Electron beam curable printing ink and method for manufacturing printed materials using the same

Abstract

To provide an electron beam curable printing ink in which the elution of unreacted components after curing is suppressed. [Solution] An electron beam curable printing ink containing (a) a compound having an ethylenically unsaturated group, (b) a pigment, and (c) a polyolefin, and substantially free of a photopolymerization initiator.

Description

Technical Field

[0001] The present invention relates to an electron beam curable ink for printing and a method for manufacturing a printed matter using the same.

Background Art

[0002] In recent years, from the perspective of environmental consideration, as printing inks, instead of solvent inks using organic solvents, water-based inks that do not use petroleum-based solvents and inks that are cured by active energy rays such as ultraviolet rays and electron beams have attracted attention. Among them, the use of electron beam curable inks for printing, which are instantaneously cured by irradiating an electron beam, has spread in many fields.

[0003] In recent years, studies have begun on applying electron beam curable inks for printing to flexible packaging printing used for daily necessities, food products, pharmaceuticals, etc. based on thin film plastic films, etc. Since electron beam curable inks for printing can be cured at room temperature and in a short time without substantially using a photoinitiator, they are considered suitable for flexible packaging printing based on plastic films with poor heat resistance.

[0004] Examples of electron beam curable inks for printing include, for example, lithographic printing inks containing pigments and resins having ethylenically unsaturated groups and hydrophilic groups (see, for example, Patent Document 1), and electron beam curable inkjet inks containing a photopolymerizable compound containing a trifunctional or higher polyfunctional compound and a linear alkyl aldehyde having 6 to 9 carbon atoms, wherein the content of the linear alkyl aldehyde is 0.001 mg / kg or more and 10 mg / kg or less in terms of toluene conversion with respect to the total mass of the electron beam curable inkjet ink (see, for example, Patent Document 2), etc. have been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] When applying these electron beam-curable printing inks to the flexible packaging printing described above, it is necessary to suppress the leaching of unreacted components remaining in the cured ink. In particular, in food applications where high safety is required, the suppression of leaching of unreacted components is even more strictly required.

[0007] Therefore, in view of the problems of the above-mentioned prior art, the present invention aims to provide an electron beam curable printing ink in which the elution of unreacted components after curing is suppressed. [Means for solving the problem]

[0008] To solve the above problems, the present invention mainly has the following configuration. <1> An electron beam curable printing ink comprising (a) a compound having an ethylenically unsaturated group, (b) a pigment, and (c) a polyolefin, and substantially free of a photopolymerization initiator. <2> The above (c) The melting point of the polyolefin is 60°C or higher. <1> The electron beam curing printing ink described in [reference]. <3> The weight-average molecular weight of the polyolefin (c) is equal to or greater than the molecular weight of the compound having an ethylenically unsaturated group (a). <1> or <2> The electron beam curing printing ink described in [reference]. <4> The (c) polyolefin contains polyethylene and / or polypropylene. <1> ~ <3> Electron beam curing printing ink as described in any of the following. <5> Furthermore, (d) contains a resin having hydrophilic functional groups. <1> ~ <4> Electron beam curing printing ink as described in any of the following. <6> (a) The compound having an ethylenically unsaturated group has at least a portion of a hydrophilic functional group. <1> ~ <5> Electron beam curing printing ink as described in any of the following. <7> The above (a) compound having an ethylenically unsaturated group has 3 to 6 ethylenically unsaturated groups. <1> ~ <6> Electron beam curing printing ink as described in any of the following. <8> <1> ~ <7> A method for manufacturing a printed material, comprising the steps of applying or transferring an electron beam-curable printing ink described in any of the above onto a substrate, and irradiating the applied or transferred electron beam-curable ink with an electron beam. <9> The substrate used is a plastic film, a plastic film laminated paper, a metal-deposited plastic film, and / or metal-deposited paper. <8> A method for manufacturing printed materials as described above. [Effects of the Invention]

[0009] According to the electron beam curable printing ink of the present invention, the elution of unreacted components after curing can be suppressed. [Modes for carrying out the invention]

[0010] The present invention will be described in detail below.

[0011] The electron beam curable printing ink according to the present invention (hereinafter sometimes abbreviated as "ink") contains (a) a compound having an ethylenically unsaturated group (hereinafter sometimes abbreviated as "(a) compound"), (b) a pigment, and (c) a polyolefin. By containing (a) the compound, the property of being curable by electron beam can be imparted. By containing (b) the pigment, a specific color can be imparted to the ink. In the present invention, by further containing (c) the polyolefin, the elution of unreacted components after curing can be suppressed, as will be described later. In the following description, the state before curing containing these components will be referred to as "ink," and the state after being cured by electron beam will be referred to as "ink cured film."

[0012] As mentioned above, in printing flexible packaging such as plastic films, unreacted components leached from the ink-cured film may contaminate the contents or adhere to surrounding objects and people during handling. Therefore, suppressing the leaching of unreacted components from the ink-cured film is more important than ever. The inventors investigated suppressing leaching by suppressing the remaining unreacted components in the ink-cured film and focused on polyolefins, in which radicals are generated in the molecular chain by electron beam irradiation. Polyolefins undergo cleavage of bonds in their molecular chains by electron beam irradiation, generating reactive radicals. On the other hand, the decomposition of polyolefins themselves by electron beam irradiation is not easily carried out. Therefore, by including (c) polyolefin in the ink, the amount of radicals generated by electron beam irradiation increases, improving the reaction rate of (a) compound and reducing the amount of remaining unreacted components in the ink-cured film.

[0013] Furthermore, one method to increase the amount of radical generation and improve the reaction rate of compound (a) is to include a large amount of additives such as photopolymerization initiators in the ink. However, in this case, there is a problem that the photopolymerization initiator itself tends to leach out from the ink cured film. Also, the tack of the ink tends to increase. In contrast, polyolefin (c), being a polymer, does not easily leach out from the ink cured film, and its compatibility with compound (a) is moderately suppressed, thus reducing the tack of the ink. The ink of the present invention substantially does not contain photopolymerization initiators. Here, "substantially does not contain photopolymerization initiators" means that the amount of photopolymerization initiator relative to the ink is less than 0.3% by mass.

[0014] (a) As for the compound, a compound having a (meth)acryloyl group as an ethylenically unsaturated group is preferred. Here, "(meth)acryloyl group" is a general term for acryloyl group and methacryloyl group. Two or more of these may be contained.

[0015] Compounds having two (meth)acryloyl groups include, for example, ditrimethylolpropane di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipentaerythritol di(meth)acrylate, dipropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, and 1,11-undecanediol di(meth)acrylate. Examples include acrylates, 1,12-dodecanediol di(meth)acrylate, 1,13-tridecanediol di(meth)acrylate, 1,14-tetradecanediol di(meth)acrylate, 1,15-pentadecanediol di(meth)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 alkylene oxide adducts thereof. Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, and tetramethylene oxide. Among these, ethylene oxide and propylene oxide are preferred from the viewpoint of compatibility with other components.

[0016] Examples of compounds having three (meth)acryloyl groups include pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, glycerin tri(meth)acrylate, diglycerin tri(meth)acrylate, and their alkylene oxide adducts.

[0017] Examples of the compound having four (meth)acryloyl groups include pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, diglycerin tetra(meth)acrylate, and alkylene oxide adducts thereof.

[0018] Examples of the compound having five or more (meth)acryloyl groups include dipentaerythritol penta(meth)acrylate, dipentaethylitol hexa(meth)acrylate, and alkylene oxide adducts thereof.

[0019] The compound (a) preferably has 3 to 6 ethylenically unsaturated groups in one molecule. By having 3 or more ethylenically unsaturated groups, the curing reaction by electron beam proceeds easily, so that unreacted components in the ink cured film can be further reduced and elution of unreacted components from the ink cured film can be further suppressed. On the other hand, by having 6 or less ethylenically unsaturated groups, interference between ethylenically unsaturated groups in the same molecule is suppressed, radical reactivity is enhanced, unreacted components in the ink cured film can be further reduced, and elution of unreacted components from the ink cured film can be further suppressed. It is more preferable to have 5 or less ethylenically unsaturated groups. When two or more kinds of the compound (a) are contained, it is preferable that at least a part of them has 3 to 6 ethylenically unsaturated groups in one molecule, and it is more preferable that 50 mass% or more of the compound (a) is a compound having 3 to 6 ethylenically unsaturated groups in one molecule.

[0020] (a) The compound preferably has hydrophilic functional groups. Having hydrophilic functional groups improves the affinity with (b) the pigment, so that (a) the compound and (b) the pigment are uniformly dispersed in the ink, and the radical reaction of (a) the compound by electron beam irradiation proceeds more uniformly, thereby reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components. In addition, compatibility with (c) polyolefin is moderately reduced, and the tack of the ink can be further reduced. Examples of hydrophilic groups include hydroxyl groups, carboxyl groups, amino groups, thiol groups, amide bonds, urethane bonds, and oxyethylene groups. Two or more of these may be present. Among these, from the viewpoint of affinity with (b) the pigment, hydroxyl groups, carboxyl groups, amino groups, amide bonds, and oxyethylene groups are preferred, and if a resin other than polyolefin, which will be described later, is included, hydroxyl groups and oxyethylene groups are more preferred from the viewpoint of affinity with such resin. (a) When two or more compounds are included, it is preferable that at least a portion of them have hydrophilic functional groups, and it is more preferable that 50% by mass or more of the compounds in (a) have hydrophilic functional groups.

[0021] (a) The molecular weight of the compound is preferably 250 or more. By setting the molecular weight to 250 or more, the distance between ethylenically unsaturated groups within the same molecule in the (a) compound is sufficiently large, so that each interference can be suppressed and the radical reactivity can be improved. As a result, the unreacted components in the ink cured film can be further reduced, and the elution of unreacted components from the ink cured film can be further suppressed. In addition, the compatibility with (c) polyolefin can be moderately reduced, and the tack of the ink can be further reduced. On the other hand, the molecular weight of the (a) compound is preferably 1,500 or less. When the molecular weight is 1,500 or less, the curing reaction by electron beam proceeds easily, so that the unreacted components in the ink cured film can be further reduced, and the elution of unreacted components from the ink cured film can be further suppressed. The "molecular weight" referred to here means the relative molecular mass. When the (a) compound has a molecular weight distribution, in the mass spectrometry described later, the relative molecular mass with the strongest relative intensity of the detection spectrum is taken as the molecular weight of the (a) compound. When two or more kinds of (a) compounds are contained, it is preferable that the relative molecular mass with the strongest relative intensity of the detection spectrum of the two or more kinds of (a) compounds as a whole is within the above range.

[0022] The content of the (a) compound in the ink is preferably 15 to 65% by mass. By setting the content of the (a) compound to 15% by mass or more, the curing reaction by electron beam proceeds easily, so that the unreacted components in the ink cured film can be further reduced, and the elution of unreacted components from the ink cured film can be further suppressed. On the other hand, by setting the content of the (a) compound to 65% by mass or less, the content of the (a) compound in the ink can be sufficiently suppressed, the unreacted components in the ink cured film can be further reduced, and the elution of unreacted components from the ink cured film can be further suppressed.

[0023] (a) The structure and molecular weight of compound (a) can be determined by the following method. First, the ink is dissolved in a suitable solvent, filtered to extract the soluble portion, centrifuged, and, if necessary, compound (a) is separated by high-performance liquid chromatography (HPLC). After dissolving the separated compound (a) in a developing solvent (tetrahydrofuran), the mass-to-charge ratio is measured using a mass spectrometer to calculate the mass of compound (a), and the molecular weight of compound (a) can be determined by subtracting the mass of the ions used in the mass spectrometry. Furthermore, the structure of compound (a) can be determined by dissolving the recovered compound (a) in a deuterated solvent and subjecting it to nuclear magnetic resonance (NMR). If the structure of compound (a) in the ink is known, the molecular weight may be determined from the known structure.

[0024] (b) Examples of pigments include organic pigments and inorganic pigments. Examples of organic pigments and inorganic pigments are those exemplified in International Publication No. 2018 / 163942, respectively. Two or more of these may be included.

[0025] The content of (b) pigment in the ink is preferably 15 to 50% by mass.

[0026] (b) The particle size of the pigment is preferably 2.0 μm or less. (b) By making the particle size of the pigment 2.0 μm or less, the pigment can be dispersed more uniformly in the ink. Here, "particle size" refers to the particle size corresponding to the cumulative frequency of 50% in the particle size distribution.

[0027] Examples of (c) polyolefins include polyethylene, polypropylene, polybutadiene, polyisoprene, and polyisobutylene. Two or more of these may be included. Among these, polyethylene and polypropylene are preferred from the viewpoint of the reactivity of radicals generated by electron beam irradiation and ease of handling. In this invention, even if a compound has an ethylenically unsaturated group in its side chain, if it has a polyolefin skeleton (aliphatic hydrocarbon), it will be classified as a (c) polyolefin. On the other hand, even if the main skeleton is an aliphatic hydrocarbon, if it has a group other than an aliphatic hydrocarbon in its side chain, it will be classified as a resin other than (c) polyolefin as described later.

[0028] In the present invention, the melting point of the polyolefin is preferably 60°C or higher. A melting point of 60°C or higher suppresses aggregation and separation in the ink. As a result, the (c) polyolefin is uniformly dispersed in the ink, and the radical reaction by electron beam irradiation proceeds more uniformly, thereby reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components. When two or more types of (c) polyolefin are contained, it is preferable that at least some of them have a melting point of 60°C or higher, and it is more preferable that 50% by mass or more of the (c) polyolefin has a melting point of 60°C or higher. On the other hand, from the viewpoint of handling, the melting point of the (c) polyolefin is preferably 180°C or lower.

[0029] Here, the melting point of (c) polyolefin can be measured by the following method. First, the ink is dissolved in a suitable solvent, filtered to recover the insoluble portion, then the insoluble portion is dispersed in the solvent and centrifuged to recover the (c) polyolefin. The melting point of the recovered (c) polyolefin can be measured by differential scanning calorimetry (DSC). More specifically, approximately 10 mg of the recovered (c) polyolefin is weighed, and using an aluminum pan and pan cover, the temperature difference between the standard sample and the polyolefin and the resulting heat difference are measured using a differential thermal analyzer (differential differential thermal balance TG8120; manufactured by Rigaku Corporation) when the temperature is increased from -20°C in a nitrogen atmosphere at a rate of 5°C / min. Based on the obtained results, the melting point is defined as the intersection of the tangent to the slope of the endothermic change at the endothermic peak and the baseline. If the structure of the (c) polyolefin in the ink is known, the melting point may be determined from the known structure using literature values, etc.

[0030] (c) The weight-average molecular weight of the polyolefin is preferably greater than or equal to the molecular weight of the compound (a). By making the weight-average molecular weight of the polyolefin (c) greater than or equal to the molecular weight of the compound (a), the molecular weight of the polyolefin (c) becomes sufficiently large, which further suppresses the elution of the polyolefin (c) itself from the ink-cured film. In addition, a sufficiently large molecular weight of the polyolefin (c) further reduces compatibility with the compound (a) and further reduces ink tack. The weight-average molecular weight of the polyolefin (c) is preferably 5,000 to 50,000 greater than the molecular weight of the compound (a). Note that if two or more types of polyolefins (c) are contained, the weight-average molecular weight of (c) refers to the total weight-average molecular weight of the two or more types.

[0031] Here, the weight-average molecular weight of (c) polyolefin can be measured by the following method. The (c) polyolefin is recovered from the ink by the method described above. The weight-average molecular weight of the recovered (c) polyolefin can be measured by subjecting it to gel permeation chromatography (GPC). More specifically, the (c) polyolefin is dissolved in a developing solvent (dichlorobenzene), and then subjected to a high-temperature GPC equipped with a column (e.g., "TSKgel®" GMHHR-H(20)HT, manufactured by Tosoh Corporation), and the weight-average molecular weight obtained using polystyrene as a standard sample is taken as the weight-average molecular weight of (c) polyolefin.

[0032] The content of (c) polyolefin in the ink is preferably 0.1 to 8.0% by mass. By setting the content of (c) polyolefin to 0.1% by mass or more, the amount of radical generation by electron beam irradiation is increased, the reaction rate of (a) compound is further improved, the unreacted components in the ink-cured film are further reduced, and the elution of unreacted components can be further suppressed. In addition, the compatibility with (a) compound is moderately suppressed, and the tack of the ink can be further reduced. On the other hand, by setting the content of (c) to 8.0% by mass or less, the (c) polyolefin is uniformly dispersed in the ink, and the radical reaction by electron beam irradiation proceeds more uniformly, so the unreacted components in the ink-cured film are further reduced, and the elution of unreacted components can be further suppressed. In addition, a significant decrease in compatibility with (a) compound can be suppressed, the fluidity of the ink can be maintained, and the ink transferability can be improved.

[0033] (c) The particle size of the polyolefin is preferably 0.5 to 30.0 μm. By setting the particle size of the polyolefin to 0.5 μm or more, aggregation of particles is suppressed, the polyolefin is uniformly dispersed in the ink, and the radical reaction by electron beam irradiation proceeds more uniformly, thereby further reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components. On the other hand, by setting the particle size of the polyolefin to 30.0 μm or less, the specific surface area increases, and the probability of reaction with the compound (a) when radicals are generated by electron beam irradiation increases, thereby further reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components.

[0034] The ink according to the present invention preferably further contains a resin other than (c) polyolefin. By containing a resin other than (c) polyolefin, (c) polyolefin is uniformly dispersed in the ink, and the radical reaction by electron beam irradiation proceeds more uniformly, thereby further reducing unreacted components in the ink cured film and further suppressing the elution of unreacted components. Examples of resins include acrylic resin, styrene acrylic resin, styrene maleic acid resin, rosin-modified maleic acid resin, rosin-modified acrylic resin, epoxy resin, polyester resin, polyurethane resin, butyral resin, polyamide resin, urea resin, phenolic resin, etc. Two or more of these may be contained. Among these, acrylic resin, styrene acrylic resin, styrene maleic acid resin, polyester resin, polyamide resin, and urea resin are preferred from the viewpoint of affinity with (a) compound.

[0035] Among these, resins having (d) hydrophilic functional groups are preferred. By having hydrophilic functional groups, the affinity with (a) compounds and (b) pigments is improved, so that (a) compounds and (b) pigments are uniformly dispersed in the ink, and the radical reaction of (a) compounds by electron beam irradiation proceeds more uniformly, thereby reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components. In addition, compatibility with (c) polyolefins is moderately reduced, and the tack of the ink can be further reduced. In addition, by having hydrophilic functional groups, compatibility with (c) polyolefins is moderately reduced, and the tack of the ink can be further reduced. Examples of hydrophilic functional groups include hydroxyl groups, carboxyl groups, amino groups, thiol groups, amide bonds, urethane bonds, and oxyethylene groups. Two or more of these may be present. Among these, from the viewpoint of affinity with (a) compounds and (b) pigments, hydroxyl groups, carboxyl groups, amino groups, and amide bonds are preferred, hydroxyl groups and carboxyl groups are more preferred, and carboxyl groups are even more preferred.

[0036] (d) When the resin having hydrophilic functional groups has carboxyl groups, the acid value is preferably 50 to 250 mg KOH / g. By setting the acid value to 50 mg KOH / g or higher, the affinity with (b) pigment contained in the ink is improved, so that each component is uniformly dispersed in the ink and the radical reaction by electron beam irradiation proceeds more uniformly, thereby further reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components. In addition, the compatibility with (c) polyolefin is moderately reduced, and the tack of the ink can be further reduced. On the other hand, by setting the acid value of the resin having hydrophilic functional groups to 250 mg KOH / g or lower, the compatibility with (a) compound is improved, so that each component is uniformly dispersed in the ink and the radical reaction by electron beam irradiation proceeds more uniformly, thereby further reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components.

[0037] (d) The acid value of a resin having hydrophilic functional groups can be determined in accordance with the neutralization titration method described in section 3.1 of the test method of JIS K 0070:1992. (d) When two or more resins having hydrophilic functional groups are included, (d) it is preferable that the acid value of the resins having hydrophilic functional groups as a whole is within the above range.

[0038] (d) The weight-average molecular weight of the resin having hydrophilic functional groups is preferably 5,000 to 100,000. By setting the weight-average molecular weight to 5,000 or more, the ink viscosity at low shear increases, (c) the polyolefin is uniformly dispersed in the ink, and the radical reaction by electron beam irradiation proceeds more uniformly, thereby reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components. On the other hand, by setting the weight-average molecular weight of the resin having hydrophilic functional groups to 100,000 or less, the compatibility with (a) the compound is improved, so each component is uniformly dispersed in the ink, and the radical reaction by electron beam irradiation proceeds more uniformly, thereby reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components.

[0039] (d) The weight-average molecular weight of the resin having hydrophilic functional groups can be measured by the following method. First, the ink is dissolved in a suitable solvent, filtered to recover the insoluble portion, then the insoluble portion is dispersed in the solvent and centrifuged to recover the resin having hydrophilic functional groups (d). The recovered resin having hydrophilic functional groups (d) can be subjected to gel permeation chromatography (GPC) to measure its weight-average molecular weight. More specifically, the resin having hydrophilic functional groups (d) is dissolved in a developing solvent (tetrahydrofrancichlorobenzene), and then subjected to a high-temperature GPC equipped with a column (for example, "TSKgel®" SuperHM-H, manufactured by Tosoh Corporation) and "TSKgel®" SuperH2000 (manufactured by Tosoh Corporation) linked in that order, and the weight-average molecular weight obtained using polystyrene as a standard sample is taken as the weight-average molecular weight of the resin having hydrophilic functional groups (d). Furthermore, if (d) a resin having hydrophilic functional groups is included in two or more types, the weight-average molecular weight of the resin having hydrophilic functional groups (d) refers to the total weight-average molecular weight of the two or more types.

[0040] The ink according to the present invention preferably contains a polymerization inhibitor. Examples of polymerization inhibitors are those exemplified in International Publication No. 2018 / 163942. Two or more of these may be included. When the ink according to the present invention contains a polymerization inhibitor, the content is preferably 0.001% by mass or more and 5% by mass or less.

[0041] The ink according to the present invention may optionally contain additives such as pigment dispersants, surfactants, defoamers, transferability enhancers, and leveling agents.

[0042] Next, a method for producing the ink according to the present invention will be described. The ink according to the present invention can be obtained by mixing and dispersing (a) a compound, (b) a pigment, (c) a polyolefin and other components as needed. Prior to mixing and dispersion, each raw material may be dissolved at 5 to 100°C, and during and / or after the mixing and dispersion process, degassing may be performed under vacuum or reduced pressure conditions. Examples of mixing and dispersion equipment include kneaders, three-roll mills, ball mills, planetary ball mills, bead mills, roll mills, attritors, sand mills, gate mixers, paint shakers, homogenizers, and agitators and kneaders such as self-rotating agitators.

[0043] Next, the method for manufacturing printed materials according to the present invention will be described. The method for manufacturing printed materials according to the present invention includes the steps of applying or transferring the ink according to the present invention onto a substrate and irradiating it with an electron beam. Since the ink according to the present invention hardens upon electron beam irradiation, a printed material having a hardened film of ink can be obtained by the electron beam irradiation step.

[0044] First, the process of applying or transferring the ink according to the present invention onto a substrate will be described.

[0045] Examples of substrates include art paper, coated paper, cast paper, synthetic paper, newsprint, plastic film, plastic film laminated paper, metal plates, metal-deposited paper, and metal-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, and polyvinyl acetal. Examples of plastic film laminated paper include those in which the aforementioned plastic film is laminated on paper. Examples of metal plates include those made of zinc, copper, and aluminum. Examples of metal-deposited paper and metal-deposited plastic film include those in which the aforementioned metal or its oxide is deposited on paper or plastic film. Among these, plastic film, plastic film laminated paper, metal-deposited plastic film, and metal-deposited paper do not absorb ink and therefore do not fix the ink by absorption, so they can be suitably used in the present invention, where the ink can be cured and fixed by electron beam irradiation.

[0046] For flexible packaging applications, the thickness of the base material is preferably between 10 μm and 100 μm.

[0047] Either sheet film or roll film can be used as the base material. When using thin film for flexible packaging applications, it is preferable to use roll film and apply or transfer the coating using a roll-to-roll method.

[0048] Methods for applying or transferring the ink according to the present invention onto a substrate include, for example, flexographic, offset, inkjet, and RI tester printing methods. Among these, offset printing is preferred from the viewpoint of image detail.

[0049] Next, we will explain the process of irradiating with an electron beam.

[0050] As for the electron beam, an energy beam of 100 to 500 keV is preferred.

[0051] Examples of printing presses used in the method for manufacturing printed materials of the present invention include single-cylinder printing presses that use separate impression cylinders for each color, and center-impression printing presses that use a single impression cylinder to print multiple colors.

[0052] In the method for manufacturing printed materials of the present invention, the thickness of the ink-cured film on the resulting printed material is preferably 0.1 to 50 μm. By setting the film thickness to 0.1 μm or more, the color density of the printed material can be appropriately increased. On the other hand, by setting the film thickness to 50 μm or less, the curing reaction by electron beam can proceed more easily, reducing unreacted components in the ink-cured film and further suppressing the elution of unreacted components from the ink-cured film. [Examples]

[0053] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

[0054] (Synthesis Example 1: (d) Resin 1 having hydrophilic functional groups) In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, 150 mol parts of propylene glycol monomethyl ether acetate, 31 mol parts of styrene, 31 mol parts of methyl methacrylate, 5 mol parts of 2-ethylhexyl acrylate, and 33 mol parts of acrylic acid were charged as solvents, and 1 mol part of 2,2'-azobis(2-methylbutyronitrile) was added as a polymerization initiator. Droplet polymerization was carried out at 140°C for 1.5 hours under reflux and stirring, and then the mixture was kept warm for another hour. After that, the temperature was raised to 160°C, and the solvent was removed by distillation while stirring continued at atmospheric pressure. Next, the pressure was reduced to 6.7 MPa or less at the same temperature, and the solvent was removed by distillation to obtain resin 1 having hydrophilic functional groups, with a weight-average molecular weight of 24,300 and an acid value of 190 mgKOH / g.

[0055] (Synthesis Example 2: (d) Resin 2 having hydrophilic functional groups) In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet, 150 mol parts of propylene glycol monomethyl ether acetate, 25 mol parts of styrene, 25 mol parts of methyl methacrylate, and 50 mol parts of methacrylic acid were charged as solvents, and 1 mol part of 2,2'-azobis(2-methylbutyronitrile) was added as a polymerization initiator. Droplet polymerization was carried out at 140°C for 1.5 hours under reflux and stirring, and then the mixture was kept warm for another hour. Subsequently, 0.55 equivalents of glycidyl methacrylate were added to the carboxyl groups, and then the mixture was reprecipitated in water to obtain resin 2 having hydrophilic functional groups with a weight-average molecular weight of 34,000 and an acid value of 105 mgKOH / g.

[0056] (Synthesis Example 3: Other Resins 1) In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet tube, 150 mol parts of propylene glycol monomethyl ether acetate, 46 mol parts of styrene, 46 mol parts of methyl methacrylate, and 8 mol parts of 2-ethylhexyl acrylate were charged as solvents, and 1 mol part of 2,2'-azobis(2-methylbutyronitrile) was added as a polymerization initiator. Droplet polymerization was carried out at 140°C for 1.5 hours under reflux and stirring, and then the mixture was kept warm for another hour. After that, the temperature was raised to 160°C, and the solvent was removed by distillation while stirring continued at atmospheric pressure. Next, the pressure was reduced to 6.7 MPa or less at the same temperature, and the solvent was removed by distillation to obtain another resin 1 with a weight-average molecular weight of 24,300 and an acid value of 0 mgKOH / g.

[0057] Other materials used in the examples and comparative examples are listed below. (a) Compound 1: Pentaerythritol ethylene oxide modified tetraacrylate “Miramer®” M4004 (manufactured by MIWON). Number of ethylenically unsaturated groups: 4, Molecular weight: 572 (a) Compound 2: Trimethylolpropaneethylene oxide-modified triacrylate “Miramer®” M3190 (manufactured by MIWON). Number of ethylenically unsaturated groups: 3, Molecular weight: 692 (a) Compound 3: Trimethylolpropaneethylene oxide-modified triacrylate “Miramer®” M3130 (manufactured by MIWON). Number of ethylenically unsaturated groups: 3, Molecular weight: 428 (a) Compound 4: Trimethylolpropanepropylene oxide-modified triacrylate “Miramer®” M360 (manufactured by MIWON). Number of ethylenically unsaturated groups: 3, Molecular weight: 470 (a) Compound 5: Neopentyl glycol diacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.). Number of ethylenically unsaturated groups: 2, Molecular weight: 240 (a) Compound 6: Polyethylene glycol diacrylate “Miramer®” M286 (manufactured by MIWON). Number of ethylenically unsaturated groups: 2, Molecular weight: 708 (a) Compound 7: Pentaerythritol triacrylate “Miramer®” M340 (manufactured by MIWON). Number of ethylenically unsaturated groups: 3, Molecular weight: 298 (a) Compound 8: Propylene oxide-modified glyceryl triacrylate “Miramer®” M320 (manufactured by MIWON). Number of ethylenically unsaturated groups: 3, Molecular weight: 428 (a) Compound 9: Diethylene glycol diacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.). Number of ethylenically unsaturated groups: 2, Molecular weight: 214 Pigment 1: Cyanine Blue 4920 (manufactured by Dainichi Seika Co., Ltd.), particle size 0.1 μm Polyolefin 1: "Sanwax (trademark registered)" 161-P (manufactured by Sanyo Chemical Industries, Ltd.). Polyethylene, weight-average molecular weight 27,000, melting point 103℃, particle size 12μm Polyolefin 2: "Viscol (trademark registered)" 660-P, classified using a 325-mesh sieve (manufactured by Sanyo Chemical Industries, Ltd.). Polypropylene, weight-average molecular weight 40,000, melting point 145°C, particle size 14 μm Polyolefin 3:Paraffin (mp. 42~44℃) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Saturated hydrocarbon compound, weight-average molecular weight 450, melting point 43℃ Other resins 2: KTL-4N (manufactured by Kitamura Co., Ltd.). Polytetrafluoroethylene, melting point 327℃, particle size 3μm, acid value 0mgKOH / g Other resins 3: "Hymer (registered trademark)" ST-95 (manufactured by Sanyo Chemical Industries, Ltd.). Polystyrene, weight-average molecular weight 4,000, no melting point, particle size 8 μm, acid value 0 mg KOH / g Other resins 4: KF96 350CS (manufactured by Shin-Etsu Chemical Co., Ltd.) Polydimethylsiloxane, weight-average molecular weight 10,000, melting point -50℃, acid value 0 mgKOH / g Photopolymerization initiator 1: "Irgacure®" 907 (manufactured by BASF).

[0058] Next, we will explain the raw materials and evaluation methods used in the examples and comparative examples.

[0059] (molecular weight) (a) Molecular weight of the compound: Compound (a) was dissolved in tetrahydrofuran to a concentration of 0.10% by mass. The mass spectrometer used was LCMS-2020 (Shimadzu Corporation), the column was Shim-packXR-C8 (Shimadzu Corporation), and the mobile phase was acetonitrile:water:formic acid = 90:10:0.1% by mass). The injection volume was 1.0 mL, the analysis time was 8 minutes, the flow rate was 1.0 mL / min, and the column temperature was 50°C.

[0060] (c) Weight-average molecular weight of polyolefin: (c) Polyolefin was dissolved in dichlorobenzene to a concentration of 1.0% by mass. A GPC (Glass Probe Co., Ltd.) HLC-8321 / HT (Tosoh Corporation) was used, and three "TSKgel®" GMHHR-H(20)HT columns (Tosoh Corporation) were linked together. RI detection was performed using the RI detector built into the GPC, with an input volume of 300 μL, an analysis time of 40 minutes, a flow rate of 1.0 mL / min, and a column temperature of 140°C. A calibration curve was created using polystyrene standards, and the weight-average molecular weight of the sample was calculated.

[0061] (d) Weight-average molecular weight of the resin having hydrophilic functional groups: The resin having hydrophilic functional groups (d) obtained by Synthesis Examples 1-2 was dissolved in tetrahydrofranglichlorobenzene to a concentration of 0.25% by mass. The GPC was HLC-8220 (manufactured by Tosoh Corporation), and the column was a combination of "TSKgel®" SuperHM-H (manufactured by Tosoh Corporation), TSKgel SuperHM-H (manufactured by Tosoh Corporation), and "TSKgel®" SuperH2000 (manufactured by Tosoh Corporation). RI detection was performed using the RI detector built into the GPC, with an input volume of 10 μL, an analysis time of 30 minutes, a flow rate of 0.4 mL / min, and a column temperature of 40°C. A calibration curve was created using polystyrene standard substances, and the weight-average molecular weight of the measured samples was calculated.

[0062] Weight-average molecular weight of other resins: (d) The weight-average molecular weight was measured in the same manner as for resins having hydrophilic functional groups.

[0063] (Acid value) (d) The acid value of resins having hydrophilic functional groups and other resins was measured by neutralization titration in accordance with the test method in Section 3.1 of JIS K 0070:1992. 1.0 g each of resins 1 and 2 having hydrophilic functional groups prepared in Synthesis Examples 1 and 2, other resin 1 prepared in Synthesis Example 3, and the aforementioned other resins 2 to 4 were weighed into Erlenmeyer flasks. 100 ml of ethanol and a few drops of phenolphthalein solution as an indicator were added, and the mixture was stirred thoroughly on a water bath until the sample was completely dissolved. However, resins that did not completely dissolve in ethanol were not subjected to the following procedure, and their acid value was set to 0 mg KOH / g. Next, the mixture was titrated with a 0.1 mol / l potassium hydroxide ethanol solution, and the endpoint was reached when the indicator turned red for 30 seconds. The acid value was then calculated using the following formula. A = [B × f × 5.611 / S] A: Acid value (mgKOH / g) B: Volume (ml) of 0.1 mol / l potassium hydroxide ethanol solution used for titration. f: Factor (concentration correction factor) of a 0.1 mol / l potassium hydroxide ethanol solution S: Mass of the sample (g).

[0064] (Particle size) (c) The particle size of polyolefin and the aforementioned other resins 2-3 was determined by placing (c) polyolefin and the aforementioned other resins 2-3 into the sample chamber of a particle size distribution analyzer (MT3300; manufactured by Nikkiso Co., Ltd.) filled with ethanol, performing ultrasonic treatment for 120 seconds, and then measuring the particle size distribution. The value that represents 50% of the cumulative distribution was defined as the particle size.

[0065] (Amount of unreacted components eluted) A waterless lithographic printing plate (TAC-VG5, manufactured by Toray Industries, Inc.) with a solid image strip measuring 400 mm (vertical direction) x 900 mm (horizontal direction) at the center of a printing plate measuring 854 mm (vertical direction) x 1,070 mm (horizontal direction) was mounted on a center-impression type offset rotary printing press (CI-8, manufactured by COMEXI). Using the inks obtained in each example and comparative example, 1,000 m of printing was performed on polyester film PTM12 (manufactured by Unitika Ltd., thickness 12 μm) at a printing speed of 200 m / min and an ink supply rate of 50%. The thickness of the solid ink cured film was measured using a contact-type film thickness gauge and was found to be 3 μm. At the point of 1,000 m printing, the solid ink cured film portion with a thickness of 3 μm was cut into 12 cm squares, and the evaluation area was 100 cm². 2 The printed surface was set in a cylindrical single-sided elutor, and 100 ml of 95% by mass ethanol was injected. The mixture was then stored in a 60°C constant temperature bath for 5 hours. After that, the ethanol was concentrated 10 times, and the amount of ink components (unreacted components) eluted into the ethanol was measured by liquid chromatography-mass spectrometry (LC-MS).

[0066] (Tack value) 1.3 ml of ink obtained from each example and comparative example was weighed onto the roller of an INKOGRAPH TYPE-V Incomometer (manufactured by Tester Sangyo Co., Ltd.), and the tack value was measured after 1 minute under conditions of roller temperature 30°C and rotation speed 400 rpm. The tack value is an indicator of ink adhesion, and a smaller value indicates suppressed tack, which is preferable.

[0067] (Ink transfer) For the printed material obtained at the 1,000m printing stage in the measurement of the amount of unreacted components eluted, the density of solid areas was measured using a reflectance densitometer (GretagMacbeth, SpectroEye, Status E), with high-quality paper used as the paper white (reflectance density 0 as the baseline), and the ink transferability was evaluated. A higher density indicates better ink transferability.

[0068] (Example 1) 19 parts by mass of (d) hydrophilic functional group resin 1, 27 parts by mass of (a) compound 1, and 27 parts by mass of (a) compound 2, prepared in Synthesis Example 1, were weighed into a container and heated and dissolved at 95°C for 390 minutes while stirring at 500 rpm using a disperser blade to obtain a varnish. To the obtained varnish, 26 parts by weight of (b) pigment 1 and 1 part by weight of (c) polyolefin 1 were weighed and added, and the mixture was kneaded three times in gap 1 using a three-roll mill "EXAKT®" M-80S (manufactured by EXAKT) to obtain an ink.

[0069] (Examples 2-9, Comparative Examples 1-7) The ink was obtained in the same manner as in Example 1, except that the types and amounts of raw materials were changed as shown in Tables 1 and 2.

[0070] The evaluation results for each example and comparative example are shown in Tables 1 and 2.

[0071] [Table 1]

[0072] [Table 2]

Claims

1. An electron beam curable printing ink comprising (a) a compound having an ethylenically unsaturated group, (b) a pigment, and (c) a polyolefin, and substantially free of a photopolymerization initiator.

2. The electron beam curable printing ink according to claim 1, wherein the melting point of the polyolefin in (c) is 60°C or higher.

3. The electron beam curable printing ink according to claim 1 or 2, wherein the weight-average molecular weight of the polyolefin (c) is equal to or greater than the molecular weight of the compound having an ethylenically unsaturated group (a).

4. The electron beam curable printing ink according to claim 1 or 2, wherein the (c) polyolefin is polyethylene and / or polypropylene.

5. Furthermore, (d) the electron beam curable printing ink according to claim 1 or 2, further comprising a resin having hydrophilic functional groups.

6. The electron beam curable printing ink according to claim 1 or 2, wherein at least a portion of the compound having an ethylenically unsaturated group has a hydrophilic functional group.

7. The electron beam curable printing ink according to claim 1 or 2, wherein the compound having an ethylenically unsaturated group (a) has 3 to 6 ethylenically unsaturated groups.

8. A method for manufacturing a printed material, comprising the steps of applying or transferring an electron beam-curable printing ink according to claim 1 or 2 onto a substrate, and irradiating the applied or transferred electron beam-curable ink with an electron beam.

9. The method for manufacturing a printed article according to claim 8, wherein a plastic film, a plastic film laminated paper, a metal-deposited plastic film, and / or metal-deposited paper are used as the substrate.

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