JP7247660B2 - Ultraviolet curable ink for inkjet and image forming method - Google Patents

Description

The present invention relates to an ultraviolet curable ink for inkjet and an image forming method.

2. Description of the Related Art An image forming method using an inkjet system is applied to various printing fields including special printing such as photography, various types of printing, marking, and color filters, because images can be easily and inexpensively formed. In particular, an image forming method using an inkjet system enables digital printing without using a plate, and is therefore particularly suitable for applications such as forming various images in small quantities.

2. Description of the Related Art As a type of inkjet ink used in an image forming method by an inkjet method, an ink containing a liquid component that cures when irradiated with ultraviolet rays (hereinafter also simply referred to as “ultraviolet curable ink”) is known. As the image forming method, droplets of the ultraviolet curable ink are allowed to land on the surface of the recording medium, and the ink droplets deposited 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 obtained by curing the ink by the above method.

Ultraviolet curable inks for inkjet for use in the above image forming method have been extensively studied, and various improvements have been made in order to form desired images. For example, Patent Document 1 describes a self-dispersing UV-polymerizable compound, a water-insoluble α-aminoketone UV-polymerization initiator, a water-insoluble sensitizer absorbing UV light in the wavelength region of 375 nm or more and 450 nm or less, and water. The above UV curable water-based ink suppresses the occurrence of offset (a phenomenon in which ink is transferred to the recording media when the recording media are stacked or transferred to a member that winds up the recording media) to achieve high-speed recording. It is said that it can be done.

JP 2015-168727 A

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

Therefore, in an image forming method involving a transfer step of transferring an image formed on the surface of an intermediate transfer body onto a recording medium, image deletion does not occur on the intermediate transfer body, and the image can be transferred from the intermediate transfer body onto the recording medium. There is a demand for an actinic radiation curable ink for inkjet that also 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 that has good transferability and is capable of forming high-definition images. A second object of the present invention is to provide an image forming method using the ultraviolet curable ink.

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

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

Another image forming method of the present invention comprises ejecting droplets of the above-described ultraviolet curable ink for inkjet from an inkjet head and landing them on the surface of a recording medium to form an image on the surface of the recording medium. a first light irradiation step in which the integrated amount of light with a wavelength of 300 nm or more and less than 400 nm applied to the image is 100 to 1000 mJ/cm ² ; and the integrated amount of light with a wavelength of 400 nm to 800 nm applied to the image is 100. and a second light irradiation step of ~1000 mJ/cm ² .

ADVANTAGE OF THE INVENTION According to this invention, the transferability is favorable and the ultraviolet curing ink which can form a high-definition image can be provided. Further, according to the present invention, it is possible to provide an image forming method using the ultraviolet curable ink.

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

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

1. Ultraviolet curable ink In one embodiment of the present invention, a phase change from solid to liquid or liquid crystal is performed by irradiating light (ultraviolet rays) of 300 nm or more and less than 400 nm, and light of 400 nm or more and 800 nm or less (visible light) is used. The present invention relates to an ultraviolet curable ink for inkjet containing a compound represented by the formula (1) that undergoes a phase change from liquid or liquid crystal to solid upon irradiation. 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 formed by curing the ultraviolet curable ink). Therefore, for example, the ultraviolet curable ink is discharged onto the intermediate transfer body, and the ultraviolet curable ink is irradiated with ultraviolet rays on the intermediate transfer body, thereby curing the ultraviolet curable ink and formula (1). The UV-curable ink cured by the represented compound can be moderately softened. At this time, it is also possible to improve transferability by moderately softening the cured product with the compound represented by the formula (1) while suppressing image deletion on the intermediate transfer member by curing the ultraviolet curable ink. can. After the transfer to the recording medium, the image is irradiated with visible light to cause a phase change of the compound represented by formula (1) into a solid, thereby increasing the hardness of the image and suppressing blocking after image formation. 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 Formula (1), X ₁ and X ₂ are each independently a nitrogen atom or a carbon atom, and R ₁ to R ₁₀ are each independently a hydrogen atom, an alkyl group, an alkoxy group, or a halogen group. , a hydroxy group, and a carboxy group, 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 or alkoxy group having 1 to 18 carbon atoms.)

In one embodiment of the present invention, the phase-change compound represented by formula ( _{1) is an azobenzene derivative in which X 1 and X 2 are nitrogen atoms} , or It is a stilbene derivative.

1-1. Azobenzene Derivatives, Stilbene Derivatives Azobenzene derivatives in which X ₁ and X ₂ are nitrogen atoms represented by the above formula (1), or stilbene derivatives in which X ₁ and X ₂ are carbon atoms, absorb light in the ultraviolet region. , by isomerizing from the trans isomer to the cis isomer, the phase changes from solid to liquid or liquid crystal, and by absorbing light in the visible light region and isomerizing from the cis isomer to the trans isomer, the liquid or liquid crystal to solid phase change to

R ₁ and R ₆ in the azobenzene derivative and the stilbene derivative represented by Structural Formula (1) in one embodiment of the present invention are alkyl groups or alkoxy groups having 1 to 18 carbon atoms, and R ₁ and R ₆ is preferably an alkyl or alkoxy group having 4 to 12 carbon atoms, more preferably an alkyl or alkoxy group having 4 to 8 carbon atoms. R ₂ to R ₅ and R ₇ to R ₁₀ are each independently a group 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.

In addition, R ₁ and R ₆ may be the same or different, but from the viewpoint of intermolecular interaction, it is preferable that the molecular arrangement has regularity, so they are preferably the same. .

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 and 1-hexylheptyl group.

Examples of the alkoxy groups include methoxy, ethoxy, n-propoxy, n-butoxy, n-pentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy, 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 group: 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 -dimethyl-4-heptyloxy, 3,5,5-trimethylhexyloxy, 1-methyldecyloxy, 1-hexylheptyloxy, and other branched alkoxy groups.

Examples of such halogen groups include fluoro, chloro, bromo, and iodo groups.

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

An azobenzene derivative and a stilbene derivative according to one embodiment of the present invention have the alkyl group or alkoxy group described above. Since the above alkyl and alkoxy groups have thermal mobility, the thermal motion of the alkyl and alkoxy groups in the periodic structure dominated by the π-π interaction of the azobenzene moiety of the azobenzene derivative and the stilbene moiety of the stilbene derivative A specific crystal structure in which isotropically disordered structures coexist can be formed. Therefore, cis-trans isomerization occurs locally, and a phase change from solid to liquid or liquid crystal, or from liquid or liquid crystal to solid proceeds, resulting in the azobenzene moiety of the azobenzene derivative and the stilbene derivative of the stilbene derivative. Since the π-π interaction of the portion is reduced, a chain reaction of isotropic melting occurs in the entire system, so that the phase change described above proceeds more easily.

In addition, an alkyl group or an alkoxy group having 4 to 12 carbon atoms in the groups (R ₁ and R ₆ ) of the azobenzene derivative and the stilbene derivative represented by Structural Formula (1) has high thermal mobility but , the intermolecular alkyl-alkyl interaction is relatively weak, so cis-trans isomerization is likely to occur, and the phase change described above is more likely to proceed. As a result, the softening speed by ultraviolet irradiation is improved, and the curing speed by visible light irradiation is also improved.

In addition, the groups (R ₂ to R ₅ , R ₇ to R ₁₀ ) of the azobenzene derivative and the stilbene derivative represented by Structural Formula (1) are each independently a group consisting of an alkyl group, an alkoxy group, and a halogen group. By substituting with a group selected from, the above-mentioned phase change can also occur, such as the generation of lattice defects that act favorably on cis-trans isomerization, the expression of free volume, and the reduction of π-π interaction. easier to progress.

Specifically, the azobenzene derivative is preferably a compound represented by the following structural formulas (2) to (10) having a structure that favors cis-trans isomerization. - Compounds represented by the following structural formulas (11) to (16) having a structure that favors trans isomerization are preferred.

A 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 in Structural Formula (1) are alkyl groups, p-alkylaniline is heated and stirred in toluene using manganese dioxide as an oxidant to give 4 , 4′-dialkylazobenzenes can be obtained.

Moreover, the method for synthesizing the stilbene derivative is not particularly limited, and a conventionally known synthesis method can be applied. For example, in the case of a stilbene derivative in which R ₁ and R ₆ in Structural Formula (1) are alkyl groups, p-alkylstyrene is heated and stirred in toluene using a Grubbs catalyst, which is an olefin metathesis reaction reagent. , 4,4′-dialkylstilbenes can be obtained.

The content of the azobenzene derivative or the stilbene derivative is preferably 0.5 to 15% by mass with respect to the total mass of the ultraviolet curable ink, and is 3.0% by mass or more and 7.0% by mass or less. It is more preferable to have

By setting the content of the azobenzene derivative or the stilbene derivative to 0.5% by mass or more, the image (cured film formed by curing the ultraviolet curable ink) has a certain degree of curing, and the intermediate transfer member A high-definition image can be obtained because the image flow on the upper surface can be suppressed. 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 formed on the intermediate transfer member (cured film obtained by curing the ultraviolet curable ink) is high. Since excessive formation is suppressed, transferability to a recording medium can be improved.

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

The UV-polymerizable compound is a compound that crosslinks or polymerizes when irradiated with UV rays. The above examples also include cationically polymerizable compounds, radically polymerizable compounds, or mixtures thereof. Among the above, radically polymerizable compounds are preferred. Incidentally, the above may be any of monomers, polymerizable oligomers, prepolymers and mixtures thereof.

A radically polymerizable compound is a compound having an ethylenically unsaturated double bond group in the molecule. Radically polymerizable compounds can be monofunctional or polyfunctional compounds. 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 methacryloyl group, and "(meth)acryl" means acrylic Or means methacrylic.

Examples of monofunctional (meth)acrylates include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomyrstyl (meth)acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-(meth) acryloyloxyethylhexahydrophthalic 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 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, polypropylene glycol di(meth)acrylate, (meth)acrylates, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, PO adduct di(meth)acrylate of bisphenol A, neopentylglycol hydroxypivalate di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, polyethylene glycol diacrylate and Bifunctional (meth) acrylates such as tripropylene glycol diacrylate; Trimethylolpropane tri (meth) acrylate, trifunctional (meth) acrylates such as pentaerythritol tri (meth) acrylate; Tri- or higher functional (meth)acrylates such as pentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerin propoxytri(meth)acrylate and pentaerythritol ethoxytetra(meth)acrylate; including polyester acrylate oligomers ( Oligomers having a meth)acryloyl group, modified products thereof, and the like are included. Examples of the modified products include ethylene oxide-modified (EO-modified) acrylates into which ethylene oxide groups are inserted, and propylene oxide-modified (PO-modified) acrylates into which propylene oxide groups are inserted.

At least part of the radically polymerizable compound is preferably an ethylene oxide-modified (meth)acrylate compound. This is because the ethylene oxide-modified (meth)acrylate compound has high photosensitivity, and in the case of ink containing a gelling agent, it easily forms a card house structure when gelling at low temperatures. In addition, the ethylene oxide-modified (meth)acrylate compound easily dissolves in other ink components at high temperatures and exhibits little curing shrinkage, so curling of printed matter is less likely to occur.

A cationically polymerizable compound is a compound having a cationically polymerizable group in its molecule. Examples of cationic polymerizable compounds include epoxy compounds, vinyl ether compounds and oxetane compounds.

Examples of the above epoxy compounds include 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene monoepoxide, ε-caprolactone-modified 3, 4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexanecarboxylate, 1-methyl-4-(2-methyloxiranyl)-7-oxabicyclo[4,1,0]heptane, 2-(3,4 -epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanone-meta-dioxane and cycloaliphatic epoxy resins such as bis(2,3-epoxycyclopentyl)ether, diglycidyl ether of 1,4-butanediol , diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, diglycidyl ether of polyethylene glycol, diglycidyl ether of propylene glycol, ethylene glycol, propylene glycol, and glycerin. Aliphatic epoxy compounds including polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides (such as ethylene oxide and propylene oxide) to aliphatic polyhydric alcohols, and bisphenol A or Examples include di- or polyglycidyl ethers of its alkylene oxide adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and aromatic epoxy compounds including novolak-type epoxy resins.

Examples of the above 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, isopropenyl. Monovinyl ether compounds, including ether-o-propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether, and ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether , butanediol divinyl ether, hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, trimethylolpropane trivinyl ether, and the like.

Examples of the oxetane compounds include 3-hydroxymethyl-3-methyloxetane, 3-hydroxymethyl-3-ethyloxetane, 3-hydroxymethyl-3-propyloxetane, 3-hydroxymethyl-3-n-butyloxetane, -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- and ethyl (3-oxetanyl)]methyl ether.

The content of the ultraviolet polymerizable compound is preferably 1.0% by mass or more and 97% by mass or less, more preferably 30% by mass or more and 90% by mass or less, relative to the total mass of the ultraviolet curable ink. preferable.

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

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

Moreover, from the following viewpoints, it is preferable that the gelling agent crystallizes in the ink at a temperature equal to or lower than the gelling temperature of the ink. Here, the term "gelling temperature" refers to the temperature at which the phase transition of the ink from sol to 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 AntonPaar), and the temperature at which the viscosity rises abruptly 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 plate-shaped crystallizing gelling agent is enclosed (such a structure is hereinafter referred to as a “card "house structure"). When the card house structure is formed, the liquid is held in the space, so that the dots formed by the impact of the ink are less likely to wet and spread, and the pinning property of the ink is further enhanced. It is thought that when the pinning property of the ink increases, it becomes difficult for the dots formed by the ink to land on the recording medium to merge.

Examples of the above gelling agents include dipentadecyl ketone, diheptadecyl ketone, dilignoceryl ketone, dibehenyl ketone, distearyl ketone, dieicosil ketone, dipalmityl ketone, dimyristyl ketone, lauryl myristyl ketone, Aliphatic ketone compounds such as lauryl palmityl ketone, myristyl palmityl ketone, myristyl stearyl ketone, myristyl behenyl ketone, palmityl stearyl ketone, palmityl behenyl ketone and stearyl behenyl ketone; cetyl palmitate, stearyl stearate, behenyl behenate, Icosyl icosanoate, behenyl stearate, palmityl stearate, lauryl stearate, stearyl palmitate, myristyl myristate, cetyl myristate, octyldodecyl myristate, stearyl oleate, stearyl erucate, stearyl linoleate, behenyl oleate and linol aliphatic ester compounds such as arachidyl acid; amide compounds such as N-lauroyl-L-glutamic acid dibutylamide and N-(2-ethylhexanoyl)-L-glutamic acid dibutylamide; 1,3:2,4-bis-O - dibenzylidene sorbitols such as benzylidene-D-glucitol; petroleum waxes such as paraffin wax, microcrystalline wax, petrolactam; candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, jojoba solid wax, and plant waxes such as jojoba esters; animal waxes such as beeswax, lanolin and whale wax; mineral waxes such as montan wax and hydrogenated wax; hydrogenated castor oil or hydrogenated castor oil derivatives; montan wax derivatives, paraffin wax derivatives, modified waxes such as microcrystalline wax derivatives or polyethylene wax derivatives; higher fatty acids such as behenic 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 derivatives; lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, 12-hydroxystearic acid amide, etc. fatty acid amide; N-stearyl stearamide, N-olei N-substituted fatty acid amides such as lupalmitic acid amide; specialties such as N,N'-ethylenebisstearylamide, N,N'-ethylenebis-12-hydroxystearylamide, and N,N'-xylylenebisstearylamide 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 compounds; sucrose fatty acid esters such as sucrose stearic acid and sucrose palmitic acid; synthetic waxes such as polyethylene wax and α-olefin maleic anhydride copolymer wax; polymeric wax; dimer acid; be These waxes may be used alone or in combination of two or more.

The content of the gelling agent is preferably 0.01% by mass or more and 7.0% by mass or less relative to the total mass of the ink, and 0.2% by mass or more and 6.8% by mass relative to the total mass of the ink. % or less. 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 ultraviolet curable ink may further contain a polymerization initiator, if necessary. The above polymerization initiator may be any one as long as it can initiate the above polymerization. For example, when the UV-curable ink contains a radically polymerizable compound, the polymerization initiator can be a photoradical initiator, and when the UV-curable ink contains a cationic polymerizable compound, the polymerization initiator can be It can be a photocationic 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-cleaving 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 -methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone, benzoin, benzoin methyl ether, and benzoin isopropyl ether. acylphosphine oxide initiators, including phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and benzyl and methylphenylglyoxyesters.

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 Benzophenone-based initiators, including sulfides, acrylated benzophenones, 3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone, and 3,3′-dimethyl-4-methoxybenzophenone, 2-isopropyl thioxanthone-based initiators including thioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone and the like; aminobenzophenone-based initiators including Michler's ketone, 4,4'-diethylaminobenzophenone and the like; 10-butyl-2-chloroacridone, 2-ethylanthraquinone, 9,10-phenanthrenequinone, camphorquinone, and the like.

Examples of cationic polymerization initiators include photoacid generators. Examples of photoacid generators include aromatic onium compounds B(C ₆ F ₅ ) ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF, including diazonium, ammonium, iodonium, sulfonium, and phosphonium. Included are sulfonates that generate sulfonic acids such as ₃ SO ₃ ^-salts , halides that photogenerate hydrogen halides, and iron allene complexes.

The content of the polymerization initiator can be arbitrarily set within a range in which the ultraviolet curing ink is sufficiently cured by irradiation with ultraviolet rays and the ejection property of the ultraviolet curing ink is not lowered. For example, the content of the polymerization initiator is preferably 0.1% by mass or more and 20% by mass or less, and is 1.0% by mass or more and 12% by mass or less with respect to the total mass of the ultraviolet curable ink. is more preferable.

1-5. Colorants Colorants include pigments and dyes. The coloring material is preferably a pigment from the viewpoint of further increasing the dispersion stability of the ink and forming an image with 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, and 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.

Examples of black pigments include Pigment Black 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, more preferably 0.4% by mass or more and 10% by mass or less, relative to the total mass of the ink. When the content of the pigment or dye is 0.1% by mass or more relative to the total mass of the ink, the resulting image has sufficient color development. When the pigment or dye content 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 dispersants include surfactants and polymeric dispersants, with polymeric dispersants being preferred.

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

The pigment may be further enhanced in dispersibility with a dispersing aid, if desired.

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 relative 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 relative to the total mass of the pigment, It becomes easy to stabilize the ejection property of the ink from the inkjet head.

1-7. Polymerization Inhibitor The ultraviolet curing ink may contain a polymerization inhibitor.

Examples of the above polymerization inhibitors include (alkyl)phenol, hydroquinone, catechol, resorcinol, p-methoxyphenol, t-butylcatechol, t-butylhydroquinone, pyrogallol, 1,1-picrylhydrazyl, phenothiazine, p- Benzoquinone, nitrosobenzene, 2,5-di-t-butyl-p-benzoquinone, dithiobenzoyl disulfide, picric acid, cupferron, aluminum N-nitrosophenylhydroxylamine, tri-p-nitrophenylmethyl, N-(3-oxyanilino -1,3-dimethylbutylidene)aniline oxide, dibutyl cresol, cyclohexanone oxime cresol, guaiacol, o-isopropylphenol, butyraldoxime, methyl ethyl ketoxime, cyclohexanone oxime.

1-8. Other Components The UV curable ink may further contain other components as necessary. Other components may be photoacid generators, various additives, other resins, and the like. Examples of additives also include surfactants, leveling additives, matting agents, infrared absorbing agents, antibacterial agents, basic compounds for enhancing the storage stability of the ink, 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 physical properties of cured films such as polyester resins, polyurethane resins, vinyl resins, acrylic resins, and rubber resins.

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

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

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

A pigment dispersion can be prepared by dispersing a pigment. Dispersion of the pigment may be performed using, for example, a ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paint shaker, or the like. At this time, a dispersant may be added.

2. Image Forming Method The image forming method according to the embodiment of the present invention is an image forming method using the ultraviolet curable ink for inkjet described above. Specifically, a step of ejecting droplets of the above-mentioned ultraviolet curable ink for inkjet from an inkjet head and landing them on the surface of the intermediate transfer body to form an image on the surface of the intermediate transfer body; A first light irradiation step in which the integrated amount of light with a wavelength of 300 nm or more and less than 400 nm applied to the image is 100 to 1000 mJ/cm ² , a step of transferring the image onto a recording medium, and the image transferred onto the recording medium. and a second light irradiation step in which the integrated amount of light having a wavelength of 400 nm or more and 800 nm or less is 100 to 1000 mJ/cm ² .

In the step of ejecting the ultraviolet curable ink and making it land on the surface of the intermediate transfer member, the above-described ultraviolet curable ink is ejected from the inkjet head.

When droplets of a plurality of types of UV-curable inks having different compositions (for example, types or amounts of colorants) are ejected and landed to form a multicolor image, the plurality of types of UV-curing At least one of the mold inks is the UV curable ink. Two or more inks among the ejected ultraviolet curable inks 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 preferred. From the above viewpoint, it is more preferable that all of the discharged ultraviolet curing ink is the ultraviolet curing ink.

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

Moreover, the inkjet head may be either a scan-type inkjet head 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 ultraviolet curable ink for inkjet contains a gelling agent, the temperature of the ultraviolet curable ink in the inkjet head is set to a temperature higher than the gelling temperature of the ultraviolet curable ink by 10° C. or more and less than 40° C. preferably. By setting the temperature of the UV curable ink in the inkjet head to the gelling 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 can be ejected satisfactorily. be able to. Further, by setting the temperature of the ultraviolet curable ink in the inkjet head to less than the gelling temperature of the ultraviolet curable ink +40° C., the thermal load of the inkjet head can be reduced. In particular, an ink jet head using a piezo element is likely to deteriorate in performance due to a thermal load, so it is particularly preferable to set the temperature of the ultraviolet curable ink within the above range.

The ejected ultraviolet curing ink lands on the surface of the intermediate transfer member.

The intermediate transfer member is made of benzene rings 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, polyvinylidene fluoride, and a mixture or copolymer thereof. In addition to the substrate layer, the intermediate transfer member includes rubber, elastomer and elastic rubber such as silicone rubber (SR), chloropene rubber (CR), nitrile rubber (NBR) and epichlorohydrin rubber (ECO) on the ink landing surface side. both or either of an elastic layer containing resin or the like, and a surface layer containing fluorine resin such as polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), and polyvinylidene fluoride (PVDF) and acrylic resin. may have.

Alternatively, the intermediate transfer member may be polyethylene terephthalate (PET) film, 1,4-polycyclohexylene dimethylene terephthalate film, polyethylene naphthalate (PEN) film, polyphenylene sulfide film, polystyrene (PS) film, polypropylene (PP) film. , resin films such as 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. may be

When the ultraviolet curable ink for inkjet includes a gelling agent, the ultraviolet curable ink that has landed on the surface of the intermediate transfer member is pinned by crystallization of the gelling agent. As a result, the dots formed by landing the ink are less likely to spread by wetting, and the dots formed by the landing of the ink on the surface of the intermediate transfer body are prevented from merging with each other.

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

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

From the viewpoint of suppressing the occurrence of poor curing of the UV curable ink due to melting of the UV curable ink by radiant heat of the light source, the UV light source is preferably a light emitting diode (LED). Examples of LED light sources capable of irradiating actinic rays for curing UV curable ink include 395 nm, water-cooled LED, Phoseon Technology, Heraeus, Kyocera, HOYA, and Integration Included are those manufactured by Technology.

From the viewpoint of sufficiently polymerizing and cross-linking the energy of ultraviolet rays, and from the viewpoint of isomerizing the azobenzene derivative or stilbene derivative contained in the above-mentioned ultraviolet curing ink, the cumulative amount of ultraviolet rays of 300 nm or more and less than 400 nm irradiated to the image is 100. It is preferably up to 1000 mJ/cm ² , more preferably 250 mJ/cm ² or more and 500 mJ/cm ² or less. By setting the integrated light quantity of the ultraviolet light to 100 mJ/cm ² or more, the ultraviolet polymerizable compound can be polymerized and crosslinked, and the phase of the azobenzene derivative or stilbene derivative can be changed from solid to liquid or liquid crystal to form an image ( A cured film obtained by curing an ultraviolet curable ink can be softened. As a result, transferability from the intermediate transfer body to the recording medium can be improved. Further, since the image has a degree of curing to some extent, it is possible to proceed to the transfer process without causing image deletion on the intermediate transfer member, so that a high-definition image can be obtained.

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

In addition, in the step of irradiating 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 with a low oxygen concentration, curing inhibition due to oxygen in the atmosphere is less likely to occur, and the curing sensitivity of the ultraviolet curing ink for inkjet can be further increased.

The step of transferring the image onto the recording medium further includes the step of pressing the image formed on the surface of the intermediate transfer member with a pressure member. The temperature of the pressing member when pressing the image 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 within the above range, even when the glass transition point (Tg) of the image (cured film formed by curing the ultraviolet curable ink) is higher than room temperature, transferability is improved. The image can be transferred from the intermediate transfer member to the recording medium without degradation.

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

In addition, from the viewpoint of causing a phase change of the azobenzene derivative or stilbene derivative contained in the above-described ultraviolet curable ink from liquid or liquid crystal to solid, the image transferred to the recording medium (cured film formed by curing the ultraviolet curable ink) The integrated amount of light (visible light) having a wavelength of 400 nm or more and 800 nm or less is preferably 100 to 1000 mJ/cm ² , more preferably 200 mJ/cm ² or more and 800 mJ/cm ² or less. By setting the cumulative amount of visible light to 100 mJ/cm ² or more, the phase change of the azobenzene derivative or the stilbene derivative can proceed rapidly. Further, by setting the cumulative amount of 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 above image forming method, the ultraviolet curable ink for inkjet is landed on an intermediate transfer member, and the ultraviolet curable ink applied to the intermediate transfer member is irradiated with ultraviolet rays to form an image. Although the method of transferring an image to a recording medium and irradiating the transferred image with visible light has been described, the present invention is not limited to this. For example, an image may be formed by directing the ultraviolet curable ink for inkjet onto the surface of a recording medium and irradiating the recording medium with ultraviolet rays and visible light. The recording medium may be any medium on which an image can be formed. Non-absorbent recording media composed of plastics, including the medium, polyester, polyvinyl chloride, polyethylene, polyurethane, polypropylene, acrylic resin, polycarbonate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate and polybutadiene terephthalate, and Non-absorbing inorganic recording media such as metals and glass can be used.

3. 1. Image Forming Apparatus FIG. 1 is a schematic diagram showing an exemplary configuration of an inkjet image forming apparatus 100 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 from an inkjet head 140 and a recording medium 110 on which the ejected ultraviolet curable ink for inkjet lands. , a transport path 130 for landing the ultraviolet curable ink on the surface of the intermediate transfer body 120, and an ultraviolet curable ink on the surface of the intermediate transfer body 120 arranged opposite to the surface of the transport path 130 on which the recording medium 110 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 the ultraviolet curable ink is transferred to the recording medium 110. a transfer section 160 that presses an intermediate image in the transfer section 160; a second light irradiation unit 180 that irradiates the intermediate image that has been transferred to the second light irradiation unit 180 with visible light; and a cleaning unit 190 for cleaning.

The transport path 130 is composed of, for example, a metal drum, and transports the recording medium 110 onto which the intermediate image is transferred. The conveying 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 pressure unit 161 to form a transfer nip. The transport path 130 may have a claw (not shown) that fixes the leading edge of the recording medium 110 . The conveying path 130 conveys the recording medium 110 to the transfer nip by fixing the tip of the recording medium 110 to the claw and rotating counterclockwise in FIG.

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

At least one of the three support rollers 170, 171 and 172 is a driving roller and rotates the intermediate transfer member 120 in the A direction.

The intermediate transfer member 120 is made of benzene, such as aromatic polyimide (PI), aromatic polyamideimide (PAI), polyphenylene sulfide (PPS), aromatic polyetheretherketone (PEEK), aromatic polycarbonate, and aromatic polyetherketone. It has a base layer containing a resin having a structural unit containing a ring, polyvinylidene fluoride, a mixture or copolymer thereof, or the like. In addition to the base layer, the intermediate transfer member 120 includes rubber such as silicone rubber (SR), chloropene rubber (CR), nitrile rubber (NBR), epichlorohydrin rubber (ECO), elastomer, and elastic resin on the ink landing surface side. and/or a surface layer containing fluororesins such as polytetrafluoroethylene (PTFE), perfluoroalkoxyalkanes (PFA), and polyvinylidene fluoride (PVDF) and acrylic resins. You may

Alternatively, the intermediate transfer member 120 may be a polyethylene terephthalate (PET) film, a 1,4-polycyclohexylene dimethylene terephthalate film, a polyethylene naphthalate (PEN) film, a polyphenylene sulfide film, a polystyrene (PS) film, or a polypropylene (PP) film. 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 may have been

The portions of the intermediate transfer member 120 that are stretched between support rollers 170 and 171 located at the left and right vertices of the inverted triangle serve as landing surfaces for ink ejected from the respective inkjet heads. A support roller 172 (pressing portion 161) positioned at the lower vertex of the inverted triangle on the intermediate transfer body 120 presses the intermediate transfer body 120 toward the conveying path 130 with a predetermined nip pressure. , and functions as a pressure unit that transfers an intermediate image formed by landing ink ejected from each inkjet head onto the recording medium 110 .

The intermediate image forming unit 141, which is also an ink ejecting unit, is an ink applying unit that forms an intermediate image by an ink jet method. It has inkjet heads 140Y, 140M, 140C and 140K that eject curable ink from nozzles and land it on the surface of the intermediate transfer member 120 . Inkjet heads 140Y, 140M, 140C, and 140K deposit the above-described ultraviolet curable inks at positions corresponding to the images to be formed on the surface of intermediate transfer member 120 to form intermediate images.

The first light irradiation section 150 is arranged downstream of the intermediate image forming section 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 member with ultraviolet rays to polymerize and crosslink the ultraviolet polymerizable compound contained in the ultraviolet curing ink forming the image, and azobenzene. A derivative or stilbene derivative undergoes a phase change from solid to liquid or liquid crystal. As a result, an image that can be transferred to a recording medium is formed on the surface of the intermediate transfer member 120 .

The transfer portion 160 includes a transfer nip where the intermediate transfer body 120 and the transport path 130 are closest to each other. A pressure unit 161 presses the surface of the transport path 130 with which the intermediate transfer member 120 contacts. The image formed on the surface of the intermediate transfer member 120 and conveyed and the recording medium 110 arranged on the surface of the conveying path 130 and conveyed come into contact at the transfer nip and are transferred to the intermediate transfer member 120 via the pressure unit 161 . By applying pressure from the transfer body 120 to the conveying path 130 side, the image is transferred to the recording medium.

The second light irradiation unit 180 is arranged downstream of the transfer unit 160 in the transport direction of the recording medium 110 along the transport path 130 and irradiates the surface of the transport path 130 with actinic rays. Thereby, the second light irradiation unit 180 irradiates the image (cured film formed by curing the ultraviolet curable ink) transferred to the recording medium 110 with visible light to convert the azobenzene derivative or the stilbene derivative from the liquid or the liquid crystal. The image (cured film formed by curing the ultraviolet curable ink) is solidified by undergoing a phase change to a solid. 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 contacts the surface of the intermediate transfer member 120 on the downstream side of the transfer unit 160 . The cleaning unit 190 removes 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 rotating the cleaning roller.

Although not shown, the image forming apparatus 100 may have a temperature adjustment unit that adjusts the surface temperature of the ink landing position of the intermediate transfer member 120 to 60° C. or lower.

Further, although not shown, the image forming apparatus 100 may have an oxygen concentration adjustment 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.

In the above description, an image forming apparatus having an intermediate transfer member has been described. It may be configured to directly land on the recording medium.

The present invention will be more specifically described using the following tests, but the present invention is not limited to the following tests.

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

1-1-2. Synthesis of compound 2 Represented by the following structural formula (3) in the same manner as compound 1 except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-butoxyaniline (1.7 g, 10 mmol) Compound 2 was obtained.

1-1-3. Synthesis of compound 3 Represented by the following structural formula (4) in the same manner as compound 1 except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-hexylaniline (1.8 g, 10 mmol) 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), and represented by the following structural formula (5). to obtain compound 4.

1-1-5. Synthesis of compound 5 In the same manner as compound 1, except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-octylaniline (2.1 g, 10 mmol), represented by the following structural formula (6) Compound 5 was obtained.

1-1-6. Synthesis of Compound 6 In the same manner as Compound 1 except that 4-butylaniline (1.5 g, 10 mmol) was changed to 4-octyloxyaniline (2.2 g, 10 mmol), represented by the following structural formula (7). to obtain compound 6.

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 while 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 20% aqueous sodium hydroxide solution was added to the above solution and stirred for 20 hours. The deposited precipitate was filtered and washed with water to obtain a pale yellow solid. The resulting solid was purified by silica gel column chromatography using a mixed solvent of ethyl acetate and hexane as a developing solvent, and then recrystallized with a mixed solvent of acetone and hexane to obtain intermediate A. 100 mL of DMF, 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), stirred at 80° C. for 2 hours, and then stirred at room temperature for 20 minutes. Stirred for an hour. After distilling off the solvent under reduced pressure, the residue was extracted with ethyl acetate, and the organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. After the organic layer was filtered, the solvent was distilled off under reduced pressure, and the obtained solid was purified by silica gel column chromatography using a mixture 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) 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 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 stirred at 80° C. for 6 hours under nitrogen atmosphere. After distilling off the solvent under reduced pressure, the residue was extracted with ethyl acetate, and the organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. After the organic layer was filtered, the solvent was distilled off under reduced pressure, and the resulting solid was purified by silica gel column chromatography using a mixture of ethyl acetate and hexane as a developing solvent to obtain a compound represented by the following structural formula (10). The represented compound 9 was obtained.

1-2. Synthesis of stilbene derivative 1-2-1. Synthesis of compound 10 1,3-dimethylpropylene urea, nickel iodide hydrate (0.53 g, 1.3 mmol), 4,4′-dimethytoxy-2,2″-bipyridine (0.3 g, 1.3 mmol) , sodium iodide (1.2 g, 8.3 mmol), 4,4′-dibromostilbene (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, then zinc powder (3.4 g, 52.0 mmol) was added and further stirred for 15 minutes. After cooling the reaction mixture, it was filtered through celite, and the organic layer was washed with saturated aqueous ammonium chloride 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 was purified by silica gel column chromatography using a mixture of ethyl acetate and hexane as a developing solvent to obtain a compound represented by the following structural formula (11). The represented compound 10 was obtained.

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

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

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

1-2-5. Synthesis of compound 14 In the same manner as compound 10 except that 1-bromobutane (3.8 g, 28.0 mmol) was changed to 1-bromooctane (5.4 g, 28.0 mmol), the following structural formula (15) The represented compound 14 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), represented by the following structural formula (16) A compound 15 was obtained.

1-3. Other Compounds As a compound 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 obtained by converting 2,2′:5′,2″-terthiophene-5,5″-dicarboxaldehyde into a dialkyne body by Cory-Fuchs alkylation reaction. , followed by Sonogashira coupling with 2-bromo-5-hexylthiophene.

1-4. Preparation of ink 1-4-1. Preparation of pigment dispersion Cyan pigment “Lionol Blue FG-7400-G” (manufactured by Toyocolor Co., Ltd.) (20 parts by mass) and dispersant “BYKJET-9151” (manufactured by BYK, “BYKJET” is a registered trademark of the company ) (6.5 parts by mass), (polyethylene glycol #400 diacrylate) (73.2 parts by mass), and a photopolymerization inhibitor "Irgastab UV10" (manufactured by BASF, "Irgastab" is a registered trademark of the company) (0 .3 parts by mass) and 0.3 mm zirconia beads “YTZ Ball” (manufactured by Nikkato Co., Ltd.) are placed in a 100 mL plastic container and dispersed for 3 hours with a paint shaker, after which the zirconia beads are removed and the pigment is 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 parts by mass), and 3PO-modified trimethylol Propane triacrylate (15.0% by mass), a photoinitiator "IRGACURE819" (manufactured by BASF, "Irgacure" is a registered trademark of the same company) (6.0% by mass), and compound 1 (5.0% by mass) and Irgastab UV10 (0.1% by mass) were added, stirred at 105° C. for 45 minutes, and then filtered through a 3 μm membrane filter (Teflon (registered trademark) manufactured by ADVANTEC) to obtain Ink 1.

Table 1 shows the content of each component of inks 1 to 10, Table 2 shows inks 11 to 19, and Table 3 shows the contents of inks 20 to 24 (in units of parts by mass).

Each abbreviation shown in Tables 1 to 3 is 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. Evaluation of Image Formation Transferability and image quality were evaluated using prepared inks 1 to 24.

(Image forming method)
Inks 1 to 24 were introduced into an inkjet recording apparatus (KM512MHX, manufactured by Konica Minolta) having an inkjet recording head equipped with a piezo inkjet nozzle, and the intermediate transfer body was heated to 25 ° C. using a Peltier cooling unit, and the resolution was 720. 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 an integrated amount of 350 mJ/cm ² , and then the intermediate transfer member is heated to 50 ° C. with a Peltier heating unit, and coated printing paper (OK top coat, basis weight 128 g/m ² , manufactured by Oji Paper Co., Ltd.).

2-1. Transfer property evaluation The amount of ink ejected (μg) used in the above image formation was calculated from the weight increase (μg) of the recording medium and the weight of the transfer residue on the intermediate transfer body (μg), and the weight increase of the recording medium was calculated. The transfer rate (%) was calculated by minutes/injected ink weight. In addition, △ or more is regarded as a pass.

(Evaluation criteria)
◎: transfer rate of 95% or more ○: transfer rate of 90 or more and less than 95% △: transfer rate of 80 or more and less than 90% ×: transfer rate of less than 80%

2-2. Image quality evaluation (image formation method)
(Evaluation method)
A 5 cm×5 cm solid image 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 was observed in the image when observed from a distance of 5 cm ○: No density unevenness was observed in the image when observed from a position 15 cm away Density unevenness is observed in part, but no density unevenness is observed from a position 30 cm away. ×: Density unevenness is observed in the image from a position 30 cm away.

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

(Evaluation criteria)
⊙: No coloration observed on coated printing paper A when observed from a distance of 5 cm ○: No coloration observed on coated printing paper A when observed from a distance of 20 cm △: A position separated by 50 cm No coloration observed on coated printing paper A ×: Coloring observed on coated printing paper A observed from a distance of 50 cm

Each evaluation result is shown in Table 4.

Compared to inks 23 and 24 containing compounds 16 and 17 that do not cause phase change, the use of inks 1 to 21 containing an azobenzene derivative or a stilbene derivative as a component of the ultraviolet curable ink results in better transferability. It was possible to form high-definition images. This is because the azobenzene derivative or stilbene derivative contained in the UV-curable ink undergoes a phase change from a solid to a liquid or a liquid crystal when irradiated with UV rays, resulting in an image (curing formed by curing the UV-curable ink). It is thought that the transferability to the recording medium was improved because the film) was softened. In addition, since the azobenzene derivative or stilbene derivative is included, the degree of curing of the image (cured film formed by curing the ultraviolet curing ink) does not become too high, so it is necessary to irradiate ultraviolet rays before transferring to the recording medium. can be done. As a result, image smearing on the intermediate transfer member can be suppressed, and high-definition images can be obtained.

In addition, as shown in inks ₁ to 15, 20, and ₂₁ , azobenzene derivatives or When a stilbene derivative was used, good transferability was obtained and a high-definition image could be formed. It is considered that this is because the carbon chain is relatively short with 4 to 8 carbon atoms and is linear, so it is less susceptible to steric hindrance and undergoes phase change easily. In addition, although an alkyl group or alkoxy group having 4 to 8 carbon atoms has high thermal mobility, the intermolecular alkyl-alkyl interaction is relatively weak, so cis-trans isomerization proceeds further. It is considered that this is because the softening speed is improved by ultraviolet irradiation. Moreover, since the curing speed by visible light is also improved, blocking can be suppressed.

In addition, by making the azobenzene derivative or stilbene derivative 0.1% by mass or more and 20% by mass or less with respect to the total mass of the ultraviolet curable ink, the 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, good transferability results were obtained. By containing the azobenzene derivative or stilbene derivative within the above range, the degree of curing of the image formed on the surface of the intermediate transfer member (cured film obtained by curing the ultraviolet curable ink) is suitable for transfer. It is thought that this is because it is possible to keep the

The UV curable ink of the present invention is expected to expand the range of application of inkjet printing and contribute to the advancement and spread of technology in the same field.

REFERENCE SIGNS LIST 100 image forming apparatus 110 recording medium 120 intermediate transfer member 130 transport path 140 inkjet head 141 intermediate image forming section 150 first light irradiation section 160 transfer section 161 pressure section 170, 171, 172 support roller 180 second light irradiation section 190 cleaning Department

Claims (10)

A compound represented by the formula (1) that undergoes a phase change from a solid to a liquid or liquid crystal by irradiation with ultraviolet rays, and undergoes a phase change from the liquid or liquid crystal to a solid by irradiation with visible light,
UV curable ink for inkjet.

(In Formula (1), X ₁ and X ₂ are each independently a carbon atom or a nitrogen atom, and R ₁ to R ₁₀ are each independently a hydrogen atom, an alkyl group, an alkoxy group, or a halogen group. , a hydroxy group, and a carboxy group, 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 or alkoxy group having 1 to 18 carbon atoms.) In the compound represented by the formula (1), R ₁ and R ₆ are each independently an alkyl group or an alkoxy group having 1 to 18 carbon atoms, and R ₂ to R ₅ and R ₇ to R ₁₀ are , each 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. 3. The ultraviolet ray for inkjet according to claim 1 or 2, wherein in the compound represented by the formula (1), R ₁ and R ₆ are each independently an alkyl group or an alkoxy group having 4 to 12 carbon atoms. curable ink. 4. The ultraviolet curable ink for inkjet according to claim 1, wherein in the compound represented by formula (1), X ₁ and X ₂ are nitrogen atoms. 4. The ultraviolet curable ink for inkjet according to claim 1, wherein in the compound represented by formula (1), X ₁ and X ₂ are carbon atoms. 6. 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 inkjet, any one of claims 1 to 5 . Ultraviolet curable ink for inkjet described in . The UV curable ink for inkjet according to any one of claims 1 to 6 , which contains a gelling agent. From an inkjet head, droplets of the ultraviolet curable ink for inkjet according to any one of claims 1 to 7 are ejected and landed on the surface of an intermediate transfer member to form an image on the surface of the intermediate transfer member. forming a
a first light irradiation step in which the integrated amount of light with a wavelength of 300 nm or more and less than 400 nm is 100 to 1000 mJ/cm ² , and the image is irradiated;
transferring the image to a recording medium;
a second light irradiation step in which the integrated light amount of light having a wavelength of 400 nm or more and 800 nm or less is 100 to 1000 mJ/cm ² , which is irradiated to the image transferred to the recording medium;
having
Imaging method. 9. The image forming method according to claim 8 , wherein the image is heated in the step of transferring the image to the recording medium. 10. The image forming method according to claim 9 , wherein the temperature for heating the image is 20[deg.] C. or higher and 90[deg.] C. or lower.

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