JP5880228B2 - Actinic ray curable inkjet ink and image forming method using the same - Google Patents

Description

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

  The ink jet recording system is used in various printing fields because it can form an image easily and inexpensively. 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. One of the methods for preventing the unification of adjacent dots is a technique of adding a gelling agent to the ultraviolet curable inkjet ink. As a gelling agent to be added to ink, stearone has been proposed (see, for example, Patent Documents 1 and 2).

  Here, when the light source for curing the ultraviolet curable ink jet ink is a light source with high radiant heat such as a metal halide lamp, the surface of the ink droplet cured by the ultraviolet ray is easily melted, and the ink droplet surface is liable to be hardened. There was a problem. Furthermore, in the case of a plastic recording medium that is easily affected by heat, there has been a problem that the ink cannot be cured by a light source having a large radiant heat.

  Thus, it has been studied to use a light source for ink curing as an LED light source with little radiant heat (for example, Patent Document 3). However, the LED light source has a small amount of light. Therefore, the ink droplets cannot be sufficiently cured to the inside. Therefore, there is a problem that the ink droplets cured by the LED light source have low adhesion to the recording medium.

  In order to solve this problem, it has been studied to add a ketone resin having a hydroxyl group and a urethane oligomer to an ultraviolet curable ink-jet ink to improve the adhesion between the cured ink droplet and the recording medium (Patent Literature). 4).

US Patent Application Publication No. 2007/0058020 International Publication No. 2007/025893 JP 2011-25684 A JP 2011-52107 A

  However, even with the ultraviolet curable inkjet ink described in Patent Document 4, the adhesion of the cured ink to a plastic recording medium such as polypropylene or polypropylene terephthalate is insufficient. In addition, when ink jet printing is performed on such a plastic substrate, there is a problem that ink droplets are likely to coalesce and image quality is poor.

The present invention has been made in view of the above circumstances , and provides an actinic ray curable inkjet ink having a low odor and excellent dissolution stability of contained components, and using the ink, after landing on a recording medium things make coalescence ink Ku, hardening film is an object to provide a method of forming a stable the images that have a recording medium and high adhesion.

The first of the present invention relates to an image forming method described below.
[1] Actinic ray curable inkjet ink droplets containing a gelling agent, a photopolymerizable compound, a photopolymerization initiator, and a non-polymerizable resin and undergoing a sol-gel phase transition with temperature are ejected from an inkjet recording head. A step of adhering to a recording medium, and a step of irradiating light from an LED light source to the droplets landed on the recording medium to cure the droplets, wherein the gelling agent has a carbon number. Including a compound containing 12 or more linear alkyl groups, wherein the photopolymerizable compound includes a (meth) acrylate compound having a molecular weight of 280 to 1500 and a ClogP value of 4.0 to 7.0. The non-polymerizable resin includes a polyester resin having one or more polar functional groups in the molecule, or a ketone resin having one or more polar functional groups in the molecule, and the gelation is performed with respect to the total amount of the ink. 0.5 to 10.0% by mass, 10 to 40% by mass of the (meth) acrylate compound, 2.0 to 15.0% by mass of the non-polymerizable resin, and the light has a peak at 370 to 410 nm. An image forming method having an illuminance of 0.5 to 10.0 W / cm ² .

[2] The image forming method according to [1], wherein the (meth) acrylate compound is at least one (meth) acrylate compound of the following (1) and (2).
(1) Trifunctional or higher (meth) acrylate compound having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule (2) cyclic in the molecule Bifunctional or higher functional (meth) acrylate compound [3] The gelling agent is at least one compound selected from the compounds represented by the following general formulas (G1) and (G2): [1] or [1] 2].
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4
(In the formula, R1 to R4 each independently represents a hydrocarbon group containing a straight chain portion having 12 or more carbon atoms.)

[4] The polar functional group of the polyester resin or the ketone resin is selected from —OH group, —COOH group, —NH ₂ group, —NO ₂ group, and —CN group, [1] to [3] The image forming method according to any one of the above.
[5] The image forming method according to any one of [1] to [4], wherein the polyester resin or the ketone resin has an —OH group and a —COOH group.
[6] The image formation according to any one of [1] to [5], wherein the polyester resin or the ketone resin has a number average molecular weight of 1000 to 5000 and an acid value or a base value of 10 to 350 mgKOH / g. Method.
[7] The temperature of the recording medium when the actinic radiation curable inkjet ink lands on the recording medium is set to a range of −10 ° C. to −20 ° C. of the sol-gel phase transition temperature of the actinic radiation curable inkjet ink. , [1] to [6].
[8] The image formation according to any one of [1] to [7], wherein the light irradiated in the step of curing the ink droplets has a peak illuminance of 0.5 to 5 W / cm ² at 370 to 410 nm. Method.
[9] The image forming method according to any one of [1] to [8], wherein the recording medium is made of polypropylene or polyethylene terephthalate.

The second aspect of the present invention relates to the following inkjet ink.
[10] An actinic ray curable ink jet containing a gelling agent, a photopolymerizable compound, a photopolymerization initiator, and a non-polymerizable resin and undergoing a sol-gel phase transition according to temperature, wherein the gelling agent has a carbon number Including a compound containing 12 or more linear alkyl groups, wherein the photopolymerizable compound includes a (meth) acrylate compound having a molecular weight of 280 to 1500 and a ClogP value of 4.0 to 7.0. The non-polymerizable resin includes a polyester resin having one or more polar functional groups in the molecule, or a ketone resin having one or more polar functional groups in the molecule, and the gelling agent is added to the total amount of the ink. An actinic ray curable inkjet ink comprising 0.5 to 10.0% by mass, 10 to 40% by mass of the (meth) acrylate compound, and 2.0 to 15.0% by mass of the non-polymerizable resin.

  According to the image forming method of the present invention, since the ink that has landed on the recording medium does not coalesce, a high-quality image can be obtained. Further, the formed image has high adhesion to the recording medium.

It is a figure which shows an example of a structure of the principal part of the inkjet recording apparatus of a line recording system. 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.

  The image forming method of the present invention is a method for forming an image by applying a specific actinic ray curable inkjet ink.

[Actinic ray curable inkjet ink]
The actinic ray curable inkjet ink applied by the image forming method of the present invention includes a photopolymerizable compound, a gelling agent, a photopolymerization initiator, and a non-polymerizable resin. Additives etc. may be included.

-About a photopolymerizable compound Actinic-light curable inkjet contains a photopolymerizable compound. A photopolymerizable compound is a compound that crosslinks or polymerizes upon irradiation 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 is a radical polymerizable compound or a cationic polymerizable compound, and preferably a radical polymerizable compound.

  The radically polymerizable compound is a compound (monomer, oligomer, polymer or mixture thereof) having a radically polymerizable ethylenically unsaturated bond. A radically polymerizable compound may be used independently and may be used in combination of 2 or more type.

  Examples of compounds having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids and salts thereof, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and anhydrides thereof, 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 but also an oligomer, a mixture of a monomer and an oligomer, a modified product, an oligomer having a polymerizable functional group, or the like. Here, “(meth) acrylate” refers to both and / or “acrylate” and “methacrylate”, and “(meth) acryl” refers to both and / or “acryl” and “methacryl”.

  The actinic ray curable inkjet ink for the image forming method of the present invention has a molecular weight within the range of 280 to 1500 and a ClogP value within the range of 4.0 to 7.0 as the photopolymerizable compound. (Meth) acrylate compounds (hereinafter also referred to as “(meth) acrylate compound A”) are included. The (meth) acrylate compound A preferably has two or more (meth) acrylate groups.

  The molecular weight of the (meth) acrylate compound A is preferably in the range of 280 to 1500, and more preferably in the range of 300 to 800. In order to stably eject ink droplets from the ink jet recording head, it is necessary that the ink viscosity at the ejection temperature be between 7 and 14 mPa · s. An ink composition containing a (meth) acrylate compound having a molecular weight of less than 280 and a gelling agent has a large change in ink viscosity before and after the ejection temperature. Therefore, it is difficult to adjust the ink viscosity within the above range. Moreover, since the (meth) acrylate compound having a molecular weight of 280 or more has less odor, the odor of the actinic ray curable inkjet ink and its cured product can be reduced. On the other hand, when a (meth) acrylate compound having a molecular weight exceeding 1500 is contained, the sol viscosity of the ink becomes excessively high.

  The ClogP value of the (meth) acrylate compound A is preferably in the range of 4.0 to 7.0, and more preferably in the range of 4.5 to 6.0. When the ClogP value of the (meth) acrylate compound A is less than 4.0, the actinic ray curable inkjet ink becomes hydrophilic and the gelling agent is hardly dissolved. Therefore, even when heated, the gelling agent is not completely dissolved, and the ink does not sufficiently undergo sol-gel phase transition. Further, defective ejection from the ink jet recording apparatus is likely to occur. On the other hand, when the ClogP value of the (meth) acrylate compound A exceeds 7.0, the solubility of the photopolymerization initiator in the ink is lowered, and the curability of the ink is lowered or the ejection property from the ink jet recording head is decreased. Or drop.

  Here, the “Log P value” is a coefficient indicating the affinity of an organic compound for water and 1-octanol. 1-octanol / water partition coefficient P is a distribution equilibrium when a trace amount of compound is dissolved as a solute in a two-liquid solvent of 1-octanol and water, and is a ratio of the equilibrium concentration of the compound in each solvent. Their logarithm LogP for the base 10 is shown. That is, the “log P value” is a logarithmic value of the 1-octanol / water partition coefficient, and is known as an important parameter representing the hydrophilicity / hydrophobicity of a molecule.

  The “CLogP value” is a LogP value calculated by calculation. The CLogP value can be calculated by a fragment method, an atomic approach method, or the like. More specifically, ClogP values can be calculated in the literature (C. Hansch and A. Leo, “Substituent Constants for Correlation Analysis in Chemistry and Biology” (John Wiley & Sons, New York, 69). Or the following commercially available software package 1 or 2 may be used.

Software Package 1: MedChem Software (Release 3.54, Aug. 1991, Medicinal Chemistry Project, Pomona College, Clarmont, CA)
Software package 2: Chem Draw Ultra ver. 8.0. (April 2003, CambridgeSoft Corporation, USA)

  The numerical value of the ClogP value described in this specification and the like is a “ClogP value” calculated using the software package 2.

  The amount of (meth) acrylate compound A contained in the actinic ray curable inkjet ink is preferably in the range of 10 to 40% by mass. When the amount of the (meth) acrylate compound A is less than 10% by mass, the ink becomes hydrophilic, the solubility of the gelling agent is lowered, and the sol-gel phase transition is not sufficiently performed. On the other hand, when the amount of the (meth) acrylate compound A exceeds 40% by mass, the solubility of the photopolymerization initiator in the ink becomes insufficient. For this reason, the ejection of ink from the ink jet recording apparatus becomes unstable, and the shrinkage when the ink droplets are cured increases. Further, the printed material is curled, and the adhesion of the image film to the recording medium is significantly deteriorated. Further, the gelling agent is difficult to deposit and the pinning property of the ink is deteriorated.

More preferable examples of the (meth) acrylate compound A include (1) a trifunctional or higher functional group having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule. Methacrylate or acrylate compounds, (2) Bifunctional or higher functional methacrylate or acrylate compounds having a cyclic structure in the molecule are included. These (meth) acrylate compounds have high photocurability and little shrinkage when cured. Furthermore, the reproducibility of the sol-gel phase transition is high.

(1) A trifunctional or higher functional methacrylate or acrylate compound having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule is, for example, 3 or more A hydroxyl group of a compound having a hydroxyl group is modified with propylene oxide, and the resulting modified product is esterified with (meth) acrylic acid. Specific examples of this compound include
3PO-modified trimethylolpropane triacrylate Photor 4072 (molecular weight 471, Clog P4.90, manufactured by Cognis),
3PO-modified trimethylolpropane triacrylate Miramer M360 (molecular weight 471, Clog P4.90, manufactured by Miwon)
Etc. are included.

(2) The bifunctional or higher functional methacrylate or acrylate compound having a cyclic structure in the molecule is obtained by esterifying the hydroxyl group of a compound having two or more hydroxyl groups and tricycloalkane with (meth) acrylic acid. is there. Specific examples of this compound include
Tricyclodecane dimethanol diacrylate NK ester A-DCP (molecular weight 304, Clog P4.69),
Tricyclodecane dimethanol dimethacrylate NK ester DCP (molecular weight 332, Clog P 5.12)
Etc. are included.

  Another specific example of the (meth) acrylate compound A includes 1,10-decanediol dimethacrylate NK ester DOD-N (molecular weight 310, Clog P5.75, manufactured by Shin-Nakamura Chemical Co., Ltd.).

  The photopolymerizable compound may further contain a photopolymerizable compound other than the (meth) acrylate compound A. Other photopolymerizable compounds include, for example, (meth) acrylate monomers or oligomers having a ClogP value of less than 4.0; (meth) acrylate monomers or oligomers having a ClogP value of more than 7.0, and other polymerizable properties There are oligomers and the like.

  Examples of (meth) acrylate monomers or oligomers include 4EO modified hexanediol diacrylate (CD561, manufactured by Sartomer, molecular weight 358); 3EO modified trimethylolpropane triacrylate (SR454, manufactured by Sartomer, molecular weight 429); 4EO modified Pentaerythritol tetraacrylate (SR494, manufactured by Sartomer, molecular weight 528); 6EO-modified trimethylolpropane triacrylate (SR499, manufactured by Sartomer, molecular weight 560); caprolactone acrylate (SR495B, manufactured by Sartomer); polyethylene glycol diacrylate (NK) Ester A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 508), (NK Ester A-600, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 708) Polyethylene glycol dimethacrylate (NK ester 9G, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 536), (NK ester 14G, manufactured by Shin-Nakamura Chemical Co., Ltd.); tetraethylene glycol diacrylate (V # 335HP, manufactured by Osaka Organic Chemical Co., Ltd., molecular weight 302) ); Stearyl acrylate (STA, manufactured by Osaka Organic Chemical Co., Ltd.); phenol EO-modified acrylate (M144, manufactured by Miwon); nonylphenol EO-modified acrylate (M166, manufactured by Miwon), and the like.

  Examples of other polymerizable oligomers include epoxy acrylate, aliphatic urethane acrylate, aromatic urethane acrylate, polyester acrylate, and linear acrylic oligomer.

-Non-polymerizable resin Actinic ray curable inkjet inks have a resin that is inert to actinic rays; that is, those that do not have groups (photopolymerizable groups) that crosslink or polymerize upon irradiation with actinic rays. Polymerizable resins are included. The actinic ray curable inkjet ink for the image forming method of the present invention includes a polyester resin or a ketone resin having at least one polar functional group in the molecule as a non-polymerizable resin. When such a polyester resin or ketone resin is contained in the actinic ray curable inkjet ink, the gelling agent is likely to be deposited after the ink has landed on the recording medium due to the polar functional group. On the other hand, the relatively weak polar site (ester site or ketone site) of the polyester resin or ketone resin has an affinity for the gelling agent. That is, the gelling agent is easily mixed uniformly in the sol ink.
Further, the polar functional group of the polyester resin or the ketone resin is bonded to the functional group on the surface of the recording medium, so that the adhesion between the cured film of the ink and the recording medium is enhanced.

The polar functional group possessed by the polyester resin or ketone resin is preferably a group selected from —OH group, —COOH group, —NH ₂ group, —NO ₂ group, and —CN group. When the polyester resin or the ketone resin has these polar functional groups, the gelling agent is more likely to precipitate in the ink after landing on the recording medium. In particular, the polyester resin or the ketone resin preferably has both —OH groups and —COOH. If the polyester resin or the ketone resin has these, the adhesiveness is likely to be increased regardless of the functional group present on the surface of the recording medium.

  The amount of the polar functional group that the polyester resin or ketone resin has is not particularly limited, but a range in which the acid value or base value of the polyester resin or ketone resin is 10 to 350 mgKOH / g is preferable. The acid value or base value of the polyester resin or ketone resin is more preferably 10 to 65 mgKOH / g. If the acid value or base value of the polyester resin or ketone resin is 10 mg KOH / g, the adhesion of the cured film to the recording medium will not be sufficient, and the ink will not sufficiently undergo sol-gel phase transition. On the other hand, it is difficult to introduce a polar functional group into a polyester resin or a ketone resin as the acid value or base value of the polyester resin or the ketone resin exceeds 350 mgKOH / g. Moreover, when the amount of polar functional groups is excessive, the compatibility of the gelling agent may be lowered in the sol-like ink. The acid value and base number are measured in accordance with the neutralization number test method described in JIS K2501.

  The number average molecular weight of the polyester resin or ketone resin having a polar functional group is preferably 1000 to 5000, and more preferably 1200 to 3000. When the number average molecular weight of the polyester resin or the ketone resin is less than 1000, the compatibility of the gelling agent is increased and the gelling agent is hardly precipitated. On the other hand, when the number average molecular weight of the polyester resin or the ketone resin is larger than 5000, the viscosity of the actinic ray curable inkjet ink is increased, and the ejection stability of the ink from the inkjet recording apparatus is lowered. The number average molecular weight is a value measured in terms of polystyrene by gel permeation chromatography (GPC).

  Specific examples of the polyester resin having a hydroxyl group and a hydroxyl group include a special ester resin (TEGOAddBond series (LTH, LTW, 1270, 2440, 3350 UV) manufactured by EVONIK INDUSTRIES, all of which have an average molecular weight of 1500 to 3000 and an acid value of 15 to 65 mgKOH. / G, base number 10 to 50 mg KOH / g).

Specific examples of the ketone resin having a hydroxyl group include a ketone resin manufactured by degussa (TEGO VARIPLUS SK (average molecular weight 1000 to 2000, acid value about 0 mgKOH / g, base number about 300 mgKOH / g)) and the like.
Specific examples of the ketone resin having a urethane group include a ketone resin (TEGO VARIPLUS PZZ-1201) manufactured by degussa.

  The amount of the polyester resin or ketone resin having a polar functional group contained in the actinic ray curable inkjet is 2.0 to 15.0% by mass, preferably 3.0 to 10.0 with respect to the total mass of the ink. % By mass. When two or more kinds of polyester resins or ketone resins having a polar functional group are contained, the total amount thereof is within the above range. If the amount of the polyester resin or ketone resin having a polar functional group is less than 2.0% by mass, the gelling agent may not be sufficiently precipitated (crystallized) in the ink after landing. On the other hand, when the amount of the polyester resin or ketone resin having a polar functional group exceeds 15.0% by mass, not only the viscosity of the sol-like ink is increased, but also the solubility of the gelling agent in the sol-like ink is increased. descend.

There is no restriction | limiting in particular in the preparation method of the polyester resin which has a polar functional group. For example, it can be obtained by preparing a polyester resin from a polyhydric alcohol having a polar functional group, a polyvalent carboxylic acid, a cyclic lactone or the like. Specifically, a polyester resin having a polar functional group can be prepared by performing the following reaction.
(I) Direct esterification reaction of bifunctional or higher polyhydric alcohol and bifunctional or higher polycarboxylic acid (ii) Transesterification reaction of bifunctional or higher polyester and bifunctional or higher polyhydric alcohol (iii) 2 Esterification reaction of polyhydric alcohol and acid anhydride higher than functional group (iv) Direct esterification reaction of hydroxycarboxylic acid having one or more hydroxyl groups and carboxyl groups in one molecule (v) Polar functional group bonded to ring Ring-opening polymerization of selected cyclic lactones

  The acid value and base value of the polyester resin are adjusted by the number of functional groups such as polyhydric alcohol, polycarboxylic acid, hydroxycarboxylic acid, and polar group-containing cyclic lactone as raw materials.

A ketone resin having a polar functional group can be prepared by reacting an aromatic ketone compound such as acetophenone with a compound having a polar functional group. For example, a ketone resin having an —OH group can be prepared by reacting an aromatic ketone compound such as acetophenone with an aldehyde compound such as formaldehyde and hydrogenating the obtained ketone resin.
The acid value and base value of the ketone resin are adjusted by the amount of the compound to be reacted with the ketone compound, the kind of the compound, and the like.

-About a gelatinizer The gelling agent contained in actinic-light curable inkjet ink has the function to carry out a sol-gel phase transition reversibly with 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 from the ink jet recording apparatus, it is necessary that the compatibility of 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 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 actinic ray curable inkjet ink for the image forming method of the present invention 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 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, gelling agents having a polar group such as —OH or —COOH at the end of the alkyl chain, such as fatty acid amide, have poor stability in sol-like ink, and may precipitate or separate layers. is there. Further, the gelling agent may gradually elute from the cured film of the ink with the passage of time. 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, when 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 ejection 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 (made by Alfa Aeser), Hentriacontan-16-on (made by Alfa Aeser), Kao wax T1 (made by Kao Corporation), and the like. Is included.

  The aliphatic ketone compound contained in the actinic ray curable inkjet ink may be only one kind, or may be a mixture of two or more kinds.

  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 (G2) include behenyl behenate (C21-C22, melting point 70 ° C.), icosyl icosylate (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-C14), Melting point 43 ° C), cetyl myristate (C13-C16, melting point 50 ° C), octyldodecyl myristate (C13-C20), stearyl oleate (C17-C18), stearyl erucate (C21-C18), stearyl linoleate ( C17-C18), behenyl oleate (C18-C 2), myricyl cellotate (C25-C16), stearyl montanate (C27-C18), behenyl montanate (C27-C22), arachidyl linoleate (C17-C20), palmityl triacontanoate (C29-C16), etc. included.

  Examples of commercially available aliphatic ester compounds represented by the formula (G2) include Unistar M-2222SL (manufactured by NOF Corporation), EXCEPARL SS (manufactured by Kao Corporation, melting point 60 ° C.), EMALEX CC-18 ( Nippon Emulsion Co., Ltd.), Amreps PC (manufactured by Higher Alcohol Industry Co., Ltd.), Exepal MY-M (manufactured by Kao Co., Ltd.), Spam Acechi (manufactured by NOF Corporation), EMALEX CC-10 (manufactured by Nippon Emulsion Co., Ltd.), etc. Is 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 actinic ray curable inkjet ink may be only one type or a mixture of two or more types.

  The amount of the gelling agent contained in the actinic ray curable inkjet ink is preferably 0.5 to 10.0% by mass, more preferably 1 to 7% by mass with respect to the total amount of the ink. If it is less than 0.5% by mass, the ink droplet cannot be gelled (sol-gel phase transition due to temperature), and if it exceeds 10% by mass, it cannot be sufficiently dissolved in the ink, and the ink droplet is ejected. This is because the sex is lowered.

-Photopolymerization initiator The actinic ray curable inkjet 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, include camphor quinone and the like.

  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 in the actinic ray curable inkjet ink is preferably 0.1% by mass to 10% by mass, although it depends on the light irradiated at the time of ink curing and the type of the photopolymerizable compound. More preferably, it is 2-8 mass%.

  The photopolymerization initiator in the actinic ray curable inkjet ink may contain a photoacid generator. Examples of photoacid generators include chemically amplified photoresists and compounds used for photocationic polymerization (Organic Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), 187. To page 192).

  The actinic ray curable inkjet ink may further contain a photopolymerization initiator auxiliary agent, a polymerization inhibitor, and the like, 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 kind of these compounds may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained.

  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.

-About a color material A color material is further contained in actinic-light curable inkjet ink. The colorant can be a dye or a pigment. A pigment is more preferable because it has good dispersibility with respect to the components of the ink and is excellent in weather resistance.

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

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

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

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

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

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

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

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

  The content of the pigment or dye is preferably 0.1 to 20% by mass, and more preferably 0.4 to 10% by mass with respect to the actinic ray curable inkjet ink. This is because if the content of the pigment or dye is too small, the color of the resulting image is not sufficient, and if it is too large, the viscosity of the ink increases and the jetting property decreases.

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

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

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

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

-Sol-gel phase transition type inkjet ink Since the actinic ray curable inkjet ink contains a gelling agent as described above, the sol-gel phase transition reversibly occurs depending on the temperature. Actinic ray curable ink that undergoes a sol-gel phase transition is a liquid (sol) at a high temperature (for example, about 80 ° C.), and therefore can be ejected in a sol state from an inkjet recording head. When actinic ray curable inkjet 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 ejection properties of the ink droplets, 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 gelation temperature of the 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 gelation temperature of the ink exceeds 70 ° C. when the ejection temperature is around 80 ° C., gelation tends to occur at the time of ejection, resulting in low ejection properties. When the gelation temperature is less than 40 ° C., the recording medium This is because it does not gel immediately after landing. The gelation temperature is a temperature at which the fluidity decreases due to gelation in the process of cooling the ink in the sol state.

  The viscosity at 80 ° C., the viscosity at 25 ° C. and the gelation temperature of the 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 gelation temperature can be determined as the temperature at which the viscosity becomes 200 mPa · s in the temperature change curve of the viscosity.

  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 °.

  In the conventional actinic radiation curable inkjet ink that undergoes sol-gel phase transition, the compatibility between the gelling agent and other components has not been studied in detail, and printing is continued even if dot coalescence can be suppressed at the beginning of printing. When printing is started after leaving the printer in a standby state without printing for a while, the image quality may deteriorate. Also, the adhesion between the ink cured film and the recording medium is insufficient, and particularly when printing is performed on a plastic recording medium such as polypropylene or polyethylene terephthalate, the ink cured film is easily peeled off from the recording medium. There was a problem.

  In general ink, a urethane acrylate oligomer, a (meth) acrylate compound having a hydroxyl group, a (meth) acrylate compound having an acrylamide structure, or the like is added in order to improve the adhesion between the cured product and the recording medium. However, when a urethane acrylate oligomer or the like is added to the ink containing the gelling agent, the compatibility of the gelling agent is reduced or the sol-gel phase transition is inhibited.

  The inventors have added a specific amount of (meth) acrylate compound A and a non-polymerizable resin to the actinic ray curable inkjet ink, so that good curability and high image quality (dot coalescence suppression, It was found that there was no character collapse), reproducibility (gelator dissolution stability = ejection stability), and the like.

  The reason why a high-quality image can be obtained by the actinic ray curable inkjet ink of the present invention is presumed as follows. When the (meth) acrylate compound A is contained in the actinic ray curable inkjet ink, the solubility of the gelling agent is improved. Further, in the actinic radiation curable ink-jet ink, a non-polymerizable resin having a weak polar group (ester group or ketone group) and a (meth) acrylate compound A having a relatively high hydrophobicity are mixed relatively uniformly. Yes. The mixing stability of the gelling agent is also increased by the weak polar group (ester group or ketone group) of the non-polymerizable resin. That is, the stability of the sol ink is excellent, and the ejection stability of the ink from the ink jet recording apparatus is good.

  In addition, the actinic ray curable ink-jet ink contains a non-polymerizable resin, and the gelling agent precipitates or crystallizes stably and rapidly after the ink lands due to the polar functional group of the non-polymerizable resin. Therefore, coalescence of ink droplets is effectively suppressed, and a high quality image can be obtained. Further, the polar functional group of the non-polymerizable resin is bonded to the functional group on the surface of the recording medium, so that the adhesion between the ink cured product and the recording medium is increased.

-Preparation method of inkjet ink Actinic ray curable inkjet ink is obtained by mixing the above-mentioned photopolymerizable compound, gelling agent, non-polymerizable resin, and coloring material under heating. Preferably, a pigment dispersant in which a color material (particularly a pigment) is dispersed in a part of the photopolymerizable compound is prepared and mixed with the pigment dispersant and other ink components. The obtained ink is preferably filtered through a predetermined filter.

2. Image Forming Method The image forming method of the present invention includes at least the following two steps.
(1) A step of ejecting an actinic ray curable ink jet ink from an ink jet recording head and adhering the ink onto a recording medium (2) The ink liquid is obtained by irradiating the droplets landed on the recording medium with light from an LED light source. Curing the drops

-(1) Process The actinic-light curable inkjet ink should just be the inkjet ink mentioned above.
Ink droplets are ejected from the ink jet recording head. In order to improve the ejection properties of the ink droplets, it is preferable to set the temperature of the inkjet ink in the inkjet recording head to a temperature that is 10 to 30 ° C. higher than the gelation temperature of the ink. When 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 the ejection properties of the ink droplets are likely to deteriorate. 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 ink is heated by an ink jet recording head of the ink jet recording apparatus, an ink flow path connected to the ink jet recording head, an ink tank connected to the ink flow path, or the like.

  The amount of droplets ejected from each nozzle of the inkjet recording head is preferably 0.5 to 10 pl, although it depends on the resolution of the image. In order to form a high-definition image, 0 More preferably, it is 5-2.5 pl. In order to form a high-definition image with such a droplet amount, the ink after landing does not coalesce; that is, the ink needs to undergo a sol-gel phase transition sufficiently. In the above-mentioned actinic ray curable inkjet ink, the sol-gel transition is rapidly performed. Therefore, a high-definition image can be stably formed even with such a droplet amount.

  The ink droplets that have landed on the recording medium are cooled and rapidly gelled by the sol-gel phase transition. As a result, the ink droplets can be pinned without diffusing. Furthermore, since it is difficult for oxygen to enter the ink droplets, 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. Conventional ink cured products have low adhesion to a recording medium made of polyethylene terephthalate or polypropylene. On the other hand, the cured product of the actinic ray curable inkjet ink used in the image forming method of the present invention has excellent adhesion to polyethylene terephthalate or polypropylene. Therefore, according to the image forming method of the present invention, a high-quality image can be formed on a recording medium made of polyethylene terephthalate or polypropylene.

  Here, by ejecting ink droplets from the ink jet recording head, the ink droplets adhere to the recording medium. The temperature of the recording medium when the ink droplet lands 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 ink droplets gel excessively and pinning, so that the ink droplets are not sufficiently leveled and the image gloss may be lowered. 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.

  In the actinic ray curable inkjet ink of the present invention, the gelling agent is stably dissolved in the ink droplets ((meth) acrylate compound A, non-polymerizable resin). Therefore, the temperature of the recording medium may be adjusted to adjust the gloss of the image.

  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 is deteriorated or the photocuring (described later) of the ink becomes insufficient.

Step (2) By irradiating light from an LED light source to ink droplets that have landed on the recording medium, the photopolymerizable compound contained in the ink droplets is crosslinked or polymerized to cure the ink droplets.

  The light applied to the 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. A metal halide lamp is an example of a general ultraviolet light source. By using an LED as a light source, ink droplets are melted by the radiant heat of the light source; it can.

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

  The light irradiation to the ink droplets is performed within 10 seconds after the ink droplets adhere on the recording medium, preferably 0.001 seconds to 5 seconds, in order to prevent the adjacent ink droplets from being united with each other. Within a range of 0.01 second to 2 seconds. The light irradiation is preferably performed after ejecting ink droplets from all the ink jet recording heads accommodated in the head carriage.

Inkjet recording apparatus The image forming method of the present invention can be carried out using an actinic ray curable inkjet 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. 1 is a diagram illustrating an example of a configuration of a main part of a line recording type ink jet recording apparatus. Among these, Fig.1 (a) is a side view, FIG.1 (b) is a top view.

  As shown in FIG. 1, the inkjet recording apparatus 10 stores a head carriage 16 that houses a plurality of inkjet recording heads 14, an ink flow path 30 connected to the head carriage 16, and ink supplied through the ink flow path 30. An ink tank 31 that covers the entire width of the recording medium 12, a light irradiation unit 18 that is disposed downstream of the head carriage 16 (in the conveyance direction of the recording medium), and a temperature control unit that is disposed on the lower surface of the recording medium 12. 19 and.

  The head carriage 16 is fixedly arranged so as to cover the entire width of the recording medium 12, and accommodates a plurality of inkjet recording heads 14 provided for each color. Ink is supplied to the ink jet recording head 14. For example, the ink may be supplied directly or by an ink supply unit (not shown) from an ink cartridge (not shown) that is detachably attached to the inkjet recording apparatus 10.

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

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

  The light irradiation unit 18 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 irradiating unit 18 irradiates the droplets ejected by the inkjet recording head 14 and landed on the recording medium 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. 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. The recording medium 12 is conveyed between the head carriage 16 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 head carriage 16 and adhered (landed) on the recording medium 12. Then, the light irradiating unit 18 irradiates the ink droplets attached on the recording medium 12 with light and cures them.

  The total ink droplet thickness after curing is preferably 2 to 25 μm. The “total ink droplet thickness” is the maximum value of the ink droplet thickness drawn on the recording medium.

  FIG. 2 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. 2, the inkjet recording apparatus 20 has a width narrower than the entire width of the recording medium, instead of the head carriage 16 fixedly arranged so as to cover the entire width of the recording medium, and a plurality of inkjet recording heads. 1 can be configured except that a head carriage 26 that accommodates 24 and a guide portion 27 for moving the head carriage 26 in the width direction of the recording medium 12 are provided.

  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 sent in the transport direction, and light is irradiated by the light irradiation unit 28. Except for these operations, an image is recorded in substantially the same manner as the line recording type inkjet recording apparatus 10 described above.

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

  The actinic ray curable ink-jet ink of each example and comparative example was prepared with the following components.

(Gelling agent)
Stearyl stearate (Exepal SS, manufactured by Kao Corporation), (Unistar M-9676, manufactured by NOF Corporation), (EMALEX CC-18, manufactured by Nippon Emulsion Co., Ltd.), (AmrepSS SS, manufactured by Higher Alcohol Industry Co., Ltd.)
Distearyl ketone (Kao wax T1, manufactured by Kao Corporation), (18-Pentatria cationone, reagent (Arfa Aeser))
Behenyl behenate (Unistar M-2222SL, NOF Corporation)
Dipalmityl ketone (Hentriacontan-16-on, reagent (Arfa Aeser))
Dilauryl ketone (12-tricosanone, reagent (Arfa Aeser))
Cetyl palmitate (Amreps PC, high alcohol industry)
Behenic acid (Lunac BA, manufactured by Kao Corporation)

(Photopolymerizable compound)
A (meth) acrylate compound having a ClogP value in the range of 4.0 to 7.0 Photomer 4072 (manufactured by Cognis): 3PO-modified trimethylolpropane triacrylate, molecular weight 471, ClogP value 4.90
Miramer M360 (manufactured by Miwon): trimethylolpropane PO-modified triacrylate, molecular weight 471, ClogP value 4.90
NK ester DOD-N (manufactured by Shin-Nakamura Chemical Co., Ltd.): 1,10-decanediol dimethacrylate, molecular weight 310, ClogP value 5.75
NK ester A-DCP (manufactured by Shin-Nakamura Chemical Co., Ltd.): tricyclodecane dimethanol diacrylate, molecular weight 304, ClogP value 4.69

Other photopolymerizable compounds NK ester A-400 (manufactured by Shin-Nakamura Chemical Co., Ltd.): polyethylene glycol diacrylate CD561 (manufactured by Sartomer): alkoxylated hexanediol diacrylate SR499 (manufactured by Sartomer): 6EO-modified trimethylolpropane tri Acrylate SR494 (manufactured by Sartomer): 4EO-modified pentaerythritol tetraacrylate

(Non-polymerizable resin)
TEGO AddBond LTH (manufactured by EVONIK, polyester resin containing hydroxyl group and carboxyl group, acid value 16 mgKOH / g, base value 25 mgKOH / g, number average molecular weight 2000 to 3000)
TEGO AddBond LTW (manufactured by EVONIK, hydroxyl group and carboxyl group-containing polyester resin, 60% xylene solution, acid value 25 mgKOH / g, base number 30 mgKOH / g, number average molecular weight 2000 to 3000)
TEGO VariPlus 3350UV (manufactured by EVONIK, hydroxyl group and carboxyl group-containing polyester resin, 50% tripropylene glycol diacrylate, acid value 18 mgKOH / g, base value 16 mgKOH / g, number average molecular weight 2000 to 3000)
TEGO VARIPLUSK SK (manufactured by degussa, hydroxyl group-containing ketone resin, acid value of less than 3 mgKOH / g, base value of 325 mgKOH / g, number average molecular weight 1000-1500)
TEGO VARIPLUS AP (manufactured by degussa, ketone resin, acid value / base value less than 3 mgKOH / g, number average molecular weight 1000-1500)

(Surfactant)
KF-352 (manufactured by Shin-Etsu Chemical Co., Ltd.)

(Photopolymerization initiator)
DAROCURE TPO (made by BASF)
ITX (manufactured by DKSH Japan)

(Sensitization aid)
KayacureEPA (Nippon Kayaku Co., Ltd.)

(Pigment dispersion)
A pigment dispersion prepared by the following procedure was used. The following two kinds of compounds were put into a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.
PB824 (Ajinomoto Fine Techno Co., Ltd.) 9 parts by mass Tripropylene glycol diacrylate (APG-200, Shin-Nakamura Chemical Co., Ltd.) 71 parts by mass

  After cooling to room temperature, 20 parts by weight of Pigment Black 7 (Mitsubishi Chemical Co., Ltd., # 52) as a pigment is added thereto, and the mixture is sealed in a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm. Time distributed processing. Thereafter, the zirconia beads were removed, and this was used as a pigment dispersion.

Example 1
In accordance with the composition (mass ratio) in Table 1 below, each component was mixed and heated to 80 ° C. and stirred. While maintaining the temperature of the obtained solution, the solution was filtered through a Teflon (registered trademark) 3 μm membrane filter manufactured by ADVATEC to prepare an actinic ray curable inkjet ink. The ink of this actinic radiation curable inkjet ink was evaluated as follows.

(Ink status)
-Gelling agent dissolution stability The actinic ray curable inkjet ink was allowed to stand in a constant temperature bath at 100 ° C for 4 hours. About the ink after stationary, the melt | dissolution state of the gelatinizer was confirmed visually and evaluated based on the following reference | standard. The results are shown in Table 1.
○: No separation or precipitation ×: Oil balls are gathered on the surface (separated layers)

Ink odor The actinic ray curable inkjet ink was heated to 100 ° C., and the odor at that time was evaluated based on the following criteria. The results are shown in Table 1.
○: Almost no odor △: Slightly irritating odor ×: Strong irritating odor

-Sol-gel phase transition temperature The sol-gel phase transition temperature was measured with a viscoelasticity measuring device MCR300 manufactured by Physica, share rate 11 (1 / s). The results are shown in Table 1.

(Image formation)
The actinic radiation curable inkjet ink was loaded into an inkjet recording apparatus having an inkjet recording head equipped with a piezo inkjet nozzle. From this apparatus, images were continuously recorded 500 m on an untreated PET and an untreated PP having a width of 600 mm and a thickness of 40 μm while performing corona treatment immediately before printing.

  As the printing apparatus, an ink supply system having an ink tank, an ink flow path, a sub ink tank immediately before the ink jet recording head, a pipe with a filter, and a piezo head was used. During image formation, the ink was heated to 100 ° C. from the ink tank to the head portion. A voltage was applied to the piezo head so that 2 pl droplets were ejected from the printing apparatus. The piezo head is composed of four heads with a resolution of 360 dpi, and a 1440 × 1440 dpi single-color solid image, 3 pt Mincho-style black characters, 3 pt Mincho-style white characters (white characters in the solid image) are formed. .

After printing, light (395 nm, 8 W / cm ² ) was irradiated from an LED lamp with a water cooling unit manufactured by Phosson Technology to cure the actinic ray curable inkjet ink. The distance from the lamp to the recording medium surface was 20 mm. The conveyance speed of the recording medium was 60 m / s. The amount of light was 200 mJ / cm ² . The amount of light was measured with a UV integrating light meter C9536, H9958 manufactured by Hamamatsu Photonics.

(Image evaluation)
・ Image quality (white blank)
Regarding the image formed on the PP film, white spots (unprinted portions due to dot coalescence) of the solid image portion at the time of printing the 10th and 500th meters were visually confirmed. Evaluation was made according to the following criteria.
○: No white spots △: There are white spots in one or two places, but there is no practical problem ×: Many white spots are generated

・ Image quality (character quality)
The image formed on the PET film was visually evaluated for the quality of 3pt Mincho characters at the time of printing the 10th and 500th meters.
○: Characters are reproduced △: Some characters are crushed ×: Characters are crushed

・ Curability evaluation (pencil hardness)
The 10 m solid image formed on the PET film was left in an environment of 25 ° C. and 60% RH for 24 hours. Thereafter, the pencil hardness of the surface was measured according to JIS-K-5400. Evaluation was made based on the following criteria.
○: Pencil hardness of 2H or more △: B, F, H
×: 2B or less

-Evaluation of bending resistance The 10 m solid image portion formed on the PET film was left in an environment of 25 ° C and 60% RH for 24 hours. Then, this was folded in half and evaluated based on the following criteria.
○: Image film was broken ×: Image film was broken at the folded part

-Substrate adhesion 3M cellophane tape was adhered to the 10 m solid image portion output to the PP film and peeled off. At this time, the adhesion between the PP film and the image was evaluated based on the following criteria.
○: No peeling of image film
Δ: Part of the image film is peeled off ×: Most part of the image film is peeled off

<< Examples 2 to 4 and Comparative Examples 1 to 6 >>
For Examples 2 to 4 and Comparative Examples 3 to 6, inks were prepared in the same manner as in Example 1 except that each component was prepared according to the composition described in Table 1 below.
In Comparative Example 1, actinic ray curable inkjet ink was used as Phaser 860 ink manufactured by Xerox.

In Comparative Example 2, an actinic radiation curable ink-jet ink was prepared from the formulation of Ink 9 of Example 1 of US Pat. No. 7,432,072 B2 by reducing tetrahydrofurfuryl acrylate by 5%, and instead using a gelling agent (stearyl stearate 3 % And distearyl ketone 2%).
With these actinic ray curable inkjet inks, images were formed in the same manner as in Example 1, and the formed images were evaluated. The results are shown in Table 1.

  As shown in Table 1, Examples containing a predetermined amount of a (meth) acrylate compound, a non-polymerizable resin, a gelling agent, and a photopolymerization initiator having a ClogP value in the range of 4.0 to 7.0. The actinic ray curable inkjet inks 1 to 4 were excellent in the dissolution stability of the gelling agent, and also had high adhesion between the cured product of the ink and the recording medium. On the other hand, in the commercially available ink (Comparative Example 1), the adhesion between the ink cured product and the recording medium was low, and the pencil hardness was also low. This is presumed to be because the curability of the commercially available ink was insufficient.

  Also in Comparative Example 2 in which a gelling agent was added to a known ink, the adhesion between the ink cured product and the recording medium was low, and the pencil hardness was also low. This is presumably because the ink of Comparative Example 2 was insufficient in curability. In addition, the character quality at the 500 m level was lower than that at the 10 m level. This is presumably because the amount of the gelling agent became non-uniform due to the separation of the ink in the ink jet recording apparatus. Moreover, it is considered that the reason why the ink odor evaluation of Comparative Examples 1 and 2 was low included a polymerizable compound having a molecular weight of less than 280.

In Comparative Examples 3 and 4 where the amount of the (meth) acrylate compound having a ClogP value in the range of 4.0 to 7.0 is not included or the content thereof is small, the dissolution stability of the gelling agent is low. It was. In addition, in the printed matter 500 m from the start of printing, white spots occurred and the character quality deteriorated. This is presumably because the ink separated in the ink jet recording apparatus and the gelling agent did not function sufficiently.
On the other hand, when the amount of the (meth) acrylate compound having a ClogP value in the range of 4.0 to 7.0 is excessive (Comparative Examples 5 and 6), the bending resistance of the cured ink is low, and the pencil hardness is evaluated. It was bad. This is presumably because the curability of the ink was insufficient.

<< Examples 5 to 7 and Comparative Examples 7 to 9 >>
For Examples 5 to 7 and Comparative Examples 7 to 9, inks were prepared in the same manner as in Example 1 except that each component was prepared according to the composition described in Table 2 below. With these actinic ray curable inkjet inks, images were formed in the same manner as in Example 1, and the formed images were evaluated. The results are shown in Table 2.

  As shown in Table 2, Examples containing a predetermined amount of (meth) acrylate compound, non-polymerizable resin, gelling agent, and photopolymerization initiator having a ClogP value in the range of 4.0 to 7.0. The actinic ray curable inkjet inks 5 to 7 were excellent in dissolution stability of the gelling agent, and also had high adhesion between the cured product of the ink and the recording medium.

  On the other hand, when the amount of non-polymerizable resin was small (Comparative Example 7), the bending resistance was low. This is presumably because the adhesion between the ink cured product and the recording medium was low. In addition, the character quality at the 500 mth was poor although the printing was good at the 10 mth. This is presumably because the ink was separated and the gelling agent did not function sufficiently.

  In addition, when the amount of the non-polymerizable resin was excessive (Comparative Example 8), the character quality of the printed matter at 500 m from the start of printing was lowered. This is presumably because the ink separated in the ink jet recording apparatus and the gelling agent did not function sufficiently. Furthermore, since the amount of non-polymerizable resin is large, the dissolution stability of the gelling agent was low. Furthermore, the curability of the ink was insufficient, and the pencil hardness was poorly evaluated.

  Further, when the non-polymerizable resin is a non-polymerizable resin having no polar functional group (Comparative Example 9), the adhesion with the base material is insufficient, and the gelling agent in the ink is used. The dispersibility of was bad. Moreover, it is surmised that the quality of the printed material from the 10th to the 500m from the start of printing is poor and the ink is further separated in the ink jet recording apparatus.

<< Examples 8 to 12 and Comparative Examples 10 and 11 >>
For Examples 8 to 12 and Comparative Examples 10 and 11, inks were prepared in the same manner as in Example 1 except that each component was prepared according to the composition described in Table 3 below. With these actinic ray curable inkjet inks, images were formed in the same manner as in Example 1, and the formed images were evaluated. The results are shown in Table 3.

  As shown in Table 3, Examples containing a predetermined amount of (meth) acrylate compound, non-polymerizable resin, gelling agent, and photopolymerization initiator having a ClogP value in the range of 4.0 to 7.0. The actinic ray curable inkjet inks 8 to 12 were excellent in the dissolution stability of the gelling agent, and further had high adhesion between the cured product of the ink and the recording medium.

  On the other hand, when the amount of the gelling agent was small (Comparative Example 10), white spots and character quality were deteriorated in both the 10th and 500th meters. This is presumably because the ink droplets did not sufficiently gel after landing on the recording medium and could not be pinned. On the other hand, when the gelling agent was large (Comparative Example 11), the polymerized property of the ink cured product was low. This is considered to be because the gelling agent inhibited the photocuring of the polymerizable compound.

<< Examples 13 to 15 and Comparative Example 12 >>
For Examples 13 to 15 and Comparative Example 12, inks were prepared in the same manner as in Example 1 except that each component was prepared according to the composition described in Table 4 below. That is, Examples 13 to 15 and Comparative Example 12 all had the same composition. With these actinic ray curable inkjet inks, images were formed under the conditions shown in Table 4 below, and the formed images were evaluated. The results are shown in Table 4.

As shown in Table 4, when the temperature of the recording medium during ink curing is in the range of sol-gel phase transition temperature −10 ° C. to −20 ° C. (Example 13), there is no white spot and character quality is high. It was.
On the other hand, in the case where the sol-gel sol-gel phase transition temperature was −9 ° C. (Example 14) and in both the 10th and 500th meters, the character quality was somewhat deteriorated. This is presumably because gelation was insufficient when the ink landed. On the other hand, when the sol-gel sol-gel phase transition temperature was −27 ° C. (Example 15), there was no white spot and the character quality was high.

  When the light source for curing the ink was a metal halide lamp (Comparative Example 12), white spots were generated at both the 10th and 500th meters, and the character quality was low. Moreover, when the obtained printed matter was observed, the surface gloss of the solid image was low. These are considered to be because the ink droplets melted due to the radiant heat of the metal halide lamp, resulting in poor curing of the cured film surface of the ink droplets.

From the above results, according to the present onset bright, odor less, excellent dissolution stability of containing components, it can also be stably form a high fine fine images in high-speed recording, good in adaptability to various recording media It can be seen that an actinic ray curable inkjet ink can be provided. It can also be seen that an image forming method using the same can be provided.

In the image forming method of the present invention, the ink that has landed on the recording medium does not coalesce, and an image with high adhesion between the ink cured film and the recording medium can be stably formed . Therefore, the present invention is suitable for producing various printed materials, particularly for forming images on plastic recording media.

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 (10)

An actinic ray curable inkjet ink droplet containing a gelling agent, a photopolymerizable compound, a photopolymerization initiator, and a non-polymerizable resin and undergoing a sol-gel phase transition with temperature is ejected from an inkjet recording head onto a recording medium. A process of adhering to,
Irradiating a droplet landed on the recording medium with light from an LED light source and curing the droplet;
The gelling agent includes a compound containing a linear alkyl group having 12 or more carbon atoms,
The photopolymerizable compound includes a (meth) acrylate compound having a molecular weight of 280 to 1500 and a ClogP value of 4.0 to 7.0.
The non-polymerizable resin includes a polyester resin having one or more polar functional groups in the molecule, or a ketone resin having one or more polar functional groups in the molecule,
The gelling agent is 0.5 to 10.0% by mass, the (meth) acrylate compound is 10 to 40% by mass, and the non-polymerizable resin is 2.0 to 15.0% by mass with respect to the total amount of the ink. Including
The image forming method, wherein the light has a peak illuminance of 0.5 to 10.0 W / cm ² at 370 to 410 nm. The image forming method according to claim 1, wherein the (meth) acrylate compound is at least one (meth) acrylate compound of the following (1) and (2).
(1) Trifunctional or higher (meth) acrylate compound having 3 to 14 structures represented by (—C (CH ₃ ) H—CH ₂ —O—) in the molecule (2) cyclic in the molecule Bifunctional or higher functional (meth) acrylate compounds The image forming method according to claim 1, wherein the gelling agent is at least one compound selected from compounds represented by the following general formulas (G1) and (G2).
General formula (G1): R1-CO-R2
General formula (G2): R3-COO-R4
(In the formula, R1 to R4 each independently represents a hydrocarbon group containing a straight chain portion having 12 or more carbon atoms.) The polar functional group of the polyester resin or the ketone resin is selected from —OH group, —COOH group, —NH ₂ group, —NO ₂ group, and —CN group. The image forming method described in 1.   The image forming method according to claim 1, wherein the polyester resin or the ketone resin has an —OH group and a —COOH group.   The image forming method according to any one of claims 1 to 5, wherein the polyester resin or the ketone resin has a number average molecular weight of 1000 to 5000 and an acid value or a base value of 10 to 350 mgKOH / g. The temperature of the recording medium when the actinic radiation curable inkjet ink lands on the recording medium is in a range lower by 10 ° C. to 20 ° C. than the sol-gel phase transition temperature of the actinic radiation curable inkjet ink. The image forming method according to claim 1. The image forming method according to claim 1, wherein the light irradiated in the step of curing the ink droplets has a peak illuminance of 0.5 to 5 W / cm ² at 370 to 410 nm.   The image forming method according to claim 1, wherein the recording medium is made of polypropylene or polyethylene terephthalate. An actinic ray curable ink jet containing a gelling agent, a photopolymerizable compound, a photopolymerization initiator, and a non-polymerizable resin and undergoing a sol-gel phase transition depending on temperature,
The gelling agent includes a compound containing a linear alkyl group having 12 or more carbon atoms,
The photopolymerizable compound includes a (meth) acrylate compound having a molecular weight of 280 to 1500 and a ClogP value of 4.0 to 7.0.
The non-polymerizable resin includes a polyester resin having one or more polar functional groups in the molecule, or a ketone resin having one or more polar functional groups in the molecule,
The gelling agent is 0.5 to 10.0% by mass, the (meth) acrylate compound is 10 to 40% by mass, and the non-polymerizable resin is 2.0 to 15.0% by mass with respect to the total amount of the ink. An actinic ray curable inkjet ink comprising:

Images