JP6303330B2 - Ink set and image forming method using the same - Google Patents

Description

  The present invention relates to an ink set and an image forming method using the ink set.

  The ink jet recording system is used in various printing fields because it can form an image easily and inexpensively. As one of the inkjet recording methods, there is an ultraviolet curable inkjet method in which droplets of inkjet ink are landed on a recording medium and then irradiated with ultraviolet rays to cure the ink and form an image. The ultraviolet curable ink jet method has been attracting attention in recent years because an image having high scratch resistance and adhesion can be formed on a recording medium having no ink absorbability.

  However, in the conventional image forming method using an ultraviolet curable ink jet system, it is not possible to suppress the union of adjacent dots during high-speed recording such as a single pass recording method using a line recording head or a high-speed serial method, There was a problem that the image quality was inferior. As one of methods for preventing unification of adjacent dots, a technique of adding a gelling agent to an ultraviolet curable inkjet ink has been proposed (see, for example, Patent Documents 1 and 2).

  In recent years, printed products such as cosmetics, confectionery and other paper containers, labels, book covers, decorative paper, posters, catalogs, and the like have been printed on cosmetics and high-gloss to high gloss, and have a deeper matte appearance. In order to give high added value to inkjet printed materials, attempts have been made to improve the quality of inkjet printed materials having a matte tone and inkjet printed materials having a glossy tone.

  Such a mat-like printed material is conventionally manufactured by coating a printed material using various coating methods using a mat varnish in which a matting agent (filler) is mixed in a varnish. Further, means for transferring the surface property of the contact member by applying heat and pressure to the surface of the resin layer having thermoplasticity in contact with a contact member having a desired surface property such as a mat, a semi-mat, or an emboss ( For example, a method of imparting a matte tone by embossing is also known, such as Patent Document 3).

In the case of ultraviolet curable ink, a method of obtaining a matte surface by adjusting the amount of ultraviolet light exposure is known (see, for example, Patent Documents 4 and 5).
In the ink jet recording method, a method of obtaining a matte surface state by adjusting the dot diameter of ink droplets is known (see, for example, Patent Document 6).

  In addition, in ultraviolet curable inkjet inks to which a gelling agent is added, a technique for applying an overcoat composition containing a gelling agent on a printed image has been proposed in order to increase the durability of the formed printed image. (For example, refer to Patent Document 7).

US Patent Application Publication No. 2007/0058020 International Publication No. 2007/025893 JP 2005-119285 A JP2012-40837A JP 2013-232529 A JP 2011-224955 A JP 2010-106275 A

  However, in the ink jet recording system, when a filler is contained in the ink in order to impart a matte tone, there are problems such as poor ejection stability and ink storage stability. Further, the application of matte tone by transfer or the like has a problem that the apparatus becomes large and complicated or cannot cope with high-speed printing.

  The adjustment based on the exposure amount in the curable ink requires high ink sensitivity or requires a light source separately from image formation, which increases the apparatus size and cost. In addition, when a matte tone is obtained by adjusting the dot diameter of ink droplets, a pattern is formed with a dot diameter smaller than one pixel, resulting in a difference in gloss between the printed portion and the portion that is not printed, and the scratch resistance of the surface Is also inferior.

  With respect to a technique for applying an overcoat composition containing a gelling agent on a printed image, the gloss is controlled by heating before UV-curing the overcoat composition. In this case, in order to obtain matte surface properties, the amount of curable wax is increased and heated. However, by increasing the amount of the curable wax, the turbidity of the overcoat layer increases, the color of the color image becomes cloudy, and the strength of the cured film cannot be obtained. In addition, when the color ink also contains a gelling agent, color bleeding or the like of the color image occurs due to heating for gloss control, and the image quality is deteriorated.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an ink set capable of forming a printed image having both good curability, high image quality, and surface matting.

1. a color ink containing a photopolymerizable compound, a photopolymerization initiator, a gelling agent, and a coloring material, having a phase transition point of 40 ° C. or higher and lower than 100 ° C., and undergoing a sol-gel phase transition depending on the temperature; , A photopolymerization initiator, and a gelling agent, having a phase transition point of 40 ° C. or higher and lower than 100 ° C., and a clear ink that undergoes a sol-gel phase transition depending on temperature, and the gel transition of the clear ink An ink set having a temperature higher than the gel transition temperature of the color ink.
2. The amount of gelling agent contained in the clear ink and the color ink is 0.1 to 10% by mass, and the amount of gelling agent contained in the clear ink is greater than the amount of gelling agent contained in the color ink. 2. The ink set described in 1 above,
3. The clear ink and the color ink contain an aliphatic ketone compound and an aliphatic ester compound as the gelling agent, and the total amount of the gelling agent contained in the clear ink contains the aliphatic ketone compound contained in the clear ink. 3. The ink set according to 1 or 2 above, which is 60 to 95% and is larger than the amount of the aliphatic ketone compound contained in the color ink.
4. The clear ink and the color ink further include a surfactant, and the amount of the surfactant contained in the clear ink is greater than the amount of the surfactant contained in the color ink. The ink set according to item 1.
5. Using the ink set according to any one of 1 to 4 above, a step of ejecting ink droplets of the color ink from an ink jet recording head and attaching the ink droplet onto a recording medium, and the clearing of the ink set A step of causing ink droplets to be ejected from an ink jet recording head and adhering to a recording medium; and irradiating actinic rays to color ink droplets and clear ink droplets that have landed on the recording medium; An image forming method comprising: curing the droplet.

  According to the present invention, an ink set capable of forming a printed image having both good curability, high image quality, and surface matting property is provided.

It is a side view of an example of the composition of the important section of a line recording type ink jet recording device. FIG. 2 is a top view of an example of a configuration of a main part of a line recording type inkjet recording apparatus. FIG. 2A is a side view of another example of the configuration of the main part of the line recording type inkjet recording apparatus. FIG. 2B is a top view of another example of the configuration of the main part of the line recording type inkjet recording apparatus. It is a figure which shows an example of a structure of the principal part of the inkjet recording device of a serial recording system.

Hereinafter, the present invention will be described with reference to embodiments, but the present invention is not limited to the following embodiments.
[1. Inkjet ink set]
The inkjet ink set according to the embodiment includes (a) a photopolymerizable compound, a photopolymerization initiator, a gelling agent, and a colorant, and has a phase transition point of 40 ° C. or higher and lower than 100 ° C. and undergoes sol-gel transition depending on temperature. And (b) a color ink containing a photopolymerizable compound, a photopolymerization initiator, a gelling agent, and a colorant, having a phase transition point at 40 ° C. or higher and lower than 100 ° C., and undergoing sol-gel transition depending on temperature. The gel transition temperature of the clear ink is preferably higher than the gel transition temperature of the color ink.
In the color ink of the ink set according to the embodiment, it is difficult for ink droplets to coalesce after landing on a recording medium. Therefore, a high-definition image without blur can be formed. On the other hand, since the clear ink of the inkjet ink set of the present invention is designed to be more difficult to unite than the color ink, it can form a uniform film with low gloss. That is, by using the ink set according to the embodiment, a printed image having both high image quality and a uniform matte feeling can be formed.
According to the ink set according to the embodiment, an image can be formed by the ink jet recording method, so that a matte tone image can be formed by using a smaller and simpler apparatus than the transfer type image forming method. Also, storage stability and discharge stability are good due to the filler free.

The content of the gelling agent contained in the clear ink is 0.1 to 10% by mass with respect to the total mass of the clear ink, and the content of the gelling agent contained in the color ink is the total mass of the color ink. The content of the gelling agent contained in the clear ink is preferably greater than the content of the gelling agent contained in the color ink. This is because it is easy to form a printed image having both high image quality and a uniform matte feeling.
It is preferable that the clear ink and the color ink each further contain a surfactant, and the content of the surfactant contained in the clear ink is larger than the content of the surfactant contained in the color ink. By adding the surfactant, precipitation of the gelling agent is promoted to form ink droplets having a concavo-convex feeling, and a mat-like surface property can be obtained. In this case, if the amount of the surfactant in the clear ink is made larger than that of the color ink, a uniform film with lower gloss can be formed.

The inkjet ink set according to the embodiment includes a color ink and a clear ink, but the color ink may be a single color or a set of a plurality of colors (for example, cyan, magenta, yellow, black, etc.). There may be. When the color ink has a plurality of colors, it is preferable that the gel transition temperature of the clear ink is higher than any of the gel transition temperatures.
Further, the components of the photopolymerizable compound, the photopolymerization initiator, and the gelling agent in the clear ink and the color ink may be the same or different independently of each other.

<About color ink>
Color ink is ink that undergoes a sol-gel phase transition with temperature.
The color ink contains a photopolymerizable compound, a photopolymerization initiator, a gelling agent, and 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, and are preferably ultraviolet rays. The photopolymerizable compound can be a radical polymerizable compound or a cationic polymerizable compound. A radical polymerizable compound is preferred.

  The radically polymerizable compound is a compound (monomer, oligomer, polymer or mixture thereof) having a radically polymerizable ethylenically unsaturated bond. Only one kind of radically polymerizable compound may be contained in the color ink, or two or more kinds thereof may be contained.

  Examples of the compound having an ethylenically unsaturated bond capable of radical polymerization include an unsaturated carboxylic acid and a salt thereof, an unsaturated carboxylic acid ester compound, an unsaturated carboxylic acid urethane compound, an unsaturated carboxylic acid amide compound and an anhydride thereof, Examples include acrylonitrile, styrene, unsaturated polyester, unsaturated polyether, unsaturated polyamide, and unsaturated urethane. 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 described later, but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, and 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 (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) ) Acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, Methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl ( Acrylate), tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2 -(Meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid, t-butylcyclohexyl (meth) acrylate, etc. Monofunctional monomers of
Triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, reethylene 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, bisphenol A bifunctional monomer such as PO adduct di (meth) acrylate of A, neopentyl glycol di (meth) acrylate hydroxypivalate, poly (tetramethylene glycol di (meth) acrylate);
Trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate And trifunctional or higher polyfunctional monomers such as pentaerythritol ethoxytetra (meth) acrylate.

  Among them, from the viewpoint of photosensitivity, stearyl (meth) acrylate, lauryl (meth) acrylate, isostearyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, isobornyl (meth) acrylate, tetraethylene glycol di (meth) acrylate , Glycerin propoxytri (meth) acrylate and the like are preferable.

  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. Among these, an ethylene oxide-modified (meth) acrylate compound is preferable from the viewpoint of high photosensitivity and easy formation of a card house structure described later when gelling at a low temperature. In addition, the ethylene oxide-modified (meth) acrylate compound is easily dissolved in other ink components at high temperatures and has little curing shrinkage, so that curling of the printed matter hardly occurs.

  Examples of ethylene oxide-modified (meth) acrylate compounds include 4EO-modified hexanediol diacrylate CD561 (molecular weight 358), 3EO-modified trimethylolpropane triacrylate SR454 (molecular weight 429), 6EO-modified trimethylolpropane triacrylate SR499 manufactured by Sartomer. (Molecular weight 560), 4EO-modified pentaerythritol tetraacrylate SR494 (molecular weight 528); polyethylene glycol diacrylate NK ester A-400 (molecular weight 508), polyethylene glycol diacrylate NK ester A-600 (molecular weight 742) manufactured by Shin-Nakamura Chemical Co., Ltd. , Polyethylene glycol dimethacrylate NK ester 9G (molecular weight 536), polyethylene glycol dimethacrylate NK ester 4G (molecular weight 770); Tetraethylene glycol diacrylate V # 335HP (molecular weight 302) manufactured by Osaka Organic Chemical Co .; 3PO-modified trimethylolpropane triacrylate Photomer 4072 (molecular weight 471) manufactured by Cognis; 1 manufactured by Shin-Nakamura Chemical Co., Ltd. , 10-decanediol dimethacrylate NK ester DOD-N (molecular weight 310), tricyclodecane dimethanol diacrylate NK ester A-DCP (molecular weight 304), tricyclodecane dimethanol dimethacrylate NK ester DCP (molecular weight 332), etc. included.

  The (meth) acrylate compound may be a polymerizable oligomer. Examples of such 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 and the like are included.

  The content of the photopolymerizable compound is preferably 1 to 97% by mass and more preferably 30 to 95% by mass with respect to the total mass of the color ink. When the amount of the photopolymerizable compound is too small, the coloring material cannot be sufficiently dispersed, and the ink dischargeability from the ink jet recording apparatus is lowered. 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.

(Photopolymerization initiator)
The color ink further contains a photopolymerization initiator.
Photopolymerization initiators 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, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone; benzoins such as benzoin, benzoin methyl ether, benzoin isopropyl ether; 2 Acylphosphine oxide systems such as 1,4,6-trimethylbenzoindiphenylphosphine oxide; benzyl and And methylphenylglyoxyester.

  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 camphorquinone, include triallyl phosphonium salts.

  When the photopolymerization initiator is acyl phosphine oxide or acyl phosphonate, the sensitivity is good. Specifically, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide, and the like are preferable.

  The content of the photopolymerization initiator contained in the color ink is 0.1% by mass to 10% by mass with respect to the total mass of the ink, although it depends on the light irradiated during ink curing and the type of the photopolymerizable compound. It is preferably 2 to 8% by mass.

  The color ink may further contain a photopolymerization initiator auxiliary agent or a polymerization inhibitor, if 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 of these compounds may be included in the color ink, or two or more of these compounds may be included.

  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.

(Gelling agent)
The gelling agent contained in the color ink has a function of reversibly sol-gel phase transition of the color ink depending on the temperature. Such a gelling agent is at least 1) soluble in a photopolymerizable compound or non-polymerizable resin at a temperature higher than the gelation temperature, and 2) crystallizes in the ink at a temperature below the gelation temperature. It is necessary.

  When the gelling agent crystallizes in the ink, it is preferable to form a space three-dimensionally surrounded by plate crystals which are crystallized products of the gelling agent, and to enclose the photopolymerizable compound in the space. Thus, the structure in which the photopolymerizable compound is encapsulated in the space three-dimensionally surrounded by the plate crystal is sometimes referred to as “card house structure”. When the card house structure is formed, the liquid photopolymerizable compound can be held and ink droplets can be pinned. Thereby, coalescence of droplets can be suppressed. In order to form the card house structure, it is preferable that the photopolymerizable compound dissolved in the ink and the gelling agent are compatible. On the other hand, when the photopolymerizable compound dissolved in the ink and the gelling agent are phase-separated, it may be difficult to form a card house structure.

  In order to stably discharge ink droplets of color ink from an ink jet recording apparatus, it is necessary that the compatibility between the photopolymerizable compound and the gelling agent is good in the sol-like ink (at a high temperature). . Furthermore, in order to stably suppress coalescence of droplets even during high-speed printing, after the ink droplets have landed on the recording medium, the gelling agent quickly crystallizes to form a strong card house structure. is necessary.

Examples of such gelling agents include
An aliphatic ketone compound;
Aliphatic ester compounds;
Petroleum waxes such as paraffin wax, microcrystalline wax, petrolactam;
Plant 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 whale wax;
Mineral waxes such as montan wax and hydrogenated wax;
Hydrogenated castor oil or hydrogenated castor oil derivative;
Modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline 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 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 manufactured by Nippon Kasei Co., Ltd.) ITOWAX series manufactured by Ito Oil Co., Ltd., FATTYAMID series manufactured by Kao Corporation, etc.);
N-substituted fatty acid amides such as N-stearyl stearamide and N-oleyl palmitate amide;
Special fatty acid amides such as N, N′-ethylenebisstearylamide, N, N′-ethylenebis-12-hydroxystearylamide, and 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, Emullex series manufactured by Nihon Emulsion Co., Ltd., Riken Vitamin Co., Ltd. Marl series, RIKEN VITAMIN POM series, etc.);
Esters of sucrose fatty acids such as sucrose stearic acid and sucrose palmitic acid (eg Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods);
Synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax (such as UNILIN series manufactured by Baker-Petrolite);
Dimer acid;
Dimer diol (such as PRIDA series manufactured by CRODA);
Fatty acid inulins such as inulin stearate;
Fatty acid dextrins such as dextrin palmitate and dextrin myristate (such as Leopard series manufactured by Chiba Flour Mills);
Glyceryl behenate eicosane diacid;
Eicosane polyglyceryl behenate (Nomshin Eulio Co., Ltd. Nomucoat series, etc.);
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);
Low molecular oil gelling agents described in JP-A-2005-126507, JP-A-2005-255821, and JP-A-2010-1111790;
Etc. are included.

  The color ink preferably contains a compound containing a linear alkyl group having 12 or more carbon atoms as a gelling agent. When the gelling agent contains a linear alkyl group having 12 or more carbon atoms, the aforementioned “card house structure” is easily formed. The structure of the gelling agent may have a branched chain.

  Specific examples of the gelling agent containing a linear alkyl group having 12 or more carbon atoms include aliphatic ketone compounds, aliphatic ester compounds, higher fatty acids, higher alcohols having a linear alkyl group having 12 or more carbon atoms, Fatty acid amides and the like are included.

However, a gelling agent having a polar group such as —OH or —COOH at the end of the alkyl chain has poor stability in a sol-like ink and may precipitate or phase-separate. In addition, the gelling agent may gradually bleed out with time from the cured film of the ink. Therefore, the gelling agent is preferably an aliphatic ketone compound or an aliphatic ester compound. That is, a compound represented by the following general formulas (G1) and (G2) is preferable.
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4
In general formulas (G1) and (G2), R1 to R4 each independently represent a hydrocarbon group having a straight chain portion having 12 or more carbon atoms. R1 to R4 may have a branched portion.

  In General Formula (G1), the hydrocarbon groups represented by R1 and R2 are each preferably an aliphatic hydrocarbon group including a straight chain portion having 12 to 25 carbon atoms. If the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group represented by R1 and R2 is less than 12, it does not function as a gelling agent because it does not have sufficient crystallinity, and the card described above In the house structure, there is a possibility that a sufficient space for encapsulating the photopolymerizable compound cannot be formed. On the other hand, if the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group exceeds 25, the melting point becomes too high, so that the ink may not be dissolved in the ink unless the ink discharge temperature is increased.

  Examples of the aliphatic ketone compound represented by the general formula (G1) include dilignoceryl ketone (C24-C24), dibehenyl ketone (C22-C22, melting point 88 ° C.), distearyl ketone (C18-C18, 84 ° C.), dieicosyl ketone (C20-C20), dipalmityl ketone (C16-C16, melting point 80 ° C.), dimyristyl ketone (C14-C14), dilauryl ketone (C12-C12, melting point 68 ° C.) , Lauryl myristyl ketone (C12-C14), lauryl palmityl ketone (C12-C16), myristyl palmityl ketone (C14-C16), myristyl stearyl ketone (C14-C18), myristyl behenyl ketone (C14-C22), palmityl Stearyl ketone (C16-C18), Valmityl behenyl ketone (C 6-C22), include stearyl and behenyl ketone (C18-C22) and the like.

  Examples of commercially available compounds represented by the general formula (G1) include 18-Pentriacontanon (manufactured by Alfa Aeser), Hentriacontan-16-on (manufactured by Alfa Aeser), Kao wax T1 (manufactured by Kao Corporation), and the like. included.

The aliphatic ketone compound contained in the color ink may be only one type or a mixture of two or more types.
In the general formula (G2), the hydrocarbon group represented by R3 and R4 is not particularly limited, but is preferably an aliphatic hydrocarbon group including a linear portion having 12 to 26 carbon atoms. When the number of carbon atoms in the straight chain portion contained in the aliphatic hydrocarbon group represented by R3 and R4 is 12 or more and 26 or less, it is necessary for the gelling agent as in the compound represented by the general formula (G1). The above-mentioned card house structure can be formed while having excellent crystallinity, and the melting point is not too high.
Examples of the aliphatic ester compound represented by the formula (2) include behenyl behenate (C21-C22, melting point 70 ° C.), icosyl icosanoate (C19-C20), stearyl stearate (C17-C18, melting point 60 ° C.). ), Palmitic acid stearate (C17-C16), lauryl stearate (C17-C12), cetyl palmitate (C15-C16, melting point 54 ° C.), stearyl palmitate (C15-C18), myristyl myristate (C13-C)
14, melting point 43 ° C), cetyl myristate (C13-C16, melting point 50 ° C), octyldodecyl myristate (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), linoleic acid Stearyl (C17-C18), behenyl oleate (C18-C22), myricyl serotate (C25-C16), stearyl montanate (C27-C18), behenyl montanate (C27-C22), arachidyl linoleate (C17-C20) ), Palmitic acid triacontanoate (C29-C16) and the like.

  Examples of commercially available products of the aliphatic ester compound represented by the formula (2) include Unistar M-2222SL (manufactured by NOF Corporation), EXCEPARL SS (manufactured by Kao Corporation, melting point 60 ° C.), EMALEXCC-18 (Japan) Emulsion Co., Ltd.), Amreps PC (manufactured by Higher Alcohol Industry Co., Ltd.), Exepal MY-M (Kao Co., Ltd.), Spalm Acechi (Nissho Co., Ltd.), EMALEX CC-10 (Nihon Emulsion Co., Ltd.) included. Since these commercial products are often a mixture of two or more types, they may be separated and purified as necessary.

  The aliphatic ester compound contained in the color ink may be only one type or a mixture of two or more types.

  The amount of the gelling agent contained in the color ink is preferably 0.1 to 10.0% by mass, more preferably 1 to 7% by mass with respect to the total amount of the color ink. If it is less than 0.5% by mass, the ink droplets cannot be gelled (sol-gel phase transition due to temperature). On the other hand, when the amount of the gelling agent exceeds 10% by mass, the gelling agent is not sufficiently dissolved in the ink, and the discharge property of the ink droplets is lowered.

(About clear ink)
Since the clear ink also contains a gelling agent, the sol-gel phase transition is reversibly caused by temperature. Since the sol-gel phase transition clear ink is a liquid (sol) at a high temperature (for example, about 80 ° C.), it can be discharged in a sol state from an inkjet recording head. When ink is ejected at a high temperature, ink droplets (dots) land on the recording medium, and then naturally cool to gel. Thereby, a cured film of clear ink can be formed in a desired region.

In order to provide a uniform matte tone on the surface of an image made of a recording medium or color ink as described above, it is necessary to form a surface having uniform graininess with the clear ink after landing. For this purpose, the gel transition temperature of the clear ink is required to be higher than the gel transition temperature of the color ink.
When the gel transition temperature of the clear ink is lower than the gel transition temperature of the color ink, leveling is easy on the color ink surface, resulting in a cured surface with high gloss.

  The gel transition temperature of the clear ink is higher than the gel transition temperature of the color ink, preferably 40 ° C. or higher and 70 ° C. or lower, and more preferably 50 ° C. or higher and 65 ° C. or lower. If the gel transition temperature of the ink exceeds 70 ° C. when the discharge temperature is in the vicinity of 80 ° C., gelation is likely to occur at the time of discharge, resulting in poor discharge properties. On the other hand, if the gel transition temperature is less than 40 ° C., the gelation is weak after landing on the recording medium, and the clear ink not only becomes a non-uniform film on the surface of the color ink, but also is susceptible to oxygen. Curing sensitivity is lowered.

The gel transition temperature is a temperature at which fluidity is lowered due to gelation in the process of cooling the ink in a sol state. The difference between the gel transition temperature of the clear ink and the gel transition temperature of the color ink is preferably within 10 ° C., more preferably within 5 ° C. When the difference between the gelation temperature of the clear ink and the gelation temperature of the color ink is large, it becomes difficult to achieve both the sharpness and gloss of the image.
In order for the gel transition temperature of the clear ink to be higher than the gel transition temperature of the color ink, for example, the amount of the gelling agent contained in the clear ink is made larger than the amount of the gelling agent contained in the color ink. Can be achieved.

As the gelling agent increases, the amount of the gelling agent deposited upon landing increases and ink droplets with a more uneven feel are formed. Therefore, a matte surface property can be obtained as compared with the case of using only color ink.
In addition to the amount of gelling agent, the gel transition temperature can be adjusted depending on the type of gelling agent and the ratio of the gelling agent when a plurality of gelling agents are used in combination. The gel transition temperature can be controlled to a desired gel transition temperature.

When a plurality of gelling agents are used in combination, surface properties with a sense of unevenness can be obtained by selecting a gelling agent with higher crystallinity (easy to crystallize). However, gelling agents with high crystallinity are often poorly soluble in ink components even at high temperatures, and tend to reduce ink ejection properties. In order to obtain high crystallinity without reducing ink ejection properties, the present inventors combine gelling agents having a similar chemical structure and different crystallinity; The present inventors have found that it is effective to combine a gelling agent having high properties with a gelling agent having low crystallinity. That is, when the ink falls below a certain temperature, first, crystal nuclei of the gelling agent having high crystallinity are precipitated. Next, a crystal of a gelling agent having low crystallinity grows and precipitates around the precipitated crystal nucleus. The sol-gel phase transition rate of the ink containing the gelling agent having different crystallinity is as high as that of the ink containing the gelling agent having high crystallinity alone. Moreover, since the ink containing the gelling agent having different crystallinity includes a gelling agent having low crystallinity, the ink has high solubility at high temperatures and high ejection properties. Furthermore, since these gelling agents having different crystallinities have chemical structures similar to each other, the crystal structure after crystallization becomes uniform, so that the film strength of the image after curing can be increased.
Of the at least two types of gelling agents having different crystallinity, the gelling agent having high crystallinity is preferably the above-mentioned aliphatic ketone compound, and the gelling agent having low crystallinity is preferably the above-mentioned gelling agent. It is preferable that it is an aliphatic ester compound.

One of the indices indicating the crystallinity of a compound is the melting point. For example, the aliphatic hydrocarbon group of R1 of the aliphatic ketone compound represented by the above general formula (G1) and the aliphatic hydrocarbon group of R3 of the aliphatic ester compound represented by the above general formula (G2) Are similar (for example, the number of carbon atoms of both is approximate), and the aliphatic hydrocarbon group of R2 in the general formula (G1) is similar to the aliphatic hydrocarbon group of R4 in the general formula (G2) ( For example, when the number of carbon atoms of both is approximate, the melting point of the aliphatic ketone compound represented by the general formula (G1) is usually higher than the melting point of the aliphatic ester compound represented by the general formula (G2). Is also expensive.
The melting point of the gelling agent having high crystallinity is more preferably 60 ° C. or more and 100 ° C. or less, and the melting point of the gelling agent having low crystallinity is preferably 30 ° C. or more and 75 ° C. or less.

  When the ratio of the gelling agent having high crystallinity is high, the crystal becomes larger, so that the hardened surface has a matte feeling. The proportion of the gelling agent having high crystallinity is preferably 80 to 95% with respect to the total amount of the gelling agent. When the ratio is small, the crystal growth of the gelling agent having high crystallinity is suppressed, so that the crystal becomes fine and has a glossy surface.

  In addition, when the clear ink and the color ink include a surfactant, the clear ink and the color ink are formed with only the color ink by making the amount of the active agent contained in the clear ink larger than the amount of the active agent contained in the color ink. Compared to images, a matte surface property can be obtained.

(Color material)
The color ink further includes a color 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 RED 130, 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, Bayer Japan), KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow AG, KAYASET Yellow EG (above, 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, Perman Yellow G
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 color ink. If the pigment or dye content is too low, the resulting image will not be sufficiently colored, and if it is too high, the viscosity of the ink will increase and the discharge properties will decrease.

  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.

  The color ink may further contain a dispersant in order to improve the dispersibility of the pigment. 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 and the like are included. Examples of commercially available dispersants include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series.

The color ink may further contain a dispersion aid as necessary. The dispersion aid may be selected according to the pigment.
The total amount of the dispersant and the dispersion aid is preferably 1 to 50% by mass with respect to the pigment.

  The color ink may further include a dispersion medium for dispersing the pigment as necessary. A solvent may be included in the color ink as a dispersion medium. However, in order to suppress residual solvent in the formed image, the above-described photopolymerizable compound (particularly a monomer having a low viscosity) is the dispersion medium. It is preferable.

(Other ingredients)
The color 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, a basic compound for enhancing the storage stability of the color ink, and the like. 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.

(Viscosity of color ink)
Since the color ink contains a gelling agent as described above, it undergoes a sol-gel phase transition reversibly depending on the temperature. Since the sol-gel phase transition color ink is a liquid (sol) at a high temperature (for example, about 80 ° C.), it can be ejected in a sol state from an inkjet recording head. When color ink is ejected at a high temperature, ink droplets (dots) land on the recording medium and then naturally cool to gel. Thereby, coalescence of adjacent dots can be suppressed and image quality can be improved.

  In order to improve the discharge property of the sol-gel phase transition type ink, it is preferable that the viscosity of the ink at a high temperature is not more than a certain level. Specifically, the actinic ray curable inkjet ink preferably has a viscosity at 80 ° C. of 3 to 20 mPa · s. On the other hand, in order to suppress coalescence of adjacent dots, it is preferable that the viscosity of the ink at normal temperature after landing is a certain level or more. Specifically, the viscosity at 25 ° C. of the actinic ray curable inkjet ink is preferably 1000 mPa · s or more.

  The gel transition temperature of the sol-gel phase transition type ink is preferably 40 ° C. or higher and 70 ° C. or lower, and more preferably 50 ° C. or higher and 65 ° C. or lower. When the ink discharge temperature is in the vicinity of 80 ° C., if the gel transition temperature of the ink exceeds 70 ° C., gelation tends to occur at the time of discharge, and the discharge property is lowered. On the other hand, if the gelation temperature is less than 40 ° C., it is difficult to quickly gel after landing on the recording medium. The gel transition temperature is a temperature at which fluidity is lowered due to gelation in the process of cooling the ink in a sol state.

  The viscosity at 80 ° C., the viscosity at 25 ° C. and the gel transition temperature of the sol-gel phase transition ink can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. Specifically, a temperature change curve of viscosity is obtained when the ink is heated to 100 ° C. and cooled to 20 ° C. under conditions of a shear rate of 11.7 (/ s) and a temperature decrease rate of 0.1 ° C./s. And the viscosity in 80 degreeC and the viscosity in 25 degreeC can be calculated | required by reading the viscosity in 80 degreeC and 25 degreeC in the temperature change curve of a viscosity, respectively. The gel transition temperature is a temperature at which the viscosity changes greatly in the temperature change curve of the viscosity. For example, the gel transition temperature can be a temperature at which the viscosity becomes 200 mPa · s.

  As the rheometer, a stress control type rheometer Physica MCR series manufactured by Anton Paar can be used. The cone plate can have a diameter of 75 mm and a cone angle of 1.0 °.

(Preparation method of color ink)
The color ink is obtained by mixing a photopolymerizable compound, a gelling agent, a photopolymerization initiator, and a color material under heating. Preferably, a pigment dispersion in which a color material (particularly a pigment) is dispersed in a part of the photopolymerizable compound is prepared and mixed with the pigment dispersion and other ink components.
The obtained color ink is preferably filtered through a predetermined filter.

<About clear ink>
Clear ink is ink that undergoes a sol-gel phase transition. The clear ink is applied so as to overlap with the color ink described above. At this time, it is possible to give the color image a matte feeling by giving the clear ink a certain granular feeling. In addition, when forming an image with color ink, the density of the image is adjusted by the amount of the color ink. Therefore, an image made of the above-described color ink has a different thickness in the shade area, and the formed image has a slight difference. A step will occur. By overlaying clear ink on the entire surface of this color image, the unevenness and steps on the surface of the color ink, as well as the portion with and without the image on the substrate, can be flattened, and the uniformity of the printed surface can be improved. it can. Moreover, the scratch resistance of the printed matter can be improved by overlaying the clear ink.

  In addition, when color ink and clear ink are applied sequentially and cured at the same time, compared to normal curable clear ink, clear ink added with a gelling agent causes pinning due to the gelling agent. There is no turbidity, high-definition images can be obtained, and since it is not easily affected by oxygen during curing, the clear ink layer has good surface curability, and even the color ink layer can be cured firmly. The image has good adhesion and is strong against bending.

  The clear ink contains a photopolymerizable compound, a photopolymerization initiator, and a gelling agent, and other components as necessary. The photopolymerizable compound, photopolymerization initiator, and gelling agent can be the same as those contained in the color ink.

  The amount of the photopolymerizable compound contained in the clear ink is preferably 1 to 97% by mass, and preferably 30 to 95% by mass with respect to the total mass of the clear ink. If the amount of the photopolymerizable compound contained in the clear ink is small, the strength and scratch resistance of the clear ink cured film may be lowered. On the other hand, when the amount of the photopolymerizable compound contained in the clear ink is excessive, the amount of the gelling agent or the photopolymerizable compound is relatively reduced. For this reason, there is a possibility that the sol-gel phase transition cannot be performed sufficiently and the ink is not sufficiently cured.

  The amount of the photopolymerization initiator contained in the clear ink is preferably 0.1 to 10% by mass, and preferably 2 to 8% by mass with respect to the total mass of the clear ink. When the amount of the photopolymerization initiator is small, the ink is not sufficiently cured. On the other hand, when the amount of the photopolymerization initiator is excessive, coloring derived from the initiator increases or the molecular weight of the polymer decreases, resulting in brittleness. In addition, since clear ink is less shielded by a colorant than color ink, an excellent cured film can be obtained in an amount smaller than the amount of initiator contained in color ink.

  Since the clear ink also contains a gelling agent, the sol-gel phase transition is reversibly caused by temperature. Since the sol-gel phase transition clear ink is a liquid (sol) at a high temperature (for example, about 80 ° C.), it can be discharged in a sol state from an inkjet recording head. When ink is ejected at a high temperature, ink droplets (dots) land on the recording medium, and then naturally cool to gel. Thereby, a cured film of clear ink can be formed in a desired region.

  In order to provide a uniform matte tone on the surface of an image made of a recording medium or color ink as described above, it is necessary to form a surface having uniform graininess with the clear ink after landing. For this purpose, the gel transition temperature of the clear ink is required to be higher than the gel transition temperature of the color ink.

  When the gel transition temperature of the clear ink is lower than the gel transition temperature of the color ink, leveling is easy on the color ink surface, resulting in a cured surface with high gloss.

  The gel transition temperature of the clear ink is lower than the gel transition temperature of the color ink, preferably 40 ° C. or more and 70 ° C. or less, and more preferably 50 ° C. or more and 65 ° C. or less. If the gel transition temperature of the ink exceeds 70 ° C. when the discharge temperature is in the vicinity of 80 ° C., gelation is likely to occur at the time of discharge, resulting in poor discharge properties. On the other hand, if the gel transition temperature is less than 40 ° C., the gelation is weak after landing on the recording medium, and the clear ink not only becomes a non-uniform film on the surface of the color ink, but also is susceptible to oxygen. Curing sensitivity is lowered.

  The gel transition temperature is a temperature at which fluidity is lowered due to gelation in the process of cooling the ink in a sol state. The difference between the gel transition temperature of the clear ink and the gel transition temperature of the color ink is preferably within 10 ° C., more preferably within 5 ° C. When the difference between the gelation temperature of the clear ink and the gelation temperature of the color ink is large, it becomes difficult to achieve both the sharpness and gloss of the image.

  In order for the gel transition temperature of the clear ink to be higher than the gel transition temperature of the color ink, for example, the amount of the gelling agent contained in the clear ink is made larger than the amount of the gelling agent contained in the color ink. Can be achieved.

  As the gelling agent increases, the amount of the gelling agent deposited upon landing increases and ink droplets with a more uneven feel are formed. Therefore, a matte surface property can be obtained as compared with the case of using only color ink.

  In addition to the amount of gelling agent, the gel transition temperature can be adjusted depending on the type of gelling agent and the ratio of the gelling agent when a plurality of gelling agents are used in combination. The gel transition temperature can be controlled to a desired gel transition temperature.

  The amount of the gelling agent contained in the clear ink is preferably 0.1 to 10.0% by mass, more preferably 1 to 7% by mass with respect to the total amount of the clear ink. If it is less than 0.5% by mass, the ink droplets cannot be gelled (sol-gel phase transition due to temperature). On the other hand, when the amount of the gelling agent exceeds 10% by mass, the gelling agent is not sufficiently dissolved in the ink, and the discharge property of the ink droplets is lowered.

  In addition, when the clear ink and the color ink include a surfactant, the clear ink and the color ink are formed with only the color ink by making the amount of the active agent contained in the clear ink larger than the amount of the active agent contained in the color ink. Compared to images, a matte surface property can be obtained.

  By including the surfactant, the activator becomes a crystal nucleus, which is considered to affect the precipitation of the gelling agent particularly near the surface of the cured film. As the amount of the surfactant increases, the precipitation of the gelling agent is promoted to form ink droplets with a sense of unevenness, and a mat-like surface property can be obtained. The addition amount of the surfactant is preferably 0.001 to 1%, more preferably 0.01 to 0.5%. When the addition amount of the surfactant is large, the ink ejection property is deteriorated and the strength of the cured layer is lowered.

  The surfactant is not particularly limited, and examples thereof include anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene. Nonionic surfactants such as glycols and polyoxyethylene / polyoxypropylene block copolymers, cationic surfactants such as alkylamine salts and quaternary ammonium salts, silicone oils and the like.

  In the present embodiment, it is particularly preferable to use a silicone oil. As the silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, carboxy-modified silicone oil, polyether-modified silicone oil, dimethylpolysiloxane and a polymethyl group. Examples include polyether-modified silicone oils introduced with ether groups, alkyl-modified silicone oils, alkoxy-modified silicone oils, fluorine-modified silicone oils, methylstyrene-modified silicone oils, olefin-modified silicone oils, and alcohol-modified silicone oils.

  Also in the clear ink, in order to improve the discharge property of the sol-gel phase transition type ink, 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. On the other hand, in order to suppress coalescence of adjacent dots, it is preferable that the viscosity of the ink at normal temperature after landing is a certain level or more. Specifically, the viscosity at 25 ° C. of the actinic ray curable inkjet ink is preferably 1000 mPa · s or more.

  The viscosity at 80 ° C., the viscosity at 25 ° C., and the gel transition temperature of the clear ink are measured in the same manner as the color ink described above.

  The clear ink is obtained by mixing a photopolymerizable compound, a gelling agent, and a photopolymerization initiator under heating. The obtained clear ink is preferably filtered through a predetermined filter.

[2. Image forming method]
The image forming method according to the embodiment includes (a) a step of using the above-described inkjet ink set, discharging ink droplets of color ink from an inkjet recording head, and depositing the ink on a recording medium; and (b) an inkjet ink set. A step of discharging the clear ink droplets from the ink jet recording head and attaching them to the recording medium; and (c) irradiating the color ink droplets and the clear ink droplets landed on the recording medium with actinic rays. And curing each droplet.

  The (c) curing step may be performed only once or in two steps. For example, (a) a step of attaching color ink to the recording medium, (c-1) a step of curing color ink droplets, (b) a step of attaching clear ink to the recording medium, and (c-2) clear ink. The color ink droplets and the clear ink droplets may be individually cured by performing the steps of curing the droplets.

  Further, (a) a step of attaching the color ink to the recording medium, (b) a step of attaching the clear ink to the recording medium, (c) a step of curing the droplets of the clear ink and the color ink are performed in this order. Color ink droplets may be cured in a lump. The droplets of the color ink and the clear ink are gelated by the sol-gel phase transition, and the viscosity of the clear ink and the color ink at 25 ° C. is a certain level or higher. Therefore, the color ink film before curing and the clear ink film before curing are difficult to mix. Therefore, a high quality image can be obtained without performing the step (c) between the steps (a) and (b). (C) When the curing step is performed only once, there is an advantage that only one exposure light source is required and the image forming time can be shortened.

(A) Step The above-described color ink droplets are ejected from the ink jet recording head portion of the ink jet recording apparatus. When a plurality of colors are included in the color ink, each color ink is ejected to form an image. In order to improve the dischargeability of the color ink droplets, it is preferable to set the temperature of the inkjet ink in the inkjet recording head to a temperature that is 10 to 30 ° C. higher than the gel transition temperature of the color ink. If the ink temperature in the ink jet recording head is less than the gelation temperature + 10 ° C., the ink gels in the ink jet recording head or on the nozzle surface, and ink droplet ejection properties tend to decrease. On the other hand, when the temperature of the ink in the ink jet recording head exceeds the gelation temperature + 30 ° C., the ink becomes too high, and the ink component may deteriorate.

  The color ink is heated by 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 per droplet of color ink ejected from each nozzle of the inkjet recording head is preferably 0.5 to 10 pl, although it depends on the resolution of the image. In order to form a high-definition image 0.5 to 4.0 pl is more preferable. In order to form a high-definition image with such a droplet amount, the ink after landing does not coalesce. That is, the color ink needs to sufficiently undergo sol-gel phase transition. The aforementioned color ink undergoes a sol-gel phase transition promptly. Therefore, a high-definition image can be stably formed even with such a droplet amount.

  The color ink droplets that have landed on the recording medium are cooled and rapidly gelled by the sol-gel phase transition. Thereby, it is possible to perform pinning without excessively spreading the color ink droplets. Furthermore, since the droplets gel quickly, it is difficult for oxygen to enter the droplets, and the curing of the photopolymerizable compound is not easily inhibited by oxygen.

  The recording medium may be paper or a resin film. Examples of paper include coated paper for printing, coated paper B for printing, and the like. Examples of the resin film include a polyethylene terephthalate film, a polypropylene film, and a vinyl chloride film.

  Here, by discharging the color ink droplets from the ink jet recording head, the color ink droplets adhere to the recording medium. The temperature of the recording medium when the color ink droplets land is preferably set to a temperature that is 10 to 20 ° C. lower than the gelation temperature of the ink. If the temperature of the recording medium is too low, the color ink droplets will gel too quickly and pinning. On the other hand, if the temperature of the recording medium is too high, the ink droplets are difficult to gel, and adjacent dots of the ink droplets may be mixed together. By appropriately adjusting the temperature of the recording medium, it is possible to achieve appropriate leveling and appropriate pinning so that adjacent dots of ink droplets do not mix with each other.

  The conveyance speed of the recording medium is preferably 30 to 120 m / 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 deteriorates and the color ink is not sufficiently cured (described later).

(B) Step The above-described clear ink droplets are ejected from the ink jet recording head portion of the ink jet recording apparatus. In order to improve the dischargeability of the clear ink droplets, it is preferable to set the temperature of the inkjet ink in the inkjet recording head to a temperature that is 10 to 30 ° C. higher than the gelation temperature of the clear ink. If the ink temperature in the ink jet recording head is less than the gelation temperature + 10 ° C., the ink gels in the ink jet recording head or on the nozzle surface, and ink droplet ejection properties tend to decrease. On the other hand, when the temperature of the ink in the ink jet recording head exceeds the gelation temperature + 30 ° C., the clear ink becomes too high, and the clear ink component may deteriorate.

  The amount of liquid droplets per clear ink ejected from each nozzle of the ink jet recording head is preferably 0.5 to 10 pl depending on the viscosity of the clear ink and the like, and is ejected only to a desired region. Is more preferably 0.5 to 4.0 pl. Even when such an amount of clear ink is applied, since the sol-gel phase transition is performed in the clear ink of the present invention, the clear ink is not excessively wetted and can be discharged only to a desired location.

  The clear ink droplets landed on the recording medium are cooled and gelled by the sol-gel phase transition. Accordingly, the pinning can be performed without the clear ink droplets diffusing. In addition, since the droplet gels quickly, it is difficult for oxygen to enter the droplet and the curing of the photopolymerizable compound is not easily inhibited by oxygen.

  The temperature of the recording medium when the clear ink is applied may be different from the temperature when the color ink is dropped, but is usually the same temperature. In the inkjet ink set of the present invention, the clear ink is sufficiently leveled even when the temperature of the recording medium when the clear ink is dropped is the same as the temperature of the recording medium when the color ink is dropped.

(C) Step By irradiating the color ink droplet and the clear ink droplet landed on the recording medium with light from the LED light source, the photopolymerizable compound contained in the color ink droplet and the clear ink droplet is crosslinked or cross-linked. Each ink droplet is cured by polymerization. As described above, the color ink droplets and the clear ink droplets may be cured together, or the color ink droplets and the clear ink droplets may be individually cured.

  The light applied to the color ink droplets and the clear ink droplets attached to the recording medium is preferably ultraviolet light from an LED light source. Specific examples include a 395 nm, water-cooled LED, etc. manufactured by Phoseon Technology. When the color ink droplet and the clear ink droplet are individually cured, they may be the same type of light source or different light sources. As a general ultraviolet light source, a metal halide lamp can be mentioned. By using an LED as a light source, droplets of color ink and clear ink are melted by the radiant heat of the light source; Can be suppressed.

LED light source has a peak illuminance in the image surface with ultraviolet rays at 360~410nm is installed such that the 0.5~10W / cm ^2, and more preferably disposed so that 1~5W / cm ^2. The amount of light applied to the image is set to be less than 500 mJ / cm ² . This is to prevent the radiant heat from being applied to the ink droplets.

(Inkjet recording device)
The image forming method can be performed by an actinic ray curable ink jet recording apparatus. Actinic ray curable ink jet recording apparatuses include a line recording method (single pass recording method) and a serial recording method. The line recording method (single-pass recording method) is preferable from the viewpoint of high-speed recording, although it may be selected according to the required image resolution and recording speed.

FIG. 1A is a side view of an example of a configuration of a main part of a line recording type ink jet recording apparatus, and FIG. 1B is a top view thereof. 2A is a side view of another example of the configuration of the main part of the line recording type ink jet recording apparatus, and FIG. 2B is a top view thereof.
As shown in FIGS. 1A, 1B, 2A, and 2B, the inkjet recording apparatus 10 includes a head carriage 16 (16a, 16b) that accommodates a plurality of inkjet recording heads 14, and an ink flow connected to the head carriage 16. The light irradiation unit 18 that covers the entire path of the path 30, the ink tank 31 that stores ink supplied through the ink flow path 30, and the downstream side of the head carriage 16 (in the conveyance direction of the recording medium). (18a, 18b) and a temperature control unit 19 disposed on the lower surface of the recording medium 12.

  1A and 1B, the color ink head carriage 16a, the color ink droplet curing light irradiation unit 18a, the clear ink head carriage 16b, and the clear ink droplet curing light irradiation. The parts 18b are arranged in this order. In this apparatus, the color ink droplet and the clear ink droplet can be individually cured.

  2A and 2B, a clear ink head carriage 16b, a color ink head carriage 16a, and a light irradiation unit 18 are arranged in this order. In this apparatus, the clear ink is first ejected onto the recording medium 12, the color ink is ejected onto the clear ink, and the color ink and the clear ink droplet are collectively exposed by the light irradiation unit 18.

  The head carriage 16 of the inkjet recording apparatus 10 includes a head carriage 16a for color ink and a head carriage 16b for clear ink. The color ink head carriage 16a includes a head carriage for each color. For example, as shown in FIG. 1B, the head carriage 16 is fixedly disposed so as to cover the entire width of the recording medium 12 and accommodates a plurality of inkjet recording heads 14.

  The ink jet recording head 14 is supplied with color ink or clear ink. 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 ink jet recording head 14 is heated to a predetermined temperature to maintain the gel state.

  The light irradiation unit 18 (18a and 18b) covers the entire width of the recording medium 12, and is disposed on the downstream side of the head carriage 16 in the conveyance direction of the recording medium. The light irradiation unit 18 irradiates the ink droplets ejected by the inkjet recording head 14 and landed on the recording medium 12 with light, thereby curing the droplets.

  The temperature control unit 19 is disposed on the lower surface of the recording medium 12 and maintains the recording medium 12 at a predetermined temperature. For example, as shown in FIG. 1A, the temperature control unit 19 may be divided into a color ink head carriage 16a side and a clear ink head carriage 16b side. The temperature control unit 19 can be, for example, various heaters.

  Hereinafter, an image forming method using the line recording type inkjet recording apparatus 10 will be described. 1A and 1B, the recording medium 12 is conveyed between the color ink head carriage 16a and the temperature control unit 19 of the inkjet recording apparatus 10. On the other hand, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19. Next, high-temperature ink droplets are ejected from the ink jet recording head 14 of the color ink head carriage 16 a and adhered (landed) on the recording medium 12. Thereafter, if necessary, the light irradiating unit 18a irradiates the ink droplets of the color ink adhering on the recording medium 12 with light, and cures.

  Further, high temperature ink droplets are ejected from the ink jet recording head 14 of the clear ink head carriage 16b onto the recording medium 12 and attached (landed) on the recording medium 12. Thereafter, the light irradiating unit 18b irradiates the ink droplets of the clear ink adhering to the recording medium 12 with light to be cured.

  2A and 2B, the recording medium 12 is transported between the clear ink head carriage 16b and the temperature control unit 19 of the inkjet recording apparatus 10. On the other hand, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19. Next, high temperature ink droplets are ejected from the ink jet recording head 14 of the clear ink head carriage 16 b and are attached (landed) on the recording medium 12.

  Further, the recording medium 12 is transported under the color ink head carriage 16a, and high-temperature ink droplets are ejected from the ink jet recording head 14 to adhere (land) on the recording medium 12. Thereafter, the light irradiating unit 18 irradiates the ink droplets of the clear ink and the color ink attached on the recording medium 12 with light and cures them.

  The total ink droplet thickness after curing is preferably 1 to 20 μm. The “total ink droplet film thickness” is the maximum value of the thickness of the cured film of color ink and clear ink drawn on the recording medium.

  FIG. 3 is a diagram illustrating an example of a configuration of a main part of the serial recording type inkjet recording apparatus 20. As shown in FIG. 3, the inkjet recording apparatus 20 has a width narrower than the entire width of the recording medium, instead of the head carriage 16 (16a and 16b) fixedly arranged so as to cover the entire width of the recording medium, and 1A except that it includes a head carriage 26 (26a and 26b) that accommodates a plurality of inkjet recording heads 24, and a guide portion 27 (27a and 27b) for moving the head carriage 26 in the width direction of the recording medium 12. 1B can be configured similarly to FIG. 1B.

  In the serial recording type inkjet recording apparatus 20, an ink droplet is ejected from the inkjet recording head 24 accommodated in the head carriage 26 while the head carriage 26 moves in the width direction of the recording medium 12 along the guide portion 27. After the head carriage 26 has completely moved in the width direction of the recording medium 12 (for each pass), the recording medium 12 is fed in the transport direction. Except for these operations, an image is recorded in substantially the same manner as the line recording type inkjet recording apparatus 10 described above.

  In the ink jet recording apparatus 20 having the configuration shown in FIG. 3, the color ink and clear ink droplets are collectively exposed by the light irradiation unit 28. If necessary, the color ink head carriage 26a and the clear ink are used. A light irradiation unit for curing the color ink droplets may be disposed between the head carriage 26b and the head carriage 26b.

<Preparation of ink composition>
Inks of the examples and comparative examples were prepared using the following components.

<Preparation of pigment dispersion>
Each pigment dispersion was prepared by the following procedure. A dispersant and a dispersion medium are put into a stainless beaker, heated and stirred for 1 hour while being heated on a hot plate at 65 ° C., cooled to room temperature, a pigment is added thereto, and 200 g of zirconia beads having a diameter of 0.5 mm are added. Sealed in a glass jar. This was subjected to a dispersion treatment with a paint shaker until a desired particle size was obtained, and then zirconia beads were removed.

(Yellow pigment dispersion)
Dispersant 1: EFKA7701 (manufactured by BASF) 5.6 parts by mass Dispersant 2: Solsperse 22000 (manufactured by Nihon Lubrizol) 0.4 parts by mass Dispersion medium: tripropylene glycol diacrylate (containing 0.2% UV-10) 80.6 parts by mass Pigment: PY185 (manufactured by BASF, Paliotor Yellow D1155) 13.4 parts by mass

(Magenta pigment dispersion)
Dispersant: JET-9151 (manufactured by BYK) 11 parts by mass Dispersion medium: Tripropylene glycol diacrylate (containing 0.2% UV-10) 69 parts by mass Pigment: PV19 / PR202 (manufactured by BASF, Seishin Kasha Magenta 2BC) 20 Parts by mass

(Cyan pigment dispersion)
Dispersant: JET-9151 (manufactured by BYK) 7 parts by weight Dispersion medium: tripropylene glycol diacrylate (containing 0.2% UV-10) 70 parts by weight Pigment: PB15: 4 (manufactured by Dainichi Seika, Chromofine Blue 6332JC) 23 parts by mass

(Black pigment dispersion)
Dispersant: JET-9151 (BYK) 7 parts by weight Dispersion medium: Tripropylene glycol diacrylate (containing 0.2% UV-10) 70 parts by weight Pigment: PB7 (Mitsubishi Chemical Corporation, MA-7) 23 parts by weight Part

(Gelling agent)
Kao Wax T1 (disoaryl ketone manufactured by Kao Corporation)
Unistar M-2222SL (behyl behenylate manufactured by NOF Corporation)
18-Pentatriacontanon (Alfa Aeser)
Hentriacontan-16-on (Alfa Aeser)
EXCEPARL SS (manufactured by Kao Corporation)

(Photopolymerizable compound (polymerizable monomer))
APG-200 (Tripropylene glycol diacrylate manufactured by Shin-Nakamura Chemical Co., Ltd.)
A-600 (manufactured by Shin-Nakamura Chemical Co., Ltd., polyethylene glycol # 600 diacrylate)
SR499 (Sartomer 6EO-modified trimethylolpropane triacrylate)
M360 (3PO modified trimethylolpropane triacrylate, manufactured by Mion)

(Photopolymerizable compound (polymerizable oligomer))
Etcure 6361-100 (Hyperbranch polyester acrylate manufactured by Eternal Chemical)
CN2270 (aliphatic polyester acrylate manufactured by Sartomer)

(Photopolymerization initiator)
TPO (BASF)
819 (BASF)
ITX (made by LAMBSON)

(Polymerization inhibitor)
Irgastab UV10 (Ciba Japan)

(Surfactant)
TSF-4442 (Toshiba Silicone)

  According to the composition of the ink described in Table 1 and Table 2, each component and each part of the pigment dispersion were mixed and heated to 80 ° C. and stirred. The obtained solution was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC under heating. Then, the image was evaluated according to the evaluation criteria described later.

<Formation of inkjet image>
Cyan ink is loaded into the cyan ink head carriage 16a of the line head type ink jet recording apparatus having the piezo ink jet recording head shown in FIGS. 1A, 1B, 2A, and 2B, and the clear ink head carriage 16b is cleared. An ink was loaded to form a cyan monochrome image.
The ink supply system of the ink jet recording apparatus includes an ink tank, a supply pipe, a front chamber ink tank immediately before the recording head, a pipe with a filter, and a piezo head. The ink was insulated from the front chamber ink tank to the recording head portion, and heated to the gelation temperature of the ink + 30 ° C. Also, a heater was incorporated in the piezo head, and the ink temperature in the recording head was heated to the above temperature. The piezo head had a nozzle diameter of 24 μm, and as shown in FIG. 1B, heads with a nozzle resolution of 600 dpi were arranged in a staggered manner to form a 1200 dpi nozzle row.

The recording medium was recorded on the following coated paper for printing.
・ OK top coat + (US basis weight 104.7g / m ² made by Oji Paper)
・ OK top coat mat N (US basis weight 104.7g / m ² made by Oji Paper)
・ OK Kanfuji + (US basis weight 127.9g / m ² made by Oji Paper)
・ SA Kanofuji + (basis weight of 127.9 g / m ² made by Oji Paper)

  The recording medium was conveyed by being adsorbed on a conveyance table. At this time, the temperature of the suction table was adjusted so that the temperature of the surface of the recording medium was constant when the ink droplet landed and during UV exposure. Table 3 shows the temperature of the recording medium in each example and comparative example.

  The amount of droplets of color ink from the head was 3.5 pl, the amount of droplets of clear ink was 4 pl, and the recording resolution was 1200 dpi × 1200 dpi. The recording speed was 800 mm / s. dpi represents the number of dots per 2.54 cm.

  Using YMCK color ink, the positive and negative characters (white characters) of 5 points and 7 points of MS Mincho, YMCKBGR gradation chart, natural image, 5cm x 5cm solid image After printing an evaluation chart including a clear ink, a clear ink was printed on the entire surface at a drawing rate of 100% to create an image.

The color ink and the clear ink were exposed to UV, and each ink was cured. Except for the sample 2, both the color ink and the clear ink were discharged onto the recording medium, and then exposure was performed collectively. For sample 2, after the color image was created, only the color ink was exposed, and then the clear ink was applied and exposed again.
The exposure was an LED lamp (emission center wavelength 395 nm, distance between recording medium and lamp 2 mm, maximum output 7000 mW / cm ² ). The above image formation was performed in an environment of 23 ° C. and 55% RH.

<Evaluation of formed image>
The formed image was evaluated by the following method.
(Evaluation of character quality)
The obtained characters were visually observed and evaluated according to the following criteria.
○: Negative and positive of 5-point characters can be reproduced without loss of detail. △: Although the collapse of details is seen with positive of 5-point characters, it is fully decipherable and 7-point characters are reproduced without being destroyed. ×: Details are crushed with negative and positive 7-point characters

(Evaluation of mat feeling)
The 60-degree gloss value was measured by the method defined by JIS K 5600.
○: Surface gloss value is 20 or less, and the entire surface has a uniform mat feeling. Δ: Surface gloss value is 20 to 30 or less, and there is slight gloss variation, but there is little discomfort overall. Higher than 40 and strong gloss

(Evaluation of relief feeling)
The obtained gradation chart was visually observed and evaluated according to the following criteria. Here, the relief feeling refers to a feeling of unevenness due to a step generated at a boundary where image density differences are different.
○: There is no relief feeling and the image is uniformly matte. Δ: There is a part that feels unevenness. ×: The unevenness is large on the whole, the relief feeling is remarkable, and the image part and the substrate are uncomfortable. Unbearable to use greatly

(Evaluation of abrasion)
In accordance with the method described in “JIS Standard K5701-1-6.2.3 Friction Resistance Test” on a 5 cm × 5 cm solid image, a recording medium cut to an appropriate size is placed on the image, and a load is applied. And rubbed together. Thereafter, the degree of image density reduction was visually observed and evaluated according to the following criteria.
○: No change in image was observed even after rubbing 100 times or more. Δ: Image density decreased at the stage of rubbing 100 times, but in a practically acceptable range. X: Clear with rubbing less than 50 times. The image density is noticeable, and the quality is unusable.

  From Table 3, about Examples 1-17, the favorable result was obtained also in any evaluation item. Although not shown, the storage stability and ejection stability were also good.

DESCRIPTION OF SYMBOLS 10, 20 Inkjet recording device 12 Recording medium 14, 24 Inkjet recording head 16, 26 Head carriage 18, 28 Light irradiation part 19 Temperature control part 27 Guide part

Claims (5)

A color ink containing a photopolymerizable compound, a photopolymerization initiator, a gelling agent, and a coloring material, having a phase transition point at 40 ° C. or more and less than 100 ° C., and undergoing a sol-gel phase transition according to temperature;
An inkjet ink set comprising a photopolymerizable compound, a photopolymerization initiator, and a gelling agent, having a phase transition point at 57 ° C. or more and less than 100 ° C., and a clear ink that undergoes a sol-gel phase transition depending on the temperature;
The gel transition temperature of the clear ink is higher than the gel transition temperature of the color ink,
Wherein in gelling agent content in the clear ink and the color ink from 0.1 to 10 wt%, said gelling agent amount contained in the clear ink is greater than the gelling agent content in the color ink An ink set characterized by A color ink containing a photopolymerizable compound, a photopolymerization initiator, a gelling agent, and a coloring material, having a phase transition point at 40 ° C. or more and less than 100 ° C., and undergoing a sol-gel phase transition according to temperature;
An inkjet ink set comprising a photopolymerizable compound, a photopolymerization initiator, and a gelling agent, having a phase transition point at 57 ° C. or more and less than 100 ° C., and a clear ink that undergoes a sol-gel phase transition depending on temperature;
The gel transition temperature of the clear ink is higher than the gel transition temperature of the color ink,
The ink set, wherein the clear ink and the color ink further contain a surfactant. The ink set according to claim 2, wherein the surfactant content in the clear ink, characterized in that more than the amount of surfactant contained in the color ink. The clear ink and the color ink contain an aliphatic ketone compound and an aliphatic ester compound as the gelling agent, and the aliphatic ketone compound contained in the clear ink contains 60 to 60 of the total amount of gelling agent contained in the clear ink. The ink set according to any one of claims 1 to 3, wherein the ink set is 95% and more than the amount of the aliphatic ketone compound contained in the color ink. Using the ink set according to any one of claims 1 to 4 , ejecting the ink droplets of the color ink from an ink jet recording head, and attaching the ink droplets onto a recording medium;
Droplets of the clear ink of the ink set are ejected from an inkjet recording head and adhered onto a recording medium;
And a step of irradiating the droplets of the color ink landed on the recording medium and the droplets of the clear ink with actinic rays to cure the droplets.

Images