JP2009096141A - Active energy ray-curable inkjet printing system and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active energy ray-curable inkjet printing system which causes little density unevenness and gloss unevenness and is excellent in curability and to provide its image forming method. <P>SOLUTION: In the active energy ray-curable inkjet printing system, a plurality of active energy ray-curable inks which are cured by active energy rays are delivered onto a recording medium by a plurality of recording heads 3, and then the active energy ray curable inks are cured by radiating active energy rays so as to form images. In this inkjet printing system, a plurality of the active energy ray irradiating parts are composed of two or more LED light sources LED 1 and 2 having different light emission characteristics. A plurality of the active energy ray curable inks are composed of two or more inks having different hues, and the composition of a photo polymerization initiator group contained by at least one of the inks has a composition that is different from the photo polymerization initiator group of the other ink. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an active energy ray-curable inkjet printing system having a novel configuration and an image forming method using the system.

  In recent years, an inkjet recording method can easily and inexpensively create an image, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as a color filter. In particular, inkjet recording devices that emit and control fine dots, ink with improved color reproduction gamut, durability, and emission suitability, ink absorbency, coloring material coloring, 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 jet ink (hereinafter also simply referred to as ink), and dedicated paper are available.

  However, in an inkjet system that requires special paper, the recording material 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, it is crosslinked by 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, or active energy rays (for example, ultraviolet rays) after recording. An active energy ray curable ink jet method or the like.

  Among them, the active energy ray curable inkjet method has been attracting attention in recent years in that 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 property and no ink absorption. Japanese Patent Publication No. 5-54667, Japanese Patent Application Laid-Open No. 6-200204, Japanese Patent Publication No. 2000-504778, etc. disclose ultraviolet curable ink-jet inks.

  The ink jet recording apparatus used for the output of the active energy ray curable ink mainly records an ink tank (also referred to as an ink cartridge) for storing and supplying the active energy ray curable ink, and records the ink as minute ink droplets. An inkjet recording head that discharges according to image information on a medium, an active energy ray irradiating light source for irradiating and curing an active energy ray curable ink droplet landed on a recording medium, and, in addition, It includes an ink supply path for feeding ink from the ink tank to the ink jet recording head, a filter, a transport mechanism for the recording medium, a control unit for controlling the output of the ink according to image information, and the like.

  As a printing method of the ink jet recording apparatus, an ink jet recording head having a carriage that reciprocates in the main scanning direction and a plurality of nozzles arranged in the sub scanning direction corresponding to each color on the carriage, and mainly active at both ends thereof. A serial system provided with an energy beam irradiation light source, an inkjet recording head in which a plurality of nozzles are arranged in the main scanning direction across the width of the recording medium to be printed, and an active energy beam irradiation light source at a position in the sub scanning direction However, there is a line system that is fixedly arranged.

  In recent years, various methods for increasing resolution or reducing density unevenness have been proposed as an attempt to improve image quality in an inkjet printing system using an active energy ray-curable ink. Although a certain level of image quality has been achieved by these technologies, the present situation is that the expectations for ever-increasing image quality, especially density unevenness reduction and gloss unevenness reduction, are not sufficiently met.

On the other hand, a method for improving the adhesion to a substrate by recording an inkjet ink containing a plurality of types of initiators with an inkjet printer having a plurality of light source types has been proposed (for example, see Patent Document 1). However, the description regarding the improvement of image quality such as reduction of density unevenness and gloss unevenness, which are the above-mentioned problems, is not recognized.
JP 2003-21370 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to use an active energy ray-curable inkjet ink set, and has an active energy ray-curable inkjet print that has less density unevenness and gloss unevenness and excellent curability. A system and an image forming method using the system are provided.

  The above object of the present invention is achieved by the following configurations.

1. After a plurality of active energy ray-curable inks that are cured with active energy rays from a plurality of recording heads are ejected onto a recording medium, the active energy ray-curable ink is irradiated with active energy rays from a plurality of active energy ray irradiation units. In an active energy ray-curable inkjet printing system for curing and forming an image,
The plurality of active energy ray irradiating units are composed of two or more types of LED light sources having different emission characteristics,
The plurality of active energy ray-curable inks are composed of two or more types of inks having different hues, and the configuration of the photopolymerization initiator group contained in at least one type of ink is a photopolymerization initiator group of another ink. An active energy ray-curable inkjet printing system, characterized by being different from the configuration of

  2. 2. The active energy ray-curable inkjet printing system according to 1 above, wherein a wavelength difference between the two or more types of LED light sources having different emission characteristics is in a range of 5 to 50 nm.

  3. 3. The above-described 1 or 2, wherein the plurality of recording heads are serial, and two types of LED light sources having different light emission characteristics are provided at both ends of a carriage on which the plurality of recording heads are mounted. Active energy ray curable inkjet printing system.

  4). The above-mentioned 1 or 2 characterized in that the plurality of recording heads are serial, have LED light sources at both ends of each recording head, and at least one of the LED light sources has different light emission characteristics from other LED light sources. An active energy ray-curable inkjet printing system according to 1.

  5). The above-described 1 or 2, wherein the plurality of recording heads are line systems and have LED light sources corresponding to the respective recording heads, and at least one of the LED light sources is different in light emission characteristics from other LED light sources. The active energy ray-curable inkjet printing system as described.

  6). Any one of the above 1 to 5, further comprising at least one irradiation light source selected from a high pressure mercury lamp, a metal halide lamp, a black light, and a cold cathode tube, in addition to the two or more types of LED light sources having different emission characteristics. 2. The active energy ray-curable inkjet printing system according to item 1.

  7. The plurality of active energy ray-curable inks are composed of at least a yellow ink, a magenta ink, a cyan ink, and a black ink, and the maximum light emission wavelength of an LED light source used for curing the yellow ink is an LED used for curing other inks. 7. The active energy ray-curable inkjet printing system according to any one of 1 to 6, wherein the wavelength is shorter than the maximum emission wavelength of the light source.

  8). 7. The wavelength difference between the maximum emission wavelength of the LED light source used for curing the yellow ink and the maximum emission wavelength of the LED light source used for curing the other ink is in the range of 5 to 50 nm. The active energy ray-curable inkjet printing system as described.

  9. 9. An image forming method comprising performing image formation using the active energy ray-curable inkjet printing system according to any one of 1 to 8 above.

  According to the present invention, an active energy ray-curable inkjet printing system using an active energy ray-curable ink-jet ink set with less density unevenness and gloss unevenness and excellent curability and an image forming method using the same are provided. I was able to.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor discharged a plurality of active energy ray-curable inks that are cured with active energy rays from a plurality of recording heads onto a recording medium, and then irradiated with a plurality of active energy rays. In the active energy ray-curable inkjet print system, the active energy ray curable ink is cured by irradiating the active energy ray from the portion to cure the active energy ray curable ink, and the plural active energy ray irradiating portions have two or more kinds of light emission characteristics. It is composed of different LED light sources, and the plurality of active energy ray-curable inks are composed of two or more kinds of inks having different hues, and the composition of the photopolymerization initiator group contained in at least one kind of ink is different from that of the other According to an active energy ray-curable inkjet printing system, which differs from the composition of the photopolymerization initiator group of the ink It was found that an active energy ray-curable inkjet printing system capable of forming a high-quality image, having low density unevenness and gloss unevenness, high productivity, and a wide range of substrate suitability can be realized. .

  As described above, Patent Document 1 proposes a method for improving adhesion to a substrate by recording an inkjet ink containing a plurality of types of initiators with an inkjet printer having a plurality of light source types. However, using multiple types of initiators in a single ink, using a single light source (for example, a metal halide lamp), the light is split into multiple types of light with different spectral spectra using a cut filter or the like, and this is used as the irradiation light source This method is effective to some extent with respect to monochromatic image formation, but it is difficult to apply to multicolor image formation in recent years, and also reduces the spectral energy amount of a single light source. In an aspect, this is a method of obtaining radiation having different wavelengths, which inevitably results in a reduction in the amount of irradiation energy.

  The present invention relates to an LED (Light Emitting Diode) that emits light with less radiant heat and easily controls the amount of light and has an extremely narrow emission wavelength width (half-value width) in image formation using two or more types of inks having different hues. ) Is used in plural types. That is, an LED having an optimal spectral spectrum is used in accordance with the spectral transmission characteristics of each color ink image formed on each recording medium, and a combination of a photopolymerization initiator and a sensitizer contained in each ink. Can be adjusted according to the characteristics of the LED to be used, so that the curing speed between the inks can be adjusted. As a result, the rate of change with the surface tension at the time of curing is set to a constant condition between the inks. It has become possible to control, the dot diameter fluctuation between each color ink after landing on the recording medium is suppressed, and it has been found that high-quality images can be obtained by greatly suppressing density unevenness and gloss unevenness It is.

  Details of the present invention will be described below.

<Multiple active energy ray curable inks>
First, the active energy ray-curable ink according to the present invention will be described.

  A plurality of active energy ray-curable inks (hereinafter, also simply referred to as inks) according to the present invention constitute an ink set composed of two or more kinds of inks having different hues, and at least one kind of ink contains photopolymerization initiation The constitution of the agent group is different from the constitution of the photopolymerization initiator group of other inks.

  The ink constituting the ink set according to the present invention is preferably at least two types selected from yellow ink, magenta ink and cyan ink, and further includes four types of yellow ink, magenta ink, cyan ink and black ink. It is preferable to include. Further, if necessary, the ink set according to the present invention may have a configuration in which light color ink (for example, light magenta ink, light cyan ink, light black ink, etc.) or white ink using a white pigment is added. .

  Each active energy ray-curable ink according to the present invention is mainly composed of an active energy ray-polymerizable compound (hereinafter also simply referred to as a polymerizable compound), a constituent compound of a photopolymerization initiator group, and a color material. The constitution of the photopolymerization initiator group referred to in the present invention is a single photopolymerization initiator, a plurality of photopolymerization initiators, a combination of a photopolymerization initiator and a sensitizer, and a photopolymerization initiator and a sensitizer. The photopolymerization initiator group is different in composition between at least two types of ink.

[Active energy ray polymerizable compound]
Examples of the active energy ray polymerizable compound applicable to the active energy ray curable ink according to the present invention include a radical polymerizable compound and a cationic polymerizable compound.

(Radically polymerizable compound)
The radically polymerizable compound applicable to the present invention is a compound having an ethylenically unsaturated bond capable of radical polymerization, and any compound having at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. In other words, those having chemical forms such as monomers, oligomers and polymers are included. Only one kind of radically polymerizable compound may be used, or two or more kinds thereof may be used in combination at an arbitrary ratio in order to improve desired properties. A polyfunctional compound having two or more functional groups is more preferable than a monofunctional compound. More preferably, two or more polyfunctional compounds are used in combination for controlling performance such as reactivity and physical properties.

  Examples of compounds having an ethylenically unsaturated bond capable of radical polymerization include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and their salts, esters, urethanes, amides. And radically polymerizable compounds such as various unsaturated polyesters, unsaturated polyethers, unsaturated polyamides and unsaturated urethanes. Specifically, acryloylmorpholine, phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate Bis (4-acryloxypolyethoxyphenyl) propane, EO-modified bisphenol A diacrylate, polyethylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerin epoxy acrylate, neopentyl glycol diacrylate, 1,6-hexane Diol diacrylate, ethylene glycol dia Relate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, trimethylolpropane triacrylate, Acrylic acid derivatives such as tetramethylol methane tetraacrylate, oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, epoxy acrylate, methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, allyl methacrylate, glycine Methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylolethane trimethacrylate, trimethylolpropane Examples include methacrylic derivatives such as trimethacrylate, 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate, and triallyl trimellitate. , Yamashita Shinzo, “Crosslinking agent handbook” (Taisei, 1981); Kato Kiyomi, “UV / EB Curing Han” Dobook (raw material edition) "(1985, Polymer publication society); Radtech study edition," Application and market of UV / EB curing technology ", p. 79, (1989, CMC); Eiichiro Takiyama," Polyester Commercially available products described in “Resin Handbook”, (1988, Nikkan Kogyo Shimbun), or radically polymerizable or crosslinkable monomers, oligomers and polymers known in the industry can be used. The amount of the radical polymerizable compound added is preferably 1 to 97% by mass, more preferably 30 to 95% by mass.

(Cationically polymerizable compound)
Examples of the cationic polymerizable compound applicable to the present invention include an epoxy compound, an oxetane compound, and a vinyl ether compound that can be polymerized by cationic polymerization.

  Examples of the epoxy compound that can be used in the present invention include JP-A No. 2001-220526, JP-A No. 2002-188025, JP-A No. 2002-317139, JP-A No. 2003-55449, and JP-A No. 2003-73481. Any known epoxy compound described in 1. can be used, and a compound having at least one cycloalkane ring such as cyclohexene or cyclopentene ring is epoxidized with a suitable oxidizing agent such as hydrogen peroxide or peracid. A cyclohexene oxide or cyclopentene oxide-containing compound obtained by this is preferable.

  As the oxetane compound that can be used in the present invention, for example, any known oxetane compound as disclosed in JP-A Nos. 2001-220526 and 2001-310937 can be used.

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

  One of the polymerizable compounds may be used alone, but two or more may be used in appropriate combination.

  In addition, as a means for preventing a decrease in sensitivity due to the light-shielding effect due to the ink color material, it is possible to combine a cationically polymerizable monomer having a long initiator lifetime with an initiator to obtain a radical-cation hybrid curable ink.

[Configuration of photopolymerization initiator group]
Examples of the additive constituting the photopolymerization initiator group according to the present invention include radical polymerization initiators, cationic polymerization initiators, initiation assistants, and sensitizers. The added amount of these photopolymerization initiator groups in the ink is required to be 1 to 10 parts by mass of the whole ink.

  Various known compounds can be used for the photopolymerization initiator group according to the present invention, and the photopolymerization initiator group is selected from those soluble in the polymerizable compound.

(Photopolymerization initiator)
<Radical polymerization initiator>
Examples of the radical polymerization initiator include triazine derivatives described in JP-B-59-1281, JP-A-69-1621, and JP-A-60-60104, JP-A-59-1504 and JP-A-61-2243807. And other publications such as JP-B Nos. 43-23684, 44-6413, 44-6413, and 47-1604, and US Pat. No. 3,567,453. Diazonium compounds described in the specification, organic azide compounds described in U.S. Pat. Nos. 2,848,328, 2,852,379 and 2,940,853, Japanese Patent Publication No. 36-22062, Ortho-quinonediazides described in JP-A-37-13109, JP-A-38-18015, JP-A-45-9610, JP-B-55-39162, JP-A-59-1 No. 023 etc. and various onium compounds described in “Macromolecules, Vol. 10, Volume 1307 (1977)”, azo compounds described in JP-A-59-142205, 1-54440, European Patent Nos. 109,851 and 126,712, “Journal of Imaging Science” (J. Imag. Sci.), Vol. 30, No. 174 Page (1986), metal allene complexes described in JP-A-4-2133861 and JP-A-4-255347, organoboron complexes described in JP-A-4-151197, and titanocene described in JP-A-61-151197. "Coordination Chemistry Review" ry Review), 84, 85-277 (1988) and JP-A-2-182701, transition metal complexes containing transition metals such as ruthenium, JP-A-3-209477 Examples include 2,4,5-triarylimidazole dimer, carbon tetrabromide, and organic halogen compounds described in JP-A-59-107344. These polymerization initiators are preferably contained in the range of 0.01 to 10 parts by mass with respect to 100 parts by mass of the compound having an ethylenically unsaturated bond capable of radical polymerization.

<Cationic polymerization initiator>
The active energy ray-curable ink according to the present invention preferably contains a cationic polymerization initiator as a photopolymerization initiator together with the cationic polymerizable compound.

  Specific examples of the cationic polymerization initiator include a photoacid generator and the like. For example, a chemical amplification type photoresist or a compound used for photocationic polymerization is used (edited by Organic Electronics Materials Research Group, “ Organic materials for imaging ", Bunshin Publishing (1993), see pages 187-192). Examples of compounds suitable for the present invention are listed below.

First, B (C ₆ F ₅ ) ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ SO ₃ ⁻ salt of aromatic onium compounds such as diazonium, ammonium, iodonium, sulfonium, phosphonium, etc. be able to.

  Specific examples of onium compounds that can be used in the present invention are shown below.

  Secondly, sulfonated compounds that generate sulfonic acid can be mentioned, and specific compounds thereof are exemplified below.

  Thirdly, halides that generate hydrogen halide can also be used, and specific compounds thereof are exemplified below.

  Fourthly, an iron allene complex can be mentioned.

(Sensitizer)
In the active energy ray-curable ink according to the present invention, it is preferable to use a sensitizer having ultraviolet spectrum absorption at a wavelength longer than 300 nm. For example, a hydroxyl group, an optionally substituted aralkyloxy group or A polycyclic aromatic compound having at least one alkoxy group, a carbazole derivative, a thioxanthone derivative, and the like can be given.

  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.

  Examples of these sensitizers that can be used in the present invention include carbazole derivatives such as carbazole, N-ethylcarbazole, N-vinylcarbazole, N-phenylcarbazole, 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 diglycid Ether, 2,7-di (2-vinyloxyethyl) naphthyl ether, 4-methoxy-1-naphthol, ESN-175 (epoxy resin manufactured by Nippon Steel Chemical Co., Ltd.) or its series, condensate of naphthol derivative and formalin, etc. Naphthalene derivatives, 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-di Ethoxyanthracene, 9-ethoxy-10-methylanthracene, 9, 0-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-dibenzyloxyanthracene, 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-hydroxyethoxy) anthracene, 2-ethyl-9,10 -Anthracene derivatives such as di (2-carboxyethoxy) anthracene, 1,4-dimethoxychrysene, 1,4-diethoxychrysene, 1,4-dipropoxychrysene, 1,4-dibenzyloxychrysene, 1,4- Examples include chrysene derivatives such as di-α-methylbenzyloxychrysene, 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 methoxy group and ethoxy group are preferable as the alkoxy group.

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

(Starting aid)
An initiator is a substance that acts as a sensitizing dye that improves the radical or acid generation efficiency of an initiator by donating energy to the initiator by light irradiation, electron donation, electron attraction, heat generation, etc. Yes, applied in combination with initiator.

  Examples of the initiator include xanthene, thioxanthone dye, ketocoumarin, thioxanthene dye, cyanine, phthalocyanine, merocyanine, porphyrin, spiro compound, ferrocene, fluorene, fulgide, imidazole, perylene, phenazine, phenothiazine, polyene, azo compound, diphenylmethane , Triphenylmethane, polymethine acridine, coumarin, ketocoumarin, quinacridone, indigo, styryl, pyrylium compound, pyromethene compound, pyrazolotriazole compound, benzothiazole compound, barbituric acid derivative, thiobarbituric acid derivative and the like can be applied.

  In addition to the above-mentioned compounds, it is well known that the initiator acts as a sensitizing dye in documents such as “Development technology of polymer additives” (CMC Publishing Co., Ltd., supervised by Junichi Daikatsu). The substance may be applied. The initiation assistant can also be regarded as a component that forms part of the photopolymerization initiator.

  In addition to these photoinitiators, an accelerator aid may be added to accelerate the photopolymerization (curing) reaction. Examples of these include ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, ethanolamine, diethanolamine, triethanolamine and the like.

  Examples of a combination of a radical polymerization initiator and an initiator that are applied to the radical polymerizable composition include a peracid ester as a radical polymerization initiator and xanthene, a thioxanthone dye, a ketocoumarin, a thiopyrylium salt as an initiator. And a combination of an onium salt such as diphenyliodonium salt which is a radical polymerization initiator and a thioxanthene dye which is an initiation assistant are well known.

  Further, when applying titanocenes as radical polymerization initiators, as initiators for sensitizing the titanocenes from visible light to near infrared light corresponding to lasers or LEDs, for example, cyanine, phthalocyanine, merocyanine, porphyrin, Spiro compound, ferrocene, fluorene, fulgide, imidazole, perylene, phenazine, phenothiazine, polyene, azo compound, diphenylmethane, triphenylmethane, polymethine acridine, coumarin, ketocoumarin, quinacridone, indigo, styryl, pyrylium compound, pyromethene compound, pyrazolotriazole A compound, a benzothiazole compound, a barbituric acid derivative, a thiobarbituric acid derivative, or the like can be applied.

  As the starting aid used in combination with titanocene, further, European Patent No. 568,993, US Patent Nos. 4,508,811, 5,227,227, JP 2001-125255 A, JP 11-271969 A, etc. The compounds described in (1) are also applicable. Specific examples of the combination of such a titanocene radical polymerization initiator and an initiation assistant include combinations described in JP-A Nos. 2001-125255 and 11-271969.

[Color material]
The coloring material used for the active energy ray-curable ink according to the present invention may be a pigment or a dye. From the viewpoint of the weather resistance of the image, it is preferable to use a pigment.

The pigments that can be preferably used in the present invention are listed below.
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.

  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. Further, a dispersing agent can be added when dispersing the pigment. As the dispersant, a polymer dispersant is preferably used, and examples of the polymer dispersant include Avecia's Solsperse series and Ajinomoto Fine-Techno's PB series. Moreover, it is also possible to use a synergist according to various pigments as a dispersion aid. These dispersants and dispersion aids are preferably added in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the pigment. The dispersion medium is used using a solvent or a polymerizable compound. However, the radiation curable ink used in the present invention is preferably solvent-free 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.

  The pigment is preferably dispersed so that the average particle diameter of the pigment particles is 0.08 to 0.2 μm, and the maximum particle diameter is 0.3 to 10 μm, preferably 0.3 to 3 μm. The selection of the dispersion medium, the dispersion conditions, and the filtration conditions are appropriately set. By controlling the particle size, clogging of the head nozzle can be suppressed, and ink storage stability, ink transparency, and curing sensitivity can be maintained.

  In the ink according to the present invention, the color material concentration is preferably 1% by mass to 30% by mass of the entire ink. For inks other than white, the content is more preferably 1% by mass to 10% by mass.

[Other additives]
A polymerization inhibitor can be added to the ink according to the present invention in an amount of 200 to 20000 ppm from the viewpoint of improving the storage stability. Since the ink according to the present invention is preferably ejected by heating and lowering the viscosity in the range of 40 to 80 ° C., it is preferable to add a polymerization inhibitor in order to prevent head clogging due to thermal polymerization.

  In addition to this, surfactants, leveling additives, matting agents, polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, and waxes are added to adjust film properties as necessary. can do.

《Active energy ray curable inkjet printing system》
Next, the configuration of the ink jet recording apparatus used in the active energy ray-curable ink jet printing system of the present invention will be described with reference to the drawings. However, the present invention is not limited to the configuration described in the drawings illustrated here.

  In the active energy ray-curable inkjet printing system of the present invention, after ejecting a plurality of active energy ray-curable inks that are cured with active energy rays from a plurality of recording heads onto a recording medium, a plurality of active energy ray irradiation units In the active energy ray-curable inkjet printing system for irradiating an active energy ray to cure the active energy ray curable ink to form an image, the plurality of active energy ray irradiating portions are two or more kinds of LEDs having different light emission characteristics. It is characterized by comprising a light source.

  In the present invention, it is preferable that a plurality of recording heads are serial and that two types of LED light sources having different light emission characteristics are provided at both ends of a carriage on which the plurality of recording heads are mounted. It is one of.

  First, the main configuration of a serial type inkjet recording apparatus applicable to the present invention will be described.

  FIG. 1 is a schematic perspective view showing an example of a main configuration of a serial type ink jet recording apparatus applicable to the present invention.

As shown in FIG. 1, the ink jet recording apparatus according to the present invention includes a conveying means (not shown) for conveying the base material 2 forward during printing, and the base material 2 with each color (in FIG. 1, yellow as an example). (Y, magenta (M), cyan (C), and black (K) are shown), and a plurality of recording heads 3 for discharging ink and the recording heads 3 for each of the plurality of colors are discharged. A carriage for storing LED light sources LED1 and LED2 composed of two types of LEDs each having different emission characteristics for irradiating the substrate 2 with active energy rays at both ends of the recording head for curing the ink. 4 and maintenance unit 5 having a capping unit 51 and a cleaning unit 52 for performing the maintenance of the recording head 3, and at the time of printing or maintenance For example, a guide rail 6 for guiding the carriage 4 along the horizontal direction (arrow A), a home position 7 having a moisturizing cap 71 serving as a standby area for the carriage 4, and a control unit (not shown) for controlling these parts. ) Etc. T ₀ is an ink tank for supplying ink, and each ink sent from the tank T ₀ is once stored in the sub-tank T and then sent to the recording head through the ink supply path P through the supply valve V. It has a configuration.

  The sub-tank T is an intermediate tank that is usually provided at a position below the recording head in order to adjust the back pressure of the ink in the recording head. The intermediate tank is also provided nearer to the recording head, and again, an intermediate damper that serves as a damper for mitigating sudden changes in ink back pressure due to movement of the carriage after scanning during scanning. (Not shown in FIG. 1) are examples of intermediate tanks.

  The conveying means conveys the substrate 2 on the printing (image forming) area C in synchronization with the operation of the carriage 4 after printing and irradiation with active energy rays, and prints and prints with ink from the recording head by image signals. Irradiation of active energy rays by the subsequent LED light sources LED1 and LED2 is performed, and the substrate 2 is transported downward (arrow B) from the printing area in accordance with the end.

  In addition, although not shown here, the base material 2 that has been printed by scanning and irradiated with active energy rays from the LEDs 1 and 2 is further provided with a second light source at a downstream position where the base material is transported after the printing area. And may be irradiated.

  The recording head has a head substrate, an ink discharge main body, a temperature sensor (temperature measuring means) that measures the temperature in the vicinity of the ink discharge main body, and a discharge port sensor for detecting clogging of the discharge port. A flexible cable for inputting and outputting signals is connected to the main body of the ink discharge unit and the sensor. A plurality of ink discharge ports are provided on the ink discharge surface of the ink discharge main body portion along the center line of the ink discharge surface so as to face the substrate 2, and the discharge ports communicate with the ink nozzles (flow paths). ing. Further, in the present invention, the recording head, the ink flow path in the recording head, the liquid feeding tube (piping), etc., particularly the recording head, in the case of the ink according to the present invention, as described above, can maintain the fluidity of the ink. It can be kept warm or heated.

  The control unit according to the inkjet recording apparatus of the present invention includes an interface, a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processing Unit), and the like, and a control program and control written in the ROM. Various devices connected to the interface are controlled according to the data.

  The recording head 3, the carriage 4, the suction pump 54, the irradiation light source LED, the heating unit, the temperature sensor, the discharge port sensor, the transport unit, the moving unit, and the like are electrically connected to the interface.

  Various control programs and control data relating to the operation of each unit of the ink jet printer are written in the ROM.

  The RAM can store a plurality of input data only while power is supplied, and includes a storage area for storing various data such as image data to be imaged and a work area for the CPU.

  The CPU develops a program designated from various programs stored in the ROM in a work area in the RAM, and executes various processes according to the program in accordance with input signals from each sensor.

As the LED light source used in the present invention, one having an emission wavelength of 200 nm to 420 nm is preferably used. Considering the cost of the light source and the output intensity, it is more preferable to use an ultraviolet to visible LED having an emission wavelength of 350 nm to 420 nm. Examples of LED light sources (light-emitting diodes) that can be applied to the present invention include LEDs with a peak wavelength of 365 nm (manufactured by Nichia Corporation) and an illuminance of 100 mW / cm ² , LED Zero (peak) manufactured by INTEGRATION Wavelength: 395 nm, illuminance: 1 to 2.5 W / cm ² ), and the like.

  In the present invention, the plurality of active energy ray irradiating portions are composed of two or more types of LED light sources having different emission characteristics, but the wavelength difference between the two or more types of LED light sources is 5 to 50 nm. It is preferable that it is the range of 10-40 nm, More preferably, it is the range of 10-40 nm, Most preferably, it is the range of 20-35 nm.

  FIG. 2 is a schematic top view and a schematic side view showing another example of the configuration of the serial carriage unit.

  FIG. 2A is a top view showing an example of a carriage configuration that moves in a serial manner on a recording medium. In FIG. 2 a, the inkjet printer 1 is a serial inkjet printer, and has a flat platen 12 that supports the non-recording surface on the back side of the recording surface of the recording medium 2 inside the housing. . The platen 12 is provided with a recording medium adsorption fan for adsorbing the non-recording surface of the recording medium 2, thereby adopting a configuration for supporting the recording medium 2. Further, before and after the platen 12, transport rollers 13a and 13b of the recording medium transport mechanism 13 are disposed, respectively. The conveyance rollers 13a and 13b are coupled by a conveyance belt 13c and rotate in a predetermined direction around the axis before and after the platen 12, and the recording medium 2 is conveyed in the conveyance direction as the conveyance rollers 13a and 13b rotate. It is conveyed along B.

  An image recording unit 4 that records an image on the recording surface of the recording medium 2 is disposed above the platen 12 inside the housing. The image recording unit 4 includes a guide member 11 extending in a direction orthogonal to the transport direction B (hereinafter referred to as a scanning direction A), and the carriage 4 is supported on the guide member 11. The carriage 4 is reciprocally movable along the scanning direction A while being guided by the guide member 11 by driving of the carriage driving mechanism.

  As an example, four recording heads 3Y and 3M that discharge yellow (Y), magenta (M), cyan (C), and black (K) inks toward the recording surface of the recording medium 2, respectively. 3C and 3K are mounted, and the four recording heads 3Y, 3M, 3C, and 3K can be moved simultaneously by the reciprocating movement of the carriage 4. A plurality of nozzles (not shown) for ejecting ink as droplets are disposed on the sides of the recording heads 5, 6, 7, 8 facing the recording surface of the recording medium 99. The plurality of nozzles are arranged along the conveyance direction B of the recording medium 2 for each of the recording heads 3Y, 3M, 3C, and 3K to form nozzle rows (not shown), and the recording head having the nozzle outlets A surface facing the recording surface of the recording medium 2 in 3Y, 3M, 3C, and 3K is a nozzle surface (not shown).

  Further, LED light sources LED1 and LED2 each composed of two types of LEDs each having different emission characteristics for irradiating the ink landed on the recording medium 2 with active energy rays are mounted on both ends in the scanning direction A of the carriage 4, respectively. The LED light sources LED1 and LED2 are also movable by the reciprocating movement of the carriage 4 in the same manner as the recording heads 3Y, 3M, 3C, and 3K. Each of the LED light sources LED1 and LED2 is provided with a plurality of LEDs (light emitting diodes) having different spectral characteristics and irradiates the recording surface of the recording medium 2 with active energy rays (ultraviolet rays) having different spectral characteristics. Be able to.

  FIG. 2B is a schematic side view of the carriage structure that moves in the serial manner shown in FIG. 2A. The light emission characteristics are provided at both ends of the recording head group composed of 3Y, 3M, 3C, and 3K. LED light sources LED1 and LED2 each composed of different LEDs are mounted.

  In the present invention, the plurality of recording heads are serial, and each recording head has an LED light source at both ends, and at least one of the LED light sources has a configuration in which light emission characteristics are different from those of other LED light sources. Is preferred.

  FIG. 2C) is a schematic cross-sectional view showing another example of the configuration of the serial carriage unit.

  In FIG. 2c), recording heads 3Y, 3M, 3C, and 3K are provided on a carriage 4 that can reciprocate in the A direction, and LED light sources are provided at both ends of each recording head. At this time, it is a preferable aspect that at least one kind of LED light source has a configuration in which light emission characteristics are different from those of other LED light sources. In the example shown in FIG. 2c), the LED light source LED1 provided at both ends of the recording head 3Y and the LED light source LED1 at the both ends of the recording heads 3M, 3C, and 3K have different light emission characteristics. It is the structure which provided LED light source LED2. In the present invention, the maximum emission wavelength of the LED light source (LED1) used for curing the yellow ink is shorter than the maximum emission wavelength of the LED light source (LED2) used for curing other inks. It is preferable from the viewpoint that the curing speed can be made uniform.

  FIG. 2D is a schematic cross-sectional view illustrating another example of the serial carriage configuration.

  The configuration shown in (d) of FIG. 2 has another active energy irradiation light source 41 different from the LED light source, specifically, a high pressure at both outer ends of the recording head group of the carriage shown in (c) of FIG. 1 shows a configuration in which at least one irradiation light source selected from a mercury lamp, a metal halide lamp, a black light, and a cold cathode tube is provided.

  In the present invention, the plurality of recording heads is a line type, has an LED light source corresponding to each recording head, and at least one of the LED light sources is configured to have different light emission characteristics from other LED light sources. One preferred embodiment.

  FIG. 3 is a top view and a side view showing an example of a main configuration of a line-type inkjet recording apparatus applicable to the present invention.

  FIG. 3A is a top view showing an example of an ink jet recording apparatus including a line type recording head and a corresponding LED light source.

  In FIG. 3 a), each recording head and its corresponding LED light source are fixed on the recording medium 2 held by the conveying roller 9 and conveyed in the B direction at a position covering the width of the recording medium. is set up.

  In FIG. 3A, a recording head 8Y that discharges yellow ink, a recording head 8M that discharges magenta ink, a recording head 8C that discharges cyan ink, and a recording head 8K that discharges black ink are sequentially installed as recording heads. LED light sources corresponding to the downstream sides of the respective recording heads are installed.

  At this time, in the present invention, the maximum emission wavelength of the LED light source (LED • Y) used for curing the yellow ink is the same as that of the LED light source (LED • M, LED • C, LED • K) used for curing other ink. A wavelength shorter than the maximum emission wavelength is preferable from the viewpoint that the curing speeds among the color inks can be made uniform. The wavelength difference between the LED light sources is preferably in the range of 5 to 50 nm, more preferably in the range of 10 to 40 nm, and particularly preferably in the range of 20 to 35 nm.

  FIG. 3B is a side view of the ink jet recording apparatus including the line-type recording head shown in FIG. 3A and the corresponding LED light source when viewed from the X direction.

"recoding media"
As a recording medium that can be used in the present invention, in addition to ordinary uncoated paper, coated paper, and the like, various non-absorbable plastics used in so-called soft packaging and films thereof can be used. For example, polyethylene terephthalate (PET) film, stretched polystyrene (OPS) film, stretched polypropylene (OPP) film, stretched nylon (ONy) film, polyvinyl chloride (PVC) film, polyethylene (PE) film, triacetyl cellulose (TAC) ) A film etc. can be mentioned. As other plastics, polycarbonate, acrylic resin, ABS, polyacetal, polyvinyl alcohol (PVA), rubbers and the like can be used. Moreover, it is applicable also to metals and glass. Among these recording media, the configuration of the present invention is effective particularly when an image is formed on a PET film, an OPS film, an OPP film, an ONy film, or a 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 energy of these various plastic films differs greatly, and it has been a problem in the past that the dot diameter after ink landing varies depending on the recording medium. The active energy ray-curable inkjet printing system of the present invention is suitable for a wide range of recording media 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. High-definition images can be formed.

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

<Image forming conditions>
The active energy ray-curable ink jet printing system of the present invention ejects and draws the ink according to the present invention on a recording medium by an ink jet recording method, and then irradiates active energy rays from two or more types of LED light sources having different light emission characteristics. This is a method of curing the ink.

(Total ink film thickness after ink landing)
In the present invention, the total ink film thickness after the ink has landed on the recording medium 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 medium is often a thin plastic material, the recording medium 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 medium, 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 discharge conditions, it is preferable from the viewpoint of discharge stability that the ink jet recording head and the ink are heated to 35 to 100 ° C. and discharged. 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.

(Activation energy ray irradiation conditions after ink landing)
In the image forming method of the present invention, as the irradiation condition of the active energy ray, the active energy ray is preferably irradiated between 0.001 second and 2.0 seconds after landing of the ink, and more preferably 0.001 second. It is -1.0 second, More preferably, it is 0.001 second-0.5 second. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<Preparation of dispersion>
[Preparation of Dispersion A]
Each of the following compounds was placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.

PB822 (dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 8 parts Tetraethylene glycol diacrylate (TEGDA, bifunctional) 72 parts After cooling to room temperature, 20 parts of Pigment Black 7 (Mitsubishi Chemical Co., Ltd. # 52) was added, 200 g of zirconia beads having a diameter of 0.3 mm were placed in a glass bottle and sealed, and dispersed for 4 hours with a paint shaker. Then, the zirconia beads were removed to prepare dispersion A.

[Preparation of dispersions B to D]
In the preparation of the above dispersion A, Pigment Black 15: 4 (Cyanine Blue 4044 manufactured by Sanyo Dye Co., Ltd.), Pigment Red 122 (CFR321 manufactured by Dainichi Seika Co., Ltd.), and Pigment Yellow 180 (Large) were used instead of Pigment Black 7 Dispersion B, dispersion C, and dispersion D were prepared in the same manner except that CFY313-2) manufactured by Nissei Kasei was used.

[Preparation of Dispersion E]
Each of the following compounds was placed in a stainless beaker and dissolved by stirring and heating for 1 hour while heating on a hot plate at 65 ° C.

PB821 (Dispersant manufactured by Ajinomoto Fine Techno Co., Ltd.) 9 parts OXT221 (Oxetane compound manufactured by Toa Gosei Co., Ltd.) 71 parts After cooling to room temperature, 20 parts of Pigment Black 7 (Mitsubishi Chemical Co., Ltd. # 52) is added to the diameter 0 Then, 200 g of 3 mm zirconia beads were placed in a glass bottle and sealed, and after a dispersion treatment for 4 hours with a paint shaker, the zirconia beads were removed to prepare dispersion E.

[Preparation of dispersions F to H]
In the preparation of the dispersion E, Pigment Black 15: 4 (Cyanine Blue 4044 manufactured by Sanyo Dye Co., Ltd.), Pigment Red 122 (CFR321 manufactured by Dainichi Seika Co., Ltd.), and Pigment Yellow 180 (Large) were used instead of Pigment Black 7 in the preparation of the dispersion E. Dispersion F, dispersion G, and dispersion H were prepared in the same manner except that CFY313-2) manufactured by Nissei Kasei was used.

<Preparation of ink set>
[Preparation of ink set 1]
Using the dispersions A to D (radical polymerizable compounds) prepared above, inks 1K, 1C, 1M, and 1Y having the configurations shown in Table 1 were prepared.

[Preparation of ink set 2]
Inks 2K, 2C, 2M, and 2Y having the configurations shown in Table 2 were prepared using the dispersions A to D (radically polymerizable compounds) prepared above, and this was designated as ink set 2.

[Preparation of ink set 3]
Inks 3K, 3C, 3M, and 3Y having the configurations shown in Table 3 were prepared using the prepared dispersions E to H (cationically polymerizable compounds).

[Preparation of ink set 4]
Inks 4K, 4C, 4M, and 4Y having the configurations shown in Table 4 were prepared using the dispersions E to H (cationically polymerizable compounds) prepared above, and this was designated as ink set 4.

  In addition, the numerical value of the said Tables 1-4 represents a mass part.

  The details of the compounds described in Tables 1 to 4 as abbreviations are as follows.

<Radically polymerizable compound>
RA: Lauryl acrylate TEGDA: Tetraethylene glycol diacrylate A-400: NK ester Shin-Nakamura Chemical Co., Ltd. <Cationically polymerizable compound>
2021P: Celloxide 2021P (alicyclic epoxy compound, bifunctional, manufactured by Daicel Chemical Industries)
OXT212: Monofunctional oxetane compound, manufactured by Toagosei Co., Ltd. OXT221: Bifunctional oxetane compound, manufactured by Toagosei Co., Ltd. <Modified silicone oil>
SDX-1843: Modified silicone oil SDX-1843, manufactured by Asahi Denka Kogyo Co., Ltd. <Photopolymerization initiator>
I-907: Irgacure 907 Ciba Specialty Chemicals UVI6992: Triarylsulfonium salt, UVI6992, Dow Chemical Co., Ltd. <sensitizer>
IPTX: Isopropylthioxanthone CPTX: 1-chloro-4-propoxythioxanthone AHC: 3-acetyl-7-hydroxycoumarin << Image formation >>
[Formation of image 1]
(Inkjet recording device)
The ink set 1 (inks 1K, 1C, 1M, 1Y) shown in Table 1 prepared above was added to the serial type ink jet recording apparatus having the configuration shown in FIG. 1 and FIG. Was discharged to each long recording medium having a width of 600 mm and a length of 20 m under the following conditions. 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, and was heated from the front chamber tank to the head portion and heated at 50 ° C. The head is heated in accordance with the viscosity of each ink, and is driven so that it can be ejected at a resolution of 720 × 720 dpi (dpi represents the number of dots per 2.54). Continuous discharge was performed to print solid images of each color. The recording material was adjusted to 40 ° C. with a surface heater and a cooling device. After landing, an active energy ray was irradiated from the following light source set A (LED light source) and cured instantaneously (less than 0.5 seconds after landing). The ink discharge amount was printed with a minimum droplet amount of 4 pl and a maximum appropriate liquid amount of 80 pl. Further, the inkjet image was formed at a temperature of 23 ° C. and a humidity of 30%.

LED light source set A: LED light source (LED2) for ink 1K, 1C, 1M uses LEDZero 395 (manufactured by INTEGRATION, peak wavelength: 395 nm, illuminance: 1 to 2.5 W / cm ² ), for ink Y1 As the LED light source (LED1), an LED with a peak wavelength of 365 nm and an illuminance of 100 mW / cm ² manufactured by Nichia Corporation (custom product) was used.

[Formation of images 2 to 4]
In the formation of the image 1, images 2 to 4 were formed in the same manner except that the ink sets 2, 3 and 4 were used in place of the ink set 1, respectively.

[Formation of images 5 to 8]
In the formation of the images 1 to 4, images 5 to 8 were formed in the same manner except that the light source set B composed of the following LEDs was used instead of the light source set A.

Light source set B: As all LED light sources (LED1 and LED2) for inks K, C, M, and Y, LEDs with a peak wavelength of 365 nm and illuminance of 100 mW / cm ² manufactured by Nichia Corporation (special order) are used. did.

[Formation of images 9 to 12]
In the formation of the images 1 to 4, images 9 to 12 were formed in the same manner except that the light source set C constituted by the following LEDs was used instead of the light source set A.

Light source set C: LEDZero 395 (manufactured by INTEGRATION, peak wavelength: 395 nm, illuminance: 1 to 2.5 W / cm ² ) is used as all LED light sources (LED1 and LED2) for inks K, C, M, and Y did.

[Formation of Image 13]
In the formation of the image 3, the irradiation light source installed at both ends of the carriage is a 120 W / cm metal halide lamp (MAL 400NL manufactured by Nippon Batteries) as a serial type ink jet recording apparatus as shown in FIG. The image 13 was formed in the same manner except that it was set to 400 mW / cm ² (referred to as the light source set D).

[Formation of Image 14]
In the formation of the image 3, the image 14 was formed in the same manner except that the line type ink jet recording apparatus shown in FIG. 3 was used instead of the serial type ink jet recording apparatus (c in FIG. 2).

The recording head for each ink has 256 nozzles, and can be ejected with a resolution of 720 × 720 dpi (dpi represents the number of dots per 2.54 cm) by a 2 to 20 pl multi-drop method. In addition, as LED light source, LED / Y (manufactured by Nichia Corporation) (special order) peak wavelength: 365 nm, illuminance: 100 mW / cm ² LED is used, LED · M, LED · C and LED · K, LEDZero 395 (manufactured by INTEGRATION, peak wavelength: 395 nm, illuminance: 1 to 2.5 W / cm ² ) is used, and this is referred to as a light source set E.

[Formation of Image 15]
In the formation of the image 3, an image 15 was formed in the same manner except that the light source set F described in d) of FIG. 2 was used instead of the ink jet recording apparatus (c) of FIG.

In the light source set F, in addition to each LED light source similar to the light source set A, a 120 W / cm metal halide lamp (MAL 400NL manufactured by Nippon Batteries) and 400 mW / cm ² were further installed at both ends of the carriage, and the LED light source was irradiated. Thereafter, light was irradiated with a metal halide lamp to form an image.

[Formation of Image 16]
An image 16 was formed in the same manner as the image 15 except that the ink set 1 was used instead of the ink set 3.

[Formation of Image 17]
In the formation of the image 3, an image 17 was formed in the same manner except that the LED light source (LED 2) for the inks 1K, 1C, and 1M was a light source set G using an LED light source having a peak wavelength of 405 nm.

[Formation of Image 18]
An image 18 was formed in the same manner as the image 17 except that the ink set 1 was used instead of the ink set 3.

[Formation of Image 19]
In the formation of the image 3, an image 19 was formed in the same manner except that the LED light source (LED 2) for the inks 1K, 1C, and 1M was a light source set H using an LED light source having a peak wavelength of 415 nm.

[Formation of Image 20]
An image 20 was formed in the same manner as the image 19 except that the ink set 1 was used instead of the ink set 3.

<Evaluation of formed image>
Each evaluation shown below was performed about each formed image formed by the above.

[Evaluation of curability]
About each formed solid image, the image printing surface immediately after active energy ray irradiation was touched with the finger, and sclerosis | hardenability was evaluated according to the following reference | standard. In addition, evaluation was calculated | required by the average value of each color ink.

◎: There is no stickiness on the surface of all formed images, and it is completely cured. ○: There is almost no stickiness on the surface of all formed images, and it is fully cured. △: Slight stickiness is recognized ×: Strong stickiness is recognized in some formed images [Evaluation of gloss unevenness resistance]
The glossiness of each formed solid color image was visually observed, and gloss unevenness resistance was evaluated according to the following criteria.

A: No difference in glossiness is observed between the formed solid images of each color. ○: A difference in glossiness is not observed between the formed solid images of each color. Δ: A part of the formed solid images of each color. A slight difference in glossiness is observed. Δ: A difference in glossiness is recognized in many of the formed solid images. Table 5 shows the results obtained as described above.

  As is clear from the results shown in Table 5, the configuration of the photopolymerization initiator group containing at least one kind of ink using a group of active light source irradiated LED light sources having two different light emission characteristics, The images formed using the ink sets 1 and 3 different from the configuration of the photopolymerization initiator group of other inks are higher in curability of the images formed by the respective inks than the comparative examples, and the gloss difference between the respective color images. Is small.

1 is a schematic perspective view illustrating an example of a main configuration of a serial type inkjet recording apparatus applicable to the present invention. It is the schematic top view and schematic side view which show another example of a serial carriage part structure. 1A and 1B are a top view and a side view showing an example of a main configuration of a line-type inkjet recording apparatus applicable to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 2 Film base material, recording medium 3 Recording head 3Y, 3M, 3C, 3K Recording head (serial system)
4 Carriage 5 Maintenance unit 8Y, 8M, 8C, 8K Recording head (line system)
9 Transport roller 11 Guide member 12 Platen 13 Recording medium transport mechanism LED1, LED2 LED light source LED • Y, LED. M, LED. C, LED. K LED light source N Nozzle

Claims (9)

After a plurality of active energy ray-curable inks that are cured with active energy rays from a plurality of recording heads are ejected onto a recording medium, the active energy ray-curable ink is irradiated with active energy rays from a plurality of active energy ray irradiation units. In an active energy ray-curable inkjet printing system for curing and forming an image,
The plurality of active energy ray irradiating units are composed of two or more types of LED light sources having different emission characteristics,
The plurality of active energy ray-curable inks are composed of two or more types of inks having different hues, and the configuration of the photopolymerization initiator group contained in at least one type of ink is a photopolymerization initiator group of another ink. An active energy ray-curable inkjet printing system, characterized by being different from the configuration of 2. The active energy ray-curable inkjet printing system according to claim 1, wherein a wavelength difference between the two or more types of LED light sources having different emission characteristics is in a range of 5 to 50 nm. 3. The two or more types of LED light sources having different light emission characteristics are provided at both ends of a carriage on which the plurality of recording heads are serial, and the plurality of recording heads are mounted. Active energy ray curable inkjet printing system. The plurality of recording heads are serial, and have LED light sources at both ends of each recording head, and at least one of the LED light sources has different light emission characteristics from other LED light sources. 2. The active energy ray-curable inkjet printing system according to 2. The plurality of recording heads are line systems and have LED light sources corresponding to the respective recording heads, and at least one of the LED light sources is different in light emission characteristics from other LED light sources. An active energy ray-curable inkjet printing system according to 1. 6. The light source according to claim 1, further comprising at least one irradiation light source selected from a high pressure mercury lamp, a metal halide lamp, a black light, and a cold cathode tube, in addition to the two or more types of LED light sources having different light emission characteristics. The active energy ray-curable ink jet printing system according to claim 1. The plurality of active energy ray-curable inks are composed of at least a yellow ink, a magenta ink, a cyan ink, and a black ink, and the maximum light emission wavelength of an LED light source used for curing the yellow ink is an LED used for curing other inks. The active energy ray-curable inkjet printing system according to claim 1, wherein the wavelength is shorter than the maximum emission wavelength of the light source. The wavelength difference between the maximum emission wavelength of the LED light source used for curing the yellow ink and the maximum emission wavelength of the LED light source used for curing the other ink is in a range of 5 to 50 nm. An active energy ray-curable inkjet printing system according to 1. An image forming method comprising performing image formation using the active energy ray-curable inkjet printing system according to claim 1.

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