JP2020139109A - Ultraviolet ray curable ink for ink jet printing and method for forming image - Google Patents

Abstract

To provide an ultraviolet curable ink having good transferability and capable of forming a high definition image.SOLUTION: There is provided an ultraviolet curable ink for ink jet printing, including a compound which changes its phase from solid to liquid or liquid crystal by irradiation with ultraviolet rays and which changes its phase from liquid or liquid crystal to solid by irradiation with visible light. The compound which changes its phase by irradiation with ultraviolet rays and visible rays is an azobenzene derivative represented by formula (1)in which X1 and X2 are nitrogen atoms, or a stilbene derivative in which the above X1 and X2 are carbon atoms.SELECTED DRAWING: Figure 1

Description

The present invention relates to UV curable inks for inkjet and image forming methods.

Since the image forming method by the inkjet method can produce an image easily and inexpensively, it is applied to various printing fields including special printing such as photography, various printing, marking, and color filter. In particular, the image forming method by the inkjet method is particularly suitable for applications in which various images are formed little by little because digital printing is possible without using a plate.

As a kind of inkjet ink used in an image forming method by an inkjet method, an ink contained as a liquid component that is cured by being irradiated with ultraviolet rays (hereinafter, also simply referred to as "ultraviolet curable ink") is known. As the above image forming method, droplets of ultraviolet curable ink are landed on the surface of a recording medium, and the ink droplets applied on the recording medium are irradiated with ultraviolet rays to cure the ink. There is a method of forming a film on the surface of a recording medium. A desired image can be formed by forming a cured film formed by curing the ink by the above method.

UV curable inks for inkjets for use in the image forming methods have been extensively studied and various improvements have been made to form the desired image. For example, Patent Document 1 describes a self-dispersing ultraviolet polymerizable compound, a water-insoluble α-aminoketone ultraviolet polymerization initiator, and a water-insoluble sensitizer having absorption in ultraviolet rays in a wavelength region of 375 nm or more and 450 nm or less. And UV curable water-based inks containing water are disclosed. The ultraviolet curable water-based ink realizes high-speed recording by suppressing the occurrence of offset (a phenomenon in which ink is transferred to a stacked recording medium or ink is transferred to a member that winds up a recording medium when the recording media are stacked). It is said that it can be done.

Japanese Unexamined Patent Publication No. 2015-168727

By using the ultraviolet curable water-based ink disclosed in Patent Document 1, a desired image can be obtained in a method of forming an image directly on a recording medium. However, in the ultraviolet curable water-based ink, when the ultraviolet curable water-based ink is ejected onto the surface of the intermediate transfer material and transferred to a recording medium, the intermediate transfer material is affected by the moisture contained in the ultraviolet curable water-based ink. It is difficult to completely suppress the image flow above.

Therefore, in the image forming method involving the transfer step of transferring the image formed on the surface of the intermediate transfer body onto the recording medium, no image flow occurs on the intermediate transfer body and the transfer from the intermediate transfer body to the recording medium is performed. There is a demand for an active photocurable ink for inkjet, which has good properties.

The present invention has been made in view of the above points, and a first object of the present invention is to provide an ultraviolet curable ink having good transferability and capable of forming a high-definition image. A second object of the present invention is to provide an image forming method using the above-mentioned ultraviolet curable ink.

The ultraviolet curable ink for inkjet of the present invention contains a compound that undergoes a phase change from solid to liquid or liquid crystal when irradiated with ultraviolet rays, and undergoes a phase change from liquid or liquid crystal to solid when irradiated with visible light.

In the image forming method of the present invention, droplets of the above-mentioned ultraviolet curable ink for inkjet are ejected from the inkjet head and landed on the surface of the intermediate transfer body to form an image on the surface of the intermediate transfer body. A step, a first light irradiation step in which the integrated light amount of light of 300 nm or more and less than 400 nm to irradiate the image is 100 to 1000 mJ / cm ² , a step of transferring the image to a recording medium, and a step of transferring the image to the recording medium. It has a second light irradiation step in which the integrated light amount of light of 400 nm or more and 800 nm or less to irradiate the image is 100 to 1000 mJ / cm ² .

In another image forming method of the present invention, droplets of the above-mentioned ultraviolet curable ink for inkjet are ejected from an inkjet head and landed on the surface of a recording medium to form an image on the surface of the recording medium. The first light irradiation step in which the integrated light amount of light of 300 nm or more and less than 400 nm irradiating the image is 100 to 1000 mJ / cm ² , and the integrated light amount of light of 400 nm or more and 800 nm or less irradiating the image is 100. It has a second light irradiation step of ~ 1000 mJ / cm ² .

According to the present invention, it is possible to provide an ultraviolet curable ink having good transferability and capable of forming a high-definition image. Further, according to the present invention, it is possible to provide an image forming method using the above-mentioned ultraviolet curable ink.

FIG. 1 is a schematic diagram showing an exemplary configuration of an image forming apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

1. 1. Ultraviolet Curable Ink One embodiment of the present invention emits light (visible light) of 400 nm or more and 800 nm or less, which undergoes a phase change from solid to liquid or liquid crystal by irradiating light (ultraviolet light) of 300 nm or more and less than 400 nm. The present invention relates to an ultraviolet curable ink for inkjet, which comprises a compound represented by the formula (1), which undergoes a phase change from a liquid or a liquid crystal to a solid when irradiated. The compound contained in the ultraviolet curable ink undergoes a phase change with light of 300 nm or more and less than 400 nm to soften the formed image (cured film obtained by curing the ultraviolet curable ink). Therefore, for example, by ejecting the ultraviolet curable ink onto the intermediate transfer body and irradiating the ultraviolet curable ink with ultraviolet rays on the intermediate transfer body, the ultraviolet curable ink is cured by the formula (1). The ultraviolet curable ink cured by the represented compound can be appropriately softened. At this time, the transferability can be improved by appropriately softening the cured product with the compound represented by the formula (1) while suppressing the image flow on the intermediate transfer material by curing the ultraviolet curable ink. it can. After the transfer to the recording medium, the image is irradiated with visible light to change the phase of the compound represented by the formula (1) into a solid, thereby increasing the hardness of the image and suppressing blocking after image formation. It is also possible.

（式（１）中、Ｘ_１、Ｘ_２は、それぞれ独立して、窒素原子または炭素原子であり、Ｒ_１〜Ｒ_１０は、それぞれ独立して、水素原子、アルキル基、アルコキシ基、ハロゲン基、ヒドロキシ基、およびカルボキシ基からなる群から選択される基であり、Ｒ_１〜Ｒ_５の少なくとも１つの基は、炭素数１〜１８のアルキル基またはアルコキシ基であり、Ｒ_６〜Ｒ_１０の少なくとも１つの置換基は、炭素数１〜１８のアルキル基またはアルコキシ基である。）

(In the formula (1), X ₁ and X ₂ are independent nitrogen atoms or carbon atoms, and R _{1 to} R ₁₀ are independent hydrogen atoms, alkyl groups, alkoxy groups, and halogen groups, respectively. , A hydroxy group, and a carboxy group, at least one of R _{1 to} R ₅ is an alkyl or alkoxy group having 1 to 18 carbon atoms, of R _{6 to} R ₁₀ . At least one substituent is an alkyl group or an alkoxy group having 1 to 18 carbon atoms.)

In the phase-changing compound represented by the above formula (1) in one embodiment of the present invention, the above X ₁ and X ₂ are azobenzene derivatives which are nitrogen atoms, or the above X ₁ and X ₂ are carbon atoms. A stilbene derivative.

1-1. Azobenzene derivative, stilbene derivative The azobenzene derivative in which X ₁ and X ₂ represented by the above formula (1) are nitrogen atoms, or the stilbene derivative in which the above X ₁ and X ₂ are carbon atoms absorb light in the ultraviolet region. By isomerizing from trans to cis, the phase changes from solid to liquid or liquid crystal, absorbs light in the visible light region, and by isomerizing from cis to trans, from liquid or liquid crystal to solid. Phase change to.

R ₁ and R ₆ in the azobenzene derivative and the stillben derivative represented by the structural formula (1) in one embodiment of the present invention are alkyl groups or alkoxy groups having 1 to 18 carbon atoms, and are R ₁ and R _6. Is preferably an alkyl group or an alkoxy group having 4 to 12 carbon atoms, and more preferably an alkyl group or an alkoxy group having 4 to 8 carbon atoms. In addition, R _{2 to} R ₅ and R _{7 to} R ₁₀ may be independently selected from the group consisting of a hydrogen atom, an alkyl group, an alkoxy group, a halogen group, a hydroxy group, and a carboxy group. More preferably, it is a group selected from the group consisting of a hydrogen atom, an alkyl group, an alkoxy group and a halogen group.

Further, R ₁ and R ₆ may be the same or different, but they are preferably the same because they preferably have regularity in the molecular arrangement from the viewpoint of intermolecular interaction. ..

Examples of the above alkyl groups include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n. Linear alkyl groups such as -decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-octadecyl group; isopropyl group, Isobutyl group, sec-butyl group, tert-butyl group, isoamyl group, tert-pentyl group, neopentyl group, 1-methylpentyl group, 4-methyl-2-pentyl group, 3,3-dimethylbutyl group, 2-ethylbutyl Group, 1-methylhexyl group, tert-octyl group, 1-methylheptyl group, 2-ethylhexyl group, 2-propylpentyl group, 2,2-dimethylheptyl group, 2,6-dimethyl-4-heptyl group, 3 , 5,5-trimethylhexyl group, 1-methyldecyl group, 1-hexylheptyl group and other branched alkyl groups are included.

Examples of the alkoxy groups include methoxy group, ethoxy group, n-propoxy group, n-butoxy group, n-pentyloxy group, n-hexyloxy group, n-heptyloxy group, n-octyloxy group and n-. Nonyloxy group, n-decyloxy group, n-undecyloxy group, n-dodecyloxy group, n-tridecyloxy group, n-tetradecyloxy group, n-pentadecyloxy group, n-hexadecyloxy group, n -Linear alkoxy groups such as octadecyloxy groups: isopropoxy group, tert-butoxy group, 1-methylpentyloxy group, 4-methyl-2-pentyloxy group, 3,3-dimethylbutyloxy group, 2- Ethylbutyloxy group, 1-methylhexyloxy group, tert-octyloxy group, 1-methylheptyloxy group, 2-ethylhexyloxy group, 2-propylpentyloxy group, 2,2-dimethylheptyloxy group, 2,6 Includes branched alkoxy groups such as −dimethyl-4-heptyloxy group, 3,5,5-trimethylhexyloxy group, 1-methyldecyloxy group, 1-hexylheptyloxy group.

Examples of the halogen group include a fluoro group, a chloro group, a bromo group, and an iodine group.

In the azobenzene derivative represented by the structural formula (1) in one embodiment of the present invention, the alkyl group or alkoxy group having 1 to 18 carbon atoms used in R ₁ and R ₆ may be linear. It may be branched or may be branched, but from the viewpoint of having a structure in which phase change is likely to proceed, it is preferably linear, which is less susceptible to steric hindrance.

The azobenzene derivative and the stilbene derivative according to the embodiment of the present invention have the above-mentioned alkyl group or alkoxy group. Since the alkyl group and the alkoxy group have thermal mobility, the thermal motion of the alkyl group and the alkoxy group causes the π-π interaction of the azobenzene moiety of the azobenzene derivative and the stilbene moiety of the stilbene derivative to predominate in the periodic structure. It is possible to form a specific crystal structure in which isotropically disordered structures coexist. Therefore, local cis-trans isomerization causes a phase change from solid to liquid or liquid crystal, or phase change from liquid or liquid crystal to solid, and the azobenzene moiety of the azobenzene derivative and the stilbene of the stilbene derivative Since the π-π interaction of the portions is reduced, isotropic melting occurs in a chain throughout the system, so that the above-mentioned phase change is more likely to proceed.

Further, the azobenzene derivative represented by the structural formula (1) and the alkyl group or alkoxy group having 4 to 12 carbon atoms in the groups (R ₁ and R ₆ ) of the stilbene derivative have high thermal motility. Since the alkyl-alkyl interaction between the molecules is relatively weak, cis-trans isomerization is likely to occur, and the above-mentioned phase change is more likely to proceed. As a result, the softening rate due to ultraviolet irradiation is improved, and the curing rate due to visible light irradiation is also improved.

Also, azobenzene derivative represented by the structural formula (1), and groups of stilbene derivative _{(R 2 ~R 5, R 7} ~R 10) are each independently an alkyl group, an alkoxy group, the group consisting of halogen group By substituting with a group selected from, it is possible to generate lattice defects that favor cis-trans isomerization, develop free volumes, reduce π-π interactions, and so on. It will be easier to proceed.

Specifically, the azobenzene derivative is preferably a compound represented by the following structural formulas (2) to (10), which has a structure that favorably acts on cis-trans isomerization, and the stilbene derivative is cis. -It is preferable that the compounds are represented by the following structural formulas (11) to (16) and have a structure that favorably acts on trans isomerization.

The method for synthesizing the azobenzene derivative is not particularly limited, and a conventionally known synthesis method can be applied. For example, in the case of an azobenzene derivative in which R ₁ and R ₆ of the structural formula (1) are alkyl groups, by heating and stirring with manganese dioxide as an oxidizing agent for p-alkylaniline in toluene, 4 , 4'-Dialkylazobenzene can be obtained.

The method for synthesizing the stilbene derivative is not particularly limited, and a conventionally known synthetic method can be applied. For example, in the case of a stilbene derivative in which R ₁ and R ₆ of the structural formula (1) are alkyl groups, by heating and stirring p-alkyl styrene in toluene using a Grubbs catalyst which is an olefin metathesis reaction reagent. , 4,4'-Dialkylstilbene can be obtained.

The content of the azobenzene derivative or the stilbene derivative is preferably 0.5 to 15% by mass, preferably 3.0% by mass or more and 7.0% by mass or less, based on the total mass of the ultraviolet curable ink. More preferably.

By setting the content of the azobenzene derivative or the stilbene derivative to 0.5% by mass or more, the image (cured film obtained by curing the ultraviolet curable ink) has a certain degree of curing, and thus the intermediate transfer product. Since the image flow on the above can be suppressed, a high-definition image can be obtained. Further, by setting the content of the azobenzene derivative or the stilbene derivative to 15% by mass or less, the degree of curing of the image (cured film formed by curing the ultraviolet curable ink) on the intermediate transfer material is high. It is possible to improve the transferability to a recording medium because it suppresses excessive formation.

1-2. Ultraviolet polymerizable compound The ultraviolet curable ink for an inkjet of the present invention contains an ultraviolet polymerizable compound.

The ultraviolet polymerizable compound is a compound that is crosslinked or polymerized by irradiation with ultraviolet rays. In addition, the above examples include cationically polymerizable compounds, radically polymerizable compounds, or mixtures thereof. Among the above, radically polymerizable compounds are preferable. The above may be any of a monomer, a polymerizable oligomer, a prepolymer and a mixture thereof.

The radically polymerizable compound is a compound having an ethylenically unsaturated double bond group in the molecule. The radically polymerizable compound can be a monofunctional or polyfunctional compound. Examples of radically polymerizable compounds include (meth) acrylates, which are unsaturated carboxylic acid ester compounds. In the present invention, "(meth) acrylate" means acrylate or methacrylate, "(meth) acryloyl group" means acryloyl group or metaacryloyl group, and "(meth) acrylic" means acrylic. Or it means 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.

Further, it is preferable that at least a part of the radically polymerizable compound is an ethylene oxide-modified (meth) acrylate compound. This is because the ethylene oxide-modified (meth) acrylate compound is highly photosensitive, and in the case of an ink containing a gelling agent, it is easy to form a cardhouse structure when gelling at a low temperature. Further, since the ethylene oxide-modified (meth) acrylate compound is easily dissolved in other ink components at a high temperature and has less curing shrinkage, curling of printed matter is less likely to occur.

The cationically polymerizable compound is a compound having a cationically polymerizable group in the molecule. Examples of cationically polymerizable compounds include epoxy compounds, vinyl ether compounds, oxetane compounds and the like.

Examples of the above epoxy compounds include 3,4-epoxycyclohexylmethyl-3', 4'-epoxycyclohexanecarboxylate, bis (3,4-epoxycyclohexylmethyl) adipate, vinylcyclohexene monoepoxyside, ε-caprolactone modified 3, 4-Epoxycyclohexylmethyl 3', 4'-epoxycyclohexanecarboxylate, 1-methyl-4- (2-methyloxylanyl) -7-oxabicyclo [4,1,0] heptane, 2- (3,4) -Epoxycyclohexyl-5,5-spiro-3,4-epoxy) Cyclohexanone-meth-dioxane and alicyclic epoxy resins such as bis (2,3-epoxycyclopentyl) ether, diglycidyl ether of 1,4-butanediol , 1,6-Hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, ethylene glycol, propylene glycol, and glycerin. An aliphatic epoxy compound containing polyglycidyl ether, which is a polyether polyol obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to an aliphatic polyhydric alcohol, and bisphenol A or Includes the alkylene oxide adduct di or polyglycidyl ether, hydrogenated bisphenol A or the alkylene oxide adduct di or polyglycidyl ether, and aromatic epoxy compounds including novolak type epoxy resins.

Examples of the vinyl ether compounds include ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexanedimethanol monovinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and isopropenyl. Monovinyl ether compounds including ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether, as well as ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether. , Butanediol divinyl ethers, hexanediol divinyl ethers, cyclohexanedimethanol divinyl ethers, and di or trivinyl ether compounds including trimethylolpropane trivinyl ethers and the like.

Examples of the above oxetane compounds include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-normalbutyloxetane, 3 -Hydroxymethyl-3-phenyloxetane, 3-hydroxymethyl-3-benzyloxetane, 3-hydroxyethyl-3-methyloxetane, 3-hydroxyethyl-3-ethyloxetane, 3-hydroxyethyl-3-propyloxetane, 3 -Hydroxyethyl-3-phenyloxetane, 3-hydroxypropyl-3-methyloxetane, 3-hydroxypropyl-3-ethyloxetane, 3-hydroxypropyl-3-propyloxetane, 3-hydroxypropyl-3-phenyloxetane, 3 -Hydroxybutyl-3-methyloxetane, 1,4 bis {[(3-ethyl-3-oxetanyl) methoxy] methyl} benzene, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane and di [1- Ethyl (3-oxetanyl)] Methyl ether and the like are included.

The content of the ultraviolet polymerizable 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, based on the total mass of the ultraviolet curable ink. preferable.

1-3. Gelling agent The ultraviolet curable ink for an inkjet of the present invention may contain a gelling agent.

The gelling agent is an organic substance that is solid at room temperature but becomes liquid when heated, so that the ultraviolet curable ink can undergo a sol-gel phase transition in response to a temperature change.

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. Here, the "gelling temperature" refers to a temperature at which the ink undergoes a phase transition from the sol to the gel and the viscosity of the ink suddenly changes when the ink that has been solified or liquefied by heating is cooled. Specifically, the solified or liquefied ink is cooled while measuring the viscosity with a rheometer "MCR302" (manufactured by AntonioPaar), and the temperature at which the viscosity rises sharply is defined as the gelation temperature of the ink. can do.

When the gelling agent crystallizes in the ink, a structure may be formed in which the three-dimensional space formed by the gelling agent crystallized in a plate shape is contained (such a structure is referred to as "card" below. House structure "). When the card house structure is formed, the liquid is held in the space, so that the dots formed by landing the ink are less likely to get wet and spread, and the pinning property of the ink is further improved. It is considered that when the pinning property of the ink is improved, it becomes difficult for the dots formed by the ink to land on the recording medium to be united with each other.

Examples of the above gelling agents include dipentadecyl ketone, diheptadecyl ketone, dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dimyristyl ketone, lauryl myristyl ketone, and the like. Aliper ketone compounds such as lauryl palmityl ketone, myristyl palmityl ketone, myristyl stearyl ketone, myristyl behenyl ketone, palmityl stearyl ketone, balmityl behenyl ketone and stearyl behenyl ketone; cetyl palmitate, stearyl stearate, behenyl behenate, Icosyl icosate, behenyl stearate, palmityl stearate, lauryl stearate, stearyl palmitate, myristyl myristate, cetyl myristate, octyldodecyl myristate, stearyl oleate, stearyl erucate, stearyl linoleate, behenyl oleate and linole Aliper ester compounds such as arachidyl acid; amide compounds such as N-lauroyl-L-glutamate dibutylamide, N- (2-ethylhexanoyl) -L-glutamate dibutylamide; 1,3: 2,4-bis-O -Benzilidene-D-Divendilidene sorbitols such as glucitol; petroleum waxes such as paraffin wax, microcrystallin wax, petrolactam; candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and Plant waxes such as jojoba ester; animal waxes such as beeswax, lanolin and whale wax; mineral waxes such as montan wax and hydride wax; hardened castor oil or hardened castor oil derivative; montan wax derivative, paraffin wax derivative, Modified waxes such as microcrystallin wax derivatives or polyethylene wax derivatives; higher fatty acids such as bechenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid; higher alcohols such as stearyl alcohol and behenyl alcohol. Hydroxystearic acid such as 12-hydroxystearic acid; 12-hydroxystearic acid derivative; lauric acid amide, stearic acid amide, bechenic acid amide, oleic acid amide, erucic acid amide, ricinolic acid amide, 12-hydroxystearic acid amide and the like. Fatty acid amides; N-stearyl stealic acid amides, N-olei N-substituted fatty acid amides such as lupalmitic acid amide; specials such as N, N'-ethylenebisstearylamide, N, N'-ethylenebis-12-hydroxystearylamide, and N, N'-xylylene bisstearylamide. Fatty acid amides; higher amines such as dodecylamine, tetradecylamine or octadecylamine; stearyl stearic acid, oleyl palmitic acid, glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, polyoxyethylene fatty acid esters, etc. Fatty acid ester compound; sucrose fatty acid ester such as sucrose stearic acid and sucrose palmitic acid; synthetic wax such as polyethylene wax and α-olefin maleic anhydride copolymer wax; polymerizable wax; dimer acid; dimer diol and the like Is done. Only one type of these waxes may be used alone, or two or more types may be used in combination.

The content of the gelling agent is preferably 0.01% by mass or more and 7.0% by mass or less with respect to the total mass of the ink, and 0.2% by mass or more and 6.8% by mass with respect to the total mass of the ink. More preferably, it is less than%. By setting the content of the gelling agent within the above range, the pinning property of the ink can be sufficiently enhanced and a higher definition image can be formed.

1-4. Polymerization Initiator The UV curable ink may further contain a polymerization initiator, if necessary. The above-mentioned polymerizable initiator may be any one capable of initiating the above-mentioned polymerization. For example, when the UV curable ink has a radically polymerizable compound, the polymerization initiator can be a photoradical initiator, and when the UV curable ink has a cationically polymerizable compound, the polymerization initiator is It can be a photocation initiator (photoacid generator).

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, benzyldimethylketal, 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. Benzyls including phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide and the like, acylphosphine oxide-based initiators, and benzyl and methylphenylglycoesters are included.

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.

Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include diazonium, ammonium, iodonium, sulfonium, and phosphonium and aromatic onium compound containing ^{_{B (C 6 F 5) 4}} -, PF 6 -, AsF 6 -, SbF 6 -, CF Includes sulfonates that generate sulfonic acids, halides that photogenerate hydrogen halides, such as ₃ SO ₃ ^- salts, and iron allen complexes.

The content of the polymerization initiator can be arbitrarily set as long as the ultraviolet curable ink is sufficiently cured by irradiation with ultraviolet rays and the ejection property of the ultraviolet curable ink is not deteriorated. For example, the content of the polymerization initiator is preferably 0.1% by mass or more and 20% by mass or less, and 1.0% by mass or more and 12% by mass or less, based on the total mass of the ultraviolet curable ink. Is more preferable.

1-5. Color material Color material includes pigments and dyes. The coloring material is preferably a pigment from the viewpoint of improving the dispersion stability of the ink and forming an image having high weather resistance.

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, 26, and 28.

Examples of dyes include various oil-soluble dyes.

The content of the pigment or dye is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.4% by mass or more and 10% by mass or less with respect to the total mass of the ink. When the content of the pigment or dye is 0.1% by mass or more with respect to the total mass of the ink, the color development of the obtained image is sufficient. When the content of the pigment or dye 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.

1-6. Dispersant The pigment may be dispersed with a dispersant.

Examples of the dispersant include a surfactant and a polymer dispersant, but a polymer dispersant is preferable.

Examples of polymer dispersants include (meth) acrylic resins, styrene- (meth) acrylic resins, hydroxyl group-containing carboxylic acid esters, long-chain polyaminoamide and high-molecular-weight acid esters salts, and high-molecular-weight polycarboxylic acid salts. , Salt of long-chain polyaminoamide and polar acid ester, high molecular weight unsaturated acid ester, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate Includes salts, polyoxyethylene alkyl phosphates, polyoxyethylene nonylphenyl ethers, stearylamine acetates, pigment derivatives and the like.

The pigment may be further enhanced in dispersibility by a dispersion aid, if necessary.

The content of the dispersant is preferably 10% by mass or more and 200% by mass or less with respect to the total mass of the pigment. When the content of the dispersant is 10% by mass or more with respect to the total mass of the pigment, the dispersion stability of the pigment is enhanced, and when the content of the dispersant is 200% by mass or less with respect to the total mass of the pigment. The ink ejection property from the inkjet head is easily stabilized.

1-7. Polymerization inhibitor The UV curable ink may contain a polymerization inhibitor.

Examples of the polymerization inhibitor 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 are included.

1-8. Other components The ultraviolet curable ink may further contain other components, if necessary. Other components may be photoacid generators, various additives, other resins and the like. Examples of additives include surfactants, leveling additives, matting agents, infrared absorbers, antibacterial agents, basic compounds for enhancing the storage stability of inks, and the like. Examples of basic compounds include basic alkali metal compounds, basic alkaline earth metal compounds, basic organic compounds such as amines, and the like. Examples of other resins include resins for adjusting the physical properties of cured films such as polyester-based resins, polyurethane-based resins, vinyl-based resins, acrylic-based resins, and rubber-based resins.

1-9. Physical Properties of UV Curable Ink The UV curable ink of the present invention has a viscosity of 3 mPa · s or more and 20 mPa · s or less at the temperature of the inkjet head at the time of ejection from the viewpoint of further improving the ejection property from the inkjet head. preferable. For example, the temperature of the inkjet head can be about 50 ° C. when the UV curable ink does not contain a gelling agent, and about 80 ° C. when the UV curable ink contains a gelling agent. can do.

1-10. Ink Preparation Method The ultraviolet curable ink can be prepared by mixing the above-mentioned azobenzene derivative or stilbene derivative with any other component under heating. At this time, it is preferable to filter the obtained mixed solution with a predetermined filter.

When preparing an ink containing a pigment, it is preferable to prepare a pigment dispersion liquid containing the pigment, and then mix the pigment dispersion liquid with other components. The pigment dispersion may further contain a dispersant.

The pigment dispersion liquid can be prepared by dispersing the pigment. The pigment may be dispersed by using, 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. At this time, a dispersant may be added.

2. 2. Image Forming Method The image forming method according to the embodiment of the present invention is an image forming method using the above-mentioned ultraviolet curable ink for inkjet. Specifically, a step of ejecting a droplet of the above-mentioned ultraviolet curable ink for inkjet from an inkjet head and landing it on the surface of the intermediate transfer body to form an image on the surface of the intermediate transfer body. The first light irradiation step in which the integrated light amount of light of 300 nm or more and less than 400 nm to irradiate the image is 100 to 1000 mJ / cm ² , the step of transferring the image to a recording medium, and the image transferred to the recording medium. This is an image forming method comprising a second light irradiation step in which the integrated light amount of light of 400 nm or more and 800 nm or less to be irradiated to is 100 to 1000 mJ / cm ² .

In the step of ejecting the ultraviolet curable ink and landing it on the surface of the intermediate transfer body, the above-mentioned ultraviolet curable ink is ejected from the inkjet head.

When a plurality of types of UV-curable ink droplets having different compositions (for example, types or amounts of coloring materials) are ejected and landed to form a multicolor image, the plurality of types of UV-curable inks are formed. At least one type of mold ink is the above-mentioned ultraviolet curable ink. In addition, two or more of the ultraviolet curable inks to be ejected are the ultraviolet curable inks (droplets of a plurality of types of the ultraviolet curable inks having different compositions are ejected and land on the recording medium. ) Is preferable. From the above viewpoint, it is more preferable that all of the ultraviolet curable inks to be ejected are the ultraviolet curable inks.

The inkjet head may be either an on-demand type or a continuous type. Examples of on-demand inkjet heads include electro-mechanical conversion methods including single cavity type, double cavity type, bender type, piston type, shared mode type and shared wall type, and thermal inkjet type and bubble jet ( Bubble jet includes an electric-heat conversion method including a registered trademark of Canon Inc.).

Further, the inkjet head may be either a scan type or a line type inkjet head.

At this time, in order to improve the ejection property of the ink droplets, the ultraviolet curable ink in the inkjet head is heated to 40 to 120 ° C., and the heated ultraviolet curable ink is ejected. From the viewpoint of ejection stability, the viscosity of the ultraviolet curable ink is preferably 3 mPa · s or more and less than 20 mPa · s at the temperature inside the inkjet head.

When the UV curable ink for inkjet contains a gelling agent, the temperature of the UV curable ink in the inkjet head is set to a temperature 10 ° C or higher and lower than 40 ° C higher than the gelation temperature of the UV curable ink. It is preferable to do so. By setting the temperature of the UV curable ink in the inkjet head to the gelation temperature + 10 ° C or higher, the UV curable ink does not gel in the inkjet head or on the nozzle surface, and the UV curable ink is ejected satisfactorily. be able to. Further, by setting the temperature of the ultraviolet curable ink in the inkjet head to less than the gelation temperature of the ultraviolet curable ink + 40 ° C., the thermal load on the inkjet head can be reduced. In particular, in an inkjet head using a piezo element, performance deterioration is likely to occur due to a thermal load, so it is particularly preferable to keep the temperature of the ultraviolet curable ink within the above range.

The ejected ultraviolet curable ink is landed on the surface of the intermediate transfer body.

The intermediate transfer material is a benzene ring such as aromatic polyimide (PI), aromatic polyamideimide (PAI), polyphenylene sulfide (PPS), aromatic polyetheretherketone (PEEK), aromatic polycarbonate, and aromatic polyetherketone. It has a substrate layer containing a resin having a structural unit containing, a polyvinylidene fluoride, and a mixture or copolymer thereof. In addition to the base material layer, the intermediate transfer material has rubber, elastomer and elasticity such as silicone rubber (SR), chloropun rubber (CR), nitrile rubber (NBR) and epichlorohydrin rubber (ECO) on the landing surface side of the ink. An elastic layer containing a resin or the like and / or a surface layer containing a fluororesin such as polytetrafluoroethylene (PTFE), perfluoroalkoxy alkane (PFA), and polyvinylidene fluoride (PVDF) and an acrylic resin. May have.

Alternatively, the intermediate transfer material is polyethylene terephthalate (PET) film, 1,4-polycyclohexylene methylene terephthalate film, polyethylene naphthalate (PEN) film, polyphenylene sulfide film, polystyrene (PS) film, polypropylene (PP) film. , Polysalphon film, aramid film, polycarbonate film, polyvinyl alcohol film, polyethylene (PE) film, polyvinyl chloride film, nylon film, polyimide film, and resin films such as ionomer films, and cellulose derivatives such as cellophane and cellulose acetate. You may be.

When the ultraviolet curable ink for inkjet contains a gelling agent, the ultraviolet curable ink that has landed on the surface of the intermediate transfer body is pinned by crystallizing the gelling agent. As a result, the dots formed by landing the ink are less likely to get wet and spread, and the dots formed by landing the ink on the surface of the intermediate transfer body are prevented from coalescing.

At this time, in order to improve the pinning property of the ink, the surface temperature of the intermediate transfer material may be set to be near or lower than the gelling temperature of the gelling agent.

In the first light irradiation step of irradiating the ultraviolet rays of the present invention, the integrated light amount of the ultraviolet rays of 300 nm or more and less than 400 nm irradiated to the image formed on the surface of the intermediate transfer body is 100 to 1000 mJ / cm ² , and the ultraviolet rays. By polymerizing and cross-linking the ultraviolet polymerizable compound contained in the curable ink and isomerizing the azobenzene derivative or stillben derivative contained in the ultraviolet curable ink from the trans form to the cis form, the phase changes from solid to liquid or liquid crystal. By changing, the image formed on the surface of the intermediate transfer body (the cured film formed by curing the ultraviolet curable ink) is softened. The integrated light amount can be determined by ultraviolet intensity (mW / cm ² ) × curing time (sec).

From the viewpoint of suppressing the occurrence of curing failure of the ultraviolet curable ink due to the melting of the ultraviolet curable ink by the radiant heat of the light source, the ultraviolet light source is preferably a light emitting diode (LED). Examples of LED light sources capable of irradiating active rays to cure UV curable inks are 395 nm, water-cooled LEDs, Phoseon Technology, Heraeus, Kyocera, HOYA, and Integration. Included from Technology.

From the viewpoint of sufficiently polymerizing and cross-linking the energy of ultraviolet rays and isomerizing the azobenzene derivative or stilbene derivative contained in the above-mentioned ultraviolet curable ink, the integrated light amount of ultraviolet rays of 300 nm or more and less than 400 nm irradiating the image is 100. is preferably to 1000 mJ / cm ^2, and more preferably 250 mJ / cm ² or more 500 mJ / cm ² or less. By setting the integrated light amount of the ultraviolet rays to 100 mJ / cm ² or more, the ultraviolet-polymerizable compound can be polymerized and crosslinked, and the azobenzene derivative or the stillben derivative is phase-changed from a solid to a liquid or a liquid crystal to obtain an image ( A cured film formed by curing an ultraviolet curable ink) can be softened. Thereby, the transferability from the intermediate transfer body to the recording medium can be improved. Further, since the image has a certain degree of hardening, it is possible to move to the transfer step without causing image flow on the intermediate transfer body, so that a high-definition image can be obtained.

Further, by setting the integrated light intensity of the ultraviolet rays to 1000 mJ / cm ² or less, deterioration and yellowing of the pigment and the ultraviolet polymerizable compound can be suppressed.

Further, in the step of irradiating the ultraviolet rays, the ultraviolet rays may be irradiated in an atmosphere having an oxygen concentration of 0.1% by volume or more and 10.0% by volume or less. By irradiating ultraviolet rays in an atmosphere having a low oxygen concentration, curing inhibition due to oxygen in the atmosphere is less likely to occur, and the curing sensitivity of the ultraviolet curable ink for an inkjet can be further increased.

The step of transferring the image to the recording medium further includes a step of pressurizing the image formed on the surface of the intermediate transfer body with a pressurizing member. When pressurizing the image, the temperature of the pressurizing member is preferably 20 ° C. or higher and 90 ° C. or lower, and more preferably 20 ° C. or higher and 80 ° C. or lower. By setting the temperature of the pressure member in the above range, the transferability can be improved even when the glass transition point (Tg) of the above image (cured film obtained by curing the ultraviolet curable ink) is higher than room temperature. The image can be transferred from the intermediate transfer body to the recording medium without deterioration.

In the second light irradiation step of irradiating light, the integrated light amount of light (visible light) of 400 nm or more and 800 nm or less to irradiate the image transferred on the recording medium is 100 to 1000 mJ / cm ² , and the light (visible). (Light rays) are irradiated to solidify the above image (cured film formed by curing ultraviolet curable ink).

Further, from the viewpoint of changing the phase of the azobenzene derivative or stillben derivative contained in the above-mentioned ultraviolet curable ink from a liquid or liquid crystal to a solid, an image transferred to the above recording medium (a cured film obtained by curing the ultraviolet curable ink). irradiating the integral light volume of 400nm or 800nm or less of the light (visible light) is preferably from 100~1000mJ / cm ^2, and more preferably 200 mJ / cm ² or more 800 mJ / cm ² or less. By setting the integrated light intensity of the visible light to 100 mJ / cm ² or more, the phase change of the azobenzene derivative or the stilbene derivative can be rapidly advanced. Further, by setting the integrated light amount of the visible light to 1000 mJ / cm ² or less, deterioration and yellowing of the pigment and the ultraviolet polymerizable compound can be suppressed.

In the image forming method, the ultraviolet curable ink for inkjet is landed on the intermediate transfer body, and the ultraviolet curable ink applied to the intermediate transfer body is irradiated with ultraviolet rays to form an image, and then the image is formed. The method of transferring an image to a recording medium and irradiating the transferred image with visible light has been described, but the method is not limited thereto. For example, the ultraviolet curable ink for an inkjet may be directly landed on the surface of a recording medium, and the recording medium may be irradiated with ultraviolet rays and visible light to form an image. The recording medium may be any medium capable of forming an image, and is, for example, an absorbent paper including art paper, coated paper, lightweight coated paper, finely coated paper and cast paper, and non-coated paper. Non-absorbable recording media composed of media, polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate and plastics including polybutadiene terephthalate, and Non-absorbable inorganic recording media such as metals and glass can be used.

3. 3. Image forming apparatus FIG. 1 is a schematic view showing an exemplary configuration of an image forming apparatus 100 for an inkjet according to an embodiment of the present invention.

The image forming apparatus 100 of the present invention conveys an ink ejection unit that ejects ultraviolet curable ink for inkjet and a recording medium 110 that lands the ejected ultraviolet curable ink for inkjet from the inkjet head 140. UV curing is performed on the surface of the intermediate transfer body 120, which is arranged so as to face the transport path 130 for landing the ultraviolet curable ink on the surface of the intermediate transfer body 120 and the surface on which the recording medium 110 of the transport path 130 is transported. An intermediate image forming unit 141 that applies mold ink to form an intermediate image, a first light irradiation unit 150 that irradiates the formed intermediate image with ultraviolet rays, and an intermediate image containing ultraviolet curable ink are transferred to a recording medium 110. The transfer unit 160, the pressure unit 161 that pressurizes the intermediate image by the transfer unit 160, the three support rollers 170, 171 and 172 that stretch the intermediate transfer body 120 having the shape of an endless belt, and the recording medium 110. The second light irradiation unit 180 that irradiates the intermediate image transferred to the image with visible light, and the ultraviolet curable ink that remains on the surface of the intermediate transfer body 120 without being transferred to the recording medium 110 are removed from the surface of the intermediate transfer body 120. It has a cleaning unit 190 and a cleaning unit 190.

The transport path 130 is composed of, for example, a metal drum, and transports a recording medium 110 on which an intermediate image is transferred. The transport path 130 is arranged in contact with a part of the surface of the intermediate transfer body 120, and the contacting surface of the intermediate transfer body 120 is pressed by the pressurizing portion 161 to form a transfer nip. The transport path 130 may have a claw (not shown) for fixing the tip of the recording medium 110. The transport path 130 transports the recording medium 110 to the transfer nip by fixing the tip of the recording medium 110 to the claw and rotating it in the counterclockwise direction in FIG.

The intermediate transfer body 120 has three support rollers 170, 171 and 172. The intermediate transfer body 120 is composed of an endless belt, is stretched in an inverted triangular shape by three support rollers 170, 171 and 172, and the intermediate image forming unit 141 transfers the intermediate image formed on the surface of the intermediate transfer body 120. Transport to section 160.

Of the three support rollers 170, 171 and 172, at least one roller is a drive roller, which rotates the intermediate transfer body 120 in the A direction.

The intermediate transfer material 120 is a benzene such as aromatic polyimide (PI), aromatic polyamideimide (PAI), polyphenylene sulfide (PPS), aromatic polyetheretherketone (PEEK), aromatic polycarbonate, and aromatic polyetherketone. It has a substrate layer containing a resin having a structural unit containing a ring, polyvinylidene fluoride, and a mixture or copolymer thereof. In addition to the base material layer, the intermediate transfer material 120 has a rubber, elastomer and elastic resin such as silicone rubber (SR), chloropun rubber (CR), nitrile rubber (NBR) and epichlorohydrin rubber (ECO) on the landing surface side of the ink. It has an elastic layer containing such as, and a surface layer containing a fluororesin such as polytetrafluoroethylene (PTFE), perfluoroalkoxy alkane (PFA), and polyvinylidene fluoride (PVDF) and an acrylic resin, or any of the above. You may.

Alternatively, the intermediate transfer member 120 may be a polyethylene terephthalate (PET) film, a 1,4-polycyclohexylene methylene terephthalate film, a polyethylene naphthalate (PEN) film, a polyphenylene sulfide film, a polystyrene (PS) film, or a polypropylene (PP). Formed from resin films such as films, polysulfone films, aramid films, polycarbonate films, polyvinyl alcohol films, polyethylene (PE) films, polyvinyl chloride films, nylon films, polyimide films, and ionomer films, and cellulose derivatives such as cellophane and cellulose acetate. It may have been done.

The portions of the intermediate transfer body 120 stretched on the support rollers 170 and 171 located at the left and right apex portions of the inverted triangle shape are the landing surfaces of the inks ejected from the respective inkjet heads. The support roller 172 (pressurizing portion 161) located at the lower apex of the inverted triangular shape of the intermediate transfer body 120 pressurizes the intermediate transfer body 120 toward the transport path 130 by a predetermined nip pressure. It functions as a pressurizing unit that transfers an intermediate image formed by landing the ink ejected from each inkjet head to the recording medium 110.

The intermediate image forming unit 141, which is also an ink ejection unit, is an ink applying unit that forms an intermediate image by an inkjet method, and is an ultraviolet ray of each color of Y (yellow), M (magenta), C (cyan), and K (black), respectively. It has inkjet heads 140Y, 140M, 140C and 140K that eject curable ink from a nozzle and land on the surface of the intermediate transfer member 120. The inkjet heads 140Y, 140M, 140C and 140K land the ultraviolet curable inks of the above colors at positions on the surface of the intermediate transfer member 120 according to the image to be formed to form an intermediate image.

The first light irradiation unit 150 is arranged on the downstream side of the intermediate image forming unit 141, and irradiates the surface of the transport path 130 with ultraviolet rays. As a result, the first light irradiation unit 150 irradiates the image formed on the intermediate transfer body with ultraviolet rays to polymerize and crosslink the ultraviolet polymerizable compounds contained in the ultraviolet curable ink constituting the image, and azobenzene. Derivatives or stylben derivatives are phase-changed from solid to liquid or liquid crystal. As a result, an image transferable to a recording medium is formed on the surface of the intermediate transfer body 120.

The transfer unit 160 is a portion including a transfer nip in which the intermediate transfer body 120 and the transfer path 130 are closest to each other, and the intermediate transfer body 120 is urged in the direction of the transfer path 130 by the pressurizing unit 161. The surface of the transport path 130 in contact with the intermediate transfer body 120 is pressurized by the pressurizing unit 161. The image formed on the surface of the intermediate transfer body 120 and conveyed and the recording medium 110 arranged on the surface of the transfer path 130 and conveyed are brought into contact with each other at the transfer nip and are intermediate via the pressurizing unit 161. By applying pressure from the transfer body 120 to the transport path 130 side, the image is transferred to the recording medium.

The second light irradiation unit 180 is arranged on the downstream side of the transfer unit 160 in the transfer direction of the recording medium 110 by the transfer path 130, and irradiates the active line toward the surface of the transfer path 130. As a result, the second light irradiation unit 180 irradiates the image transferred to the recording medium 110 (a cured film formed by curing the ultraviolet curable ink) with visible light to release the azobenzene derivative or the stillben derivative from the liquid or liquid crystal. The phase is changed to a solid to solidify the image (cured film formed by curing the ultraviolet curable ink). As a result, the image is fixed on the surface of the recording medium 110.

The cleaning unit 190 is a cleaning roller such as a web roller or a sponge roller, and comes into contact with the surface of the intermediate transfer body 120 on the downstream side of the transfer unit 160. The cleaning unit 190 removes the residual ink (residual coating material) remaining on the surface of the intermediate transfer body 120 without being transferred to the recording medium 110 in the transfer unit 160 by driving and rotating the cleaning roller.

Although not shown, the image forming apparatus 100 may have a temperature adjusting unit that adjusts the surface temperature of the intermediate transfer body 120 at the position where the ink lands to 60 ° C. or lower.

Further, although not shown, the image forming apparatus 100 may have an oxygen concentration adjusting unit capable of adjusting the oxygen concentration of the atmosphere to a desired value of 0.1% by volume or more and 10% by volume or less.

Further, although the image forming apparatus having the intermediate transfer body has been described in the above description, the image forming apparatus of the present invention does not have the intermediate transfer body and conveys the ultraviolet curable ink ejected from the ink ejection portion along the conveying path. It may be configured to land directly on the recording medium to be printed.

The present invention will be described in more detail with reference to the following tests, but the present invention is not limited to the following tests.

1-1. Synthesis of azobenzene derivatives 1-1-1. Synthesis of Compound 1 To 4-butylaniline (1.5 g, 10 mmol), 100 mL of toluene and active manganese dioxide (3.0 g, 35 mmol) were added, and the mixture was stirred at 120 ° C. for 8 hours. The solvent was distilled off under reduced pressure, the mixture was extracted with ethyl acetate, the organic layer was washed with saturated brine, and dried over anhydrous magnesium sulfate. After filtering this, the solvent was distilled off under reduced pressure, and the obtained solid was purified by silica gel column chromatography using a mixed solution of ethyl acetate and hexane as a developing solvent. Then, the solvent was removed to obtain Compound 1 represented by the following structural formula (2).

1-1-2. Synthesis of Compound 2 Similar to Compound 1, except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-butoxyaniline (1.7 g, 10 mmol), which is represented by the following structural formula (3). Compound 2 was obtained.

1-1-3. Synthesis of Compound 3 Similar to Compound 1, except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-hexylaniline (1.8 g, 10 mmol), which is represented by the following structural formula (4). Compound 3 was obtained.

1-1-4. Synthesis of Compound 4 In the same manner as Compound 1, except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-hexyloxyaniline (1.9 g, 10 mmol), it is represented by the following structural formula (5). Compound 4 was obtained.

1-1-5. Synthesis of Compound 5 Similar to Compound 1, except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-octylaniline (2.1 g, 10 mmol), which is represented by the following structural formula (6). Compound 5 was obtained.

1-1-6. Synthesis of Compound 6 4-Butylaniline (1.5 g, 10 mmol) is changed to 4-octyloxyaniline (2.2 g, 10 mmol) in the same manner as in Compound 1, and is represented by the following structural formula (7). Compound 6 was obtained.

1-1-7. Synthesis of Compound 7 After adding 75 mL of 2.4N hydrochloric acid to 4-aminophenol (6.54 g, 60 mmol), sodium nitrite (4.98 g, 72 mmol) was dissolved in 6 mL of distilled water with stirring at 0 ° C. The solution was added and stirred at 0 ° C. for 60 minutes. A mixed solution of o-cresol (6.48 g, 60 mmol) and 24 mL of a 20% aqueous sodium hydroxide solution was added to the above solution, and the mixture was stirred for 20 hours. The precipitated precipitate was filtered and washed with water to give a pale yellow solid. The obtained solid was purified by silica gel column chromatography using a mixed solution of ethyl acetate and hexane as a developing solvent, and then recrystallized from a mixed solvent of acetone and hexane to obtain Intermediate A. DMF 100 mL, 1-bromohexane (9.9 g, 60 mmol) and potassium carbonate (6.9 g, 50 mmol) were added to the intermediate A (2.28 g, 10 mmol), and the mixture was stirred at 80 ° C. for 2 hours and then 20 at room temperature. Stirred for hours. The solvent was distilled off under reduced pressure, the mixture was extracted with ethyl acetate, the organic layer was washed with saturated brine, and dried over anhydrous magnesium sulfate. After filtering the organic layer, the solvent was distilled off under reduced pressure, and the obtained solid substance was purified by silica gel column chromatography using a mixed solution of ethyl acetate and hexane as a developing solvent to obtain the following structural formula (8). The represented compound 7 was obtained.

1-1-8. Synthesis of Compound 8 A compound represented by the following structural formula (9) in the same manner as Compound 7 except that o-cresol (6.48 g, 60 mmol) was changed to 2-bromophenol (10.4 g, 60 mmol). I got 8.

1-1-9. Synthesis of Compound 9 After adding 70 mL of DMF to tris (dibenzylideneacetone) dipalladium (0.46 g, 0.5 mmol), 2-di-tert-butylphosphino-2'was stirred under a nitrogen atmosphere at room temperature. , 4', 6'-triisopropylbiphenyl (0.85 g, 2 mmol) was added, and the mixture was stirred at room temperature for 10 minutes. Compound 8 (2.3 g, 5 mmol), methanol (0.80 g, 25 mmol) and cesium carbonate (8.15 g, 25 mmol) were added to this solution, and the mixture was stirred at 80 ° C. for 6 hours under a nitrogen atmosphere. The solvent was distilled off under reduced pressure, the mixture was extracted with ethyl acetate, the organic layer was washed with saturated brine, and dried over anhydrous magnesium sulfate. After filtering the organic layer, the solvent was distilled off under reduced pressure, and the obtained solid substance was purified by silica gel column chromatography using a mixed solution of ethyl acetate and hexane as a developing solvent to obtain the following structural formula (10). Compound 9 represented was obtained.

1-2. Synthesis of stilbene derivatives 1-2-1. Synthesis of Compound 10 Nickel iodide hydrate (0.53 g, 1.3 mmol) in 1,3-dimethylpropylene urea, 4,4'-dimethitoxy 2,2''-bipyridine (0.3 g, 1.3 mmol) , Sodium iodide (1.2 g, 8.3 mmol), 4,4'-dibromostilben (8.6 g, 25.5 mmol), pyridine (0.1 mL, 1.3 mmol), 1-bromobutane (3.8 g, 28.0 mmol) was added and stirred at 60 ° C. for 30 minutes, zinc powder (3.4 g, 52.0 mmol) was added, and the mixture was further stirred for 15 minutes. The reaction mixture was cooled, filtered through Celite, and the organic layer was washed with saturated aqueous ammonium chloride solution and then saturated brine, and dried over anhydrous magnesium sulfate. After filtering the organic layer, the solvent was distilled off under reduced pressure, and the obtained solid substance was purified by silica gel column chromatography using a mixed solution of ethyl acetate and hexane as a developing solvent to obtain the following structural formula (11). The represented compound 10 was obtained.

1-2-2. Synthesis of Compound 11 In the same manner as in Compound 10, except that 1-bromobutane (3.8 g, 28.0 mmol) was changed to 1-butanol (2.1 g, 28.0 mmol), it is represented by the following structural formula (12). Compound 11 was obtained.

1-2-3. Synthesis of Compound 12 Similar to Compound 10, except that 1-bromobutane (3.8 g, 28.0 mmol) was changed to 1-bromohexane (4.6 g, 28.0 mmol), using the following structural formula (13). Compound 12 represented was obtained.

1-2-4. Synthesis of Compound 13 In the same manner as in Compound 9, except that 1-bromobutane (3.8 g, 28.0 mmol) was changed to 1-hexanol (2.9 g, 28.0 mmol), it is represented by the following structural formula (14). Compound 13 was obtained.

1-2-5. Synthesis of Compound 14 Similar to Compound 10, except that 1-bromobutane (3.8 g, 28.0 mmol) was changed to 1-bromooctane (5.4 g, 28.0 mmol), using the following structural formula (15). Compound 14 represented was obtained.

1-2-6. Synthesis of Compound 15 In the same manner as Derivative 11, except that 1-bromobutane (3.8 g, 28.0 mmol) was changed to 1-octanol (3.6 g, 28.0 mmol), it is represented by the following structural formula (16). Compound 15 was obtained.

1-3. Other Compounds As compounds other than the above derivatives 1 to 15, a commercially available compound 16 (4-cyano-4'-hexylbiphenyl, manufactured by Tokyo Chemical Industry Co., Ltd.) represented by the following structural formula (17) was obtained.

In addition, compound 17 represented by the following structural formula (18) is a dialkyne compound obtained by converting 2,2': 5', 2''-terthiophene-5,5''-dicarboxyaldehyde by Corey-Fuchs alkyneization reaction. Then, a sonogashira coupling with 2-bromo-5-hexylthiophene could be performed.

1-4. Ink preparation 1-4-1. Preparation of Pigment Dispersion Solution Cyan pigment "Lionol Blue FG-7400-G" (manufactured by Toyo Color Co., Ltd.) (20 parts by mass) and dispersant "BYKJET-9151" (manufactured by BYK, "BYKJET" are registered trademarks of the same company. ) (6.5 parts by mass), (polyethylene glycol # 400 diacrylate) (73.2 parts by mass), and a photopolymerization inhibitor "IrgastabUV10" (manufactured by BASF, "Irgastab" is a registered trademark of the same company) (0) .3 parts by mass) and 0.3 mm zirconia beads "YTZ ball" (manufactured by Nikkato Co., Ltd.) were placed in a 100 mL plastic container, dispersed in a paint shaker for 3 hours, then the zirconia beads were removed and the pigment was removed. A dispersion was obtained.

1-4-2. Preparation of Ink The above pigment dispersion (10.0% by mass), polyethylene glycol # 400 diacrylate (38.9% by mass), 4EO-modified pentaerythritol tetraacrylate (25.0% by mass), and 3PO-modified trimethylolpropane. Propanetriacrylate (15.0% by mass), photoinitiator "IRGACURE819" (BASF, "Irgacare" is a registered trademark of the company) (6.0% by mass), and compound 1 (5.0% by mass). And IrgastabUV10 (0.1% by mass) were added, and the mixture was stirred at 105 ° C. for 45 minutes and then filtered with a 3 μm membrane filter (Teflon (registered trademark) manufactured by ADVANTEC) to obtain ink 1.

Table 1 shows the contents of inks 1 to 10, Table 2 shows the contents of inks 11 to 19, and Table 3 shows the contents (unit: parts by mass) of inks 20 to 24.

The abbreviations shown in Tables 1 to 3 are as follows.
PEG400DA: Polyethylene glycol # 400 diacrylate 4EO-PETTA: 4EO modified pentaerythritol tetraacrylate TMP (PO) 3TA: 3PO modified trimethylolpropane triacrylate 819: Irgacure 819
UV10: Irgastab UV10

2. 2. Image formation evaluation Transferability and image quality were evaluated using the prepared inks 1 to 24.

(Image formation method)
Inks 1 to 24 were introduced into an inkjet recording device (KM512MHX, manufactured by Konica Minolta) having an inkjet recording head equipped with a piezo type inkjet nozzle, and the resolution was 720 with respect to an intermediate transfer body at 25 ° C. using a Perche cooling unit. A solid image (100% printing) was printed under the condition of × 720 dpi. The above solid image is irradiated with ultraviolet rays of 395 nm at a cumulative total of 350 mJ / cm ² , and then the intermediate transfer material is heated to 50 ° C. with a Perche heating unit, and printing coated paper (OK top coat, paper density). Pressure transfer was performed on 128 g / m ² , manufactured by Oji Paper Co., Ltd.).

2-1. Evaluation of transferability The amount of ink ejected (μg) used during image formation is calculated from the weight increase of the recording medium (μg) and the weight of the transfer residue on the intermediate transfer medium (μg), and the weight of the recording medium is increased. The transfer rate (%) was calculated from the minutes / weight of the ejected ink. In addition, △ or more is regarded as a pass.

(Evaluation criteria)
⊚: Transfer rate 95% or more ○: Transfer rate 90 or more and less than 95% Δ: Transfer rate 80 or more and less than 90% ×: Transfer rate less than 80%

2-2. Image quality evaluation (image formation method)
(Evaluation method)
A solid image of 5 cm × 5 cm obtained by the above image forming method was visually evaluated to evaluate density unevenness. In addition, △ or more is regarded as a pass.

(Evaluation criteria)
⊚: No density unevenness is observed in the image when observed from a position 5 cm away ○: No density unevenness is observed in the image when observed from a position 15 cm away Δ: When observed from a position 15 cm away, the image Density unevenness is observed in some parts, but no density unevenness is observed from a position 30 cm away. ×: Density unevenness is observed in the image when observed from a position 30 cm away.

2-3. Set-off property evaluation (image formation method)
(Evaluation method)
A printing coated paper A (OK top coat, rice basis weight 128 g / m ² , manufactured by Oji Paper Co., Ltd.) is placed on the 5 cm × 5 cm solid image obtained by the above image forming method, and the weight of 800 kPa / cm ² is changed. The set-off property was evaluated. In addition, △ or more is regarded as a pass.

(Evaluation criteria)
⊚: No coloring is observed on the printing coated paper A when observed from a position 5 cm away ○: No coloring is observed on the printing coated paper A when observed from a position 20 cm away Δ: 50 cm away position No coloring is observed on the printing coated paper A when observed. ×: Coloring is observed on the printing coated paper A when observed from a position 50 cm away.

The results of each evaluation are shown in Table 4.

Compared with the inks 23 and 24 containing the compounds 16 and 17 that do not cause a phase change, the transferability is improved by using the inks 1 to 21 containing the azobenzene derivative or the stilbene derivative as the constituent components of the ultraviolet curable ink. It was possible to form a high-definition image. This is because the azobenzene derivative or stilbene derivative contained in the ultraviolet curable ink undergoes a phase change from a solid to a liquid or liquid crystal when irradiated with ultraviolet rays, and the image (curing obtained by curing the ultraviolet curable ink). Since the film) was softened, it is considered that the transferability to the recording medium was improved. In addition, since the degree of curing of the image (cured film obtained by curing the ultraviolet curable ink) does not become too high by containing the azobenzene derivative or the stilbene derivative, it is necessary to irradiate the image with ultraviolet rays before transfer to the recording medium. Can be done. As a result, the image flow on the intermediate transfer body can be suppressed, and it is considered that a high-definition image can be obtained.

Further, as shown in inks 1 to 15, 20 and 21, an azobenzene derivative having a linear alkyl group or alkoxy group having 4 to 8 carbon atoms in R ₁ and R _{6 represented} by the structural formula (1) or When the stilbene derivative was used, the transferability was good and a high-definition image could be formed. It is considered that this is because the carbon chain has a relatively short carbon number of 4 to 8 and is linear, so that it is not easily affected by steric hindrance and the phase change is likely to proceed. Further, an alkyl group or an alkoxy group having 4 to 8 carbon atoms has high thermal motility, but the alkyl-alkyl interaction between molecules is relatively weak, so that cis-trans isomerization proceeds more. It is considered that this is because it becomes easier and the softening rate by irradiation with ultraviolet rays is improved. In addition, since the curing speed by visible light is also improved, blocking can be suppressed.

Further, by setting the azobenzene derivative or the stilbene derivative to 0.1% by mass or more and 20% by mass or less with respect to the total mass of the ultraviolet curable ink, transferability is good and a high-definition image can be formed. did it. In particular, when the content was 5.0% by mass to 10% by mass, the transferability was good. This is suitable for transferring the degree of curing of the image (cured film formed by curing the ultraviolet curable ink) formed on the surface of the intermediate transfer body by containing the azobenzene derivative or the stilbene derivative within the above range. It is thought that this is because it can be put into a state of being

According to the ultraviolet curable ink of the present invention, it is expected to broaden the range of application of printing by the inkjet method and contribute to the advancement and popularization of technology in the same field.

100 Image forming apparatus 110 Recording medium 120 Intermediate transfer body 130 Transport path 140 Inkjet head 141 Intermediate image forming part 150 First light irradiation part 160 Transfer part 161 Pressurizing part 170, 171, 172 Support roller 180 Second light irradiation part 190 Cleaning Department

Claims (12)

A compound that undergoes a phase change from a solid to a liquid or liquid crystal by irradiation with ultraviolet rays and a phase change from a liquid or liquid crystal to a solid by irradiation with visible light.
UV curable ink for inkjet. The ultraviolet curable ink for an inkjet according to claim 1, wherein the compound whose phase changes upon irradiation with ultraviolet rays and visible light is a compound represented by the formula (1).

(In formula (1), X ₁ and X ₂ are independent carbon atoms or nitrogen atoms, and R _{1 to} R ₁₀ are independent hydrogen atoms, alkyl groups, alkoxy groups, and halogen groups, respectively. , A hydroxy group, and a group selected from the group consisting of a carboxy group, and at least one group of R _{1 to} R ₅ is an alkyl group or an alkoxy group having 1 to 18 carbon atoms, and R _{6 to} R ₁₀ . At least one substituent is an alkyl group or an alkoxy group having 1 to 18 carbon atoms.) In the compound represented by the formula (1), R ₁ and R ₆ are independently alkyl groups or alkoxy groups having 1 to 18 carbon atoms, and R _{2 to} R ₅ and R _{7 to} R ₁₀ are. The UV curing for inkjet according to claim 1 or 2, which is a group independently selected from the group consisting of a hydrogen atom, an alkyl group, an alkoxy group, a halogen group, a hydroxy group, and a carboxy group. Mold ink. The compound represented by the formula (1) according to any one of claims 1 to 3, wherein R ₁ and R ₆ are independently alkyl groups or alkoxy groups having 4 to 12 carbon atoms. UV curable ink for inkjet. The ultraviolet curable ink for an inkjet according to any one of claims 1 to 4, wherein the compound represented by the formula (1) has X ₁ and X ₂ as nitrogen atoms. The ultraviolet curable ink for an inkjet according to any one of claims 1 to 5, wherein the compound represented by the formula (1) is a carbon atom in which X ₁ and X ₂ are carbon atoms. Any one of claims 1 to 6, wherein the content of the compound represented by the formula (1) is 0.5 to 15% by mass with respect to the total mass of the ultraviolet curable ink for an inkjet. UV curable ink for inkjet described in. The ultraviolet curable ink for an inkjet according to any one of claims 1 to 7, which contains a gelling agent. A droplet of the ultraviolet curable ink for inkjet according to any one of claims 1 to 8 is ejected from the inkjet head, landed on the surface of the intermediate transfer body, and an image is formed on the surface of the intermediate transfer body. And the process of forming
The first light irradiation step in which the integrated light amount of light of 300 nm or more and less than 400 nm to irradiate the image is 100 to 1000 mJ / cm ² .
The step of transferring the image to a recording medium and
A second light irradiation step in which the integrated light amount of light of 400 nm or more and 800 nm or less to irradiate the image transferred to the recording medium is 100 to 1000 mJ / cm ² .
Have,
Image formation method. A droplet of the ultraviolet curable ink for inkjet according to any one of claims 1 to 8 is ejected from the inkjet head and landed on the surface of the recording medium to form an image on the surface of the recording medium. And the process of
The first light irradiation step in which the integrated light amount of light of 300 nm or more and less than 400 nm to irradiate the image is 100 to 1000 mJ / cm ² .
The second light irradiation step in which the integrated light amount of the light of 400 nm or more and 800 nm or less to irradiate the image is 100 to 1000 mJ / cm ² .
Have,
Image formation method. The image forming method according to claim 9, wherein the image is heated in the step of transferring the image to a recording medium. The image forming method according to claim 10, wherein the temperature at which the image is heated is 20 ° C. or higher and 90 ° C. or lower.

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