JP2009040830A - Uv-curing ink composition for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a UV-curing ink composition for inkjet recording, the composition achieving formation of a cured coating film with excellent curing property and flexibility. <P>SOLUTION: The UV-curing ink composition for inkjet recording comprises a urethane prepolymer (A) having a structure expressed by general formula (1) and a photo-cation polymerization initiator (B). In the formula, a represents 0 or 1, when a is 0, each of R<SB>1</SB>and R<SB>2</SB>independently represents an alkylene group, and when a is 1, each of R<SB>1</SB>and R<SB>2</SB>independently represents a residue of a divalent phenol; b represents 0 or 1; and R<SB>3</SB>represents an alkyl group or a hydrogen atom. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultraviolet curable ink composition for ink jet recording, and more specifically, an ultraviolet curable ink composition for ink jet recording capable of forming a cured coating film having excellent curability and flexibility. It is about.

  Printing by an ink jet recording apparatus is a method in which ink is ejected from a nozzle and adhered to a recording material. Since the nozzle and the recording material are in a non-contact state, the surface has an irregular shape with a curved surface or unevenness. In contrast, good printing can be performed. For this reason, the printing method is expected to be used in a wide range of industrial applications. Examples of the ink composition for inkjet recording include water-based inks using water as a main solvent and oil-based inks using an organic solvent as a main solvent, or water-based and oil-based inks that are cured and dried with active energy rays such as ultraviolet rays. Proposed.

  Among them, the ultraviolet curable ink composition for ink jet recording is excellent in terms of drying property and coating film curability, and can be widely applied even when the recording material is a non-absorbing member such as metal, glass, and plastic. Certain characteristics cannot be obtained with other ink jet recording methods. These UV curable ink jet recording systems require high sensitivity because of the necessity of curing by applying a very small amount of energy rays immediately after ink droplets land on the printing substrate due to the structure of the printing device. Is done.

The ultraviolet curable resin composition used for the ultraviolet curable ink composition for inkjet recording is roughly classified into radically polymerizable ones and cationic polymerizable ones.
As an ultraviolet curable ink jet recording ink composition excellent in coating properties after curing such as flexibility, adhesion, solvent resistance, and high toughness using a radical polymerizable ultraviolet curable resin composition, an acetal bond, An active energy ray-curable ink comprising a polyvinyl acetal having an ethylenically unsaturated group via at least one bond selected from a urethane bond, an ester bond, and an ether bond is disclosed. (For example, see Patent Document 1)
However, radical polymerization of the ultraviolet curable resin composition sometimes stops due to a radical termination reaction or the like before the curing of the composition sufficiently proceeds.
In addition, radical polymerization of the ultraviolet curable resin composition sometimes stops due to radical deactivation due to the influence of oxygen in the atmosphere before the curing of the composition sufficiently proceeds. For this reason, in order to sufficiently cure the composition by irradiating the composition with ultraviolet rays, it is necessary to take measures, for example, in an environment purged with nitrogen.

  On the other hand, since the cationic polymerizable ultraviolet curable resin composition is not a curing reaction due to radicals, it does not cause radical deactivation due to the radical termination reaction or the influence of oxygen as described above. The cationic polymerization of the ultraviolet curable resin composition continues to proceed even after the ultraviolet irradiation is stopped during the polymerization. Therefore, the cationic polymerizable ultraviolet curable resin composition is expected to be applied in various fields, and various compositions are proposed as the ultraviolet curable resin composition used for the ink for the ultraviolet curable ink jet recording system. However, the present situation is that a composition having sufficient curability and flexibility has not been obtained.

Examples of the cationic polymerizable ultraviolet curable resin composition include a cationic polymerizable compound such as bisphenol A type epoxy resin, a compound having at least two hydroxyl groups in a molecule such as polytetramethylene glycol, and initiation of photo cationic polymerization. An adhesive containing an agent is known (for example, see Patent Document 2).
The document 2 describes that the adhesive composition has advantages such as curing in a short time by ultraviolet irradiation. However, the obtained cured product could not be said to have sufficient performance in terms of flexibility and adhesion to the substrate.

  Further, as the cationic polymerizable ultraviolet curable resin composition, for example, a composition containing a urethane resin and a photopolymerization initiator has been studied. Urethane resins are generally excellent in properties such as adhesion to a substrate and flexibility. Therefore, if it becomes possible to cure the urethane resin by ultraviolet irradiation, it is possible to express excellent adhesion to the base material, flexibility and the like, and it is possible to proceed with curing without going through a heating step. It is possible to provide high value-added products such as adhesives and paints.

  Examples of the cationic polymerizable ultraviolet curable resin composition containing such a urethane resin and a photopolymerization initiator include alicyclic epoxy group-containing urethane resins, cationic polymerizable substances and / or (meth) acrylates, and photopolymerization initiators. It is known that a resin composition containing a resin can form a cured product having excellent curability and excellent glossiness and adhesion to a substrate (see, for example, Patent Document 3). .

  Although the resin composition described in Document 3 is cured to some extent by irradiation with ultraviolet rays, curing cannot proceed to a practically sufficient level. Therefore, the obtained cured product has a problem that it is easily deteriorated due to the influence of an organic solvent or the like. Further, the obtained cured product was not sufficient in terms of flexibility and the like.

  In addition, as the cationic polymerizable ultraviolet curable resin composition, a curable composition for a liquid crystal display device containing a cationic polymerizable compound having a hydrogen bonding functional group and a cationic polymerizable group in one molecule, and a cationic polymerization initiator. Resin compositions are known, and as such cationically polymerizable compounds, those having an average molecular weight of 300 or more having a urethane group as a hydrogen-bonding functional group and an oxetane group and / or an epoxy group as a cationically polymerizable group It is known that can be used (for example, refer patent document 4).

  However, it is difficult to say that the curable resin composition for liquid crystal display elements described in Patent Document 4 still has sufficient curability, and can be applied to various applications using the composition. It was difficult to obtain a cured product.

JP 2004-269690 A JP-A-10-330717 Japanese Patent Laid-Open No. 9-87357 JP 2005-227367 A

  The problem to be solved by the present invention is to provide an ultraviolet curable ink composition for ink-jet recording capable of forming a cured coating film having excellent curability and flexibility.

In order to develop excellent curability, it is important for the present inventors to proceed sufficiently with cationic polymerization, and therefore various studies are made on the cationic polymerizable group of the urethane prepolymer that is directly involved in cationic polymerization. In view of this, the above-mentioned problems may be solved, and a combination of urethane prepolymers having various cationic polymerizable groups and a photocationic polymerization initiator was studied.
While proceeding with the examination, the urethane prepolymer having an epoxy group as a cationically polymerizable group as described in the above-mentioned Reference 3 can be used when producing the urethane prepolymer. Was also abundant and had the advantage of being relatively easy to obtain. For this reason, the present inventors proceeded with studies based on urethane prepolymers having epoxy groups, which can be studied with various raw materials.

  As the urethane prepolymer having an epoxy group, one obtained by reacting polyisocyanate and glycidol as described in, for example, Document 3 is known. In order to confirm the curability of a resin composition containing a urethane prepolymer and a cationic photopolymerization initiator as the polyisocyanate, the present inventors performed ultraviolet irradiation on the resin composition. However, even if the resin composition was irradiated with ultraviolet rays, it could not be cured to a practically sufficient level. Moreover, in order to improve the sclerosis | hardenability of this resin composition, using together various reactive diluents, such as an oxetane compound, was examined. However, the resin composition containing the urethane prepolymer, the cationic photopolymerization initiator, and the reactive diluent was not sufficiently cured by ultraviolet irradiation.

  As a result of studying various types of epoxy groups possessed by the urethane prepolymer, the present inventors have found a resin comprising a urethane prepolymer having an epoxy group having a specific structure as described later and a photocationic polymerization initiator. It has been found that the composition is excellent in curability and the obtained cured product is excellent in flexibility.

  That is, this invention relates to the ultraviolet curable resin composition characterized by including the urethane prepolymer (A) which has a structure shown by following General formula (1), and a photocationic polymerization initiator (B).

（ａは、０または１を表す。ａが０の時、Ｒ_１及びＲ_２は、それぞれ独立してアルキレン基を表す。ａが１の時、Ｒ_１及びＲ_２は、それぞれ独立して２価フェノール類の残基を表す。ｂは、０または１を表す。Ｒ_３は、アルキル基または水素原子を表す。）

(A represents 0 or 1. When a is 0, R ₁ and R ₂ each independently represent an alkylene group. When a is 1, R ₁ and R ₂ each independently represents 2 .b representing the residue of valence phenols, .R ₃ represents 0 or 1 represents an alkyl group or a hydrogen atom.)

  The ink composition for ultraviolet curable ink jet recording of the present invention is excellent in curability and can form a cured coating film having a practically sufficient level of flexibility. Moreover, the ultraviolet curable ink composition for inkjet recording of this invention has favorable adhesiveness with respect to various base materials besides the above-mentioned outstanding effect.

  The present invention contains a urethane prepolymer (A) having a structure represented by the general formula (1) and a cationic photopolymerization initiator (B) as main components, and additionally contains various additives as necessary. An ultraviolet curable ink composition for inkjet recording.

（ａは、０または１を表す。ａが０の時、Ｒ_１及びＲ_２は、それぞれ独立してアルキレン基を表す。ａが１の時、Ｒ_１及びＲ_２は、それぞれ独立して２価フェノール類の残基を表す。ｂは、０または１を表す。Ｒ_３は、アルキル基または水素原子を表す。）

(A represents 0 or 1. When a is 0, R ₁ and R ₂ each independently represent an alkylene group. When a is 1, R ₁ and R ₂ each independently represents 2 Represents a residue of a monovalent phenol, b represents 0 or 1. R ₃ represents an alkyl group or a hydrogen atom.)

  First, the urethane prepolymer (A) having the structure represented by the general formula (1) used in the present invention will be described.

The urethane prepolymer (A) used in the present invention has a structure represented by the general formula (1) in the molecule. The urethane prepolymer (A) used in the present invention does not have to have various epoxy groups, but has a specific epoxy group-containing structure represented by the general formula (1). It is important to obtain an ultraviolet curable resin composition having excellent curability and capable of forming a cured coating film excellent in flexibility.
For example, in an ultraviolet curable resin composition containing an epoxy group-containing urethane prepolymer and a photocationic initiator obtained by reacting a urethane prepolymer having an isocyanate group with glycidol, It is difficult to form a cured product that cannot exhibit curability comparable to the ultraviolet curable resin composition of the present invention and has sufficient flexibility.

  The urethane prepolymer (A) may have the structure represented by the general formula (1) at any position in the molecule. In particular, as the urethane prepolymer (A), use of a urethane prepolymer having the structure represented by the general formula (1) at both ends of the molecule has excellent curability due to ultraviolet irradiation. In addition, it is more preferable to obtain an ultraviolet curable resin composition capable of forming a cured product having excellent flexibility.

  In addition, what is called a urethane prepolymer generally has a relatively low molecular weight, but those skilled in the art also refer to those having a number average molecular weight of tens of thousands as a urethane prepolymer. Also, urethane prepolymers having a number average molecular weight of tens of thousands can be used. The number average molecular weight measured by size exclusion chromatography of the urethane prepolymer (A) used in the present invention is preferably in the range of 500 to 100,000, more preferably in the range of 1,000 to 50,000. By using the urethane prepolymer (A) having a number average molecular weight within the above range, the obtained cured product is excellent in flexibility and has good adhesion to organic materials, inorganic materials, and metal materials. An ultraviolet curable resin composition can be obtained. The number average molecular weight as used in the present invention is measured in terms of polystyrene with a known molecular weight using an RI detector (refractive method) with tetrahydrofuran (THF) as an eluent and a flow rate of 1 ml / min. Represents a value.

  In the urethane prepolymer (A), for example, the polyol (a) and the polyisocyanate (b), the isocyanate group of the polyisocyanate (b) is excessive with respect to the hydroxyl group of the polyol (a). By reacting under conditions, a urethane prepolymer (aa) having an isocyanate group at the terminal is produced, and then the urethane prepolymer (aa) is reacted with a compound (ab) represented by the following general formula (2) Can be manufactured.

（ａは、０または１を表す。ａが０の時、Ｒ_１及びＲ_２は、それぞれ独立してアルキレン基を表す。ａが１の時、Ｒ_１及びＲ_２は、それぞれ独立して２価フェノール類の残基を表す。ｂは、０または１を表す。Ｒ_３は、アルキル基または水素原子を表す。）

(A represents 0 or 1. When a is 0, R ₁ and R ₂ each independently represent an alkylene group. When a is 1, R ₁ and R ₂ each independently represents 2 Represents a residue of a monovalent phenol, b represents 0 or 1. R ₃ represents an alkyl group or a hydrogen atom.)

  Examples of the polyol (a) that can be used in producing the urethane prepolymer (A) include polyether polyol, polyester polyol, polycarbonate polyol, polybutadiene polyol, hydrogenated polybutadiene polyol, and the like. These can be used alone or in combination of two or more.

  Examples of the polyether polyol that can be used in the polyol (a) include compounds obtained by reacting a reaction initiator having two or more active hydrogen-containing groups in the molecule with an alkylene oxide.

  Examples of the reaction initiator include water, ethylene glycol, propylene glycol, butanediol, glycerin, trimethylolpropane, hexanetriol, triethanolamine, diglycerin, pentaerythritol, methyl glucoside, sorbitol, sucrose, and aliphatic amine compounds. , Aromatic amine compounds, sucrose amine compounds, phosphoric acid, acidic phosphate esters and the like may be used, and these may be used alone or in combination of two or more.

  As said alkylene oxide, ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran etc. can be used, for example, These may be used individually or may use 2 or more types together.

  Specific examples of the polyether polyol obtained by the reaction of the reaction initiator having two or more active hydrogen-containing groups in the molecule with an alkylene oxide include, for example, polypropylene glycol, polyethylene glycol, polybutylene glycol, and their co-polymers. Examples include coalescence.

  Moreover, as said polyether polyol, the polytetramethylene glycol obtained by the ring-opening polymerization of tetrahydrofuran other than what was mentioned above can also be used.

  Examples of the polyester polyol that can be used in the polyol (a) include a polyester polyol obtained by reacting a low molecular weight polyol and a polycarboxylic acid, a polyester polyol obtained by ring-opening polymerization of a cyclic ester compound, and the like. It is done.

  Examples of the low molecular weight polyol include ethylene glycol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 3,3-dimethylol heptane, 1,4-cyclohexanedimethanol, neopentyl glycol, diethylene glycol, dipropylene glycol, glycerin, trimethylol propane, etc. can be used, and these can be used alone or in combination of two or more. Can do.

  As the polycarboxylic acid, for example, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, orthophthalic acid, isophthalic acid, terephthalic acid and the like can be used, and these are used alone or in combination of two or more. be able to.

  As said cyclic ester compound, (epsilon) -caprolactone, (delta) -valerolactone etc. can be used, for example, These can be used individually or can be used together 2 or more types.

  Examples of other polyols that can be used in the polyol (a) include polymer polyols, modified polyols of polyether polyols, PHD (abbreviation of polyharnsoff dispersion) polyether polyols, urethane-modified polyether polyols, polyether ester copolymer polyols. Etc. can be used. The polymer polyol is a polyether polyol obtained by graft polymerization of a monomer having a vinyl group such as acrylonitrile or styrene monomer in the polyol. The PHD polyether polyol is a polyol in which polyurea produced is stably dispersed by reacting diamine and diisocyanate in polyether.

  Moreover, when manufacturing the said urethane prepolymer (A), the compound which has an active hydrogen which can react with an isocyanate group other than the said polyol (a) as needed can be used.

  As the compound having active hydrogen capable of reacting with the isocyanate group, for example, a compound generally known as a chain extender, such as a low molecular weight polyol, an aliphatic amine, an aromatic amine, or an alkanolamine, may be used. it can.

  As said low molecular weight polyol, the thing similar to the low molecular weight polyol illustrated as what can be used when manufacturing the said polyester polyol can be used.

  Examples of the polyisocyanate (b) that can be used for producing the urethane prepolymer (A) include 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethane diisocyanate, and polymethylene poly (polyethylene). Aromatic diisocyanates such as phenyl polyisocyanate, carbodiimidized diphenylmethane polyisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,5-naphthalene diisocyanate, or aroma such as xylylene diisocyanate, tetramethylxylene diisocyanate Diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate having an isocyanate group bonded to the ring via an alkyl group , Alicyclic diisocyanates such as hydrogenated xylylene diisocyanate and norbornene diisocyanate, and aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate and dimer acid diisocyanate. These may be used alone or in combination of two or more. can do.

Among the compounds (ab) represented by the general formula (2) that can be used for producing the urethane prepolymer (A), a in the formula is 0, and R ₁ and R ₂ are each independently As the alkylene group, for example, glycerol polyglycidyl ether and trimethylolpropane polyglycidyl ether can be used alone or in combination of two or more. The alkylene group preferably has 1 to 3 carbon atoms.

Moreover, among the compounds (ab) represented by the general formula (2) that can be used when the urethane prepolymer (A) is produced, a in the formula is 1, and R ₁ and R ₂ are each independently Examples of the residues of divalent phenols include polycondensates of 4-t-butylpyrocatechol and 1-chloro-2,3-epoxypropane, bisphenol A type epoxy compounds, and hydrogenated bisphenols. Glycidyl ether type epoxy compounds such as A type epoxy compounds and bisphenol F type epoxy compounds can be used alone or in combination of two or more.

As the compound (ab) represented by the general formula (2), glycerol polyglycidyl ether is preferably used. In the general formula (1) obtained by using glycerol polyglycidyl ether, a is 0, b is 0, R ₁ and R ₂ are methylene groups, R ₃ is a hydrogen atom A urethane prepolymer having a certain structure can reduce the viscosity of the ink composition for ultraviolet curable ink jet recording of the present invention, and it is easy to lower the viscosity necessary for dischargeability as an ink for ink jet recording.

  Examples of the glycerol polyglycidyl ether include Denacol EX-313, Denacol EX-314 (manufactured by Nagase ChemteX Corp.), SR-GLG (manufactured by Sakamoto Pharmaceutical Co., Ltd.), and the like. .

  As the trimethylolpropane polyglycidyl ether, for example, Denacol EX-321 (manufactured by Nagase ChemteX Corporation) is commercially available.

  As the polycondensate of 4-t-butylpyrocatechol and 1-chloro-2,3-epoxypropane, for example, Epicron HP-820 (manufactured by Dainippon Ink & Chemicals, Inc.) is commercially available.

  The urethane prepolymer (aa) having an isocyanate group at the molecular end, which can be used when the urethane prepolymer (A) is produced, replaces the polyol (a) and the polyisocyanate (b) with, for example, nitrogen substitution. It can manufacture by making it react with stirring in the ratio from which the equivalent of the isocyanate group which the said polyisocyanate (b) has becomes excess with respect to the equivalent of the hydroxyl group which the said polyol (a) has within the flask made.

  In the polyol (a) and the polyisocyanate (b), the equivalent ratio of the isocyanate group of the polyisocyanate (b) is 1.1 to 5.0 with respect to 1 equivalent of the hydroxyl group of the polyol (a). It is preferable to make it react in the range which becomes, and it is more preferable to make it react in the range of 1.3-3.0. By using a urethane prepolymer obtained by reacting at an equivalent ratio within the above range, a cured coating film having excellent curability and dischargeability when used as an ink for inkjet recording and having excellent flexibility An ultraviolet curable ink composition for inkjet recording that can be formed can be produced.

  In addition, the urethane prepolymer (A) is obtained by stirring the urethane prepolymer (aa) obtained by the reaction and the compound (ab) represented by the general formula (2), for example, in a nitrogen atmosphere. It can be produced by reacting.

  The urethane prepolymer (aa) and the compound (ab) have an equivalent ratio of isocyanate groups of the urethane prepolymer (aa) of 0.5 to 1 equivalent to 1 equivalent of the hydroxyl group of the compound (ab). The reaction is preferably performed in the range of 1.2, and more preferably in the range of 0.8 to 1.0. By using a urethane prepolymer obtained by reacting at an equivalent ratio within the above range, UV curing capable of forming a cured product having excellent curability and ejectability as an ink for inkjet recording and excellent flexibility. Resin composition can be obtained.

  In addition, the polyol (a) and the polyisocyanate (b), and the urethane prepolymer (aa) and the compound (ab) are each reacted in the range of about 70 to 100 ° C. for about 2 to 15 hours. Is preferred.

Next, the photocationic polymerization initiator (B) used in the present invention will be described.
The cationic photopolymerization initiator (B) used in the present invention can initiate cationic polymerization of the urethane prepolymer (A) when the ultraviolet curable resin composition of the present invention is irradiated with ultraviolet rays.

As the photocationic polymerization initiator (B), for example, the cation moiety may be aromatic sulfonium, aromatic iodonium, aromatic diazonium, aromatic ammonium, thianthrhenium, thioxanthonium, (2,4-cyclopentadiene- 1-yl) [(1-methylethyl) benzene] -Fe cation, and the anion moiety is BF ₄ −, PF ₆ −, SbF ₆ −, [BX ₄ ] ⁻ (where X is at least two or more An onium salt composed of a phenyl group substituted with a fluorine or trifluoromethyl group) can be used alone or in combination of two or more.

  Examples of the aromatic sulfonium salt include bis [4- (diphenylsulfonio) phenyl] sulfide bishexafluorophosphate, bis [4- (diphenylsulfonio) phenyl] sulfide bishexafluoroantimonate, and bis [4- (diphenyl). Sulfonio) phenyl] sulfide bistetrafluoroborate, bis [4- (diphenylsulfonio) phenyl] sulfide tetrakis (pentafluorophenyl) borate, diphenyl-4- (phenylthio) phenylsulfonium hexafluorophosphate, diphenyl-4- (phenylthio) ) Phenylsulfonium hexafluoroantimonate, diphenyl-4- (phenylthio) phenylsulfonium tetrafluoroborate, diphenyl-4- (phenylthio) ) Phenylsulfonium tetrakis (pentafluorophenyl) borate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrafluoroborate, triphenylsulfonium tetrakis (pentafluorophenyl) borate, bis [4- (di (4- (2-hydroxyethoxy)) phenylsulfonio) phenyl] sulfide bishexafluorophosphate, bis [4- (di (4- (2-hydroxyethoxy)) phenylsulfonio) phenyl] sulfide bishexafluoroantimonate Bis [4- (di (4- (2-hydroxyethoxy)) phenylsulfonio) phenyl] sulfide bistetrafluoroborate, bis [4- ( (4- (2-hydroxyethoxy)) can be used phenylsulfonio) phenyl] sulfide tetrakis (pentafluorophenyl) borate.

  Examples of the aromatic iodonium salt include diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, diphenyliodonium tetrafluoroborate, diphenyliodonium tetrakis (pentafluorophenyl) borate, bis (dodecylphenyl) iodonium hexafluorophosphate, Bis (dodecylphenyl) iodonium hexafluoroantimonate, bis (dodecylphenyl) iodonium tetrafluoroborate, bis (dodecylphenyl) iodonium tetrakis (pentafluorophenyl) borate, 4-methylphenyl-4- (1-methylethyl) phenyliodonium Hexafluorophosphate, 4-methylphenyl-4- (1-methyl Ethyl) phenyliodonium hexafluoroantimonate, 4-methylphenyl-4- (1-methylethyl) phenyliodonium tetrafluoroborate, 4-methylphenyl-4- (1-methylethyl) phenyliodonium tetrakis (pentafluorophenyl) borate Etc. can be used.

  Examples of the aromatic diazonium salt include phenyldiazonium hexafluorophosphate, phenyldiazonium hexafluoroantimonate, phenyldiazonium tetrafluoroborate, and phenyldiazonium tetrakis (pentafluorophenyl) borate.

  Examples of the aromatic ammonium salt include 1-benzyl-2-cyanopyridinium hexafluorophosphate, 1-benzyl-2-cyanopyridinium hexafluoroantimonate, 1-benzyl-2-cyanopyridinium tetrafluoroborate, 1-benzyl 2-cyanopyridinium tetrakis (pentafluorophenyl) borate, 1- (naphthylmethyl) -2-cyanopyridinium hexafluorophosphate, 1- (naphthylmethyl) -2-cyanopyridinium hexafluoroantimonate, 1- (naphthylmethyl) -2-Cyanopyridinium tetrafluoroborate, 1- (naphthylmethyl) -2-cyanopyridinium tetrakis (pentafluorophenyl) borate, and the like can be used.

  Moreover, S-biphenyl 2-isopropyl thioxanthonium hexafluorophosphate etc. can be used as said thioxanthonium salt.

  The (2,4-cyclopentadien-1-yl) [(1-methylethyl) benzene] -Fe salt includes (2,4-cyclopentadien-1-yl) [(1-methylethyl) benzene. ] -Fe (II) hexafluorophosphate, (2,4-cyclopentadien-1-yl) [(1-methylethyl) benzene] -Fe (II) hexafluoroantimonate, 2,4-cyclopentadiene-1- Yl) [(1-methylethyl) benzene] -Fe (II) tetrafluoroborate, 2,4-cyclopentadien-1-yl) [(1-methylethyl) benzene] -Fe (II) tetrakis (pentafluorophenyl) ) Borate and the like can be used.

  Examples of the photocationic polymerization initiator (B) include CPI-100P, CPI-100A, CPI-110P (manufactured by San Apro Co., Ltd.), Syracure photocuring initiator UVI-6990, and Syracure photocuring initiator UVI. -6992, Cyracure photocuring initiator UVI-6976 (above, manufactured by Dow Chemical Japan), Adekaoptomer SP-150, Adekaoptomer SP-170 (above, Asahi Denka Kogyo Co., Ltd.), FC -508, FC-512 (manufactured by 3M), CI-5102, CI-2855 (manufactured by Nippon Soda Co., Ltd.), Sun-Aid SI-60L, Sun-Aid SI-80L, Sun-Aid SI-100L, Sun-Aid SI- 110L, Sun-Aid SI-180L, Sun-Aid SI-110, Sun-Aid SI-180 Sanshin Chemical Industry Co., Ltd.), Esacure 1064, Esacure 1187 (above, manufactured by Lamberti Co., Ltd.), Omnicat 550 (produced by IG Resin Co., Ltd.), Irgacure 250 (produced by Ciba Specialty Chemicals Co., Ltd.), Rhodosil Photoinitiator 2074 (RHODORSIL PHOTOINITIATOR 2074, manufactured by Rhodia Japan Co., Ltd.) is commercially available.

In addition, in the ultraviolet curable ink composition for inkjet recording of the present invention, in addition to the urethane prepolymer (A) and the cationic photopolymerization initiator (B), in order to obtain a discharge viscosity suitable for the inkjet head to be used, A cationically polymerizable compound (C) can be used in combination.
By using the cationic polymerizable compound (C), it is possible to improve the dischargeability as an ink for ink jet recording without impairing the curability of the ultraviolet curable ink composition for ink jet recording of the present invention.

  Examples of the cationic polymerizable compound (C) include an aliphatic polyol polyglycidyl ether compound, an alicyclic epoxy compound, an oxetane compound having an oxetane ring structure represented by the following structural formula (3) in the molecule, and a bisphenol A type epoxy. A compound, hydrogenated bisphenol A type epoxy compound, glycidyl ether type epoxy compound such as bisphenol F type epoxy compound, etc. can be used alone or in combination of two or more.

  Examples of the aliphatic polyol polyglycidyl ether compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, neopentyl glycol. Use diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, etc. can do.

  Among the above-described aliphatic polyol polyglycidyl ether compounds, it is preferable to use an aliphatic polyol polyglycidyl ether compound having 2 to 4 epoxy groups.

  Examples of the aliphatic polyol polyglycidyl ether compound having 2 to 4 epoxy groups include, for example, Epicron 705, Epicron 707, Epicron 720, Epicron 725, Epicron 726 (above, Dainippon Ink & Chemicals, Inc.), Denacol EX-611, Denacol EX-614B, Denacol EX-512, Denacol EX-411, Denacol EX-421, Denacol EX-313, Denacol EX-321, Denacol EX-212, Denacol EX-212, Denacol EX-212L, Denacol EX-214L, Denacol EX-810, Denacol EX-850L, Denacol EX-911 (above, manufactured by Nagase ChemteX Corp.), SR-NPG, SR-16H, SR-16HL, SR-TMP, SR- G, SR-TPG, SR-4PG, SR-2EG, SR-8EG, SR-8EGS, SR-GLG, SR-DGE, SR-DGE, SR-4GL, SR-4GLS, SR-SEP (above, Sakamoto Yakuhin Kogyo Co., Ltd.), YED205, YED216 (above, Japan Epoxy Resin Co., Ltd.), Rica Resin W-100 (above, Shin Nippon Rika Co., Ltd.) are commercially available.

Moreover, as said alicyclic epoxy compound, what has multiple alicyclic epoxy groups, Preferably 2-4 pieces can be used.
As an alicyclic epoxy compound having two alicyclic epoxy groups, for example, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate represented by the following general formula (4) (wherein c is 0), its caprolactone-modified product (wherein c is 1), its trimethylcaprolactone-modified product (Structural Formula (5) and Structural Formula (6)), and its valerolactone-modified product (Structural Formula) (7) and the structural formula (8)) and the compound represented by the structural formula (9) can be used.

  In the general formula (4), c represents 0 or 1.

  Examples of the 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate represented by the general formula (4) and its caprolactone-modified product include, for example, Celoxide 2021, Celoxide 2021A, Celoxide 2021P, Celoxide 2080, Celoxide 2081, Celoxide 2083, Celoxide 2085 (manufactured by Daicel Chemical Industries, Ltd.), Cyracure UVR-6105, Cyracure UVR-6107, Silacure UVR-6110 (manufactured by Dow Chemical Japan Co., Ltd.) and the like are commercially available.

  Examples of the adipic acid ester-based alicyclic epoxy compound represented by the general formula (9) include commercially available Cyracure UVR-6128, ERL4289, ERL4299 (above, manufactured by Dow Chemical Japan Co., Ltd.) and the like. Yes.

  As the alicyclic epoxy compound having three alicyclic epoxy groups, a compound represented by the following general formula (10) can be used.

  In general formula (10), d and e are each independently 0 or 1, and they may be the same or different.

  As the alicyclic epoxy compound represented by the general formula (10), for example, Epadido GT300, Epadido GT301, Epadido GT302 (manufactured by Daicel Chemical Industries, Ltd.) are commercially available.

  As the alicyclic epoxy compound having four alicyclic epoxy groups, for example, a compound represented by the following general formula (11) can be used.

  In the general formula (11), f to i each independently represent 0 or 1, and they may be the same or different.

  As the alicyclic epoxy compound represented by the general formula (11), for example, Epolide GT400, Epolide GT401, Epolide GT403 (manufactured by Daicel Chemical Industries, Ltd.) and the like are commercially available.

As the oxetane compound having an oxetane ring structure, a compound having a plurality of oxetane ring structures, preferably 2 to 4 can be used.
As the oxetane compound having an oxetane ring structure having 2 to 4 oxetane ring structures, for example, compounds represented by the following general formulas (12) and (13) can be used alone or in combination of two or more. .

In the general formulas (12) and (13), R ₄ represents a hydrogen atom, a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group, an aralkyl group, a furyl group, or It represents a thienyl group, R ₅ represents a divalent organic residue, Z is an oxygen atom or a sulfur atom.

Examples of the linear, branched or cyclic alkyl group having 1 to 6 carbon atoms represented by R ₄ include a methyl group, an ethyl group, an n- or i-propyl group, an n-, i- or t- group. A butyl group, a pentyl group, a hexyl group, a cyclohexyl group, and the like; and an aryl group such as a phenyl, naphthyl, tolyl, and xylyl group; and an aralkyl group such as a benzyl and phenethyl group It is.

In the general formula (12), examples of the divalent organic residue represented by R ₅ include a linear, branched or cyclic alkylene group and a poly (oxy) having 4 to 30 carbon atoms. Alkylene) group, phenylene group, xylylene group, and structures represented by the following general formulas (14) and (15).

The linear, branched, or cyclic alkylene group constituting R ₅ has 1 carbon atom such as a methylene group, an ethylene group, a 1,2- or 1,3-propylene group, a butylene group, and a cyclohexylene group. An alkylene group of ˜15 is preferred. The poly (oxyalkylene) group having 4 to 30 carbon atoms is preferably one having 4 to 8 carbon atoms, for example, a poly (oxyethylene) group or a poly (oxypropylene) group. Is preferred.

In the general formula (14), R ₆ represents an oxygen atom, a sulfur atom, CH ₂ , NH, SO, SO ₂ , C (CF ₃ ) ₂ or C (CH ₃ ) ₂ .

In the general formula (15), R ₇ represents an alkylene group having 1 to 6 carbon atoms, an arylene group, and a functional group represented by the following general formula (16).

  In the general formula (16), j represents an integer of 1 to 6, and k represents an integer of 1 to 15.

  As said general formula (16), it is preferable that k is an integer of 1-3.

  As the oxetane compound having 2 to 4 oxetane ring structures, for example, Aron oxetane OXT-221 and Aron oxetane OXT-121 (manufactured by Toagosei Co., Ltd.) are commercially available.

  Examples of the bisphenol A type epoxy compound include Epicron 840, Epicron 840-S, Epicron 850, Epicron 850-S, Epicron 850-CRP, Epicron 850-LC (manufactured by Dainippon Ink & Chemicals, Inc.), Denacol EX-252 (above, manufactured by Nagase ChemteX Corporation), Epicoat 825, Epicoat 827, Epicoat 828, Epicoat 828EL, Epicoat 828XA, Epicoat 834 (above, manufactured by Japan Epoxy Resins Co., Ltd.), Rica Resin BPO-20E, Rikaresin BEO-60E (manufactured by Shin Nippon Rika Co., Ltd.) and the like are commercially available.

  Examples of the hydrogenated bisphenol A type epoxy compound include, for example, Epicron EXA-7015 (above, manufactured by Dainippon Ink & Chemicals, Inc.), Denacol EX-252 (above, manufactured by Nagase ChemteX Corporation), SR-HBA. (Established by Hangen Pharmaceutical Co., Ltd.), Epicote YX-8000, Epicote RXE-21 (above, Japan Epoxy Resin Co., Ltd.), Rica Resin HBE-100 (above, Shin Nippon Rika Co., Ltd.), etc. Is commercially available.

  Examples of the bisphenol F-type epoxy compound include Epicron 830, Epicron 830-S, Epicron 830-LVP, Epicron 835, Epicron 835-LV (above, manufactured by Dainippon Ink & Chemicals, Inc.), Epicoat 806, Epicoat 806L Epicoat 807 (manufactured by Japan Epoxy Resin Co., Ltd.) and the like are commercially available.

  As the cationic polymerizable compound (C), it is more preferable to use an aliphatic polyol polyglycidyl ether compound having 2 to 4 epoxy groups or an oxetane compound having 2 to 4 oxetane ring structures. The aliphatic polyol polyglycidyl ether compound having an epoxy group within the above range and the oxetane compound having an oxetane ring structure within the above range further improve the curability of the ultraviolet curable ink composition for inkjet recording of the present invention, and Since the viscosity of the composition can be reduced, it is easy to lower the viscosity necessary for the dischargeability as an ink for inkjet recording.

Next, the manufacturing method of the ultraviolet curable ink composition for inkjet recording of this invention is demonstrated.
In order to produce the ultraviolet curable ink composition for inkjet recording of the present invention, basically, the urethane prepolymer (A), the photocationic polymerization initiator (B), and if necessary, the cation polymerizable compound (C). The UV curable resin composition is used as a main component, and various additives such as a pigment, a dispersant, and a surface tension adjuster may be added as necessary, and mixed, stirred or dispersed.

  The photocationic polymerization initiator (B) is preferably used in the range of 0.5 to 20% by mass, preferably in the range of 1 to 10% by mass, based on the total amount of the ultraviolet curable resin composition of the present invention. More preferably. The ultraviolet curable resin composition containing the cationic photopolymerization initiator (B) within the above range has good curability, and the amount of acid remaining in the obtained cured product is almost negligible. Therefore, it is possible to suppress deterioration of the base material such as metal due to the acid.

  When the cationic polymerizable compound (C) is used in combination, the mass ratio [(A) / (C)] of the urethane prepolymer (A) and the cationic polymerizable compound (C) is 60/40. It is preferably in the range of ˜5 / 95, more preferably in the range of 50/50 to 10/90.

The colorant used in the ultraviolet curable ink composition for inkjet recording of the present invention is not particularly limited as long as it is a colorant such as a pigment and a dye that have been conventionally used in inkjet for color image formation. However, it is preferable to use a pigment because it can impart good water resistance and light resistance to the pattern formed by the ink. Examples of the pigment used include azo pigments such as azo lake pigments, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, anthraquinone pigments, perylene pigments, quinacridone pigments, isoindoline pigments, benzimidazolone pigments, thioindigo pigments, Examples include polycyclic pigments such as dioxazine pigments and quinophthalone pigments, organic pigments such as nitro pigments, nitroso pigments, aniline black and fluorescent pigments, and inorganic pigments such as titanium oxide, iron oxide and carbon black. It is not limited. In the ink used in the present embodiment, the colorant concentration varies depending on the type of pigment used and the hue required at the time of printing, but is preferably 0.1 to 30 parts by mass of the entire ink.
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 mass with respect to 100 parts by mass of the pigment.
When the pigment is used as the colorant, the dispersion of the pigment is preferably performed so that the average particle diameter of the pigment particles is 0.08 to 0.5 μm in the process, and the maximum particle diameter is 0.3 to The selection of the pigment, the dispersant, the dispersion medium, the dispersion conditions, the filtration conditions, and the like can be appropriately set so as to be 10 μm, preferably 0.3 to 3 μm. By adjusting and managing the particle size after dispersion of the pigment so as to fall within the above particle size range, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained. .

  For the dispersion of the coloring material, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like can be used. Further, a dispersing agent can be added when dispersing the coloring material. As the dispersant, a polymer dispersant is preferably used, and examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine Techno's PB series.

When forming an image made of the ink composition for ultraviolet curable ink jet recording of the present invention on a substrate made of glass, metal, plastic or the like as a non-absorbing recording material, the critical surface tension of the surface of these recording materials By considering the surface tension of the ink composition and setting the surface tension of the ink composition lower than the assumed critical surface tension of the recording material, an image of the ink composition is formed on the recording material without repellency. can do.
Therefore, the surface tension of the ink composition for ultraviolet curable ink jet recording of the present invention is such that the surface of the ink is wet with an absorbent medium such as glass, plastic, metal, etc. It is necessary to consider the resolution of the image formed after the droplets land on the medium and are cured. In the present invention, the recording material is particularly flexible and is effective when it is a film or plastic. Therefore, the recording material is set to be larger than 22 mN / m and smaller than 35 mN / m. Because it is important to control the spread of dots from the viewpoint of image clarity and resolution maintenance, the lower limit of the surface tension is usually adjusted to be larger than 22 mN / m, and stable ejection properties are ensured. It is because it adjusts smaller than 35 mN / m in order to reduce the repelling on the member to be absorbed. The surface tension is adjusted mainly by using a surfactant as a surface tension adjusting agent, and changing the type and amount of the surface tension to a predetermined numerical range for applying the surface tension of the ink to the film or plastic as the application object. Can be adjusted.

  As the compound used as the surface tension adjusting agent in the present invention, known compounds generally used for adjusting the surface tension can be used without any particular problem. Examples thereof include organic solvents such as alcohols and glycol ethers, ionic surfactants, nonionic surfactants, and modified silicone oils.

Examples of the modified silicone oil include polyether modified silicone oil, methylstyrene modified silicone oil, olefin modified silicone oil, alcohol modified silicone oil, alkyl modified silicone oil, and the like.
Although the use of organic solvents as surface tension modifiers is possible, one of the characteristics of UV-curable ink compositions that do not contain volatile components or have low volatile components is lost, so surface tensions other than organic solvents It is preferable to use a regulator, and modified silicone oils into which various organic groups have been introduced are particularly preferable because they are easily dissolved in an ultraviolet curable compound.
These surface tension adjusting agents are preferably used in the range of 0.05 to 1% by mass of the total amount of ink.

  An organic solvent can also be used in the ink composition of the present invention for the purpose of adjusting the viscosity. As the organic solvent, a solvent that does not deteriorate the ejection stability and the excellent ink wettability (repellence prevention) when landed on the surface of the recording material in the present invention must be selected. Examples of the organic solvent include, but are not limited to, ketones, esters, ethers, alcohols, aliphatic and aromatic hydrocarbons. These organic solvents can be used alone or in combination of two or more. However, the excessive use of these organic solvents loses one of the characteristics of the ultraviolet curable ink jet recording ink composition that does not contain a volatile component or has a small amount of a volatile component. .

  Various additives other than those described above can be used for the ink used in the present embodiment. For example, in order to improve the storage stability of the ink composition, a polymerization inhibitor can be added at 200 to 20000 ppm. Since the UV curable ink is preferably ejected by heating and lowering the viscosity, it is preferable to add a polymerization inhibitor in order to prevent head clogging due to thermal polymerization.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[Synthesis Example 1] (Synthesis Example of Urethane Prepolymer (I))
A clean flask was charged with 504 parts by weight of polypropylene glycol (hydroxyl equivalent = 1000), then 189 parts by weight of 4,4′-diphenylmethane diisocyanate (isocyanate equivalent / hydroxyl equivalent = 3.00), and stirred under a nitrogen atmosphere. Then, a urethane prepolymer having an isocyanate group at the molecular end was prepared by reacting them at 90 ° C. for 3 hours.

Next, 307 parts by mass of Denacol EX-313 (manufactured by Nagase ChemteX Corporation) was charged into the flask (isocyanate group equivalent / hydroxyl group equivalent = 0.90), and the isocyanate was added to the molecular terminal while stirring under a nitrogen atmosphere. Urethane prepolymer (I) was prepared by reacting a urethane prepolymer having a group with Denacol EX-313 at 90 ° C. for 10 hours. The number average molecular weight measured by size exclusion chromatography (SEC) of the obtained urethane prepolymer (I) was 2000. The obtained urethane prepolymer (I) is, at both ends of the molecule, among the structures represented by the general formula (1), a is 0, b is 0, R ₁ and R ₂ It had a structure that was a methylene group and R ₃ was a hydrogen atom.

[Synthesis Example 2] (Synthesis Example of Urethane Prepolymer (II))
A clean flask was charged with 504 parts by mass of polycaprolactone polyol (hydroxyl equivalent = 1000), and then 189 parts by mass of 4,4′-diphenylmethane diisocyanate (isocyanate equivalent / hydroxyl equivalent = 3.00) under a nitrogen atmosphere. A urethane prepolymer having an isocyanate group at the molecular end was prepared by reacting them at 90 ° C. for 3 hours with stirring at ˜.

Next, 307 parts by mass of Denacol EX-313 (manufactured by Nagase ChemteX Corporation) was charged into the flask (isocyanate group equivalent / hydroxyl group equivalent = 0.90), and the isocyanate was added to the molecular terminal while stirring under a nitrogen atmosphere. A urethane prepolymer (II) was prepared by reacting a urethane prepolymer having a group with Denacol EX-313 at 90 ° C. for 10 hours. The number average molecular weight measured by size exclusion chromatography (SEC) of the obtained urethane prepolymer (II) was 2000. The obtained urethane prepolymer (I) is, at both ends of the molecule, among the structures represented by the general formula (1), a is 0, b is 0, R ₁ and R ₂ It had a structure that was a methylene group and R ₃ was a hydrogen atom.

[Synthesis Example 3] (Synthesis Example of Urethane Prepolymer (III))
A clean flask was charged with 648 parts by weight of polypropylene glycol (hydroxyl equivalent = 1000) and then with 244 parts by weight of 4,4′-diphenylmethane diisocyanate (isocyanate equivalent / hydroxyl equivalent = 3.00) under a nitrogen atmosphere. A urethane prepolymer having an isocyanate group at the molecular end was prepared by reacting them at 90 ° C. for 3 hours with stirring.

  Next, 108 parts by mass of glycidol was charged (isocyanate group equivalent / hydroxyl group equivalent = 0.90), and the urethane prepolymer having an isocyanate group at the molecular terminal and glycidol were reacted at 90 ° C. for 4 hours while stirring in a nitrogen atmosphere. Thus, a urethane prepolymer (III) was prepared. The number average molecular weight measured by size exclusion chromatography (SEC) of the obtained urethane prepolymer (III) was 2000.

[Synthesis Example 4] (Synthesis Example of Urethane Prepolymer (IV))
A clean flask was charged with 601 parts by weight of polypropylene glycol (hydroxyl equivalent = 1000), then 227 parts by weight of 4,4′-diphenylmethane diisocyanate (isocyanate group equivalent / hydroxyl equivalent = 3.00), and stirred under a nitrogen atmosphere. Then, a urethane prepolymer having an isocyanate group at the molecular end was prepared by reacting them at 90 ° C. for 3 hours.

  Next, 172 parts by mass of a compound represented by the following structural formula (17) (ETHB, manufactured by Daicel Chemical Industries, Ltd.) was charged (isocyanate group equivalent / hydroxyl group equivalent = 0.90), and the molecules were stirred while being stirred in a nitrogen atmosphere. Urethane prepolymer (IV) was prepared by reacting a urethane prepolymer having an isocyanate group at the terminal with a compound represented by the following structural formula (17) at 90 ° C. for 3 hours. The number average molecular weight measured by size exclusion chromatography (SEC) of the obtained urethane prepolymer (IV) was 2000.

[Synthesis Example 5] (Synthesis Example of Urethane Prepolymer (V))
A clean flask was charged with 615 parts by weight of polypropylene glycol (hydroxyl equivalent = 1000), then 228 parts by weight of 4,4′-diphenylmethane diisocyanate (isocyanate group equivalent / hydroxyl equivalent = 3.00), and stirred under a nitrogen atmosphere. Then, a urethane prepolymer having an isocyanate group at the molecular end was prepared by reacting them at 90 ° C. for 3 hours.

  Next, 157 parts by mass of a compound of the following structural formula (18) (Aron Oxetane OXT-101, manufactured by Toagosei Co., Ltd.) was charged (isocyanate group equivalent / hydroxyl group equivalent = 0.90) and stirred under a nitrogen atmosphere. The urethane prepolymer (V) was prepared by reacting the urethane prepolymer having an isocyanate group at the molecular terminal with a compound of the following structural formula (18) at 90 ° C. for 3 hours. The number average molecular weight measured by size exclusion chromatography (SEC) of the obtained urethane prepolymer (V) was 2000.

[Example]
The mixture was sufficiently stirred and dissolved with the formulation shown in Table 1 below, and then filtered using a 1.2 μm membrane filter to obtain a clear ink for an ultraviolet curable ink jet printer.

Aron Oxetane OXT-221: Bis [1-ethyl (3-oxetanyl)] methyl ether EX-214L manufactured by Toa Gosei Co., Ltd. 1,4-butanediol diglycidyl ether celoxide 2021P manufactured by Nagase ChemteX Corporation Daicel Chemical Industries, Ltd. 3,4-epoxycyclohexylmethyl-3,4-cyclohexanecarboxylate UVI-6992: Dow Chemical Japan Co., Ltd. Photocationic polymerization initiator KF-351A: Shin-Etsu Chemical Co., Ltd. Polyether modified silicone oil

As a result of evaluating the ejection properties of the inks of Examples 1 to 3 and Comparative Examples 1 to 4 using a piezo-type inkjet printer in which the inkjet head was heated to 45 ° C., all of the inks had good ejection properties.

Next, the following items were evaluated for the ultraviolet curable ink jet recording inks produced in Example 1, Example 2, Example 3, and Comparative Examples 1 to 4. The evaluation results are shown in Table 1 above.

[Curing property]
The ink obtained in Examples and Comparative Examples was applied to an easy-adhesion treated PET film (HK-31WF 100 μm thickness, manufactured by Higashiyama Film Co., Ltd.) using a spin coater with a film thickness of about 6 μm, and then applied to the coating film Irradiation was performed under the condition of an energy amount of 200 J / m ² per pass with a belt conveyor type ultraviolet irradiator, and the integrated value of the irradiation energy amount until tack free was confirmed while touching the coating film surface with a finger. Normally, it is considered that there is no problem in actual use if it is cured at an irradiation dose of 700 J / m ² or less and becomes tack-free.

[Flexibility]
The following criteria evaluated the presence or absence of a crack when the cured film apply | coated to the easily-adhesive process PET film which evaluated curability was bent at 90 degreeC by hand.
○: No cracking occurs even when bent by 90 °, and the bent ridge portion remains transparent.
X: Cracking occurs when bent 90 °. Or white streaks appear on the bent ridges.

  As is apparent from Table 1, Examples 1, 2, and 3 have good curability and flexibility, whereas Comparative Examples 1, 2, and 3 have insufficient curability, and Comparative Example 4 is cured. It can be seen that the properties are good but the flexibility is insufficient.

INDUSTRIAL APPLICABILITY The present invention is useful for providing an ultraviolet curable ink composition for ink jet recording, which is excellent in ejection stability and excellent in flexibility and curability in an ink composition for ultraviolet curable ink jet recording.

Claims (6)

An ultraviolet curable ink composition for ink jet recording, comprising a urethane prepolymer (A) having a structure represented by the following general formula (1) and a cationic photopolymerization initiator (B).

(A represents 0 or 1. When a is 0, R ₁ and R ₂ each independently represent an alkylene group. When a is 1, R ₁ and R ₂ each independently represents 2 Represents a residue of a monovalent phenol, b represents 0 or 1. R ₃ represents an alkyl group or a hydrogen atom.) The ink composition for ultraviolet curable ink jet recording according to claim 1, wherein the urethane prepolymer (A) has a structure represented by the general formula (1) at both ends of the molecule. The urethane prepolymer (A) has a structure in which a in the general formula (1) is 0, b is 0, R ₁ and R ₂ are methylene groups, and R ₃ is a hydrogen atom. The ink composition for ultraviolet curable ink jet recording according to claim 1, which is contained. The urethane prepolymer (A) is a compound represented by the urethane prepolymer (aa) having an isocyanate group at the terminal obtained by reacting the polyol (a) and the polyisocyanate (b), and the following general formula (2) The ink composition for ultraviolet curable ink jet recording according to claim 1, which is obtained by reacting (ab).

(A represents 0 or 1. When a is 0, R ₁ and R ₂ each independently represent an alkylene group. When a is 1, R ₁ and R ₂ each independently represents 2 Represents a residue of a monovalent phenol, b represents 0 or 1. R ₃ represents an alkyl group or a hydrogen atom.) Furthermore, the ultraviolet curable ink composition for inkjet recording of Claim 1 containing other cationically polymerizable compounds (C) other than the said urethane prepolymer (A). The other cationic polymerizable compound (C) is at least one selected from the group consisting of an aliphatic polyol polyglycidyl ether compound having 2 to 4 epoxy groups and an oxetane compound having 2 to 4 oxetane ring structures. The ultraviolet curable ink composition for ink jet recording according to claim 5, which is a seed.