained in the polymerization process needs to be neutralized with alkali at a high temperature of 70°C. Therefore, there is a problem of low solubility of the (meth)acrylic acid copolymer in alkaline water.

[0014] The present invention aims to provide a (meth)acrylic copolymer that exhibits good solubility in alkaline water, good ink storage stability, and good opacity in film printing; a (meth)acrylic copolymer composition containing the (meth)acrylic copolymer; and an ink containing the (meth)acrylic copolymer composition.

[0015] Technical solutions to the problem

[0016] The present invention has the following aspects:

[0017] [1] A (meth)acrylic acid copolymer having structural units derived from alkyl (meth)acrylic acid esters having 1 to 8 alkyl carbon atoms, structural units derived from vinyl compounds containing acid groups, and chemical structures derived from trifunctional or higher thiols, wherein the (meth)acrylic acid copolymer is a particulate solid.

[0018] [2] A (meth)acrylic acid copolymer having structural units derived from alkyl (meth)acrylic acid esters having 1 to 8 alkyl carbon atoms, structural units derived from vinyl compounds containing acid groups, and chemical structures derived from trifunctional or higher thiols, wherein the (meth)acrylic acid copolymer also has one or more chemical structures selected from chemical structures derived from monofunctional thiols and chemical structures derived from difunctional thiols.

[0019] [3] According to [1] or [2], the (meth)acrylic acid copolymer has a secondary glass transition temperature of 35°C or higher.

[0020] [4] The (meth)acrylic acid copolymer according to any one of [1] to [3] further comprises structural units derived from compounds having two or more polymerizable double bonds.

[0021] [5] The (meth)acrylic acid copolymer according to any one of [1], [3], [4] also has one or more chemical structures selected from the chemical structures derived from monofunctional thiols and the chemical structures derived from difunctional thiols.

[0022] [6] A (meth)acrylic acid copolymer according to any one of [1] to [5], wherein the mass average particle size of the (meth)acrylic acid copolymer is 20 to 2000 μm.

[0023] [7] A (meth)acrylic acid copolymer according to any one of [1] to [6], wherein the water content of the (meth)acrylic acid copolymer is 0.01 to 10% by mass.

[0024] [8] A (meth)acrylic acid copolymer according to any one of [1] to [7], wherein the acid value of the (meth)acrylic acid copolymer is 20 to 140 mg KOH / g.

[0025] [9] A (meth)acrylic acid copolymer according to any one of [1] to [8], wherein the weight-average molecular weight of the (meth)acrylic acid copolymer is 15,000 to 80,000.

[0026]

[10] A (meth)acrylic acid copolymer composition comprising: any one of [1] to [9] a (meth)acrylic acid copolymer, water, and an alkaline compound.

[0027]

[11] The (meth)acrylic copolymer composition according to

[10] further comprises a pigment.

[0028]

[12] An ink containing a (meth)acrylic copolymer composition of

[10] or

[11] .

[0029] Invention Effects

[0030] According to the present invention, it is possible to provide a (meth)acrylic copolymer that has good solubility in alkaline water, good ink storage stability and good opacity in film printing, a (meth)acrylic copolymer composition containing said (meth)acrylic copolymer, and an ink containing said (meth)acrylic copolymer composition. Detailed Implementation

[0031] The present invention will now be described in detail. The following embodiments are merely illustrative examples and are not intended to limit the invention to these embodiments only. The present invention can be practiced in various ways without departing from its spirit.

[0032] In this specification, "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. "(meth)acrylic acid derivatives" is a general term for acrylic acid derivatives and methacrylic acid derivatives. "(meth)acrylic acid copolymers" refers to copolymers having at least one of, for example, acryloyl and methacryloyl groups.

[0033] In this specification, "(meth)acrylate" is a general term for acrylates and methacrylates.

[0034] In this specification, the proportions of each structural unit of the (meth)acrylic acid copolymer and the proportions of the chemical structures derived from thiols are calculated from the mass ratios of the monomers and thiols used in the polymerization raw materials.

[0035] In this manual, "room temperature" means a temperature within the range of 23℃±2℃ unless otherwise stated.

[0036] [(Meth)acrylic acid copolymer]

[0037] <First-type (meth)acrylic acid copolymer>

[0038] The (meth)acrylic acid copolymer of the first embodiment of the present invention has a structural unit derived from an alkyl (meth)acrylic acid ester (hereinafter also referred to as "monomer (a)") having 1 to 8 alkyl carbon atoms, a structural unit derived from a vinyl compound containing an acid group (hereinafter also referred to as "monomer (b)"), and a chemical structure derived from a trifunctional or higher thiol.

[0039] The (meth)acrylic acid copolymer of the first embodiment preferably also has one or more chemical structures selected from those derived from monofunctional thiols and those derived from difunctional thiols. Furthermore, the (meth)acrylic acid copolymer may also have structural units derived from monomers other than monomers (a) and monomers (b) (hereinafter also referred to as "monomer (c)").

[0040] <Second-type (meth)acrylic acid copolymer>

[0041] The second embodiment of the (meth)acrylic acid copolymer of the present invention has structural units derived from monomer (a), structural units derived from monomer (b), and chemical structures derived from trifunctional or higher thiols. The (meth)acrylic acid copolymer further has one or more chemical structures selected from monofunctional thiols and difunctional thiols. Furthermore, the second embodiment of the (meth)acrylic acid copolymer may also have structural units derived from monomer (c).

[0042] <alkyl methacrylates with 1 to 8 carbon atoms>

[0043] The (meth)acrylic copolymers of the first and second embodiments of the present invention have structural units derived from alkyl (meth)acrylic esters having 1 to 8 alkyl carbon atoms, i.e., structural units derived from monomer (a).

[0044] Monomer (a) in the (meth)acrylic copolymers of the first and second embodiments can be exemplified by, for example: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, and isooctyl methacrylate.

[0045] Among these, methyl methacrylate, n-butyl methacrylate, and 2-ethylhexyl acrylate are preferred from the perspective that (meth)acrylic acid copolymers have better solubility in alkaline water and are more readily available.

[0046] These can be used individually or in combination with two or more.

[0047] Of the total 100% by mass of structural units derived from monomer (a) and structural units derived from monomer (b), the proportion of structural units derived from monomer (a) in the (meth)acrylic copolymers of the first and second embodiments is preferably 60 to 97% by mass, more preferably 80 to 95% by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0048] If the proportion of structural units derived from monomer (a) is within the above range, the film-forming properties and water resistance of the ink become good.

[0049] <Vinyl compounds containing acid groups>

[0050] The (meth)acrylic acid copolymers of the first and second embodiments of the present invention have structural units derived from vinyl compounds containing acid groups, i.e., structural units derived from monomer (b).

[0051] Examples of monomers (b) include, for example, vinyl compounds having acid groups such as carboxylic acids or sulfonic acids.

[0052] Specific examples of vinyl compounds having carboxylic acid groups in (meth)acrylic acid copolymers of the first and second methods include: monocarboxylic acids such as (meth)acrylic acid and crotonic acid; dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid; and some esters of these dicarboxylic acids.

[0053] Specific examples of vinyl compounds having a sulfonic acid group include vinyl sulfonic acid and 2-acrylamide-2-methylpropanesulfonic acid.

[0054] Among these, from the perspective of improving the water solubility of (meth)acrylic acid copolymers, vinyl compounds having carboxylic acid groups are preferred, and (meth)acrylic acid is more preferred.

[0055] These can be used individually or in combination with two or more.

[0056] Of the total 100% by mass of structural units derived from monomer (a) and structural units derived from monomer (b), the proportion of structural units derived from monomer (b) in the (meth)acrylic copolymers of the first and second embodiments is preferably 3 to 40% by mass, more preferably 5 to 20% by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0057] If the proportion of structural units derived from monomer (b) is within the above range, the solubility of (meth)acrylic acid copolymers in alkaline water and in other solvents becomes better.

[0058] Relative to the total mass of all structural units constituting the (meth)acrylic acid copolymer, the combined proportion of structural units derived from monomer (a) and structural units derived from monomer (b) in the (meth)acrylic acid copolymer of the first and second embodiments is preferably 70 to 99.9% by mass, more preferably 80 to 99% by mass, and even more preferably 85 to 95% by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0059] If the total ratio of structural units derived from monomer (a) to structural units derived from monomer (b) is within the above range, the solubility in alkaline water becomes very good.

[0060] In this specification, the total mass of all structural units constituting the (meth)acrylic acid copolymers of the first and second embodiments also includes the proportion of chemical structures derived from thiols, which will be described later.

[0061] <Thiols>

[0062] The (meth)acrylic acid copolymers of the first and second methods have chemical structures derived from trifunctional or higher thiols.

[0063] As detailed below, in the manufacture of the (meth)acrylic acid copolymers of the first and second methods, trifunctional or higher thiols are used as chain transfer agents in the polymerization reaction. The trifunctional or higher thiols become the initiation sites for polymerization, and the chemical structures derived from the trifunctional or higher thiols are introduced into the (meth)acrylic acid copolymers.

[0064] Thiols with three or more functions are compounds that have three or more thiol groups in a single molecule.

[0065] Examples of trifunctional or higher thiols in (meth)acrylic acid copolymers as the first and second methods include: 1,2,3-trimercaptopropane, 2,2-bis(mercaptomethyl)-1-mercaptobutane, 1,2,3,4-tetramercaptobutane, 2,2-bis(mercaptomethyl)-1,3-dimercaptopropane, triglycerides (3-mercaptopropionic acid), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), dipentaerythritol hexa(3-mercaptopropionate), triglycerides (mercaptoacetic acid), trimethylolpropane tris(mercaptoacetic acid), pentaerythritol tetra(mercaptoacetic acid), dipentaerythritol hexa(mercaptoacetic acid), trimethylolpropane tris(2-mercaptobutyrate), pentaerythritol tetra(2-mercaptobutyrate), dipentaerythritol hexa(2-mercaptobutyrate), etc.

[0066] Among these, from the perspective that (meth)acrylic acid copolymers have better solubility in alkaline water and are more readily available, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionic acid) ester, and pentaerythritol tetra(mercaptoacetic acid) ester are preferred.

[0067] These can be used individually or in combination with two or more.

[0068] Relative to a total of 100 parts by mass of structural units comprising all monomers derived from the (meth)acrylic acid copolymer, the proportion of chemical structures derived from trifunctional or higher thiols in the (meth)acrylic acid copolymer of the first and second embodiments is preferably 0.1 to 20 parts by mass, more preferably 1 to 6 parts by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0069] If the proportion of chemical structures derived from trifunctional or higher thiols is above the lower limit mentioned above, the solubility of (meth)acrylic acid copolymers in alkaline water tends to improve. If the proportion of chemical structures derived from trifunctional or higher thiols is below the upper limit mentioned above, the off-odor of (meth)acrylic acid copolymers is suppressed.

[0070] In addition to having a chemical structure derived from a trifunctional or higher thiol, the (meth)acrylic acid copolymer of the first embodiment preferably also has one or more chemical structures selected from monofunctional thiols and difunctional thiols. When the (meth)acrylic acid copolymer of the first embodiment also has one or more chemical structures selected from monofunctional and difunctional thiols, its viscosity when dissolved in alkaline water decreases, and it becomes easier to incorporate pigments, etc.

[0071] The second type of (meth)acrylic acid copolymer, in addition to having a chemical structure derived from trifunctional or higher thiols, also has one or more chemical structures selected from monofunctional and difunctional thiols. Therefore, according to the second type of (meth)acrylic acid copolymer, the viscosity is lower when dissolved in alkaline water, and it is easier to incorporate pigments, etc.

[0072] Monofunctional thiols are compounds that have one thiol group within a single molecule.

[0073] Examples of monofunctional thiols in (meth)acrylic acid copolymers of the first and second methods include: n-octylthiol, n-dodecylthiol, tert-dodecylthiol, n-butylthiol, mercaptoacetic acid, 3-mercaptopropionic acid, 2-mercaptoethanol, 2-ethylhexyl 3-mercaptopropionic acid, 2-ethylhexyl 3-mercaptopropionic acid, isooctyl 3-mercaptopropionic acid, isooctyl 3-mercaptopropionic acid, 2-methoxybutyl 3-mercaptopropionic acid, etc.

[0074] These can be used individually or in combination with two or more.

[0075] Relative to a total of 100 parts by mass of structural units comprising all monomers derived from the (meth)acrylic acid copolymer, the proportion of chemical structures derived from monofunctional thiols in the (meth)acrylic acid copolymers of the first and second embodiments is preferably 0.1 to 20 parts by mass, more preferably 1 to 6 parts by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0076] If the proportion of chemical structures derived from monofunctional thiols is above the lower limit mentioned above, the solubility of (meth)acrylic acid copolymers in alkaline water tends to improve. If the proportion of chemical structures derived from monofunctional thiols is below the upper limit mentioned above, the off-odor of (meth)acrylic acid copolymers is suppressed.

[0077] Bifunctional thiols are compounds that have two thiol groups in a single molecule.

[0078] Examples of bifunctional thiols in (meth)acrylic acid copolymers, such as those in the first and second methods, include: 1,4-dimercaptobutane, 3-oxo-1,5-pentanedithiol, 3-thia-1,5-pentanedithiol, ethylene glycol bis(3-mercaptopropionic acid), di(mercaptoacetic acid)-1,4-butanediol, etc.

[0079] These can be used individually or in combination with two or more.

[0080] Relative to a total of 100 parts by mass of structural units comprising all monomers derived from the (meth)acrylic acid copolymer, the proportion of chemical structures derived from bifunctional thiols in the (meth)acrylic acid copolymers of the first and second embodiments is preferably 0.1 to 20 parts by mass, more preferably 1 to 6 parts by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0081] If the proportion of chemical structures derived from difunctional thiols is above the lower limit mentioned above, the solubility of (meth)acrylic acid copolymers in alkaline water tends to improve. If the proportion of chemical structures derived from difunctional thiols is below the upper limit mentioned above, the off-odor of (meth)acrylic acid copolymers is suppressed.

[0082] <Other Individuals>

[0083] In addition to having structural units derived from monomer (a) and monomer (b), the (meth)acrylic acid copolymers of the first and second methods may also have structural units derived from other monomers (monomer (c)).

[0084] Examples of monomers (c) in the (meth)acrylic acid copolymers of the first and second embodiments include compounds having one polymerizable double bond (hereinafter also referred to as "monomer (c1)"), compounds having two or more polymerizable double bonds (hereinafter also referred to as "monomer (c2)"), etc. Among these, monomer (c2) is preferred as monomer (c). That is, in addition to having structural units derived from monomer (a) and structural units derived from monomer (b), the (meth)acrylic acid copolymer preferably also has structural units derived from monomer (c2).

[0085] Examples of monomers (c1) in the (meth)acrylic copolymers of the first and second embodiments include: styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, 4-(tert-butyl)styrene, p-(tert-butoxy)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, phenyl methacrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, stearyl methacrylate, lauryl methacrylate, etc.

[0086] These can be used individually or in combination with two or more.

[0087] Relative to a total of 100 parts by mass of structural units derived from monomer (a) and structural units derived from monomer (b), the proportion of structural units derived from monomer (c1) in the (meth)acrylic acid copolymers of the first and second embodiments is preferably 0.1 to 20 parts by mass, more preferably 1 to 6 parts by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0088] If the proportion of structural units derived from monomer (c1) is above the lower limit mentioned above, the storage stability of the ink tends to improve. If the proportion of structural units derived from monomer (c1) is below the upper limit mentioned above, the viscosity of the ink can be reduced, and the operability during printing becomes better.

[0089] Monomers (c2) in the (meth)acrylic acid copolymers of the first and second embodiments include, for example: ethylene glycol di(meth)acrylate, 1,2-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4-cyclohexanediethanol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, etc. Acrylates, pentaerythritol tetra(meth)acrylate, bisphenol A di(meth)acrylate, 2,2-bis{4-[2-(acryloyloxy)ethoxy)]phenyl}propane, 2,2-bis{4-[2-(methacryloyloxy)ethoxy)]phenyl}propane, tricyclodecanediethanol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, glycerol tri(meth)acrylate, ethoxy-modified isocyanuric acid tri(meth)acrylate, pentaerythritol hexa(meth)acrylate, 1,4-divinylbenzene, 1,3,5-trivinylbenzene, etc.

[0090] Among these, ethylene glycol diacrylate, 1,6-hexanediol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate are preferred from the perspective of lower viscosity when dissolved in alkaline water and easier incorporation of pigments.

[0091] These can be used individually or in combination with two or more.

[0092] Relative to a total of 100 parts by mass of structural units derived from monomer (a) and structural units derived from monomer (b), the proportion of structural units derived from monomer (c2) in the (meth)acrylic copolymers of the first and second embodiments is preferably 0.1 to 20 parts by mass, more preferably 1 to 6 parts by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0093] If the proportion of structural units derived from monomer (c2) is above the lower limit mentioned above, the storage stability of the ink tends to improve. If the proportion of structural units derived from monomer (c2) is below the upper limit mentioned above, the viscosity of the ink can be reduced, and the operability during printing becomes better.

[0094] <Physical Properties>

[0095] The (meth)acrylic acid copolymer of the first embodiment is a solid at room temperature. Since the (meth)acrylic acid copolymer of the first embodiment is a solid at room temperature, VOCs when dissolved in alkaline water can be reduced. Furthermore, compared to its dissolved state (aqueous solution) and dispersed state (dispersion), volume increase can be suppressed, making it suitable for transportation and storage.

[0096] The (meth)acrylic acid copolymer of the second type is also preferably solid at room temperature. When the (meth)acrylic acid copolymer of the second type is solid at room temperature, VOCs can be reduced when dissolved in alkaline water. Furthermore, compared to its dissolved state (aqueous solution) and dispersed state (dispersion), volume increase can be suppressed, making it suitable for transportation and storage.

[0097] Specific shapes of solid (meth)acrylic acid copolymers include: powder, plate, fragment, sphere, particle, granule, and pellet. Among these, powder, fragment, sphere, particle, and granule solids are preferred from the perspective of ease of handling when dissolved in solvents and alkaline water.

[0098] The (meth)acrylic acid copolymers of the first and second methods can be readily dissolved in water or in a mixture of water and an auxiliary solvent described later, by neutralization with the alkaline compound described later.

[0099] The secondary glass transition temperature (Tg) of the (meth)acrylic acid copolymers of the first and second embodiments is preferably 35°C or higher, more preferably 40°C or higher, and even more preferably 45°C or higher. The secondary glass transition temperature (Tg) of the (meth)acrylic acid copolymers of the first and second embodiments is preferably 70°C or lower, more preferably 60°C or lower, and even more preferably 55°C or lower. These lower and upper limits can be combined arbitrarily.

[0100] If the secondary glass transition temperature (Tg) of the (meth)acrylic acid copolymers of the first and second methods is within the above range, the aggregation between copolymer particles is suppressed when dissolved in alkaline water, and the solubility in alkaline water becomes better.

[0101] The secondary glass transition temperature (Tg) of the (meth)acrylic acid copolymers of the first and second methods can be determined using differential scanning calorimetry (DSC), and the specific determination method is as described in the examples.

[0102] The mass-average particle size of the (meth)acrylic acid copolymers in the first and second embodiments is preferably 20–2000 μm, more preferably 50–850 μm, even more preferably 80–700 μm, and particularly preferably 150–600 μm. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0103] If the mass average particle size of the (meth)acrylic acid copolymer is above or above the lower limit mentioned above, the formulation process becomes easier. Furthermore, if the mass average particle size of the (meth)acrylic acid copolymer is below or below the upper limit mentioned above, the dissolution time in alkaline water is shortened.

[0104] The mass average particle size of (meth)acrylic acid copolymers can be calculated by sieving 20g of granular resin by shaking for 5 minutes using a standard sieve.

[0105] The water content of the (meth)acrylic acid copolymers in the first and second embodiments is preferably 0.01 to 10% by mass relative to the total mass of the acrylic copolymer, more preferably 0.02 to 8.0% by mass, even more preferably 0.1 to 5.0% by mass, and particularly preferably 0.5 to 5.0% by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0106] If the moisture content of the (meth)acrylic acid copolymer is above the lower limit mentioned above, its solubility in alkaline water becomes good. Furthermore, if the moisture content of the (meth)acrylic acid copolymer is below the upper limit mentioned above, the water resistance of the printed material increases. Additionally, if the moisture content of the (meth)acrylic acid copolymer is within the above range, the workability of the copolymer becomes good when obtaining particulate (meth)acrylic acid copolymers.

[0107] The specific method for determining the moisture content of (meth)acrylic acid copolymers is as described in the Examples section.

[0108] The acid value of the (meth)acrylic acid copolymers in the first and second methods is preferably 20–140 mg KOH / g, more preferably 50–100 mg KOH / g, and even more preferably 55–90 mg KOH / g. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0109] If the acid value of the (meth)acrylic acid copolymer is above the lower limit mentioned above, its solubility in alkaline water becomes better. If the acid value of the (meth)acrylic acid copolymer is below the upper limit mentioned above, the amount of alkaline compound required for neutralization and dissolution can be reduced, and the water resistance of the printed material also becomes good.

[0110] The acid value of (meth)acrylic acid copolymers refers to the mass of potassium hydroxide required to neutralize 1 g of the (meth)acrylic acid copolymer, expressed in milligrams. The acid value of the (meth)acrylic acid copolymers in both methods can be determined by neutralization titration with potassium hydroxide solution based on the phenolphthalein color change point. Specific determination methods are as described in the Examples section.

[0111] The weight-average molecular weight (Mw) of the (meth)acrylic acid copolymers in the first and second embodiments is preferably 15,000 to 80,000, more preferably 15,000 to 60,000, further preferably 20,000 to 60,000, particularly preferably 25,000 to 60,000, and most preferably 25,000 to 40,000. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0112] If the weight-average molecular weight of the (meth)acrylic acid copolymer is above the lower limit mentioned above, the storage stability of the ink tends to be better. If the weight-average molecular weight of the (meth)acrylic acid copolymer is below the upper limit mentioned above, the viscosity of the ink decreases and the film-forming properties tend to be better.

[0113] The weight-average molecular weight (Mw) of the (meth)acrylic acid copolymers in both methods was determined by gel permeation chromatography (GPC) (converted to polystyrene). Specific determination methods are as described in the Examples section.

[0114] The number-average molecular weight (Mn) of the (meth)acrylic acid copolymers in the first and second embodiments is preferably 5,000 to 120,000, more preferably 8,000 to 80,000, further preferably 12,000 to 70,000, particularly preferably 15,000 to 60,000, and most preferably 20,000 to 50,000. The lower and upper limits of these numerical ranges can be combined arbitrarily.

[0115] If the number average molecular weight of the (meth)acrylic acid copolymer is above the lower limit mentioned above, the storage stability of the ink tends to be better. If the number average molecular weight of the (meth)acrylic acid copolymer is below the upper limit mentioned above, the viscosity of the ink decreases and the film-forming properties tend to be better.

[0116] The number-average molecular weight (Mn) of the (meth)acrylic acid copolymers in both methods was determined by gel permeation chromatography (GPC) (converted to polystyrene). Specific determination methods are as described in the Examples section.

[0117] <Manufacturing Method>

[0118] The (meth)acrylic acid copolymers of the first and second methods can be manufactured by known polymerization methods such as bulk polymerization, suspension polymerization, and emulsion polymerization. Among these polymerization methods, bulk polymerization and suspension polymerization are preferred from the perspective of easily obtaining copolymers in the form of powders, spheres, and particles that are easy to handle.

[0119] <Manufacturing method using suspension polymerization>

[0120] The (meth)acrylic acid copolymers of the first and second methods preferably include a suspension polymerization step, a first dehydration step, a washing step, a second dehydration step, and a drying step.

[0121] (Suspension polymerization process)

[0122] The suspension polymerization process involves dispersing the aforementioned monomers (a) and (b) and, as needed, monomer (c) in water and polymerizing them in the presence of trifunctional or higher thiols to obtain the (meth)acrylic acid copolymers of the first and second methods.

[0123] As a method for suspension polymerization, known methods can be employed. Examples of methods for suspension polymerization include: polymerizing monomers (a), (b), and, as needed, monomers (c) in water in the presence of a polymerization auxiliary in a reactor equipped with polymerization temperature control and stirring functions.

[0124] Examples of polymerization aids that can be used in the manufacture of (meth)acrylic acid copolymers in both the first and second methods include polymerization initiators, chain transfer agents, dispersants, and dispersing aids. However, at least as a chain transfer agent, a trifunctional or higher thiol is used.

[0125] As a polymerization aid, by using trifunctional or higher thiols, (meth)acrylic acid copolymers having chemical structures derived from trifunctional or higher thiols can be obtained in a first and second manner.

[0126] Examples of polymerization initiators that can be used in the manufacture of (meth)acrylic acid copolymers in the first and second methods include: 2,2'-azobis(2-isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), benzoyl peroxide, lauroyl peroxide, tert-butyl peroxide-2-ethylhexanoate, tert-amyl hydroxy-2-ethylhexanoate, tert-hexyl peroxide-2-ethylhexanoate, 1,1,3,3-tetramethyl butyl peroxide-2-ethylhexanoate, etc.

[0127] These can be used individually or in combination with two or more.

[0128] As a chain transfer agent that can be used in the manufacture of (meth)acrylic acid copolymers in the first and second methods, at least a trifunctional or higher thiol is used.

[0129] In addition, as a chain transfer agent, besides trifunctional or higher thiols, at least one of the above-mentioned monofunctional and difunctional thiols can also be used together.

[0130] In addition to these thiols, they can also be further combined with diphenyl disulfide, dibenzyl disulfide, and α-methylstyrene dimer.

[0131] These can be used individually or in combination with two or more.

[0132] Dispersants that can be used in the manufacture of (meth)acrylic acid copolymers in the first and second methods include, for example, surfactants that stably disperse monomers in water. Specifically, examples include copolymers of sodium 2-ethanesulfonate methacrylate with potassium methacrylate and methyl methacrylate, copolymers of sodium 3-propionic acid methacrylate with methyl methacrylate, copolymers of sodium methacrylate with methacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.

[0133] These can be used individually or in combination with two or more.

[0134] Examples of dispersing agents that can be used in the manufacture of (meth)acrylic acid copolymers in the first and second methods include: sodium sulfate, sodium carbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium chloride, calcium acetate, magnesium sulfate, manganese sulfate, etc.

[0135] These can be used individually or in combination with two or more.

[0136] (Meth)acrylic copolymers of the first and second methods are obtained in a slurry state through suspension polymerization. By dehydrating the slurry, (meth)acrylic copolymer particles with an approximately spherical shape are typically obtained.

[0137] (First dehydration process, second dehydration process)

[0138] The first dehydration process is a process of separating the (meth)acrylic acid copolymer particles of the first and second methods from the reaction solution by dehydrating the slurry after suspension polymerization using a dehydrator or the like.

[0139] The second dehydration process involves using a dehydrator or similar equipment to dehydrate the (meth)acrylic acid copolymer particles after the washing process, thereby separating the (meth)acrylic acid copolymer particles from the washing liquid.

[0140] Various dewatering machines can be used in each dewatering process, such as centrifugal dewatering machines and devices that remove water by suction on a porous belt, etc.

[0141] One dewatering machine can be used, or two of the same model can be prepared and used in different dewatering processes, or a variety of different models of dewatering machines can be used. From the perspectives of product quality, equipment investment cost, productivity, and operating costs, the appropriate model can be selected. When emphasizing a balance between product quality and production speed, it is preferable to use dedicated dewatering machines for each dewatering process.

[0142] (Washing process)

[0143] The washing process is a process of washing the (meth)acrylic acid copolymer particles separated from the reaction solution.

[0144] By washing, components other than the (meth)acrylic acid copolymer are removed to obtain the (meth)acrylic acid copolymers of the first and second methods.

[0145] Examples of washing methods include: adding washing liquid to the (meth)acrylic acid copolymer particles dehydrated in the first dehydration step, then slurrying and mixing the (meth)acrylic acid copolymer again; and continuing to add washing liquid after the dehydration step in a dehydrator with a washing function. Furthermore, these washing methods can be combined.

[0146] The type and amount of washing solution should be selected to achieve the purpose of the washing process. Examples of washing solutions include: water (ion-exchanged water, distilled water, purified water, etc.), aqueous solutions containing dissolved sodium salts, buffer solutions that can be adjusted to any pH, methanol, etc.

[0147] (Drying process)

[0148] The drying process is a process of drying the (meth)acrylic acid copolymer particles of the first and second methods after the second dehydration process.

[0149] Water remains on the surface of the (meth)acrylic acid copolymer particles after the second dehydration process. Furthermore, the interior of the (meth)acrylic acid copolymer is nearly saturated with water. Therefore, drying is preferable to further reduce the moisture content of the (meth)acrylic acid copolymers obtained in both the first and second methods.

[0150] Various dryers can be used in the drying process, such as: dryers that dry under reduced pressure and heat; dryers that dry (meth)acrylic acid copolymer particles while using heated air to transport them in the tube; and dryers that dry (meth)acrylic acid copolymer particles on the upper side while blowing heated air into the lower side of a perforated plate to make them flow.

[0151] The drying process is preferably carried out in a manner that brings the moisture content of the (meth)acrylic acid copolymers after the first and second drying processes to 0.01 to 10% by mass.

[0152] <Manufacturing methods utilizing bulk polymerization>

[0153] The bulk polymerization method for manufacturing (meth)acrylic acid copolymers preferably includes a bulk polymerization step and a pulverization step. A devolatilization step may be included between the bulk polymerization step and the pulverization step.

[0154] (Bulk polymerization process)

[0155] The bulk polymerization process is a process of polymerizing the above-mentioned monomers (a) and (b) and the required monomer (c) in the presence of trifunctional or higher thiols to obtain the (meth)acrylic acid copolymers of the first and second methods.

[0156] As a method for bulk polymerization, known methods can be employed. Examples of methods for bulk polymerization include: a method in which monomers (a), (b), and, as needed, monomers (c) are polymerized in a reactor equipped with polymerization temperature control, in the presence of a polymerization auxiliary agent.

[0157] Examples of polymerization aids include polymerization initiators and chain transfer agents. However, as at least chain transfer agents, thiols with trifunctionality or higher are used.

[0158] As polymerization initiators, examples of polymerization initiators previously exemplified in the description of the suspension polymerization process can be cited.

[0159] As chain transfer agents, examples can be cited from the previous description of the suspension polymerization process.

[0160] The reactor shape used in the bulk polymerization process is arbitrary. For example, as a laboratory-level method, a glass tank consisting of a rubber tube with loops at both ends clamped between two tempered glass plates and secured at the four corners can be used as a reactor. Furthermore, as an industrially usable reactor, a closed container with a stirring mechanism can be cited.

[0161] Regarding the polymerization temperature control function, for example, if the aforementioned glass tank is used as a reactor, a commercially available thermostatic water tank can be used. When using a closed container with a stirring mechanism, temperature control can be achieved through heat exchange between the outer surface of the reaction vessel and the temperature-regulated heat and cold media.

[0162] (Devourering process)

[0163] The devolatilization process is a process of removing (devolatilizing) volatile components (such as unreacted monomers, moisture, etc.) contained in the first and second type (meth)acrylic acid copolymers obtained in the bulk polymerization process.

[0164] As a devolatilization method, known methods can be used. Examples of devolatilization methods include: treating (meth)acrylic acid copolymers using an extruder with venting holes, etc.

[0165] The set temperature of the extruder can be determined by taking into account the boiling point of the volatile components that you want to remove.

[0166] (Grinding process)

[0167] The pulverization process is the process of pulverizing the (meth)acrylic acid copolymers of the first and second methods, which have undergone devolatilization treatment as needed, into the desired particle size.

[0168] As a pulverizing method, any pulverizing method corresponding to the required particle size can be used.

[0169] From the perspective of forming a slurry with water during neutralization and dissolution, the maximum diameter of the pulverized particles is preferably 5 mm or less, and more preferably 2 mm or less.

[0170] <Effects>

[0171] The (meth)acrylic acid copolymers of the first and second embodiments of the present invention described above exhibit excellent solubility and powder properties, thus showing good solubility in various solvents, particularly alkaline water. Furthermore, compositions and inks containing the (meth)acrylic acid copolymers of the first and second embodiments of the present invention exhibit excellent coatability, storage stability, and excellent opacity in film printing, thus reducing the likelihood of pinholes and uneven printing during printing.

[0172] Furthermore, the (meth)acrylic acid copolymers of the first and second embodiments of the present invention also exhibit excellent productivity.

[0173] <Application>

[0174] The (meth)acrylic acid copolymers of the first and second embodiments of the present invention can be used as raw materials for, for example, inks and coatings. They are particularly suitable as raw materials for water-based inks.

[0175] [(Meth)acrylic acid copolymer composition]

[0176] The (meth)acrylic acid copolymer composition of the present invention contains: one or more selected from the (meth)acrylic acid copolymers of the first and second embodiments of the present invention described above, water, and an alkaline compound.

[0177] (Meth)acrylic acid copolymer compositions may also contain pigments and solvents other than water (hereinafter also referred to as "auxiliary solvents").

[0178] Hereinafter, (meth)acrylic copolymer compositions containing pigments will also be specifically referred to as "pigment-containing compositions".

[0179] The content of the (meth)acrylic acid copolymer relative to the total mass of the (meth)acrylic acid copolymer composition is preferably 10-60% by mass, more preferably 15-50% by mass. The lower and upper limits of these ranges can be combined arbitrarily. If the content of the (meth)acrylic acid copolymer is above the lower limit, the film-forming properties become good, and the texture when printed on the substrate becomes good. If the content of the (meth)acrylic acid copolymer is below the upper limit, the film-forming properties become good, exhibiting good printing performance on various substrates.

[0180] The water content relative to the total mass of the (meth)acrylic acid copolymer composition is preferably 20-80% by mass, more preferably 30-70% by mass. The lower and upper limits of these ranges can be combined arbitrarily. If the water content is above the lower limit, the miscibility with the pigment becomes good. If the water content is below the upper limit, the viscosity of the dissolved (meth)acrylic acid polymer is low, and the miscibility with other materials becomes good.

[0181] The basic compound neutralizes the solid (meth)acrylic acid copolymer and dissolves it in water or in a mixture of water and an auxiliary solvent.

[0182] Examples of alkaline compounds include alkali metal hydroxides, ammonia, ammonia water, and amine compounds.

[0183] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0184] Examples of amine compounds include: triethylamine, 1-propylamine, diethylamine, triisopropylamine, dibutylamine, pentanamine, 1-octylamine, 2-(dimethylamino)ethanol, 2-(ethylamino)ethanol, 2-(diethylamino)ethanol, 1-amino-2-propanol, 2-amino-1-propanol, 3-amino-1-propanol, 1-(dimethylamino)-2-propanol, 3-(dimethylamino)-1-propanol, 2-(propylamino)ethanol, bis(3-ethoxypropyl)amine, aminobenzyl alcohol, morpholine, N-methylmorpholine, tetrabutylammonium hydroxide, etc.

[0185] Among these, triethylamine and 2-(dimethylamino)ethanol are preferred from the perspectives of high amine value per unit usage, reduced amount of amine required for neutralization, ability to achieve low VOC in ink, and easy volatilization after drying of printed matter, making them less likely to remain on printed matter.

[0186] These can be used individually or in combination with two or more.

[0187] The content of the basic compound relative to the total mass of the (meth)acrylic acid copolymer composition is preferably 0.1 to 10% by mass, more preferably 2 to 5% by mass. The lower and upper limits of these ranges can be combined arbitrarily. If the content of the basic compound is above the lower limit, the solubility of the (meth)acrylic acid polymer composition becomes good. If the content of the basic compound is below the upper limit, the water resistance after printing becomes good.

[0188] Examples of pigments include: titanium dioxide, carbon black, phthalocyanine blue, phthalocyanine green, chrome yellow, cadmium yellow, lead chromate, cobalt blue, chrome green, cobalt green, benzidine yellow, and zinc white. In addition, any commercially available pigment can also be used.

[0189] These can be used individually or in combination with two or more.

[0190] When the (meth)acrylic acid copolymer composition contains pigment, the pigment content is preferably 20-60% by mass, more preferably 20-50% by mass, relative to the total mass of the (meth)acrylic acid copolymer composition. The lower and upper limits of these ranges can be combined arbitrarily. If the pigment content is above the lower limit, the opacity to the substrate is improved, and the color development of the coating film becomes better. If the pigment content is below the upper limit, the ink with dispersed pigment can be uniformly adjusted, resulting in a coating film with fewer pinholes.

[0191] The (meth)acrylic acid copolymer compositions of the present invention contain water as a solvent, but may also contain solvents other than water as auxiliary solvents as needed.

[0192] Examples of auxiliary solvents include water-soluble organic solvents such as alcohols, glycols, ethers, ketones, esters, and carbitols.

[0193] These can be used individually or in combination with two or more.

[0194] When the (meth)acrylic acid copolymer composition contains an auxiliary solvent, the content of the auxiliary solvent relative to the total mass of the (meth)acrylic acid copolymer composition is preferably 1 to 40% by mass, more preferably 2 to 30% by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily. If the content of the auxiliary solvent is above the aforementioned lower limit, the leveling properties of the (meth)acrylic acid copolymer composition can be further improved. If the content of the auxiliary solvent is below the aforementioned upper limit, the amount of volatile organic compounds (VOCs) contained in the (meth)acrylic acid copolymer composition can be reduced.

[0195] (Meth)acrylic acid copolymer compositions can be obtained, for example, by dissolving the (meth)acrylic acid copolymer together with a basic compound in water or in a mixture of water and an auxiliary solvent. Pigments may also be added as needed. A specific manufacturing method is to mix and stir the components constituting the (meth)acrylic acid copolymer composition using a commonly used mixer.

[0196] The (meth)acrylic copolymer compositions of the present invention described above are less prone to pinholes and uneven printing due to their excellent coatability, storage stability, and opacity in film printing.

[0197] [Ink]

[0198] The ink of the present invention contains the above-described (meth)acrylic acid copolymer composition.

[0199] In the case where the (meth)acrylic copolymer composition does not contain pigment, the ink preferably contains pigment in addition to the (meth)acrylic copolymer composition.

[0200] When the (meth)acrylic acid copolymer composition is a pigment-containing composition, the pigment-containing composition itself can be used as an ink, and it can be further diluted with water or an auxiliary solvent.

[0201] In addition, depending on the purpose, inks may also contain auxiliary solvents, binders, and other additives.

[0202] Relative to the total mass of the ink, the content of the (meth)acrylic copolymer of the first and second embodiments of the present invention in the ink is preferably 5 to 30% by mass, more preferably 10 to 25% by mass. The lower and upper limits of these numerical ranges can be combined arbitrarily. If the content of the (meth)acrylic copolymer is above the aforementioned lower limit, the aggregation of primary pigment particles can be suppressed. If the content of the (meth)acrylic copolymer is below the aforementioned upper limit, it becomes an ink with low viscosity and easy handling.

[0203] The water content in the ink is preferably 20-60% by mass relative to the total mass of the ink, more preferably 25-50% by mass. The lower and upper limits of these ranges can be combined arbitrarily. If the water content is above the lower limit, the ink has low viscosity and is easy to print. If the water content is below the upper limit, the printed matter dries well.

[0204] The content of alkaline compounds in the ink is preferably 0.1 to 10% by mass relative to the total mass of the ink, more preferably 2 to 5% by mass. The lower and upper limits of these ranges can be combined arbitrarily. If the content of the alkaline compounds is above the lower limit, the ink exhibits good film-forming properties. If the content of the alkaline compounds is below the upper limit, an image with good water resistance can be formed.

[0205] As pigments, examples can be found in the description of (meth)acrylic acid copolymer compositions previously provided.

[0206] The pigment content in the ink is preferably 10-50% by mass relative to the total mass of the ink, more preferably 20-40% by mass. The lower and upper limits of these ranges can be combined arbitrarily. If the pigment content is above the lower limit, it becomes an ink with excellent opacity to the substrate. If the pigment content is below the upper limit, agglomeration during printing is suppressed, resulting in an ink with less color unevenness.

[0207] The ink of the present invention contains water as a solvent, but may also contain solvents other than water as auxiliary solvents as needed.

[0208] As auxiliary solvents, examples include those previously exemplified in the description of (meth)acrylic acid copolymer compositions.

[0209] When the ink contains an auxiliary solvent, the content of the auxiliary solvent relative to the total mass of the ink is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass. The lower and upper limits of these ranges can be combined arbitrarily. If the content of the auxiliary solvent is above the aforementioned lower limit, the leveling properties of the water-based ink can be further improved. If the content of the auxiliary solvent is below the aforementioned upper limit, the amount of volatile organic compounds (VOCs) contained in the ink can be reduced.

[0210] The ink of the present invention may contain a binder to compensate for the adhesion of the ink substrate.

[0211] Examples of binders include: polyurethane dispersions (PUD), polyurethane-acrylate composite dispersions (PUA), acrylic emulsions, polyester dispersions, polyolefin dispersions, polyolefin-acrylate composite dispersions, and polyolefin-polyester dispersions.

[0212] These can be used individually or in combination with two or more.

[0213] Other additives include, for example, defoamers, leveling agents, pigment dispersants, film-forming aids, and adhesion promoters.

[0214] These can be used individually or in combination with two or more.

[0215] Inks are obtained, for example, by adding pigments and one or more auxiliary solvents, binders, and other additives, as needed, to a (meth)acrylic copolymer composition and mixing them. At this point, pigment dispersion treatment may be performed, if necessary. Furthermore, it may be further diluted with water, if required.

[0216] As a method for pigment dispersion, any dispersion method can be adopted, such as using commercially available rocking shakers, planetary bead mills, intermittent stirred bead mills, or continuous stirred bead mills.

[0217] The inks of the present invention described above are excellent in terms of coatability, storage stability, and opacity in film printing, thus making them less prone to pinholes and uneven printing during printing.

[0218] Example

[0219] The present invention will now be described in more detail through embodiments, but the present invention is not limited thereto.

[0220] The various measurement and evaluation methods in the following examples and comparative examples are shown below.

[0221] Please note that in the following description, unless otherwise stated, "parts" refers to parts by mass and "%" refers to percentage by mass.

[0222] [Measurement / Evaluation Methods]

[0223] <Determination of Secondary Glass Transition Temperature (Tg)>

[0224] Using a differential scanning calorimeter (manufactured by Seiko Instruments Co., Ltd., "EXSTAR DSC-6200"), 5 mg of (meth)acrylic acid copolymer was subjected to heating and cooling operations according to the temperature scanning conditions described below. When plotting the DSC data measured in step (3) under the temperature scanning conditions described below with temperature (°C) on the horizontal axis and DSC measurement value (Mw) on the vertical axis, a tangent line was drawn at the low-temperature side point where the slope of the curve changed by 0. The temperature (°C) corresponding to the intersection of this tangent line and the tangent line at the point where the slope of the curve changed by the maximum (inflection point) was taken as the secondary glass transition temperature (Tg) of the (meth)acrylic acid copolymer.

[0225] (Temperature scan conditions)

[0226] • Step (1): Stabilize at -10℃ for 5 minutes, then raise the temperature to 110℃.

[0227] Step (2): Cool to -10°C.

[0228] Step (3): Heat up to 110℃ again.

[0229] Step (4): Cool to room temperature.

[0230] • Heating rate: +10℃ / minute.

[0231] • Cooling rate: -10℃ / minute.

[0232] <Determination of Acid Value>

[0233] Accurately weigh approximately 0.5 g (A(g)) of the (meth)acrylic acid copolymer into a beaker and add 50 mL of a mixed solution of toluene and ethanol (mass ratio 1:1). Add a few drops of phenolphthalein and titrate with a 0.05 equivalent concentration KOH solution (solvent: ethanol). (Titration amount = B(mL), potency of KOH solution = f). Similarly, perform a blank determination (titation amount = C(mL)) and calculate the result according to the following formula.

[0234] Acid value (mgKOH / g) = {(BC) × 0.05 × 56.11 × f} / A

[0235] <Determination of weight-average molecular weight (Mw) and number-average molecular weight (Mn)>

[0236] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of (meth)acrylic acid copolymers were determined by gel permeation chromatography (GPC), and the values ​​were calculated in polystyrene using a calibration curve of standard polystyrene. The GPC determination conditions are shown below.

[0237] (GPC measurement conditions)

[0238] • Device: HLC-8220GPC manufactured by Tosoh Corporation.

[0239] • Chromatographic column: TSKgel G5000HXL manufactured by Tosoh Corporation "and GMHXL-L" It is formed by connecting in series.

[0240] • Eluent: Tetrahydrofuran.

[0241] • Sample concentration: 0.4%.

[0242] • Measurement temperature: 40℃.

[0243] • Injection volume: 100μL.

[0244] • Flow rate: 1.0 mL / min.

[0245] • Detectors: RI (built into the device), UV (Tosoh UV-8220).

[0246] <Determination of Moisture Content>

[0247] The moisture content of (meth)acrylic acid copolymers is calculated based on the moisture content of the (meth)acrylic acid copolymer being 0% after drying at 105°C for 2 hours, and is obtained from the weight loss of the (meth)acrylic acid copolymer before and after drying at 105°C for 2 hours.

[0248] <Evaluation of solubility in alkaline water>

[0249] 65.5 g of water and 30.0 g of (meth)acrylic acid copolymer were placed together with a stir bar into a glass bottle (manufactured by Kashiwagawa Glass Co., Ltd., "M-225"), the bottle was capped, and the mixture was stirred in a water bath at 30°C for 10 minutes to prepare a slurry. 4.5 g of 2-(dimethylamino)ethanol was added to the resulting slurry, and the mixture was further stirred at 30°C for 3 hours. The solubility was visually confirmed by checking the state of the solution. If precipitate was found in the solution, stirring was continued for another 3 hours, and the solubility in alkaline water was evaluated according to the following criteria.

[0250] A: After stirring for 3 hours initially, no precipitate could be visually identified, indicating excellent solubility.

[0251] A-: After stirring for 3 hours initially, precipitate could be visually identified, but after stirring for another 3 hours, the precipitate disappeared, indicating excellent solubility.

[0252] B: After stirring for 6 hours, there was obvious insoluble precipitate, indicating poor solubility.

[0253] <Evaluation of Storage Stability and Shielding>

[0254] (Preparation of (meth)acrylic acid copolymer compositions)

[0255] 65.5 g of water and 30.0 g of (meth)acrylic acid copolymer were placed together with a stir bar into a glass bottle (manufactured by Kashiwagawa Glass Co., Ltd., "M-225"), the bottle was capped, and the mixture was stirred at room temperature for 10 minutes to prepare a slurry. 4.5 g of 2-(dimethylamino)ethanol was added to the obtained slurry, and the mixture was further placed in a water bath at 60°C and stirred until no dissolved residue remained, yielding a (meth)acrylic acid copolymer composition with a (meth)acrylic acid copolymer concentration of 30%.

[0256] (Ink preparation)

[0257] 50g of the obtained (meth)acrylic acid copolymer composition, 30g of titanium dioxide CR-90 (manufactured by Ishihara Sangyo Co., Ltd.), 20g of 2-propanol, and 60g of glass microspheres were mixed in a container and then dispersed using a rocking shaker for 1 hour. Next, the glass microspheres were removed from the resulting mixture to obtain a pigment paste.

[0258] 60g of the obtained pigment paste was diluted with 11g of 2-propanol and 13g of water to obtain a water-based ink. The storage stability of the ink and the opacity of the printed matter were evaluated using the obtained water-based ink.

[0259] (Evaluation of storage stability)

[0260] The ink was left to stand at room temperature for 3 days. Visual inspection was performed to check for any pigment settling. Storage stability was then evaluated according to the following evaluation criteria.

[0261] A: After 3 days, the pigments in the ink are also in a dispersed state.

[0262] B: After 3 days, some or all of the pigment in the ink will have settled.

[0263] (Evaluation of the concealment)

[0264] Ink was applied to a gravure printing press (RK PRINTCOAT INSTRUMENTS, "GP-100") for printing. A printing plate with 150 lines per inch was used. Acrylic film (Toyobo Co., Ltd., "PYLEN Film OT P2108") was used as the substrate for printing.

[0265] For the printed coating, the color difference of transmitted light was measured using a spectrophotometer (Konica Minolta, Inc., "CM-5"). Then, the color difference was measured from L... * The ΔL value is obtained by subtracting 100 from the measured value of brightness, and the opacity is evaluated according to the following evaluation criteria. The smaller the ΔL value, the better the opacity of the printed material.

[0266] A: △L value ≦-22.5.

[0267] B: △L value > -22.5.

[0268] [Preparation of dispersant (1)]

[0269] In a polymerization apparatus equipped with a stirrer, cooling pipe, and thermometer, 1230 g of deionized water, 60 g of sodium 2-ethanesulfonate methacrylate, 10 g of potassium methacrylate, and 12 g of methyl methacrylate were added and stirred. The apparatus was purged with nitrogen, and the temperature was raised to the polymerization temperature of 50°C. 0.08 g of 2,2'-azobis(2-methylpropylimidazolium) dihydrochloride, used as a polymerization initiator, was added, and the temperature was further raised to the polymerization temperature of 60°C. Simultaneously with the addition of the polymerization initiator, methyl methacrylate was continuously added dropwise at a rate of 0.24 g / min for 75 minutes using a drop pump. The polymerization temperature was maintained at 60°C for 6 hours, and then cooled to room temperature to obtain dispersant (1). The solid content of the obtained dispersant (1) was 7.5%.

[0270] [Example 1]

[0271] In a polymerization apparatus equipped with a stirrer, cooling pipe, and thermometer, a monomer mixture containing 40 parts methyl methacrylate, 40 parts n-butyl methacrylate, 5 parts n-butyl acrylate, 15 parts methacrylic acid, and 1.2 parts trimethylolpropane trimethacrylate, 0.4 parts 2,2'-azobis(2-methylbutyronitrile), 2 parts 2-ethylhexyl 3-mercaptopropionate, 2 parts trimethylolpropane tri(3-mercaptopropionate), and 2 parts pentaerythritol tetra(mercaptoacetic acid) ester was added and stirred until homogeneous. Further, a liquid consisting of 160 parts homogeneous pure water, 0.1 parts sodium sulfate, and 0.6 parts dispersant (1) was added, and nitrogen was purged while stirring. Then, the temperature inside the flask was controlled at 80°C to initiate suspension polymerization. After detecting the polymerization heating peak, the mixture was treated at 90°C for 30 minutes to obtain a slurry-like (meth)acrylic acid copolymer (suspension polymerization step).

[0272] After polymerization, the reactor is cooled to room temperature, and the resulting slurry is dehydrated using a centrifugal dewatering machine (first dewatering step).

[0273] The obtained (meth)acrylic acid copolymer and pure water as washing liquid are added to the washing tank at a mass ratio of ((meth)acrylic acid copolymer: washing liquid) of 1:2. After stirring and mixing for 20 minutes for washing (washing step), the mixture is dehydrated using a centrifugal separator (second dehydration step).

[0274] After dehydration, the dehydrated (meth)acrylic acid copolymer is placed in a fluidized bed dryer with an internal temperature set at 40°C for drying so that the moisture content of the (meth)acrylic acid copolymer particles is below 10% (drying process).

[0275] For the obtained particulate solid (meth)acrylic acid copolymer particles, the secondary glass transition temperature (Tg), acid value, weight-average molecular weight (Mw), and number-average molecular weight (Mn) were measured, and their solubility in alkaline water was evaluated. Furthermore, water-based inks were prepared using the above method, and the storage stability of the inks and the opacity of the printed materials were evaluated. The results are shown in Table 1.

[0276] [Examples 2, 3, 5, 6; Comparative Examples 1-7]

[0277] In addition to using the formulations shown in Tables 1 and 2, particulate solid (meth)acrylic acid copolymer particles were prepared in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0278] [Example 4]

[0279] In a glass bath equipped with a thermometer, a homogeneous mixture of 70 parts methyl methacrylate, 5 parts n-butyl acrylate, 12 parts 2-ethylhexyl acrylate, 13 parts methacrylic acid, 1.2 parts trimethylolpropane triacrylate, 0.4 parts tert-butyl peroxide (manufactured by Nippon Oil Co., Ltd., "PERBUTYL O"), 4 parts 2-ethylhexyl 3-mercaptopropionate, and 2 parts pentaerythritol tetra(mercaptoacetic acid) ester was placed. After sealing, the temperature inside the glass bath was controlled at 83°C in a water bath to initiate bulk polymerization. After detecting the polymerization exothermic peak, the mixture was treated at 90°C for 30 minutes to obtain a blocky solid (meth)acrylic acid copolymer (bulk polymerization process).

[0280] After polymerization, the glass bath is cooled to room temperature. The blocky solid (meth)acrylic copolymer is removed from the bath, crushed with Sanitary Crusher SC-01 (manufactured by Sansho Kogyo Co., Ltd.), and then shaken on a 2mm sieve. The portion that passes through is collected to obtain particulate solid (meth)acrylic copolymer (crushing process).

[0281] For the obtained particulate solid (meth)acrylic acid copolymers, the secondary glass transition temperature (Tg), acid value, weight-average molecular weight (Mw), and number-average molecular weight (Mn) were determined, and their solubility in alkaline water was evaluated. Furthermore, water-based inks were prepared using the above method, and the storage stability of the inks and the opacity of the printed materials were evaluated. The results are shown in Table 1.

[0282] [Example 5]

[0283] The particulate solid (meth)acrylic acid copolymer obtained in Example 4 was agitated on a sieve with a pore size of 1 mm for 5 minutes, and the portion that passed through was collected to obtain particulate solid (meth)acrylic acid copolymer.

[0284] [Example 6]

[0285] The particulate (meth)acrylic acid copolymer obtained in Example 4 was agitated on a sieve with a pore size of 750 μm for 5 minutes, and the portion that passed through was collected to obtain particulate solid (meth)acrylic acid copolymer.

[0286] [Table 1]

[0287]

[0288] [Table 2]

[0289]

[0290] The abbreviations in the table are shown below. Additionally, blank columns in the table indicate that the ingredient was not included (the amount included is 0 parts).

[0291] MMA: Methyl methacrylate.

[0292] n-BMA: n-Butyl methacrylate.

[0293] n-BA: n-Butyl acrylate.

[0294] ·2-EHA: 2-Ethylhexyl acrylate.

[0295] •IBXMA: Isoborneol methacrylate.

[0296] MAA: Methacrylic acid.

[0297] ·TMPTMA: Trimethylolpropane trimethacrylate.

[0298] •HDDA: 1,6-hexanediol diacrylate.

[0299] • TMPTA: Trimethylolpropane triacrylate.

[0300] EHMP: 2-Ethylhexyl 3-mercaptopropionic acid.

[0301] ·EGMP: Ethylene glycol bis(3-mercaptopropionic acid) ester.

[0302] • TMPMP: Trimethylolpropane tris(3-mercaptopropionate).

[0303] ·PEMP: Pentaerythritol tetra(3-mercaptopropionic acid) ester.

[0304] •PETG: Pentaerythritol tetra(mercaptoacetic acid) ester.

[0305] ·AMBN: 2,2'-Azobis(2-methylbutyronitrile).

[0306] ·PERBUTYL O: tert-butyl peroxide-2-ethylhexanoate.

[0307] It should be noted that IBXMA is a substitute for monomer (a) (monomer (a')).

[0308] As shown in Table 1, the (meth)acrylic acid copolymers obtained in each example exhibit good solubility in alkaline water. Furthermore, the inks containing these (meth)acrylic acid copolymers demonstrate good storage stability and excellent opacity in film printing.

[0309] On the other hand, as can be seen from the results in Table 2, when using Comparative Examples 1 and 2, which are (meth)acrylic acid copolymers that do not have a chemical structure derived from trifunctional or higher thiols but instead have a chemical structure derived from monofunctional thiols, the storage stability of the ink and the opacity of the printed matter are poor.

[0310] Although it does not have a chemical structure derived from trifunctional or higher thiols, but instead has a chemical structure derived from monofunctional thiols, the (meth)acrylic acid copolymer of Comparative Example 3, which has a structural unit derived from HDDA (1,6-hexanediol diacrylate) as a structural unit derived from the monomer (C2), exhibits poor solubility in alkaline water. Furthermore, in the case of Comparative Example 3, although a (meth)acrylic acid copolymer composition was obtained, its viscosity was very high, making it impossible to perform pigment dispersion treatment and thus impossible to evaluate the storage stability of the ink and the opacity of the printed material.

[0311] Although Comparative Examples 4 and 5 do not possess chemical structures derived from trifunctional or higher-functional thiols, but instead have chemical structures derived from monofunctional or difunctional thiols, the (meth)acrylic acid copolymers in proportions lower than those in Comparative Examples 1 and 2 are insoluble in the eluent and cannot be used for GPC determination. Furthermore, they exhibit poor solubility in alkaline water. Moreover, in the cases of Comparative Examples 4 and 5, although (meth)acrylic acid copolymer compositions were obtained, their viscosity was extremely high, making pigment dispersion treatment impossible and thus hindering the evaluation of ink storage stability and print opacity.

[0312] The (meth)acrylic acid copolymers of Comparative Examples 6 and 7, which do not have structural units derived from monomer (a) or from monomer (b), exhibit poor solubility in alkaline water. Furthermore, in the cases of Comparative Examples 6 and 7, since the (meth)acrylic acid copolymers were not completely dissolved in alkaline water, (meth)acrylic acid copolymer compositions and inks could not be prepared, thus making it impossible to evaluate the storage stability of the ink and the opacity of the printed matter.

[0313] Industrial availability

[0314] According to the present invention, a (meth)acrylic copolymer with good solubility in alkaline water, good ink storage stability and good opacity in film printing, a (meth)acrylic copolymer composition containing said (meth)acrylic copolymer, and an ink containing said (meth)acrylic copolymer composition can be provided. Therefore, the (meth)acrylic copolymer of the present invention is also applicable to the field of resin compositions that can be developed by alkaline aqueous solutions, and is of great industrial importance.

Claims

1. A (meth)acrylic acid copolymer, characterized in that, It has structural units derived from alkyl esters of (meth)acrylate with 1 to 8 alkyl carbon atoms, structural units derived from vinyl compounds containing acid groups, chemical structures derived from trifunctional or higher thiols, and structural units derived from compounds having two or more polymerizable double bonds; the (meth)acrylate copolymer is a particulate solid with a secondary glass transition temperature of 35°C or higher and 67°C or lower.

2. A (meth)acrylic acid copolymer, characterized in that, It has structural units derived from alkyl esters of (meth)acrylate with 1 to 8 alkyl carbon atoms, structural units derived from vinyl compounds containing acid groups, chemical structures derived from trifunctional or higher thiols, and structural units derived from compounds having two or more polymerizable double bonds; the (meth)acrylate copolymer also has one or more chemical structures selected from chemical structures derived from monofunctional thiols and chemical structures derived from difunctional thiols, and its secondary glass transition temperature is above 35°C and below 67°C.

3. The (meth)acrylic acid copolymer according to claim 1 or 2, wherein the compound having two or more polymerizable double bonds is selected from one or more of ethylene glycol diacrylate, 1,6-hexanediol di(meth)acrylate and trimethylolpropane tri(meth)acrylate.

4. The (meth)acrylic acid copolymer according to claim 1, further having one or more chemical structures selected from the chemical structures derived from monofunctional thiols and difunctional thiols.

5. The (meth)acrylic acid copolymer according to any one of claims 1, 2, and 4, wherein, The mass-average particle size of the (meth)acrylic acid copolymer is 20–2000 μm.

6. The (meth)acrylic acid copolymer according to any one of claims 1, 2, and 4, wherein, The water content of the (meth)acrylic acid copolymer is 0.01 to 10% by mass.

7. The (meth)acrylic acid copolymer according to any one of claims 1, 2, and 4, wherein, The acid value of the (meth)acrylic acid copolymer is 20-140 mgKOH / g.

8. The (meth)acrylic acid copolymer according to any one of claims 1, 2, and 4, wherein, The weight-average molecular weight of the (meth)acrylic acid copolymer is 15,000 to 80,000.

9. A (meth)acrylic acid copolymer composition comprising: the (meth)acrylic acid copolymer according to any one of claims 1, 2, and 4, water, and an alkaline compound.

10. The (meth)acrylic copolymer composition according to claim 9, further comprising a pigment.

11. An ink comprising the (meth)acrylic acid copolymer composition of claim 9.

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