JP4835004B2 - Actinic ray curable inkjet ink set, image forming method, and inkjet recording apparatus - Google Patents

Description

  The present invention relates to an actinic ray curable ink jet ink set capable of stably reproducing high-definition images on various recording materials, an image forming method using the ink set, and an ink jet recording apparatus.

  In recent years, the inkjet recording method can be easily and inexpensively produced images, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, a recording device that emits and controls fine dots, ink that has improved color reproduction gamut, durability, and emission suitability, and ink absorbability, coloring material color development, surface gloss, etc. have been dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper. The image quality improvement of today's ink jet recording system is achieved only when all of the recording apparatus, ink, and special paper are available.

  However, in an inkjet system that requires dedicated paper, the recording medium is limited, and the cost of the recording medium increases. Therefore, many attempts have been made to record on a transfer medium different from dedicated paper by an ink jet method. Specifically, a phase change ink jet method using a wax ink solid at room temperature, a solvent ink jet method using an ink mainly composed of a fast-drying organic solvent, a UV ink jet method in which crosslinking is performed by ultraviolet (UV) light after recording, etc. It is.

  Among them, the UV inkjet method has been attracting attention in recent years because it has a relatively low odor compared to the solvent-based inkjet method, and can be recorded on a recording medium having no quick drying and no ink absorption. Ink is disclosed (for example, refer to Patent Documents 1 and 2).

  However, even if these inks are used, the dot diameter after landing greatly changes depending on the type of recording material and the working environment, and it is not possible to form high-definition images on various recording materials. Is possible.

  In particular, in an ultraviolet curable ink-jet ink, for example, an ink using a cationic polymerizable compound (see, for example, Patent Documents 3 to 6) does not receive an oxygen-inhibiting action, but has a molecular level moisture (humidity). There is a problem that it is easily affected by.

And at least one compound selected from a polycyclic aromatic compound having at least one hydroxyl group, optionally substituted aralkyloxy group or alkoxy group as a substituent, a carbazole derivative, a phenothiazine derivative, and a thioxanthone derivative. Although it is well known to use as (for example, refer to Patent Documents 4 to 6), when a high-definition image is formed using the ink-jet ink, it is not a configuration capable of stably forming an image. Further, particularly in black ink and white ink, there is a problem that ejection / curability tends to be unstable due to the environment (temperature, humidity).
JP-A-6-200204 (Claims, Examples) JP 2000-504778 (Claims, Examples) JP 2002-188025 A (pages 2 to 7) Japanese Patent No. 3437069 (Claims and Examples) JP 2000-239648 A (Claims, Examples) JP 2002-239309 A (Claims, Examples)

  The present invention has been made in view of the above-described problems, and an object thereof is an actinic ray capable of recording a high-definition image with excellent reproducibility and excellent stability with excellent character quality and no color mixing. It is an object to provide a curable inkjet ink set, an image forming method, and an inkjet recording apparatus.

  The above object of the present invention can be achieved by the following configuration.

(Claim 1)
An actinic radiation curable inkjet ink set comprising four or more actinic radiation curable inkjet inks containing a photoinitiator, a photopolymerizable compound, and a pigment, wherein the actinic radiation curable inkjet included in the actinic radiation curable inkjet ink set The black ink uses at least one selected from an oxetane compound and an alicyclic epoxy compound as a photopolymerizable compound in combination with a (meth) acrylate compound, and further has an activity of three or more colors excluding the actinic ray curable inkjet black ink. An activity characterized by containing a sensitizer having ultraviolet spectrum absorption at a wavelength longer than 330 nm in the photocurable ink-jet ink or in all active photocurable ink-jet inks including the active photocurable ink-jet black ink. Light curing type Ink jet ink set.

(Claim 2)
The sensitizer is at least one compound selected from a polycyclic aromatic compound having at least one hydroxyl group, an optionally substituted aralkyloxy group or an alkoxy group as a substituent, a carbazole derivative, a phenothiazine derivative, and a thioxanthone derivative. The actinic ray curable inkjet ink set according to claim 1, wherein

(Claim 3)
1 to 10% by mass of an onium salt photoacid generator such as iodonium salt or sulfonium salt as a photoinitiator in the actinic ray curable inkjet black ink, and 0 to 1% by mass of a photoradical generator. The actinic ray curable inkjet ink set according to claim 1 or 2,

(Claim 4)
When the actinic radiation curable inkjet ink set has an actinic radiation curable inkjet white ink, at least one selected from an oxetane compound and an alicyclic epoxy compound as a photopolymerizable compound in the actinic radiation curable inkjet white ink; The actinic ray curable inkjet ink set according to any one of claims 1 to 3, wherein a (meth) acrylate compound is used in combination.

(Claim 5)
1 to 10% by mass of an onium salt photoacid generator such as iodonium salt or sulfonium salt as a photoinitiator in the actinic ray curable inkjet white ink, and 0 to 1% by mass of a photoradical generator. The actinic ray curable inkjet ink set according to claim 4.

(Claim 6)
A photopolymerizable compound in an actinic ray curable inkjet ink of three or more colors other than actinic ray curable inkjet black ink and actinic ray curable inkjet white ink, which contains a sulfonium salt that does not generate benzene after light irradiation as a photoinitiator As a compound containing 30 to 95% by mass of a compound having at least one oxetane ring, 5 to 70% by mass of at least one alicyclic epoxy compound, and 0 to 40% by mass of at least one vinyl ether compound. The actinic ray curable inkjet ink set according to any one of claims 1 to 5.

(Claim 7)
The actinic ray curable inkjet ink set according to claim 1, wherein each actinic ray curable inkjet color ink has a viscosity at 25 ° C. of 7 to 50 mPa · s.

(Claim 8)
An image forming method in which the actinic radiation curable inkjet ink of the actinic radiation curable inkjet ink set according to any one of claims 1 to 7 is jetted onto a recording material from an inkjet recording head, and printing is performed on the recording material. Then, after the actinic ray curable ink jet ink has landed, an actinic ray is irradiated for 0.001 to 1.0 seconds.

(Claim 9)
An image forming method for performing printing on a recording material by jetting the actinic radiation curable inkjet ink set according to any one of claims 1 to 7 onto the recording material from an ink jet recording head, the active light curing An image forming method, wherein the total actinic ray curable inkjet ink film thickness after the ink jet ink is landed and cured by irradiation with actinic rays is 2 to 20 μm.

(Claim 10)
An image forming method in which the actinic ray curable ink jet ink set according to any one of claims 1 to 7 is jetted onto a recording material from an ink jet recording head, and printing is performed on the recording material. An image forming method, wherein the amount of actinic ray curable inkjet ink droplets discharged from each nozzle is 2 to 15 pl.

(Claim 11)
An image forming method in which the actinic ray curable inkjet ink set according to any one of claims 1 to 7 is jetted onto a recording material from an inkjet recording head, and printing is performed on the recording material. An image forming method comprising forming an image by ejecting from a recording head.

(Claim 12)
It is an inkjet recording device used for the image forming method of any one of Claims 8-11, Comprising: It discharges, after heating actinic-light curable inkjet ink and a recording head to 35-100 degreeC. An inkjet recording apparatus.

  According to the present invention, there is provided an actinic ray curable inkjet ink set, an image forming method, and an inkjet recording apparatus that are capable of recording a high-definition image that is excellent in character quality and free of color mixing with high reproducibility and extremely stably. We were able to.

  The present invention will be described in more detail.

  In the actinic ray curable inkjet ink set comprising actinic ray curable inkjet inks (hereinafter also simply referred to as inks) of four or more colors, the inventor of the present invention presents an actinic ray curable inkjet black ink (hereinafter also simply referred to as a black ink). An oxetane compound and / or an alicyclic epoxy compound and a (meth) acrylate compound are used in combination as a photopolymerizable compound, and more than 330 nm in three or more colors of inks other than black ink or in all inks including black ink. It has been found that the above problem can be solved by containing a sensitizer having ultraviolet spectrum absorption at a wavelength.

  Further, as the photoinitiator in the black ink, it is more preferable to use only an onium salt photoacid generator such as an iodonium salt or a sulfonium salt and no substantial photoradical generator (1% by mass or less). It is preferable that the actinic ray curable inkjet white ink (hereinafter also simply referred to as white ink) has a composition similar to that of the black ink.

  As a most preferable configuration, a sulfonium salt that does not generate benzene after irradiation with actinic rays is used as a photoinitiator, and at least one oxetane ring is used as a photopolymerizable compound in inks of three or more colors other than black ink. Examples include using 30 to 95% by mass of the compound, 5 to 70% by mass of the compound having at least one oxirane group, and 0 to 40% by mass of at least one vinyl ether compound.

  Each ink used in the actinic ray curable inkjet ink set of the present invention contains a photoinitiator, a photopolymerizable compound, and a pigment.

  As the photopolymerizable compound in the black ink, an oxetane compound and / or an alicyclic epoxy compound and a (meth) acrylate compound are used in combination. More preferably, as the photopolymerizable compound in the white ink, an oxetane compound and / or an alicyclic epoxy compound and a (meth) acrylate compound are used in combination.

  Any known oxetane compound can be used, and examples thereof include OXT221, OXT121, RSOX, HQOX, BPOX, OXT212, OXT101, OXT213 manufactured by Toagosei Co., Ltd., but are not limited thereto.

  Examples of the epoxy compound include the following aromatic epoxides, alicyclic epoxides, and aliphatic epoxides.

  A preferable aromatic epoxide is a di- or polyglycidyl ether produced by the reaction of a polyhydric phenol having at least one aromatic nucleus or an alkylene oxide adduct thereof and epichlorohydrin, such as bisphenol A or an alkylene oxide thereof. Examples thereof include di- or polyglycidyl ethers of adducts, di- or polyglycidyl ethers of hydrogenated bisphenol A or its alkylene oxide adducts, and novolak-type epoxy resins. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

  As the alicyclic epoxide, cyclohexene oxide obtained by epoxidizing a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring with a suitable oxidizing agent such as hydrogen peroxide or peracid. Or a cyclopentene oxide containing compound is preferable.

  Preferred aliphatic epoxides include di- or polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, and typical examples thereof include diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol or Diglycidyl ether of alkylene glycol such as diglycidyl ether of 1,6-hexanediol, polyglycidyl ether of polyhydric alcohol such as di- or triglycidyl ether of glycerin or its alkylene oxide adduct, polyethylene glycol or its alkylene oxide adduct Diglycidyl ethers of polyalkylene glycols such as diglycidyl ethers, polypropylene glycols or diglycidyl ethers of adducts thereof Tel and the like. Here, examples of the alkylene oxide include ethylene oxide and propylene oxide.

  Among these epoxides, in view of fast curability, aromatic epoxides and alicyclic epoxides are preferable, and alicyclic epoxides are particularly preferable. In the present invention, one of the epoxides may be used alone, or two or more may be used in appropriate combination.

  As the (meth) acrylate compound, any known (meth) acrylate monomer and / or oligomer can be used.

  For example, isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isomyristyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid , Butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2 Hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, t- Monofunctional monomers such as butylcyclohexyl acrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6- Hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecane diacrylate Bifunctional monomers such as EO adduct diacrylate of bisphenol A, PO adduct diacrylate of bisphenol A, neopentyl glycol diacrylate hydroxypivalate, polytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EO-modified trimethylolpropane Triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, caprolactone modified trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate, caprolactam modified dipentaerythritol hexa Acrylate, etc. A trifunctional or higher polyfunctional monomer may be mentioned. In addition, polymerizable oligomers can be blended in the same manner as the monomer. Examples of the polymerizable oligomer include epoxy acrylate, aliphatic urethane acrylate, aromatic urethane acrylate, polyester acrylate, and linear acrylic oligomer.

  As a preferable formulation example of the photopolymerizable compound in the black ink, the oxetane compound and / or the alicyclic epoxy compound is 50 to 90% by mass, and the (meth) acrylate compound is 5 to 40% by mass.

  In the present invention, the ink of three or more colors excluding black ink or all inks including black ink is a polycyclic aromatic compound having at least one hydroxyl group, optionally substituted aralkyloxy group or alkoxy group as a substituent, It contains at least one compound selected from carbazole derivatives, phenothiazine derivatives, and thioxanthone derivatives as a sensitizer. By containing these, the dischargeability and curability due to changes in the environment (temperature, humidity) are stabilized, and a high-definition image can be stably formed.

  As the polycyclic aromatic compound that can be used in the present invention, naphthalene derivatives, anthracene derivatives, chrysene derivatives, and phenanthrene derivatives are preferable. As an alkoxy group which is a substituent, a C1-C18 thing is preferable and a C1-C8 thing is especially preferable. As the aralkyloxy group, those having 7 to 10 carbon atoms are preferable, and benzyloxy groups and phenethyloxy groups having 7 to 8 carbon atoms are particularly preferable. Specific examples include 1-naphthol, 2-naphthol, 1-methoxynaphthalene, 1-stearyloxynaphthalene, 2-methoxynaphthalene, 2-dodecyloxynaphthalene, 4-methoxy-1-naphthol, glycidyl-1-naphthyl ether. 2- (2-naphthoxy) ethyl vinyl ether, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 2,7-dimethoxynaphthalene, 1,1 ′ -Thiobis (2-naphthol), 1,1'-bi-2-naphthol, 1,5-naphthyl diglycidyl ether, 2,7-di (2-vinyloxyethyl) naphthyl ether, 4-methoxy-1-naphthol ESN-175 (Epoxy resin manufactured by Nippon Steel Chemical Co., Ltd.) The series, naphthalene derivatives such as condensates of naphthol derivatives and formalin, 9,10-dimethoxyanthracene, 2-ethyl-9,10-dimethoxyanthracene, 2-tbutyl-9,10-dimethoxyanthracene, 2,3- Dimethyl-9,10-dimethoxyanthracene, 9-methoxy-10-methylanthracene, 9,10-diethoxyanthracene, 2-ethyl-9,10-diethoxyanthracene, 2-tbutyl-9,10-diethoxyanthracene 2,3-dimethyl-9,10-diethoxyanthracene, 9-ethoxy-10-methylanthracene, 9,10-dipropoxyanthracene, 2-ethyl-9,10-dipropoxyanthracene, 2-tbutyl-9 , 10-dipropoxyanthracene, 2,3-dimethyl 9,10-dipropoxyanthracene, 9-isopropoxy-10-methylanthracene, 9,10-dibenzyloxyanthracene, 2-ethyl-9,10-dibenzyloxyanthracene, 2-tbutyl-9,10-di Benzyloxyanthracene, 2,3-dimethyl-9,10-dibenzyloxyanthracene, 9-benzyloxy-10-methylanthracene, 9,10-di-α-methylbenzyloxyanthracene, 2-ethyl-9,10- Di-α-methylbenzyloxyanthracene, 2-tbutyl-9,10-di-α-methylbenzyloxyanthracene, 2,3-dimethyl-9,10-di-α-methylbenzyloxyanthracene, 9- (α -Methylbenzyloxy) -10-methylanthracene, 9,10-di (2-hydro) Ciethoxy) anthracene, anthracene derivatives such as 2-ethyl-9,10-di (2-carboxyethoxy) anthracene, 1,4-dimethoxychrysene, 1,4-diethoxychrysene, 1,4-dipropoxychrysene, 1, Examples include chrysene derivatives such as 4-dibenzyloxychrysene and 1,4-di-α-methylbenzyloxychrysene, and phenanthrene derivatives such as 9-hydroxyphenanthrene, 9,10-dimethoxyphenanthrene, and 9,10-diethoxyphenanthrene. . Among these derivatives, 9,10-dialkoxyanthracene derivatives which may have an alkyl group having 1 to 4 carbon atoms as a substituent are particularly preferable, and the alkoxy group is preferably a methoxy group or an ethoxy group.

  Examples of the carbazole derivative include the following compounds. N-methylcarbazole, N-ethylcarbazole, N-propylcarbazole, N-butylcarbazole, N-vinylcarbazole, 1,3,6,8,9-pentamethylcarbazole, 1,4,5,8,9-penta Methylcarbazole (hereinafter referred to as “NMPC”), 3-formyl-N-ethylcarbazole, N-phenylcarbazole, N-ethyl-3,6-bis (benzoyl) -carbazole (hereinafter referred to as “NEBC”), 9,9′-diethyl-3,3′-dicarbazole (hereinafter referred to as “NEDC”).

  Examples of the phenothiazine derivatives include 2-methoxyphenothiazine, 2-chlorophenothiazine, 2-cyanophenothiazine, 2-acetylphenothiazine, 2-trifluoromethylphenothiazine, 2-methylthiophenothiazine, 2-dimethylaminosulfanylphenothiazine, and the like. .

  Examples of the thioxanthone derivative include thioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone 2-chlorothioxanthone, and the like.

  In the present invention, as the photoinitiator, all known photoacid generators published in “Application and Market of UV / EB Curing Technology” (CMC Publishing Co., Ltd., edited by Yoneho Tabata / edited by Radtech Research Association), etc. A photo radical generator can be used.

  The photoinitiator in the black ink or the white ink contains 1 to 10% by mass of an onium salt photoacid generator such as iodonium salt or sulfonium salt, and 0 to 1% by mass of a photo radical generator (substantially (Not contained) is preferable. If a photoradical generator is present (particularly if it exceeds 1% by mass), the photoacid generation efficiency of the onium salt becomes poor, and the reactivity of the polymerizable compound is remarkably lowered, which is not preferable.

In the ink set of the present invention, as a particularly preferable example in terms of dischargeability and curability, the photoinitiator of all inks contains a sulfonium salt that does not generate benzene after light irradiation, and has three or more colors other than black ink. The photopolymerizable compound in the ink is 30 to 95% by mass of a compound having at least one oxetane ring, 5 to 70% by mass of at least one alicyclic epoxy compound, and 0 to 40 of at least one vinyl ether compound. % By mass. In the present invention, “does not generate benzene by light irradiation” means that benzene is not substantially generated. Specifically, an ink containing 5% by mass of a sulfonium salt (photoinitiator) in the ink composition. The amount of benzene generated when printing an image having a thickness of 15 μm and about 100 m ² using an irradiating amount of actinic rays sufficient to decompose the photoacid generator with the ink film surface kept at 30 ° C. It indicates that there is no trace amount of 5 μg or less, or none. The sulfonium salt satisfies the above conditions as long as it has a substituent on the benzene ring bonded to S ^+, and examples thereof include the following.

In either case, X = PF ₆ ⁻
Any known vinyl ether compound may be used as the vinyl ether compound.

  Examples of the vinyl ether compound that can be used in the present invention include ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, propylene glycol divinyl ether, dipropylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, and cyclohexane. Di- or trivinyl ether compounds such as dimethanol divinyl ether and trimethylolpropane trivinyl ether, ethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinyl ether, cyclohexyl vinyl ether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexane dimethanol Vinyl, n- propyl vinyl ether, isopropyl vinyl ether, isopropenyl ether -O- propylene carbonate, dodecyl vinyl ether, diethylene glycol monovinyl ether, and octadecyl vinyl ether.

  Among these vinyl ether compounds, in consideration of curability, adhesion, and surface hardness, di- or trivinyl ether compounds are preferable, and divinyl ether compounds are particularly preferable. In the present invention, one of the above vinyl ether compounds may be used alone, or two or more thereof may be used in appropriate combination.

Specific examples of the pigment include those listed below, but the present invention is not limited to these.
C. I. Pigment Yellow
1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 81, 83, 87, 93, 95, 97, 98, 109, 114, 120, 128, 129, 138, 150, 151, 154, 180, 185
C. I. Pigment Red
5, 7, 12, 22, 38, 48: 1, 48: 2, 48: 4, 49: 1, 53: 1, 57: 1, 63: 1, 101, 112, 122, 123, 144, 146, 168, 184, 185, 202
C. I. Pigment Violet
19, 23
C. I. Pigment Blue
1, 2, 3, 15: 1, 15: 2, 15: 3, 15: 4, 18, 22, 27, 29, 60
C. I. Pigment Green
7,36
C. I. Pigment White
6, 18, 21
C. I. Pigment Black 7
In the present invention, it is preferable to use white ink in order to improve the color concealment property on a transparent substrate such as a plastic film. In particular, it is preferable to use white ink in soft packaging printing and label printing.

  The pigment may be subjected to various known surface treatments as necessary.

  For the dispersion of the pigment, 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 can be used. Moreover, it is also possible to use a synergist according to various pigments as a dispersion aid if necessary. These dispersants and dispersion aids are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment.

  The dispersion medium is used using a solvent or a polymerizable compound, but the actinic ray curable ink used in the present invention is preferably solventless because it reacts and cures immediately after ink landing. If the solvent remains in the cured image, the solvent resistance deteriorates and the VOC of the remaining solvent arises. Therefore, it is preferable in view of dispersibility that the dispersion medium is not a solvent but a polymerizable compound, and among them, a monomer having the lowest viscosity is selected.

  In the ink of the present invention, it is preferable that the viscosity at 25 ° C. is 7 to 50 mPa · s in order to obtain stable discharge and good curability regardless of the curing environment (temperature / humidity).

  As a recording material that can be used in the present invention, in addition to ordinary uncoated paper, coated paper, etc., various non-absorbable plastics and films used for so-called soft packaging can be used. Examples thereof include PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, PVA, rubbers and the like can be used. Moreover, it is applicable also to metals and glass. Among these recording materials, the configuration of the present invention is effective particularly when an image is formed on a PET film, OPS film, OPP film, ONy film, or PVC film that can be shrunk by heat. These substrates are not only susceptible to curling and deformation of the film due to ink curing shrinkage and heat generation during the curing reaction, but also the ink film is difficult to follow the substrate shrinkage.

  The surface energies of these various plastic films differ greatly, and it has been a problem in the past that the dot diameter after ink landing varies depending on the recording material. With the configuration of the present invention, a good high-definition image can be formed on a wide range of recording materials having a surface energy of 35 to 60 mN / m, including OPP films having a low surface energy, OPS films, and PET having a relatively large surface energy. .

  In the present invention, it is more advantageous to use a long (web) recording material in terms of the cost of the recording material such as packaging cost and production cost, the production efficiency of the print, and the ability to cope with printing of various sizes. is there.

  Next, the image forming method of the present invention will be described.

  In the image forming method of the present invention, a method is preferred in which the ink set is ejected and drawn on a recording material by an ink jet recording method, and then the ink is cured by irradiation with actinic rays such as ultraviolet rays.

(Total ink film thickness after ink landing)
In the present invention, the total ink film thickness after the ink has landed on the recording material and cured by irradiation with actinic rays is preferably 2 to 20 μm. In the actinic ray curable inkjet recording in the screen printing field, the total ink film thickness currently exceeds 20 μm, but in the flexible packaging printing field where the recording material is often a thin plastic material, the recording material described above is used. In addition to the problem of curling and wrinkles, there is a problem in that the entire printed material is changed in its strain and texture.

  Here, “total ink film thickness” means the maximum value of the film thickness of the ink drawn on the recording material, and even for a single color, other two colors are superimposed (secondary color), three colors are superimposed, four colors are used. Even when recording is performed by the overlapping (white ink base) inkjet recording method, the meaning of the total ink film thickness is the same.

(Ink ejection conditions)
As the ink ejection conditions, it is preferable from the viewpoint of ejection stability that the recording head and ink are heated to 35 to 100 ° C. and ejected. Actinic radiation curable ink has a large viscosity fluctuation range due to temperature fluctuations, and the viscosity fluctuations directly affect the droplet size and droplet ejection speed, causing image quality degradation. It is necessary to keep. The control range of the ink temperature is set temperature ± 5 ° C., preferably set temperature ± 2 ° C., more preferably set temperature ± 1 ° C.

  Moreover, in this invention, it is preferable that the amount of droplets discharged from each nozzle is 2 to 15 pl.

  Originally, in order to form a high-definition image, it is necessary for the amount of droplets to be within this range, but when discharging with this amount of droplets, the above-described discharge stability becomes particularly severe. According to the present invention, even when ejection is performed with a small droplet amount such as 2 to 15 pl, the ejection stability is improved and a high-definition image can be stably formed.

(Light irradiation conditions after ink landing)
In the image forming method of the present invention, the actinic ray is preferably irradiated for 0.001 second to 1.0 second after the ink landing, more preferably 0.001 second to 0. .5 seconds. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

  As a method for irradiating actinic rays, the basic method is disclosed in JP-A-60-132767. According to this, the light source is provided on both sides of the head unit, and the head and the light source are scanned by the shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In US Pat. No. 6,145,979, as an irradiation method, a method using an optical fiber or a method of applying a collimated light source to a mirror surface provided on the side of the head unit and irradiating the recording unit with UV light is disclosed. Yes. Any of these irradiation methods can be used in the image forming method of the present invention.

  Next, an ink jet recording apparatus (hereinafter simply referred to as a recording apparatus) of the present invention will be described.

  The recording apparatus of the present invention will be described below with reference to the drawings as appropriate. Note that the recording apparatus of the drawings is merely one aspect of the recording apparatus of the present invention, and the recording apparatus of the present invention is not limited to this drawing.

  FIG. 1 is a front view showing the configuration of the main part of the recording apparatus of the present invention. The recording apparatus 1 includes a head carriage 2, a recording head 3, an irradiation unit 4, a platen unit 5, and the like. In the recording apparatus 1, the platen unit 5 is installed under the recording material P. The platen unit 5 has a function of absorbing ultraviolet rays, and absorbs excess ultraviolet rays that have passed through the recording material P. As a result, a high-definition image can be reproduced very stably.

  The recording material P is guided by the guide member 6 and moves from the near side to the far side in FIG. 1 by the operation of the conveying means (not shown). A head scanning unit (not shown) scans the recording head 3 held by the head carriage 2 by reciprocating the head carriage 2 in the Y direction in FIG.

  The head carriage 2 is installed on the upper side of the recording material P, and stores a plurality of recording heads 3 to be described later according to the number of colors used for image printing on the recording material P, with the discharge ports arranged on the lower side. The head carriage 2 is installed with respect to the main body of the recording apparatus 1 in such a manner that it can reciprocate in the Y direction in FIG. 1, and reciprocates in the Y direction in FIG. 1 by driving the head scanning means.

  In FIG. 1, the head carriage 2 is white (W), yellow (Y), magenta (M), cyan (C), black (K), light yellow (Ly), light magenta (Lm), and light cyan (Lc). Although the drawing is carried out assuming that the recording heads 3 of light black (Lk) and white (W) are accommodated, the number of colors of the recording heads 3 accommodated in the head carriage 2 is determined as appropriate. Is.

  The recording head 3 has a discharge port by operating a discharge means (not shown) provided with a plurality of actinic ray curable inks (for example, UV curable ink) supplied by an ink supply means (not shown). To the recording material P. The UV ink ejected by the recording head 3 is composed of a coloring material, a polymerizable monomer, an initiator, and the like, and the monomer crosslinks when the initiator acts as a catalyst when irradiated with ultraviolet rays. It has the property of being cured by a polymerization reaction.

  During the scanning in which the recording head 3 moves from one end of the recording material P to the other end of the recording material P in the Y direction in FIG. 1 by driving the head scanning means, a certain area (landing possible area) in the recording material P On the other hand, UV ink is ejected as ink droplets, and ink droplets are landed on the landable area.

  The above scanning is performed as many times as necessary, and after UV ink is ejected toward one landable area, the recording material P is appropriately moved from the front to the back in FIG. 1, the recording head 3 discharges UV ink to the next landable area adjacent in the depth direction in FIG.

  By repeating the above operation and ejecting the UV ink from the recording head 3 in conjunction with the head scanning means and the conveying means, an image composed of an aggregate of UV ink droplets is formed on the recording material P.

  The irradiation unit 4 includes an ultraviolet lamp that emits ultraviolet light in a specific wavelength region with stable exposure energy and a filter that transmits ultraviolet light of a specific wavelength. Here, as the ultraviolet lamp, a mercury lamp, a metal halide lamp, an electrodeless lamp, an excimer laser, an ultraviolet laser, a cold cathode tube, a hot cathode tube, a black light, an LED (light emitting diode), etc. can be applied, A metal halide lamp, a cold cathode tube, a hot cathode tube, a mercury lamp or black light is preferred.

  The irradiating means 4 has substantially the same shape as the maximum one that can be set by the recording apparatus (UV inkjet printer) 1 among the landable areas in which the recording head 3 ejects UV ink by one scan driven by the head scanning means. , Having a shape larger than the landable area.

  The irradiation means 4 is fixed on both sides of the head carriage 2 so as to be substantially parallel to the recording material P.

  As described above, as a means for adjusting the illuminance of the ink discharge portion, not only the entire recording head 3 is shielded, but in addition, the ink discharge of the recording head 3 is determined from the distance h1 between the irradiation means 4 and the recording material P. It is effective to increase the distance h2 between the portion 31 and the recording material P (h1 <h2), or to increase the distance d between the recording head 3 and the irradiation means 4 (d is increased). Further, it is more preferable to provide a bellows structure 7 between the recording head 3 and the irradiation means 4.

  Here, the wavelength of the ultraviolet rays irradiated by the irradiation means 4 can be changed as appropriate by replacing the ultraviolet lamp or filter provided in the irradiation means 4.

  The ink of the present invention has excellent ejection stability and is particularly effective when an image is formed using a line head type recording apparatus.

  FIG. 2 is a top view illustrating another example of the configuration of the main part of the ink jet recording apparatus.

  The ink jet recording apparatus shown in FIG. 2 is called a line head system, and a plurality of recording heads 3 of each color are fixedly arranged on the head carriage 2 so as to cover the entire width of the recording material P. Yes.

  On the other hand, an irradiation unit 4 is provided on the downstream side of the head carriage 2 so as to cover the entire width of the recording material P.

  In this line head system, the head carriage 2 and the irradiating means 4 are fixed, and only the recording material P is conveyed, and ink ejection and curing are performed to form an image.

  Examples of the present invention will be specifically described below, but the embodiments of the present invention are not limited to these examples.

<< Preparation of Dispersion A >>
The pigment was dispersed with the following composition. The following two compounds were placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a 65 ° C. hot plate.
PB822 (dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 9 parts OXT-221 (manufactured by Toagosei Co., Ltd.) 71 parts After cooling to room temperature, 20 parts of the following pigment is added to this and placed in a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm. Sealed and dispersed with a paint shaker for the following time, after which zirconia beads were removed.
Pigment 1: Pigment Black 7 (Mitsubishi Chemical Corporation, # 52) 10 hours Pigment 2: Pigment Blue 15: 4
(Sanyo Color Co., Ltd., Cyanine Blue 4044) 6 hours Pigment 3: Pigment Yellow 150
(Manufactured by LANXESS, E4GN-GT CH20003) 10 hours Pigment 4: Pigment Red 122 (manufactured by Dainichi Seika Co., Ltd., special order) 10 hours Pigment 5: Titanium oxide (anatase type: particle size 0.2 μm) 10 hours << Dispersion B Preparation of
The pigment was dispersed with the following composition. The following two compounds were placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a 65 ° C. hot plate.
PB822 (dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 9 parts OXT-221 (manufactured by Toagosei Co., Ltd.) 71 parts After cooling to room temperature, 20 parts of the following pigment is added to this and placed in a glass bottle with 200 g of zirconia beads having a diameter of 0.5 mm. Sealed and dispersed with a paint shaker for the following time, after which zirconia beads were removed.
Pigment 1: Pigment Black 7 (Mitsubishi Chemical Corporation, # 52) 10 hours Pigment 2: Pigment Blue 15: 4
(Daiichi Seika Co., Ltd., Blue No. 32) 6 hour pigment 3: Pigment Yellow 180 (Daiichi Seika Co., Ltd., special order) 10 hour pigment 4: Pigment Red 19 (Daiichi Seika Co., Ltd., custom order) 10 hour pigment 5 : Titanium oxide (anatase type: particle size 0.2 μm) 10 hours << Preparation of ink composition >>
Inks were prepared with the ink compositions 1 to 6 described in Table 1 and Table 2, and filtered with a PP3 μm disk filter manufactured by Loki Techno. Each ink viscosity is as shown in the table. In addition, the number of each component in a table | surface is the mass%.

  In the table, the ink symbols are as follows.

K: Dark black ink C: Dark cyan ink M: Dark magenta ink Y: Dark yellow ink Lk: Light black ink Lc: Light cyan ink Lm: Light magenta ink Ly: Light yellow ink

<< Inkjet image forming method >>
Each of the ink composition sets 1 to 3 prepared above is loaded into an ink jet recording apparatus having the structure shown in FIG. 1 having a piezo type ink jet nozzle, and the length is 600 mm and 500 m long as shown in Table 3. The following image recording was continuously performed on each recording material. As the image data, “high-definition color digital standard image data“ N5 / bicycle ”(issued in December 1995 by the Japanese Standards Association) was used. The ink supply system was composed of an ink tank, a supply pipe, a front chamber ink tank immediately before the head, a pipe with a filter, and a piezo head. The ink was insulated from the front chamber tank to the head portion and heated at 50 ° C. The piezo head was driven so that 2 to 15 pl multi-size dots could be ejected at a resolution of 720 × 720 dpi, and each ink was ejected continuously. After landing, it is cured instantaneously (less than 1 second after landing) by the lamp units on both sides of the carriage. After recording, the total ink film thickness was measured and found to be in the range of 2.3 to 13 μm. In the present invention, dpi represents the number of dots per 2.54 cm. Inkjet images were formed according to the above method in an environment of 10 ° C. and 20% RH, an environment of 25 ° C. and 50% RH, and an environment of 27 ° C. and 80% RH, respectively.

  The details of the abbreviations of the recording materials listed in Table 3 are as follows.

PET: Polyethylene terephthalate
PVC: poly vinyl chloride
Further, in the same manner, an image was formed using the ink composition sets 4 to 6 using the line head recording type ink jet recording apparatus shown in FIG.

<Evaluation of inkjet recording image>
Each image recorded by the above image forming method was subjected to the following evaluations when outputting 1 m and 100 m.

(Character quality)
Using each color ink of Y, M, C, and K, a 6-point MS Mincho character was printed at a target density, and the character roughness was enlarged and evaluated with a loupe, and character quality was evaluated according to the following criteria.

◎: No rusting ○: Slight rustling is visible △: Gashesiness is visible, but it can be recognized as characters, but it can be used at the last minute ×: Levels that are extremely gritty and characters are faint and cannot be used (Color mixing (bleeding, 皺))
At 720 dpi, printing is performed so that one dot of each color of Y, M, C, and K is adjacent to each other, each adjacent color dot is enlarged with a loupe, the degree of bleeding is visually observed, and color mixing is evaluated according to the following criteria. .

◎: Adjacent dot shape keeps perfect circle and no blur ○: Adjacent dot shape keeps almost perfect circle and almost no blur △: Adjacent dots are slightly blurred and dot shape is slightly displaced , The level that can be used at last x: Table 4 shows the evaluation results obtained when the adjacent dots are blurred and mixed, and the overlapping portion has wrinkles and is not usable.

  The configuration of the present invention can form high-definition images very stably on various recording materials regardless of the printing environment.

It is a front view which shows an example of a structure of the principal part of the inkjet recording device of this invention. It is a top view which shows another example of a structure of the principal part of the inkjet recording device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording apparatus 2 Head carriage 3 Recording head 31 Ink ejection port 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure 8 Irradiation light source P Recording material

Claims (12)

An actinic radiation curable inkjet ink set comprising four or more actinic radiation curable inkjet inks containing a photoinitiator, a photopolymerizable compound, and a pigment, wherein the actinic radiation curable inkjet included in the actinic radiation curable inkjet ink set The black ink uses at least one selected from an oxetane compound and an alicyclic epoxy compound as a photopolymerizable compound in combination with a (meth) acrylate compound, and further has an activity of three or more colors excluding the actinic ray curable inkjet black ink. An activity characterized by containing a sensitizer having ultraviolet spectrum absorption at a wavelength longer than 330 nm in the photocurable ink-jet ink or in all active photocurable ink-jet inks including the active photocurable ink-jet black ink. Light curing type Ink jet ink set. The sensitizer is at least one compound selected from a polycyclic aromatic compound having at least one hydroxyl group, an optionally substituted aralkyloxy group or an alkoxy group as a substituent, a carbazole derivative, a phenothiazine derivative, and a thioxanthone derivative. The actinic ray curable inkjet ink set according to claim 1, wherein 1 to 10% by mass of an onium salt photoacid generator such as iodonium salt or sulfonium salt as a photoinitiator in the actinic ray curable inkjet black ink, and 0 to 1% by mass of a photoradical generator. The actinic ray curable inkjet ink set according to claim 1 or 2, When the actinic radiation curable inkjet ink set has an actinic radiation curable inkjet white ink, at least one selected from an oxetane compound and an alicyclic epoxy compound as a photopolymerizable compound in the actinic radiation curable inkjet white ink; The actinic ray curable inkjet ink set according to any one of claims 1 to 3, wherein a (meth) acrylate compound is used in combination. 1 to 10% by mass of an onium salt photoacid generator such as iodonium salt or sulfonium salt as a photoinitiator in the actinic ray curable inkjet white ink, and 0 to 1% by mass of a photoradical generator. The actinic ray curable inkjet ink set according to claim 4. A photopolymerizable compound in an actinic ray curable inkjet ink of three or more colors other than actinic ray curable inkjet black ink and actinic ray curable inkjet white ink, which contains a sulfonium salt that does not generate benzene after light irradiation as a photoinitiator As a compound containing 30 to 95% by mass of a compound having at least one oxetane ring, 5 to 70% by mass of at least one alicyclic epoxy compound, and 0 to 40% by mass of at least one vinyl ether compound. The actinic ray curable inkjet ink set according to any one of claims 1 to 5. The actinic ray curable inkjet ink set according to claim 1, wherein each actinic ray curable inkjet color ink has a viscosity at 25 ° C. of 7 to 50 mPa · s. An image forming method in which the actinic radiation curable inkjet ink of the actinic radiation curable inkjet ink set according to any one of claims 1 to 7 is jetted onto a recording material from an inkjet recording head, and printing is performed on the recording material. Then, after the actinic ray curable ink jet ink has landed, an actinic ray is irradiated for 0.001 to 1.0 seconds. An image forming method for performing printing on a recording material by jetting the actinic radiation curable inkjet ink set according to any one of claims 1 to 7 onto the recording material from an ink jet recording head, the active light curing An image forming method, wherein the total actinic ray curable inkjet ink film thickness after the ink jet ink is landed and cured by irradiation with actinic rays is 2 to 20 μm. An image forming method in which the actinic ray curable ink jet ink set according to any one of claims 1 to 7 is jetted onto a recording material from an ink jet recording head, and printing is performed on the recording material. An image forming method, wherein the amount of actinic ray curable inkjet ink droplets discharged from each nozzle is 2 to 15 pl. An image forming method in which the actinic ray curable inkjet ink set according to any one of claims 1 to 7 is jetted onto a recording material from an inkjet recording head, and printing is performed on the recording material. An image forming method comprising forming an image by ejecting from a recording head. It is an inkjet recording device used for the image forming method of any one of Claims 8-11, Comprising: It discharges, after heating actinic-light curable inkjet ink and a recording head to 35-100 degreeC. An inkjet recording apparatus.

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