JPWO2016088703A1 - Primer, ink set and image forming method - Google Patents

Abstract

An object of the present invention is to provide a primer that has high adhesion to a recording medium, high photocurability, and hardly causes curling of the recording medium even when cured. The above object is a primer that is cured by irradiation with active energy rays, which contains a tri- or higher functional (meth) acrylate, a vinyl ether compound having two or more vinyl ether groups, and a photoinitiator. This primer is achieved by a primer containing (meth) acrylate in an amount of 10% by mass to 50% by mass and a vinyl ether compound in an amount of 3% by mass to 40% by mass with respect to the total mass of the primer.

Description

  The present invention relates to a primer, an ink set, and an image forming method.

  The ink jet recording method is used in various printing fields because it can form an image easily and inexpensively. As one of the ink jet recording methods, droplets of an ink jet ink composition (hereinafter also simply referred to as “ink jet ink”) having a property of being cured by irradiation with active energy rays are landed on a recording medium, and then active energy rays are used. There is a method of forming an image by irradiating and curing the ink-jet ink. When the active energy ray-curable inkjet ink composition is used, an image having high scratch resistance and adhesion can be formed even on a non-absorbing recording medium having no ink absorbability.

  In recent years, in order to further improve the adhesion of the ink to the non-absorbing recording medium, the primer which has adhesion to both the recording medium and the inkjet ink and is cured by irradiation with energy rays (hereinafter simply referred to as “primer”). ") Has been developed. In this method, a primer layer formed by adhering a primer composition to a recording medium is formed, and an ink jet ink is landed thereon and cured to form an ink layer.

  For example, Patent Document 1 optionally includes a monomer containing a monofunctional monomer and 2-hydroxy-3-phenoxypropyl acrylate, and having an oxetane group, an oxirane group or a vinyl ether group and a (meth) acryl group in the molecule. Have been disclosed. Patent Document 2 contains at least one adhesion promoting component selected from the group consisting of an N-vinyl lactam compound, an acrylamide compound and an N-vinylamide compound, and 2-hydroxy-3-phenoxypropyl acrylate. Primers are disclosed. According to Patent Documents 1 and 2, by using these primer inks to form a primer layer, the fixability and drawability (color unevenness and line width) of an image recorded with an inkjet ink on a non-permeable recording medium (Characteristics related to image quality such as non-uniformity).

JP 2013-119585 A JP 2012-140615 A

  As described in the cited documents 1 and 2, the primer is required to have adhesion to a recording medium as a base material. On the other hand, since a primer is hardened | cured by superposition | polymerization of the photopolymerizable compound by light irradiation, it is calculated | required that photocurability is high. Further, the primer is also required to be less likely to curl the recording medium due to large shrinkage of the primer due to photocuring in the state of being in close contact with the recording medium.

  In view of the above problems, the present invention provides a primer that has high adhesion to a recording medium, high photocurability, and hardly causes curling of the recording medium even when cured in a state of being in close contact with the recording medium. It is an object of the present invention to provide an ink set including a primer and an image forming method using such a primer.

In view of the above problems, the first of the present invention relates to the following primers.
[1] A primer that is cured by irradiation with an active energy ray, comprising a tri- or higher-functional (meth) acrylate, a vinyl ether compound having two or more vinyl ether groups, and a photoinitiator, On the other hand, the primer which contains the said (meth) acrylate in the quantity of 10 to 50 mass% and the said vinyl ether compound in the quantity of 3 to 40 mass%.
[2] The trifunctional or higher functional (meth) acrylates are trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipenta The primer according to [1], which is at least one selected from the group consisting of erythritol penta (meth) acrylate and dipentaerythritol hexa (meth) acrylate.
[3] The primer according to [1] or [2], wherein the vinyl ether compound has at least one selected from the group consisting of an ethylene oxide group, a propylene oxide group, and an ester group.

The second aspect of the present invention relates to the following ink set.
[4] An ink set comprising the primer according to any one of [1] to [3] and an inkjet ink that is cured by being irradiated with active energy rays.

The third aspect of the present invention relates to the following image forming method.
[5] A step of attaching the primer according to any one of [1] to [3] on a recording medium, a step of irradiating the primer attached on the recording medium with an active energy ray to form a primer layer, A step of ejecting ink droplets of an ink jet ink that is cured by irradiation with an active energy ray to land on the primer layer, and an ink jet ink that is irradiated with active energy rays And a step of forming an image formed by curing.
[6] At least a portion of the recording medium on which an image is to be formed is a non-absorbing recording medium composed of at least one selected from the group consisting of polypropylene, polyethylene, and polyethylene terephthalate. , [5] The image forming method.

  According to the present invention, a primer having high adhesion to a recording medium, high photocurability, and hardly causing curling of the recording medium even when cured in a state of being in close contact with the recording medium, and an ink including such a primer Sets and imaging methods using such primers are provided.

1. Primer The primer of the present invention contains a trifunctional or higher functional (meth) acrylate, a vinyl ether compound having two or more vinyl ether groups, and a photoinitiator. The primer of the present invention comprises 10% by mass to 50% by mass of a tri- or higher functional (meth) acrylate, 3% by mass to 40% by mass of a vinyl ether compound having two or more vinyl ether groups, based on the total mass of the primer. Contains in the following amounts. In the present invention, “(meth) acryl” means one or both of “acryl” and “methacryl”, “(meth) acrylate” means one or both of “acrylate” and “methacrylate”, “(Meth) acryloyl” means one or both of “acryloyl” and “methacryloyl”.

[Trifunctional or higher (meth) acrylate]
The primer of the present invention contains a tri- or higher functional (meth) acrylate. The trifunctional or higher functional (meth) acrylate means a compound having three or more (meth) acryloyl groups in the molecule. As a result, the adhesion of the primer layer to a recording medium, particularly a non-absorbing recording medium composed of plastic (hereinafter also simply referred to as “plastic substrate”) is enhanced, and the photocurability of the primer is enhanced. be able to. This is considered to be due to the following reasons. Trifunctional or higher (meth) acrylates have low polarity. Since the primer of the present invention contains such a low polarity compound, it has a high affinity for a plastic substrate composed of a low polarity material. Therefore, the adhesion between the plastic substrate and the primer layer obtained by curing the primer of the present invention is also increased. Trifunctional or higher (meth) acrylates are polyfunctional and thus have excellent photocurability. In addition, when a tri- or higher functional (meth) acrylate is used, a crosslinking site is likely to occur when cured. Therefore, the primer layer obtained by curing or semi-curing the primer of the present invention has higher hardness and more It can adhere firmly. The primer of the present invention may contain only one kind of tri- or more functional (meth) acrylate or two or more kinds.

  The content of the trifunctional or higher functional (meth) acrylate is 10% by mass or more and 50% by mass or less with respect to the total mass of the primer. By adjusting the content of the trifunctional or higher (meth) acrylate to 10% by mass or more based on the total mass of the primer, the adhesion of the primer layer to the plastic substrate and the curability of the primer are enhanced. Also, by setting the content of trifunctional or higher (meth) acrylate to 50% by mass or less based on the total mass of the primer, the trifunctional or higher functional (meth) acrylate is excessively cross-linked and the primer layer shrinks. This suppresses curling of the recording medium. From the viewpoint of further improving the adhesion, the content of the trifunctional or higher functional (meth) acrylate in the primer of the present invention is preferably 30% by mass or more and 40% by mass or less with respect to the total mass of the primer.

  Examples of tri- or higher functional (meth) acrylates include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, and PO-modified trimethylolpropane tri (meth). Acrylate, pentaerythritol tetra (meth) acrylate, EO-modified pentaerythritol tetra (meth) acrylate, PO-modified pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylol Propane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, caprolactone-modified trimethylolpropane tri (meth) acrylate DOO, include pentaerythritol ethoxy tetra (meth) acrylate and caprolactam modified dipentaerythritol hexa (meth) acrylate.

  Among these, a compound having a trimethylolethane structure, a trimethylolpropane structure, a pentaerythritol structure or a dipentaerythritol structure has a high affinity for a plastic substrate having a low polarity because the entire compound has a low polarity. Therefore, by using a tri- or higher functional (meth) acrylate having a trimethylolethane structure, a trimethylolpropane structure, a pentaerythritol structure or a dipentaerythritol structure, the adhesion of the primer layer to the plastic substrate is further increased.

  Examples of preferred compounds having a trimethylolethane structure, a trimethylolpropane structure, a pentaerythritol structure or a dipentaerythritol structure include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, ditrimethylolpropane tetra (meta ) Acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and the like.

[Vinyl ether compound having two or more vinyl ether groups]
The primer of the present invention contains a vinyl ether compound having two or more vinyl ether groups. As a result, the adhesion between the primer layer and the ink layer is enhanced, and curling of the recording medium is suppressed. This is considered to be due to the following reasons. That is, when the vinyl ether compound has two or more vinyl ether groups in the same molecule, one of the vinyl ether groups is hardly used for polymerization and may remain unreacted after curing. Since the vinyl ether group has a polarity, this unreacted vinyl ether group is easily removed from the non-polar primer layer, near the cured film of the primer layer, that is, near the surface on the side that comes into contact with the active energy ray-curable inkjet ink later. Easy to exist. Because the vinyl ether group collected near the surface increases the polarity near the surface of the primer layer, the polarity between the functional group having the polarity of the compound contained in the active energy ray-curable inkjet ink and the vicinity of the surface of the primer layer is increased. Thus, a relatively loose bond such as a hydrogen bond or van der Waals bond is generated, and the adhesion between the primer layer and the active energy ray-curable inkjet ink is enhanced. The primer of the present invention may contain only one kind of vinyl ether compound having two or more vinyl ether groups, or may contain two or more kinds.

  Moreover, although the reactivity of a vinyl ether group is comparatively high, it is lower than the reactivity of a (meth) acryloyl group. Therefore, when the primer of the present invention is cured or semi-cured, excessive polymerization or cross-linking formation due to the (meth) acryloyl group of a tri- or higher-functional (meth) acrylate can be inhibited by an unreacted vinyl ether group. . Thereby, it is suppressed that the primer layer shrinks due to excessive cross-linking by the (meth) acryloyl group and the curling is generated on the recording medium.

  Content of the vinyl ether compound which has a 2 or more vinyl ether group is 3 to 40 mass% with respect to the total mass of a primer. By setting the content of the vinyl ether compound having two or more vinyl ether groups to 3% by mass or more based on the total mass of the primer, the adhesion to the ink layer is increased without reducing the adhesion to the plastic substrate. In addition, curling of the recording medium when the primer layer is formed is suppressed. In addition, since the content of the vinyl ether compound having two or more vinyl ether groups is 40% by mass or less with respect to the total mass of the primer, polymerization or crosslinking of a tri- or higher functional (meth) acrylate is not inhibited too much. , The curability of the primer is sufficient. The content of the vinyl ether compound having two or more vinyl ether groups is preferably 10% by mass or more and 35% by mass or less, more preferably 20% by mass or more and 35% by mass or less with respect to the total mass of the primer. More preferably, the content is 30% by mass or more and 35% by mass or less.

Examples of vinyl ether compounds having two or more vinyl ether groups include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butylene glycol divinyl ether. , Hexanediol divinyl ether, cyclohexane dimethanol divinyl ether, divinyl ethers such as bisphenol A alkylene oxide divinyl ether and bisphenol F alkylene oxide divinyl ether, and trimethylol ethane trivinyl ether, trimethylol propane trivinyl ether, ditrimethylol propane tetra Vinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol hexavinyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added trimethylolpropane trivinyl ether, ethylene oxide-added ditrimethylolpropane tetravinyl ether, With propylene oxide-added ditrimethylolpropane tetravinyl ether, ethylene oxide-added pentaerythritol tetravinyl ether, propylene oxide-added pentaerythritol tetravinyl ether, ethylene oxide-added dipentaerythritol hexavinyl ether and propylene oxide They include polyfunctional vinyl ethers such as dipentaerythritol hexa ether.

  Among these, a compound having a trimethylolethane structure, a trimethylolpropane structure, a pentaerythritol structure or a dipentaerythritol structure has a high affinity for a plastic substrate having a low polarity because the entire compound has a low polarity. Therefore, by using a vinyl ether compound having two or more vinyl ether groups having a trimethylolethane structure, a trimethylolpropane structure, a pentaerythritol structure or a dipentaerythritol structure, the vinyl ether present on the plastic substrate side in the primer layer A primer in which a relatively loose bond such as a hydrogen bond or van der Waals bond as described above occurs between the functional group having a low polarity in the compound and the plastic substrate, and the primer of the present invention is cured. It is considered that the adhesion of the layer to the plastic substrate is further increased.

  In addition, in a compound having a polar structure, such as an ethylene oxide group, a propylene oxide group, and an ester group, the polar structure is likely to be eliminated in the upper layer of the primer layer. A loose bond is formed between the polar structure and the functional group having polarity in the compound contained in the active energy ray-curable inkjet ink and the vicinity of the surface of the primer layer, so that the primer layer and the ink layer are separated from each other. The adhesion between them is further increased. Therefore, by using a vinyl ether compound having two or more vinyl ether groups having an ethylene oxide group, a propylene oxide group or an ester group, the adhesion between the primer layer and the active energy ray-curable inkjet ink is further increased.

  Examples of vinyl ether compounds having two or more vinyl ether groups having ethylene oxide groups include ethylene oxide-added trimethylolpropane trivinyl ether, ethylene oxide-added ditrimethylolpropane tetravinyl ether, ethylene oxide-added pentaerythritol tetravinyl ether, and ethylene oxide-added divinyl ether. Pentaerythritol hexavinyl ether and the like are included.

  Examples of vinyl ether compounds having two or more vinyl ether groups having propylene oxide groups include propylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added ditrimethylolpropane tetravinyl ether, propylene oxide-added pentaerythritol tetravinyl ether, and propylene oxide-added divinyl ether. Pentaerythritol hexavinyl ether and the like are included.

  The vinyl ether compound having two or more vinyl ether groups having an ester group may be a monomer or an oligomer. Examples of the monomer include compounds STERVE-1 to 8 shown below. EsterVE-1 to -5 are commercially available from Sigma Aldridge as VEctomer 4010, VEctomer 4020, VEctomer 4040, VEctomer 4060, and VEctomer 5015, respectively. Examples of the oligomer include those commercially available from Nippon Carbide as the Crossmer U series.

  By setting the content of the vinyl ether compound having two or more vinyl ether groups having an ethylene oxide group, a propylene oxide group or an ester group to 10% by mass or more and 35% by mass or less based on the total mass of the primer, The adhesion between the primer layer and the ink layer can be further improved without reducing the adhesion between the primer layer obtained by curing the primer and the recording medium. The content of the vinyl ether compound having two or more vinyl ether groups having an ethylene oxide group, a propylene oxide group or an ester group is more preferably 20% by mass or more and 35% by mass or less with respect to the total mass of the primer.

[Other photopolymerizable compounds]
The primer of the present invention may further contain other photopolymerizable compounds as long as the effects of the present invention are obtained. Examples of other photopolymerizable compounds include bifunctional (meth) acrylates and radical polymerizable compounds including a vinyl ether compound having only one vinyl ether group in the molecule, and epoxy compounds, vinyl ether compounds, and oxetane compounds. And other cationically polymerizable compounds. The photopolymerizable compound other than the above may be a monomer, oligomer, polymer, or a mixture thereof. The primer of the present invention may contain only one type of photopolymerizable compound other than the above, or may contain two or more types.

Examples of bifunctional or lower (meth) acrylates include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomyristyl (meth) acrylate, iso Stearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate , Methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl ( Acrylate), tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2 -Acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible (meth) acrylate and t-butylcyclohexyl (meth) acrylate Monofunctional (meth) acrylates such as triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,4-butanedio 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, Bifunctional (meth) acrylates such as PO adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate hydroxypivalate, and polytetramethylene glycol di (meth) acrylate are included.

  Examples of vinyl ether compounds having only one vinyl ether group in the molecule include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl Vinyl ether, cyclohexyl methyl vinyl ether, 4-methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxy Ethyl vinyl ether, methoxypo Ethylene glycol vinyl ether, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether Chloroethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxypolyethylene glycol vinyl ether, and the like.

[Photoinitiator]
The primer of the present invention contains a photoinitiator. The photoinitiator (photopolymerization initiator) in the present invention is a polymerization of a photopolymerizable compound (trifunctional or higher functional (meth) acrylate, vinyl ether compound having two or more vinyl ether groups and other photopolymerizable compounds) by light. As photoinitiators, all known light published in “Applications and Markets of UV / EB Curing Technology” (CMC Publishing Co., Ltd., edited by Yoneho Tabata, edited by Radtech Research Association), etc. An initiator can be used. The photoinitiator is preferably a radical polymerization initiator, but may further contain a cationic polymerization initiator. The primer of the present invention may contain only one kind of photoinitiator or two or more kinds.

  The radical polymerization initiator contained in the primer of the present invention may be either a molecular cleavage type polymerization initiator or a hydrogen abstraction type polymerization initiator.

  Examples of molecular cleavage type radical polymerization initiators include benzoin isobutyl ether, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, benzyl, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-benzyl-2-dimethyl. Amino-1- (4-morpholinophenyl) -butan-1-one, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, bis (2,4,6-trimethylbenzoyl)- Phenylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2 -Methyl Pan-1-one, 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one and 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl -1-propan-1-one and the like are included.

  Examples of the hydrogen abstraction type radical polymerization initiator include benzophenone, 4-phenylbenzophenone, isophthalphenone, 4-benzoyl-4′-methyl-diphenyl sulfide, and bis (2,4-cyclohexane) which is a metallocene type polymerization initiator. Pentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium, an oxime ester type polymerization initiator 1,2-octanedione, 1- ( 4- (phenylthio) -2- (O-benzoyloxime)), ethanone and 1- (9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl) -1- (O-acetyloxime ) Etc. are included.

Examples of cationic polymerization initiators include B (C ₆ F ₅ ) ⁴⁻ , PF ⁶⁻ , AsF ⁶⁻ , SbF ⁶⁻ or CF ₃ SO of aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium and phosphonium. ^3- Salts, sulfonates that generate sulfonic acid, halides that generate hydrogen halide, and iron allene complexes are included.

  The content of the photoinitiator is preferably 0.1 to 20% by mass and more preferably 1 to 12% by mass with respect to the total mass of the primer.

[Other additives]
The primer of the present invention is a sensitizer, a radical polymerization inhibitor, a cationic polymerization inhibitor, a colorant, a pigment dispersant, an organic solvent, a surfactant, and other additives as long as the effects of the present invention are obtained. Contains lubricants, fillers, antifoaming agents, gelling agents, thickeners, specific resistance adjusting agents, film forming agents, UV absorbers, antioxidants, anti-fading agents, anti-fouling agents and rust-proofing agents. Also good.

  Examples of sensitizers include trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzylamine and 4,4. Examples include amines that do not cause an addition reaction with a photopolymerizable compound, such as' -bis (diethylamino) benzophenone.

  Examples of radical polymerization inhibitors include phenolic hydroxyl group-containing compounds, quinones or hydroquinones, phenothiazines, N-oxyls, aromatic amines or phenylenediamines, imines, sulfonamides, oximes, hydroxylamines, urea derivatives (eg urea Or thiourea), phosphorus-containing compounds (eg triphenylphosphine, triphenylphosphite, hypophosphorous acid, trinonyl phosphite, triethylphosphite or diphenylisopropylphosphine), sulfur-containing compounds (eg diphenyl sulfide, phenothiazine) and Sulfur-containing natural substances (for example, cysteine) and the like are included.

  Examples of the cationic polymerization inhibitor include amines such as alkanolamines, N, N-dimethylalkylamines, N, N-dimethylalkenylamines and N, N-dimethylalkynylamines.

  The colorant can be a dye or a pigment.

  Examples of pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow and pyrazolone red, soluble azo pigments such as ritole red, heliobordeaux, pigment scarlet and permanent red 2B, alizarin, indanthrone and Derivatives from vat dyes such as thioindigo maroon, phthalocyanine organic pigments such as phthalocyanine blue and phthalocyanine green, quinacridone organic pigments such as quinacridone red and quinacridone magenta, perylene organic pigments such as perylene red and perylene scarlet, isoindo Isoindolinone-based organic pigments such as linone yellow and isoindolinone orange, and pylanthrone such as pyranslon red and pyranslon orange Organic pigments such as organic pigments, thioindigo organic pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments such as quinophthalone yellow, and isoindoline organic pigments such as isoindoline yellow, and flavanthron yellow, Inorganic pigments such as acylamide yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet, carbon black, titanium oxide and calcium carbonate are included.

Examples of the dyes include MS Magenta VP, MS Magenta HM-1450 and MS Magenta HSo-147 manufactured by Mitsui Toatsu Co., AIZEN SOT Red-1, AIZEN SOT Red-2, AIZEN SOT Red-3 manufactured by Hodogaya Chemical Co., Ltd. AIZEN SOT Pin-1 and SPIRONRED GEH SPECIAL, Bayer Japan RESOLIN Red FB 200%, MACROLEX Red Violet R and MACROEXROT5B, Nippon Kayaku Kayase Red 80, Kayase Red 80, Kayase Red 130 PHLOXIN, ROSE BENGAL, ACID Red, Mitsubishi Kasei HSR-31, DIARESINRed K Magenta dye of OilRed such as manufactured by BASF Japan Ltd. in beauty,
MS Cyan HM-1238, MS Cyan HSo-16, Cyan HSo-144 and MS Cyan VPG, AIZEN SOT Blue-4 manufactured by Hodogaya Chemical Co., Ltd., RESOLIN BR. Manufactured by Bayer Japan. Blue BGLN 200%, MACROLEX Blue RR, CERES Blue GN, SIRIUS SUPRATURQ. BlueZ-BGL and SIRIUS SUPRATURQ. Blue FB-LL 330%, KAYASET Blue FR, KAYASET Blue N, KAYASET Blue 814, Turq. BlueGL-5 200 and LightBlue BGL-5 200, Daiwa Kasei DAIWA Blue 7000 and Oleosol Fast Blue GL, Mitsubishi Kasei DIARESIN Blue P and BASF Japan SUDAN Blue 80B ONE 80E Cyan dyes, etc.
MS Yellow HSm-41, Yellow KX-7 and Yellow EX-27 (Mitsui Toatsu) manufactured by Mitsui Toatsu, AIZEN SOT Yellow-1, AIZEN SOT YellowW-3 and AIZEN SOT Yellow-6 manufactured by Hodogaya Chemical Co., Ltd. MACROLEX Yellow 6G and MACROLEX FLUOR. Yellow 10GN, KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow A-G and KAYASET Yellow E-G, manufactured by Nippon Kayaku Co., Ltd., DAIWA Yellow 330HB, manufactured by Daiwa Kasei Co., Ltd. 146 and NEOPEN Yellow 075, etc., and MS Black VPC manufactured by Mitsui Toatsu, AIZEN SOT Black-1 and AIZEN SOT Black-5 manufactured by Hodogaya Chemical Co., and RESORIN Black GSN 200% manufactured by Bayer Japan RESOLIN BlackBS, KAYASET Black A-N manufactured by Nippon Kayaku Co., Ltd., D manufactured by Daiwa Kasei Co., Ltd. Oil-soluble dyes such as AIWA Black MSC, HSB-202 manufactured by Mitsubishi Kasei Co., Ltd., NEPTUNE BlackX60 and NEOPEN BlackX58 manufactured by BASF Japan are included.

  Of these, pigments are preferred because they have good dispersibility with respect to the constituent components of the primer of the present invention and are excellent in weather resistance.

  The content of the color material can be arbitrarily set within a range in which the effect of the present invention can be obtained. The coloring material may not be substantially contained in the primer of the present invention, and can be, for example, less than 0.1% by mass with respect to the total mass of the primer.

  Examples of pigment dispersants include hydroxyl group-containing carboxylic acid esters, salts of long chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long chain polyaminoamides and polar acid esters, high molecular weight unsaturated acids. Ester, polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalenesulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxy Ethylene nonylphenyl ether, stearylamine acetate, pigment derivatives and the like are included.

  Examples of the organic solvent include ester solvents, ether solvents, ether ester solvents, ketone solvents, aromatic hydrocarbon solvents, nitrogen-containing organic solvents, and the like.

  Examples of surfactants include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates and fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols and polyoxy Nonionic surfactants such as ethylene / polyoxypropylene block copolymers, cationic surfactants such as alkylamine salts and quaternary ammonium salts, and silicone-based and fluorine-based surfactants are included.

  Among these, when the primer of the present invention contains a silicone-based or fluorine-based surfactant, when printing on a recording medium made of a hydrophobic resin such as a vinyl chloride sheet or a recording medium that absorbs slowly such as printing paper. , Primer mixing can be suppressed, and high-quality printing is possible.

  Examples of the silicone-based surfactant include polyether-modified polysiloxane compounds, specifically, KF-351A, KF-352A, KF-642 and X-22-4272 manufactured by Shin-Etsu Chemical, BYK307 manufactured by Big Chemie. , BYK345, BYK347 and BYK348, and TSF4452 manufactured by Toshiba Silicone Co., Ltd. are included.

  The fluorine-based surfactant means a compound in which a part or all of the surfactant is substituted with fluorine in place of hydrogen bonded to carbon of the hydrophobic group of a normal surfactant. Examples of fluorosurfactants include Megafac F from DIC, Surflon from Asahi Glass, Fluorad FC from Minnesota Mining and Manufacturing Company, Monflor, manufactured by Imperial Chemical Industry, Zonyls, manufactured by EI Dupont Nemeras & Company, Licowet VPF, manufactured by Rubevelke Hoechst, and footers manufactured by Neos Gents etc. are included.

  The surfactant content is preferably 0.001% by mass or more and less than 1.0% by mass with respect to the total mass of the primer.

[Physical properties]
When the primer of the present invention has a viscosity at 25 ° C. of 10 m · pas or more and 500 m · pas or less, handling such as ease of spreading when coated with a bar coder or the like is further improved. As the viscosity of the primer of the present invention, a value measured using a commercially available rotational viscometer (for example, R500 rotational viscometer manufactured by Toki Sangyo Co., Ltd.) can be used. The viscosity of the primer of the present invention can be adjusted by selecting a photopolymerizable compound or changing the blending ratio.

[Preparation method]
The primer of the present invention can be prepared by stirring and dissolving a tri- or higher functional (meth) acrylate, a vinyl ether compound having two or more vinyl ether groups, a photoinitiator and other additives while heating. . Specifically, the primer of the present invention can be prepared by putting these materials in a stainless beaker and stirring and dissolving for 1 hour while heating on a hot plate at 65 ° C.

[Usage]
The primer of the present invention is applied or printed on a recording medium, and then cured or semi-cured by irradiating active energy rays such as ultraviolet rays to form a primer layer. The recording medium and the active energy ray curable inkjet ink By adhering to both, an image having high adhesion can be formed. In particular, the primer of the present invention can be suitably used when an image having high adhesion is formed on a non-absorbent recording medium composed of a plastic substrate.

2. Ink Set When the primer of the present invention is attached to a recording medium by an inkjet method, the primer of the present invention can be combined with an inkjet ink to form an ink set. The ink set means a combination of the primer of the present invention and the inkjet ink configured to be installed in the inkjet recording apparatus to form an image. Examples of ink sets include those in which the primer and ink jet ink of the present invention are individually stored in a plurality of ink cartridges, or a plurality of ink storage portions are integrally configured, and the ink storage portions of the present invention are integrally formed. An ink cartridge containing a primer and inkjet is included. The ink set of the present invention may contain a combination of a plurality of inkjet inks that can apply or print different colors depending on the type of image to be formed.

  The inkjet ink is not particularly limited, and a known inkjet ink can be used. The inkjet ink contains, for example, a photopolymerizable compound, a photoinitiator, a coloring material, or other additives as necessary.

  Examples of the photopolymerizable compound that the inkjet ink can contain include radically polymerizable compounds such as (meth) acrylate and vinyl ether compounds, and cationically polymerizable compounds such as epoxy compounds, vinyl ether compounds, and oxetane compounds. It is. These compounds may be monomers, oligomers, polymers or mixtures thereof.

  When the inkjet ink contains a radically polymerizable compound as a photopolymerizable compound, it can contain a radical polymerization initiator as a photoinitiator. When the inkjet ink contains a cationically polymerizable compound as a photopolymerizable compound, it can contain a photoacid generator as a photoinitiator.

  The coloring material that can be contained in the ink-jet ink can be a dye or a pigment, but is preferably a pigment because it has good dispersibility with respect to other components of the ink-jet ink and is excellent in weather resistance.

  Examples of other additives include crosslinking accelerators, sensitizers, radical polymerization inhibitors, cationic polymerization inhibitors, pigment dispersants, organic solvents, surfactants, lubricants, fillers, antifoaming agents, gelling agents. , Thickeners, specific resistance adjusting agents, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifouling agents, rust preventives and the like.

  Examples of the photopolymerizable compound, photoinitiator, colorant, and other additives that can be contained in the inkjet ink can be used for the primer of the present invention as long as it can be used as an inkjet ink. Included are the compounds or products exemplified.

[Physical properties of inkjet ink]
The surface tension of the inkjet ink is preferably 15 mN / m or more and less than 35 mN / m. If the surface tension of the ink-jet ink is 15 mN / m or more, it is difficult for the discharge capability to be lowered due to the area around the nozzles of the ink-jet head being wet. Further, if the surface tension of the ink-jet ink is less than 35 mN / m, whitening is unlikely to occur because the surface energy of the ink-jet ink is well wetted with a coated paper or resin recording medium lower than that of ordinary paper. The surface tension of the inkjet ink was measured using a commercially available surface tension meter (eg, Kyowa Interface Science Co., Ltd., surface tension meter FACE SURFACE TENSIOMETER CBVB-A3, etc.) using the Wilhelmy method (plate method) with a liquid temperature of 25 ° C. The value measured at 60% RH can be used. The surface tension of the inkjet ink can be adjusted by selecting a photocurable compound, changing the blending ratio of each component, or adding a surfactant.

  The viscosity of the inkjet ink is preferably 2 mPa · s or more and 50 mPa · s or less at 25 ° C., and in the temperature range of 20 ° C. or more and less than 100 ° C., which is the ink temperature when discharging from the inkjet head, 7 mPa · s or more and 15 mPa · s. It is more preferable that it can be s or less, more preferably 8 mPa · s or more and 13 mPa · s or less. As the viscosity of the inkjet ink, a value measured using a commercially available rotational viscometer (for example, R500 rotational viscometer manufactured by Toki Sangyo Co., Ltd.) can be used. The viscosity of the inkjet ink can be adjusted by selecting a photopolymerizable compound or changing the blending ratio.

  When a pigment is used as the color material, it is preferable that there is no gel-like substance having an average particle size exceeding 1.0 μm other than the pigment particles in the inkjet ink.

  In order to suppress the electrical corrosion of the inkjet ink inside the inkjet head, the conductivity of the inkjet ink is preferably 10 μS / cm or less. In a continuous type ink jet apparatus, it is necessary to adjust the electric conductivity with an electrolyte. In this case, the electric conductivity of the ink jet ink is preferably 0.5 mS / cm or more as necessary. The electric conductivity of the ink-jet ink can be determined by immersing two electrodes separated by a certain distance in the ink, applying a certain voltage between both electrodes, and measuring the value of the current flowing between the electrodes. The electrical conductivity of the inkjet ink can be adjusted by selecting a photopolymerizable compound, a polymerization initiator or a sensitizer, changing the blending ratio, or adjusting the water content of the inkjet ink.

  The calorific value per unit mass when inkjet DSC (Differential Scanning Calorimetry) measurement is performed in the range from 25 ° C. to −25 ° C. at a rate of 5 ° C. per minute of the ink jet ink is 10 mJ / mg or more. It is preferable not to show a peak. By setting it as such a structure, generation | occurrence | production of a gel or precipitation can be suppressed when an ink is preserve | saved at low temperature.

[Preparation method of inkjet ink]
The ink-jet ink can be produced by mixing various materials and well dispersing them using an ordinary dispersing machine such as a sand mill. When a pigment is used as the color material, a concentrated solution containing a high concentration pigment may be prepared in advance, and the concentrated solution may be diluted with a photopolymerizable compound. Even with a normal disperser such as a sand mill, the material can be sufficiently dispersed, does not require excessive dispersion energy, and does not require a long dispersion time. Can be prepared. The prepared ink is preferably filtered with a filter having a pore diameter of 3 μm or less, preferably 1 μm or less.

3. Image Forming Method The image forming method of the present invention can be performed in the same manner as a known image forming method in which an ink jet ink is landed and cured after forming a primer layer, except that the primer of the present invention described above is used.

  For example, the image forming method of the present invention comprises a step of adhering the above-described primer of the present invention on a recording medium, a step of irradiating the primer adhering to the recording medium with an active energy ray to form a primer layer, an active energy A step of ejecting ink droplets of ink jet ink that is cured by irradiation with a line from the ink jet head and landing on the primer layer, and an image obtained by irradiating the landed ink jet ink with active energy rays and curing the ink jet ink Forming a step.

[Step of attaching the primer of the present invention onto a recording medium]
In this step, the primer of the present invention is deposited on the recording medium. The primer of the present invention is a printing medium by a method using a plate such as bar coating, spray coating, curtain coating, roll coating, screen printing, offset printing, gravure printing, letterpress and intaglio, and a method not using a plate such as inkjet. Can be deposited on top. Among these, it is preferable to attach the primer by screen printing, offset printing, gravure printing, and bar coating because the work is easy and uniform adhesion becomes possible.

[Step of forming a primer layer by irradiating active energy rays to a primer deposited on a recording medium]
In this step, active energy rays are irradiated to the primer of the present invention attached on the recording medium in the previous step to polymerize, copolymerize and crosslink the photopolymerizable compound contained in the primer. By this step, the primer is cured or semi-cured to form a primer layer on the recording medium. At this time, active energy rays may be irradiated until the primer is completely cured, or active energy rays may be irradiated to such a degree that the primer is not completely cured. The latter is preferable from the viewpoint of further improving the adhesion between the inkjet ink to be printed in a later step and the primer layer.

The active energy ray irradiated to the primer can be selected from, for example, an electron beam, an ultraviolet ray, an α ray, a γ ray, and an X-ray, and among these, it is preferable to irradiate the ultraviolet ray. The active energy rays are adjusted and applied so that an energy amount of 100 mJ / cm ² or more and 1000 mJ / cm ² or less is applied. In order to bring the primer of the present invention into a semi-cured state, it is preferable to irradiate while adjusting so that an energy amount of 100 mJ / cm ² or more and 400 mJ / cm ² or less is applied.

[Process of ejecting ink jet ink droplets from the ink jet head and landing on the primer layer]
In this step, inkjet ink droplets are ejected from the inkjet head and land on the primer layer formed in the previous step. In this step, the inkjet ink is landed at a position corresponding to the image to be formed.

  The ejection method from the ink jet head may be either an on-demand method or a continuous method. On-demand inkjet heads include electro-mechanical conversion systems such as single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, and thermal inkjet type and bubble jet. Any of electric-thermal conversion methods such as Canon Inc. (registered trademark) type may be used.

  The ejection stability of the inkjet ink droplets can be improved by ejecting the droplets from the inkjet head in a heated state. The temperature of the inkjet ink at the time of ejection is preferably 35 ° C. or more and 100 ° C. or less, and more preferably 35 ° C. or more and 80 ° C. or less in order to further improve ejection stability. In particular, it is preferable to emit at an ink temperature such that the viscosity of the inkjet ink is 7 mPa · s or more and 15 mPa · s or less, more preferably 8 mPa · s or more and 13 mPa · s or less.

  The method for heating the inkjet ink to a predetermined temperature is not particularly limited. For example, at least one of an ink tank constituting the head carriage, an ink supply system such as a supply pipe and an anterior chamber ink tank just before the head, a pipe with a filter, a piezo head, etc., is used among a panel heater, a ribbon heater, and warm water Either can be heated to a predetermined temperature.

  The droplet amount of the inkjet ink when ejected is preferably 2 pL or more and 20 pL or less from the viewpoint of recording speed and image quality.

[Process of forming an image formed by irradiating the landed inkjet ink with active energy rays and curing the inkjet ink]
In this step, the ink jet ink landed in the previous step is irradiated with active energy rays to form an image formed by curing the ink jet ink. The active energy ray is preferably irradiated for 0.001 second or more and 1.0 second or less after ink landing. In order to form a high-definition image, 0.001 second or more and 0.5 second or less. It is more preferable to irradiate in between.

  The active energy ray applied to the inkjet ink can be selected from, for example, an electron beam, an ultraviolet ray, an α ray, a γ ray, an X-ray, and the like. Ultraviolet rays can be irradiated by a 395 nm, water-cooled LED, etc., manufactured by Phoseon Technology. By using the LED as the light source, it is possible to suppress the occurrence of ink curing failure due to the ink-jet ink being melted by the radiant heat of the light source.

The LED light source is installed such that the peak illuminance on the image surface is 0.5 to 10 W / cm ² with ultraviolet rays of 370 to 410 nm, and more preferably 1 to 5 W / cm ² . The amount of light applied to the image is preferably less than 350 mJ / cm ² . This is to prevent the radiant heat from being applied to the inkjet ink.

  Also, the irradiation of active energy rays is divided into two stages. First, after the ink jet ink has landed, the active ink rays are irradiated by the above-described method for 0.001 second to 2.0 seconds to temporarily cure the ink jet ink. The ink jet ink may be fully cured by irradiating an active energy ray after completion of all printing. By dividing the irradiation of active energy rays into two stages, the shrinkage of the recording material that occurs during ink curing can be more efficiently suppressed.

  In the image forming method of the present invention, when the total ink film thickness after being cured by irradiating active energy rays to the primer and inkjet ink of the present invention landed on a recording medium is 2 μm or more and 20 μm or less, The occurrence of curling and wrinkling of the recording medium and the change in texture of the recording medium can be prevented more efficiently. The “total ink film thickness” means the total value of the film thicknesses of the primer and all inkjet inks applied or printed on the recording medium.

  When recording on a wide area of the recording medium, the recording medium may be divided into a plurality of areas, and the image forming method of the present invention may be performed independently for each area, or collectively over the entire area of the recording medium. You may perform the image forming method of this invention. By dividing the recording medium into a plurality of regions and independently performing the image forming method of the present invention for each region, it is possible to prevent a decrease in adhesion with the ink-jet ink composition due to drying of the primer. . On the other hand, the process can be simplified by carrying out the image forming method of the present invention all over the recording medium.

[Conveying process]
When the formation of the primer layer and the formation of the ink layer are performed by different machines, a recording medium on which the primer layer is formed is formed between the step of forming the primer layer and the step of landing the droplets of the second ink. The process to convey may be included.

[recoding media]
The recording medium used in the image forming method of the present invention is not particularly limited, and examples thereof include polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, and polybutadiene. Non-absorptive recording medium (plastic substrate) composed of plastic such as terephthalate, non-absorbing inorganic recording medium such as metals and glass, and papers (for example, coated paper for printing and coated paper B for printing) Etc.) can be used. In particular, the primer of the present invention has good adhesion to a plastic substrate. As the plastic substrate, it is preferable to use polypropylene, polyethylene, polyethylene terephthalate, and a substrate obtained by stretching these. Although all parts of the recording medium may be non-absorbing, the part where an image is to be formed by the image forming method of the present invention is non-absorbing, and the other part is made of a water-soluble resin or the like. Absorption may be achieved by providing an ink receiving layer.

That the recording medium is non-absorbing means that the amount of water absorption of the recording medium from the start of contact to 30 msec ^1/2 measured by the Bristow method is 0.3 g / m ² or less.

  Conventional primers have low adhesion to plastic substrates. On the other hand, according to the image forming method including the step of curing the primer of the present invention on a recording medium, a primer layer having high adhesion to a plastic substrate can be formed and formed on the primer layer. Adhesiveness between the image by the inkjet ink and the recording medium is also increased. Further, according to the image forming method including the step of curing the primer of the present invention on the recording medium, the recording medium is hardly curled when the primer layer is formed.

[Example 1]
1. Preparation of primers Acrylates (A) to (I), vinyl ether compounds (A) to (F), intramolecular cleavage type initiators, hydrogen abstraction type initiators, etc. prepared according to the compositions shown in Tables 1 and 2 Primers 1 to 20 were prepared by dissolving with heating and stirring on a 65 ° C. hot plate.

[Trifunctional or higher (meth) acrylate]
Acrylate (A): Trimethylolpropane (3EO) triacrylate Acrylate (B): Trimethylolpropane (3PO) triacrylate Acrylate (C): Pentaerythritol triacrylate Acrylate (D): Pentaerythritol tetraacrylate Acrylate (E): Di Pentaerythritol pentaacrylate

[Other (meth) acrylates]
Acrylate (F): Tetrahydrofurfuryl acrylate Acrylate (G): Benzyl acrylate Acrylate (H): Phenoxyethyl acrylate Acrylate (I): 1,6-hexanediol diacrylate

[Vinyl ether compounds having two or more vinyl ether groups]
Vinyl ether compound (A): Cyclohexanedimethanol divinyl ether Vinyl ether compound (B): Triethylene glycol divinyl ether Vinyl ether compound (C): Dipropylene glycol divinyl ether Vinyl ether compound (D): Trimethylolpropane trivinyl ether

[Other vinyl ether compounds]
Vinyl ether compound (E): Diethylene glycol monovinyl ether Vinyl ether compound (F): 2- (2-vinyloxyethoxy) ethyl acrylate

[Intramolecular cleavage type initiator]
TPO: DAROCUR TPO (manufactured by BASF, DAROCUR is a registered trademark of the company)

[Hydrogen extraction type initiator]
ITX: SPEEDCURE ITX (manufactured by DKSH)

2. Method for forming primer coating film Using the above-prepared primers 1-20, white PET # 50 (manufactured by Maru Adhesive Co., Ltd.) having a width of 75 mm and a length of 130 mm, a corona-treated biaxially stretched polypropylene film OPP (manufactured by Okamoto Corporation) ) And YUPO (manufactured by YUPO Corporation) so as to have a thickness of 10 μm. After the application, it was cured by applying an energy amount of 400 mJ / cm ^{2 with} an LED lamp (8 W / cm ² , water cooled unit) manufactured by Phoseon Technology.

3. Evaluation of properties [Evaluation of adhesion to recording materials]
About each hardened | cured material of the primers 1-20 recorded with the said coating-film formation method, it is an adhesive tape (Scotch # 250, Sumitomo) to the hardening composition sample obtained by the cross-cut tape peeling residue adhesion test (cross cut test of JISK5400). 3M) and pasted once with a 2kg roller, peeled off at once, investigated the number of remaining grid-like samples, evaluated the adhesion rate with the following rank, and was one of the indicators of adhesion did. Δ or more is a practically favorable range.

A: Adhesive residual rate of 80% or more and 100%
○: Adhesion residual rate 60% or more and less than 80% △: Adhesion residual rate 40% or more and less than 60% ×: Adhesion residual rate 40% or less

[Curl evaluation]
About each recording medium in which the primers 1-20 were made effective by the said coating-film formation method, the generation | occurrence | production degree of curl of the recording medium by hardening shrinkage was observed visually, and the following reference | standard evaluated.

◎: No warpage in the recording medium ○: Slight warping at the edge is within the allowable range △: Slight warping as a whole ×: Warping of the recording medium is large and NG level

[Curability evaluation (pencil hardness)]
About each hardened | cured material of the primers 1-20 recorded with the said coating-film formation method, after leaving to stand in 25 degreeC60% RH environment for 24 hours, the pencil hardness of a surface was measured according to JIS-K-5400, and the following rank Was evaluated as one of the indicators of curability.

◎: Pencil hardness 2H or more ○: Pencil hardness B or more and less than 2H △: Pencil hardness 2B or more and less than B ×: Pencil hardness 2B or less

  The obtained results are shown in Table 3.

  As shown in Table 3, the sample which is an example of the present invention obtained a good evaluation in any evaluation item. In particular, when the tri- or higher functional (meth) acrylate has a pentaerythritol or dipentaerythritol structure, the adhesion of the primer of the present invention to a plastic substrate was high (primer Nos. 5 to 12).

  On the other hand, when the content of the vinyl ether compound having two or more vinyl ether groups in the molecule was less than 3% by weight with respect to the total mass of the primer, the curl evaluation was lowered (primer No. 13 to 15). This seems to be because inhibition of crosslinking of the acrylate by the vinyl ether group is less likely to occur. Further, when the content of the vinyl ether compound having two or more vinyl ether groups in the molecule was more than 40% by weight with respect to the total mass of the primer, the curability of the primer was poor (Primer No. 16). In addition, when the amount of tri- or higher functional (meth) acrylate was less than 10% by mass with respect to the total mass of the primer, the adhesion of the primer to the plastic substrate was reduced (Primer Nos. 17 to 19). Further, when the amount of tri- or higher functional (meth) acrylate was more than 50% by mass with respect to the total mass of the primer, the curl evaluation deteriorated (primer No. 20). This is considered to be because the primer layer contracted due to excessive crosslinking of the tri- or higher functional (meth) acrylate.

[Example 2]
1. Preparation of Pigment Dispersion A pigment dispersant and an organic solvent prepared according to the composition shown in Table 4 were placed in a stainless beaker and dissolved with stirring and heating for 1 hour while heating on a hot plate at 65 ° C.

[Pigment dispersant]
Pigment dispersant: Ajisper PB824, manufactured by Ajinomoto Fine Techno Co. (Ajisper is a registered trademark of Ajinomoto Co., Inc.)

[Organic solvent]
Organic solvent: Tripropylene glycol diacrylate

  After the solution was cooled to room temperature, the pigments described below were added according to the composition described in Table 4, put in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, and sealed with a paint shaker. After the dispersion treatment for the time described in 1., zirconia beads were removed to prepare pigment dispersions 1 to 4.

[Pigment]
Pigment (A): Pigment Black 7 (# 52, manufactured by Mitsubishi Chemical Corporation)
Pigment (B): Pigment Blue 15: 4 (Chromofine Blue 6332JC, manufactured by Dainichi Seika Kogyo Co., Ltd., Chromofine is a registered trademark of the company)
Pigment (C): Pigment Yellow 150 (E4GN-GT CH20015, manufactured by LANXESS)
Pigment (D): Pigment Red 122 (Chromofine Red 6112JC, manufactured by Dainichi Seika Kogyo Co., Ltd.)

2. Preparation of Ink Composition An ink-jet ink is prepared by mixing a pigment dispersion prepared according to the composition shown in Table 5 and an ink composition, and a polytetrafluoroethylene type membrane filter (pore size: 3 μm, manufactured by Advantech) And filtered.

[Photopolymerizable compound]
Photopolymerizable compound (IA): Polyethylene glycol # 400 diacrylate (A-400, manufactured by Shin-Nakamura Chemical Co., Ltd.)
Photopolymerizable compound (IB): trimethylolpropane (9EO) triacrylate (A-TMPT-9EO, manufactured by Shin-Nakamura Chemical Co., Ltd.)
Photopolymerizable compound (IC): Trimethylolpropane (6PO) triacrylate (A-TMPT-6PO, manufactured by Shin-Nakamura Chemical Co., Ltd.)

[Silicone-based surfactant]
KF-352: KF-352 (manufactured by Shin-Etsu Chemical Co., Ltd.)

[Intramolecular cleavage type initiator]
TPO: DAROCUR TPO (BASF)

[Hydrogen extraction type initiator]
ITX: SPEEDCURE ITX (manufactured by DKSH)

[Sensitizer]
EPA: Kayacure EPA (manufactured by Nippon Kayaku Co., Ltd., Kayacure is a registered trademark of the company)

3. Inkjet image formation In the same procedure as in Example 1, primer 1 on white PET # 50 (manufactured by Maru Adhesion Co., Ltd.), corona-treated biaxially stretched polypropylene film OPP (manufactured by Okamoto Co., Ltd.) and YUPO (manufactured by YUPO Corporation) 20 was applied and cured. An ink jet recording apparatus having an ink jet recording head equipped with a piezo ink jet nozzle was loaded with the ink jet inks K, C, M and Y prepared above, and images were formed on the cured products of the respective primers. The conveyance speed of the recording material was 30 m / s.

  Although not shown, the ink supply system is composed of an ink tank, a supply pipe, a sub ink tank just before the head, a pipe with a filter, and a piezo head. The piezo head applied a voltage so as to form a droplet of 2 pl, and ejected it using four heads each having a resolution of 360 dpi, forming a 1440 × 1440 dpi RGB secondary color solid image.

After printing, an energy amount of 600 mJ / cm ² was applied with an LED lamp (8 W / cm ² , water cooled unit) manufactured by Phoseon Technology to completely cure the image surface. Irradiation was performed at a distance of 5 mm from the tube surface (irradiation width 20 mm in the conveying direction).

4). Evaluation of properties [Evaluation of adhesion to recording materials]
For images formed on the cured products of the primers 1 to 20, adhesive tape (Scotch # 250, manufactured by Sumitomo 3M Co., Ltd.) was applied to the cured composition sample obtained in the cross-cut tape peeling residual adhesion test (cross cut test of JIS K 5400). ) And then reciprocally pressed with a 2 kg roller, and then peeled off at a stretch. The number of remaining grid-like samples was investigated, and the adhesion rate was evaluated according to the following rank, which was used as an index of adhesion. Δ or more is a practically favorable range.

A: Adhesive residual rate of 80% or more and 100%
○: Adhesion residual rate 60% or more and less than 80% △: Adhesion residual rate 40% or more and less than 60% ×: Adhesion residual rate 40% or less

[Curl evaluation]
About the image formed on each hardened | cured material of the said primers 1-20, the generation | occurrence | production degree of the curl of the recording medium by hardening shrinkage was observed visually, and the following reference | standard evaluated.

◎: No warpage in the recording medium ○: Slight warping at the edge is within the allowable range △: Slight warping as a whole ×: Warping of the recording medium is large and NG level

  The results obtained are shown in Table 6.

  As shown in Table 6, when an image was formed on a cured product obtained by curing the primer which is an example of the present invention, good evaluation was obtained in any evaluation item. In particular, when the trifunctional or higher functional (meth) acrylate has a pentaerythritol or dipentaerythritol structure, the adhesion of the image to the plastic substrate by the inkjet ink was high (primer Nos. 5 to 12).

  The primer of the present invention can be suitably used for image formation on a recording medium, particularly a non-absorbing recording medium.

  This application claims the priority based on Japanese application No. 2014-243301 filed on Dec. 1, 2014, and the contents described in the specification of the application are incorporated in this application.

Claims (6)

A primer that cures when irradiated with active energy rays,
A trifunctional or higher (meth) acrylate, a vinyl ether compound having two or more vinyl ether groups, and a photoinitiator,
The primer which contains the said (meth) acrylate in the quantity of 10 to 50 mass% and the said vinyl ether compound in the quantity of 3 to 40 mass% with respect to the total mass of a primer.   The trifunctional or higher functional (meth) acrylate is trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta ( The primer according to claim 1, wherein the primer is at least one selected from the group consisting of (meth) acrylate and dipentaerythritol hexa (meth) acrylate.   The primer according to claim 1 or 2, wherein the vinyl ether compound has at least one selected from the group consisting of an ethylene oxide group, a propylene oxide group, and an ester group.   The ink set containing the primer of any one of Claims 1-3, and the inkjet ink which is irradiated and irradiated with an active energy ray. Attaching the primer according to any one of claims 1 to 3 on a recording medium;
Irradiating active energy rays to the primer deposited on the recording medium to form a primer layer;
A step of ejecting droplets of an inkjet ink that is cured by irradiation with active energy rays from an inkjet head to land on the primer layer, and irradiating active energy rays to the deposited inkjet ink to form the inkjet ink And a step of forming an image formed by curing.   The non-absorbing recording medium comprising at least one part selected from the group consisting of polypropylene, polyethylene, and polyethylene terephthalate, at least a portion of the recording medium on which an image is to be formed. 6. The image forming method according to 5.