JP6038430B2 - Active energy ray-curable inkjet ink set and image forming method - Google Patents

Description

  The present invention relates to an active energy ray-curable inkjet ink set and an image forming method using the same.

  In recent years, inkjet recording methods can be used to produce images easily and inexpensively, and thus have been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters.

  Among them, the inkjet method using an active energy ray-curable ink that is cured by active energy rays such as ultraviolet rays and electron beams or heat has a relatively low odor compared to the solvent-type inkjet method, and does not have quick drying and ink absorption. Recently, active energy ray-curable ink-jet ink used in this method has been widely disclosed in that it can be recorded on a recording medium, and in particular, a recording device that emits and controls fine dots, It is possible to obtain a high-definition color image by using an ink having improved color reproduction range and emission suitability. In addition, long-term preservation of the created image is also required.

  In particular, when images are used outdoors, excellent weather resistance that can cope with all natural conditions is required. Weather resistance is the property that even when exposed to sunlight, heat, oxygen in the air, or moisture, the printed image will not be altered or discolored for a certain period of time, such as discoloration or fading, cracking or outflow of the image. This is the performance required for printed materials used outdoors. The same applies to ink-jet images, but in particular, ink-jet images form an image with a collection of fine dots, and therefore have a larger image surface area than the uniform image surface created by a general printing method. When used for outdoor signboards and the like, the area that comes into contact with sunlight and oxygen and moisture in the air increases, so the influence on deterioration that is experienced over time becomes more prominent.

  As a means for improving the weather resistance of ink, the weather resistance of an image has been improved by using a dye or an organic pigment having a structure excellent in weather resistance as a colorant. However, since it is exposed to sunlight for a long time in outdoor applications, it is difficult to avoid image degradation even when organic pigments are used. In addition, when a plurality of colorants having different color tones are used, each colorant has different weather resistance, so that the color balance is lost after outdoor exposure, resulting in an unnatural image.

  Further, although a means for providing a clear layer containing an ultraviolet absorber or a light stabilizer on an image is also known (see, for example, Patent Document 1), a step of providing a clear layer and a step of drying are required. Therefore, cost increase and energy consumption increase.

  It is known that an ultraviolet absorber, an antioxidant, or the like is added or used in combination for improving the weather resistance of the active energy ray-curable inkjet ink (see, for example, Patent Document 2). The amount of the inhibitor added is large, and the amount of the initiator added is increased in order to maintain sensitivity, which is problematic from the viewpoints of ink storage stability and ink ejection properties. Further, from the viewpoint of sensitivity, there is a document using a small amount of a highly basic hindered amine antioxidant and a metal complex-based yellow pigment with good weather resistance (see, for example, Patent Document 3), but a solvent after outdoor exposure. It was found that the wiping resistance due to the water resistance and the weather resistance of the pigments other than this yellow pigment were insufficient. In addition, all the examples in the literature describe only the single color ink, and no description about the weather resistance in an image using a plurality of color inks is found.

International Publication No. 2002/100652 Pamphlet JP 2005-179416 A JP 2009-275080 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an active energy ray-curable inkjet ink set capable of maintaining good image quality while achieving both color balance, weather resistance, and sensitivity after a long period of time. An object of the present invention is to provide an image forming method using the above.

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

  1. In an active energy ray-curable inkjet ink set composed of black ink and color ink, the absorbance at 340 nm when the color ink cured film is measured at 3 μm thickness is 340 nm when the black ink cured film is measured at 3 μm thickness. An active energy ray-curable inkjet ink set, characterized in that the absorbance is 80 to 110% with respect to the absorbance.

  2. 2. The active energy ray-curable ink jet ink set as described in 1 above, wherein the color ink comprises two or more kinds and contains an ultraviolet absorber.

  3. 3. The active energy ray-curable inkjet ink set described in 1 or 2 above, which contains a light stabilizer.

  4). 4. The active energy ray-curable inkjet ink set described in any one of 1 to 3 above, which comprises an acid generator and a cationic polymerizable monomer.

  5. 5. The active energy ray-curable inkjet ink set described in 4 above, wherein the content of the light stabilizer is 2 to 15% by mass of the content of the acid generator.

  6). 6. The active energy ray-curable ink jet ink set according to any one of 1 to 5, further comprising a sensitizer.

  7). An image is formed by irradiating a low-pressure mercury lamp after ejecting an image by an inkjet method using the active energy ray-curable inkjet ink set described in any one of 1 to 6 above on a substrate. An image forming method.

  8). After discharging an image by an inkjet system using the active energy ray-curable inkjet ink set described in any one of 1 to 6 above on a substrate, forming an image by irradiating an LED An image forming method.

  According to the present invention, it was possible to provide an active energy ray-curable ink jet ink set capable of achieving both good color balance after a long period of time, weather resistance, and sensitivity, and maintaining good image quality, and an image forming method using the same.

It is a front view showing an example of the composition of the principal part of the ink jet recording device used for the image forming method of the present invention. It is a top view which shows another example of a structure of the principal part of the inkjet recording device used for the image forming method of this invention.

  The present invention measures the absorbance at 340 nm when a color ink cured film is measured at a thickness of 3 μm in an active energy ray-curable ink jet ink set composed of a black ink and a color ink, and the black ink cured film is measured at a thickness of 3 μm. It was found that the absorbance at 340 nm was 80 to 110%, and that it was possible to maintain a good color image with a maintained color balance even after being used outdoors for a long time.

  Images placed outdoors are deteriorated by ultraviolet rays, moisture, oxygen in the air, and large-scale pollutants. In particular, the deterioration due to ultraviolet rays is caused by the absorption of ultraviolet rays of 290 to 400 nm reaching the surface of the earth, whereby the energy of the photons is given, and the colorant is decomposed and the polymer chain is broken.

  The absorption spectrum of black ink is generally broad in the entire wavelength range, and has absorption evenly in the above-mentioned wavelength range of 290 to 400 nm. Ultraviolet rays hardly reach the inside of the cured layer and are not easily deteriorated. On the other hand, color ink has absorption in a specific range, and absorption in the ultraviolet region is low or not, so it tends to be affected by ultraviolet rays to the inside of the cured layer and tends to deteriorate compared to black ink. It is in.

  The absorbance is preferably measured in a state where it is actually exposed to the outside air, that is, in a state where the active energy ray-curable ink is cured. In such a case, the comparison can be made in the original state of exposure without considering the absorption of a photoinitiator or the like that is required only at the time of curing and decreases in absorption by light irradiation for curing. In addition, when measuring the absorbance in the state of the ink before curing, the absorbance close to the cured film can be obtained by subtracting the absorbance of substances whose absorption decreases due to light irradiation for curing such as a photoinitiator. Can be measured.

  The absorbance is measured using a spectrophotometer that can measure from a general ultraviolet to infrared range. For example, a transparent film that does not absorb more than 300 nm, such as polyethylene terephthalate (PET), is coated with ink using a wire bar and irradiated with light to produce a 3 μm thick ink cured film. For example, U-3300 type self-recording spectrophotometer The absorbance of the cured film is measured using a meter (manufactured by Hitachi, Ltd.). At this time, the black ink and the color ink are preferably applied using the same wire bar. Further, when the absorbance is 1-2, an accurate absorbance is obtained.

[Ultraviolet absorber]
The present invention relates to an active energy ray-curable ink jet ink set, wherein at least two kinds of color inks contain an ultraviolet absorber, and the color ink cured film measured at a thickness of 3 μm has an absorbance at 340 nm of black ink cured. It is preferable to be 80 to 110% with respect to the absorbance at 340 nm when the film is measured at a thickness of 3 μm.

  As the ultraviolet absorber used in the present invention, an ultraviolet absorber having an absorption wavelength at 220 to 400 nm can be preferably used. By containing the ultraviolet absorber, absorption at around 340 nm is imparted to the active energy ray-curable inkjet ink, and the weather resistance of the cured film is improved.

  Conventionally known compounds can be used, for example, UV-absorbing inorganic compounds such as cerium oxide described in JP-A Nos. 9-157560, 9-279075, and 2001-181528, benzophenone-based UV absorbers, Examples include salicylic acid ester ultraviolet absorbers, cyanoacrylate ultraviolet absorbers, benzotriazole ultraviolet absorbers, and nickel complex ultraviolet absorbers. The ultraviolet absorber used in the present invention is preferably an organic compound from the image quality of the obtained inkjet image, and a benzophenone ultraviolet absorber, a benzotriazole ultraviolet absorber, and a triazine ultraviolet absorber are preferable.

  Specific examples of the benzophenone ultraviolet absorber include 2-hydroxy-4-n-octoxybenzophenone (sumisorb130), 2,4-dihydroxybenzophenone (SEESORB100), 2-hydroxy-4-methoxybenzophenone (SEESORB101, CYASORB (R ) UV-9), 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid trihydrate (SEESORB101S), 2-hydroxy-4-octoxybenzophenone (SEESORB102), 4-dodecyloxy-2-hydroxybenzophenone (SEESORB103) ), 4-benzyloxy-2-hydroxybenzophenone (SEESORB105), 2,2 ', 4,4'-tetrahydroxybenzophenone (SEESORB106), 2 2'-dihydroxy-4,4'-dimethoxybenzophenone (SEESORB107), 1,4-bis (4-benzoyl-3-hydroxyphenoxy) butane (SEESORB151), 2,2'-dihydroxy-4-methoxybenzophenone (CYASORB ( R) UV-24) and the like.

  Specific examples of the benzotriazole ultraviolet absorber include 2- (2-hydroxy-5-methylphenyl) benzotriazole (sumisorb200), 2- [2-hydroxy-3- (3,4,5,6-tetrahydrophthalimide). -Methyl) -5-methylphenyl] benzotriazole (sumisorb250), 2- (3-tert-butyl-2-hydroxy-5-methylphenyl) -5-chlorobenzotriazole (sumisorb300), 2- (2-hydroxy- 5-tert-octylphenyl) benzotriazole (sumisorb 340), 2- (2-hydroxy-3,5-di-tert-pentylphenyl) benzotriazole (sumisorb 350), 2- (2-hydroxy-5-methylphenyl)- 2H-Be Zotriazole (SEESORB701), 2- (3-tert-butyl-2-hydroxy-5-methylphenyl) -5-chloro-2H-benzotriazole (SEESORB703), 2- (3,5-di-tert-pentyl- 2-hydroxyphenyl) -2H-benzotriazole (SEESORB 704), 2- (2H-benzotriazol-2-yl) -4-methyl-6- (3,4,5,6-tetrahydrophthalimidylmethyl) phenol ( SEESORB 706), 2- (2-hydroxy-4-octyloxyphenyl) -2H-benzotriazole (SEESORB 707), 2- (2-hydroxy-5-tert-octylphenyl) -2H-benzotriazole (SEESORB 709), 2- (2-hydroxy-5-t rt-butylphenyl) -2H-benzotriazole (TINUVIN PS), 2- (2H-benzotriazol-2-yl) -4,6-bis (1-methyl-1-phenylethyl) phenol (TINUVIN900), 2- (2H-benzotriazol-2-yl) -6- (1-methyl-1-phenylethyl) -4- (1,1,3,3-tetramethylbutyl) phenol (TINUVIN 928), 2,5-bis ( 5'-tert-butyl-2'-benzoxazolyl) thiophene (UVITEX OB), 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole (TINUVIN 327, SEESORB 702) 2- [2′-hydroxy-3 ′, 5′-bis (α, α-dimethylbenzyl) Phenyl] -2H-benzotriazole (TINUVIN234), 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole (TINUVIN320, Eversorb77), 2,2′-methylenebis [6- ( 2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol] (TINUVIN 360, Eversorb 78), 2- (2'-hydroxy-3'-sec-butyl-5 ' -Tert-butylphenyl) benzotriazole (Eversorb79) and the like.

  Specific examples of the benzoate ultraviolet absorber include 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate (sumisorb 400), phenyl salicylate, and the like.

  Specific examples of the triazine-based ultraviolet absorber include 2- [4,6-bis (2,4-dimethylphenyl) -1,3,5-triazin-2-yl] -5- (octyloxy) phenol (CYASORB ( R) UV-1164), 2- [4-[(2-hydroxy-3-dodecyloxypropyl) oxy] -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1, 3,5-triazine (TINUVIN 400), 2- [4-[(2-hydroxy-3-tridecyloxypropyl) oxy] -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1 , 3,5-triazine (TINUVIN 400), 2- [4-[(2-hydroxy-3- (2′-ethyl) hexyl) oxy] -2-hydroxyphenyl] -4,6- (2,4-dimethylphenyl) -1,3,5-triazine (TINUVIN405), 2,4-bis (2-hydroxy-4-butoxyphenyl) -6- (2,4-bis-butyroxyphenyl) ) -1,3,5-triazine (TINUVIN 460), 2- (2-hydroxy-4- [1-octyloxycarbonylethoxy] phenyl) -4,6-bis (4-phenylphenyl) -1,3,5 -Triazine (TINUVIN479) etc. are mentioned. Most preferred is a hydroxyphenyltriazine-based compound, especially 2- (2-hydroxy-4- [1-octyloxycarbonylethoxy] phenyl) -4,6-bis (4-phenylphenyl) -1,3,5. -Triazine (TINUVIN479) has a large ultraviolet absorption coefficient, and a large effect can be obtained by adding a small amount.

  The above-mentioned sumisorb is manufactured by Sumitomo Chemical Co., SEESORB is manufactured by Cypro Kasei Co., Ltd., CYASORB (R) is manufactured by Cytec Industries, TINUVIN and UVITEX are manufactured by BASF Japan (formerly Ciba Specialty Chemicals), and Eversorb is Taiwan Eilong It is a product made by Photochemical Industry.

  These may be used alone or in combination of two or more.

  The addition amount of these ultraviolet absorbers is such that the absorbance at 340 nm when the color ink cured film is measured at a thickness of 3 μm is 80 to 110% relative to the absorbance at 340 nm when the black ink cured film is measured at a thickness of 3 μm. It is preferable to add so as to be different depending on the color of the ink.

  For example, yellow ink is 0.5 to 2.0% by mass, more preferably 0.8 to 1.5% by mass with respect to the total solid content of the active energy ray-curable composition, and magenta ink is 0.2 to 1.% by mass. 5% by mass, more preferably 0.4 to 1.0% by mass, and for cyan ink, 0.05 to 0.8% by mass, and more preferably 0.1 to 0.5% by mass. For other colors as well, they are appropriately added so as to be 80 to 110% with respect to the absorbance of the black ink cured film.

  In any color, if the addition amount is small, good weather resistance cannot be obtained, and if the addition amount is large, the sensitivity is lowered or the ink is precipitated in the ink.

(Light stabilizer)
The ultraviolet absorber used in the present invention absorbs harmful ultraviolet rays prior to the polymer chain of the cured film and converts it into heat energy that is harmless to the cured film, but radicals are inevitably generated near the surface. The weather resistance can be further improved by using a light stabilizer that traps radicals in combination.

  As such a light stabilizer, a kind selected from a hindered amine light stabilizer (HALS), a hindered phenol antioxidant, a phosphorus antioxidant, a sulfur antioxidant, and a hindered amide antioxidant. The above is preferable. In particular, HALS having a function of scavenging radicals may be used. HALS has a radical scavenging mechanism that returns to the original form before scavenging again after scavenging radicals, so that radicals can be repeatedly captured. Hindered phenol radical scavengers and hindered amide radical scavengers having the same radical scavenging mechanism as HALS are also suitable as stabilizers.

  Specific examples of the light stabilizer having a radical scavenging mechanism are given below. HALS includes bis (1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate (TINUVIN123), 2,4-bis [N-butyl-N- (1-cyclohexyloxy-2, 2,6,6-tetramethylpiperidin-4-yl) amino] -6- (2-hydroxyethylamine) -1,3,5-triazine (TINUVIN152), dimethyl-1- (2-hydroxyethyl) -succinate 4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (TINUVIN 622), bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate (TINUVIN 770), N, N′-bis (3-Aminopropyl) ethylenediamine-2,4-bis [N-butyl-N- (1,2,2,6,6-pentamethyl) 4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate (CHIMASSORB 119), poly [{6- (1,1,3,3-tetramethylbutyl) amino-1,3,5- Triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}] hexamethyl (CHIMASSORB 944), and the like. As a hindered amine-based + hindered phenol-based radical scavenger, bis (1,2,2,6,6-pentamethyl-4-piperidinyl)-[[3,5-bis (1,1-dimethylethyl) -4- And hydroxyphenyl] methyl] butyl malonate (TINUVIN 144). Examples of the hindered phenol radical scavenger include triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] (IRGANOX245), 1,6-hexanediol-bis. [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (IRGANOX259), 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di- t-butylanilino) -1,3,5-triazine (IRGANOX565), pentaerythrityl tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (IRGANOX1010), 2,2- Thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propyl Pionate] (IRGANOX1035), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (IRGANOX1076), N, N′-hexamethylenebis (3,5-di-t-butyl- 4-hydroxy-hydrocinnamamide) (IRGANOX 1098), 3,5-di-tert-butyl-4-hydroxybenzylphosphonate-diethyl ester (IRGANOX1222), 1,3,5-trimethyl-2,4,6 -Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (IRGANOX1330), 2,4-bis [(octylthio) methyl] -O-cresol (IRGANOX1520), isooctyl-3- (3,5 -Di-t-butyl-4-hydroxyphenyl) propione Doo (IRGANOX1135), and the like. The above TINUVIN (R), CHIMASSORB (R) and IRGANOX (R) are manufactured by BASF Japan (formerly Ciba Specialty Chemicals).

  In the present invention, tertiary amine HALS and amino ether type (NOR) HALS, which are particularly weak in basicity and close to neutrality, are preferred from the viewpoints of storage properties and sensitivity. Such a HALS is represented by the following structure, and commercially available products such as “TINUVIN 111 FDL”, “TINUVIN 123”, “TINUVIN 144”, “TINUVIN 152”, “TINUVIN 152” manufactured by BASF Japan, “TINUVIN 292”, “TINUVIN 5100” and the like can be mentioned.

  The amount of these light stabilizers to be added is preferably 0.01 to 1.5% by mass, more preferably 0.1 to 0.5% by mass, based on the total solid content of the active energy ray-curable composition. . When the addition amount is less than 0.05% by mass, sufficient weather resistance cannot be obtained, and when it is more than 1.0% by mass, the polymerization initiating ability of the initiator is inhibited and the sensitivity is lowered. Moreover, it is preferable that the addition amount of the light stabilizer in the active energy ray-curable ink is 2 to 15% by mass with respect to the addition amount of the acid generator.

(Polymerizable compound)
The active energy ray-curable ink jet ink in the present invention preferably contains a polymerizable compound and a polymerization initiator. Examples of the polymerizable compound include a cationic polymerizable compound and a radical polymerizable compound.

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

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

  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.

  Examples of the alicyclic epoxide include cyclohexene oxide or cyclopentene 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. Oxide-containing compounds are preferred.

  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 Of polyalkylene glycols such as diglycidyl ether, polypropylene glycol or diglycidyl ether of its alkylene oxide adduct Glycidyl ether, 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.

  In the present invention, from the viewpoint of safety such as AMES and sensitization, at least one of an epoxidized fatty acid ester and an epoxidized fatty acid glyceride may be used as an epoxy compound having an oxirane group.

  The epoxidized fatty acid ester and the epoxidized fatty acid glyceride are not particularly limited as long as an epoxy group is introduced into the fatty acid ester or fatty acid glyceride.

  The epoxidized fatty acid ester is produced by epoxidizing an oleic acid ester, and examples thereof include methyl epoxy stearate, butyl epoxy stearate, octyl epoxy stearate and the like. Similarly, the epoxidized fatty acid glyceride is produced by epoxidizing soybean oil, linseed oil, castor oil and the like, and epoxidized soybean oil, epoxidized linseed oil, epoxidized castor oil and the like are 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, cyclohexanedimethanol 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 Ete , 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, etc. And monovinyl ether compounds.

(Cationic polymerization initiator (acid generator))
In the active energy ray-curable inkjet ink of the present invention, an acid generator is used as a photoinitiator. As the acid generator, any known one can be used, for example, a chemical amplification type photoresist or a compound used for photocationic polymerization (edited by Organic Electronics Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), see pages 187-192).

  As the acid generator, for example, a chemical amplification type photoresist or a compound used for photocationic polymerization is used (Organic Materials Research Group, “Organic Materials for Imaging”, Bunshin Publishing (1993), 187- (See page 192). Examples of compounds suitable for the present invention are listed below.

First, diazonium, ammonium, iodonium, sulfonium, aromatic onium compounds such as phosphonium ^{_{B (C 6 F 5) 4}} -, PF 6 -, AsF 6 -, SbF 6 -, CF 3 SO 3 - and salts be able to.

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

  Secondly, sulfonated substances 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.

(Radically polymerizable compound)
The radical polymerizable compound is a compound having an ethylenically unsaturated bond capable of radical polymerization, and may be any compound as long as it has at least one ethylenically unsaturated bond capable of radical polymerization in the molecule. , Oligomers, polymers and the like having a chemical form. 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.

  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, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, bis (4-acryloxypolyethoxyphenyl) propane, neopentyl glycol Diacrylate, 1,6-hexanediol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol Tetraacrylate, dipentaery Acrylic acid derivatives such as lithol tetraacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, oligoester acrylate, N-methylol acrylamide, diacetone acrylamide, epoxy acrylate, methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate , Lauryl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylol Methacryl derivatives such as tan trimethacrylate, trimethylolpropane trimethacrylate, 2,2-bis (4-methacryloxypolyethoxyphenyl) propane, and other derivatives of allyl compounds such as allyl glycidyl ether, diallyl phthalate, triallyl trimellitate More specifically, Shinzo Yamashita, “Cross-linking agent handbook”, (1981 Taiseisha); Kato Kiyomi, “UV / EB curing handbook (raw material)” (1985, Polymer publication) ); Rad-Tech Study Group, “Application and Market of UV / EB Curing Technology”, p. 79, (1989, CMC); Eiichiro Takiyama, “Polyester Resin Handbook”, (1988, Nikkan Kogyo Shimbun) Commercially available products described in the above, or radically polymerizable or crosslinkable monomers known in the industry, Oligomers and polymers can be used.

(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 US 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, 38-18015, and 45-9610, JP-B-55-39162, JP-A-59- Various onium compounds described in each publication of No. 4023 and “Macromolecules”, Vol. 10, page 1307 (1977), azo compounds described in JP-A-59-142205, 1-54440, European Patent Nos. 109,851, 126,712, etc., “Journal of Imaging Science (J. Imag. Sci.)”, Vol. 30, page 174 (1986), (oxo) sulfonium organoboron complexes described in JP-A-5-213861 and JP-A-5-255347, and titanocenes described in JP-A-61-151197. , "Coordination Chemistry R review), 84, 85-277 (1988) and transition metal complexes containing transition metals such as ruthenium described in JP-A-2-182701, described in JP-A-3-209477 2,4,5-triarylimidazole dimer, carbon tetrabromide, and organic halogen compounds described in JP-A-59-107344.

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

  As for the addition amount of the said polymerization initiator, 0.5-10 mass% is preferable with respect to the total solid of an active energy ray curable composition.

(Sensitizer)
The active energy ray-curable inkjet ink of the present invention can use a sensitizer having an ultraviolet spectrum absorption at a wavelength longer than 300 nm, and more preferably has a high absorption in the wavelength region of the LED light source. And compounds having a peak in a different region.

  Specific examples such as polycyclic aromatic compounds, carbazole derivatives, and thioxanthone derivatives having at least one hydroxyl group or optionally substituted aralkyloxy group or alkoxy group that can be used as such a sensitizer Examples of the compound include the following compounds. As the polycyclic aromatic compound, 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 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 Cis-resin) or series thereof, 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- t-butyl-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- Anthracene derivatives such as (2-hydroxyethoxy) anthracene and 2-ethyl-9,10-di (2-carboxyethoxy) anthracene, 1,4-dimethoxychrysene, 1,4-diethoxychrysene, 1,4-dipropoxy Chrysene derivatives such as chrysene, 1,4-dibenzyloxychrysene, 1,4-di-α-methylbenzyloxychrysene, phenanthrenes such as 9-hydroxyphenanthrene, 9,10-dimethoxyphenanthrene, 9,10-diethoxyphenanthrene Derivatives and the like can be mentioned. 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 carbazole derivative include carbazole, N-ethylcarbazole, N-vinylcarbazole, N-phenylcarbazole and the like. Examples of the thioxanthone derivative include thioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone 2-chlorothioxanthone, and the like.

  In addition, when an ink sensitizer using a cationic polymerizable compound and a sulfonium salt as a photoinitiator, anthracene and anthracene derivatives (ADEKA OPTOMESP SP-100, diethoxyanthracene, dibutoxyanthracene manufactured by ADEKA) are used. Etc.). When used as an iodonium salt photoinitiator, thioxanthones and the like can be used.

  These sensitizers can be used alone or in combination. The addition amount is preferably 0.2 to 5% by mass, more preferably 0.5 to 4% by mass, based on the total solid content of the active energy ray-curable composition. If the amount is less than 0.2% by mass, the sensitizing effect is poor. If the amount exceeds 5% by mass, coloring of the sensitizer itself and coloring by a sensitizer decomposition product become a problem.

(Coloring agent)
The active energy ray-curable inkjet ink used in the present invention contains various known dyes and / or pigments together with the above-described polymerizable compound, but preferably contains 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, 151, 154
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, in soft packaging printing and label printing, it is preferable to use white ink. There is a limit.

  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 active energy ray-curable ink jet ink of 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.

  The pigment is preferably dispersed so that the average particle diameter of the pigment particles is 0.08 to 0.5 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 active energy ray-curable inkjet ink of the present invention, the colorant concentration is preferably 1 to 10% by mass of the total ink.

  The ink set in the present invention is composed of black ink and one or more color inks.

  The ink set of the present invention may have a plurality for each color. For example, in addition to the basic four colors of yellow, magenta, cyan, and black, when adding the same series of dark and light colors for each color, in addition to light magenta, dark red, and cyan, in addition to magenta In addition to light light cyan, dark blue, and black, light gray, light black, and dark matte black can be used.

(Other additives)
In the active energy ray-curable inkjet ink of the present invention, in addition to the above description, if necessary, emission stability, print head and ink packaging container compatibility, storage stability, image storage stability, and other performance improvements Depending on the purpose, various known additives such as surfactants, lubricants, fillers, antifoaming agents, gelling agents, thickeners, specific resistance adjusting agents, film forming agents, antioxidants, anti-fading An agent, a fungicide, a rust inhibitor and the like can be appropriately selected and used.

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

  In the image forming method of the present invention, ink is ejected and drawn on a recording material by an ink jet recording method, and then irradiated with actinic rays such as ultraviolet rays to cure the ink and form an image.

  In the present invention, ink is ejected onto a recording material, and actinic rays are irradiated in a state where the ink landed on the recording material is heated. By this image forming method, the stability of the ink itself containing the UV absorber, the stability at the time of ejection that is not affected by the environment (temperature / humidity), and the stability at the time of curing are maintained in a well-balanced manner, and a high-definition image is obtained. Can be formed stably.

  In the present invention, the recording head and ink are heated to 35 to 80 ° C. and ejected, and the ink is irradiated with actinic rays in a state where the ink is kept at 35 to 80 ° C. after landing on the recording material. Active energy ray-curable ink has a large viscosity fluctuation range due to temperature fluctuation, and the viscosity fluctuation directly affects the droplet size and droplet discharge speed, causing image quality degradation. It is important to keep on. The control range of the ink temperature is set temperature ± 5 ° C., preferably set temperature ± 2 ° C., more preferably set temperature ± 1 ° C. In addition, it is preferable that the ink supply system from the ink container to the recording head be a sealed system in order to achieve the effect of the present invention.

(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 active energy ray curable ink jet 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, In addition to the problem of curling and wrinkles, there is a problem that the entire printed matter is changed in its texture and texture, so that it is not preferable to eject ink with an excessive film thickness. Here, the “total ink film thickness” means the maximum value of the film thickness of the ink drawn on the recording material, and it is a single color or other two-color overlay (secondary color), three-color overlay, four colors 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)
In the present invention, the amount of liquid droplets discharged from each nozzle is preferably 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.

  In the present invention, it is preferable that the total power consumption of the light source for irradiating actinic rays is less than 1 kW · hr. Examples of the light source having a total power consumption of less than 1 kW · hr include, but are not limited to, a low-pressure mercury lamp, a fluorescent tube, a cold cathode tube, a hot cathode tube, and an LED.

  Next, an ink jet recording apparatus (hereinafter also simply referred to as a recording apparatus) used in the image forming method of the present invention will be described.

  Hereinafter, a recording apparatus used in the image forming method of the present invention will be described with reference to the drawings as appropriate. Note that the recording apparatus shown in the drawings is only one aspect of the recording apparatus used in the present invention, and the recording apparatus used in the present invention is not limited to this drawing.

  FIG. 1 is a front view showing an example of a configuration of a main part of an ink jet recording apparatus used in the image forming method 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.

  Moreover, in this invention, it is preferable that the platen part is a heater plate. The active energy ray-curable ink that has landed on the recording material receives actinic rays at a predetermined temperature or higher, so that the curability is kept constant regardless of the environment (temperature, humidity). Can be reproduced stably. This is particularly effective when the ink of the present invention stored by the above-described storage method that is stable in ejection is used.

  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 discharges active energy ray curable ink (for example, UV curable ink) supplied by an ink supply means (not shown) by the operation of a discharge means (not shown) provided therein. The ink is discharged from the outlet toward 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. The monomer crosslinks and polymerizes when the initiator acts as a catalyst when irradiated with ultraviolet rays. It has the property of curing by 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 means 4 in the present invention includes an ultraviolet lamp that emits ultraviolet light in a specific wavelength region with exposure energy that is stabilized, and a filter that transmits ultraviolet light of a specific wavelength. Here, as the ultraviolet lamp, a low-pressure mercury lamp, a metal halide 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 cathode tube, a hot cathode tube, a mercury lamp or black light is preferred.

  In particular, a low-pressure mercury lamp, a hot cathode tube, a cold cathode tube, and a germicidal lamp that emit ultraviolet light having a wavelength of 254 nm are preferable because they can effectively prevent bleeding and control the dot diameter. By using black light as the radiation source of the irradiation means 4, the irradiation means 4 for curing the UV ink can be produced at low cost.

  In addition, the LED can be turned on instantaneously, has a long life, has little radiant heat, can easily control the amount of light, has a very narrow emission wavelength width (half-value width), and has a small amount of power consumption, and is preferable as a light source.

  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 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 portion 31 of the recording head 3 and the recording are determined from the distance h1 between the irradiation means 4 and the recording material P. It is effective to increase the distance h2 from the 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 that a bellows structure 7 is provided between the recording head 3 and the irradiation means 4.

  Here, the wavelength of the ultraviolet rays irradiated by the irradiation unit 4 can be changed as appropriate by exchanging the ultraviolet lamp or the filter provided in the irradiation unit 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 showing another example of the configuration of the main part of the ink jet recording apparatus used in the image forming method of the present invention.

  The ink jet recording apparatus shown in FIG. 2 is called a line head system, and a plurality of ink jet 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. ing.

  On the other hand, on the downstream side of the head carriage 2, there is provided irradiation means 4 arranged so as to cover the entire width of the recording material P and cover the entire area of the ink printing surface. A metal halide lamp light source 8 was used as an irradiation light source used for the illumination means 4.

  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.

  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 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.

  The present invention will be specifically illustrated by the following examples, but is not limited thereto. In addition, although the display of "%" is used in an Example, unless otherwise indicated, "mass%" is represented.

Hereinafter, the active energy ray curable inkjet ink and the active energy ray curable inkjet ink set are also simply referred to as ink and ink set, respectively)
Example 1
[Preparation of ink]
For each component shown in the ink composition below, and Y, M, and C inks, UV absorbers and light stabilizers shown in Table 1 below were used, respectively, and OXT221 (manufactured by Toagosei Co., Ltd., oxetane compound) was added. A total amount of 100 parts was mixed to prepare an ink.

  The pigment was prepared as a high-concentration dispersion with oxetane (OXT221) together with the pigment dispersant and added. At this time, OXT 221 added excessively was previously reduced so that the composition ratio of the polymerizable composition in the case of ink was not changed.

<Ink Y1-Y6>
Celoxide 2021P (produced by Daicel Chemical Industries, alicyclic epoxy resin) 10 parts by mass Celoxide 3000 (produced by Daicel Chemical Industries, alicyclic epoxy resin) 20 parts by mass OXT212 (produced by Toagosei Co., Ltd., oxetane compound) 15 parts by mass Pigment Yellow 150 (Yellow pigment) 3.4 parts by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.2 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass IRGANOX 1076 (manufactured by BASF Japan) , Sensitization aid) 1 part by weight CPI-100P (propylene carbonate 50% solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by weight DEA (manufactured by Kawasaki Kasei Co., Ltd., 9.10-diethoxyanthracene) Sensitizer) 2 parts by weight UV absorber Table 1 Light stabilization Table 1 <Ink M1~M5>
Celoxide 2021P (produced by Daicel Chemical Industries, alicyclic epoxy resin) 10 parts by mass Celoxide 3000 (produced by Daicel Chemical Industries, alicyclic epoxy resin) 20 parts by mass OXT212 (produced by Toagosei Co., Ltd., oxetane compound) 15 parts by mass Pigment Red 122 (Magenta pigment) 4.1 parts by mass Azisper PB822 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.6 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass IRGANOX 1076 (manufactured by BASF Japan) , Sensitization aid) 1 part by weight CPI-100P (propylene carbonate 50% solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by weight DEA (manufactured by Kawasaki Kasei Co., Ltd., 9.10-diethoxyanthracene) Sensitizer) 2 parts by weight UV absorber Table 1 Light stabilization Table 1 <Ink C1~C2>
Celoxide 2021P (produced by Daicel Chemical Industries, alicyclic epoxy resin) 10 parts by mass Celoxide 3000 (produced by Daicel Chemical Industries, alicyclic epoxy resin) 20 parts by mass OXT212 (produced by Toagosei Co., Ltd., oxetane compound) 15 parts by mass Pigment Blue 15 : 4 (cyan pigment) 2.5 parts by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.0 part by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass IRGANOX 1076 (BASF Japan) 1 part by weight CPI-100P (propylene carbonate 50% solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by weight DEA (manufactured by Kawasaki Kasei Co., Ltd., 9.10-diethoxy) Anthracene, sensitizer) 2 parts by mass UV absorber Table 1 <Ink 1>
Celoxide 2021P (produced by Daicel Chemical Industries, alicyclic epoxy resin) 10 parts by mass Celoxide 3000 (produced by Daicel Chemical Industries, alicyclic epoxy resin) 20 parts by mass OXT221 (produced by Toagosei Co., Ltd., oxetane compound) 40.5 parts by mass OXT212 (Oxetane compound, manufactured by Toagosei Co., Ltd.) 15 parts by mass Pigment Black 7 (black pigment) 2.5 parts by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 0.9 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., Surfactant) 0.04 parts by mass IRGANOX 1076 (manufactured by BASF Japan, sensitization aid) 1 part by mass CPI-100P (50% propylene carbonate solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by mass DEA (diethoxyanthracene, sensitizer) 2 quality Amount part N-ethyldiethanolamine (polymerization inhibitor) 0.04 part by mass [Evaluation of ink]
The obtained ink was subjected to the following measurements and evaluations.

(Measurement of absorbance of ink cured layer)
The ink was applied on a PET film having a thickness of 50 μm with a wire bar so that the thickness of the cured film was 3 μm. Next, the coated film was cured by passing it under an LED lamp (385 nm, 2 W / cm ² ) at 400 mm / s in an environment of 25 ° C. and 50% RH. Thereafter, the absorbance of the cured film in a wavelength region of 200 to 600 nm was measured using a U-3300 type self-recording spectrophotometer (manufactured by Hitachi, Ltd.), and the color ink of black ink (ink K1) from the following equation was measured. The ratio of absorbance and the absorbance ratio (%) were calculated.

Absorbance ratio (%) = (Color ink absorbance at 340 nm) ÷ (Black ink absorbance at 340 nm) × 100 (%)
(Weatherability)
Each of the inks prepared above was loaded into a recording apparatus having the configuration shown in FIG. 1 equipped with a piezo-type inkjet nozzle, and the following image recording was continuously performed on a hard vinyl chloride sheet.

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 to eject 4 pl dots at a resolution of 1440 × 1440 dpi (dpi represents the number of dots per 2.54 cm), and each ink was ejected continuously. After landing, it is cured instantaneously (less than 0.5 seconds after landing) by the lamp units on both sides of the carriage. An LED lamp (385 nm, 2 W / cm ² ) was used as the light source. The inkjet image was formed in an environment of 25 ° C. and 50% RH according to the above method.

  Printed images are yellow, magenta, cyan, and black wedge images, and solid images of B, R, G (blue, red, green), 3C (third color by YMC), and 4C (quaternary color by YMCK) A test chart consisting of

Using a UVA-340 lamp (illuminance: 0.68 W / m ² ), UV irradiation (60 ° C.) and UV non-irradiation / temperature 50 ° C./humidity 100% 4 in a QUV Accelerated Weathering Tester (manufactured by Q-LAB) 4 The time was repeated for 2000 hours, and the weather resistance was evaluated. The weather resistance was evaluated by the concentration change rate with respect to the initial concentration using a densitometer 938 spectrophotometer manufactured by X-rite.

Concentration remaining rate = (density after light irradiation) / (density before light irradiation) × 100 (%)
From this concentration residual ratio, the following criteria were used for evaluation.

A: Density remaining rate is 90% or more. O: Density remaining rate is 80% or more and less than 90%. Δ: Density remaining rate is 70% or more and less than 80%. X: Density remaining rate is less than 70% (Color balance)
The ink prepared above was used as an ink set with the combinations shown in Table 2, filled in the recording apparatus, and two photographic image samples were prepared. One of them was put into the QUV used in the weather resistance evaluation for 2000 hours, arranged side by side with an unfilled image sample, and visually evaluated for color balance according to the following criteria.

◎: Natural density image with little density reduction and color balance maintained ○: Slight density reduction is observed, but color balance is maintained and natural image △: Color balance is maintained However, the density drop is large and the difference from the area where the black ink is used is large. X: The hue is greatly shifted to one of the cyan component, magenta component, and yellow component, the color balance is lost, and the image is unnatural. The results are shown in Tables 1 and 2.

  From the table, the ink of the present invention has an absorbance at 340 nm when the color ink cured film is measured at a thickness of 3 μm and 80 to 110% of the absorbance at 340 nm when the black ink cured film is measured at a thickness of 3 μm. It can be seen that the weather resistance and color balance after long-term aging are superior to those of the comparative examples.

Example 2
[Preparation of ink]
In the same manner as in Example 1, an ink was prepared according to the following formulation.

<Ink Y7>
Celoxide 2021P (manufactured by Daicel Chemical Industries, alicyclic epoxy resin, molecular weight 252)
20 parts by mass Celoxide 3000 (Daicel Chemical Industries, alicyclic epoxy resin, molecular weight 168)
10 parts by mass OXT221 (manufactured by Toagosei Co., Ltd., oxetane compound) 44 parts by mass OXT212 (manufactured by Toagosei Co., Ltd., oxetane compound) 5 parts by mass E4030 (manufactured by Nippon Nippon Chemical Co., Ltd., epoxidized vegetable oil) 10 parts by mass Pigment Yellow 150 (yellow pigment) ) 3.4 parts by mass Ajisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.4 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass IRGANOX 1076 (manufactured by BASF Japan Ltd., sensitization) Auxiliary agent) 1 part by mass Triisopropanolamine (polymerization inhibitor) 0.005 part by mass SPG (67% propylene carbonate solution, acid generator) 3.8 parts by mass

Tinuvin 479 (manufactured by BASF Japan, UV absorber) 1.0 part by mass Tinuvin 123 (manufactured by BASF Japan, light stabilizer) 0.2 part by mass <Ink M6>
EPR (alicyclic epoxy resin) 10 parts by mass

Celoxide 2021P (manufactured by Daicel Chemical Industries, Ltd., alicyclic epoxy resin) 10 parts by mass OXT221 (manufactured by Toagosei Co., Ltd., oxetane compound) 58 parts by mass OXT212 (manufactured by Toagosei Co., Ltd., oxetane compound) 10 parts by mass Pigment Red 122 (magenta pigment) 4.1 parts by mass Ajisper PB822 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.6 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass IRGANOX 1076 (manufactured by BASF Japan Ltd., sensitization assistant) Agent) 1 part by mass SPG (67% propylene carbonate solution, acid generator) 4.5 parts by mass Tinuvin 479 (manufactured by BASF Japan, UV absorber) 0.4 part by mass Tinuvin 123 (manufactured by BASF Japan, light stabilizer) 0.2 parts by mass <Ink C3>
EPR (alicyclic epoxy resin) 5 parts by mass Celoxide 2021P (manufactured by Daicel Chemical Industries, Ltd., alicyclic epoxy resin) 5 parts by mass Celoxide 3000 (manufactured by Daicel Chemical Industries, Ltd., alicyclic epoxy resins) 10 parts by mass OXT221 (Toagosei Co., Ltd.) Manufactured, Oxetane compound) 42 parts by mass EX-211 (manufactured by Nagase ChemteX Corporation, epoxy compound) 10 parts by mass E4030 (manufactured by Nippon Nippon Chemical Co., Ltd., epoxidized vegetable oil) 10 parts by mass Pigment Blue 15: 4 (cyan pigment) 2.5 Part by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.0 part by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass IRGANOX 1076 (manufactured by BASF Japan, sensitizer) 1 Parts by mass Triisopropanolamine (polymerization inhibitor) 0.025 parts by mass SP G (67% propylene carbonate solution, acid generator) 3.8 parts by mass Tinuvin 123 (manufactured by BASF Japan, light stabilizer) 0.2 parts by mass <Ink K2>
EPR (alicyclic epoxy resin) 20 parts by mass OXT221 (manufactured by Toagosei Co., Ltd., oxetane compound) 62 parts by mass E4030 (manufactured by Nippon Nippon Chemical Co., Ltd., epoxidized vegetable oil) 10 parts by mass Pigment Black 7 (black pigment) 2.5 parts by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 0.9 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass IRGANOX 1076 (manufactured by BASF Japan, sensitizing aid) 1 part by mass SPG (67% propylene carbonate solution, acid generator) 3.8 parts by mass 2-methylaminoethanol (polymerization inhibitor) 0.04 parts by mass Tinuvin 123 (manufactured by BASF Japan, light stabilizer) 0.1 parts by mass [ (Evaluation of ink)
The obtained ink was evaluated in the same manner as in Example 1. However, in measuring the absorbance of the ink cured layer, the LED lamp was changed to a low-pressure mercury lamp (254 nm, the illuminance of the substrate surface was 10 mW / cm ² ) and cured by placing it under the low-pressure mercury lamp for 30 seconds to evaluate the weather resistance. Then, the image was formed by changing the LED lamp to a low-pressure mercury lamp having a main peak at 254 nm (illuminance of the substrate surface was 10 mW / cm ² ).

  For the evaluation of color balance, the ink prepared above was evaluated as an ink set with the combinations shown in Table 4.

  The results of evaluation are shown in Tables 3 and 4.

  From the table, the ink of the present invention has an absorbance at 340 nm when the color ink cured film is measured at a thickness of 3 μm and 80 to 110% of the absorbance at 340 nm when the black ink cured film is measured at a thickness of 3 μm. It can be seen that the color balance after weathering and long-term aging is excellent.

Example 3
[Preparation of ink]
In the preparation of the Y1, M1, and C1 inks of Example 1, the types and amounts of the UV absorber and the light stabilizer were changed as shown in Table 5, and OXT221 (manufactured by Toagosei Co., Ltd., oxetane compound) was added thereto. A total amount of 100 parts was mixed to prepare Y8 to Y16, M7 to M8, and C4 inks, respectively.

[Evaluation of ink]
The obtained ink was evaluated in the same manner as in Example 1.

  For the evaluation of color balance, the ink prepared above was evaluated as an ink set with the combinations shown in Table 6.

  The results of evaluation are shown in Tables 5 and 6.

  From the table, the ink of the present invention has an absorbance at 340 nm when the color ink cured film is measured at a thickness of 3 μm and 80 to 110% of the absorbance at 340 nm when the black ink cured film is measured at a thickness of 3 μm. It can be seen that the color balance after weathering and long-term aging is excellent.

Example 4
[Preparation of ink]
In the preparation of Y7 and M6 in Example 2, the amounts of acid generator (polymerization initiator) and light stabilizer were changed as shown in Table 7, and OXT221 (manufactured by Toagosei Co., Ltd., oxetane compound) was added thereto. Those with a total amount of 100 parts were mixed to prepare Y7-1 to Y7-4 and M6-1 to M6-2 inks, respectively.

[Evaluation of ink]
The obtained ink was evaluated in the same manner as in Example 1. Furthermore, the sensitivity (curing sensitivity) was evaluated by the following method.

(sensitivity)
After applying the ink composition on a PET film having a thickness of 50 μm with a wire bar so as to have a thickness of 3 μm, the ink composition was placed immediately under a low-pressure mercury lamp (254 nm, substrate surface illuminance of 10 mW / cm ² ). The time when tack disappears (state in which no fingerprint mark is left by the finger) was used as an index of sensitivity, and evaluation was performed according to the following criteria.

A: Curing time is less than 10 seconds B: Curing time is 10 or more and less than 20 seconds B: Curing time is 20 or more and less than 30 seconds X: Curing time is 30 seconds or more Table 7 shows the evaluation results.

  From the table, the ink of the present invention in which the content of the light stabilizer, which is a color ink of the ink set used in combination with the ink K1, is 2 to 15% by mass of the content of the acid generator is compared with the comparative example. It can be seen that both weather resistance and sensitivity can be achieved.

Example 5: VE cationic ink [Preparation of ink]
Each component shown in the following ink composition, and each of the Y, M, and C inks uses an ultraviolet absorber and a light stabilizer shown in Table 5 below, respectively, and triethylene glycol divinyl ether (VE-1) is used for these. In addition, the total amount of 100 parts was mixed to prepare an ink.

  The pigment was prepared and added as a high-concentration dispersion with Tri-VE-1 together with a pigment dispersant. At this time, the amount of VE-1 added excessively was reduced in advance so that the composition ratio of the polymerizable composition in the case of ink was not changed.

<Ink Y17>
Triethylene glycol divinyl ether 59.1 parts by weight Diethylene glycol divinyl ether 10 parts by weight Ethylene oxide-modified trimethylolpropane triacrylate trivinyl ether
15 parts by mass Pigment Yellow 150 (yellow pigment) 3.4 parts by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.2 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass CPI-100P (propylene carbonate 50% solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by mass DEA (produced by Kawasaki Kasei Co., Ltd., 9.10-diethoxyanthracene, sensitizer) 2 parts by mass 2- Methylaminoethanol (polymerization inhibitor) 0.02 parts by mass Tinuvin 479 (manufactured by BASF Japan, UV absorber) 1.0 part by mass Tinuvin 123 (manufactured by BASF Japan, light stabilizer) 0.2 parts by mass <Ink M9>
Triethylene glycol divinyl ether 58.6 parts by mass Diethylene glycol divinyl ether 10 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate trivinyl ether
15 parts by mass Pigment Red 122 (magenta pigment) 4.1 parts by mass Azisper PB822 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.6 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass CPI-100P (propylene carbonate 50% solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by mass DEA (produced by Kawasaki Kasei Co., Ltd., 9.10-diethoxyanthracene, sensitizer) 2 parts by mass 2- Methylaminoethanol (polymerization inhibitor) 0.02 parts by mass Tinuvin 479 (manufactured by BASF Japan, UV absorber) 0.4 parts by mass Tinuvin 123 (manufactured by BASF Japan, light stabilizer) 0.2 parts by mass <Ink C5>
Triethylene glycol divinyl ether 61.1 parts by mass Diethylene glycol divinyl ether 10 parts by mass Ethylene oxide-modified trimethylolpropane triacrylate trivinyl ether
15 parts by mass Pigment Blue 15: 4 (cyan pigment) 2.5 parts by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 1.0 part by mass KF351 (surfactant manufactured by Shin-Etsu Chemical Co., Ltd.) 0.04 CPI-100P (propylene carbonate 50% solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by mass DEA (manufactured by Kawasaki Kasei Co., Ltd., 9.10-diethoxyanthracene, sensitizer) 2 parts by mass 2-methylaminoethanol (polymerization inhibitor) 0.02 parts by mass Tinuvin 479 (manufactured by BASF Japan, UV absorber) 0.3 parts by mass <Ink K3>
Triethylene glycol divinyl ether 61.5 parts by mass Diethylene glycol divinyl ether 10 parts by mass Ethylene oxide modified trimethylolpropane triacrylate trivinyl ether
15 parts by mass Pigment Black 7 (black pigment) 2.5 parts by mass Azisper PB824 (manufactured by Ajinomoto Fine Techno Co., Ltd., pigment dispersant) 0.9 parts by mass KF351 (manufactured by Shin-Etsu Chemical Co., Ltd., surfactant) 0.04 parts by mass CPI-100P (propylene carbonate 50% solution of triallylsulfonium salt, manufactured by San Apro, acid generator) 8 parts by weight DEA (diethoxyanthracene, sensitizer) 2 parts by weight 2-methylaminoethanol (polymerization inhibitor) 0 .04 parts by mass [Evaluation of ink]
The obtained ink was evaluated in the same manner as in Example 1.

  For color balance evaluation, the ink prepared above was evaluated as an ink set with the combinations shown in Table 9.

  The results of evaluation are shown in Tables 8 and 9.

  From the table, the ink of the present invention has an absorbance at 340 nm when the color ink cured film is measured at a thickness of 3 μm and 80 to 110% of the absorbance at 340 nm when the black ink cured film is measured at a thickness of 3 μm. It can be seen that the color balance after weathering and long-term aging is excellent.

DESCRIPTION OF SYMBOLS 1 Recording device 2 Head carriage 3 Recording head 4 Irradiation means 5 Platen part 6 Guide member 7 Bellows structure 8 Metal halide lamp line light source P Recording material

Claims (8)

In the active energy ray-curable inkjet ink set consisting of black ink and color ink,
Each of the black ink and the color ink contains a colorant, a polymerizable compound, and a polymerization initiator,
The content of the polymerization initiator contained in the black ink is 0.5 to 10% by mass with respect to the total solid mass of the black ink,
The content of the polymerization initiator contained in the color ink is 0.5 to 10% by mass with respect to the total solid content mass of the color ink,
The colorant contained in the black ink is carbon black,
The black ink does not contain an ultraviolet absorber,
The absorbance at 340 nm when the cured film of the color ink cured by an LED light source having a peak wavelength of 385 nm or a low-pressure mercury lamp having a peak wavelength of 254 nm is measured at a thickness of 3 μm has an LED light source having the peak wavelength of 385 nm Alternatively, the cured film of the black ink cured by the low-pressure mercury lamp having the peak wavelength of 254 nm is 80 to 110% with respect to the absorbance at 340 nm when measured at a thickness of 3 μm. Type ink set for inkjet.   The active energy ray-curable ink jet ink set according to claim 1, wherein the color ink comprises two or more types and contains an ultraviolet absorber.   The active energy ray-curable inkjet ink set according to claim 1, further comprising a light stabilizer. The polymerizable compound includes a cationic polymerizable monomer;
Furthermore, the said polymerization initiator contains an acid generator, The active energy ray hardening-type ink set for inkjets of any one of Claims 1-3 characterized by the above-mentioned.   The active energy ray-curable ink jet ink set according to claim 4, wherein the content of the light stabilizer is 2 to 15% by mass of the content of the acid generator.   6. The active energy ray-curable inkjet ink set according to claim 1, further comprising a sensitizer.   An image is formed on a substrate by irradiating a low-pressure mercury lamp after ejecting the image by an inkjet method using the active energy ray-curable inkjet ink set according to any one of claims 1 to 6. An image forming method.   After discharging an image by an inkjet system using the active energy ray-curable inkjet ink set according to any one of claims 1 to 6 on a substrate, an image is formed by irradiating an LED. An image forming method.

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