Water-based ink

Abstract

The present invention relates to an aqueous ink. In the aqueous ink, the aqueous ink contains a pigment, a fixing resin, and water. The fixing resin contains a structural unit derived from (meth)acrylic acid (A), a structural unit derived from a cycloalkyl (meth)acrylate (B), and a structural unit derived from an alkyl (meth)acrylate (C) having a glass transition temperature (Tg) of 0 °C or lower when made into a homopolymer. The content of the structural unit derived from (meth)acrylic acid (A) is 6 to 25% by mass in all the structural units of the fixing resin, and the content of the structural unit derived from the cycloalkyl (meth)acrylate (B) is 30 to 90% by mass in all the structural units of the fixing resin.

Description

Technical Field

[0001] The present invention relates to an aqueous ink. Background Art

[0002] In industrial printing markets such as packaging printing, resin films are mainly used as printing media from the viewpoint of durability. When the printing medium is a resin film, different from paper media, considering aspects such as the resin film not absorbing ink, poor wettability of the ink, and the constituent resin of the resin film being low in polarity, the fixability of the ink can be cited as an issue. Insufficient fixability of the ink to the resin film means that the ink coating film is easily peeled off from the resin film, and the peeling of the ink impairs the beauty of the printed matter and reduces the preservability of contents such as food. Therefore, the fixability of the ink to the resin film is required.

[0003] Conventionally, by using solvent-based inks or UV inks, fixing to the resin film has been possible, but volatile organic solvents and residual monomers impose a large burden on the environment and the human body. Therefore, the use of aqueous inks with a small environmental load is being promoted. However, the fixability of aqueous inks to resin films is a major issue, and new techniques for imparting fixability to aqueous inks are required.

[0004] For example, as an aqueous ink for inkjet that can record images with excellent fixability and rub resistance, Japanese Patent Laid-Open No. 2017-210604 (Patent Document 1) discloses an aqueous ink containing resin particles having: a first layer (inner side) formed of a first resin containing units derived from an ethylenically unsaturated monomer containing a specific amount of a cyclic aliphatic group, and a second layer (outer side) formed of a second resin having units derived from an ethylenically unsaturated monomer containing a specific amount of an ionic group. Summary of the Invention

[0005] The present invention relates to an aqueous ink, wherein the aqueous ink contains a pigment, a fixing resin, and water, and the fixing resin contains a structural unit derived from (meth)acrylic acid (A), a structural unit derived from (meth)acrylic cycloalkyl ester (B), and a structural unit derived from (meth)acrylic alkyl ester (C) having a glass transition temperature (Tg) of 0°C or lower when made into a homopolymer. The content of the structural unit derived from (meth)acrylic acid (A) is 6% by mass or more and 25% by mass or less in all the structural units of the fixing resin, and the content of the structural unit derived from (meth)acrylic cycloalkyl ester (B) is 30% by mass or more and 90% by mass or less in all the structural units of the fixing resin. Detailed Description

[0006] When printing a resin film with an aqueous ink, it is necessary for the aqueous ink to be sufficiently fixed to the resin film. However, in the technique of Patent Document 1, the fixability of the ink is insufficient.

[0007] The present invention relates to an aqueous ink having excellent fixing property to a resin film.

[0008] The present inventors have found that by using a resin containing a structural unit derived from (meth)acrylic acid, a structural unit derived from a cycloalkyl (meth)acrylate, and a structural unit derived from an alkyl (meth)acrylate having a glass transition temperature of 0°C or lower when made into a homopolymer as the fixing resin, the above problems can be solved.

[0009] That is, the present invention relates to an aqueous ink containing a pigment, a fixing resin, and water.

[0010] The fixing resin contains a structural unit derived from (meth)acrylic acid (A), a structural unit derived from a cycloalkyl (meth)acrylate (B), and a structural unit derived from an alkyl (meth)acrylate (C) having a glass transition temperature (Tg) of 0°C or lower when made into a homopolymer.

[0011] The content of the structural unit derived from (meth)acrylic acid (A) is 6% by mass or more and 25% by mass or less in all the structural units of the fixing resin.

[0012] The content of the structural unit derived from the cycloalkyl (meth)acrylate (B) is 30% by mass or more and 90% by mass or less in all the structural units of the fixing resin.

[0013] According to the present invention, an aqueous ink having excellent fixing property to a resin film can be provided.

[0014] [Aqueous ink]

[0015] The aqueous ink of the present invention is an aqueous ink containing a pigment, a fixing resin, and water.

[0016] The fixing resin contains a structural unit derived from (meth)acrylic acid (A), a structural unit derived from a cycloalkyl (meth)acrylate (B), and a structural unit derived from an alkyl (meth)acrylate (C) having a glass transition temperature (Tg) of 0°C or lower when made into a homopolymer.

[0017] The content of the structural unit derived from (meth)acrylic acid (A) is 6% by mass or more and 25% by mass or less in all the structural units of the fixing resin.

[0018] The content of the structural unit derived from the cycloalkyl (meth)acrylate (B) is 30% by mass or more and 90% by mass or less in all the structural units of the fixing resin.

[0019] It should be noted that "aqueous" means that water accounts for the largest proportion in the medium.

[0020] According to the present invention, an aqueous ink having excellent fixing property to a resin film can be provided. The reason is not necessarily clear, but it is considered as follows.

[0021] The fixing resin contained in the aqueous ink of the present invention contains a structural unit derived from a cycloalkyl (meth)acrylate (B). It is considered that the cycloalkyl ester moiety of the cycloalkyl (meth)acrylate (B) interacts closely with the resin film, and thus the fixing property is improved.

[0022] In addition, it is considered that the fixing resin contains a structural unit derived from an alkyl (meth)acrylate (C) having a glass transition temperature (Tg) of 0°C or lower when made into a homopolymer. Therefore, the Tg of the fixing resin can be lowered, thereby improving the wettability to the resin film and the fixing property.

[0023] <Aqueous Ink>

[0024] The aqueous ink of the present invention contains at least a pigment, a fixing resin, and water, and exhibits excellent fixing property in inkjet printing. Therefore, it is preferably used for inkjet printing.

[0025] As a preferred form of the pigment used in the aqueous ink of the present invention, the following can be cited: (i) a pigment capable of maintaining a dispersed state without a dispersant, that is, in the form of a self-dispersing pigment; (ii) in the form of pigment particles obtained by dispersing a pigment with a low molecular weight or high molecular weight surfactant; (iii) in the form of polymer particles containing a pigment. Among them, from the viewpoints of dispersion stability and fixing property of the pigment, the form of polymer particles containing a pigment is preferred.

[0026] Here, the "polymer particles containing a pigment" (hereinafter also referred to as "polymer particles containing a pigment") refers to particles in a form in which the polymer contains the pigment, particles in a form in which a part of the pigment is exposed on the surface of the particles composed of the polymer and the pigment, particles in a form in which the polymer is adsorbed on a part of the pigment, and may also be a mixture thereof. Among them, particles in a form in which the polymer contains the pigment are more preferred.

[0027] [Pigment]

[0028] The pigment used in the present invention can be either an inorganic pigment or an organic pigment.

[0029] As the inorganic pigment, for example, carbon black, metal oxides, etc. can be cited. In black ink, carbon black is preferred. As carbon black, furnace black, lamp black, acetylene black, channel black, etc. can be cited. In white ink, metal oxides such as titanium dioxide, zinc oxide, silicon dioxide, aluminum oxide, magnesium oxide, etc. can be cited.

[0030] Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, violanthrone pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, and the like.

[0031] The hue is not particularly limited, and any one of colored pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used in the colored ink.

[0032] The above pigments can be used alone or in combination of two or more.

[0033] [Polymer particles containing a pigment]

[0034] The polymer (hereinafter also referred to as "polymer a") constituting the polymer particles containing a pigment is not particularly limited as long as it has at least pigment dispersion ability.

[0035] Examples of polymer a include vinyl resins, polyester resins, polyurethane resins, etc. obtained by addition polymerization of vinyl monomers. Among them, from the viewpoints of pigment dispersion stability and fixing property, one or more selected from vinyl resins and polyester resins are preferred, and vinyl resins are more preferred.

[0036] Polymer a can be a synthetic product synthesized appropriately or a commercially available product.

[0037] The polymer particles containing a pigment are more preferably crosslinked polymer particles containing a pigment (hereinafter also referred to as "crosslinked polymer particles containing a pigment") obtained by further crosslinking the polymer particles containing a pigment with a crosslinking agent, and further preferably crosslinked vinyl polymer particles containing a pigment.

[0038] The polymer a before crosslinking can be a water-soluble polymer or a water-insoluble polymer, but a water-insoluble polymer is more preferred. Even if the polymer used is a water-soluble polymer, as long as it is crosslinked, the polymer becomes a water-insoluble polymer.

[0039] In this specification, the "water-insolubility" of a polymer means that when a polymer dried at 105 °C for 2 hours to a constant weight is dissolved in 100 g of water at 25 °C, the dissolved amount is less than 10 g. In the case where the polymer is an anionic polymer, the dissolved amount is the dissolved amount when the anionic group of the polymer is neutralized 100% with sodium hydroxide.

[0040] [Vinyl resin]

[0041] When the polymer a is a vinyl resin, from the viewpoint of improving the dispersion stability of the pigment, the vinyl resin preferably contains a structural unit derived from (a-1) an ionic monomer, and more preferably has a structural unit derived from (a-2) a hydrophobic monomer and / or (a-3) a nonionic monomer.

[0042] [(a-1) ionic monomer]

[0043] As the (a-1) ionic monomer, an anionic monomer is preferred, and examples thereof include carboxylic acid monomers and sulfonic acid monomers, and carboxylic acid monomers are more preferred.

[0044] As the carboxylic acid monomer, one or more selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid are exemplified, and (meth)acrylic acid is preferred. "(Meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

[0045] [(a-2) hydrophobic monomer]

[0046] The "hydrophobicity" of the (a-2) hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25 °C until saturation, its dissolved amount is less than 10 g.

[0047] Specific examples of the (a-2) hydrophobic monomer include the hydrophobic monomers described in paragraphs

[0020] to

[0022] of Japanese Patent Laid-Open No. 2018-83938. Among them, (meth)acrylic acid alkyl esters having an alkyl group with 1 to 18 carbon atoms, particularly 1 to 10 carbon atoms, aromatic group-containing monomers having an aromatic group with 6 to 22 carbon atoms, and macromonomers having a polymerizable functional group at a single terminal are preferred, and more preferably one or more selected from styrene, α-methylstyrene, and benzyl (meth)acrylate.

[0048] The macromonomer having a polymerizable functional group at a single terminal is a compound having a number average molecular weight of 500 or more and 100,000 or less, preferably 1,000 or more and 10,000 or less. As the polymerizable functional group, acryloyloxy or methacryloyloxy can be cited.

[0049] As the macromonomer, aromatic group-containing monomer-based macromonomers are preferred, and as the aromatic group-containing monomer constituting the same, the above-mentioned aromatic group-containing monomers can be cited.

[0050] Specific examples of commercially available styrene-based macromonomers include AS-6(S), AN-6(S), HS-6(S), etc. manufactured by Toagosei Co., Ltd.

[0051] [(a-3) nonionic monomer]

[0052] (a-3) The nonionic monomer is a monomer having a high affinity for water or a water-soluble organic solvent, for example, a monomer containing a hydroxyl group or a polyalkylene glycol chain.

[0053] As a specific example of the component (a-3), the nonionic monomers described in paragraph

[0018] of Japanese Patent Application Laid-Open No. 2018-83938 can be cited. Among them, one or more selected from methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferred.

[0054] The above components (a-1) to (a-3) can be used by separately using the monomer components contained in each component or by mixing two or more of them.

[0055] (Content of each structural unit in the vinyl resin)

[0056] From the viewpoint of improving the dispersion stability of the pigment, the content of the structural units derived from the components (a-1) to (a-3) in the vinyl resin is as follows.

[0057] The content of the component (a-1) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 12% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less.

[0058] The content of the component (a-2) is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less.

[0059] When the component (a-3) is contained, its content is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less.

[0060] The mass ratio of the component (a-1) to the component (a-2) [(a-1) component / (a-2) component] is preferably 0.15 or more, more preferably 0.2 or more, still more preferably 0.25 or more, and preferably 1.2 or less, more preferably 0.8 or less, still more preferably 0.5 or less.

[0061] (Manufacture of vinyl resin)

[0062] The vinyl resin can be produced by copolymerizing a monomer mixture using a known polymerization method. As the polymerization method, a solution polymerization method is preferred.

[0063] There is no restriction on the solvent used in the solution polymerization method. Polar solvents such as water, aliphatic alcohols, ketones, ethers, esters, etc. are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone, etc. are more preferred.

[0064] During polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. As the polymerization initiator, examples include persulfates such as ammonium persulfate and potassium persulfate, water-soluble azo polymerization initiators, etc. As the polymerization chain transfer agent, examples include thiols, etc.

[0065] The polymerization temperature varies depending on the types of polymerization initiator, monomer, solvent, etc. It is preferably 30 °C or higher, more preferably 50 °C or higher, and preferably 95 °C or lower, more preferably 80 °C or lower.

[0066] The polymerization atmosphere is preferably a nitrogen or inert gas atmosphere.

[0067] The vinyl resin is preferably neutralized with a neutralizing agent as described later.

[0068] From the viewpoints of dispersion stability and fixing property, the weight-average molecular weight of the vinyl resin is preferably 5000 or more, more preferably 8000 or more, further preferably 10,000 or more, and preferably 150,000 or less, more preferably 100,000 or less, further preferably 80,000 or less.

[0069] From the same viewpoints as above, the acid value of polymer a is preferably 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, further preferably 90 mgKOH / g or more, and preferably 400 mgKOH / g or less, more preferably 300 mgKOH / g or less, further preferably 200 mgKOH / g or less.

[0070] The measurement of the weight-average molecular weight and acid value of the polymer can be carried out by the methods described in the examples.

[0071] [Polyester resin]

[0072] When polymer a is a polyester resin, the polyester resin contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid.

[0073] (Alcohol component)

[0074] As the alcohol component of the raw material monomer of the polyester resin, polyhydric alcohols such as aromatic polyhydric alcohols and aliphatic polyhydric alcohols can be cited, and aromatic diols are preferably contained.

[0075] As the aromatic diol, an alkylene oxide adduct of bisphenol A is preferred.

[0076] The alkylene oxide adduct of bisphenol A is preferably specifically a compound represented by the following general formula (I-1).

[0077]

[0078] In the general formula (I-1), OR 1 and R 2 O are each oxyalkylene groups, preferably each independently oxyalkylene groups having 1 or more and 4 or less carbon atoms, more preferably oxyethylene or oxypropylene groups.

[0079] x and y are the molar numbers of addition of alkylene oxide. From the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more, and preferably 7 or less, more preferably 5 or less, and further preferably 3 or less.

[0080] In addition, x OR 1 and y R 2 O may be the same or different from each other, and are preferably the same from the viewpoint of fixability to the printing medium. The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct and an ethylene oxide adduct, and more preferably a propylene oxide adduct of bisphenol A.

[0081] From the viewpoint of improving fixability, the content of the alkylene oxide adduct of bisphenol A in the alcohol component is preferably 50 mol% or more, more preferably 60 mol% or more, further preferably 70 mol% or more, and 100 mol% or less.

[0082] As the alcohol component as a raw material monomer of the polyester resin, other alcohol components may also be used in addition to the alkylene oxide adduct of bisphenol A. Examples of other alcohol components include ethylene glycol, propylene glycol (1,2-propylene glycol), glycerin, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, or their alkylene oxide (having 2 or more and 4 or less carbon atoms) adducts (average addition molar number is 1 or more and 16 or less), etc.

[0083] (Carboxylic acid component)

[0084] In the carboxylic acid component as a raw material monomer of the polyester resin, carboxylic acids, their acid anhydrides, and their alkyl (having 1 or more and 3 or less carbon atoms) esters, etc. are included.

[0085] Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and polycarboxylic acids having 3 or more carbon atoms, etc., and preferably 1 or more selected from aromatic dicarboxylic acids and aliphatic dicarboxylic acids.

[0086] As the aromatic dicarboxylic acid, phthalic acid, isophthalic acid, and terephthalic acid are preferred, and terephthalic acid is more preferred.

[0087] As the aliphatic dicarboxylic acid, unsaturated aliphatic dicarboxylic acids and saturated aliphatic dicarboxylic acids can be mentioned. As the unsaturated aliphatic dicarboxylic acid, fumaric acid and maleic acid are preferred, and fumaric acid is more preferred. As the saturated aliphatic dicarboxylic acid, adipic acid and succinic acid are preferred. As the alicyclic dicarboxylic acid, cyclohexanedicarboxylic acid, decahydronaphthalenedicarboxylic acid, and tetrahydrophthalic acid are preferred. As the polycarboxylic acid having 3 or more carboxyl groups, trimellitic acid and pyromellitic acid are preferred.

[0088] The above carboxylic acid components can be used alone or in combination of two or more.

[0089] Among the above carboxylic acid components, aromatic dicarboxylic acids and aliphatic dicarboxylic acids are preferred, aliphatic dicarboxylic acids are more preferred, unsaturated aliphatic dicarboxylic acids are further preferred, and fumaric acid is even more preferred. In addition, it is also preferred to use an aromatic dicarboxylic acid and / or an alicyclic dicarboxylic acid in combination with an unsaturated aliphatic dicarboxylic acid.

[0090] The content of the unsaturated aliphatic dicarboxylic acid in the carboxylic acid component is preferably 25 mol% or more, more preferably 40 mol% or more, further preferably 60 mol% or more, even more preferably 70 mol% or more, and 100 mol% or less.

[0091] (Manufacture of polyester resin)

[0092] The polyester resin can be obtained by polycondensing at least an alcohol component and a carboxylic acid component. For example, it can be manufactured by polycondensing the above alcohol component and the above carboxylic acid component at a temperature of 180°C or higher and 250°C or lower in an inert gas atmosphere using an esterification catalyst as needed. The preferred embodiments and preferred contents of the alcohol component and the carboxylic acid component are as described above.

[0093] In the polycondensation reaction of the polyester resin, it is preferred to use an esterification catalyst.

[0094] As the esterification catalyst, metal compounds such as tin catalysts, titanium catalysts, antimony trioxide, zinc acetate, and germanium dioxide can be mentioned. From the viewpoint of the esterification reaction efficiency, tin catalysts are preferred. As the tin catalyst, dibutyltin oxide, tin(II) bis(2-ethylhexanoate), or their salts are preferred, and tin(II) bis(2-ethylhexanoate) is more preferred.

[0095] In addition, as needed, an esterification cocatalyst such as 3,4,5-trihydroxybenzoic acid can be further used, and a radical inhibitor such as 4-tert-butylcatechol and hydroquinone can be used in combination.

[0096] From the viewpoint of improving fixability, the acid value of the polyester resin is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, still more preferably 15 mgKOH / g or more, and is preferably 70 mgKOH / g or less, more preferably 50 mgKOH / g or less, still more preferably 40 mgKOH / g or less.

[0097] From the viewpoint of improving fixability, the weight-average molecular weight of the polyester resin is preferably 8,000 or more, more preferably 10,000 or more, still more preferably 12,000 or more, and from the viewpoint of the dispersion stability of the pigment, it is preferably 200,000 or less, more preferably 100,000 or less, still more preferably 50,000 or less.

[0098] The acid value and weight-average molecular weight of the polyester resin can be adjusted by appropriately adjusting the types of monomers used, the compounding ratio, the temperature of polycondensation, and the reaction time to prepare a desired resin. In addition, the acid value and weight-average molecular weight of the polyester resin are measured by the methods described in the examples.

[0099] [Preparation of Polymer Particles Containing Pigment]

[0100] Polymer particles containing a pigment can be effectively produced as a pigment aqueous dispersion by a method having the following steps 1 and 2.

[0101] Step 1: A step of subjecting a pigment mixture containing a pigment, polymer a, an organic solvent, and water to a dispersion treatment to obtain a dispersion-treated product

[0102] Step 2: A step of removing the organic solvent from the dispersion-treated product obtained in Step 1 to obtain an aqueous dispersion of polymer particles A containing a pigment (hereinafter, also referred to as "pigment aqueous dispersion (i)")

[0103] When polymer a is a vinyl resin, it is preferable to further perform the following Step 3.

[0104] Step 3: A step of adding a crosslinking agent to the pigment aqueous dispersion (i) obtained in Step 2 to crosslink the polymer particles containing a pigment to obtain an aqueous dispersion of crosslinked polymer particles containing a pigment (I) (hereinafter, also referred to as "pigment aqueous dispersion (I)")

[0105] The polymer particles containing a pigment according to the present invention also include the crosslinked polymer particles containing a pigment obtained in Step 3.

[0106] (Step 1)

[0107] The pigment mixture in Step 1 is preferably obtained by dissolving Polymer a in an organic solvent, and then adding a pigment, water, and, if necessary, a neutralizing agent, a surfactant, etc. to the obtained organic solvent solution for mixing to obtain an oil-in-water dispersion.

[0108] There is no limitation on the organic solvent used in Step 1. It is preferably a ketone, an ether, an ester, an aliphatic alcohol having 1 to 3 carbon atoms, etc. From the viewpoint of improving the wettability of the pigment and the adsorption of Polymer a to the pigment, it is more preferably a ketone having 4 to 8 carbon atoms, further preferably methyl ethyl ketone or methyl isobutyl ketone, and even more preferably methyl ethyl ketone. In the case where a vinyl resin is synthesized by a solution polymerization method as Polymer a, the solvent used in the polymerization can also be directly used.

[0109] When Polymer a has an acid group, at least a part of the acid group is preferably neutralized with a neutralizing agent. Thus, it is considered that the charge repulsion exhibited after neutralization becomes larger, the aggregation of pigment particles in the aqueous ink can be suppressed, and the dispersion stability of the pigment can be improved.

[0110] In the case of neutralization, it is preferably neutralized so that the pH becomes 7 or more and 11 or less.

[0111] Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, and sodium hydroxide and ammonia are preferred.

[0112] In addition, Polymer a can also be pre-neutralized.

[0113] From the viewpoint of improving the dispersion stability, the use equivalent of the neutralizing agent is preferably 20 mol% or more, more preferably 30 mol% or more, further preferably 40 mol% or more, and preferably 150 mol% or less, more preferably 120 mol% or less, and further preferably 100 mol% or less.

[0114] Here, when the polymer a before neutralization is defined as "Polymer a'", the use equivalent of the neutralizing agent can be calculated by the following formula.

[0115] Use equivalent of neutralizing agent (mol%) = [{Added mass of neutralizing agent (g) / Equivalent of neutralizing agent} / [{Acid value of Polymer a' (mgKOH / g) × Mass of Polymer a' (g)} / (56 × 1,000)]] × 100

[0116] In Step 1, the dispersion treatment can also micronize the pigment particles to a desired particle size only by primary dispersion using shear stress. However, from the viewpoint of obtaining a uniform pigment aqueous dispersion, it is preferred to pre-disperse the pigment mixture and then further perform primary dispersion.

[0117] As a disperser for predispersion, commonly used mixing and stirring devices such as anchor blades and dispersing blades can be used.

[0118] As a device for providing shear stress for main dispersion, for example, kneading machines such as roll mills and kneaders, high-pressure homogenizers such as microfluidic homogenizers, paint stirrers, and media dispersers such as bead mills can be cited. Among them, from the viewpoint of reducing the particle size of the pigment, a high-pressure homogenizer and a bead mill are preferably used.

[0119] In the case of performing dispersion treatment using a high-pressure homogenizer, by controlling the number of passes at a dispersion pressure of 20 MPa or more, it is possible to control the pigment to have a desired particle size, and it is also possible to adjust the average particle size of the pigment aqueous dispersion (I) described later.

[0120] (Step 2)

[0121] The removal of the organic solvent in Step 2 can be carried out by a known method. The organic solvent in the obtained pigment aqueous dispersion (i) is preferably substantially removed, but as long as the object of the present invention is not impaired, for example, it may remain at 0.1% by mass or less.

[0122] In addition, in order to remove coarse particles and the like, it is preferable to further centrifuge the aqueous dispersion from which the organic solvent has been removed, filter the liquid layer portion with a filter or the like, and obtain the substance passed through the filter or the like as the pigment aqueous dispersion (i).

[0123] (Step 3)

[0124] Step 3 is optional. A crosslinking agent is added to the pigment aqueous dispersion (i) obtained in Step 2 to crosslink a part of the carboxyl groups of the polymer a constituting the polymer particles containing the pigment, and a crosslinked structure is formed on the surface layer portion of the polymer particles containing the pigment, thereby obtaining a pigment aqueous dispersion (I) containing crosslinked polymer particles containing the pigment. Thus, it is considered that the polymer crosslinked from the polymer a is firmly adsorbed or immobilized on the pigment surface, and the aggregation of the pigment is suppressed. As a result, the dispersion stability of the obtained ink is further improved.

[0125] As the crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in the molecule is preferred, a compound having two or more glycidyl ether groups is more preferred, and a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 4 carbon atoms is further preferred.

[0126] From the viewpoint of improving the ease of reaction and the like, the molecular weight of the crosslinking agent is preferably 120 or more, more preferably 150 or more, and preferably 2,000 or less, more preferably 1,500 or less.

[0127] The epoxy equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, and preferably 300 or less, more preferably 200 or less.

[0128] Preferred examples of the crosslinking agent include polyglycidyl ethers such as trimethylolpropane polyglycidyl ether (water solubility 27% by mass) and pentaerythritol polyglycidyl ether (water solubility 0% by mass).

[0129] From the viewpoint of improving the fixing property and the like, the crosslinking rate in Step 3 is preferably 15 mol% or more, more preferably 20 mol% or more, further preferably 25 mol% or more, and preferably 80 mol% or less, more preferably 60 mol% or less, further preferably 50 mol% or less, based on the ratio of the molar equivalent number of the crosslinking functional groups of the crosslinking agent to the molar equivalent number of the carboxyl groups of Polymer a.

[0130] From the same viewpoint as above, the temperature of the crosslinking treatment is preferably 40°C or more, more preferably 50°C or more, and preferably 90°C or less, more preferably 80°C or less.

[0131] In the pigment aqueous dispersion (I) of the crosslinked polymer particles containing a pigment obtained in Step 3, from the viewpoint of ensuring the storage stability when the pigment aqueous dispersion (I) is used in the aqueous ink of the present invention, when the polymer constituting the crosslinked polymer particles containing a pigment has a crosslinked structure, the acid value is preferably 40 mgKOH / g or more, more preferably 60 mgKOH / g or more, further preferably 80 mgKOH / g or more, and preferably 160 mgKOH / g or less, more preferably 130 mgKOH / g or less, further preferably 100 mgKOH / g or less. In the present invention, the acid value when the polymer has a crosslinked structure can be calculated by multiplying the acid value of Polymer a before crosslinking by the crosslinking rate.

[0132] From the viewpoint of improving the dispersion stability of the pigment aqueous dispersion, the non-volatile component concentration (solid component concentration) of the obtained pigment aqueous dispersion (I) is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less.

[0133] The solid component concentration is measured by the method described in the examples.

[0134] From the viewpoint of dispersion stability, the content of the pigment in the pigment aqueous dispersion (I) is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 12% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less.

[0135] The mass ratio of the (crosslinked) polymer containing pigment particles to the pigment [(crosslinked) polymer / pigment] in the pigment aqueous dispersion (I) is preferably 0.08 or more, more preferably 0.1 or more, and preferably 0.8 or less, more preferably 0.7 or less.

[0136] From the viewpoint of dispersion stability, the average particle diameter of the (crosslinked) polymer particles containing the pigment is preferably 50 nm or more, more preferably 70 nm or more, further preferably 80 nm or more, and preferably 400 nm or less, more preferably 300 nm or less, further preferably 200 nm or less.

[0137] The average particle diameter is measured by the method described in the examples.

[0138] <Fixing resin>

[0139] From the viewpoints of improving fixing properties and improving the rub resistance of the obtained printed matter, the aqueous ink of the present invention contains a fixing resin.

[0140] The fixing resin more preferably contains a structural unit derived from (meth)acrylic acid, a structural unit derived from a cycloalkyl (meth)acrylate, and a structural unit derived from an alkyl (meth)acrylate having a glass transition temperature (Tg) of 0°C or lower when made into a homopolymer, and is composed only of the resin. That is, the fixing resin is preferably in the form of resin particles B that do not contain pigments (hereinafter also referred to as "resin particles B").

[0141] The structure of the resin particles B may be a structure in which the composition changes from the center of the resin particles toward the outer shell part, such as a core-shell structure, or a structure in which the composition is substantially homogeneous from the center of the resin particles toward the outer shell part, and more preferably a homogeneous structure.

[0142] The fixing resin is preferably used as an aqueous dispersion in which the resin particles B are dispersed in water.

[0143] The (meth)acrylic acid (A) constituting the fixing resin is one or more selected from acrylic acid and methacrylic acid. Among them, acrylic acid is preferred.

[0144] The cycloalkyl group of the cycloalkyl (meth)acrylate (B) constituting the fixing resin preferably has 4 or more and 12 or less carbon atoms, more preferably 5 or more and 8 or less carbon atoms. Preferred examples of the cycloalkyl (meth)acrylate include one or more selected from cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate. Among them, one or more selected from cyclopentyl acrylate, cyclohexyl acrylate, and cycloheptyl acrylate are preferred, and cyclohexyl acrylate is more preferred.

[0145] As the (meth)acrylic acid alkyl ester (C) having a glass transition temperature (Tg) of 0 °C or lower when made into a homopolymer, preferably, a (meth)acrylic acid alkyl ester having 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms in the alkyl group can be cited. As a preferred example thereof, one or more selected from ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (iso)butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate can be cited, and preferably, one or more selected from ethyl acrylate, butyl acrylate, isobutyl acrylate, and hexyl acrylate are used.

[0146] The above monomer components (A) to (C) can be used by separately using the monomers contained in each component alone or by mixing two or more of them.

[0147] Within the range not impairing the effects of the present invention, the fixing resin may contain structural units derived from other monomers other than the above monomers A to C. As other monomers, ionic monomers, hydrophobic monomers having an aromatic group, and nonionic monomers other than the above monomers A to C can be cited.

[0148] (Content of each structural unit in the fixing resin)

[0149] From the viewpoint of improving the fixability to the printing medium, the content of the structural units derived from each monomer in the fixing resin is as follows.

[0150] The content of the structural unit derived from (meth)acrylic acid (A) is 6% by mass or more, preferably 7% by mass or more, more preferably 8% by mass or more, further preferably 9% by mass or more, and 25% by mass or less, preferably 24% by mass or less, more preferably 23% by mass or less, further preferably 22% by mass or less.

[0151] The content of the structural unit derived from (meth)acrylic acid cycloalkyl ester (B) is 30% by mass or more, preferably 35% by mass or more, more preferably 40% by mass or more, further preferably 45% by mass or more, and 90% by mass or less, preferably 85% by mass or less, more preferably 80% by mass or less, further preferably 75% by mass or less.

[0152] The content of the structural unit derived from (meth)acrylic acid alkyl ester (C) is preferably 2% by mass or more, more preferably 4% by mass or more, further preferably 6% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, further preferably 50% by mass or less.

[0153] The resin for fixing can be produced by copolymerizing a monomer mixture containing the above-mentioned monomers (A), (B), (C), etc. by using a known polymerization method or the like.

[0154] From the viewpoint of improving the fixing property, the weight-average molecular weight of the resin for fixing is preferably 20,000 or more, more preferably 40,000 or more, still more preferably 80,000 or more, and preferably 2,000,000 or less, more preferably 1,000,000 or less, still more preferably 500,000 or less, and even more preferably 200,000 or less.

[0155] From the viewpoint of improving the fixing property, the acid value of the resin for fixing is preferably 20 mgKOH / g or more, more preferably 30 mgKOH / g or more, still more preferably 40 mgKOH / g or more, and preferably 200 mgKOH / g or less, more preferably 180 mgKOH / g or less, still more preferably 150 mgKOH / g or less, and even more preferably 120 mgKOH / g or less.

[0156] The weight-average molecular weight and acid value of the resin for fixing are measured by the methods described in the examples.

[0157] From the viewpoint of improving the fixing property, the glass transition temperature (Tg) of the resin for fixing is preferably -20°C or more, more preferably -15°C or more, still more preferably -10°C or more, and even more preferably -5°C or more, and preferably 50°C or less, more preferably 40°C or less, still more preferably 30°C or less, and even more preferably 20°C or less.

[0158] The glass transition temperature of the resin for fixing can be calculated according to the following Fox equation based on the mass ratio of the monomers in each polymer part.

[0159] 1 / Tg = (W1 / Tg1) + (W2 / Tg2) + ··· + (W m / Tg m )

[0160] W1 + W2 + ··· W m = 1

[0161] In the above Fox equation, Tg is the glass transition temperature of the polymer, and Tg1, Tg2, ···, Tg m are the glass transition temperatures of the homopolymers of the respective polymerization monomers. The unit of temperature is K. In addition, W1, W2, ···, W m represent the mass ratios of the respective monomers.

[0162] As the glass transition temperature of the homopolymer of each monomer in the above-mentioned Fox formula, for example, the values described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

[0163] From the viewpoint of the storage stability of the ink, the average particle diameter of the resin particles B in the aqueous ink is preferably 10 nm or more, more preferably 20 nm or more, further preferably 30 nm or more, and preferably 300 nm or less, more preferably 200 nm or less, and further preferably 150 nm or less.

[0164] The aqueous ink of the present invention may contain various additives such as water-soluble organic solvents, surfactants, humectants, wetting agents, viscosity regulators, defoamers, preservatives, fungicides, and rust inhibitors that are commonly used in aqueous inks.

[0165] (Water-soluble organic solvent)

[0166] Examples of the water-soluble organic solvent include glycol ethers, polyhydric alcohols, nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, and alkanolamines. Among them, one or more selected from glycol ethers and polyhydric alcohols are preferred.

[0167] As the glycol ether, alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers are preferred, and alkylene glycol monoalkyl ethers are more preferred. Preferred examples of the alkylene glycol monoalkyl ether include ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, and the like.

[0168] Examples of the polyhydric alcohol include alkylene glycols having 2 to 6 carbon atoms such as propylene glycol, diethylene glycol, 1,2-hexanediol, and glycerol.

[0169] (Surfactant)

[0170] As the surfactant, a nonionic surfactant is preferred, and one or more selected from acetylenic alcohol surfactants and silicone surfactants are more preferred.

[0171] Examples of the acetylenic alcohol surfactant include acetylenic diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, and their ethylene oxide adducts.

[0172] Examples of commercially available products of the acetylenic alcohol surfactant include the "Surfynol" series and "OLFINE" series manufactured by Nissin Chemical Industry Co., Ltd.

[0173] As the silicone surfactant, polyether-modified silicone is preferred. As its commercially available product examples, KF series manufactured by Shin-Etsu Chemical Co., Ltd. can be cited: KF-353, KF-355A, KF-642, KF-6011, etc., Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd., BYK series manufactured by BYK-Chemie Japan K.K., etc.

[0174] The aqueous ink of the present invention can be efficiently manufactured by mixing a pigment, a fixing resin, water, a water-soluble organic solvent as needed, a surfactant, and other additives, etc. There is no particular limitation on their mixing method.

[0175] <Content of each component in the aqueous ink, etc.>

[0176] From the viewpoint of improving the fixing property to the printing medium, the content of each component in the aqueous ink of the present invention and the ink physical properties are as follows.

[0177] (Content of the pigment)

[0178] The content of the pigment in the aqueous ink is preferably 2% by mass or more, more preferably 3% by mass or more, further preferably 4% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, further preferably 10% by mass or less.

[0179] (Content of the polymer particles containing the pigment)

[0180] The content of the polymer particles containing the pigment in the aqueous ink is preferably 3% by mass or more, more preferably 4% by mass or more, further preferably 5% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, further preferably 12% by mass or less.

[0181] (Content of the fixing resin)

[0182] The content of the fixing resin in the aqueous ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, further preferably 2% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, further preferably 6% by mass or less.

[0183] The mass ratio of the fixing resin to the polymer particles containing the pigment [fixing resin / polymer particles containing the pigment] is preferably 0.1 or more, more preferably 0.2 or more, and preferably 2 or less, more preferably 1 or less.

[0184] The content of the water-soluble organic solvent in the aqueous ink is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less.

[0185] The total content of surfactants in the aqueous ink is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 0.8% by mass or more, and is preferably 5% by mass or less, more preferably 4% by mass or less, still more preferably 3% by mass or less.

[0186] The content of water in the aqueous ink is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less.

[0187] (Physical properties of the aqueous ink)

[0188] From the viewpoint of fixability, the viscosity of the aqueous ink at 32 °C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, still more preferably 4 mPa·s or more, and is preferably 20 mPa·s or less, more preferably 15 mPa·s or less, still more preferably 12 mPa·s or less.

[0189] From the viewpoint of fixability, the pH of the aqueous ink at 20 °C is preferably 5.5 or more, more preferably 6.0 or more, still more preferably 6.5 or more, and from the viewpoints of component tolerance and skin irritation, it is preferably 11.0 or less, more preferably 10.5 or less, still more preferably 10.0 or less.

[0190] The aqueous ink of the present invention is filled in a known inkjet printing apparatus and can be ejected in the form of ink droplets onto a printing medium such as a resin film to print an image or the like. As a method of ejecting the ink droplets, any one of a piezoelectric method, a thermal method, and an electrostatic method can be adopted.

[0191] As the resin film, a transparent synthetic resin film can be mentioned, for example, a polyester film, a vinyl chloride film, a polypropylene film, a polyethylene film, a nylon film, etc. These films can be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film. Among them, a polyester film and a stretched polypropylene film are preferred, and a corona discharge-treated polyethylene terephthalate (PET) film and a corona discharge-treated biaxially stretched polypropylene (OPP) film are more preferred.

[0192] Examples

[0193] In the following production examples, preparation examples, examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. It should be noted that the measurement and calculation methods of each physical property and the like are as described below.

[0194] (1) Measurement of the number-average molecular weight and weight-average molecular weight of the polymer

[0195] In N,N-dimethylformamide, phosphoric acid and lithium bromide were dissolved at concentrations of 60 mmol / L and 50 mmol / L, respectively, and the resulting liquid was used as an eluent. By gel permeation chromatography [GPC device (HLC-8320GPC) manufactured by Tosoh Corporation, chromatographic columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolum Super AW-H) manufactured by Tosoh Corporation, flow rate: 0.5 mL / min], a monodisperse polystyrene kit with known molecular weights [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), manufactured by Tosoh Corporation] was used as a reference substance for measurement.

[0196] For the measurement sample, 0.1 g of the polymer was mixed with 10 mL of the above eluent in a glass bottle, stirred with a magnetic stirrer at 25 °C for 10 hours, and filtered through a syringe filter (DISMIC-13HP, PTFE, 0.2 μm, manufactured by ADVANTEC Co., Ltd.) to obtain the sample.

[0197] (2) Measurement of the average particle diameter of the pigment-containing polymer particles in the aqueous dispersion

[0198] Cumulative analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.) to measure the average particle diameter. A dispersion liquid diluted with water to a concentration of 5×10 -3 wt% (in terms of solid component concentration) was used. The measurement conditions were a temperature of 25 °C, an angle between the incident light and the detector of 90°, and 100 cumulative counts. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent, and the resulting cumulative average particle diameter was taken as the average particle diameter of the pigment-containing polymer particles.

[0199] (3) Measurement of the solid component concentration of the aqueous dispersion

[0200] Using an infrared moisture meter "FD-230" (manufactured by Kett Electric Laboratory Co., Ltd.), after drying 5 g of the measurement sample under the conditions of a drying temperature of 150 °C and a measurement mode of 96 (monitoring time 2.5 minutes / variation range 0.05%), the moisture (%) of the measurement sample was measured, and the solid component concentration was calculated by the following formula.

[0201] Solid component concentration (%) = 100 - moisture (%) of the measurement sample

[0202] (4) Determination of the acid value of the polymer

[0203] Dissolve the resin in a titration solvent prepared by mixing toluene and acetone (2:1) in an automatic potentiometric titrator (manufactured by Kyoto Electronics Industry Co., Ltd., automatic burette, model: APB - 610), and perform titration with a 0.1N potassium hydroxide / ethanol solution using potentiometric titration method. Take the inflection point on the titration curve as the end point. Calculate the acid value (mgKOH / g) from the titration volume up to the end point of the potassium hydroxide solution.

[0204] Production Example 1 (Production of Fixing Resin Emulsion 1)

[0205] (1) Charge 0.96 parts of acrylic acid, 4.80 parts of cyclohexyl acrylate, 2.24 parts of isobutyl acrylate, 5.89 parts of methyl ethyl ketone (MEK), and 0.65 parts of water as the initial charge into a reaction vessel equipped with a stirrer, reflux condenser, and dropping tank. Maintain the temperature of the reaction vessel at 77°C and stir for 10 minutes.

[0206] Then, continuously add the monomer mixture shown in Table 1, that is, 8.64 parts of acrylic acid, 43.2 parts of cyclohexyl acrylate, 20.16 parts of isobutyl acrylate, 53.0 parts of MEK, 5.89 parts of water, and 2.64 parts of 4,4'-azobis(4-cyanovaleric acid) as a polymerization initiator, into the reaction vessel over 5 hours. After the addition is completed, continue the polymerization reaction for 1 hour and then cool to room temperature to end the polymerization reaction.

[0207] (2) Add 4.2 parts of MEK to 15.8 parts of the copolymer obtained above so that the solid content concentration of the polymer solution becomes 40 wt%, and perform dilution. Then, add 1.6 parts of 5N sodium hydroxide aqueous solution and stir well at 25°C. Then, add 70.8 parts of water over 1 hour. After the addition is completed, evaporate MEK using an evaporator to obtain Fixing Resin Emulsion 1.

[0208] Production Examples 2 - 9, 11, 12 and Comparative Production Examples 1 - 4

[0209] Change the monomer composition of the fixing resin in Production Example 1 to the conditions shown in Table 1, and perform the same operations as in Production Example 1 to obtain Fixing Resin Emulsions 2 - 9, 11, 12, 21 - 24.

[0210] Production Example 10 (Production of Fixing Resin Emulsion 10)

[0211] (1) Charge 0.36 part of acrylic acid, 1.80 parts of cyclohexyl acrylate, 0.84 part of isobutyl acrylate, 4.29 parts of an emulsifier (sodium polyoxyethylene alkyl ether sulfate, manufactured by Kao Corporation, LATEMUL E-118B), 7.44 parts of a polymerization initiator (potassium persulfate), and 98.11 parts of water, which are the initial charges, into a reaction vessel equipped with a stirrer, a reflux condenser, and a dropping funnel. Maintain the temperature of the reaction vessel at 80 °C and stir for 30 minutes.

[0212] Next, continuously add the mixture of monomers and the like described in Table 1, namely 6.84 parts of acrylic acid, 34.2 parts of cyclohexyl acrylate, 15.96 parts of isobutyl acrylate, 2.63 parts of the above emulsifier (LATEMUL E-118B), 4.56 parts of a polymerization initiator (potassium persulfate), and 24.89 parts of water, to the reaction vessel over 3 hours. After the addition is completed, continue the polymerization reaction for 3 hours and then cool to room temperature to complete the polymerization reaction.

[0213] (2) Add 1.35 parts of a 5N aqueous sodium hydroxide solution to 10.0 parts of the emulsion copolymer obtained above, and stir well at 25 °C to obtain a fixing resin emulsion 10.

[0214]

[0215] Preparation Example 1 (Preparation of an aqueous dispersion of polymer particles 1 containing a pigment)

[0216] (1) Synthesis of a water-insoluble polymer

[0217] Mix 16 parts of methacrylic acid, 44 parts of styrene, 30 parts of a styrene macromonomer (manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight 6,000, solid content 50%), and 25 parts of methoxypolyethylene glycol methacrylate (manufactured by NOF Corporation, trade name: Blemmer PME-200) to prepare 115 parts of a monomer mixture.

[0218] Add 18 parts of MEK, 0.03 part of a chain transfer agent (2-mercaptoethanol), and 10% (11.5 parts) of the above monomer mixture to the reaction vessel, mix them, and perform sufficient nitrogen replacement.

[0219] On the other hand, a mixed solution containing the remaining 90% (103.5 parts) of the monomer mixture, 0.27 part of the above chain transfer agent, 42 parts of MEK, and 3 parts of a polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Fuji Film Wako Pure Chemical Corporation, trade name: V-65) was placed in a dropping funnel. Under a nitrogen atmosphere, the mixed solution in the reaction vessel was stirred while heating to 75°C, and the mixed solution in the dropping funnel was added dropwise over 3 hours. Then, after 2 hours at 75°C, a solution obtained by dissolving 3 parts of the above polymerization initiator in 5 parts of MEK was added, and the mixture was further cured at 75°C for 2 hours and at 80°C for 2 hours. Further, 50 parts of MEK was added to obtain a solution of a water-insoluble polymer (weight average molecular weight: 50,000, acid value: 104 mgKOH / g) (solid content concentration: 45%).

[0220] (2) Preparation of an aqueous dispersion of polymer particles 1 containing a pigment

[0221] 95.2 parts of the water-insoluble polymer solution obtained in the above (1) was dissolved in 53.7 parts of MEK, and 13.7 parts of 5N aqueous sodium hydroxide solution as a neutralizing agent, 0.5 part of 25% ammonia water, and 341.8 parts of ion-exchanged water were added thereto. Further, 100 parts of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 15:3) was added to obtain a pigment mixture (polymer neutralization degree: 72 mol%).

[0222] After the obtained pigment mixture was mixed at 7000 rpm and 20°C for 1 hour using a dispersion blade, it was further subjected to 15 passes of dispersion treatment at a pressure of 180 MPa using a microfluidizer (manufactured by Microfluidics Corporation, high-pressure homogenizer, trade name: M-140K).

[0223] The obtained dispersion of polymer particles containing a pigment was deaerated at 60°C under reduced pressure to remove MEK, and further a part of the water was removed. Then, centrifugation was performed, and the liquid layer was filtered through a membrane filter (manufactured by Sartorius Corporation, trade name: Minisart syringe filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous dispersion of polymer particles containing a pigment (solid content concentration: 22%).

[0224] To 100 parts of the aqueous dispersion of the obtained polymer particles containing a pigment, 0.45 part of a crosslinking agent (trimethylolpropane polyglycidyl ether, trade name: Denacol EX321L, epoxy equivalent: 130, manufactured by Nagase ChemteX Corporation), corresponding to a crosslinking ratio of 30 mol%, and 15.23 parts of ion-exchanged water were added, and heat treatment was carried out at 70 °C for 3 hours with stirring (solid content concentration: 22%). After cooling to room temperature, the liquid layer part was filtered through a membrane filter (trade name: Minisart syringe filter) to remove coarse particles, and an aqueous dispersion of polymer particles 1 containing a pigment was obtained (solid content concentration: 22%, pigment: 15.2%, polymer: 6.8%, average particle size: 110 nm).

[0225] Production Example 2 (Production of an aqueous dispersion of polymer particles 2 containing a pigment)

[0226] (1) Production of a polyester resin

[0227] Using polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane as the alcohol component, fumaric acid as the carboxylic acid component, tin(II) bis(2-ethylhexanoate) as the esterification catalyst, and 3,4,5-trihydroxybenzoic acid as the esterification co-catalyst, the reaction was carried out at 210 °C for 10 hours to obtain a polyester resin with an acid value of 22.4 mgKOH / g and a weight-average molecular weight of 13,700 ([molar ratio of carboxylic acid component / alcohol component]: 1.04).

[0228] (2) Production of an aqueous dispersion of polymer particles 2 containing a pigment

[0229] In a 2 L container, 66.7 g of the polyester resin obtained in the above (1) was dissolved in 198.6 g of MEK, and 5N sodium hydroxide aqueous solution was added thereto so that 85 mol% of the acid value of the polyester resin was neutralized. Further, 390.5 g of ion-exchanged water was added dropwise over 30 minutes, and the mixture was stirred and mixed at 1,500 r / min for 15 minutes at 10 to 15 °C using a dispersion blade.

[0230] Next, 100 g of C.I. Pigment Blue 15:3 (manufactured by Dainichi Seika Kogyo Co., Ltd., trade name: CFB6338JC) was added, and the mixture was stirred and mixed at 6,500 r / min for 2 hours at 10 - 15 °C using a dispersion blade to obtain a predispersion.

[0231] The obtained predispersion was filtered through a 200-mesh sieve, diluted by adding 36.1 g of ion-exchanged water, and then subjected to 15 passes of dispersion treatment at a pressure of 150 MPa using a microfluidic homogenizer (manufactured by Microfluidics, high-pressure homogenizer, trade name: M-110EH-30XP) to obtain an aqueous dispersion of polymer particles 2 containing pigments.

[0232] All of the obtained pigment aqueous dispersion was added to a 2-L eggplant-shaped flask, ion-exchanged water was added so that the solid content concentration became 15%, and using a rotary distillation apparatus (manufactured by Tokyo Rika Kikai Co., Ltd., rotary evaporator, trade name: N-1000S), it was maintained at a pressure of 0.09 MPa (abs) in a temperature-controlled bath adjusted to 32°C at a rotation speed of 50 r / min for 3 hours to remove the organic solvent. Further, the temperature-controlled bath was adjusted to 62°C, the pressure was reduced to 0.07 MPa (abs), and it was concentrated to a solid content concentration of 25% to obtain a concentrate.

[0233] The obtained concentrate was put into a 500-mL angle rotor, centrifuged at 3,660 r / min for 20 minutes using a high-speed cooling centrifuge (manufactured by Hitachi Koki Co., Ltd., trade name: himac CR22G, set temperature 20°C), and the liquid layer part was filtered using a membrane filter (trade name: Minisart syringe filter), and diluted with water so that the solid content concentration became 22% to obtain an aqueous dispersion of polymer particles 2 containing pigments (solid content concentration: 22%, pigment: 13.2%, polymer: 8.8%, average particle size: 95 nm).

[0234] Example 1 (Preparation of Aqueous Ink 1)

[0235] An aqueous dispersion of polymer particles 1 containing pigments (8.17 parts by solid content), 2.83 parts of the fixing resin emulsion obtained in Production Example 1, 32 parts of propylene glycol, 2 parts of diethylene glycol monoisobutyl ether (iBDG), 1 part of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol 440 (average number of moles of EO added: 3.5)), 0.25 part of a polyether-modified silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-6011), 0.2 part of a polyether-modified silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-353A), and ion-exchanged water were added to make up the ink composition (total 100 parts) shown in Table 2, and stirred well, and then filtered using a membrane filter (trade name: Minisart syringe filter) to obtain aqueous ink 1 (solid content concentration: 11%, pigment: 5.6%, polymer: 5.4%).

[0236] Examples 2 to 14 and Comparative Examples 1 to 4

[0237] Except in Example 1 where the conditions were changed to those shown in Table 2, the procedure was the same as in Example 1 to obtain aqueous inks 2 to 14 and 21 to 24.

[0238] It should be noted that the aqueous dispersion 1 described in Table 2 is an aqueous dispersion of polymer particles 1 containing a pigment, the aqueous dispersion 2 is an aqueous dispersion of polymer particles 2 containing a pigment, and the self-dispersing pigment is a cyan pigment (trade name: CAB-O-JET 450C) manufactured by Cabot Corporation.

[0239] Using the aqueous inks 1 - 14 and 21 - 24 obtained in the above Examples and Comparative Examples, prints were made by the method shown in (1) below, and the peel strength and transparent tape peel were evaluated by the methods shown in (2) and (3) below. The results are shown in Table 2.

[0240] It should be noted that the values in Table 2 are the amounts of active ingredients (solid component amounts).

[0241] (1) Production of Prints

[0242] Using a tabletop coater (manufactured by Mitsui Electric Precision Co., Ltd., trade name: TC-1 type) and a bar coater No. 3, the aqueous ink was coated on the corona discharge treated surfaces of a PET film (manufactured by Futamura Chemical Co., Ltd., trade name: FE2001#25) and an OPP film (manufactured by Futamura Chemical Co., Ltd., trade name: FOR-AQ#25), and dried at 50°C for 3 minutes to produce prints.

[0243] It should be noted that as a substitute for the inkjet printing test, a tabletop coater test, which is a simple evaluation method, was conducted. Regarding the tabletop coater test, it is considered relevant to the inkjet printing test in terms of fixability.

[0244] (2) Measurement of Peel Strength

[0245] A double-sided tape (manufactured by Nichiban Co., Ltd., trade name: Nice Tack, No. 4) was pasted on the obtained print, and a T-peel test was performed using a Tensilon universal material testing machine (manufactured by A&D Co., Ltd., trade name: RTC-1150A) to measure the peel strength (N / 15 mm).

[0246] The peel strength is preferably 1.5 N / 15 mm or more, more preferably 2 N / 15 mm or more.

[0247] (3) Measurement of Transparent Tape Peel

[0248] Attach a transparent tape (manufactured by NICHIBAN Co., Ltd., product name: CT-18) to the obtained printed matter and quickly peel it off. Visually confirm the peeled sample and evaluate it according to the following criteria.

[0249] (Evaluation criteria)

[0250] 〇: No peeling of the ink.

[0251] △: Areas where the ink has peeled off.

[0252] ×: All the ink has peeled off.

[0253] If the evaluation is 〇 or △, there is no practical obstacle.

[0254] It should be noted that there is no strong correlation between the above (2) peel strength and (3) transparent tape peeling. Preferably, the (2) peel strength is 1.5 N / 15 mm or more, and the evaluation of transparent tape peeling is 〇 or △.

[0255]

[0256] As can be seen from Table 2, compared with the water-based inks 21 to 24 obtained in the comparative examples, the water-based inks 1 to 14 obtained in the examples have excellent fixing properties. Therefore, a printed matter with excellent peel strength can be obtained.

[0257] Industrial applicability

[0258] According to the present invention, a water-based ink having excellent fixing properties for a resin film can be provided. The water-based ink for inkjet printing of the present invention is particularly useful for image formation on a resin film by inkjet printing.

Claims

1. An aqueous ink, wherein, the aqueous ink contains a pigment, a resin for fixing, and water, the resin for fixing comprises: a structural unit derived from (meth)acrylic acid (A), a structural unit derived from (meth)acrylic cycloalkyl ester (B), and a structural unit derived from (meth)acrylic alkyl ester (C) having a glass transition temperature Tg of 0 °C or lower when made into a homopolymer, the content of the structural unit derived from (meth)acrylic acid (A) is 6% by mass or more and 25% by mass or less in all the structural units of the resin for fixing, the content of the structural unit derived from (meth)acrylic cycloalkyl ester (B) is 60% by mass or more and 90% by mass or less in all the structural units of the resin for fixing, (meth)acrylic cycloalkyl ester (B) is one or more selected from cyclohexyl (meth)acrylate and cycloheptyl (meth)acrylate, the glass transition temperature Tg of the resin for fixing is -20 °C or higher and 40 °C or lower, the weight average molecular weight of the resin for fixing is 100,000 or more and 1,000,000 or less.

2. The aqueous ink according to claim 1, wherein, (meth)acrylic alkyl ester (C) is one or more selected from ethyl acrylate, butyl acrylate, isobutyl acrylate, and hexyl acrylate.

3. The aqueous ink according to claim 1 or 2, wherein, the content of the structural unit derived from (meth)acrylic alkyl ester (C) is 4% by mass or more and 60% by mass or less in all the structural units of the resin for fixing.

4. The aqueous ink according to claim 1 or 2, wherein, the acid value of the resin for fixing is 20 mgKOH / g or higher and 200 mgKOH / g or lower.

5. The aqueous ink according to claim 1 or 2, wherein, the resin for fixing is in the form of resin particles, and the average particle diameter of the resin particles is 10 nm or more and 300 nm or less.

6. The aqueous ink according to claim 5, wherein, the resin particles have a homogeneous structure.

7. The aqueous ink according to claim 1 or 2, wherein, the content of the resin for fixing in the aqueous ink is 0.5% by mass or more and 10% by mass or less.

8. The aqueous ink according to claim 1 or 2, wherein, the aqueous ink further contains a water-soluble organic solvent.

9. The aqueous ink according to claim 8, wherein, the water-soluble organic solvent is one or more selected from glycol ethers and polyols.

10. The aqueous ink according to claim 8, wherein, the content of the water-soluble organic solvent in the aqueous ink is 10% by mass or more and 50% by mass or less.

11. The aqueous ink according to claim 1 or 2, wherein, the aqueous ink further contains a surfactant.

12. The aqueous ink according to claim 11, wherein, the surfactant is one or more selected from alkynediol surfactants and silicone surfactants.

13. The aqueous ink according to claim 11, wherein, the total content of the surfactant in the aqueous ink is 0.1% by mass or more and 5% by mass or less.

14. The aqueous ink according to claim 1 or 2, wherein, The pigment is in the form of polymer particles containing the pigment.

15. The aqueous ink according to claim 14, wherein the polymer constituting the polymer particles containing the pigment is a vinyl resin.

16. The aqueous ink according to claim 15, wherein the vinyl resin has a structural unit derived from (a-1) an ionic monomer, a structural unit derived from (a-2) a hydrophobic monomer and / or (a-3) a nonionic monomer.

17. The aqueous ink according to claim 16, wherein the content of the (a-1) component in the vinyl resin is 5% by mass or more and 45% by mass or less.

18. The aqueous ink according to claim 16, wherein the content of the (a-2) component in the vinyl resin is 30% by mass or more and 90% by mass or less.

19. The aqueous ink according to claim 16, wherein as the mass ratio of the (a-1) component to the (a-2) component, (a-1) component / (a-2) component is 0.15 or more and 1.2 or less.

20. The aqueous ink according to claim 16, wherein the weight average molecular weight of the vinyl resin is 5,000 or more and 150,000 or less.

21. The aqueous ink according to claim 14, wherein the acid value of the polymer constituting the polymer particles containing the pigment is 50 mgKOH / g or more and 400 mgKOH / g or less.

22. The aqueous ink according to claim 14, wherein the polymer particles containing the pigment are crosslinked polymer particles containing the pigment obtained by further crosslinking the polymer particles containing the pigment with a crosslinking agent.

23. The aqueous ink according to claim 14, wherein the polymer constituting the polymer particles containing the pigment is a polyester resin containing a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid.

24. The aqueous ink according to claim 23, wherein the structural unit derived from the alcohol component contains an aromatic diol.

25. The aqueous ink according to claim 23, wherein the structural unit derived from the carboxylic acid contains one or more selected from aromatic dicarboxylic acids and aliphatic dicarboxylic acids.

26. The aqueous ink according to claim 14, wherein as the mass ratio of the fixing resin to the polymer particles containing the pigment, fixing resin / polymer particles containing the pigment is 0.1 or more and 2 or less.

27. The aqueous ink according to claim 1 or 2, wherein the water content in the aqueous ink is 30% by mass or more and 90% by mass or less.

28. The aqueous ink according to claim 1 or 2, wherein for resin film.

29. The aqueous ink according to claim 1 or 2, wherein for inkjet printing.

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