JP6070698B2 - Actinic ray curable inkjet ink and image forming method using the same - Google Patents

Description

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

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

  However, in these image forming methods using an ultraviolet curable ink jet system, unification of adjacent dots cannot be suppressed 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 was inferior. One of the methods for preventing unification of adjacent dots is a technique of adding a gelling agent to the ultraviolet curable inkjet ink (see, for example, Patent Documents 1 and 2).

  On the other hand, if 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 rays is likely to melt, and the curing of the ink droplet surface is likely to occur. There was a problem. Furthermore, in the case of a plastic recording medium which is easily affected by heat, there is a problem that the ink cannot be cured with 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, the image cured with the LED light source has a problem of low adhesion to the recording medium.

  In order to solve such a problem, an inkjet ink in which a trifunctional or higher acrylate monomer and an acrylamide derivative are added has been proposed (for example, Patent Document 4). According to the technique of Patent Document 4, the curable monomer is enhanced with an acrylate monomer having three or more functions, and the ejection stability of the ink is enhanced with an acrylamide derivative.

  On the other hand, for the purpose of 1) increasing the ink ejection stability and 2) increasing the strength of the cured film, the photopolymerizable compound having a (meth) acrylamide group in an ultraviolet curable inkjet ink containing a water-soluble solvent. It is also considered to add (Patent Document 5).

US Patent Application Publication No. 2007/0058020 International Publication No. 2007/025893 JP 2011-25684 A JP 2008-163342 A JP 2011-174013 A

  In the techniques of Patent Documents 1 and 2, the compatibility between the gelling agent and the photopolymerizable compound has not been studied in detail, and depending on the type of the photopolymerizable compound, the gelling agent is difficult to be compatible. There are problems that the ejection becomes unstable, the gelling agent cannot sufficiently undergo the sol-gel phase transition, and the coalescence of the droplets cannot be suppressed.

  On the other hand, in the inks described in Patent Documents 4 and 5, the viscosity of the ink droplet after landing on the recording medium is low. Therefore, there is a problem that oxygen is easily diffused into the ink droplets during polymerization of the photopolymerizable compound, and the photopolymerization reaction is easily inhibited by oxygen. In particular, a light source with a low light quantity such as an LED cannot sufficiently cure the ink, and has a problem that adhesion between a printed image and a recording medium is low and scratch resistance is also low.

  The present invention has been made in view of the above circumstances. An actinic ray curable inkjet ink in which ink droplets after landing on a recording medium do not coalesce, the cured film has high adhesion to the recording medium, and the cured film also has excellent scratch resistance, and the same An object is to provide an image forming method.

The first of the present invention relates to the actinic ray curable inkjet ink shown below.
[1] An actinic ray curable inkjet ink that contains a gelling agent, a photopolymerizable compound, and a photopolymerization initiator and that reversibly undergoes sol-gel phase transition depending on temperature, and the content of the gelling agent is 0.5% by mass or more and less than 10% by mass with respect to the mass, and the photopolymerizable compound has 1) ClogP in the range of −4.0 to less than 1.0, and (meth) acrylamide group in the molecule And 2) a polymerizable compound B having ClogP in the range of −1.0 or more and less than 4.0, a molecular weight of 200 or more and less than 1200, and having a (meth) acrylate group in the molecule. An actinic ray curable inkjet ink comprising:

[2] The actinic ray curable inkjet ink according to [1], wherein the polymerizable compound A is contained in an amount of 5% by mass to less than 50% by mass with respect to the total mass of the ink.
[3] The actinic ray curable inkjet ink according to [1] or [2], wherein the polymerizable compound B is contained in an amount of 10% by mass to less than 70% by mass with respect to the total mass of the ink.
[4] The actinic ray curable inkjet ink according to any one of [1] to [3], wherein the polymerizable compound B has two or more (meth) acrylate groups.

[5] The activity according to any one of [1] to [4], wherein the polymerizable compound B contains 3 or more and less than 25 a structure represented by (—CH ₂ —CH ₂ —O—) in the molecule. Light curable inkjet ink.
[6] The actinic ray curable inkjet ink according to any one of [1] to [5], wherein the molecular weight of the polymerizable compound B is 300 or more and less than 800.
[7] The actinic ray curable inkjet ink according to any one of [1] to [6], wherein the polymerizable compound B has a ClogP value of 0 or more and less than 3.6.

[8] The actinic ray curable inkjet ink according to any one of [1] to [7], which contains the gelling agent in an amount of 1% by mass to less than 6% by mass with respect to the total mass of the ink.
[9] The actinic ray curable inkjet ink according to any one of [1] to [8], wherein the gelling agent is a wax having a polar group in the molecule.
[10] The gelling agent is at least one selected from the group consisting of aliphatic ketone compounds, aliphatic monoester compounds, higher fatty acids, higher alcohols, fatty acid amides, and polyhydric alcohol fatty acid esters. [1] -The actinic-light curable inkjet ink in any one of [9].

The second of the present invention relates to an image forming method described below.
[11] A step of ejecting ink droplets of the actinic radiation curable inkjet ink according to any one of the above [1] to [10] from an inkjet recording head to adhere to the recording medium; Irradiating the landed ink droplets with actinic rays from an LED light source to cure the ink droplets.

  In the actinic ray curable inkjet ink of the present invention, ink droplets after landing on a recording medium are difficult to coalesce during image formation. Furthermore, the adhesion between the cured film (printed image) of the ink and the recording medium is high, and the scratch resistance of the cured film is also excellent. That is, it is possible to form a high-quality image with good adhesion to the recording medium and high hardness.

It is a figure (side view) which shows an example of a structure of the principal part of the inkjet recording apparatus of a line recording system. FIG. 2 is a diagram (top view) illustrating an example of a configuration of a main part of a line recording type inkjet recording apparatus. It is a figure which shows an example of a structure of the principal part of the inkjet recording device of a serial recording system.

[Actinic ray curable ink]
The actinic ray curable inkjet ink of the present invention includes a gelling agent, a photopolymerizable compound, and a photopolymerization initiator.

-Photopolymerizable compound A photopolymerizable compound is a compound which bridge | crosslinks or superposes | polymerizes by irradiation of actinic light. The actinic rays are, for example, electron beams, ultraviolet rays, α rays, γ rays, and X-rays, and are preferably ultraviolet rays.

The actinic ray curable inkjet ink of the present invention contains at least the following polymerizable compound A and polymerizable compound B.
1) Polymerizable compound A having ClogP in the range of −4.0 to less than 1.0 and having a (meth) acrylamide group in the molecule.
2) Polymerizable compound B having ClogP in the range of -1.0 or more and less than 4.0, molecular weight of 200 or more and less than 1200, and having a (meth) acrylate group in the molecule.

  Here, “(meth) acrylate” refers to both and / or “acrylate” and “methacrylate”, and “(meth) acryl” refers to both and / or “acryl” and “methacryl”.

  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 relative to the base 10 is indicated. 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.

  In the conventional sol-gel phase transition type UV curable ink, the compatibility between the gelling agent and the photopolymerizable compound has not been studied in detail. Therefore, when the photopolymerizable compound and the gelling agent are difficult to be compatible, the ink ejection becomes unstable or the gelling agent has a desired gel structure (card house structure or fibrous network structure). There was a problem that the ink droplets that could not be formed were difficult to gel after landing. On the other hand, when the compatibility between the photopolymerizable compound and the gelling agent is too high, there is a problem that the gelling agent cannot be sufficiently crystallized after the ink has landed on the recording medium. Further, even when the gelling agent is compatible with the photopolymerizable compound in the initial stage of printing, the gelling agent gradually becomes incompatible with the continued printing, and the ink ejection property may be lowered.

  On the other hand, the present inventors use a certain amount of the polymerizable compound A and a certain amount of the polymerizable compound B in combination with the gelling agent, so that the gelling agent is stably compatible, and the ink ejection property. And the gelling agent quickly crystallized after the ink landed on the recording medium, and it was found that coalescence of droplets could be suppressed. The reason is guessed as follows.

  The polymerizable compound A ((meth) acrylamide compound) has a relatively high hydrophilicity. On the other hand, the polymerizable compound B ((meth) acrylate compound) is relatively hydrophobic. These polymerizable compound A and polymerizable compound B both have a (meth) acryloyl group and are easily compatible with each other. On the other hand, the gelling agent contained in the actinic ray curable inkjet ink has both a hydrophobic part and a hydrophilic part in its molecular structure. The hydrophobic part and the hydrophilic part of the gelling agent tend to have affinity with the polymerizable compound B and the polymerizable compound A, respectively. Therefore, the gelling agent can exist stably in the sol ink.

  On the other hand, since the ink contains a highly hydrophilic polymerizable compound A, when the ink lands on the recording medium, the gelling agent quickly precipitates and crystallizes. That is, coalescence of the droplets after landing is suppressed, and a high quality image is obtained.

  In addition, since the actinic ray curable inkjet ink of the present invention contains the polymerizable compound A (acrylamide compound), the adhesion between the cured ink (printed image) and the recording medium is good. Furthermore, the scratch resistance of the cured film is also increased. Furthermore, since the highly flexible polymerizable compound B is included, the flexibility (bending resistance) of the printed image is also improved.

About the polymerizable compound A The polymerizable compound A is a (meth) acrylamide compound. As described above, when the polymerizable compound A is contained in the actinic ray curable inkjet ink, the adhesion between the cured ink and the recording medium is increased. Further, the scratch resistance of the ink cured film is also increased.

  The ClogP value of the polymerizable compound A is −4.0 or more and less than 1.0, preferably −3.0 or more and less than 1.0. When the ClogP value of the polymerizable compound A is less than −4.0, the hydrophilicity becomes excessively high, and the compatibility with the gelling agent and the polymerizable compound B decreases. Therefore, the solubility of the gelling agent becomes unstable, the ink ejection property becomes unstable, or a desired gel structure (card house structure or fibrous network structure) is not formed after landing on the recording medium, In some cases, dot coalescence cannot be suppressed. On the other hand, when the ClogP value of the polymerizable compound A is 1.0 or more, the adhesion between the printed image and the recording medium is hardly increased.

  The number of (meth) acrylamide groups contained in the molecule of the polymerizable compound A is not particularly limited. Only one (meth) acrylamide group may be contained in the polymerizable compound A, and two or more (meth) acrylamide groups may be contained.

  The molecular weight of the polymerizable compound A is not particularly limited, but is preferably 100 or more and less than 1000, and more preferably 100 or more and less than 500. Some acrylamide compounds having a molecular weight of 100 or less are harmful to living organisms. On the other hand, when the molecular weight of the acrylamide compound is 1000, the viscosity of the ink tends to be excessively high.

Preferred examples of the polymerizable compound A include the following compounds. However, the polymerizable compound A is not limited to the following compounds.
N, N-dimethylacrylamide (molecular weight 99, ClogP value: -0.17), N, N-diethylacrylamide (molecular weight 127, ClogP value: 0.89), acryloylmorpholine (molecular weight 141, ClogP value: -0.07) ), N- (2-hydroxyethyl) acrylamide (molecular weight 115, ClogP value: -1.03), N-isopropylacrylamide (molecular weight 113, ClogP value: 0.25), diacetone acrylamide (molecular weight 169, ClogP value: 0.29), N-methylolacrylamide (molecular weight 101, ClogP value: -0.93), N- [3- (dimethylamino) propyl] acrylamide (molecular weight 156, ClogP value: 0.20), N, N ' -Methylenebisacrylamide (molecular weight 154, ClogP value: -0 92), N, N ′-(1,2-dihydroxyethylene) bisacrylamide (molecular weight 200, ClogP value: −3.00), N, N′-ethylenebisacrylamide (molecular weight 154, ClogP value: −0.94). ), N, N′-propylenebisacrylamide (molecular weight 182; ClogP value: −0.43), N, N′-dimethylmethacrylamide (molecular weight 113, ClogP value: 0.14), N- (2-hydroxyethyl) ) Methacrylamide (molecular weight 129, ClogP value: -0.17).

N- {3- [4- (3-acryloylamino-2-hydroxy-propoxy) -butoxy] -2-hydroxy-propyl} -acrylamide represented by the following general formula (1) (molecular weight 344, ClogP value: − 2.09)

N- (3- {2- [2- (3-acryloylamino-propoxy) -ethoxy] -ethoxy} -propyl) -acrylamide represented by the following general formula (2) (molecular weight 328, ClogP value: −0. 32)

N- {2- [2- (2-acryloylamino-ethoxy) -ethoxy] -ethyl} -acrylamide represented by the following general formula (3) (molecular weight 256, ClogP value: -0.76)

N- {3- [2- (3-acryloylamino-propoxy) -ethoxy] -propyl} -acrylamide represented by the following general formula (4) (molecular weight 284, ClogP value: -0.19)

N- {3- [2- (3- (3-acryloylamino-2-hydroxy-propoxy) -ethoxy] -2-hydroxy-propyl} -acrylamide represented by the following general formula (5) (molecular weight 316, ClogP value: − 2.41)

N- {3- [3- (3-acryloylamino-2-hydroxy-propoxy) -2,2-bis- (3-acryloylamino-2-hydroxy-propoxymethyl) represented by the following general formula (6) -Propoxy] -2-hydroxy-propyl} -acrylamide (molecular weight 645, Clog P value: -3.81)

N- {3- [2- [3- (3-acryloylamino-2-hydroxy-propoxy) -1- (2-hydroxy-5-oxo-hept-6-enyloxymethyl) represented by the following general formula (7) -Ethoxy] -2-hydroxy-propyl} -acrylamide (molecular weight 472, ClogP value: -3.05)

N- [2- (2- {2- {2- [2- (acryloylamino-methoxy) -ethoxy] -ethoxymethyl} -2- [2- (acryloylamino-) represented by the following general formula (8) Methoxy) -ethoxymethyl] -butoxy} -ethoxy) -ethoxymethyl] -acrylamide (molecular weight 604, ClogP value: -0.62)

N- {3- [2,2-bis- (3-acryloylamino-2-hydroxy-propoxymethyl) -butoxy] -2-hydroxy-propyl} -acrylamide (molecular weight 516) represented by the following general formula (9) ClogP value: -1.56)

N- {2- [2- (2- {2- [2- (acryloylamino-methoxy) -ethoxy] -ethoxy} -1- {2- [2- (acryloyl) represented by the following general formula (10) Amino-methoxy) -ethoxy] -ethoxymethyl} -ethoxy) -ethoxy] -ethoxymethyl} -acrylamide (molecular weight 606, Clog P value: -2.99)

N- (2- {3- [2- (acryloylamino-methoxy) -ethoxy] -2,2-bis- [2- (acryloylamino-methoxy) -ethoxymethyl] represented by the following general formula (11) -Propoxy} -ethoxymethyl) -acrylamide (molecular weight 645, ClogP value: -2.20)

  The content of the polymerizable compound A is preferably 5% by mass or more and less than 50% by mass, and more preferably 10 to 40% by mass with respect to the total mass of the actinic ray curable inkjet ink. When the content of the polymerizable compound A is 50% by mass or more, the hydrophilicity of the ink increases and the solubility of the gelling agent tends to become unstable. For this reason, ink ejection becomes unstable, or in the ink droplets after landing, the gel structure (card house structure or fibrous network structure) is not sufficiently formed, and it is difficult to suppress dot coalescence. On the other hand, when the amount of the polymerizable compound A is less than 5% by mass, the adhesion between the cured ink film and the recording medium is not sufficiently improved.

About the polymerizable compound B The polymerizable compound B is a (meth) acrylate compound. When the polymerizable compound B is contained in the actinic ray curable inkjet ink, the gelling agent is stably dissolved in the ink. When the polymerizable compound B is contained, the flexibility of the ink cured film is increased. The ClogP value of the polymerizable compound B is −1.0 or more and less than 4.0, preferably 0 or more and less than 3.6. When the ClogP value of the (meth) acrylate compound is less than −1.0, the polymerizable compound B and the gelling agent are hardly compatible. For this reason, ink ejection becomes unstable, or a gel structure (card house structure or fibrous network structure) is not sufficiently formed in the ink droplets after landing, and it is difficult to suppress dot coalescence. On the other hand, when the ClogP value of the (meth) acrylate compound is 4.0 or more, the polymerizable compound A and the polymerizable compound B are hardly compatible.

  The molecular weight of the polymerizable compound B is 200 or more and less than 1200, and preferably 300 or more and less than 800. If the molecular weight of the polymerizable compound B is less than 200, the polymerizable compound B tends to volatilize in the ink jet recording apparatus, and ink ejection tends to become unstable. On the other hand, if the molecular weight of the (meth) acrylate compound exceeds 1200, the viscosity of the ink becomes excessively high, and ink ejection tends to become unstable.

  The number of (meth) acrylate groups contained in the molecule of the polymerizable compound B is not particularly limited, but it is preferable to have two or more (meth) acrylate groups in the molecule. Specifically, it is preferable to have 2, 3 or 4 (meth) acrylate groups from the viewpoint of the curability of the ink.

Preferred examples of the polymerizable compound B include the following compounds. However, the polymerizable compound B is not limited to the following compounds.
4EO-modified pentaerythritol tetraacrylate (SR494, manufactured by Sartomer, molecular weight 528, ClogP value: 2.28), tetraethylene glycol diacrylate (V # 335HP, manufactured by Osaka Organic Chemical Co., Ltd., molecular weight 302, ClogP value: 1.15) Polyethylene glycol # 400 diacrylate (NK ester A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 508, Clog P value: 0.47), polyethylene glycol # 600 diacrylate (NK ester A-600, manufactured by Shin-Nakamura Chemical Co., Ltd.) Molecular weight 708, ClogP value: -0.16), polyethylene glycol # 200 dimethacrylate (NK ester 4G, Shin-Nakamura Chemical Co., Ltd., molecular weight 330, ClogP: 0.59), polyethylene glycol # 400 dimethacrylate (NKE) Ter 9G, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 536, ClogP: 1.09), 4EO modified hexanediol diacrylate (CD561, manufactured by Sartomer, molecular weight 358, ClogP value: 2.52), 3EO modified trimethylolpropane triacrylate (SR454, manufactured by Sartomer, molecular weight 429, ClogP value: 3.97), 6EO-modified trimethylolpropane triacrylate (SR499, manufactured by Sartomer, molecular weight 560, ClogP value: 3.57), tripropylene glycol diacrylate (APG) -200, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 300, ClogP value: 2.21), tris (2-hydroxyethyl) isocyanurate triacrylate (SR368, manufactured by Sartomer, molecular weight 423, ClogP value) 2.59), glycerin propoxyacrylate (OTA480, manufactured by Daicel-Cytec, Inc., molecular weight 428, ClogP value: 2.66), dioxane glycol diacrylate (CD536, manufactured by Sartomer, molecular weight 326, ClogP value: 3.03), 3PO modified neopentyl glycol diacrylate (SR9003, manufactured by Sartomer, molecular weight 328, ClogP value: 3.38), dipropylene glycol diacrylate (APG-100, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 242, ClogP value 2.04) , Neopentyl glycol diacrylate (A-NPG, Shin-Nakamura Chemical Co., Ltd., molecular weight 212, ClogP value: 2.58), 2-hydroxy-3-acryloyloxypropyl methacrylate (701A, Shin-Nakamura Chemical Co., Ltd., molecular weight) 214, ClogP value: 0.84), glycerin dimethacrylate (701, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 228, ClogP value: 1.15), 1,6-hexanediol diacrylate (A-HD, Shin-Nakamura Chemical Co., Ltd.) Manufactured, molecular weight 226, ClogP value: 3.02), caprolactone acrylate (SR495B, manufactured by Sartomer, molecular weight 344, ClogP value: 2.09), phenol 4EO modified acrylate (Miramer M144, manufactured by Miwon, molecular weight 324, ClogP value) : 2.45), methoxytriethylene glycol acrylate (AM-30G, Shin-Nakamura Chemical, molecular weight 218, ClogP value 0.49), methoxytriethylene glycol methacrylate (V-MTG, Osaka Organic Chemistry, molecular weight 232, ClogP value: 0.79 ), Alkoxylated neopentyl glycol diacrylate (for example, manufactured by Sartomer, CD9043, CD9045), EO-modified pentanediol di (meth) acrylate, EO-modified hexanediol di (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate EO-modified pentaerythritol tri (meth) acrylate, EO-modified pentaerythritol tetra (meth) acrylate, tetramethylolmethane triacrylate.

In the molecule of the polymerizable compound B, the structure represented by (—CH ₂ —CH ₂ —O—) is preferably contained in a range of 3 or more and less than 25, more preferably 3 or more and less than 15. When three or more structures represented by (—CH ₂ —CH ₂ —O—) are contained in the molecule of the polymerizable compound B, the flexibility of the cured film of the ink is increased. On the other hand, when 25 or more structures represented by (—CH ₂ —CH ₂ —O—) are contained in the molecule of the polymerizable compound B, the hydrophilicity of the polymerizable compound B tends to become excessively high, and the gelling agent There is a possibility that it becomes difficult to be compatible with.

  Therefore, the polymerizable compound B includes tetraethylene glycol diacrylate (V # 335HP, manufactured by Osaka Organic Chemical Co., Ltd., molecular weight 302, ClogP value: 1.15), polyethylene glycol # 400 diacrylate (NK ester A-400, Shin Nakamura). Chemical company, molecular weight 508, ClogP value: 0.47), polyethylene glycol # 600 diacrylate (NK ester A-600, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 708, ClogP value: -0.16), polyethylene glycol # 200 Dimethacrylate (NK ester 4G, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 330, ClogP value: 0.59), polyethylene glycol # 400 dimethacrylate (NK ester 9G, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 536, ClogP value: 1.09) ) 4EO modified hexanediol di Chryrate (CD561, manufactured by Sartomer, molecular weight 358, ClogP value: 2.52), 3EO modified trimethylolpropane triacrylate (SR454, manufactured by Sartomer, molecular weight 429, ClogP value: 3.97), 6EO modified trimethylolpropane tri More preferred is acrylate (SR499, manufactured by Sartomer, molecular weight 560, ClogP value: 3.57).

  Content of the polymeric compound B is 10 mass% or more and less than 70 mass% with respect to the actinic-light curable inkjet ink total mass, More preferably, it is 20-50 mass%. When the content of the polymerizable compound B is 70% by mass or more, the amount of the polymerizable compound A having an acrylamide group is relatively small, and the adhesion to the recording medium is hardly increased. On the other hand, when the content of the polymerizable compound B is less than 10% by mass, the solubility of the gelling agent becomes unstable, and ink ejection tends to become unstable. Further, the flexibility of the printed image is not sufficiently increased, and the bendability of the printed matter is lowered.

Other Polymerizable Compound The actinic ray curable inkjet ink may further contain a photopolymerizable compound other than the polymerizable compound A and the polymerizable compound B. The other polymerizable compound can be a radical polymerizable compound.

  The other polymerizable compound may be a compound (monomer, oligomer, polymer, or mixture thereof) having a radically polymerizable ethylenically unsaturated bond. One type of other polymerizable compound may be contained in the actinic ray curable inkjet ink, or two or more types may be contained.

  Examples of other polymerizable compounds (compounds having an ethylenically unsaturated bond) include unsaturated carboxylic acids and their salts, unsaturated carboxylic acid ester compounds, unsaturated carboxylic acid urethane compounds, unsaturated carboxylic acid amide compounds and their Examples include anhydrides, acrylonitrile, styrene, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like.

  The other polymerizable compound is particularly preferably a (meth) acrylate monomer and / or oligomer or other polymerizable oligomer.

Examples of (meth) acrylate monomers and / or oligomers include, for example, isoamyl (meth) acrylate, behenyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) Acrylate, dodecyl (meth) acrylate, isooctyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, 2-acryloyloxyethyl succinic acid, 2- Acryloyloxyethylphthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, 2-ethylhexyl (meth) acrylate, 2-ethylhexyl-diglyco (Meth) acrylate, 2-hydroxybutyl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, N-vinylcaprolactam, dimethyl Aminoethyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) Acrylate, ethyl carbitol (meth) acrylate, benzyl acrylate, γ-butyrolactone (meth) acrylate, Morpholine (meth) acrylate, nonylphenol EO modified (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, t-butylcyclohexyl ( Monofunctional monomers such as (meth) acrylates;
1,4-butanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, 1,12-dodecanediol di (meth) acrylate, dimethylol- Bifunctional monomers such as tricyclodecane di (meth) acrylate, PO adduct diacrylate of bisphenol A, neopentyl glycol diacrylate hydroxypivalate, polytetramethylene glycol diacrylate;
PO-modified trimethylolpropane tri (meth) acrylate, PO-modified pentaerythritol tri (meth) acrylate, PO-modified pentaerythritol tetra (meth) acrylate, PO-modified dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate Trifunctional or more polyfunctional monomers such as glycerin propoxytri (meth) acrylate, caprolactone-modified trimethylolpropane tri (meth) acrylate, caprolactam-modified dipentaerythritol hexa (meth) acrylate;
And oligomers thereof.

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

Gelling agent The actinic ray curable inkjet ink of the present invention contains a gelling agent. Therefore, the ink undergoes a sol-gel phase transition reversibly depending on the temperature. The sol-gel phase transition referred to in the present invention is a solution state having fluidity at a high temperature, but when cooled below the gelation temperature, the entire liquid is gelled and changes to a state in which the fluidity is lost. It refers to the phenomenon of returning to a fluid liquid state when heated above.

In the present invention, gelation means forming any of the following structures.
1) Lamella structure 2) Polymer network structure formed by non-covalent bond or hydrogen bond 3) Polymer network structure formed by physical aggregation state 4) Interaction such as aggregation structure of fine particles or precipitated microcrystal A structure in which substances lose their independent movements due to the interaction of, for example, gel, that is, a gel indicates a solidified, semi-solidified, or thickened state with a sudden increase in viscosity or elasticity. On the other hand, the sol means a state in which the interaction formed by the gelation is eliminated and the liquid has fluidity.

  When the ink that has landed on the recording medium is gelled, coalescence between adjacent dots is suppressed, and image quality is improved. Further, when the ink gels, it becomes difficult for oxygen to diffuse into the ink droplets. Therefore, the photopolymerization of the photopolymerizable compound is less likely to be inhibited by oxygen and the curability of the ink is increased.

  The amount of gelling agent added to the actinic ray curable inkjet ink in the present invention is 0.5% by mass or more and less than 10% by mass, more preferably 1% by mass or more and less than 6% by mass with respect to the total mass of the ink. When the actinic ray curable inkjet ink contains two or more kinds of gelling agents, the total amount of the gelling agents is preferably in the above range.

  When the content of the gelling agent is less than 0.5% by mass, the actinic ray curable inkjet ink may not sufficiently undergo sol-gel phase transition. On the other hand, if the content of the gelling agent exceeds 10% by mass, the solubility of the gelling agent becomes unstable, and ink ejection tends to become unstable.

  The gelling agent contained in the actinic ray curable ink jet may be either a wax or a hydrogen bonding gelling agent, but is preferably a wax from the viewpoint of sol-gel phase transition, and is particularly photopolymerizable. From the viewpoint of compatibility with the compound, a wax having a polar group in the molecule is preferable.

About Wax In the present invention, “wax” refers to an organic substance that is solid at room temperature and becomes liquid when heated. The melting point of the wax is preferably 30 ° C. or higher and lower than 150 ° C. The wax contained in the actinic radiation curable ink-jet ink is at least 1) dissolved in the photopolymerizable compound at a temperature higher than the gelation temperature, and 2) crystallized in the ink at a temperature lower than the gelation temperature. ,is necessary.

  When the wax is crystallized in the ink, it is preferable to form a space three-dimensionally surrounded by plate crystals which are crystallized wax, 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 a card house structure, it is preferable that the photopolymerizable compound and the wax are compatible. On the other hand, when the photopolymerizable compound and the wax are phase-separated, it may be difficult to form a card house structure.

  The type of wax is not particularly limited. Preferred examples of the wax include dibehenyl ketone, distearyl ketone, dipalmityl ketone, dimyristyl ketone, dilauryl ketone, palmityl stearyl ketone, stearyl behenyl ketone, 18-Pentriacontanon (for example, a reagent manufactured by Alfa Aeser), ketone Aliphatic ketone compounds such as wax (for example, Kao Wax T1 manufactured by Kao Corporation); behenyl behenate (for example, Unistar M-2222SL manufactured by NOF Corporation), stearyl stearate (for example, EXPARAL SS manufactured by Kao Corporation), cetyl palmitate (For example, Amreps PC, manufactured by Higher Alcohol Industry Co., Ltd.), aliphatic models such as palmitic acid stearate, myristyl myristate, lauryl laurate, myricyl serinate, and behenyl montanate. Ester compounds; petroleum waxes such as paraffin wax, microcrystalline wax and petrolactam; plant waxes such as candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and jojoba ester; beeswax; Animal waxes such as lanolin and whale wax; mineral waxes such as montan wax and hydrogenated wax; hardened castor oil or hardened castor oil derivatives; montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives or polyethylene wax derivatives, etc. Modified wax; higher fatty acids such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid; stearyl alcohol, behenyl alcohol Higher alcohols such as coal; hydroxystearic acid such as 12-hydroxystearic acid; 12-hydroxystearic acid derivatives; lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, 12- Fatty acid amides such as hydroxystearic acid amide (eg Nikka Amide series manufactured by Nippon Kasei Co., Ltd. ITOHWAX series manufactured by Ito Oil Co., Ltd., FATTYAMID series manufactured by Kao Co., Ltd.); N-stearyl stearic acid amide, N-oleyl palmitic acid amide N- Substituted fatty acid amides; special fatty acid amides such as N, N′-ethylenebisstearylamide, N, N′-ethylenebis-12-hydroxystearylamide, and N, N′-xylylenebisstearylamide; dodecylamine, tetradecyl Ami Or higher amines such as octadecylamine; polyhydric alcohol fatty acid esters such as glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, polyoxyethylene fatty acid ester (for example, EMALLEX series manufactured by Nihon Emulsion Co., Ltd., RIKEN VITAMIN CO., LTD.) Riquemar series manufactured by Riken Vitamin Co., Ltd. Poem series, etc.); Esters of sucrose fatty acids such as sucrose stearic acid and sucrose palmitic acid (for example, Ryoto Sugar Ester series manufactured by Mitsubishi Chemical Foods); polyethylene wax, α-olefin Synthetic waxes such as maleic anhydride copolymer wax (such as UNILIN series manufactured by Baker-Petrolite); dimer acid; dimer diol (CRO DA's PRIPOR series, etc.).

  Only one kind of these waxes may be contained in the actinic ray curable inkjet ink, or two or more kinds thereof may be contained. Commercially available waxes are often a mixture of two or more types of waxes. Therefore, commercially available wax may be used after separation and purification as necessary.

  As described above, the wax preferably has a polar group in the molecule. The polar group is preferably a ketone group, —OH group, carboxyl group, amide group, carbonyl group, ester bond or the like. In particular, the wax is preferably an aliphatic ketone compound, an aliphatic monoester compound, a higher fatty acid, a fatty acid amide, a higher alcohol, or a polyhydric alcohol fatty acid ester, and is an aliphatic ketone compound or an aliphatic monoester compound. More preferably. In waxes containing protons in the polar group, the polar group may form hydrogen bonds with the acrylamide group, and the solubility of the wax may become excessively high. For this reason, in the ink droplet after landing on the recording medium, precipitation of the gelling agent is hindered, and the sol-gel phase transition may not be sufficiently performed. In contrast, with a wax having a ketone group or an ester group (aliphatic ketone compound or aliphatic monoester compound), the gelling agent tends to precipitate in the ink droplets after landing on the recording medium, and the sol-gel phase transition is sufficient. Is done.

Regarding the hydrogen bonding gelling agent The gelling agent may be a hydrogen bonding gelling agent. In the present invention, the “hydrogen bonding gelling agent” refers to a compound that forms a fibrous metastable structure by intermolecular hydrogen bonding in ink and gels by encapsulating a solvent in the network of the fiber structure. .

  Examples of hydrogen bonding gelling agents include 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; glyceryl behenate; Sunpolyglyceryl (Nomshin Eulio Co., Ltd. Nomucoat series, etc.); N-lauroyl-L-glutamic acid dibutylamide, N- (2-ethylhexanoyl) -L-glutamic acid dibutylamide and other amide compounds (available from Ajinomoto Fine Techno) ); 1,3: 2,4-bis-O-benzylidene-D-glucitol (Gelol D available from Shin Nippon Chemical Co., Ltd.) and the like; JP-A 2005-126507, JP-A 2005-255821 Gazette and JP 2010-1111790 It includes the like; low molecular oil-gelling agents described.

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.

  The content of the photopolymerization initiator in the actinic ray curable ink-jet ink is preferably 0.01% by mass to 10% by mass, although it depends on the type of actinic ray or photopolymerizable compound.

  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 Electronics Materials Study 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.

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

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

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

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

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

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

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

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

  The 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 pigment may be dispersed in a solvent or the like, but is more preferably dispersed in the aforementioned photopolymerizable compound (particularly a monomer having a low viscosity).

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

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.

Organic solvent The actinic ray curable inkjet ink may contain water or an organic solvent as necessary. When the organic solvent is contained in the ink, effects such as easy penetration of the ink into the recording medium can be obtained.

  Examples of the organic solvent include, for example, glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, 1,3-butanediol, 2,3-butanediol, 2-ethyl-2- Methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 2,2, Alkanediols (polyhydric alcohols) such as 4-trimethyl-1,3-pentanediol; sugar alcohols; alkyl alcohols having 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, isopropanol; ethylene glycol monomethyl ether , Ethylene glycol monoethyl ether, ethylene glycol Monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether , Ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether , Propylene glycol mono- -Propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether, Glycol ethers such as tripropylene glycol monomethyl ether; and the like. These can be used individually by 1 type or in combination of 2 or more types.

-Physical property of actinic-light curable inkjet ink Actinic-light curable inkjet ink is an ink which reversibly changes sol-gel phase with temperature as described above. Since the sol-gel phase transition type actinic ray curable ink is a sol at a high temperature (for example, about 80 ° C.), it can be ejected from an ink jet 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 discharge property of the sol-gel phase transition type ink, it is preferable that the viscosity of the ink at a high temperature is not more than a certain level. Specifically, the actinic ray curable inkjet ink preferably has a viscosity at 80 ° C. of 3 to 20 mPa · s. On the other hand, in order to suppress coalescence of adjacent dots, it is preferable that the viscosity of the ink at normal temperature after landing is a certain level or more. Specifically, the viscosity at 25 ° C. of the actinic ray curable inkjet ink is preferably 1000 mPa · s or more.

  The gelation temperature of the sol-gel phase transition ink is preferably 40 ° C. or higher and 70 ° C. or lower, and more preferably 50 ° C. or higher and 65 ° C. or lower. When the ink discharge temperature is in the vicinity of 80 ° C., if the gelation temperature of the ink exceeds 70 ° C., gelation tends to occur at the time of discharge, and the discharge performance is lowered. On the other hand, if the gelation temperature is less than 40 ° C., it is difficult to quickly gel after landing on the recording medium. The 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 sol-gel phase transition type 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 (1 / 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 is a temperature at which the viscosity changes greatly in the temperature change curve of the viscosity. For example, the gelation temperature can be a temperature at which the viscosity becomes 200 mPa · s.

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

-Preparation method of actinic ray curable inkjet ink Actinic ray curable inkjet ink is prepared by heating the above-mentioned photopolymerizable compound, gelling agent, photopolymerization initiator, colorant, and each optional component under heating. It can obtain by mixing in. It is preferable to filter the obtained liquid mixture with a predetermined filter.

[Image forming method]
The image forming method of the present invention is not particularly limited, but 1) a step of discharging the actinic radiation curable inkjet ink onto a recording medium, and 2) irradiating the ink landed on the recording medium with actinic rays to cure the ink. It is preferable to include the process.

1) Process The above-mentioned actinic ray curable inkjet ink accommodated in the inkjet recording head is ejected as droplets toward the recording medium through the nozzle. At this time, the temperature of the inkjet ink accommodated in the ejection recording head is set to a temperature at which the gelling agent does not precipitate. That is, the temperature is such that the saturated dissolution amount of the gelling agent in the ink is greater than the amount of the gelling agent contained in the ink.

  In order to improve the ejection property of the ink droplets, it is preferable to set the temperature of the inkjet ink in the inkjet recording head to a temperature that is 10 to 30 ° C. higher than the gelation temperature. When the ink temperature in the ink jet recording head is less than (gelation temperature + 10) ° C., the ink gels in the ink jet recording head or on the nozzle surface, and the discharge property of ink droplets is likely to deteriorate. On the other hand, when the temperature of the ink in the ink jet recording head exceeds (gelation temperature + 30) ° C., the ink becomes too hot and the ink component may deteriorate.

  It is preferable to discharge the ink jet ink droplets at a predetermined temperature by heating the ink jet recording head, the ink flow path connected to the ink jet recording head, or the ink tank connected to the ink flow path.

  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, it becomes difficult for oxygen to diffuse into the ink droplets. Therefore, in the step 2) described later, the photopolymerization of the photopolymerizable compound is less likely to be inhibited by oxygen, and the curability of the ink is increased, so that even a low light source such as an LED can be sufficiently cured.

  The temperature of the recording medium when the ink droplets land is preferably set to a temperature that is 10 to 20 ° C. lower than the gelation temperature of the ink. If the temperature of the recording medium is too low, the 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 may be mixed together. By appropriately adjusting the temperature of the recording medium, it is possible to achieve appropriate leveling and appropriate pinning so that adjacent dots of ink droplets do not mix with each other.

  The 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 and a vinyl chloride film.

  The conveyance speed of the recording medium is preferably 30 to 120 m / min. The higher the conveyance speed, the higher the image forming speed, which is preferable. However, when the conveyance speed is too high, the image quality is deteriorated or the ink is not sufficiently cured.

2) Step By irradiating the ink landed on the recording medium with an actinic ray, the photopolymerizable compound contained in the ink droplet is crosslinked or polymerized to cure the ink droplet.

  The active light to be irradiated may be appropriately selected depending on the type of the photopolymerizable compound, and may be ultraviolet rays or electron beams. As an ultraviolet light source, a metal halide lamp or the like may be used. However, by using an LED as a light source, it is possible to suppress dissolution of the ink droplet surface by the radiant heat of the light source.

Light from the LED light source preferably has a peak irradiance 1.0~10W / cm ² in the wavelength 370～410Nm, it is more preferable peak irradiance is 1~5W / cm ^2. The peak illuminance is the illuminance on the surface of the recording medium. The conveyance speed of the recording medium during light irradiation is preferably 30 to 120 m / min. The higher the conveyance speed, the less the influence of radiant heat, and the higher the image forming speed, which is preferable. However, if the conveying speed is too high, photocuring may be insufficient.

  During irradiation with actinic rays, the temperature of the recording medium can be arbitrarily adjusted. The temperature of the recording medium in the ejection process and the temperature of the recording medium in the curing process are not necessarily the same, and may be controlled independently.

Inkjet recording apparatus An actinic ray curable inkjet recording apparatus is described. 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.

  1A and 1B are diagrams illustrating an example of a configuration of a main part of a line recording type inkjet recording apparatus. Among these, FIG. 1A is a side view, and FIG. 1B is a top view. As shown in FIGS. 1A and 1B, the inkjet recording apparatus 10 includes a head carriage 16 that accommodates a plurality of inkjet recording heads 14 and the entire width of the recording medium 12, and the head carriage 16 (the recording medium conveyance direction). ) An actinic ray irradiation unit 18 disposed on the downstream side, and a temperature control unit 19 (19a and 19b) disposed on the lower surface of the recording medium 12.

  The head carriage 16 is connected to an ink tank 31 that stores ink via an ink flow path 30. 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 ejection recording heads 14 are arranged so as to be shifted with respect to the conveyance direction of the recording medium 12. do it. 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 actinic ray 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 recording medium conveyance direction. The actinic ray irradiation unit 18 irradiates the droplets ejected by the inkjet recording head 14 and landed on the recording medium 12 with actinic rays to cure the droplets.

When the actinic ray is ultraviolet ray, examples of the actinic ray irradiating unit 18 (ultraviolet ray irradiating means) include a fluorescent tube (low pressure mercury lamp, germicidal lamp), a cold cathode tube, an ultraviolet laser, and an operating pressure of several hundred Pa to 1 MPa. These include low pressure, medium pressure, high pressure mercury lamps, metal halide lamps and LEDs. From the viewpoint of curability, ultraviolet irradiation means for irradiating ultraviolet rays having an illuminance of 100 mW / cm ² or more; specifically, a high-pressure mercury lamp, a metal halide lamp, and an LED are preferable. The ultraviolet irradiation means is particularly preferably an LED from the viewpoint of low power consumption and low radiant heat. Specific examples of the LED that is the ultraviolet irradiation means include 395 nm, water-cooled LED, etc. manufactured by Phoseon Technology.

  When the actinic ray is an electron beam, examples of the actinic ray irradiating unit 18 (electron beam irradiating unit) include electron beam irradiating means such as a scanning method, a curtain beam method, and a broad beam method. Therefore, a curtain beam type electron beam irradiation means is preferable. Examples of the electron beam irradiation means include “Curetron EBC-200-20-30” manufactured by Nissin High Voltage Co., Ltd., “Min-EB” manufactured by AIT Co., Ltd., and the like.

  The temperature control unit 19 (19a and 19b) 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 recording method using the line recording type inkjet recording apparatus 10 will be described. The recording medium 12 is conveyed between the head carriage 16 of the inkjet recording apparatus 10 and the temperature control unit 19a. On the other hand, the recording medium 12 is adjusted to a predetermined temperature by the temperature control unit 19a. Next, high-temperature ink is ejected from the ink jet recording head 14 of the head carriage 16 to adhere (land) on the recording medium 12. Then, the actinic ray irradiating unit 18 irradiates the ink droplets attached on the recording medium 12 with an actinic ray to cure.

  When the ink is ejected from the ink jet recording head 14, the temperature of the ink in the ink jet recording head 14 is set to a temperature that is 10 to 30 ° C. higher than the gelation temperature of the ink in order to improve the ink ejectability. It is preferable. If the ink temperature in the ink jet recording head 14 is less than (gelation temperature + 10) ° C., the ink gels in the ink jet recording head 14 or on the nozzle surface, and the ink ejection properties tend to decrease. On the other hand, when the temperature of the ink in the inkjet recording head 14 exceeds (gelling temperature + 30) ° C., the ink becomes too high, and the ink component may be deteriorated.

  The amount of droplets ejected from each nozzle of the inkjet recording head 14 is preferably 0.5 pl to 10 pl in order to form a high resolution image, although it depends on the resolution of the image. It is more preferably 1 pl to 4.0 pl.

  Irradiation of actinic rays from the actinic ray irradiating unit 18 is performed within 10 seconds after the ink droplets adhere on the recording medium, preferably from 0.001 second to prevent the adjacent ink droplets from coalescing. It is preferable to carry out within 5 seconds, more preferably within 0.01 second to 2 seconds. Irradiation with actinic rays is preferably performed after ink is ejected from all the inkjet recording heads 14 accommodated in the head carriage 16. At this time, the temperature of the recording medium 12 is appropriately adjusted by the temperature controller 19b. The temperature of the recording medium 12 at this time may be the same as or different from the temperature of the recording medium 12 at the time of ink ejection; that is, the temperature adjusted by the temperature control unit 19a.

  When the actinic ray is an electron beam, the acceleration voltage for electron beam irradiation is preferably 30 to 250 kV and more preferably 30 to 100 kV in order to perform sufficient curing. When the acceleration voltage is 100 to 250 kV, the electron beam irradiation amount is preferably 30 to 100 kGy, and more preferably 30 to 60 kGy.

  The total film thickness of the image after ink curing is preferably 2 to 25 μm. The “total film thickness” is the maximum film thickness of the cured ink that has landed 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 includes a plurality of inkjet recording heads that are narrower than the entire width of the recording medium, instead of the head carriage 16 that is fixedly arranged so as to cover the entire width of the recording medium. 2 can be configured except that a head carriage 26 that accommodates the head 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, the head carriage 26 discharges ink from the inkjet recording head 24 accommodated in the head carriage 26 while moving in the width direction of the recording medium 12 along the guide portion 27. After the head carriage 26 has completely moved in the width direction of the recording medium 12 (for each pass), the recording medium 12 is fed in the transport direction. Thereafter, the active light irradiation unit 28 irradiates the active light. 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.

  In Examples and Comparative Examples, actinic ray curable inkjet inks were prepared with the following components (photopolymerizable compound, gelling agent, photopolymerization initiator, polymerization inhibitor, and pigment dispersion).

(Photopolymerizable compound)
Polymerizable compound A
N- (2-hydroxyethyl) acrylamide (manufactured by Tokyo Chemical Industry, molecular weight 115, ClogP value: -1.03)
N, N-diethylacrylamide (manufactured by Tokyo Chemical Industry, molecular weight 127, ClogP value: 0.89)
N-isopropylacrylamide (manufactured by Kojin Co., Ltd., molecular weight 113, ClogP value: 0.25)
Diacetone acrylamide (manufactured by Nippon Kasei Co., Ltd., molecular weight 169, ClogP value: 0.29)
N, N ′-(1,2-dihydroxyethylene) bisacrylamide (manufactured by Tokyo Chemical Industry, molecular weight 200, ClogP value: −3.00)
N- {3- [4- (3-acryloylamino-2-hydroxy-propoxy) -butoxy] -2-hydroxy-propyl} -acrylamide (molecular weight 344, ClogP: −2.09)

Polymerizable compound B
Polyethylene glycol diacrylate (NK ester A-400, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 508, EO unit amount 9, ClogP value: 0.47)
4EO-modified pentaerythritol tetraacrylate (SR494, manufactured by Sartomer, molecular weight 528, ClogP value: 2.28)
6EO-modified trimethylolpropane triacrylate (SR499, manufactured by Sartomer, molecular weight 560, ClogP value: 3.57)
Tripropylene glycol diacrylate (APG-200, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 300, Clog P value: 2.21)

Other polymerizable compounds 3PO modified trimethylolpropane triacrylate (Photomer 4072, manufactured by Cognis, molecular weight 471, Clog P value: 4.90)
1,9-nonanediol diacrylate (V # 260, manufactured by Osaka Organic Chemical Co., Ltd., molecular weight 268, Clog P value 5.22)

(Gelling agent)
Wax behenic acid (Lunac BA, manufactured by Kao Corporation, molecular weight 340, Clog P value: 10.1)
Palmitic acid amide (Diamid KP, Nippon Kasei Co., Ltd., molecular weight 255, ClogP value: 6.3)
Aliphatic ketone (Kao wax T1, manufactured by Kao Corporation, Clog P value of 15 or more)
Behenyl behenate (Unistar M-2222SL, NOF Corporation, Clog P value of 15 or more)
-Hydrogen bonding gelling agent N-lauroyl-L-glutamic acid dibutyramide (GP-1, Ajinomoto Co., Inc., molecular weight 439, ClogP value: 5.4)

(Photopolymerization initiator)
DAROCURE TPO (Ciba Specialty Chemicals)
(Polymerization inhibitor)
Irgastab UV10 (manufactured by Ciba Specialty Chemicals)

(Pigment dispersion)
-Preparation of pigment dispersion 1 (K: black) In a composition ratio shown below, a dispersant, a photopolymerizable compound, and a polymerization inhibitor are placed in a stainless beaker and heated on a hot plate at 65 ° C for 1 hour. The mixture was dissolved by heating and stirring. After cooling the obtained solution to room temperature, the following black pigment 1 was added, and it was put in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm and sealed. This was dispersed in a paint shaker for 5 hours. Thereafter, zirconia beads were removed to prepare Pigment Dispersion Liquid 1.

-Composition of Pigment Dispersion 1 Dispersant: Azisper PB824 (Ajinomoto Fine Techno Co., Ltd.) 9 parts by mass Photopolymerizable compound: Tripropylene glycol diacrylate (APG-200, Shin-Nakamura Chemical Co., Ltd., molecular weight 300, ClogP value 2. 21) 70 parts by mass Polymerization inhibitor: Irgastab UV10 (manufactured by Ciba Specialty Chemicals) 0.02 parts by mass Black pigment 1: Pigment Black 7 (manufactured by Mitsubishi Chemical Corporation, # 52) 21 parts by mass

-Preparation of pigment dispersion 2 Dispersant, photopolymerizable compound, and polymerization inhibitor were placed in a stainless beaker at the composition ratio shown below, and dissolved by heating and stirring for 1 hour while heating on a 65 ° C hot plate. I let you. The resulting solution was cooled to room temperature, then the following black pigment 1 was added, 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. Thereafter, zirconia beads were removed to prepare pigment dispersion 2.

-Composition of Pigment Dispersion 2 Dispersant: Azisper PB824 (Ajinomoto Fine Techno Co., Ltd.) 9 parts by weight Photopolymerizable compound: 1,9-nonanediol diacrylate (V # 260, Osaka Organic Chemical Co., Molecular weight 268, ClogP Value 5.22) 70 parts by mass Polymerization inhibitor: Irgastab UV10 (manufactured by Ciba Specialty Chemicals) 0.02 part by mass Black pigment 1: Pigment Black 7 (manufactured by Mitsubishi Chemical Corporation, # 52) 21 parts by mass

[Preparation of ink]
According to the composition described in Table 1 and Table 2, after mixing each component, the mixture was heated to 80 ° C. and stirred. The obtained solution was filtered through a # 3000 metal mesh filter under heating, and then cooled to prepare an ink. In Table 1 and Table 2, the unit of the blending amount of each component is mass%.

[Image formation]
The actinic ray curable inkjet ink was loaded into a line type inkjet recording apparatus. The temperature of the ink jet recording head of the ink jet recording apparatus was set to 80 ° C. As the ink jet recording head, a piezo head having a nozzle diameter of 20 μm and a nozzle number of 512 nozzles (256 nozzles × 2 rows, staggered arrangement, 1 row nozzle pitch 360 dpi) was used. The amount of one droplet was 2.5 pl, the droplet discharge speed was about 6 m / s, the resolution was 1440 dpi × 1440 dpi, and the recording speed was 500 mm / s. Image formation was performed in an environment of 23 ° C. and 55% RH. dpi represents the number of dots per 2.54 cm.

  A solid image of 5 cm × 5 cm was printed on a PET (polyethylene terephthalate) film subjected to corona treatment immediately before printing from an ink jet recording apparatus. After the image was formed, the ink was cured by irradiating the image with ultraviolet light using an LED lamp (395 nm manufactured by Phoseon Technology, water-cooled LED) disposed in the downstream portion of the recording apparatus. The integrated light quantity during irradiation was 200 mJ.

[Image Evaluation]
(Evaluation of density unevenness)
The density unevenness of the solid image of 5 cm × 5 cm printed on the PET film was visually confirmed. Evaluation was performed according to the following criteria. The results are shown in Tables 1 and 2.
○: Observed from a position 15 cm away, no density unevenness is observed in the image Δ: Observed from a position 15 cm away, density unevenness is observed in a part of the image, but from the position 30 cm away, the density unevenness is observed X: Observed from a position 30 cm away, density unevenness is observed in the image

(Evaluation of adhesion)
A 3M cellophane tape was adhered to a 5 cm × 5 cm solid image printed on a PET film and peeled off. The adhesion between the PET film and the image at this time was evaluated based on the following criteria. The results are shown in Tables 1 and 2.
○: No peeling of the image film Δ: Part of the image film is peeled ×: Most of the image film is peeled off

(Scratch resistance evaluation)
A solid image of 5 cm × 5 cm printed on a PET film was rubbed with a nail, and the scratch resistance of the image was evaluated based on the following criteria. The results are shown in Tables 1 and 2.
◎: The image film is not peeled off even when rubbed with a strong force. ◯: The image film is peeled off when rubbed with a strong force. △: The entire image film is peeled off when rubbed with a strong force. Does not peel off when rubbed with weak force ×: The entire image film is easily peeled off even when rubbed with weak force

(Evaluation of bending resistance)
The printed part of a solid image of 5 cm × 5 cm printed on a PET film was folded in half, and bending resistance was evaluated according to the following criteria. The results are shown in Table 1.
○: Image film is not cracked △: Fracture is thin and cracked ×: Image film is cracked at the folded part

[Evaluation of ejection stability]
Ink was ejected from the ink jet head of the ink jet recording apparatus loaded with each ink. At this time, the presence or absence of nozzle missing and discharge bending was visually observed and evaluated based on the following criteria. The results are shown in Tables 1 and 2.
○: No nozzle missing was observed Δ: Nozzle missing was observed in 1 to 4 nozzles in all nozzles 512 ×: Nozzle missing was observed in 5 or more nozzles in all nozzles 512 The

As shown in Table 2, when the polymerizable compound A was not included (Comparative Example 1), the adhesion between the recording medium and the formed image was low. Furthermore, the scratch resistance was low.
On the other hand, when the polymerizable compound B was not included (Comparative Example 2), density unevenness was slightly generated, and ink ejection stability was further reduced. Since the polymerizable compound B is not contained, the gelling agent is hardly dissolved, and it is assumed that the gelling agent is precipitated in the sol-like ink.
Moreover, when the quantity of the polymeric compound A exceeded 70% (comparative example 2), the coating film became hard and the bending tolerance of the coating film fell.

  Furthermore, when the gelling agent was not included (Comparative Example 3), the ink after landing on the recording medium could not be pinned, resulting in density unevenness. Moreover, when the gelling agent was not included, the adhesion of the coating film was also low. This is presumed that because the viscosity of the ink landed on the recording medium was low, oxygen easily diffused into the ink, and photopolymerization of the photopolymerizable compound was inhibited by oxygen.

  On the other hand, as shown in Tables 1 and 2, when a predetermined amount of the gelling agent, the polymerizable compound A, and the polymerizable compound B are included (Examples 1 to 12), the ink is generally stable. The coating film was excellent in bending resistance and adhesion, and density unevenness was hardly generated in the image. In particular, when the gelling agent was an aliphatic ketone compound or an aliphatic monoester compound (Examples 4 to 6), the scratch resistance was good. Further, when the gelling agent is an aliphatic ketone compound or an aliphatic monoester compound, the scratch resistance is good. Since the ink has sufficiently undergone sol-gel phase transition, oxygen is not diffused within the ink droplets, and it is surmised that the photopolymerization has been sufficiently performed to increase the curing density.

  On the other hand, when the amount of the polymerizable compound A was 50% by mass or more based on the total mass of the ink (Examples 7 and 8), the adhesion was slightly lowered. Furthermore, the coating film became hard and the bending resistance slightly decreased.

  Further, when the amount of the polymerizable compound B was less than 10% by mass with respect to the total mass of the ink (Example 8), the ejection stability was slightly lowered. It is inferred that the amount of the polymerizable compound B was small and the gelling agent was hardly compatible.

  On the other hand, when the amount of the polymerizable compound A was less than 5% by mass with respect to the total mass of the ink (Example 9), the adhesion between the recording medium and the printed image was somewhat low, and the scratch resistance was also reduced. At this time, since the amount of the polymerizable compound B exceeded 70% by mass with respect to the total mass of the ink, the gelling agent hardly deposited in the ink landed on the recording medium, and density unevenness was slightly generated.

  When the amount of the gelling agent was 6.0% by mass or more (Example 10), the ejection stability of the ink was slightly lowered. It is inferred that the gelling agent amount was excessive and the dissolution stability in the ink was lowered.

  Furthermore, when the gelling agent was a hydrogen bonding gelling agent (Example 11), some unevenness in density occurred. The hydrogen bonding gelling agent is presumed to be slightly inferior in the pinning property of the ink as compared with the wax (for example, Example 1).

Even when the molecular weight of the polymerizable compound A was as large as 645 (Example 12), good adhesion, scratch resistance and bending resistance were obtained, but the discharge stability was slightly deteriorated.
This application is accompanied by a priority claim based on a Japanese patent application previously filed by the same applicant, ie, Japanese Patent Application No. 2012-102768 (filing date: April 27, 2012). The contents of which are incorporated herein as part of the present invention.

  In the actinic ray curable inkjet ink of the present invention, ink droplets after landing on a recording medium are difficult to coalesce. Further, the adhesion between the cured image and the recording medium is good. Therefore, it is suitable for production of various printed materials.

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

Claims (8)

An actinic ray curable inkjet ink comprising a gelling agent, a photopolymerizable compound, and a photopolymerization initiator, and reversibly sol-gel phase transition with temperature,
The gelling agent content is 0.5% by mass or more and less than 10% by mass with respect to the total mass of the ink,
The photopolymerizable compound is
1) ClogP is in the range of -4.0 to less than 1.0, and the polymerizable compound A having a (meth) acrylamide group in the molecule is 5% by mass or more and less than 50% by mass with respect to the total mass of the ink . And 2) ClogP is in the range of -1.0 or more and less than 4.0, the molecular weight is 300 or more and less than 800 , and the polymerizable compound B having a (meth) acrylate group in the molecule is added to the total mass of the ink. An actinic ray curable inkjet ink containing 10% by weight or more and less than 70% by weight .   The actinic ray curable inkjet ink according to claim 1, wherein the polymerizable compound B has two or more (meth) acrylate groups. The polymerizable compound B comprises 3 or more and less than 25 the structure represented by in the molecule _{(-CH 2} -CH 2 -O-), actinic radiation curable inkjet ink according to claim 1 or 2. The actinic ray curable inkjet ink according to any one of claims 1 to 3, wherein the polymerizable compound B has a ClogP value of 0 or more and less than 3.6. The actinic ray curable inkjet ink according to claim 1, wherein the gelling agent is contained in an amount of 1% by mass or more and less than 6% by mass with respect to the total mass of the ink. The actinic ray curable inkjet ink according to any one of claims 1 to 5, wherein the gelling agent is a wax having a polar group in a molecule. The gelling agent is any one or more selected from the group consisting of an aliphatic ketone compound, an aliphatic monoester compound, a higher fatty acid, a higher alcohol, a fatty acid amide, and a polyhydric alcohol fatty acid ester . The actinic ray curable inkjet ink according to any one of the above. A step of causing ink droplets of the actinic radiation curable inkjet ink according to any one of claims 1 to 7 to be ejected from an inkjet recording head and adhered onto a recording medium;
Irradiating the ink droplets landed on the recording medium with an actinic ray from an LED light source to cure the ink droplets.

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