JP5880244B2 - Image forming method - Google Patents

Description

  The present invention relates to an image forming method using an actinic ray curable inkjet ink.

  The ink jet recording system is used in various printing fields because it can form an image easily and inexpensively. One ink jet recording method is a method of forming an image by applying an ink that is liquid at high temperature and solid at room temperature; so-called “hot melt ink”. In this method, hot melt ink is heated to 130 to 140 ° C. and discharged from an ink jet recording head to an intermediate transfer medium of an ink jet recording apparatus. The ink droplets are partially cooled by the intermediate transfer medium, and then transferred to a recording medium to form an image.

  Conventional “hot melt inks” are mainly composed of crystalline wax, and in order to be ejected from an ink jet recording head, it was necessary to heat the ink to a high temperature. Furthermore, the conventional image made of hot melt ink has a problem of low abrasion resistance. In order to solve such a problem, it has been proposed to apply a phase change ink jet ink containing a photopolymerizable component and a wax to an ink jet system (Patent Documents 1 and 2). A phase change ink-jet ink containing a photopolymerizable component can eject ink at a relatively low temperature. In addition, since the ink droplets are transferred to the recording medium and then the ultraviolet rays are irradiated to cure the droplets, the printed image has high scratchability.

JP 2007-297625 A JP 2006-176882 A

  However, the phase change inkjet inks described in Patent Documents 1 and 2 contain a large amount of gelling agent and have a high storage modulus of ink droplets. Therefore, when transferring the ink from the intermediate transfer medium to the recording medium, there is a problem that the ink hardly adheres to the recording medium and the transferability of the ink is low. Furthermore, the ink droplets are hard and the ink droplets are difficult to smooth. Therefore, there is a problem that thickness unevenness and thickness difference are likely to occur in the printed image, and gloss unevenness is likely to occur.

  The present invention has been made in view of the above circumstances, and provides an image forming method that is excellent in gloss uniformity of an image and has a small thickness difference (so-called relief feeling).

The present invention relates to an image forming method described below.
[1] An ink attachment step in which ink droplets of an actinic radiation curable inkjet ink containing a photopolymerizable compound, a photopolymerization initiator, and a gelling agent are ejected from an inkjet recording head and adhered to an intermediate transfer medium; A transfer step of transferring the ink droplets attached to the intermediate transfer medium to the recording medium, and an exposure step of irradiating the ink droplets transferred to the recording medium with actinic rays to cure each droplet. The actinic ray curable inkjet ink includes the gelling agent in an amount of 0.5% by mass or more and less than 10% by mass with respect to the total mass of the ink. The viscosity is 1 × 10 ³ mPa · s or more and less than 5 × 10 ⁴ mPa · s, and the storage elastic modulus of the ink is 3 × 10 ¹ PaPa or more and less than 3 × 10 ³ Pa. , Image forming method.
[2] The image forming method according to [1], wherein the temperature of the intermediate transfer medium in the ink adhering step is 30 ° C. or higher and lower than 55 ° C.
[3] The image forming method according to [1] or [2], wherein a nip pressure between the intermediate transfer medium and the recording medium in the transfer step is 0.1 MPa or more and less than 0.5 MPa.
[4] The image forming method according to any one of [1] to [3], wherein the temperature of the recording medium in the transfer step is lower than the temperature of the intermediate transfer medium in the transfer step.
[5] The image forming method according to any one of [1] to [4], wherein the temperature of the recording medium in the transfer step is 5 ° C. or more and less than 15 ° C. lower than the temperature of the intermediate transfer medium in the transfer step.

  According to the image forming method of the present invention, it is possible to obtain a printed image having high sharpness, excellent surface gloss uniformity, and less relief.

It is a figure which shows an example of a structure of the principal part of an inkjet recording device, Fig.1 (a) shows a side view, FIG.1 (b) shows a top view. It is a figure which shows the other example of a structure of the principal part of an inkjet recording device. It is a figure which shows the other example of a structure of the principal part of an inkjet recording device.

  In the image forming method of the present invention, an actinic ray curable inkjet ink is discharged onto an intermediate transfer medium of an inkjet recording apparatus to form a coating film. Thereafter, the coating film is transferred from the intermediate transfer medium to the recording medium, and the ink transferred to the recording medium is irradiated with actinic rays to cure the ink.

1. Actinic ray curable inkjet ink The actinic ray curable inkjet ink contains a photopolymerizable compound, a gelling agent, and a photopolymerization initiator. The actinic ray curable inkjet ink contains a coloring material and other additives as necessary.

(Photopolymerizable compound)
The photopolymerizable compound is a compound that crosslinks or polymerizes when irradiated with actinic rays. The actinic rays are, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays, preferably ultraviolet rays or electron rays, and particularly preferably ultraviolet rays. The photopolymerizable compound can be a radical polymerizable compound or a cationic polymerizable compound. A radical polymerizable compound is preferred.

Cationic polymerizable compound The cationic polymerizable compound may be an epoxy compound, a vinyl ether compound, an oxetane compound, or the like. These are disclosed in JP-A-6-9714, JP-A-2001-31892, JP-A-2001-40068, JP-A-2001-55507, JP-A-2001-310938, JP-A-2001-310937. And compounds exemplified in JP-A-2001-220526. Only one kind of the cationic polymerizable compound may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  The epoxy compound is an aromatic epoxide, an alicyclic epoxide, an aliphatic epoxide, or the like, and an aromatic epoxide or an alicyclic epoxide is preferable in order to increase curability.

  The aromatic epoxide may be a di- or polyglycidyl ether obtained by reacting a polyhydric phenol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the polyhydric phenol to be reacted or an alkylene oxide adduct thereof include bisphenol A or an alkylene oxide adduct thereof, hydrogenated bisphenol A or an alkylene oxide adduct thereof, and a novolac type epoxy resin. The alkylene oxide in the alkylene oxide adduct can be ethylene oxide, propylene oxide, and the like.

  The alicyclic epoxide can be a cycloalkane oxide-containing compound obtained by epoxidizing a cycloalkane-containing compound with an oxidizing agent such as hydrogen peroxide or peracid. The cycloalkane in the cycloalkane oxide-containing compound can be cyclohexene or cyclopentene.

  The aliphatic epoxide can be a di- or polyglycidyl ether obtained by reacting an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof with epichlorohydrin. Examples of the aliphatic polyhydric alcohol include alkylene glycol such as ethylene glycol, propylene glycol, 1,6-hexanediol, polyethylene glycol, and polypropylene glycol, glycerin, and the like. Examples of the alkylene oxide in the alkylene oxide adduct include ethylene oxide and propylene oxide.

Examples of vinyl ether compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, triethylene glycol Di- or trivinyl ether compounds such as methylolpropane trivinyl ether;
Ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether-o-propylene carbonate, dodecyl Monovinyl ether compounds such as vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether; The vinyl ether compound is preferably a di- or trivinyl ether compound in consideration of curability and adhesion.

  An oxetane compound is a compound having an oxetane ring, and examples thereof include oxetane compounds described in JP-A Nos. 2001-220526 and 2001-310937. When an oxetane compound having 5 or more oxetane rings is included, the viscosity of the actinic radiation curable inkjet ink is increased, and the handling tends to be difficult. In addition, the glass transition temperature of the oxetane compound increases, and the tackiness of the cured product of the actinic ray curable inkjet ink may not be sufficient. Therefore, the oxetane compound is preferably a compound having 1 to 4 oxetane rings.

The oxetane compound is a compound represented by general formula (1) described in paragraph No. 0089 of JP-A-2005-255821, and a compound represented by general formula (2) described in paragraph No. 0092 of the same publication. , A compound represented by general formula (7) in paragraph number 0107, a compound represented by general formula (8) in paragraph number 0109, a compound represented by general formula (9) in paragraph number 0116, and the like. Specifically, there are exemplified compounds 1 to 6 described in paragraph numbers 0104 to 0119 of the same publication and compounds described in paragraph number 0121 of the publication. General formulas (1), (2), and (7) to (9) described in JP-A-2005-255821 are shown below.

-Radical polymerizable compound A radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization. The compound is not limited as long as it is a compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. The radical polymerizable compound may be any of a monomer, an oligomer, a polymer and the like. Examples of the radical polymerizable compound include radical polymerizable compounds described in JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, and JP-A-10-863. sell. The actinic ray curable inkjet ink may contain only one type of radical polymerizable compound or two or more types thereof.

  Examples of compounds having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids and salts thereof, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and anhydrides thereof, Acrylonitrile, styrene, unsaturated polyester, unsaturated polyether, unsaturated polyamide, unsaturated urethane and the like are included. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like.

  Especially, it is preferable that a radically polymerizable compound is an unsaturated carboxylic acid ester compound, and it is more preferable that it is a (meth) acrylate compound. The (meth) acrylate compound may be not only a monomer but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, or the like. Here, “(meth) acrylate” refers to both and / or “acrylate” and “methacrylate”, and “(meth) acryl” refers to both and / or “acryl” and “methacryl”.

Examples of (meth) acrylate compounds include isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isomyristyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, 2-hydroxybutyl acrylate, 2- Acryloyloxyethyl hexahydrophthalic acid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate 2-hydro Cypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modifiable Monofunctional monomers such as flexible acrylate, t-butylcyclohexyl acrylate;
Triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9- Bifunctional monomers such as nonanediol diacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecane diacrylate, PO adduct diacrylate of bisphenol A, neopentyl glycol diacrylate of hydroxypivalate, polytetramethylene glycol diacrylate;
Trimethylolpropane triacrylate, pentaerythritol triacrylate, EO modified trimethylolpropane triacrylate, pentaerythritol tetraacrylate, EO modified pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, caprolactone modified And a trifunctional or higher functional monomer such as trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate, caprolactam-modified dipentaerythritol hexaacrylate, and the like.

  The (meth) acrylate compound may be a modified product. Examples thereof include ethylene oxide-modified (meth) acrylate compounds such as ethylene oxide-modified trimethylolpropane tri (meth) acrylate and ethylene oxide-modified pentaerythritol tetraacrylate; Caprolactone-modified (meth) acrylate compounds such as caprolactone-modified trimethylolpropane tri (meth) acrylate; and caprolactam-modified (meth) acrylate compounds such as caprolactam-modified dipentaerythritol hexa (meth) acrylate and the like are included.

  The radical polymerizable compound may be a mixture of vinyl ether monomer and / or oligomer and (meth) acrylate monomer and / or oligomer. Examples of vinyl ether monomers include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, triethylene glycol Di- or trivinyl ether compounds such as methylolpropane trivinyl ether; ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl Contains etc.; vinyl ether, isopropyl vinyl ether, isopropenyl ether -o- propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether.

  The vinyl ether oligomer is preferably a bifunctional compound having a molecular weight of 300 to 1000 and having 2 to 3 ester groups in the molecule. Examples of vinyl ether oligomers include, but are not limited to, compounds available as a VEctomer series from ALDRICH (such as VEctomer 4010, VEctomer 4020, VEctomer 4040, VEctomer 4060, VEctomer 5015, etc.).

  The radical polymerizable compound may be a mixture of a vinyl ether monomer and / or oligomer and a maleimide compound. Examples of maleimide compounds include N-methylmaleimide, N-propylmaleimide, N-hexylmaleimide, N-laurylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N, N′-methylenebismaleimide, polypropylene glycol-bis (3-maleimidopropyl) ether, tetraethylene glycol-bis (3-maleimidopropyl) ether, bis (2-maleimidoethyl) carbonate, N, N ′-(4,4′-diphenylmethane) bismaleimide, N, N ′ Examples include -2,4-tolylene bismaleimide, and ester compounds of maleimide carboxylic acid and various polyols described in JP-A-11-124403, but are not limited thereto.

  The radical polymerizable compound may be a polymerizable oligomer. Examples of polymerizable oligomers include epoxy (meth) acrylate oligomers, aliphatic urethane (meth) acrylate oligomers, aromatic urethane (meth) acrylate oligomers, polyester (meth) acrylate oligomers, and linear (meth) acrylic oligomers. included. Specifically, Yamashita Shinzo, “Cross-linking agent handbook” (Taisei, 1981); Kato Kiyosumi, “UV / EB curing handbook (raw material)” (185, Polymer publication society); Commercial editions described in the conference edition, “Application and Market of UV / EB Curing Technology”, p. 79, (1989, CMC); Eiichiro Takiyama, “Polyester Resin Handbook”, (1988, Nikkan Kogyo Shimbun) Products, or known radically polymerizable or crosslinkable oligomers and polymers.

  Since radically polymerizable compounds are particularly high in photosensitivity and have little cure shrinkage, polyethylene glycol di (meth) acrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, ethylene oxide-modified pentaerythritol tetra (meth) acrylate Etc.

-Content of a photopolymerizable compound It is preferable that content of a photopolymerizable compound is 1-97 mass% with respect to the actinic-light curable inkjet total mass, More preferably, it is 30-95 mass%. When there is too little quantity of a photopolymerizable compound, the discharge property of the ink from an inkjet recording device will fall. On the other hand, when the amount of the photopolymerizable compound is excessive, the amount of the gelling agent and the photopolymerization initiator is relatively small, and the sol-gel phase transition may not be sufficiently performed or the curing is insufficient. there is a possibility.

(Gelling agent)
The actinic ray curable inkjet ink contains a gelling agent. The gelling agent has a function of causing the actinic ray curable inkjet ink to reversibly undergo a sol-gel phase transition depending on temperature. When the actinic ray curable ink-jet ink of the present invention is ejected from the ink-jet recording head and then lands on the intermediate transfer medium, gelation; that is, the viscosity increases. By increasing the viscosity of the droplet, mixing of dots and dot coalescence are suppressed. Further, since the viscosity of the droplet is increased, it is difficult for oxygen to enter the droplet, and the inhibition of the polymerization of the photopolymerizable compound by oxygen can be suppressed.

  The term “gel” as used in the present invention refers to an interaction such as a lamellar structure; a polymer network formed by non-covalent bonds or hydrogen bonds; a polymer network formed by a physical aggregation state; Or a structure in which substances have lost their independent motion due to the interaction of precipitated microcrystals. Further, “gelation” means solidification, semi-solidification, or thickening with a sudden increase in viscosity or elasticity.

  The gelling agent contained in the actinic radiation curable inkjet ink may be a high molecular compound or a low molecular compound, but a low molecular compound is preferable from the viewpoint of ejection from an inkjet recording apparatus.

  Examples of gelling agents composed of a polymer compound include fatty acid inulins such as inulin stearate; fatty acid dextrins such as dextrin palmitate and dextrin myristate (available from Chiba Flour as the Leopard series); eicosane diacid glyceryl behenate; And polyglyceryl behenate (available from Nisshin Oilio as Nomcoat series); and the like.

Examples of the gelling agent comprising a low molecular compound include, for example, low molecular oil gelling agents described in JP-A-2005-126507, JP-A-2005-255821, and JP-A-2010-1111790;
Amide compounds such as N-lauroyl-L-glutamic acid dibutylamide and N-2 ethylhexanoyl-L-glutamic acid dibutylamide (available from Ajinomoto Fine-Techno);
Dibenzylidene sorbitols such as 1,3: 2,4-bis-O-benzylidene-D-glucitol (available from Gelol D Shin Nippon Chemical);
Paraffin wax, microcrystalline wax, petrolactam, candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, jojoba ester, beeswax, lanolin, whale wax, montan wax, hydrogenated wax, hardened castor Various waxes such as oil or hydrogenated castor oil derivative, montan wax derivative, paraffin wax derivative, microcrystalline wax derivative or polyethylene wax (derivative), α-olefin maleic anhydride copolymer wax (UNILIN series manufactured by Baker-Petrolite, LUNAC BA Kao Corporation, Kao Wax T1 Kao Corporation);
Higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, erucic acid;
Higher alcohols such as stearyl alcohol and behenyl alcohol;
Hydroxystearic acid, such as 12-hydroxystearic acid, 12-hydroxystearic acid derivatives;
Fatty acid amides such as lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, 12-hydroxystearic acid amide (for example, Nikka Amide series Nippon Kasei Co., Ltd., ITOHWAX series Ito Oil N-substituted fatty acid amides such as N-stearyl stearamide, N-oleyl palmitate, N, N'-ethylenebisstearylamide, N, N'-ethylenebis-12 Special fatty acid amides such as -hydroxystearylamide, N, N'-xylylenebisstearylamide;
Higher amines such as dodecylamine, tetradecylamine or octadecylamine;
Stearyl stearic acid, oleyl palmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, polyoxyethylene fatty acid ester, and other fatty acid ester compounds (for example, EMALLEX series manufactured by Nihon Emulsion Co., Ltd. Rikenmar series RIKEN Vitamin And Poem series manufactured by RIKEN VITAMINS);
Sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid (for example, Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods);
Dimer acid, dimer diol (PRIPOR series manufactured by CRODA);
Etc. are included. The actinic ray curable inkjet ink may contain only one kind of gelling agent or two or more kinds.

  The content of the gelling agent is 0.5% by mass or more and less than 10% by mass with respect to the total mass of the ink, preferably 1% by mass or more and less than 10% by mass, and more preferably 2-7% by mass. By setting the content of the gelling agent to 0.5% by mass or more, the storage elastic modulus of the droplet after landing on the intermediate transfer medium is sufficiently increased. Moreover, by making the content of the gelling agent less than 10% by mass, the uncured component hardly remains after irradiation with actinic rays. Further, the flexibility of the ink droplet before curing is relatively high.

(Photopolymerization initiator)
The actinic ray curable inkjet ink contains a photopolymerization initiator. The photopolymerization initiator is appropriately selected depending on the type of the photopolymerizable compound and the type of actinic rays irradiated when the ink is cured.

  Photopolymerization initiators contained in radical polymerization type actinic ray curable inkjet inks include an intramolecular bond cleavage type and an intramolecular hydrogen abstraction type. Examples of intramolecular bond cleavage type photopolymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1- (4-isopropylphenyl) -2. -Hydroxy-2-methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4 Acetophenones such as -thiomethylphenyl) propan-1-one and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoins such as benzoin, benzoin methyl ether and benzoin isopropyl ether; 2 , 4,6-Trimethylbenzoindiphenylphosphine Acylphosphine oxide, such as Sid; as benzyl and methyl phenylglyoxylate esters include.

  Examples of intramolecular hydrogen abstraction type photopolymerization initiators include benzophenone, methyl 4-phenylbenzophenone o-benzoylbenzoate, 4,4′-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4′-methyl-diphenyl. Benzophenones such as sulfide, acrylated benzophenone, 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 3,3′-dimethyl-4-methoxybenzophenone; 2-isopropylthioxanthone, 2,4 -Thioxanthone series such as dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone; Aminobenzophenone series such as Michler ketone, 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethyl Anthraquinone, 9,10-phenanthrene Non, include camphor quinone and the like.

  Examples of the photopolymerization initiator contained in the radical polymerization type actinic ray curable ink jet ink include Japanese Patent Publication No. 59-1281, Japanese Patent Publication No. 61-9621, and Japanese Patent Publication No. 60-60104. Triazine derivatives described in JP-A-59-1504, and organic peroxides described in JP-A-61-243807; JP-B-43-23684, JP-B-44-6413, The diazonium compounds described in JP-B-44-6413, JP-B-47-1604, and US Pat. No. 3,567,453; US Pat. No. 2,848,328, US Pat. , 852, 379, and U.S. Pat. No. 2,940,853, etc .; Japanese Patent Publication No. 36-22062, Japanese Patent Publication No. 37- Ortho-quinonediazides described in Japanese Patent No. 3109, Japanese Patent Publication No. 38-18015, Japanese Patent Publication No. 45-9610, etc .; Japanese Patent Publication No. 55-39162, Japanese Patent Application Laid-Open No. 59-14023, and “Macromolecule” Various onium compounds described in Macromolecules, Vol. 10, page 1307 (1977), etc .; azo compounds described in JP-A-59-142205; JP-A-1-54440, European Patent No. No. 109,851, European Patent No. 126,712, and “Journal of Imaging Science” (J. Imag. Sci.), Vol. 30, 174 (1986), etc. Metal allene complexes described in the above; (oxo) sulfonium described in Japanese Patent Nos. 2711491 and 2803454 Machine boron complex; titanocenes described in JP-A-61-151197; “Coordination Chemistry Review”, 84, 85-277 (1988), and JP-A-2 Transition metal complexes containing a transition metal such as ruthenium as described in JP-A No. 182701; 2,4,5-triarylimidazole dimer as described in JP-A-3-209477; carbon tetrabromide and JP And organic halogen compounds described in JP-A-59-107344.

  The amount of the photopolymerizable compound contained in the radical polymerization type actinic ray curable inkjet ink is 0.01% by mass to 10% by mass with respect to the total mass of the ink, although it depends on the type of actinic ray or photopolymerizable compound. % Is preferred.

  The actinic ray curable inkjet ink of the cationic polymerization system contains an acid generation type photopolymerization initiator (photo acid generator). Examples of acid-generating photopolymerization initiators include chemically amplified photoresists and compounds used for photocationic polymerization (edited by Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993). Year), pages 187-192).

Examples of acid-generating photopolymerization initiators include aromatic onium compounds (cations) such as aromatic diazonium, aromatic ammonium, aromatic iodonium, aromatic sulfonium, aromatic phosphonium, and B ( C ₆ F ₅ ) ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , salts with anions such as CF ₃ SO ₃ ⁻ (onium salts) are included. The aromatic onium compound may be a compound described in paragraph number 0134 of JP-A No. 2005-255821.

  The acid-generating photopolymerization initiator may be a sulfonated product that generates sulfonic acid; a halide that generates hydrogen halide; an iron allene complex, or the like. Examples of the sulfonated product include compounds described in paragraph No. 0136 of JP-A No. 2005-255821. Examples of the halide include compounds described in paragraph No. 0138 of JP-A No. 2005-255821. Examples of the iron allene complex include compounds described in paragraph No. 0140 of JP-A No. 2005-255821.

  The amount of the acid-generating photopolymerization initiator contained in the actinic ray curable inkjet ink of the cationic polymerization method is 0.01 mass relative to the total mass of the ink, although it depends on the type of actinic rays and photopolymerizable compounds. It is preferable that it is% -10 mass%.

  The actinic ray curable inkjet ink may further contain a photopolymerization initiator auxiliary agent, a sensitizer, a polymerization inhibitor, and the like as necessary. The photopolymerization initiator assistant may be a tertiary amine compound, preferably an aromatic tertiary amine compound. Examples of aromatic tertiary amine compounds include N, N-dimethylaniline, N, N-diethylaniline, N, N-dimethyl-p-toluidine, N, N-dimethylamino-p-benzoic acid ethyl ester, N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester, N, N-dihydroxyethylaniline, triethylamine, N, N-dimethylhexylamine and the like are included. Of these, N, N-dimethylamino-p-benzoic acid ethyl ester and N, N-dimethylamino-p-benzoic acid isoamyl ethyl ester are preferred. Only one kind of these compounds may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  The sensitizer is preferably a compound having ultraviolet spectrum absorption on the longer wavelength side than the wavelength of 300 nm. Examples of the sensitizer include a polycyclic aromatic compound having at least one hydroxyl group, an aralkyloxy group which may have a substituent, or an alkoxy group; a carbazole derivative; a thioxanthone derivative; an anthracene derivative.

  Examples of polymerization inhibitors include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p-benzoquinone , Nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperone, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N- (3-oxyanilino- 1,3-dimethylbutylidene) aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraloxime, methyl ethyl ketoxime, cyclohexanone oxime and the like.

(Color material)
The actinic ray curable inkjet ink may further contain a coloring material. The colorant can be a dye or a pigment. A pigment is more preferable because it has good dispersibility with respect to the components of the ink and is excellent in weather resistance.

  The dye can be an oil-soluble dye or the like. Examples of oil-soluble dyes include the following various dyes. Examples of magenta dyes include MS Magenta VP, MS Magenta HM-1450, MS Magenta HSo-147 (manufactured by Mitsui Toatsu), AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, and AIZEN SOT. Pink-1, SPIRON Red GEH SPECIAL (above, manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN Red FB 200%, MACROLEX Red Violet R, MACROLEX ROT5B (above, manufactured by Bayer Japan), KAYASET Red B, KAYASE RED130, 802 (above, Nippon Kayaku Co., Ltd.), PHLOXIN, ROSE Bengal, ACID Red (above, Daiwa Kasei Co., Ltd.), H R-31, DIARESIN Red K (manufactured by Mitsubishi Kasei Corp.), include Oil Red (manufactured by BASF Japan Ltd.).

  Examples of cyan dyes include MS Cyan HM-1238, MS Cyan HSo-16, Cyan HSo-144, MS Cyan VPG (manufactured by Mitsui Toatsu), AIZEN SOT Blue-4 (manufactured by Hodogaya Chemical Co., Ltd.), RESOLIN BR. Blue BGLN 200%, MACROLEX Blue RR, CERES Blue GN, SIRIUS SUPRATURQ. Blue Z-BGL, SIRIUS SUTRA TURQ. Blue FB-LL 330% (above, Bayer Japan), KAYASET Blue FR, KAYASET Blue N, KAYASET Blue 814, Turq. Blue GL-5 200, Light Blue BGL-5 200 (above, Nippon Kayaku Co., Ltd.), DAIWA Blue 7000, Oleosol Fast Blue GL (above, Daiwa Kasei), DIARESIN Blue P (Mitsubishi Kasei), SUDAN Blue 670, NEOPEN Blue 808, ZAPON Blue 806 (above, manufactured by BASF Japan Ltd.) and the like are included.

  Examples of yellow dyes include MS Yellow HSm-41, Yellow KX-7, Yellow EX-27 (Mitsui Toatsu), AIZEN SOT Yellow-1, AIZEN SOT Yellow W-3, AIZEN SOT Yellow-6 (above, Hodogaya) Chemical Co., Ltd.), MACROLEX Yellow 6G, MACROLEX FLUOR. Yellow 10GN (above, manufactured by Bayer Japan), KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow AG, KAYASET Yellow EG (above, manufactured by Nippon Kayaku), DAIWA YELLOW 330H HSY-68 (manufactured by Mitsubishi Kasei Co., Ltd.), SUDAN Yellow 146, NEOPEN Yellow 075 (above, manufactured by BASF Japan Ltd.) and the like.

  Examples of black dyes include MS Black VPC (Mitsui Toatsu Co., Ltd.), AIZEN SOT Black-1, AIZEN SOT Black-5 (above, manufactured by Hodogaya Chemical Co., Ltd.), RESORIN Black GSN 200%, RESOLIN BlackBS (above, Bayer Japan), KAYASET Black A-N (Nippon Kayaku), DAIWA Black MSC (Daiwa Kasei), HSB-202 (Mitsubishi Kasei), NEPTUNE Black X60, NEOPEN Black X58 (above, BASF Japan product).

  The pigment is not particularly limited, and may be, for example, an organic pigment or an inorganic pigment having the following numbers described in the color index.

  Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53. : 1, 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13, 16, 20, 36, etc. are included. Examples of blue or cyan pigments include Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36. , 60 and the like. Examples of green pigments include Pigment Green 7, 26, 36, 50. Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137. 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193 and the like. Examples of the black pigment include Pigment Black 7, 28, 26, and the like.

Examples of commercially available pigments include chromofine yellow 2080, 5900, 5930, AF-1300, 2700L, chromofine orange 3700L, 6730, chromofine scarlet 6750, chromofine magenta 6880, 6886, 6891N, 6790, 6887, chromo Fine Violet RE, Chromo Fine Red 6820, 6830, Chromo Fine Blue HS-3, 5187, 5108, 5197, 5085N, SR-5020, 5026, 5050, 4920, 4927, 4937, 4824, 4933GN-EP, 4940, 4972, 5205, 5208, 5214, 5221, 5000P, Chromofine Green 2GN, 2GO, 2G-550D, 5310, 5370, 6830, Chromofine Black A-1103, Seika Fast Yellow 10GH, A-3, 2035, 2054, 2200, 2270, 2300, 2400 (B), 2500, 2600, ZAY-260, 2700 (B), 2770, Seica Fast Red 8040, C405 (F), CA120, LR-116, 1531B, 8060R, 1547, ZAW-262, 1537B, GY, 4R-4016, 3820, 3891, ZA-215, Seika Fast Carmine 6B1476T-7, 1483LT, 3840, 3870, Seika Fast Bordeaux 10B-430, Seikalite Rose R40, Seikalite Violet B800, 7805, Seika Fast Maroon 460N, Seika Fast Orange 900, 2900, Seika Light Blue C718, A6 2, Cyanine Blue 4933M, 4933GN-EP, 4940,4973 (manufactured by Dainichiseika Color & Chemicals Mfg.);
KET Yellow 401, 402, 403, 404, 405, 406, 416, 424, KET Orange 501, KET Red 301, 302, 303, 304, 305, 306, 307, 308, 309, 310, 336, 337, 338, 346, KET Blue 101, 102, 103, 104, 105, 106, 111, 118, 124, KET Green 201 (Dainippon Ink Chemical Co., Ltd.);
Colortex Yellow 301, 314, 315, 316, P-624, 314, U10GN, U3GN, UNN, UA-414, U263, Finecol Yellow T-13, T-05, Pigment Yellow 1705, Colortex Orange 202, Color103 Red, 101 115, 116, D3B, P-625, 102, H-1024, 105C, UFN, UCN, UBN, U3BN, URN, UGN, UG276, U456, U457, 105C, USN, Colortex Maroon601, Colortex Brownex600 Red 122, Colortex Blue 516, 517, 518, 519, A8 8, P-908,510, Colortex Green402,403, Colortex Black 702, U905 (manufactured by Sanyo Color Works);
Lionol Yellow 1405G, Lionol Blue FG7330, FG7350, FG7400G, FG7405G, ES, ESP-S (manufactured by Toyo Ink),
Toner Magenta E02, Permanent RubinF6B, Toner Yellow HG, Permanent Yellow GG-02, Hostapeam Blue B2G (manufactured by Hoechst Industry);
Novoperm P-HG, Hostaperm Pink E, Hostaperm Blue B2G (manufactured by Clariant);
Carbon black # 2600, # 2400, # 2350, # 2200, # 1000, # 990, # 980, # 970, # 960, # 950, # 850, MCF88, # 750, # 650, MA600, MA7, MA8, MA11 , MA100, MA100R, MA77, # 52, # 50, # 47, # 45, # 45L, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, # 44, CF9 (Mitsubishi Chemical).

  The average particle size of the pigment is preferably 0.08 to 0.5 μm, and the maximum particle size of the pigment is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. By adjusting the particle size of the pigment, clogging of the nozzles of the ink jet recording head can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  The content of the pigment or dye is preferably 0.1 to 20% by mass, and more preferably 0.4 to 10% by mass with respect to the total mass of the actinic ray curable inkjet ink. This is because when the content of the pigment or dye is too small, the resulting image is not sufficiently colored, and when it is too large, the viscosity of the ink is increased and the dischargeability is lowered.

  The pigment can be dispersed by, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker. The pigment is dispersed so that the average particle size of the pigment particles is preferably 0.08 to 0.5 μm, and the maximum particle size is preferably 0.3 to 10 μm, more preferably 0.3 to 3 μm. Is preferred. The dispersion of the pigment is adjusted by the selection of the pigment, the dispersant, and the dispersion medium, the dispersion conditions, the filtration conditions, and the like.

  In order to improve the dispersibility of the pigment, the actinic ray curable inkjet ink may further contain a dispersant. Examples of the dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a salt of a long chain polyaminoamide and a polar acid ester, a high molecular weight unsaturated acid ester , Polymer copolymer, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene Nonylphenyl ether, stearylamine acetate, pigment derivatives and the like are included.

  Examples of commercially available dispersants include “Anti-Terra-U (polyaminoamide phosphate)”, “Anti-Terra-203 / 204 (high molecular weight polycarboxylate)” manufactured by BYK Chemie, “Disperbyk-101”. (Polyaminoamide phosphate and acid ester), 107 (hydroxyl group-containing carboxylic acid ester), 110 (copolymer containing an acid group), 130 (polyamide), 161, 162, 163, 164, 165, 166, 170 (high Molecular copolymer) ”,“ 400 ”,“ Bykumen ”(high molecular weight unsaturated acid ester),“ BYK-P104, P105 (high molecular weight unsaturated acid polycarboxylic acid) ”,“ P104S, 240S (high molecular weight unsaturated) Acid polycarboxylic acid and silicon) "," Lactimon (long-chain amine and unsaturated acid polycarboxylic acid) Include silicon), "it said.

  Examples of commercially available dispersants include “Efka CHEMICALS” “Efka 44, 46, 47, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766”, “Efka Polymer 100 (modified) Polyacrylate), 150 (aliphatic modified polymer), 400, 401, 402, 403, 450, 451, 452, 453 (modified polyacrylate), 745 (copper phthalocyanine)); "710 (urethane oligomer)", "Furonon SH-290, SP-1000", "Polyflow No. 50E, No. 300 (acrylic copolymer)"; "Disparon KS-860, 873SN, 874" manufactured by Enomoto Kasei Co., Ltd. Polymer dispersant), # 2150 (aliphatic polyvalent carboxylic acid), # 7004 (polyether S) Le type) "and the like are also included.

  Furthermore, examples of commercially available dispersants include “Demol RN, N (Naphthalenesulfonic acid formalin condensate sodium salt), MS, C, SN-B (aromatic sulfonic acid formalin condensate sodium salt), manufactured by Kao Corporation, "EP", "Homogenol L-18 (polycarboxylic acid type polymer)", "Emulgen 920, 930, 931, 935, 950, 985 (polyoxyethylene nonylphenyl ether)", "Acetamine 24 (coconut amine acetate), 86 (stearylamine acetate) ”;“ Solspers 5000 (phthalocyanine ammonium salt type), 13240, 13940 (polyesteramine type), 17000 (fatty acid amine type), 24000, 32000 ”manufactured by Zeneca;“ Nikkor T106 (Nikko Chemical Co., Ltd.) ” Polyoxyethylene sorbi Nmonooreto), MYS-IEX (polyoxyethylene monostearate), also includes Hexagline4-0 (hexaglyceryl ruthenate Huwei rate) "and the like.

  The actinic ray curable inkjet ink may contain a dispersion aid. Examples of the dispersion aid include Avecia's Solsperse series and Ajinomoto Fine Techno's PB series.

  The total amount of the dispersant and the dispersion aid is preferably 1 to 50% by mass with respect to the pigment.

  The actinic radiation curable inkjet ink may further include a dispersion medium for dispersing the pigment as necessary. The dispersion medium may be a solvent, but in order to suppress the residual solvent in the formed image, the above-described photopolymerizable compound (particularly a monomer having a low viscosity) is preferably the dispersion medium.

Other components The actinic ray curable inkjet ink may further contain other components as necessary. Other components may be various additives, other resins, and the like. Examples of the additive include a surfactant, a leveling additive, a matting agent, an ultraviolet absorber, an infrared absorber, an antibacterial agent, and a basic compound for enhancing the storage stability of the ink. Examples of basic compounds include basic alkali metal compounds, basic alkaline earth metal compounds, basic organic compounds such as amines, and the like. Examples of other resins include resins for adjusting the physical properties of the cured film, such as polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes. It is.

-About the physical property of actinic-light curable inkjet ink Since actinic-light curable inkjet ink contains the gelatinizer as mentioned above, it carries out a sol-gel phase transition reversibly with temperature. Actinic ray curable ink that undergoes a sol-gel phase transition is a liquid (sol) at a high temperature (for example, about 80 ° C.), and is thus ejected from an inkjet recording head in a sol state. On the other hand, ink droplets (dots) land on the intermediate transfer medium, and are then naturally cooled to gel. Therefore, the ink droplets do not coalesce, and an image with high sharpness is formed on the intermediate transfer medium. Further, since the ink is gelled, the ink droplets do not coalesce until the ink is transferred from the intermediate transfer medium to the recording medium without being cured. Accordingly, a sharp image is transferred to the recording medium.

  In general, the sol-gel ink phase transition ink has high viscosity and storage elastic modulus of the ink droplets after gelation, and thus the droplets are difficult to coalesce. On the other hand, ink droplets after gelation are difficult to level and fine irregularities are likely to occur on the surface of the coating film. When the storage elastic modulus of the ink droplet is high, even when the coating film is transferred from the intermediate transfer medium to the recording medium, the unevenness is difficult to be smoothed, and uneven glossiness tends to occur.

  Also, the coating film made of the sol-gel ink phase transition ink tends to be thin in a region where the image density is high; that is, a region where the ink application amount is large, and a region where the image density is low; that is, a region where the ink application amount is small. . If the storage elastic modulus of the ink droplet is high, even if the coating film is transferred from the intermediate transfer medium to the recording medium, the thickness difference is difficult to be smoothed. That is, a step (so-called relief feeling) tends to occur at the boundary between regions having different image densities.

  Furthermore, ink droplets having a high storage elastic modulus are difficult to adhere to the recording medium during transfer, and transfer residue is likely to occur.

On the other hand, in the present invention, the storage elastic modulus of the ink at the temperature of the intermediate transfer medium at the time of ink landing; that is, the storage elastic modulus of the ink after gelation is 3 × 10 ¹ Pa or more and less than 3 × 10 ³ Pa. It is preferably 3 × 10 ² Pa or more and less than 1 × 10 ³ Pa. Since the storage elastic modulus is 3 × 10 ¹ Pa or more, the ink droplets after gelation are difficult to coalesce. On the other hand, the storage elastic modulus is less than 3 × 10 ³ Pa, and the ink droplets after gelation have appropriate flexibility. For this reason, when transferring from the intermediate transfer medium to the recording medium, the ink tends to adhere to the recording medium. Furthermore, the ink droplets are appropriately deformed during the transfer, and the coating film is easily smoothed. Therefore, it is easy to obtain a printed image with excellent gloss uniformity and less relief. The storage elastic modulus of the actinic ray curable ink-jet ink can be adjusted by the type of the gelling agent, the content of the gelling agent, the type of the photopolymerizable compound, and the like.

  In the present invention, “high gloss homogeneity” does not indicate that an absolute gloss value, for example, a 60 ° specular gloss value is high. “High gloss homogeneity” means that the gloss is not uniform in some parts of the image, such as unnatural glitter caused by microscopic gloss differences on the image, unnecessary reduction in gloss, and streaky gloss unevenness. This means that the gloss of the entire image, particularly the solid print portion, is uniform.

In the present invention, the viscosity of the ink at the temperature of the intermediate transfer medium upon landing of the ink is 1 × 10 ³ mPa · s or more and less than 5 × 10 ⁴ mPa · s, preferably 3 × 10 ³ mPa · s. As described above, it is less than 1 × 10 ⁴ mPa · s. When the viscosity of the intermediate transfer medium at the time of ink landing is 1 × 10 ³ mPa · s or more, the droplets that have landed on the intermediate transfer medium are difficult to spread and the droplets are difficult to coalesce. On the other hand, when it is less than 5 × 10 ⁴ mPa · s, the dischargeability from the ink jet recording head is improved.

  In addition, in order to improve the discharge property of the ink droplets, it is preferable that the viscosity of the ink at a high temperature is not more than a certain value. Specifically, the actinic ray curable inkjet ink preferably has a viscosity at 80 ° C. of 3 to 20 mPa · s. The viscosity of the actinic ray curable inkjet ink can be adjusted by the type of gelling agent, the content of the gelling agent, the type of the photopolymerizable compound, and the like.

The viscosity and storage elastic modulus can be measured with a stress control type rheometer using a cone plate, Physica MCR series, manufactured by Anton Paar). The viscosity is measured at a shear rate of 11.7 s ⁻¹ while changing the temperature from 90 ° C. at a temperature drop rate of 0.1 ° C. in the rotation mode. The storage elastic modulus is measured at a strain of 5% and an angular frequency of 10 radian / s while changing the temperature from 90 ° C. at a temperature drop rate of 0.1 ° C. / in the oscillation mode.

  The gelling temperature of the actinic ray curable inkjet ink is preferably 40 ° C. or higher and lower than 90 ° C., and more preferably 45 ° C. or higher and 70 ° C. or lower. Considering the summer temperature, if the phase transition temperature of the ink is 40 ° C. or higher, the ink can be stably ejected without being influenced by the environmental temperature. If the phase transition temperature of the ink is less than 90 ° C., the ink can be stably ejected without heating the ink to an excessively high temperature. Therefore, it is possible to reduce the thermal load on the ink jet recording head of the ink jet recording apparatus and the members of the ink supply system. The gelation temperature of the ink can be appropriately adjusted depending on the type of gelling agent used, the amount of gelling agent added, and the type of photopolymerizable compound.

  The gelation temperature of ink refers to a temperature at which the viscosity of the ink suddenly changes from a fluid solution state to a gel state. It is synonymous with terms called gel transition temperature, gel dissolution temperature, phase transition temperature, sol-gel phase transition temperature, and gel point. Further, “solation” means that the interaction formed by the gelation is eliminated and the liquid state changes to a fluid state. The solubilization temperature is a temperature at which fluidity develops due to the sol formation when the gelled ink is heated.

  The gelation temperature of the ink can be measured with a rheometer similar to the viscosity and storage modulus measurement (for example, a stress-controlled rheometer using a cone plate, Physica MCR series, manufactured by Anton Paar). While gradually lowering the temperature of the ink, the viscosity is measured at a low shear rate to create a temperature change curve of the viscosity. Then, from the temperature change curve of the viscosity, a temperature at which the viscosity rapidly increases is obtained and used as the gelation temperature.

  In addition, a method in which a small iron piece sealed in a glass tube is placed in an dilatometer together with ink to lower the ink temperature, and a point at which the small iron piece does not naturally drop in the ink liquid is used as a gelation temperature (J. Polym. Sci., 21, 57 (1956)). In addition, a method of setting the temperature at which an aluminum cylinder naturally falls when an aluminum cylinder is placed on the ink and heating the ink to the gelation temperature (Journal of Japanese Society of Rheology, Vol. 17, 86 (1989)) is also obtained. It is done. As an example of a simpler method, there is a method in which a gel ink test piece is placed on a heat plate, the heat plate is heated, and the temperature at which the shape of the test piece collapses is set as the gelation temperature.

-About the preparation method of an inkjet ink Actinic-light curable inkjet ink is obtained by mixing the above-mentioned photopolymerizable compound, a gelatinizer, a photoinitiator, a coloring material, etc. under a heating. Preferably, a pigment dispersant in which a color material (particularly a pigment) is dispersed in a part of the photopolymerizable compound is prepared and mixed with the pigment dispersant and other ink components. The obtained ink is preferably filtered through a predetermined filter.

2. Image Forming Method The image forming method of the present invention includes at least the following three steps.
(1) Ink adhesion step of ejecting ink droplets of actinic ray curable inkjet ink from an inkjet recording head and adhering to the intermediate transfer medium (2) Ink droplets adhering to the intermediate transfer medium are applied to the recording medium Transfer step for transferring (3) Curing step for curing the ink droplets by irradiating the droplets landed on the recording medium with light from an LED light source.

(1) Ink attachment process Ink droplets of actinic ray curable inkjet ink are ejected from an inkjet recording head portion of an inkjet recording apparatus onto an intermediate transfer medium. The ink is the actinic ray curable inkjet ink described above. The ink droplets that have landed on the intermediate transfer medium are quickly gelled by the sol-gel phase transition. When the ink droplets are gelled, coalescence of the ink droplets is suppressed. Further, when the ink droplet is gelled, it is difficult for oxygen to enter the ink droplet, and in the (3) curing step, curing of the photopolymerizable compound is not easily inhibited by oxygen.

  In order to improve the discharge property of the ink droplets, it is preferable to set the temperature of the inkjet ink in the inkjet recording head to a temperature that is 10 ° C. or more and less than 40 ° C. higher than the gelation temperature of the ink. By setting the gelation temperature of the ink in the ink jet recording head to 10 ° C. or higher, the ink can be well ejected without causing the ink to gel in the ink jet recording head or on the nozzle surface. Moreover, the thermal load of the ink jet recording head can be reduced by setting the temperature of the ink in the ink jet recording head to less than the gelation temperature of ink + 40 ° C. Particularly, in an ink jet recording head using a piezo element, the performance is likely to deteriorate due to a thermal load. Therefore, the ink temperature is particularly preferably within the above range. From the viewpoint of ejection stability, the viscosity of the ink is preferably 3 mPa · s or more and less than 20 mPa · s at the temperature in the inkjet recording head.

  The ink is preferably heated in an ink jet recording head of an ink jet recording apparatus, an ink flow path connected to the ink jet recording head, an ink tank connected to the ink flow path, or the like. The amount of droplets ejected from each nozzle of the inkjet recording head is preferably 1 to 10 pl, although it depends on the resolution of the image.

  The surface temperature of the intermediate transfer medium at the time of ink landing is not particularly limited as long as it is lower than the gelation temperature of the ink. However, considering the sharpness of the image, the surface temperature is 5 ° C. or lower than the gelation temperature of the ink. It is preferable. In particular, the temperature of the intermediate transfer medium is preferably 30 ° C. or higher and lower than 55 ° C., more preferably 40 to 50 ° C.

  There is no particular limitation on the temperature control method of the intermediate transfer medium. For example, a cooling device and a heating device may be provided inside the intermediate transfer medium, and the temperature may be adjusted from the inside of the intermediate transfer medium. A refrigerant, a heater, or the like may be provided on the outer periphery of the intermediate transfer medium to adjust from the outside. May be warm.

  The shape of the intermediate transfer medium is not particularly limited as long as the ink landing surface is smooth. For example, the intermediate transfer medium may have an endless belt shape as shown in FIG. 1 or a drum shape as shown in FIG. May be.

The intermediate transfer medium usually has a substrate and a release layer formed on the surface thereof.
The material of the base material of the intermediate transfer medium is appropriately selected in consideration of the shape and strength of the intermediate transfer medium. Examples of base materials include metals such as iron, stainless steel, and aluminum; polyimide (PI), polyphenylene sulfide (PPS), polyethersulfone (PES), polyamide (PA), polyethylene terephthalate (PET), and polyimide amide Resins such as (PIA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP); ethylene propylene rubber (EPDM) In addition, elastomers such as silicone rubber and fluororubber are included.

  The release layer formed on the surface of the substrate is preferably a layer having releasability with respect to the actinic ray curable inkjet ink. The release layer can be a silicone resin layer or a fluororesin layer.

  The silicone resin layer is preferably a layer obtained by curing a solvent addition type silicone or a condensation curable type silicone, and particularly preferably a layer obtained by curing a solvent addition type silicone.

  Examples of the solvent addition type silicone include KS-887, KS-779H, KS-778, KS-835, X-62-2456, X-62-2494, X-62-2461, KS- manufactured by Shin-Etsu Silicone. 3650, KS-3655, KS-3600, KS-847, KS-770, KS-770L, KS-776A, KS-856, KS-775, KS-830, KS-830E, KS-839, X-62- 2404, X-62-2405, KS-3702, X-62-2232, KS-3503, KS-3502, KS-3703, KS-5508, and the like.

  Examples of the condensation curable silicone include silicones such as KS-881, KS-882, KS-883, X-62-9490, and X-62-9028 manufactured by Shin-Etsu Silicone.

  The thickness of the silicone resin layer (release layer) is preferably 1 to 50 μm, and more preferably 10 to 30 μm.

  Examples of the fluororesin contained in the fluororesin layer (release layer) include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer Combined (FEP) is included. In the fluororesin layer, only one type of fluororesin may be included, or two or more types may be included.

  The thickness of the fluororesin layer (release layer) is preferably 5 to 30 μm, and more preferably 10 to 20 μm.

  The surface contact angle of the release layer with respect to pure water is preferably 100 to 120 °, and more preferably 105 to 115 °. The surface contact angle is a contact angle between the measurement surface and pure water 0.5 seconds after about 15 μl of pure water is gently dropped on the measurement surface. Automatic contact angle meter DAC-VZ (manufactured by Kyowa Interface Science Co., Ltd.) ).

(2) Transfer process The ink droplets formed on the intermediate transfer medium are transferred to the recording medium. In the present invention, as described above, since the ink droplets have an appropriate flexibility (storage modulus), the ink easily adheres to the recording medium, and the transfer residue does not easily occur. Furthermore, since the ink droplets have an appropriate flexibility (storage modulus), the coating film surface is easily smoothed during transfer.

  During ink transfer, it is preferable to apply a pressure (nip pressure) between the intermediate transfer medium and the recording medium. The nip pressure is preferably 0.1 MPa or more and less than 0.5 MPa, and more preferably 0.1 MPa or more and less than 0.3 MPa. If the nip pressure is less than 0.1 MPa, the ink may not be sufficiently transferred from the intermediate transfer medium to the recording medium side. On the other hand, when the nip pressure is low, the image surface transferred to the recording medium cannot be sufficiently smoothed and gloss uniformity may be lowered. On the other hand, if the nip pressure is 0.5 MPa or more, the ink droplets are crushed and the image is blurred, and the image quality sharpness may be reduced. The ink hardness of the actinic ray curable inkjet ink is sufficiently smaller than the hardness of the hot melt ink. Therefore, according to the present invention, the image surface can be smoothed with a lower nip pressure than in the conventional hot melt ink transfer.

  The temperature of the recording medium when transferring an image from the intermediate transfer medium to the recording medium is preferably lower than the temperature of the intermediate transfer medium. Specifically, it is preferably 5 ° C. or more and less than 15 ° C., more preferably 5 ° C. or more and less than 10 ° C. lower than the temperature of the intermediate transfer medium. When the temperature of the recording medium is lower than the temperature of the intermediate transfer medium, the ink is easily transferred to the recording medium side, and the transfer residue is reduced.

  The temperature control method for the recording medium is not particularly limited, and for example, a cooling device or a heating device may be provided on the recording medium conveying member, and the temperature may be adjusted from the back surface (ink non-transfer surface) side of the recording medium. In addition, a refrigerant, a heater, an IR laser, or the like may be provided in the recording medium conveyance path to control the temperature from the ink transfer surface side of the recording medium. Furthermore, the recording medium before being installed in the ink jet recording apparatus may be adjusted to a predetermined temperature. From the viewpoint that the temperature of the recording medium can be adjusted even during ink transfer, temperature control from the back side of the recording medium is preferable.

  The type of recording medium is not particularly limited. Examples of recording media include: base materials made of paper such as plain paper, fine paper, coated paper, art paper; resin-coated paper in which both sides of the base paper are coated with resin; various laminating papers; synthetic papers; various plastics Film; Metal substrate; Glass substrate and the like are included. Examples of plastic films include polyethylene terephthalate (PET) film, biaxially oriented polystyrene (OPS) film, biaxially oriented polypropylene (OPP) film, biaxially oriented nylon (ONY) film, polyvinyl chloride (PVC) film, polyethylene (PE) film, triacetyl cellulose (TAC) film and the like are included.

  The conveyance speed of the recording medium when transferring ink from the intermediate transfer medium to the recording medium is preferably 500 to 3000 mm / s. The higher the conveyance speed, the higher the image forming speed, which is preferable. However, when the conveyance speed is too high, the image quality is deteriorated or the ink is not sufficiently cured.

(3) Curing Step The ink transferred from the intermediate transfer medium to the recording medium is irradiated with actinic rays to cure the ink; that is, the photopolymerizable compound contained in the ink droplets is crosslinked or polymerized. By curing the ink, a printed image having high hardness and excellent abrasion resistance can be obtained.

  The irradiation with actinic rays is preferably performed after all images have been transferred to the recording medium. For example, as shown in FIG. 1 or FIG. 2, when transferring a plurality of colors of ink onto one intermediate transfer medium 11, an actinic ray irradiation device is disposed on the downstream side of the intermediate transfer medium 11, and all images are displayed. It is preferable to irradiate actinic rays after the transfer is completed. As shown in FIG. 3, when transferring ink from a plurality of intermediate transfer media 11 to a recording medium 12, it is preferable to irradiate actinic rays after transferring the ink from all the intermediate transfer media.

  When actinic rays are irradiated before all the ink is transferred, ink droplets transferred later may be repelled by the previously cured film, and the image quality may be disturbed or the gloss uniformity may be lowered.

There is no particular limitation on the actinic ray applied to the ink, and it is preferably, for example, an electron beam or ultraviolet rays.
The electron beam irradiation method is not particularly limited and may be, for example, a scanning method, a curtain beam method, or a broad beam method, but the curtain beam method is preferable from the viewpoint of processing capability. Moreover, it is preferable to set the acceleration voltage at the time of electron beam irradiation to the range of 30-250 kV, More preferably, it is 30-100 kV. Moreover, when performing normal electron beam irradiation whose acceleration voltage is 100-250 kV, it is preferable that electron beam irradiation amount is 30-100 kGy, and it is more preferable that it is 30-60 kGy.

  Examples of the electron beam irradiation means include “Curetron EBC-200-20-30” manufactured by Nissin High Voltage Co., Ltd., “Min-EB” manufactured by AIT Co., Ltd., and the like.

The light source for ultraviolet irradiation is not particularly limited. Examples of light sources include fluorescent tubes (low pressure mercury lamps, germicidal lamps), cold cathode tubes, ultraviolet lasers, low pressure, medium pressure, high pressure mercury lamps, metal halide lamps, LEDs, etc. with operating pressures from several hundred Pa to 1 MPa. It is. From the viewpoint of curing the actinic ray curable ink satisfactorily, a light source having an illuminance of 100 mW / cm ² or more is preferable, and a high-pressure mercury lamp, a metal halide lamp, and an LED are preferable. Among them, an LED with low power consumption is preferable.

  The total film thickness of the image after curing is preferably 2 to 25 μm. The “total film thickness of the image” is the maximum film thickness of the cured film formed on the recording medium. Whether the image is a single color image or an image in which a plurality of colors are superimposed, the total film thickness is preferably in the above range.

Inkjet recording apparatus The image forming method of the present invention can be performed using an actinic ray curable inkjet recording apparatus.
1A and 1B are diagrams illustrating an example of the configuration of an ink jet recording apparatus, in which FIG. 1A is a side view and FIG. 1B is a top view. As shown in FIG. 1, the inkjet recording apparatus 10 stores a head carriage 16 that houses a plurality of inkjet recording heads 14, an ink flow path 30 connected to the head carriage 16, and ink supplied through the ink flow path 30. Of the ink tank 31, the intermediate transfer medium 11 that receives the ink discharged from the ink jet recording head 14 and transfers it to the recording medium 12, the conveying member 15 that conveys the recording medium 12, and the (recording of the intermediate transfer medium 11 The light irradiation unit 18 disposed on the downstream side in the medium conveyance direction) and the temperature control unit 19 disposed on the lower surface of the recording medium 12 are provided. Further, a cleaning member 13 is disposed downstream of the intermediate transfer medium 11 (in the recording medium conveyance direction).

  The head carriage 16 is fixedly arranged so as to cover the entire width of the intermediate transfer medium 11 and accommodates a plurality of ink jet recording heads 14. Ink is supplied to the ink jet recording head 14. For example, the ink may be supplied directly or by an ink supply unit (not shown) from an ink cartridge (not shown) that is detachably attached to the inkjet recording apparatus 10.

  A plurality of inkjet recording heads 14 are arranged in the conveyance direction of the recording medium 12 for each color. The number of inkjet recording heads 14 arranged in the conveyance direction of the recording medium 12 is set according to the nozzle density of the inkjet recording head 14 and the resolution of the print image. For example, when an image having a resolution of 1440 dpi is formed using the inkjet recording head 14 having a droplet amount of 2 pl and a nozzle density of 360 dpi, the four inkjet recording heads 14 may be arranged so as to be shifted with respect to the conveyance direction of the recording medium 12. That's fine. Further, when an image having a resolution of 720 × 720 dpi is formed using the ink jet recording head 14 having a droplet amount of 6 pl and a nozzle density of 360 dpi, the two ink jet recording heads 14 may be arranged in a shifted manner. dpi represents the number of ink droplets (dots) per 2.54 cm.

  The ink tank 31 is connected to the head carriage 16 via the ink flow path 30. The ink flow path 30 is a path for supplying the ink in the ink tank 31 to the head carriage 16. In order to stably eject ink droplets, the ink in the ink tank 31, the ink flow path 30, the head carriage 16, and the inkjet recording head 14 is heated to a predetermined temperature to maintain the sol state.

  The intermediate transfer medium 11 is disposed between the head carriage 16 and the recording medium 12. The intermediate transfer medium 11 has an ink landing surface on which ink ejected from the ink jet recording head 14 lands, and this ink landing surface is conveyed in a certain direction (the direction indicated by the arrow in FIG. 1) after ink landing. The recording medium 12 is pressure-bonded. At this time, a predetermined pressure (nip pressure) is applied between the recording medium 12 and the ink landing surface. The nip pressure is adjusted by adjusting the distance between the recording medium 12 and the intermediate transfer medium 11 or the like. An intermediate transfer medium temperature control unit (not shown) for adjusting the temperature of the intermediate transfer medium 11 at the time of ink landing is provided inside or outside the intermediate transfer medium 11. The intermediate transfer medium temperature control unit may be various heaters, for example.

  The conveying member 15 is arranged to convey the recording medium 12 to the intermediate transfer medium 11 and the light irradiation unit 18 side at a constant speed. A temperature control unit 19 is disposed on the lower surface of the conveying member 15. The temperature control unit 19 maintains the temperature of the recording medium 12 at a predetermined temperature. The temperature control unit 19 can be, for example, various heaters.

  The light irradiation unit 18 covers the entire width of the recording medium 12 and is disposed on the downstream side of the intermediate transfer medium 11 in the conveyance direction of the recording medium 12. The light irradiation unit 18 irradiates the ink droplet transferred to the recording medium 12 with light, and cures the droplet.

  The cleaning member 13 is disposed downstream of the intermediate transfer medium 11 (in the recording medium conveyance direction) and wipes and removes transfer residue (active light curable inkjet ink, etc.) adhering to the surface of the intermediate transfer medium 11 with a blade or the like. To do. The cleaning member 13 is usually provided with a collection unit (not shown) for collecting the transfer residue. The member for wiping and removing the transfer residue is not limited to the blade, and may be, for example, a brush roll, an air knife, an adhesive roll, or the like.

Hereinafter, an image forming method using the inkjet recording apparatus 10 will be described. The recording medium 12 is conveyed between the conveying member 15 of the inkjet recording apparatus 10 and the intermediate transfer medium 11. At this time, the temperature of the recording medium 12 is adjusted by the temperature control unit 19.
On the other hand, high-temperature ink droplets are ejected from the inkjet recording head 14 of the head carriage 16 and adhered (landed) on the intermediate transfer medium 11. After the ink droplet discharge is completed, the ink landing surface of the intermediate transfer medium 11 is rotated in a certain direction (the direction indicated by the arrow in FIG. 1). Then, the recording medium 12 and the intermediate transfer medium 11 are pressed to transfer the ink droplets on the intermediate transfer medium 11 to the recording medium 12. The recording medium 12 is moved to the light irradiation unit 18 side, and the ink droplets attached on the recording medium 12 are irradiated with light to be cured. The transfer residue adhering to the intermediate transfer medium 11 is wiped away by the cleaning member 13.

  FIG. 2 is a diagram illustrating another example of the configuration of the main part of the ink jet recording apparatus. As shown in FIG. 2, the inkjet recording apparatus 20 is configured in the same manner as in FIG. 1 except that it has a drum-shaped intermediate transfer medium 11 instead of the belt-shaped intermediate transfer medium 11.

  FIG. 3 is a diagram illustrating another example of the configuration of the main part of the ink jet recording apparatus. As shown in FIG. 3, the ink jet recording apparatus 30 includes a plurality of drum-shaped intermediate transfer media 11 instead of the belt-shaped intermediate transfer medium 11. Each head carriage 16 and each intermediate transfer medium 11 correspond to each other and are configured in the same manner as in FIG. 1 except that the ink is transferred from the respective intermediate transfer medium 11 to the recording medium 12.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not construed as being limited by these descriptions.

  Each actinic ray curable inkjet ink was prepared with the following components.

(Photopolymerizable compound)
Monomer / NK ester A-400 (manufactured by Shin-Nakamura Chemical Co., Ltd.): Polyethylene glycol diacrylate (Clog P value: 0.47)
SR499 (manufactured by Sartomer): 6EO-modified trimethylolpropane triacrylate (Clog P value: 3.57)
SR494 (manufactured by Sartomer): 4EO-modified pentaerythritol tetraacrylate (Clog P value: 2.28)
OXT221 (manufactured by Toa Gosei Co., Ltd.): 3-ethyl-3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane celoxide 2021P (manufactured by Daicel): 3,4-epoxycyclohexenylmethyl-3 ', 4'-Epoxycyclohexenecarboxylate oligomer, urethane acrylate oligomer, epoxy acrylate oligomer

(Gelling agent)
Lunac BA (manufactured by Kao Corporation): behenic acid, cao wax T1 (manufactured by Kao Corporation): distearyl ketone, stearamide, ITOHWAX J-700 (manufactured by Ito Oil Co., Ltd.): N, N'-xylylene-bis-12 Hydroxystearylamide

(Photopolymerization initiator)
・ DAROCUR TPO (BASF)
・ ITX (manufactured by DKSH Japan)
・ DAROCUR EDB (manufactured by BASF)
・ CPI-100P (manufactured by Sun Apro)

(Surfactant)
・ KF-352 (manufactured by Shin-Etsu Chemical Co., Ltd.)
・ X-22-4272 (manufactured by Shin-Etsu Chemical Co., Ltd.)

(Sensitization aid)
・ DEA (diethoxyanthracene, manufactured by Kawasaki Chemical Industries)

(Preparation of pigment dispersion 1)
The following pigment dispersant, photopolymerizable compound, and polymerization inhibitor were placed in a stainless beaker and stirred for 1 hour while heating on a hot plate at 65 ° C.
Pigment dispersant: 9 parts of Ajisper PB824 (Ajinomoto Fine Techno Co.) Photopolymerizable compound: APG-200 (Tripropylene glycol diacrylate, Shin Nakamura Chemical Co.) 70 parts Polymerization inhibitor: Irgastab UV10 (Ciba 0.02 parts from Japan)

  After cooling the mixed solution to room temperature, 21 parts by mass of Pigment Red 122 (manufactured by Dainichi Seika, Chromofine Red 6112JC) was added thereto. The mixed solution was put in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm and sealed, and dispersed with a paint shaker for 8 hours. Thereafter, the zirconia beads were removed to prepare a pigment dispersion 1.

(Preparation of pigment dispersion 2)
The pigment dispersant and photopolymerizable compound shown below were placed in a stainless beaker and stirred for 1 hour while heating with a hot plate at 65 ° C.
Pigment dispersant: 9 parts by weight of Ajisper PB824 (Ajinomoto Fine Techno Co., Ltd.) Photopolymerizable compound: OXT221 (Oxetane compound, manufactured by Toagosei Co., Ltd.) 70 parts by weight

  After cooling the mixed solution to room temperature, 21 parts by mass of Pigment Red 122 (manufactured by Dainichi Seika, Chromofine Red 6112JC) was added thereto. The mixed solution was put in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm and sealed, and dispersed with a paint shaker for 8 hours. Thereafter, the zirconia beads were removed to prepare a pigment dispersion 2.

[Preparation of radical polymerization type ink-jet ink]
Each compound was mixed with the composition ratio described in Table 1 below, and the mixture was heated to 100 ° C. and stirred. Thereafter, the obtained liquid was filtered through a # 3000 metal mesh filter under heating. This was cooled to prepare a radical curable inkjet ink.

About the ink prepared by the said method, the gelation temperature and the ink viscosity were measured with the following method.
The ink was set in a stress-controllable rheometer (Physica MCR300, manufactured by Anton Paar) capable of controlling temperature, and heated to 100 ° C. Thereafter, the viscosity and dynamic viscoelasticity were measured while cooling to 25 ° C. at a cooling rate of 0.1 ° C./s. At this time, the share rate was 11.7 s ⁻¹ . For the measurement, a cone plate (CP75-1, manufactured by Anton Paar) having a diameter of 75 mm and a cone angle of 1 ° was used. The temperature was controlled by a Peltier element type temperature controller (TEK150P / MC1) attached to the Physica MCR300. The temperature at which the viscosity rapidly increased was read from the viscosity curve obtained by the measurement, and the temperature at which the viscosity showed 500 mPa · s was defined as the gelation temperature. Moreover, the value of the storage elastic modulus in temperature 25 degreeC, 47 degreeC, and 60 degreeC was read from the temperature change curve obtained by the dynamic viscoelasticity measurement. The results obtained by the above method are shown in Table 1.

[ Examples 1-5, 7 , 8 , Comparative Examples 1-7 , and Reference Examples 1-5 ]
A magenta ink was loaded into a magenta head carriage of a line head type ink jet recording apparatus including the piezo type ink jet recording head shown in FIG. 1 to form a single color image. The ink supply system is composed of an ink tank, a supply pipe, a front chamber ink tank immediately before the print head, a pipe with a filter, and a piezo head, and is insulated from the front chamber ink tank of the ink supply system to the print head portion. Warmed to ° C. Also, a heater was incorporated in the piezo head, and the ink in the recording head was also heated.

  In addition, the recording head has a nozzle diameter of 24 μm and a resolution of 512 dpi arranged in a staggered manner to achieve a recording resolution of 1200 dpi × 1200 dpi. The amount of magenta ink droplets ejected from the head was 3.5 pl per droplet, and the droplet ejection speed was 6 m / sec. The intermediate transfer medium was a belt having a polyimide film coated with a silicone resin.

Recording medium, coated printing paper A (manufactured by OK top coat rice basis weight of 84.9g / ^{m 2} Oji Paper Co., Ltd.), coated printing paper B (manufactured by New Age rice basis weight of 104.7g / ^{m 2} Oji Paper Co., Ltd.) , Art paper (SA Kanfuji, US basis weight 104.7 g / m ² manufactured by Oji Paper Co., Ltd.).

First, ink droplets were ejected from the recording head onto an intermediate transfer medium to form a predetermined image. Thereafter, the ink droplets were transferred from the intermediate transfer medium to the recording medium. After transferring the ink droplets to the recording medium, an LED lamp (385 nm, manufactured by Hamamatsu Photonics, a distance of 2 mm between the recording medium and the lamp, a maximum output of 3800 mW / cm ² (UV integrated photometer manufactured by Hamamatsu Photonics) : Measured by C9536-02)), and the ink droplets were cured by irradiation with ultraviolet rays. The conveyance speed of the recording medium was 500 mm / s. The image formation was performed in an environment of 23 ° C. and 55% RH.

  The temperature of the intermediate transfer medium when the ink droplets are attached, the temperature of the recording medium when transferring the ink droplets from the intermediate transfer medium, and the intermediate transfer medium when transferring the ink droplets from the intermediate transfer medium to the recording medium The nip pressure with the recording medium is shown in Table 2 below.

  For images printed under each condition, character quality, gloss uniformity, and relief were evaluated as follows.

(Evaluation of character quality)
On the coated paper A, the coated paper B, and the art paper for printing, the characters “excellent” of 3 points and 5 points of MS Mincho were printed. The obtained characters were visually observed and evaluated according to the following criteria.
○: Even if it is a 3-point character, the details can be reproduced without being crushed. △: The details are crushed if the 3-point characters are crushed.

(Evaluation of gloss uniformity)
Density floors with the dot rate changed to 0%, 10%, 20%, 30%, 50%, 70%, 100% on a 2cm x 2cm area on coated paper A, coated paper B, and art paper A toned patch was prepared. The produced image was visually confirmed and evaluated according to the following criteria. The dot rate means the pixel density of output data.
○: Uniform gloss is obtained at all dot ratios, and the gloss is uniform. Δ: Some parts are worried about glitter and matte. ×: Glitter and matte are noticeable and glossy. Heterogeneous and unacceptable quality

(Evaluation of relief feeling)
Convert natural images (high-definition color digital standard image data “Cafeteria” published by the Japanese Standards Association) to gray scale in Adobe Photoshop 7.0 on coated paper A, coated paper B, and art paper for printing Images were produced. The produced image was visually observed and evaluated according to the following criteria.
◯: Smooth image quality without a feeling of relief Δ: Slightly uneven part ×: The whole surface has large unevenness and a remarkable relief feeling, and the quality is not practical.

As shown in Table 2, when the viscosity of the ink at the temperature of the intermediate transfer medium was lower than 1 × 10 ³ mPa · s (Comparative Examples 1, 2, 4, and 7), the character quality was low. It is presumed that the character quality deteriorated because adjacent droplets were mixed on the intermediate transfer medium. Moreover, when the storage elastic modulus of the ink at the temperature of the intermediate transfer medium was lower than 3 × 10 ¹ Pa (Comparative Example 1), the evaluation of gloss uniformity was also low. Since the elasticity after gelation is small, it is inferred that the liquid droplets coalesced to cause uneven gloss.

On the other hand, when the storage elastic modulus of the ink at the temperature of the intermediate transfer medium was 3 × 10 ³ Pa or more (Comparative Examples 3, 5, and 6), the character quality was good, but the gloss uniformity was good. And the evaluation of the feeling of relief was bad. Since the storage modulus of the ink was too high, the ink droplets were not easily deformed, and it was assumed that the coating film was not smoothed during ink transfer.

  Further, when the nip pressure between the intermediate transfer medium and the recording medium at the time of ink transfer is less than 0.1 MPa (Example 1 and Example 4), although there is no practical problem, the character quality and the gloss uniformity are good. There was a case of decline. It is inferred that the coating film was not smoothed during ink transfer because the nip pressure was too small.

  On the other hand, when the nip pressure at the time of ink transfer was 0.5 MPa or more (Examples 7 and 8), the sharpness of characters was slightly lowered. It is inferred that the image was blurred because the nip pressure was too high.

When the temperature of the intermediate transfer medium at the time of ink landing is relatively low (25 ° C.) ( Reference Examples 2 and 4 ), the character quality was relatively good, but the gloss homogeneity may be small and the relief feeling may be slightly It was seen. When the temperature of the intermediate transfer medium at the time of ink landing is low, the sol-gel phase transition is performed quickly. For this reason, it is assumed that the coating film on the intermediate transfer medium has relatively large irregularities and steps, and these steps and irregularities were not sufficiently smoothed during the transfer.

On the other hand, when the temperature of the intermediate transfer medium at the time of ink landing was relatively high (60 ° C.) ( Reference Example 5 ), the gloss homogeneity feeling was relatively good and the relief feeling was small. On the other hand, the character quality slightly decreased. Since the temperature of the intermediate transfer medium at the time of ink landing is high, it is presumed that the pinning property of the landed ink is slightly lowered.

  Further, at the time of ink transfer, if the temperature of the recording medium was higher than the temperature of the intermediate recording medium, the characters were likely to spread slightly. In addition, the gloss homogeneity was slightly lowered, and a relief was also observed. The temperature of the recording medium is higher than the temperature of the intermediate recording medium, so it is presumed that the ink transferability has decreased.

[Preparation of cationic polymerization type ink]
The respective compounds were mixed at the composition ratio shown in Table 3 below, heated to 100 ° C. and stirred. Thereafter, the obtained liquid was filtered through a # 3000 metal mesh filter under heating. This was cooled to prepare an ink. For each ink, the gelation temperature, ink viscosity, and storage elastic modulus were measured in the same manner as for the radical polymerization type ink.

[Examples 13 and 14 , Comparative Examples 8 to 10 , Reference Example 6 ]
A magenta head carriage of the ink jet recording apparatus shown in FIG. 3 was loaded with magenta ink to form a single color image. The ink supply system is composed of an ink tank, a supply pipe, a front chamber ink tank immediately before the print head, a pipe with a filter, and a piezo head, and is insulated from the front chamber ink tank of the ink supply system to the print head portion. Warmed to ° C. Also, a heater was incorporated in the piezo head, and the ink in the recording head was also heated.

  In addition, the recording head has a nozzle diameter of 24 μm and a resolution of 512 dpi arranged in a staggered manner to achieve a recording resolution of 1200 dpi × 1200 dpi. The amount of magenta ink droplets ejected from the head was 3.5 pl per droplet, and the droplet ejection speed was 6 m / sec. As the intermediate transfer medium, a surface of a stainless steel drum was coated with a silicone resin.

Recording medium, coated printing paper A (manufactured by OK top coat rice basis weight of 84.9g / ^{m 2} Oji Paper Co., Ltd.), coated printing paper B (manufactured by New Age rice basis weight of 104.7g / ^{m 2} Oji Paper Co., Ltd.) , Art paper (SA Kanfuji, US basis weight 104.7 g / m ² manufactured by Oji Paper Co., Ltd.).

First, ink droplets were ejected from the recording head onto an intermediate transfer medium to form a predetermined image. Thereafter, the ink droplets were transferred from the intermediate transfer medium to the recording medium. After transferring the ink droplets to the recording medium, an LED lamp (385 nm, manufactured by Hamamatsu Photonics, a distance of 2 mm between the recording medium and the lamp, a maximum output of 3800 mW / cm ² (UV integrated photometer manufactured by Hamamatsu Photonics) : Measured with C9536-02)), and the ink was cured by irradiation with ultraviolet rays. The conveyance speed of the recording medium was 600 mm / s. The image formation was performed in an environment of 23 ° C. and 55% RH.

  The temperature of the intermediate transfer medium when the ink droplets are attached, the temperature of the recording medium when transferring the ink droplets from the intermediate transfer medium, and the intermediate transfer medium when transferring the ink droplets from the intermediate transfer medium to the recording medium Table 4 below shows the nip pressure with the recording medium.

  The obtained printed image was evaluated in the same manner as Example 1 for character quality, gloss uniformity, and relief. The results are shown in Table 4.

As shown in Table 4, when the ink storage elastic modulus at the temperature of the intermediate transfer medium was 3 × 10 ³ Pa or more (Comparative Examples 8 and 9), the character quality was good, but the gloss level was good. The evaluation of texture and relief was bad. It is presumed that the hardness of the ink was high and the coating film was difficult to smooth.

On the other hand, when the viscosity of the intermediate transfer medium at a temperature lower than 1 × 10 ³ mPa · s (Comparative Example 10), the character quality was low and gloss unevenness was observed. Since the viscosity of the intermediate transfer medium is too low, it is presumed that adjacent droplets are mixed on the intermediate transfer medium.

In addition, when the temperature of the intermediate transfer medium at the time of ink landing is relatively low (25 ° C.) ( Reference Example 6 ), the character quality is relatively good, but the gloss uniformity may be small, and the relief feeling may also be low. Somewhat seen. When the temperature of the intermediate transfer medium at the time of ink landing is low, the sol-gel phase transition is performed quickly. For this reason, it is assumed that the coating film on the intermediate transfer medium has relatively large irregularities and steps, and these steps and irregularities were not sufficiently smoothed during the transfer.

  An image formed from the actinic ray curable ink-jet ink of the present invention is excellent in gloss uniformity and is unlikely to have a step between the recording portion and the non-recording portion. Therefore, the present invention is suitable for producing various printed materials that require uniform gloss and smoothness.

DESCRIPTION OF SYMBOLS 10, 20, 30 Inkjet recording apparatus 11 Intermediate transfer medium 12 Recording medium 13 Cleaning member 14 Inkjet recording head 15 Conveying member 16 Head carriage 18 Light irradiation part 19 Temperature control part

Claims (3)

An ink attachment step in which ink droplets of an actinic radiation curable inkjet ink containing a photopolymerizable compound, a photopolymerization initiator, and a gelling agent are ejected from an inkjet recording head and adhered to an intermediate transfer medium;
A transfer step of transferring ink droplets attached to the intermediate transfer medium to a recording medium;
A curing step of irradiating the ink droplets transferred to the recording medium with actinic rays to cure each droplet,
The actinic radiation curable inkjet ink contains the gelling agent in an amount of 0.5% by mass or more and less than 10% by mass with respect to the total mass of the ink,
The viscosity of the ink at the temperature of the intermediate transfer medium in the ink adhering step is 1 × 10 ³ mPa · s or more and less than 5 × 10 ⁴ mPa · s, and the storage modulus of the ink is 3 × 10 ^1. Pa or more, Ri 3 × ¹⁰ 3 Pa less than der,
The image forming method , wherein the temperature of the recording medium in the transfer step is 5 ° C. or more and less than 15 ° C. lower than the temperature of the intermediate transfer medium in the transfer step .   The image forming method according to claim 1, wherein the temperature of the intermediate transfer medium in the ink adhering step is 30 ° C. or higher and lower than 55 ° C.   The image forming method according to claim 1 or 2, wherein a nip pressure between the intermediate transfer medium and the recording medium in the transfer step is 0.1 MPa or more and less than 0.5 MPa.

Images