JP2007254546A - Ink cleaning liquid and cleaning method - Google Patents

Abstract

To provide an ink cleaning liquid for a photocurable ink having an excellent cleaning property with respect to cleaning of a photocurable ink, and an ink jet printer cleaning method.
An ink cleaning liquid for a photocurable ink, which contains at least one ether compound. The ether compound is preferably a glycol ether compound. The photocurable ink is preferably a radical polymerizable ink. Furthermore, the inkjet printer cleaning method which cleans an inkjet printer using the said ink washing | cleaning liquid.

Description

  The present invention relates to a novel ink cleaning liquid and an inkjet printer cleaning method.

As an image recording method for forming an image on a recording medium such as paper based on an image data signal, there are an electrophotographic method, a sublimation type and a melt type thermal transfer method, an ink jet method and the like. The electrophotographic system requires a process of forming an electrostatic latent image on a photosensitive drum by charging and exposure, and there is a problem that the system becomes complicated and consequently the manufacturing cost becomes expensive. In addition, although the thermal transfer system is inexpensive, there are problems such as high running costs and waste materials due to the use of ink ribbons.
On the other hand, the ink jet method is an inexpensive apparatus and ejects an ink composition only to a required image portion to form an image directly on a recording medium, so that ink can be used efficiently and running cost is low. . Furthermore, there is little noise and it is excellent as an image recording method.

  Examples of the ink used in the ink jet printer include a wax ink that is solid at room temperature, a solvent ink mainly composed of an aqueous solvent or an organic solvent, and a photocurable ink that is cured by light irradiation. Among them, the photocurable ink is attracting attention because it has a lower odor than other recording methods and can be recorded on a recording medium having no quick drying property and ink absorption property other than dedicated paper.

  Photocurable inks include radically polymerizable photocurable inks that polymerize monomers and oligomers using radicals generated by light irradiation as growth active species, and monomers that use cations generated by light irradiation as growth active species. And cationically polymerizable photocurable inks in which oligomers are polymerized.

  By the way, since an ink jet printer discharges ink from a small-diameter discharge port formed in the head, the ink adheres to the head, the periphery of the discharge port, and other parts of the ink jet printer, or the ink is cured at the discharge port. As a result, the discharge port is blocked. Various measures are taken to deal with such a situation.

  As a countermeasure technique for preventing the ink from being clogged in the discharge port, there is a technique of covering the discharge port with a cap when the ink jet printer is not performing an image recording operation. Document 4 describes. As another countermeasure technique, there is a technique of wiping off ink adhering to the vicinity of an ejection port when an ink jet printer is performing an image recording operation or trying to end an image recording operation. 2 to Patent Document 5. Further, Patent Document 5 discloses a technique that uses silicon oil or ethylene glycol as a cleaning liquid when wiping off the ink at the ejection port. Patent Document 6 discloses a cleaning solution for an ink jet printer that contains isothiazolone, has an excellent detergency, and has an antifungal and antibacterial effect.

JP 57-117964 A Japanese Patent Laid-Open No. 57-80064 JP 59-111856 A JP-A-8-1953 Japanese Examined Patent Publication No. 62-9030 JP-A-4-261476

However, none of the techniques disclosed in Patent Documents 1 to 6 is sufficient for cleaning the ink composition. In particular, the cleaning property was not sufficient for the photocurable oil-soluble ink.
SUMMARY OF THE INVENTION An object of the present invention is to provide an ink cleaning liquid for photocurable ink and an ink jet printer cleaning method having excellent cleaning properties for cleaning photocurable ink.

The above object of the present invention has been achieved by the means described in <1> and <4> below. It is described below together with <2> and <3> which are preferred embodiments.
<1> An ink cleaning liquid for a photocurable ink, which contains at least one ether compound,
<2> The ink cleaning liquid according to <1>, wherein the ether compound is a glycol ether compound,
<3> The ink cleaning liquid according to <1> or <2>, wherein the photocurable ink is a radical polymerizable ink,
<4> A method for cleaning an ink jet printer, comprising: cleaning the ink jet printer using the ink cleaning liquid according to any one of <1> to <3>.

  ADVANTAGE OF THE INVENTION According to this invention, the ink cleaning liquid for photocurable ink which has the outstanding cleaning property with respect to washing | cleaning of photocurable ink, and the cleaning method of an inkjet printer can be provided. In particular, the ink cleaning liquid of the present invention is suitable for cleaning radically polymerizable photocurable ink.

Hereinafter, the present invention will be described in further detail.
The ink cleaning liquid of the present invention is an ink cleaning liquid for photo-curable ink, and contains at least one ether compound.
(1) Ink Cleaning Liquid The ink cleaning liquid of the present invention (hereinafter also simply referred to as “cleaning liquid”) contains at least an ether compound, and cleans the photocurable ink from an inkjet printer that discharges the photocurable ink from the head. Therefore, it can be suitably used.
The ink cleaning liquid of the present invention has an action of dissolving and / or dispersing uncured or cured photocurable ink, and thus can be used as a cleaning liquid for photocurable ink before and after curing.

The ink cleaning liquid of the present invention will be described.
(Ether compound)
Examples of the ether compound that can be used in the present invention include monoethers and ether compounds composed of polyols such as glycol, triol, and tetraol.
When the cleaning liquid contains an ether compound, it can be cleaned without agglomerating insoluble components in the ink, and the head is clogged in situations where cleaning is necessary, such as when the liquid is changed or the machine is restarted after a long pause. In this way, stable operation can be performed without causing any trouble, and further, by using it for cleaning after clogging of the head, the reliability of continuous ejection during drawing is improved.
In the present invention, as the ether compound, any compound having an ether group (—O—) in the molecule can be used, and among these, a glycol ether compound is preferably used as the ether compound. .

Examples of the glycol ether compound include compounds represented by the following formula [I] or [II]. However, it is not limited to these.
[I] _{^{R 1 O- (CH 2 CH (}} R 2) -O) m -R 3
[II] R ⁴ O— (CH ₂ CH ₂ —O) _p —CO—CH ₃
In the formula, R ^{1 to} R ⁴ are independently a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a benzyl group, a phenyl group, a vinyl group, an allyl group, an acrylic group, a methacryl group, or a cyclic group having 5 to 10 carbon atoms. Represents an alkyl group, and m and p represent an integer of 1 to 20.

  Specific examples include triethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol diacrylate, diethylene glycol diacrylate, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, ethylene Glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, diethylene glycol diethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, trie Lenglycol monobutyl ether, diethylene glycol dibutyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, propylene glycol Monoethyl ether, Dipropylene glycol monoethyl ether, Tripropylene glycol monoethyl ether, Dipropylene glycol diethyl ether, Tripropylene glycol divinyl ether, Dipropylene glycol divinyl ether, Tripropylene glycol diacrylate, Dipropi Glycol diacrylate and the like.

  Among these, preferable glycol ether compounds include tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, triethylene glycol divinyl ether, dipropylene glycol diacrylate, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol Examples thereof include ethylene glycol monobutyl ether, ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, tripropylene glycol divinyl ether, dipropylene glycol divinyl ether and tripropylene glycol diacrylate.

  Examples of ether compounds that can be used in the present invention include polyethylene glycol and polypropylene glycol having a molecular weight of 200 to 1,000, and monomethyl ether, monoethyl ether, monopropyl ether, isopropyl ether, and monobutyl ether of these compounds.

  Furthermore, in the present invention, it is also preferable to use an alkoxy alcohol as the ether compound. C1-C6 alkoxy alcohol is preferable and 3-methoxybutanol and 3-methyl-3-methoxybutanol can be illustrated preferably.

  In the present invention, the ether compound used in the ink cleaning liquid preferably has a viscosity of 1 to 40 mPa · s at 25 ° C., and more preferably 2 to 30 mPa · s. It is preferable that the viscosity is within the above-mentioned range since a particularly excellent cleaning effect is exhibited in cleaning in the head.

  In the present invention, the ether compound preferably has a boiling point of 50 to 150 ° C, more preferably 60 to 130 ° C. It is preferable that the boiling point is within the above-mentioned range since there is little remaining cleaning liquid after use, and it can be used safely and effectively without volatilization during use.

In the present invention, the addition amount of the ether compound is preferably 100 to 30 wt%, more preferably 100 to 40 wt%, and further preferably 100 to 50 wt% of the entire ink cleaning liquid. It is preferable for the amount added to be in the above-mentioned range since member modification by other components can be suppressed and the effect expected in the present invention can be maintained. That is, it is preferable because other components can suppress the denaturation of an object such as an ink jet head for washing ink.
In the present invention, when glycol ethers are used as the ether compound, the addition amount thereof is preferably 100 to 30 wt%, more preferably 100 to 40 wt%, further preferably 100, based on the entire ink cleaning liquid. ~ 50 wt%. It is preferable for the amount added to be in the above-mentioned range since further member modification by other components can be suppressed and the effect expected in the present invention can be maintained.

The ink cleaning liquid of the present invention can contain other components in addition to the ether compound. Examples of other components include alcohols, ketones, lactones and cyclic imides, and other components.
(Alcohols)
In the ink cleaning liquid of the present invention, alcohols having 1 to 6 carbon atoms are preferably used as alcohols.
As alcohols having 1 to 6 carbon atoms, linear alcohols, branched chain alcohols, cyclic alcohols, branched cyclic alcohols, and the like can be used. For example, tetrahydrofurfuryl alcohol, methyl alcohol, ethyl alcohol, propyl alcohol and its isomer, butyl alcohol and its isomer, pentyl alcohol and its isomer, hexyl alcohol and its isomer, and the like can be used.
In the ink cleaning liquid of the present invention, alcohols having 1 to 6 carbon atoms can be used singly or in combination of two or more. Of these, propyl alcohol and its isomer, and butyl alcohol and its isomer are preferable. Since alcohol having 7 or more carbon atoms tends to have poor ink removability, alcohols having 1 to 6 carbon atoms are preferable.
The amount of the alcohol having 1 to 6 carbon atoms in the ink cleaning liquid of the present invention is preferably 3 to 30% by weight, more preferably 5 to 12% by weight based on the whole ink cleaning liquid.
It is preferable for the amount added to be in the above-mentioned range since member modification can be suppressed and the cleaning effect expected in the present invention can be maintained.

(Esters)
Specific examples of esters that can be used in the present invention include amyl acetate, isoamyl acetate, methyl isoamyl acetate, sec-hexyl acetate, 2-ethyl-butyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, and methylcyclohexyl acetate. Benzyl acetate, butyl propionate, isoamyl propionate, butyl butyrate, isobutyl butyrate, isoamyl butyrate, methyl lactate, ethyl lactate, butyl lactate, amyl lactate, isoamyl lactate, and the like.
The added amount of esters is preferably 0 to 50% by weight, more preferably 0 to 40% by weight, and still more preferably 0 to 30% by weight of the total ink cleaning liquid. It is preferable for the amount added to be in the above-mentioned range since member modification can be suppressed and the cleaning effect expected in the present invention can be maintained.

(Ketones)
Specific examples of ketones that can be used in the present invention include methyl amyl ketone, methyl-n-hexyl ketone, di-n-propyl ketone, diacetone alcohol, acetonyl acetone, isophorone, phorone, cyclohexanone, methylcyclohexanone, Acetophenone is mentioned.
The amount of ketones added is preferably 0 to 40% by weight, more preferably 0 to 30% by weight, and still more preferably 0 to 20% by weight of the total ink cleaning liquid. It is preferable for the amount added to be in the above-mentioned range since member modification can be suppressed and the cleaning effect expected in the present invention can be maintained.

(Lactone and cyclic imide)
Specific examples of the lactone having 3 to 6 carbon atoms and the cyclic imide having 4 to 7 carbon atoms that can be used in the present invention include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ- Examples include caprolactone, γ-laurolactone, δ-valerolactone, hexanolactone, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and N-octyl-2-pyrrolidone.
The addition amount of the lactone and the cyclic imide is preferably 0 to 50% by weight, more preferably 0 to 40% by weight, and further preferably 0 to 30% by weight of the whole ink cleaning liquid. It is preferable for the amount added to be in the above-mentioned range since member modification can be suppressed and the cleaning effect expected in the present invention can be maintained.

(Other)
Other components can also be added to the ink cleaning liquid of the present invention.
Examples of other components include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl sulfoxide, tetramethylurea, dimethylimidazolidinone, and the like. .
The amount of other components added is preferably 0 to 40% by weight, more preferably 0 to 30% by weight, and still more preferably 0 to 20% by weight of the total ink cleaning liquid. It is preferable for the amount added to be in the above-mentioned range since member modification can be suppressed and the cleaning effect expected in the present invention can be maintained.

  Further, a surfactant and an antifoaming agent may be added to the ink cleaning liquid containing the ether compound. By adding a surfactant to the ink cleaning liquid, the surface energy of the ink cleaning liquid can be adjusted, and when the ink cleaning liquid is applied to the ink jet printer, the wettability of the ink cleaning liquid to the ink jet printer can be improved. preferable. Further, it is preferable to add an antifoaming agent to the cleaning liquid because bubbles can be prevented from being generated in the ink cleaning liquid.

The above is the description of the cleaning liquid. Hereinafter, the photocurable ink used in the ink jet printer (in the present invention, “photocurable ink” is also referred to as “ink composition”) will be described.
In the present invention, the “photocurable ink” means both before and after curing. In addition, the “ink composition” refers to a photocurable ink before being cured.

(2) Photo-curable ink In the present invention, the photo-curable ink is curable by radiation or heat, and contains (a) a polymerizable compound and (b) a polymerization initiator. It may contain (c) a colorant, (d) a sensitizing dye, (e) a co-sensitizer, and (f) other components.
In the present invention, the “radiation” is not particularly limited as long as it is an actinic radiation that can impart energy capable of generating a polymerization initiating species in the photocurable ink by the irradiation, and widely includes α rays, γ rays, X-rays, ultraviolet rays (UV), visible rays, electron beams and the like are included, and among these, ultraviolet rays and electron beams are preferable from the viewpoint of curing sensitivity and device availability, and ultraviolet rays are particularly preferable. Therefore, in the present invention, the photocurable ink is preferably a photocurable ink that can be cured by irradiating ultraviolet rays as radiation.

(A) Polymerizable compound In the present invention, the photocurable ink contains (a) a polymerizable compound. Examples of the polymerizable compound that can be used in the present invention include a radical polymerizable compound or a cationic polymerizable compound. Examples of the radical polymerizable compound are described in JP-A-7-159983, JP-B-7-31399, JP-A-8-224982, JP-A-10-863, JP-A-7-231444, and the like. A photocurable material using a photopolymerizable composition is known, and as a cationic polymerizable compound, for example, a cationic polymerization type photocurable resin is known, and recently visible light having a wavelength of 400 nm or more is known. Photo-cationic polymerization type photocurable resins sensitized in the above long wavelength range are also disclosed in, for example, JP-A-6-43633 and JP-A-8-324137.
In the present invention, it is preferable to use a radical polymerizable compound as the polymerizable compound. A radical polymerizable compound is preferable as the polymerizable compound because it has high curing sensitivity and has a high curing rate.
Therefore, in the present invention, the photocurable ink is preferably a radical polymerizable ink.

<Radically polymerizable compound>
The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization, and may be any compound as long as it has at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. , Oligomers, polymers and the like having a chemical form. Only one kind of radically polymerizable compound may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties. In addition, it is preferable to use a polyfunctional compound having two or more functional groups in combination rather than using a monofunctional compound alone. It is also preferable to use two or more polyfunctional compounds in combination in order to control performance such as reactivity and physical properties.

Examples of the polymerizable compound having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, and salts thereof, Examples thereof include radically polymerizable compounds such as anhydrides having a saturated group, acrylonitrile, styrene, various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes.
Specifically, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, bis (4-acryloxypolyethoxyphenyl) propane, neopentyl glycol Diacrylate, 1,6-hexanediol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol Tetraacrylate, dipentaery Acrylic acid derivatives such as lithol tetraacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, epoxy acrylate, methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate , Lauryl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylol Methacryl derivatives such as tan trimethacrylate, trimethylolpropane trimethacrylate, 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate, triallyl trimellitate More specifically, Shinzo Yamashita “Cross-linking agent handbook” (1981, Taiseisha); Kato Kiyosumi “UV / EB curing handbook (raw material)” (1985, Polymer publication society) Radtech Research Group, “Application and Market of UV / EB Curing Technology”, page 79 (1989, CMC); Eiichiro Takiyama “Polyester Resin Handbook” (1988, Nikkan Kogyo Shimbun) Radically polymerizable or crosslinkable monomers, oligomers and Polymers can be used.

  Furthermore, in this invention, it is preferable that a photocurable ink contains N-vinyl lactam as a radically polymerizable compound. Preferable examples of N-vinyl lactams include compounds represented by the following formula (I).

  In the formula (I), n represents an integer of 1 to 5, and n is 2 to 4 from the viewpoints of flexibility after the ink composition is cured, adhesion to a recording medium, and availability of raw materials. It is preferable that n is an integer of 2 or 4, and it is particularly preferable that n is 4, that is, N-vinyl-ε-caprolactam. N-vinyl-ε-caprolactam is preferable because it is excellent in safety, is general-purpose and can be obtained at a relatively low cost, and provides particularly good ink curability and adhesion of a cured film to a recording medium.

  The N-vinyl lactams may have a substituent such as an alkyl group or an aryl group, and may be linked with a saturated or unsaturated ring structure.

In the present invention, the photocurable ink composition preferably contains N-vinyl lactams in an amount of 10% by weight or more based on the entire photocurable ink. It is preferable to contain N-vinyl lactams in an amount of 10% by weight or more based on the whole ink because a photocurable ink having excellent curability, cured film flexibility, and cured substrate adhesion can be provided. A more preferable content of the N-vinyl lactam in the photocurable ink is in the range of 10% by weight to 40% by weight. N-vinyl lactams are compounds having a relatively high melting point. It is preferable that the content of N-vinyl lactam is 40% by weight or less because good solubility is exhibited even at a low temperature of 0 ° C. or less, and the temperature range in which the ink composition can be handled becomes wide. More preferably, it is in the range of 12 wt% or more and 40 wt% or less, and particularly preferably in the range of 15 wt% or more and 35 wt% or less.
The N-vinyl lactams may be included in the ink composition alone or in a plurality of types.

  The ink cleaning liquid of the present invention can be suitably used as a cleaning liquid for a photocurable ink containing N-vinyl lactam as a polymerizable compound. Since these N-vinyllactams are monomers that are solid at room temperature, they are liable to cause problems such as precipitation. In addition to the limited cleaning solution as in the present invention, precipitation is accelerated by contact with the cleaning solution during cleaning. In many cases, cleaning is difficult except for the cleaning liquid of the present invention. By using the ink cleaning liquid of the present invention, a photocurable ink containing N-vinyl lactam as a polymerizable compound can be effectively cleaned.

<Cationically polymerizable compound>
The cationically polymerizable compound that can be used in the present invention is not particularly limited as long as it is a compound that initiates a polymerization reaction with an acid generated from a photoacid generator (cationic polymerization initiator) described later and cures. Various known cationically polymerizable monomers known as ionic monomers can be used. Examples of the cationic polymerizable monomer include JP-A-6-9714, JP-A-2001-31892, JP-A-2001-40068, JP-A-2001-55507, JP-A-2001-310938, JP-A-2001-310937, and 2001-2001. Examples thereof include epoxy compounds, vinyl ether compounds, oxetane compounds and the like described in each publication such as No. 220526.

  Examples of the epoxy compound include aromatic epoxides, alicyclic epoxides, aliphatic epoxides, and the like. As the aromatic epoxide, a polyhydric phenol having at least one aromatic nucleus or an alkylene oxide adduct thereof and epichlorohydrin are used. Di- or polyglycidyl ethers produced by reaction, for example, di- or polyglycidyl ethers of bisphenol A or its alkylene oxide adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and novolaks Type epoxy resin. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

As the alicyclic epoxide, cyclohexene oxide obtained by epoxidizing a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring with a suitable oxidizing agent such as hydrogen peroxide or peracid. Or a cyclopentene oxide containing compound is mentioned preferably.
Examples of aliphatic epoxides include dihydric polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, and typical examples thereof include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol, or 1,6. -Diglycidyl ether of alkylene glycol such as diglycidyl ether of hexanediol, polyglycidyl ether of polyhydric alcohol such as di- or triglycidyl ether of glycerin or its alkylene oxide adduct, diglycidyl of polyethylene glycol or its alkylene oxide adduct Diglycidyl of polyalkylene glycol typified by diglycidyl ether of ether, polypropylene glycol or its alkylene oxide adduct Ether and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

The monofunctional and polyfunctional epoxy compounds that can be used in the present invention are exemplified in detail.
Examples of monofunctional epoxy compounds include, for example, phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, 1,2-butylene oxide, 1,3-butadiene Monooxide, 1,2-epoxydodecane, epichlorohydrin, 1,2-epoxydecane, styrene oxide, cyclohexene oxide, 3-methacryloyloxymethylcyclohexene oxide, 3-acryloyloxymethylcyclohexene oxide, 3-vinylcyclohexene oxide, 4-vinylcyclohexene oxide etc. are mentioned.

  Examples of polyfunctional epoxy compounds include, for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, and brominated bisphenol. S diglycidyl ether, epoxy novolac resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxy 2- (3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, bis (3,4-epoxy Hexylmethyl) adipate, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 3,4-epoxy-6-methylcyclohexyl-3 ′, 4′-epoxy-6′-methylcyclohexanecarboxylate, methylenebis ( 3,4-epoxycyclohexane), dicyclopentadiene diepoxide, di (3,4-epoxycyclohexylmethyl) ether of ethylene glycol, ethylene bis (3,4-epoxycyclohexanecarboxylate), dioctyl epoxyhexahydrophthalate, epoxy Di-2-ethylhexyl hexahydrophthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane Liglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ethers, 1,13-tetradecadiene dioxide, limonene dioxide, 1,2,7,8-diepoxyoctane, 1,2,5,6 -Diepoxycyclooctane and the like.

  Among these epoxy compounds, aromatic epoxides and alicyclic epoxides are preferable from the viewpoint of excellent curing speed, and alicyclic epoxides are particularly preferable.

  Examples of vinyl ether compounds include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, and trimethylol. Di- or trivinyl ether compounds such as propane trivinyl ether, ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-pro Vinyl ether, isopropyl vinyl ether, isopropenyl ether -O- propylene carbonate, dodecyl vinyl ether, and a monovinyl ether compounds such as diethylene glycol monovinyl ether.

Below, monofunctional vinyl ether and polyfunctional vinyl ether are illustrated in detail.
Examples of monofunctional vinyl ethers include, for example, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, lauryl vinyl ether, cyclohexyl vinyl ether, cyclohexyl methyl vinyl ether, 4 -Methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl D Ter, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, chloro Examples thereof include ethoxyethyl vinyl ether, phenylethyl vinyl ether, phenoxy polyethylene glycol vinyl ether and the like.

Examples of polyfunctional vinyl ethers include ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, and bisphenol F. Divinyl ethers such as alkylene oxide divinyl ether; trimethylolethane trivinyl ether, trimethylolpropane trivinyl ether, ditrimethylolpropane tetravinyl ether, glycerin trivinyl ether, pentaerythritol tetravinyl ether, dipentaerythritol pentavinyl ether, dipentaerythritol Hexavinyl ether, ethylene oxide-added trimethylolpropane trivinyl ether, propylene oxide-added trimethylolpropane trivinyl ether, ethylene oxide-added ditrimethylolpropane tetravinyl ether, propylene oxide-added ditrimethylolpropane tetravinyl ether, ethylene oxide-added pentaerythritol tetravinyl ether, propylene oxide addition Examples thereof include polyfunctional vinyl ethers such as pentaerythritol tetravinyl ether, ethylene oxide-added dipentaerythritol hexavinyl ether, and propylene oxide-added dipentaerythritol hexavinyl ether.
As the vinyl ether compound, a di- or trivinyl ether compound is preferable from the viewpoints of curability, adhesion to a recording medium, surface hardness of the formed image, and the like, and a divinyl ether compound is particularly preferable.

The oxetane compound that can be used in the present invention refers to a compound having at least one oxetane ring, and known oxetane as described in JP-A Nos. 2001-220526, 2001-310937, and 2003-341217. A compound can be arbitrarily selected and used.
As the compound having an oxetane ring that can be used in the present invention, a compound having 1 to 4 oxetane rings in its structure is preferable. By using such a compound, it becomes easy to maintain the viscosity of the ink composition in a good handling range, and to obtain high adhesion of the cured ink composition to the recording medium. Can do.

  Examples of the compound having 1 to 2 oxetane rings in the molecule include compounds represented by the following formulas (1) to (3).

R ^a1 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group, a furyl group, or a thienyl group. When two R ^a1 are present in the molecule, they may be the same or different.
Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. Preferred examples of the fluoroalkyl group include those in which any hydrogen of these alkyl groups is substituted with a fluorine atom.
R ^a2 is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, a group having an aromatic ring, an alkylcarbonyl group having 2 to 6 carbon atoms, or 2 to 6 carbon atoms. Represents an alkoxycarbonyl group, and an N-alkylcarbamoyl group having 2 to 6 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. Examples of the alkenyl group include a 1-propenyl group, a 2-propenyl group, a 2-methyl-1-propenyl group, and 2-methyl-2. -Propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group and the like. Examples of the group having an aromatic ring include phenyl group, benzyl group, fluorobenzyl group, methoxybenzyl group, phenoxyethyl group and the like. Can be mentioned. As the alkylcarbonyl group, an ethylcarbonyl group, a propylcarbonyl group, a butylcarbonyl group, etc., as an alkoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, a butoxycarbonyl group, etc., as an N-alkylcarbamoyl group, Examples thereof include an ethylcarbamoyl group, a propylcarbamoyl group, a butylcarbamoyl group, and a pentylcarbamoyl group. R ^a2 may have a substituent, and examples of the substituent include an alkyl group of 1 to 6 and a fluorine atom.

R ^a3 represents a linear or branched alkylene group, a linear or branched poly (alkyleneoxy) group, a linear or branched unsaturated hydrocarbon group, a carbonyl group or an alkylene group containing a carbonyl group, a carboxyl group Represents an alkylene group containing, an alkylene group containing a carbamoyl group, or a group shown below. Examples of the alkylene group include an ethylene group, a propylene group, and a butylene group. Examples of the poly (alkyleneoxy) group include a poly (ethyleneoxy) group and a poly (propyleneoxy) group. Examples of the unsaturated hydrocarbon group include a propenylene group, a methylpropenylene group, and a butenylene group.

When R ^a3 is the above polyvalent group, R ^a4 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a halogen atom, a nitro group, a cyano group, a mercapto group, Represents a lower alkyl carboxyl group, a carboxyl group, or a carbamoyl group.
R ^a5 represents an oxygen atom, a sulfur atom, a methylene group, NH, SO, SO ₂ , C (CF ₃ ) ₂ , or C (CH ₃ ) ₂ .
R ^a6 represents an alkyl group having 1 to 4 carbon atoms or an aryl group, and n is an integer of 0 to 2,000. R ^a7 represents an alkyl group having 1 to 4 carbon atoms, an aryl group, or a monovalent group having the following structure. In the following formula, R ^a8 is an alkyl group having 1 to 4 carbon atoms or an aryl group, and m is an integer of 0 to 100.

  As a compound represented by the formula (1), 3-ethyl-3-hydroxymethyloxetane (OXT-101: manufactured by Toagosei Co., Ltd.), 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane (OXT) -212: manufactured by Toagosei Co., Ltd.) and 3-ethyl-3-phenoxymethyloxetane (OXT-211: manufactured by Toagosei Co., Ltd.). Examples of the compound represented by the formula (2) include 1,4-bis [(3-ethyl-3-oxetanylmethoxy) methyl] benzene (OXT-121: Toagosei Co., Ltd.). ), Bis (3-ethyl-3-oxetanylmethyl) ether (OXT-221: Toagosei Co., Ltd.) is exemplified.

  Examples of the compound having 3 to 4 oxetane rings in the molecule include compounds represented by the following formula (4).

In the formula (4), R ^a1 has the same ^{meaning as} in the formula (1). In addition, as R ^a9 which is a polyvalent linking group, for example, a branched polyalkylene group having 1 to 12 carbon atoms such as groups represented by the following A to C, a branched poly ( An alkyleneoxy) group or a branched polysiloxy group such as a group represented by E below. j is 3 or 4.

In the above A, R ^a10 represents a methyl group, an ethyl group or a propyl group. Moreover, in said D, p is an integer of 1-10.

  Another embodiment of the oxetane compound that can be suitably used in the present invention includes a compound represented by the following formula (5) having an oxetane ring in the side chain.

In the formula (5), R ^a1 and R ^a8 have the same ^{meaning as} in the above formula. R ^a11 is an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group or a trialkylsilyl group, and r is 1 to 4.

The compound having such an oxetane ring is described in detail in JP-A No. 2003-341217, paragraph numbers 0021 to 0084, and the compound described herein can be suitably used in the present invention.
Oxetane compounds described in JP 2004-91556 A can also be used in the present invention. This is described in detail in paragraphs 0022 to 0058.
Among the oxetane compounds used in the present invention, it is preferable to use a compound having one oxetane ring from the viewpoint of the viscosity and tackiness of the ink composition.

The cationically polymerizable compound that can be used in the present invention may be used alone or in combination of two or more, but from the viewpoint of effectively suppressing shrinkage when the ink composition is cured, It is preferable to use a vinyl ether compound in combination with at least one compound selected from an oxetane compound and an epoxy compound.
The content of the cationically polymerizable compound in the ink composition is preferably 10 to 95% by weight, more preferably 30 to 90% by weight, still more preferably 50 to 85% by weight, based on the total solid content of the composition. is there.

<Preferable polymerizable compound>
As the polymerizable compound that can be used in the present invention, a (meth) acrylic monomer or prepolymer, an epoxy monomer or prepolymer, an oxetane monomer or prepolymer, or a urethane monomer or prepolymer is preferably used. . More preferably, they are the following compounds.

  2-ethylhexyl-diglycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-hydroxybutyl acrylate, hydroxypivalate neopentyl glycol diacrylate, 2-acryloyloxyethylphthalic acid, methoxy-polyethylene glycol acrylate, tetramethylol Methane triacrylate, 2-acryloyloxyethyl-2-hydroxyethylphthalic acid, dimethylol tricyclodecane diacrylate, ethoxylated phenyl acrylate, 2-acryloyloxyethyl succinic acid, nonylphenol EO adduct acrylate, modified glycerin triacrylate Bisphenol A diglycidyl ether acrylic acid adduct, modified bisphenol A diacrylate, phenoxy-polyethylene Glycol acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, bisphenol A PO adduct diacrylate, bisphenol A EO adduct diacrylate, 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, penta Erythritol triacrylate hexamethylene di Socia sulfonates urethane prepolymer, stearyl acrylate, isoamyl acrylate, isomyristyl acrylate, isostearyl acrylate.

  These acrylate compounds can lower the viscosity relatively than the polymerizable compounds conventionally used in UV curable inks, provide stable ink ejection properties, and good polymerization sensitivity and adhesion to the recording medium. It is. In the present invention, when the acrylate compound is used as the polymerizable compound, the content of the acrylate compound is preferably 20 to 95% by weight, more preferably 50 to 95% by weight, based on the total weight of the ink composition. More preferably, the content is 70 to 95% by weight.

In the present invention, the monomers listed as the polymerizable compounds described above are low in sensitization even with a low molecular weight, and have high reactivity, low viscosity, and adhesion to a recording medium. Excellent in properties.
Furthermore, in order to further improve the sensitivity, bleeding, and adhesion to the recording medium, the above monoacrylate is used in combination with a polyfunctional acrylate monomer or polyfunctional acrylate oligomer having a molecular weight of 400 or more, preferably 500 or more. It is preferable in terms of improving adhesion. Furthermore, it is particularly preferable to use a monofunctional, bifunctional, or trifunctional or higher polyfunctional monomer in combination. It is preferable because sensitivity, bleeding, and adhesion to the recording medium can be further improved while maintaining safety. As the oligomer, an epoxy acrylate oligomer and a urethane acrylate oligomer are particularly preferable.

When recording on a flexible recording medium such as a PET film or PP film, a combination of a monoacrylate selected from the above compound group and a polyfunctional acrylate monomer or polyfunctional acrylate oligomer gives the film flexibility and adhesion. It is preferable because the film strength can be increased while improving the properties. As monoacrylates, stearyl acrylate, isoamyl acrylate, isomystil acrylate, and isostearyl acrylate have high sensitivity and low shrinkage to prevent curling, and are preferable in terms of prevention of bleeding, odor of printed matter, and cost reduction of irradiation apparatus. .
In addition, methacrylate has better skin irritation than acrylate.
Of the above-mentioned compounds, when alkoxy acrylate is used in an amount of less than 70% by weight and the remainder is acrylate, it is preferable because it has good sensitivity, bleeding characteristics and odor characteristics.

(B) Polymerization initiator In the present invention, the photocurable ink contains (b) a polymerization initiator. As a polymerization initiator that can be used in the present invention, a known radical polymerization initiator or cationic polymerization initiator (photoacid generator) can be used. The said polymerization initiator may be used independently and may use 2 or more types together.
In the present invention, the radical polymerization initiator or cationic polymerization initiator that can be used in the ink composition is a compound that absorbs external energy to generate a polymerization initiating species. External energy used for initiating polymerization is roughly divided into heat and actinic radiation, and a thermal polymerization initiator and a photopolymerization initiator are used, respectively. Examples of the active radiation include γ rays, β rays, electron beams, ultraviolet rays, visible rays, and infrared rays.

<Radical polymerization initiator>
The radical polymerization initiator that can be used in the present invention includes (a) aromatic ketones, (b) aromatic onium salt compounds, (c) organic peroxides, (d) thio compounds, and (e) hexaarylbiphenyls. An imidazole compound, (f) a ketoxime ester compound, (g) a borate compound, (h) an azinium compound, (i) a metallocene compound, (j) an active ester compound, (k) a compound having a carbon halogen bond, and (l) Preferred examples include alkylamine compounds. These radical polymerization initiators may be used alone or in combination with the above compounds (a) to (l). The radical polymerization initiator in the present invention is preferably used alone or in combination of two or more.

<Cationic polymerization initiator>
Preferred examples of the cationic polymerization initiator (photoacid generator) that can be used in the present invention include chemically amplified photoresists and compounds used for photocationic polymerization (edited by Organic Electronics Materials Research Group, “Imaging”). Organic Materials ", Bunshin Publishing (1993), see pages 187-192). Examples of the cationic polymerization initiator suitable for the present invention are listed below.

First, B (C ₆ F ₅ ) ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ and CF ₃ SO ₃ ⁻ salts of aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium and phosphonium are listed. be able to. Secondly, sulfonated products that generate sulfonic acid can be mentioned. Thirdly, a halide that generates hydrogen halide can also be used. Fourthly, an iron allene complex can be mentioned.

(C) Colorant In the present invention, the photocurable ink (ink composition) preferably contains (c) a colorant.
The colorant that can be used in the present invention is not particularly limited, but pigments and oil-soluble dyes that are excellent in weather resistance and excellent in color reproducibility are preferable, and selected from any known colorants. Can do. In the present invention, the colorant that can be suitably used in the ink composition or the ink composition for inkjet recording preferably does not function as a polymerization inhibitor in a polymerization reaction that is a curing reaction. This is because the sensitivity of the curing reaction by actinic radiation is not reduced.

<Pigment>
The pigment is not particularly limited, and all commercially available organic and inorganic pigments or pigments dispersed in an insoluble resin or the like as a dispersion medium, or the resin is grafted onto the pigment surface Can be used. Moreover, what dye | stained the resin particle with dye can be used.
Examples of these pigments include, for example, “Pigment Dictionary” (2000), edited by Seijiro Ito. Herbst, K.M. Hunger “Industrial Organic Pigments”, JP 2002-12607 A, JP 2002-188025 A, JP 2003-26978 A, and JP 2003-342503 A3.

  Specific examples of organic pigments and inorganic pigments that can be used in the present invention include C.I. I. Pigment Yellow 1 (Fast Yellow G etc.), C.I. I. A monoazo pigment such as C.I. Pigment Yellow 74; I. Pigment Yellow 12 (disaji yellow AAA, etc.), C.I. I. Disazo pigments such as C.I. Pigment Yellow 17; I. Non-benzidine type azo pigments such as CI Pigment Yellow 180; I. Azo lake pigments such as C.I. Pigment Yellow 100 (eg Tartrazine Yellow Lake); I. Condensed azo pigments such as CI Pigment Yellow 95 (Condensed Azo Yellow GR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Yellow 115 (such as quinoline yellow lake); I. Basic dye lake pigments such as CI Pigment Yellow 18 (Thioflavin Lake, etc.), anthraquinone pigments such as Flavantron Yellow (Y-24), isoindolinone pigments such as Isoindolinone Yellow 3RLT (Y-110), and quinophthalone yellow Quinophthalone pigments such as (Y-138), isoindoline pigments such as isoindoline yellow (Y-139), C.I. I. Nitroso pigments such as C.I. Pigment Yellow 153 (nickel nitroso yellow, etc.); I. And metal complex salt azomethine pigments such as CI Pigment Yellow 117 (copper azomethine yellow, etc.).

  C. As a thing which exhibits red or magenta color, C.I. I. Monoazo pigments such as CI Pigment Red 3 (Toluidine Red, etc.); I. Disazo pigments such as C.I. Pigment Red 38 (Pyrazolone Red B, etc.); I. Pigment Red 53: 1 (Lake Red C, etc.) and C.I. I. Azo lake pigments such as C.I. Pigment Red 57: 1 (Brilliant Carmine 6B); I. Condensed azo pigments such as C.I. Pigment Red 144 (condensed azo red BR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Red 174 (Phloxine B Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Red 81 (Rhodamine 6G 'lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Red 177 (eg, dianthraquinonyl red); I. Thioindigo pigments such as C.I. Pigment Red 88 (Thioindigo Bordeaux, etc.); I. Perinone pigments such as C.I. Pigment Red 194 (perinone red, etc.); I. Perylene pigments such as C.I. Pigment Red 149 (perylene scarlet, etc.); I. Pigment violet 19 (unsubstituted quinacridone), C.I. I. Quinacridone pigments such as CI Pigment Red 122 (quinacridone magenta, etc.); I. Isoindolinone pigments such as CI Pigment Red 180 (isoindolinone red 2BLT, etc.); I. And alizarin lake pigments such as CI Pigment Red 83 (Mada Lake, etc.).

  As a pigment exhibiting blue or cyan, C.I. I. Disazo pigments such as C.I. Pigment Blue 25 (Dianisidine Blue, etc.); I. Phthalocyanine pigments such as C.I. Pigment Blue 15 (phthalocyanine blue, etc.); I. Acidic dye lake pigments such as C.I. Pigment Blue 24 (Peacock Blue Lake, etc.); I. Basic dye lake pigments such as C.I. Pigment Blue 1 (Viclotia Pure Blue BO Lake, etc.); I. Anthraquinone pigments such as C.I. Pigment Blue 60 (Indantron Blue, etc.); I. And alkali blue pigments such as CI Pigment Blue 18 (Alkali Blue V-5: 1).

As a pigment exhibiting green, C.I. I. Pigment green 7 (phthalocyanine green), C.I. I. Phthalocyanine pigments such as C.I. Pigment Green 36 (phthalocyanine green); I. And azo metal complex pigments such as CI Pigment Green 8 (Nitroso Green).
As a pigment exhibiting an orange color, C.I. I. An isoindoline pigment such as C.I. Pigment Orange 66 (isoindoline orange); I. And anthraquinone pigments such as CI Pigment Orange 51 (dichloropyrantron orange).

Examples of the black pigment include carbon black, titanium black, and aniline black.
Specific examples of the white pigment include basic lead carbonate (2PbCO ₃ Pb (OH) ₂ , so-called silver white), zinc oxide (ZnO, so-called zinc white), titanium oxide (TiO ₂ , so-called titanium white), Strontium titanate (SrTiO ₃ , so-called titanium strontium white) or the like can be used.

  Here, titanium oxide has a smaller specific gravity than other white pigments, a large refractive index, and is chemically and physically stable, so that it has a large hiding power and coloring power as a pigment. Excellent durability against other environments. Therefore, it is preferable to use titanium oxide as the white pigment. Of course, other white pigments (may be other than the listed white pigments) may be used as necessary.

For dispersing the pigment, for example, a dispersion device such as a ball mill, a sand mill, an attritor, a roll mill, a jet mill, a homogenizer, a paint shaker, a kneader, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, or a wet jet mill is used. be able to.
It is also possible to add a dispersant when dispersing the pigment. Examples of the dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long-chain polyaminoamide and a high molecular weight acid ester, a salt of a high molecular weight polycarboxylic acid, a high molecular weight unsaturated acid ester, a high molecular copolymer, a modified polyacrylate, an aliphatic Examples thereof include polyvalent carboxylic acids, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate esters, and pigment derivatives. It is also preferable to use a commercially available polymer dispersant such as the Solsperse series from Zeneca.
Moreover, it is also possible to use a synergist according to various pigments as a dispersion aid. These dispersants and dispersion aids are preferably added in an amount of 1 to 50 parts by weight with respect to 100 parts by weight of the pigment.

  In the ink composition, as a dispersion medium for various components such as a pigment, a solvent may be added, or the cationic polymerizable compound which is a low molecular weight component without a solvent may be used as a dispersion medium. In the present invention, the ink composition is preferably a radiation curable ink, and is preferably solvent-free in order to be cured after the ink is applied to a recording medium. This is because if the solvent remains in the cured ink image, the solvent resistance is deteriorated or a VOC (Volatile Organic Compound) problem of the remaining solvent occurs. From such a viewpoint, as the dispersion medium, (a) a cationically polymerizable compound is used, and among them, it is preferable to select a cationically polymerizable monomer having the lowest viscosity in terms of dispersion suitability and handling properties of the ink composition. .

The average particle diameter of the pigment is preferably 0.02 to 0.4 μm, more preferably 0.02 to 0.1 μm, and more preferably 0.02 to 0.07 μm.
Selection of pigments, dispersants, and dispersion media, dispersion conditions, and filtration conditions are set so that the average particle diameter of the pigment particles falls within the above preferred range. By controlling the particle size, clogging of the head nozzle can be suppressed, and the storage stability, transparency, and curing sensitivity of the ink composition can be maintained.

(D) Sensitizing dye In the present invention, a sensitizing dye may be added to the ink composition in order to absorb specific actinic radiation and promote decomposition of the polymerization initiator. A sensitizing dye absorbs specific actinic radiation and enters an electronically excited state. The sensitizing dye in an electronically excited state comes into contact with the polymerization initiator, and effects such as electron transfer, energy transfer, and heat generation occur. As a result, the polymerization initiator undergoes a chemical change and decomposes to generate radicals, acids or bases.
Examples of preferred sensitizing dyes include those belonging to the following compounds and having an absorption wavelength in the 350 nm to 450 nm region.
Polynuclear aromatics (eg, pyrene, perylene, triphenylene), xanthenes (eg, fluorescein, eosin, erythrosine, rhodamine B, rose bengal), cyanines (eg, thiacarbocyanine, oxacarbocyanine), merocyanines ( For example, merocyanine, carbomerocyanine), thiazines (eg, thionine, methylene blue, toluidine blue), acridines (eg, acridine orange, chloroflavin, acriflavine), anthraquinones (eg, anthraquinone), squalium (eg, squalium) ), Coumarins (eg 7-diethylamino-4-methylcoumarin).

  More preferable examples of the sensitizing dye include compounds represented by the following formulas (IX) to (XIII).

In the formula (IX), A ¹ represents a sulfur atom or NR ⁵⁰ , R ⁵⁰ represents an alkyl group or an aryl group, and L ² forms a basic nucleus of the dye together with the adjacent A ² and the adjacent carbon atom. R ⁵¹ and R ⁵² each independently represent a hydrogen atom or a monovalent nonmetallic atomic group, and R ⁵¹ and R ⁵² may be bonded to each other to form an acidic nucleus of the dye. Good. W represents an oxygen atom or a sulfur atom.

In formula (X), Ar ¹ and Ar ² each independently represent an aryl group and are linked via a bond with —L ³ —. Here, L ³ represents —O— or —S—. W is synonymous with that shown in Formula (IX).

In the formula (XI), A ₂ represents a sulfur atom or NR ⁵⁹ , L ⁴ represents a nonmetallic atomic group that forms a basic nucleus of the dye together with adjacent A ₂ and a carbon atom, R ⁵³ , R ⁵⁴ , R ⁵⁵ , R ⁵⁶ , R ⁵⁷ and R ⁵⁸ each independently represent a monovalent nonmetallic atomic group, and R ⁵⁹ represents an alkyl group or an aryl group.

In formula (XII), A ³ and A ⁴ each independently represent —S—, —NR ⁶² — or —NR ⁶³ —, wherein R ⁶² and R ⁶³ each independently represent a substituted or unsubstituted alkyl group, substituted or represents an unsubstituted aryl group, L to ^5, L ⁶ are each independently, together with the adjacent a ^3, A4 ^及 beauty adjacent carbon atoms represent a non-metallic atomic group forming a basic nucleus of a dye, R ⁶⁰ , R ⁶¹ each independently represents a hydrogen atom or a monovalent non-metallic atomic group, or may be bonded to each other to form an aliphatic or aromatic ring.

In formula (XIII), R ⁶⁶ represents an aromatic ring or a hetero ring which may have a substituent, and A ⁵ represents an oxygen atom, a sulfur atom or —NR ⁶⁷ —. R ⁶⁴ , R ⁶⁵ and R ⁶⁷ each independently represent a hydrogen atom or a monovalent nonmetallic atomic group, and R ⁶⁷ and R ⁶⁴ , and R ⁶⁵ and R ⁶⁷ each represent an aliphatic or aromatic ring. Can be combined to form.

Preferable specific examples of the compounds represented by formulas (IX) to (XIII) include (E-1) to (E-20) shown below.
In some of the following specific examples, the hydrocarbon chain is described by a simplified structural formula in which symbols of carbon (C) and hydrogen (H) are omitted.

  The addition amount is appropriately selected according to the purpose, but generally it is preferably 0.1 to 20% by weight in terms of solid content.

(E) Co-sensitizer In the present invention, the ink composition preferably contains a co-sensitizer. In the present invention, the co-sensitizer has functions such as further improving the sensitivity of the sensitizing dye to actinic radiation or suppressing polymerization inhibition of the polymerizable compound by oxygen.
Examples of such co-sensitizers include amines such as MR Sander et al., “Journal of Polymer Society”, Vol. 10, page 3173 (1972), Japanese Examined Patent Publication No. 44-20189, Japanese Patent Laid-Open No. 51-82102. Publication, JP 52-134692, JP 59-138205, JP 60-84305, JP 62-18537, JP 64-33104, Research Disclosure 33825 Specifically, triethanolamine, p-dimethylaminobenzoic acid ethyl ester, p-formyldimethylaniline, p-methylthiodimethylaniline and the like can be mentioned.

  Other examples of co-sensitizers include thiols and sulfides such as thiol compounds described in JP-A-53-702, JP-B-55-500806, JP-A-5-142772, No. 56-75643, such as 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzimidazole, 2-mercapto-4 (3H) -quinazoline, β-mercapto. And naphthalene.

Other examples include amino acid compounds (eg, N-phenylglycine), organometallic compounds described in Japanese Patent Publication No. 48-42965 (eg, tributyltin acetate), and hydrogen described in Japanese Patent Publication No. 55-34414. Donors, sulfur compounds described in JP-A-6-308727 (eg, trithiane), phosphorus compounds described in JP-A-6-250387 (diethylphosphite, etc.), Si-- described in Japanese Patent Application No. 6-191605 H, Ge-H compound, etc. are mentioned.
The addition amount is appropriately selected according to the purpose, but generally it is preferably 0.1 to 20% by weight in terms of solid content.

(F) Other components In the present invention, other components can be added to the ink composition as necessary. Examples of other components include ultraviolet absorbers, antioxidants, anti-fading agents, conductive salts, solvents, polymer compounds, surfactants, basic compounds, and the like.

[Ultraviolet absorber]
In the present invention, an ultraviolet absorber can be used from the viewpoint of improving the weather resistance of the obtained image and preventing discoloration.
Examples of the ultraviolet absorber are described in JP-A-58-185679, JP-A-61-190537, JP-A-2-782, JP-A-5-97075, JP-A-9-34057, and the like. Benzotriazole compounds, benzophenone compounds described in JP-A No. 46-2784, JP-A No. 5-194843, US Pat. No. 3,214,463, etc., JP-B Nos. 48-30492 and 56-21141 Cinnamic acid compounds described in JP-A-10-88106, JP-A-4-298503, JP-A-8-53427, JP-A-8-239368, JP-A-10-182621, JP The triazine compounds described in JP-A-8-501291, Research Disclosure No. Examples thereof include compounds described in US Pat. No. 24239, compounds that emit fluorescence by absorbing ultraviolet rays typified by stilbene and benzoxazole compounds, and so-called fluorescent brighteners.
The addition amount is appropriately selected according to the purpose, but generally it is preferably 0.5 to 15% by weight in terms of solid content.

〔Antioxidant〕
An antioxidant can be added to improve the stability of the ink composition. Examples of the antioxidant include European published patents, 223739, 309401, 309402, 310551, 310552, 359416, and 3435443. JP, 54-85535, 62-262417, 63-113536, 63-163351, JP-A-2-262654, JP-A-2-71262, Examples thereof include those described in Kaihei 3-121449, JP-A-5-61166, JP-A-5-119449, US Pat. No. 4,814,262, US Pat. No. 4,980,275, and the like.
Although the addition amount is appropriately selected according to the purpose, it is preferably 0.1 to 8% by weight in terms of solid content.

[Anti-fading agent]
In the present invention, various organic and metal complex anti-fading agents can be used in the ink composition. Examples of the organic anti-fading agent include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocycles. Examples of the metal complex anti-fading agent include nickel complexes and zinc complexes. No. 17643, VII, I to J, No. 15162, ibid. No. 18716, page 650, left column, ibid. No. 36544, page 527, ibid. No. 307105, page 872, ibid. The compounds described in the patent cited in No. 15162 and the compounds included in the general formulas and compound examples of representative compounds described in JP-A-62-215272, pages 127 to 137 can be used. .
Although the addition amount is appropriately selected according to the purpose, it is preferably 0.1 to 8% by weight in terms of solid content.

[Conductive salts]
In the present invention, conductive salts such as potassium thiocyanate, lithium nitrate, ammonium thiocyanate, and dimethylamine hydrochloride can be added to the ink composition for the purpose of controlling ejection properties.

〔solvent〕
In the present invention, it is also effective to add a trace amount of an organic solvent to the ink composition in order to improve the adhesion to the recording medium.
In the present invention, the solvent that can be used in the ink composition is preferably such that the difference between the value of the solubility parameter of rubber in the rubber particles (SP value) and the value of the solubility parameter of the solvent to be used is 2 or more. More preferably, it is 3 or more.
Examples of the solvent include ketone solvents such as acetone, methyl ethyl ketone, and diethyl ketone, alcohol solvents such as methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, and tert-butanol, and chlorine such as chloroform and methylene chloride. Solvents, aromatic solvents such as benzene and toluene, ester solvents such as ethyl acetate, butyl acetate and isopropyl acetate, ether solvents such as diethyl ether, tetrahydrofuran and dioxane, glycols such as ethylene glycol monomethyl ether and ethylene glycol dimethyl ether Examples include ether solvents.
In this case, it is effective to add the solvent within the range that does not cause the problem of solvent resistance and VOC, and the amount is preferably 0.1 to 5% by weight, more preferably 0.1 to 3% by weight based on the whole ink composition. % Range.

[Polymer compound]
In the present invention, various polymer compounds can be added to the ink composition in order to adjust film physical properties. Examples of polymer compounds include acrylic polymers, polyvinyl butyral resins, polyurethane resins, polyamide resins, polyester resins, epoxy resins, phenol resins, polycarbonate resins, polyvinyl butyral resins, polyvinyl formal resins, shellacs, vinyl resins, acrylic resins. Rubber resins, waxes and other natural resins can be used. Two or more of these may be used in combination. Of these, vinyl copolymer obtained by copolymerization of acrylic monomers is preferred. Furthermore, a copolymer containing “carboxyl group-containing monomer”, “methacrylic acid alkyl ester”, or “acrylic acid alkyl ester” as a structural unit is also preferably used as the copolymer composition of the polymer binder.

[Surfactant]
In the present invention, a surfactant may be added to the ink composition.
Examples of the surfactant include those described in JP-A Nos. 62-173463 and 62-183457. For example, anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene blocks Nonionic surfactants such as copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. An organic fluoro compound may be used instead of the surfactant. The organic fluoro compound is preferably hydrophobic. Examples of the organic fluoro compounds include fluorine surfactants, oily fluorine compounds (eg, fluorine oil) and solid fluorine compound resins (eg, tetrafluoroethylene resin). No. (columns 8 to 17) and those described in JP-A Nos. 62-135826.

[Basic compounds]
The basic compound is preferably added from the viewpoint of improving the storage stability of the ink composition. As the basic compound that can be used in the present invention, known basic compounds can be used. For example, basic inorganic compounds such as inorganic salts and basic organic compounds such as amines can be preferably used. .

In addition to this, if necessary, for example, leveling additives, matting agents, waxes for adjusting film physical properties, polymerization to inhibit the adhesion to recording media such as polyolefin and PET, and the like, The tackifier which does not do can be contained.
As a tackifier, specifically, a high molecular weight adhesive polymer (for example, (meth) acrylic acid and an alkyl group having 1 to 20 carbon atoms) described in JP-A-2001-49200, 5-6p. An ester with an alcohol having, an ester of (meth) acrylic acid and an alicyclic alcohol having 3 to 14 carbon atoms, a copolymer comprising an ester of (meth) acrylic acid and an aromatic alcohol having 6 to 14 carbon atoms) Or a low molecular weight tackifying resin having a polymerizable unsaturated bond.

(3) Properties of Photocurable Ink (Ink Composition) In the present invention, the photocurable ink (ink composition) requires (a) a polymerizable compound and (b) a polymerization initiator as described above. It is contained as a component and optionally contains a colorant and the like. These components are preferably (a) a polymerizable compound, preferably 20 to 90% by weight, more preferably 30 to 80% by weight, and (b) a polymerization initiator, based on the total weight of the ink composition. 0.1 to 30% by weight, more preferably 0.5 to 20% by weight, and further containing a colorant, the colorant is preferably 0.1 to 30% by weight, more preferably 0.5 to 20% by weight. It is appropriate that the total amount of each component is 100% by weight.

  Further, in the present invention, since the photocurable ink (ink composition) is used for inkjet recording, in consideration of dischargeability, at a discharge temperature (for example, 40 to 80 ° C., preferably 25 to 30 ° C.), In the present invention, the viscosity of the ink composition is preferably 7 to 30 mPa · s, more preferably 7 to 20 mPa · s. For example, in the present invention, the viscosity of the ink composition at room temperature (25 to 30 ° C.) is preferably 35 to 500 mPa · s, more preferably 35 to 200 mPa · s. In the present invention, it is preferable that the composition ratio of the ink composition is appropriately adjusted so that the viscosity is in the above range. By setting the viscosity at room temperature high, even when a porous recording medium is used, penetration into the recording medium can be avoided, and uncured monomers and odors can be reduced. Furthermore, it is preferable because bleeding at the time of landing of a discharged droplet can be suppressed, and as a result, the image quality is improved.

  In the present invention, the surface tension of the ink composition is, for example, preferably 20 to 30 mN / m, and more preferably 23 to 28 mN / m. When recording on various recording media such as polyolefin, PET, coated paper, and non-coated paper, 20 mN / m or more is preferable from the viewpoint of bleeding and penetration, and the wettability is preferably 30 mN / m or less.

(4) Inkjet recording method and apparatus The photocurable ink (ink composition) of the present invention is used for inkjet recording.
An ink jet recording method that can be suitably employed in the present invention will be described below.

(4-1) Inkjet recording method In the present invention, as an inkjet recording method, a photocurable ink is ejected onto a recording medium (support, recording material, etc.), and the ink composition ejected onto the recording medium is used. Examples of the method include forming an image by irradiating actinic radiation and curing the ink. That is,
(A) a step of discharging a photocurable ink (ink composition) onto a recording medium; and (b) a photocurable ink (ink composition) by irradiating the discharged photocurable ink (ink composition) with active radiation. A step of curing the ink composition),
An ink jet recording method including
The peak wavelength of the active radiation is preferably 200 to 600 nm, more preferably 300 to 450 nm, and more preferably 350 to 420 nm. The output of active radiation is preferably 2,000 mJ / cm ² or less, more preferably from 10 to 2,000 mJ / cm ^2, more preferably, be 20 to 1,000 mJ / cm ² Particularly preferably, it is 50 to 800 mJ / cm ² .

(4-1-1) Step of discharging photocurable ink onto a recording medium In the present invention, when the photocurable ink is discharged from an inkjet head onto a recording medium, the photocurable ink (ink composition) Is preferably heated to 25 to 80 ° C., more preferably 25 to 50 ° C., and the viscosity of the ink composition is preferably lowered to 7 to 30 mPa · s, more preferably 7 to 20 mPa · s, and then discharged. preferable. In particular, it is preferable to use an ink composition having an ink viscosity of 35 to 500 mP · s at 25 ° C. because a great effect can be obtained. By using this method, high ejection stability can be realized. A radiation curable ink composition such as the ink composition used in the present invention generally has a higher viscosity than a water-based ink that is usually used in an ink composition or an ink for ink jet recording. Is big. Viscosity fluctuation of the ink has a great influence on the change of the droplet size and the change of the droplet discharge speed, and consequently causes the image quality deterioration. Therefore, it is necessary to keep the temperature of the ink at the time of ejection as constant as possible. Therefore, in the present invention, it is appropriate that the temperature control range is set to ± 5 ° C. of the set temperature, preferably ± 2 ° C. of the set temperature, more preferably set temperature ± 1 ° C.

(4-1-2) A step of irradiating the ejected photocurable ink (ink composition) with actinic radiation to cure the photocurable ink (ink composition) The above ejected onto the surface of the recording medium The photocurable ink (ink composition) is cured by irradiation with actinic radiation. This is because the sensitizing dye in the polymerization initiation system contained in the ink composition used in the present invention absorbs actinic radiation to be in an excited state and comes into contact with the polymerization initiator in the polymerization initiation system. This is because the agent is decomposed and the polymerizable compound is radically polymerized and cured.
Here, α rays, γ rays, electron beams, X rays, ultraviolet rays, visible light, infrared rays, or the like can be used as the active radiation used. The peak wavelength of the actinic radiation is, for example, from 200 to 600 nm, preferably from 300 to 450 nm, more preferably from 350 to 450 nm, although it depends on the absorption characteristics of the sensitizing dye. In the present invention, the polymerization initiation system has sufficient sensitivity even with a low-power active radiation. Thus, the output of the actinic radiation is, for example, 2,000 mJ / cm ² or less, preferably, 10 to 2,000 mJ / cm ^2, more preferably, 20 to 1,000 mJ / cm ^2, more preferably, 50 to 800 mJ An irradiation energy of / cm ² is appropriate. The active radiation, the illumination intensity on the exposed surface is, for example, 10 to 2,000 mW / cm ^2, preferably, it is suitable to be irradiated at 20 to 1,000 mW / cm ^2.

In the present invention, it is appropriate that the ink composition is irradiated with such actinic radiation for, for example, 0.01 to 120 seconds, preferably 0.1 to 90 seconds.
Actinic radiation irradiation conditions and a basic irradiation method are disclosed in JP-A-60-132767. Specifically, the light source is provided on both sides of the head unit including the ink ejection device, and the head unit and the light source are scanned by a so-called shuttle method. Irradiation with actinic radiation takes a certain time (for example, 0.01 to 0.5 seconds, preferably 0.01 to 0.3 seconds, more preferably 0.01 to 0.15 seconds) after ink landing. Will be done. In this way, by controlling the time from ink landing to irradiation to an extremely short time, it is possible to prevent the ink that has landed on the recording medium from spreading before curing. Further, since the ink can be exposed to a porous recording medium before the ink penetrates to a deep part where the light source does not reach, residual unreacted monomer can be suppressed, and as a result, odor can be reduced. .
Further, the curing may be completed by another light source that is not driven. In WO99 / 54415, as an irradiation method, a method using an optical fiber or a method in which a collimated light source is applied to a mirror surface provided on the side surface of the head unit to irradiate the recording unit with UV light is disclosed.

By adopting the ink jet recording method as described above, the dot diameter of the landed ink can be kept constant even on various recording media having different surface wettability, and the image quality is improved. In addition, in order to obtain a color image, it is preferable to superimpose in order from a color with low brightness. By superimposing the inks in the order of low lightness, the irradiation line can easily reach the lower ink, and good curing sensitivity, reduction of residual monomers, reduction of odor, and improvement of adhesion can be expected. In addition, irradiation can be performed by discharging all colors and collectively exposing, but exposure for each color is preferable from the viewpoint of promoting curing.
In this way, in the present invention, the ink composition is cured by irradiation with actinic radiation to form a hydrophobic image on the hydrophilic support surface.

(4-2) Inkjet printer (inkjet recording apparatus)
The inkjet printer used in the present invention (hereinafter also referred to as “inkjet recording apparatus”) is not particularly limited, and a commercially available inkjet recording apparatus can be used. That is, in the present invention, recording can be performed on a recording medium using a commercially available inkjet recording apparatus.
Examples of the ink jet recording apparatus that can be used in the present invention include an ink supply system, a temperature sensor, and an actinic radiation source.
The ink supply system includes, for example, an original tank containing the photocurable ink (ink composition), a supply pipe, an ink supply tank immediately before the inkjet head, a filter, and a piezo-type inkjet head. The piezo-type inkjet head has a multi-size dot of 1 to 100 pl, preferably 8 to 30 pl, for example, 320 × 320 to 4,000 × 4,000 dpi, preferably 400 × 400 to 1,600 × 1,600 dpi. More preferably, it can be driven so as to discharge at a resolution of 720 × 720 dpi. In the present invention, dpi represents the number of dots per 2.54 cm.

  As described above, since it is desirable that the radiation curable ink has a constant temperature for the ejected ink, heat insulation and heating can be performed from the ink supply tank to the inkjet head portion. The temperature control method is not particularly limited, but for example, it is preferable to provide a plurality of temperature sensors at each piping site and perform heating control according to the ink flow rate and the environmental temperature. The temperature sensor can be provided near the ink supply tank and the nozzle of the inkjet head. Moreover, it is preferable that the head unit to be heated is thermally shielded or insulated so that the apparatus main body is not affected by the temperature from the outside air. In order to shorten the printer start-up time required for heating or to reduce the loss of thermal energy, it is preferable to insulate from other parts and reduce the heat capacity of the entire heating unit.

As the active radiation source, a mercury lamp, a gas / solid laser or the like is mainly used, and a mercury lamp and a metal halide lamp are widely known as the ultraviolet light curable ink jet. However, from the viewpoint of environmental protection, mercury-free is strongly desired, and replacement with a GaN-based semiconductor ultraviolet light-emitting device is very useful industrially and environmentally. Furthermore, LED (UV-LED) and LD (UV-LD) are small, have a long lifetime, high efficiency, and low cost, and are expected as light sources for photo-curable ink jets.
Further, a light emitting diode (LED) and a laser diode (LD) can be used as the active radiation source. In particular, when an ultraviolet light source is required, an ultraviolet LED and an ultraviolet LD can be used. For example, Nichia Corporation has introduced a purple LED whose main emission spectrum has a wavelength between 365 nm and 420 nm. When even shorter wavelengths are required, US Pat. No. 6,084,250 discloses an LED that can emit actinic radiation centered between 300 nm and 370 nm. Other ultraviolet LEDs are also available and can emit radiation in different ultraviolet bands. The actinic radiation source particularly preferred in the present invention is a UV-LED, particularly preferably a UV-LED having a peak wavelength at 350 to 420 nm.
It is preferable that maximum illumination intensity of the LED on a recording medium is 10 to 2,000 mW / cm ^2, more preferably 20 to 1,000 mW / cm ^2, particularly preferably 50 to 800 mW / cm ² .

  Next, a method for cleaning an ink jet printer will be described. An ink jet printer or some parts are cleaned using the ink cleaning liquid of the present invention. As a cleaning method, a method of wiping the inkjet printer or its parts with a cloth or a cleaning blade wetted with the ink cleaning liquid of the present invention, a method of immersing the ink jet printer or its parts in the ink cleaning liquid of the present invention, and an ink cleaning liquid of the present invention by inkjet. A method in which an absorbent material is brought into contact with an ink jet printer or its parts after being applied to the printer or its parts, and the cleaning liquid is sucked with the absorbent material. After the ink cleaning liquid of the present invention is applied to the ink jet printer or its parts, the ink jet printer or its parts are applied. For example, a method of removing the cleaning liquid by performing air suction, air supply, etc.

  Further, when the ink jet printer is provided with a cleaning mechanism for cleaning the head of the ink jet printer with the cleaning liquid, the head is cleaned by the cleaning mechanism when the ink cleaning liquid of the present invention is supplied to the cleaning mechanism. Further, when the ejection port of the head is covered with a cap, a cap coated with the ink cleaning liquid of the present invention may be used.

Further, by filling the ink cleaning liquid of the present invention into the head of the ink jet printer and discharging it from the nozzle, it is possible to clean the inside of the head and the vicinity of the nozzle by discharging the ink from the nozzle. In this case, it is preferable to apply a pressure of about 1 kPa to 100 kPa. Specifically, the cleaning liquid is fed into the head from the ink supply path connected to the head. At that time, adjusting the pressure to discharge the cleaning liquid from the nozzle, or forcibly sucking the filled cleaning liquid with a rubber tube or the like so as not to damage the nozzle surface from the nozzle surface is included. In some cases, it is possible to drive the printer head and perform the same operation as the ink discharge to discharge the ink cleaning liquid.
On the other hand, a method of cleaning the inside of the printer (nozzle, head, tube, pump, etc.) by circulating the ink cleaning liquid can also be exemplified.
Alternatively, the cleaning liquid may be discharged or collected after filling the head with the cleaning liquid and applying external vibration by ultrasonic waves to promote the solubility of the solids in the head.

In the present invention, as the method of using the ink jet recording apparatus, when the ink jet recording apparatus is not used for several hours, the method of using the ink jet recording apparatus in which the ink cleaning liquid of the present invention is filled in the head of the ink jet printer is preferable. As described above, it is preferable to fill the head with the ink cleaning liquid of the present invention because the curing of the photocurable ink can be prevented and clogging of the head can be suppressed.
In addition, it is preferable that the head is automatically cleaned with an ink cleaning liquid when ejection is not performed for a certain period of time (preferably 12 to 168 hours, more preferably 24 to 36 hours). More preferably, it is filled with a cleaning liquid. In use, the photocurable ink can be discharged by discharging or collecting the filled ink cleaning liquid.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.
The “parts” described below represent “parts by weight” unless otherwise specified.
Chromophthal Yellow LA, Cinquasia Magenta RT-355D, Irgalite Blue GLVO, Microlith Black C-K, and Irgacure 184 used in the present invention are commercially available products from Ciba Specialty Chemicals (CSC).
The following examples relate to UV inkjet inks of each color.

[Example 1]
<< Preparation of radical polymerizable ink >>
<Yellow ink 1>
N-vinyl-ε-caprolactam (Aldrich) 25.0 parts Actilane 421 29.4 parts (Akcros polyfunctional acrylate monomer)
Photomer 4017 (UV diluent manufactured by EChem) 10.0 parts (1,6-hexanediol diacrylate)
・ Solsperse 32000 (Noveon dispersant) 0.4 part ・ Chromophthalal Yellow LA (CSC pigment) 3.6 part ・ Genorad 16 (Rahn stabilizer) 0.05 part ・ Lucirin TPO (BASF light) 8.5 parts · Benzophenone (photopolymerization initiator) 4.0 parts · Irgacure 184 (CSC photopolymerization initiator) 4.0 parts · Byk 307 (BYK Chemie antifoam) 0. 05 parts9,10-dibutoxyanthracene 3.0 parts

<Magenta ink 1>
・ N-vinyl-ε-caprolactam (manufactured by Aldrich) 25.0 parts ・ Activane 421 21.4 parts (manufactured by Akcros polyfunctional acrylate monomer)
Photomer 4017 (UV diluent manufactured by EChem) 10.0 parts (1,6-hexanediol diacrylate)
Solsperse 32000 (Noveon dispersant) 0.4 part Cinquasia Magenta RT-355D (CSC pigment) 3.6 part Genorad 16 (Rahn stabilizer) 0.05 part Rapi-Cure DVE- 3
(Vinyl ether manufactured by ISP Europe) 8.0 parts / Lucirin TPO (photopolymerization initiator manufactured by BASF) 8.5 parts / benzophenone (photopolymerization initiator) 4.0 parts / Irgacure 184 (photopolymerization initiator manufactured by CSC) ) 4.0 parts • Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts • 9,10-dibutoxyanthracene 3.0 parts

<Cyan ink 1>
・ N-vinyl-ε-caprolactam (manufactured by Aldrich) 25.0 parts ・ Activane 421 21.4 parts (manufactured by Akcros polyfunctional acrylate monomer)
Photomer 4017 (UV diluent manufactured by EChem) 10.0 parts (1,6-hexanediol diacrylate)
・ Solsperse 32000 (Noveon dispersant) 0.4 part ・ Irgalite Blue GLVO (CSC pigment) 3.6 part ・ Genorad 16 (Rahn stabilizer) 0.05 part ・ Rapi-Cure DVE-3
(Vinyl ether manufactured by ISP Europe) 8.0 parts / Lucirin TPO (photopolymerization initiator manufactured by BASF) 8.5 parts / benzophenone (photopolymerization initiator) 4.0 parts / Irgacure 184 (photopolymerization initiator manufactured by CSC) ) 4.0 parts • Byk 307 (defoamer manufactured by BYK Chemie) 0.05 parts • 9,10-dibutoxyanthracene 3.0 parts

<Black ink 1>
N-vinyl-ε-caprolactam (Aldrich) 25.0 parts Actilane 421 25.4 parts (Akcros polyfunctional acrylate monomer)
Photomer 4017 (UV diluent manufactured by EChem) 10.0 parts (1,6-hexanediol diacrylate)
・ Solsperse 32000 (Noveon's dispersant) 0.4 part ・ Microlith Black CK (pigment made by CSC) 2.6 part ・ Genorad 16 (Rahn stabilizer) 0.05 part ・ Rapi-Cure DVE- 3 5.0 parts (vinyl ether made by ISP Europe)
• Lucirin TPO (BASF photopolymerization initiator) 8.5 parts • Benzophenone (photopolymerization initiator) 4.0 parts • Irgacure 184 (CSC photopolymerization initiator) 4.0 parts • Byk 307 (BYK Chemie) Defoaming agent manufactured by the company) 0.05 parts, 9,10-dibutoxyanthracene 3.0 parts

<White ink 1>
N-vinyl-ε-caprolactam (manufactured by Aldrich) 25.0 parts Actylane 421 18.0 parts (Akcros polyfunctional acrylate monomer)
Photomer 4017 (UV diluent manufactured by EChem) 5.0 parts (1,6-hexanediol diacrylate)
-Solsperse 32000 (Noveon Co. dispersant) 0.4 part-KRONOS 2300 (KRONOS titanium oxide) 15.0 parts-Genorad 16 (Rahn Stabilizer) 0.05 part-Rapi-Cure DVE-3 5 0.0 part (vinyl ether made by ISP Europe)
• Lucirin TPO (BASF photopolymerization initiator) 8.5 parts • Benzophenone (photopolymerization initiator) 4.0 parts • Irgacure 184 (CSC photopolymerization initiator) 4.0 parts • Byk 307 (BYK Chemie) Defoaming agent manufactured by the company) 0.05 parts, 9,10-dibutoxyanthracene 3.0 parts

  The crude color inks 1 prepared as described above were filtered with a filter having an absolute filtration accuracy of 2 μm to obtain inks 1 of the respective colors.

<< Preparation of cationically polymerizable ink >>
<Yellow ink 2>
・ C. I. Pigment Yellow 13 5 parts • DISPERBYK 168 (pigment dispersant manufactured by BYK Chemie) 4 parts • Photocationic polymerization initiator: triphenylsulfonium salt (UVI-6922, manufactured by Dow Chemical Co.) 6 parts • Sensitizing dye: 9, 3 parts of 10-dibutoxyanthracene / polymerizable compound Monomer: 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UCB) 30 parts Monomer: 3,7-bis (3-Oxetanyl) -5-oxanonane (OXT-221: manufactured by Toagosei Co., Ltd.) 37 parts

<Magenta ink 2>
・ C. I. Pigment Red 57: 1 5 parts DISPERBYK 168 (pigment dispersant manufactured by BYK Chemie) 4 parts Photocationic polymerization initiator: triphenylsulfonium salt (UVI-6992, manufactured by Dow Chemical Co.) 6 parts Sensitizing dye: 9,10-dibutoxyanthracene 3 parts, polymerizable compound Monomer: 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UCB) 30 parts Monomer: 3,7 -Bis (3-oxetanyl) -5-oxanonane (OXT-221: manufactured by Toagosei Co., Ltd.) 37 parts

<Cyan ink 2>
・ C. I. Pigment Blue 15: 3 4 parts DISPERBYK 168 (pigment dispersant manufactured by BYK Chemie) 3 partsPhotocationic polymerization initiator: triphenylsulfonium salt (UVI-6992, manufactured by Dow Chemical Co.) 6 parts 9,10-dibutoxyanthracene 3 parts, polymerizable compound Monomer: 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UCB) 30 parts Monomer: 3,7 39 parts of bis (3-oxetanyl) -5-oxanonane (OXT-221: manufactured by Toagosei Co., Ltd.)

<Black ink 2>
・ C. I. Pigment Black 7 4 parts • DISPERBYK 168 (pigment dispersant manufactured by BYK Chemie) 3 parts • Photocationic polymerization initiator: Triphenylsulfonium salt (UVI-6922, manufactured by Dow Chemical Co.) 6 parts • Sensitizing dye: 9, 3 parts of 10-dibutoxyanthracene / polymerizable compound Monomer: 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UCB)
30 parts Monomer: 3,7-bis (3-oxetanyl) -5-oxanonane (OXT-221: manufactured by Toagosei Co., Ltd.) 39 parts

<White ink 2>
· KRONOS 2300 (KRONOS titanium oxide) 15.0 parts · DISPERBYK 168 (BYK Chemie pigment dispersant) 3 parts · Photocationic polymerization initiator: Triphenylsulfonium salt (UVI-6992, manufactured by Dow Chemical) 6 parts-sensitizing dye: 9,10-dibutoxyanthracene 3 parts-polymerizable compound Monomer: 3,4-epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexanecarboxylate (Celoxide 2021A: manufactured by Daicel UCB) 28 parts Monomer: 3,7-bis (3-oxetanyl) -5-oxanonane (OXT-221: manufactured by Toagosei Co., Ltd.) 30 parts

  The crude yellow ink 2, magenta ink 2, cyan ink 2, black ink 2 and white ink 2 prepared as described above were filtered with a filter having an absolute filtration accuracy of 2 μm to obtain inks of respective colors.

<Inkjet image recording>
When drawing, three shear mode piezo heads (KM 512SH manufactured by Konica Minolta, minimum droplet volume 4 pL, number of nozzles 512, nozzle density 360 nozzles / 25.4 mm) are arranged as a head so that the nozzles are arranged in a staggered manner. A drawing apparatus equipped with 15 sets of one-pass head units (recording width 542 mm) so that printing can be performed across the recording medium width direction with a nozzle density 1080 dpi head unit in which the heads are arranged in the recording medium moving direction. used.
Ink was introduced into an ink tank having a capacity of 10 L having a pressure reducing function, depressurized to -38 kPa and degassed dissolved gas in the ink, and an ink having an inner diameter of 2 mm was passed through a static pressure type pressure control tank (capacity 50 mL). The head unit was introduced by a polytetrafluoroethylene flexible tube. By controlling the height of the hydrostatic pressure tank with respect to the head, the internal pressure of the head was adjusted to −5.0 kPa, and the meniscus shape at the nozzle portion of the head was controlled. The ink temperature in the head was set to 55 ° C. in the heater built in the head. The head drive voltage was 26 V, and ejection was performed in a binary mode with a drive frequency of 23 kHz.
The drawing pitch was 1080 dpi in the recording medium width × 2000 dpi in the recording medium conveyance direction (head scan speed 292 mm / s), that is, one-pass printing was performed while continuously conveying the recording medium. Also, a UV light source (two VTechnology Technologies Vzero270s arranged in the width direction of the recording medium) is arranged downstream of the head in the recording medium conveyance direction, and the ink drawn on the recording medium is irradiated with UV light. Yes. Further, as the above-mentioned head cleaning means, there was means for performing head nozzle suction and preliminary discharge, and cleaning was carried out as appropriate.

The following two types (A, B) were evaluated using the above-described inkjet discharge device.
<Evaluation A (Continuous discharge reliability)>
Before the ink jet apparatus was operated, the liquid circulation with the ink cleaning liquid was repeated for 15 minutes to remove the ink remaining at the ink contact portion in the apparatus. Thereafter, continuous use for 8 hours was performed, and the number of nozzles that caused drawing defects (non-ejection, twisting, etc.) was counted.
◎ ・ ・ ・ No discharge failure ○ ・ ・ ・ Discharge failure 3 nozzles or less △ ・ ・ ・ Discharge failure exceeding 3 nozzles and less than 10 nozzles × ・ ・ ・ Discharge failure 10 nozzles or more

<Evaluation B (Reset nozzle clogging)>
The head was continuously used without cleaning for one week, and was repeatedly circulated and ejected with an ink cleaning liquid for 15 minutes. The ink was supplied again, drawing was performed, and the number of non-ejection nozzles was confirmed.
◎ ・ ・ ・ No discharge failure ○ ・ ・ ・ Discharge failure 3 nozzles or less △ ・ ・ ・ Discharge failure exceeding 3 nozzles and less than 10 nozzles × ・ ・ ・ Discharge failure 10 nozzles or more

  Evaluation A and B using the ink cleaning liquid (1) were carried out using the drawing apparatus and drawing with five colors (cyan, magenta, yellow, black, white) of ink. The results are shown in Table 1. In addition, drawing was performed using both radial polymerizable ink and cationic polymerizable ink.

Ink cleaning liquid (1):
Tripropylene glycol monomethyl ether (Dow Chemical) 100wt%

[Examples 2 to 12]
Evaluation was carried out in the same manner except that the ink cleaning liquid (1) was replaced with the ink cleaning liquids (2) to (12) shown in Table 1.
The results are shown in Table 1.

[Comparative Example 1]
Evaluation was carried out in the same manner except that the ink cleaning liquid (1) was not used.
The results are shown in Table 1.

[Comparative Example 2]
Evaluation was carried out in the same manner except that the liquid (1) of the present invention was replaced with Isopar G (isoparaffin solvent, manufactured by ExxonMobil).
The results are shown in Table 1.

Claims (4)

An ink cleaning liquid for photocurable ink,
An ink cleaning liquid comprising at least one ether compound.   The ink cleaning liquid according to claim 1, wherein the ether compound is a glycol ether compound.   The ink cleaning liquid according to claim 1, wherein the photocurable ink is a radical polymerizable ink. An ink jet printer cleaning method using the ink cleaning liquid according to claim 1.