Radiation-curable inkjet composition and inkjet recording method

Abstract

To provide a radiation-curable inkjet composition that is suitable for signature and gives a coating having flexibility, adhesion, and scratch resistance, and an inkjet recording method.SOLUTION: A radiation-curable inkjet composition has a monofunctional monomer of 86 mass% or more relative to the total monomer content. When calculated from a glass transition temperature of the monomer, the radiation-curable inkjet composition has a glass transition temperature of 42°C or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a radiation-curable ink jet composition and an ink jet recording method using the composition. [Background technology]

[0002] Conventionally, radiation-curable inkjet compositions that have little odor and exhibit good curability and flexibility after curing have been known, as described in, for example, Patent Document 1. In particular, Example 9 (Table 3) describes a radiation-curable inkjet composition that contains, as monomers, 39% by mass of phenoxyethyl acrylate, 20% by mass of acryloylmorpholine, 15% by mass of n-vinylcaprolactam, 10% by mass of 2-(2-vinyloxyethoxy)ethyl acrylate, and a bifunctional urethane acrylate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-9142 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the radiation-curable inkjet composition described in Patent Document 1 has the problem that when used for signage, the flexibility and adhesion of the coating film tend to be insufficient. Also, when the proportion of monofunctional monomers relative to the total monomers is increased in order to improve flexibility and adhesion, the scratch resistance of the coating film may decrease. [Means for solving the problem]

[0005] The radiation-curable inkjet composition of the present application contains 86% by mass or more of monofunctional monomers based on the total mass of the monomers, and has a glass transition temperature of 42° C. or higher calculated from the glass transition temperature of the monomers.

[0006] The radiation-curable ink jet composition preferably contains a monomer represented by the following general formula (1). CH2=CR 1 -COOR 2 -O-CH=CH-R 3 ···(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0007] In the radiation-curable ink jet composition, the monofunctional monomer preferably includes a monomer having a glass transition temperature of 90° C. or higher.

[0008] In the radiation-curable ink jet composition, the monofunctional monomer is preferably n-vinylcaprolactam or acryloylmorpholine.

[0009] One aspect of the inkjet recording method according to the present invention preferably includes the steps of: attaching the radiation-curable inkjet composition described above to a recording medium; and irradiating the radiation-curable inkjet composition with UV-LED light. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described. The embodiment described below is an example of the present invention. The present invention is not limited to the following embodiment, and includes various modified forms that are implemented within the scope of the present invention. Note that not all of the configurations described below are necessarily essential configurations of the present invention.

[0011] In this specification, "(meth)acryloyl" means at least one of acryloyl and its corresponding methacryloyl, "(meth)acrylate" means at least one of acrylate and its corresponding methacrylate, and "(meth)acrylic" means at least one of acrylic and its corresponding methacrylic.

[0012] 1. Radiation-curable inkjet composition The radiation-curable inkjet composition according to this embodiment is a composition that is ejected from an inkjet head by an inkjet method. Hereinafter, a radiation-curable inkjet composition will be described as one embodiment of the radiation-curable inkjet composition, but the composition may be a composition other than an ink composition, for example, a composition used for 3D modeling.

[0013] The radiation-curable inkjet composition of this embodiment is cured by irradiation with radiation. Examples of radiation include ultraviolet light, infrared light, visible light, and X-rays. As the radiation, ultraviolet light is preferred because radiation sources are readily available and widely used, and materials suitable for curing by ultraviolet radiation are readily available and widely used.

[0014] The radiation-curable inkjet composition according to this embodiment contains 86% by mass or more of monofunctional monomers relative to the total mass of the monomers, and has a glass transition temperature of 42°C or higher calculated from the glass transition temperature of the monomers.

[0015] The components that may be contained in the radiation-curable ink jet composition according to this embodiment, its physical properties, and a production method will be described below.

[0016] 1.1.Monomer The monomers exemplified in this embodiment include monofunctional monomers having one polymerizable functional group and polyfunctional monomers having multiple polymerizable functional groups.

[0017] The radiation-curable inkjet composition according to this embodiment contains 86% by mass or more of a monofunctional monomer relative to the total amount of monomers. The content of the monofunctional monomer is preferably 86% by mass or more and 99% by mass or less, more preferably 94% by mass or more and 99% by mass or less, and even more preferably 96% by mass or more and 99% by mass or less, relative to the total amount of monomers. When the content of the monofunctional monomer relative to the total amount of monomers is 86% by mass or more, the flexibility and adhesion of the coating film can be improved. When the content is 94% by mass or more, the flexibility and adhesion can be further improved, and when the content is 96% by mass or more, the adhesion can be further improved. The content of the monofunctional monomer is preferably 99% by mass or less, relative to the total amount of monomers. When the content is 99% by mass or less, the abrasion resistance can be improved.

[0018] Furthermore, the radiation-curable inkjet composition according to this embodiment has a glass transition temperature of 42° C. or higher, calculated from the glass transition temperature of the monomer. This can improve the scratch resistance of the coating film at room temperature.

[0019] The method for calculating the glass transition temperature of the radiation-curable ink jet composition will be described. The glass transition temperature of the radiation-curable ink jet composition is calculated as Tg All The glass transition temperature of each monomer contained in the radiation-curable inkjet composition is represented by Tg N , and its content is X N (% by mass). N is a number starting from 1 depending on the type of monomer contained in the radiation-curable inkjet composition. For example, when three types of monomers are used, Tg1, Tg2, and Tg3 are generated. The glass transition temperature of each monomer was obtained from the safety data sheet (SDS) or catalog information of the monomer. The glass transition temperature Tg of the radiation-curable inkjet composition All is the glass transition temperature Tg calculated for each monomer. N and content X N Therefore, the following equation (2) holds true. Tg All =ΣTg N ×X N ···(2)

[0020] 1.1.1. Monofunctional Monomers The radiation-curable inkjet composition according to this embodiment contains a monofunctional monomer.

[0021] The monofunctional monomer of this embodiment is not particularly limited, but a conventionally known monofunctional monomer having a polymerizable functional group, particularly a polymerizable functional group having a carbon-carbon unsaturated double bond, can be used. In addition, the monofunctional monomer may contain, for example, a monofunctional (meth)acrylate having an aromatic ring skeleton.

[0022] The monofunctional (meth)acrylate having an aromatic ring skeleton is a compound having an aromatic ring skeleton and one (meth)acryloyl group as a polymerizable functional group in one molecule. Examples of the monofunctional (meth)acrylate having an aromatic ring skeleton include, but are not limited to, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate (PEA), alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, p-cumylphenol EO-modified (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Examples of commercially available products include Viscoat #192 (trade name: phenoxyethyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.), SR340 (phenoxyethyl methacrylate), SR339A (phenoxyethyl acrylate), SR504 (ethoxylated nonylphenyl acrylate), CD614 (alkoxylated nonylphenyl acrylate), and CD9087 (alkoxylated 2-phenoxyethyl acrylate) (all of which are trade names manufactured by Sartomer Corporation).

[0023] Other examples of the monofunctional monomer include compounds represented by the following general formula (3) and compounds represented by the following general formula (4).

[0024] CH2=CR 4 -COOR5 -Ar···(3) CH2=CR 4 -COO-Ar ···(4) (In the above formulas (3) and (4), R 4 In the above formula (3), Ar representing the aromatic ring skeleton has at least one aryl group, and the carbon atoms constituting the aryl group are R 5 is a monovalent organic residue bonded to a group represented by R 5 is a divalent organic residue having 1 to 4 carbon atoms. In the above formula (4), Ar, which represents an aromatic ring skeleton, is a monovalent organic residue having at least one aryl group, and the carbon atom constituting the aryl group is bonded to -COO- in the formula.

[0025] In the above general formula (3), R 5 Preferred examples of the group represented by the formula (I) include linear, branched, or cyclic alkylene groups having 1 to 4 carbon atoms, which may be substituted, and alkylene groups having 1 to 4 carbon atoms and which have an oxygen atom via an ether bond and / or an ester bond in their structure. Among these, alkylene groups having 1 to 4 carbon atoms, such as ethylene, n-propylene, isopropylene, and butylene, and alkylene groups having 1 to 4 carbon atoms and which have an oxygen atom via an ether bond in their structure, such as oxyethylene, oxy-n-propylene, oxyisopropylene, and oxybutylene, are preferably used. When the organic residue is an optionally substituted group, the substituent is not particularly limited, and examples include a carboxyl group, an alkoxy group, a hydroxyl group, and a halo group. When the substituent is a group containing a carbon atom, the carbon atom is counted as part of the carbon number of the organic residue.

[0026] In the above general formulas (3) and (4), the aryl group contained in at least one Ar (aryl) (aromatic ring skeleton) is not limited to the following, but examples thereof include a phenyl group and a naphthyl group. The number of aryl groups is 1 or more, preferably 1 or 2. The aryl group is formed by arranging the carbon atoms constituting the group at positions R in formula (3). 5The substituent may be substituted on a carbon atom other than the carbon atom bonded to the organic residue represented by the formula (1), the carbon atom bonded to -COO- in formula (4), and the carbon atom bonding the aryl groups together when there are multiple aryl groups. When substituted, the number of substitutions per aryl group is 1 or more, preferably 1 or 2. The substituent is not particularly limited, but examples include linear, branched, or cyclic alkyl and alkoxy groups having 1 to 10 carbon atoms, carboxyl groups, halo groups, and hydroxyl groups.

[0027] The inclusion of a monofunctional (meth)acrylate having an aromatic ring skeleton tends to improve the solubility of the polymerization initiator described below, which tends to improve curability, making it preferable. In particular, when an acylphosphine oxide-based polymerization initiator or a thioxanthone-based polymerization initiator is used, the solubility tends to be improved. Among the monofunctional (meth)acrylates having an aromatic ring skeleton, phenoxyethyl (meth)acrylate and benzyl (meth)acrylate are preferred, with phenoxyethyl (meth)acrylate being even more preferred due to its lower odor. Furthermore, phenoxyethyl (meth)acrylate is preferred, with phenoxyethyl acrylate (PEA) being particularly preferred, because it has good compatibility with additives such as polymerization initiators, can further reduce viscosity and odor, and can further improve reactivity (curability).

[0028] Furthermore, monofunctional monomers without an aromatic ring skeleton can also be used. Specific examples thereof include unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid; salts of the unsaturated carboxylic acids; esters, urethanes, amides, and anhydrides of unsaturated carboxylic acids; acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes; N-vinyl compounds such as N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, and N-vinylcaprolactam; and acrylamides such as dimethylacrylamide (DMAA) and dimethylaminoethyl acrylate benzyl chloride quaternary salt (DMAEA). These monofunctional monomers may be used alone or in combination of two or more.

[0029] As the monofunctional monomer, from the viewpoint of improving the curability of the radiation-curable ink jet composition, a monofunctional (meth)acrylic acid ester, that is, a monofunctional (meth)acrylate may be used.

[0030] Monofunctional (meth)acrylates include tert-butylcyclohexanol acrylate (TBCHA), isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate (IDA), isomyristyl (meth)acrylate, isostearyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and butoxyethyl (meth)acrylate. , tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, lactone-modified flexible (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl, and the like.

[0031] The monofunctional monomer contained in the radiation-curable ink jet composition of this embodiment preferably contains a monomer having a glass transition temperature of 90° C. or higher.

[0032] By including a monomer having a glass transition temperature of 90° C. or higher, the glass transition temperature of the radiation-curable ink jet composition, calculated from the glass transition temperature of the monomer, can be easily increased to 42° C. or higher, thereby achieving the effect of improving the scratch resistance of the coating film at room temperature.

[0033] Examples of monofunctional monomers having a glass transition temperature of 90°C or higher include n-vinylcaprolactam (NVC), acryloylmorpholine (ACMO), dicyclopentanyl acrylate, dicyclopentadienyl acrylate, and isobornyl acrylate. N-vinylcaprolactam (NVC) and acryloylmorpholine (ACMO) are particularly preferred. n-Vinylcaprolactam or acryloylmorpholine can further enhance the scratch resistance of the coating film at room temperature. Furthermore, n-vinylcaprolactam further enhances the flexibility of the coating film, and acryloylmorpholine can reduce the odor of the radiation-curable inkjet composition.

[0034] The content of the monofunctional monomer having a glass transition temperature of 90°C or higher is not particularly limited, but it is preferable to adjust the content so that the glass transition temperature of the radiation-curable inkjet composition calculated from the glass transition temperature of the monomer is 42°C or higher.

[0035] 1.1.2. Polyfunctional Monomers The radiation-curable ink jet composition of this embodiment may contain a polyfunctional monomer.

[0036] The polyfunctional monomer preferably contains a polyfunctional monomer (vinyl ether group-containing (meth)acrylate) represented by the following general formula (1). CH2=CR 1 -COOR 2 -O-CH=CH-R3 ···(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0037] By including a monomer represented by general formula (1), the viscosity of the radiation-curable ink jet composition can be easily reduced. The reduced viscosity allows the radiation-curable ink jet composition to be stably ejected from an inkjet head when printing using the composition. In addition, by including a monomer represented by general formula (1), the curability can be improved. The improved curability allows for faster printing speeds. Therefore, a radiation-curable ink jet composition suitable for printing can be obtained.

[0038] In the above general formula (1), R 2 Suitable divalent organic residues having 2 to 20 carbon atoms and represented by the formula (I) are linear, branched, or cyclic alkylene groups having 2 to 20 carbon atoms, which may be substituted; alkylene groups having 2 to 20 carbon atoms and having an oxygen atom via an ether bond and / or an ester bond in the structure, which may be substituted; and divalent aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkylene groups having 2 to 6 carbon atoms, such as ethylene, n-propylene, isopropylene, and butylene, and alkylene groups having 2 to 9 carbon atoms and having an oxygen atom via an ether bond in the structure, such as oxyethylene, oxy-n-propylene, oxyisopropylene, and oxybutylene, are preferably used. Furthermore, from the viewpoint of further reducing the viscosity and further improving the curability of the radiation-curable inkjet composition, R 2 is an alkylene group having 2 to 9 carbon atoms and having an oxygen atom by an ether bond in the structure, such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, or an oxybutylene group, and more preferred are compounds having a glycol ether chain.

[0039] In the above general formula (1), R 3 Suitable monovalent organic residues having 1 to 11 carbon atoms and represented by the formula (I) are linear, branched, or cyclic alkyl groups having 1 to 10 carbon atoms, which may be substituted, and aromatic groups having 6 to 11 carbon atoms, which may be substituted. Among these, alkyl groups having 1 to 2 carbon atoms, such as methyl or ethyl groups, and aromatic groups having 6 to 8 carbon atoms, such as phenyl and benzyl groups, are preferably used.

[0040] When each of the above organic residues is a group that may be substituted, the substituent is divided into a group containing carbon atoms and a group not containing carbon atoms. First, when the above substituent is a group containing carbon atoms, the carbon atom is counted in the number of carbon atoms of the organic residue. Examples of the group containing carbon atoms include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing carbon atoms include, but are not limited to, a hydroxyl group and a halo group.

[0041] Specific examples of the compound of formula (1) include, but are not limited to, 2-vinyloxyethyl (meth)acrylate, 3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl (meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl (meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl (meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate, 3-vinyloxybutyl acrylate, 1-methyl-2-vinyloxypropyl (meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl (meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate, 3-vinyloxymethylcyclohexylmethyl (meth)acrylate, 2-vinyloxymethylcyclohexylmethyl (meth)acrylate, p-vinyloxymethylphenylmethyl (meth)acrylate, m-vinyloxymethylphenylmethyl (meth)acrylate 2-(vinyloxyethoxy)ethyl acrylate (VEEA), 2-(vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethyl)acrylate (meth)acrylate 2-(vinyloxyethoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)ethyl, (meth)acrylate 2-(vinyloxyethoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyethoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyethoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)propyl, (meth)acrylate 2-(vinyloxyisopropoxyisopropoxy)propyl2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate, 2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate ethyl, 2-(isopropenoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate. Of these specific examples, VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferred, as it allows for easy balancing of the curability and viscosity of the radiation-curable inkjet composition.

[0042] The radiation-curable ink jet composition of this embodiment may contain other polyfunctional monomers.

[0043] Examples of bifunctional (meth)acrylates include diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol dimethacrylate, dipropylene glycol diacrylate (DPGDA), tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6 -hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, EO (ethylene oxide) adduct di(meth)acrylate of bisphenol A, PO (propylene oxide) adduct di(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate.

[0044] Examples of trifunctional or higher polyfunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate.

[0045] Furthermore, as the tri- or higher functional polyfunctional (meth)acrylate, an oligomer (including a dimer, a trimer, etc.), a prepolymer, etc. can be used. As the oligomer or prepolymer, for example, those containing the above-mentioned monomers as constituent components can be used.

[0046] The radiation-curable ink jet composition may contain a polyfunctional oligomer. This can improve the storage stability of the radiation-curable ink jet composition and also improve the abrasion resistance and other properties of the pattern formed. Preferred oligomers include urethane oligomers, which have a urethane repeating unit, and epoxy oligomers, which have an epoxy repeating unit.

[0047] Furthermore, examples of polyfunctional acrylate oligomers include oligoester acrylates, such as urethane acrylate oligomers, polyester acrylate oligomers, and epoxy acrylate oligomers. Examples of urethane acrylate oligomers include aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers, with aliphatic urethane acrylate oligomers being more preferred. Furthermore, the urethane acrylate oligomer is preferably a tetrafunctional or lower urethane acrylate oligomer, and more preferably a difunctional urethane acrylate oligomer.

[0048] 1.2.Polymerization initiator The radiation-curable inkjet composition according to this embodiment preferably contains a polymerization initiator that generates active species upon irradiation with radiation. The polymerization initiator is not particularly limited, but examples include known polymerization initiators such as alkylphenone-based polymerization initiators, acylphosphine oxide-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone-based polymerization initiators. Among these, acylphosphine oxide-based polymerization initiators are preferred. By containing an acylphosphine oxide-based polymerization initiator, the radiation-curable inkjet composition tends to have excellent curability, and in particular, even better curability in a curing process using UV-LED light.

[0049] Examples of the acylphosphine oxide polymerization initiator include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0050] Commercially available acylphosphine oxide polymerization initiators include, for example, IRGACURE 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), IRGACURE 1800 (a mixture of bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 25:75), and IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (all manufactured by BASF).

[0051] The polymerization initiator may be used alone or in combination of two or more. The total content of the polymerization initiators is preferably from 1 to 20% by mass, more preferably from 3 to 15% by mass, even more preferably from 5 to 10% by mass, and particularly preferably from 7 to 9% by mass, relative to the total mass (100% by mass) of the radiation-curable inkjet composition, in order to achieve excellent curability and solubility.

[0052] 1.3. Other additives The radiation-curable ink jet composition according to this embodiment may further contain additives such as a colorant, a dispersant, a polymerization inhibitor, a slip agent, a photosensitizer, and a polymerization inhibitor, as needed.

[0053] 1.3.1.Colorants The radiation-curable ink jet composition according to this embodiment may further contain a coloring material. The radiation-curable ink jet composition according to this embodiment can be used as a colored radiation-curable ink jet composition by containing a coloring material. The coloring material can be at least one of a pigment and a dye.

[0054] <Pigments> By using a pigment as the coloring material, the light resistance of the radiation-curable ink jet composition can be improved. Both inorganic and organic pigments can be used as the pigment.

[0055] As inorganic pigments, carbon blacks (CI (Colour Index Generic Name) Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, iron oxide, and titanium oxide can be used.

[0056] Examples of organic pigments include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye chelates (for example, basic dye chelates, acid dye chelates, etc.); dye lakes (basic dye lakes, acid dye lakes), nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments.

[0057] More specifically, carbon blacks used for the black include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. (all manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (all manufactured by Carbon Columbia), Rega1 400R, Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. (manufactured by CABOT JAPAN). KK), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black 4A, and Special Black 4 (all manufactured by Degussa).

[0058] Pigments used for white include CI Pigment White 6, 18, and 21.

[0059] Pigments used for yellow include CI Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, and 180.

[0060] Pigments used for magenta include CI Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, and CI Pigment Violet. Examples include 19, 23, 32, 33, 36, 38, 43, and 50.

[0061] Pigments used for cyan include CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, and CI Vat Blue 4 and 60.

[0062] Examples of pigments other than magenta, cyan, and yellow include CI Pigment Green 7 and 10, CI Pigment Brown 3, 5, 25, and 26, and CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, and 63.

[0063] The above pigments may be used alone or in combination of two or more. When the above pigments are used, the average particle size thereof is preferably 300 nm or less, more preferably 50 nm to 200 nm. When the average particle size is within the above range, the reliability of the discharge stability and dispersion stability of the radiation-curable ink jet composition is further improved, and images of excellent quality can be formed. Here, the average particle size in this specification is defined as the Dv measured by dynamic light scattering. 50 The value was set as:

[0064] <dye> Dyes can be used as colorants. The dyes are not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. Examples of dyes include CI Acid Yellow 17, 23, 42, 44, 79, 142, CI Acid Red 52, 80, 82, 249, 254, 289, CI Acid Blue 9, 45, 249, CI Acid Black 1, 2, 24, 94, CI Food Black 1, 2, CI Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, CI Direct Red 1, 4, 9, 80, 81, 225, 227, CI Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, CI Direct Black 19, 38, 51, 71, 154, 168, 171, 195, CI Reactive Red 14, 32, 55, 79, 249, CI Reactive Black 3, 4, 35.

[0065] The above dyes may be used alone or in combination of two or more.

[0066] The total content of coloring materials is preferably 1% by mass or more and 20% by mass or less, based on the total mass (100% by mass) of the radiation-curable inkjet composition. The ink may be a clear ink that does not contain coloring materials, or that contains coloring materials to an extent that coloring is not intended (for example, 0.1% by mass or less).

[0067] Dispersants When the radiation-curable inkjet composition contains a pigment, it may further contain a dispersant to improve pigment dispersibility. The dispersant is not particularly limited, but examples include dispersants commonly used in preparing pigment dispersions, such as polymeric dispersants. Specific examples include those containing one or more of the following as the main component: polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins. Commercially available polymeric dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Solsperse series (e.g., Solsperse 36000) available from Avecia and Noveon, the Disperbyk series manufactured by BYK Additives & Instruments, and the Disparlon series manufactured by Kusumoto Chemicals Co., Ltd.

[0068] 1.3.3. Polymerization inhibitors The radiation-curable inkjet composition according to this embodiment may further contain a hindered amine compound or other polymerization inhibitor. Examples of polymerization inhibitors include, but are not limited to, p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, hydroquinone, cresol, t-butylcatechol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-butylphenol), and 4,4'-thiobis(3-methyl-6-t-butylphenol). The polymerization inhibitors may be used alone or in combination of two or more.

[0069] The total content of the polymerization inhibitor is preferably 0.05% by mass or more and 0.5% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, relative to the total mass (100% by mass) of the radiation-curable inkjet composition.

[0070] 1.3.4.Slip agents The radiation-curable inkjet composition according to this embodiment may further contain a slip agent. As the slip agent, a silicone surfactant is preferred, and a polyester-modified silicone or a polyether-modified silicone is more preferred. Examples of polyester-modified silicones include BYK-347, 348, BYK-UV3500, 3510, and 3530 (all manufactured by BYK Additives & Instruments), and examples of polyether-modified silicones include BYK-3570 (manufactured by BYK Additives & Instruments). One type of slip agent may be used alone, or two or more types may be used in combination.

[0071] The total content of the slip agent is preferably 0.01% by mass or more and 2% by mass, and more preferably 0.05% by mass or more and 1% by mass or less, relative to the total mass (100% by mass) of the radiation-curable inkjet composition.

[0072] Photosensitizers The radiation-curable inkjet composition according to this embodiment may further contain a photosensitizer. Examples of the photosensitizer include amine compounds (aliphatic amines, amines containing an aromatic group, piperidine, reaction products of epoxy resins and amines, triethanolamine triacrylate, etc.), urea compounds (allylthiourea, o-tolylthiourea, etc.), sulfur compounds (sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acids, etc.), nitrile compounds (N,N-diethyl-p-aminobenzonitrile, etc.), phosphorus compounds (tri-n-butylphosphine, sodium diethyldithiophosphide, etc.), nitrogen compounds (Michler's ketone, N-nitrisohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, condensates of formaldehyde or acetaldehyde with diamines, etc.), and chlorine compounds (carbon tetrachloride, hexachloroethane, etc.).

[0073] 1.4.Physical Properties The viscosity of the radiation-curable ink jet composition according to this embodiment at 20° C. is preferably 25 mPa·s or less, and more preferably 5 mPa·s to 25 mPa·s. When the viscosity of the composition at 20°C is within this range, an appropriate amount of the composition is ejected from the nozzle, and deflection and scattering of the composition can be further reduced, making it suitable for use in inkjet recording devices. The viscosity can be measured using a viscoelasticity tester MCR-300 (manufactured by Pysica) in an environment of 20°C, by increasing the shear rate from 10 to 1000 and reading the viscosity at a shear rate of 200.

[0074] The surface tension of the radiation-curable inkjet composition according to this embodiment at 20°C is preferably 20 mN / m or more and 40 mN / m or less. When the surface tension of the radiation-curable inkjet composition at 20°C is within this range, the composition is less likely to wet a nozzle surface that has been treated with a liquid repellent. This allows the composition to be ejected normally and in an appropriate amount from the nozzle, further reducing deflection and scattering of the composition, making the composition suitable for use in inkjet recording devices. The surface tension can be measured by wetting a platinum plate with the radiation-curable inkjet composition at 20°C using an automatic surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[0075] 1.5. Method for producing the composition The production (preparation) of the radiation-curable ink jet composition is carried out by mixing the components contained in the composition and stirring the mixture to ensure a sufficient homogeneous mixture. In this embodiment, the preparation of the radiation-curable ink jet composition preferably includes a step of subjecting a mixture of a polymerization initiator and at least a portion of the monomers to at least one of ultrasonic treatment and heating treatment during the preparation process. This reduces the amount of dissolved oxygen in the prepared composition, resulting in a radiation-curable ink jet composition with excellent ejection stability and storage stability. The mixture may contain at least the components described above, and may further contain other components contained in the radiation-curable ink jet composition, or may contain all of the components contained in the radiation-curable ink jet composition. The monomer contained in the mixture may be at least a portion of the monomers contained in the radiation-curable ink jet composition.

[0076] 2. Inkjet recording method The inkjet recording method according to this embodiment includes a step of applying the radiation-curable inkjet composition to a recording medium, and a step of irradiating the radiation-curable inkjet composition on the recording medium with light from a UV-LED (ultraviolet light-emitting diode) after the application step. In this way, a coating film is formed at the location on the recording medium where the radiation-curable inkjet composition has been applied.

[0077] 2.1.Attachment process In the step of depositing the radiation-curable inkjet composition on the recording medium, a known inkjet recording apparatus can be used. When ejecting the radiation-curable inkjet composition, as described above, the viscosity of the radiation-curable inkjet composition at 20°C is preferably 25 mPa·s or less, and more preferably 5 mPa·s to 25 mPa·s. If the viscosity of the radiation-curable inkjet composition is within this range, the composition can be ejected at room temperature or without heating. Alternatively, the radiation-curable ink jet composition may be heated to a predetermined temperature to achieve a suitable viscosity for ejection, thereby achieving good ejection stability.

[0078]

[0003] Radiation-curable inkjet compositions have higher viscosities than aqueous ink compositions generally used in inkjet applications, and therefore undergo large viscosity fluctuations due to temperature fluctuations during ejection. Such viscosity fluctuations of radiation-curable inkjet compositions have a significant effect on changes in droplet size and droplet ejection speed, which can ultimately cause deterioration in image quality. Therefore, it is preferable to keep the temperature of the radiation-curable inkjet composition as constant as possible during ejection.

[0079] The material of the recording medium is not particularly limited, but examples include plastics such as polyvinyl chloride, polyethylene terephthalate, polypropylene, polyethylene, polycarbonate, cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose nitrate, polyethylene terephthalate, polyethylene, polystyrene, polypropylene, polycarbonate, and polyvinyl acetal, as well as plastics with treated surfaces, glass, paper, metal, and wood.

[0080] The form of the recording medium is not particularly limited, and examples include film, board, cloth, etc.

[0081] The coating film formed on these recording media for sign applications is subjected to post-processing such as cutting and folding. The inkjet composition has good flexibility and adhesion, so that cracking and chipping of the coating film can be suppressed when such post-processing is performed. Therefore, the radiation-curable inkjet composition of this embodiment can be suitably used for sign applications.

[0082] 2.2.Curing process (light irradiation process) Next, in the curing step, the radiation-curable inkjet composition coated on the recording medium is cured by irradiation with UV-LED light to form a coating film. This is because the polymerization initiator that may be contained in the radiation-curable inkjet composition decomposes upon irradiation with UV light to generate active species (initiating species) such as radicals, acids, and bases, and the polymerization reaction of the monomer is accelerated by the function of the initiating species. Alternatively, this is because the photopolymerization reaction of the monomer is initiated by irradiation with UV light. At this time, if a sensitizing dye is present in the radiation-curable inkjet composition together with the polymerization initiator, the sensitizing dye in the system absorbs actinic radiation and becomes excited, and upon contact with the polymerization initiator, it accelerates the decomposition of the polymerization initiator, thereby achieving a curing reaction with higher sensitivity.

[0083] Furthermore, by using UV-LEDs as the ultraviolet light source, it is possible to reduce the size and cost of the device. Because UV-LEDs as ultraviolet light sources are compact, they can be installed inside the inkjet recording device. For example, they can be installed on a carriage (at both ends along the medium width direction and / or on the medium transport direction side) on which an inkjet head that ejects the radiation-curable inkjet composition is mounted. Furthermore, due to the composition of the radiation-curable inkjet composition described above, low-energy, high-speed curing can be achieved. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity. This allows the irradiation time to be shortened, increasing the printing speed. On the other hand, the irradiation intensity can also be reduced. This reduces the temperature rise of the printed material, which also leads to a reduced odor of the cured film.

[0084] 3. Working Example The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to these examples.

[0085] 3.1. Preparation of Inkjet Composition First, the colorant, dispersant, and a portion of each monomer were weighed and placed in a pigment dispersion tank. A 1 mm diameter ceramic bead mill was then placed in the tank and stirred to obtain a pigment dispersion in which the colorant was dispersed in the monomer. Next, the remaining monomers, polymerization initiator, and polymerization inhibitor were placed in a stainless steel mixing tank so as to obtain the composition shown in Table 1, and mixed and stirred to completely dissolve. After that, the pigment dispersion obtained above was added, and the mixture was further mixed and stirred at room temperature for an hour, and then filtered through a 5 μm membrane filter to obtain the radiation-curable inkjet composition of each example. Note that the numerical values for each component shown in each example in the table represent mass %.

[0086] [Table 1]

[0087] The abbreviations and product ingredients used in Table 1 are as follows:

[0088] <Monomer> PEA (product name "Viscoat #192, manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate") NVC (N-vinylcaprolactam, manufactured by ISP Japan Co., Ltd.) ACMO (Acryloylmorpholine, manufactured by KJ Chemicals Co., Ltd.) IBXA (Osaka Organic Chemical Industry, Ltd., isobornyl acrylate) TBCHA (product name "SR217", manufactured by Sartomer Corporation, tert-butyl cyclohexanol acrylate) VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd.) DPGDA (product name "SR508", manufactured by Sartomer Corporation, dipropylene glycol diacrylate) CN991 (Sartomer Corporation, bifunctional urethane acrylate oligomer) <Polymerization initiator> Irg.819 (trade name "IRGACURE 819" manufactured by BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) TPO (product name "IRGACURE TPO", manufactured by BASF, 2,4,6-trimethylbenzoyldiphenylphosphine oxide) <Polymerization inhibitor> MEHQ (product name "p-methoxyphenol", manufactured by Kanto Chemical Co., Ltd., hydroquinone monomethyl ether) <Slip agent> BYK-UV3500 (BYK Additives & Instruments, polyether-modified polydimethylsiloxane with acryloyl groups) <Coloring materials (pigments)> Carbon black (product name "MA-100", manufactured by Mitsubishi Chemical Corporation) <Dispersant> Solsperse 36000 (polymer dispersant, manufactured by Lubrizol).

[0089] Example 1 is a radiation-curable inkjet composition containing the monomers shown in Table 1, with the proportion of monofunctional monomers being 86% by mass relative to the total monomers, and with a glass transition temperature of 42°C.

[0090] Example 2 is a radiation-curable ink jet composition in which the content ratio of the monomers was adjusted, and the proportion of the monofunctional monomer relative to the total monomer content was changed from Example 1 to 94 mass %.

[0091] Example 3 is a radiation-curable ink jet composition in which the content ratio of the monomers was adjusted, and the proportion of the monofunctional monomer relative to the total amount of the monomers in Example 1 was changed to 96 mass %.

[0092] Example 4 is a radiation-curable ink jet composition in which the content ratio of the monomers was adjusted, and the proportion of the monofunctional monomer relative to the total monomer content was changed from Example 1 to 99 mass %.

[0093] Example 5 is a radiation-curable ink jet composition in which the content ratio of the monomer was adjusted and the glass transition temperature was changed from Example 3 to 45°C.

[0094] Example 6 is a radiation-curable ink jet composition obtained by removing NVC from Example 3 and changing the content ratio of the monomer.

[0095] Example 7 is a radiation-curable ink jet composition obtained by removing ACMO from Example 3 and changing the content ratio of the monomer.

[0096] Example 8 is a radiation-curable ink jet composition obtained by using IBXA instead of NVC in Example 3 and by changing the content ratio of the monomer.

[0097] Example 9 is a radiation-curable ink jet composition obtained by using DPGDA instead of VEEA in Example 3 and changing the content ratio of the monomer.

[0098] Comparative Example 1 is a radiation-curable inkjet composition obtained by removing TBCHA from Example 1 and changing the proportion of the monomers contained such that the proportion of the monofunctional monomer relative to the total amount of the monomers was changed to 83 mass %.

[0099] Comparative Example 2 is a radiation-curable inkjet composition obtained by removing TBCHA, VEEA, and CN991 from Example 1 and changing the content of the monomers so that the proportion of the monofunctional monomer relative to the total amount of the monomers was 100% by mass.

[0100] Comparative Example 3 is a radiation-curable inkjet composition in which the content ratio of the monomer was adjusted and the glass transition temperature was changed to 32°C from Example 3.

[0101] Comparative Example 4 is a radiation-curable inkjet composition in which the content ratio of the monomer was adjusted and the glass transition temperature was changed to 39°C from Example 3.

[0102] 3.2.Evaluation Method 3.2.1. Flexibility Assessment Each radiation-curable inkjet composition was applied to a vinyl chloride film (JT5829R, manufactured by MACtac) using a bar coater to a thickness of 10 μm. Then, a metal halide lamp (manufactured by iGraphics) was used to apply the composition to the film at 400 mJ / cm. 2 The coating was cured with an energy of 100 keV to form a coating film. The release paper was peeled off from the PVC film on which the coating was formed, and the film was cut into a strip of 1 cm wide and 8 cm long to prepare a test piece. The elongation percentage, which indicates flexibility, was measured for each test piece using a tensile tester (TENSILON, manufactured by ORIENTEC). The elongation percentage was the value at which a crack occurred when pulled at 5 mm / min. The value was calculated by {(length at crack - length before stretching) / length before stretching × 100}. The evaluation criteria were as follows, and the results are shown in Table 1.

[0103] A: 300% or more B: 250% or more but less than 300% C: 200% or more but less than 250% D: Less than 200%

[0104] 3.2.2. Evaluation of Adhesion The cured coating films prepared in the above flexibility evaluation were subjected to a cross-cut test in accordance with JIS K5600-5-6. The evaluation criteria were as follows. The evaluation results are shown in Table 1.

[0105] A: Classification 0, 1 B: Classification 2, 3 C: Classification 4, 5 D: No paint film remaining

[0106] 3.2.3. Evaluation of abrasion resistance The cured coating films prepared for the flexibility evaluation were subjected to a micro-scratch test in accordance with JIS R3255. An ultra-thin film scratch tester (CSR-5000, manufactured by Nanotec Co., Ltd.) was used to measure the load capacity as a measure of abrasion resistance. Micro-scratching was performed while applying a load, and the load capacity was determined as the load when the stylus reached the media surface. Measurements were performed with a stylus diameter of 15 μm, an amplitude of 100 μm, and a scratch speed of 10 μm / sec. The evaluation criteria were as follows. The evaluation results are shown in Table 1.

[0107] A :35mN or more B: 30mN or more and less than 35mN C: 25mN or more and less than 30mN D: Less than 25mN

[0108] 3.3.Evaluation Results Table 1 shows the composition of the radiation-curable inkjet composition used in each example, as well as the evaluation results. Table 1 shows that the radiation-curable inkjet compositions of Examples 1 to 9, which contained 86% by mass or more of monofunctional monomers relative to the total monomer content and had glass transition temperatures of 42°C or higher, calculated from the glass transition temperatures of the monomers, all achieved ratings of C or higher in flexibility, adhesion, and abrasion resistance, making them favorable. A comparison of Examples 1 to 4 with Comparative Examples 1 and 2 reveals that the ratio of monofunctional monomers to the total monomer content was 86% by mass or higher in Examples 1 to 4, thereby improving flexibility and adhesion. Comparative Example 2, on the other hand, had favorable flexibility and adhesion, but was poor in abrasion resistance, earning a rating of D. A comparison of Examples 3, 5, Comparative Examples 3, and 4 reveals that a radiation-curable inkjet composition with a glass transition temperature of 42°C or higher ensures abrasion resistance.

[0109] The following describes the results derived from the embodiments.

[0110] The radiation-curable ink jet composition of the present invention contains 86% by mass or more of monofunctional monomers based on the total mass of the monomers, and has a glass transition temperature of 42° C. or higher calculated from the glass transition temperature of the monomers.

[0111] This configuration improves the flexibility and adhesion of the coating film while ensuring abrasion resistance. Specifically, because the monofunctional monomer accounts for 86 mass % or more of the total monomer content, the flexibility and adhesion of the coating film are improved. Furthermore, because the glass transition temperature of the radiation-curable inkjet composition, calculated from the glass transition temperature of the monomer, is 42°C or higher, the abrasion resistance of the coating film at room temperature is improved. Therefore, it is possible to provide a radiation-curable inkjet composition that can give a coating film with flexibility, adhesion, and abrasion resistance suitable for sign applications.

[0112] The radiation-curable ink jet composition preferably contains a monomer represented by the following general formula (1). CH2=CR 1 -COOR 2 -O-CH=CH-R 3 ···(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

[0113] According to this configuration, since the radiation-curable ink jet composition contains a monomer represented by general formula (1), the viscosity of the radiation-curable ink jet composition can be easily reduced. The reduced viscosity allows the radiation-curable ink jet composition to be stably ejected from an inkjet head when printing is performed using the radiation-curable ink jet composition. In addition, the inclusion of a monomer represented by general formula (1) can improve the curability. The improved curability can increase the printing speed. Therefore, a radiation-curable ink jet composition suitable for printing can be obtained.

[0114] In the radiation-curable ink jet composition, the monofunctional monomer preferably includes a monomer having a glass transition temperature of 90° C. or higher.

[0115] According to this configuration, since the radiation-curable ink jet composition contains a monomer with a glass transition temperature of 90° C. or higher, the glass transition temperature of the radiation-curable ink jet composition calculated from the glass transition temperature of the monomer can be easily set to 42° C. or higher, thereby achieving the effect of improving the scratch resistance of the coating film at room temperature.

[0116] In the radiation-curable ink jet composition, the monofunctional monomer is preferably n-vinylcaprolactam or acryloylmorpholine.

[0117] According to this configuration, n-vinylcaprolactam or acryloylmorpholine has a glass transition temperature of 90° C. or higher, and therefore the scratch resistance of the coating film at room temperature can be further improved. In addition, n-vinylcaprolactam further increases the flexibility of the coating film, and acryloylmorpholine can reduce the odor of the radiation-curable inkjet composition.

[0118] One aspect of the inkjet recording method according to the present invention preferably includes the steps of: attaching the radiation-curable inkjet composition described above to a recording medium; and irradiating the radiation-curable inkjet composition with UV-LED light.

[0119] This configuration makes it possible to obtain a coating film that is excellent in flexibility, adhesion, and abrasion resistance.

Claims

1. The content of monofunctional monomers is 94% by mass or more based on the total amount of monomers, The glass transition temperature of the radiation-curable ink jet composition is calculated from the glass transition temperature of the monomer. The lattice transition temperature is 42°C or higher, the monofunctional monomer includes acryloylmorpholine; the monofunctional monomer includes phenoxyethyl acrylate; The phenoxyethyl acrylate is contained in an amount of 39.0 mass % or more relative to the total amount of the monomers. Contains 7% by mass or less, The monomer includes a monomer represented by the following general formula (1): Acylphosphine oxide polymerization initiators and thioxanthone polymerization initiators are used and either one of Radiation-curable inkjet compositions. CH 2 =CR 1 -COOR 2 -O-CH=CH-R 3 ・・・(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue with 2 to 20 carbon atoms group, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms.

2. The composition contains 94% by mass or more of monofunctional monomers based on the total amount of monomers, The glass transition temperature of the radiation-curable ink jet composition is calculated from the glass transition temperature of the monomer. The lattice transition temperature is 42°C or higher, the monofunctional monomer includes acryloylmorpholine; The monomer is a radiation-curable ink containing a monomer represented by the following general formula (1): Coujet composition. CH 2 =CR 1 -COOR 2 -O-CH=CH-R 3 ・・・(1) (In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a divalent organic residue with 2 to 20 carbon atoms group, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. However, the radiation-curable ink contains a monomer represented by the following general formula (A) as the monomer: Excludes ink jet compositions. ...(A) (n in formula (A) represents an integer of 2 to 6.)

3. The acryloylmorpholine is present in an amount of 24.0 mass % or more and 36.1 mass % or less based on the total amount of the monomers.

3. The radiation-curable inkjet printer according to claim 1, wherein the content is 1% by weight or less. Jet composition.

4. The monomer represented by the general formula (1) is contained in an amount of 1.2 mass % or more and 11.0 mass % or less based on the total amount of the monomers.

4. The radiation according to claim 1, wherein the radiation contains 0.5 wt % or less of the ion beam. Curable inkjet composition.

5. The radiation-curable inkjet recording medium according to any one of claims 1 to 4, which is used for signs. composition.

6. The radiation-curable ink-jet composition according to any one of claims 1 to 5, a step of attaching the recording medium to the recording medium; irradiating the radiation-curable inkjet composition with UV-LED light; An inkjet recording method comprising:

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