Radiation-curable inkjet composition and recording method

Abstract

To provide a radiation ray-curable inkjet composition and an inkjet recording method capable of obtaining a coating film which has low odor and has color development, flexibility, adhesiveness and scratch resistance.SOLUTION: There is provided a radiation ray-curable inkjet composition which comprises a polymerizable compound containing a monofunctional monomer and a polyfunctional monomer, wherein the content of the monofunctional monomer is 87 mass% or more based on the total amount of the polymerizable compound, the monofunctional monomer contains a nitrogen-containing monofunctional monomer, the content of the nitrogen-containing monofunctional monomer is 14 mass% or less based on the total amount of the radiation ray-curable inkjet composition and the weighted average of the glass transition temperature of a homopolymer of each of the polymerizable compounds with the content mass ratio of each of the polymerizable compounds taken as a weight is 42°C or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a radiation-curable inkjet composition and a recording method.

Background Art

[0002] Conventionally, for example, as described in Patent Document 1, studies have been conducted on radiation-curable inkjet compositions that exhibit good curability and flexibility after curing. In particular, in Example 9 (Table 3), a radiation-curable inkjet composition containing 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 as monomers is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the radiation-curable inkjet composition described in Patent Document 1 has a problem that when used for signature applications, the flexibility and adhesion of the coating film tend to be insufficient. In addition, it has been found that when the ratio of monofunctional monomers to the total monomers is increased to improve flexibility and adhesion, the abrasion resistance and color development of the coating film may decrease.

Means for Solving the Problems

[0005] The radiation-curable inkjet composition of the present invention contains a polymerizable compound including a monofunctional monomer and a polyfunctional monomer, the content of the monofunctional monomer is 87% by mass or more based on the total amount of the polymerizable compound, the monofunctional monomer includes a nitrogen-containing monofunctional monomer, the content of the nitrogen-containing monofunctional monomer is 14% by mass or less based on the total amount of the radiation-curable inkjet composition, and the weighted average of the glass transition temperatures of the homopolymers of the respective polymerizable compounds, with the content mass ratio of each polymerizable compound as the weight, is 42°C or higher.

[0006] In the above radiation-curable inkjet composition, it is preferable that the nitrogen-containing monofunctional monomer includes a monomer having a nitrogen-containing heterocyclic structure.

[0007] In the above radiation-curable inkjet composition, it is preferable that the content of the polyfunctional monomer is 1 to 10% by mass based on the total amount of the polymerizable compound.

[0008] In the above radiation-curable inkjet composition, it is preferable that the polyfunctional monomer includes vinyl ether group-containing (meth)acrylic acid esters represented by the following formula (1). The radiation-curable inkjet composition according to any one of claims 1 to 3. CH2=CR 1 -COOR 2 -O-CH=CH-R 3 ··· (1) (In the formula, R 1 is a hydrogen atom or a methyl group, 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.)

[0009] In the above radiation-curable inkjet composition, it is preferable that the content of the nitrogen-containing monofunctional monomer is 3 to 14% by mass based on the total amount of the radiation-curable inkjet composition.

[0010] Preferably, the radiation-curable inkjet composition contains a nitrogen-containing monofunctional monomer including a nitrogen-containing monofunctional acrylate monomer.

[0011] Preferably, the radiation-curable inkjet composition contains a nitrogen-containing monofunctional monomer including a nitrogen-containing monofunctional vinyl monomer.

[0012] Preferably, the radiation-curable inkjet composition contains a monofunctional monomer including a monofunctional acrylate having a polycyclic hydrocarbon group. The radiation-curable inkjet composition according to any one of claims 1 to 7.

[0013] Preferably, the content of the monofunctional acrylate having a polycyclic hydrocarbon group in the radiation-curable inkjet composition is 40% by mass or less based on the total amount of the radiation-curable inkjet composition.

[0014] Preferably, the radiation-curable inkjet composition contains a pigment.

[0015] Further, the recording method of the present invention includes a discharging step of discharging the radiation-curable inkjet composition from an inkjet head and attaching it to a recording medium, and an irradiating step of irradiating radiation to the radiation-curable inkjet composition attached to the recording medium.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiment") will be described in detail, but the present invention is not limited thereto, and various modifications are possible without departing from the gist thereof.

[0017] In this specification, “(meth)acryloyl” means at least either acryloyl or the corresponding methacryloyl, “(meth)acrylate” means at least either acrylate or the corresponding methacrylate, and “(meth)acrylic” means at least either acrylic or the corresponding methacrylic.

[0018] 1. Radiation-curable inkjet composition The radiation-curable inkjet composition according to this embodiment (hereinafter, also simply referred to as “composition”) contains a polymerizable compound including a monofunctional monomer and a polyfunctional monomer, the content of the monofunctional monomer is 87% by mass or more with respect to the total amount of the polymerizable compound, the monofunctional monomer includes a nitrogen-containing monofunctional monomer, the content of the nitrogen-containing monofunctional monomer is 14% by mass or less with respect to the total amount of the radiation-curable inkjet composition, and the weighted average of the glass transition temperatures of the homopolymers of the respective polymerizable compounds, with the content mass ratio of each polymerizable compound as the weight, is 42° C. or higher.

[0019] Thus, in this embodiment, by setting the content of the monofunctional monomer within a predetermined range, the flexibility and adhesion of the coating film can be improved. On the other hand, when the content of the monofunctional monomer is within the above range, the abrasion resistance of the coating film decreases. However, by configuring the polymerizable compound such that the weighted average of the glass transition temperatures of the homopolymers of the respective polymerizable compounds falls within a predetermined range, it is possible to improve the abrasion resistance of the coating film. Furthermore, when the content of the functional monomer is within the above range, odor is likely to occur. In this regard, the odor can be suppressed by using a nitrogen-containing monofunctional monomer.

[0020] The radiation-curable inkjet composition according to this embodiment is a composition that is ejected from an inkjet head by an inkjet method and used. Hereinafter, the radiation-curable ink composition will be described as one embodiment of the radiation-curable inkjet composition. However, the composition according to this embodiment may be a composition other than the ink composition, for example, a composition used for 3D printing.

[0021] The radiation-curable inkjet composition of this embodiment cures by irradiation with radiation. Examples of the radiation include ultraviolet rays, infrared rays, visible light, X-rays, etc. Ultraviolet rays are preferred as the radiation because the radiation source is easily available and widely used, and materials suitable for curing by ultraviolet radiation are easily available and widely used.

[0022] Hereinafter, in the radiation-curable inkjet composition according to this embodiment, the components, physical properties, and manufacturing method that may be included will be described.

[0023] 1.1. Polymerizable compound The polymerizable compound includes a monofunctional monomer having one polymerizable functional group and a polyfunctional monomer having a plurality of polymerizable functional groups, and may optionally include an oligomer having one or more polymerizable functional groups. Each polymerizable compound may be used alone or in combination of two or more.

[0024] In this embodiment, the weighted average of the glass transition temperatures of the homopolymers of the respective polymerizable compounds, with the content mass ratio of each polymerizable compound as the weight, is 42°C or higher, preferably 44°C or higher, more preferably 46°C or higher. By the weighted average of the glass transition temperature being 42°C or higher, the abrasion resistance of the coating film at room temperature can be enhanced. Also, the upper limit of the weighted average of the glass transition temperature is not particularly limited, but is preferably 60°C or lower, more preferably 55°C or lower, still more preferably 55°C or lower.

[0025] The calculation method of the weighted average of the glass transition temperature will be described. Let the value of the weighted average of the glass transition temperature be Tg All , the glass transition temperature of the homopolymer of each polymerizable compound be Tg N and the content mass ratio of the polymerizable compound be X N(in mass %). N is numbered sequentially from 1 according to the types of polymerizable compounds contained in the radiation-curable inkjet composition. For example, when three types of polymerizable compounds are used, Tg1, Tg2, and Tg3 occur. The glass transition temperature of the homopolymer of each polymerizable compound can be obtained from the safety data sheet (SDS) or catalog information of the polymerizable compound. The weighted average Tg of the glass transition temperature All is the glass transition temperature Tg calculated for each polymerizable compound N and the content X N and is the sum of the products. Therefore, the following formula (2) holds. Tg All =ΣTg N ×X N ···(2)

[0026] Note that the weighted average of the glass transition temperature can be adjusted by the glass transition temperature of the polymerizable compound used and the mass ratio of the polymerizable compound used.

[0027] 1.1.1. Monofunctional monomer The monofunctional monomer of this embodiment includes a nitrogen-containing monofunctional monomer, and may include other monofunctional monomers as necessary. The other monofunctional monomers are not particularly limited, but monofunctional monomers having a conventionally known polymerizable functional group, particularly a polymerizable functional group having an unsaturated double bond between carbons, can be used.

[0028] The content of the monofunctional monomer is 87% by mass or more, preferably 90% by mass or more, more preferably 94% by mass or more, and still more preferably 96% by mass or more, based on the total amount of the polymerizable compounds. When the content of the monofunctional monomer is 87% by mass or more based on the total amount of the polymerizable compounds, the flexibility and adhesion of the coating film are further improved. The upper limit of the content of the monofunctional monomer is not particularly limited, but is preferably 99% by mass or less, more preferably 98% by mass or less, and still more preferably 97% by mass or less, based on the total amount of the polymerizable compounds. When the content of the monofunctional monomer is 99% by mass or less based on the total amount of the polymerizable compounds, the abrasion resistance of the coating film tends to be further improved.

[0029] In addition, the content of the monofunctional monomer is preferably 78% by mass or more, more preferably 80% by mass or more, and still more preferably 82% by mass or more with respect to the total amount of the composition. When the content of the monofunctional monomer is 78% by mass or more with respect to the total amount of the composition, the flexibility and adhesion of the coating film tend to be further improved. Further, the upper limit of the content of the monofunctional monomer is preferably 92% by mass or less, more preferably 90% by mass or less, and still more preferably 88% by mass or less with respect to the total amount of the composition. When the content of the monofunctional monomer is 90% by mass or less with respect to the total amount of the composition, the scratch resistance of the coating film tends to be further improved.

[0030] Hereinafter, the monofunctional monomer will be exemplified, but the monofunctional monomer in the present embodiment is not limited to the following.

[0031] 1.1.1.1. Nitrogen-containing monofunctional monomer The nitrogen-containing monofunctional monomer is not particularly limited. For example, nitrogen-containing monofunctional vinyl monomers such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholine; (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, and quaternary salts of dimethylaminoethyl acrylate benzyl chloride, etc. nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide are exemplified.

[0032] Among these, it is preferable to contain either a nitrogen-containing monofunctional vinyl monomer or a nitrogen-containing monofunctional acrylate monomer, and monomers having a nitrogen-containing heterocyclic structure such as N-vinylcaprolactam, N-vinylcarbazole, N-vinylpyrrolidone, or acryloylmorpholine are more preferable, and it is still more preferable to contain either N-vinylcaprolactam or acryloylmorpholine.

[0033] By using such a nitrogen-containing monofunctional monomer, the scratch resistance of the coating film tends to be further improved. Furthermore, a nitrogen-containing monofunctional vinyl monomer having a nitrogen-containing heterocyclic structure such as N-vinylcaprolactam further improves the flexibility of the coating film, and a nitrogen-containing monofunctional acrylate monomer having a nitrogen-containing heterocyclic structure such as acryloylmorpholine tends to further reduce the odor of the composition.

[0034] The content of the nitrogen-containing monofunctional monomer is preferably 1 to 25% by mass, more preferably 5 to 20% by mass, and still more preferably 10 to 15% by mass with respect to the total amount of the polymerizable compounds. When the content of the nitrogen-containing monofunctional monomer is within the above range, the odor is reduced and the scratch resistance of the coating film tends to be further improved.

[0035] The content of the nitrogen-containing monofunctional monomer is 14% by mass or less, preferably 3 to 14% by mass, more preferably 12% by mass or less, still more preferably 3 to 12% by mass, and still more preferably 5 to 12% by mass with respect to the total amount of the composition. When the content of the nitrogen-containing monofunctional monomer is 14% by mass or less with respect to the total amount of the composition, the adhesion is further improved. Also, when the content of the nitrogen-containing monofunctional monomer is 3% by mass or more with respect to the total amount of the composition, the odor is reduced and the scratch resistance of the coating film tends to be further improved.

[0036] 1.1.1.2. Monofunctional acrylate having a polycyclic hydrocarbon group Examples of other monofunctional monomers include monofunctional acrylates having a polycyclic hydrocarbon group. The monofunctional acrylate having a polycyclic hydrocarbon group is not particularly limited as long as it has a plurality of cyclic hydrocarbons in its structure. For example, acrylates having an unsaturated polycyclic hydrocarbon group such as dicyclopentenyl acrylate and dicyclopentenyl oxyethyl acrylate; acrylates having a saturated polycyclic hydrocarbon group such as dicyclopentanyl acrylate and isobornyl acrylate can be mentioned. Among these, acrylates having an unsaturated polycyclic hydrocarbon group are preferred, and it is more preferred to contain at least dicyclopentenyl acrylate. By using such a monofunctional acrylate having a polycyclic hydrocarbon group, the scratch resistance, flexibility, and adhesion of the coating film tend to be further improved. In addition, when an acrylate having an unsaturated polycyclic hydrocarbon group is used, the adhesion tends to be better, which is preferable.

[0037] The content of the monofunctional acrylate having a polycyclic hydrocarbon group is preferably 20 to 55% by mass, more preferably 25 to 50% by mass, and still more preferably 30 to 45% by mass with respect to the total amount of the polymerizable compounds. When the content of the monofunctional acrylate having a polycyclic hydrocarbon group is 20% by mass or more with respect to the total amount of the polymerizable compounds, the scratch resistance of the coating film tends to be further improved. In addition, when the content of the monofunctional acrylate having a polycyclic hydrocarbon group is 55% by mass or less with respect to the total amount of the polymerizable compounds, the odor tends to be more suppressed.

[0038] The content of the monofunctional acrylate having a polycyclic hydrocarbon group is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 20 to 40% by mass, and still more preferably 25 to 40% by mass with respect to the total amount of the composition. When the content of the monofunctional acrylate having a polycyclic hydrocarbon group is 50% by mass or less, the odor tends to be more suppressed. In addition, when the content of the monofunctional acrylate having a polycyclic hydrocarbon group is 20% by mass or more, the scratch resistance of the coating film tends to be further improved.

[0039] 1.1.1.3. Monofunctional monomer containing an aromatic group As one of the other monofunctional monomers, a monofunctional monomer containing an aromatic group can be mentioned. In this embodiment, the monofunctional monomer containing an aromatic group is not a compound having a polycyclic hydrocarbon group.

[0040] The monofunctional monomer containing an aromatic group is not particularly limited. For example, it includes phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, 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. Among these, phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are preferred, phenoxyethyl (meth) acrylate is more preferred, and phenoxyethyl acrylate (PEA) is even more preferred. By using such a monofunctional monomer containing an aromatic group, the solubility of the polymerization initiator is further improved, and the curability of the composition tends to be further improved. In particular, when an acylphosphine oxide-based polymerization initiator or a thioxanthone-based polymerization initiator is used, its solubility tends to be good. Also, by using phenoxyethyl (meth) acrylate, the odor can be further reduced.

[0041] Illustrating the monofunctional monomer containing an aromatic group in other expressions, examples of the monofunctional monomer containing an aromatic group include a compound represented by the following general formula (3) and a compound represented by general formula (4).

[0042] CH2=CR 4 -COOR 5 -Ar ···(3) CH2=CR 4 -COO-Ar ···(4) (In the above formulas (3) and (4), R 4is a hydrogen atom or a methyl group. In the above formula (3), Ar representing an aromatic ring skeleton has at least one aryl group, and the carbon atom constituting the aryl group is R 5 is a monovalent organic residue bonded to the group represented by, and R5 is a divalent organic residue having 1 to 4 carbon atoms. In the above formula (4), Ar representing an aromatic ring skeleton has at least one aryl group, and the carbon atom constituting the aryl group is a monovalent organic residue bonded to -COO- in the formula.)

[0043] In the above general formula (3), R 5 Examples of the group represented by 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 having an oxygen atom due to an ether bond and / or an ester bond in the structure, which may be substituted. Among these, alkylene groups having 1 to 4 carbon atoms such as an ethylene group, an n-propylene group, an isopropylene group, and a butylene group, and alkylene groups having 1 to 4 carbon atoms having an oxygen atom due to an ether bond in the structure such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group are preferably used. When the above organic residue is a group that may be substituted, 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 the number of carbon atoms of the organic residue.

[0044] In the above general formulas (3) and (4), examples of the aryl group contained at least once in Ar (aryl) (aromatic ring skeleton) include, but are not limited to, a phenyl group and a naphthyl group. The number of aryl groups is 1 or more, preferably 1 or 2. The aryl group may be substituted at carbon atoms other than the carbon atom bonding to the organic residue represented by R5 in formula (3), the carbon atom bonding to -COO- in formula (4), and, when having a plurality of aryl groups, the carbon atom connecting the aryl groups to each other. When substituted, the number of substitutions per aryl group is 1 or more, preferably 1 or 2. The substituents are not particularly limited, and examples thereof include linear, branched, or cyclic alkyl groups and alkoxy groups having 1 to 10 carbon atoms, a carboxyl group, a halo group, and a hydroxyl group.

[0045] The content of the aromatic group-containing monofunctional monomer is preferably 25 to 60% by mass, more preferably 30 to 55% by mass, and still more preferably 35 to 50% by mass with respect to the total amount of the polymerizable compounds. When the content of the aromatic group-containing monofunctional monomer is 25% by mass or more with respect to the total amount of the polymerizable compounds, the odor tends to be more suppressed. Further, when the content of the aromatic group-containing monofunctional monomer is 60% by mass or less with respect to the total amount of the polymerizable compounds, the scratch resistance of the coating film tends to be more improved.

[0046] The content of the aromatic group-containing monofunctional monomer is preferably 20 to 55% by mass, more preferably 25 to 50% by mass, and still more preferably 30 to 45% by mass with respect to the total amount of the composition. When the content of the aromatic group-containing monofunctional monomer is 20% by mass or more with respect to the total amount of the composition, the odor tends to be more suppressed. Further, when the content of the aromatic group-containing monofunctional monomer is 55% by mass or less with respect to the total amount of the composition, the scratch resistance of the coating film tends to be more improved.

[0047] 1.1.1.4. Saturated aliphatic group-containing monofunctional monomer As one of the other monofunctional monomers, a monofunctional monomer containing a saturated aliphatic group can be mentioned. In the present embodiment, the monofunctional monomer containing a saturated aliphatic group is not a compound having a polycyclic hydrocarbon group.

[0048] The monofunctional monomer containing a saturated aliphatic group is not particularly limited. For example, alicyclic group-containing monofunctional monomers such as tert-butylcyclohexanol acrylate (TBCHA) and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl; straight-chain or branched-chain aliphatic group-containing monofunctional monomers such as isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate; and lactone-modified flexible (meth)acrylate can be mentioned. Among these, alicyclic group-containing monofunctional monomers are preferred. By using such a monofunctional monomer containing a saturated aliphatic group, the curability of the composition tends to be further improved.

[0049] The content of the monofunctional monomer containing a saturated aliphatic group is preferably 2.5 to 17.5% by mass, more preferably 5 to 15% by mass, and still more preferably 7.5 to 12.5% by mass with respect to the total amount of the polymerizable compounds.

[0050] The content of the monofunctional monomer containing a saturated aliphatic group is preferably 1 to 10% by mass, more preferably 2 to 7.5% by mass, and still more preferably 2.5 to 5% by mass with respect to the total amount of the composition.

[0051] 1.1.1.5. Others As other monofunctional monomers, in addition to the above, for example, 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 the unsaturated carboxylic acids; acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes may also be used.

[0052] 1.1.2. Polyfunctional monomers Examples of the polyfunctional monomers of the present embodiment include vinyl ether group-containing (meth)acrylates, bifunctional (meth)acrylates, and polyfunctional (meth)acrylates having three or more functional groups. The polyfunctional monomers are not limited to the above.

[0053] The content of the polyfunctional monomer is preferably 0.5% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass or more with respect to the total amount of the polymerizable compounds. When the content of the polyfunctional monomer is 0.5% by mass or more with respect to the total amount of the polymerizable compounds, the scratch resistance tends to be further improved. The upper limit of the content of the polyfunctional monomer is preferably 10% by mass or less, more preferably 7.5% by mass or less, and still more preferably 5% by mass or less with respect to the total amount of the polymerizable compounds. When the content of the polyfunctional monomer is 10% by mass or less with respect to the total amount of the polymerizable compounds, the flexibility and adhesion of the coating film tend to be further improved.

[0054] Also, the content of the polyfunctional monomer is preferably 0.5% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass or more with respect to the total amount of the composition. When the content of the polyfunctional monomer is 0.5% by mass or more with respect to the total amount of the composition, the scratch resistance tends to be further improved. The upper limit of the content of the polyfunctional monomer is preferably 10% by mass or less, more preferably 7.5% by mass or less, and still more preferably 5% by mass or less with respect to the total amount of the composition. When the content of the polyfunctional monomer is 10% by mass or less with respect to the total amount of the composition, the flexibility and adhesion of the coating film tend to be further improved.

[0055] Examples of the polyfunctional monomer are given below, but the polyfunctional monomer in this embodiment is not limited to those below.

[0056] 1.1.2.1 (Meth)acrylate containing vinyl ether group The (meth)acrylate containing a vinyl ether group is not particularly limited, and examples thereof include compounds represented by the following formula (1). By including such a (meth)acrylate containing a vinyl ether group, the viscosity of the composition tends to decrease, and the discharge stability tends to be further improved. In addition, the curability of the composition is further improved, and with the improvement of the curability, the recording speed can be further increased. CH2=CR 1 -COOR 2 -O-CH=CH-R 3 ··· (1) (In the formula, R 1 is a hydrogen atom or a methyl group, 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.)

[0057] In the above formula (1), examples of the divalent organic residue having 2 to 20 carbon atoms represented by R 2 include linear, branched or cyclic alkylene groups having 2 to 20 carbon atoms, which may be substituted; alkylene groups having 2 to 20 carbon atoms, which may be substituted and have an oxygen atom due to an ether bond and / or an ester bond in the structure; 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 an ethylene group, an n-propylene group, an isopropylene group, and a butylene group, and alkylene groups having 2 to 9 carbon atoms, which may be substituted and have an oxygen atom due to an ether bond in the structure such as an oxyethylene group, an oxy-n-propylene group, an oxyisopropylene group, and an oxybutylene group are preferable. Further, from the viewpoint of further reducing the viscosity of the composition and further improving the curability of the composition, R 2More preferably, the compound has a glycol ether chain in which the alkylene group having 2 to 9 carbon atoms having an oxygen atom by an ether bond in the structure is an oxyethylene group, an oxy n-propylene group, an oxyisopropylene group, an oxybutylene group, or the like.

[0058] In the above formula (1), R 3 As the monovalent organic residue having 1 to 11 carbon atoms represented by, a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms, which may be substituted, and an aromatic group having 6 to 11 carbon atoms, which may be substituted, are preferable. Among these, an alkyl group having 1 to 2 carbon atoms such as a methyl group or an ethyl group, and an aromatic group having 6 to 8 carbon atoms such as a phenyl group and a benzyl group are preferably used.

[0059] When each of the above organic residues is a group that may be substituted, the substituent is classified into a group containing a carbon atom and a group not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted as the number of carbon atoms of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

[0060] Specific examples of the compound of formula (1) are not particularly limited, but for example, 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 (meth)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, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl methacrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, 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-(vinyloxyethoxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxyethoxy)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,(Meth)acrylic acid 2-(vinyloxyethoxyethoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyethoxyisopropoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyisopropoxyethoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyisopropoxyisopropoxy)isopropyl, (meth)acrylic acid 2-(vinyloxyethoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxyethoxyethoxy)ethyl, (meth)acrylic acid 2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate are exemplified. Among these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferable in terms of easy balance of curability and viscosity of the composition. In this embodiment, 2-(2-vinyloxyethoxy)ethyl acrylate is sometimes referred to as VEEA.,

[0061] The content of the vinyl ether group-containing (meth)acrylate is preferably 0.5 to 10% by mass, more preferably 1 to 7.5% by mass, and still more preferably 2 to 5% by mass with respect to the total amount of the polymerizable compounds. When the content of the vinyl ether group-containing (meth)acrylate with respect to the total amount of the polymerizable compounds is within the above range, the viscosity of the composition decreases and the discharge stability tends to be further improved.

[0062] The content of the vinyl ether group-containing (meth)acrylate is preferably 0.5 to 10% by mass, more preferably 1 to 7.5% by mass, and still more preferably 2 to 5% by mass with respect to the total amount of the composition. When the content of the vinyl ether group-containing (meth)acrylate with respect to the total amount of the composition is within the above range, the viscosity of the composition decreases and the discharge stability tends to be further improved.

[0063] 1.1.2.2 Difunctional (meth)acrylate The difunctional (meth)acrylate is not particularly limited. For example, dipropylene glycol diacrylate (DPGDA), diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol dimethacrylate, 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 of bisphenol A di(meth)acrylate, PO (propylene oxide) adduct of bisphenol A di(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate can be mentioned.

[0064] 1.1.2.3 Polyfunctional (meth)acrylate with three or more functional groups The polyfunctional (meth)acrylate with three or more functional groups is not particularly limited. For example, 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 propoxylate tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol ethoxytetra(meth)acrylate, and caprolactam-modified dipentaerythritol hexa(meth)acrylate can be mentioned.

[0065] 1.2.3. Oligomer The oligomers of this embodiment are multimers such as dimers and trimers that contain a polymerizable compound as a constituent component, and refer to compounds having one or more polymerizable functional groups. Note that the polymerizable compounds referred to here are not limited to the above-mentioned monofunctional monomers and polyfunctional monomers. In this embodiment, those with a molecular weight of 1000 or more are defined as oligomers, and those with a molecular weight of less than 1000 are defined as monomers.

[0066] Such oligomers are not particularly limited. For example, there are urethane acrylate oligomers with a urethane repeating structure, polyester acrylate oligomers with an ester repeating structure, epoxy acrylate oligomers with an epoxy repeating structure, and the like.

[0067] Among these, urethane acrylate oligomers are preferred, aliphatic urethane acrylate oligomers and aromatic urethane acrylate oligomers are more preferred, and aliphatic urethane acrylate oligomers are even more preferred. Also, the urethane acrylate oligomer is preferably a urethane acrylate oligomer with 4 or fewer functional groups, and more preferably a bifunctional urethane acrylate oligomer.

[0068] By using such oligomers, the storage stability of the composition is further improved, and the abrasion resistance tends to be further improved.

[0069] The content of the oligomer is preferably 1 to 10% by mass, more preferably 3 to 9% by mass, and even more preferably 5 to 7% by mass with respect to the total amount of the polymerizable compound. When the content of the oligomer with respect to the total amount of the polymerizable compound is within the above range, the storage stability of the composition is further improved, and the abrasion resistance of the coating film tends to be further improved.

[0070] The content of the oligomer is preferably 1 to 10% by mass, more preferably 3 to 9% by mass, and still more preferably 5 to 7% by mass with respect to the total amount of the composition. When the content of the oligomer with respect to the total amount of the composition is within the above range, the storage stability of the composition is further improved, and the scratch resistance of the coating film tends to be further improved.

[0071] 1.2. Polymerization initiator The radiation-curable inkjet composition according to the present embodiment preferably contains a polymerization initiator that generates active species by irradiating radiation. The polymerization initiator may be used alone or in combination of two or more.

[0072] The polymerization initiator is not particularly limited, and examples thereof include known polymerization initiators such as acylphosphine oxide-based polymerization initiators, alkylphenone-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone-based polymerization initiators. Among these, acylphosphine oxide-based polymerization initiators are preferred. By using such a polymerization initiator, the curability of the composition is further improved, and particularly the curability by the curing process using the light of UV-LED tends to be further improved.

[0073] Examples of the acylphosphine oxide-based polymerization initiator include, but are not particularly limited to, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like.

[0074] Examples of commercially available acylphosphine oxide-based polymerization initiators include 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-hydroxy-cyclohexyl-phenylketone at a mass ratio of 25:75), IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (all of the above are manufactured by BASF), and the like.

[0075] The content of the polymerization initiator is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, still more preferably 5 to 10% by mass, and particularly preferably 7 to 9% by mass with respect to the total amount of the composition. When the content of the polymerization initiator is within the above range, the curability of the composition and the solubility of the polymerization initiator tend to be further improved.

[0076] 1.3. Other Additives The radiation-curable inkjet composition according to this embodiment may further contain additives such as colorants, dispersants, polymerization inhibitors, slip agents, photosensitizers, and polymerization inhibitors, as necessary.

[0077] 1.3.1. Colorants The radiation-curable inkjet composition according to this embodiment may further contain a colorant. By including a colorant in the radiation-curable inkjet composition according to this embodiment, it can be used as a colored radiation-curable inkjet composition. At least one of a pigment and a dye can be used as the colorant.

[0078] The total content of the colorant is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, and still more preferably 2 to 10% by mass with respect to the total amount of the composition. Note that the radiation-curable inkjet composition according to this embodiment may be a clear ink that does not contain a colorant or contains a colorant to such an extent that it is not intended to be colored (for example, 0.1% by mass or less).

[0079] 1.3.1.1. Pigment By using a pigment as a colorant, the light resistance of the radiation-curable inkjet composition can be improved. As the pigment, either an inorganic pigment or an organic pigment can be used. The pigment may be used alone or in combination of two or more.

[0080] As the inorganic pigment, carbon blacks (C.I. (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.

[0081] Examples of the organic pigment include azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, and chelate azo pigments; phthalocyanine pigments; perylene and perinone pigments; anthraquinone pigments; quinacridone pigments; dioxane pigments; thioindigo pigments; isoindolinone pigments; quinophthalone pigments and other polycyclic pigments; dye chelates (e.g., basic dye type chelates, acid dye type chelates, etc.); dyed lakes (basic dye type lakes, acid dye type lakes); nitro pigments; nitroso pigments; aniline black; and daylight fluorescent pigments.

[0082] More specifically, as the carbon black used for black, there are No.2300, No.900, MCF88, No.33, No.40, No.45, No.52, MA7, MA8, MA100, No.2200B, etc. (manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (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 K.K.), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color B1ack S150, ColorBlack S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, SpecialBlack 6, Special Black 5, Special Black 4A, Special Black 4, etc. (manufactured by Degussa).

[0083] As the pigments used for white, there are C.I. Pigment White 6, 18, 21 mentioned.

[0084] Examples of pigments used for yellow include C.I. 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, 180.

[0085] Examples of pigments used for magenta include C.I. 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, or C.I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50.

[0086] Examples of pigments used for cyan include C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, C.I. Vat Blue 4, 60.

[0087] Examples of pigments other than magenta, cyan, and yellow include, for example, C.I. Pigment Green 7, 10, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

[0088] As for pigments, it is preferable to use non-metallic pigments such as carbon black and organic pigments because of their good storage stability.

[0089] The content of the pigment is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, and even more preferably 2 to 10% by mass based on the total amount of the composition.

[0090] 1.3.1.2. 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. The dyes may be used alone or in combination of two or more.

[0091] The dyes are not particularly limited. For example, C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35 can be mentioned.

[0092] 1.3.2. Dispersant When the radiation-curable inkjet composition contains a pigment, a dispersant may be further contained to make the pigment dispersibility better. The dispersant may be used alone or in combination of two or more.

[0093] The dispersant is not particularly limited, and examples thereof include dispersants commonly used for preparing pigment dispersions such as polymer dispersants. Specific examples thereof include those mainly composed of one or more of polyoxyalkylene polyalkylene polyamine, 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.

[0094] Commercially available products of polymer dispersants include the AJISPER series manufactured by Ajinomoto Fine-Techno Co., the Solsperse series (such as Solsperse 36000) available from Avecia and Noveon, the DISPERBYK series manufactured by BYK Additives & Instruments, and the DISPARON series manufactured by Kusumoto Chemicals.

[0095] The content of the dispersant is preferably 0.1 to 2% by mass, more preferably 0.1 to 1% by mass, and still more preferably 0.1 to 0.5% by mass based on the total amount of the composition.

[0096] 1.3.3. Polymerization inhibitor The radiation-curable inkjet composition according to the present embodiment may further contain a polymerization inhibitor. The polymerization inhibitor may be used alone or in combination of two or more.

[0097] The polymerization inhibitor is not limited to the following, and examples thereof include 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), hindered amine compounds, and the like.

[0098] The content of the anti-coalescence agent is preferably 0.05 to 1% by mass, more preferably 0.05 to 0.5% by mass, based on the total amount of the composition.

[0099] 1.3.4. Slip agent The radiation-curable inkjet composition according to this embodiment may further contain a slip agent. The slip agent may be used alone or in combination of two or more.

[0100] As the slip agent, a silicone surfactant is preferable, and a polyester-modified silicone or a polyether-modified silicone is more preferable. Examples of the polyether-modified silicone include BYK-378, 3455, BYK-UV3500, 3510, 3530 (manufactured by BYK Additives&Instruments), etc., and examples of the polyester-modified silicone include BYK-3570 (manufactured by BYK Additives&Instruments), etc.

[0101] The content of the slip agent is preferably 0.01 to 2% by mass, more preferably 0.05 to 1% by mass, based on the total amount of the composition.

[0102] 1.3.5. Photosensitizer The radiation-curable inkjet composition according to this embodiment may further contain a photosensitizer. Examples of the photosensitizer include amine compounds (such as aliphatic amines, amines containing aromatic groups, piperidine, reaction products of epoxy resins and amines, triethanolamine triacrylate, etc.), urea compounds (such as allylthiourea, o-tolylthiourea, etc.), sulfur compounds (such as sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acids, etc.), nitrile compounds (such as N,N-diethyl-p-aminobenzonitrile, etc.), phosphorus compounds (such as tri-n-butylphosphine, sodium diethyldithiophosphide, etc.), nitrogen compounds (such as Michler's ketone, N-nitrosohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds, condensates of formaldehyde or acetaldehyde and diamines, etc.), chlorine compounds (such as carbon tetrachloride, hexachloroethane, etc.).

[0103] 1.4. Physical properties The viscosity of the radiation-curable inkjet composition according to this embodiment at 20°C is preferably 25 mPa·s or less, more preferably 5 mPa·s to 25 mPa·s. When the viscosity of the composition at 20°C is within the above range, an appropriate amount of the composition is ejected from the nozzle, and the flight curve and scattering of the composition can be further reduced, so it can be suitably used in an inkjet recording apparatus. The viscosity can be measured by using a viscoelasticity tester MCR-300 (manufactured by Pysica), in an environment of 20°C, increasing the Shear Rate from 10 to 1000, and reading the viscosity at Shear Rate 200.

[0104] 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 the nozzle surface that has been subjected to the liquid-repellent treatment. As a result, the composition is discharged from the nozzle normally and in an appropriate amount, and the flight deflection and scattering of the composition can be further reduced, so that it can be suitably used in an inkjet recording apparatus. The surface tension can be measured by using an automatic surface tension meter CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) to check the surface tension when a platinum plate is wetted with the radiation-curable inkjet composition in an environment of 20°C.

[0105] 1.5. Manufacturing method of the composition The production (preparation) of the radiation-curable inkjet composition is carried out by mixing each component contained in the composition and stirring so that the components are mixed sufficiently uniformly. In this embodiment, the preparation of the radiation-curable inkjet composition preferably has a step of subjecting at least one of ultrasonic treatment and heating treatment to a mixture in which at least a part of the polymerization initiator and the monomer are mixed during the preparation process. Thereby, the amount of dissolved oxygen in the prepared composition can be reduced, and a radiation-curable inkjet composition excellent in discharge stability and storage stability can be obtained. The above mixture only needs to contain at least the above components, and may further contain other components contained in the radiation-curable inkjet composition, or may contain all the components contained in the radiation-curable inkjet composition. The monomer contained in the mixture only needs to be at least a part of the monomer contained in the radiation-curable inkjet composition.

[0106] 2. Inkjet recording method The inkjet recording method according to this embodiment includes a discharging step of discharging a radiation-curable inkjet composition from an inkjet head and attaching it to a recording medium, and an irradiation step of irradiating the radiation-curable inkjet composition attached to the recording medium with radiation. Thereby, a coating film can be formed at the location where the radiation-curable inkjet composition on the recording medium is applied. Hereinafter, the details of each step will be described.

[0107] 2.1. Discharging step In the discharging step, the composition is discharged from the inkjet head and attached to the recording medium. More specifically, the pressure generating means is driven to discharge the composition filled in the pressure generating chamber of the inkjet head from the nozzles. Such a discharging method is also called an inkjet method.

[0108] Examples of the inkjet head used in the discharging step include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0109] In the line method using a line head, for example, an inkjet head having a width equal to or greater than the recording width of the recording medium is fixed to the recording apparatus. Then, the recording medium is moved along the sub-scanning direction (the longitudinal direction of the recording medium, the conveyance direction), and ink droplets are discharged from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0110] In the serial method using a serial head, for example, an inkjet head is mounted on a carriage movable in the main scanning direction (the lateral direction of the recording medium, the width direction). Then, the carriage is moved along the main scanning direction, and ink droplets are discharged from the nozzle openings of the head in conjunction with this movement, whereby an image can be recorded on the recording medium.

[0111] 2.2. Irradiation step In the irradiation step, radiation is irradiated onto the radiation-curable inkjet composition adhered to the recording medium. When the radiation is irradiated, the polymerization reaction of the monomer starts, causing the composition to cure and form a coating film. At this time, if a polymerization initiator is present, active species (starting species) such as radicals, acids, and bases are generated, and the polymerization reaction of the monomer is promoted by the function of the starting species. Also, if a photosensitizer is present, it absorbs radiation and enters an excited state, and by contacting the polymerization initiator, it promotes the decomposition of the polymerization initiator, enabling the achievement of a more curing reaction.

[0112] Here, examples of the radiation include ultraviolet rays, infrared rays, visible light, X-rays, etc. The radiation source irradiates the composition by a radiation source provided downstream of the inkjet head. The radiation source is not particularly limited, and for example, a UV-LED can be mentioned. By using such a radiation source, miniaturization of the device and cost reduction can be realized. Since the UV-LED as an ultraviolet source is small, it can be installed inside the inkjet recording device.

[0113] For example, it can be attached to a carriage (both ends along the medium width direction and / or on the medium conveyance direction side) equipped with an inkjet head that discharges the radiation-curable inkjet composition. Furthermore, due to the composition of the above-mentioned radiation-curable inkjet composition, curing at low energy and high speed can be realized. The irradiation energy is calculated by multiplying the irradiation time by the irradiation intensity. Therefore, the irradiation time can be shortened and the printing speed can be increased. On the other hand, the irradiation intensity can also be decreased. This can reduce the temperature rise of the printed matter, which also leads to a reduction in the odor of the cured film.

[0114] 3. Recorded Matter The recorded matter of this embodiment is one in which the above-mentioned radiation-curable inkjet composition adheres to the recording medium and cures. Since the above composition has good flexibility and adhesion, it is possible to suppress cracking and chipping of the coating film when post-processing such as cutting and bending is performed. Therefore, the recorded matter of this embodiment can be suitably used for sign applications and the like.

[0115] The material of the recording medium is not particularly limited, and examples thereof 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, polyvinyl acetal, etc., and those with their surfaces processed, glass, paper, metal, wood, etc.

[0116] Also, the form of the recording medium is not particularly limited. Examples thereof include film, board, cloth, etc.

Examples

[0117] Hereinafter, the present invention will be described more specifically using examples. The present invention is not limited by the following examples in any way.

[0118] 1. Preparation of Inkjet Composition First, a part of the coloring material, dispersant, and each monomer were weighed and put into a tank for pigment dispersion. A ceramic bead mill with a diameter of 1 mm was put into the tank and stirred to obtain a pigment dispersion liquid in which the coloring material was dispersed in the monomer. Next, the remaining monomers, polymerization initiator, and polymerization inhibitor were put into a tank for mixture, which is a stainless steel container, so as to have the composition shown in Table 1, and mixed and stirred until completely dissolved. Then, the pigment dispersion liquid obtained above was added, and further mixed and stirred at room temperature for 1 hour, and then filtered through a 5 μm membrane filter to obtain the radiation-curable inkjet composition of each example. In addition, the numerical values of each component shown in each example in the table represent mass% unless otherwise specified.

[0119]

Table 1

[0120] The abbreviations and components of the products used in Table 1 are as follows.

[0121] <Mono-functional monomer> ·PEA (Trade name: "Biscote #192", manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate) ·NVC (manufactured by ISP Japan Co., Ltd., N-vinylcaprolactam) ·ACMO (manufactured by KJ Chemicals Co., Ltd., acryloylmorpholine) ·TBCHA (Trade name: "SR217", manufactured by Sartomer Co., Ltd., tert-butylcyclohexanol acrylate) ·IBXA (manufactured by Osaka Organic Chemical Industry Co., Ltd., isobornyl acrylate) ·DCPA (manufactured by Hitachi Chemical Co., Ltd., dicyclopentenyl acrylate) <Multi-functional monomer> ·VEEA (manufactured by Nippon Shokubai Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate) <Oligomer> ·CN991 (manufactured by Sartomer Co., Ltd., bifunctional urethane acrylate oligomer) <Polymerization initiator> ·Irg.819 (Trade name: "IRGACURE 819", manufactured by BASF, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) ·TPO (Trade name: "IRGACURE TPO", manufactured by BASF, 2,4,6-trimethylbenzoyldiphenylphosphine oxide) <Polymerization inhibitor> ·MEHQ (Trade name: "p-methoxyphenol", manufactured by Kanto Chemical Co., Inc., hydroquinone monomethyl ether) <Slip agent> ·BYK-UV3500 (manufactured by BYK Additives&Instruments, polyether-modified polydimethylsiloxane having an acryloyl group) <Colorant (pigment)> ·Carbon black (Trade name: "MA-100", manufactured by Mitsubishi Chemical Corporation) <Dispersant> ·Solsperse36000 (manufactured by Lubrizol, polymeric dispersant).

[0122] In Table 1, the "monofunctional monomer ratio" represents the content of the monofunctional monomer with respect to the total amount of the polymerizable compounds. Specifically, as the polymerizable compounds, it refers to the monofunctional monomers, polyfunctional monomers, and bifunctional urethane acrylates in Table 1.

[0123] In Table 1, the "N-containing monomer amount" represents the content of the nitrogen-containing monofunctional monomer with respect to the total amount of the ink composition.

[0124] In Table 1, the "glass transition temperature" in the physical property column represents the weighted average of the glass transition temperatures of the homopolymers of the respective polymerizable compounds, with the content mass ratio of the polymerizable compounds as the weight.

[0125] 2. Evaluation Method 2.1. Curing Property Cotton swab weighted tackiness evaluation was carried out. Specifically, the ink composition was applied to a PVC medium with a bar coater so that the coating thickness of the ink composition was 10 μm, and ultraviolet light was irradiated at a speed of 0.04 sec / cm with a predetermined irradiation intensity. At that time, an LED having a peak wavelength at 395 nm was used as the light source. Then, the surface of the coating film was rubbed with a cotton swab, and the curing property was evaluated based on the irradiation intensity at which the cotton swab did not get colored. The evaluation criteria are as follows. A: Irradiation intensity is less than 0.5 W / cm 2 less than B: Irradiation intensity is 0.5 W / cm or more and less than 1.1 W / cm 2 and less than 2 1.1 W / cm C: Irradiation intensity is 1.1 W / cm or more and less than 2.5 W / cm 2 and less than 2 2.5 W / cm D: Irradiation intensity is 2.5 W / cm or more 2 or more

[0126] 2.2. Color Development Property For the coating film obtained by the above evaluation of curability, the L* value was measured using a colorimeter (trade name "Gretag Macbeth Spectrolino", manufactured by X-RITE). Note that a cured coating film was used. When the L* value is 15 or less, it can be said that good color development is obtained.

[0127] 2.3. Odor In accordance with JIS K 0102, the odor intensity of each radiation-curable inkjet composition was determined. More specifically, the sample was added to water maintained at 40°C, and the dilution multiple value when the odor was clearly felt, that is, the dilution multiple of the odor threshold value, was obtained. In order to reduce individual differences in olfaction, the test was conducted on at least 10 people for the same sample. Based on the obtained values, the odor was evaluated according to the following evaluation criteria. (Evaluation Criteria) A: 0 or more and less than 2 B: 2 or more and less than 3 C: 3 or more and less than 4 D: 4 or more

[0128] 2.4. Evaluation of Flexibility Using a bar coater, each radiation-curable inkjet composition was coated on a PVC film (JT5829R, manufactured by MACtac) to a thickness of 10 μm. Next, using a metal halide lamp (manufactured by Eye Graphics), it was cured with an energy of 400 mJ / cm 2 to form a coating film. The release paper of the PVC film on which the above coating film was formed was peeled off, and test pieces were prepared by cutting it into strips 1 cm wide and 8 cm long. For each test piece, the elongation rate as flexibility was measured using a tensile tester (TENSILON, manufactured by ORIENTEC). The elongation rate was the value at the time when cracks occurred when pulled at 5 mm / min. The value was calculated from {(length at the time of crack - length before stretching) / length before stretching × 100}. The evaluation criteria are shown below. (Evaluation Criteria) A: 300% or more B: 250% or more and less than 300% C: 200% or more and less than 250% D: Less than 200%

[0129] 2.5. Evaluation of Adhesion Except for using a polypropylene board (manufactured by Corplast) and a polyethylene terephthalate film (manufactured by Toray) as the recording media respectively, a cured coating film was prepared on each film in the same manner as the above evaluation of flexibility. For the obtained coating film, evaluation of the cross-cut test was carried out according to JIS K5600-5-6.

[0130] More specifically, with a cutter, the blade of the cutting tool was applied perpendicularly to the coating film to make a grid with a pitch of 1 mm between cuts, creating a 10×10 grid. A transparent adhesive tape (width 25 mm) with a length of about 75 mm was attached to the grid, and the tape was rubbed well with fingers so that the cured film could be seen through. Next, within 5 minutes after attaching the tape, the tape was surely peeled off from the cured film at an angle close to 60° in 0.5 - 1.0 seconds, and the state of the grid was observed visually. The evaluation criteria are as follows. (Evaluation Criteria) A: No peeling of the cured film was observed in the grid for both the polypropylene film and the polyethylene terephthalate film. B: Peeling of the cured film was observed in less than 50% of the grid for either the polypropylene film or the polyethylene terephthalate film. C: Peeling of the cured film was observed in less than 50% of the grid for both the polypropylene film and the polyethylene terephthalate film. D: Peeling of the cured film was observed in 50% or more of the grid for either the polypropylene film or the polyethylene terephthalate film. E: Peeling of the cured film was observed in 50% or more of the grid for both the polypropylene film and the polyethylene terephthalate film.

[0131] 2.6. Evaluation of Abrasion Resistance In the evaluation of the flexibility, the cured coating film prepared was evaluated for micro scratch test in accordance with JIS R3255. For the measurement, a ultra-thin film scratch tester (CSR-5000, manufactured by Nanotech Corporation) was used to measure the load resistance as scratch resistance. The load resistance was measured as the load at the time when a micro scratch was made while applying a load and the stylus reached the media surface. The greater the load resistance, the better the scratch resistance. The measurement was carried out with a stylus diameter of 15 μm, an amplitude of 100 μm, and a scratch speed of 10 μm / sec. The evaluation criteria are as follows. (Evaluation Criteria) A: 30 mN / cm 2 or more B: 25 mN / cm 2 or more and less than 30 mN / cm 2 less than C: 20 mN / cm 2 or more and less than 25 mN / cm 2 less than D: less than 20 mN / cm 2 less than

[0132] Each radiation-curable inkjet composition was filled into an inkjet printer PX-G930 (manufactured by Seiko Epson Corporation) for recording. For each radiation-curable inkjet composition, it was confirmed that inkjet ejection was possible and image formation was possible.

[0133] 3. Evaluation Results Table 1 shows the composition of the radiation-curable inkjet compositions used in each example and the evaluation results. From Table 1, the radiation-curable inkjet compositions of Examples 1 to 11, in which the monofunctional monomer contains 87% by mass or more based on the total amount of the polymerizable compounds, the monofunctional monomer contains a nitrogen-containing monofunctional monomer, and the content of the nitrogen-containing monofunctional monomer is 14% by mass or less based on the total amount of the radiation-curable inkjet composition, and the weighted average of the glass transition temperatures of the homopolymers of the respective polymerizable compounds with the content mass ratio of each polymerizable compound as the weight is 42°C or more, all had flexibility, adhesion, and scratch resistance of C or more, and also had good color development.

[0134] Specifically, when comparing each example with Comparative Examples 1 and 2, it can be seen that the color developability is improved by the fact that the ratio of the nitrogen-containing monofunctional monomer is 14% by mass or less with respect to the composition. Further, when comparing each example with Comparative Example 2, it can be seen that the flexibility and adhesion are improved by the fact that the ratio of the monofunctional monomer is 87% by mass or more with respect to the whole polymerizable compound. Furthermore, when comparing each example with Comparative Example 4, it can be seen that the abrasion resistance is improved by the fact that the weighted average of the glass transition temperature is 42°C or higher.

Claims

1. A radiation-curable inkjet composition containing a monofunctional monomer and a polyfunctional monomer (excluding those containing vinylcaprolactam and / or an acrylated amine compound having two photopolymerizable functional groups and two amino groups in the molecule), wherein the content of the monofunctional monomer is 87% by mass or more based on the total amount of the polymerizable compound, the monofunctional monomer includes a nitrogen-containing monofunctional monomer and an aromatic monofunctional monomer, the content of the nitrogen-containing monofunctional monomer is 14% by mass or less based on the total amount of the radiation-curable inkjet composition, the content of the aromatic monofunctional monomer is 25 to 45% by mass based on the total amount of the radiation-curable inkjet composition, the weighted average of the glass transition temperatures of the homopolymers of the respective polymerizable compounds, with the content mass ratio of each polymerizable compound as the weight, is 42°C or higher, a radiation-curable inkjet composition (excluding those containing at least one polymer of polythiourethane, polyurethane, and polyurea having a thiol structure at both ends of the main chain).

2. The nitrogen-containing monofunctional monomer includes a monomer having a nitrogen-containing heterocyclic structure, The radiation-curable inkjet composition according to Claim 1.

3. The content of the polyfunctional monomer is 1 to 10% by mass based on the total amount of the polymerizable compound, The radiation-curable inkjet composition according to Claim 1 or 2.

4. The polyfunctional monomer includes vinyl ether group-containing (meth)acrylate esters represented by the following formula (1), The radiation-curable inkjet composition according to any one of Claims 1 to 3. CH 2 =CR 1 -COOR 2 -O-CH=CH-R 3 ... (1) (wherein, 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.)

5. The content of the nitrogen-containing monofunctional monomer is 3 to 14% by mass based on the total amount of the radiation-curable inkjet composition, The radiation-curable inkjet composition according to any one of Claims 1 to 4.

6. The nitrogen-containing monofunctional monomer includes a nitrogen-containing monofunctional acrylate monomer, The radiation-curable inkjet composition according to any one of Claims 1 to 5.

7. The nitrogen-containing monofunctional monomer includes a nitrogen-containing monofunctional vinyl monomer, The radiation-curable inkjet composition according to any one of Claims 1 to 6.

8. The monofunctional monomer includes a monofunctional acrylate having a polycyclic hydrocarbon group, The radiation-curable inkjet composition according to any one of Claims 1 to 7.

9. The content of the monofunctional acrylate having the polycyclic hydrocarbon group is 40% by mass or less based on the total amount of the radiation-curable inkjet composition. The radiation-curable inkjet composition according to claim 8.

10. Containing a pigment The radiation-curable inkjet composition according to any one of claims 1 to 9.

11. A discharging step of discharging the radiation-curable inkjet composition according to any one of claims 1 to 10 from an inkjet head and attaching it to a recording medium, and An irradiation step of irradiating radiation to the radiation-curable inkjet composition attached to the recording medium. Recording method.

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