JP7720191B2 - Inkjet ink composition - Google Patents

Description

The present invention relates to an inkjet ink composition.

Conventionally, inkjet ink compositions (hereinafter also referred to as ink compositions) have been put to practical use in a variety of applications, including coatings for plastics, paper, woodworking, and inorganic materials, adhesives, printing inks, printed circuit boards, and electrical insulation. In recent years, the development of various inkjet ink compositions compatible with olefin-based substrates such as polyethylene and polypropylene has also become important, and there is a particular demand for inkjet ink compositions that not only have low viscosity but also allow the ejected ink to wet and spread well over the olefin substrate and adhere well after drying.

Conventional inkjet inks have the problem of insufficient adhesion to olefin substrates. To address this issue, it has been proposed to use a mixture of chlorinated polyolefin resin and chlorinated ethylene vinyl acetate copolymer resin as an inkjet ink (see, for example, Patent Document 1), or a mixture of styrene acrylic resin, chlorinated polyolefin, and epoxy resin as an inkjet ink (see, for example, Patent Document 2).

However, in recent years, there has been growing emphasis on addressing environmental issues, and there is a strong desire to reduce the generation of hazardous substances during the disposal of used products. However, because chlorinated polyolefins contain chlorine, there is a problem in that hazardous substances are generated when incinerated, which could pollute the environment. For this reason, there has been a demand for inkjet ink compositions that do not contain chlorinated polyolefins but have excellent adhesion to substrates such as olefin substrates.

Japanese Patent Application Laid-Open No. 2018-165328 JP 2012-072236 A

The present invention aims to provide an inkjet ink composition that has low initial viscosity, excellent ejection properties, excellent adhesion to substrates such as olefin substrates, excellent stability during low-temperature storage and when containing water, and excellent alcohol resistance when dried and solidified after solvent removal.

The present inventors have conducted research to achieve the above object and have arrived at the present invention.
That is, the present invention provides a composition comprising a (co)polymer (A) having a weight average molecular weight of 40,000 to 90,000, a solvent (B), a water-insoluble dye (C), and a (co)polymer (D) having a weight average molecular weight of 700 to 10,000,
The ink-jet ink composition is one in which the content of the (co)polymer (A) is 5 to 20% by weight, the content of the solvent (B) is 70 to 85% by weight, the content of the water-insoluble dye (C) is 3 to 10% by weight, and the content of the (co)polymer (D) is 5 to 12% by weight, based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer (D).

The inkjet ink composition of the present invention has low initial viscosity, excellent ejection properties, and excellent stability during low-temperature storage and when containing water. Furthermore, the dried solidified product after solvent removal has excellent adhesion to substrates and alcohol resistance.

The inkjet ink composition of the present invention is characterized by containing a (co)polymer (A) having a weight-average molecular weight of 40,000 to 90,000, a solvent (B), a water-insoluble dye (C), and a (co)polymer (D) having a weight-average molecular weight of 700 to 10,000.

In this specification, "(meth)acrylate" means "acrylate or methacrylate," and "(meth)acryloyl group" means "acryloyl group or methacryloyl group."

The (co)polymer (A), solvent (B), water-insoluble dye (C), and (co)polymer (D) are explained in this order below.

In the present invention, the (co)polymer (A) having a weight-average molecular weight of 40,000 to 90,000 preferably contains a (meth)acrylate (a1) having an alicyclic skeleton as a constituent monomer.

The (meth)acrylate (a1) having an alicyclic skeleton has a homopolymer glass transition temperature of more than 20° C. and not more than 170° C., preferably 30 to 160° C., and more preferably 40 to 150° C. If the homopolymer has a glass transition temperature of 20° C. or less, the alcohol resistance is poor, and if it exceeds 170° C., the adhesion to the substrate is poor. The glass transition temperature may be abbreviated as Tg.
Here, the Tg of a homopolymer refers to the value measured by the method specified in ASTM D3418-82 (DSC method) using a DSC20, SSC/580 manufactured by Seiko Instruments Inc. for a polymer obtained by homopolymerizing the monomer.
When two or more types of (meth)acrylates (a1) having an alicyclic skeleton are contained, the Tg of the homopolymer of each (meth)acrylate falls within the above range.

Examples of the (meth)acrylate (a1) having an alicyclic skeleton include isobornyl acrylate (Tg 94°C), cyclohexyl methacrylate (Tg 66°C), t-butylcyclohexyl acrylate (Tg 65°C), t-butylcyclohexyl methacrylate (Tg 145°C), trimethylcyclohexyl acrylate (Tg 43°C), trimethylcyclohexyl methacrylate (Tg 145°C), dicyclopentanyl acrylate (Tg 120°C), and dicyclopentenyl acrylate (Tg 120°C).
Of these, from the viewpoint of adhesion to the substrate, at least one selected from the group consisting of isobornyl acrylate, t-butylcyclohexyl acrylate, trimethylcyclohexyl acrylate, cyclohexyl methacrylate and trimethylcyclohexyl methacrylate is preferred.

The (co)polymer (A) may contain, as a constituent monomer, a monomer (a2) other than the (meth)acrylate (a1) having an alicyclic skeleton, to the extent that it does not affect the physical properties. Examples of the monomer (a2) include (meth)acrylates (a21) having a linear or branched aliphatic skeleton, (meth)acrylates (a22) having an aromatic skeleton, (meth)acrylates (a23) having an alicyclic skeleton other than the (meth)acrylates (a1) having an alicyclic skeleton, and (meth)acrylates (a24) having a heterocyclic skeleton.

Examples of the (meth)acrylate (a21) having a linear or branched aliphatic skeleton include methyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl diglycol (meth)acrylate, butoxyethyl (meth)acrylate, butoxymethyl (meth)acrylate, methoxymethyl (meth)acrylate, methyl ... Examples of the acrylate copolymer include dipropylene mono(meth)acrylate, 3-methoxybutyl(meth)acrylate, 2-(2-methoxyethoxy)ethyl(meth)acrylate, 2-(2-butoxyethoxy)ethyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, polyethylene oxide monomethyl ether(meth)acrylate, methoxydipropylene glycol(meth)acrylate, polyethylene glycol (PEG) mono(meth)acrylate, polypropylene glycol (PPG) mono(meth)acrylate, and polycaprolactone 2-hydroxyethyl(meth)acrylate ester.
Examples of the (meth)acrylate (a22) having an aromatic skeleton include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, methylphenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenyl (meth)acrylate, phenoxymethyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.
Examples of the (meth)acrylate (a23) having an alicyclic skeleton other than the (meth)acrylate (a1) having an alicyclic skeleton include cyclohexyl acrylate (Tg 16° C.) and isobornyl methacrylate (Tg 180° C.).
Examples of the (meth)acrylate (a24) having a heterocyclic skeleton include glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and cyclic trimethylolpropane formal (meth)acrylate.

Among the (meth)acrylates (a21) having a linear or branched aliphatic skeleton, (meth)acrylates (a22) having an aromatic skeleton, (meth)acrylates (a23) having an alicyclic skeleton other than (meth)acrylates (a1) having an alicyclic skeleton, and (meth)acrylates (a24) having a heterocyclic skeleton, from the viewpoint of adhesion to the substrate, preferred are isobornyl methacrylate, 2-ethylhexyl methacrylate, lauryl acrylate, benzyl acrylate, cyclohexyl acrylate, t-butyl methacrylate, and phenoxyethyl acrylate, and more preferred are 2-ethylhexyl methacrylate, lauryl acrylate, benzyl acrylate, cyclohexyl acrylate, t-butyl methacrylate, and phenoxyethyl acrylate.

The weight average molecular weight (hereinafter, may be referred to as Mw) of the (co)polymer (A) in the present invention is 40,000 to 90,000, and preferably 40,000 to 80,000. If the weight average molecular weight of the (co)polymer (A) is less than 40,000, the alcohol resistance may be poor, and if it exceeds 90,000, the solubility in the solvent (B) may be poor.
The Mw of the (co)polymer (A) and the (co)polymer (D) described below is measured by gel permeation chromatography under the following conditions.
<Conditions for measuring Mw of (co)polymer (A) and (co)polymer (D) described below>
Device: "HLC-802A" [manufactured by Tosoh Corporation]
Color: 2 tubes of "TSK gel GMH6" [manufactured by Tosoh Corporation] Measurement temperature: 40°C
Sample solution: 0.25 wt% tetrahydrofuran solution Solution injection amount: 100 μl
Detector: Refractive index detector Reference material: Standard polystyrene (TSKstandard POLYSTYRENE)
12 points (molecular weight: 500, 1,050, 2,800, 5,970, 9,100, 18,100, 37,900, 96,400, 190,000, 355,000, 1,090,000, 2,890,000) [manufactured by Tosoh Corporation]

From the viewpoint of adhesion to a substrate, the content of the (meth)acrylate (a1) having an alicyclic skeleton is preferably 65% by weight or more, more preferably 70 to 100% by weight, and even more preferably 80 to 100% by weight, based on the total weight of the monomers constituting the (co)polymer (A).
From the viewpoint of adhesion to a substrate, the content of the monomer (a2) as a constituent monomer based on the weight of the (co)polymer (A) is preferably 35% by weight or less, more preferably 0 to 30% by weight, and particularly preferably 0 to 20% by weight.

The (co)polymer (A) can be obtained by a known production method, specifically a method of solution polymerization of the above-mentioned monomers in a solvent in the presence of a polymerization catalyst.
Examples of the solvent include toluene, xylene, alkylbenzene having 9 to 10 carbon atoms, methyl ethyl ketone, diethyl ketone, methyl isopropyl ketone, methyl propyl ketone, methyl isobutyl ketone, propylene glycol monomethyl ether acetate, and mixtures thereof.
Examples of the polymerization catalyst include azo catalysts (2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile), etc.), peroxide catalysts (benzoyl peroxide, cumyl peroxide, lauryl peroxide, etc.), and redox catalysts (mixtures of benzoyl peroxide and tertiary amine, etc.). Furthermore, if necessary, known chain transfer agents (e.g., alkyl mercaptans having 2 to 20 carbon atoms, such as dodecyl mercaptan) can also be used to adjust the molecular weight.
The polymerization temperature is preferably 25 to 140° C., more preferably 50 to 120° C. In addition to the above solution polymerization, the (co)polymer (A) can also be obtained by bulk polymerization, emulsion polymerization or suspension polymerization.
The polymerization form of the (co)polymer (A) may be either a random addition polymer or an alternating copolymer, and may also be either a graft copolymer or a block copolymer.

The SP value of the (co)polymer (A) is preferably from 8.0 to 9.5, more preferably from 8.3 to 9.3, from the viewpoint of alcohol resistance.
The SP value can be calculated by the method described in Polymer Engineering and Science, Vol. 14, pp. 151-154, by Robert F. Fedors et al.

Examples of the solvent (B) used in the present invention include ketone solvents, ester solvents, alcohol solvents, ether solvents, glycol solvents, carbonate solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and mixed solvents of two or more of these.

Ketone solvents include methyl ethyl ketone, diethyl ketone, methyl isopropyl ketone, dimethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl t-butyl ketone, methyl n-butyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone.

Ester solvents include methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.

Alcohol solvents include methanol, ethanol, n-propanol, i-propanol, 1-butanol, 2-butanol, isobutanol, t-butanol, n-pentanol, 2-pentanol, 3-methyl-3-pentanol, 2-hexanol, 2-ethylhexanol, cyclopentanol, cyclohexanol, and methylcyclohexanol.

Examples of ether solvents include dimethyl ether, methyl ethyl ether, methyl t-butyl ether, methyl normal butyl ether, diethyl ether, ethyl t-butyl ether, diisopropyl ether, dipropyl ether, tetrahydrofuran, tetrahydropyran, 4-methyltetrahydropyran, and methoxycyclopentane.

Glycol solvents include dimethoxymethane, dimethoxyethane, 2,2-dimethoxypropane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether acetate.

Carbonate solvents include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

Aromatic hydrocarbon solvents include toluene and xylene.

Aliphatic hydrocarbon solvents include hexane, heptane, octane, isooctane, and methylcyclohexane.

Among these solvents (B), from the viewpoint of the solubility of the (co)polymer (A) and the quick-drying properties of the ink, preferred are ketone solvents, ester solvents, alcohol solvents, ether solvents, carbonate solvents, and mixtures thereof, more preferred are ketone solvents, and particularly preferred are at least one solvent selected from the group consisting of methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isopropyl ketone, and methyl isobutyl ketone.

In the present invention, water-insoluble dye (C) refers to a dye whose solubility in water at 25°C (the mass of dye dissolved in 100 g of water) is 1 g or less. The solubility in water at 25°C is preferably 0.5 g or less, and more preferably 0.1 g or less. Therefore, so-called water-insoluble oil-soluble dyes are preferably used.

Specific examples of the water-insoluble dye (C) include C.I. Solvent Yellow 16, 21, 25, 29, 33, 51, 56, 82, 88, 89, 150, 163, C.I. Solvent Red 7, 8, 18, 24, 27, 49, 109, 122, 125, 127, 130, 132, 135, 218, 225, 230, C.I. Solvent Blue 14, 25, 35, 38, 48, 67, 68, 70, 132, and C.I. Solvent Black 3, 5, 7, 27, 28, 29, 34, and the like.
Among these, Solvent Black 3, 27, 29 and 34 are preferred from the viewpoints of solubility in the solvent (B) and visibility of the printed matter.

The (co)polymer (D) is preferably at least one resin selected from the group consisting of styrene (maleic anhydride) resin, styrene (meth)acrylic resin, polystyrene, and ketone aldehyde resin.
Styrene (maleic anhydride) resin is a polymer containing styrene and maleic acid and/or maleic anhydride as essential constituent monomers.
Styrene (meth)acrylic resin is a polymer containing styrene and (meth)acrylate as essential constituent monomers.
Polystyrene is a polymer whose constituent monomer is styrene.
Ketone aldehyde resins are condensation products of ketones and aldehydes.
Of these, from the viewpoint of alcohol resistance of the printed matter, styrene (meth)acrylic resin, polystyrene, and ketone aldehyde resin are preferred.
The weight average molecular weight of the (co)polymer (D) is 700 to 10000. If the weight average molecular weight is less than 700, the alcohol resistance may be poor, and if it exceeds 10000, the solubility may be poor.
Among the (co)polymers (D), styrene (maleic anhydride) resin, styrene (meth)acrylic resin, and polystyrene can be synthesized by known polymerization methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization using the constituent monomers and a radical polymerization initiator. Solution polymerization, suspension polymerization and bulk polymerization, or a combination thereof are preferred. Ketone aldehyde resins can be obtained by condensing a ketone and an aldehyde under basic conditions.
The polymerization temperature is preferably 60 to 230° C., more preferably 80 to 230° C. The polymerization time is preferably 1 to 30 hours, more preferably 2 to 20 hours.

Examples of the radical polymerization initiator include azo polymerization initiators (e.g., azobisisobutyronitrile, azobisvaleronitrile, and azobiscyanovaleric acid) and organic peroxide polymerization initiators (e.g., benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane).
Of these, di-t-butyl peroxide and 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane are preferred.
The amount of the polymerization initiator used is preferably 0.01 to 10% by weight, more preferably 0.05 to 8% by weight, and particularly preferably 0.1 to 6% by weight, based on the total amount of the monomers.

Examples of the solvent used in solution polymerization include cycloalkane solvents having 5 to 12 carbon atoms (cyclohexane, methylcyclohexane, etc.); aromatic solvents having 6 to 12 carbon atoms (benzene, toluene, xylene, ethylbenzene, cumene, etc.); ester solvents (ethyl acetate, butyl acetate, etc.); and ether solvents (methyl cellosolve, ethyl cellosolve, butyl cellosolve, etc.).
Of these, aromatic solvents are preferred, and toluene, xylene and ethylbenzene are more preferred.
In addition, when suspension polymerization is carried out, polymerization can be carried out in water using an inorganic acid salt dispersant (calcium carbonate, calcium phosphate, etc.) and an organic dispersant (polyvinyl alcohol, methyl cellulose, etc.).

From the viewpoint of ink viscosity, the content of the (co)polymer (A) is 5 to 20% by weight, preferably 5 to 18% by weight, and particularly preferably 7 to 15% by weight, based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer (D).
From the viewpoint of ink viscosity, the content of the solvent (B) is 70 to 85% by weight, preferably 75 to 88% by weight, and particularly preferably 77 to 86% by weight, based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer (D).
From the viewpoint of visibility and adhesion of the printed matter, the content of the water-insoluble dye (C) is 3 to 10% by weight, preferably 3.3 to 9% by weight, and particularly preferably 3.5 to 8% by weight, based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer (D).
The content of the (co)polymer (D) is 5 to 12% by weight, and preferably 7 to 12% by weight, based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer (D), from the viewpoints of ink viscosity and alcohol resistance.

From the viewpoint of suppressing the generation of harmful substances, the inkjet ink composition of the present invention preferably contains no more than 5% by weight, more preferably no more than 2% by weight, of a chlorine-containing resin based on the total weight of the (co)polymer (A), solvent (B), water-insoluble dye (C), and (co)polymer (D), and it is particularly preferred that the inkjet ink composition does not contain any chlorine-containing resin. Examples of chlorine-containing resins include chlorinated polyolefin resins, chlorinated ethylene vinyl acetate copolymer resins, and vinyl chloride vinyl acetate copolymer resins.

The ink-jet ink composition of the present invention may contain a leveling agent (E) from the viewpoint of reducing the surface tension and improving the wettability with the recording medium.
Examples of the leveling agent (E) include silicone surfactants, fluorine surfactants, and polyoxyethylene adducts of nonionic surfactants.
Among these leveling agents (E), silicone surfactants are preferred from the viewpoints of wettability and prevention of foaming.

From the viewpoint of wettability and foamability, the content of the leveling agent (E) is preferably 0.01 to 1.0% by weight, more preferably 0.03 to 0.5% by weight, and particularly preferably 0.05 to 0.3% by weight, based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer (D).

(Other additives)
Various additives may be added to the inkjet ink composition of the present invention, if necessary, to impart various functionalities. Specific examples include charge adjusters (such as diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate), light stabilizers, surface treatment agents, antioxidants (such as Irganox 1010), antioxidants, crosslinking accelerators, plasticizers (such as polytetramethylene glycol), preservatives, pH adjusters, antifoaming agents, and moisturizers.

(Method of Preparing Inkjet Ink Composition)
The method for preparing the inkjet ink composition of the present invention is not particularly limited, and the inkjet ink composition can be prepared by adding all of the above-mentioned materials and mixing them in a bead mill, a triple roll mill, etc. When a pigment is used, the pigment, pigment dispersant, photopolymerizable compound, etc. can be mixed to obtain a base ink in advance, and the remaining components can be added to the base ink so as to obtain the desired composition.

(Inkjet ink composition)
From the viewpoint of imparting favorable jetting properties, the inkjet ink composition of the present invention preferably has an initial viscosity in the range of 2 to 7 mPa s, more preferably 2.3 to 6 mPa s or less, even more preferably 2.4 to 5 mPa s or less, and particularly preferably 2.5 to 4 mPa s.
The initial viscosity is the viscosity of the ink composition immediately after preparation, and can be measured, for example, with an E-type viscometer (trade name: TVE-35, manufactured by Toki Sangyo Co., Ltd.).

The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to these.

<Production Example 1: Production of (co)polymer (A-1)>
Into a reaction vessel equipped with a stirrer, a heating/cooling device, a thermometer, a dropping funnel, a nitrogen inlet tube, and a pressure reducing device, 100 parts by weight of methyl ethyl ketone was placed as a solvent, and in another glass beaker, 30 parts by weight of isobornyl acrylate, 30 parts by weight of t-butylcyclohexyl acrylate, 29.3 parts by weight of trimethylcyclohexyl acrylate, 10 parts by weight of 2-ethylhexyl methacrylate, 0.2 parts by weight of dodecyl mercaptan as a chain transfer agent, and 0.5 parts by weight of 2,2′-azobis(2-methylbutyronitrile) were placed, and the mixture was stirred and mixed at 20° C. to prepare a monomer solution, which was then placed in the dropping funnel.
After the gas phase of the reaction vessel was purged with nitrogen (gas phase oxygen concentration: 100 ppm or less), the monomer solution was added dropwise over 2 hours while maintaining the temperature inside the sealed system at 70 to 75°C, and the mixture was aged at 75°C for 8 hours from the end of the addition to obtain a 50 wt% solution of a polymer composition containing copolymer (A-1). The resulting copolymer (A-1) had an Mw of 50,000 and an SP value of 8.7.

<Production Examples 2 to 9, Comparative Production Examples 1 and 2: Production of (Co)polymers (A-2) to (A-9), (A'-1), and (A'-2)>
A 50 wt % solution of a polymer composition containing the (co)polymers (A-2) to (A-9), (A′-1) and (A′-2) was obtained in the same manner as in Production Example 1, except that the raw materials listed in Table 1 were used.

The raw materials used in Table 1 are as follows:
(a1-1) Isobornyl acrylate [trade name: Light Acrylate IB-XA, Kyoeisha Chemical Co., Ltd.] Tg 94°C
(a1-2) Cyclohexyl methacrylate [trade name: Light Ester CH, Kyoeisha Chemical Co., Ltd.] Tg 66°C
(a1-3) t-Butylcyclohexyl acrylate [trade name: Miramer M1150, manufactured by Miwon Co., Ltd.] Tg 65°C
(a1-4) Trimethylcyclohexyl acrylate [trade name: Miramer M1130, manufactured by Miwon Co., Ltd.] Tg 43°C
(a1-5) Trimethylcyclohexyl methacrylate [trade name: Satomer CD421, manufactured by Arkema] Tg 145°C
(a2-1) 2-Ethylhexyl methacrylate [trade name: Light Ester 2EH, manufactured by Nippon Shokubai Co., Ltd.]
(a2-2) Lauryl acrylate [trade name: Light Acrylate LA, Kyoeisha Chemical Co., Ltd.]
(a2-3) Benzyl acrylate [trade name: Miramer M1182, manufactured by Miwon Co., Ltd.]
(a2-4) Cyclohexyl acrylate [trade name: Blenmer CHA, manufactured by NOF Corporation] Tg 16°C
(a2-5) t-Butyl methacrylate [trade name: Light Ester TB, Kyoeisha Chemical Co., Ltd.]
(a2-6) Phenoxyethyl acrylate [trade name: Viscoat #192, PEA, Osaka Organic Chemical Industry Co., Ltd.]

<Production Example 10: Production of (co)polymer (D-1)>
An autoclave was charged with 250 parts by weight of xylene, and the air was replaced with nitrogen. The autoclave was then heated to 185°C in a sealed state with stirring. A mixed solution of 472 parts by weight of styrene, 15 parts by weight of n-butyl acrylate, 13 parts by weight of acrylic acid, 15 parts by weight of di-t-butyl peroxide, and 100 parts by weight of xylene was added dropwise over 3 hours while controlling the temperature inside the autoclave at 185°C, allowing polymerization to occur. The same temperature was maintained for another 1 hour to complete the polymerization, and the temperature was then raised to 170°C while distilling off the xylene, after which the pressure was reduced. Desolvation was continued at a pressure of 1 kPa or less, and the xylene content in the (co)polymer was confirmed to be 400 ppm or less, yielding a styrene (meth)acrylic resin (co)polymer (D-1). The Mw of the (co)polymer (D-1) was 10,000.

<Production Example 11: Production of (co)polymer (D-2)>
An autoclave was charged with 250 parts by weight of xylene, and the air was replaced with nitrogen. The autoclave was then heated to 170°C in a sealed state with stirring. A mixed solution of 411 parts by weight of styrene, 150 parts by weight of n-butyl acrylate, 9 parts by weight of methacrylic acid, 25 parts by weight of di-t-butyl peroxide, and 100 parts by weight of xylene was added dropwise over 3 hours while controlling the temperature inside the autoclave at 170°C, allowing polymerization to occur. The same temperature was maintained for another 1 hour to complete the polymerization, and the temperature was then raised to 170°C while distilling off the xylene, after which the pressure was reduced. Desolvation was continued at a pressure of 1 kPa or less, and the xylene content in the (co)polymer was confirmed to be 400 ppm or less, yielding a styrene (meth)acrylic resin (co)polymer (D-2). The Mw of the (co)polymer (D-2) was 850.

<Production Example 12: Production of (co)polymer (D-3)>
An autoclave was charged with 250 parts by weight of xylene, and the air was replaced with nitrogen. The autoclave was then heated to 200°C in a sealed state with stirring. A mixed solution of 487 parts by weight of styrene, 13 parts by weight of maleic anhydride, 25 parts by weight of di-t-butyl peroxide, and 110 parts by weight of xylene was added dropwise over 3 hours while controlling the temperature inside the autoclave at 200°C, allowing polymerization to occur. The temperature was maintained for another 1 hour to complete the polymerization, and the temperature was then raised to 170°C while distilling off the xylene, after which the pressure was reduced. Desolvation was continued at a pressure of 1 kPa or less, and the xylene content in the (co)polymer was confirmed to be 400 ppm or less, yielding a styrene-maleic anhydride resin (co)polymer (D-3). The Mw of the (co)polymer (D-3) was 5,000.

<Production Example 13: Production of (co)polymer (D-4)>
An autoclave was charged with 250 parts by weight of xylene, and the air was replaced with nitrogen. The autoclave was then heated to 200°C in a sealed state with stirring. A mixed solution of 500 parts by weight of styrene, 50 parts by weight of di-t-butyl peroxide, and 110 parts by weight of xylene was added dropwise over 3 hours while controlling the temperature inside the autoclave at 200°C, allowing polymerization to occur. The temperature was maintained for another 1 hour to complete the polymerization, and the temperature was then raised to 170°C while distilling off the xylene, after which the pressure was reduced. Desolvation was continued at a pressure of 1 kPa or less, and it was confirmed that the xylene content in the (co)polymer was 400 ppm or less, yielding a polystyrene (co)polymer (D-4). The Mw of the (co)polymer (D-4) was 3,000.

<Comparative Production Example 3>
Polymerization and solvent removal were carried out in the same manner as in Production Example 13, except that 50 parts by weight of di-t-butyl peroxide was changed to 200 parts by weight of di-t-butyl peroxide, thereby obtaining a polystyrene (co)polymer (D'-1). The Mw of the obtained polymer was 650.

Comparative Production Example 4
Polymerization and solvent removal were carried out in the same manner as in Production Example 13, except that 50 parts by weight of di-t-butyl peroxide was changed to 8 parts by weight of di-t-butyl peroxide, thereby obtaining a polystyrene (co)polymer (D'-2). The Mw of the obtained polymer was 22,000.

(Examples 1 to 9 and Comparative Examples 1 to 4)
A 50 wt % solution of a polymer composition containing (co)polymer (A) or (A') (the solids content of (co)polymer (A) or (A') is shown in the table), solvent (B), and (co)polymer (D) or (D') were uniformly mixed, and then other additives and the water-insoluble dye (C) were added and mixed uniformly to prepare each ink composition having the formulation (parts by weight) shown in Table 2. The amount of solvent in the polymer composition containing (co)polymer (A) or (A') was included in the amount of solvent (B).

The raw materials used in Table 2 are as follows:
(B-1) Methyl ethyl ketone [Tokyo Chemical Industry Co., Ltd.]
(B-2) Diethyl ketone [Tokyo Chemical Industry Co., Ltd.]
(B-3) Methyl propyl ketone [Tokyo Chemical Industry Co., Ltd.]
(B-4) Methyl isopropyl ketone [Tokyo Chemical Industry Co., Ltd.]
(B-5) Ethanol [Tokyo Chemical Industry Co., Ltd.]
(B-6) Dimethyl carbonate [Tokyo Chemical Industry Co., Ltd.]
(C-1) Solvent Black 3 [trade name: Oil Black 860, Orient Chemical Industry Co., Ltd.]
(C-2) Solvent Black 27 [product name: VALI FAST Black 3820, Orient Chemical Industry Co., Ltd.]
(C-3) Solvent Black 29 [product name: VALI FAST Black 3810, Orient Chemical Industry Co., Ltd.]
(C-4) Solvent Black 34 [Product name: VALI FAST Black 3804, Orient Chemical Industry Co., Ltd.]
(D-5) Ketone aldehyde resin [trade name Variplus SK, manufactured by Evonik] Mw is 990.
(D-6) Ketone aldehyde resin [trade name Variplus AP, manufactured by Evonik] Mw is 950.
(E-1) Silicone surfactant [trade name: BYK-333, manufactured by BYK Japan Co., Ltd.] (E-2) Fluorosurfactant [trade name: Megafac F-563, manufactured by DIC Corporation]
(F-1) Antioxidant [trade name: Irganox 1010, manufactured by BASF Japan Ltd.]
(G-1) Plasticizer [Polytetramethylene glycol, manufactured by]
(H-1) Charge adjuster [diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate, trade name: CPI-110P, manufactured by San-Apro Co., Ltd.]

<Initial viscosity measurement>
The viscosity (initial viscosity) of each inkjet ink composition of the Examples and Comparative Examples at 25°C immediately after preparation was measured using an E-type viscometer (trade name: TVE-35, manufactured by Toki Sangyo Co., Ltd.) with a cone rotor of 1°34' x R24. The results are shown in Table 3.

<Solubility of (Co)polymer (A) and (Co)polymer (D)>
The (co)polymer (A), solvent (B), and (co)polymer (D) in each inkjet ink composition of the Examples and Comparative Examples were mixed in the weight ratios shown in Table 2, stirred at 60°C for 6 hours, and then allowed to stand at room temperature for 1 hour. Thereafter, the mixture was visually observed to check for any undissolved residue. The results are shown in Table 3.
○: No residual dissolution ×: Some residual dissolution

<Low temperature stability test>
The (co)polymer (A), solvent (B), and (co)polymer (D) in each inkjet ink composition of the Examples and Comparative Examples were mixed in the weight ratios shown in Table 2, stirred at 60°C for 6 hours, and then allowed to stand at -5°C for 24 hours. Thereafter, the mixture was visually observed to check for any undissolved residue. The results are shown in Table 3.
○: No residual dissolution ×: Some residual dissolution

<Stability test when wet>
The (co)polymer (A), solvent (B), and (co)polymer (D) in each inkjet ink composition of the Examples and Comparative Examples were mixed in the weight ratios shown in Table 2, and stirred at 60°C for 6 hours. Water was then added to the mixture in 0.1 wt% increments at room temperature while visually observing the mixture, and the amount of water added at which cloudiness occurred (the total weight of (co)polymer (A), solvent (B), and (co)polymer (D) is taken as 100 wt%) was confirmed. The results are shown in Table 3.
◎: 7.5% by weight or more ○: 4.0 to less than 7.5% by weight △: 3.0 to less than 4.0% by weight ×: Less than 3.0% by weight

<Dry coating film performance evaluation>
<Evaluation of Adhesion (PET)>
Each of the inkjet ink compositions of the Examples and Comparative Examples was applied to one side of a 100 μm thick PET film substrate (trade name "Cosmoshine A4300", manufactured by Toyobo Co., Ltd.) using a bar coater so that the film thickness after drying would be 2 μm, thereby producing a film having a dried coating layer of the inkjet ink composition on the surface of the PET film substrate.
The adhesion (PET) was evaluated in accordance with JIS K 5600-5-6:1999.
The resulting coating film was allowed to stand for 24 hours in an environment of 23°C and 50% relative humidity, and then 2 mm wide cuts were made with a cutter knife to form a grid (10 x 10 pieces).
An adhesive tape was applied to the grid and peeled off at a 90-degree angle. The peeling state of the coating film from the PET film substrate was visually observed. The number of squares in which the coating film was not peeled off and adhered was counted out of 100 squares and evaluated. The results are shown in Table 3.
◎: No peeling in 100 squares ○: Peeling in 1 to 10 squares △: Peeling in 11 to 49 squares ×: Peeling in 50 squares or more

<Evaluation of Adhesion (PP)>
Each of the inkjet ink compositions of the Examples and Comparative Examples was applied to one side of a 60 μm thick PP film substrate (trade name "2500H Torayfan" manufactured by Toray Industries, Inc.) using a bar coater so that the film thickness after drying would be 1 μm, thereby producing a film having a dried coating film of the inkjet ink composition on the surface of the PP film substrate.
In accordance with JIS K 5600-5-6:1999, the coating film formed on the surface of the PP film substrate was left to stand for 24 hours in an environment of 23°C and a relative humidity of 50%, and then 2 mm wide cuts were made with a cutter knife to create a grid (10 x 10 pieces).
An adhesive tape was applied to the grid and peeled at a 90-degree angle, and the state of peeling of the coating film from the PP film substrate was visually observed. The number of squares in which the coating film was not peeled off and adhered was counted out of 100 squares and evaluated. The results are shown in Table 3.
◎: No peeling in 100 squares ○: Peeling in 1 to 10 squares △: Peeling in 11 to 49 squares ×: Peeling in 50 squares or more

<Evaluation of alcohol wiping resistance>
The grid of a coating film prepared in the same manner as that used in the evaluation of adhesion (PET) above was rubbed 20 times with gauze soaked in ethanol, and the state of peeling of the coating film from the PET film substrate was visually observed and evaluated according to the following criteria. The results are shown in Table 3. Alcohol wiping resistance is also simply referred to as alcohol resistance.
◎: No peeling in 100 squares ○: Peeling in 1 to 10 squares △: Peeling in 11 to 49 squares ×: Peeling in 50 squares or more

The results in Table 3 show that the inkjet ink compositions of Examples 1 to 9 have low initial viscosities and excellent jetting properties due to the high dissolution rate of the (co)polymer, and are stable even when stored at low temperatures or when containing water. Furthermore, the dried coating films of these compositions have excellent adhesion (to PET and PP films) and resistance to alcohol wiping.
On the other hand, the inkjet ink composition of Comparative Example 1, which uses a (co)polymer (A'-1) having a weight-average molecular weight of less than 40,000, shows that the dried coating film has insufficient resistance to alcohol wiping.
Furthermore, the inkjet ink composition of Comparative Example 2, which uses a (co)polymer (A'-2) having a weight-average molecular weight of more than 90,000, exhibits reduced adhesion to the substrate and is also insufficient in stability when stored at low temperatures and when containing water.
Furthermore, it is clear that the inkjet ink composition of Comparative Example 3, which uses a (co)polymer (D'-1) having a weight-average molecular weight of less than 700, exhibits insufficient resistance to alcohol wiping of the dried coating film.
Furthermore, the inkjet ink composition of Comparative Example 4, which uses a (co)polymer (D'-2) having a weight-average molecular weight of more than 10,000, exhibits reduced adhesion to the substrate and is insufficient in stability when stored at low temperatures and when containing water.

The inkjet ink composition of the present invention has low initial viscosity, excellent ejection properties, and excellent stability during low-temperature storage and when containing water. Furthermore, its dried solid exhibits excellent adhesion to substrates and alcohol resistance. The inkjet ink composition of the present invention is extremely useful, as it can be used in a wide range of inkjet printing applications, for example, in industrial and commercial applications.

Claims (5)

The composition contains a (co)polymer (A) having a weight average molecular weight of 40,000 to 90,000, a solvent (B), a water-insoluble dye (C), and a (co)polymer (D) having a weight average molecular weight of 700 to 10,000,
the (co)polymer (A) contains, as a constituent monomer, a (meth)acrylate (a1) having an alicyclic skeleton,
the (co)polymer (D) is at least one resin selected from the group consisting of styrene (maleic anhydride) resin, styrene (meth)acrylic resin, polystyrene, and ketone aldehyde resin,
an ink-jet ink composition, wherein the content of the (co)polymer (A) is 5 to 20% by weight, the content of the solvent (B) is 70 to 85% by weight, the content of the water-insoluble dye (C) is 3 to 10% by weight, and the content of the (co)polymer (D) is 5 to 12% by weight, based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer (D). 2. The ink-jet ink composition according to claim 1, wherein a homopolymer of the (meth)acrylate (a1) having an alicyclic skeleton has a glass transition temperature of more than 20°C and not more than 170°C, and the content of the (meth)acrylate ( a1 ) having an alicyclic skeleton is 65% by weight or more based on the total weight of the monomers constituting the (co)polymer (A). 3. The ink-jet ink composition according to claim 1 , wherein the (meth)acrylate (a1) having an alicyclic skeleton is at least one selected from the group consisting of isobornyl acrylate, t-butylcyclohexyl acrylate, trimethylcyclohexyl acrylate, cyclohexyl methacrylate, and trimethylcyclohexyl methacrylate. 4. The ink-jet ink composition according to claim 1 , wherein the solvent (B) is at least one selected from the group consisting of methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isopropyl ketone, and methyl isobutyl ketone. 5. The ink-jet ink composition according to claim 1, further comprising a leveling agent (E), wherein the content of the leveling agent (E) is 0.01 to 1.0 wt % based on the total weight of the (co)polymer (A), the solvent (B), the water-insoluble dye (C), and the (co)polymer ( D ).