JP2020139071A - Active ray curable inkjet ink - Google Patents

Abstract

To provide an active ray curable inkjet ink that can form an image with improved light resistance.SOLUTION: An active ray curable inkjet ink contains a radical photopolymerizable compound, a radical photopolymerization initiator, an a colorant, and further contains at least one thiocarbonyl compound selected from the group consisting of general formulae (1)-(4).SELECTED DRAWING: None

Description

The present invention relates to an active photocurable inkjet ink.

The inkjet recording method is used in various printing fields because it can form an image easily and inexpensively. As one of the inkjet recording methods, there is an active light-curable inkjet method in which droplets of active light-curable inkjet ink are landed on a recording medium and then irradiated with active light (ultraviolet rays) to cure the image. .. The active ray-curable inkjet method has been attracting attention in recent years because it can form an image having high scratch resistance and adhesion even on a recording medium having no ink absorption.

Since active ray-curable ink has higher water resistance than water-based ink, it is often used for printing signboards installed outdoors. However, since the signboard installed outdoors is exposed to sunlight, not only water resistance but also light resistance is required. In order to meet such a demand for light resistance, for example, in the invention described in Patent Document 1, a thioxanthone-based photopolymerization initiator is contained in an active photocurable ink composition.

Japanese Unexamined Patent Publication No. 2009-227968

However, the present inventors have found that the invention described in Patent Document 1 may not always have sufficient light resistance. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an active ray-curable inkjet ink capable of forming an image having better light resistance.

The present invention is an active photocurable inkjet ink containing a radical photopolymerizable compound, a radical photopolymerization initiator, and a coloring material, and is selected from the group consisting of the following general formulas (1) to (4). This is an active photocurable inkjet ink further containing at least one of the above thiocarbonyl compounds.

(In the general formula (1), X ₁ and X ₂ are independently any of a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, an alkenyl group having 2 or more and 10 or less carbon atoms, or a substituent Y ₁ shown below. Represents

(In the substituent Y ₁ , R ₁ , R ₂ , and R ₃ each independently represent a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, or any of the following substituents Y ₂ , and n is 1 to 10. Represents an integer.)

(Among the substituents _{Y 2,} m represents an integer of 1 to 10.)

(In the general formula (2), R ₄ , R ₅ , R ₆ and R ₇ are independently any of a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, an alkyl group having 1 to 10 carbon atoms, and a methyl ester group. , And l independently represents an integer from 1 to 10.)

(In the general formula (3), R ₈ , R ₉ , and R ₁₀ are independently hydrogen atoms, methyl groups, hydroxyl groups, carbonyl group-containing groups having 1 or more and 10 or less carbon atoms, chlorine atoms, and 1 to 10 carbon atoms. Represents either an alkyl group or a carboxyl group, Z ₁ represents a nitrile group or an aromatic ring having 3 or more and 15 or less carbon atoms, and k independently represents an integer of 0 to 10).

(In the general formula (4), R _{11 to} R ₁₅ are independently hydrogen atom, methyl group, hydroxyl group, carbonyl group-containing group having 1 or more and 10 or less carbon atoms, chlorine atom, and alkyl having 1 to 10 carbon atoms. Represents any of the groups, Z ₂ represents a nitrile group or an aromatic ring with 3 or more and 15 or less carbon atoms.)

According to the active light-curable inkjet ink of the present invention, an image having excellent light resistance can be formed.

[Activated light-curable inkjet ink]
The active photocurable inkjet ink according to the embodiment of the present invention contains a radical photopolymerizable compound, a radical photopolymerization initiator, a coloring material, and a thiocarbonyl compound. Further, the activated photocurable inkjet ink according to the embodiment of the present invention may further contain a gelling agent.

The reason why the above problems can be solved by the present invention is considered as follows.

One of the causes of the deterioration of the light resistance of the image is that the radical photopolymerization initiator remaining in the image formed without contributing to the curing of the image is decomposed by the ultraviolet rays contained in sunlight and the like to generate radical species. It is thought that this radical species attacks the color material and destroys the structure of the color material. On the other hand, in the image formed by the ink of the present invention, the thiocarbonyl compound reacts with the radical species derived from the radical photopolymerization initiator remaining in the image to convert it into an inactive dormant species. It captures the radical species and irreversibly inactivates them. As a result, the concentration of radical species in the image is kept low even when irradiated with sunlight or the like, and the radicals that attack the coloring material are reduced, so that it is considered that the light resistance of the image can be improved.

Hereinafter, each component will be described.

(Thiocarbonyl compound)
The thiocarbonyl compound is at least one compound selected from the group consisting of the following general formulas (1) to (4).

The content of the thiocarbonyl compound is preferably 0.5 or more and 1.0 or less, and more preferably 0.6 or more and 0.9 or less in terms of the molar ratio with respect to the content of the radical photopolymerization initiator. , 0.7 or more and 0.8 or less is more preferable. When the content of the thiocarbonyl compound is 0.5 or more in terms of the molar ratio to the content of the radical photopolymerization initiator, the concentration of radical species in the formed image is kept low, and the light resistance of the image is good. Become. Further, since the content of the thiocarbonyl compound is 1.0 or less in terms of the molar ratio to the content of the radical photopolymerization initiator, the thiocarbonyl compound is formed without excessively inhibiting the polymerization of the radical photopolymerizable compound. The curability of the image is improved.

When the active photocurable inkjet ink contains a gelling agent, it is considered that the thiocarbonyl compound retains the gelling agent in the ink before and after curing by hydrophobically interacting with the gelling agent. Be done. As a result, the thiocarbonyl compound can suppress the precipitation of the gelling agent when the image is formed, and can suppress the blooming of the image surface.

Hereinafter, the thiocarbonyl compound will be described in detail.

The thiocarbonyl compound is a compound represented by any of the following general formulas (1) to (4).

(In the general formula (1), X ₁ and X ₂ are independently any of a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, an alkenyl group having 2 or more and 10 or less carbon atoms, or a substituent Y ₁ shown below. Represents

(In the substituent Y ₁ , R ₁ , R ₂ , and R ₃ each independently represent a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, or any of the following substituents Y ₂ , and n is 1 to 10. Represents an integer.)

(Among the substituents _{Y 2,} m represents an integer of 1 to 10.)

(In the general formula (2), R ₄ , R ₅ , R ₆ and R ₇ are independently any of a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, an alkyl group having 1 to 10 carbon atoms, and a methyl ester group. , And l independently represents an integer from 1 to 10.)

(In the general formula (3), R ₈ , R ₉ , and R ₁₀ are independently hydrogen atoms, methyl groups, hydroxyl groups, carbonyl group-containing groups having 1 or more and 10 or less carbon atoms, chlorine atoms, and 1 to 10 carbon atoms. Represents either an alkyl group or a carboxyl group, Z ₁ represents a nitrile group or an aromatic ring having 3 or more and 15 or less carbon atoms, and k independently represents an integer of 0 to 10).

(In the general formula (4), R _{11 to} R ₁₅ are independently hydrogen atom, methyl group, hydroxyl group, carbonyl group-containing group having 1 or more and 10 or less carbon atoms, chlorine atom, and alkyl having 1 to 10 carbon atoms. Represents any of the groups, Z ₂ represents a nitrile group or an aromatic ring with 3 or more and 15 or less carbon atoms.)

In the thiocarbonyl compound of the general formula (1), examples of the alkenyl group having 2 or more and 10 or less carbon atoms include a vinyl group, an allyl group, a butenyl group and the like.

From the viewpoint of facilitating the capture of radical species in the formed image and further enhancing the light resistance of the image, in the thiocarbonyl compound of the above general formula (1), X ₁ and X ₂ are alkenyl groups and hydroxyl groups. preferably, and a substituent Y _1, and more preferably an alkenyl group having 3 carbon atoms.

Further, the substituent Y _1, n is preferably 1 or more 10 or less, more preferably 1 to 5.

Further, the substituents _{Y 1, R 1, R 2} , R 3 represents a hydroxyl group, preferably a carboxyl group and a substituent _{Y 2,} and more preferably hydroxyl group of these. Further, the substituent Y _2, m is preferably 1 or more 10 or less, more preferably 1 to 5.

From the viewpoint of facilitating the capture of radical species in the formed image and further enhancing the light resistance of the image, the thiocarbonyl compounds of the above general formula (1) are the same as X ₁ and X ₂ . It is preferably a functional group.

In the thiocarbonyl compound of the general formula (2), the methyl ester group means a functional group having an ester structure and a methyl group bonded to either an oxygen atom or a carbon atom constituting the ester structure. Examples of methyl ester groups include those having a structure of a carboxyl group (-COOCH ₃ ) esterified with methanol and those having a structure of a hydroxyl group (-OCOCH ₃ ) esterified with acetic acid.

Further, in the thiocarbonyl compound of the general formula (2), l is preferably 1 or more and 10 or less, and more preferably 1 or more and 5 or less.

From the viewpoint of facilitating the capture of radical species in the formed image and further enhancing the light resistance of the image, in the thiocarbonyl compound of the above general formula (2), R ₄ , R ₅ , R ₆ , R ₇ Is preferably a hydroxyl group, a carboxyl group and an ethyl group, and more preferably a hydroxyl group among these. _{Incidentally, R 4, R 5, R} 6, R 7 is preferably one or more than three substituents among these are hydrogen.

From the viewpoint of facilitating the capture of radical species in the formed image and further enhancing the light resistance of the image, the thiocarbonyl compounds of the above general formula (2) are the same as R ₄ and R ₅ . It is preferable that it is a functional group, and it is preferable that R ₆ and R ₇ are the same functional group.

In the thiocarbonyl compounds of the general formulas (3) and (4), the carbonyl group-containing group preferably has 1 or more and 10 or less carbon atoms, and more preferably 1 or more and 5 or less. Examples of the carbonyl group-containing group having 1 or more and 10 or less carbon atoms include a carboxyl group (-COOH), an esterified carboxyl group (-COOR), an aldehyde group (-COH) and the like. The R in the esterified carboxyl group is preferably an alkyl group having 1 to 9 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms.

In the thiocarbonyl compounds of the general formulas (3) and (4), the number of carbon atoms in the aromatic ring is preferably 3 or more and 15 or less, more preferably 6 or more and 13 or less, and 7 or more and 10 or less. Is even more preferable. Examples of the aromatic ring having 3 or more and 15 or less carbon atoms include a benzene ring, a benzene ring which may have a substituent, and the like. Examples of the benzene ring which may have a substituent include benzoic acid, derivatives of benzoic acid, phenol, derivatives of phenol and the like.

In the thiocarbonyl compound of the general formula (3), k is preferably 0 or more and 10 or less, more preferably 1 or more and 10 or less, and more preferably 1 or more and 5 or less.

From the viewpoint of facilitating the capture of radical species in the formed image and further enhancing the light resistance of the image, in the thiocarbonyl compound of the above general formula (3), R ₈ and R ₉ are hydroxyl groups and carbon. The alkyl group of numbers 1 to 5 is preferable, and the hydroxyl group is more preferable. Similarly, in the thiocarbonyl compound of the general formula (3), R ₁₀ is preferably a hydroxyl group and an alkyl group having 1 to 5 carbon atoms, and more preferably a hydroxyl group.

From the viewpoint of facilitating the capture of radical species in the formed image and further enhancing the light resistance of the image, the thiocarbonyl compound of the above general formula (3) is the same as R ₈ and R ₉ . It is preferably a functional group.

From the viewpoint of facilitating the capture of radical species in the formed image and further enhancing the light resistance of the image, in the thiocarbonyl compound of the above general formula (4), R _{11 to} R ₁₅ are methyl groups and hydrogen. It is preferably an alkyl group having 1 to 5 atoms and 1 to 5 carbon atoms, and more preferably a methyl group. In R _{11 to} R ₁₅ , it is preferable that one or more and three or less substituents are hydrogen.

Specific examples of the thiocarbonyl compound include bis [4- (allyloxycarbonyl) benzyl] trithiocarbonate, bis [4- (2,3-dihydroxypropoxycarbonyl) benzyl] trithiocarbonate, and bis {4- [ethyl-]. (2-Acetyloxyethyl) carbamoyl] benzyl} trithiocarbonate, bis {4- [ethyl- (2-hydroxyethyl) carbamoyl] benzyl} trithiocarbonate, bis [4- (2-hydroxyethoxycarbonyl) benzyl] tri Thiocarbonate, 4-[(2-carboxyethyl sulfanylthiocarbonyl) sulfanyl] -4-cyanopentanoic acid, 2-{[(2-carboxyethyl) sulfanylthiocarbonyl] sulfanyl} propanoic acid, 2'-cyanobutane-2' -Il 4-chloro-3,5-dimethylpyrazole-1-carbodithioate, 2'-cyanobutane-2'-yl 3,5-dimethylpyrazole-1-carbodithioate, 4-cyano-4-[(dodecyl) Sulfanylthiocarbonyl) Sulfanyl] pentanoic acid, cyanomethyl 3,5-dimethylpyrazole-1-carbodithioate, cyanomethyl N-methyl-N-phenyldithiocarbamate, S, S-dibenzyltrithiocarbonate, 2-[(dodecylsulfanyl) Includes methyl 4-cyano-4-[(dodecyl sulfanyl thiocarbonyl) sulfanyl] pentanoate, such as thiocarbonyl) sulfanyl] propanoate.

Among these thiocarbonyl compounds, bis [4- (allyloxycarbonyl) benzyl] trithiocarbonate, bis [4- (2,3-dihydroxypropoxycarbonyl) benzyl] trithiocarbonate, bis {4- [ethyl-( 2-Acetyloxyethyl) carbamoyl] benzyl} trithiocarbonate, bis {4- [ethyl- (2-hydroxyethyl) carbamoyl] benzyl} trithiocarbonate, preferably bis [4- (allyloxycarbonyl) benzyl] tri Thiocarbonate, 4-[(2-carboxyethylsulfanylthiocarbonyl) sulfanyl] -4-cyanopentanoic acid, 2'-cyanobutane-2'-yl 4-chloro-3,5-dimethylpyrazole-1-carbodithioate, 2'cyanobutane-2'-yl 3,5-dimethylpyrazole-1-carbodithioate is more preferred.

(Radical photopolymerizable compound)
The radical photopolymerizable compound is not particularly limited as long as it is a compound that is crosslinked or polymerized by irradiation with active light.

The content of the radical photopolymerizable compound is preferably 1.0% by mass or more and 97% by mass or less, and more preferably 30% by mass or more and 90% by mass or less with respect to the total mass of the ink.

The radical photopolymerizable compound is a compound (monomer, oligomer, polymer or a mixture thereof) having an ethylenically unsaturated bond capable of radical polymerization. The radical photopolymerizable compound may be used alone or in combination of two or more. The radical photopolymerizable compound can be a monofunctional monomer or a polyfunctional monomer.

The radical photopolymerizable compound is preferably an unsaturated carboxylic acid ester compound, more preferably a (meth) acrylate. In the present specification, "(meth) acrylate" means acrylate or methacrylate, "(meth) acryloyl group" means acryloyl group or metaacryloyl group, and "(meth) acrylic" means. Means acrylic or methacrylic.

Examples of monofunctional (meth) acrylates include isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, isomilstill (meth) acrylate, and isostearyl. (Meta) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) ) Acrylate, methoxydiethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxy Ethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl phthal Includes acids, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid and t-butylcyclohexyl (meth) acrylate.

Examples of polyfunctional (meth) acrylates include triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, and polypropylene glycol di. (Meta) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, Dimethylol-tricyclodecanedi (meth) acrylate, PO adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate of hydroxypivalate, polytetramethylene glycol di (meth) acrylate, polyethylene glycol diacrylate and Bifunctional (meth) acrylates such as tripropylene glycol diacrylate; trifunctional (meth) acrylates such as trimethylolpropantri (meth) acrylates and pentaerythritol tri (meth) acrylates; pentaerythritol tetra (meth) acrylates, di. Contains trifunctional or higher functional (meth) acrylates such as pentaerythritol hexa (meth) acrylate, ditrimethylol propanetetra (meth) acrylate, glycerin propoxytri (meth) acrylate and pentaerythritol ethoxytetra (meth) acrylate; polyester acrylate oligomers ( Meta) oligomers having an acryloyl group, and modified products thereof are included. Examples of the modified product include ethylene oxide-modified (EO-modified) acrylate with an ethylene oxide group inserted and propylene oxide-modified (PO-modified) acrylate with a propylene oxide inserted.

The radical photopolymerizable compound preferably contains an ethylene oxide structure or a propylene oxide structure. That is, the radical photopolymerizable compound preferably contains ethylene oxide or a (meth) acrylate modified with propylene oxide (hereinafter, also simply referred to as "modified (meth) acrylate").

When the radical photopolymerizable compound contains an ethylene oxide structure or a propylene oxide structure, the compatibility between the radical photopolymerizable compound and the thiocarbonyl compound is enhanced, and coarse particles formed by agglomeration of the thiocarbonyl compound are precipitated in the ink. It becomes difficult.

(Radical photopolymerization initiator)
The radical photopolymerization initiator is not particularly limited as long as it can initiate the polymerization of the radical photopolymerizable compound.

The content of the radical photopolymerization initiator can be arbitrarily set as long as the radical photopolymerizable compound is sufficiently cured by irradiation with active light and the ejection property of the ink is not deteriorated. For example, the content of the radical photopolymerization initiator is preferably 0.1% by mass or more and 20% by mass or less, and preferably 1.0% by mass or more and 12% by mass or less, based on the total mass of the ink. More preferred.

The radical polymerization initiator includes an intramolecular bond cleavage type radical polymerization initiator and an intramolecular hydrogen abstraction type radical polymerization initiator.

Examples of intramolecular bond cleavage type radical polymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1- (4-isopropylphenyl) -2. -Hydroxy-2-methylpropan-1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4) Acetphenone-based initiators including −methylthiophenyl) propan-1-one and 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone, benzoin, benzoin methyl ether, benzoin isopropyl ether, etc. Includes benzoins, including 2,4,6-trimethylbenzoindiphenylphosphine oxides, acylphosphine oxide-based initiators, and benzyl and methylphenylglycoesters.

Examples of intramolecular hydrogen abstraction-type radical polymerization initiators include benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4,4'-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl. 2-Isopropyl, a benzophenone-based initiator containing sulphide, acrylicized benzophenone, 3,3', 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, and 3,3'-dimethyl-4-methoxybenzophenone. A thioxanthone-based initiator containing thioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, etc., an aminobenzophenone-based initiator containing Michler ketone, 4,4'-diethylaminobenzophenone, etc. Includes 10-butyl-2-chloroacrydone, 2-ethylanthraquinone, 9,10-phenanslenquinone, and camphorquinone.

(Color material)
Coloring materials include pigments and dyes.

The content of the coloring material is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 20% by mass or less, and 2% by mass or more and 10% by mass with respect to the total mass of the ink. The following is more preferable. When the content of the coloring material is 2% by mass or more with respect to the total mass of the ink, the color development of the obtained image becomes sufficient. Further, when the content of the coloring material is 20% by mass or less with respect to the total mass of the ink, the viscosity of the ink does not increase too much.

Examples of pigments include the following organic and inorganic pigments listed in the Color Index.

Examples of red or magenta pigments include Pigment Red 3, 5, 19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53. 1, 57: 1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108, 112, 122, 123, 144 , 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, and 88, Also included are Pigment Orange 13, 16, 20, and 36.

Examples of blue or cyan pigments include pigment Blue 1, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36. , And 60 are included.

Examples of green pigments include Pigment Green 7, 26, 36, and 50.

Examples of yellow pigments include Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137. 138, 139, 153, 154, 155, 157, 166, 167, 168, 180, 185, and 193 are included.

Examples of black pigments include Pigment Blacks 7, 28, and 26.

Examples of dyes include various oil-soluble dyes.

(Gel agent)
The activated light-curable inkjet ink according to the embodiment of the present invention may contain a gelling agent. The gelling agent is an organic substance that is solid at room temperature but becomes a liquid when heated, so that the ink can undergo a sol-gel phase transition in response to a temperature change. When the gelling agent is contained in the active photocurable inkjet ink, the gelling agent forms a card house-like crystal structure near the surface of the ink dots to suppress oxygen inhibition during polymerization, so that the image is formed. The curability of the ink is improved.

The content of the gelling agent is preferably 1.0% by mass or more and 10.0% by mass or less with respect to the total mass of the ink. By setting the content of the gelling agent to 1.0% by mass or more, the pinning property of the ink can be sufficiently enhanced and a higher-definition image can be formed. By setting the content of the gelling agent to 10.0% by mass or less, the gelling agent is less likely to precipitate on the surface of the formed image, and the gloss of the image can be made closer to the gloss of the image by other inks. Moreover, the ink ejection property from the inkjet head can be further improved. From the above viewpoint, the content of the gelling agent in the ink of the present invention is preferably 1.0% by mass or more and 5.0% by mass or less, and 2.5% by mass or more and 5.0% by mass or less. It is more preferable that the content is 2.5% by mass or more and 4.0% by mass or less.

From the following viewpoints, the gelling agent preferably crystallizes in the ink at a temperature equal to or lower than the gelation temperature of the ink. When the gelling agent crystallizes in the ink, a structure in which the photopolymerizable compound is contained in the three-dimensional space formed by the gelling agent crystallized in a plate shape may be formed (such a structure). , Hereinafter referred to as "card house structure"). When the card house structure is formed, the liquid photopolymerizable compound is held in the space, so that the ink droplets are less likely to get wet and spread, and the ink pinning property is further improved. When the pinning property of the ink is improved, it becomes difficult for the ink droplets that have landed on the recording medium to coalesce with each other, and a higher-definition image can be formed.

In order to form the card house structure, it is preferable that the photopolymerizable compound dissolved in the ink and the gelling agent are compatible with each other. On the other hand, if the photopolymerizable compound dissolved in the ink and the gelling agent are phase-separated, it may be difficult to form a cardhouse structure.

Examples of gelling agents suitable for forming a curdhouse structure by crystallization include ketone wax, ester wax, petroleum wax, plant wax, animal wax, mineral wax, hardened castor oil, modified wax, and higher fatty acid. , Higher alcohols, hydroxystearic acid, fatty acid amides including N-substituted fatty acid amides and specialty fatty acid amides, higher amines, sucrose fatty acid esters, synthetic waxes, dibenzylidene sorbitol, dimer acids and dimer diols.

Examples of the above-mentioned ketone wax include dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristyl palmityl ketone and palmityl stearyl ketone. Is done.

Examples of the above ester wax include behenyl behenylate, icosyl icosate, stearyl stearate, palmityl stearate, cetyl palmitate, myristyl myristate, cetyl myristate, myricyl serotate, stearyl stearate, oleyl palmitate, and glycerin fatty acid. Includes esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters and polyoxyethylene fatty acid esters.

Examples of the above-mentioned commercial products of ester wax include Nippon Emulsion Co., Ltd., EMALEX series (“EMALEX” is a registered trademark of the same company), and Riken Vitamin Co., Ltd., Rikemar series and Poem series (“Rikemar” and “Poem”). Both are registered trademarks of the same company).

Examples of the petroleum wax include paraffin wax, microcrystalline wax and petroleum wax containing petroleum lactam.

Examples of the plant-based waxes include candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax and jojoba ester.

Examples of animal waxes include beeswax, lanolin and whale wax.

Examples of the above-mentioned mineral waxes include montan wax and hydrogenated wax.

Examples of the modified wax include a montan wax derivative, a paraffin wax derivative, a microcrystalline wax derivative, a 12-hydroxystearic acid derivative and a polyethylene wax derivative.

Examples of the higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

Examples of the higher alcohols include stearyl alcohol and behenyl alcohol.

Examples of the hydroxystearic acid include 12-hydroxystearic acid.

Examples of the fatty acid amides include lauric acid amides, stearic acid amides, bechenic acid amides, oleic acid amides, erucic acid amides, ricinoleic acid amides and 12-hydroxystearic acid amides.

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

Examples of the N-substituted fatty acid amides include N-stearyl stearic acid amides and N-oleyl palmitate amides.

Examples of the above-mentioned special fatty acid amides include N, N'-ethylenebisstearylamide, N, N'-ethylenebis-12-hydroxystearylamide and N, N'-xylylene bisstearylamide.

Examples of the higher amines include dodecylamine, tetradecylamine and octadecylamine.

Examples of the sucrose fatty acid ester include sucrose stearic acid and sucrose palmitic acid.

Examples of commercially available products of the sucrose fatty acid ester include Mitsubishi Chemical Foods Co., Ltd.'s Ryoto Sugar Ester series (“Ryoto” is a registered trademark of the company).

Examples of the synthetic wax include polyethylene wax and α-olefin maleic anhydride copolymer wax.

Examples of commercial products of the synthetic wax include the UNILIN series manufactured by Baker-Petrolite (“UNILIN” is a registered trademark of the company).

Examples of the above dibenzylidene sorbitol include 1,3: 2,4-bis-O-benzylidene-D-glucitol.

Examples of commercial products of dibenzylideneacetone sorbitol include Gelol D (“Gelol” is a registered trademark of the company) manufactured by New Japan Chemical Co., Ltd.

Examples of commercially available dimerdiols include the PRIPOR series manufactured by CRODA (“PRIPOR” is a registered trademark of the company).

Among these gelling agents, ketone wax, ester wax, higher fatty acid, higher alcohol and fatty acid amide are preferable from the viewpoint of further enhancing the pinning property, and from the above viewpoint, the ketone represented by the following general formula (G1) is preferable. Waxes and ester waxes represented by the following general formula (G2) are more preferable. The ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may contain only one type or two or more types in the ink of the present invention. May be. Further, only one of the ketone wax represented by the following general formula (G1) and the ester wax represented by the following general formula (G2) may be contained in the ink of the present invention, or both. May be included.

General formula (G1): R1-CO-R2
In the general formula (G1), R1 and R2 are both linear or branched hydrocarbon groups having 9 or more and 25 or less carbon atoms.

General formula (G2): R3-COO-R4
In the general formula (G2), R3 and R4 are both linear or branched hydrocarbon groups having 9 or more and 25 or less carbon atoms.

The ketone wax represented by the general formula (G1) or the ester wax represented by the general formula (G2) is gelled because the linear or branched hydrocarbon group has 9 or more carbon atoms. The crystallinity of the agent is further increased, and more sufficient space is created in the card house structure. Therefore, the photopolymerizable compound is likely to be sufficiently encapsulated in the space, and the pinning property of the ink is further improved. Further, since the linear or branched hydrocarbon group has 25 or less carbon atoms, the melting point of the gelling agent does not rise excessively, so that it is not necessary to excessively heat the ink when ejecting the ink. .. From the above viewpoint, it is particularly preferable that R1 and R2 are linear hydrocarbon groups having 11 or more and less than 23 carbon atoms.

Further, from the viewpoint of raising the gelation temperature of the ink and gelling the ink more rapidly after landing, the number of carbon atoms in which either R1 or R2 or R3 or R4 is saturated is 11 or more. It is preferably less than 23 hydrocarbon groups. From the above viewpoint, it is more preferable that both R1 and R2, or both R3 and R4 are saturated hydrocarbon groups having 11 or more and less than 23 carbon atoms.

Examples of the ketone wax represented by the above general formula (G1) include dilignoceryl ketone (carbon number: 23-24), dibehenyl ketone (carbon number: 21-22), and distearyl ketone (carbon number: 17). -18), Dieicosyl ketone (carbon number: 19-20), dipalmityl ketone (carbon number 15-16), dimyristyl ketone (carbon number 13-14), dilauryl ketone (carbon number: 11) -12), Lauryl myristyl ketone (carbon number: 11-14), Lauryl palmityl ketone (11-16), Myristyl palmityl ketone (13-16), Myristyl stearyl ketone (13-18), Myristyl behenyl ketone (13) -22), palmityl stearyl ketone (15-18), balmityl behenyl ketone (15-22) and stearyl behenyl ketone (17-22). The carbon number in parentheses represents the carbon number of each of the two hydrocarbon groups separated by the carbonyl group.

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

Examples of fatty acids or ester waxes represented by the general formula (G2) include behenyl behenylate (carbon number: 21-22), icosyl icosanate (carbon number: 19-20), stearyl stearate (carbon number: 17). -18), palmityl stearate (carbon number: 17-16), lauryl stearate (carbon number: 17-12), cetyl palmitate (carbon number 15-16), stearyl palmitate (carbon number 15-18) ), Myristyl myristate (13-14 carbons), cetyl myristate (13-16 carbons), octyldodecyl myristate (13-20 carbons), stearyl oleate (17-18 carbons) , Stearyl erkaate (21-18 carbon atoms), stearyl linoleate (17-18 carbon atoms), behenyl oleate (18-22 carbon atoms) and arachidyl linoleate (17-20 carbon atoms) Is done. The number of carbon atoms in parentheses represents the number of carbon atoms of each of the two hydrocarbon groups separated by the ester group.

Examples of commercially available ester wax products represented by the general formula (G2) include Nichiyu Co., Ltd., Unistar M-2222SL and Spalm Aceti (“Unistar” is a registered trademark of the company), Kao Corporation, Exepearl SS and Exepearl MY-M ("Exepearl" is a registered trademark of the company), Nippon Emulsion Co., Ltd., EMALEX CC-18 and EMALEX CC-10 ("EMALEX" is a registered trademark of the company), and Higher Alcohol Industry Co., Ltd., Amreps PC ("Amrepus" is a registered trademark of the company) is included. Since these commercially available products are often a mixture of two or more types, they may be separated and purified and contained in the ink as necessary.

(Polymerization inhibitor)
The activated light-curable inkjet ink according to the embodiment of the present invention may contain a polymerization inhibitor.

The content of the polymerization inhibitor is preferably 0.05% by mass or more and 0.2% by mass or less with respect to the total mass of the ink.

Examples of anti-polymerization agents include (alkyl) phenol, hydroquinone, catechol, resorcin, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiline, p-benzoquinone. , Nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cuperon, aluminum N-nitrosophenyl hydroxylamine, tri-p-nitrophenylmethyl, N- (3-oxyanilino-) 1,3-Dimethylbutylidene) aniline oxide, dibutylcresol, cyclohexanone oxime cresol, guayacol, o-isopropylphenol, butyraldoxime, methylethylketoxim, cyclohexanone oxime.

(Physical properties)
The activated light-curable inkjet ink preferably has a viscosity at 25 ° C. of 2 mPa · s or more and 50 mPa · s or less. The viscosity of the active light-curable inkjet ink is preferably 7 mPa · s or more and 15 mPa · s or less in a temperature range of 20 ° C. or higher and lower than 100 ° C., which is the ink temperature at the time of ejection from the inkjet head, and is preferably 8 mPa. -It is more preferable that it is s or more and 13 mPa · s or less.

When the active ray-curable inkjet ink contains a gelling agent, the viscosity at 80 ° C. is preferably 3 mPa · s or more and 20 mPa · s, and 6.0 mPa · s or more and 15.0 mPa · s or less. More preferably, it is more preferably 7.0 mPa · s or more and 12.0 mPa · s or less. On the other hand, in order to suppress the coalescence of adjacent ink droplets, it is preferable that the viscosity of the ink at room temperature after landing is constant or higher. Specifically, when the active photocurable inkjet ink contains a gelling agent, the viscosity at 25 ° C. is preferably 1000 mPa · s or more.

The viscosity of the active photocurable inkjet ink at 25 ° C., the viscosity at 80 ° C., and the gelation temperature can be determined by measuring the temperature change of the dynamic viscoelasticity of the ink with a rheometer. Specifically, a temperature change curve of viscosity is obtained when the ink is heated to 100 ° C. and cooled to 25 ° C. under the conditions of a shear rate of 11.7 (1 / s) and a temperature lowering rate of 0.1 ° C./s. .. Then, the viscosity can be obtained by reading the viscosity at 80 ° C. and the viscosity at 25 ° C., respectively. The gelation temperature can be determined as the temperature at which the viscosity becomes 200 mPa · s in the temperature change curve of the viscosity.

As the rheometer, a stress-controlled rheometer Physica MCR series manufactured by Antonio Par can be used. The diameter of the cone plate can be 75 mm and the cone angle can be 1.0 °.

(Manufacturing method of activated light-curable inkjet ink)
In the method for producing an active photocurable inkjet ink, a radical photopolymerizable compound, a radical photopolymerization initiator, and a coloring material are mixed. At this time, the gelling agent may be mixed at the same time, or the other components described above may be mixed at the same time. It is preferable to filter the mixed solution obtained with the gelling agent with a predetermined filter. At this time, in order to increase the solubility of the gelling agent and the like, it is preferable to mix the above components while heating.

It is preferable that each component to be mixed at this time has a high purity.

A dispersion containing a pigment and a dispersant may be prepared in advance, and the remaining components may be added thereto and mixed. Also at this time, in order to enhance the solubility of the dispersant and the like, it is preferable to prepare the dispersion by mixing the pigment and the dispersant while heating.

The dispersion can be prepared by, for example, a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, or the like. The dispersion is preferably carried so that the average particle size of the pigment particles is 0.08 μm or more and 0.5 μm or less, and the maximum particle size is 0.3 μm or more and 10 μm or less, preferably 0.3 μm or more and 3 μm or less.

[Image formation method]
The image forming method according to another embodiment of the present invention includes 1) a step of ejecting droplets of the above-mentioned activated photocurable inkjet ink from a nozzle of an inkjet recording device and landing them on the surface of a recording medium, and 2) a recording medium. The step of irradiating the droplets of the active light-curable inkjet ink landed on the surface with active light to cure the droplets of the active light-curable inkjet ink is included.

(First step)
In the first step, droplets of the inkjet ink are ejected from the inkjet head and landed on the recording medium at a position corresponding to the image to be formed.

The ejection method from the inkjet head may be either an on-demand method or a continuous method. On-demand inkjet heads include electro-mechanical conversion methods such as single cavity type, double cavity type, bender type, piston type, shared mode type and shared wall type, as well as thermal inkjet type and bubble jet (bubble jet is Any of the electric-heat conversion methods such as Canon's registered trademark) type may be used.

By ejecting the ink droplets from the inkjet head in a heated state, the ejection stability can be improved. The temperature of the ink at the time of ejection is preferably 35 ° C. or higher and 100 ° C. or lower, and more preferably 35 ° C. or higher and 80 ° C. or lower in order to further improve the ejection stability. In particular, it is preferable to eject the ink at an ink temperature such that the viscosity of the ink is 7 mPa · s or more and 15 mPa · s or less, more preferably 8 mPa · s or more and 13 mPa · s or less.

When the active light-curable inkjet ink contains a gelling agent, in order to improve the ejection property of the ink from the inkjet head, the temperature of the ink when the ink is filled in the inkjet head is set to the gelation temperature of the ink + 10 ° C. As described above, it is preferable to set the gelation temperature to + 30 ° C. or lower. If the temperature of the ink in the inkjet head is less than the gelation temperature + 10 ° C., the ink gels in the inkjet head or on the nozzle surface, and the ink ejection property tends to decrease. On the other hand, if the temperature of the ink in the inkjet head exceeds the gelation temperature + 30 ° C., the ink becomes too high, and the ink component may deteriorate.

The method of heating the ink is not particularly limited. For example, at least one of the ink tank, the supply pipe, the ink supply system such as the front chamber ink tank immediately before the head, the pipe with a filter, and the piezo head, which constitute the head carriage, is heated by a panel heater, a ribbon heater, and heat insulating water. be able to.

The amount of ink droplets to be ejected is preferably 2 pL or more and 20 pL or less from the viewpoint of recording speed and image quality.

The recording medium is not particularly limited, and in addition to ordinary uncoated paper and coated paper, synthetic paper YUPO (registered trademark), various plastics used for flexible packaging, and films thereof can be used. Examples of various plastic films include PP film, PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubber and the like can be used. It can also be applied to metals and glasses.

It is preferable that the temperature of the recording medium when the ink droplets land is controlled to 20 ° C. or higher and 40 ° C. or lower from the viewpoint of ink gelation.

(Second step)
In the second step, the ink landed on the recording medium in the first step is irradiated with active rays to form an image made of a cured film of the ink.

The active ray can be selected from, for example, electron beam, ultraviolet ray, α ray, γ ray, and X-ray, but is preferably ultraviolet ray, and irradiates light having a peak wavelength of 360 nm or more and 410 nm or less from the LED light source. Is preferable. An example of an LED light source is a water-cooled LED (peak wavelength 395 nm) manufactured by Phoseon Technology. LEDs have less radiant heat than conventional light sources (such as metal halide lamps). Therefore, when irradiated with active light, the ink is hard to melt and uneven gloss is hard to occur.

Here, the case of irradiating light having a peak wavelength 360nm or 410nm or less, a peak illuminance in the recording medium surface or the ink droplet surface, it is preferable that a 0.5 W / cm ² or more 10.0 W / cm ² or less it is preferable to 1.0 W / cm ² or more 5.0 W / cm ² or less.

The irradiation of the active light is preferably performed within 0.001 seconds to 1.0 seconds after the ink lands on the recording medium, and 0.001 seconds to 0 seconds in order to form a high-definition image. More preferably, it is performed within 5 seconds.

On the other hand, the irradiation of the active light may be performed in two stages. In this case, the ink is tentatively cured by irradiating the ink with an active ray from 0.001 seconds to 2.0 seconds after the ink lands on the recording medium, and after all printing is completed, the ink is further irradiated with an active ray. Can be finally cured. By dividing the irradiation of the active light into two stages, the curing shrinkage of the ink is less likely to occur.

Hereinafter, specific examples of this embodiment will be described together with comparative examples. However, the technical scope of the present invention is not limited to the following examples.

1. 1. Active light-curable inkjet ink 1-1. Preparation of Pigment Dispersion Solution (M: Magenta) The following dispersants, active photocurable compounds and polymerization inhibitors were placed in a stainless steel beaker and dissolved by heating and stirring for 1 hour on a hot plate at 65 ° C. .. After cooling the obtained solution to room temperature, 21 parts by mass of the following magenta pigment 1 was added, and the solution was placed in a glass bottle together with 200 g of zirconia beads having a diameter of 0.5 mm, sealed, and dispersed with a paint shaker for 8 hours. Then, the zirconia beads were removed to prepare a pigment dispersion having the following composition.

[Composition of pigment dispersion]
・ Dispersant: Azisper PB824 (manufactured by Ajinomoto Fine-Techno) 9 parts by mass ・ Radical photopolymerizable compound: APG-200 (tripropylene glycol diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.) 70 parts by mass ・ Polymerization inhibitor: Irgastab UV10 (manufactured by Shin-Nakamura Chemical Co., Ltd.) Ciba Japan Co., Ltd.) 0.02 parts by mass ・ Magenta pigment: Pigment Red 122 (manufactured by Dainichi Seika Co., Ltd., Chromofine Red 6112JC) 21 parts by mass

1-2. Preparation of active photocurable inkjet ink Using the following gelling agent, radical photopolymerizable compound, polymerization inhibitor, radical photopolymerization initiator, thiocarbonyl compound, and the above pigment dispersion, an active photocurable inkjet ink is prepared. Prepared.

The following gelling agents were used.
・ Aliphatic diketone (Kaowax T1, manufactured by Kao Corporation)

The following radical photopolymerizable compounds were used.
-Polyethylene glycol # 400 diacrylate-4EO-modified pentaerythritol tetraacrylate-6EO-modified trimethylolpropane triacrylate-methoxypolyethylene glycol # 550 acrylate-1,9-nonanediol diacrylate-Trimethylolpropane triacrylate-Pentaerythritol triacrylate

The following polymerization inhibitors were used.
・ Irgastab UV10 (manufactured by Chivas Specialty Chemical Co., Ltd.)

The following radical photopolymerization initiators were used.
・ DAROCURE TPO (manufactured by Chivas Specialty Chemical Co., Ltd.)

The following thiocarbonyl compounds were used.

-Compound (1)

-Compound (2)

・ Compound (3)

The mixture obtained by mixing each of the above components according to the composition shown in Table 1 was heated to 80 ° C. and stirred. The obtained solution was filtered under heating with a # 300 metal mesh filter and then cooled to prepare inks 1-10.

2. 2. Image preparation 2-1. Recording media Inks 1 to 10 were used to form images on the following recording media.
・ Coated paper for printing A (OK top coat, rice basis weight 128 g / m ² manufactured by Oji Paper Co., Ltd.)

2-2. Image Preparation Conditions Inks 1 to 10 were recorded on a recording medium using an inkjet recording device having a piezo type inkjet nozzle. The ink supply system consisted of a former tank, a supply pipe, an ink supply tank immediately before the inkjet head, a filter, and a piezo type inkjet head, and heat-insulated and heated the ink supply tank to the inkjet head portion. The temperature sensors were provided near the nozzles of the ink supply tank and the inkjet head, respectively, and controlled at 80 ° C. ± 2 ° C. The ejection conditions were an appropriate amount of liquid of 14 pl, a printing speed of 0.5 m / sec, an injection frequency of 10.5 kHz, and a printing rate of 100%, and a solid printing portion of 5 cm × 5 cm was formed on the recording medium. After landing, UV light is focused on the exposure surface illuminance of 1,200 mW / cm ² , and the exposure system, main scanning speed, and emission frequency are adjusted so that irradiation starts 0.1 seconds after the ink composition lands on the recording medium. did. In addition, the exposure time was made variable and the exposure energy was applied. An LED lamp (manufactured by GS Yuasa Corporation) was used as the ultraviolet lamp.

3. 3. Evaluation (light resistance)
An image formed with each ink was subjected to a light resistance test based on the change in the reflection density of the image before and after exposure to strong light conditions. Specifically, first, the reflection density of the image in the vicinity of the print density 1 was measured using X-Rite900 (manufactured by Nippon Flat Plate Equipment Co., Ltd.). Next, using a low-temperature Xe weather meter XL75 (manufactured by Suga Test Instruments Co., Ltd.), each image was exposed under strong light conditions of 20 ° C. and 50 RH for 7 days at an illuminance of 70,000 lux. Next, the reflection density of the image after being exposed to strong light conditions was measured using X-Rite900 (manufactured by Nippon Flat Plate Equipment). The residual reflection density (%) was determined from the change in the reflection density before and after exposure to strong light conditions. For images with insufficient density, changes in the reflection density at the highest density portion were measured instead of around 1 print density. The level of light resistance was ranked as follows. For the print density, the ratio of the reflected light amount to the incident light amount (reflectance) is obtained using the X-Rite900, and the common logarithm with respect to the inverse number of the reflectance (incident light intensity / reflected light intensity). I asked for it by taking.

A: Reflective density residual rate is 85% or more B: Reflective density residual rate is less than 70 to 85% C: Reflective density residual rate is less than 50 to 70% D: Reflective density residual rate is less than 50% In the present invention, rank B The above is practical.

(Rubbing resistance (hardness))
The images formed with each ink were evaluated for rubbing resistance according to the method described in "JIS standard K5701-1 6.2.3 friction resistance test". Specifically, a recording medium cut out to an appropriate size was placed on the image, and a load was applied to rub it together. Then, the degree of decrease in image density was visually observed and evaluated based on the following criteria.

⊚: Even if the image is rubbed 100 times or more, no change in the image is visually recognized.
◯: When rubbed 100 times or more, some traces are left on the surface, but the concentration does not decrease, which is within the practically acceptable range.
Δ: A decrease in image density is observed after rubbing 100 times, but it is within a practically acceptable range.
X: A clear decrease in image density was observed after rubbing less than 50 times, and the quality was not practical.

(Blooming)
Using the above ink, a 5 cm x 5 cm solid image formed on printing coated paper A (OK top coat rice basis weight 128 g / m ² manufactured by Oji Paper Co., Ltd.), which is a recording medium, is formed in an environment of 40 ° C. Stored for months. The image after storage was visually observed, and blooming was evaluated according to the following criteria.
◯: No deposit is observed on the image surface.
Δ: Thin deposits are present on the surface of the image and can be visually confirmed.
X: The surface of the image is covered with a powdery substance and can be clearly confirmed visually.

(Dispersion stability)
Each ink was applied onto a polyethylene terephthalate film using a wire bar so as to have a wet film thickness of 20 μm. After that, observation was performed using a magnifying glass (100 times) to confirm the presence or absence of coarse particles.

The evaluation results are shown in Table 2 below.

Since the inks 1 to 7 of the examples had thiocarbonyl compounds, the images formed with these inks had a good light resistance evaluation of A or B.

Since the inks 8 to 10 of the comparative examples do not have the thiocarbonyl compound, the images formed with these inks had a poor light resistance evaluation of C.

Comparing the inks 2 to 7 of the examples and the inks 8 to 10 of the comparative examples, all the inks contain a gelling agent, but in the image of the inks 2 to 7 of the examples, the gelling agent is precipitated (blooming). I couldn't see it. It is considered that this is because the inks 2 to 7 of the examples contain the thiocarbonyl compound, and the thiocarbonyl compound suppresses the precipitation of the gelling agent by the hydrophobic interaction.

Comparing the inks 1 to 4, 6 and 7 of the examples with the inks 5 of the examples, the inks 1 to 4, 6 and 7 of the examples have a thiocarbonyl compound content with respect to the radical photopolymerization initiator. Since the molar ratio was 0.5 or more, the images formed with these inks had better light resistance.

Comparing the inks 2 to 5 and 7 of the examples with the inks 1 of the examples, since the inks 2 to 5 and 7 of the examples contain a gelling agent, the curability is better than that of the first example. there were.

Although the ink 6 of the example contains a gelling agent, the content of the thiocarbonyl compound is more than 1.0 in terms of the molar ratio to the radical photopolymerization initiator, so that it is compared with the inks 2 to 5 and 7 of the example. Poor curability. It is considered that this is because the amount of the thiocarbonyl compound in the ink of Example 6 was too large and the polymerization of the radical photopolymerizable compound was inhibited.

Comparing the inks 1 to 6 of the examples with the inks 7 of the examples, coarse particles were not observed in the inks 1 to 6 of the examples, and the dispersion stability of the ink was better. It is considered that this is because the radical photopolymerizable compounds of the inks 1 to 6 of the examples contain polyethylene oxide.

According to the active light-curable inkjet ink of the present invention, an image having high light resistance can be obtained. Therefore, the present invention is expected to contribute to the development and popularization of active ray-curable inkjet inks.

Claims (5)

An active photocurable inkjet ink containing a radical photopolymerizable compound, a radical photopolymerization initiator, and a coloring material.
An active photocurable inkjet ink further containing at least one thiocarbonyl compound selected from the group consisting of the following general formulas (1) to (4).

(In the general formula (1), X ₁ and X ₂ are independently any of a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, an alkenyl group having 2 or more and 10 or less carbon atoms, or a substituent Y ₁ shown below. Represents

(In the substituent Y ₁ , R ₁ , R ₂ , and R ₃ each independently represent a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, or any of the following substituents Y ₂ , and n is 1 to 10. Represents an integer.)

(Among the substituents _{Y 2,} m represents an integer of 1 to 10.)

(In the general formula (2), R ₄ , R ₅ , R ₆ and R ₇ are independently any of a hydrogen atom, a methyl group, a hydroxyl group, a carboxyl group, an alkyl group having 1 to 10 carbon atoms, and a methyl ester group. , And l independently represents an integer from 1 to 10.)

(In the general formula (3), R ₈ , R ₉ , and R ₁₀ are independently hydrogen atoms, methyl groups, hydroxyl groups, carbonyl group-containing groups having 1 or more and 10 or less carbon atoms, chlorine atoms, and 1 to 10 carbon atoms. Represents either an alkyl group or a carboxyl group, Z ₁ represents a nitrile group or an aromatic ring having 3 or more and 15 or less carbon atoms, and k independently represents an integer of 0 to 10).

(In the general formula (4), R _{11 to} R ₁₅ are independently hydrogen atom, methyl group, hydroxyl group, carbonyl group-containing group having 1 or more and 10 or less carbon atoms, chlorine atom, and alkyl having 1 to 10 carbon atoms. Represents any of the groups, Z ₂ represents a nitrile group or an aromatic ring with 3 or more and 15 or less carbon atoms.) The active photocurable inkjet ink according to claim 1, wherein the content of the thiocarbonyl compound is 0.5 or more and 1.0 or less in terms of the molar ratio with respect to the radical photopolymerization initiator. The active photocurable inkjet ink according to claim 1 or 2, further comprising a gelling agent. The active photocurable inkjet ink according to any one of claims 1 to 3, wherein the radical photopolymerizable compound contains a polypropylene oxide structure or a polyethylene oxide structure. A step of ejecting droplets of the active ray-curable inkjet ink according to any one of claims 1 to 4 from a nozzle of an inkjet head and landing them on the surface of a recording medium.
The step of irradiating the landed droplet with an active ray to cure the droplet, and
An image forming method having.