Active ray-curable resin composition for printing and lithographic printing ink using the same

Abstract

To provide an active ray-curable resin composition for printing which demonstrates superior adhesion with plastic films, stability in long-term storage, and tack stability under changes in humidity, and a lithographic printing ink using the same.SOLUTION: An active ray-curable resin composition for printing, comprises: an acrylic copolymer being a copolymer of a monomer group comprising (a) styrene, (b) acrylic acid, and (c) methyl methacrylate; and pentaerythritol triacrylate, wherein the proportion of each component in the monomer group is (a) styrene 20 to 40 mol%, (b) acrylic acid 20 to 40 mol%, and (c) methyl methacrylate 20 to 60 mol%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an actinic radiation-curable printing resin composition and a printing ink using the same. [Background technology]

[0002] Lithographic printing is a printing method that has become widespread as a system for producing printed materials at high speed, in large quantities, and at low cost. In recent years, the use of actinic radiation-curable lithographic printing inks, which cure instantly upon exposure to actinic radiation from sources such as mercury lamps, metal halide lamps, light-emitting diodes, and electron beams, has spread to many fields due to their advantages in terms of equipment, safety, the environment, and productivity.

[0003] In recent years, studies have begun to apply lithographic printing to flexible packaging made of thin plastic film used for everyday items, food, pharmaceuticals, etc. Actinic radiation-curable lithographic printing inks can be cured at room temperature in a short time, and are therefore considered to be suitable for printing on flexible packaging made of plastic film, which has poor heat resistance.

[0004] As an ink suitable for printing on flexible packaging, an active energy ray-curable composition has been proposed (see, for example, Patent Document 1), which contains a resin and an ethylenically unsaturated compound (A), the resin being a copolymer of a monomer group including styrenes (a) and a vinyl monomer (c) having a hydrophilic group, in which the content of styrenes (a) in the monomer group is 50.0 mol % or more and 85.0 mol % or less, and the glass transition temperature Tg is 100°C or more and 150°C or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2023 / 54322 Summary of the Invention [Problem to be solved by the invention]

[0006] Plastic films used in flexible packaging are flexible and easily bendable. Therefore, in so-called front printing, in which ink is applied to the front side of the film, the printed surface is easily rubbed, and high adhesion between the ink film and the plastic film is required. Furthermore, in so-called back printing, in which ink is applied to the back side of the plastic film, high adhesion between the ink film and the plastic film is required to prevent ink peeling during post-processing such as sealant lamination and handling. Pentaerythritol triacrylate is an example of a compound that exhibits excellent adhesion to substrates such as plastic films. However, according to the inventors' studies, pentaerythritol triacrylate has poor compatibility with conventional acrylic resins used in actinic radiation-curable printing resin compositions such as those described in Patent Document 1, and has problems such as clouding of the composition depending on the storage environment and significant tack fluctuation due to humidity.

[0007] In view of the problems of the prior art, the present invention aims to provide an actinic radiation-curable printing resin composition that has excellent adhesion to plastic films, long-term storage stability, and tack stability against humidity fluctuations, and a lithographic printing ink using the same. [Means for solving the problem]

[0008] The present invention mainly has the following configuration. (1) An actinic radiation-curable printing resin composition containing pentaerythritol triacrylate and an acrylic copolymer, which is a copolymer of a monomer group including (a) styrene, (b) acrylic acid, and (c) methyl methacrylate, wherein the content of each component in the monomer group is (a) styrene 20 to 40 mol%, (b) acrylic acid 20 to 40 mol%, and (c) methyl methacrylate 20 to 60 mol%. (2) The actinic radiation-curable printing resin composition according to (1), wherein the monomer group further comprises (d) at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, and the total content of ethyl acrylate and butyl acrylate in component (d) is 10 mol% or less, and the content of 2-ethylhexyl acrylate is 6 mol% or less. (3) The actinic radiation-curable printing resin composition according to (1) or (2), further comprising a polyfunctional (meth)acrylate other than pentaerythritol triacrylate. (4) The actinic radiation-curable printing resin composition according to (3), which contains 10 to 30% by mass of the acrylic copolymer, 30 to 60% by mass of the pentaerythritol triacrylate, and 20 to 40% by mass of the other polyfunctional (meth)acrylate. (5) Viscosity (viscosity N 0.1 ) is 100 to 1,000 Pa·s. (6) Viscosity N when the moisture content is 0.5% by mass 0.5 The viscosity N 0.1 Ratio to (N 0.5 / N 0.1 ) is 0.4 to 0.7. (7) The actinic radiation-curable printing resin composition according to any one of (1) to (6), wherein the acrylic copolymer has a weight-average molecular weight of 5,000 to 50,000. (8) A lithographic printing ink containing the actinic radiation-curable printing resin composition according to any one of (1) to (7) and a pigment. [Effects of the Invention]

[0009] The actinic radiation-curable printing resin composition according to the present invention and the lithographic printing ink using the same are excellent in adhesion to plastic films, long-term storage stability, and tack stability against humidity fluctuations. DETAILED DESCRIPTION OF THE INVENTION

[0010] The actinic radiation-curable printing resin composition (hereinafter sometimes abbreviated as "resin composition") of the present invention contains an acrylic copolymer, which is a copolymer of a monomer group including (a) styrene, (b) acrylic acid, and (c) methyl methacrylate, and pentaerythritol triacrylate. The acrylic copolymer imparts elasticity to the resin composition, thereby adjusting the viscosity of the resin composition and improving pigment dispersibility. As mentioned above, pentaerythritol triacrylate significantly improves adhesion to plastic films, but has the problem of poor compatibility with conventional acrylic resins. Therefore, in the present invention, from the perspective of compatibility with pentaerythritol triacrylate, we focus on the copolymerization composition of the acrylic copolymer. By using the copolymerization components described below in the copolymerization ratio described below, it is possible to achieve both adhesion to plastic films, long-term storage stability, and tack stability against humidity changes. The resin composition of the present invention can be suitably used, for example, in lithographic printing inks (hereinafter sometimes abbreviated as "inks"), overcoat varnishes such as ultraviolet-curable overcoat varnishes and electron beam-curable overcoat varnishes, and adhesives such as ultraviolet-curable adhesives and electron beam-curable adhesives.

[0011] The acrylic copolymer contains structural units derived from (a) styrene, which imparts high elasticity derived from the aromatic skeleton to the resin composition of the present invention. Therefore, when the resin composition is used in an ink, tackiness and background scumming can be suppressed. Furthermore, the stringiness of the ink can be suppressed, and misting can be suppressed.

[0012] The content of (a) styrene in the group of monomers constituting the acrylic copolymer is 20 to 40 mol %. If the content of (a) styrene is less than 20 mol %, the compatibility with pentaerythritol triacrylate will be excessively improved, resulting in increased tackiness of the ink. Furthermore, when used in an ink, background scumming and misting will be more likely to occur. The content of (a) styrene is preferably 25 mol % or more. On the other hand, if the content of (a) styrene exceeds 40 mol %, the viscosity of the resin composition will decrease and the compatibility with pentaerythritol triacrylate will decrease, resulting in a decrease in the long-term storage stability of the resin composition. The content of (a) styrene is preferably 35 mol % or less.

[0013] The acrylic copolymer contains structural units derived from (b) acrylic acid, which improves compatibility with pentaerythritol triacrylate and improves tack stability against humidity fluctuations when the resin composition is used in an ink. This effect is unique to acrylic acid and is not achieved by other structurally similar compounds, such as methacrylic acid. This is thought to be due to the higher water solubility of acrylic acid compared to methacrylic acid, which maintains high compatibility with pentaerythritol triacrylate even when the moisture content of the resin composition increases, thereby stabilizing tack. Furthermore, the presence of structural units derived from (b) acrylic acid improves pigment dispersibility, suppressing ink viscosity loss under high shear stress and reducing background scumming.

[0014] The content of (b) acrylic acid in the group of monomers constituting the acrylic copolymer is 20 to 40 mol %. If the content of (b) acrylic acid is less than 20 mol %, compatibility with pentaerythritol triacrylate decreases, and when the resin composition is used in an ink, tack stability against humidity fluctuations decreases. Furthermore, the viscosity at high shear decreases, so background scumming tends to occur when used in an ink. The content of (b) acrylic acid is preferably 25 mol % or more. On the other hand, if the content of (b) acrylic acid exceeds 40 mol %, the viscosity of the resin composition increases due to interactions between polar groups. When other polyfunctional (meth)acrylates described below are contained, compatibility with the other polyfunctional (meth)acrylates decreases, and long-term storage stability decreases. The content of (b) acrylic acid is preferably 35 mol % or less.

[0015] By including structural units derived from (c) methyl methacrylate, the acrylic copolymer can improve compatibility with pentaerythritol triacrylate, thereby improving long-term storage stability and tack stability against humidity fluctuations. Furthermore, when the resin composition is used in ink, background scumming can be suppressed. This effect is unique to methyl methacrylate and is not achieved by other compounds with similar structures, such as methyl acrylate. This is thought to be because structural units derived from methyl methacrylate have a higher glass transition temperature and relatively high elasticity compared to structural units derived from methyl acrylate, thereby improving the elasticity of the resin composition.

[0016] The content of (c) methyl methacrylate in the group of monomers constituting the acrylic copolymer is 20 to 60 mol %. If the content of (c) methyl methacrylate is less than 20 mol %, the compatibility with pentaerythritol triacrylate decreases, resulting in a decrease in the long-term storage stability and tack stability against humidity fluctuations of the resin composition. Furthermore, the elasticity of the resin composition decreases, making background scumming more likely to occur when the resin composition is used in ink. The content of (c) methyl methacrylate is preferably 25 mol % or more. On the other hand, if the content of (c) methyl methacrylate exceeds 60 mol %, the contents of (a) styrene and (b) acrylic acid become relatively small, resulting in increased tackiness and decreased tack stability against humidity fluctuations when the resin composition is used in ink. Furthermore, background scumming and misting are more likely to occur. The content of (c) methyl methacrylate is preferably 45 mol % or less, and more preferably 35 mol % or less.

[0017] The group of monomers constituting the acrylic copolymer preferably further includes (d) at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. The acrylic copolymer contains structural units derived from these monomers, which further improves compatibility with pentaerythritol triacrylate and the long-term storage stability of the resin composition. Furthermore, the acrylic copolymer also improves affinity with plastic films, thereby improving ink smudging when used as an ink.

[0018] The total content of (d) ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate in the group of monomers constituting the acrylic copolymer is preferably 1 mol% or more, more preferably 3 mol% or more. Meanwhile, the total content of ethyl acrylate and butyl acrylate in component (d) is preferably 10 mol% or less, which can suppress tack and background scumming and misting when used as an ink. Furthermore, the content of 2-ethylhexyl acrylate in component (d) is preferably 6 mol% or less, which can suppress tack and background scumming when used as an ink. The content of 2-ethylhexyl acrylate is more preferably 3 mol% or less.

[0019] The weight-average molecular weight of the acrylic copolymer is preferably 5,000 or more, which can appropriately increase the viscosity of the resin composition under high shear. Therefore, when used as an ink, background scumming can be suppressed. The weight-average molecular weight is more preferably 10,000 or more, and even more preferably 15,000 or more. On the other hand, the weight-average molecular weight of the acrylic copolymer is preferably 50,000 or less, which can appropriately maintain the fluidity of the resin composition. In addition, it has excellent compatibility with pentaerythritol triacrylate, which can further improve long-term storage stability. The average molecular weight is more preferably 35,000 or less, and even more preferably 25,000 or less. The weight-average molecular weight of the acrylic copolymer can be measured using gel permeation chromatography (GPC) in terms of polystyrene.

[0020] The acrylic copolymer can be obtained by copolymerizing (a) styrene, (b) acrylic acid, (c) methyl methacrylate, and, if necessary, (d) at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, using a radical polymerization initiator.

[0021] The content of the acrylic copolymer in the resin composition according to the present invention is preferably 10 to 30% by mass. By making the content of the acrylic copolymer 10% by mass or more, the viscosity of the resin composition can be appropriately increased, and when used as an ink, scumming and misting can be suppressed. On the other hand, by making the content 30% by mass or less, the curability of the resin composition and adhesion to plastic films can be improved.

[0022] The resin composition according to the present invention contains pentaerythritol triacrylate. By including pentaerythritol triacrylate, adhesion to plastic films is significantly improved. Furthermore, when used as an ink, it exhibits excellent curability and pigment dispersibility, and can suppress background scumming. The effects of pentaerythritol triacrylate are believed to be due to its extremely high hydroxyl value and double bond ratio per molecular weight. This is thought to be due to the fact that hydrogen bonds of the hydroxyl groups facilitate bonding with carbonyl groups, amino groups, and the like present on the surface of the film. Furthermore, the high curability ensures that the resin composition and ink cure reliably, contributing to the development of adhesion to plastic films.

[0023] The content of pentaerythritol triacrylate in the resin composition according to the present invention is preferably 30 to 60% by mass. By making the content of pentaerythritol triacrylate 30% by mass or more, the adhesion of the resin composition to a plastic film can be further improved. Furthermore, when used as an ink, the curability and pigment dispersibility can be further improved, and background scumming can be further suppressed. On the other hand, by making the content 60% by mass or less, tackiness of the resin composition can be suppressed.

[0024] The resin composition according to the present invention preferably contains, together with pentaerythritol triacrylate, other polyfunctional (meth)acrylates (hereinafter sometimes abbreviated as "polyfunctional (meth)acrylates"). By including such polyfunctional (meth)acrylates, tackiness of the resin composition can be suppressed. Here, "(meth)acrylate" is a general term for acrylates and methacrylates.

[0025] Examples of polyfunctional (meth)acrylates include pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane di(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, polyethylene glycol di(meth)acrylate, dipentaerythritol di(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaethylitol hexa(meth)acrylate, dipropylene glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, neopentyl glycol propoxylate, glycerin propoxy triacrylate, glycerin di(meth)acrylate, glycerin tri(meth)acrylate, diglycerin tri( Di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,11-undecanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 1,13-tridecanediol di(meth)acrylate, 1,14-tetradecanediol di(meth)acrylate, 1,15-pentadecanediol di(meth)acrylate acrylate, 1,16-hexadecanediol di(meth)acrylate, 1,17-heptadecanediol di(meth)acrylate, 1,18-octadecanediol di(meth)acrylate, 4-methyl-1,10-decanediol di(meth)acrylate, 4-ethyl-1,10-decanediol di(meth)acrylate, and ethylene oxide adducts, propylene oxide adducts, butylene oxide adducts, tetramethylene oxide adducts thereof, etc. Two or more of these may be contained.

[0026] The content of the polyfunctional (meth)acrylate in the resin composition according to the present invention is preferably 20 to 40% by mass. By making the content of the polyfunctional (meth)acrylate 20% by mass or more, the fluidity of the resin composition can be improved and tackiness can be suppressed. On the other hand, by making the content 40% by mass or less, the viscosity of the resin composition can be maintained high under high shear stress, and adhesion to plastic films can be further improved. Furthermore, when used as an ink, background scumming can be suppressed.

[0027] The resin composition according to the present invention may further contain an organic solvent and various additives, if necessary.

[0028] The resin composition according to the present invention has a viscosity (viscosity N 0.1 ) is preferably 100 to 1,000 Pa·s. In addition, the viscosity N 0.5 The viscosity N 0.1 Ratio to (N 0.5 / N 0.1 ) is preferably 0.4 to 0.7. Here, the viscosity at 25°C is the viscosity at a temperature that is a general temperature in the environment in which the resin composition or ink is used. The viscosity of the resin composition varies depending on the moisture content in the resin composition, which is affected by the humidity of the environment in which the resin composition is used. When the temperature is controlled at 25°C, the humidity generally varies within a range of about 30 to 70%. In an atmosphere with a temperature of 25°C and a humidity of 30%, the moisture content that the resin composition or ink is expected to reach when kneaded with a roller or the like is 0.1% by mass, and in an atmosphere with a temperature of 25°C and a humidity of 70%, the moisture content that the resin composition or ink is expected to reach when kneaded with a roller or the like is 0.5% by mass. Therefore, in the present invention, the viscosity N at these moisture contents is 0.1 and N 0.5 We focused on N 0.1indicates the viscosity of a resin composition at 25°C and a Brookfield viscometer at a rotation speed of 0.4 (1 / s) when the moisture content is 0.1% by mass. If the moisture content of the resin composition is less than 0.1% by mass, distilled water is added to make the moisture content 0.1% by mass before measurement. If the moisture content of the resin composition exceeds 0.1% by mass, the moisture content is adjusted to 0.1% by mass by vacuum drying or the like before measurement. 0.5 refers to the viscosity of a resin composition measured with a Brookfield viscometer at a rotation speed of 0.4 (1 / s) when the moisture content is 0.5% by mass. If the moisture content of the resin composition is less than 0.5% by mass, distilled water is added to adjust the moisture content to 0.5% by mass before measurement. If the moisture content of the resin composition is more than 0.5% by mass, the moisture content is adjusted to 0.5% by mass by vacuum drying or the like before measurement. Note that although it is believed that the viscosity of a resin composition changes little with shear rate, in the present invention, attention is focused on the viscosity at a rotation speed of 0.4 (1 / s) as a condition under which excessive torque is not applied.

[0029] Viscosity N 0.1 If the viscosity is 100 Pa·s or more, background scumming can be suppressed when used as an ink. 0.1 By making the viscosity 1,000 Pa·s or less, the resin composition becomes easy to handle.

[0030] N 0.1 As a means for adjusting the content to the above range, for example, a method of using the above-mentioned preferred acrylic copolymer or a method of adjusting the content thereof to the above-mentioned preferred range can be mentioned.

[0031] N 0.5 / N 0.1 When the moisture content of the resin composition is 0.4 or more, the tack stability against humidity fluctuations can be further improved. On the other hand, the tack of the resin composition tends to increase as the compatibility between the acrylic copolymer and the monomer component such as pentaerythritol triacrylate increases. When the moisture content of the resin composition increases, the compatibility improves and the tack tends to increase. 0.5 / N 0.1 N 0.5 / N0.1 When the tackiness is 0.7 or less, the decrease in tackiness due to the decrease in viscosity and the increase in tackiness due to the improvement in compatibility are offset, and it is believed that the tackiness stability against humidity fluctuations can be further improved.

[0032] N 0.5 / N 0.1 As a means for adjusting the content of the acrylic copolymer, pentaerythritol triacrylate, and polyfunctional (meth)acrylate to fall within the above range, for example, a method of adjusting the content of the acrylic copolymer, pentaerythritol triacrylate, and polyfunctional (meth)acrylate to fall within the above-mentioned preferred range may be mentioned.

[0033] The resin composition of the present invention can be obtained, for example, by heating and dissolving the above-mentioned acrylic copolymer, pentaerythritol triacrylate, and, if necessary, the above-mentioned polyfunctional (meth)acrylate and other components at 50 to 110°C for 1 to 6 hours, and then cooling to room temperature.

[0034] The ink of the present invention contains the resin composition of the present invention and a pigment. Examples of the pigment include organic pigments and inorganic pigments. Examples of the organic pigment and inorganic pigment include those exemplified as organic pigments and inorganic pigments in WO 2018 / 163942. Two or more of these pigments may be contained. In the case of inks used as base colors for transparent plastic films, white pigments such as titanium dioxide, zinc oxide, and alumina white, which impart hiding properties, are preferred.

[0035] The content of the pigment in the ink of the present invention is preferably 15 to 40 mass % for organic pigments or carbon black with a specific gravity of 2 or less, and preferably 40 to 50 mass % for inorganic pigments with a specific gravity of more than 2.

[0036] The ink of the present invention may contain an acylphosphine oxide compound. Examples of acylphosphine oxide compounds include those exemplified in WO 2018 / 163942. Two or more of these compounds may be contained.

[0037] When the ink of the present invention contains an acylphosphine oxide compound, the content thereof is preferably 5 to 10% by mass.

[0038] The ink of the present invention may contain a sensitizer. Examples of sensitizers include those exemplified in WO 2018 / 163942. Two or more of these may be contained.

[0039] When the ink of the present invention contains a sensitizer, the content thereof is preferably 3 to 10% by mass.

[0040] The ink of the present invention preferably contains a polymerization inhibitor. Examples of polymerization inhibitors include those exemplified in WO 2018 / 163942. Two or more of these may be contained.

[0041] When the ink of the present invention contains a polymerization inhibitor, the content thereof is preferably 0.001 to 5% by mass.

[0042] The ink of the present invention preferably contains a pigment dispersant, which can improve the dispersibility of the pigment and improve the fluidity of the ink. Examples of pigment dispersants include those exemplified in WO 2018 / 163942. Two or more of these may be contained.

[0043] When the ink of the present invention contains a pigment dispersant, the content thereof is preferably 5 to 50 parts by mass relative to 100 parts by mass of the pigment.

[0044] The ink of the present invention may contain additives such as wax, antifoaming agent, transferability improver, leveling agent, etc., as required.

[0045] The viscosity of the ink of the present invention under low shear conditions, for example, the low shear viscosity (A) measured using a cone-plate rotational viscometer at 35°C and a shear rate of 3 (1 / s), is preferably 20 to 100 Pa·s. When the low shear viscosity (A) is 20 Pa·s or higher, the transferability between rollers is improved. On the other hand, when the low shear viscosity (A) is 100 Pa·s or lower, the flowability is improved.

[0046] The viscosity of the ink of the present invention under high shear, for example, the high shear viscosity (B) measured using a cone-plate rotational viscometer at 35°C and a shear rate of 418 (1 / s), is preferably 15 to 30 Pa·s. When the high shear viscosity (B) is 15 Pa·s or higher, background scumming can be suppressed. On the other hand, when the high shear viscosity (B) is 30 Pa·s or lower, transferability to a lithographic printing plate is improved.

[0047] Next, a method for producing the ink of the present invention will be described. The ink of the present invention can be obtained by mixing and dispersing the pigment and other components into the resin composition of the present invention. Prior to mixing and dispersing, the components may be dissolved at 5 to 100°C, or degassing may be performed under vacuum or reduced pressure conditions during and / or after mixing and dispersing. Examples of mixing and dispersing devices include agitators and kneaders such as a kneader, three-roll mill, ball mill, planetary ball mill, bead mill, roll mill, attritor, sand mill, gate mixer, paint shaker, homogenizer, and planetary agitator.

[0048] Next, a method for producing a printed matter using the ink of the present invention will be described. The method preferably includes a step of transferring the ink onto a substrate and a step of irradiating the ink with actinic rays. Since the ink of the present invention is cured by irradiation with actinic rays, a printed matter having a cured ink film can be obtained by the step of irradiating with actinic rays.

[0049] First, the process of transferring the ink according to the present invention onto a substrate will be described.

[0050] Examples of substrates include art paper, coated paper, cast paper, synthetic paper, newsprint, plastic film, plastic film-laminated paper, metal, metal-vapor-deposited paper, and metal-vapor-deposited plastic film. Two or more of these may be used. Examples of plastic films include films made of polyethylene terephthalate, polyethylene, polyester, polyamide, polyimide, polystyrene, polypropylene, polycarbonate, polyvinyl acetal, and the like. Examples of plastic film-laminated paper include paper on which the aforementioned plastic film is laminated. Examples of metal plates include plates made of zinc, copper, and the like. Examples of metal-vapor-deposited paper and metal-vapor-deposited plastic film include paper or plastic film on which the aforementioned metals or their oxides are vapor-deposited. Among these, plastic film, plastic film-laminated paper, and metal-vapor-deposited plastic film do not absorb ink and therefore do not adhere to the ink due to ink absorption. Therefore, they are suitable for use in the present invention, where the ink can be cured and adhered by exposure to actinic rays.

[0051] The substrate may be subjected to an adhesion-facilitating treatment to improve ink transferability to the substrate. Examples of the adhesion-facilitating treatment include surface treatments such as primer application, corona discharge treatment, and plasma treatment, and formation of an adhesion-facilitating layer.

[0052] When used for flexible packaging, the thickness of the substrate is preferably 10 to 30 μm.

[0053] The substrate may be either a sheet or a roll film. When a thin film is used for flexible packaging, it is preferable to use a roll film and transfer the film by roll-to-roll transfer.

[0054] The method for transferring the ink according to the present invention onto a substrate is preferably lithographic printing, and examples of lithographic printing methods include water-based printing and waterless printing.

[0055] Next, the step of irradiating with actinic rays will be described.

[0056] Examples of actinic rays include ultraviolet rays and electron beams. Examples of ultraviolet irradiation devices include high-pressure mercury lamps, xenon lamps, metal halide lamps, and light-emitting diodes (LEDs). From the viewpoint of power saving, it is preferable to use ultraviolet rays (LED-UV) using a light-emitting diode that emits an emission line with a wavelength of 350 to 420 nm as a light source. As for electron beams, energy rays of 100 to 500 eV are preferred.

[0057] Examples of printing presses include single-cylinder printing presses that use an independent impression cylinder for each color, and center-impression printing presses that use a single impression cylinder for multiple colors. Center-impression printing presses have a short printing interval (distance) between each color, which means that the time required for the ink to be leveled after being transferred to the substrate is short, making it difficult to achieve high ink density with conventional inks. The ink of the present invention is particularly suitable for use in center-impression printing presses, as it moderately reduces the ink viscosity at low shear, shortens the time required for the ink to be leveled after being transferred to the substrate, and facilitates high ink density.

[0058] The thickness of the ink coating on the printed matter is preferably 0.1 to 50 μm, which allows for both good print quality and reduced ink consumption. [Example]

[0059] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0060] First, the raw materials of the resin composition and ink will be described.

[0061] Resin 1: A reaction vessel equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet was charged with 100 mol of copolymerized monomers, 150 mol of propylene glycol monomethyl ether acetate as solvent, 33 mol of styrene, 33 mol of acrylic acid, 33 mol of methyl methacrylate, and 1 mol of 2-ethylhexyl acrylate. 1 mol of 2,2'-azobis(2-methylbutyronitrile) was added as a polymerization initiator. The mixture was refluxed and stirred at 140°C for 1.5 hours, followed by an incubation period of 1 hour. The temperature was then raised to 160°C, and the solvent was distilled off at normal pressure while stirring. The pressure was then reduced to below 6.7 kPa at the same temperature, and the solvent was completely distilled off to obtain Resin 1 with a weight-average molecular weight of 20,000.

[0062] Resins 2 to 14: Resins 2 to 14 were obtained in the same manner as for Resin 1, except that the types of copolymerized monomers and copolymerization ratios were changed as shown in Table 1.

[0063] Table 1 shows the copolymer compositions and weight average molecular weights of Resins 1 to 14.

[0064] [Table 1]

[0065] Pentaerythritol triacrylate: "Miramer" (registered trademark) M340 (manufactured by MIWON). Multifunctional (meth)acrylate 1: Pentaerythritol ethylene oxide modified tetraacrylate "DOUBLEMER" (registered trademark) PET5EO4A (manufactured by Double Bond Chemical Co., Ltd.) Multifunctional (meth)acrylate 2: Glycerin propoxytriacrylate "Miramer" (registered trademark) M320 (manufactured by MIWON Co., Ltd.) Pigment 1: Carmine 6B 393 (manufactured by Dainichi Seika Color & Chemicals Co., Ltd.) Pigment 2: Mica A-11 (manufactured by Yamaguchi Mica Co., Ltd.).

[0066] Next, the evaluation methods used in the examples and comparative examples will be described.

[0067] (1) Weight-average molecular weight of resin The weight-average molecular weight of the resin was measured by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase. The resin was diluted with tetrahydrofuran to a concentration of 0.25% by mass. The diluted solution was dissolved by stirring at 100 rpm for 5 minutes using a mix rotor (MIX-ROTAR VMR-5, AS ONE Corporation). The filtrate was then filtered through a 0.2 μm filter (Z227536-100EA, SIGMA Corporation) to obtain the measurement sample. The GPC used was an HLC-8220 (Tosoh Corporation), and the columns were a TSKgel SuperHM-H (Tosoh Corporation), a TSKgel SuperHM-H (Tosoh Corporation), and a TSKgel SuperH2000 (Tosoh Corporation) column connected in this order. RI detection was performed using the RI detector built into the GPC. The load volume was 10 μL, the analysis time was 30 minutes, the flow rate was 0.4 mL / min, and the column temperature was 40°C. A calibration curve was prepared using polystyrene standards.

[0068] (2) Viscosity N of the resin composition 0.1 , N 0.5 The moisture content of the resin compositions obtained in each of the Examples and Comparative Examples was measured using a moisture measuring device (AQ-2200A, manufactured by Hiranuma Sangyo Co., Ltd.) and a moisture vaporizer (EV-2000, manufactured by Hiranuma Sangyo Co., Ltd.) If necessary, drying was performed using a vacuum dryer or distilled water was added so that the moisture content was 0.1% by mass or 0.5% by mass.

[0069] The resin composition with the adjusted moisture content was measured for viscosity N at a moisture content of 0.1% by mass at 25°C and a shear rate of 0.4 (1 / s) using a Brookfield viscometer (DV-II, manufactured by Brookfield) with a spindle (SC4-14, diameter 8.74 mm, manufactured by Brookfield). 0.1 and viscosity N at a moisture content of 0.5% by mass 0.5 The viscosity ratio (N 0.5 / N 0.1 ) was calculated.

[0070] (3) Adhesion of resin composition The resin compositions obtained in each Example and Comparative Examples 1, 3, and 5 were applied to a polyamide substrate (ONM, manufactured by Unitika Ltd.) using a #8 bar coater to a thickness of approximately 10 μm, and then the resin compositions were cured by irradiating them with an electron beam at an acceleration voltage of 110 kV and a dose of 30 kGy. A 3 cm long piece of cellophane tape (CT-24, manufactured by Nichiban Co., Ltd.) was applied to the surface of the cured product and immediately peeled off. The area of ​​the cured product peeled off from the polyamide substrate together with the cellophane tape (peeled area) was calculated, and adhesion was evaluated as the ratio of the peeled area to the attached area. The smaller the peeled area, the better the adhesion; a peeled area of ​​50% or less is preferred, and 20% or less is more preferred.

[0071] (4) Long-term storage stability of the resin composition The resin compositions obtained in each of the Examples and Comparative Examples were transferred to transparent glass containers and stored in an incubator (KMH-050, manufactured by AS ONE Corporation) at -15°C. The appearance was visually inspected after one day, one week, and one month, and the long-term storage stability was evaluated according to the following criteria. D (very poor): Cloudy and does not flow even when the container is tilted C (bad): The liquid is cloudy and flows when the container is tilted, but the end of the container cannot be seen through. B (fairly good): Cloudy, flows when the container is tilted, and the tip of the container is visible A (Good): Transparent.

[0072] (5) Ink tack and tack stability against humidity fluctuations At a temperature of 25°C and humidity of 30%, and a temperature of 25°C and humidity of 70%, 1.3 ml of ink obtained in each Example and Comparative Examples 1 and 3 to 5 was applied to the roller of an Inkometer INKOGRAPH TYPE-V (Tester Sangyo Co., Ltd.), operated at a roller temperature of 30°C and a rotation speed of 400 rpm, and the tack value was measured after 1 minute. The lower the tack value, the more suppressed the tack, and a tack value of 16 or less is preferable.

[0073] The tack stability against humidity fluctuations was evaluated based on the difference in the tack measurement values ​​under each humidity condition. The smaller the difference in the tack measurement values, the better the tack stability. The difference in the tack measurement values ​​is preferably 3 or less, and more preferably 1 or less.

[0074] (6) Ink viscosity The viscosity of the inks obtained in each of the Examples and Comparative Examples 1 and 3 to 5 was measured at 35°C using a rheometer (MCR301, manufactured by Anton Paar) with a cone plate (CR25-2, diameter 25 mm, angle 2 degrees, manufactured by Anton Paar) in shear measurement mode (shear rate was increased from 1 (1 / s) to 490 (1 / s) in 5-second intervals in logarithmic increase mode), and the low shear viscosity (A) at a rotation speed of 3 (1 / s) and the high shear viscosity (B) at a rotation speed of 418 (1 / s) were measured.

[0075] (7) Background smearing and misting A waterless lithographic printing plate (TAC-VG5, manufactured by Toray Industries, Inc.) was mounted on an offset web press (CI-8, manufactured by COMEXI). Using the inks obtained in each Example and Comparative Examples 1, 3, and 5, a test pattern with a solid area was printed on a polyester film PTM12 (manufactured by Unitika, 12 μm thick) at a printing temperature of 30°C, a printing speed of 200 m / min, and an ink supply rate of 50%. A 1,000-m reverse print was then performed. The print was then irradiated with an electron beam at an accelerating voltage of 110 kV and a dose of 30 kGy to cure the ink and obtain a printed product. The ink supply rate was adjusted so that the reflection density of the solid area was 1.6. The reflection density of the solid area was measured using a reflection densitometer (SpectroEye, Status E, manufactured by GretagMacbeth) with white coated paper as the paper white (reflection density 0 as the reference). The coated paper was also placed near the mixing roll.

[0076] The reflection density of the non-printing area located 1 cm from the solid area of ​​the test pattern on the obtained print was measured using a reflection densitometer (SpectroEye, Status E, manufactured by GretagMacbeth) to evaluate background scumming. The lower the reflection density, the more suppressed the background scumming, and a reflection density of 0.10 or less is preferred, and 0.05 or less is more preferred.

[0077] After printing the test pattern, the reflection density of the coated paper placed near the mixing roll was measured using a reflection densitometer (SpectroEye, Status E, manufactured by GretagMacbeth) to evaluate misting. The lower the reflection density, the more suppressed the misting, and a reflection density of 0.10 or less is preferred, and 0.05 or less is more preferred.

[0078] [Example 1] The resin, pentaerythritol triacrylate, and polyfunctional (meth)acrylate 1 shown in Table 2 were weighed and dissolved by heating at 95°C for 390 minutes while stirring at 500 rpm using a disperser blade to obtain a resin composition. The viscosity, adhesion, and long-term storage stability of the obtained resin composition were evaluated. The evaluation results are shown in Table 2.

[0079] To 100 parts by mass of the obtained resin composition, 20 parts by mass of pigment 1 and 1 part by mass of pigment 2 were added, and the mixture was kneaded three times at a gap of 1 using a three-roll mill "EXAKT" (registered trademark) M-80S (manufactured by EXAKT) to obtain an ink. The obtained ink was evaluated for tack, shear viscosity, background scumming, and misting. The evaluation results are shown in Table 2.

[0080] [Examples 2 to 7] Resin compositions and inks were obtained in the same manner as in Example 1, except that the components were changed as shown in Table 2. The results of evaluation in the same manner as in Example 1 are shown in Table 2.

[0081] [Examples 8 to 16, Comparative Examples 1 to 5] Resin compositions and inks were obtained in the same manner as in Example 1, except that the compositions were changed as shown in Tables 3 and 4. The results of evaluations similar to those in Example 1 are shown in Tables 3 and 4.

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

Claims

1. An actinic radiation-curable printing resin composition containing pentaerythritol triacrylate and an acrylic copolymer which is a copolymer of a monomer group including (a) styrene, (b) acrylic acid, and (c) methyl methacrylate, wherein the content of each component in the monomer group is (a) 20 to 40 mol % of styrene, (b) 20 to 40 mol % of acrylic acid, and (c) 20 to 60 mol % of methyl methacrylate.

2. 2. The actinic radiation-curable printing resin composition according to claim 1, wherein the monomer group further comprises (d) at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, and the total content of ethyl acrylate and butyl acrylate in component (d) is 10 mol % or less, and the content of 2-ethylhexyl acrylate is 6 mol % or less.

3. The actinic radiation-curable printing resin composition according to claim 1 or 2, further comprising a polyfunctional (meth)acrylate other than pentaerythritol triacrylate.

4. 4. The actinic radiation-curable printing resin composition according to claim 3, comprising 10 to 30% by mass of the acrylic copolymer, 30 to 60% by mass of the pentaerythritol triacrylate, and 20 to 40% by mass of the other polyfunctional (meth)acrylate.

5. The viscosity (viscosity N ０．１ 3. The actinic radiation-curable printing resin composition according to claim 1, wherein the viscosity of the resin composition is 100 to 1,000 Pa·s.

6. Viscosity N when moisture content is 0.5% by mass ０．５ The viscosity N ０．１ Ratio to (N ０．５ / N ０．１ 6. The actinic radiation-curable printing resin composition according to claim 5, wherein the value of (a) is 0.4 to 0.

7.

7. 3. The actinic radiation-curable printing resin composition according to claim 1, wherein the weight-average molecular weight of the acrylic copolymer is 5,000 to 50,000.

8. A lithographic printing ink comprising the actinic radiation-curable printing resin composition according to claim 1 or 2 and a pigment.

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