JP2013147023A - Image forming method using active energy ray-curable inkjet ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality image that is high definition, and reduced in concave and convex impression by injecting the active energy ray-curable inkjet ink that is hard to receive an environmental influence such as inhibition of polymerizations by the oxygen by the liquid droplet.SOLUTION: An image forming method contains: a step to inject a droplet of an active energy ray-curable inkjet ink which contains two or more kinds of polymerizable monomers having unsaturated bonds by the size of 0.1-12 pl to reach a recording medium; and a step to irradiate the droplet reached to the recording medium with an active ray to be cured. In the image forming method, the difference of a maximum value X and minimum value Y is 0.24 or more and 0.46 or less when assuming the maximum value of the charge of the carbon atom that composes an unsaturated bond as X and the minimum value of the charge of the carbon atom that composes an unsaturated bond as Y out of the two kinds of polymerizable monomers included in the inkjet ink, and viscosityof the inkjet ink at 25°C is 20-500 mPa.

Description

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

  In recent years, inkjet recording methods have been used in various printing fields such as photographs, various printing, marking, and special printing such as color filters from the viewpoint of being able to create images easily and inexpensively. An example of an ink jet ink used in the ink jet recording method is an aqueous ink jet ink containing water as a main solvent. In addition, non-volatile inkjet solvents that do not volatilize at room temperature are mainly oil-based inkjet inks that do not substantially contain water, non-aqueous inkjet inks that do not substantially contain water that volatilizes at room temperature, and solid inks heat and melt at room temperature. There is hot melt ink that prints. Furthermore, there are active energy ray-curable inkjet inks that are cured by an actinic ray such as ultraviolet rays after printing, and they are properly used depending on the application.

  Among these, the active energy ray-curable ink-jet ink has a fast curing property and can print on a wide variety of recording media. Therefore, it has been attracting attention as a next-generation inkjet ink that replaces water-based inkjet ink, oil-based inkjet ink, and non-aqueous inkjet ink, which have a large drying load and the recording medium is limited.

  As means for improving the image quality of the ink jet recording method, a substrate (for example, a water-based ink absorbing substrate) for stabilizing the dot diameter of the ejected ink is selected, a dark ink set is used, It is conceivable to reduce the droplet size. In the ink jet recording system using the active energy ray curable ink jet ink, the base material cannot be limited. Therefore, it is preferable to improve the image quality by using a dark or light ink or by reducing the ink droplet size.

  With the recent development of ink jet, the nozzle of the head can be made small, and ejection of a droplet size of less than 2 pl is possible. For this reason, attempts have been made to form an image by ejecting several pl droplets even in the active energy ray-curable inkjet ink.

  Active energy ray-curable ink-jet inks are mainly classified into radical polymerization types and cationic polymerization types. Radical polymerization type ink-jet inks are widely researched and developed and put to practical use because they have a wide range of material choices and a high degree of freedom in ink design. However, radical polymerization inks are susceptible to polymerization inhibition by oxygen. When the droplet size is reduced, the sensitivity is greatly reduced due to further polymerization inhibition by oxygen. As a result, blurring between uncured inks occurs, resulting in problems such as deterioration in image quality, residual unreacted monomer and a monomer odor, and inability to obtain solvent resistance and scratch resistance.

  As a technique for suppressing oxygen inhibition of the radical polymerization type ink, it is conceivable to increase the illuminance of the nitrogen purge or the light source. However, these means cause problems such as an increase in the size of the apparatus, heat generation of the light source, an increase in the cost of the apparatus, and restriction on the use of a substrate that is vulnerable to heat. In addition, methods have been proposed to increase the amount of polymerization initiator and attempt to increase sensitivity, but there are problems such as residual polymerization initiator, precipitation during low-temperature storage, and poor curing with a low illuminance light source (Patent Document) 1).

  On the other hand, the cationic polymerization type ink-jet ink is not affected by the inhibition of polymerization by oxygen, but the polymerization reaction is inhibited by the influence of humidity. For this reason, when the droplet size is reduced to improve the image quality, the sensitivity is greatly reduced particularly under high humidity (see Patent Document 2).

  In addition, an attempt has been made to apply a charge transfer complex polymerization compound (referred to as a CT polymerization compound) as a new polymerization method to a polymerization monomer of an active energy ray-curable composition (for example, Non-Patent Document 1). reference). Furthermore, it is also proposed to CT polymerize a monomer composition containing a combination of an electron-rich monomer (donor monomer) such as vinyl ether and an electron-deficient monomer (acceptor monomer) such as maleimide (Patent Documents 3 and 4). See).

  In the advertising industry, output products to be used (large format signs, product labels, etc.) are placed outdoors for a long period of time, so that weather resistance of images is required to prevent image fading. As a base material for these output materials, a heat-sensitive plastic film or vinyl chloride is often used. However, when an image having weather resistance is formed on such a substrate, if the light irradiation during ink curing is increased, the substrate is curled due to thermal damage.

  In order to form an image having weather resistance on a heat-sensitive substrate, the light irradiation to the ink is required to have a low illuminance and a low integrated light amount. However, radical polymerization and cationic polymerization ink jet inks that are susceptible to polymerization inhibition due to oxygen, humidity, etc. cannot obtain images with weather resistance when the light irradiation during image formation is low illuminance and low integrated light quantity. There was a problem (see Patent Document 5).

JP 2005-154537 A JP 2005-144790 A Japanese Patent No. 3353020 Japanese Patent Laid-Open No. 11-124403 JP 2009-263603 A

Sonny Jonsson, et.al, Polymer Materials Sci. & Enginer. 1995, 72, 470-472

The first object of the present invention is to eject active energy ray-curable inkjet ink that is not easily affected by the environment, such as polymerization inhibition by oxygen, in small droplets, resulting in high definition and high quality with reduced unevenness. Is to provide a good image. Furthermore, the irradiation amount of active energy for curing the ink is reduced.
The second object of the present invention is to use an actinic radiation energy ray curable inkjet ink that is not susceptible to polymerization inhibition due to oxygen, humidity, etc., even when light irradiation during image formation has a low illuminance and a low integrated light amount. It is to provide an image having weather resistance. Thereby, the thermal damage to the heat-sensitive substrate can be reduced, and curling of the substrate is suppressed.

The present invention relates to the following contents.
[1] A step of ejecting droplets of an active energy ray-curable inkjet ink containing two or more polymerizable monomers having an unsaturated bond in a size of 0.1 to 12 pl and landing on a recording medium; Irradiating an actinic ray to a droplet landed on a recording medium and curing it, and an image forming method comprising:
Among the two or more kinds of polymerizable monomers contained in the inkjet ink, when the maximum value X of the charge of the carbon atom constituting the unsaturated bond and the minimum value Y of the charge of the carbon atom constituting the unsaturated bond are set, The image forming method, wherein the difference between the maximum value X and the minimum value Y is 0.24 or more and 0.46 or less, and the viscosity of the inkjet ink at 25 ° C. is 20 to 500 mPa.
[2] The ink droplet that has landed on the recording medium is irradiated with the actinic ray with an integrated light amount of 200 mJ / cm ² or less within 0.001 to 1.0 seconds after landing. Image forming method.
[3] The image forming method according to [1] or [2], wherein an illuminance of the actinic ray is 5 W or less.
[4] The image forming method according to any one of [1] to [3], wherein the active light is light using an LED as a light source.
[5] The image forming method according to any one of [1] to [4], wherein droplets of the active energy ray-curable inkjet ink are ejected in a size of 0.1 to 4 pl.
[6] The image forming method according to any one of [1] to [5], wherein the inkjet ink has a surface tension at 25 ° C. of 15 mN / m or more and less than 35 mN / m.
[7] The image forming method according to any one of [1] to [6], which is performed by a serial head type inkjet recording apparatus.
[8] The image forming method according to any one of [1] to [6], which is performed by a line head type ink jet recording apparatus.

According to the present invention, it is possible to provide a high-quality image with high definition and reduced unevenness. In addition, since the ink can be cured with a light source with low illuminance, the system can be made compact and energy saving.
ADVANTAGE OF THE INVENTION According to this invention, the image which has a weather resistance can be provided, without giving a heat damage also to the base material weak to a heat | fever.

1 is a front view illustrating an example of a configuration of a main part of a serial head type inkjet recording apparatus according to the present invention. FIG. 2 is a top view illustrating an example of a configuration of a main part of the line head type ink jet recording apparatus of the present invention.

Hereinafter, the present invention will be described with reference to embodiments, but the present invention is not limited to the following embodiments.
The image forming method according to the embodiment includes: 1) a step of ejecting droplets of an active energy ray-curable inkjet ink and landing on the recording medium; and 2) irradiating the droplets landing on the recording medium with actinic rays. And curing.

About the active energy ray-curable inkjet ink The active energy ray-curable inkjet ink contains two or more polymerizable monomers. Two or more kinds of polymerizable monomers each have an unsaturated bond (usually a carbon-carbon double bond).

  Two or more kinds of polymerizable monomers contained in the active energy ray-curable inkjet ink each have an unsaturated bond. Among the two or more kinds of polymerizable monomers, the polymerizable monomer having the maximum charge of the carbon atom constituting the unsaturated bond is referred to as “a monomer having a high electron density”. Among two or more kinds of polymerizable monomers, a polymerizable monomer having a minimum charge of carbon atoms constituting an unsaturated bond is referred to as “a monomer having a low electron density”. When the charge of the carbon atom constituting the unsaturated bond of the “monomer having a high electron density” is defined as charge X, and the charge of the carbon atom constituting the unsaturated bond of the “monomer having a low electron density” is defined as charge Y, the charge X And the charge Y is set to be 0.24 or more and 0.46 or less.

  The charge of the carbon atom constituting the unsaturated bond in the polymerizable monomer means an atomic charge in the ground state obtained by calculation based on the molecular orbital theory. The charge on the carbon atom of the unsaturated bond in the ground state of the polymerizable monomer can be obtained by calculation using a computer. In the present invention, SPARTAN'08 for Windows (registered trademark) which is molecular orbital calculation software can be used, and the calculation method can be Equilibrium Geometry at Ground state with Hartree-Fock 3-21G in Vacuum. The value of the charge is Natural atomic charge.

  The “carbon constituting the unsaturated bond” in the monomer having a low electron density means a carbon having a larger charge value out of two carbons on the unsaturated bond to which the electron attractive group is bonded. The “carbon constituting the unsaturated bond” in the monomer having a high electron density means a carbon having a smaller charge value out of two carbons on the unsaturated bond to which the electron donating group is bonded. When a plurality of unsaturated bonds are present in one molecule of the polymerizable monomer, “carbon constituting the unsaturated bond” means an average value of electric charges of carbon constituting each unsaturated bond.

  If the difference between the charge X and the charge Y is 0.24 or more, CT polymerization tends to occur. Further, if the difference between the charge X and the charge Y is 0.46 or less, the charge transfer complex is not excessively stabilized, and the polymerization rate is sufficiently high.

  In order to increase the difference between the charge X and the charge Y, a monomer having an excessively high unsaturated bond electron density or a monomer having an excessively low unsaturated bond electron density must be used. A monomer having an excessively high electron density is susceptible to hydrolysis in the presence of an acid, and polymerization is also likely to occur. On the other hand, a monomer having an excessively low electron density is susceptible to hydrolysis in the presence of an alkali (base). Therefore, an ink combining a monomer having an excessively high electron density and a monomer having an excessively low electron density may be easily deteriorated by both acid and alkali.

  In the present embodiment, the active energy ray-curable inkjet ink contains at least two polymerizable monomers having an unsaturated bond, and the difference between the charge X and the charge Y is appropriately adjusted. High stability (high sensitivity) and excellent stability (for example, viscosity stability) when the ink is stored for a long period of time.

<Monomer with low electron density>
The monomer having a low electron density in the present embodiment is a monomer having an electron-deficient unsaturated bond. The value of the atomic charge of the carbon atom constituting the unsaturated bond in the monomer having a low electron density is preferably −0.3 or more, more preferably −0.28 or more.

In the inkjet ink according to the embodiment, the monomer having a low electron density (the polymerizable monomer having the maximum charge of the carbon atom constituting the unsaturated bond) is represented by the general formula (4) or the general formula (5). A compound having a bond is preferable.

In the general formula (4) or the general formula (5), EWG ₁ and EWG ₂ each represent a partial structure in which an electron-withdrawing group is directly connected to an unsaturated bond. A part of EWG ₁ or EWG ₂ may be bonded to have a cyclic structure. The electron-withdrawing group represents a cyano group, a halogen group, a pyridyl group, a pyrimidyl group, a nitro group, a group represented by the following general formula (a), or a group represented by the following general formula (b).

Further, EWG ₁ and EWG ₂ may be bonded to each other to form the following electron-withdrawing linking group to form a cyclic structure. Examples of the electron-withdrawing linking group include —CO—O—CO—, —CO—N (R _X ) —CO—, —S (O) _n —O—CO—, —S (O) _n —. N (R) —CO—, —S (O) _n —O—S (O) _n —, or —S (O) _n —N (R _X ) —S (O) _n — and the like are included.

EWG ₁ and EWG ₂ may form a cyclic structure via a linking group such as a linear alkylene group, a branched alkylene group, a cyclic alkylene group, an alkylene group having a hydroxyl group, an arylene group or an arylalkylene group, and a substituent. You may have. Further, a part of EWG ₁ or EWG ₂ may form a polyfunctional polymerizable compound having two or more unsaturated bonds through a linking group.

In the above general formulas (a) and (b), Q ₁ represents OH, OR ′, NR′R ″ or R ′. R ′ and R ″ each represent a hydrogen atom, a linear alkyl group, a branched alkyl group, a cyclic alkyl group, an alkyl group having a hydroxyl group, an aryl group or an arylalkyl group, and may further have a substituent.

  Specific examples of the unsaturated compound represented by the general formula (4) or the general formula (5) include a vinylene imide compound, a vinylene dicarboxylic acid, a vinylene dicarboxylic acid ester, a vinylene monocarboxylic acid amide monocarboxylic acid, and a vinylene monocarboxylic acid amide. Monocarboxylic acid esters, vinylene dicarboxylic acid amides, vinylene nitrile compounds substituted with nitrile groups at both ends of the vinylene skeleton, vinyl halide compounds substituted with halogen groups at both ends of the vinylene skeleton, vinylene ketone compounds substituted with carbonyl at both ends of the vinylene skeleton, vinyl Range thiocarboxylic acid anhydride, vinylene thioimide compound, vinylene thiocarboxylic acid, vinylene thiocarboxylic acid ester, vinylene monothiocarboxylic acid amide monothiocarboxylic acid, vinylene monothiocarboxylic acid amide monothiocarbo Ester, vinyl range thio carboxylic acid amide, compounds pyridyl group which is substituted vinylene backbone ends, but such compounds structure pyrimidyl group is substituted on vinylene skeleton ends include, but are not limited to.

  Preferred examples of the unsaturated compound which is a monomer having a low electron density include vinylene imides such as maleic anhydride and maleimide, vinylene dicarboxylic acids such as maleic acid and fumaric acid, vinylene dicarboxylic acid esters such as maleic acid esters and fumaric acid esters, etc. Is included. More preferably, maleic anhydride, maleic acid, fumaric acid, maleic acid esters, fumaric acid esters, and maleimide compounds are preferable from the viewpoint of increasing sensitivity.

  Moreover, in this invention, the unsaturated compound represented by General formula (4) or General formula (5) is at least 1 sort (s) chosen from following General formula (A-1)-General formula (A-13). An unsaturated compound is preferred.

In General Formula (A-1) to General Formula (A-13), R ₁ , R ₂ , R ₃ , and R ₄ are each independently a hydrogen atom, a linear alkyl group, a branched alkyl group, or a cyclic alkyl group. Represents a hydroxyl group-containing alkyl group, an aryl group or an arylalkyl group, which may further have a substituent, and a linking group for forming a polyfunctional polymerizable compound having two or more unsaturated bond portions; can do. X ₁ represents a halogen atom.

  The monomer having a low electron density is represented by the general formula (A-1), the general formula (A-2), or the general formula among the unsaturated compounds represented by the general formula (A-1) to the general formula (A-13). The unsaturated compound represented by (A-6) is more preferable.

  Although the unsaturated compound represented with general formula (A-1)-general formula (A-13) below is demonstrated below, it is not limited to these. The charge of the carbon atom of the unsaturated bond which the unsaturated compound demonstrated below shows all values of -0.3 or more.

  Examples of monofunctional unsaturated compounds represented by the general formulas (A-1) to (A-13) include maleic anhydride as an example of a compound having vinylene dicarboxylic anhydride, and an example of a compound having vinylene imide. Maleimide, N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, N-2-ethylhexylmaleimide, N-dodecylmaleimide, N-octadecylmaleimide, N-phenylmaleimide, N-cyclohexylmaleimide, N- (p-carbo Methoxyphenyl) maleimide, 4,4′-dimaleimidobisphenol F, N-butylmaleimide, N- (2-chlorophenyl) maleimide, N- (4-chlorophenyl) maleimide, 2,3-dimethyl-1-N- (2 -Methacryloxyethylmaleimide; maleic acid, fumaric acid; Examples of dicarboxylic acid esters include dimethyl maleate, diethyl maleate, diisopropyl maleate, di-n-butyl maleate, di-tert-butyl maleate, di (2-ethylhexyl) maleate, dimethyl fumarate, fumarate Examples include diethyl acid, diisopropyl fumarate, di-n-butyl fumarate, di-tert-butyl fumarate, and di (2-ethylhexyl) fumarate, but these are not limited to these specific examples.

  The polyfunctional polymerizable monomer which is a monomer having a low electron density has a conventionally known linking group skeleton. For example, it may be a polyfunctional maleimide derivative as described in US Pat. No. 6,034,150, JP-A-11-124403, and the like.

  Hereinafter, maleimide derivatives preferable as monomers having a low electron density will be described. The maleimide derivative as a monomer having a low electron density is preferably a maleimide compound having a chiral structure in the molecule from the viewpoints of solubility, low viscosity, and injection stability required for inkjet inks.

  The maleimide compound having a chiral group is not particularly limited as long as it has at least one chiral carbon atom in the molecule. As this preferred maleimide compound, a compound represented by the following general formula (1) is preferable.

In the general formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ₁ and R ₂ may be linked to form a ring. Y ₁ , Y ₃ and Z represent a divalent organic linking group in which groups selected from an alkylene group, an alkyleneoxy group, a phenylene group, an ester group, an ether group and a thioether group are combined. Y ₂ represents a divalent group having an asymmetric carbon. n represents an integer of 1 to 6, n1 represents 0 or 1, and n2 represents 0 or 1.

Examples of the alkyl group represented by R ₁ and R ₂ include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group. R ₁ and R ₂ may combine to form a cyclopropylene ring, a cyclobutylene ring, a cyclopentene ring, a cyclohexene ring, or the like.

The divalent organic linking group represented by Y ₁ and Y ₃ is an alkylene group (eg, methylene group, ethylene group, butylene group, hexylene group, etc.), an alkyleneoxy group (eg, ethyleneoxy group, polyethyleneoxy group, Butyleneoxy group, polybutyleneoxy group), alkyleneoxycarbonyl group (for example, ethyleneoxycarbonyl group, hexyleneoxycarbonyl group, etc.), alkylene ester group (for example, methylene ester group, hexylene ester group, phenylene group), phenyl Group (for example, methylphenylene group, oxycarbonylphenylenecarbonyloxy group, carbonyloxyphenyleneoxycarbonyl group, etc.).

Y ₂ represents a divalent group having an asymmetric carbon (chiral carbon). Specifically, it is represented by the following formula.

  In the above formula, X represents an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, an alkyloxy group having 1 to 18 carbon atoms, an alkylcarbonyloxy group having 1 to 18 carbon atoms, or a hydroxyl group. Preferably, a C1-C4 methyl group, an ethyl group, a propyl group, and an isobutyl group are mentioned.

In the general formula (1), Z represents an n-valent linking group. In the case of n = 1, Z is a hydrogen atom, an alkyl group (methyl group, ethyl group, hexyl group), a hydroxyl group, a carboxyl group, or an alkyl ester group. In the case of n = 2, Z is synonymous with the divalent organic linking group represented by the above Y ₁ and Y ₃ . In the case of n = 3, Z is a glycerol group, a trimethylol alkyl group, a triazine group, or the like. When n = 4, Z is a pentaerythritol group or the like, and when n = 6, Z is a bistrimethylolalkyl group or the like.

  In order to eject the ink jet ink from the ink jet head, the molecular weight of the maleimide compound having a chiral group is preferably 200 to 1,000, more preferably 200 to 800. If it is smaller than 200, it is easy to crystallize and clogging is likely to occur during injection. On the other hand, if the molecular weight is larger than 1000, the viscosity becomes high and injection becomes difficult.

More preferred examples of the maleimide compound having a chiral group include a maleimide compound represented by the following structural formula.

n11 and n12 are integers of 0 to 6, and n13 is preferably an integer of 1 to 30. R _{1, R 2,} Z is synonymous with _{R 1, R} 2, Z in the general formula (1). X has the same meaning as X in the formula given as an example of the divalent group having an asymmetric carbon (chiral carbon) represented by Y ₂ . Particularly preferably, R ₁ and R ₂ are a hydrogen atom, X is an alkyl group having 1 to 4 carbon atoms, n12 is 0, and Z is an alkylene or polyoxyalkylene having 1 to 18 carbon atoms.

Although the specific example of the maleimide compound which has a chiral group represented by General formula (1) below is shown, it is not limited to this.

  Methods for synthesizing these maleimide compounds are known, and can be synthesized, for example, using the method described in JP-A-11-124403 or Macromolecular Chemical and physics, 2009, 210, 269-278.

In the inkjet ink according to the embodiment, as a more preferable maleimide derivative applicable as a monomer having a low electron density, a maleimide derivative represented by the following general formula (2) is preferable from the viewpoint of low viscosity, solubility, and injection stability. Can be mentioned.

In the general formula (2), R ₁₁ and R ₁₂ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ₁₁ and R ₁₂ may be bonded to each other to form a ring. . A ₁₁ and A ₁₃ each independently represent an alkylene group, and A ₁₂ represents a trivalent hydrocarbon group having an asymmetric center. Y represents carbonyloxy (—C (═O) —O—) or oxycarbonyl (—O—C (═O) —). p represents 1 or 2. R ₁₃ represents an alkyl group or alkyleneoxy group having a molecular weight of 15 to 600 when p is 1, and an alkylene group or alkyleneoxy group having a molecular weight of 14 to 600 when p is 2. m represents 0 or 1, and n represents 0 or 1.

In the general formula (2), examples of the alkyl group represented by R ₁₁ and R ₁₂ include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group. R ₁₁ and R ₁₂ may be bonded to form a cyclopropene ring, a cyclobutylene ring, a cyclopentene ring, a cyclohexene ring, or the like.

Examples of the divalent organic linking group represented by A ₁₁ and A ₁₃ include a methylene group, an ethylene group, a butylene group, a hexylene group, an ethyleneoxy group, a polyethyleneoxy group, a butyleneoxy group, a polybutyleneoxy group, and an ethyleneoxycarbonyl group. Hexyleneoxycarbonyl group, methylene ester group, hexylene ester group, phenylene group, methylphenylene group, oxycarbonylphenylenecarbonyloxy group, and carbonyloxyphenyleneoxycarbonyl group.

A ₁₂ represents a trivalent group having an asymmetric carbon (chiral carbon).

In the general formula (2), A ₁₁ and A ₁₃ are preferably a methylene group, A ₁₂ is —CHR ₁₄ —, and R ₁₃ is an alkyl group having 2 to 12 carbon atoms or an alkylene group. At this time, R ₁₄ represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, an alkyloxy group having 1 to 18 carbon atoms, an alkylcarbonyloxy group having 1 to 18 carbon atoms, or a hydroxyl group. Preferably, R ₁₄ is an alkyl group having 1 to 4 carbon atoms (such as a methyl group, an ethyl group, a propyl group, or an isobutyl group).

When p is 1, the alkyl group having a molecular weight of 15 to 600 represented by R ₁₃ is a linear or branched alkyl group having 1 to 18 carbon atoms, specifically, methyl group, ethyl group, propyl group. Group, butyl group, hexyl, group, neopentyl group, dodecyl group, 2,2,4-octyl group, and the like.

The alkylene group having a molecular weight of 14 to 600 represented by R ₁₃ when p is 2 is a linear or branched alkylene group having 1 to 18 carbon atoms, specifically a methylene group, an ethylene group, or a propylene group. Butylene group, hexylene group, nepopentylene group, dodecylene group, 2,2,4-octylene group and the like.

Examples of the alkyleneoxy group represented by R ₁₃ when p is 1 include a hydroxy or alkoxy polyethyleneoxy group, a hydroxy or alkoxypolyproleneoxy group, a hydroxy or alkoxypolybutyleneoxy group, and the like. It is not limited.

R ₁₃ is preferably a linear or branched alkylene group having 1 to 18 carbon atoms, or a linear or branched alkyl group having 1 to 18 carbon atoms, and more preferably a linear or branched alkyl group having 4 to 12 carbon atoms. An alkylene group is a linear or branched alkyl group having 4 to 12 carbon atoms.

Further preferred maleimide derivatives include maleimide derivatives represented by the following general formulas (II) to (IV).

In the general formulas (II) to (IV), R ₁₄ is an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, an alkyloxy group having 1 to 18 carbon atoms, or an alkyl group having 1 to 18 carbon atoms. Represents an alkylcarbonyloxy group or a hydroxyl group. Preferably, an alkyl group having 1 to 4 carbon atoms (methyl group, ethyl group, propyl group, isobutyl group, etc.) can be used. p represents 1 or 2. R ₁₅ represents a linear alkyl group having 4 to 12 carbon atoms or an alkylene group.

The specific example of the maleimide derivative represented by General formula (2) in embodiment below is shown.

<Monomer with high electron density>
A monomer having a high electron density in this embodiment is a monomer having an unsaturated bond with an excess of electrons, and the value of an atomic charge of the unsaturated bond is −0.45 or less. Preferably, it is −0.50 or less.

Among two or more kinds of polymerizable monomers having an unsaturated bond, a monomer having a high electron density (a polymerizable monomer having a minimum charge of carbon atoms constituting the unsaturated bond) is represented by the following general formula (6). An unsaturated compound is preferred.

In the general formula (6), X represents —O—, —NR ₄ —, —S—, or —SO—. Y represents a hydrogen atom, a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkyl group having a hydroxyl group, an aryl group, or an arylalkyl group, and may further have a substituent. R ₁ , R ₂ , and R ₃ each independently represent a hydrogen atom, a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkyl group having a hydroxyl group, an aryl group, or an arylalkyl group; You may have. Further, a part of R ₂ or R ₃ and Y may be bonded to form a cyclic structure. Moreover, you may form the polyfunctional donor monomer which one part of Y has a 2 or more unsaturated bond through a coupling group.

  Specific examples of the unsaturated compound represented by the general formula (6) include alkenyl ethers such as vinyl ether and propenyl ether, alkenyl thioethers such as vinyl thioether and propenyl thioether, and alkenyl sulfoxides such as vinyl sulfoxide and propenyl sulfoxide. , Vinyl esters in which a vinyl group is bonded to the oxygen atom of a carboxylate ester, vinylamines in which a vinyl group is bonded to a nitrogen atom in an amino group, vinylamides in which a vinyl group is bonded to a nitrogen atom in an amide group, nitrogen atoms in an imidazole ring And vinyl imidazole having a vinyl group bonded thereto, vinyl carbazole having a vinyl group bonded to a nitrogen atom of a carbazole ring, a cyclic 5-membered ring containing a vinylene skeleton and an oxygen atom in the ring, and a cyclic 6-membered ring compound.

The compound represented by the general formula (6) is more preferably a compound represented by the following general formulas (D-1) to (D-9).

In General Formulas (D-1) to (D-9), R ₅ to R ₉ are each independently a hydrogen atom, a linear alkyl group, a branched alkyl group, a cyclic alkyl group, an alkyl group having a hydroxyl group, or aryl. Represents a group or an arylalkyl group, and may further have a substituent. R ₅ to R ₉ may be a linking group for forming a polyfunctional polymerizable compound having two or more unsaturated bond moieties. Z represents —O—, —N (R ₁₀ ) — or —S—. R ₁₀ represents a hydrogen atom, a linear alkyl group, a branched alkyl group, a cyclic alkyl group, an alkyl group having a hydroxyl group, an aryl group, or an arylalkyl group, and may further have a substituent.

Among the unsaturated compounds represented by the general formula (6), in the monofunctional unsaturated compound, Y is a hydrogen atom, a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkyl group having a hydroxyl group, an aryl group, or Represents an arylalkyl group. X represents —O—, —N (R ₁₁ ) CO—, —NR ₄ —, —S—, or —SO—, R ₁₁ represents a hydrogen atom, an alkyl group, a cycloalkyl group, or an aryl group; R ₁₁ may be linked to Y to form a ring.

  Specific examples of the monofunctional unsaturated compound represented by the general formula (6) include vinyl thioether; vinyl methyl sulfoxide as a polymerizable monomer containing vinyl sulfoxide; vinyl-tert-butyl sulfide, vinyl methyl sulfide, vinyl ethyl sulfide, and the like. Is included.

  The monofunctional unsaturated compound represented by the general formula (6) may be a polymerizable monomer having a vinylene skeleton and a 5-membered or 6-membered ring compound containing a nitrogen atom or an oxygen atom in the ring. Examples of the 5-membered or 6-membered ring compound include imidazole, pyrrole, furan, dihydrofuran, pyran, dihydropyran and the like.

  Specific examples of N-vinyl compounds having a structure in which a vinyl group is substituted on a nitrogen atom include N-vinylformamide, N-vinylcarbazole, N-vinylindole, N-vinylpyrrole, N-vinylacetamide, N-vinyl. Pyrrolidone, N-vinylcaprolactam, N-vinyl-N-ethylurea, N-vinyloxazolidone, N-vinylsuccinimide, N-vinylethylcarbamate and derivatives thereof are included. Among these compounds, N-vinylcaprolactam and N-vinylformamide are particularly preferable. N-vinylformamide can be obtained from, for example, Arakawa Chemical Industries, Ltd.

The compound represented by the general formula (6) may be a monofunctional vinyl ether compound represented by the general formula (3). A monofunctional vinyl ether compound is particularly preferable because it can enhance the storage stability of the inkjet ink.

In the general formula (3), R ₃ , R ₄ and R ₅ represent a hydrogen atom, an alkyl group, a cycloalkyl group or an aryl group, and R ₆ represents an alkyl group, a cycloalkyl group or an aryl group.

  Examples of monofunctional vinyl ether compounds include n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, allyl vinyl ether, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, 9-hydroxy Nonyl vinyl ether, 4-hydroxycyclohexyl vinyl ether, cyclohexanedimethanol monovinyl ether, triethylene glycol monovinyl ether and the like are included.

  Furthermore, various known vinyl ether compounds may be used. For example, a compound containing a (meth) acryloyl group and a vinyl ether group in the molecule disclosed in Japanese Patent No. 3461501, a vinyl ether compound having an alicyclic skeleton containing at least an oxygen atom disclosed in Japanese Patent No. 4037856, A vinyl ether having an alicyclic skeleton disclosed in JP-A-2005-015396, a 1-indanyl vinyl ether disclosed in JP-A-2008-137974, and disclosed in JP-A-2008-150341 4-acetoxycyclohexyl vinyl ether and the like.

  The ink-jet ink in the present embodiment preferably contains a polyfunctional monomer with a high electron density in addition to a monofunctional monomer with a high electron density. Thereby, curing sensitivity, weather resistance and solvent resistance can be improved.

Examples of the polyfunctional unsaturated compound in the unsaturated compound represented by the general formula (6) are represented by the above general formula (D-1) to general formula (D-9), and R ^{5 to} R ⁹ are 2 It becomes a linking group for forming a polyfunctional polymerizable compound having one or more unsaturated bond moieties. Especially, it is especially preferable that it is a compound represented by general formula (D-1).

  Although the example of the polyfunctional unsaturated compound which has an unsaturated bond represented by general formula (D-1)-general formula (D-9) is shown, it is not limited to this. All of the charges of the carbon atoms constituting the unsaturated bond of the polymerizable monomer exemplified below are −0.40 or less.

  Examples of bifunctional vinyl ether compounds include 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, neopentyl glycol divinyl ether, nonanediol divinyl ether, cyclohexanediol divinyl ether, cyclohexanedimethanol divinyl ether, diethylene glycol Examples include divinyl ether, triethylene glycol divinyl ether (TEGDVE), trimethylolpropane divinyl ether, ethylene oxide-modified trimethylolpropane divinyl ether, pentaerythritol divinyl ether, and the like.

  Examples of the bifunctional vinyl ether compound include a vinyl ether compound having an alicyclic skeleton containing at least an oxygen atom disclosed in Japanese Patent No. 4037856, and an alicyclic skeleton disclosed in Japanese Patent Application Laid-Open No. 2005-015396. There are also vinyl ethers, 1-indanyl vinyl ether disclosed in JP 2008-137974 A, 4-acetoxycyclohexyl vinyl ether disclosed in JP 2008-150341 A, and the like.

  Introduce a substituent at the α-position or β-position of the vinyl ether group by substituting the vinyl ether group of the above-mentioned bifunctional vinyl ether compound with a propenyl ether group, an isopropenyl ether group, a butenyl ether group or an isobutenyl ether group. These compounds can also be used as polyfunctional unsaturated compounds.

  Among these bifunctional vinyl ether compounds, in consideration of curability, adhesion, and surface hardness, diethylene glycol divinyl ether, triethylene glycol divinyl ether, cyclohexanediol divinyl ether, cyclohexane dimethanol divinyl ether, and the like are curable. Are excellent in terms of compatibility, odor, and safety.

  Specific examples of the trifunctional or higher polyfunctional vinyl ether compound include trimethylolpropane trivinyl ether, ethylene oxide modified trimethylolpropane trivinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, ethylene oxide modified pentaerythritol trivinyl ether, ethylene oxide modified Examples include pentaerythritol tetravinyl ether, dipentaerythritol hexavinyl ether, and ethylene oxide-modified dipentaerythritol hexavinyl ether.

The trifunctional vinyl ether compound can be represented by the following general formula (A). As represented by the general formula (A), a compound having an oxyalkylene group in the molecule is preferable for obtaining compatibility and solubility with other ink components and adhesion to a substrate. The total number of oxyalkylene groups in the compound represented by formula (A) is preferably 10 or less. If it exceeds 10, the water resistance of the cured film may be lowered. The compound represented by the general formula (A) has an oxyethylene group, but the oxyethylene group may be another oxyalkylene group having a different carbon number. 1-4 are preferable and, as for carbon number of an oxyalkylene group, it is more preferable that it is 1 or 2.

In the above general formula (A), R ₁₁ represents hydrogen or an organic group. Examples of the organic group represented by R ₁₁ include an alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, or a butyl group, a fluoroalkyl group having 1 to 6 carbon atoms, an aryl group, and a furyl group. Or thienyl group, allyl group, 1-propenyl group, 2-propenyl group, 2-methyl-1-propenyl group, 2-methyl-2-propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, etc. An alkenyl group having 1 to 6 carbon atoms, phenyl group, benzyl group, fluorobenzyl group, aryl group such as methoxybenzyl group or phenoxyethyl group, alkoxy group such as methoxy group, ethoxy group and butoxy group, propylcarbonyl group, An alkylcarbonyl group having 1 to 6 carbon atoms such as a butylcarbonyl group or a pentylcarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group; Includes a group such as an alkoxycarbamoyl group having 1 to 6 carbon atoms such as a butoxycarbonyl group, an alkoxycarbamoyl group having 1 to 6 carbon atoms such as an ethoxycarbamoyl group, a propylcarbamoyl group or a butylpentylcarbamoyl group. It is not limited. Among these, as the organic group, a hydrocarbon group containing no hetero atom is preferable from the viewpoint of curability. Moreover, p, q, and r are 0 or an integer greater than or equal to 1, and p + q + r is an integer of 3-10.

Examples of the polyfunctional vinyl ether compound having four or more vinyl ether groups include compounds represented by the following general formulas (B) and (C).

In the general formula (B), R ₁₂ is a linking group containing any one of a methylene group, an alkylene group having 1 to 6 carbon atoms, an oxyalkylene group, and an ester group. p, q, l and m are each 0 or an integer of 1 or more, and the total number of p + q + l + m is an integer of 3 to 10.

In General Formula (C), R ₁₃ represents a linking group containing any of a methylene group, an alkylene group having 1 to 6 carbon atoms, an oxyalkylene group, and an ester group. p1, q1, r1, l1, m1, and s1 are each 0 or an integer of 1 or more, and the total number of p1 + q1 + r1 + l1 + m1 + s1 is an integer of 3 to 10.

  In the general formulas (B) and (C), an oxyethylene group is exemplified, but an oxyalkylene group having a different carbon number may be used. The number of carbon atoms in the oxyalkylene group is preferably 1 to 4, and more preferably 1 or 2.

<Other polymerizable compounds>
The inkjet ink according to the embodiment may contain other polymerizable compound as long as the effects of the embodiment are not impaired. The charge of the carbon atom constituting the unsaturated bond of the other polymerizable compound is more than −0.40 and preferably less than −0.30. By adding other polymerizable compounds, it is possible to achieve reduction in curing shrinkage, viscosity adjustment, substrate adhesion, flexibility, and the like.

  The other polymerizable compound is preferably a compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule, and may be any of a monomer, an oligomer and a polymer. Only one type of radically polymerizable monomer may be used, or two or more types may be used in combination at an arbitrary ratio in order to improve the desired properties. It is preferable to use two or more kinds in combination for controlling performance such as reactivity and physical properties. The cyclic allyl sulfide monomer can be copolymerized with other methacrylate monomers and acrylate monomers.

  Examples of polymerizable monomers having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid and methacrylic acid and their salts; anhydrides having ethylenically unsaturated groups, acrylonitrile, styrene, and various Unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, unsaturated urethanes, and the like.

  Specifically, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, tridecyl acrylate, 2-phenoxyethyl acrylate, bis (4-acryloxypolyethoxyphenyl) Propane, polyethylene glycol diacrylate, polypropylene glycol diacrylate, dipentaerythritol tetraacrylate, trimethylolpropane triacrylate, oligoester acrylate, N-methylolacrylamide, diacetone acrylamide, epoxy acrylate, isobornyl acrylate, dicyclopentenyl acrylate, Dicyclopentenyloxyethyl acrylate, disic Acrylic acid derivatives such as lopentanyl acrylate; methyl methacrylate, n-butyl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis (4- Methacryl derivatives such as methacryloxypolyethoxyphenyl) propane; and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate and triallyl trimellitate.

  More specifically, Shinzo Yamashita, “Crosslinker Handbook”, (1981 Taiseisha); Kato Kiyosumi, “UV / EB Curing Handbook (Materials)” (1985, Polymer Publications); Radtech Study Group, “Application and Market of UV / EB Curing Technology”, p. 79, (1989, CMC); Eiichiro Takiyama, “Polyester Resin Handbook”, (1988, Nikkan Kogyo Shimbun) Commercially available products or radically polymerizable and crosslinkable monomers, oligomers and polymers known in the industry can be used.

  Among these acrylates and methacrylates, from the viewpoint of curability and film properties after curing, acrylates of alcohols having ether oxygen atoms such as tetrahydrofurfuryl acrylate and 2-phenoxyethyl acrylate are adhesive, flexible, It is preferable from the viewpoint of curability. For the same reason, an acrylate of an alcohol having an alicyclic structure is also preferable, and a bicyclo ring structure or a tricyclo ring structure such as isobornyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, etc. An acrylate having is preferable. Of these, dicyclopentenyl acrylate and dicyclopentenyloxyethyl acrylate having a double bond in the alicyclic structure are particularly preferable.

  Examples of the radical polymerizable monomer include JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, JP-A-10-863, JP-A-9-134011, JP-T-2004. There are photocurable polymerizable monomers used in the photopolymerizable composition described in each publication such as 5114014, and these can also be applied to the polymerizable monomer of the ink inkjet ink in the present embodiment.

  Further, other polymerizable compounds include (meth) acrylic monomers or prepolymers, (meth) acrylic acid esters such as epoxy monomers or prepolymers, urethane monomers or prepolymers (hereinafter appropriately referred to as acrylate compounds). It may be. Specific examples thereof include 2-ethylhexyl-diglycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxybutyl acrylate, hydroxypivalate neopentyl glycol diacrylate, 2-acryloyloxyethyl phthalate, methoxy -Polyethylene glycol acrylate, tetramethylol methane triacrylate, 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, dimethylol tricyclodecane diacrylate, ethoxylated phenyl acrylate, 2-acryloyloxyethyl succinic acid, nonylphenol EO addition Acrylate, modified glycerin triacrylate, bisphenol A diglycidyl ether acrylic acid adduct, modified bisphenol A diacrylate, phenoxy-poly Ethylene glycol acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, PO adduct diacrylate of bisphenol A, EO adduct diacrylate of bisphenol A, dipentaerythritol hexaacrylate, pentaerythritol triacrylate tolylene diisocyanate urethane prepolymer Lactone-modified flexible acrylate, butoxyethyl acrylate, propylene glycol diglycidyl ether acrylic acid adduct, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, 2-hydroxyethyl acrylate, methoxydipropylene glycol acrylate, ditrimethylolpropane Tetraacrylate, pentaerythritol triacrylate hexamethyle Diisocyanate urethane prepolymer, stearyl acrylate, isoamyl acrylate, isomyristyl acrylate, isostearyl acrylate, and the like lactone-modified acrylate.

  These acrylate compounds are polymerizable compounds used in conventional UV curable inks, and have low skin irritation and sensitization (ease of rash). Further, since it has a relatively low viscosity, it can stabilize the ink ejection properties, and the polymerization sensitivity and the adhesion to the substrate are also good. Furthermore, (meth) acrylic monomers have lower skin irritation than acrylic monomers.

  Among them, monofunctional acrylates are often low-viscosity, and can be adjusted from the standpoint of improving injection properties. Also, the cured film can be made flexible even on flexible substrates, and shrinkage can be cured. Since generation | occurrence | production can be prevented, it is preferable.

  As the oligomer that can be used in combination with the monofunctional acrylate, an epoxy acrylate oligomer and a urethane acrylate oligomer are particularly preferable. The polyfunctional monomer has good sensitivity and cured film strength. In such a polyfunctional monomer, examples of the bifunctional monomer include bifunctional acrylate, polyethylene glycol diacrylate, and polypropylene glycol diacrylate. Mention may be made of polyfunctional acrylates, dipentaerythritol tetraacrylate, trimethylolpropane triacrylate, oligoester acrylate.

<Photopolymerization initiator>
The ink jet in the present embodiment preferably contains a radical photopolymerization initiator or a sensitizer as a photopolymerization initiator from the viewpoint of obtaining high sensitivity.

  The radical photopolymerization initiator contained in the inkjet ink according to the embodiment is preferably a molecular cleavage type or a hydrogen abstraction type. Specific examples of the radical photopolymerization initiator include benzoin isobutyl ether, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, benzyl, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-benzyl-2-dimethylamino- 1- (4-morpholinophenyl) -butan-1-one, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine An oxide or the like is preferably used.

  Further, as molecular cleavage type photopolymerization initiators, 1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzyldimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-Hydroxy-2-methylpropan-1-one and 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-Hydroxy-2-methyl-1-propan-1-one may be used in combination.

  Further, examples of the hydrogen abstraction type photopolymerization initiator include benzophenone, 4-phenylbenzophenone, isophthalphenone, 4-benzoyl-4′-methyl-diphenyl sulfide, and bis (2,4- 1,2-octanedione, a polymerization initiator of cyclopentadiene-1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium, an oxime ester type -(4- (phenylthio) -2- (O-benzoyloxime)), ethanone, 1- (9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl)-, 1- (O -Acetyl oxime).

  A sensitizer can be used in combination with the radical photopolymerization initiator. Examples of sensitizers include trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzylamine and 4, Amines that do not cause an addition reaction with a radically polymerizable monomer such as 4′-bis (diethylamino) benzophenone are included. Of course, it is preferable to select and use a radical photopolymerization initiator and a sensitizer that are excellent in solubility in the polymerizable monomer.

  The content of the photo radical polymerization initiator and the sensitizer in the inkjet ink is preferably 0.1 to 20% by mass, more preferably 1 to 12% by mass with respect to the total mass of the inkjet ink.

  Other examples of the radical photopolymerization initiator include a type in which an amine-based initiator aid is bonded as an initiator structure to a dendrimer core described in European Patent 1,674,499A, European Patent 2,161. , 264A, European Patent 2,189,477A, an initiator having a polymerizable group, an amine-based initiator, a plurality of those described in European Patent 1,927,632B1 A type having an amine-based initiator in one molecule, a type containing a plurality of thioxanthones in the molecule described in WO 2009/060235, represented by ESACURE ONE and ESACUR KIP150 commercially available from Lamberti Also included is an oligomer type polymerization initiator in which α-hydroxypropiophenone is bonded to the side chain.

  Moreover, the maleimide compound which is a polymerizable monomer itself can act as a photopolymerization initiator.

<Colorant>
When coloring the inkjet ink which concerns on embodiment, it is preferable that a pigment is included as a coloring agent. The pigment may be a colorless inorganic pigment such as carbon black, titanium oxide, calcium carbonate, or a colored organic pigment.

  Examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, pyrazolone red, soluble azo pigments such as ritol red, heliobordeaux, pigment scarlet, permanent red 2B; alizarin, indanthrone 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; Isoindolinone organic pigments such as indolinone yellow and isoindolinone orange; pyranthrone organic pigments such as pyranthrone red and pyranthrone orange; thioindigo Machine pigments, condensed azo organic pigments, benzimidazolone organic pigments, quinophthalone organic pigments such as quinophthalone yellow; isoindoline organic pigments such as isoindoline yellow; other pigments such as flavanthron yellow, acylamide yellow, nickel Azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet and the like are included.

  Organic pigments are exemplified below by color index (CI) numbers.

C. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 180, 185;
C. I. Pigment orange 16, 36, 43, 51, 55, 59, 61;
C. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 177, 180, 192, 202, 206, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240;
C. I. Pigment violet 19, 23, 29, 30, 37, 40, 50;
C. I. Pigment blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64;
C. I. Pigment green 7, 36;
C. I. Pigment Brown 23, 25, 26.

  Among the above pigments, quinacridone-based, phthalocyanine-based, benzimidazolone-based, isoindolinone-based, condensed azo-based, quinophthalone-based, and isoindoline-based organic pigments are preferable because of excellent light resistance.

  The organic pigment is preferably fine particles having an average particle diameter in the ink of 10 to 150 nm as measured by laser scattering. When the average particle size of the pigment is less than 10 nm, the light resistance is lowered due to the small particle size, and when it exceeds 150 nm, it is difficult to stably maintain the dispersion, and the pigment is likely to precipitate. Stability is lowered, and a problem that minute mist called satellite occurs. However, in the case of titanium oxide, the average particle diameter is 150 to 300 nm, preferably 180 to 250 nm, in order to provide whiteness and concealment.

  In addition, it is preferable that coarse particles are removed by sufficient dispersion or filtration so that the maximum particle size of the pigment in the ink does not exceed 1.0 μm. When coarse particles are present, the injection stability tends to decrease.

  The organic pigment can be refined by the following method. That is, a mixture comprising at least three components of an organic pigment, a water-soluble inorganic salt of 3 mass times or more of the organic pigment, and a water-soluble solvent is made into a clay, kneaded with a kneader or the like, and then poured into water. Stir with a speed mixer to make a slurry. Next, filtration and washing of the slurry are repeated, and the water-soluble inorganic salt and the water-soluble solvent are removed by aqueous treatment. In the miniaturization step, a resin, a pigment dispersant and the like may be added.

  Examples of the water-soluble inorganic salt include sodium chloride and potassium chloride. These inorganic salts are used in the range of 3 to 20 times the mass of the organic pigment, but after the dispersion treatment, chlorine ions (halogen ions) are removed by washing with water. When the amount of the inorganic salt is less than 3 times by mass, a treated pigment having a desired size cannot be obtained. When the amount is more than 20 times by mass, the cleaning process in the subsequent step is enormous, and the substantial processing amount of the organic pigment is reduced.

  The water-soluble solvent is not particularly limited as long as it is a solvent that can be used for making an appropriate clay state of an organic pigment and a water-soluble inorganic salt used as a crushing aid and performing sufficient crushing efficiently, and is soluble in water. However, since the temperature rises during kneading and the solvent easily evaporates, a high boiling point solvent having a boiling point of 120 to 250 ° C. is preferable from the viewpoint of safety. As water-soluble solvent, 2- (methoxymethoxy) ethanol, 2-butoxyethanol, 2- (i-pentyloxy) ethanol, 2- (hexyloxy) ethanol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether , Triethylene glycol, triethylene glycol monomethyl ether, liquid polyethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, low molecular weight Examples include polypropylene glycol.

  The pigment may be surface-treated by a known technique such as an acid treatment or a basic treatment, a synergist, or various coupling agents. This is because the adsorption with the pigment dispersant is promoted to ensure dispersion stability.

  The pigment content in the ink-jet ink is preferably 1.5 to 8% by mass in order to obtain a sufficient concentration and sufficient light resistance, but in the case of a white ink containing titanium oxide as a pigment, it is 10 to 30% by mass. % Is preferably included.

<Pigment dispersant>
Pigment dispersants include hydroxyl group-containing carboxylic acid esters, salts of long chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, Polymer 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 nonyl Examples thereof include phenyl ether, stearylamine acetate, and pigment derivatives.

  Specific examples of the pigment dispersant include “Anti-Terra-U (polyaminoamide phosphate)”, “Anti-Terra-203 / 204 (high molecular weight polycarboxylate)” manufactured by BYK Chemie, “Disperbyk-101”. (Polyaminoamide phosphate and acid ester), 107 (hydroxyl group-containing carboxylic acid ester), 110 (copolymer containing an acid group), 130 (polyamide), 161, 162, 163, 164, 165, 166, 170 (high Molecular copolymer) ”,“ 400 ”,“ Bykumen ”(high molecular weight unsaturated acid ester),“ BYK-P104, P105 (high molecular weight unsaturated acid polycarboxylic acid) ”,“ P104S, 240S (high molecular weight unsaturated) Acid polycarboxylic acid and silicone) "," Lactimon (long-chain amine and unsaturated acid polycal And the like and phosphate Silicone) ".

  “Efka 44, 46, 47, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766” manufactured by Efka CHEMICALS, “Efka Polymer 100 (modified polyacrylate), 150 (aliphatic) Modified polymer), 400, 401, 402, 403, 450, 451, 452, 453 (modified polyacrylate), 745 (copper phthalocyanine type) ”;“ Floren TG-710 (urethane oligomer) ”manufactured by Kyoei Chemical Co., Ltd.,“ “Flonon SH-290, SP-1000”, “Polyflow No. 50E, No. 300 (acrylic copolymer)”; “Disparon KS-860, 873SN, 874 (polymer dispersing agent)” manufactured by Enomoto Kasei Co., Ltd., # 2150 (aliphatic polyvalent carboxylic acid), # 7004 (polyether ester type) "etc. are also pigments It can be a powder.

  Furthermore, “Demol RN, N (Naphthalenesulfonic acid formalin condensate sodium salt), MS, C, SN-B (aromatic sulfonic acid formalin condensate sodium salt), EP”, “Homogenol L-18” manufactured by Kao Corporation. (Polycarboxylic acid type polymer) "," Emulgen 920, 930, 931, 935, 950, 985 (polyoxyethylene nonyl phenyl ether) "," Acetamine 24 (coconut amine acetate), 86 (stearyl amine acetate) "; “Solspers 5000 (phthalocyanine ammonium salt type), 13240, 13940 (polyesteramine type), 17000 (fatty acid amine type), 24000, 32000, 7000” manufactured by Zeneca Corporation; “Nikkor T106 (polyoxyethylene sorbitan) manufactured by Nikko Chemical Co., Ltd.” mono Rate), MYS-IEX (polyoxyethylene monostearate), Hexagline4-0 (hexaglyceryl ruthenate Huwei rate) ", also manufactured by Ajinomoto Fine-Techno Co., of AJISPER 821,822,824 etc. can be a pigment dispersing agent.

  The content of the pigment dispersant in the inkjet ink is 5 to 70 parts by mass, preferably 10 to 50 parts by mass with respect to 100 parts by mass of the pigment. If the amount is less than 5 parts by mass, dispersion stability may be difficult to obtain. If the amount is more than 70 parts by mass, the injection stability may deteriorate.

<Radical polymerization inhibitor>
The ink-jet ink in this embodiment may contain a radical polymerization inhibitor from the viewpoint of storage stability. Ink jet ink may generate radicals under the influence of heat or light during storage, and radical polymerization reaction may occur. By adding a radical polymerization inhibitor to the inkjet ink, radical polymerization that occurs during storage is suppressed. Since the ink-jet ink in this embodiment is extremely excellent in photocurability, it is very preferable to add a radical polymerization inhibitor.

  Examples of radical polymerization inhibitors include phenolic hydroxyl group-containing compounds, methoquinone (hydroquinone monomethyl ether), hydroquinone, 4-methoxy-1-naphthol, hindered amine antioxidants, 1,1-diphenyl-2-picrylhydrazyl. Free radicals, N-oxide compounds, piperidine 1-oxyl free radical compounds, pyrrolidine 1-oxyl free radical compounds, N-nitrosophenylhydroxylamines, nitrogen-containing heterocyclic mercapto compounds, thioether antioxidants, hinders Dophenol antioxidants, ascorbic acids, zinc sulfate, thiocyanates, thiourea derivatives, various sugars, phosphate antioxidants, nitrites, sulfites, thiosulfates, hydroxylamine derivatives, dicyandiamide and polyalkylene poly Polycondensates of emissions, include phenothiazines, and the like.

  Specific examples of the radical polymerization inhibitor include the following compounds.

  Examples of phenolic compounds as radical polymerization inhibitors include phenol, alkylphenols such as o-, m- or p-cresol (methylphenol), 2-t-butyl-4-methylphenol, 6-t-butyl. -2,4-dimethylphenol, 2,6-di-t-butyl-4-methylphenol, 2-t-butylphenol, 4-t-butylphenol, 2,4-di-t-butylphenol, 2-methyl-4 -t-butylphenol, 4-t-butyl-2,6-dimethylphenol, or 2,2'-methylene-bis- (6-t-butyl-methylphenol), 4,4'-oxydiphenyl, 3,4 -Methylenedioxydiphenol (sesame oil), 3,4-dimethylphenol, benzcatechin (1,2-dihydroxybenzol), 2- (1'-methylcyclohexyl-1'-yl) -4,6-dimethylphenol 2- (1'-F Nyleth-1'-yl) phenol, 4- (1'-phenyleth-1'-yl) phenol, 2-t-butyl-6-methylphenol, 2,4,6-tris-t-butylphenol, 2,6 -Di-t-butylphenol, nonylphenol [CAS-Nr. 11066-49-2], octylphenol [CAS-Nr. 140-66-9], 2,6-dimethylphenol, bisphenol A, bisphenol B, bisphenol C, bisphenol F, bisphenol S, 3,3 ′, 5,5′-tetrabromobisphenol A, 2,6-di- t-Butyl-p-cresol, BASF Aktiengesellschaft, Koresin, 3,5-di-t-butyl-4-hydroxybenzoic acid methyl ester, 4-t-butylbenzcatechin, 2-hydroxybenzyl alcohol, 2- Methoxy-4-methylphenol, 2,3,6-trimethylphenol, 2,4,5-trimethylphenol, 2,4,6-trimethylphenol, 2-isopropylphenol, 4-isopropylphenol, 6-isopropyl-m- Cresol, n-octadecyl-β- (3,5-di-t-butyl-4-hydroxyphenyl) Pionate, 1,1,3-tris- (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris- (3,5-di-) -t-butyl-4-hydroxybenzyl) benzol, 1,3,5-tris- (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris- (3, 5-Di-tert-butyl-4-hydroxyphenyl) propionyloxyethyl-isocyanurate, 1,3,5-tris- (2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate or penta Erythlit-tetrakis- [β- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,6-di-t-butyl-4-dimethylaminomethylphenol, 6-s-butyl- 2,4-dinitrophenol, Firma Ciba Specialiaetenc Emie Irganox 565, 1010, 1076, 1141, 1192, 1222 and 1425, 3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionic acid octadecyl ester, 3- ( 3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionic acid hexadecyl ester, 3- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionic acid octyl ester, 3-thia-1,5-pentanediol-bis- [3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate], 4,8-dioxa-1,11-undecandiol-bis- [3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate], 4,8-dioxa-1,11-undecandiol-bis-[(3'-t-butyl-4'-hydroxy -5′-methylphenyl) propionate], , 9-nonanediol-bis-[(3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate], 1,7-heptanediamine-bis [3- (3 ′, 5′-di -t-butyl-4'-hydroxyphenyl) propionic acid amide], 1,1-methanediamine-bis [3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionic acid amide] 3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionic acid hydrazide, 3- (3 ′, 5′-dimethyl-4′-hydroxyphenyl) propionic acid hydrazide, bis- ( 3-t-butyl-5-ethyl-2-hydroxyphen-1-yl) methane, bis- (3,5-di-t-butyl-4-hydroxyphen-1-yl) methane, bis- [3- (1′-Methylcyclohex-1′-yl) -5-methyl-2-hydroxyphen-1-yl] methane, bis- (3-tert-butyl-2-hydroxy-5-methyl) Ruphen-1-yl) methane, 1,1-bis- (5-tert-butyl-4-hydroxy-2-methylphen-1-yl) ethane, bis- (5-tert-butyl-4-hydroxy-2-) Methylphen-1-yl) sulfide, bis- (3-tert-butyl-2-hydroxy-5-methylphen-1-yl) sulfide, 1,1-bis- (3,4-dimethyl-2-hydroxypheny-1) -Yl) -2-methylpropane, 1,1-bis- (5-tert-butyl-3-methyl-2-hydroxyphen-1-yl) butane, 1,3,5-tris- [1 ′-( 3 ", 5" -di-t-butyl-4 "-hydroxyphen-1" -yl) methy-1'-yl] -2,4,6-trimethylbenzol, 1,1,4- Aminophenols such as tris- (5′-t-butyl-4′-hydroxy-2′-methylphen-1′-yl) butane, t-butylcatechol, p-aminophenol, p-nitrosophenol and p-nitroso- -Nitrosophenol such as cresol, 2-methoxyphenol (guaiacol, benzcatechin monomethyl ether), 2-ethoxyphenol, 2-isopropoxyphenol, 4-methoxyphenol (hydroquinone monomethyl ether), mono- or di-t-butyl- 4-methoxyphenol, 3,5-di-t-butyl-4-hydroxyanisole, 3-hydroxy-4-methoxybenzyl alcohol, 2,5-dimethoxy-4-hydroxybenzyl alcohol (syringa alcohol), 4-hydroxy -3-Methoxybenzaldehyde (vanillin), 4-hydroxy-3-ethoxybenzaldehyde (ethylvanillin), 3-hydroxy-4-methoxybenzaldehyde (isovanillin), 1-((4-hydroxy-3-methoxyphenyl) ethanone (aceto Vanillin), Eugeno , Alkoxyphenols such as dihydroeugenol and isoeugenol, tocopherols such as α-, β-, γ-, δ- and ε-tocopherol, tocol, α-tocopherol hydroquinone, and 2,3-dihydro-2,2- Dimethyl-7-hydroxybenzofuran (2,2-dimethyl-7-hydroxycoumaran) and the like are included.

  Examples of quinones and hydroquinones as radical polymerization inhibitors include hydroquinone or hydroquinone monomethyl ether (4-methoxyphenol), methylhydroquinone, 2,5-di-t-butylhydroquinone, 2-methyl-p-hydroquinone, 2, 3-dimethylhydroquinone, trimethylhydroquinone 4-methylbenzcatechin, t-butylhydroquinone, 3-methylbenzcatechin, benzoquinone, 2-methyl-p-hydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone, t-butylhydroquinone, 4 -Ethoxyphenol, 4-butoxyphenol, hydroquinone monobenzyl ether, p-phenoxyphenol, 2-methylhydroquinone, tetramethyl-p-benzoquinone, diethyl-1,4-cyclohexanedione-2,5-dicarboxylate, phenyl -p-benzoquinone, 2,5-dimethyl-3-benzyl-p-benzoquinone, 2-isopropyl-5-methyl-p-benzoquinone (thymoquinone), 2,6-diisopropyl-p-benzoquinone, 2,5-dimethyl- 3-hydroxy-p-benzoquinone, 2,5-dihydroxy-p-benzoquinone, embellin, tetrahydroxy-p-benzoquinone, 2,5-dimethoxy-1,4-benzoquinone, 2-amino-5-methyl-p-benzoquinone 2,5-bisphenylamino-1,4-benzoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 2-anilino-1,4-naphthoquinone, anthraquinone, N, N-dimethylindoaniline, N, N -Diphenyl-p-benzoquinonediimine, 1,4-benzoquinonedioxime, cerlignon, 3,3'-di-t-butyl-5,5'-dimethyldiphenoquinone, p-rosoleic acid (orin), 2, 6- Di-t-butyl-4-benzylidene-benzoquinone, 2,5-di-t-butyl-amylhydroquinone and the like are included.

  Examples of N-oxyl compounds as radical polymerization inhibitors (nitroxyl- or N-oxyl-groups, compounds having at least one> NO- group) include 4-hydroxy-2,2,6, 6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 2,2,6,6-tetramethylpiperidine-N-oxyl, BASF Aktinengesellschaft Ubinul 4040P, 4,4 ′, 4 ″ -tris- (2,2,6,6-tetramethylpiperidine-N-oxyl) phosphite, 3-oxo-2,2,5,5-tetramethylpyrrolidine-N-oxyl, 1-oxyl- 2,2,6,6-tetramethyl-4-me Toxipiperidine, 1-oxyl-2,2,6,6-tetramethyl-4-trimethylsilyloxypiperidine, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-2-ethylhexanoate 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-sebacate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-stearate, 1-oxyl- 2,2,6,6-tetramethylpiperidin-4-yl-benzoate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl- (4-t-butyl) benzoate, bis- ( 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate, bis- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipate, 1,10 -Decandioic acid-bis- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl Esters, bis- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) n-butylmalonate, bis- (1-oxyl-2,2,6,6-tetramethylpiperidine- 4-yl) phthalate, bis- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) isophthalate, bis- (1-oxyl-2,2,6,6-tetramethylpiperidine -4-yl) terephthalate, bis- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) hexahydroterephthalate, N, N′-bis- (1-oxyl-2,2, 6,6-tetramethylpiperidin-4-yl) adipinamide, N- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) caprolactam, N- (1-oxyl-2,2) , 6,6-Tetramethylpiperidin-4-yl) dodecylsuccinimide, 2,4,6-tris- [N-butyl -N- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl] triazine, N, N'-bis- (1-oxyl-2,2,6,6-tetramethylpiperidine- 4-yl) -N, N′-bis-formyl-1,6-diaminohexane, 4,4′-ethylene-bis- (1-oxyl-2,2,6,6-tetramethylpiperazin-3-one ) Etc. are included.

  Examples of aromatic amines or phenylenediamines as radical polymerization inhibitors include N, N-diphenylamine, N-nitroso-diphenylamine, nitrosodiethylaniline, p-phenylenediamine, N, N′-diisobutyl-p-phenylenediamine, N, N′-dialkyl-p-phenylenediamine, such as N, N′-diisopropyl-p-phenylenediamine (the two alkyl groups may be the same or different, each containing 1 to 4 carbon atoms, Or Irganox 5057 (Firma Ciba Spezialitaetenchemie), N-phenyl-p-phenylenediamine, N, N′-diphenyl-p-phenylenediamine, N-isopropyl-N-phenyl-p-phenylenediamine N, N'-di-s-butyl-p-phenylenediamine (BASF Aktiengesellschaft's Kerobit BPD), N-pheny -N'-isopropyl-p-phenylenediamine (Vulkanox 4010 from Bayer AG), N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, N-phenyl-2-naphthylamine , Iminodibenzyl, N, N′-diphenylbenzidine, N-phenyltetraaniline, acridone, 3-hydroxydiphenylamine, 4-hydroxydiphenylamine and the like.

  Examples of imines as radical polymerization inhibitors include methylethylimine, (2-hydroxyphenyl) benzoquinoneimine, (2-hydroxyphenyl) benzophenoneimine, N, N-dimethylindoaniline, thionine (7-amino-3- Imino-3H-phenothiazine), methylene violet (7-dimethylamino-3-phenothiazine) and the like.

  Examples of sulfonamides as radical polymerization inhibitors include N-methyl-4-toluolsulfonamide, Nt-butyl-4-toluolsulfonamide, Nt-butyl-N-oxyl-4-toluene. Allsulfonamide, N, N′-bis (4-sulfanylamide) piperidine, 3-{[5- (4-aminobenzoyl) -2,4-dimethylbenzoylsulfonyl] ethylamino} -4-methylbenzolsulfonic acid, etc. Is included.

  Examples of oximes as radical polymerization inhibitors include aldoxime, ketoxime or amidoxime, preferably diethyl ketoxime, acetoxime, methyl ethyl ketoxime, cyclohexanone oxime, benzaldehyde oxime, benzyldioxime, dimethylglyoxime, 2-pyridine aldoxime, salicyl. Aldoxime, phenyl-2-pyridylketoxime, 1,4-benzoquinone dioxime, 2,3-butanedione dioxime, 2,3-butanedione monooxime, 9-fluorenone oxime, 4-t-butyl-cyclohexanone oxime N-ethoxy-acetimidic acid ethyl ester, 2,4-dimethyl-3-pentanone oxime, cyclododecanone oxime, 4-heptanone oxime and di-2-furanylethanedione dioxime. Other examples of oximes include their reaction with other aliphatic or aromatic oximes or alkyl transfer agents such as alkyl halogenides, -triflate, -sulfonate, -tosylate, -carbonate, -sulfate, -phosphate, etc. It may be a product.

  Examples of hydroxylamine as a radical polymerization inhibitor include N, N-diethylhydroxylamine, compounds described in the international patent application PCT / EP2003 / 03139.

  The urea derivative as the radical polymerization inhibitor is, for example, urea or thiourea.

  Examples of phosphorus-containing compounds as radical polymerization inhibitors include triphenylphosphine, triphenyl phosphite, hypophosphorous acid, trinonyl phosphite, triethyl phosphite or diphenylisopropylphosphine.

  Examples of sulfur-containing compounds as radical polymerization inhibitors include diphenyl sulfide, phenothiazine and sulfur-containing natural materials such as cysteine.

  Complexing agents based on tetraazaannulene (TAA) as radical polymerization inhibitors are described, for example, in Chem. Soc. Rev. 1998, 27, 105-115, for example, dibenzotetraaza [14] ring and porphyrin.

  Other examples of radical polymerization inhibitors include carbon salts, chlorides, dithiocarbamic acid, sulfuric acid, salicylic acid, acetic acid, stearic acid, ethylhexanoic acid and other metal salts (copper, manganese, cerium, nickel, chromium, etc.) It is.

  Further, the N-oxyl free radical compound having a vinyl ether functional group described in Macromol. Rapid Commun., 28, 1929 (2007) has both a polymerizable function and a radical scavenging function in the same molecule. This compound can also be added to the inkjet ink according to the embodiment from the viewpoints of curability and ink storage stability. The polymer obtained by polymerizing this compound has a free radical in the side chain. This polymer can also be added to the inkjet ink according to the embodiment from the viewpoints of cured film properties such as solvent resistance, scratch resistance, and weather resistance, and ink storage stability.

  The content of the radical polymerization inhibitor in the inkjet ink (per 1 g) is preferably 1.0 to 5000 μg, and more preferably 10 to 2000 μg. If it is 1.0 μg / g or more, desired storage stability can be obtained, ink thickening and liquid repellency with respect to the ink jet nozzle can be obtained, and this is preferable from the viewpoint of ejection stability. Moreover, if it is 5000 microgram / g ink or less, the high generation sensitivity can be maintained, without impairing the acid generation efficiency of a polymerization initiator.

<Other additives>
The ink-jet ink may further contain various additives as necessary. Examples of various additives include surfactants, lubricants, fillers, antifoaming agents, gelling agents, thickeners, specific resistance adjusting agents, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, Anti-corrosive agent, rust preventive agent, etc. are included. These are added depending on the purpose of improving the injection stability, compatibility with the print head and ink packaging container, storage stability, image storage stability, and other various performances. Furthermore, it can contain a small amount of solvent such as ester solvent, ether solvent, ether ester solvent, ketone solvent, aromatic hydrocarbon solvent, nitrogen-containing organic solvent.

  Specific examples of the solvent include dimethyl sulfoxide, diethyl sulfoxide, methyl ethyl sulfoxide, diphenyl sulfoxide, tetraethylene sulfoxide, dimethyl sulfone, methyl ethyl sulfone, methyl-isopropyl sulfone, methyl-hydroxyethyl sulfone, sulfolane, or N-methyl- 2-pyrrolidone, 2-pyrrolidone, β-lactam, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2 -Oxazolidinone, γ-butyrolactone, γ-valerolactone, isophorone, cyclohexanone, propylene carbonate, anisole, methyl ethyl ketone, acetone, ethyl lactate, butyl lactate, dioxane, ethyl acetate, butyl acetate, diethylene glycol Methyl ether, dibasic ester, methoxybutyl acetate, and the like. When a solvent is added to the ink in an amount of 1.5 to 30%, preferably 1.5 to 15%, adhesion to a resin recording medium such as polyvinyl chloride is improved.

  Other specific examples of the solvent include alkylene glycol monoalkyl ethers such as diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, ethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, etc. Alkylene glycol dialkyl ethers, alkylene glycol monoalkyl ether acetates such as ethylene glycol monobutyl ether acetate, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, ethylene glycol diacetate, propylene glycol diacetate .

  Examples of the surfactant contained in the inkjet ink in the present embodiment include anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkylallyl Nonionic surfactants such as ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, cationic surfactants such as alkylamine salts and quaternary ammonium salts, silicone-based and fluorine-based surfactants Agents and the like. In particular, a silicone-based or fluorine-based surfactant is preferable.

  By adding a silicone-based or fluorine-based surfactant, it is possible to further suppress ink mixing on recording media made of various hydrophobic resins such as vinyl chloride sheets and recording media that absorb slowly such as printing paper. And high-quality printed images can be obtained. These surfactants are particularly preferably used in combination with a water-soluble organic solvent having a low surface tension.

  Preferred examples of the silicone-based surfactant include polyether-modified polysiloxane compounds such as KF-351A, KF-642, X-22-4272 manufactured by Shin-Etsu Chemical Co., Ltd., BYK307, BYK345, BYK347 manufactured by Big Chemie. BYK348, TSF4452 manufactured by Toshiba Silicone Co., and the like.

  The fluorosurfactant means one obtained by substituting a part or all of hydrogen bonded to carbon of the hydrophobic group of a normal surfactant with fluorine. The fluorine-based surfactant preferably has a perfluoroalkyl group in the molecule.

  Fluorosurfactants are available from DIC under the name Megafac F; from Asahi Glass under the name Surflon; from Minnesota Mining & Manufacturing Company Fluorad Under the trade name FC; under the trade name Monflor from Imperial Chemical Industry; under the trade name Zonyls from EI DuPont Nemeras &Company; Ricobet from Farbeberke Hoechst (Licowet) under the trade name VPF; also commercially available from Neos under the trade name Fantage.

  The addition amount of the surfactant in the inkjet ink is preferably 0.1% by mass or more and less than 2.0% by mass with respect to the total mass of the ink.

  If the surface tension of the ink-jet ink is 15 mN / m or more (25 ° C.), the area around the nozzle of the ink-jet head gets wet and the ejection performance is unlikely to decrease. Further, it is preferable that the surface tension of the ink-jet ink is less than 35 mN / m (25 ° C.) because it is well wetted with a coated paper or a resin-made recording medium whose surface energy is lower than that of normal paper, and whitening hardly occurs.

<Ink physical properties>
The inkjet ink in the present embodiment preferably has the same physical properties as a normal active energy ray-curable inkjet ink.

  The viscosity of the inkjet ink is preferably 20 to 500 mPa · s at 25 ° C. Or it is 20-500 mPa * s in 25 degreeC, and it is preferable that it is 5-30 mPa * s above 40 degreeC. Furthermore, it is preferable that the share rate dependency be as small as possible.

  By increasing the viscosity of the inkjet ink at room temperature, it can suppress the penetration of the ink into the absorbent recording medium, reduce the uncured monomer, reduce the odor, and suppress the dot bleeding upon landing, Image quality is improved. Moreover, even if the surface tension of the base material changes, similar dots can be formed, so that similar image quality can be formed. If it is less than 20 mPa · s, the effect of preventing bleeding is small. If it is higher than 500 mPa · s, there will be a problem in the supply of the ink liquid. Further, since the viscosity of the ink at 25 ° C. is within the range of the present invention, when the ejected ink lands on the recording medium, the viscosity increases and it is difficult to receive oxygen inhibition. For this reason, the ink droplets can be cured more easily, and even with a small droplet ink having a relatively large surface area relative to the ink droplet, image formation can be performed without any problem. On the other hand, the conventional ink is greatly affected by the inhibition of curing due to the small droplets, and it has not been possible to prevent the occurrence of poor curing only by setting the viscosity range to the range of the present invention. Further, in order to obtain a stable ejection property at the time of ejection, the ink is preferably 5 to 30 mPa · s.

  The inkjet ink in the present embodiment preferably does not contain a gel-like substance having an average particle size exceeding 1.0 μm, excluding pigment particles.

  The electrical conductivity of the inkjet ink in this embodiment is preferably 10 μS / cm or less. This is to suppress electrical corrosion inside the inkjet head. In the continuous type, the conductivity of the inkjet ink needs to be adjusted to 0.5 mS / cm or more. In this case, it is necessary to adjust the conductivity with the electrolyte.

  The ink-jet ink according to the embodiment shows a heat generation peak with a calorific value per unit mass of 10 mJ / mg or more when DSC measurement of the ink is performed in a range of 25 ° C. to −25 ° C. at a rate of 5 ° C. per minute. Preferably not. By doing in this way, generation | occurrence | production of a gel and generation | occurrence | production of a precipitate can be suppressed when an inkjet ink is preserve | saved at low temperature. The calorific value in the DSC measurement is adjusted by selecting the components of the inkjet ink.

<Ink preparation method>
Ink jet ink is produced by dispersing a polymerizable monomer, a photopolymerization initiator, a colorant, and, when the colorant is a pigment, a pigment dispersant using a normal disperser such as a sand mill. .

  Preferably, a pigment concentrate is prepared in advance, and the pigment concentrate is diluted with a polymerizable monomer to prepare an inkjet ink. According to this method, sufficient dispersion can be performed with a normal disperser, and excessive dispersion energy and a great amount of dispersion time are not required. As a result, it is possible to prepare an ink that is less likely to be deteriorated during the dispersion step and has excellent stability.

  The prepared ink is preferably filtered through a filter having a pore diameter of 3 μm or less (preferably 1 μm or less).

<Recording medium>
In the image forming method according to the embodiment, the active energy ray-curable inkjet ink is ejected as a droplet onto a recording medium by an inkjet method. The ejected liquid droplets land on the recording medium, and the landed liquid droplets are irradiated with actinic rays.

  The recording medium in the image forming method according to the embodiment may be any of a wide range of synthetic resins conventionally used for various applications. Specific examples of the recording medium include polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, polybutadiene terephthalate, and the like. The thickness and shape of these synthetic resin base materials are not limited at all. In addition, metals, glass, printing paper, etc. can be used.

  Specific examples of polyvinyl chloride which is one of the recording media in the image forming method according to the embodiment include KSM-VS, KSM-VST, KSM-VT (above, manufactured by Kimoto Co., Ltd.), P-223RW, P- 224RW, P-249ZW, P-284ZC (above, manufactured by Lintec Corporation), MPI3023 (produced by Toyo Corporation), NIJ-CAPVC, NIJ-SPVCGT (above, manufactured by Nichie Corporation), JT5129PM, JT5728P, JT5822P, JT5829P, JT5829R, JT5829PM, JT5829RM, JT5929PM (manufactured by Mactac), VGL-137, SVGS-137, MD3-200, MD3-301M, MD5-100, MD5-101M, MD5-105 (and above, Metam) rk), 640M, 641G, 641M, 3105M, 3105SG, 3162G, 3164G, 3164M, 3164XG, 3164XM, 3165G, 3165SG, 3165M, 3169M, 3451SG, 3551G, 3551M, 3631, 3641M, 3651G, 3651G, 3651SG, 3951G 3641M (manufactured by Orafol), IJ180CV2 (manufactured by 3M), and the like.

  The recording medium may be a resin substrate containing no plasticizer or a non-absorbing inorganic substrate. There are no particular restrictions on various properties such as the thickness, shape, color, softening temperature, and hardness of the substrate.

  Examples of resin substrates that do not contain a plasticizer include ABS resin, polycarbonate (PC) resin, polyacetal (POM) resin, polyamide (PA) resin, polyethylene terephthalate (PET) resin, polyimide (PI) resin, acrylic resin, Examples include polyethylene (PE) resin, polypropylene (PP) resin, and hard polyvinyl chloride (PVC) resin that does not contain a plasticizer.

  Examples of non-absorbing inorganic base materials include glass plates, metal plates such as iron and aluminum, ceramic plates, and the like. These inorganic substrates are characterized by not having an ink-absorbing layer on the surface.

  These substrates can be used alone or in combination of a plurality of types of substrates.

<Injection of inkjet ink>
Ink jet ink is ejected as droplets from a nozzle (eject port) of an ink jet head onto a recording medium. The ink jet head system may be an on-demand system or a continuous system. In addition, the injection method is an electro-mechanical conversion method (for example, single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), electro-thermal conversion method (for example, thermal ink jet) Any of a type | mold, a bubble jet (trademark) type | mold etc. may be sufficient.

  The droplet size ejected from the nozzles of the inkjet head can be adjusted by the nozzle diameter of the head, the magnitude of the voltage applied to the inkjet head, and the pattern. For example, by using a “pulling” method in which the pressure chamber communicating with the nozzle opening is expanded and then contracted, the mass of the ink droplet can be reduced, so that the droplet size can be reduced.

  In order to form a high-definition and high-quality image with little unevenness, the droplet size is preferably 0.1 to 12 pl. If the droplet size is smaller than 0.1 pl, the number of droplets for image formation becomes excessive, the time required for image formation becomes long, and nozzle clogging is likely to occur. In addition, when the droplet size is smaller than 0.1 pl, the surface area per unit volume when the ink jet ink is ejected from the nozzle or when it is landed on the base material is increased, so that it is easily affected by outside air. On the other hand, if the droplet size is larger than 12 pl, the dot diameter per dot increases, so the resolution of the formed image decreases. For this reason, there are problems in the roughness of image quality and the reproducibility of fine characters when viewed from close.

  In the image forming method according to the embodiment, the inkjet ink may be ejected in a heated state. Since the viscosity of the inkjet ink is reduced by heating, the injection stability is increased. The heating temperature of the inkjet ink is preferably 35 to 100 ° C, more preferably 35 to 80 ° C. A method for heating and keeping the ink-jet ink at a predetermined temperature is not particularly limited. For example, insulate the ink supply system such as the ink tank, supply pipe, front chamber ink tank just before the head, pipe with filter, piezo head, etc. that make up the inkjet head carriage, and use panel heater, ribbon heater, warm water, etc. There is a method of heating to a predetermined temperature.

  The inkjet ink is preferably heated and kept at a control width of a set temperature ± 5 ° C., more preferably a control width of a set temperature ± 2 ° C., and particularly preferably a control width of a set temperature ± 1 ° C. .

<Irradiation of active energy rays to ink landed on recording medium>
The inkjet ink droplets ejected onto the recording medium are irradiated with active energy rays such as ultraviolet rays, and the components contained in the ink are cured.

  Examples of the active energy rays to be irradiated include ultraviolet rays, near ultraviolet rays, natural light (including filter cut products), and the like, and ultraviolet rays are preferable. Examples of the ultraviolet light irradiation light source include a light emitting diode (LED), a metal halide lamp, a xenon lamp, a carbon arc lamp, a chemical lamp, a low pressure mercury lamp, a high pressure mercury lamp, and the like. For example, H lamps, D lamps, V lamps, etc. manufactured by Fusion System are commercially available.

  The LED can be turned on instantaneously, has a long life, has little radiant heat, is easy to control the amount of light, has a very narrow emission wavelength width (half-value width), and has low power consumption. LED light sources are also commercially available. The wavelength of the irradiation light source is preferably 350 nm to 450 nm, and more preferably 365 nm to 400 nm. This is because it is safe because it is on the long wavelength side in the light ultraviolet region.

In the image forming method according to the present embodiment, it is preferable that the integrated light amount applied to the inkjet ink droplets landed on the recording medium is 200 mJ / cm ² or less per droplet. The inkjet ink in the present embodiment can sufficiently undergo a curing reaction even when the integrated light amount per drop is 200 mJ / cm ² or less. Therefore, it is advantageous from the viewpoint of energy saving / space saving and cost.

In the image forming method in the present embodiment, the illuminance of the active energy ray irradiation light source is preferably 5 W / cm ² or less. A light source with an illuminance higher than 5 W / cm ² has a large amount of heat generation, which may cause problems such as deformation of a recording medium with low heat resistance, or increased leakage of light and ink curing on the head nozzle surface. . In addition, a light source with high illuminance has high energy consumption, a large light source space, and cost increases.

  In the image forming method according to the embodiment, the active energy ray is preferably irradiated between 0.001 second and 1.0 second after the ink droplet has landed on the recording medium, and more preferably 0.001. Irradiation between 2 seconds and 0.5 seconds. In order to form a high-definition image, it is preferable that the interval from landing to irradiation is as short as possible.

  The irradiation method of an active energy ray is not specifically limited, For example, it can carry out with the following method. A light source is provided on both sides of the head unit, the head and the light source are scanned by a shuttle method, and irradiation is performed after a certain time from ink landing. Further, the curing is completed by irradiating light from another light source that is not driven (see Japanese Patent Application Laid-Open No. 60-132767). Alternatively, light may be irradiated using an optical fiber, or ultraviolet light from a collimated light source may be reflected by a mirror surface provided on the side of the head unit and irradiated to the recording unit (US Pat. No. 6, 145,979).

  Moreover, you may divide active energy ray irradiation into two steps. For example, a method of first irradiating active energy rays by the above-described method between 0.001 and 2.0 seconds after ink landing, and further irradiating active energy rays after the completion of all printing is one of preferred embodiments. is there. By dividing the irradiation of the active energy ray into two stages, it is possible to further suppress the shrinkage of the recording material that occurs during ink curing.

<Total ink film thickness after ink landing>
In the ink jet recording method according to the embodiment, the total ink film thickness after the ink has landed on the recording medium and cured by irradiation with active energy rays is preferably 2 to 20 μm. This is for suppressing curling and wrinkling of the recording medium and changes in the texture of the recording medium. “Total ink film thickness” means the maximum value of the film thickness of ink drawn on a recording medium. Whether it is a single color or a two-color overlap (secondary color), a three-color overlap, or a four-color overlap (white ink base), the total ink film thickness is preferably 2 to 20 μm.

(1) Total ink film thickness 1
In the image forming method according to the embodiment, 1) the polymerizable monomer is a combination of a monomer having a low electron density and a monomer having a high electron density, and 2) the droplet size to be ejected is 0.1 to 12 pl. Therefore, regardless of the printing environment, it is possible to form a high-definition and high-quality image with reduced unevenness, and to reduce the amount of irradiation light.

  First, 1) Since a monomer having a low electron density and a monomer having a high electron density are combined as the polymerizable monomer, the photosensitivity is high. It is considered that the reason why the photosensitivity is high is that charge transfer complex polymerization occurs. In addition, the light sensitivity does not deteriorate depending on the printing environment. Therefore, 2) Even if the droplet size to be ejected is reduced to 0.1 pl to 12 pl, it is easily photocured.

  On the other hand, the radical polymerization type inkjet ink reacts with oxygen in the printing environment at the end of polymerization to produce hydroperoxy radicals with poor reactivity, and thus the progress of the polymerization reaction is hindered. Further, in the cationic polymerization type ink-jet ink, moisture in the outside air binds to an acid generated from the polymerization initiator and inhibits the progress of the polymerization reaction. For this reason, especially when the droplet size to be ejected is 12 pl or less, the photocuring sensitivity is greatly lowered, and the image quality is likely to be lowered.

  In contrast, since the image forming method according to the embodiment combines a monomer having a low electron density and a monomer having a high electron density, the reactivity with oxygen at the growth end during polymerization is slow. That is, it is difficult to receive polymerization inhibition by oxygen. Moreover, there is little influence on the polymerization reaction by moisture. Therefore, even if the droplet size to be ejected is 12 pl or less, high curing sensitivity is maintained and a high-quality image is formed. This is presumably because the image forming method according to the embodiment uses an active energy ray-curable inkjet ink by a charge transfer complex polymerization method (CT polymerization method).

(2) Total ink film thickness 2
In the image forming method according to the embodiment, 1) a monomer having a low electron density and a monomer having a high electron density are combined as a polymerizable monomer, and 2) an actinic ray energy ray at the time of image formation has a wavelength of 305 to 410 nm. The illuminance is 8 W / cm ² or less and the integrated light quantity is in the range of ^{20 to} 200 mJ / cm ² . As a result, an image having weather resistance can be provided without causing thermal damage even to a heat-sensitive substrate.

  First, 1) Since a monomer having a low electron density and a monomer having a high electron density are combined as the polymerizable monomer, the photosensitivity is high. It is considered that the reason why the photosensitivity is high is that charge transfer complex polymerization occurs. In addition, the light sensitivity does not deteriorate depending on the printing environment. Therefore, 2) it is possible to form an image having weather resistance even if the active energy ray to be irradiated is made to have a low illuminance and a low integrated light amount.

  On the other hand, the radical polymerization type inkjet ink reacts with oxygen in the printing environment at the end of polymerization to produce hydroperoxy radicals with poor reactivity, and thus the progress of the polymerization reaction is hindered. Further, in the cationic polymerization type ink-jet ink, moisture in the outside air binds to an acid generated from the polymerization initiator and inhibits the progress of the polymerization reaction. For this reason, when the active energy ray is set to a low illuminance, the photocuring sensitivity is greatly lowered, and the weather resistance of the image tends to be lowered.

  In contrast, since the image forming method according to the embodiment combines a monomer having a low electron density and a monomer having a high electron density, the reactivity with oxygen at the growth end during polymerization is slow. That is, it is difficult to receive polymerization inhibition by oxygen. Moreover, there is little influence on the polymerization reaction by moisture. For this reason, even if the active energy ray to be irradiated has a low illuminance, high curing sensitivity is maintained, and an image having weather resistance is formed even with a low integrated light amount. This is presumably because the image forming method according to the embodiment uses an active energy ray-curable inkjet ink by a charge transfer complex polymerization method (CT polymerization method).

<Inkjet recording apparatus>
The ink jet recording method according to the embodiment can be performed using an ink jet recording apparatus (ink jet printer). Examples of the ink jet recording apparatus include, but are not limited to, a serial head type recording apparatus and a line head type recording apparatus. Hereinafter, each recording apparatus will be described with reference to the drawings, but the ink jet recording apparatus is not limited thereto.

  FIG. 1 is a front view of a serial head type ink jet recording apparatus and shows a configuration of a main part of the apparatus. The recording apparatus 1 includes a head carriage 2, a recording head 3, an irradiation unit 4, a platen unit 5, and the like. In the recording apparatus 1, the platen unit 5 is installed under the recording medium P. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs the ultraviolet rays that have passed through the recording medium P. As a result, a high-definition image can be stably reproduced.

  The recording medium P is guided by the guide member 6 and moves from the front side to the back side in FIG. 1 by the operation of the conveying means (not shown). A head scanning means (not shown) scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction.

  The head carriage 2 is installed facing the upper side of the recording medium P, and includes a plurality of recording heads 3 according to the number of colors of images to be printed on the recording medium P. The recording head 3 is arranged with the ejection port 31 facing the recording medium P. The head carriage 2 of the recording apparatus of FIG. 1 accommodates four types of recording heads 3 of yellow (Y), magenta (M), cyan (C), and black (K), but is accommodated in the head carriage 2. The number of colors of the recording head 3 is appropriately set.

  Inside the recording head 3, a plurality of ink chambers are arranged, and each ink chamber is provided with ejection means (not shown). The injection means is, for example, a piezo element. The ink chamber disposed inside the recording head 3 is supplied with active energy ray-curable ink by an ink supply means (not shown). The active energy ray-curable ink supplied to the ink chamber is ejected from the ejection port 31 toward the recording medium P by the operation of the ejection unit.

  The inkjet ink ejected from the ejection port 31 of the recording head 3 is the above-described active energy ray-curable inkjet ink, and when irradiated with the active energy ray, the polymerizable monomer is crosslinked or polymerized by the action of the polymerization initiator. It has the property of causing a reaction to cure.

  The recording head 3 can scan from one end to the other end of the recording medium P along the Y direction by driving the head scanning means. The recording head 3 ejects ink-jet ink droplets to land on a certain area (landing possible area) of the recording medium P while scanning.

  After the recording head 3 is scanned as many times as necessary and ink is ejected to one landable area, the recording medium P is appropriately moved from the front side to the back side in FIG. The ink jet ink droplets are ejected and landed on the landable area adjacent to the one landable area by the recording head 3 while scanning the recording head 3 again.

  By repeating the above-described operation, an image composed of an aggregate of inkjet ink droplets is formed on the recording medium P.

  The irradiation unit 4 is installed on both sides of the head carriage 2 so as to be fixed substantially parallel to the recording medium P. The irradiation means 4 includes an irradiation light source 8 that emits ultraviolet light in the specific wavelength region described above, and a filter (not shown) that transmits ultraviolet light of a specific wavelength.

  The irradiation area of the irradiation unit 4 may be the same as or larger than the landing possible area by the recording head 3.

  In order to prevent the ink ejection unit 31 from being exposed to light, the entire recording head 3 is shielded from light, and the ink ejection unit 31 and the recording material of the recording head 3 are further separated from the distance h1 between the irradiation unit 4 and the recording medium P. It is preferable to increase the distance h2 from P (h1 <h2) or to increase the distance between the recording head 3 and the irradiation means 4. Further, it is preferable that a bellows structure 7 is provided between the recording head 3 and the irradiation means 4.

  FIG. 2 is a top view of the line head type ink jet recording apparatus, and shows the main configuration of the apparatus. The recording apparatus 1 includes a head carriage 2 in which a plurality of recording heads 3 are fixedly disposed, and an irradiation unit 4.

  The plurality of recording heads 3 provided in the head carriage 2 are arranged so as to cover the entire width of the recording medium P.

  The irradiation unit 4 is disposed downstream of the head carriage 2 in the conveyance direction of the recording medium P. The irradiation means 4 has a plurality of LED light sources, and the plurality of LED light sources are arranged so as to cover the entire width of the recording medium P. That is, the irradiation means 4 is arranged so as to cover the entire area of the ink print surface. Each LED light source has a maximum illuminance, for example, at 395 nm.

  In the line head type ink jet recording apparatus 1, the head carriage 2 and the irradiation means 4 are fixed, and only the recording medium P is conveyed. Ink droplets ejected from the fixedly arranged recording head 3 land on the transported recording medium P, and light from the irradiation unit 4 is irradiated to the landed ink, so that the ink is cured. Thereby, an image is formed.

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

マレイミド化合物１ Synthesis Example 1 Synthesis of maleimide compound 1

Maleimide compound 1

  N-β-hydroxypropylmaleimide was synthesized by the method described in the document “Organization of Synthetic Organic Chemistry, Vol. 23, No. 2 (1965)”. Next, in a 300 mL eggplant-shaped flask equipped with a stirrer, a decompression device and a trap, 5.0 g of the aforementioned N-β-oxyisopropylmaleimide, 3.03 g of sebacic acid, 0.7 g of p-toluenesulfonic acid monohydrate, 2 , 6-tert-butyl-p-cresol 0.05 g and toluene 20 mL were sequentially charged. Then, the reaction was carried out by stirring for 12 hours at a reaction temperature of 80 ° C. while azeotropically distilling off generated water and toluene under reduced pressure. The solution after completion of the reaction was cooled to room temperature, dissolved in 300 mL of ethyl acetate, and washed three times with 100 mL of saturated aqueous sodium hydrogen carbonate solution and once with 100 mL of saturated brine. The obtained organic layer was dried over magnesium sulfate and then concentrated to obtain 3.3 g of maleimide compound 1. Maleimide compound 1 was a solid at room temperature.

The NMR measurement results of the obtained maleimide compound 1 are shown below.
1H NMR (400 MHz, CDCl ₃ ): 6.72 (s, 4H, —CH═CH—), 5.12-5.14 (m, 2H, — (C═O) —O—CH—), 3 .58-3.71 (m, 4H, N—CH ₂ —), 2.22 (t, 4H, —O— (C═O) —CH ₂ —), 1.54 (brs, 4H, —CH _{2 -), 1.22-1.42 (m,} 8H, -CH 2 -), 1.24 (d, 6H, -CH 3).
13C NMR (100 MHz, CDCl ₃ ): 173.3 [— (C═O) —O—], 170.5 [N— (C═O)], 134.1 (—CH═CH—), 68. 0 [— (C═O) —O—CH—], 41.9 (—N—CH ₂ —), 34.2 [—O— (C═O) —CH ₂ —], 29.0 (— _{CH 2 -), 28.9 (-CH} 2 -), 24.6 (-CH 2 -), 17.6 (-CH 3).

マレイミド化合物２ Synthesis Example 2 Synthesis of Maleimide Compound 2

Maleimide compound 2

  Maleimide compound 2 was prepared in the same manner as in Synthesis Example 1 except that 4.55 g of N-β-hydroxyethylmaleimide synthesized in the same manner as described above was used instead of 5.0 g of N-β-hydroxypropylmaleimide described above. 3.3 g was obtained. This maleimide compound 2 was solid at room temperature.

The NMR measurement results of the obtained maleimide compound 2 are shown below.
1H NMR (400 MHz, CDCl ₃ ): 6.73 (s, 4H, —CH═CH—), 4.23 (t, 4H, — (C═O) —O—CH ₂ —), 3.79 ( t, 4H, N—CH ₂ —), 2.26 (t, 4H, —O— (C═O) —CH ₂ —), 1.57 (t, 4H, —CH ₂ —), 1.27 _{(s, 8H, -CH 2 -} ).
13C NMR (100 MHz, CDCl ₃ ): 173.5 [— (C═O) —O—], 170.4 [N— (C═O)], 134.2 (—CH═CH—), 61. 1 [— (C═O) —O—CH ₂ —], 36.9 (—N—CH ₂ —), 33.9 [—O— (C═O) —CH ₂ —], 28.9 ( _{2C) (- CH 2 -)} , 24.6 (-CH 2 -).

マレイミド化合物３ Synthesis Example 3 Synthesis of Maleimide Compound 3

Maleimide compound 3

  2-maleimido-2-methylacetic acid was synthesized by the method described in Japanese Patent No. 3599160. Next, in a 300 mL eggplant-shaped flask equipped with a stirrer, a decompression device and a trap, 33.8 g of the above-mentioned 2-maleimido-2-methylacetic acid, 10.2 g of diethylene glycol, 4.47 g of p-toluenesulfonic acid monohydrate, , 6-tert-butyl-p-cresol 0.35 g and toluene 20 mL were sequentially charged. Then, the reaction was carried out by stirring at a reaction temperature of 80 ° C. for 5 hours while azeotropically distilling off the water and toluene produced under reduced pressure. After completion of the reaction, the resulting solution was cooled to room temperature, dissolved in 300 mL of ethyl acetate, and washed 3 times with 100 mL of saturated aqueous sodium hydrogen carbonate solution and once with 100 mL of saturated brine. The obtained organic layer was dried over magnesium sulfate and then concentrated to obtain 24.7 g of maleimide compound 3. This maleimide compound 3 was solid at room temperature.

The NMR measurement results of the obtained maleimide compound 3 are shown below.
1H NMR (400 MHz, CDCl ₃ ): 6.75 (s, 4H, —CH═CH—), 4.82 (q, 2H, N—CH—), 4.20-4.32 (m, 4H, _{- (C = O) -O-} CH 2 -), 3.58-3.67 (m, 4H, -CH 2 -O -), 1.59 (d, 2H, -CH 3).
13C NMR (100 MHz, CDCl ₃ ): 169.7 [N— (C═O)], 169.5 [— (C═O) —O—], 134.3 (—CH═CH—), 68. 7 [— (C═O) —O—CH ₂ —], 64.6 (—CH ₂ —O—), 47.4 (—CH—), 15.1 (—CH ₃ ).

マレイミド化合物４ Synthesis Example 4 Synthesis of Maleimide Compound 4

Maleimide compound 4

  25.4 g of maleimide compound 4 was obtained in the same manner as in Synthesis Example 3 except that 11.4 g of 1,6-hexanediol was used instead of 10.2 g of diethylene glycol. Maleimide compound 4 was a solid at room temperature.

The NMR measurement results of the obtained maleimide compound 4 are shown below.
1H NMR (400 MHz, CDCl ₃ ): 6.75 (s, 4H, —CH═CH—), 4.77 (q, 2H, N—CH—), 4.07-4.17 (m, 4H, _{- (C = O) -O-} CH 2 -), 1.63 (d, 6H, -CH 3), 1.58-1.63 (m, 4H, -CH 2 -), 1.24-1 _{.33 (m, 4H, -CH 2} -).
13C NMR (100 MHz, CDCl ₃ ): 169.8 [N— (C═O)], 169.5 [— (C═O) —O—], 134.2 (—CH═CH—), 65. 5 [— (C═O) —O—CH ₂ —], 47.4 (N—CH—), 28.1 (—CH ₂ —), 25.1 (—CH ₂ —), 15.0 ( -CH _3).

マレイミド化合物５ Synthesis Example 5 Synthesis of maleimide compound 5

Maleimide compound 5

  22.3 g of maleimide compound 5 was obtained in the same manner as in Synthesis Example 3 except that 16.7 g of 1,10-decanediol was used instead of 10.2 g of diethylene glycol. Maleimide compound 5 was solid at room temperature.

The NMR measurement results of the obtained maleimide compound 5 are shown below.
1H NMR (400 MHz, CDCl ₃ ): 6.74 (s, 4H, —CH═CH—), 4.78 (q, 2H, N—CH—), 4.08-4.18 (m, 4H, _{- (C = O) -O-} CH 2 -), 1.58-1.65 (m, 10H, -CH 2 -, - CH 3), 1.20-1.28 (m, 12H, -CH _2- ).
13C NMR (100 MHz, CDCl ₃ ): 169.8 [N— (C═O)], 169.6 [— (C═O) —O—], 134.3 (—CH═CH—), 65. 8 [— (C═O) —O—CH ₂ —], 47.5 (N—CH—), 29.1 (—CH ₂ —), 28.9 (—CH ₂ —), 28.0 ( _{-CH 2 -), 25.4 (-CH} 2 -), 25.0 (-CH 2 -), 15.1 (-CH 3).

マレイミド化合物６ Synthesis Example 6 Synthesis of maleimide compound 6

Maleimide compound 6

  Maleimide compound 6 was synthesized using a method for synthesizing maleimide derivatives described in Examples of JP-A-11-124403 and a method described in Macromolecular Chemical and Physics, 2009, 210, 269-278.

<Ink Preparation A>
Inks 1 to 9 having the composition described in Table A1 and inks 10 to 13 constituting the ink set 1 were prepared according to the following method. Part of the dispersant, basic compound, and photopolymerizable compound listed in Table A1 was placed in a stainless beaker, and stirred and mixed for 1 hour while heating on a hot plate at 60 ° C. to dissolve. Next, after adding the coloring materials 1 to 4 shown in Table 1 to this solution, the mixture was sealed in a plastic bottle together with zirconia beads having a diameter of 0.5 mm, and dispersed for 6 hours with a paint shaker, and then zirconia beads. Was removed to obtain a pigment dispersion.

  A monomer solution in which the remaining photopolymerizable compound, polymerization initiator, surfactant and polymerization inhibitor were mixed and dissolved was added to the obtained pigment dispersion with stirring. The obtained solution was filtered through a 1 μm membrane filter to prepare inks 1 to 13. In the inks 1 to 13 having the composition shown in Table A1, the difference between the charge of the carbon atom constituting the unsaturated bond of the maleimide compound and the charge of the carbon atom constituting the unsaturated bond of the vinyl ether compound is 0.27 to 0 .45.

  Inks 14 to 17 (composing ink set 2) having the composition described in Table A2 and inks 18 to 21 (composing ink set 3) having the composition described in Table A3 are described in Table A1. It was prepared in the same manner as the ink having the composition.

  The components of the inks listed in Tables A1 to A3 are as follows.

[Color material]
Color material 1: C.I. I. pigment Black 7
Color material 2: C.I. I. pigment Blue 15: 4
Color material 3: C.I. I. pigment Red 122
Color material 4: C.I. I. pigment Yellow 150

  [Basic compound] TIPA: Triisopropanolamine

[Pigment dispersant]
D1: Pigment dispersant Solsperse 24000GR, manufactured by Lubrizol, Inc. D2: Pigment dispersant, BYKJET-9150, manufactured by Big Chemie Japan Co., Ltd. D3: Pigment dispersant, Azisper PB824, manufactured by Ajinomoto Fine Techno Co., Ltd.

[Maleimide compound]
Maleimide compound 1 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 2 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 3 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 4 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 5 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 6 (charge of carbon atom constituting unsaturated bond -0.09)
DEM: diethyl maleate (charge of carbon atom constituting unsaturated bond -0.27)

[Vinyl ether compounds]
TEGDVE: Triethylene glycol divinyl ether (charge of carbon atom constituting unsaturated bond -0.54)
DEGDVE: Diethylene glycol divinyl ether (charge of carbon atom constituting unsaturated bond -0.54)
DDVE: dodecyl vinyl ether (charge of carbon atom constituting unsaturated bond -0.54)
DEGV: Diethylene glycol monovinyl ether (charge of carbon atom constituting unsaturated bond -0.54)

[Cationic photopolymerizable compound]
CEL2021P: Alicyclic epoxy compound Daicel Chemical Industries, Ltd. OXT-221: Oxetane compound, Toagosei Chemical Co., Ltd. OXT-212: Oxetane compound, Toagosei Chemical Co., Ltd. OXT-101: Oxetane compound, manufactured by Toagosei

[Radical photopolymerizable compound]
A-1: Phenoxyethyl acrylate A-2: Tetrahydrofurfuryl acrylate A-3: Isobornyl acrylate A-4: PO-modified NPG diacrylate

[Photopolymerization initiator]
TPO: 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (BASF)
Irg819: Bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (manufactured by BASF)
Irg369: 2-Benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (BASF)
ITX: 2-Isopropylthioxanthone (Nippon Kayaku Co., Ltd.)
CPI-100P: Photoacid generator (manufactured by Sun Apro)

[Surfactant]
KF351: Side chain polyether-modified silicone oil, Shin-Etsu Silicone W260: Ether ester plasticizer, DIC

[Polymerization inhibitor]
Irgastab UV-10 (BASF)

  For the obtained inks 1 to 9, ink 14 and ink 18, the ink composition was loaded into a serial type ink jet recording apparatus equipped with a piezo type ink jet nozzle, and the curability immediately after ink ejection was evaluated.

  The ink supply system includes an ink tank, a supply pipe, a front chamber ink tank immediately before the head, a pipe with a filter, and a piezo head. The temperature from the front chamber tank to the head portion was controlled by a heater, and the viscosity of the inkjet ink was adjusted to a jettable viscosity (about 10 mPa · s).

  The nozzle pitch of the piezo head was 360 dpi (dpi represents the number of dots per inch), and the droplet size was 4 pl, 6 pl, 14 pl, or 42 pl.

  A solid image having an image resolution of 1440 × 1440 dpi was formed using a PET film as the recording medium. Image formation was carried out in an environment of 25 ° C./30% RH and 28 ° C./80% RH, respectively.

Air-cooled LEDs (manufactured by Foseon) having a wavelength of 395 nm were mounted on both ends of the carriage, and actinic rays were irradiated within 0.5 seconds after ink landing while scanning the head. The exposure surface illuminance was 2 W / cm ² . Further, the integrated light quantity was adjusted by changing the speed of the head carriage, and the curability of each ink was evaluated. The illuminance on the exposed surface and the integrated light intensity were measured in the UVA2 region using a UV POWER PUCK II manufactured by EIT.

The carriage speed was gradually increased to form an image. The integrated light quantity value to the ink droplet was determined when the carriage speed was such that an image with no rub marks was obtained when the cured film surface was rubbed with a finger. The results are shown in Table A4.
A: Less than 50 mJ / cm ² ○: 50 mJ / cm ² or more and less than 200 mJ / cm ² Δ: 200 mJ / cm ² or more and less than 500 mJ / cm ² ×: 500 mJ / cm ² or more and less than 1000 mJ / cm ² ××: 1000 mJ / cm ² Even above, there was a rub mark

  Next, the ink jet ink of ink set 1, 2 or 3 was loaded into a serial type ink jet recording apparatus provided with a four-color piezo-type head having an ink nozzle capable of ejecting a droplet size of 6 pl.

A color image (N3 “fruit basket” of high-definition color digital standard image conforming to JISX 9201-1995) having an image resolution of 1440 × 1440 dpi was printed on a vinyl chloride sheet as a recording medium. The carriage speed was 500 mm / s. Within 0.5 seconds after landing, the ink droplets were irradiated with light from LEDs (wavelength 395 nm, 2 W / cm ² ) mounted on both ends of the carriage to form an image. Image formation was performed in an environment of 25 ° C./30% RH and 25 ° C./80% RH, respectively. The integrated light quantity on the substrate was 80 mJ / cm ² .

  The image quality of the obtained image was evaluated. The image output with the ink set 1 was a clear image with no trace when the print surface was rubbed immediately after printing in any environment, and no blur between colors. Further, even when the surface was wiped with a non-woven cloth moistened with a cleaner solution containing an alcohol solvent, no color transfer occurred and no change in the gloss of the image was observed.

  The image output with Ink Set 2 was a good image at 25 ° C. and 30% RH, but at 28 ° C. and 80% RH, the image surface remained tacky, and the print surface was rubbed. It was. Further, when wiped with the above cleaner liquid, it was observed that the non-woven fabric was faintly transferred and the gloss of the image surface was lowered.

  The image output by the ink set 3 was rubbed when the print surface was rubbed immediately after printing in any environment, and bleeding between colors was also observed. As a result, the image was totally blurred. Also, when wiped with the above cleaner liquid, an image was taken and white spots were lost.

  Next, the inkjet of the ink set 1 or 3 was loaded into a line head type inkjet recording apparatus having a four-color piezo-type head having an ink nozzle capable of ejecting a droplet size of 6 pl.

The resolution is 1400dpi x 1440dpi, 4 points, 5 points and 6 points MS Mincho style, M, C, Kanji "Mouth, Fourth, Day, Time, Cause, Hard, Country, Eye, Figure, Country" K, B, G, R, 3C characters and blank characters and the color image were printed on art paper. The character reproducibility and image quality were evaluated visually. The exposure was performed using an LED having a width wider than the width of the head (manufactured by Foseon, wavelength 395 nm, 4 W / cm ² ).

The light source was arranged in parallel to the head in the downstream direction in which the base material was conveyed (where actinic rays hit after printing). Printing was performed by conveying the substrate at a carriage speed such that the integrated light amount was 100 mJ / cm ² on the substrate.

  When ink set 1 was used, all four-point characters and blank characters were clearly recorded in detail. Further, a clear image having good rubbing property on the surface of the color image was formed.

  In the image formed using the ink set 3, 6-point characters and blank characters were crushed, and some images could not be read. Further, the surface of the color image remained rubbing and the image was blurred overall.

<Ink Preparation B>
Pigment dispersions of Examples B1 to B8 and Comparative Examples B1 and B2 having the compositions described in Table B1 were prepared according to the following method. The pigment dispersant, the polymerizable compound and the polymerization inhibitor described in Table B1 were placed in a stainless beaker, stirred and mixed for 1 hour while being heated on a hot plate at 60 ° C., and dissolved. Then, after adding the coloring material described in Table A1 to this solution, put it in a plastic bottle together with zirconia beads having a diameter of 0.5 mm, and after carrying out a dispersion treatment with a paint shaker for 6 hours, remove the zirconia beads, A pigment dispersion was obtained.

  A polymerization initiator (5.0 g of TPO, 2.0 g of ITX) was added to 92.0 g of the obtained pigment dispersion with stirring. The obtained solution was filtered through a 1 μm membrane filter to prepare inks of Examples B1 to B8 and Comparative Examples B1 and B2.

  In the inks of Examples B1 to B8, the difference between the charge of the carbon atom constituting the unsaturated bond of the maleimide compound and the charge of the carbon atom constituting the unsaturated bond of the vinyl ether compound is 0.24 to 0.45. .

  The components used for the preparation of the ink are as follows.

[Color material]
C. I. pigment Black 7

[Pigment dispersant]
Solsperse 24000GR: (made by Lubrizol)

[Electron-accepting compound]
Maleimide compound 1 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 2 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 3 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 4 (charge of carbon atom constituting unsaturated bond -0.27)
Maleimide compound 5 (charge of carbon atom constituting unsaturated bond -0.27)
Maleic anhydride (charge of carbon atom constituting unsaturated bond -0.29)

ＴＥＧＭＶＥ：トリエチレングリコールモノメチルビニルエーテル（不飽和結合を構成する炭素原子の電荷−０．５２）

[Electron donating compound]
TEGDVE: Triethylene glycol divinyl ether (charge of carbon atom constituting unsaturated bond -0.54)

TEGVE: Triethylene glycol monomethyl vinyl ether (charge of carbon atom constituting unsaturated bond -0.52)

[Other polymerizable compounds]
Tetrafurfuryl alcohol oligoacrylate (Biscoat V # 150, manufactured by Osaka Organic Chemical Industry Co., Ltd.)
Trimethylolpropane ethoxytriacrylate Trimethylolpropane triacrylate Trimethylolpropane formal acrylate Phenoxyethyl acrylate Dodecyl acrylate N-Vinylcaprolactam PO-modified NPG diacrylate (manufactured by Daicel Cytec Co., Ltd.)

[Polymerization initiator]
TPO (phosphine oxide photoinitiator, manufactured by BASF)
ITX (thioxanthone photosensitizer, manufactured by Aceto Chemical)

[Polymerization inhibitor]
TEMPO (2,2,6,6-tetramethylpiperidinyl-N-oxyl)

<Evaluation method>
[Weatherability]
The inks of Example B and Comparative Example B described above were printed on a soft vinyl chloride sheet (MD5 Metamark) under the conditions of 720 dpi × 720 dpi (4 Pass bidirectional printing) using an inkjet printer loaded with an ultraviolet lamp. The printed matter was irradiated with ultraviolet rays and cured to obtain an image. As the ultraviolet lamp, a Fusion H bulb (LH-6) or Hi-Cure-N (manufactured by Neopto) was used, and the illuminance was adjusted by a filter. The cumulative amount of ultraviolet rays in the UVA2 region (320 nm to 390 nm) was the amount of light irradiated until whitening or stickiness did not occur when the cured film was rubbed with a finger. The accumulated light quantity at that time is described in “” of Table B2. Further, the illuminance and the integrated light amount in the UVA2 region (320 nm to 390 nm) were measured using an integrated light meter UV Power Pack S / N8202.

The OD value α of the image obtained using the ink jet printer was measured using X-rite 528 (manufactured by X-Rite). Further, the obtained image was put into a weather resistance tester (Xe fade meter) for 300 hours. Thereafter, the OD value β of the image after the weather resistance test was measured. The ratio of the OD value before and after the weather resistance test “OD value β / OD value α” was defined as the residual rate. The following evaluation results are shown in Table B2.
"Evaluation criteria"
○: Residual rate 95% or more ×: Residual rate less than 95% −: Ink does not cure

[curl]
The inks of Example B and Comparative Example B described above were printed on 35 μm PET under the conditions of 720 dpi × 720 dpi (8 Pass bidirectional printing) using an inkjet printer loaded with an ultraviolet lamp. The printed matter was irradiated with ultraviolet rays at 1 Pass to obtain an image. The illuminance of the ultraviolet lamp was set to 7 levels in the range of 0.5 to 50W. The image was irradiated with ultraviolet light in the UVA2 region. In this case, the integrated light quantity was the amount until whitening or stickiness did not occur when the cured film was rubbed with a finger in the weather resistance test. The accumulated light quantity at that time is shown in “” of Table 2. As an ultraviolet lamp, a Fusion H bulb (LH-6) or Hi-Cure-N (manufactured by Neopto) was used, and the illuminance was adjusted by a filter. Further, the illuminance and the integrated light amount in the UVA2 region (320 nm to 390 nm) were measured using an integrated light amount meter UV Power Pack S / N8202. The curl state of the substrate was visually evaluated according to the following evaluation criteria. The following evaluation results are shown in Table B3.
"Evaluation criteria"
◎: Not curled ○: Slightly curled △: Largely curled curly ×: Waved curled −: Ink does not cure

The evaluation results on the weather resistance of Examples B1 to B8 and Comparative Examples B1 and B2 are shown in Table B2.

The evaluation results for the curls of Examples B1 to B8 and Comparative Examples B1 and B2 are shown in Table B3.

In Comparative Examples B1 and B2 in Table B2, it was necessary to set the integrated light amount to 200 mJ / cm ² or more in order to form an image without whitening or stickiness at any illuminance. On the other hand, Examples B1 to B8 can form an image without whitening or stickiness with an integrated light quantity of 150 mJ / cm ² or less at any illuminance. In particular, when the polymerizable compound in the ink is only a bifunctional maleimide compound and a bifunctional vinyl ether compound as in Examples B1 to B5, an image can be formed with an integrated light amount of 50 mJ / cm ² regardless of the illuminance. It was.

In Comparative Examples B1 and B2 of Table B2, when the illuminance was 8 W or less, the residual rate in the weather resistance test showed a result of less than 95%, and the irradiation was continued until the integrated light amount became 200 mJ / cm ² . The residual rate never exceeded 95%. On the other hand, Examples B1 to B8 showed the result that the residual ratio of ink was 95% or more even when the illuminance was 8 W or less. The inks of Examples B1 to B8 can form an image that can withstand the outdoor environment even when cured at low illuminance.

  In Comparative Examples B1 and B2 in Table B3, the ink was not cured when the illuminance was 8 W or less. In addition, when the illuminance is 25 W or more, the ink is cured, but the base material is curled due to thermal damage. On the other hand, in Examples B1 to B8, the ink can be cured even when the illuminance is 8 W or less, and curling of the substrate can be suppressed. Further, when the illuminance is 25 W, the accumulated light amount for curing the ink is lower than those in Comparative Examples B1 and B2, and thus curling of the substrate can be suppressed. The inks of Examples B1 to B8 are suitable for forming an image with low illuminance without causing thermal damage to the substrate.

  According to the ink-jet ink of the present invention, a high-quality image with high definition and reduced unevenness can be obtained. In addition, since the ink can be cured with a light source with low illuminance, the system can be made compact and energy saving.

DESCRIPTION OF SYMBOLS 1 Recording device 2 Head carriage 3 Recording head 31 Injection port 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure 8 Irradiation light source P Recording medium

Claims (8)

A step of ejecting droplets of an active energy ray-curable inkjet ink containing two or more polymerizable monomers having an unsaturated bond in a size of 0.1 to 12 pl and landing on a recording medium;
Irradiating an actinic ray to a droplet landed on the recording medium and curing it, and an image forming method comprising:
Among the two or more kinds of polymerizable monomers contained in the inkjet ink, when the maximum value X of the charge of the carbon atom constituting the unsaturated bond and the minimum value Y of the charge of the carbon atom constituting the unsaturated bond are set, The image forming method, wherein the difference between the maximum value X and the minimum value Y is 0.24 or more and 0.46 or less, and the viscosity of the inkjet ink at 25 ° C. is 20 to 500 mPa. ^2. The image forming method according to claim 1, wherein the ink droplets that have landed on the recording medium are irradiated with the actinic light with an integrated light amount of 200 mJ / cm ² or less within 0.001 to 1.0 seconds after landing. .   The image forming method according to claim 1, wherein an illuminance of the active light is 5 W or less.   The image forming method according to claim 1, wherein the active light is light using an LED as a light source.   The image forming method according to claim 1, wherein droplets of the active energy ray-curable inkjet ink are ejected in a size of 0.1 to 4 pl.   The image forming method according to claim 1, wherein a surface tension of the inkjet ink at 25 ° C. is 15 mN / m or more and less than 35 mN / m.   The image forming method according to claim 1, wherein the image forming method is performed by a serial head type inkjet recording apparatus.   The image forming method according to claim 1, which is performed by a line head type ink jet recording apparatus.

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