JP2016172819A - Active ray-curable inkjet ink, image forming method, and ink set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active ray-curable inkjet ink which contains a gelatinizer and more enhances surface energy of a cured product forming an image, and thereby can suppress repelling of an overcoating liquid.SOLUTION: An active ray-curable inkjet ink contains a photopolymerizable compound, a non-polymerizable polyoxyethylene alkyl compound having a straight-chain alkyl group, a gelatinizer, and a photoinitiator; and causes reversible sol-gel phase transition by a temperature. The photopolymerizable compound contains 30-70 mass% of (meth)acrylate having a molecular weight of 300-1,500 and 3-14 EO groups with respect to the total mass of the ink. The non-polymerizable polyoxyethylene alkyl compound contains 0.01-10.0 mass% or less of a compound having an HLB value of 6 or more with respect to the total mass of the ink.SELECTED DRAWING: None

Description

  The present invention relates to an actinic ray curable inkjet ink, an image forming method, and an ink set.

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

  When the ink-jet ink contains a gelling agent, the ink gels due to crystallization of the gelling agent when it cools after landing on the recording medium. Hard to occur. In addition, since the viscosity of the ink containing the gelling agent is high even at a low temperature, it is possible to improve the scratching property of the formed image at room temperature.

  In inkjet inks containing a gelling agent, it is known that crystals of the gelling agent are deposited on the surface of the cured product when the ink is cured by irradiation with actinic rays (see, for example, Patent Document 1). In Patent Document 1, the non-polymerizable liquid component is contained in the ink-jet ink, and the gelling agent is dissolved in the liquid component, thereby suppressing the precipitation of the gelling agent.

  In addition, in order to improve the storage stability, dischargeability, and adhesion to a recording medium of an ink-jet ink, a technique for containing a polyoxyethylene alkyl compound in the ink-jet ink is known (for example, see Patent Document 2).

  In addition, on the image formed by irradiating actinic ray curable ink with actinic rays for the purpose of giving the printed image gloss or resistance to external impacts, an overcoat is further formed. Techniques for applying and coating a liquid are known. As an example, a technique for controlling the gloss of an image with an overcoat liquid containing a gelling agent, a curable monomer, a curable wax, and a photoinitiator is known (for example, see Patent Document 3).

JP 2013-2221048 A JP 2006-299212 A JP 2010-792 A

  When an overcoat solution is applied on the image, the adhesion and wettability with the overcoat solution on the formed image are low, and the overcoat solution may be repelled and its adhesion may be weakened.

  If the surface tension of the overcoat solution is weakened, the repelling of the overcoat solution can be reduced. However, when an overcoat liquid is applied to an image formed by irradiating an inkjet ink containing a gelling agent with an actinic ray, the repelling may not be suppressed even if the surface tension of the overcoat liquid is reduced.

  Even if the surface energy of the cured product that forms an image by corona treatment is increased, the repelling of the overcoat solution can be reduced. However, since a dedicated device is required for the corona treatment, the cost of image formation increases, the printing system becomes larger, and the image formation speed becomes slower. Therefore, a method for increasing the surface energy of the cured product by a simpler method is desired.

  In view of the above-mentioned problems, the present invention can more easily increase the surface energy of a cured product that forms an image and suppress the repelling of an overcoat liquid in an actinic ray curable inkjet ink containing a gelling agent. It is an object of the present invention to provide an ink, an image forming method using such an actinic radiation curable inkjet ink, and an ink set including such an actinic radiation curable inkjet ink.

In view of the above problems, a first aspect of the present invention relates to the following actinic ray curable inkjet ink.
[1] An actinic ray curable inkjet ink containing a photopolymerizable compound, a non-polymerizable polyoxyethylene alkyl compound having a linear alkyl group, a gelling agent and a photoinitiator,
The photopolymerizable compound has a structure represented by (—CH ₂ —CH ₂ —O—) _m (m is an integer of 3 or more and 14 or less) in the molecule, and has a molecular weight of 300 to 1500 (meth). Including acrylate,
The non-polymerizable polyoxyethylene alkyl compound has an HLB value of 6 or more,
The ink contains 30% by mass or more and 70% by mass or less of the (meth) acrylate based on the total mass of the ink,
The ink contains 0.01% by mass or more and 10.0% by mass or less of the non-polymerizable polyoxyethylene alkyl compound with respect to the total mass of the ink.
[2] The gelling agent is at least one selected from the group consisting of general formula (G1) to general formula (G5), and the ink is 2% by mass or more and 10% by mass with respect to the total mass of the ink. % Of the actinic ray curable ink-jet ink according to [1], containing a gelling agent represented by the general formula (G1) to the general formula (G5) in an amount of% or less.
General formula (G1): R1a-CO-R1b
General formula (G2): R1a-COO-R1b
General formula (G3): R1a-COOH
General formula (G4): R1a-OH
Formula _{(G5): R2a- (CH 2} CH 2 O) n-R2b
(R1a and R1b independently represent an alkyl group having a straight chain portion having 12 to 24 carbon atoms, and R2a and R2b are independently an alkyl ketone group having a straight chain portion having 12 to 24 carbon atoms or Represents an alkyl ester group, and n represents 1 or 2.)
[3] The number of carbon atoms in the straight chain portion of R1a, R1b, R2a or R2b of the gelling agent, and the number of carbon atoms in the straight chain alkyl group of the non-polymerizable polyoxyethylene alkyl compound, The actinic ray curable inkjet ink according to [2], wherein the difference is 3 or less.
[4] The non-polymerizable polyoxyethylene alkyl compound is a compound represented by the general formula (A1) and having an HLB value of 10 or more and 18 or less, [1] to [3] The actinic ray curable inkjet ink according to any one of the above.
Formula _{(A1): R3-X -} ((CH 2 CH 2 O) p -H) q H r
(R3 represents an alkyl group having a straight chain portion having 12 to 24 carbon atoms, X represents one structure selected from the group consisting of C, N and a sugar structure, and p and q are independently 2 or more. And r represents (valence of X−q−1).)
[5] The ink contains 2.0% by mass or more and 6.0% by mass or less of the non-polymerizable polyoxyethylene alkyl compound based on the total mass of the ink. 4] The actinic ray curable inkjet ink according to any one of [4].

The second aspect of the present invention relates to the following image forming method.
[6] A step of landing droplets of the actinic ray curable inkjet ink according to any one of [1] to [5] on a recording medium by an inkjet method, and actinic rays are applied to the droplets that have landed on the recording medium An image forming method comprising: a step of forming a lower layer constituting an image by irradiation; and a step of applying an overcoat liquid on the lower layer.
[7] The image forming method according to [6], wherein the overcoat liquid contains a non-polymerizable polyoxyethylene alkyl compound having an HLB value of 6 or more.
[8] The overcoat solution contains at least one gelling agent selected from the group consisting of general formula (G1) to general formula (G5), and the overcoat solution is a total mass of the overcoat solution. The method according to [7], wherein the gelling agent is contained in an amount of 2% by mass to 10% by mass based on
General formula (G1): R1a-CO-R1b
General formula (G2): R1a-COO-R1b
General formula (G3): R1a-COOH
General formula (G4): R1a-OH
Formula _{(G5): R2a- (CH 2} CH 2 O) n-R2b
(R1a and R1b independently represent an alkyl group having a straight chain portion having 12 to 24 carbon atoms, and R2a and R2b are independently an alkyl ketone group having a straight chain portion having 12 to 24 carbon atoms or Represents an alkyl ester group, and n represents 1 or 2.)
[9] The difference between the number of carbon atoms of the linear alkyl group of the non-polymerizable polyoxyethylene alkyl compound and the number of carbon atoms of the linear portion of R1a, R1b, R2a and R2b of the gelling agent is 3 [8] The method according to [8], wherein
[10] The nonpolymerizable polyoxyethylene alkyl compound is a compound represented by the general formula (A1) and having an HLB value of 10 or more and 18 or less, [7] to [9] The method according to any one.
Formula _{(A1): R3-X -} ((CH 2 CH 2 O) p -H) q H r
(R3 represents an alkyl group having a straight chain portion having 12 to 24 carbon atoms, X represents one structure selected from the group consisting of C, N and a sugar structure, and p and q are independently 2 or more. And r represents (valence of X−q−1).)
[11] The overcoat liquid contains 0.01% by mass or more and 10.0% by mass or less of the non-polymerizable polyoxyethylene alkyl compound with respect to the total mass of the overcoat liquid. 6. The method according to any one of [10] to [10].
[12] The method according to any one of [6] to [11], wherein the overcoat liquid is an actinic ray curable ink.

The third aspect of the present invention relates to the following ink set.
[13] An ink set comprising the actinic ray curable inkjet ink according to any one of [1] to [5] and an inkjet discharge overcoat liquid.
[14] The ink set according to [13], wherein the inkjet discharge overcoat liquid contains a non-polymerizable polyoxyethylene alkyl compound having an HLB value of 6 or more.

  According to the present invention, in an actinic ray curable inkjet ink containing a gelling agent, an ink that can more easily increase the surface energy of a cured product that forms an image and suppress the repelling of an overcoat liquid, such as An image forming method using such actinic ray curable inkjet ink and an ink set including such an actinic ray curable inkjet ink are provided.

  As a result of intensive studies, the present inventor repels the overcoat liquid due to crystals of the gelling agent deposited on the surface of the cured product in the image formed using the actinic ray curable ink containing the gelling agent. I found out. That is, since the gelling agent is hydrophobic, the surface energy of the cured product is lowered by precipitation of crystals of the gelling agent. If the surface energy is low, the wettability of the overcoat liquid to the surface of the cured product is low, and the overcoat liquid is difficult to adhere, so that it is considered that repelling is likely to occur.

  On the other hand, the present invention has the following composition, and despite having a gelling agent, the surface energy of a cured product formed by irradiating actinic rays is high, and an overcoat applied on the cured product The present inventors have found an ink composition that improves liquid wettability and adhesion, and found that such an ink can be applied to an image forming method and an ink set.

  In addition, since the present invention can increase the surface energy of the cured product without including a special process such as corona treatment, there are problems including an increase in image formation cost, an increase in size of a printing system system, and a decrease in image formation speed. Is unlikely to occur.

1. Actinic ray curable inkjet ink The actinic ray curable inkjet ink of the present invention (hereinafter also simply referred to as “the ink of the present invention”) is a photopolymerizable compound and a non-polymerizable polyoxyethylene alkyl compound having a linear alkyl group. Contains a gelling agent and a photoinitiator. The photopolymerizable compound has a molecular weight of 300 or more and 1500 or less, and has a structure represented by (—CH ₂ —CH ₂ —O—) _m (m is an integer of 3 to 14) in the molecule. Includes 300 to 1500 (meth) acrylate (hereinafter also simply referred to as “EO (meth) acrylate”). The non-polymerizable polyoxyethylene alkyl compound is a compound having an HLB value of 6 or more (hereinafter also simply referred to as “EO alkyl compound”). The ink of the present invention contains 30% by mass to 70% by mass of the EO (meth) acrylate with respect to the total mass of the ink, and 0.01% by mass to 10% by mass with respect to the total mass of the ink. The non-polymerizable polyoxyethylene alkyl compound is contained. In the present invention, “(meth) acrylate” means one or both of “acrylate” and “methacrylate”.

  Although the ink of the present invention contains a gelling agent, the surface energy of the cured product formed by irradiating actinic rays is high, and the wettability and adhesion of the overcoat liquid applied on the cured product are increased. . The reason for this is not clear, but the present inventors consider as follows. That is, since both the EO (meth) acrylate and the EO alkyl compound have a highly polar EO group, their affinity for each other is low. Therefore, when the EO (meth) acrylate is polymerized by irradiation with actinic rays to form a hydrocarbon chain (when the ink is cured), the EO alkyl compound is hardly taken into the hydrocarbon chain, and the outside of the ink ( Easy to move in the vicinity of the surface). Thereby, since many EO alkyl compounds which have EO group exist in the surface vicinity of the hardened | cured material which the ink of this invention hardened | cured, the surface energy of hardened | cured material increases. When the surface energy of the cured product increases, intermolecular forces such as hydrogen bonding or van der Waals force act on the composition of the overcoat liquid, and the wettability and adhesion of the overcoat liquid increase.

  Further, in the gelling agent having an alkyl group, the difference between the number of carbon atoms constituting the alkyl group and the number of carbon atoms constituting the alkyl group of the EO alkyl compound is 3 or less in absolute value. The wettability and adhesion of the overcoat liquid are further increased. The present inventors believe that this is because the affinity between the gelling agent and the EO alkyl compound is increased, and the EO alkyl compound easily moves to the vicinity of the surface of the ink being cured together with the gelling agent. ing.

1-1. Photopolymerizable compound 1-1-1. EO (meth) acrylate EO (meth) acrylate is a (meth) acrylate having 3 to 14 EO groups and a molecular weight of 300 to 1500. 3 or more and 14 or less EO groups may exist as one connected segment, or may exist in two or more segments. However, from the viewpoint of making it difficult for the EO alkyl compound to be taken into the hydrocarbon chain when the ink is cured, when the EO group is divided into two or more segments, a segment having three or more EO groups is present. It is preferable that there are two or more in the molecule. The ink of the present invention may contain only one type of EO (meth) acrylate or two or more types.

  Since EO (meth) acrylate has three or more EO groups, when the ink is cured, it is difficult to incorporate the EO alkyl compound into the hydrocarbon chain, and it is easy to move the EO alkyl compound to the vicinity of the surface of the cured product. Moreover, since EO (meth) acrylate has three or more EO groups, it is considered that curling of the printed matter due to curing shrinkage can be further reduced. Since EO (meth) acrylate has the number of EO groups of 14 or less, the molecular weight of EO (meth) acrylate can be adjusted to the said range, and discharge stability can be improved. Further, since EO (meth) acrylate has 14 or less EO groups, it is considered that the gelling agent can be sufficiently dissolved in the ink and the ejection stability can be improved.

  Since EO (meth) acrylate has a molecular weight of 300 or more, the amount of change in ink viscosity near the discharge temperature does not become too large, and the temperature range in which stable ink discharge is possible can be widened. It is considered that the temperature can be easily adjusted. In addition, since EO (meth) acrylate has a molecular weight of 300 or more, it is considered that the odor of the ink itself and the odor from the printed matter formed using the ink can be suppressed.

  The ink of the present invention contains 30% by mass or more and 70% by mass or less of EO (meth) acrylate with respect to the total mass of the ink. When the amount of EO (meth) acrylate is 30% by mass or more, repulsion between EO groups is sufficiently generated, so that many EO alkyl compounds can exist in the vicinity of the surface of the cured product. Further, when the amount of EO (meth) acrylate is 30% by mass or more, it is considered that curling of the printed matter due to curing shrinkage can be further reduced. It is considered that when the amount of EO (meth) acrylate is 70% by mass or less, the gelling agent can be sufficiently dissolved in the ink, and the ejection stability can be improved. From the above viewpoint, the amount of EO (meth) acrylate is more preferably 35% by mass or more and 60% by mass or less, and further preferably 40% by mass or more and 50% by mass or less.

  Examples of EO (meth) acrylate include 4EO modified hexanediol diacrylate (molecular weight 358), 3EO modified trimethylolpropane triacrylate (molecular weight 429), 6EO modified trimethylolpropane triacrylate (molecular weight 560), 4EO modified pentaerythritol tetra. Acrylate (molecular weight 528), 5EO-modified pentaerythritol tetraacrylate (molecular weight 572), polyethylene glycol diacrylate having 4 to 14 EO groups (molecular weight 302 to 742), and polyethylene glycol dimethacrylate having 4 to 14 EO groups (molecular weight) 332-772).

1-1-2. Other Photopolymerizable Compound The photopolymerizable compound may contain a photopolymerizable compound other than EO (meth) acrylate as long as the effects of the present invention are obtained. Examples of photopolymerizable compounds other than EO (meth) acrylate include radically polymerizable compounds containing (meth) acrylates having 2 or less EO groups, and cationic polymerizable compounds containing epoxy compounds and vinyl ether compounds Is included. The photopolymerizable compound other than the above may be a monomer, oligomer, polymer, or a mixture thereof. The ink of the present invention may contain only one type of photopolymerizable compound other than EO (meth) acrylate, or may contain two or more types.

  Examples of (meth) acrylates having 2 or less EO groups 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-acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxy Diethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (Meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-acryloyloxyethyl succinic acid, Monofunctional (meth) acrylates including 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible (meth) acrylate and t-butylcyclohexyl (meth) acrylate , And 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol- Includes bifunctional (meth) acrylates including licyclodecane di (meth) acrylate, PO adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate hydroxypivalate and poly (tetramethylene glycol di (meth) acrylate) .

  Examples of epoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenol (polyethyleneoxy) 5-glycidyl ether, butylphenyl glycidyl ether, glycidyl hexahydrophthalate, lauryl glycidyl ether, 1,2-epoxycyclohexane, Monofunctional epoxy compounds including 1,4-epoxycyclohexane, 1,2-epoxy-4-vinylcyclohexane and norbornene oxide, and neopentyl glycol diglycidyl ether, 1,6 hexanediol diglycidyl ether, polyglycerol triglycidyl ether, Polyfunctional epoxy compounds including sorbitol polyglycidyl ether and pentaerythritol polyglycidyl ether are included.

  Examples of vinyl ether compounds include monofunctional vinyl ethers including butyl vinyl ether, butyl propenyl ether, butyl butenyl ether, hexyl vinyl ether, ethyl hexyl vinyl ether, phenyl vinyl ether, benzyl vinyl ether, ethyl ethoxy vinyl ether, acetyl ethoxy ethoxy vinyl ether, cyclohexyl vinyl ether and adamantyl vinyl ether Compound, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol vinyl ether, butylene divinyl ether, dibutylene glycol divinyl ether, neopentyl glycol divinyl ether , Cyclohexanediol divinyl ether, cyclohexane dimethanol divinyl ether, norbornyl dimethanol divinyl ether, isovinyl divinyl ether, divinyl resorcin, divinyl hydroquinone, glycerin trivinyl ether, glycerin ethylene oxide adduct trivinyl ether (addition moles of ethylene oxide 6) , Trimethylol propane trivinyl ether, trivinyl ether ethylene oxide adduct trivinyl ether (addition mole number of ethylene oxide 3), pentaerythritol trivinyl ether and ditrimethylol propane hexavinyl ether and polyfunctional vinyl ether compounds including their oxyethylene adducts.

1-2. EO alkyl compound The EO alkyl compound is a non-polymerizable polyoxyethylene alkyl compound having an EO group in the molecule, an HLB value of 6 or more, and a linear alkyl group. The ink of the present invention may contain only one type of EO alkyl compound or two or more types.

  Since the EO alkyl compound has an EO group in the molecule, it has a low affinity with EO (meth) acrylate and is difficult to be taken into the hydrocarbon chain when EO (meth) acrylate is polymerized. Easy to move near the surface. Therefore, the number of EO groups near the surface of the cured product can be increased, the surface energy of the cured product can be increased, and the wettability and adhesion of the overcoat liquid can be increased.

  Further, since the EO alkyl compound has an HLB value of 6 or more and the lipophilicity level is not so high, it is difficult to be taken into the hydrocarbon chain formed by polymerization of EO (meth) acrylate, and the vicinity of the surface of the ink being cured. Easy to move to. Therefore, the number of EO groups near the surface of the cured product can be increased, the surface energy of the cured product can be increased, and the wettability and adhesion of the overcoat liquid can be increased. From the above viewpoint, the HLB value of the EO alkyl compound is more preferably 10 or more, and further preferably 12 or more.

  From the viewpoint of setting the HLB value within the above range, the EO alkyl compound preferably has 8 or more EO groups.

  In addition, since the EO alkyl compound is non-polymerizable, it does not easily react with EO (meth) acrylate when EO (meth) acrylate is polymerized, and is not easily taken into the hydrocarbon chain. Thereby, the EO alkyl compound easily moves to the vicinity of the surface of the ink being cured. Therefore, the number of EO groups near the surface of the cured product can be increased, the surface energy of the cured product can be increased, and the wettability and adhesion of the overcoat liquid can be increased. “Non-polymerizable” means that the amount of radical polymerizable functional group contained per mole of EO alkyl compound is 0.1 molar equivalent or less.

  The molar equivalent of the polymerizable functional group possessed by the EO alkyl compound can be determined by dividing the amount of the polymerizable functional group possessed by the EO alkyl compound by the weight average molecular weight of the EO alkyl compound. The amount of the polymerizable functional group can be estimated using ordinary analysis methods including nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and mass spectrometry (MS). it can. The weight average molecular weight of the EO alkyl compound can be measured by performing gel permeation chromatography (GPC) using a column with o-dichlorobenzene as the solvent and substituting the obtained value into a calibration curve using polystyrene. .

  Further, since the EO alkyl compound has a linear alkyl group, the affinity between the gelling agent and the EO alkyl compound is increased, and the EO alkyl compound easily moves to the vicinity of the surface of the ink being cured together with the gelling agent. It is considered to be.

  The ink of the present invention contains 0.01% by mass to 10.0% by mass of an EO alkyl compound with respect to the total mass of the ink. When the amount of the EO alkyl compound is 0.01% by mass or more, the amount of the EO alkyl compound existing in the vicinity of the surface of the cured product increases, so that the surface energy of the cured product is increased and the wettability and adhesion of the overcoat liquid are increased. Increases nature. When the amount of the EO alkyl compound is 10.0% by mass or less, the film hardness of the cured product increases. The amount of the EO alkyl compound in the ink of the present invention is 2.0% by mass or more and 6.0% by mass from the viewpoint of achieving both higher wettability and adhesion of the overcoat liquid and film hardness of the cured product. More preferably, it is 3.0 mass% or more and 5.0 mass% or less.

  Examples of EO alkyl compounds include: Nymene S-204 (HLB value: 8), manufactured by NOF Corporation (“Naymin” is a registered trademark of the company), and EMALEX CWS-3 (HLB value: 3) and EMALEX LWS- 3 (HLB value: 3), manufactured by Nippon Emulsion Co., Ltd. ("EMALEX" is a registered trademark of the company).

  From the viewpoint of increasing the affinity between the gelling agent and the EO alkyl compound and facilitating the transfer of the EO alkyl compound to the vicinity of the surface of the ink being cured together with the gelling agent, the EO alkyl compound is represented by the following general formula (A1). It is more preferable that it is a compound represented by these.

Formula _{(A1): R3-X -} ((CH 2 CH 2 O) p -H) q H r

  In General Formula (A1), R3 represents an alkyl group having a straight chain portion having 12 to 24 carbon atoms, X represents one structure selected from the group consisting of C, N, and a sugar structure, and p and q Independently represents an integer of 2 or more, and r represents (valence of X−q−1).

  In addition, the said sugar structure in this invention means the structure more than bivalence derived from these derivatives containing the monosaccharide, disaccharide, and trisaccharide containing 1 or more and 3 or less sugar, and a dehydration thing.

  Examples of sugar structures include sorbitan and sucrose.

  From the viewpoint of facilitating movement of the EO alkyl compound near the surface of the ink being cured, the HLB value of the EO alkyl compound represented by the general formula (A1) is preferably 10 or more. It is preferable that it is 18 or less. From the viewpoint of further increasing the solubility of the EO alkyl compound in the ink, the HLB value of the EO alkyl compound represented by the general formula (A1) is preferably 17 or less.

  Examples of commercially available EO alkyl compounds represented by the general formula (A1) having an HLB value of 10 or more and 18 or less include Naimine S-210 (X = N), Naimine S-215 (X = N), Naimine S-220 (X = N), manufactured by NOF Corporation, Emulgen 109P (X = C), Emulgen 120 (X = C), Emulgen 147 (X = C), Emulgen 210P (X = C), Emulgen 320P (X = C), manufactured by Kao Corporation (“Emulgen” is a registered trademark of the company), EMALEX BHA-10 (X = C), manufactured by Nippon Emulsion Co., Ltd., Tween 20 (X = sugar structure), Tween 40 (X = sugar) Structure), Tween 60 (X = sugar structure) and Tween 80 (X = sugar structure). The description in parentheses indicates the type of X (any of C, N and sugar structure) in each commercial product.

1-3. Gelling agent A gelling agent is a compound that reversibly undergoes a sol-gel phase transition due to a temperature change even within the use temperature range of the ink. The gelling agent can temporarily fix (pinning) ink droplets of the present invention landed on a recording medium in a gel state. When the ink is pinned in a gel state, wetting and spreading of the ink is suppressed and adjacent dots are less likely to be the same, so that a higher definition image can be formed. In addition, when the ink is in a gel state, the entry of oxygen in the environment into the ink droplets is suppressed and it becomes difficult for the ink to inhibit curing, so that a high-definition image can be formed at a higher speed. Only one kind of gelling agent may be contained in the ink of the present invention, or two or more kinds may be contained.

  The amount of the gelling agent contained in the ink of the present invention may be in a range where the ink can be sufficiently pinned and the gloss of the image is not excessive due to the gelling agent deposited on the surface of the cured product. It can be 1.0 mass% or more and 10.0 mass% or less with respect to the total mass of an ink. When the amount of the gelling agent is 1.0% by mass or more, the pinning property of the ink is sufficiently increased, and a higher definition image can be formed. When the amount of the gelling agent is 10.0% by mass or less, the amount of the gelling agent deposited on the surface of the formed image is reduced, so that excessive gloss generation can be suppressed. From the above viewpoint, the amount of the gelling agent contained in the ink of the present invention is more preferably 2.0% by mass or more and 10.0% by mass or less, and 2.0% by mass or more and 5.0% by mass or less. More preferably, it is 2.0 mass% or more and 3.5 mass% or less.

  From the following viewpoint, the gelling agent is preferably crystallized in the ink at a temperature not higher than the gelation temperature of the ink. The gelation temperature refers to a temperature at which the viscosity of the ink changes suddenly when the ink sol- lated or liquefied by heating is cooled and the gelling agent undergoes phase transition from sol to gel. Specifically, the sol or liquefied ink is cooled while measuring the viscosity with a viscoelasticity measuring device (for example, MCR300, manufactured by Physica), and the temperature at which the viscosity rapidly increases is measured. The gelation temperature can be set.

  When the gelling agent is crystallized in the ink, a structure in which the photopolymerizable compound is included in the three-dimensional space formed by the gelling agent that has been crystallized in a plate shape may be formed (such a structure). , Hereinafter referred to as "card house structure"). When the card house structure is formed, since the liquid photopolymerizable compound is held in the space, the ink droplets are less likely to spread and the pinning property of the ink is further increased. When the pinning property of the ink is increased, the ink droplets that have landed on the recording medium are less likely to coalesce, and a higher definition image can be formed.

  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.

Examples of gelling agents suitable for forming a card house structure by crystallization include
Ketone waxes including dilignoseryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone;
Behenyl behenate, icosyl icosanoate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, myristyl myristate, stearyl stearate, oleyl palmitate, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol Ester waxes including fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters;
Petroleum-based waxes including paraffin wax, microcrystalline wax and petrolactam;
Plant waxes including candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax and jojoba ester;
Animal waxes including beeswax, lanolin and whale wax;
Mineral waxes including montan wax and hydrogenated wax;
Hydrogenated castor oil;
Modified waxes including hardened castor oil derivatives, montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, 12-hydroxystearic acid derivatives and polyethylene wax derivatives;
Higher alcohols including stearyl alcohol and behenyl alcohol;
Hydroxystearic acid including 12-hydroxystearic acid;
Fatty acid amides including lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide and 12-hydroxystearic acid amide;
N-substituted fatty acid amides including N-stearyl stearamide and N-oleyl palmitate amide;
Special fatty acid amides including N, N′-ethylenebisstearylamide, N, N′-ethylenebis-12-hydroxystearylamide and N, N′-xylylenebisstearylamide;
Higher amines including dodecylamine, tetradecylamine and octadecylamine;
Esters of sucrose fatty acids including sucrose stearic acid and sucrose palmitic acid;
Synthetic waxes including polyethylene waxes and alpha-olefin maleic anhydride copolymer waxes;
Dimer acid; and dimer diol.

  Examples of commercially available fatty acid amides include the Nikka Amide series, manufactured by Nippon Kasei Co., Ltd. (“Nikka Amide” is a registered trademark of the company), ITOWAX series, manufactured by Ito Oil Co., Ltd., and FATTYAMID series, manufactured by Kao Corporation.

  Examples of commercially available fatty acid ester compounds include EMALLEX series, Riquemar series and Poem series manufactured by Nippon Emulsion, and Riken Vitamin ("Riquemar" and "Poem" are registered trademarks of the same company).

  Examples of commercially available esters of sucrose fatty acid esters include the Ryoto Sugar Ester series, manufactured by Mitsubishi Chemical Foods (“Ryoto” is a registered trademark of the company).

  Examples of commercially available synthetic waxes include the UNILIN series, manufactured by Baker-Petrolite ("UNILIN" is a registered trademark of the company).

  Examples of commercially available dimer diol include the PRIPOR series, manufactured by CRODA ("PRIPOR" is a registered trademark of the company).

  Of these gelling agents, ketone wax, ester wax, higher fatty acid and higher alcohol are preferred from the viewpoint of further improving pinning properties, and the ketone wax and ester wax may have an EO group. From the above viewpoint, the gelling agent is more preferably at least one of the compounds represented by the following general formula (G1) to general formula (G5). At least one of the compounds represented by the following general formulas (G1) to (G5) may be included in the ink of the present invention, and two or more types may be included. Also good.

General formula (G1): R1a-CO-R1b
General formula (G2): R1a-COO-R1b
General formula (G3): R1a-COOH
General formula (G4): R1a-OH
Formula _{(G5): R2a- (CH 2} CH 2 O) n-R2b

  In General Formulas (G1) to (G5), R1a and R1b independently represent an alkyl group having a straight chain portion having 12 to 24 carbon atoms, and R2a and R2b independently represent 12 or more carbon atoms. An alkyl ketone group or an alkyl ester group having a straight chain portion of 24 or less is represented, and n represents 1 or 2.

  Since the gelling agent represented by the general formula (G1) to the general formula (G5) includes a linear alkyl structure having 12 or more carbon atoms, it has high crystallinity and is sufficient in the card house structure. Create a space. For this reason, the photopolymerizable compound can be easily contained in the space, and the pinning property of the ink becomes higher. In addition, since the gelling agent represented by the above general formula (G1) to general formula (G5) has a linear or branched hydrocarbon group having 24 or less carbon atoms, the gelling agent has a melting point. The ink does not rise excessively, and it is not necessary to heat the ink excessively when ejecting the ink.

  Examples of the ketone wax represented by the general formula (G1) include 25-nonatetracontanone (carbon number: 24-24), 22-tritetracontanone (carbon number: 21-21), 19-heptatria. Contanone (carbon number: 18-18), 18-pentatriacontanone (carbon number: 17-17), 21-hentetracontanone (carbon number: 20-20), 16-hentriacontanone (carbon number) 15-15), 14-heptacosanone (carbon number: 13-13), 13-heptacosanone (carbon number: 12-14), 13-nonacosanone (carbon number: 12-16), 13-hentriacontanone (carbon Number: 12-18), 13-pentatriacontanone (carbon number: 12-22), 15-hentriacontanone (carbon number: 14-16), 15-propatriacontanone Carbon number: 14-18), 15-heptatriacontanone (carbon number: 14-22), 17-heptatriacontanone (carbon number: 16-18), 17-nonatriacontanone (carbon number: 16-22) ) And 19-hentetracontanone (carbon number: 18-22). In addition, the carbon number in the said parenthesis represents the carbon number of R1a and R1b each divided by a carbonyl group.

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

  Examples of the ester wax represented by the general formula (G2) include behenyl behenate (carbon number: 21-22), icosyl icosanoate (carbon number: 19-20), stearyl stearate (carbon number: 17-18). ), Palmitic acid stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number: 15-16), stearyl palmitate (carbon number: 15-18), Myristyl myristate (carbon number: 13-14), cetyl myristate (carbon number: 13-16), octyldodecyl myristate (carbon number: 13-20), stearyl oleate (carbon number: 17-18), Elca Stearyl acid (carbon number: 21-18), stearyl linoleate (carbon number: 17-18), isostearyl palmitate (carbon number: 1) -18) are included. In addition, the carbon number in the said parenthesis represents the carbon number of R1a and R1b each divided by an ester group.

  Examples of commercially available ester waxes represented by the general formula (G2) include UNISTAR M-2222SL and SPALM ACETI, manufactured by NOF Corporation (“UNISTAR” is a registered trademark of the company), EXCEPARL SS and EXCEPARL MY-M, Kao ("EXPEARL" is a registered trademark of the company), EMALEX CC-18 and EMALEX CC-10, manufactured by Nippon Emulsion ("EMALEX" is a registered trademark of the company), Amreps PC, and Higher Alcohol Industry ("Amreps") Are registered trademarks of the company. Since these commercially available products are often a mixture of two or more types, they may be separated and purified as necessary and contained in the ink.

  Examples of higher fatty acids represented by the general formula (G3) include behenic acid (carbon number: 22).

  Examples of the higher alcohol represented by the general formula (G4) include behenyl alcohol (carbon number: 22).

  Examples of the ketone wax and ester wax having an EO group represented by the general formula (G5) include diethylene glycol dilaurate (carbon number: 12-12, n = 2), diethylene glycol distearate (carbon number: 17-17, n = 2) and diethylene glycol diisostearate (carbon number: 17-17, n = 2). In addition, the carbon number in the said parenthesis represents carbon number of each of two R2 divided by EO group.

  Examples of commercially available products of ketone wax and ester wax having an EO group represented by the general formula (G5) include EMALEX DEG-di-L, EMALEX DEG-di-S, EMALEX EG-di-L, EMALEX EG- di-S and EMALEX DEG-di-IS, manufactured by Nippon Emulsion Co., Ltd. are included. Since these commercially available products are often a mixture of two or more types, they may be separated and purified as necessary and contained in the ink.

  From the viewpoint of sufficiently increasing the pinning property of the ink and suppressing excessive gloss caused by the gelling agent deposited on the surface of the cured product, the gelling agent represented by the above general formula (G1) to general formula (G5) Is preferably 2.0% by mass or more and 10.0% by mass or less, more preferably 2.0% by mass or more and 5.0% by mass or less, based on the total mass of the ink. More preferably, it is 0 mass% or more and 3.5 mass% or less.

  From the viewpoint of enhancing the affinity between the gelling agent and the EO alkyl compound and facilitating the transfer of the EO alkyl compound to the vicinity of the surface of the ink being cured together with the gelling agent, the above general formulas (G1) to (G5) The difference between the carbon number of at least one of the alkyl groups R1a, R1b, R2a and R2b possessed by the gelling agent represented by) and the carbon number of at least any linear alkyl group possessed by the EO alkyl compound is The absolute value is preferably 3 or less.

1-4. Photoinitiator [Photoinitiator]
A photoinitiator (photopolymerization initiator) is capable of initiating polymerization of a photopolymerizable compound upon irradiation with actinic rays. The photoinitiator is preferably a radical polymerization initiator, but may further contain a cationic polymerization initiator. The ink of the present invention may contain only one kind of photoinitiator or two or more kinds.

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

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

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

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

  The amount of the photoinitiator can be arbitrarily set as long as the effect of the present invention is obtained. For example, it can be 0.1 mass% or more and 20 mass% or less, preferably 1.0 mass% or more and 12 mass% or less with respect to the total mass of the ink.

1-5. Other Components The ink of the present invention may contain components other than those described above as long as the effects of the present invention are obtained. Examples of compounds other than those described above that may be contained in the ink of the present invention include non-polymerizable polyoxyethylene alkyl compounds other than the EO alkyl compounds, sensitizers, colorants, and surfactants. Only one kind of these components may be contained in the ink of the present invention, or two or more kinds thereof may be contained.

  Examples of non-polymerizable polyoxyethylene alkyl compounds other than the EO alkyl compound include Naimine S-202, manufactured by NOF Corporation, EMALEX CWS-3 and EMALEX LWS-3, and Nippon Emulsion Co., Ltd.

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

  The colorant can be a dye or a pigment.

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

Examples of dyes include MS Magenta VP, MS Magenta HM-1450 and MS Magenta HSo-147, manufactured by Mitsui Toatsu Co., Ltd., AIZENSOT Red-1, AIZEN SOT Red-2, AIZEN SOTRed-3, AIZENSOT PINGAL and SPIRONRED GSP , Manufactured by Hodogaya Chemical Co., Ltd., RESOLIN Red FB 200%, MACROLEX Red Violet R and MACROLEX ROT5B, manufactured by LANXESS ("MACROLEX" is a registered trademark of the company), KAYASETRed B, KAYASET Red 130, and KAYASET Japan Red 80 Manufactured ("Kayaset" is a registered trademark of the company), PHLOXIN, ROSEBENGAL and ACID Red, Iva Kasei Co., Ltd., HSR-31 and DIARESINRed K, Mitsubishi Kasei Co., Ltd. ( "DIARESIN" is registered trademark of the company), as well as OilRed, magenta dye, including manufactured by BASF Japan Ltd.,
MS Cyan HM-1238, MS Cyan HSo-16, Cyan HSo-144 and MS Cyan VPG, manufactured by Mitsui Toatsu, AIZEN SOTBlue-4, manufactured by Hodogaya Chemical Co., Ltd., RESOLIN BR. Blue BGLN 200%, MACROLEX Blue RR, CERES Blue GN, SIRIUS SUPRATURQ. BlueZ-BGL and SIRIUS SUPRATURQ. Blue FB-LL 330%, manufactured by LANXESS, KAYASET Blue FR, KAYASET Blue N, KAYASET Blue 814, Turq. BlueGL-5 200 and LightBlue BGL-5 200, manufactured by Nippon Kayaku Co., Ltd., DAIWA Blue 7000 and Oleosol Fast Blue GL, manufactured by Daiwa Kasei Co., Ltd., DIARESIN Blue P, manufactured by Mitsubishi Kasei Co., Ltd., and SUDUAN Blue 670ZE 806, a cyan dye containing BASF Japan,
MS Yellow HSm-41, Yellow KX-7 and YellowEX-27, manufactured by Mitsui Toatsu Co., Ltd., AIZEN SOT Yellow-1, AIZEN SOT YellowW-3 and AIZEN SOT Yellow-6, manufactured by Hodogaya Chemical Co., Ltd. MACROLEX Yellow ELU 6F MAC . Yellow 10GN, manufactured by Bayer Japan, KAYASET Yellow SF-G, KAYASET Yellow 2G, KAYASET Yellow A-G and KAYASET Yellow E-G, manufactured by Nippon Kayaku Co., Ltd., DAIWA Yellow 330HB, manufactured by Daisei Kasei Co., Ltd. 146 and NEOPEN Yellow 075, yellow dyes including BASF Japan, and MS Black VPC, Mitsui Toatsu, AIZEN SOT Black-1, AIZEN SOT Black-5, Hodogaya Chemical Co., Resorin Black GSN 200% and RESOLIN BlackBS, manufactured by LANXESS, KAYASET Black A-N, manufactured by Nippon Kayaku Co., Ltd., Oil-soluble dyes including DAIWA Black MSC, Daiwa Kasei Co., Ltd., HSB-202, Mitsubishi Kasei Co., Ltd., NEPTUNE BlackX60 and NEOPEN BlackX58, manufactured by BASF Japan are included.

  The amount of the color material can be arbitrarily set as long as the effect of the present invention is obtained. The color material may not be substantially contained in the ink of the present invention, and can be, for example, less than 0.1% by mass with respect to the total mass of the ink.

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

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

  Examples of silicone-based surfactants include polyether-modified polysiloxane compounds, specifically KF-351A, KF-352A, KF-642 and X-22-4272, manufactured by Shin-Etsu Chemical Co., Ltd., BYK307, BYK345, BYK347 and BYK348, manufactured by Big Chemie ("BYK" is a registered trademark of the company), and TSF4452, manufactured by Toshiba Silicone Co., Ltd. are included.

  The fluorine-based surfactant means a compound in which a part or all of the surfactant is substituted with fluorine in place of hydrogen bonded to carbon of the hydrophobic group of a normal surfactant. Examples of fluorosurfactants include Megafac F, manufactured by DIC ("Megafac" is a registered trademark of the company), Surflon, manufactured by AGC Seikagaku ("Surflon" is a registered trademark of the company), Fluorad FC, 3M (“Fluorad” is a registered trademark of the company), Monflor, manufactured by Imperial Chemical Industry, Zonyls, manufactured by Ei Dupont Nemeras & Company, Licowet VPF, manufactured by Rubevelke Hoechst, and FTERGENT And Neos ("FTERGENT" is a registered trademark of the company).

  The amount of the surfactant can be arbitrarily set as long as the effect of the present invention is obtained. For example, the amount of the surfactant can be 0.001% by mass or more and less than 1.0% by mass with respect to the total mass of the ink.

1-6. Physical Properties The surface tension of the ink of the present invention is preferably 15 mN / m or more and less than 35 mN / m. If the surface tension of the ink is 15 mN / m or more, it is difficult for the discharge capability to be lowered due to the area around the nozzles of the inkjet head being wet. Further, if the surface tension of the ink is less than 35 mN / m, the ink is well wetted with a coated paper or a resin-made recording medium whose surface energy is lower than that of ordinary paper, so that whitening is unlikely to occur. The surface tension of the ink is measured by a Wilhelmy method (plate method) at a liquid temperature of 25 ° C., 60 ° C. using a commercially available surface tension meter (for example, surface tension meter FACE SURFACE TENSIOMETER CBVB-A3 manufactured by Kyowa Interface Science Co., Ltd.). A value measured by% RH can be used. The surface tension of the ink can be adjusted by selecting a photocurable compound, changing the blending ratio of each component, or adding a surfactant.

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

  When a pigment is used as the color material, it is preferable that the ink of the present invention does not contain a gel material having an average particle size exceeding 1.0 μm other than the pigment particles.

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

  The calorific value per unit mass of the ink of the present invention when the DSC (Differential Scanning Calorimetry) measurement of the ink is performed in the range from 25 ° C. to −25 ° C. at a rate of 5 ° C. per minute is 10 mJ / mg or more. It is preferable that no exothermic peak is exhibited. By setting it as such a structure, generation | occurrence | production of a gel or precipitation can be suppressed when an ink is preserve | saved at low temperature.

1-7. Preparation Method The ink of the present invention can be produced by mixing various materials and thoroughly dispersing them using a normal dispersing machine such as a sand mill. When a pigment is used as the color material, a concentrated solution containing a high concentration pigment may be prepared in advance, and the concentrated solution may be diluted with a photopolymerizable compound. Even with a normal disperser such as a sand mill, the material can be sufficiently dispersed, does not require excessive dispersion energy, and does not require a long dispersion time. Can be prepared. The prepared ink is preferably filtered with a filter having a pore diameter of 3 μm or less, preferably 1 μm or less.

2. Image Forming Method The image forming method of the present invention is carried out in the same manner as a known image forming method in which an image is formed using inkjet ink and an overcoat liquid is applied thereon, except that the ink of the present invention described above is used. obtain.

  For example, in the image forming method of the present invention, a step of landing ink jet ink droplets on a recording medium by the ink jet method, an actinic ray is irradiated to the ink jet ink landed on the recording medium, and a lower layer constituting an image is formed. In the image forming method including a step and a step of applying an overcoat liquid onto the lower layer, the inkjet ink may be the above-described ink of the present invention.

2-1. Step of Landing Inkjet Ink Drops on a Recording Medium In this step, ink jet ink droplets are ejected from an inkjet head and landed on a recording medium. The ink jet ink droplets are preferably landed on a position corresponding to the image to be formed on the recording medium.

  The ejection method from the ink jet head may be either an on-demand method or a continuous method. Examples of on-demand inkjet heads include single-cavity, double-cavity, bender, piston, shear-mode, and shared-wall electro-mechanical conversion, and thermal inkjet and bubble jet (bubble) The jet includes an electric-thermal conversion system including a Canon (registered trademark) type.

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

  Examples of the method of heating the inkjet ink to a predetermined temperature include at least one of an ink tank constituting a head carriage, an ink supply system such as a supply pipe and an anterior chamber ink tank immediately before the head, a pipe with a filter, and a piezo head Is heated to a predetermined temperature by any one of a panel heater, a ribbon heater, warm water and the like.

  From the viewpoint of increasing the recording speed and improving the image quality, it is preferable that the droplet amount of the ink-jet ink when ejected is 2 pL or more and 20 pL or less.

2-2. The process of forming the lower layer constituting the image by irradiating the ink jet ink landed on the recording medium with the active light In this step, the lower layer constituting the image by irradiating the ink jet ink landed in the previous step with the active light Form. By irradiating the inkjet ink with actinic rays, the inkjet ink is cured and a lower layer is formed.

  From the viewpoint of enhancing the curability of the inkjet ink, the actinic ray is preferably applied for 0.001 second or more and 1.0 second or less after ink landing. It is more preferable to irradiate between 001 seconds and 0.5 seconds.

  Examples of actinic rays that can be applied to the inkjet ink include electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among these, it is preferable to irradiate ultraviolet rays from the viewpoint of easy handling and little influence on the human body. The light source is preferably a light emitting diode (LED) from the viewpoint of suppressing the occurrence of ink curing failure due to melting of the inkjet ink by the radiant heat of the light source. Examples of LED light sources capable of irradiating with ultraviolet light for forming the lower layer include 395 nm, water-cooled LED, manufactured by Phoseon Technology.

From the viewpoint of further suppressing the irradiation of the radiant heat to the ink-jet ink, the LED light source is set so that the peak illuminance on the image surface is 0.5 to 10 W / cm ² using ultraviolet rays of 370 to 410 nm, and 1 to 5 W / cm. ² is more preferable, or it is preferable that the amount of light applied to the image is less than 350 mJ / cm ² .

  From the viewpoint of more efficiently suppressing the shrinkage of the recording material that occurs during ink curing, it is preferable to divide the irradiation of actinic rays into two stages. For example, first, after the ink jet ink has landed, actinic light is irradiated by the above-described method for 0.001 second or more and 2.0 seconds or less to temporarily cure the ink jet ink. The ink-jet ink can be fully cured.

2-3. Step of applying overcoat liquid on lower layer In this step, an overcoat liquid is applied on the lower layer. The overcoat liquid includes the overcoat liquid for inkjet discharge and an overcoat liquid applied by a method other than inkjet discharge (hereinafter also simply referred to as “non-inkjet discharge overcoat liquid”). Applying on the lower layer means applying an overcoat liquid so as to contact the surface of the lower layer formed on the side opposite to the recording medium.

2-3-1. Overcoat Liquid In this step, a known overcoat liquid can be appropriately used depending on the purpose of giving the printed image gloss or resistance to external impacts. The overcoat liquid may be a color ink containing a color material (for example, a white ink containing a white pigment) or a clear ink substantially free of a color material.

  At this time, when the ink of the present invention is used as an overcoat liquid, the wettability and adhesion of the inkjet discharge overcoat are further increased. This is because the image and the overcoat formed by the interaction between the EO group existing in the vicinity of the surface of the cured film forming the image and the EO group contained in the overcoat liquid, such as hydrogen bond or van der Waals force. This is thought to be because the affinity with the liquid is further increased.

  For example, the overcoat liquid for inkjet discharge may contain the following EO alkyl compound, and may further contain the following gelling agent.

  The EO alkyl compound is a non-polymerizable polyoxyethylene alkyl compound having a linear alkyl group having an HLB value of 6 or more.

  From the viewpoint of further improving the wettability and adhesion of the overcoat liquid for inkjet discharge, the number of EO groups contained in the EO alkyl compound contained in the overcoat liquid for inkjet discharge may be 12 or more, or 15 or more. it can.

  From the viewpoint of further improving the wettability and adhesion of the overcoat liquid for inkjet discharge, the HLB value of the EO alkyl compound contained in the overcoat liquid for inkjet discharge can be 10 or more, or 12 or more.

  The inkjet discharge overcoat liquid is 0.01% by mass or more and 10.0% by mass or less and 2.0% by mass or more with respect to the total mass of the inkjet discharge overcoat liquid from the viewpoint of further improving wettability and adhesion. An EO alkyl compound of 6.0% by mass or less, or 3.0% by mass or more and 5.0% by mass or less can be contained.

  From the viewpoint of increasing the affinity between the gelling agent and the EO alkyl compound and facilitating movement of the EO alkyl compound together with the gelling agent to the vicinity of the surface of the ink being cured, the EO alkyl contained in the overcoat liquid for inkjet discharge The compound can be a compound represented by the general formula (A1).

  From the viewpoint of facilitating movement of the EO alkyl compound in the vicinity of the surface of the ink being cured, the HLB value of the EO alkyl compound represented by the general formula (A1) contained in the overcoat liquid for inkjet discharge is 10 or more and 18 or less. It can be.

  The type of the gelling agent is not particularly limited as long as excessive wetting and spreading after discharge can be suppressed. For example, any one or more of the above-described general formula (G1) to general formula (G5) may be used. It can be set as a gelling agent, The quantity of these gelling agents can be 2 mass% or more and 10 mass% or less with respect to the total mass of the overcoat liquid for inkjet discharge.

  From the viewpoint of enhancing the resistance to external impact, the overcoat liquid for inkjet discharge is preferably a curable ink that is cured by light or heat. Further, from the viewpoint of enhancing the ease of handling, the above EO (Metal A) An actinic ray curable ink which contains an acrylate or other photopolymerizable compound and is cured by irradiation with actinic rays. From the viewpoint of further improving the affinity with the ink of the present invention and further improving wettability and adhesion, the inkjet discharge overcoat liquid may contain 30% by mass or more and 70% by mass or less of EO (meth) acrylate. preferable.

  The overcoat liquid may be an inkjet overcoat liquid that can be applied by an ink jet method, or may be a non-inkjet overcoat liquid that can be applied by a method other than the ink jet method. Non-inkjet overcoat liquid is applied by methods such as bar coating, spray coating, curtain coating, roll coating, screen printing, offset printing, gravure printing, relief printing and intaglio printing, and other printing methods. can do. In the case of using a non-inkjet overcoat liquid, it is preferably applied by screen printing, offset printing, gravure printing or bar coating from the viewpoint of ease of work and uniform application.

  From the viewpoint of simplifying the apparatus configuration and reducing the cost of image formation, the overcoat liquid is preferably an inkjet overcoat liquid.

2-4. The step of irradiating the overcoat solution with actinic rays to cure the overcoat solution When the overcoat solution is an actinic ray curable ink, the overcoat solution is applied to the overcoat solution after the step of applying the overcoat solution on the lower layer. The overcoat liquid may be cured by irradiation with actinic rays. From the viewpoint of facilitating the setting of the apparatus and efficiently forming an image, the conditions for irradiating the overcoat liquid with actinic rays are preferably the same as the conditions for irradiating the inkjet ink with actinic rays.

2-5. When carrying out the formation of the lower layer and the application of the overcoat liquid with different machines, or when these processes are carried out in different places of the same machine, the process of forming the lower layer and the process of applying the overcoat liquid, A step of conveying the recording medium on which the lower layer is formed may be included.

2-6. Recording medium The recording medium used in the image forming method of the present invention only needs to be able to form an image with the ink of the present invention. For example, polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile -Non-absorbing recording media composed of plastics containing butadiene-styrene copolymer, polyethylene terephthalate and polybutadiene terephthalate, non-absorbing inorganic recording media such as metals and glass, and papers (for example, coats for printing) Paper and coated paper B for printing).

3. Ink Set The ink of the present invention can be combined with the above-described inkjet discharge overcoat liquid to form an ink set. The ink set means a combination of the ink of the present invention and an overcoat liquid for inkjet discharge, which is configured to be installed in an inkjet recording apparatus to form an image. Examples of the ink set include those in which the ink of the present invention and the overcoat liquid for inkjet discharge are individually accommodated in a plurality of ink cartridges, or a plurality of ink accommodating portions are integrally configured to each of the ink accommodating portions. Includes an ink cartridge containing the ink of the present invention or an overcoat liquid for inkjet discharge. The ink set of the present invention may contain a combination of a plurality of inks that can apply or print different colors depending on the type of image to be formed.

[Example 1]
1. Preparation of inks Inks 1 to 20 were prepared using the photopolymerizable compounds listed in Table 1, the gelling agents listed in Table 2, the non-polymerizable polyoxyethylene alkyl compounds listed in Table 3, and the following components. did.

  In addition, “EO number” in Table 1 represents the number of continuous EO groups possessed by each (meth) acrylate. Moreover, the linear carbon number described in Table 2 and Table 3, and the HLB value described in Table 3 are values described in the catalog.

[Photoinitiator]
TPO: DAROCUR TPO, manufactured by BASF (DAROCUR is a registered trademark of BASF)
ITX: ITX, manufactured by BASF

[Photopolymerization inhibitor]
UV-10: Irgastab UV-10, manufactured by BASF ("Irgastab" is a registered trademark of the company)

1-1. Preparation of Pigment Dispersion Liquid 1 The following two types of compounds were placed in a stainless beaker and dissolved by stirring with heating for 1 hour while heating on a 65 ° C. hot plate.
Azisper PB824 9 parts Diethylene glycol diacrylate 71 parts After cooling to room temperature, 20 parts of the following pigment is added to the above solution, sealed in a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm, and dispersed in a paint shaker for 5 hours. After the treatment, the zirconia beads were removed to obtain a pigment dispersion 1.
Pigment Blue 15: 4 (Chromo Fine Blue 6332JC, manufactured by Dainichi Seika Kogyo Co., Ltd.)

1-2. Preparation of Inks 1 to 24 The gelling agent, EO alkyl compound, photopolymerizable compound, polymerization inhibitor and photoinitiator described in Tables 4 to 6 in the amounts described in Tables 4 to 6 and a hot plate at 65 ° C. After dissolving with heating and stirring above, the pigment dispersion 1 was added and stirred. The obtained ink was filtered with a 3 μm membrane filter manufactured by ADVATEC (Teflon is a registered trademark of EI DuPont) to obtain inks 1 to 24.

2. Image formation A line-type inkjet recording apparatus having an inkjet recording head (each color 42 pL, 360 dpi) provided with a piezo-type inkjet nozzle was loaded. The ink supply system was composed of 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, and the ink was heated to 100 ° C. The substrate carrier was heated to 40 ° C.

  A transparent polyethylene terephthalate (PET) film roll having a width of 300 mm and a thickness of 50 μm was prepared as a substrate. The transmittance of this PET film with respect to light having a wavelength of 350 to 400 nm is 80% or more. A 100% solid image (resolution: 360 × 360 dpi) having a size of 50 × 200 mm was formed on the substrate using inks 1 to 20.

After printing, the image surface was completely cured by applying an energy amount of 600 mJ / cm ² with an LED lamp (4 W / cm ² , water cooled unit, manufactured by Phoseon Technology). Irradiation was performed at a distance of 5 mm from the tube surface (irradiation width 20 mm in the conveying direction). The integrated light amount was measured using an ultraviolet integrated light meter (C9536-2 and H9958-2; Hamamatsu Photonics Co., Ltd.), and the substrate conveyance speed was adjusted.

3. Evaluation [Surface energy]
Three types of liquids with known γ _L ^D , γ _L ^P and γ _L ^H are dropped on the ink cured product constituting the formed image, and the contact angle at that time is measured by a contact angle meter measuring device “contact angle meter”. “CA-V, manufactured by Kyowa Interface Science Co., Ltd.” was measured five times at normal temperature and humidity (20 ° C., 50% RH), and the average value was defined as the contact angle θ. The three types of liquid gamma _L ^D, obtains a γ _L ^P, γ _L and ^H and θ by solving the simultaneous equations are substituted into equation ^{_{(1) γ S D, γ}} S P , and _gamma ^{S H,} the resulting gamma _S ^D, the gamma _S ^P and _gamma ^{S H} to calculate the surface energy gamma _S of the cured product are substituted into equation (2). , Γ _L ^D is the surface energy (dispersion force component) of the liquid, γ _L ^P is the surface energy of the liquid (dipole component), γ _L ^H is the surface energy of the liquid (hydrogen bond component), and γ _S ^D is the surface energy of the ink cured product (dispersion force component), the gamma _S ^P surface energy (dipole component) of the ink cured product, gamma _S ^H represents the surface energy of the ink cured product (hydrogen bonding component), respectively.
Formula (1) γ _L (1 + cos θ) = 2 (γ _S ^D γ _L ^D ) ^1/2 +2 (γ _S ^P γ _L ^P ) ^1/2 +2 (γ _S ^H γ _L ^H ) ^1/2
Equation _{(2) γ S = γ S} D + γ S P + γ S H

[Wettability]
When the upper layer liquid was applied on the formed image, the time until repelling occurred and the degree of white spots (unprinted portions due to flipping) were visually confirmed. Evaluation was performed according to the following criteria.

  As the upper layer liquid, UV VECTA coat varnish PC-3KW2, which is a general-purpose varnish not containing an EO alkyl compound, manufactured by T & K TOKA Corporation was used. The upper layer liquid was uniformly coated on each cured ink using a bar coater. After the application, a metal halide lamp lamp 120 W / cm manufactured by GS Yuasa Co., Ltd. was used to irradiate light with a maximum illuminance of 280 mW / cm 2 on the image surface to be cured. The conveyance speed of the recording medium was 30 m / min. The amount of light irradiated was 350 mJ / cm 2.

1: Repelling occurs immediately after application, causing a problem in practical use.
2: Repelling occurs after 5 seconds after application, and there are several white spots.
3: Repelling occurs after 10 seconds after application, and there are several white spots.
4: Repelling occurs after 15 seconds after application, and there are several white spots.
5: No repelling occurs until 20 seconds after application, and there are almost no white spots.
6: No repelling occurs after application and no white spots are observed.

[Adhesion]
Cross-cut the surface of the image formed above into 25 squares, paste cellophane, 3M ("Cellotape" is a registered trademark of the company), peel it off in the vertical direction, count the number of squares peeled off, The adhesion of the image to was evaluated.

1: All peeled off.
2: 1-15 squares remain.
3: 16-20 squares remain.
4: 21-24 squares remain.
5: All remains.

[Film hardness]
The formed image was left in an environment of 25 ° C. and 60% RH for 24 hours. Thereafter, the pencil hardness of the image surface was measured according to JIS-K-5400. Evaluation was performed according to the following criteria.

1: The pencil hardness was 2B or less.
2: The pencil hardness was B, F or H.
3: The pencil hardness was 2H or more.

  The results obtained are shown in Table 7.

  The image formed with the ink having the composition of the present invention had high surface energy and film hardness (35 mN / m or more) and high wettability and adhesion of the overcoat liquid (ink Nos. 1 to 15).

  On the other hand, when the ink does not contain an EO alkyl compound or the amount of the EO alkyl compound is less than 0.1% by mass, the surface energy is low (less than 35 mN / m), and the wettability and adhesion of the overcoat liquid are low. It was low (Ink Nos. 16, 17, 19 to 24).

  Further, the ink having an amount of the EO alkyl compound larger than 10.0% by mass had high surface energy and high wettability and adhesion of the overcoat liquid, but the film hardness was low (ink No. 18).

  The ink with less (meth) acrylate content than 30% by mass had low surface energy and low wettability and adhesion of the overcoat liquid (ink Nos. 22 to 24).

  When the gelling agent is at least one of the compounds represented by the general formula (G1) to the general formula (G5), the wettability and the adhesion became higher (Ink Nos. 4 to 15 and Ink No. 4). 1 to 3).

  The number of carbon atoms of the linear alkyl group that the EO alkyl compound has, and the number of carbon atoms of the linear portion of R1a, R1b, R2a, or R2b that the gelling agent represented by general formula (G1) to general formula (G5) has When the difference was 3 or less, the wettability and adhesion of the overcoat liquid were higher (by comparison between ink Nos. 9 to 15 and inks Nos. 1 to 8).

  When the EO alkyl compound is a compound represented by the general formula (A1) and having an HLB value of 10 or more and 18 or less, the wettability and adhesion of the overcoat liquid are further increased (ink Nos. 10 to 10). 15 and ink Nos. 1 to 9).

  When the amount of the EO alkyl compound was 2% by mass or more, the surface energy of the image was higher (by comparison between Ink Nos. 2 to 12 and Ink No. 1). When the amount of the EO alkyl compound was 6% by mass or less, the film hardness of the image was higher (by comparison between ink No. 1, 2, 4 to 9, 12 and ink No. 3, 10, 11). .

[Example 2]
1. 1. Preparation of overcoat solution 1-1. Preparation of White Pigment Dispersion Liquid 1 The following two types of compounds were placed in a stainless beaker and dissolved by heating and stirring for 1 hour while heating on a 65 ° C. hot plate.
Azisper PB824 9 parts 3PO-modified trimethylolpropane triacrylate 71 parts After cooling to room temperature, 60 parts of the following pigment was added to the above solution, sealed in a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm, and sealed in a paint shaker. After 5 hours of dispersion treatment, the zirconia beads were removed to obtain a white pigment dispersion 1.
Titanium oxide (TCR-52, manufactured by Sakai Chemical Industry Co., Ltd.)

1-2. Preparation of White Pigment Dispersion 2 Same as White Pigment Dispersion 1 except that Azisper PB824 was changed to BYKJET-9151, a block polymer having a tertiary amine, manufactured by BYK (“BYKJET” is a registered trademark of the company). Thus, a white pigment dispersion 2 was prepared.

1-3. Preparation of Overcoat Liquids 1-15 Ink No. 1 was used except that Pigment Dispersion 1 was changed to White Pigment Dispersion 1, White Pigment Dispersion 2, or diethylene glycol diacrylate (DEGDA). Overcoat liquids 1, 2, 4, 5, 9, 10 and 13-15 were obtained in the same manner as 1, 2, 4, 5, 9, 10 and 13-15, respectively. The overcoat liquids 3, 7, 8, 11 and 12 were UV VECTA coat varnish PC-3KW2, a varnish containing an EO alkyl compound, manufactured by T & K TOKA Corporation as an overcoat liquid.

2. Image Formation Overcoat liquids 1 to 15 were applied on images formed with inks 1 to 15 in Example 1.

  The overcoat liquids 1, 2, 4-6, 9-12 and 14 are the same as the image formation by applying the overcoat liquid under the same conditions as the image formation using the same type of piezo head as that used for the image formation. Actinic rays were irradiated under conditions.

The overcoat liquids 3, 7, 8, 13 and 15 were uniformly applied using a bar coater. After the application, a metal halide lamp lamp 120 W / cm manufactured by GS Yuasa Co., Ltd. was used to irradiate light with a maximum illuminance of 280 mW / cm 2 on the image surface to be cured. The conveyance speed of the recording medium was 30 m / min. The amount of light irradiated was 350 mJ / cm ² .

3. Evaluation The surface energy, wettability, adhesion and film hardness of the formed overcoat layer were evaluated by the same means as in Example 1.

  Table 9 shows the obtained results.

  When the overcoat liquid contained an EO alkyl compound, the wettability and adhesion of the image became higher.

  An image formed using the ink of the present invention has high wettability and adhesion of the overcoat liquid applied thereon, and therefore can be used for forming an image that requires aesthetics and high durability.

Claims (14)

An actinic ray curable inkjet ink containing a photopolymerizable compound, a non-polymerizable polyoxyethylene alkyl compound having a linear alkyl group, a gelling agent and a photoinitiator,
The photopolymerizable compound has a structure represented by (—CH ₂ —CH ₂ —O—) _m (m is an integer of 3 or more and 14 or less) in the molecule, and has a molecular weight of 300 to 1500 (meth). Including acrylate,
The non-polymerizable polyoxyethylene alkyl compound has an HLB value of 6 or more,
The ink contains 30% by mass or more and 70% by mass or less of the (meth) acrylate based on the total mass of the ink,
The ink contains 0.01% by mass or more and 10.0% by mass or less of the non-polymerizable polyoxyethylene alkyl compound with respect to the total mass of the ink. The gelling agent includes at least one selected from the group consisting of general formula (G1) to general formula (G5), and the ink is 2% by mass to 10% by mass with respect to the total mass of the ink. The actinic ray curable inkjet ink according to claim 1, further comprising a gelling agent represented by the general formula (G1) to the general formula (G5).
General formula (G1): R1a-CO-R1b
General formula (G2): R1a-COO-R1b
General formula (G3): R1a-COOH
General formula (G4): R1a-OH
Formula _{(G5): R2a- (CH 2} CH 2 O) n-R2b
(R1a and R1b independently represent an alkyl group having a straight chain portion having 12 to 24 carbon atoms, and R2a and R2b independently represent an alkyl ketone group having a straight chain portion having 12 to 24 carbon atoms or Represents an alkyl ester group, and n represents 1 or 2.)   The difference between the number of carbon atoms in the straight chain portion of R1a, R1b, R2a or R2b of the gelling agent and the number of carbon atoms in the straight chain alkyl group of the non-polymerizable polyoxyethylene alkyl compound is The actinic ray curable inkjet ink according to claim 2, wherein the actinic ray curable inkjet ink is 3 or less. The non-polymerizable polyoxyethylene alkyl compound is a compound represented by the general formula (A1) and having an HLB value of 10 or more and 18 or less, according to any one of claims 1 to 3. The actinic ray curable inkjet ink described.
Formula _{(A1): R3-X -} ((CH 2 CH 2 O) p -H) q H r
(R3 represents an alkyl group having a straight chain portion having 12 to 24 carbon atoms, X represents one structure selected from the group consisting of C, N and a sugar structure, and p and q are independently 2 or more. And r represents (valence of X−q−1).)   5. The ink according to claim 1, wherein the ink contains 2.0% by mass or more and 6.0% by mass or less of the non-polymerizable polyoxyethylene alkyl compound with respect to the total mass of the ink. 2. The actinic ray curable inkjet ink according to item 1.   A step of landing droplets of the actinic ray curable inkjet ink according to any one of claims 1 to 5 on a recording medium by an inkjet method, irradiating the droplets that have landed on the recording medium with active rays An image forming method comprising: forming a lower layer constituting an image; and applying an overcoat liquid on the lower layer.   The image forming method according to claim 6, wherein the overcoat liquid contains a non-polymerizable polyoxyethylene alkyl compound having an HLB value of 6 or more. The overcoat liquid contains at least one gelling agent selected from the group consisting of general formula (G1) to general formula (G5), and the overcoat liquid is based on the total mass of the overcoat liquid. The method according to claim 7, comprising 2 to 10% by mass of the gelling agent.
General formula (G1): R1a-CO-R1b
General formula (G2): R1a-COO-R1b
General formula (G3): R1a-COOH
General formula (G4): R1a-OH
Formula _{(G5): R2a- (CH 2} CH 2 O) n-R2b
(R1a and R1b independently represent an alkyl group having a straight chain portion having 12 to 24 carbon atoms, and R2a and R2b are independently an alkyl ketone group having a straight chain portion having 12 to 24 carbon atoms or Represents an alkyl ester group, and n represents 1 or 2.)   The difference between the number of carbon atoms of the linear alkyl group of the non-polymerizable polyoxyethylene alkyl compound and the number of carbon atoms of the linear portion of R1a, R1b, R2a and R2b of the gelling agent is within 3. The method according to claim 8, wherein: The non-polymerizable polyoxyethylene alkyl compound is a compound represented by the general formula (A1) and having an HLB value of 10 or more and 18 or less, according to any one of claims 7 to 9. The method described.
Formula _{(A1): R3-X -} ((CH 2 CH 2 O) p -H) q H r
(R3 represents an alkyl group having a straight chain portion having 12 to 24 carbon atoms, X represents one structure selected from the group consisting of C, N and a sugar structure, and p and q are independently 2 or more. And r represents (valence of X−q−1).)   The said overcoat liquid contains 0.01 mass% or more and 10.0 mass% or less of the said non-polymerizable polyoxyethylene alkyl compound with respect to the total mass of an overcoat liquid. 11. The method according to any one of items 10.   The method according to claim 6, wherein the overcoat liquid is an actinic ray curable ink.   An ink set comprising the actinic ray curable inkjet ink according to any one of claims 1 to 5 and an overcoat liquid for inkjet discharge.   The ink set according to claim 13, wherein the ink jet discharge overcoat liquid contains a non-polymerizable polyoxyethylene alkyl compound having an HLB value of 6 or more.