JP2010047636A - Active energy ray-curing type inkjet ink composition for forming clear layer, and printed article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active energy ray-curing type inkjet ink composition for forming clear layers, which is excellent in curability and adhesiveness even by low energy irradiation means, and is also excellent in continuous dischargeability, when printing by an inkjet method, and to provide a printed article having a clear layer formed by using the active energy ray-curing type inkjet ink composition for forming the clear layers and having excellent gloss. <P>SOLUTION: There is provided the active energy ray-curing type inkjet ink composition for forming the clear layers, which does not contain a colorant and is used for covering images formed on a recording medium with an active energy ray-curing type inkjet ink composition used for forming the clear layers and containing a colorant, characterized by comprising a (meth)acrylate monomer compound, an N-substituted (meth)acrylamide compound, a photopolymerization initiator, and a surface tension-adjusting agent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is used for a clear layer for covering images such as characters, marks, patterns, and patterns formed using an active energy ray-curable inkjet ink composition for image formation containing a coloring material on a recording medium. The present invention relates to an active energy ray-curable inkjet ink composition for forming a clear layer that does not contain a coloring material, and a printed matter formed using the same. In particular, the present invention relates to an active energy ray-curable inkjet ink composition for forming a clear layer, which can be suitably used for an inkjet recording apparatus including a low energy irradiation unit such as an ultraviolet LED or an ultraviolet laser.

  As an ink composition for image formation applied to an ink jet method, a water-based ink containing a dye or a pigment as a coloring material and water as a main component or an oil-based ink mainly containing an organic solvent as a solvent has been used. However, in order to suppress bleeding of an image, a solventless type active energy ray-curable inkjet ink composition that cures ink by irradiation with an active energy ray (for example, ultraviolet rays) has attracted attention.

  Since this type of active energy ray-curable inkjet ink composition does not contain a solvent, it is not necessary for the solvent to penetrate into the recording medium, and the ink can be cured in a very short time. Although it is possible to obtain high print quality with little bleeding, it is difficult for ink to penetrate into the recording medium, so there is a problem that irregularities are likely to occur on the surface of the image, the image becomes matte, and gloss is liable to decrease. .

In order to solve the above-mentioned gloss problem, conventionally, after forming an image, a clear layer is formed on the image by a screen printing method or a spray printing method to smooth the surface of the printed matter. However, these printing methods require an apparatus for forming a clear layer in addition to the ink jet recording apparatus, which makes the apparatus large and expensive. For this reason, a method of forming a clear layer on an image by an inkjet method in the same manner as in the case of forming an image using an active energy ray-curable inkjet ink composition that does not contain a colorant as the clear layer forming ink can be considered. However, the ink composition for image formation is required to suppress the spread of the ink in order not to deteriorate the print quality, whereas the ink composition for forming the clear layer is excellent in ink to uniformly cover the image. Therefore, it is necessary to use ink compositions having different characteristics. For this reason, for example, an energy ray-curable compound, a photopolymerization initiator, and a surface tension adjuster, energy that does not contain a colorant having a viscosity at 25 ° C. of 100 mPa · s or less and a surface tension of 22 to 27 mN / m. It has been proposed to improve the gloss of printed matter by forming a clear layer on an image using an ink-jet method using a linear curable ink-jet ink composition (for example, Patent Document 1).
JP 2007-31667 A

  By the way, as an irradiation means of an inkjet recording apparatus in which the active energy ray-curable inkjet ink composition as described above is used, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a xenon lamp, a metal halide lamp, and the like have been used. When ultraviolet rays are irradiated by these irradiation means, heat is likely to be generated. Therefore, in applications where a polymer base material is used as a recording medium, curling or waviness is likely to occur on the base material. For this reason, in recent years, low energy irradiation means such as ultraviolet LEDs and ultraviolet lasers which are small and generate little heat have been used instead of the mercury lamps and metal halide lamps described above.

  However, in Patent Document 1, radical polymerization type monofunctional or polyfunctional (meth) acrylate monomers, cationic polymerization type vinyl ether compounds or oxetane compounds are used as energy beam curable compounds. The linear curable compound has low reactivity, and there is a problem that sufficient curability cannot be obtained by the low energy irradiation means as described above, and a problem that adhesion between the clear layer and the image is low. When using energy ray curable compounds such as radical polymerization type (meth) acrylate monomers, polyfunctional (meth) acrylate monomers with many ethylenic double bonds in the molecule to improve curability and adhesion It is conceivable to increase the content of the ink, but as a result, the ink becomes highly viscous, and in an ink jet recording apparatus having a small-diameter nozzle for forming a fine image, the continuous discharge property is lowered and the ink is formed on the image. Is difficult to spread, and the uniformity of the clear layer is likely to deteriorate.

  The present invention has been made in order to solve the above-described problems. The object of the present invention is to form a clear layer on an image by an ink jet method, and to prevent the curability and the image from being irradiated even by a low energy irradiation means. Provided is an active energy ray-curable inkjet ink composition for forming a clear layer which has excellent adhesion and excellent continuous ejection when printing by an inkjet method, and also provides the active energy ray-curable inkjet ink for forming a clear layer. An object of the present invention is to provide a printed matter having excellent gloss by forming a clear layer using the composition.

The present invention relates to a colorant for coating an image formed by using an active energy ray-curable inkjet ink composition for image formation (hereinafter referred to as “image formation ink composition”) containing a colorant on a recording medium. A clear layer-forming active energy ray-curable inkjet ink composition (hereinafter referred to as “clear layer-forming ink composition”),
A clear layer forming ink composition comprising (meth) acrylate monomers, N-substituted (meth) acrylamides, a photopolymerization initiator, and a surface tension adjusting agent.

  The clear layer forming ink composition may contain 55 to 85% by mass of the (meth) acrylate monomers and 10 to 40% by mass of the N-substituted (meth) acrylamides with respect to the whole ink composition. preferable.

  The photopolymerization initiator preferably contains at least one selected from the group consisting of acylphosphine oxides, α-aminoalkylphenones, and thioxanthones.

  The surface tension modifier preferably contains a silicone compound, and particularly preferably contains a silicone compound having an ethylenic double bond in the molecule.

  The N-substituted (meth) acrylamides preferably contain at least one selected from the group consisting of N, N-dimethyl (meth) acrylamide and N, N-diethyl (meth) acrylamide.

  The viscosity of the clear layer forming ink composition is preferably 4 to 50 mPa · s at 25 ° C., and the surface tension is preferably 23 to 34 mN / m at 25 ° C.

  Further, the clear layer forming ink composition does not need to contain a substantially non-reactive solvent.

  The image forming ink composition preferably contains (meth) acrylate monomers and N-substituted (meth) acrylamides as the polymerizable compound.

  And this invention is printed matter which has a clear layer formed using the ink composition for clear layer formation as described above.

  According to the present invention, when a clear layer is formed on an image by an ink jet method, it is excellent in curability and adhesion to an image even by a low energy irradiation means, and is continuously ejected when printing by an ink jet method. It is possible to provide an ink composition for forming a clear layer excellent in the above. Moreover, the printed matter which has the outstanding gloss can be provided by forming a clear layer using the said ink composition for clear layer formation.

  The clear layer forming ink composition of the present embodiment contains (meth) acrylate monomers as the polymerizable compound. The (meth) acrylate monomers may be monofunctional (meth) acrylate monomers having one ethylenic double bond in the molecule, or polyfunctional having two or more ethylenic double bonds in the molecule ( It may be a (meth) acrylate monomer. Among these, higher polyfunctional (meth) acrylate monomers having 3 or more ethylenic double bonds in the molecule are preferable, bifunctional (meth) acrylate monomers having 2 ethylenic double bonds in the molecule, and molecules The combined use with a higher polyfunctional (meth) acrylate monomer having 3 or more ethylenic double bonds therein is more preferred. By using a higher polyfunctional (meth) acrylate monomer having three or more ethylenic double bonds in the molecule, an ink composition having excellent curability and adhesion can be obtained. Further, the viscosity is likely to increase by containing such a polyfunctional (meth) acrylate monomer, but the clear layer forming ink composition of the present embodiment is N-substituted (meth) acrylamides as other polymerizable compounds. Therefore, the viscosity of the ink composition obtained even when a large amount of the polyfunctional (meth) acrylate monomer is contained can be reduced to a viscosity suitable for the ink jet system.

  Specific examples of the monofunctional (meth) acrylate monomer having one ethylenic double bond in the molecule include amyl (meth) acrylate, isoamyl (meth) acrylate, octyl (meth) acrylate, and isooctyl (meth) ) Acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, isomyristyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) Acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, neopentyl glycol (meth) acrylic acid benzoate, butoxyethyl (meth) acrylate, ethoxy-diethylene glycol (meth) acrylate Rate, methoxy-triethylene glycol (meth) acrylate, methoxy-polyethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxy-polyethylene glycol (meth) acrylate, nonylphenol ethylene oxide addition Product (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy -3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl-succinic acid, 2- (meth) acryloyloxye Le - phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl - phthalic acid, and the like functional group, such as phosphorus and fluorine has been imparted (meth) acrylate monomer and the like thereto. These may be used alone or in combination.

  Specific examples of the bifunctional (meth) acrylate monomer having two ethylenic double bonds in the molecule include hydroxypivalate neopentyl glycol di (meth) acrylate and polytetramethylene glycol di (meth) acrylate. , Trimethylolpropane (meth) acrylic acid benzoate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol (200) di (meth) acrylate, polyethylene Glycol (400) di (meth) acrylate, polyethylene glycol (600) di (meth) acrylate, polyethylene glycol (1000) di (meth) acrylate, dipropylene glycol di (Meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol (400) di (meth) acrylate, polypropylene glycol (700) di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,3-butanediol Di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate Dimethylol-tricyclodecane di (meth) acrylate, bisphenol A ethylene oxide adduct di (meth) acrylate, bisphenol A propylene oxide adduct di (meth) acrylate, and the like. These may be used alone or in combination.

  Specific examples of the trifunctional (meth) acrylate monomer having three ethylenic double bonds in the molecule include, for example, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tris (2- Hydroxyethyl) isocyanurate tri (meth) acrylate, glyceryl tri (meth) acrylate, ethylene oxide modified products, propylene oxide modified products, caprolactone modified products, and the like. These may be used alone or in combination.

  Specific examples of the tetrafunctional (meth) acrylate monomer having four ethylenic double bonds in the molecule include, for example, ditrimethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, and ethylene thereof. An oxide modified body, a propylene oxide modified body, a caprolactone modified body, etc. are mentioned. These may be used alone or in combination.

  Specific examples of pentafunctional (meth) acrylate monomers having five ethylenic double bonds in the molecule include dipentaerythritol hydroxypenta (meth) acrylate, and their ethylene oxide modified products and propylene oxide modified products. Body, modified caprolactone, and the like. These may be used alone or in combination.

  Specific examples of the hexafunctional (meth) acrylate monomer having six ethylenic double bonds in the molecule include dipentaerythritol hexa (meth) acrylate, ethylene oxide-modified products, and propylene oxide-modified products. And caprolactone-modified products. These may be used alone or in combination.

  The content of the (meth) acrylate monomers in the clear layer forming ink composition is not particularly limited, but is preferably 55 to 85 mass% with respect to the entire ink composition. If content of (meth) acrylate monomers is the said range, while being able to reduce a viscosity further, sclerosis | hardenability and adhesiveness can be improved.

  The clear layer forming ink composition of the present embodiment contains N-substituted (meth) acrylamides as the polymerizable compound. By using N-substituted (meth) acrylamides together with (meth) acrylate monomers, the viscosity of the ink composition can be reduced, and an ink composition excellent in continuous ejection properties can be obtained. N-substituted (meth) acrylamides have a small number of ethylenic double bonds in the molecule, but if (meth) acrylate monomers and N-substituted (meth) acrylamides are used in combination, even with low energy irradiation. A clear layer forming ink composition having excellent curability can be obtained. Furthermore, when (meth) acrylate monomers and N-substituted (meth) acrylamides are used in combination, adhesion to an image can be improved as compared to the case of (meth) acrylate monomers alone. The reason why the adhesion to the image is improved is not necessarily clear, but the polymerizable compound contained in the image forming ink composition is completely cured by oxygen inhibition when the polymerizable compound on the outermost surface is cured. This is probably because the reactive group remains, and the N-substituted (meth) acrylamides easily react with the remaining reactive group. Specific examples of such N-substituted (meth) acrylamides include N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dipropyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-dihexyl (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-hexyl (meth) Acrylamide, (meth) acryloylmorpholine, N, N-dimethylaminomethyl (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N, N-dimethylamino Hexyl (meth) acrylamide, N, -Diethylaminomethyl (meth) acrylamide, N, N-diethylaminoethyl (meth) acrylamide, N, N-diethylaminopropyl (meth) acrylamide, N, N-diethylaminohexyl (meth) acrylamide, N-methoxymethyl acrylamide, N-n -Butoxymethyl acrylamide, N-isobutoxymethyl acrylamide, N-methoxyethyl acrylamide, N-methoxypropyl acrylamide, N-methoxyhexyl acrylamide, diacetone acrylamide, N-methylol acrylamide, etc. are mentioned. These may be used alone or in combination. Among these, at least one N-substituted (meth) acrylamide selected from the group consisting of N, N-dimethyl (meth) acrylamide and N, N-diethyl (meth) acrylamide has low viscosity and high viscosity. It is particularly preferable because of its reactivity.

  The content of N-substituted (meth) acrylamides in the clear layer forming ink composition is not particularly limited, but is preferably 10 to 40% by mass with respect to the entire ink composition. When the content of N-substituted (meth) acrylamides is in the above range, an ink composition having a lower viscosity can be obtained, and curability and adhesion with an image can be further improved. In particular, if the content of N-substituted (meth) acrylamides is 20 to 40% by mass, the scratch resistance can also be improved.

  As long as the clear layer forming ink composition of the present embodiment contains the above (meth) acrylate monomers and N-substituted (meth) acrylamides, an oligomer or a prepolymer is further added as another polymerizable compound. You may contain. However, since viscosity tends to increase when oligomers and prepolymers are used, the total amount of these polymerizable compounds is preferably 30% by mass or less with respect to the entire ink composition.

  The clear layer forming ink composition of the present embodiment contains a photopolymerization initiator in order to initiate polymerization by irradiation with active energy rays. As photopolymerization initiators, acyl phosphine oxides, α-aminoalkylphenones, thioxanthones, arylalkyl ketones, oxime ketones, acyl phosphonates, thiobenzoic acid S-phenyls, titanocenes, aromatic ketones , Benzyls, quinone derivatives, ketocoumarins and the like. Among these, when used together with the polymerizable compound, at least one light selected from the group consisting of acylphosphine oxides, α-aminoalkylphenones, and thioxanthones capable of initiating polymerization with low energy. A polymerization initiator is preferable, and acylphosphine oxides or a mixture of α-aminoalkylphenones and thioxanthones is more preferable.

  Specific examples of acylphosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,3, 5,6-tetramethylbenzoyldiphenylphosphine oxide, 2,6-dimethylbenzoyldiphenylphosphine oxide, 4-methylbenzoyldiphenylphosphine oxide, 4-ethylbenzoyldiphenylphosphine oxide, 4-isopropylbenzoyldiphenylphosphine oxide, 1-methylcyclohexa Noylbenzoyldiphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxa 2,4,6-trimethylbenzoylphenylphosphinic acid methyl ester, 2,4,6-trimethylbenzoylphenylphosphinic acid isopropyl ester, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide Etc. These may be used alone or in combination. Examples of the acylphosphine oxides available on the market include DAROCURE TPO manufactured by Ciba.

  Specific examples of α-aminoalkylphenones include 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) butanone-1,2-methyl-1- [4- (methoxythio) -phenyl] -2-morpholinopropan-2-one and the like. These may be used alone or in combination. Examples of α-aminoalkylphenones available on the market include IRGACURE 369 and IRGACURE 907 manufactured by Ciba.

  Specific examples of the thioxanthones include thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4- Examples include diethylthioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone. These may be used alone or in combination. Examples of commercially available thioxanthones include KAYACURE DETX-S manufactured by Nippon Kayaku Co., and Chivacure ITX manufactured by Double Bond Chemical.

  The content of the photopolymerization initiator in the clear layer forming ink composition depends on the content of polymerizable compounds such as (meth) acrylate monomers and N-substituted (meth) acrylamides, but the entire ink composition On the other hand, the total amount is preferably 2 to 15% by mass. When the content of the photopolymerization initiator is less than 2% by mass, the curability and adhesiveness are likely to be lowered by low energy irradiation. On the other hand, when the content of the photopolymerization initiator exceeds 15% by mass, unreacted components tend to remain.

  The clear layer forming ink composition of the present embodiment contains a surface tension adjusting agent. Examples of such surface tension adjusting agents include silicone compounds and fluorine compounds. Of these, silicone compounds are preferred. If a silicone compound is used together with the polymerizable compound, the liquid physical properties such as surface tension can be adjusted to a range suitable for the ink jet system, and the ink composition for forming a clear layer is excellent in leveling on the image. Can be obtained. Of the silicone compounds, silicone compounds having an ethylenic double bond in the molecule are preferred. By using the polymerizable compound and a silicone compound having an ethylenic double bond in the molecule, the adhesion to an image can be further improved.

  Specific examples of the silicone compound include BYK-300, BYK-302, BYK-306, BYK-307, BYK-310, BYK-315, BYK-320, and BYK-322 manufactured by BYK Chemie. BYK-323, BYK-325, BYK-330, BYK-331, BYK-333, BYK-337, BYK-344, BYK-370, BYK-375, BYK-377, BYK-UV3500, BYK-UV3510, BYK -UV3570, Degussa TEGO-Rad2100, TEGO-Rad2200N, TEGO-Rad2250, TEGO-Rad2300, TEGO-Rad2500, TEGO-Rad2600, TEGO-Rad2700, Kyoeisha Chemical's Granol 100, Granol 15, Granol 400, Granol 410, Granol 435, Granol 440, Granol 450, B-1484, and the like Polyflow ATF-2, KL-600, UCR-L72, UCR-L93. These may be used alone or in combination.

  The content of the surface tension adjusting agent in the clear layer forming ink composition is not particularly limited, but is preferably 2% by mass or less, and 0.01 to 2% by mass with respect to the entire ink composition. More preferred. When there is more content of a surface tension modifier than 2 mass%, an undissolved substance may arise or foaming may be caused.

  The ink composition for forming a clear layer of the present embodiment may further include a surfactant, a leveling agent, an antifoaming agent, an antioxidant, a pH adjuster, a charge imparting agent, a bactericide, an antiseptic, a deodorant, Known general additives such as charge control agents, wetting agents, anti-skinning agents, and perfumes may be included as optional components.

  As a method for preparing the clear layer forming ink composition, conventionally known methods can be used. For example, the above (meth) acrylate monomers, N-substituted (meth) acrylamides, a photopolymerization initiator, a surface tension adjuster, and other additives as necessary are uniformly mixed using a stirrer. By doing so, an ink composition for forming a clear layer can be prepared. Specific examples of the stirrer include a three-one motor, a magnetic stirrer, a disperser, and a homogenizer.

  The viscosity of the clear layer forming ink composition is preferably 4 to 50 mPa · s at 25 ° C. Since the clear layer forming ink composition of the present embodiment contains N-substituted (meth) acrylamides as the polymerizable compound, even if it contains a large amount of polyfunctional (meth) acrylate monomers as described above, A low viscosity clear layer forming ink composition can be obtained. For this reason, the ink composition for forming a clear layer of the present embodiment is excellent in continuous discharge properties. The surface tension of the clear layer forming layer ink composition is preferably 23 to 34 mN / m at 25 ° C. The clear layer forming ink composition of the present embodiment contains (meth) acrylate monomers and N-substituted (meth) acrylamides and a surface tension adjusting agent, and thus has liquid properties suitable for an ink jet system. An ink composition having a surface tension excellent in leveling property on an image can be obtained.

  In addition, since the clear layer forming ink composition of the present embodiment has a low viscosity as described above, there is no need to dilute with a substantially non-reactive solvent, and the viscosity increases during storage and use. It has good stability that does not cause any troubles. The phrase “not containing a substantially non-reactive solvent” means that a non-reactive solvent that is inevitably mixed when an industrial product is used is not excluded. The amount of the non-reactive solvent inevitably mixed is usually 3% by mass or less based on the total amount of the clear layer forming ink composition.

  The inkjet method is not particularly limited, but is a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezo element, and an electrical signal. An acoustic ink jet method using a radiation pressure that irradiates the ink by changing the sound beam into an acoustic beam, and a thermal ink jet method using the pressure generated by heating the ink to form bubbles.

In the present embodiment, as the irradiation means, an ultraviolet LED, an ultraviolet laser, or the like can be used in addition to a mercury lamp or a metal halide lamp. In particular, since the ultraviolet LED and the ultraviolet laser have low energy and high curing sensitivity is required for the ink composition, the above-described clear layer forming ink composition is effective. For example, in the clear layer forming ink composition of the present embodiment, low energy of 400 mJ / cm ² or less can be used as the cumulative amount of ultraviolet light.

  In the present embodiment, when forming a printed material, first, an image forming ink composition containing a coloring material is ejected by an ink jet recording apparatus, and an image coating film in which characters, marks, patterns, designs, etc. are formed in a predetermined pattern is formed. Then, the image coating film is cured by irradiating active energy rays such as ultraviolet rays. Then, the clear layer forming ink composition which does not contain the colorant is discharged onto the image by an ink jet recording apparatus, and the clear layer coating film is irradiated with active energy rays and cured. Since the clear layer forming ink composition of the present embodiment tends to spread uniformly on an image, a printed matter having excellent gloss can be obtained.

  Conventionally known various dyes may be used as the colorant used in the image forming ink composition, but it is preferable to use either or both of an inorganic pigment and an organic pigment from the viewpoint of weather resistance. The content of the coloring material in the image forming ink composition is preferably 1 to 10% by mass, more preferably 2 to 7% by mass, and most preferably 3 to 6% by mass with respect to the entire ink composition. When the content of the coloring material is too small, the coloring power of the image tends to be reduced. On the other hand, when there is too much content of a coloring material, a viscosity will rise and fluidity | liquidity will be easy to be impaired. Further, when a pigment is used as the colorant, a pigment derivative or a pigment dispersant may be used in order to improve the dispersibility of the pigment.

  The polymerizable compound used in the image forming ink composition can be used without particular limitation as long as it is a polymerizable compound that starts radical polymerization or cationic polymerization by active energy rays and cures. Among these, a polymerizable compound that is cured by radical polymerization is preferable, and at least one selected from the group consisting of (meth) acrylate monomers and N-substituted (meth) acrylamides used in the above-described clear layer forming ink composition. It is more preferable to use a polymerizable compound, and a polymerizable compound containing both (meth) acrylate monomers and N-substituted (meth) acrylamides is more preferable. If the ink composition for image formation contains (meth) acrylate monomers and N-substituted (meth) acrylamides as the polymerizable compound, the adhesion between the clear layer and the image can be further improved. When the above-mentioned (meth) acrylate monomers and N-substituted (meth) acrylamides are used as the polymerizable compound, the content of (meth) acrylate monomers is preferably 10 to 50% by mass, and N-substituted (meth) acrylamides The content of is preferably 10 to 50% by mass.

  Further, as the photopolymerization initiator used in the image forming ink composition, the same photopolymerization initiator as used in the above clear layer forming ink composition can be used. Among these, at least one photopolymerization initiator selected from the group consisting of acylphosphine oxides, α-aminoalkylphenones, and thioxanthones capable of initiating polymerization with low energy is preferable, and acylphosphine oxides Or a mixture of α-aminoalkylphenones and thioxanthones is more preferred. The total content of the photopolymerization initiator is preferably 5 to 15% by mass with respect to the entire ink composition.

  The image forming ink composition preferably contains a surface tension adjusting agent. As such a surface tension adjusting agent, the same surface tension adjusting agent as that used in the clear layer forming ink composition can be used. The content of the surface tension adjusting agent is not particularly limited, but is preferably 2.5% by mass or less, and more preferably 0.01 to 2.5% by mass with respect to the entire ink composition.

  Hereinafter, the present invention will be described more specifically based on examples. The present invention is not limited to these examples. In the following, “part” means “part by mass”.

  The components used for preparing the clear layer forming ink and the image forming ink are shown in Table 1 below.

<Image formation>
In a plastic bottle, colorant, pigment dispersant, and isooctyl acrylate are weighed in the amounts shown in Table 2, 100 parts of zirconia beads are added thereto, and the mixture is mixed with a paint conditioner (manufactured by Toyo Seiki Co., Ltd.) for 2 hours. Dispersion gave a primary dispersion. Next, the remaining components were added to the obtained primary dispersion in the amounts shown in Table 2, and the mixture was stirred for 30 minutes with a magnetic stirrer. After stirring, the mixture was suction filtered using a glass filter (manufactured by Kiriyama Seisakusho) to prepare each image forming ink. The viscosity of these inks was 7.9 to 8.6 mPa · s, and the surface tension was 29.8 to 30.8 mN / m.

Each of the image forming inks was solid-printed on a PET film (Toyobo Co., Ltd., A-4300) using an ink jet recording apparatus to form an image coating film. An ultraviolet ray LED (manufactured by Nichia Chemical Co., Ltd., NLBU21W01-E2) is used as an irradiation means on this image coating film, and an ultraviolet ray is irradiated and cured so that the total irradiation light amount becomes 400 mJ / cm ² , thereby forming an image. did.

<Preparation of clear layer forming ink>
Each component was measured with the compounding quantity shown in Table 3, and this mixture was stirred for 30 minutes with the magnetic stirrer. After stirring, the mixture was suction filtered using a glass filter (manufactured by Kiriyama Seisakusho) to prepare each clear layer forming ink.

<Evaluation>
For the clear layer forming ink prepared as described above, first, the following viscosity, surface tension, and continuous dischargeability were measured.

〔viscosity〕
Using an R100 viscometer (manufactured by Toki Sangyo Co., Ltd.), the viscosity was measured under the conditions of 25 ° C. and cone rotation speed of 20 rpm.

〔surface tension〕
The surface tension at 25 ° C. was measured using a fully automatic balance type electro surface tension meter ESB-V (manufactured by Kyowa Kagaku).

[Continuous discharge]
Using an ink jet recording apparatus equipped with a piezo type ink jet nozzle, a discharge property test was performed in which ink was continuously discharged for 30 minutes, and the continuous discharge property was evaluated according to the following criteria. This ink jet recording apparatus includes an ink tank, a supply pipe, a front chamber ink tank immediately before the head, and a piezo head as an ink supply system. Further, the ink jet recording apparatus was driven at a driving frequency of 10 KHz so that ink could be ejected with a droplet size of about 7 pl and a resolution of 600 × 600 dpi.
○: No discharge failure occurs. Δ: No nozzle chipping occurs but satellites are generated. ×: Nozzle chipping occurs.

  Next, a clear layer is formed using the clear layer forming ink on the image formed using the above image forming ink, and wettability to the following images, clear layer curability, gloss, and scratch resistance. The adhesion between the image and the clear layer was evaluated.

[Wettability]
On the image formed using the image forming ink (P-1), the clear layer forming ink was solid-printed using an ink jet recording apparatus to form a clear layer coating film. The ink repelled by the clear layer coating before curing was visually observed for repelling, and the wettability was evaluated according to the following criteria.
○: No repellency occurs on landed ink ×: Repels occur on landed ink

[Curing, gloss, and scratch resistance]
The above-described evaluation sample for evaluating the wettability is cured by irradiating with ultraviolet rays so that the total irradiation light amount becomes 400 mJ / cm ² using an ultraviolet LED (manufactured by Nichia Corporation, NLBU21W01-E2) as an irradiation means. A clear layer was formed.
The clear layer thus cured was touched with a finger and visually checked for the presence or absence of ink adhesion to the finger, and the curability was evaluated according to the following criteria.
○: Ink does not adhere to the finger ×: Ink does not adhere to the finger, but the surface of the clear layer is scratched. Further, the cured clear layer is 60 ° using Micro-TRI-gross (by BYK Gardner). The gloss value was measured, and the gloss was evaluated according to the following criteria.
○: Gloss value of 35 or more △: Gloss value of more than 25, less than 35 ×: Gloss value of 25 or less Further, the clear layer is rubbed 20 times with an eraser (Plastic Eraser Mono PE-10A manufactured by Dragonfly Pencil Co., Ltd.) Observe and evaluate the scratch resistance according to the following criteria.
○: The clear layer is not scraped and the image is not deteriorated. △: A part of the clear layer is peeled off, and a part of the image is deteriorated.

[Adhesion]
On the respective images formed using the image forming inks (P-1) to (P-5), the clear layer forming ink was solid-printed using the ink jet recording apparatus in the same manner as described above. This, ultraviolet LED (Nichia Chemical Co., NLBU21W01-E2) as an irradiation means using the total irradiation light amount so that the 400 mJ / cm ^2, and then cured by irradiation with ultraviolet rays to form a clear layer. The obtained printed matter was subjected to a cross-cut test (1 mm square, 100 pieces) for confirming the peeled state with cello tape (registered trademark) according to JIS-K-5400. The number of peels in 100 pieces was examined, and the adhesion was evaluated according to the following criteria.
○: The number of peels in the cross cut test is 10 or less Δ: The number of peels in the cross cut test is 11 to 20 ×: The number of peels in the cross cut test is 21 or more

  Table 4 shows the evaluation results.

  As shown in the above table, by using (meth) acrylate monomers, N-substituted (meth) acrylamides, a photopolymerization initiator, and a surface tension modifier, the viscosity is 4.5 to 13.5 mPa · It can be seen that an ink for forming a clear layer having liquid physical properties suitable for an ink jet system having a surface tension of 26.4 to 27.6 mN / m can be obtained. For this reason, although the clear layer forming ink of the example contains a large amount of polyfunctional (meth) acrylate monomer, it is excellent in continuous discharge property. Further, it can be seen that the clear layer forming inks of these examples are excellent in wettability, and a printed matter having good gloss can be produced.

  In addition, clear layer forming inks containing (meth) acrylate monomers and N-substituted (meth) acrylamides as polymerizable compounds can be cured and adhesive even when cured using a low energy UV LED. It turns out that it is excellent in. In particular, it is found that when the clear layer forming ink containing 20 to 40% by mass of N-substituted (meth) acrylamides is used, the scratch resistance is also excellent.

  Further, as a surface tension adjusting agent, the clear layer forming ink containing a silicone compound having an ethylenic double bond in the molecule is further compared with a silicone compound having no ethylenic double bond in the molecule. It can be seen that the adhesion can be improved.

  On the other hand, it can be seen that the clear layer forming ink of Comparative Example which does not contain N-substituted (meth) acrylamides as the polymerizable compound is inferior in curability and adhesion. Moreover, it turns out that the ink for clear layer formation of the comparative example which increased content of the polyfunctional (meth) acrylate monomer as (meth) acrylate monomers becomes very high viscosity, and is inferior to continuous discharge property. For this reason, when this clear layer forming ink was used, appropriate printing could not be performed, and the curability and the like could not be evaluated.

  Furthermore, the clear layer forming ink of the comparative example not containing the surface tension adjusting agent has a high surface tension, and the ink repelling becomes remarkable, so that a uniform clear layer cannot be formed.

Claims (11)

An active energy ray-curable inkjet ink composition for forming a clear layer that does not contain a colorant that covers an image formed using an active energy ray-curable inkjet ink composition for image formation containing a colorant on a recording medium There,
An active energy ray-curable inkjet ink composition for forming a clear layer, comprising (meth) acrylate monomers, N-substituted (meth) acrylamides, a photopolymerization initiator, and a surface tension modifier.   The content of the (meth) acrylate monomers is 55 to 85% by mass and the content of the N-substituted (meth) acrylamides is 10 to 40% by mass with respect to the entire ink composition. An active energy ray-curable inkjet ink composition for forming a clear layer.   The active energy ray curing for forming a clear layer according to claim 1, wherein the photopolymerization initiator contains at least one selected from the group consisting of acylphosphine oxides, α-aminoalkylphenones, and thioxanthones. Type inkjet ink composition.   The active energy ray-curable inkjet ink composition for forming a clear layer according to any one of claims 1 to 3, wherein the surface tension adjusting agent contains a silicone compound.   The active energy ray-curable inkjet ink composition for forming a clear layer according to claim 4, wherein the silicone compound has an ethylenic double bond in the molecule.   The N-substituted (meth) acrylamides contain at least one selected from the group consisting of N, N-dimethyl (meth) acrylamide and N, N-diethyl (meth) acrylamide. 2. The active energy ray-curable inkjet ink composition for forming a clear layer according to item 1.   The active energy ray-curable inkjet ink composition for forming a clear layer according to any one of claims 1 to 6, wherein the viscosity at 25 ° C is 4 to 50 mPa · s.   8. The active energy ray-curable inkjet ink composition for forming a clear layer according to claim 1, wherein the surface tension at 25 ° C. is 23 to 34 mN / m.   The active energy ray-curable inkjet ink composition for forming a clear layer according to any one of claims 1 to 8, which contains substantially no non-reactive solvent.   The active energy ray-curable inkjet ink composition for image formation contains (meth) acrylate monomers and N-substituted (meth) acrylamides as the polymerizable compound, according to any one of claims 1 to 9. An active energy ray-curable inkjet ink composition for forming a clear layer.   The printed matter which has a clear layer formed using the active energy ray hardening-type inkjet ink composition for clear layer formation of any one of Claims 1-10.