Method for manufacturing printed matter, laminate using the same, and method for manufacturing packaging bag

Abstract

This method for manufacturing printed matter comprises, in this order, a transfer step for transferring ink onto a polyolefin film having a tensile elasticity in the MD direction of 200 MPa to 1,000 MPa by a central impression printing method; and a curing step for irradiating the ink with electron beam to cure the ink.　Provided is a method for manufacturing printed matter, the method making it possible to obtain printed matter that, even when a flexible film like a polyolefin film is used, exhibits excellent register accuracy and that can suppress packaging bag tearing.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a printed matter, and a method for producing a laminate and a packaging bag using the same. [Background technology]

[0002] Various printing methods, such as gravure printing, flexographic printing, offset printing, inkjet printing, silkscreen printing, and roll coater printing, are widely used to apply designs to packaging materials for food and hygiene products. Gravure printing and flexographic printing have been used particularly for flexible packaging materials that use plastic film. However, gravure printing and flexographic printing generally use inks containing solvents or water, and the drying process generates increased emissions of VOCs and carbon dioxide, raising concerns about the environmental impact.

[0003] Therefore, in recent years, the use of active energy ray-curable printing inks, which can instantly cure inks by irradiating them with active energy rays such as electron beams or ultraviolet rays, has been promoted. For the purpose of improving adhesion to plastic films in lithographic printing, which has conventionally been commonly used as a printing method for paper, there have been proposed an active energy ray-curable offset printing ink composition characterized by containing a compound having an ethylenically unsaturated bond and a photopolymerization initiator, and further containing 8% by mass to 12% by mass of a sensitizing compound having a specific structure, a method for producing a printed matter comprising a printing step of offset printing a resin film using such an active energy ray-curable offset printing ink composition, and a curing step of irradiating the resin film after the printing step with active energy rays (see, for example, Patent Document 1), and a method for producing a printed matter comprising a printing step of offset printing a resin film using such an active energy ray-curable offset printing ink composition and a curing step of irradiating the resin film after the printing step with active energy rays (see, for example, Patent Document 1). and (2) the indentation modulus of the cured coating film is in the range of 100 to 1,000 MPa. Also proposed are an active energy ray-curable composition, characterized in that (1) the (meth)acryloyl group concentration in the composition is in the range of 0.5 to less than 2.2 mmol / g, and (2) the indentation modulus of the cured coating film is in the range of 100 to less than 1,000 MPa; a method for producing a cured ink product, characterized in that such an ink is used for offset printing and the printed ink is cured using active energy rays (see, for example, Patent Document 2); and a method for producing a printed product by printing ink onto a film, which uses a film having a nitrogen element concentration of 0.5 to 10.0 atomic % on the film surface, and includes a step of irradiating the film with active energy rays after printing (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-168730 [Patent Document 2] Japanese Patent Publication No. 2020-33465 [Patent Document 3] International Publication No. 2018 / 163941 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the expansion of flexible packaging materials, there has been a demand for packaging materials using more flexible plastic films. In particular, when printing on flexible films such as polyolefin films using the conventional roll-to-roll method, there is a limit to the tension that can be applied to the film, which causes the ink cohesive force to cause film misalignment, resulting in insufficient register accuracy. On the other hand, when a harder film is selected to improve register accuracy, there is an issue that when used for packaging bags, the packaging bags are more likely to tear.

[0006] Therefore, the object of the present invention is to provide a method for producing printed matter that can produce printed matter with excellent registration accuracy and that can prevent packaging bags from breaking, even when using a flexible film such as a polyolefin film. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following configuration: (1) A method for producing a printed matter, comprising, in order, a transfer step of transferring ink onto a polyolefin film having a tensile modulus in the MD direction of 200 MPa or more and 1,000 MPa or less by a center impression printing method, and a curing step of irradiating the ink with an electron beam to cure the ink. (2) The method for producing a printed matter according to (1), wherein the thickness of the polyolefin film is 20 μm or more and 60 μm or less. (3) A method for producing a printed matter described in (1) or (2), in which the ratio (C2 / C1) of the crystallinity C2 of the polyolefin film after irradiating the polyolefin film with an electron beam under conditions of an acceleration voltage of 110 kV and an irradiation dose of 40 kGy to the crystallinity C1 of the polyolefin film is 0.8 or more and 1.2 or less. (4) A method for producing a printed matter according to any one of (1) to (3), wherein the polyolefin film has a crystallinity C2 of 20% or more and 50% or less after being irradiated with an electron beam at an acceleration voltage of 110 kV and an exposure dose of 40 kGy. (5) The method for producing a printed matter according to any one of (1) to (4), wherein the polyolefin film contains 10% by mass or more of a polyethylene resin. (6) The method for producing a printed matter according to (5), wherein the polyolefin film further contains 90% by mass or less of a polypropylene-based resin. (7) The method for producing a printed matter according to any one of (1) to (6), wherein the content of the crystal nucleating agent in the polyolefin film is 0.01% by mass or less. (8) The method for producing a printed matter according to any one of (1) to (7), wherein in the curing step, electron beam irradiation is performed under conditions of an acceleration voltage of 70 kV or more and 90 kV or less and an exposure dose of 20 kGy or more and 60 kGy or less. (9) The method for producing a printed matter according to any one of (1) to (8), wherein the ink contains an anionic surfactant. (10) The method for producing a printed matter according to any one of (1) to (9), wherein the ink contains urethane (meth)acrylate. (11) The method for producing a printed matter according to any one of (1) to (10), wherein in the transferring step, the ink is transferred by lithographic printing. (12) A method for producing a laminate, comprising the steps of producing a printed matter by the method according to any one of (1) to (11) and laminating a non-oriented polyolefin film onto the printed matter. (13) The method for producing a laminate according to (12), wherein the unstretched polyolefin film has a tensile modulus of elasticity of 50 MPa or more and 400 MPa or less. (14) The method for producing a laminate according to (12) or (13), wherein the thickness of the unstretched polyolefin film is 30 μm or more and 100 μm or less. (15) A method for producing a packaging bag, comprising the steps of producing a laminate by the method for producing a laminate according to any one of (12) to (14) above, and producing a bag from the laminate, in this order. [Effects of the Invention]

[0008] According to the method for producing a printed matter of the present invention, even when a flexible film such as a polyolefin film is used, a printed matter can be obtained that has excellent register accuracy and can prevent packaging bags from breaking. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the method for producing printed matter according to the present invention will be described in detail below. However, the present invention should not be construed as being limited to the embodiments shown below as examples, and various modifications can be made depending on the purpose and application without departing from the gist of the present invention.

[0010] A method for producing a printed matter according to an embodiment of the present invention includes, in order, a transfer step (hereinafter sometimes abbreviated as "transfer step") in which ink is transferred onto a polyolefin film having a tensile modulus in the MD direction of 200 MPa to 1,000 MPa using a center impression printing method, and a curing step (hereinafter sometimes abbreviated as "curing step") in which the ink is cured by irradiating it with an electron beam. The ink transferred to the polyolefin film in the transfer step can be cured in a short time in the curing step, thereby reducing the environmental impact. A surface treatment step, such as a corona discharge treatment, may be further performed on the surface of the polyolefin film prior to the transfer step.

[0011] First, the transfer step is described. In the transfer step, ink is transferred onto a polyolefin film having a tensile modulus in the MD direction of 200 MPa to 1,000 MPa by a center impression printing method.

[0012] The center impression printing method is a printing method that uses a common impression cylinder for each printing unit. Center impression printing is basically a wet-on-wet printing method in which the ink is cured after all colors are printed. The ink film that has been transferred to the substrate first is pressed by the blanket on the rear cylinder while it is still uncured. This reduces the unevenness of the ink film surface and suppresses diffuse reflection of light, making it possible to achieve high density with a small amount of ink and providing excellent resistance to scumming. In addition, the short distance between each color unit during printing improves registration accuracy.

[0013] In the present invention, a flexible polyolefin film is used as the printing substrate. Examples of polyolefin films include unstretched polypropylene film, biaxially stretched polypropylene film, unstretched polyethylene film, and biaxially stretched polyethylene film. Among these, unstretched polyolefin film is preferred, and unstretched polypropylene film is more preferred, as it is easy to adjust the tensile modulus to the range described below.

[0014] The present invention is characterized by using a polyolefin film having a tensile modulus in the MD (machine direction) of 200 MPa or more and 1,000 MPa or less. In the transfer process, high tension is generally applied to the substrate in the MD to prevent sagging of the substrate and misalignment during ink transfer. Therefore, the present invention focuses on the tensile modulus of the polyolefin film in the MD relative to the MD tension. If the tensile modulus in the MD is less than 200 MPa, the polyolefin film is likely to be misaligned, resulting in reduced registration accuracy. The tensile modulus in the MD is preferably 400 MPa or more, more preferably 600 MPa or more. On the other hand, if the tensile modulus in the MD exceeds 1,000 MPa, the packaging bag is likely to tear when processed.

[0015] The tensile modulus of elasticity in the MD direction of a polyolefin film can be determined in accordance with JIS K7161-1:2014 and JIS K7127:1999. More specifically, a tensile test is performed in the MD direction on a 15 mm wide strip-shaped test piece using a Tensilon universal testing machine with a chuck distance of 50 mm and a test speed of 300 mm / min, and the tensile modulus is determined from a stress-strain diagram. Measurements are performed on five test pieces, and the average value is used as the tensile modulus of elasticity in the MD direction of the polyolefin film.

[0016] The tensile modulus of a polyolefin film in the MD direction tends to increase, for example, as the MD stretch ratio increases, and also tends to increase with heat treatment. Therefore, the tensile modulus can be adjusted to a desired range by performing stretching or heat treatment as necessary and adjusting the conditions appropriately. In addition, polyolefin films with various tensile moduli are commercially available from various companies, and one with the desired tensile modulus can be selected from these. In particular, unstretched polyolefin films are preferred, and unstretched polypropylene films are more preferred.

[0017] The thickness of the polyolefin film is preferably 20 μm or more, which has high strength and can further improve register accuracy, while the thickness of the polyolefin film is preferably 60 μm or less, which can produce more flexible printed matter.

[0018] Polyolefin is a crystalline resin, and polyolefin films have a certain degree of crystallinity. In the present invention, it is preferable to select a polyolefin film whose crystallinity changes little due to electron beam irradiation. That is, when the crystallinity of the polyolefin film used in the transfer process is C1 [%] and the crystallinity after the polyolefin film is irradiated with an electron beam under conditions of an acceleration voltage of 110 kV and an irradiation dose of 40 kGy is C2 [%], the ratio of the crystallinity C2 after electron beam irradiation to the crystallinity C1 before electron beam irradiation (C2 / C1) is preferably 0.8 to 1.2. In addition to applying a certain tension in the MD direction to the polyolefin film in the transfer process, the polyolefin film is irradiated with an electron beam to cure the ink in the curing process described below. It is expected that the crystalline state of the polyolefin will change due to electron beam irradiation. The closer the crystallinity ratio (C2 / C1) before and after electron beam irradiation is to 1, the more effectively the strength reduction and embrittlement caused by changes in crystallinity can be suppressed. In the present invention, an acceleration voltage of 110 kV and an irradiation dose of 40 kGy are selected as conditions under which changes in crystallinity that may occur due to electron beam irradiation are fully manifested. If C2 / C1 is 0.8 or more, a decrease in strength due to a decrease in crystallinity can be suppressed, and registration accuracy can be further improved. On the other hand, if C2 / C1 is 1.2 or less, embrittlement due to an increase in crystallinity can be suppressed, and breakage of the packaging bag when processed can be further suppressed.

[0019] Furthermore, C2 of the polyolefin film is preferably 20% or more and 50% or less. If C2 is 20% or more, a decrease in strength due to a decrease in crystallinity in the curing process described below can be suppressed, and registration accuracy can be further improved. On the other hand, if C2 is 50% or less, embrittlement due to an increase in crystallinity in the curing process described below can be suppressed, and breakage of the packaging bag when processed can be further suppressed.

[0020] The crystallinity values ​​C1 and C2 of polyolefin films can be determined by X-ray diffraction. First, a 25 mm x 15 mm rectangular specimen (each side oriented in any direction) is taken from the polyolefin film for C1, and from the polyolefin film after electron beam irradiation at an accelerating voltage of 110 kV and an exposure dose of 40 kGy for C2. The obtained specimen is attached to an aluminum sample holder of an X-ray diffraction apparatus so that the film thickness direction corresponds to the normal direction to the sample holder surface. The diffraction peaks are measured by the reflection method using 2θ-θ continuous scanning while changing the X-ray incidence angle. The measurement conditions are as follows, and measurements are taken at five randomly selected locations on the specimen. Measurement range (2θ): 5 to 60° Measurement step (2θ): 0.05° Accumulation time: 2 seconds.

[0021] Next, the obtained diffraction peaks are separated into peaks derived from crystalline components and peaks derived from amorphous components using analytical software, and the crystallinity is calculated from the areas of each peak, and the average value is calculated. The crystallinity [%] can be calculated by multiplying the peak area of ​​the crystalline component by 100 / (peak area of ​​the crystalline component + peak area of ​​the amorphous component). The analytical software is not particularly limited as long as it can separate the target peaks, but for example, JADE 5.0 or JADE 2010 (MDI) can be used.

[0022] The polyolefin film of the present invention preferably contains 10% by mass or more of a polyethylene-based resin. Compared to polypropylene, polyethylene is less susceptible to an increase in crystallinity due to electron beam irradiation, so by containing 10% by mass or more of a polyethylene-based resin, it is possible to reduce the change in crystallinity due to electron beam irradiation. On the other hand, the content of the polyethylene-based resin is preferably 80% by mass or less, which makes it possible to easily adjust the tensile modulus to the aforementioned preferred range. The content of the polyethylene-based resin is more preferably 50% by mass or less.

[0023] The polyolefin film of the present invention preferably further contains 90% by mass or less of a polypropylene-based resin. By containing 90% by mass or less of a polypropylene-based resin, it is possible to reduce the change in crystallinity due to electron beam irradiation. The tensile modulus can be easily adjusted to the above-mentioned preferred range. On the other hand, the content of the polypropylene-based resin is preferably 20% by mass or more, which allows the tensile modulus to be easily adjusted to the above-mentioned preferred range. The content of the polyethylene-based resin is more preferably 50% by mass or more. Note that when the content of the polyethylene-based resin is 50% by mass or more and the content of the polypropylene-based resin is 50% by mass or less, it is preferable to uniaxially or biaxially stretch the polyolefin film to adjust the tensile modulus of the film to the above-mentioned range.

[0024] Furthermore, the content of the nucleating agent in the polyolefin film of the present invention is preferably 0.01% by mass or less. Nucleating agents are generally used to increase the crystallinity of films, but in the present invention, by setting the content to 0.01% by mass or less, it is possible to reduce the change in crystallinity due to electron beam irradiation. In particular, when the content of polypropylene-based resin is high, it is preferable to not contain a nucleating agent in order to reduce the change in crystallinity due to electron beam irradiation.

[0025] Examples of nucleating agents include inorganic particles such as silica and talc, nucleating agents containing metal salts of rosins as the main component, sorbitol-based nucleating agents, and nucleating agents consisting of metal salts of aromatic organic phosphates.

[0026] In response to recent environmental concerns and carbon neutrality, the polyolefin film of the present invention preferably contains recycled raw materials. The recycled raw materials may be those recycled by mechanical recycling or chemical recycling, and are not particularly limited. Furthermore, the polyolefin film may contain biomass-derived (plant-derived) raw materials, and it is also preferable to use them in combination with conventional petrochemical-derived raw materials.

[0027] The surface of the polyolefin film is preferably subjected to a surface treatment such as corona discharge treatment, which can improve the wetting tension of the film surface. A pre-surface-treated polyolefin film may be used, or a surface treatment step may be performed before the transfer step, in which the surface of the polyolefin film is subjected to a surface treatment such as corona discharge treatment. Examples of atmospheric gases during the corona discharge treatment include air, carbon dioxide, and nitrogen, and two or more of these may be used.

[0028] Examples of methods for transferring ink onto a polyolefin film include printing methods such as lithographic printing, letterpress printing, intaglio printing, etc. Among these, lithographic printing is preferably used because it is suitable for high-speed printing.

[0029] Lithographic printing methods include a method using a waterless lithographic printing plate and a method using a water-based lithographic printing plate. In the present invention, the method using a waterless lithographic printing plate is preferred. In the method using a waterless lithographic printing plate, no dampening water is used during printing, so radicals can be stably generated by electron beam irradiation in the curing step described below. As a result, the ink can be sufficiently cured, and the adhesion between the ink and the polyolefin film can be improved.

[0030] The ink used in the present invention is preferably an electron beam curable printing ink that is cured by electron beam irradiation in the curing step described below, and preferably contains an acrylic resin, a pigment, and a polyfunctional (meth)acrylate. Here, "(meth)acrylate" is a general term for acrylate and methacrylate. Furthermore, it is preferable that the ink contains a urethane (meth)acrylate and a monofunctional (meth)acrylate.

[0031] The acrylic resin preferably has an ethylenically unsaturated group and a carboxyl group. The weight-average molecular weight of the acrylic resin is preferably 5,000 or more, more preferably 15,000 or more, from the viewpoints of improving pigment dispersibility, reducing ink cohesion, and further improving register accuracy. On the other hand, the weight-average molecular weight of the acrylic resin is preferably 40,000 or less, from the viewpoints of suppressing entanglement of molecular chains, reducing ink cohesion, and further improving register accuracy.

[0032] The content of the acrylic resin in the ink is preferably 6% by mass or more and 15% by mass or less.

[0033] Examples of pigments include inorganic pigments and organic pigments. Examples of inorganic pigments include titanium oxide and carbon black, and examples of organic pigments include phthalocyanine pigments, soluble azo pigments, insoluble azo pigments, and lake pigments. Two or more of these pigments may be contained.

[0034] The content of the pigment in the ink is preferably 10% by mass or more and 50% by mass or less.

[0035] The polyfunctional (meth)acrylate refers to one having a molecular weight of less than 5,000 and a plurality of (meth)acryloyl groups. The molecular weight of the polyfunctional (meth)acrylate is preferably 1,000 or less. Pentaerythritol tri(meth)acrylate, diglycerin tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, tricyclodecane dimethanol diacrylate, trimethylolpropane EO-modified triacrylate, and dipentaerythritol hexaacrylate are preferred because they provide excellent pigment dispersibility and improved background smear resistance.

[0036] Urethane (meth)acrylate refers to a (meth)acrylate containing a urethane bond, preferably an oligomer with a weight-average molecular weight of 2,000 or more but less than 5,000. In the present invention, even if a (meth)acrylate contains one or more (meth)acryloyl groups, if it contains a urethane bond, it is classified as a urethane (meth)acrylate. The hydrogen bonds between the urethane bonds contained in the urethane (meth)acrylate form hard segments, which impart toughness to the cured ink film and also bond strongly to the surface of the plastic film, thereby improving adhesion to the polyolefin film. Furthermore, the polyol residues contained in the urethane (meth)acrylate form soft segments, which impart flexibility to the cured ink film, thereby further reducing bag breakage when processed into packaging bags.

[0037] The content of urethane (meth)acrylate in the ink is preferably 5% by mass or more, which can further prevent bags from breaking when processed into packaging bags, while the content of urethane (meth)acrylate in the ink is preferably 15% by mass or less, which can further improve register accuracy.

[0038] The monofunctional (meth)acrylate acts as an auxiliary agent to reduce the cohesive force of the ink, and can further improve the registration accuracy.

[0039] The monofunctional (meth)acrylate refers to a compound having a molecular weight of less than 5,000 and having one (meth)acryloyl group. For example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, heneicosyl (meth)acrylate, docosyl (meth)acrylate, isopropyl (meth)acrylate, Examples of such acrylates include butyl (meth)acrylate, isobutyl (meth)acrylate, isopentyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isoundecyl (meth)acrylate, isododecyl (meth)acrylate, isotridecyl (meth)acrylate, isotetradecyl (meth)acrylate, isopentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, isoheptadecyl (meth)acrylate, isooctadecyl (meth)acrylate, isononadecyl (meth)acrylate, isoeicosyl (meth)acrylate, isoheneicosyl (meth)acrylate, and isodocosyl (meth)acrylate. Two or more of these may be contained. Among these, alkyl(meth)acrylates having an aliphatic skeleton with 13 to 22 carbon atoms are preferred.

[0040] The content of monofunctional (meth)acrylate in the ink is preferably 1 part by mass or more per 100 parts by mass of polyfunctional (meth)acrylate, which moderately promotes the progression of phase separation and makes it easier to stably form a microphase-separated structure, thereby further improving register accuracy.On the other hand, the content of monofunctional (meth)acrylate is preferably 7 parts by mass or less, which moderately suppresses the progression of phase separation and makes it easier to stably maintain a microphase-separated structure, thereby further improving register accuracy.

[0041] The ink used in the present invention preferably further contains a surfactant, which improves the dispersibility of the pigment, further reduces the ink cohesive force, and further improves the register accuracy.

[0042] When the ink used in the present invention is a white ink, the surfactant is preferably an anionic surfactant, which improves the dispersibility of white pigments such as titanium oxide, zinc oxide, and alumina white, thereby further reducing the ink cohesive force and further improving register accuracy.

[0043] Examples of anionic surfactants include "Disperbyk" (registered trademark) 111 (trade name) manufactured by BYK Japan K.K., "Aqualon" (registered trademark) AR-10 (trade name) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., sodium dodecylbenzenesulfonate, sodium laurate, sodium myristate, sodium palmitate, sodium stearate, sodium oleate, potassium laurate, potassium myristate, potassium palmitate, potassium stearate, potassium oleate, sodium N-stearoyl-L-glutamate, sodium N-stearoyl-N-methyl taurate, and sodium N-lauroyl-L-glutamate. Two or more of these may be contained.

[0044] The content of the surfactant in the ink is preferably 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the pigment.

[0045] The ink used in the present invention may contain other ingredients.

[0046] In the transfer step, the thickness of the ink transferred onto the polyolefin film is preferably 0.1 to 50 μm. If the ink thickness is 0.1 mm or more, the ink can be easily transferred uniformly to the film surface, improving print quality. On the other hand, if the ink thickness is 50 μm or less, the adhesion between the ink and the film is not reduced.

[0047] When transferring white ink onto a substrate, it is preferable to transfer the white ink two or more times, which improves the hiding power, reduces the amount of ink transferred per transfer, and further improves register accuracy.

[0048] Next, the curing step will be described.

[0049] When an electron beam is irradiated onto ink transferred onto a polyolefin film, radicals are generated in the ink, causing the ink to harden and obtain a printed product. The electron beam that penetrates the ink also acts on the surface layer of the polyolefin film, generating radicals from the surface layer of the polyolefin film. The radicals present on the surface layer of the polyolefin film facilitate the crosslinking reaction between the ink and the surface layer of the film, which is thought to further improve the adhesion between the ink and the polyolefin film in the printed product.

[0050] In the curing step, it is preferable to irradiate the film with electron beams so that the crystallinity of the cured polyolefin film is 20% or more and 50% or less. If the crystallinity of the cured polyolefin film is 20% or more, a decrease in strength due to a decrease in crystallinity can be suppressed, and registration accuracy can be further improved. On the other hand, if the crystallinity of the cured polyolefin film is 50% or less, embrittlement due to an increase in crystallinity can be suppressed, and breakage of the packaging bag when processed can be further suppressed.

[0051] The crystallinity of the cured polyolefin film tends to increase as the electron beam irradiation conditions such as acceleration voltage and dose are increased. For example, by selecting a polyolefin film having a C1 within a desired range and appropriately adjusting the electron beam irradiation conditions such as acceleration voltage and dose, the crystallinity of the cured polyolefin film can be adjusted to a desired range.

[0052] In the curing step, the acceleration voltage of the electron beam irradiation is preferably 70 kV or more and 90 kV or less, and the irradiation dose is preferably 20 kGy or more and 60 kGy or less. By setting the acceleration voltage to 70 kV or more, the ink is sufficiently cured, and the adhesion between the ink and the polyolefin film is further improved. In addition, bag breakage when processed into packaging bags can be further suppressed. On the other hand, by setting the acceleration voltage to 90 kV or less, the change in crystallinity of the polyolefin film during the curing step can be easily adjusted to the above-mentioned preferred range, further improving registration accuracy and further suppressing bag breakage when processed into packaging bags. In addition, by setting the irradiation dose to 20 kGy or more, the ink is sufficiently cured, and the adhesion between the ink and the polyolefin film is further improved. The irradiation dose is more preferably 30 kGy or more. In addition, bag breakage when processed into packaging bags can be further suppressed. On the other hand, by setting the irradiation dose to 60 kGy or less, the change in crystallinity of the polyolefin film during the curing process can be easily adjusted to fall within the preferred range described above, thereby further improving the registration accuracy and further suppressing breakage of the packaging bag when processed into the bag.

[0053] The printed matter obtained by the method of the present invention is preferably used for laminates having a sealant layer laminated thereon, and various packaging bags.

[0054] Next, a method for producing the laminate of the present invention will be described.

[0055] The method for producing a laminate of the present invention includes a step of laminating a non-stretched polyolefin film on a printed matter obtained by the above-mentioned method. It is preferable to laminate the non-stretched polyolefin film on the ink side of the printed matter. The laminate is a laminate of the printed matter obtained by the above-mentioned method and a non-stretched polyolefin film, with the non-stretched polyolefin film serving as a sealant layer. Examples of non-stretched polyolefin films include non-stretched low-density polyethylene film, non-stretched medium-density polyethylene film, non-stretched high-density polyethylene film, non-stretched linear low-density polyethylene film, and non-stretched polypropylene film.

[0056] The tensile modulus of the laminated unstretched polyolefin film is preferably 50 MPa or more and 400 MPa or less. If the tensile modulus is 50 MPa or more, breakage of the bag when processed into a packaging bag can be further suppressed. On the other hand, if the tensile modulus is 400 MPa or less, the bag can be easily produced. The tensile modulus of the unstretched polyolefin film can be measured in the same manner as the tensile modulus of the polyolefin film described above.

[0057] The thickness of the laminated unstretched polyolefin film is preferably 30 μm or more and 100 μm or less. If the thickness is 30 μm or more, breakage of the bag when processed into a packaging bag can be further suppressed. Also, moisture resistance is further improved. On the other hand, if the thickness is 100 μm or less, the bag can be easily produced.

[0058] Next, a method for producing the packaging bag of the present invention will be described.

[0059] The method for producing a packaging bag of the present invention preferably includes the steps of producing a laminate by the above-described method and forming the laminate into a bag. Examples of the step of forming a bag from the laminate include a method of heat-sealing the peripheral portions of the unstretched polyolefin films of two laminates. Specifically, the two laminates are stacked with the unstretched polyolefin films facing each other, and then the peripheral portions on three sides are heat-sealed. After filling the contents, the remaining opening is heat-sealed to produce a packaging bag. [Example]

[0060] The present invention will be specifically described below with reference to examples, but the present invention should not be construed as being limited to these examples. It should be noted that Examples 1, 5-8, and 12-21 are currently reference examples, and Examples 2-4 and 9-11 are examples of the present invention. First, the raw materials used in each example and comparative example will be shown.

[0061] <Ink raw materials> Pigment 1: "Tipake" (registered trademark) CR58-2 (manufactured by Ishihara Sangyo Kaisha, Ltd.) Pigment 2: Carmine 6B 1483LT (manufactured by Dainichi Seika Color & Chemicals Co., Ltd.) Acrylic resin: An acrylic resin with ethylenically unsaturated groups and hydrophilic groups was obtained by addition reaction of 0.55 equivalents of glycidyl methacrylate to the carboxyl groups of a copolymer consisting of 25% by weight of methyl methacrylate, 25% by weight of styrene, and 50% by weight of methacrylic acid. The resulting resin had a weight-average molecular weight of 34,000, an acid value of 105 mg KOH / g, and an iodine value of 2.0 mol / kg. Multifunctional (meth)acrylate 1: Mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate "Miramer" (registered trademark) M340 (manufactured by MIWON Co., Ltd.) Molecular weight: 298 Multifunctional (meth)acrylate 2: Trimethylolpropane EO-modified triacrylate (manufactured by MIWON, "Miramer" (registered trademark) M3190) molecular weight 692 Multifunctional (meth)acrylate 3: Dipentaerythritol hexaacrylate (manufactured by MIWON, "Miramer" (registered trademark) M600) molecular weight 578 Urethane (meth)acrylate 1: A urethane (meth)acrylate consisting of an alicyclic diisocyanate (hydrogenated XDI), a carboxylic acid (isophthalic acid and adipic acid), a polyol, and 2-hydroxyethyl acrylate, with a urethane bond fraction of 8% by mass. Weight average molecular weight (Mw) 3,600. Urethane (meth)acrylate 2: Polyester-based urethane acrylate (Kyoeisha Chemical Co., Ltd., UF-3007M) Weight average molecular weight (Mw) 3,800 Monofunctional (meth)acrylate: octadecyl acrylate (Tokyo Chemical Industry Co., Ltd.), molecular weight 325, melting point 28°C Surfactant 1: "Disperbyk" (registered trademark) 111 (manufactured by BYK Japan Co., Ltd.) anionic surfactant Surfactant 2: "Aqualon" (registered trademark) AR-10 (Dai-ichi Kogyo Seiyaku Co., Ltd.) Anionic surfactant.

[0062] <Film Preparation> A specified mixture of polyethylene, polypropylene, and additives was melt-extruded at 280°C, extruded into a sheet from a die with a slit-shaped outlet, and cooled and molded on a cooling drum with a surface temperature of 30°C to obtain an unstretched polyolefin film. The unstretched polyolefin film was then preheated as needed and stretched 5 times in the longitudinal direction at 135°C as needed to obtain a uniaxially stretched polyolefin film. The uniaxially stretched film was then stretched 10 times in the width direction in a tenter heated to 160°C as needed, and then heat-treated at 150°C while allowing a few percent relaxation in the width direction as needed to obtain a biaxially stretched polyolefin film.

[0063] The tensile modulus and film thickness measured by the methods described below were as follows: Polyolefin film 1: MD tensile modulus 754 MPa, film thickness 25 μm, polypropylene ratio 95 mass%, polyethylene ratio 5 mass%, nucleating agent ratio 0.05 mass% Polyolefin film 2: MD tensile modulus 949 MPa, film thickness 25 μm, polypropylene ratio 100% by mass, nucleating agent ratio 0.00% by mass Polyolefin film 3: MD tensile modulus 488 MPa, film thickness 25 μm, polypropylene ratio 80 mass%, polyethylene ratio 20 mass%, nucleating agent ratio 0.05 mass% Polyolefin film 4: MD tensile modulus 250 MPa, film thickness 25 μm, polypropylene ratio 20 mass%, polyethylene ratio 80 mass%, nucleating agent ratio 0.05 mass% Polyolefin film 5: MD tensile modulus 184 MPa, film thickness 25 μm, polypropylene ratio 10 mass%, polyethylene ratio 90 mass%, nucleating agent ratio 0.05 mass% Polyolefin film 6: MD tensile modulus 1,230 MPa, film thickness 25 μm, polypropylene ratio 100% by mass, nucleating agent ratio 0.05% by mass Polyolefin film 7: MD tensile modulus 215 MPa, TD tensile modulus 234 MPa, film thickness 60 μm, unstretched polypropylene film <Ink preparation> The acrylic resin, polyfunctional (meth)acrylate, monofunctional (meth)acrylate, urethane (meth)acrylate, and surfactant listed in Table 1 were each weighed out, and heated at 95°C for 390 minutes while stirring at 500 rpm using a disper blade to obtain a varnish. The pigment listed in Table 1 was added to the obtained varnish, and the mixture was passed through a three-roll mill "EXAKT" (registered trademark) M-80S (manufactured by EXAKT) five times at a gap of 1 to obtain red ink and white inks 1 to 7, which are lithographic printing inks.

[0064] [Table 1]

[0065] Next, the evaluation method will be described.

[0066] <Film tensile modulus> Strip-shaped test pieces measuring 15 mm wide and 60 mm long were cut from each of the films 1 to 7. Tensile tests were performed in the machine direction (MD) of the film using a tensile tester (Orientec's universal testing machine "Tensilon" (registered trademark)) in accordance with JIS K7161-1:2014 and JIS K7127:1999 "Plastics - Determination of tensile properties" and "Plastics - Testing methods for tensile properties" at a temperature of 23°C, a chuck distance of 50 mm, and a speed of 300 mm / min. The tensile modulus was then calculated from the stress-strain diagram. Five test pieces were measured for each film, and the arithmetic average value was used as the tensile modulus of the film.

[0067] <Film crystallinity> For each of the polyolefin films 1 to 6, rectangular test specimens measuring 25 mm x 15 mm (each side could be oriented in any direction) were prepared. Each polyolefin film was irradiated with an electron beam using an electron beam irradiation system (LB1036, manufactured by i-Electron Beam Co., Ltd.) at various accelerating voltages and doses as shown in Table 1, followed by the preparation of rectangular test specimens measuring 25 mm x 15 mm (each side could be oriented in any direction). The resulting test specimens were attached to an aluminum sample holder of an X-ray diffractometer (4036A2, manufactured by Rigaku Denki Co., Ltd.) with the film thickness direction normal to the sample holder surface. The diffraction peaks were measured by the reflection method using CuKa radiation (with a Ni filter) as the X-ray source at an output of 40 kV and 30 mA, with 2θ-θ continuous scanning while varying the angle of incidence of the X-rays. Measurement conditions were as follows: Five randomly selected locations on the sample were measured. Measurement range (2θ): 5 to 60° Measurement step (2θ): 0.05° Accumulation time: 2 seconds The diffraction peaks obtained by the measurement were separated into peaks derived from crystalline components and peaks derived from amorphous components using analysis software (JADE5.0, MDI Corporation), and the crystallinity was calculated from each peak area using the following formula, and the arithmetic mean value was taken as the crystallinity. Crystallinity (%) = Peak area of ​​crystalline component × 100 / (Peak area of ​​crystalline component + Peak area of ​​amorphous component) The results are shown in Table 2.

[0068] [Table 2]

[0069] <Register accuracy> In each example and comparative example, the register accuracy confirmation cross marks (register marks) for each color were aligned in the same position during printing, and printing was continued without any adjustments. After 30 seconds, the distance between the red cross mark (register mark) and the white cross mark (register mark) that was furthest from the red cross mark (register mark) was measured for the printed product. The smaller the distance between the register marks, the better the register accuracy, and a distance of 0.3 mm or less was evaluated as good register accuracy.

[0070] <Adhesion> Dry laminating adhesive A-953 / A-93 (Mitsui Chemicals, Inc.) was diluted with ethyl acetate to a nonvolatile content of 50% by mass, and the diluted solution was applied onto the ink of the printed matter obtained in each example and comparative example using a bar coater No. 6, and then dried with hot air. The dry weight of the applied adhesive was 2.3 g / cm. 2 Polyolefin film 7 was laminated onto the printed material coated with the adhesive using a calendar roll (manufactured by Matsumoto Kikai Seisaku Co., Ltd.), and aging was carried out at 40° C. for 3 days to obtain a laminate.

[0071] From the resulting laminate, strip-shaped test pieces 15 mm wide were cut using a cutter. In accordance with JIS K 6854-2:1999, Standard Name: Adhesives - Test Method for Peel Adhesion Strength - Part 2: 180° Peel, a 180° peel test was performed using a tensile tester at a loading rate of 200 mm / min to measure the peel strength between the ink and polyolefin film 1-6. A peel strength of 1 N / 15 mm was evaluated as good adhesion.

[0072] <Bag breakage due to packaging bag falling> Two rectangular test pieces measuring 570 mm in length and 360 mm in width were taken from the laminate produced by the above method, and the polyolefin films 7 were stacked facing each other, and the peripheral edges on three sides were sealed to a width of 10 mm at a pressure of 0.1 MPa using a heat seal tester (manufactured by Tester Sangyo Co., Ltd.). 10 kg of rice was filled into the test pieces, and the remaining peripheral edge on one side was sealed in the same manner to produce a rice-filled packaging bag.

[0073] Each of the rice-containing packaging bags obtained was dropped a total of three times from heights of 0.5 m, 1.0 m, and 1.5 m in each direction: vertical (with the lengthwise direction vertical), horizontal (with the widthwise direction vertical), and horizontal (with the length x width plane horizontal), and the presence or absence of bag breakage was checked. Bags that did not break all three times were rated as good, and bags that broke even once were rated as bad. If no breakage was observed at a height of 0.5 m, it was evaluated as having prevented bag breakage.

[0074] [Example 1] A waterless lithographic printing plate (TAN-E, manufactured by Toray Industries, Inc.) measuring 1,070 mm in width (width direction) and 674 mm in length (printing direction) and having a 0.1 mm line-thick cross mark (register mark) for checking register accuracy located at the center in the printing direction and 50 mm from both ends of the plate in the width direction was placed on the first cylinder of a center impression printing press (CI-8, manufactured by COMEXI). A waterless lithographic printing plate (TAN-E, manufactured by Toray Industries, Inc.) measuring 1,070 mm horizontally (widthwise) and 674 mm vertically (printing direction), with a 100% solid image area measuring 900 mm horizontally (widthwise) and 500 mm vertically (printing direction) in the center of the plate, and with 0.1 mm line-thick cross marks (register marks) for checking register accuracy positioned in the center in the printing direction and 50 mm from both ends of the plate in the widthwise direction, was placed on the sixth and seventh cylinders of the center impression printing press. The red ink obtained by the above method was placed on cylinder 1, and white ink 1 obtained by the above method was placed on cylinders 6 and 7.

[0075] After irradiating the polyolefin film substrate (1) with a corona treatment device attached to the printing press at an irradiation intensity of 8.00 kW, red ink and white ink were printed wet-on-wet at a speed of 100 m / min using a T414 blanket (Kinyosha Co., Ltd., thickness 1.95 mm) under the following conditions: ink feed rate for cylinder 1: 5%, ink feed rate for cylinders 6 and 7: 40%, chiller temperature for the impression cylinder: 25°C, chiller temperature for the oscillating roller and ink fountain: 28°C. After printing all the inks, the ink was cured by irradiating it with an electron beam using the electron beam irradiation device attached to the printing press at an acceleration voltage of 80 kV and a dose of 40 kGy to obtain a printed product.

[0076] The obtained prints were evaluated by the above-mentioned methods, and the results are shown in Table 3. Example 1 was good in both register accuracy and adhesion, and no breaks were observed.

[0077] [Example 2-4] Printed matter was obtained in the same manner as in Example 1, except that the polyolefin film shown in Table 3 was used instead of Polyolefin Film 1. The obtained printed matter was evaluated using the above-mentioned method, and the results are shown in Table 3. In Examples 2 to 4, the higher the tensile modulus, the better the register accuracy. The adhesion was good in all cases, and no breakage was observed.

[0078] [Examples 5-8] Printed matter was obtained in the same manner as in Example 1, except that the accelerating voltage of the electron beam irradiation was changed as shown in Table 3. The results of evaluation of the obtained printed matter using the above-mentioned method are shown in Table 3. In Examples 5 to 8, the register accuracy was good in all cases, and the higher the accelerating voltage, the better the adhesion. On the other hand, bag breakage tended to be better when the accelerating voltage was lower.

[0079] [Examples 9-11] Printed matter was obtained in the same manner as in Example 8, except that the polyolefin film shown in Table 3 was used instead of Polyolefin Film 1. The results of evaluation of the obtained printed matter using the above-mentioned method are shown in Table 3. In Examples 9 to 11, the higher the tensile modulus, the better the register accuracy. Adhesion was good in all cases, and no breakage was observed.

[0080] [Examples 12-15] Printed matter was obtained in the same manner as in Example 1, except that the dose of electron beam irradiation was changed as shown in Table 4. The obtained printed matter was evaluated using the above-mentioned method, and the results are shown in Table 4. In Examples 12-15, the register accuracy was good in all cases, and the higher the dose of irradiation, the better the adhesion. On the other hand, the lower the dose of irradiation, the better the bag breakage.

[0081] [Examples 16-21] Printed matter was obtained in the same manner as in Example 1, except that the white inks shown in Table 4 were used instead of White Ink 1. The results of evaluation of the obtained printed matter using the above-mentioned method are shown in Table 4. In Examples 16-21, the inks containing anionic surfactants tended to have better register accuracy, and the inks containing urethane acrylates tended to be less prone to tearing. Peel strength was good in all cases.

[0082] [Comparative Examples 1 to 2] Printed matter was obtained in the same manner as in Example 1, except that the polyolefin film shown in Table 4 was used instead of Polyolefin Film 1. The obtained printed matter was evaluated by the above-mentioned method, and the results are shown in Table 4. In Comparative Example 1, a film with a tensile modulus in the MD direction of less than 200 MPa was used, so the register accuracy was poor. In Comparative Example 2, a film with a tensile modulus in the MD direction of more than 1,000 MPa was used, so the bag was prone to tearing.

[0083] [Table 3]

[0084] [Table 4]

[0085] In Tables 3 and 4, "Crystallization degree (%) after electron beam irradiation" refers to the crystallinity after electron beam irradiation under the conditions of the irradiation dose (kGy) and acceleration voltage (kV) described in the "Electron beam irradiation conditions" section in the same tables.

Claims

1. A method for producing a printed matter, comprising, in order, a transfer step of transferring ink onto a polyolefin film using a center impression printing method, the polyolefin film having a tensile modulus in the MD direction of 200 MPa or more and 1,000 MPa or less, wherein the ratio (C2 / C1) of the crystallinity C2 of the polyolefin film after irradiating the polyolefin film with an electron beam under conditions of an acceleration voltage of 110 kV and an irradiation dose of 40 kGy to the crystallinity C1 of the polyolefin film is 0.8 or more and 1.2 or less, and a curing step of irradiating the ink with an electron beam to cure the ink.

2. The method for producing a printed matter according to claim 1 , wherein the polyolefin film has a thickness of 20 μm or more and 60 μm or less.

3. The method for producing a printed matter according to claim 1 or 2, wherein the polyolefin film has a crystallinity C2 of 20% or more and 50% or less after being irradiated with an electron beam at an acceleration voltage of 110 kV and an exposure dose of 40 kGy.

4. The method for producing a printed matter according to claim 1 or 2, wherein the polyolefin film contains 10% by mass or more of a polyethylene-based resin.

5. The method for producing a printed matter according to claim 4 , wherein the polyolefin film further contains 90% by mass or less of a polypropylene-based resin.

6. The method for producing a printed matter according to claim 1 or 2, wherein the content of the crystal nucleating agent in the polyolefin film is 0.01% by mass or less.

7. The method for producing a printed matter according to claim 1 or 2, wherein the curing step involves irradiating the electron beam at an acceleration voltage of 70 kV to 90 kV and at an exposure dose of 20 kGy to 60 kGy.

8. The method for producing a printed matter according to claim 1 or 2, wherein the ink contains an anionic surfactant.

9. The method for producing a printed matter according to claim 1 or 2, wherein the ink contains urethane (meth)acrylate.

10. The method for producing a printed matter according to claim 1 or 2, wherein the ink is transferred by lithographic printing in the transferring step.

11. A method for producing a laminate, comprising the steps of producing a printed matter by the method according to claim 1 or 2, and laminating an unstretched polyolefin film onto the printed matter.

12. The method for producing a laminate according to claim 11, wherein the unstretched polyolefin film has a tensile modulus of elasticity of 50 MPa or more and 400 MPa or less.

13. The method for producing a laminate according to claim 11, wherein the thickness of the unstretched polyolefin film is 30 μm or more and 100 μm or less.

14. A method for producing a packaging bag, comprising the steps of: producing a laminate by the laminate production method according to claim 11; and producing a bag from the laminate, in this order.

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