Radiation-curable ink-jet composition and ink-jet method

Abstract

To provide a radiation-curable inkjet composition capable of giving a coating film having shielding properties, flexibility, adhesion and scratch resistance, and to provide an inkjet method.SOLUTION: The radiation-curable inkjet composition contains polymerizable compounds including a monofunctional monomer and a polyfunctional monomer, a photopolymerization initiator, and titanium oxide as a white coloring material. The content of the monofunctional monomer is 90 mass% or more based on the total amount of the polymerizable compounds. The weighted average of the glass transition temperatures of homopolymers of the respective polymerizable compounds with the content mass ratio of each of the polymerizable compounds as a weight is 48°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 method. [Background technology]

[0002] It has been known that, as described in Patent Document 1, for example, a radiation-curable inkjet composition that contains 2 to 3 mass % of a colorant and contains a vinyl ether group-containing (meth)acrylic acid ester, acryloylmorpholine or the like, and vinyl caprolactam or the like can be obtained that has little odor and exhibits good curability and flexibility after curing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-9142 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since a white ink composition is required to have a shielding property, the pigment content may be made higher than that of other colors, but the higher the pigment content, the lower the adhesion of the ink coating film becomes. Furthermore, when a white ink contains a large amount of a white coloring material with a high specific gravity, clogging easily occurs when a conventional inkjet head is used, and there is also a problem that the ejection stability is poor. [Means for solving the problem]

[0005] The radiation-curable inkjet composition of the present invention contains a polymerizable compound containing a monofunctional monomer and a polyfunctional monomer, a photopolymerization initiator, and titanium oxide as a white colorant, wherein the content of the monofunctional monomer is 90 mass% or more based on the total amount of the polymerizable compounds, and the weighted average of the glass transition temperatures of homopolymers of the polymerizable compounds, where the weights are the mass ratios of the polymerizable compounds, is 48° C. or more.

[0006] The radiation curable ink jet composition preferably contains the titanium oxide in an amount of 15% by mass or more relative to the total amount of the radiation curable ink jet composition.

[0007] In the radiation curable ink jet composition, the polyfunctional monomer preferably contains a vinyl ether group-containing (meth)acrylate represented by the following formula (1). 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.

[0008] The content of the polyfunctional monomer in the radiation curable ink jet composition is preferably 0.10 to 10% by mass relative to the total amount of the radiation curable ink jet composition.

[0009] In the radiation curable ink jet composition, the monofunctional monomer preferably includes a nitrogen-containing monofunctional monomer.

[0010] In the radiation-curable ink jet composition, the nitrogen-containing monofunctional monomer preferably includes a monomer having a nitrogen-containing heterocyclic structure.

[0011] In the radiation curable ink jet composition, the monofunctional monomer preferably contains a monofunctional (meth)acrylate having a crosslinked condensed ring structure.

[0012] In the radiation curable ink jet composition, the monofunctional (meth)acrylate having a crosslinked condensed ring structure preferably contains dicyclopentenyl (meth)acrylate.

[0013]

[0023] Furthermore, the inkjet method of the present invention is an inkjet method that uses a liquid jet head including a nozzle that ejects the radiation curable inkjet composition, a pressure chamber to which the radiation curable inkjet composition is supplied, and a circulation flow path that enables the radiation curable inkjet composition in the pressure chamber to circulate, and includes a ejection step of ejecting the heated radiation curable inkjet composition from the liquid jet head to adhere it to a recording medium, and an irradiation step of irradiating the radiation curable inkjet composition adhered to the recording medium with radiation.

[0014] The above inkjet method preferably includes a heating step of heating the radiation curable inkjet composition in the liquid jet head to 40° C. or higher. [Brief description of the drawings]

[0015] [Figure 1] 1A and 1B are schematic diagrams illustrating a configuration of a liquid jet head that can be used in the present embodiment. [Diagram 2] 1 is a perspective view showing a serial type inkjet device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary, but the present invention is not limited to this, and various modifications are possible without departing from the gist of the present invention. In the drawings, the same elements are given the same symbols, and duplicated explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings, unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0017] In this specification, "(meth)acryloyl" means at least one of acryloyl and the corresponding methacryloyl, "(meth)acrylate" means at least one of acrylate and the corresponding methacrylate, and "(meth)acrylic" means at least one of acrylic and the corresponding methacrylic.

[0018] 1. Radiation-curable inkjet composition The radiation-curable inkjet composition according to this embodiment (hereinafter also simply referred to as the "composition") contains a polymerizable compound including a monofunctional monomer and a polyfunctional monomer, a photopolymerization initiator, and titanium oxide as a white colorant, in which the content of the monofunctional monomer is 90 mass % or more relative to the total amount of the polymerizable compounds, and the weighted average of the glass transition temperatures of homopolymers of the polymerizable compounds, where the weights are the content mass ratios of the respective polymerizable compounds, is 48° C. or higher.

[0019] A white ink composition used for sign applications and the like is required to have a shielding property, but there is a problem that the adhesion and flexibility of the ink coating film decrease as the pigment content increases. In contrast, in this embodiment, the adhesion and flexibility of the coating film can be improved by setting the content of the monofunctional monomer within a predetermined range. On the other hand, when the content of the monofunctional monomer is within the above range, the scratch resistance of the coating film decreases, but by configuring the polymerizable compounds so that the weighted average of the glass transition temperatures of the homopolymers of each polymerizable compound is within a predetermined range, it is possible to improve the scratch resistance of the coating film. As a result, in this embodiment, the adhesion, flexibility and scratch resistance of the coating film can be ensured while ensuring the shielding property, even when titanium oxide, which has poor adhesion to media, is used.

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

[0021] The radiation-curable inkjet composition of the present embodiment is cured by irradiation with radiation. Examples of radiation include ultraviolet light, electron beams, infrared light, visible light, X-rays, etc. 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.

[0022] 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.

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

[0024] In this embodiment, the weighted average of the glass transition temperatures of the homopolymers of the polymerizable compounds, weighted by the content mass ratio of each polymerizable compound, is 48° C. or higher, preferably 50° C. or higher, and more preferably 52° C. or higher. By having the weighted average of the glass transition temperatures of 48° C. or higher, the scratch resistance of the coating film at room temperature can be improved. In addition, the upper limit of the weighted average of the glass transition temperatures is not particularly limited, but is preferably 65° C. or lower, more preferably 60° C. or lower, and even more preferably 55° C. or lower.

[0025] The method for calculating the weighted average of the glass transition temperature is explained. The weighted average of the glass transition temperature is called Tg All The glass transition temperature of the homopolymer of each polymerizable compound is Tg N The content mass ratio of the polymerizable compound is X N (% by mass). N is a number starting from 1 depending on the type of polymerizable compound contained in the radiation curable inkjet composition. For example, when three types of polymerizable compounds are used, Tg1, Tg2, and Tg3 are obtained. 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 All is the glass transition temperature (Tg) calculated for each polymerizable compound. N and the mass ratio X N Therefore, the following formula (2) holds. Tg All =ΣTg N X N (2)

[0026] The weighted average of the glass transition temperatures can be adjusted by the glass transition temperatures of the polymerizable compounds used and the mass ratio of the polymerizable compounds used.

[0027] 1.1.1. Monofunctional monomers The monofunctional monomer of the present embodiment is not particularly limited, but may be, for example, a nitrogen-containing monofunctional monomer, a monofunctional (meth)acrylate having a crosslinked condensed ring structure, an aromatic group-containing monofunctional monomer, or a saturated aliphatic group-containing monofunctional monomer. In addition, other monofunctional monomers may be included as necessary instead of or in addition to these. The other monofunctional monomer is not particularly limited, but may be a monofunctional monomer having a polymerizable functional group, particularly a polymerizable functional group having an unsaturated double bond between carbon atoms, which is known in the art.

[0028] The content of the monofunctional monomer is 90% by mass or more, preferably 92% by mass or more, more preferably 94% by mass or more, based on the total amount of the polymerizable compounds. When the content of the monofunctional monomer is 90% by mass or more, based on the total amount of the polymerizable compounds, the flexibility and adhesion of the coating film are further improved. In addition, 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 even 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 scratch resistance of the coating film tends to be further improved.

[0029] The content of the monofunctional monomer is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 67% by mass or more, based on the total amount of the composition. When the content of the monofunctional monomer is 60% by mass or more, based on the total amount of the composition, the flexibility and adhesion of the coating film tend to be improved. The upper limit of the content of the monofunctional monomer is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 73% by mass or less, based on the total amount of the composition. When the content of the monofunctional monomer is 80% by mass or less, based on the total amount of the composition, the scratch resistance of the coating film tends to be improved.

[0030] Examples of monofunctional monomers are given below, but the monofunctional monomers in this embodiment are not limited to the following.

[0031] 1.1.1.1. Nitrogen-containing monofunctional monomers The nitrogen-containing monofunctional monomer is not particularly limited, and examples thereof include 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; and nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetone acrylamide, N,N-dimethyl(meth)acrylamide, and dimethylaminoethyl acrylate benzyl chloride quaternary salt.

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

[0033] By using such nitrogen-containing monofunctional monomers, the scratch resistance of the coating film tends to be improved.Furthermore, the nitrogen-containing monofunctional vinyl monomers having a nitrogen-containing heterocyclic structure such as N-vinylcaprolactam and the nitrogen-containing monofunctional acrylate monomers having a nitrogen-containing heterocyclic structure such as acryloylmorpholine tend to improve the flexibility and adhesion of the coating film.

[0034] The content of the nitrogen-containing monofunctional monomer is preferably 8 to 25 mass %, more preferably 10 to 20 mass %, and further preferably 12 to 18 mass %, based on the total amount of the polymerizable compounds. When the content of the nitrogen-containing monofunctional monomer is within the above range, the scratch resistance of the coating film tends to be further improved.

[0035] The content of the nitrogen-containing monofunctional monomer is preferably 5 to 20 mass % relative to the total amount of the composition, more preferably 8 to 16 mass %, and even more preferably 10 to 14 mass %. When the content of the nitrogen-containing monofunctional monomer is 20 mass % or less relative to the total amount of the composition, the adhesion tends to be further improved. Also, when the content of the nitrogen-containing monofunctional monomer is 5 mass % or more relative to the total amount of the composition, the scratch resistance of the coating film tends to be further improved.

[0036] 1.1.1.2. Monofunctional (meth)acrylates with bridged condensed ring structures As one of the other monofunctional monomers, there can be mentioned monofunctional (meth)acrylates having a bridged condensed ring structure. In the present invention, the bridged condensed ring structure means a structure in which two or more ring structures share a side in a one-to-one relationship and two or more non-adjacent elements of the same ring structure or different ring structures are linked. Examples of the monofunctional (meth)acrylates having a bridged condensed ring structure include dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate and dicyclopentanyl (meth)acrylate. In addition to the above, the following can be mentioned as examples of the bridged condensed ring structure. [ka]

[0037] Among these, it is more preferable to contain dicyclopentenyl (meth)acrylate. By using such a monofunctional (meth)acrylate having a crosslinked condensed ring structure, the scratch resistance, flexibility and adhesion of the coating film tend to be further improved.

[0038] The content of the monofunctional (meth)acrylate having a crosslinked condensed ring structure is preferably 1 to 25 mass %, more preferably 3 to 20 mass %, and further preferably 5 to 15 mass %, based on the total amount of the polymerizable compounds. When the content of the monofunctional (meth)acrylate having a crosslinked condensed ring structure based on the total amount of the polymerizable compounds is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0039] The content of the monofunctional (meth)acrylate having a crosslinked condensed ring structure is preferably 15 to 45 mass %, more preferably 20 to 40 mass %, and even more preferably 25 to 35 mass %, relative to the total amount of the composition. When the content of the monofunctional (meth)acrylate having a crosslinked condensed ring structure relative to the total amount of the composition is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0040] 1.1.1.3. Aromatic group-containing monofunctional monomers The aromatic group-containing monofunctional monomer is not particularly limited, but examples thereof include 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.

[0041] 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 aromatic group-containing monofunctional monomers, the solubility of the photopolymerization initiator is improved, and the curability of the composition tends to be improved. In particular, when an acylphosphine oxide-based photopolymerization initiator or a thioxanthone-based photopolymerization initiator is used, the solubility tends to be good.

[0042] The content of the aromatic group-containing monofunctional monomer is preferably 25 to 55 mass %, more preferably 30 to 50 mass %, and further preferably 35 to 45 mass %, based on the total amount of the polymerizable compounds. When the content of the aromatic group-containing monofunctional monomer based on the total amount of the polymerizable compounds is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0043] The content of the aromatic group-containing monofunctional monomer is preferably 15 to 45 mass %, more preferably 20 to 40 mass %, and even more preferably 25 to 35 mass %, relative to the total amount of the composition. When the content of the aromatic group-containing monofunctional monomer relative to the total amount of the composition is within the above range, the adhesion and abrasion resistance of the coating film tend to be further improved.

[0044] 1.1.1.4. Monofunctional monomers containing saturated aliphatic groups The saturated aliphatic group-containing monofunctional monomer is not particularly limited, and examples thereof include alicyclic group-containing monofunctional monomers such as isobornyl (meth)acrylate (IBXA), tert-butylcyclohexanol acrylate (TBCHA), and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl; isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, and decyl (meth)acrylate. Examples of the monofunctional monomer include linear or branched aliphatic group-containing monofunctional monomers such as acrylate, isodecyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate; and lactone-modified flexible (meth)acrylate. Among these, the monofunctional monomer containing an alicyclic group is preferred. By using such a monofunctional monomer containing a saturated aliphatic group, the curing property of the composition tends to be further improved. In this embodiment, the monofunctional monomer containing a saturated aliphatic group is not a compound having a crosslinked condensed ring structure.

[0045] The content of the saturated aliphatic group-containing monofunctional monomer is preferably 1 to 6 mass %, more preferably 2 to 5 mass %, and further preferably 3 to 4 mass %, based on the total amount of the polymerizable compounds.

[0046] The content of the saturated aliphatic group-containing monofunctional monomer is preferably from 2 to 8 mass %, more preferably from 3 to 7 mass %, and further preferably from 4 to 6 mass %, based on the total amount of the composition.

[0047] Other Other monofunctional monomers that may be used in addition to the above include, 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 unsaturated carboxylic acids; acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes.

[0048] 1.1.2. Multifunctional monomers Examples of the polyfunctional monomer of the present embodiment include vinyl ether group-containing (meth)acrylate and polyfunctional (meth)acrylate. Note that the polyfunctional monomer is not limited to the above.

[0049] The content of the polyfunctional monomer is preferably 1 to 10% by mass or more, more preferably 2 to 8% by mass, and even more preferably 3 to 6% by mass, based on the total amount of the polymerizable compounds. When the content of the polyfunctional monomer is 1% by mass or more based on the total amount of the polymerizable compounds, the scratch resistance tends to be further improved. Also, when the content of the polyfunctional monomer is 10% by mass or less based on the total amount of the polymerizable compounds, the flexibility and adhesion of the coating film tends to be further improved.

[0050] The content of the polyfunctional monomer is preferably 0.1 to 10% by mass or more, more preferably 1 to 8% by mass, and even more preferably 2 to 6% by mass, based on the total amount of the composition. When the content of the polyfunctional monomer is 0.1% by mass or more, based on the total amount of the composition, the scratch resistance tends to be further improved. When the content of the polyfunctional monomer is 10% by mass or less, based on the total amount of the composition, the flexibility and adhesion of the coating film tend to be further improved.

[0051] Examples of polyfunctional monomers are given below, but the polyfunctional monomers in this embodiment are not limited to the following.

[0052] 1.1.2.1 Vinyl ether group-containing (meth)acrylates The vinyl ether group-containing (meth)acrylate is not particularly limited, but may be, for example, a compound represented by the following formula (1). By including such a vinyl ether group-containing (meth)acrylate, the viscosity of the composition tends to be reduced and the ejection stability tends to be improved. In addition, the curability of the composition is improved, and the improved curability allows the recording speed to be 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.

[0053] In the above formula (1), R 2Examples of the divalent organic residue having 2 to 20 carbon atoms represented by the formula (I) include a linear, branched or cyclic alkylene group having 2 to 20 carbon atoms, which may be substituted, an alkylene group having 2 to 20 carbon atoms, which has an oxygen atom due to an ether bond and / or an ester bond in the structure, which may be substituted, and a divalent aromatic group 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 have an oxygen atom due to an ether bond in the structure, such as an oxyethylene group, an oxyn-propylene group, an oxyisopropylene group, and an oxybutylene group, are preferred. Furthermore, from the viewpoint of further reducing the viscosity of the composition and further improving the curability of the 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 oxyn-propylene group, an oxyisopropylene group, or an oxybutylene group, is more preferred.

[0054] In the above formula (1), R 3 Preferred examples of the monovalent organic residue having 1 to 11 carbon atoms and represented by the formula (1) 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 a methyl group or an ethyl group, and aromatic groups having 6 to 8 carbon atoms, such as a phenyl group and a benzyl group, are preferably used.

[0055] When each of the organic residues is a group that may be substituted, the substituent is divided into a group that contains carbon atoms and a group that does not contain carbon atoms.First, when the substituent is a group that contains carbon atoms, the carbon atom is counted in the number of carbon atoms of the organic residue.As the group that contains carbon atoms, but is not limited to the following, for example, a carboxyl group and an alkoxy group can be mentioned.Next, as the group that does not contain carbon atoms, but is not limited to the following, for example, a hydroxyl group and a halo group can be mentioned.

[0056] 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-vinyloxymethylphenyl (meth)acrylate Methyl, o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 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-(vinyloxyisopropoxy)isopropyl (meth)acrylate, 2-(vinyloxyeth (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 2-(vinyloxyisopropoxyisopropoxy)propyl,2-(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, 2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate, polyethylene glycol monovinyl ether (meth)acrylate, and polypropylene glycol monovinyl ether (meth)acrylate. Of these specific examples, 2-(2-vinyloxyethoxy)ethyl acrylate is particularly preferred in that it is easy to balance the curability and viscosity of the composition. In this embodiment, 2-(2-vinyloxyethoxy)ethyl acrylate is also referred to as VEEA.

[0057] The content of the vinyl ether group-containing (meth)acrylate relative to the total amount of the polymerizable compounds is preferably 1 to 10% by mass or more, more preferably 2 to 8% by mass, and even more preferably 3 to 6% by mass. When the content of the vinyl ether group-containing (meth)acrylate relative to the total amount of the polymerizable compounds is within the above range, the viscosity of the composition tends to decrease and the discharge stability tends to be improved.

[0058] The content of the vinyl ether group-containing (meth)acrylate relative to the total amount of the composition is preferably 0.1 to 10% by mass or more, more preferably 1 to 8% by mass, and even more preferably 2 to 6% by mass. When the content of the vinyl ether group-containing (meth)acrylate relative to the total amount of the composition is within the above range, the viscosity of the composition tends to decrease, and the ejection stability tends to be improved.

[0059] 1.1.2.2 Multifunctional (meth)acrylates The polyfunctional (meth)acrylate is not particularly limited, and examples thereof include 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 di(meth)acrylate of bisphenol A, PO(propylene) di(meth)acrylate of bisphenol A, and the like. bifunctional (meth)acrylates such as hydroxypivalic acid neopentyl glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate; and polyfunctional (meth)acrylates having three or more functional groups such as 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.

[0060] The content of the polyfunctional (meth)acrylate is preferably 1 to 10% by mass or more, more preferably 2 to 8% by mass, and even more preferably 3 to 6% by mass, based on the total amount of the polymerizable compounds. When the content of the polyfunctional (meth)acrylate is 1% by mass or more, based on the total amount of the polymerizable compounds, the scratch resistance tends to be further improved. Also, when the content of the polyfunctional (meth)acrylate is 10% by mass or less, based on the total amount of the polymerizable compounds, the flexibility and adhesion of the coating film tends to be further improved.

[0061] The content of the polyfunctional (meth)acrylate is preferably 0.1 to 10% by mass or more, more preferably 1 to 8% by mass, and even more preferably 2 to 6% by mass, based on the total amount of the composition. When the content of the polyfunctional (meth)acrylate is 0.1% by mass or more, based on the total amount of the composition, the scratch resistance tends to be further improved. When the content of the polyfunctional (meth)acrylate is 10% by mass or less, based on the total amount of the composition, the flexibility and adhesion of the coating film tend to be further improved.

[0062] 1.2. Photoinitiator The photopolymerization initiator is not particularly limited as long as it generates active species by irradiation with radiation, and examples thereof include known photopolymerization initiators such as acylphosphine oxide-based photopolymerization initiators, alkylphenone-based polymerization initiators, titanocene-based polymerization initiators, and thioxanthone-based photopolymerization initiators. Among these, acylphosphine oxide-based photopolymerization initiators are preferred. By using such a photopolymerization initiator, the curability of the composition is improved, and in particular, the curability by the curing process using UV-LED light tends to be improved. The photopolymerization initiator may be used alone or in combination of two or more.

[0063] The acylphosphine oxide photopolymerization initiator is not particularly limited, but examples thereof include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like.

[0064] Commercially available products of such acylphosphine oxide photopolymerization 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-hydroxy-cyclohexyl-phenyl ketone in a mass ratio of 25:75), and IRGACURE TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (all manufactured by BASF).

[0065] The content of the photopolymerization initiator is preferably 3 to 12 mass %, more preferably 5 to 10 mass %, and further preferably 7 to 9 mass %, based on the total amount of the composition. When the content of the photopolymerization initiator is within the above range, the curability of the composition and the solubility of the photopolymerization initiator tend to be further improved.

[0066] 1.3.White color material The radiation-curable ink jet composition of the present embodiment contains titanium oxide as a white coloring material. Although titanium oxide tends to reduce the adhesion of a coating film, it has a higher whiteness and a higher refractive index than other white coloring materials such as silica, and therefore has high shielding properties.

[0067] The content of titanium oxide is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the total amount of the composition. When the content of titanium oxide is 5% by mass or more, the shielding property tends to be further improved. In addition, the content of titanium oxide is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the composition. When the content of titanium oxide is 30% by mass or less, the adhesion, abrasion resistance, and flexibility of the coating film tend to be further improved.

[0068] 1.4. Other Additives The radiation curable ink jet composition according to this embodiment may further contain additives such as a dispersant, a polymerization inhibitor, and a slip agent, if necessary.

[0069] Dispersants The radiation-curable ink jet composition of this embodiment may further contain a dispersant to improve the dispersibility of the white colorant. The dispersant may be used alone or in combination of two or more kinds.

[0070] The dispersant is not particularly limited, but examples thereof include dispersants commonly used for preparing pigment dispersions, such as polymer dispersants, etc. Specific examples thereof include those containing one or more of 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 as the main component.

[0071] Commercially available polymer dispersants include the Ajisper series manufactured by Ajinomoto Fine-Techno Co., Ltd., the Solsperse series (Solsperse 36000, etc.) available from Avecia and Noveon, the Disperbyk series manufactured by BYK Additives & Instruments, and the Disparlon series manufactured by Kusumoto Chemicals Co., Ltd.

[0072] The content of the dispersant is preferably 0.1 to 2 mass %, more preferably 0.1 to 1 mass %, and further preferably 0.1 to 0.5 mass %, relative to the total amount of the composition.

[0073] 1.4.2. Polymerization inhibitors The radiation-curable ink jet composition according to this embodiment may further contain a polymerization inhibitor. The polymerization inhibitor may be used alone or in combination of two or more kinds.

[0074] Examples of the polymerization inhibitor 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), and hindered amine compounds.

[0075] The content of the polymerization inhibitor is preferably 0.05 to 1 mass %, and more preferably 0.05 to 0.5 mass %, based on the total amount of the composition.

[0076] 1.4.3. Slip agents The radiation curable ink jet composition according to this embodiment may further contain a slipping agent. The slipping agent may be used alone or in combination of two or more kinds.

[0077] The slip agent is preferably a silicone surfactant, more preferably a polyester-modified silicone or a polyether-modified silicone. Examples of the polyester-modified silicone include BYK-347, 348, BYK-UV3500, 3510, and 3530 (all manufactured by BYK Additives & Instruments), and examples of the polyether-modified silicone include BYK-3570 (manufactured by BYK Additives & Instruments).

[0078] The content of the slip agent is preferably 0.01 to 2 mass %, more preferably 0.05 to 1 mass %, based on the total amount of the composition.

[0079] 1.5.Physical Properties The viscosity of the radiation curable ink jet composition according to this embodiment at 40°C is 10 mPa·s or more, preferably 10 to 15 mPa·s, and more preferably 10 to 14 mPa·s. When the viscosity of the composition at 40°C is within the above range, the ejection stability is further improved. The viscosity can be measured using a viscoelasticity tester MCR-300 (manufactured by Pysica) in an environment at 40°C by increasing the shear rate from 10 to 1000 and reading the viscosity at a shear rate of 200. The viscosity at 40°C may be estimated from the viscosities measured in environments at 35°C and 45°C.

[0080] 1.6. Method for producing the composition The radiation curable ink jet composition is manufactured (prepared) by mixing the components contained in the composition and stirring the mixture so that the components are sufficiently uniformly mixed. In the present embodiment, the radiation curable ink jet composition is preferably prepared by subjecting a mixture of a polymerization initiator and at least a part of the monomers to at least one of ultrasonic treatment and heating treatment during the preparation process. This can reduce the amount of dissolved oxygen in the composition after preparation, and can provide a radiation curable ink jet composition with excellent ejection stability and storage stability. The mixture may contain at least the above components, 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 part of the monomers contained in the radiation curable ink jet composition.

[0081] 2. Inkjet method The inkjet method according to this embodiment includes a discharge step of discharging a predetermined radiation curable inkjet composition (hereinafter also simply referred to as "composition") using a predetermined liquid ejecting head to cause the composition to adhere to a recording medium, and an irradiation step of irradiating the radiation curable inkjet composition adhered to the recording medium with radiation.

[0082] In the inkjet method according to the present embodiment, as described above, the use of an ink composition containing titanium oxide as a white coloring material can improve the shielding properties. However, because titanium oxide has a large specific gravity, clogging and the like tend to occur easily when a conventional non-circulating type liquid ejection head is used, and ejection stability tends to be poor.

[0083] In contrast, in the inkjet method according to the present embodiment, by using a circulation type liquid ejection head, the ink composition containing titanium oxide can be circulated within the head, thereby maintaining ejection stability.

[0084] In addition, in the inkjet method according to the present embodiment, the flexibility, adhesion, and abrasion resistance can be improved by using a composition having a high monofunctional monomer ratio and a high weighted average of the glass transition temperature of the polymerizable compound. However, such a composition tends to have a relatively high viscosity. Therefore, from the viewpoint of enabling the composition to be discharged from a liquid jet head, it is required to heat the composition to a higher temperature than before to reduce the viscosity to a predetermined value or less. However, the higher the heating temperature, the larger the temperature difference between the temperature near the liquid jet head and the environmental temperature. In this case, when a non-circulating type liquid jet head is used, the heat dissipation conditions differ for each nozzle due to the difference in the usage rate (discharge duty) for each nozzle that discharges the composition and the position of the nozzle in the head (difference between the center part, the end part, etc.), so the temperature fluctuation of the discharged composition becomes large, resulting in a problem of reduced discharge stability.

[0085] In contrast, in the inkjet method according to the present embodiment, by using a circulation type liquid ejection head, it is possible to stabilize the above-mentioned temperature fluctuation and maintain ejection stability, while simultaneously achieving flexibility, adhesion, and abrasion resistance, which are inherent properties of the composition. Each step will be described in detail below.

[0086] 2.1.Discharge process In the ejection process, the heated composition is ejected from a liquid ejection head and adhered to a recording medium. More specifically, a pressure generating means is driven to eject the composition filled in the pressure generating chamber of the liquid ejection head from a nozzle. This ejection method is also called an ink jet method.

[0087] The liquid jet head used in this embodiment will be described. Fig. 1 shows a schematic diagram for explaining the configuration of a liquid jet head 10. Fig. 1 shows an outline of one nozzle 1 for ejecting a composition, a pressure chamber 2 to which the composition is supplied, and a circulation flow path 3 that enables the composition in the pressure chamber 2 to circulate. In the example of Fig. 1, the nozzle 1 and the pressure chamber 2 are in communication with each other via a communication path 4.

[0088] The nozzle 1 is a through hole for ejecting the composition. More specifically, the nozzle 1 is a through hole formed in a nozzle plate. A plurality of nozzles are formed in the nozzle plate, and a pressure chamber 2 is provided for each of the nozzles. The pressure chamber 2 is formed individually for each nozzle 1. The composition is supplied to the pressure chamber 2. When the pressure in the pressure chamber 2 fluctuates due to a pressure generating means (not shown), a part of the composition flowing in the communication passage 4 is ejected from the nozzle 1 to the outside, and the remaining part flows into the circulation flow passage 3. The path of the circulation flow passage 3 is not particularly limited, but the flow passage can be configured so that the composition that flows into the circulation flow passage 3 is supplied to the pressure chamber 2. Note that the composition that flows into the circulation flow passage 3 does not necessarily need to be resupplied to the same pressure chamber, and may be supplied to a pressure chamber corresponding to another nozzle. In addition, all of the circulation flow passages 3 do not need to be inside the liquid jet head 10, and some of the flow passages may be outside the liquid jet head 10 as long as the composition that flows out of the pressure chamber 2 is supplied to the pressure chamber 2 again.

[0089] In this way, according to the liquid jet head 10 of the present embodiment, the composition inside the pressure chamber 2, more specifically, the composition in the vicinity of the nozzle 1, can be efficiently circulated inside the head. This makes it possible to suppress temperature fluctuations of the composition for each nozzle even if there are differences in the usage rate or nozzle position for each nozzle.

[0090] The liquid jet head 10 used in the ejection process may be a line head that performs recording by a line method, or a serial head that performs recording by a serial method.

[0091] In the line method using a line head, for example, a liquid jet head having a width equal to or greater than the recording width of a recording medium is fixed to an inkjet device. Then, the recording medium is moved in the sub-scanning direction (the vertical direction of the recording medium, the transport direction), and ink droplets are ejected from the nozzles of the liquid jet head in conjunction with this movement to record an image on the recording medium.

[0092] In the serial method using a serial head, for example, a liquid ejection head is mounted on a carriage that can move in the width direction of the recording medium. The carriage is then moved along the main scanning direction (the lateral direction or width direction of the recording medium), and ink droplets are ejected from the nozzle openings of the head in conjunction with this movement, thereby recording an image on the recording medium.

[0093] 2.2.Heating process The inkjet method of the present embodiment may include a heating step of heating the composition in the liquid jet head. More specifically, the method may include a heating step of heating the composition in the circulation flow path composed of the pressure chamber 2, the circulation flow path 3, and the communication path 4. The heating means is not particularly limited, and may be provided, for example, in the pressure chamber 2, the circulation flow path 3, or the communication path 4. In addition, a heating means for heating the nozzle plate may be provided, or in the case where the circulation flow path 3 passes through the outside of the liquid jet head 10, a heating means may be provided in the circulation flow path 3 present outside the liquid jet head 10. Furthermore, a heating means may be provided in the ink flow path upstream of the pressure chamber. Here, the ink flow path refers to a flow path for distributing the ink. The ink flow path also includes, for example, an ink supply path for supplying ink from an ink storage container that stores ink to an ink jet recording head.

[0094] The lower limit of the heating temperature of the composition is preferably 35° C. or higher, more preferably 40° C. or higher, and even more preferably 45° C. or higher. The upper limit is preferably 70° C. or lower, more preferably 60° C. or lower, and even more preferably 50° C. or lower. By combining such a heating step with a liquid jet head that circulates the composition, it is possible to suppress temperature fluctuations of the composition.

[0095] 2.3.Irradiation process In the irradiation step, radiation is irradiated to the radiation-curable inkjet composition attached to the recording medium. When radiation is irradiated, a polymerization reaction of the monomer is initiated, curing the composition and forming a coating film. If a polymerization initiator is present, it generates active species (initiation species) such as radicals, acids, and bases, and the polymerization reaction of the monomer is promoted by the function of the initiation species. If a photosensitizer is present, it absorbs radiation and becomes excited, and by coming into contact with the polymerization initiator, it promotes the decomposition of the polymerization initiator, thereby achieving a more effective curing reaction.

[0096] Here, examples of the radiation include ultraviolet light, infrared light, visible light, and X-rays. The radiation source is provided downstream of the liquid jet head and irradiates the composition with the radiation. The radiation source is not particularly limited, but may be, for example, an ultraviolet light emitting diode. By using such a radiation source, it is possible to reduce the size and cost of the device. The ultraviolet light emitting diode as the ultraviolet light source is small, so it can be installed in the inkjet device.

[0097] For example, the ultraviolet light emitting diodes can be attached to a carriage (both ends along the medium width direction and / or the medium transport direction side) on which a liquid jet head that ejects the radiation curable ink jet composition is mounted. Furthermore, due to the composition of the radiation curable ink jet composition described above, curing can be achieved at low energy and high speed. 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 reduced. This can reduce the temperature rise of the printed matter, which also leads to a low odor of the cured film.

[0098] 3. Inkjet device The inkjet device of the present embodiment comprises a liquid ejecting head having a nozzle for ejecting the composition, a pressure chamber to which the composition is supplied, and a circulation flow path capable of circulating the composition in the pressure chamber, a heating unit capable of heating the composition, and a radiation source for irradiating the composition with radiation, and uses the above-described radiation-curable inkjet composition as the composition.

[0099] As shown in Fig. 1, the liquid jet head has a nozzle 1, a pressure chamber 2 to which a composition is supplied, and a circulation flow path 3 that allows the composition in the pressure chamber 2 to circulate. The heating unit may be installed in any position as long as it is capable of heating the composition in the circulation flow path including the pressure chamber 2 and the circulation flow path 3, and may be provided in the liquid jet head or the ink flow path, for example. When a heating unit is provided in the liquid jet head, the heating unit may be provided in either the pressure chamber or the circulation flow path. In addition, the ink jet device of this embodiment is preferably one in which the ink flow path or the ink tank is filled with the radiation curable ink jet composition.

[0100] As an example of an inkjet device, a perspective view of a serial printer is shown in Fig. 2. As shown in Fig. 2, the serial printer 20 includes a conveying unit 220 and a recording unit 230. The conveying unit 220 conveys the recording medium F fed to the serial printer to the recording unit 230, and ejects the recording medium after recording outside the serial printer. Specifically, the conveying unit 220 has feed rollers and conveys the fed recording medium F in the sub-scanning direction T1.

[0101] The recording unit 230 also includes an inkjet head 231 that ejects a composition onto the recording medium F sent from the conveying unit 220, a radiation source 232 that irradiates the deposited composition with radiation, a carriage 234 that carries these, and a carriage movement mechanism 235 that moves the carriage 234 in the main scanning directions S1 and S2 of the recording medium F.

[0102] In the case of a serial printer, an inkjet head 131 having a length smaller than the width of the recording medium is provided, and the head moves to perform recording in multiple passes (multi-pass). In addition, in a serial printer, the head 231 and radiation source 232 are mounted on a carriage 234 that moves in a predetermined direction, and the head moves with the movement of the carriage to eject the composition onto the recording medium. In this way, recording is performed in two or more passes (multi-pass). A pass is also called a main scan. A sub-scan is performed between passes to transport the recording medium. In other words, main scans and sub-scans are performed alternately.

[0103] Although FIG. 2 shows an embodiment in which the radiation source is mounted on the carriage, the present invention is not limited to this, and the radiation source may be one that is not mounted on the carriage.

[0104] Furthermore, the inkjet device of the present embodiment is not limited to the serial type printer, but may be the line type printer described above.

[0105] 4. Records The recorded matter of the present embodiment is obtained by adhering the radiation curable inkjet composition onto a recording medium and curing the composition. The composition has good flexibility and adhesion, and thus cracks and chips in the coating film can be suppressed when post-processing such as cutting or bending is performed. Therefore, the recorded matter of the present embodiment can be suitably used for signage and the like.

[0106] The material for 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, polyvinyl acetal, and the like, as well as plastics whose surfaces have been treated, glass, paper, metal, wood, and the like.

[0107] The form of the recording medium is not particularly limited, and examples include film, board, cloth, etc. EXAMPLES

[0108] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0109] 1. Preparation of Inkjet Composition First, the colorant, dispersant, and a portion of each monomer were weighed and placed in a pigment dispersion tank, and a ceramic bead mill with a diameter of 1 mm was 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 container for mixing, and mixed and stirred to completely dissolve, so as to obtain the composition shown in Table 1. The pigment dispersion obtained above was then added, and further mixed and stirred at room temperature for 1 hour, and further filtered through a 5 μm membrane filter to obtain a radiation-curable inkjet composition of each example. The numerical values ​​of each component shown in each example in the table represent mass % unless otherwise specified.

[0110] [Table 1]

[0111] The abbreviations and product components used in Table 1 are as follows:

[0112] <Monofunctional monomer> PEA (product name "Viscoat #192, manufactured by Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate") ·NVC (ISP Japan Co., Ltd., N-vinylcaprolactam) ACMO (Acryloylmorpholine, manufactured by KJ Chemicals Co., Ltd.) TBCHA (product name "SR217", manufactured by Sartomer Corporation, tert-butyl cyclohexanol acrylate) IBXA (Osaka Organic Chemical Industry, Ltd., isobornyl acrylate) DCPA (dicyclopentenyl acrylate, manufactured by Hitachi Chemical Co., Ltd.) <Polyfunctional Monomer> · VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, manufactured by Nippon Shokubai Co., Ltd.) DPGDA (product name "SR508", Sartomer Corporation, dipropylene glycol diacrylate) <Polymerization initiator> Irg.819 (product 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 material (pigment)> Titanium oxide (product name "CI Pigment White 6", manufactured by Tika) The silica particles (colloidal silica) used were commercially available colloidal silica, which was classified as necessary to have a volume average particle size of 90 nm. <Dispersant> Solsperse 36000 (polymeric dispersant, manufactured by Lubrizol).

[0113] In Table 1, the "monofunctional monomer ratio" in the physical properties column indicates the content of the monofunctional monomer relative to the total amount of the polymerizable compound. Specifically, the polymerizable compound refers to the monofunctional monomers and polyfunctional monomers in Table 1.

[0114] In Table 1, the "weighted average glass transition temperature" in the physical properties column indicates a weighted average of the glass transition temperatures of homopolymers of each polymerizable compound, with the content mass ratio of the polymerizable compound being used as the weight.

[0115] In Table 1, the "Viscosity at 40°C" in the physical properties column was measured using a viscoelasticity tester MCR-300 (manufactured by Pysica) in an environment of 40°C, by increasing the shear rate from 10 to 1000 and reading the viscosity at a shear rate of 200.

[0116] 2. Evaluation Method 2.1. Evaluation of curability A cotton swab weighted tackiness evaluation was carried out. Specifically, each radiation curable inkjet composition was applied to a PVC medium using a bar coater so that the coating thickness of the inkjet composition was 10 μm, and ultraviolet light was irradiated at a speed of 0.04 sec / cm with a predetermined irradiation intensity. In this case, an LED having a peak wavelength at 395 nm was used as the light source. The coating surface was then rubbed with a cotton swab, and the curability was evaluated based on the irradiation intensity at which the cotton swab was not colored. The evaluation criteria were as follows: A: Irradiation intensity is 0.5W / cm 2 less than B: Irradiation intensity is 0.5W / cm 2 More than 1.1W / cm 2 less than C: Irradiation intensity is 1.1 W / cm 2 More than 2.5W / cm 2 less than D: Irradiation intensity is 2.5W / cm 2 End

[0117] 2.2. Evaluation of shielding properties The ink composition obtained as described above was filled into an inkjet printer (product name "PX-G930", manufactured by Seiko Epson Corporation). Then, an image made of the ink composition was formed on a film (product name "Clearproof Film", manufactured by Seiko Epson Corporation, cut to A4 size). As the print pattern of the image, a solid fill pattern that could be printed at a duty of 100% with a resolution of 720 dpi horizontally and 720 dpi vertically was formed.

[0118] The images obtained as described above were subjected to integration of transmitted light from wavelengths of 380 to 800 nm using a goniochromatic colorimeter (product name "ARM-500V", manufactured by JASCO Corporation). The evaluation criteria are as follows. A: Less than 300 B: 300 or more and less than 350 C: 350 or more and less than 500 D: 400 or more and less than 500 E: 500 or more

[0119] 2.3. Flexibility Assessment Each radiation-curable inkjet composition was applied to a vinyl chloride film (JT5829R, manufactured by MACtac) with 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 MPa 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 width and 8 cm length to prepare a test piece. The flexibility of each test piece was measured using a tensile tester (TENSILON, manufactured by ORIENTEC). The elongation was the value at the point where a crack occurred when pulled at 5 mm / min. The value was calculated by {(length at crack - length before stretching) / length before stretching x 100}. The evaluation criteria are as follows: (Evaluation Criteria) A: 300% or more B: 250% or more but less than 300% C: 200% or more but less than 250% D: 100% or more but less than 200% E: Less than 100%

[0120] 2.4.Evaluation of adhesion A cured coating film was prepared on each film in the same manner as in the evaluation of flexibility above, except that a polypropylene board (manufactured by Coroplast) and a polyethylene terephthalate film (manufactured by Toray Industries, Inc.) were used as the recording medium. The obtained coating films were evaluated by a cross-cut test in accordance with JIS K5600-5-6.

[0121] More specifically, the blade of a cutting tool was applied perpendicular to the coating film with a cutter, and a grid of 10 x 10 grids was created with a grid of 1 mm spacing between the cuts. A transparent adhesive tape (25 mm wide) of about 75 mm in length was applied to the grid, and the tape was rubbed with a finger sufficiently so that the cured film could be seen through. Next, within 5 minutes of applying the tape, the tape was peeled off from the cured film at an angle close to 60° in 0.5 to 1.0 seconds, and the state of the grid was visually observed. The evaluation criteria are as follows. (Evaluation Criteria) A: No peeling of the cured film was observed on the lattice 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 on either the polypropylene film or the polyethylene terephthalate film. C: Peeling of the cured film was observed in less than 50% of the lattice for both the polypropylene film and the polyethylene terephthalate film. D: Peeling of the cured film was observed in 50% or more of the lattice on either the polypropylene film or the polyethylene terephthalate film. E: Peeling of the cured film was observed in more than 50% of the lattice for both the polypropylene film and the polyethylene terephthalate film.

[0122] 2.5. Evaluation of abrasion resistance The cured coating film prepared in the above flexibility evaluation was subjected to a micro-scratch test in accordance with JIS R3255. For the measurement, an ultra-thin film scratch tester (CSR-5000, Nanotech) was used to measure the load capacity as abrasion resistance. The load capacity was determined by performing micro-scratching while applying a load, and the load was determined as the load when the stylus reached the media surface. The higher the load capacity, the better the abrasion resistance. The measurement was performed with a stylus diameter of 15 μm, amplitude of 100 μm, and scratch speed of 10 μm / sec. The evaluation criteria were as follows: (Evaluation Criteria) A: 30mN / cm 2 End B: 25mN / cm 2 More than 30mN / cm 2 less than C: 20mN / cm 2 More than 25mN / cm 2 less than D: 20mN / cm 2 less than

[0123] 2.6.Discharge stability The ink compositions of the examples and comparative examples were evaluated for ejection stability as the reliability of the inkjet device (printer). First, an inkjet printer PX-G930 (Seiko Epson Corporation) equipped with a circulation head and an inkjet printer PX-G930 (Seiko Epson Corporation) equipped with a non-circulation head having no circulation flow path were prepared. More specifically, the circulation head shown in Figures 2 and 5 of JP 2018-103602 A was used as the circulation head.

[0124] Each ink composition was filled into each inkjet printer and set in the printer. Then, the head temperature was set to 45°C, and a plurality of test patterns were continuously printed for 1 hour under an external environmental temperature of 25°C, and the occurrence of ejection defects such as non-ejection in the nozzles of the head was confirmed. The ratio of the number of nozzles that had ejection defects to the total number of nozzles that had ejected was evaluated according to the following criteria. (Evaluation Criteria) A: The number of nozzles where ejection defects occurred was less than 1%. B: The number of nozzles where ejection defects occurred was 1% or more but less than 3%. C: The number of nozzles where ejection defects occurred was 3% or more but less than 5%. D: 5% or more nozzles have discharge problems

[0125] 3. Evaluation results The composition and evaluation results of the radiation-curable inkjet composition used in each example are shown in Table 1. As can be seen from Table 1, the radiation-curable inkjet compositions of Examples 1 to 11, which contain titanium oxide as a white colorant, contain 90 mass% or more of a monofunctional monomer relative to the total amount of polymerizable compounds, and have a weighted average of the glass transition temperatures of homopolymers of each polymerizable compound of 48°C or higher, with the weight being the content mass ratio of each polymerizable compound, were evaluated to have good levels of shielding property, flexibility, adhesion, and abrasion resistance.

[0126] In detail, when comparing each Example with Comparative Example 1, it is found that the flexibility and adhesion are improved by the ratio of monofunctional monomers to the total monomers being 90 mass% or more. Also, when comparing each Example with Comparative Example 2, it is found that the scratch resistance is further improved when the weighted average of the glass transition temperature is 48°C or more. Furthermore, when comparing each Example with Comparative Example 3, it is found that the problem of reduced flexibility and adhesion does not occur when no white coloring material is included. Also, Comparative Example 3 did not have shielding properties. Furthermore, when comparing each Example with Comparative Example 4, it is found that sufficient shielding properties cannot be obtained when silica, which is a white coloring material other than titanium oxide, is used.

[0127] Furthermore, evaluation of the ejection stability of each example showed that by using a circulating head, the ejection stability of the composition of this embodiment, which has flexibility, adhesion, and abrasion resistance, is improved compared to when a non-circulating head is used.

[0128] The circulation head used in the examples of the present invention has a communication passage 4 and generates a circulation flow by the pressure at which the composition is sprayed, but it may be of a type that generates a circulation flow by a pressure difference due to a head pressure difference or the like within the circulation flow path 3. Also, a circulation head of a type that does not have a communication passage 4 and in which the pressure chamber 2 and the nozzle 1 are directly connected may be used, and the same effects as in this example are achieved when such a type of circulation head is used.

[0129] In the embodiments of the present invention, the composition was heated by heating the liquid ejection head itself, but it is sufficient to heat the composition in the circulation flow path. For example, in cases where the circulation flow path passes outside the head, the same effect can be achieved by heating the circulation flow path outside the head without heating the head. [Explanation of symbols]

[0130] 1... nozzle, 2... pressure chamber, 3... circulation flow path, 4... communication path, 10... liquid jet head, 20... serial printer, 220... transport section, 230... recording section, 231... ink jet head, 232, 233... light source, 234... carriage, 235... carriage movement mechanism, F... recording medium, S1, S2... main scanning direction, T1... sub-scanning direction

Claims

1. A polymerizable compound including a monofunctional monomer and a polyfunctional monomer; A photopolymerization initiator; Contains titanium oxide as a white coloring material, The content of the monofunctional monomer is 90% by mass or more based on the total amount of the polymerizable compound, a weighted average of glass transition temperatures of homopolymers of the polymerizable compounds, the weight being determined by the content mass ratio of each of the polymerizable compounds, is 48° C. or higher; The polyfunctional monomer contains a vinyl ether group-containing (meth)acrylate represented by the following formula (1): CH 2 =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, R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. the content of the polyfunctional monomer is 1 to 8% by mass based on the total amount of the polymerizable compound; the content of the titanium oxide is 15% by mass or more and 30% by mass or less with respect to the total amount of the radiation curable ink jet composition, The monofunctional monomer includes a nitrogen-containing monofunctional monomer including a monomer having a nitrogen-containing heterocyclic structure, and a monofunctional (meth)acrylate having a crosslinked condensed ring structure. Radiation curable ink jet compositions.

2. The monofunctional (meth)acrylate having a bridged condensed ring structure includes dicyclopentenyl (meth)acrylate. The radiation curable ink jet composition according to claim 1.

3. 3. An inkjet method using a liquid ejecting head comprising: a nozzle for ejecting the radiation curable inkjet composition according to claim 1 or 2; a pressure chamber to which the radiation curable inkjet composition is supplied; and a circulation flow path for circulating the radiation curable inkjet composition in the pressure chamber, a discharge step of discharging the heated radiation curable ink jet composition from the liquid ejection head and depositing the composition on a recording medium; an irradiation step of irradiating the radiation curable ink jet composition attached to the recording medium with radiation, Inkjet method.

4. a heating step of heating the radiation curable ink jet composition in the liquid jet head to 40° C. or higher; The ink-jet method according to claim 3.

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