Image formation method

Abstract

To provide an image forming method capable of suppressing strike-through and oozing-out of ink in forming an image by using active ray-curable ink.SOLUTION: An image forming method includes: a process for applying pretreatment liquid to a recording medium 110; a process for applying active ray-curable ink to a surface of the recording medium to which the pretreatment liquid is applied; and a process for irradiating the applied active ray-curable ink with an active ray. The pretreatment liquid includes water and resin, and the active ray-curable ink includes a two-functional monomer or a polyfunctional monomer. The active ray-curable ink is applied to the surface of the recording medium to which the pretreatment liquid set to a temperature lower than a glass transition temperature (Tg) of the resin is applied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming method. [Background technology]

[0002] The inkjet method can easily and inexpensively produce images, and is therefore applied to various printing fields, including various types of printing, marking, fine line formation, and special printing such as color filters, etc. The inkjet method is particularly suitable for applications in which a variety of images are formed in small quantities, since it allows digital printing without using a plate.

[0003] When an image is formed by the inkjet method on a recording medium that absorbs ink, such as paper, the components (e.g., actinic radiation polymerizable compound, coloring material, etc.) in the ink that is discharged from an inkjet head and landed on the recording medium are likely to be absorbed into the recording medium, which can easily cause strike-through of the landed ink, ink bleeding, and uneven density of the formed image. Therefore, in order to prevent the ink from being absorbed into the recording medium, a method has been considered in which a pretreatment liquid is applied to the surface of the recording medium to form a pretreatment layer, and then ink is applied to the surface of the pretreatment layer.

[0004] For example, Patent Document 1 describes an image forming method in which an oil-based ink is applied onto a recording medium coated with a pretreatment liquid containing polyolefin-based resin particles. According to Patent Document 1, the solvent in the oil-based ink is absorbed by the polyolefin-based resin particles, suppressing penetration into the recording medium, and the coloring material remains on the surface of the recording medium, thereby suppressing ink strike-through and bleeding.

[0005] Patent Document 2 describes an image forming method including a step of forming a pretreatment layer on the surface of a recording medium using a pretreatment layer forming material containing a resin, and a step of applying ink onto the formed pretreatment layer by an ink applying means. According to Patent Document 2, the ink applying means is heated to a temperature higher than the glass transition temperature of the resin contained in the pretreatment layer, so that a part of the ink components is impregnated into the inside of the pretreatment layer and the ink is quickly fixed on the pretreatment layer, thereby suppressing ink bleeding.

[0006] Patent Document 3 describes an image forming method including a step of applying a reaction liquid containing an aggregating agent for aggregating components of a water-based ink composition to the surface of a recording medium, and a step of applying a water-based ink to the surface of the reaction liquid applied to the surface of the recording medium. According to Patent Document 3, the water-based ink contains a surface-treated pigment, which improves reactivity with the aggregating agent contained in the reaction liquid, so that a sufficient image quality can be obtained even if the amount of the reaction liquid applied is reduced. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-104872 A [Patent Document 2] JP 2018-138347 A [Patent Document 3] JP 2018-165029 A Summary of the Invention [Problem to be solved by the invention]

[0008] As described in Patent Documents 1 to 3, when forming an image on a recording medium, it is required to suppress ink bleed-through and bleeding. Here, the methods described in Patent Documents 1 and 3 are intended for oil-based ink and water-based ink, respectively. However, ink bleed-through and bleeding also occur when forming an image using actinic ray curable ink, and the methods described in these documents cannot suppress bleed-through and bleeding of actinic ray curable ink.

[0009] On the other hand, it is expected that the method described in Patent Document 2 can also suppress strike-through and bleeding of actinic ray curable ink. However, according to the study by the present inventors, even the method described in Patent Document 2 cannot completely suppress strike-through and bleeding of actinic ray curable ink.

[0010] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide an image forming method capable of suppressing ink strike-through and bleeding when forming an image using actinic ray-curable ink. [Means for solving the problem]

[0011] In order to solve the above problems, an image forming method according to one embodiment of the present invention includes the steps of applying a pretreatment liquid to a recording medium, applying an actinic ray curable ink to a surface of the recording medium to which the pretreatment liquid has been applied, and irradiating the applied actinic ray curable ink with actinic rays, wherein the pretreatment liquid contains water and a resin, the actinic ray curable ink contains a bifunctional monomer or a polyfunctional monomer, and the actinic ray curable ink is applied to a surface of the recording medium set to a temperature lower than the glass transition temperature (Tg) of the resin. Effect of the Invention

[0012] According to the present invention, it is possible to provide an image forming method capable of suppressing ink strike-through and bleeding when forming an image using actinic ray curable ink. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus for carrying out an image forming method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described in detail.

[0015] 1. Image forming method An image forming method according to one embodiment of the present invention includes the steps of (1) applying a pretreatment liquid to a recording medium, (2) applying an actinic ray curable ink to the surface of the recording medium to which the pretreatment liquid has been applied, and (3) irradiating the applied actinic ray curable ink with actinic rays. Each step will be described below.

[0016] 1-1. Step of applying pretreatment liquid The step of applying a pretreatment liquid is a step of applying the pretreatment liquid to the surface of the recording medium.

[0017] [Pretreatment liquid] The pretreatment liquid according to one embodiment of the present invention is a liquid containing water and a resin. The pretreatment liquid may also contain a water-soluble organic solvent and additives such as a surfactant, a preservative, and a fungicide.

[0018] (resin) Examples of the resin include water-soluble resins and aqueous resin emulsions. The types of water-soluble resins and aqueous resin emulsions are not particularly limited, and known or commercially available water-soluble resins and aqueous resin emulsions can be used. The water-soluble resins and aqueous resin emulsions can also be used in combination.

[0019] Examples of water-soluble resins include polyacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid-acrylic acid ester copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene-maleic acid copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-crotonic acid copolymer, vinyl acetate-acrylic acid copolymer, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, sugars, and the like, and salts thereof. The water-soluble resins may be used alone or in combination of two or more kinds. In addition, the copolymer may be in the form of any of random copolymer, block copolymer, alternating copolymer, and graft copolymer.

[0020] Examples of commercially available water-soluble acrylic resins include Joncryl 63J (weight average molecular weight (Mw): 12,500, acid value: 213), Joncryl 67 (weight average molecular weight (Mw): 12,500, acid value: 213), Joncryl 678 (weight average molecular weight (Mw): 8,500, acid value: 215), Joncryl 586 (weight average molecular weight (Mw): 4,600, acid value: 108), Joncryl 611 (weight average molecular weight (Mw): 8,100, acid value: 53), Joncryl 680 (weight average molecular weight (Mw): 4,900, acid value: 215), and Joncryl 682 (weight average molecular weight (Mw): 4,900, acid value: 215), all manufactured by BASF. These include Joncryl 683 (weight average molecular weight (Mw): 8,000, acid value: 160), Joncryl 690 (weight average molecular weight (Mw): 16,500, acid value: 240) ("Joncryl" is a registered trademark of the company), Jurymer AT-210, AT-510, AT-613, and ARUFON series ("Jurymer" and "ARUFON" are registered trademarks of the company) manufactured by Toagosei Co., Ltd., and X-1, X-200, X-205, X-220, YS-1274, VS-1047, RS-1191, TS-1315, and RS-1190 manufactured by Seiko PMC Corporation. These include solid resins, which can be used by neutralizing and dissolving them in water or the like with a base or by dissolving them in a solvent.

[0021] Examples of the aqueous resin emulsion include (meth)acrylic resin emulsions, urethane resin emulsions, polyester resin emulsions, and polyolefin resin emulsions.

[0022] Examples of commercially available products of the (meth)acrylic resin emulsion include Vinyblan 2580, Vinyblan 2585, Vinyblan 2680, Vinyblan 2682, Vinyblan 2684, Vinyblan 2685, Vinyblan 2687, Vinyblan GA-6610 (all manufactured by Nissin Chemical Industry Co., Ltd.), Joncryl 741, Joncryl 790, Joncryl 537J (all manufactured by BASF, "Joncryl" is a registered trademark of the company), etc. The (meth)acrylic resin emulsion may be used alone or in combination of two or more kinds.

[0023] Examples of the urethane resin emulsion include WBR-016U (manufactured by Taisei Fine Chemical Co., Ltd.), Superflex 150HS, Superflex 620, Superflex 650, Superflex 500M, Superflex E-2000 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Superflex" being a registered trademark of the company), Permarine UC-20 (manufactured by Sanyo Chemical Industries, Ltd., "Permarine" being a registered trademark of the company), Parasurf UP-22 (manufactured by Ohara Palladium Chemical Co., Ltd.), etc. The urethane resin emulsions may be used alone or in combination of two or more kinds.

[0024] Examples of commercially available polyester resin emulsions include ELITEL KA-5034, ELITEL KA-5071S, ELITEL KA-1449, ELITEL KA-0134, ELITEL KA-3556, ELITEL KA-6137, ELITEL KZA-6034, ELITEL KT-8803, ELITEL KT-8701, ELITEL KT-9204, ELITEL KT-8904, ELITEL KT-0507, and ELITEL KT-9511 (all manufactured by Unitika Ltd., "ELITEL" is a registered trademark of the company). The polyester resin emulsions may be used alone or in combination of two or more kinds.

[0025] Examples of the polyolefin resin emulsion include Arrowbase SB-1200 (manufactured by Unitika Ltd., "Arrowbase" is a registered trademark of the company), Auroren 150A, Auroren AE-301 (manufactured by Nippon Paper Industries Co., Ltd., "Auroren" is a registered trademark of the company), Superclone E-415 (manufactured by Nippon Paper Industries Co., Ltd., "Superclone" is a registered trademark of the company), Hardlen Na-1001 (manufactured by Toyobo Co., Ltd., "Hardlen" is a registered trademark of the company), etc. The polyolefin resin emulsions may be used alone or in combination of two or more types.

[0026] The weight average molecular weight (Mw) of the water-soluble resin is preferably from 1000 to 100000, and more preferably from 3000 to 50000. When the weight average molecular weight (Mw) of the water-soluble resin is within the above range, the storage stability of the pretreatment liquid can be maintained good, and the pretreatment liquid can be uniformly applied to the recording medium due to appropriate fluidity, so that the ink can be retained on the surface of the recording medium and a decrease in image density can be suppressed.

[0027] Among the above resins, aqueous resin emulsions are preferred. Among the above aqueous resin emulsions, (meth)acrylic resin emulsions, styrene-(meth)acrylic resin emulsions, and urethane resin emulsions are preferred. When (meth)acrylic resin emulsions, styrene-(meth)acrylic resin emulsions, and urethane resin emulsions are used as aqueous resin emulsions, the adhesion of the pretreatment liquid to the recording medium is improved, and the emulsion is also excellent in storage stability, such as being less likely to settle.

[0028] In addition, the water-soluble resin and the resin contained in the aqueous resin emulsion preferably have a glass transition temperature (Tg).

[0029] The resin contained in the water-soluble resin and the aqueous resin emulsion according to one embodiment of the present invention preferably has a glass transition temperature (Tg) of 15°C or more and 90°C or less, and more preferably has a glass transition temperature (Tg) of 45°C or more and 65°C or less. When the glass transition temperature (Tg) of the resin is 15°C or more and 90°C or less, the ink is prevented from penetrating into the recording medium or the resin, so that an image with high density can be formed with almost no uneven density on the image surface, and the ink is prevented from penetrating into the back surface of the recording medium and striking through. Furthermore, when the glass transition temperature (Tg) of the resin is 45°C or more and 65°C or less, the resin is unlikely to soften at room temperature, so that the scratch resistance of the formed image can be improved.

[0030] The glass transition temperature (Tg) of the water-soluble resin and the resin contained in the aqueous resin emulsion can be measured using a commercially available measuring device such as "Diamond DSC" (manufactured by PerkinElmer).

[0031] The content of the resin contained in the pretreatment liquid is more preferably 5% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less, in terms of the solid content, relative to the total mass of the pretreatment liquid. When the content of the resin contained in the pretreatment liquid is 5% by mass or more, the surface of the recording medium set at a temperature lower than the glass transition temperature (Tg) of the resin is covered with the resin contained in the pretreatment liquid. Therefore, the actinic radiation curable ink is less likely to be absorbed by the recording medium, and therefore the strike-through of the actinic radiation curable ink can be suppressed. Furthermore, when the content of the resin contained in the pretreatment liquid is 20% by mass or less, the pretreatment liquid is easily discharged even when the inkjet method, spray coating, or the like is used as the coating method, and in the case of an aqueous resin emulsion, the resin can be suppressed from coagulating and precipitating, resulting in good storage stability.

[0032] (Water-soluble organic solvent) The pretreatment liquid according to an embodiment of the present invention may contain a water-soluble organic solvent.

[0033] Examples of the water-soluble organic solvent include glycerols such as glycerin, diglycerin, and polyglycerin; glycols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol glycerin, trimethylolethane, trimethylolpropane, tributyrolpropane, pentaerythritol, and polyfunctional glycols including sorbitol; methanol, ethanol, propanol, isopropanol, butanol, 2-butanol, tert-butanol, isobutanol, pentanol, isopentanol, hexanol, isohexanol, octanol, isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol, tert-nonyl alcohol, decanol, dodecanol, dodecahexanol, dodecaoctanol, allyl alcohol, oleyl alcohol, 1-methoxy-1-propanol, monoalcohols such as 1,2-butanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,2-hexanediol, 1,8-octanediol, 1,2-octanediol, 1, Alkanediols such as 9-nonanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-dibutyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 2-methyl-1,8-octanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol; imidazolidinones such as 1,3-dimethyl-2-imidazolidinone;Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monodiethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monophenyl ether, dipropylene glycol monomethyl ether glycol ethers such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine; and amides such as formamide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0034] Among the above water-soluble organic solvents, glycerins and glycols are preferred. Among the glycerins and glycols, glycerin and propylene glycol are preferred. By using a water-soluble organic solvent having two or more hydroxyl groups in one molecule, which is contained in glycerins and glycols, the hydrophilicity of the pretreatment liquid can be increased, and the pretreatment liquid can be made less compatible with the actinic ray curable ink applied to the surface of the pretreatment liquid. Therefore, the actinic ray curable ink applied to the surface of the pretreatment liquid is less likely to penetrate into the pretreatment liquid, and therefore the strike-through of the actinic ray curable ink can be suppressed. In addition, the actinic ray curable ink is more likely to remain on the surface of the pretreatment liquid, and therefore the bleeding of the ink can be suppressed.

[0035] The water-soluble organic solvent is preferably 0% by mass or more and 80% by mass or less, more preferably 50% by mass or more and 80% by mass or less, based on the total mass of the pretreatment liquid. By making the content of the water-soluble organic solvent 50% by mass or more based on the total mass of the pretreatment liquid, the water-soluble organic solvent and the resin contained in the pretreatment liquid are well compatible with each other, and the resin can be applied uniformly to the surface of the recording medium. Therefore, the voids present on the surface of the recording medium can be filled with the resin contained in the pretreatment layer, so that the actinic radiation curable ink can be prevented from being absorbed into the recording medium and causing strike-through. In addition, by making the content of the water-soluble organic solvent 80% by mass or less based on the total mass of the pretreatment liquid, a decrease in fluidity can be prevented, and in the case where an aqueous resin emulsion is contained, aggregation and sedimentation of the aqueous resin emulsion can be prevented.

[0036] [Other ingredients] The pretreatment liquid according to an embodiment of the present invention may contain a surfactant, a preservative, and an antifungal agent.

[0037] (Surfactant) Examples of surfactants include anionic surfactants including dialkyl sulfosuccinates, alkyl naphthalene sulfonates, and fatty acid salts; nonionic surfactants including polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, and polyoxyethylene-polyoxypropylene block copolymers; cationic surfactants including alkylamine salts and quaternary ammonium salts, silicone surfactants, and fluorine-based surfactants.

[0038] The surfactant is preferably present in an amount of 0% by mass or more and 5% by mass or less, and more preferably in an amount of 0% by mass or more and 2% by mass or less, based on the total mass of the pre-treatment liquid.

[0039] (Preservatives and antifungal agents) Examples of the preservative or antifungal agent include aromatic halogen compounds (eg, Preventol CMK manufactured by Lancs), methylene dithiocyanate, halogen-containing nitrogen-sulfur compounds, and 1,2-benzisothiazolin-3-one (eg, PROXELGXL manufactured by Lonza).

[0040] The amount of the preservative or antifungal agent is preferably 0.1% by mass or more and 1% by mass or less, and more preferably 0.1% by mass or more and 0.5% by mass or less, based on the total mass of the pretreatment liquid.

[0041] (Properties of pretreatment liquid) The viscosity of the pretreatment liquid is preferably 1000 cPs or more and 10000 cPs or less at 20° C. If the viscosity of the pretreatment liquid is 1000 Ps or more, the pretreatment liquid can be applied uniformly to the entire surface of the recording medium or to the area to which the surface treatment liquid is to be applied. The viscosity of the pretreatment liquid at 20° C. can be measured using a stress-controlled rheometer "Physica MCR301" (manufactured by Anton Paar, cone plate diameter: 75 mm, cone angle: 1.0°).

[0042] [Method of applying pretreatment liquid] The pretreatment liquid can be applied by a known liquid application method such as spray application, spiral application using a nozzle or a slit, dipping application, roll coater application, gravure application, flexo application, or inkjet application.

[0043] The amount of the pretreatment liquid applied was 1 g / m 2 More than 50g / m 2 It is preferable that the content is 2 g / m or less. 2 More than 30g / m 2 It is more preferable that the amount of the pretreatment liquid applied is 1 g / m or less. 2 When the amount of the pretreatment liquid applied is 50 g / m or more, the voids present on the surface of the recording medium can be filled with the resin contained in the pretreatment layer. 2If the amount of resin contained in the pretreatment layer is less than this, the voids in the pretreatment layer will be reduced, making it difficult for ink to penetrate into the applied pretreatment layer, and ink bleed-through can be suppressed.

[0044] [Recording Media] The recording medium according to an embodiment of the present invention is not particularly limited, and any known recording medium can be used.

[0045] Examples of the recording medium include paper that does not have a surface layer such as an ink receiving layer or a film layer, such as copy paper, wood-free paper, recycled paper, etc. Examples of the copy paper, wood-free paper, and recycled paper include Xerox 4200, Xerox 4024 (both manufactured by Xerox Corporation), GeoCycle (Georgia-Pacific), Recyclecut R-100 (manufactured by Oji Paper Co., Ltd.), and 55PW (manufactured by Lintec Corporation).

[0046] Furthermore, medium-quality paper, wood-based paper, coated paper, art paper, cast-coated paper, and the like may also be used.

[0047] The absorbent recording medium is a recording medium that is absorbed in a liquid for 30 msec from the start of contact with the pretreatment liquid in the Bristow method. 1 / 2 The amount of water absorbed by the pretreatment solution is less than 10ml / m 2 More than 30ml / m 2 It is preferable that:

[0048] The amount of water absorbed by the pretreatment liquid can be determined in accordance with Standard No. 51 "Paper and paperboard - Liquid absorbency test method - Bristow method" of the "JAPAN TAPPI Paper and Pulp Testing Method" adopted by the Japan Pulp and Paper Technology Association (JAPANTAPPI).

[0049] 1-2. Step of applying actinic radiation curable ink for inkjet printing The process of applying an actinic ray curable ink for inkjet (hereinafter also simply referred to as the "ink application process") is a process of applying an actinic ray curable ink to the surface of a pretreatment liquid applied to the surface of a recording medium to form an intermediate image.

[0050] In an ink application step according to an embodiment of the present invention, the actinic radiation curable ink is applied to the surface of a recording medium set at a temperature lower than the glass transition temperature (Tg) of the resin contained in the pretreatment liquid. By setting the temperature of the recording medium in this way, the resin applied by the pretreatment liquid does not soften significantly, and the ink can be applied to a surface in a state in which gaps between the resin molecules due to the movement of the resin are unlikely to occur. Therefore, it is considered that the resin sufficiently suppresses unintended diffusion of the ink, and thus the ink strike-through and bleeding can be sufficiently suppressed. From the above viewpoint, the temperature of the recording medium is preferably 10° C. to 30° C. lower than the glass transition temperature (Tg) of the resin contained in the pretreatment liquid, and more preferably 10° C. to 20° C. lower.

[0051] In the present invention, the phrase "set to a temperature lower than the glass transition temperature (Tg) of the resin contained in the pretreatment liquid" means that, when the pretreatment liquid contains multiple resins, the temperature is set to a temperature lower than the maximum glass transition temperature among those resins.

[0052] The temperature lower than the glass transition temperature (Tg) of the resin contained in the pretreatment liquid is preferably lower than the glass transition temperature (Tg) of the resin contained in the most abundant amount of the resins contained in the pretreatment liquid, and is preferably lower than the glass transition temperature (Tg) of all the resins contained in the pretreatment liquid.

[0053] In the present invention, it is preferable to further include a step of drying the pretreatment liquid applied to the surface of the recording medium after the step of applying the pretreatment liquid to the recording medium. Examples of the method for drying the pretreatment liquid include a method using a non-contact heating type drying device such as a drying oven or a hot air blower, and a method using a contact heating type drying device such as an infrared heater, a hot plate, or a heat roller. The above method can be appropriately selected depending on the type of water-soluble organic solvent contained in the pretreatment liquid.

[0054] [Actinic radiation curable ink] An actinic ray-curable ink according to one embodiment of the present invention is an ink that contains an actinic ray-polymerizable compound, and is cured by being polymerized and crosslinked by irradiation with actinic rays.

[0055] The actinic ray-polymerizable compound contained in the actinic ray-curable ink according to one embodiment of the present invention is preferably a monomer having a solubility parameter (SP value) of 20 or less, and more preferably the SP value of the monomer is 17 or more and 20 or less. By having an SP value of 17 or more and 20 or less, it is possible to increase the difference with the SP value of the resin contained in the pretreatment liquid. As a result, the monomer contained in the actinic ray-curable ink and the resin contained in the pretreatment liquid are less likely to be compatible with each other, so that it is possible to suppress strike-through due to penetration of the actinic ray-curable ink. In addition, since the actinic ray-curable ink is more likely to remain on the surface of the pretreatment liquid, it is possible to suppress bleeding of the ink.

[0056] Moreover, the actinic ray polymerizable compound contained in the actinic ray curable ink according to one embodiment of the present invention can include a monofunctional monomer, a bifunctional monomer, or a polyfunctional monomer.

[0057] The actinic ray curable ink preferably contains a bifunctional monomer or a polyfunctional monomer. The actinic ray curable ink preferably contains 30% by mass or more and 80% by mass or less of the bifunctional monomer or the polyfunctional monomer, and more preferably contains 50% by mass or more and 80% by mass or less of the bifunctional monomer or the polyfunctional monomer, based on the total mass of the actinic ray curable ink. By containing 30% by mass or more of the bifunctional monomer or the polyfunctional monomer, when the ink is cured by irradiation with actinic rays, the cured product formed by curing the ink forms a network structure, and the surface becomes hard, so that the scratch resistance of the formed image can be improved. In addition, by containing 80% by mass or less of the bifunctional monomer or the polyfunctional monomer, based on the total mass of the actinic ray curable ink, the cured product formed by curing the ink does not become too hard, so that the fixability to the recording medium is not easily impaired.

[0058] (Active radiation polymerizable compound) The actinic radiation polymerizable compound is a compound that crosslinks or polymerizes by irradiation with actinic radiation. Examples of actinic radiation include electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among the actinic radiation, ultraviolet rays or electron beams are preferred, and ultraviolet rays are more preferred. Examples of the actinic radiation polymerizable compound include radical polymerizable compounds, cation polymerizable compounds, or mixtures thereof. Among the actinic radiation polymerizable compounds, radical polymerizable compounds are preferred. The actinic radiation polymerizable compound may be any of a monomer, a polymerizable oligomer, a prepolymer, and a mixture thereof.

[0059] The radical polymerizable compound is a compound having an ethylenically unsaturated double bond group in the molecule. The radical polymerizable compound may be a monofunctional or polyfunctional compound. Examples of the radical polymerizable compound include (meth)acrylate, which is an unsaturated carboxylic acid ester compound. In the present invention, "(meth)acrylate" means acrylate or methacrylate, "(meth)acryloyl group" means acryloyl group or methacryloyl group, and "(meth)acrylic" means acrylic or methacrylic.

[0060] Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, benzyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomylstyryl (meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, Methoxypolyethyleneglycol(meth)acrylate, methoxypropyleneglycol(meth)acrylate, phenoxyethyl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate, isobornyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl(meth)acrylate. The monofunctional (meth)acrylate may be used alone or in combination of two or more kinds.

[0061] Examples of bifunctional and polyfunctional (meth)acrylates include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, PO adduct di(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene These include difunctional (meth)acrylates such as glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; tri- or higher functional (meth)acrylates such as pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxy tri(meth)acrylate, and pentaerythritol ethoxy tetra(meth)acrylate; oligomers having a (meth)acryloyl group, including polyester acrylate oligomers, and modified products thereof. Examples of the modified products include ethylene oxide modified (EO modified) (meth)acrylates in which ethylene oxide groups are inserted, and propylene oxide modified (PO modified) (meth)acrylates in which propylene oxide groups are inserted. The bifunctional and polyfunctional (meth)acrylates may be used alone or in combination of two or more kinds.

[0062] The cationic polymerizable compound is a compound having a cationic polymerizable group in the molecule. Examples of the cationic polymerizable compound include epoxy compounds, vinyl ether compounds, and oxetane compounds.

[0063] Examples of the epoxy compounds include cycloaliphatic epoxy resins such as 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene monoepoxide, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate, 1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meta-dioxane and bis(2,3-epoxycyclopentyl)ether, diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, and the like. and aliphatic epoxy compounds including polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin; and aromatic epoxy compounds including di- or polyglycidyl ethers of bisphenol A or its alkylene oxide adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and novolac-type epoxy resins.

[0064] Examples of the vinyl ether compound include monovinyl ether compounds including 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 vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether, as well as di- or trivinyl ether compounds including 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, and trimethylolpropane trivinyl ether.

[0065] Examples of the oxetane compound include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-n-butyloxetane, 3-hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3-hydroxyethyl -3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3-hydroxybutyl-3-methyloxetane, 1,4 bis{[(3-ethyl-3-oxetanyl)methoxy]methyl}benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane and di[1-ethyl(3-oxetanyl)]methyl ether.

[0066] Of the radically polymerizable compounds and cationically polymerizable compounds, it is preferable to use a radically polymerizable compound.

[0067] (Polymerization initiator) The actinic ray curable ink according to one embodiment of the present invention may contain a polymerization initiator. The polymerization initiator may be any initiator capable of initiating polymerization of the actinic ray polymerizable compound by irradiation with actinic rays. For example, when the actinic ray curable ink contains a radical polymerizable compound, the polymerization initiator may be a photoradical initiator, and when the actinic ray curable ink contains a cationic polymerizable compound, the polymerization initiator may be a photocationic initiator (photoacid generator).

[0068] The radical polymerization initiator includes an intramolecular bond cleavage type radical polymerization initiator and an intramolecular hydrogen abstraction type radical polymerization initiator.

[0069] Examples of the intramolecular bond cleavage type radical polymerization initiator include acetophenone-based initiators including diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, benzoins including benzoin methyl ether, and benzoin isopropyl ether, acylphosphine oxide-based initiators including 2,4,6-trimethylbenzoin diphenylphosphine oxide, and benzyl and methylphenyl glyoxyesters.

[0070] Examples of the intramolecular hydrogen abstraction type radical polymerization initiator include benzophenone-based initiators including benzophenone, o-benzoylmethylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, acrylated benzophenone, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone-based initiators including 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone; aminobenzophenone-based initiators including Michler's ketone and 4,4'-diethylaminobenzophenone; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, and camphorquinone.

[0071] Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium, and phosphonium, such as B(C6F5)4. - , PF6 - , AsF6 - , SbF6 - , CF3SO3 - These include salts, sulfonates which generate sulfonic acids, halides which photogenerate hydrogen halides, and iron-allene complexes.

[0072] (Gelling agent) The actinic ray curable ink according to one embodiment of the present invention may contain a gelling agent, which is an organic substance that is solid at room temperature but becomes liquid when heated, thereby causing the actinic ray curable ink to undergo a sol-gel phase transition in response to a change in temperature.

[0073] Moreover, the gelling agent preferably crystallizes in the ink at a temperature equal to or lower than the gelling temperature of the ink. Here, the gelling temperature refers to the temperature at which the ink undergoes a phase transition from sol to gel and the viscosity of the ink suddenly changes when the ink that has been solated or liquefied by heating is cooled. Specifically, the ink that has been solated or liquefied is cooled while the viscosity is measured using, for example, a rheometer "MCR300" (manufactured by Anton Paar), and the temperature at which the viscosity suddenly increases can be determined as the gelling temperature of the ink.

[0074] When the gelling agent crystallizes in the ink, a structure may be formed in which the actinic radiation polymerizable compound is encapsulated in a three-dimensional space formed by the gelling agent and wax crystallized into plate shapes (such a structure will be referred to as a "house of cards structure" hereinafter). When a house of cards structure is formed, the liquid actinic radiation polymerizable compound is held within the space, making it difficult for the actinic radiation polymerizable compound to be compatible with the resin contained in the pretreatment liquid, and therefore it becomes difficult for the actinic radiation curable ink to penetrate into the pretreatment liquid, making it possible to suppress ink bleed-through.

[0075] Examples of gelling agents include aliphatic ketone waxes such as dipentadecyl ketone, diheptadecyl ketone (stearone), dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dimyristyl ketone, lauryl myristyl ketone, lauryl palmityl ketone, myristyl palmityl ketone, myristyl stearyl ketone, myristyl behenyl ketone, palmityl stearyl ketone, palmityl behenyl ketone and stearyl behenyl ketone; cetyl palmitate, stearyl stearate, behenic acid Aliphatic ester waxes such as behenyl, icosanoic acid ethyl ester, behenyl stearate, palmityl stearate, lauryl stearate, stearyl palmitate, myristyl myristate, cetyl myristate, octyldodecyl myristate, stearyl oleate, stearyl erucate, stearyl linoleate, behenyl oleate and arachidyl linoleate; amide compounds such as N-lauroyl-L-glutamic acid dibutylamide and N-(2-ethylhexanoyl)-L-glutamic acid dibutylamide; 1,3:2,4-bis-O-benzene dibenzylidene sorbitols such as sorbitol-D-glucitol; petroleum waxes such as paraffin wax, microcrystalline wax, and petrolactam; vegetable waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as montan wax and hydrogenated wax; hydrogenated castor oil or derivatives of hydrogenated castor oil; montan wax derivatives, paraffin wax derivatives, microcrystalline wax, and other vegetable waxes. modified waxes such as wax derivatives or polyethylene wax derivatives; higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid; higher alcohols such as stearyl alcohol and behenyl alcohol; hydroxystearic acids 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, ricinoleic acid amide, and 12-hydroxystearic acid amide;N-substituted fatty acid amides such as N-stearylstearamide and N-oleylpalmitamide; special fatty acid amides such as N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide, and N,N'-xylylenebisstearylamide; higher amines such as dodecylamine, tetradecylamine, and octadecylamine; fatty acid ester compounds such as stearylstearic acid, oleylpalmitic acid, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, and polyoxyethylene fatty acid ester; sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid; synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax; polymerizable wax; dimer acid; dimer diol, etc. These waxes may be used alone or in combination of two or more kinds.

[0076] Of these, from the viewpoint of further enhancing the pinning properties of the ink, aliphatic ketone waxes, aliphatic ester waxes, higher fatty acids, higher alcohols, and fatty acid amides are preferred, and aliphatic ketone waxes or aliphatic ester waxes in which the carbon chains on both sides of the keto group or ester group each have 9 or more and 25 or less carbon atoms are more preferred.

[0077] The content of the gelling agent is preferably 0.5% by mass or more and less than 10.0% by mass, more preferably 1.0% by mass or more and less than 10.0% by mass, and even more preferably 2.0% by mass or more and 7.0% by mass or less, relative to the total mass of the actinic ray curable ink.

[0078] (Polymerization inhibitor) The actinic ray curable ink may contain a polymerization inhibitor.

[0079] Examples of the polymerization inhibitor include (alkyl)phenols, 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, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino-1,3-dimethylbutylidene)aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0080] The content of the polymerization inhibitor may be 0.05% by mass or more and 0.2% by mass or less with respect to the total mass of the ink.

[0081] (Colorant) The actinic radiation curable ink may contain a coloring material. The coloring material may include a pigment and a dye. From the viewpoint of further increasing the dispersion stability of the actinic radiation curable ink and forming an image with high weather resistance, the coloring material is preferably a pigment. Examples of the pigment include organic pigments and inorganic pigments. Examples of the dye include various oil-soluble dyes.

[0082] The pigment can be selected, for example, from red or magenta pigments, yellow pigments, green pigments, blue or cyan pigments, and black pigments listed in the Color Index, depending on the color of the image to be formed.

[0083] The content of the pigment or dye is preferably 0.1% by mass or more and 20.0% by mass or less, more preferably 0.4% by mass or more and 10.0% by mass or less, based on the total mass of the ink. When the content of the pigment or dye is 0.1% by mass or more, based on the total mass of the ink, the color development of the resulting image is sufficient. When the content of the pigment or dye is 20.0% by mass or less, based on the total mass of the ink, the viscosity of the ink does not become too high.

[0084] (Dispersant) The pigment may be dispersed with a dispersant. The dispersant may be any one that can disperse the pigment sufficiently. Examples of 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 acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ethers, and stearylamine acetate.

[0085] (fixing resin) The actinic radiation curable ink may contain a fixing resin in order to further improve the scratch resistance and blocking resistance of the coating film.

[0086] Examples of the fixing resin include (meth)acrylic resin, epoxy resin, polysiloxane resin, maleic acid resin, vinyl resin, polyamide resin, nitrocellulose, cellulose acetate, ethyl cellulose, ethylene-vinyl acetate copolymer, urethane resin, polyester resin, and alkyd resin.

[0087] The content of the fixing resin can be, for example, from 1.0% by mass to 10.0% by mass based on the total mass of the actinic radiation-polymerizable compound.

[0088] (Surfactant) The actinic ray curable ink may contain a surfactant.

[0089] The surfactant can adjust the surface tension of the ink to adjust the wettability of the ink to a substrate after application, and can suppress the coalescence of adjacent ink droplets.

[0090] Examples of the surfactant include silicone-based surfactants, acetylene glycol-based surfactants, and fluorine-based surfactants having a perfluoroalkenyl group.

[0091] The content of the surfactant is preferably from 0.001% by mass to 10% by mass, and more preferably from 0.001% by mass to 1.0% by mass, based on the total mass of the actinic ray curable ink.

[0092] (Other Ingredients) In addition to the above components, the actinic ray curable ink may contain, as necessary, polysaccharides, viscosity modifiers, resistivity modifiers, film-forming agents, UV absorbers, antioxidants, color-fading inhibitors, antifungal agents, rust inhibitors, etc. The composition may contain only one type of the above other components, or two or more types of them.

[0093] In the present invention, the actinic radiation curable ink can be used as an inkjet ink.

[0094] (Physical properties of actinic radiation curable ink) From the viewpoint of further improving the ejection property from the inkjet head, when the actinic ray curable ink does not contain a gelling agent, the viscosity of the actinic ray curable ink at 40°C is preferably 3 mPa·s or more and 20 mPa·s or less. Furthermore, when the actinic ray curable ink contains a gelling agent, the viscosity of the actinic ray curable ink at 80°C is preferably 3 mPa·s or more and 20 mPa·s or less. When the viscosity at 80°C is 3 mPa·s or more and 20 mPa·s or less, the actinic ray curable ink is less likely to gel when ejected from the inkjet head, so that the actinic ray curable ink can be ejected more stably. Furthermore, when the actinic ray curable ink contains a gelling agent, from the viewpoint of sufficiently gelling the ink when it lands and is cooled to room temperature, the viscosity of the actinic ray curable ink at 25°C is preferably 1000 mPa·s or more. If the viscosity at 25° C. is 1000 mPa·s or more, the ink droplets applied to the recording medium having the pretreatment layer are unlikely to spread out and are unlikely to coalesce with each other.

[0095] The viscosities of the actinic ray curable ink at 40°C and at 80°C are determined by heating the actinic ray curable ink to 100°C, measuring the viscosity using a stress-controlled rheometer "Physica MCR301" (manufactured by Anton Paar), and then cooling the ink to 40°C under conditions of a shear rate of 11.7 (1 / s) and a cooling rate of 0.1°C / s, and reading the viscosities at 40°C and 80°C, respectively, on the viscosity temperature change curve obtained.

[0096] [Method of preparing actinic radiation curable ink] The actinic radiation curable ink can be prepared by mixing the actinic radiation polymerizable compound, polymerization initiator, polymerization inhibitor, colorant, and any other components under heating. At this time, it is preferable to filter the obtained mixture through a predetermined filter. When preparing an ink containing a pigment, it is preferable to prepare a pigment dispersion containing the pigment and the actinic radiation polymerizable compound, and then mix the pigment dispersion with other components. The pigment dispersion may further contain a dispersant.

[0097] The pigment dispersion can be prepared by dispersing a pigment in an actinic radiation polymerizable compound. The pigment can be dispersed using, 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, a paint shaker, etc. At this time, a dispersant may be added.

[0098] [Method of applying actinic ray curable ink] The method of applying the actinic ray curable ink to the surface of the liquid pretreatment layer is not particularly limited, and known methods such as spray coating, dipping, screen printing, gravure printing, offset printing, inkjet method, etc. In one embodiment of the present invention, in the step of applying the actinic ray curable ink to the surface of the liquid pretreatment layer to form an intermediate image, it is preferable to use an inkjet method in which the actinic ray curable ink is ejected from an inkjet head and applied to the surface of the liquid pretreatment layer.

[0099] The inkjet head used in the inkjet method may be either an on-demand type or a continuous type inkjet head. Examples of on-demand type inkjet heads include electro-mechanical conversion types including single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type, and electro-thermal conversion types including thermal inkjet type and bubble jet type ("Bubble Jet" is a registered trademark of Canon Inc.).

[0100] The inkjet head may be either a scanning type or a line type inkjet head.

[0101] At this time, in order to improve the ejection properties of droplets of the actinic ray curable ink, it is preferable to heat the actinic ray curable ink in the inkjet head to 40 to 90° C. and eject the heated actinic ray curable ink.

[0102] Furthermore, when the actinic ray curable ink contains a gelling agent, it is preferable to set the temperature of the actinic ray curable ink in the inkjet head to a temperature 10°C or more and less than 40°C higher than the gelling temperature of the gelling agent contained in the actinic ray curable ink. By setting the temperature of the actinic ray curable ink in the inkjet head to a gelling temperature + 10°C or more, the actinic ray curable ink does not gel inside the inkjet head or on the nozzle surface, and the actinic ray curable ink can be ejected well. Furthermore, by setting the temperature of the actinic ray curable ink in the inkjet head to a temperature less than the gelling temperature of the actinic ray curable ink + 40°C, the thermal load of the inkjet head can be reduced. In particular, in an inkjet head using a piezoelectric element, performance degradation due to thermal load is likely to occur, so it is particularly preferable to set the temperature of the actinic ray curable ink within the above range.

[0103] When the actinic ray curable ink contains a gelling agent, the gelling agent in the actinic ray curable ink applied to the surface of the recording medium is crystallized and pinned, and therefore the applied ink remains on the surface of the pretreatment layer formed on the surface of the recording medium, making it possible to significantly suppress ink strike-through.

[0104] 1-3. Step of exposing actinic radiation-curable ink to actinic radiation In the step of irradiating the actinic ray curable ink with actinic rays, the actinic ray curable ink (intermediate image) applied to the surface of the recording medium is irradiated with actinic rays (e.g., ultraviolet rays) to completely cure the actinic ray curable ink (intermediate image). The wavelength of the actinic ray irradiated in this step is preferably 350 nm or more and 450 nm or less, and more preferably 380 nm or more and less than 430 nm. This allows the actinic ray curable ink to be fully cured, thereby improving the fixability of the actinic ray curable ink to the recording medium.

[0105] 2. Image forming equipment FIG. 1 is a schematic diagram showing an exemplary configuration of an inkjet image forming apparatus 100 according to an embodiment of the present invention.

[0106] An image forming apparatus 100 according to one embodiment of the present invention includes a recording medium 110, a pretreatment liquid application unit 120 that applies a pretreatment liquid to the surface of the recording medium 110, an ink application unit 130 that applies an actinic ray curable ink to the surface to which the pretreatment liquid has been applied, an actinic ray irradiation unit 140 that irradiates the surface to which the actinic ray curable ink has been applied with actinic rays, and a temperature adjustment unit 150 that adjusts the temperature of the recording medium.

[0107] In FIG. 1, a pretreatment liquid deposition section 120, an ink deposition section 130, and an actinic ray irradiation section 140 are arranged in this order from the upstream side along the transport direction of the substrate (direction of the arrow in the figure).

[0108] The pretreatment liquid deposition unit 120 may be configured to deposit the pretreatment liquid onto an area larger than the area on the recording medium 110 onto which the droplets of the actinic ray-curable ink land. For example, the pretreatment liquid deposition unit 120 may include a dispenser 122 that supplies the pretreatment liquid to the application roller 121, and the application roller 121 that applies the supplied pretreatment liquid in the form of a film. Note that the pretreatment liquid deposition unit 120 may use a method using a bar coater or an inkjet method.

[0109] In one embodiment of the present invention, the ink application unit 130 is an ink application unit that forms an image by an inkjet method, and has inkjet heads 132Y, 132M, 132C, and 132K for ejecting actinic radiation curable compositions (inkjet inks) of the respective colors of Y (yellow), M (magenta), C (cyan), and K (black) from nozzles 131 and applying them onto a pretreatment layer formed on the surface of the recording medium 110. The inkjet heads 132Y, 132M, 132C, and 132K apply the actinic radiation curable inks of the respective colors to positions on the pretreatment layer formed on the surface of the recording medium 110 according to the image to be formed, thereby forming an image.

[0110] The actinic ray irradiation unit 140 is disposed downstream of the ink application unit 130 in the transport direction of the recording medium 110, and irradiates actinic rays (ultraviolet rays) toward the surface of the recording medium 110 on which the pretreatment liquid and the actinic ray curable ink are applied. In this way, the actinic ray irradiation unit 140 irradiates the pretreatment liquid and the actinic ray curable ink applied to the surface of the recording medium 110 with actinic rays, thereby curing the pretreatment liquid and the actinic ray curable ink.

[0111] The temperature adjustment unit 150 is for adjusting the temperature of the recording medium 110. The temperature adjustment unit 150 may be a known device capable of adjusting the temperature to a temperature lower than the glass transition temperature (Tg) of the resin contained in the pretreatment liquid. Examples of the temperature adjustment unit 150 include a heater, a cooling device, and a blower.

[0112] In the above description, an image is formed on the surface of the pretreatment liquid applied to the surface of the recording medium by an inkjet method. However, the method of forming the image is not particularly limited, and any known method such as spray coating, a dipping method, screen printing, gravure printing, or offset printing can be used. EXAMPLES

[0113] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

[0114] 1. Preparation of Pretreatment Solution (Preparation of pretreatment solutions 1 to 16) The components shown in Table 1 were mixed and stirred with a stirrer for 1 hour. The resulting solutions were filtered through a 5 μm membrane filter to obtain pretreatment solutions 1 to 16. The units of values ​​shown in Table 1 are parts by mass, the resin content is a solid content equivalent value, the additive is a preservative (Proxel GXL(S), manufactured by Lonza Japan Co., Ltd.), and the water is ion-exchanged water. The values ​​shown in Table 1 are values ​​assuming a total amount of 100 parts by mass.

[0115] The abbreviations shown in Table 1 are as follows. (resin) Resin 1: Water-dispersible acrylic resin emulsion "Joncryl 790" (manufactured by BASF) Resin 2: Styrene-acrylic acid copolymer "Joncryl 63J" Resin 3: Water-dispersible acrylic resin emulsion "Joncryl 537J" Resin 4: Polyurethane water dispersion "Superflex 150HS" (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Resin 5: Water-dispersible acrylic resin emulsion "Joncryl 741"

[0116] The glass transition temperatures (Tg) of resins 1 to 5 shown in Table 1 are catalog values.

[0117] (Water-soluble organic solvent) Gly: Glycerin PG: Propylene glycol (Surfactant) E1010: Acetylene glycol surfactant "Olfine E1010" (manufactured by Nissin Chemical Industry Co., Ltd.)

[0118] [Table 1]

[0119] 2. Preparation of actinic radiation curable ink An actinic radiation curable ink was prepared according to the following procedure.

[0120] 2-1. Preparation of pigment dispersion (Preparation of Cyan Pigment Dispersion 1) 72.7 parts by mass of lauryl acrylate "Light Acrylate LA" (Kyoeisha Chemical Co., Ltd.), 7.0 parts by mass of pigment dispersant "BYKJET-9151" (manufactured by BYK Japan Co., Ltd., "BYKJET" is a registered trademark of the company), and 0.3 parts by mass of polymerization inhibitor "Igastab UV-10" (manufactured by BASF, "Igastab" is a registered trademark of the company) were placed in a stainless steel beaker and stirred for 1 hour while heating on a hot plate at 65 ° C. The resulting solution was cooled to room temperature, and then 20.0 parts by mass of cyan pigment "Chromofine Blue 6332JC" (Pigment Blue 15:4, manufactured by Dainichi Seika Chemicals Co., Ltd.) and 200 g of zirconia beads with a diameter of 0.5 mm were placed in a plastic container, which was then sealed and dispersed for 3 hours using a paint shaker. The zirconia beads were removed from the dispersion to obtain cyan pigment dispersion 1.

[0121] (Preparation of Cyan Pigment Dispersion 2) Cyan pigment dispersion liquid 2 was obtained in the same manner as in the preparation of cyan pigment dispersion liquid 1, except that lauryl acrylate was changed to tripropylene glycol diacrylate.

[0122] 2-2. Preparation of actinic radiation curable ink (Preparation of actinic ray curable ink 1) 33.3 parts by mass of cyan pigment dispersion 1, 33.6 parts by mass of the actinic radiation polymerizable compound "lauryl acrylate", 20 parts by mass of tripropylene glycol diacrylate, 8 parts by mass of dipropylene glycol diacrylate, 5 parts by mass of the polymerization initiator "IRGACURE 819" (manufactured by BASF, "IRGACURE" is a registered trademark of the company), and 0.15 parts by mass of the polymerization inhibitor "Irgastab UV-10" were placed in a stainless steel beaker and stirred at 105°C for 45 minutes. The mixture was then filtered through a 3 μm Teflon (registered trademark) membrane filter manufactured by ADVATEC, thereby obtaining actinic radiation curable ink 1.

[0123] (Preparation of actinic radiation curable inks 2 to 4) The content (unit: parts by mass) of each component of actinic ray curable ink 1 and actinic ray curable inks 2 to 4 is shown in Table 2. The total amount of bifunctional and polyfunctional monomers includes the bifunctional and polyfunctional monomers contained in dispersion liquid 1 and dispersion liquid 2.

[0124] The abbreviations shown in Table 2 are as follows. (Cyan pigment dispersion) Dispersion 1: Cyan pigment dispersion 1 Dispersion 2: Cyan pigment dispersion 2 (Monofunctional Monomer) LA: Lauryl acrylate BA: Benzyl acrylate (Difunctional Monomer) TPGDA: Tripropylene glycol diacrylate (SP value: 17.5) DPGDA: Dipropylene glycol diacrylate (SP value: 17.7) 1,9-NDDA: 1,9-nonanediol diacrylate (SP value: 17.1) (Polyfunctional Monomer) TMP(EO)9TA: Trimethylolpropane EO modified (9) triacrylate (SP value: 19.0) TMP(EO)3TA: Trimethylolpropane EO modified (3) triacrylate (SP value: 17.7) (Polymerization initiator) 819:IRGACURE 819 (Polymerization inhibitor) UV-10: Irgastab UV-10 (Gelling agent) SS: Stearyl stearate

[0125] [Table 2]

[0126] 3. Evaluation Images were formed using pretreatment liquids 1 to 16 and inks 1 to 4, and the image density, strike-through, bleeding and abrasion resistance were evaluated under the following conditions.

[0127] 3-1. Image forming method (Method of applying pretreatment liquid) Using a bar coater No. 8, pretreatment liquids 1 to 16 were applied to a recording medium "Xerox 4024" (copy paper, basis weight 105 g / m) so as to obtain a wet film thickness (18 μm). 2 The mixture was applied to the surface of a substrate (manufactured by Xerox) and dried at 60°C.

[0128] (Image forming method) Ink 1 was loaded into a single-pass inkjet image forming apparatus having an inkjet head equipped with a piezoelectric inkjet nozzle. The ink supply system had an ink tank, an ink flow path, a sub-ink tank immediately before the inkjet head, a pipe with a filter, and an inkjet head, and the temperature of the inkjet head was set to 80°C. The inkjet head used was a piezoelectric head with a nozzle diameter of 20 μm and 1024 nozzles (512 nozzles x 2 rows, staggered arrangement, nozzle pitch of 600 dpi per row). Inks 1 to 4 were ejected at a droplet speed of about 6 m / s under ejection conditions in which the amount of liquid per droplet was 3.0 pl. The conveying section of the recording medium was set so that the temperature of the recording medium to which the pretreatment liquid was applied was 82°C, and the actinic radiation curable ink that had landed on the recording medium was irradiated with ultraviolet light from an LED lamp (Phoseon Technology, 395 nm, water-cooled LED) arranged downstream of the inkjet head to obtain a solid image (resolution: 1200 dpi x 1200 dpi). The image formation was carried out in an environment of 23° C. and 55% RH.

[0129] Further, a solid image was formed in the same manner as in the image forming method using ink 1, except that ink 1 was changed to inks 2 to 4 and the temperature of the recording medium was changed to that shown in Table 3.

[0130] 3-2.Evaluation of image density (Evaluation method) The solid images obtained by the above image forming method were each visually observed.

[0131] (Evaluation Criteria) A: The image surface is almost completely free of uneven density and has high density. B: There is some unevenness in density on the surface of the image, and the density seems a little low. C: The image surface has uneven density and low density.

[0132] 3-3. Evaluation of bleed-through (Evaluation method) An image was formed with a resolution of 1200 dpi x 1200 dpi and a printing ratio of 70%, and was visually observed from the back side.

[0133] (Evaluation Criteria) A: No bleed-through is observed at all B: Slight ink bleeding or bleed-through is observed on the back side. C: Ink bleeding and bleed-through are observed on the back side.

[0134] 3-4. Evaluation of bleeding (Evaluation method) Eight-point alphanumeric characters were printed at a resolution of 1200 dpi x 1200 dpi, and the characters were visually inspected for any thickening.

[0135] (Evaluation Criteria) A: The characters are clearly readable without any bleeding. B: The letters are slightly thickened, but still legible. C: Some characters are thick and difficult to read. D: The letters are blurred and difficult to read.

[0136] 3-5. Evaluation of abrasion resistance (Evaluation method) In accordance with JIS K5701-1 6.2.3, a recording paper of an appropriate size was placed on the solid image obtained by the above image forming method, and a load was applied to rub the recording paper and the solid image together. The degree of density of the image after rubbing was visually observed.

[0137] (Evaluation Criteria) A: No change in image observed after rubbing 100 times or more B: After rubbing 100 times or more, a decrease in image density is observed, but this does not pose a problem in practical use. C: After less than 50 rubs, a clear decrease in image density was observed, and there was a problem in practical use.

[0138] The evaluation results are shown in Table 3.

[0139] [Table 3]

[0140] From the above evaluation results, it was found that the occurrence of ink strike-through, bleeding, and uneven image density can be suppressed by lowering the temperature of the recording medium below the glass transition temperature of the resin. This is believed to be because, even if heated ink is applied to the surface of a recording medium having a pretreatment layer, the resin contained in the pretreatment layer is not easily softened, and the ink tends to remain on the surface without penetrating the pretreatment layer.

[0141] It was also found that the use of ink containing a gelling agent can significantly suppress ink bleed-through. This is because the gelling agent of the ink applied to the surface of the pretreatment layer, where the temperature of the recording medium is lower than the glass transition temperature of the resin (below the gelling temperature), quickly crystallizes in the ink to form a three-dimensional space called a house of cards structure, and the actinic radiation polymerizable compound contained in the actinic radiation curable ink is held within the space, making it difficult for the actinic radiation polymerizable compound to be compatible with the resin contained in the pretreatment liquid. This makes it difficult for the actinic radiation curable ink to penetrate into the pretreatment liquid, which is thought to suppress ink bleed-through.

[0142] It was also found that the scratch resistance of the image was improved by making the total amount of the bifunctional monomer and polyfunctional monomer 30% by mass or more based on the total mass of the actinic radiation curable ink. This is believed to be because when the ink is cured by irradiating it with actinic radiation, the cured product formed by curing the ink forms a network structure, making the surface hard and dense. [Industrial Applicability]

[0143] By using the pretreatment liquid of the present invention, even when actinic radiation curable ink is used on an absorbent recording medium, it is possible to suppress ink strike-through and ink bleeding, and therefore it is possible to suppress uneven density of the formed image. Therefore, it is expected that the present invention will broaden the range of application of image forming methods using actinic radiation curable ink, and will contribute to the advancement and spread of technology in this field. [Explanation of symbols]

[0144] 100 Image forming device 110 Recording media 120 Pretreatment liquid application section 121 Application roller 122 Dispenser 130 Ink application section 131 Nozzle 132 Inkjet head 140 Active ray irradiation section 150 Temperature adjustment section

Claims

1. A process for applying a pretreatment liquid to a recording medium, which is paper; applying an actinic ray curable ink to the surface of the recording medium on which the pretreatment liquid has been applied; a step of irradiating the applied actinic ray curable ink with actinic ray; having The pretreatment liquid contains water and a resin, the actinic ray curable ink contains a bifunctional monomer or a polyfunctional monomer, The actinic ray curable ink is applied to a surface of a recording medium to which the pretreatment liquid, which is set to a temperature lower than the glass transition temperature (Tg) of the resin, has been applied. Image forming method.

2. The image forming method according to claim 1 , wherein the pretreatment liquid contains a resin having a glass transition temperature (Tg) of 15° C. or more and 90° C. or less.

3. 3. The image forming method according to claim 1, wherein the pretreatment liquid contains a resin having a glass transition temperature (Tg) of 45° C. or higher and 65° C. or lower.

4. 4. The image forming method according to claim 1, wherein the actinic ray curable ink is applied to a surface of the recording medium at a temperature set to be 10° C. or more lower than a glass transition temperature (Tg) of the resin.

5. applying a pretreatment liquid to a recording medium; applying an actinic ray curable ink to the surface of the recording medium on which the pretreatment liquid has been applied; a step of irradiating the applied actinic ray curable ink with actinic ray; having the pretreatment liquid contains water and a resin having a glass transition temperature (Tg) of 45° C. or higher and 65° C. or lower; the actinic ray curable ink contains a bifunctional monomer or a polyfunctional monomer, The actinic ray curable ink is applied to a surface of a recording medium to which the pretreatment liquid, which is set to a temperature lower than the glass transition temperature (Tg) of the resin, has been applied. Image forming method.

6. The image forming method according to claim 5 , wherein the actinic ray curable ink is applied to the surface of the recording medium, the temperature of which is set to be 10° C. or more lower than the glass transition temperature (Tg) of the resin.

7. The image forming method according to claim 5 or 6, wherein the recording medium is a paper (excluding mixed paper) on whose surface the pretreatment liquid and the actinic ray curable ink are applied.

8. The image forming method according to any one of claims 1 to 7, wherein the pretreatment liquid further contains a water-soluble organic solvent.

9. The image forming method according to claim 8 , wherein the pretreatment liquid contains the water-soluble organic solvent in an amount of 50% by mass or more based on the total mass of the pretreatment liquid.

10. 10. The image forming method according to claim 1, further comprising a step of drying the pretreatment liquid applied to the surface of the recording medium.

11. The image forming method according to any one of claims 1 to 10, wherein the actinic ray curable ink contains the bifunctional monomer or polyfunctional monomer in an amount of 30 mass % or more based on the total mass of the actinic ray curable ink.

12. The image forming method according to any one of claims 1 to 11, wherein the actinic ray curable ink contains a gelling agent.

13. The recording medium to which the pretreatment liquid is applied is subjected to a Bristow method in which the recording medium is subjected to a Bristow method in which the pretreatment liquid is applied within 30 msec from the start of contact with the recording medium. １／２ The amount of water absorbed by the pretreatment liquid within 10 ml / m ２ 30ml / m or more ２ The image forming method according to any one of claims 1 to 12, wherein:

Images