Resin composition for aqueous inkjet ink

Abstract

To provide a resin composition for aqueous inkjet ink, aqueous inkjet ink and a printed matter which have satisfactory nozzle clogging recoverability of an inkjet head even in printing on an impermeable substrate such as a film substrate, and impart excellent water and abrasion resistance and alcohol abrasion resistance.SOLUTION: A resin composition for aqueous inkjet ink has a core-shell structure which contains a core polymer (A) and a shell polymer (B) covering the core polymer (A), where the glass-transition temperature of the core polymer (A) is 65°C or higher, and the glass-transition temperature of the core polymer (A) is higher than the glass-transition temperature of the shell polymer (B), the acid value of the shell polymer (B) is 200 mgKOH / g or more, the mass ratio of the core polymer (A) and the shell polymer (B) is 90 / 10 to 60 / 40.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition for aqueous inkjet inks, an ink made using the same, and a printed matter thereof. [Background technology]

[0002] Digital printing methods are rapidly becoming more popular as printing runs become smaller and needs become more diverse. Because digital printing methods do not require plates, they enable small-lot production, cost reduction, and the miniaturization of printing equipment.

[0003] Inkjet printing, a type of digital printing method, is a method in which tiny droplets of ink are ejected from an inkjet head and landed on a recording medium to form images or characters (hereinafter collectively referred to as "printed matter") on the recording medium. Compared to other digital printing methods, inkjet printing is superior in terms of the size and cost of the printing device, running costs during printing, and ease of full-color printing, and has recently been increasingly used in industrial printing applications.

[0004] The inks used in inkjet printing methods vary widely, including oil-based, solvent-based, active energy ray-curable, and water-based inks. Until now, solvent-based and active energy ray-curable inks have been used for industrial printing applications. However, in recent years, there has been an increasing demand for water-based inks due to concerns about the harmful effects on the environment and people.

[0005] In recent years, there has been a demand for inkjet printing to be used in a wider range of applications, including packaging applications such as paper containers, labels, and wrapping films, in addition to industrial printing applications. In these cases, it is necessary to produce printed materials with properties that can withstand practical use on poorly permeable substrates such as coated paper and art paper, as well as non-permeable substrates such as polypropylene film and polyethylene terephthalate (PET) film.

[0006] When using inkjet printing to manufacture packaging materials, it is essential to form images on a film substrate. The water-based inks used in inkjet printing to date are designed to form images on highly permeable substrates such as plain paper or specialty paper (e.g., glossy photo paper). When printing on non-permeable substrates such as film substrates, the ink droplets do not penetrate the substrate at all after landing, and the pigments (coloring materials) remain attached to the substrate surface, resulting in low resistance to abrasion. Furthermore, to ensure ink stability, inks with high water solubility are generally used, which creates problems such as low resistance to water and alcohol.

[0007] To address the issue of low resistance, for example, Patent Documents 1 and 2 disclose that the use of emulsion in the ink can improve resistance to a certain extent. However, in both cases, problems arise such as the nozzles of the inkjet head being prone to clogging and being difficult to recover from the clogging.

[0008] Regarding the issue of nozzle clogging, for example, Patent Documents 3 and 4 disclose that the use of a core-shell emulsion in the ink can improve the recovery from clogging, but none of them provide sufficient resistance to friction when wet (water abrasion resistance and alcohol abrasion resistance). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 1991-160068 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-256194 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-101690 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-187235 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0010] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a resin composition for an aqueous inkjet ink, an aqueous inkjet ink, and a printed matter that exhibit good recovery from nozzle clogging in an inkjet head and that impart excellent water abrasion resistance and alcohol abrasion resistance, even when printing on a non-permeable substrate such as a film substrate.

[0011] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, they found that the above-mentioned problems can be solved suitably by a printed matter produced using a resin composition for an aqueous inkjet ink, which has a core-shell structure with a specific glass transition temperature, acid value, and core polymer / shell polymer mass ratio, and thus completed the present invention. [Means for solving the problem]

[0012] Specifically, the present invention relates to a resin composition for an aqueous inkjet ink having a core-shell structure containing a core polymer (A) and a shell polymer (B) that coats the core polymer (A), wherein the glass transition temperature of the core polymer (A) is 65°C or higher and is higher than the glass transition temperature of the shell polymer (B), the acid value of the shell polymer (B) is 200 mgKOH / g or higher, and the mass ratio of the core polymer (A) to the shell polymer (B) is 90 / 10 to 60 / 40.

[0013] The present invention also relates to a resin composition for a water-based inkjet ink, wherein the core polymer (A) contains 15 to 50 mass % of vinyl monomer units selected from styrene and α-methylstyrene.

[0014] The present invention also relates to a resin composition for a water-based inkjet ink, wherein the core polymer (A) has a content of hydrophilic vinyl monomer units of 1 to 5% by mass.

[0015] The present invention also relates to a resin composition for a water-based inkjet ink, wherein the core polymer (A) has a content of polyfunctional vinyl monomer units of 0 to 2% by mass.

[0016] The present invention also relates to a resin composition for use in a water-based inkjet ink, which has a 50% volume average particle size of 40 to 90 nm.

[0017] The present invention also relates to an aqueous inkjet ink containing the resin composition for an aqueous inkjet ink.

[0018] The present invention also relates to a printed matter using an aqueous inkjet ink containing the resin composition for an aqueous inkjet ink. [Effects of the Invention]

[0019] The resin composition for aqueous inkjet ink of the present invention has good recovery properties from nozzle clogging and can impart excellent water abrasion resistance and alcohol abrasion resistance to printed matter. DETAILED DESCRIPTION OF THE INVENTION

[0020] The resin composition for aqueous inkjet ink, which is an embodiment of the present invention, will be described below by taking preferred forms.

[0021] <Core-shell type emulsion resin> The resin composition for aqueous inkjet inks of the present invention contains an emulsion resin. Emulsion resins can exhibit abrasion resistance by forming an ultra-high molecular weight resin film on a substrate. However, problems arise, such as the tendency for inkjet head nozzles to clog and the difficulty in recovering from the clogged nozzles. Furthermore, it is difficult to achieve both water abrasion resistance and alcohol abrasion resistance, which are more advanced resistances. This results in the printed product not achieving the required resistance, resulting in poor appearance.

[0022] As a result of extensive research, the present inventors have discovered that a resin composition for an aqueous inkjet ink having a core-shell structure containing a core polymer (A) and a shell polymer (B) coating the core polymer (A), wherein the glass transition temperature of the core polymer (A) is 65°C or higher and is higher than the glass transition temperature of the shell polymer (B), the acid value of the shell polymer (B) is 200 mgKOH / g or higher, and the mass ratio of the core polymer (A) to the shell polymer (B) is 90 / 10 to 60 / 40, can provide printed matter that exhibits good recovery from inkjet head nozzle clogging and excellent water- and alcohol-based abrasion resistance. While the detailed mechanism is unclear, the following is believed to be one example.

[0023] First, the role of each component in the resin composition for a water-based inkjet ink of the present invention is as follows. In this emulsion resin with a core-shell structure containing a core polymer (A) and a shell polymer (B) that coats the core polymer (A), the glass transition temperature of the core polymer (A) is 65°C or higher, and the glass transition temperature of the core polymer (A) is higher than that of the shell polymer (B). This allows the shell polymer (B) to melt first during printing and drying, acting as a film-forming aid for the core polymer (A). This allows the emulsion resin to form a film even under high-speed production and low drying energy conditions, resulting in printed materials with excellent water and alcohol abrasion resistance. Furthermore, by increasing the acid value of the shell polymer (B) to 200 mg KOH / g or higher, redispersibility in water is improved. Furthermore, the glass transition temperature of the core polymer (A) is 65°C or higher, preventing fusion of the core polymer (A) with itself at temperatures near the operating temperature of aqueous inkjet heads. This is believed to improve nozzle clogging recovery in inkjet heads and provide good ejection stability. Furthermore, it is believed that the mass ratio of the core polymer (A) to the shell polymer (B) of 90 / 10 to 60 / 40 has solved the difficult problem of achieving both excellent durability of the printed matter and good ejection stability.

[0024] As described above, the resin composition for an aqueous inkjet ink of the present invention is essential for obtaining printed matter that exhibits good recovery from nozzle clogging in an inkjet head and has the excellent water abrasion resistance and alcohol abrasion resistance required for printed packaging.

[0025] <Core polymer (A)> The polymer constituting the core polymer (A) may be a homopolymer or a copolymer. The glass transition temperature of the core polymer (A) must be 65°C or higher in order to provide good water abrasion resistance, alcohol abrasion resistance, and good ejection stability by preventing fusion of the core polymers (A) together at temperatures near the operating temperature of an aqueous inkjet head. The glass transition temperature is more preferably 90°C or higher, and particularly preferably 100°C or higher. The glass transition temperature of the core polymer (A) is preferably at least 5° C. higher than the glass transition temperature of the shell polymer (B), more preferably at least 10° C. The difference in glass transition temperature between the core polymer (A) and the shell polymer (B) is preferably 50° C. or less, more preferably 40° C. or less.

[0026] When the polymer constituting the core polymer (A) is a homopolymer, the glass transition temperature of the homopolymer can be that described in various documents (e.g., Polymer Handbook, etc.). When the polymer constituting the core polymer is a copolymer, the glass transition temperature of the copolymer can be calculated from the glass transition temperatures of various homopolymers and the mass fractions of the monomers using the following FOX formula:

[0027]

number

[0028] The vinyl monomer constituting the core polymer (A) can be either a hydrophobic or hydrophilic vinyl monomer. Examples of the hydrophobic vinyl monomer include linear or branched alkyl group-containing vinyl monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, and tetradecyl (meth)acrylate; Alicyclic alkyl group-containing vinyl monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic vinyl monomers such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl acrylate, benzyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol acrylate, phenoxydiethylene glycol methacrylate, phenoxytetraethylene glycol acrylate, phenoxytetraethylene glycol methacrylate, phenoxyhexaethylene glycol acrylate, phenoxyhexaethylene glycol methacrylate, phenyl acrylate, and phenyl methacrylate; These may be used alone or in combination of two or more. In the present invention, "(meth)acrylate" refers to at least one selected from "acrylate" and "methacrylate".

[0029] As these hydrophobic vinyl monomers, aromatic vinyl monomers are preferred. The content of aromatic vinyl monomer units is preferably in the range of 15 to 50 mass% and more preferably 20 to 40 mass% per 100 parts by mass of core polymer (A). By setting the content within the above range, the water resistance and alcohol resistance of the core-shell resin emulsion are further improved. Furthermore, compatibility with shell polymer (B) is improved, resulting in improved gloss of printed matter. As the aromatic vinyl monomer, styrene and α-methylstyrene are preferred, and the total content of vinyl monomer units selected from styrene and α-methylstyrene is preferably 15 to 50 mass %. In the present invention, the vinyl monomer unit means a structural unit derived from a vinyl monomer.

[0030] Examples of the hydrophilic vinyl monomer include (meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N-pentoxymethyl-(meth)acrylamide, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethylmethacrylamide, N,N-di(ethoxymethyl)acrylamide, N-ethoxymethyl-N-propoxymethylmethacrylamide, and N,N-di(propoxymethyl)acrylamide. amide group-containing vinyl monomers such as N-butoxymethyl-N-(propoxymethyl)methacrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide, N,N-di(pentoxymethyl)acrylamide, N-methoxymethyl-N-(pentoxymethyl)methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, and N-(1,1-dimethyl-3-oxobutyl)acrylamide; hydroxyl group-containing vinyl monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, and allyl alcohol; anionic group-containing vinyl monomers such as dicarboxylic acid vinyl monomers, such as acrylic acid, methacrylic acid, carboxymethyl (meth)acrylate, carboxyethyl (meth)acrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, methacryloyloxyethyl phthalate, acryloyloxyisobutyrate, methacryloyloxyisobutyrate, 2-sulfoethyl (meth)acrylate, acryloyloxyethyl phosphonate, methacryloyloxyethyl phosphonate, 2-(phosphonooxy)ethyl (meth)acrylate, vinyl sulfonic acid, styrene carboxylic acid, styrene sulfonic acid, styrene phosphonate, itaconic acid, maleic acid, and fumaric acid, and anhydrides or half esters thereof; However, the present invention is not limited to these. These may be used alone or in combination of two or more. Among these, the use of an amide group-containing vinyl monomer can further improve the storage stability of the core-shell resin emulsion.

[0031] The content of these hydrophilic vinyl monomer units is preferably in the range of 1 to 5 mass % relative to 100 parts by mass of the core polymer (A), and more preferably 2 to 4 mass %. By keeping the content within this range, the balance between hydrophilicity and hydrophobicity can be adjusted and the storage stability of the core-shell resin emulsion can be further improved. Furthermore, compatibility with the shell polymer (B) is improved, resulting in improved gloss of printed materials.

[0032] In the core polymer (A) of the present invention, a polyfunctional vinyl monomer can be used. Specific examples include allyl (meth)acrylate, 1-methylallyl (meth)acrylate, 2-methylallyl (meth)acrylate, 1-butenyl (meth)acrylate, 2-butenyl (meth)acrylate, 3-butenyl (meth)acrylate, 1,3-methyl-3-butenyl (meth)acrylate, 2-chloroallyl (meth)acrylate, 3-chloroallyl (meth)acrylate, o-allylphenyl (meth)acrylate, 2-(allyloxy)ethyl (meth)acrylate, allyl lactyl (meth)acrylate, citronellyl (meth)acrylate, geranyl (meth)acrylate, rosinyl (meth)acrylate, cinnamyl (meth)acrylate, diallyl maleate, diaryl itaconic acid, vinyl (meth)acrylate, vinyl monomers having two or more vinyl groups, such as vinyl acrylate, vinyl crotonate, vinyl oleate, vinyl linoleate, 2-(2'-vinyloxyethoxy)ethyl (meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol (meth)acrylate, tetraethylene glycol (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, 1,1,1-trishydroxymethylethane diacrylate, 1,1,1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylpropane triacrylate, divinylbenzene, divinyl adipate, diallyl isophthalate, diallyl phthalate, and diallyl maleate; These may be used alone or in combination of two or more.

[0033] The content of these polyfunctional vinyl monomer units is in the range of 0 to 2 mass %, more preferably 0.5 to 1 mass %, relative to 100 parts by mass of the core polymer (A). By keeping the content within the above range, water resistance and alcohol resistance are further improved.

[0034] <Shell polymer (B)> The shell polymer (B) used in the core-shell resin emulsion of the present invention functions as a polymeric surfactant that copolymerizes the monomers used in the core polymer (A). Therefore, it is preferable to use a vinyl monomer containing an anionic group with moderate hydrophilicity and a vinyl monomer containing an aromatic vinyl monomer with moderate hydrophobicity. The acid value of the shell polymer (B) must be 200 mgKOH / g or higher to ensure good redispersibility of the core-shell resin emulsion in water. It is more preferably 210 mgKOH / g or higher, and particularly preferably 220 mgKOH / g or higher. By keeping the acid value within the above range, the nozzle recovery performance of inkjet heads is further improved. The acid value refers to the number of milligrams of potassium hydroxide (mgKOH / g) required to neutralize the acidic components contained in 1 g of sample. The acid value of a resin can be calculated from the respective structural units (monomers) that make up the resin.

[0035] Examples of the vinyl monomer containing an anionic group include, but are not limited to, dicarboxylic acid vinyl monomers such as acrylic acid, methacrylic acid, carboxymethyl (meth)acrylate, carboxyethyl (meth)acrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, methacryloyloxyethyl phthalate, acryloyloxyisobutyrate, methacryloyloxyisobutyrate, 2-sulfoethyl (meth)acrylate, acryloyloxyethyl phosphonate, methacryloyloxyethyl phosphonate, 2-(phosphonooxy)ethyl (meth)acrylate, vinyl sulfonic acid, styrene carboxylic acid, styrene sulfonic acid, styrene phosphonate, itaconic acid, maleic acid, and fumaric acid, as well as their anhydrides and half esters. These may be used alone or in combination of two or more.

[0036] Examples of the aromatic vinyl monomer include, but are not limited to, styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl acrylate, benzyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol acrylate, phenoxydiethylene glycol methacrylate, phenoxytetraethylene glycol acrylate, phenoxytetraethylene glycol methacrylate, phenoxyhexaethylene glycol acrylate, phenoxyhexaethylene glycol methacrylate, phenyl acrylate, and phenyl methacrylate. These may be used alone or in combination of two or more.

[0037] The shell polymer (B) may further contain other vinyl monomers. Specific examples thereof include linear or branched alkyl group-containing vinyl monomers such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, and tetradecyl (meth)acrylate; Alicyclic alkyl group-containing vinyl monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; (Meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N-pentoxymethyl-(meth)acrylamide, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethylmethacrylamide, N,N-di(ethoxymethyl)acrylamide, N-ethoxymethyl-N-propoxymethylmethacrylamide, N,N-di(propoxymethyl)acrylamide, N-butoxymethyl amide group-containing vinyl monomers such as N,N-dimethyl-N-(propoxymethyl)methacrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide, N,N-di(pentoxymethyl)acrylamide, N-methoxymethyl-N-(pentoxymethyl)methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, and N-(1,1-dimethyl-3-oxobutyl)acrylamide; Examples of the hydroxyl group-containing vinyl monomers include, but are not limited to, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, and allyl alcohol. These may be used alone or in combination of two or more.

[0038] The mass ratio of the core polymer (A) to the shell polymer (B) must be 90 / 10 to 60 / 40 in order to achieve both excellent durability and good ejection stability in printed matter. It is more preferably 85 / 15 to 65 / 35, and particularly preferably 80 / 20 to 70 / 30. Furthermore, by keeping the mass ratio within the above range, emulsion polymerization becomes easier, a uniform core-shell resin emulsion can be obtained, and good storage stability can be achieved.

[0039] The core-shell resin emulsion of the present invention has a 50% volume average particle diameter in the range of 40 to 90 nm, and more preferably 50 to 80 nm. By setting the 50% volume average particle diameter in this range, the gloss of printed matter is further improved. The 50% volume average particle diameter is the cumulative 50% diameter on a volume basis, and can be determined, for example, using a Nanotrac UPA-EX150 manufactured by Nikkiso Co., Ltd.

[0040] A known polymerization initiator can be used for synthesizing the shell polymer (B), and it is preferable to use 0.1 to 10 parts by mass of the polymerization initiator relative to 100 parts by mass of the vinyl monomer.

[0041] The polymerization initiator is preferably an organic peroxide or an azo compound. Examples of the organic peroxide include benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl hydroperoxide, tert-butylperoxy(2-ethylhexanoate), tert-butylperoxy-3,5,5-trimethylhexanoate, and di-tert-butyl peroxide. Examples of the azo compound include, but are not limited to, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 1,1'-azobis-cyclohexane-1-carbonitrile.

[0042] The shell polymer (B) preferably has a weight-average molecular weight of 5,000 to 30,000, more preferably 7,000 to 20,000. A weight-average molecular weight in the range of 5,000 to 30,000 can improve the copolymerization of the core portion. Furthermore, the core polymer (A) functions as a film-forming aid, further improving water resistance and alcohol resistance. The weight-average molecular weight refers to a polystyrene-equivalent value measured by GPC (gel permeation chromatography).

[0043] Alternatively, commercially available shell polymers (B) may be used, such as JONCRYL67, JONCRYL678, JONCRYL586, JONCRYL611, JONCRYL683, JONCRYL690, JONCRYL57J, JONCRYL60J, JONCRYL61J, JONCRYL62J, JONCRYL63J, JONCRYLHPD-96J, JONCRYL501J, and JONCRYLPDX-6102B manufactured by BASF; and DISPERBYK, DISPERBYK180, and DISPE manufactured by BYK-Chemie. Examples include RBYK187, DISPERBYK190, DISPERBYK191, DISPERBYK194, DISPERBYK2010, DISPERBYK2015, DISPERBYK2090, DISPERBYK2091, DISPERBYK2095, DISPERBYK2155, SOLSPERS41000 manufactured by Zena, and SMA1000H, SMA1440H, SMA2000H, SMA3000H, and SMA17352H manufactured by Sartomer.

[0044] The core-shell resin emulsion of the present invention can be synthesized using water-soluble polymerization initiators such as persulfates, peroxides, and azo compounds. Specific examples include ammonium persulfate (APS), potassium persulfate (KPS), hydrogen peroxide, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride. The water-soluble polymerization initiator is preferably used in an amount of 0.1 to 10 parts by mass per 100 parts by mass of vinyl monomer.

[0045] In addition, by using a reducing agent in combination with a water-soluble polymerization initiator, the polymerization rate can be increased or The reducing agent can be polymerized at a low reaction temperature. Specific examples include reducing inorganic compounds such as scorbic acid, erythorbic acid, tartaric acid, citric acid, glucose, sodium sulfite, sodium bisulfite, and sodium metabisulfite. The reducing agent is preferably used in an amount of 0.05 to 5 parts by mass per 100 parts by mass of the vinyl monomer.

[0046] In synthesizing the core-shell resin emulsion of the present invention, the shell polymer (B) can be neutralized before use. The shell polymer (B) can be made water-soluble by the neutralization. A basic compound can be used for the neutralization. Specific examples include amines such as ammonia, trimethylamine, triethylamine, butylamine, 2-dimethylaminoethanol, 2-diethylaminoethanol, diethanolamine, triethanolamine, aminomethylpropanol, and morpholine; Hydroxide salts such as potassium hydroxide and sodium hydroxide, etc. Among these, ammonia is preferred because it is easy to remove by drying after printing.

[0047] A buffer and a chain transfer agent can be used as appropriate to synthesize the core-shell resin emulsion (C) of the present invention. Examples of the buffer include sodium acetate, sodium citrate, and sodium bicarbonate. Examples of the chain transfer agent include mercaptans such as octyl mercaptan, 2-ethylhexyl thioglycolate, octyl thioglycolate, stearyl mercaptan, lauryl mercaptan, and t-dodecyl mercaptan.

[0048] The core-shell resin emulsion of the present invention preferably has a weight average molecular weight of 200,000 to 1,000,000, more preferably 300,000 to 500,000. By having the weight average molecular weight in the range of 200,000 to 1,000,000, water resistance and alcohol resistance can be further improved.

[0049] <Water-based inkjet ink> Next, the aqueous inkjet ink of the present invention will be described. The aqueous inkjet ink (hereinafter simply referred to as "aqueous ink" or "ink") contains the core-shell resin emulsion, a pigment, a pigment dispersion resin, a water-soluble organic solvent, a surfactant, and water.

[0050] The content of the core-shell resin emulsion of the present invention is in the range of 5% by mass to 40% by mass, more preferably 8% by mass to 30% by mass, and particularly preferably 10% by mass to 20% by mass, based on the total amount of the aqueous inkjet ink. By setting the content of the core-shell resin emulsion within the above range, it is possible to obtain a printed matter having excellent water abrasion resistance and alcohol abrasion resistance, and further to obtain an aqueous inkjet ink having improved nozzle clogging recovery properties of the inkjet head and good ejection stability.

[0051] <Pigments> The pigment used in the aqueous inkjet ink of the present invention may be either inorganic or organic, and is not particularly limited. Examples of organic pigments include azo, phthalocyanine, anthraquinone, perylene, perinone, quinacridone, thioindigo, dioxazine, isoindoline, quinophthalone, azomethine azo, and dicetpyrrolopyrrole pigments. Examples of inorganic pigments include carbon black, titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, silica, red iron oxide, aluminum, and mica. Titanium oxide preferably has its surface coated with at least silica or alumina. Pigments listed as CI pigments in the Color Index can be used as needed.

[0052] It is also suitable to use hollow resin particles as the white pigment. Hollow resin particles have a lower specific gravity (apparent density) than titanium oxide and the like, and are therefore less likely to settle over time, resulting in an ink with excellent storage stability.

[0053] These pigments can be used alone or in combination. Except for white inks, the pigment content is preferably in the range of 2% to 20% by mass, more preferably 2.5% to 15% by mass, and particularly preferably 3% to 10% by mass. In white inks, the pigment content is preferably in the range of 5% to 40% by mass, more preferably 8% to 30% by mass, based on the total amount of the white ink. By ensuring that the pigment content is 2% by mass or more (5% by mass or more for white inks), sufficient color development (hiding ability for white inks) can be achieved even with single-pass printing. By ensuring that the pigment content is 20% by mass or less (40% by mass or less for white inks), the ink viscosity can be kept within a range suitable for inkjet printing.

[0054] <Pigment dispersing resin> Methods for stably dispersing and maintaining pigments in aqueous inks include (1) a method in which a pigment dispersing resin is adsorbed onto the pigment surface and dispersed therein, (2) a method in which a water-soluble and / or water-dispersible surfactant is adsorbed onto the pigment surface and dispersed therein, (3) a method in which hydrophilic functional groups are chemically or physically introduced onto the pigment surface and the pigment is dispersed in the ink without a dispersing resin or surfactant (self-dispersing pigment), and (4) a method in which the pigment is coated with a water-insoluble resin and, if necessary, further dispersed in the ink using another pigment dispersing resin or surfactant.

[0055] For the aqueous inkjet ink used in the present invention, methods (1) or (4) are more preferred from the viewpoint of water resistance and alcohol resistance. When the pigment dispersion resin contains a structure derived from a vinyl monomer containing an anionic group as a constituent unit, solubility in water and water-soluble organic solvents can be ensured. Furthermore, this is also preferred in that the pigment dispersion state is favorable, thereby reducing the viscosity of the pigment dispersion. Furthermore, the acid value of the pigment dispersion resin is preferably 30 to 375 mgKOH / g, more preferably 65 to 350 mgKOH / g, and even more preferably 100 to 300 mgKOH / g, in order to more favorably exhibit the above-mentioned effects.

[0056] The type of the pigment dispersion resin is not particularly limited, and examples thereof include (meth)acrylic resins, styrene (meth)acrylic resins, (maleic anhydride) resins, styrene (maleic anhydride) resins, olefin (maleic anhydride) resins, polyurethane resins, and polyester resins. Among these, (meth)acrylic resins, styrene (meth)acrylic resins, polyurethane resins, and polyester resins are particularly preferred in terms of the wide range of material options and ease of synthesis. The pigment dispersion resins can be synthesized by known methods, or commercially available products can be used. In the present invention, "(maleic anhydride)" refers to maleic acid or maleic anhydride.

[0057] When a water-soluble pigment dispersion resin is used as the pigment dispersion resin to stably disperse and maintain the pigment in the aqueous ink, it is preferable to neutralize the acid groups in the pigment dispersion resin with a base to increase the solubility in the ink. The pH of the inkjet ink is preferably 7 to 11, and more preferably 7.5 to 10.0.

[0058] Examples of bases for neutralizing the pigment dispersing resin include alkanolamines such as diethanolamine, triethanolamine, and N-methyldiethanolamine; aqueous ammonia; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; and alkali metal carbonates such as sodium carbonate, sodium hydrogencarbonate, and potassium carbonate.

[0059] The weight-average molecular weight of the pigment dispersing resin is preferably within the range of 1,000 to 200,000, and more preferably within the range of 5,000 to 100,000. When the weight-average molecular weight is within this range, the pigment is stably dispersed in water, and viscosity adjustment when applied to inkjet inks is easy.

[0060] In the present invention, the blending amount of the pigment dispersing resin is preferably 1 to 50% by mass relative to the pigment. By blending the pigment dispersing resin in an amount of 1 to 50% by mass relative to the pigment, the viscosity of the pigment dispersion can be reduced, and the viscosity stability and dispersion stability of the pigment dispersion and inkjet ink can be improved. The blending amount of the pigment dispersing resin relative to the pigment is more preferably 2 to 45% by mass, even more preferably 3 to 40% by mass, and most preferably 4 to 35% by mass.

[0061] The pigment dispersing resin used in the present invention preferably contains, as a structural unit, a structure derived from a vinyl monomer containing an anionic group. The "anionic group" may be a carboxylic acid (carboxyl) group, a sulfonic acid group, a phosphonic acid group, or the like, any of which may be selected in the present invention. Among these, a carboxyl group is preferred from the viewpoints of ensuring solubility in water and water-soluble organic solvents, providing excellent dispersion stability, and improving water resistance and alcohol resistance.

[0062] Known vinyl monomers containing an anionic group can be used. Specific examples include acrylic acid, methacrylic acid, carboxymethyl (meth)acrylate, carboxyethyl (meth)acrylate, acryloyloxyethyl succinic acid, methacryloyloxyethyl succinic acid, acryloyloxyethyl phthalic acid, methacryloyloxyethyl phthalic acid, acryloyloxyisobutyric acid, methacryloyloxyisobutyric acid, 2-sulfoethyl (meth)acrylate, acryloyloxyethyl phosphonic acid, methacryloyloxyethyl phosphonic acid, 2-(phosphonooxy)ethyl (meth)acrylate, vinyl sulfonic acid, styrene carboxylic acid, styrene sulfonic acid, and styrene phosphonic acid, but are not limited to these. These vinyl monomers containing an anionic group can be used alone or in combination.

[0063] <Water-soluble organic solvent> The water-soluble organic solvent is not particularly limited, and any known solvent can be used. However, from the viewpoint of compatibility and affinity with the material components such as the core-shell resin emulsion, the pigment dispersion resin, and the surfactant, it is preferable that the water-soluble organic solvent contains a glycol ether solvent and / or an alkyl polyol solvent. Examples of alkyl polyol solvents include 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methylpentane-2,4-diol, 2-ethyl-1,3-hexanediol, diethylene glycol, and dipropylene glycol.Examples of glycol ether solvents include glycol monoalkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monobutyl ether; and glycol dialkyl ethers such as diethylene glycol diethyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol butyl methyl ether, and tetraethylene glycol dimethyl ether.

[0064] These water-soluble organic solvents can be used alone or in combination of two or more. The content of the water-soluble organic solvents is preferably 3% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 35% by mass or less, and particularly preferably 8% by mass or more and 30% by mass or less, relative to the total amount of the ink. By making the total amount of water-soluble organic solvents 3% by mass or more, the ink's moisture retention, ejection stability, and wettability of the aqueous ink on the printing substrate are improved. Furthermore, by making the total content of water-soluble organic solvents 40% by mass or less, the drying properties and color bleeding are improved, and printed matter with good blocking resistance can be obtained.

[0065] <Surfactant> The aqueous inkjet ink used in the present invention preferably contains a surfactant to adjust the surface tension, ensure wettability on the film substrate, and improve print quality. On the other hand, if the surface tension is too low, the nozzle surface of the inkjet head will become wet with the aqueous ink, impairing ejection stability. Therefore, the selection of the type and amount of surfactant is important. From the viewpoint of ensuring optimal wettability and achieving stable ejection from the inkjet head, it is preferable to use surfactants such as siloxane-based, acetylene-based, acrylic-based, fluorine-based, and polyoxyalkylene alkyl ether-based surfactants, with siloxane-based and / or acetylene-based surfactants being particularly preferable. The amount of surfactant added is preferably 0.05% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 3.0% by mass or less, based on the total amount of the aqueous inkjet ink. A content of 0.05% by mass or more allows the surfactant to fully exert its functions, while a content of 5.0% by mass or less allows the storage stability and ejection stability of the aqueous ink to be maintained at an appropriate level.

[0066] The aqueous inkjet ink used in the present invention may contain a hydrazide additive for the purposes of improving adhesion to the substrate, room temperature crosslinking of the resin (if it contains a keto group), etc. Examples of hydrazide additives include adipic acid hydrazide.

[0067] <Other ingredients> The aqueous inkjet ink of the present invention may further contain pH adjusters, antifoaming agents, thickeners, preservatives, waxes, and the like, as appropriate.

[0068] <Printed material> The aqueous inkjet ink of the present invention is printed on a substrate by an inkjet printing method. In this case, printing by a single-pass printing method (also called a line printing method) is preferred. The single-pass printing method requires fewer scans than a multi-pass method in which an inkjet head is scanned multiple times, allowing for increased printing speed, making it suitable for industrial applications requiring high printing speed. It is also suitable because high-quality prints can be obtained at a high recording resolution of 600 dpi or more. Note that "recording resolution" is expressed in units of dpi (dots per inch) and represents the number of aqueous inkjet ink droplets printed per inch. Furthermore, "recording resolution" in this specification refers to both the recording resolution in the transport direction of the substrate and the recording resolution in the direction perpendicular to the transport direction within the plane of the substrate (hereinafter referred to as the recording width direction).

[0069] When printing with aqueous ink using a one-pass printing method, the drop volume of the aqueous ink depends largely on the performance of the inkjet head, but to obtain printed matter with high resolution and excellent color development, it is preferably in the range of 0.6 to 60 pL, more preferably 1 to 50 pL, and particularly preferably 1.4 to 40 pL. Furthermore, to obtain high-quality images, it is particularly preferable to use an inkjet head with gradation specifications that allows the drop volume to be changed.

[0070] <Base material> The substrate on which the ink of the present invention is printed is not particularly limited, and any known substrate can be used. Among them, for packaging applications, non-permeable substrates or poorly permeable substrates are suitable, and the ink of the present invention can be particularly suitable for use on non-permeable substrates. In this specification, the permeability of a recording medium is determined by the amount of water absorption measured by a dynamic scanning absorptivity meter. Specifically, the amount of pure water absorption measured by the following method for a contact time of 100 msec is 1 g / m 2 Recording media with a permeability of less than 1 to 10 g / m are considered "impermeable substrates." 2 The recording medium having the above properties is called a "hardly permeable substrate."

[0071] The amount of water absorbed by a recording medium can be measured, for example, under the following conditions: Using a dynamic scanning absorptivity meter, a KM500win manufactured by Kumagai Riki Kogyo Co., Ltd., and using a recording medium approximately 15-20 cm square at 23°C and 50% RH, the amount of transferred pure water is measured under the conditions shown below. Measurement method: Spiral method ·Measurement start radius: 20mm Measurement end radius: 60mm ·Contact time: 10~1,000msec Number of sampling points: 19 (measured at approximately equal intervals relative to the square root of the contact time) Scanning interval: 7mm Rotating table speed change angle: 86.3 degrees Headbox conditions: width 5mm, slit width 1mm

[0072] Examples of impermeable or poorly permeable substrates include plastic substrates such as polyvinyl chloride, polyethylene terephthalate (PET), polypropylene, polyethylene, nylon, polystyrene, and polyvinyl alcohol; coated paper substrates such as coated paper, art paper, and cast paper; metal substrates such as aluminum, iron, stainless steel, and titanium; and glass substrates.

[0073] The substrate may have a smooth or textured surface, and may be transparent, translucent, or opaque. Two or more of these recording media may be laminated together. A release adhesive layer may be provided on the side opposite the printed surface, or an adhesive layer may be provided on the printed surface after printing. The recording medium used in the inkjet recording method of the present invention may be in the form of a roll or sheets.

[0074] It is also preferable to subject the non-permeable substrates or poorly permeable substrates exemplified above to a surface modification method such as corona treatment or plasma treatment, as this improves the wettability of the aqueous inkjet ink of the present invention, improves image quality and drying properties, and also improves abrasion resistance and adhesion due to the uniformity of the printed surface. [Example]

[0075] The aqueous inkjet ink resin composition according to the present invention will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" represent "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0076] (acid number) This is the amount of potassium hydroxide required in mg to neutralize the acidic components contained in 1 g of resin solids. For dried resin, potassium hydroxide is used according to the method described in JIS K2501. -Calculated by potentiometric titration in ethanol solution.

[0077] (Weight average molecular weight) The weight-average molecular weight is a polystyrene-equivalent value measured by GPC (gel permeation chromatography). The resin was dissolved in tetrahydrofuran to prepare a 0.1% solution, and the weight-average molecular weight was measured using a Tosoh HLC-8320-GPC (column: TSKgel-SuperMultiporeHZ-M, molecular weight measurement range: approximately 2,000 to approximately 2,000,000).

[0078] (50% volume average particle size) The particle size was measured using a Nanotrac UPA150 manufactured by Microtrac Bell, using a particle distribution measurement method based on dynamic light scattering, and the D50 value was taken as the average particle size.

[0079] <Synthesis example of shell polymer (B)1> A reaction vessel equipped with a stirrer, thermometer, two dropping funnels, and a reflux condenser was charged with 60.7 parts of isopropyl alcohol and heated to 80°C under nitrogen reflux while stirring. Next, two dropping funnels were prepared. 50.0 parts of styrene, 15.5 parts of methyl methacrylate, 6.9 parts of butyl acrylate, and 27.6 parts of acrylic acid were charged into one of them and added dropwise over 3 hours. 10.0 parts of dimethyl 2,2'-azobisisobutyrate dissolved in 6.0 parts of isopropyl alcohol was charged into the other and added dropwise over 4 hours. After completion of the dropwise addition, the reaction was continued at reflux temperature for 10 hours and then terminated. After cooling to room temperature, 25% aqueous ammonia was added to completely neutralize the mixture, and 150 parts of water was added to make it aqueous. The mixture was then heated to 100°C, and the isopropyl alcohol was azeotropically distilled off with water, adjusting the solids concentration to 30%. This gave Shell Polymer (B) 1, a water-soluble polymer compound with a solid content of 30%. Shell Polymer (B) 1 had a Tg of 85° C., a weight-average molecular weight of 9000, and an acid value of 215 mg KOH / g.

[0080] <Synthesis Examples of Shell Polymers (B) 2 to 5> Shell polymers (B) 2 to 5 were obtained by carrying out the reaction in the same manner as shell polymer (B) 1, except that the raw materials and compounding ratios were changed as shown in Table 1.

[0081] [Table 1]

[0082] <Synthesis Example of Core-Shell Resin Emulsion 1 Having Core Polymer (A) 1 Covered with Shell Polymer (B) 1> A reaction vessel equipped with a stirrer, thermometer, two dropping funnels, and a reflux condenser was charged with 111.1 parts of shell polymer (B)1 and 55.5 parts of ion-exchanged water, and the temperature was raised to 80°C under nitrogen reflux. Next, two dropping funnels were prepared, and 25.0 parts of styrene, 73.0 parts of methyl methacrylate, and 2.0 parts of diacetone acrylamide were charged into one of them and added dropwise over 2 hours. 1.0 parts of a 20% aqueous ammonium persulfate solution was charged into the other and added dropwise over 2 hours. After the addition was completed, the reaction was continued at 80°C for 2 hours and then terminated. The nonvolatile content of the solution was then adjusted to 40% with ion-exchanged water to obtain a core-shell resin emulsion 1 having a core polymer (A)1 coated with shell polymer (B)1. The mass ratio of core polymer (A) 1 to shell polymer (B) 1 was 75 / 25, the Tg of core polymer (A) 1 was 103°C, the weight average molecular weight of core-shell resin emulsion 1 was 530,000, and the 50% volume average particle size was 62 nm.

[0083] <Synthesis examples of core-shell type resin emulsions 2 to 21> Core-shell type resin emulsions 2 to 21 were obtained by carrying out the reaction in the same manner as for core-shell type resin emulsion 1, except that the raw materials and compounding ratios were changed as shown in Table 2.

[0084] The monomers listed in Tables 1 and 2 are shown below. St: Styrene MMA: Methyl methacrylate BA: Butyl acrylate AA: Acrylic acid IB-X: Isobornyl methacrylate DAAM: Diacetone acrylamide DVB: Divinylbenzene

[0085] [Table 2]

[0086] <Production of water-based inkjet inks> <Synthesis example of pigment dispersing resin> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 95 parts of butanol and purged with nitrogen gas. The reaction vessel was heated to 110°C, and a mixture of 35 parts of styrene as polymerizable monomers, 35 parts of acrylic acid, 30 parts of behenyl acrylate, and 6 parts of V-601 (Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added dropwise over 2 hours to carry out the polymerization reaction. After the addition was completed, the reaction was continued for another 3 hours at 110°C, followed by the addition of 0.6 parts of V-601. The reaction was continued for another 1 hour at 110°C to obtain a pigment dispersion resin solution. After cooling to room temperature, dimethylaminoethanol was added to completely neutralize the solution, and 100 parts of water was added to make the solution aqueous. The solution was then heated above 100°C, and the butanol was evaporated off by azeotropy with water, adjusting the solids concentration to 30%. This resulted in an aqueous solution of pigment dispersion resin with a solids concentration of 30%. The pigment dispersing resin had a weight average molecular weight of 28,000 and an acid value of 273 mgKOH / g.

[0087] <Example of manufacturing pigment dispersion liquid (C, M, Y, K)> Twenty parts of Toyocolor Lionol Blue 7358G (CIPI Imprint Blue 15:4), 15 parts of an aqueous solution of pigment dispersion resin (solids concentration 30%), and 65 parts of water were mixed and pre-dispersed using a disperser. After that, the main dispersion was carried out using a 0.6 L Dyno-Mill filled with 1800 g of 0.5 mm diameter zirconia beads to obtain pigment dispersion C (cyan). Pigment dispersions M (magenta), Y (yellow), and K (black) were also obtained in the same manner as pigment dispersion C, except that the above-mentioned CIP Imprint Blue 15:3 was replaced with the pigments shown below. ·Magenta: FASTGEN SUPER MAGENTA RGT manufactured by DIC (CIPIgment Red 122) Yellow: Toyo Color LIONOL YELLOW TT-1405G (CIPIgment Yellow 14) Black: Orion Engineered Carbons Printex 85 (CIPIgment Black 7)

[0088] <Production example of pigment dispersion W> 40 parts of CR-90-2 (titanium oxide) manufactured by Ishihara Sangyo Kaisha, Ltd., 30 parts of an aqueous solution of pigment dispersion resin (solid content concentration 30%), and 30 parts of water were mixed and dispersed in the same manner as in Pigment Dispersion Liquid C to obtain Pigment Dispersion Liquid W.

[0089] <Inkjet ink manufacturing example> The materials listed for inkjet ink C below were added sequentially to a mixing container while stirring with a disperser, and stirred until sufficiently uniform. Ink C was then obtained by filtering through a membrane filter with a pore size of 1 μm. Ink M, Ink Y, and Ink K were obtained by using pigment dispersions M, Y, and K, respectively, instead of pigment dispersion C. Ink W was also obtained from the materials listed for inkjet ink W below. In total, inkjet inks 1 consisting of five colors were obtained. Inkjet Ink C Pigment dispersion C 25.0 parts Core-shell resin emulsion 1 (solid concentration 40%) 30.0 parts 1,2-propanediol 20.0 parts Surfynol 465 1.0 parts BYK-349 1.0 part Proxel GXL 0.05 parts 22.95 parts ion-exchanged water Inkjet Ink W Pigment dispersion W 40.0 parts Core-shell resin emulsion 1 (solid concentration 40%) 30.0 parts 1,2-propanediol 20.0 parts Surfynol 465 1.0 parts BYK-349 1.0 part Proxel GXL 0.05 parts 7.95 parts ion-exchanged water BYK-349: Siloxane surfactant manufactured by BYK Japan Surfynol 465: An acetylene diol surfactant manufactured by Air Products

[0090] <Production example of inkjet inks 2 to 21> Inkjet inks 2 to 21 were obtained in the same manner as inkjet ink 1, except that the materials listed in Table 3 were used.

[0091] [Table 3]

[0092] <Examples of printed materials and coated materials for evaluation> Using the resulting inkjet ink, a printed matter was produced as follows.

[0093] An inkjet head KJ4B-1200 (Kyocera Corporation, resolution 1200 dpi, maximum drive frequency 64 kHz) was installed above a conveyor capable of transporting the printing substrate. The inkjet inks prepared above were loaded in the following order from the upstream side: W (white), K (black), C (cyan), M (magenta), and Y (yellow). Next, a film substrate was fixed onto the conveyor, and the conveyor was driven at 50 m / min. The inkjet inks were ejected as the film passed the inkjet head installation area, thereby performing printing. The drop volume during printing was adjusted to achieve the desired layer thickness within the range of 1.5 pL to 5 pL. The printed material was then immediately placed in an air oven at 70°C and dried for 3 minutes to obtain a printed material for evaluation. Avery Dennison OPP film label AE406 was used as the film substrate.

[0094] [Examples 1 to 17, Comparative Examples 1 to 4] The inkjet inks and printed materials for evaluation produced above were subjected to the following evaluations 1 to 6.

[0095] <Evaluation 1: Storage stability> The inkjet inks were evaluated for storage stability by measuring the change in viscosity over time at 70°C for 6 weeks. The viscosity was measured using a rheometer (TA Instruments AR-2000). The evaluation criteria were as follows, with ◎ and ◯ being in the practical usable range. The results are shown in Table 3. ◎: Viscosity change of inkjet ink is less than ±3% ○: Viscosity change of inkjet ink is ±3% or more and less than ±5% △: Viscosity change of inkjet ink is ±5% or more and less than ±10% ×: The viscosity change of the inkjet ink is ±10% or more

[0096] <Evaluation 2: Clogging recovery> Inkjet ink was filled into an inkjet head KJ4B-1200 (manufactured by Kyocera Corporation, resolution 1200 dpi, maximum drive frequency 64 kHz), and it was confirmed that there were no clogged nozzles and that normal printing was possible. The head was then left to stand at room temperature for one week with the cap removed. After leaving the head, inkjet ink was again ejected from all nozzles, and the number of cleanings required until printing was possible at the same level as initially was measured. The evaluation criteria were as follows, with ◎ and ◯ being in the practical usable range. The results are shown in Table 3. ◎: All nozzles recovered without cleaning ○: All nozzles recovered within 1 to 3 cleanings △: All nozzles recovered within 4 to 9 cleanings ×: Did not recover after 10 cleanings

[0097] <Rating 3: Water abrasion resistance> The resulting prints were subjected to a rub fastness test using a Gakushin-type rub fastness tester, with the coated surface being 500g / cm2 with water-containing Kanakin No. 3. 2 The surface was rubbed 20 times and the water abrasion resistance was evaluated based on the percentage of peeled area of ​​the coating layer. The evaluation criteria were as follows, with ⊚ and ◯ being in the range of practical use. The results are shown in Table 3. ◎: No peeling of coating film ○: Peeling of the coating film is less than 10% △: Peeling of the coating film is 10% or more but less than 50% ×: Peeling of the coating film is 50% or more

[0098] <Rating 4: Alcohol abrasion resistance> The resulting prints were rubbed at 200g / cm using a Gakushin-type rub fastness tester with Kanakin No. 3, a mixed solvent of water and ethanol (weight ratio: 50 / 50) on the coated surface. 2 The surface was rubbed 10 times and the water abrasion resistance was evaluated based on the percentage of peeled area of ​​the coating layer. The evaluation criteria were as follows, with ⊚ and ◯ being in the range of practical use. The results are shown in Table 3. ◎: No peeling of coating film ○: Peeling of the coating film is less than 10% △: Peeling of the coating film is 10% or more but less than 50% ×: Peeling of the coating film is 50% or more

[0099] <Rating 5: Scratch resistance> The resulting prints were subjected to a rub fastness test using a Gakushin type rub fastness tester, with Kanakin No. 3 on the coated surface at 500 g / cm 2 The surface was rubbed 100 times, and the abrasion resistance was evaluated based on the percentage of peeled area of ​​the coating layer. The evaluation criteria were as follows, with ⊚ and ◯ being in the range of practical use. The results are shown in Table 3. ◎: No peeling of coating film ○: Peeling of the coating film is less than 10% △: Peeling of the coating film is 10% or more but less than 50% ×: Peeling of the coating film is 50% or more

[0100] <Rating 6: Gloss> The 60° gloss of the obtained coated product was measured using a gloss meter (Micro-TRI-gloss manufactured by BYK Gardner). The evaluation criteria were as follows, with ⊚ and ◯ being in the practical usable range. The results are shown in Table 3. ◎: Glossiness is 80 or more ○: Gloss is 65 or more and less than 80 △: Gloss is 50 or more and less than 65 ×: Glossiness is less than 50

Claims

1. A resin composition for an aqueous inkjet ink, having a core-shell structure, containing a core polymer (A) and a shell polymer (B) that coats the core polymer (A), characterized in that the glass transition temperature of the core polymer (A) is 65°C or higher and is 5 to 40°C higher than the glass transition temperature of the shell polymer (B), the acid value of the shell polymer (B) is 200 mgKOH / g or higher, and the mass ratio of the core polymer (A) to the shell polymer (B) is 90 / 10 to 60 / 40.

2. 2. The resin composition for a water-based inkjet ink according to claim 1, wherein the content of vinyl monomer units selected from styrene and α-methylstyrene in the core polymer (A) is 15 to 50% by mass.

3. 3. The resin composition for a water-based inkjet ink according to claim 1, wherein the core polymer (A) has a content of hydrophilic vinyl monomer units of 1 to 5% by mass.

4. 3. The resin composition for a water-based inkjet ink according to claim 1, wherein the content of the polyfunctional vinyl monomer unit in the core polymer (A) is 0 to 2% by mass.

5. A resin composition for aqueous inkjet ink as described in claim 1 or 2, characterized in that the glass transition temperature of the core polymer (A) is 90°C or higher.

6. An aqueous inkjet ink comprising the resin composition for an aqueous inkjet ink according to claim 1 or 2.

7. A printed matter using the aqueous inkjet ink according to claim 6.

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