Laminate and its manufacturing method, packaging bag and packaging body

Abstract

To provide a laminate capable of sufficiently suppressing discoloration to occur during heat sealing.SOLUTION: A laminate 300 provided with a base film 10, an adhesive layer 30, and a sealant film 20 in this order, and is provided with a printed surface 52 of an electrostatic ink composition adhering to the adhesive layer 30. In the laminate 300, the adhesive layer 30 is composed of at least one of an adhesive composition containing a polyol, a polyisocyanate and an epoxy compound and its cured materials. When the sealant film 20 on the printed surface 52 is heated and pressurized under a predetermined heat seal condition, a color difference (ΔE) before and after that, obtained by the following formula (A), is smaller than 3.0. In the formula (A), each of ΔL*, Δa*, and Δb* represents differences in brightness, chromaticity, and chroma before and after heating and pressurizing under a predetermined heat seal condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a laminate, a method for manufacturing the same, a packaging bag, and a package. [Background technology]

[0002] Packaging bags for sealing and preserving packaged items such as food are known. Packages made of thin films or sheets are used as packaging bags. Various information such as product, brand, and manufacturer is printed on such packaging bags. Digital printers using electrostatic ink compositions are known as a printing method for such packaging bags.

[0003] For example, Patent Document 1 proposes applying a primer resin to a first flexible substrate such as a PET film to obtain a coated surface, performing electrostatic printing on the coated surface using a digital printer (HP's Indigo 20000 label and packaging digital printer), and then applying a crosslinking composition. After performing the predetermined steps in this manner, the proposed technology involves laminating the first flexible substrate coated with the predetermined components and a second flexible substrate to obtain a packaging material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-530478 Summary of the Invention [Problem to be solved by the invention]

[0005] Since digital printing using an electrostatic ink composition allows for small-lot production, digitally printed laminates are used for various packaging materials. However, it has been found that when packaging bags and the like are produced using a laminate having a surface printed with an electrostatic ink composition by a digital printer, discoloration may occur depending on the heat-sealing conditions.

[0006] Therefore, the present disclosure provides a laminate that has a surface printed by a digital printer but is capable of sufficiently suppressing discoloration that occurs during heat sealing, and also provides a packaging bag and a package that have a surface printed by a digital printer but are sufficiently suppressed from discoloring. [Means for solving the problem]

[0007] A laminate according to one aspect of the present disclosure is a laminate comprising a base film, an adhesive layer, and a sealant film in this order, and a printed surface of an electrostatic ink composition adhered to the adhesive layer, wherein the adhesive layer is composed of at least one of an adhesive composition containing a polyol, a polyisocyanate, and an epoxy compound, and a cured product thereof, and wherein the color difference (ΔE) calculated by the following formula (A) is less than 3.0 before and after the sealant film on the printed surface is heated and pressed under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds.

[0008]

number

[0009] Electrostatic ink compositions used in digital printing machines tend to have inferior heat resistance and strength compared to other inks. For this reason, when a sealant film of a laminate having a printed surface of an electrostatic ink composition is heated and pressurized under heat-sealing conditions, it discolors. In the above laminate, the adhesive layer that adheres to the printed surface of the electrostatic ink composition is composed of an adhesive composition containing a polyol, a polyisocyanate, and an epoxy compound. This adhesive composition is believed to have the effect of aggregating the electrostatic ink composition to improve the strength of the electrostatic ink composition and the effect of improving the adhesive strength between layers. Therefore, when heated and pressurized under heat-sealing conditions, it is possible to prevent gaps from forming near the printed surface and the electrostatic ink composition from breaking. Therefore, discoloration of the sealed portion due to gaps and breakage is suppressed, and discoloration of the digital print can be sufficiently suppressed.

[0010] The number of discoloration points with a size of 20 μm or more that appear on the printed surface due to the heat and pressure under the above heat sealing conditions is 1 mm 2 It is preferable that the number of particles is 10 or less per unit area. This prevents discoloration of the sealed portion, and can adequately prevent discoloration due to heat sealing.

[0011] A laminate according to one aspect of the present disclosure is a laminate comprising a substrate film, an adhesive layer, and a sealant film in this order, and a printed surface of an electrostatic ink composition adhered to the adhesive layer, wherein the adhesive layer is composed of at least one of an adhesive composition containing a polyol, a polyisocyanate, and an epoxy compound, and a cured product thereof, and wherein when the sealant film on the printed surface is heated and pressed under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds, the number of discoloration points having a size of 20 μm or more that are generated is 1 mm 2 There are 10 or fewer per item.

[0012] The surface of an electrostatic ink composition printed by a digital printer tends to have inferior heat resistance and strength compared to other inks. Therefore, when a laminate including a sealant film is heated and pressurized under heat-sealing conditions, the sealed portion discolors. The laminate has an adhesive layer that adheres to the printed surface of the electrostatic ink composition, and the adhesive layer is composed of an adhesive composition containing a polyol, a polyisocyanate, and an epoxy compound. This adhesive layer is believed to have the effect of aggregating the electrostatic ink composition and improving the strength of the electrostatic ink composition. Therefore, when heat-sealing is performed, it is possible to prevent gaps from forming near the printed surface and the electrostatic ink composition from breaking. Furthermore, the laminate has a sufficiently reduced number of discoloration points that occur when heat-sealed. Therefore, discoloration of the sealed portion can be sufficiently suppressed.

[0013] The polyol may include an aliphatic polyester polyol, and the epoxy compound may include one having epoxy groups at both ends. Such an adhesive layer has high adhesive strength, especially in high-temperature environments. Therefore, the occurrence of gaps near the printed surface and the rupture of the electrostatic ink composition during heat sealing can be sufficiently suppressed. Therefore, discoloration of digital prints due to heat sealing can be further suppressed.

[0014] The epoxy compound may include a bifunctional alicyclic epoxy compound. The bifunctionality of such an epoxy compound increases the number of crosslinking points with the electrostatic ink composition, thereby firmly adhering to the printed surface. Furthermore, the alicyclic nature of the epoxy compound can suppress reaction with polyisocyanate due to steric hindrance. This allows for stable curing, resulting in excellent adhesion at the interface between the printed surface and the adhesive layer.

[0015] The polyisocyanate may include a xylylene diisocyanate derivative. Such polyisocyanate and polyol have excellent reactivity. This improves the curing properties of the adhesive composition and further suppresses discoloration of digital prints due to heat sealing.

[0016] A packaging bag according to one aspect of the present disclosure is constructed by heat-sealing the sealant films of any of the laminates described above. Because such a packaging bag includes the laminate, discoloration of the sealed portion formed by heat sealing can be sufficiently suppressed. This reduces the color difference between the unsealed portion and the sealed portion, allowing the bag to maintain a clean appearance.

[0017] A package according to one aspect of the present disclosure includes a packaging bag and an item to be packaged in the packaging bag. Because the package includes the packaging bag, discoloration of the heat-sealed portion can be sufficiently suppressed. This reduces the color difference between the unsealed portion and the sealed portion, allowing the laminate to maintain a clean appearance.

[0018] A method for producing a laminate according to one aspect of the present disclosure includes the steps of printing an electrostatic ink composition on one side of a substrate film to obtain a printed surface, and bonding the printed surface and a substrate including a sealant film together using an adhesive composition including a polyol, a polyisocyanate, and an epoxy compound to obtain a laminate, wherein the color difference (ΔE) calculated by the following formula (A) before and after the sealant film on the printed surface is heated and pressed under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds is less than 3.0, based on the color difference before heat-sealing.

[0019]

number

[0020] The surface of an electrostatic ink composition printed by a digital printer tends to have inferior heat resistance and strength compared to other inks. For this reason, when a sealant film of a laminate having a printed surface of an electrostatic ink composition is heated and pressurized under heat-sealing conditions, it discolors. In the laminate, the adhesive composition used to adhere the printed surface of the electrostatic ink composition contains a polyol, a polyisocyanate, and an epoxy compound. This adhesive composition is believed to have the effect of aggregating the electrostatic ink composition to improve the strength of the electrostatic ink composition and the effect of improving the adhesive strength between layers. Therefore, when heated and pressurized under heat-sealing conditions, it is possible to prevent gaps from forming near the printed surface and the electrostatic ink composition from breaking. Therefore, discoloration of the sealed portion due to the occurrence of gaps and breaks is suppressed, and discoloration of the digital print can be sufficiently suppressed.

[0021] A method for producing a laminate according to one aspect of the present disclosure includes the steps of printing an electrostatic ink composition on one side of a substrate film to obtain a printed surface, and bonding the printed surface and a substrate including a sealant film together using an adhesive composition including a polyol, a polyisocyanate, and an epoxy compound to obtain a laminate, wherein the sealant film on the printed surface is heated and pressed under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds, and the number of discoloration points having a size of 20 μm or more that are produced is 1 mm 2 There are 10 or fewer per item.

[0022] The surface of an electrostatic ink composition printed by a digital printer tends to have inferior heat resistance and strength compared to other inks. Therefore, when a laminate including a sealant film is heated and pressurized under heat-sealing conditions, it discolors. In the laminate, the adhesive composition used to adhere the electrostatic ink composition to the printed surface contains a polyol, a polyisocyanate, and an epoxy compound. This adhesive layer is believed to have the function of aggregating the electrostatic ink composition to improve the strength of the electrostatic ink composition and the function of improving the adhesive strength between layers. Therefore, when heated and pressurized under heat-sealing conditions, it is possible to prevent gaps from forming near the printed surface and the electrostatic ink composition from breaking. Furthermore, the laminate has a sufficiently reduced number of discoloration points that occur when heat-sealed. Therefore, discoloration of the sealed portion can be sufficiently suppressed. [Effects of the Invention]

[0023] It is possible to provide a laminate that has a surface printed by a digital printer but is capable of sufficiently suppressing discoloration that occurs during heat sealing. It is also possible to provide a packaging bag and a package that have a surface printed by a digital printer but are sufficiently suppressed from discoloration. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 2 is a cross-sectional view showing an example of a laminate. [Figure 2] FIG. 10 is a cross-sectional view showing another example of a laminate. [Figure 3] 1 is an optical microscope photograph showing an enlarged view of the surface of the laminate after heating and pressing. [Figure 4] FIG. 2 is a plan view showing an example of a packaging bag and a packaging body. [Figure 5] FIG. 10 is a plan view showing another example of a packaging bag. [Figure 6] (A) is an optical microscope photograph showing an enlarged view of the surface of the laminate (before heat sealing) used in Example 7. (B) is an optical microscope photograph showing an enlarged view of the surface of the sealed portion of the laminate of Example 7 after heat sealing. [Figure 7] (A) is an optical microscope photograph showing an enlarged view of the surface of the laminate (before heat sealing) used in Comparative Example 7. (B) is an optical microscope photograph showing an enlarged view of the surface of the sealed portion of the laminate of Comparative Example 7 after heat sealing. DETAILED DESCRIPTION OF THE INVENTION

[0025] Embodiments of the present disclosure will be described below with reference to the drawings where appropriate. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same elements or elements having the same functions will be designated by the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0026] Fig. 1 is a cross-sectional view schematically illustrating an example of a laminate. Fig. 1 shows a cross section along the lamination direction (thickness direction) of the laminate. The laminate 300 has a base film 10, a primer layer 40, an adhesive layer 30, and a sealant film 20, in this order. The primer layer 40 is provided on one surface of the base film 10, closer to the sealant film 20.

[0027] The base film 10 and the sealant film 20 may be flexible substrates. The flexible substrate may include, for example, one or both of a metal foil such as aluminum foil and a thermoplastic polymer film. Examples of flexible substrates include films of biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), oriented polyamide (OPA), solid polypropylene (CPP), linear low-density polyethylene (LLDPE), and low-density polyethylene (LDPE).

[0028] The base film 10 may be, for example, a vapor-deposited film (transparent vapor-deposited film) in which aluminum or aluminum oxide is vapor-deposited on a PET film. Examples of the sealant film 20 include a CPP film, an LLDPE film, and an OPP film. The thickness of the base film 10 and the sealant film 20 may be 7 to 150 μm, 15 to 90 μm, or 20 to 80 μm.

[0029] The primer layer 40 may contain a resin. Examples of the resin include polyvinyl alcohol resin, cellulose-based resin, polyester, polyamine, polyethyleneimine resin, polyamide resin, polyurethane, polyacrylic polymer, hydroxyl-containing resin, carboxyl-containing resin, and amine-based polymer. The presence of the primer layer 40 allows smooth printing of the electrostatic ink composition using a digital printer. The amount of resin applied to the primer layer 40 is, for example, 0.01 to 1.5 g / m. 2 and may be 0.05 to 1.0 g / m 2 may be.

[0030] The laminate 300 has a printing surface 52 on the primer layer 40. An electrostatic ink layer 50 is provided on the printing surface 52. The electrostatic ink layer 50 may be composed of halftone dots of an electrostatic ink composition. The electrostatic ink layer 50 is provided by electrostatic printing using a digital printing machine. The multiple electrostatic ink layers 50 shown in FIG. 1 may have the same composition, or may have different compositions and thus different colors. The electrostatic ink layer 50 may be provided so as to be dotted on the primer layer 40, or may be provided so as to cover the entire one side of the primer layer 40.

[0031] The printing surface 52 having the electrostatic ink layer 50 is covered with an adhesive layer 30. The adhesive layer 30 may be composed of an adhesive composition, a cured product thereof, or a mixture thereof. The adhesive composition contains a polyol, a polyisocyanate, and an epoxy compound. At least a portion of these three components (polyol, polyisocyanate, and epoxy compound) may react with each other and cure to form a cured product. On the printing surface 52, the adhesive layer 30 containing the above three components and the electrostatic ink layer 50 are in direct contact. The epoxy compound contained in the adhesive layer 30 and the ink composition contained in the electrostatic ink layer 50 crosslink with each other, thereby sufficiently increasing the adhesive strength between the adhesive layer 30 and the electrostatic ink layer 50 on the printing surface 52.

[0032] The laminate 300 has a color difference of less than 3.0 before and after the sealant films 20 are heated and pressed together under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds, with the color difference before heat-sealing as the reference. The "color difference (ΔE)" in this disclosure is a measurement calculated from measurements taken with a spectrophotometer (for example, an eXact (device name) manufactured by X-rite). The specific calculation procedure is described below.

[0033] A laminate 300 having a printing surface 52 of an electrostatic ink composition is prepared. The lightness (L * ), and Chromaticity (a * and b * ) is measured.

[0034] Thereafter, the laminate 300 is heated and pressed from the surface 300A side under the above heat sealing conditions using a heat sealing device. Before and after the heating and pressing, the lightness (L * ), and Chromaticity (a * and b * The measurement position on the surface 300A is the same before and after heating and pressing by the heat sealing device. The difference in brightness (ΔL* ), chromaticity difference (Δa * and Δ b * ), the color difference (ΔE) is calculated by the following formula (A): The color difference calculated in this way is the "color difference (ΔE)" in the present disclosure.

[0035]

number

[0036] From the viewpoint of sufficiently suppressing discoloration during heat sealing, the color difference may be less than 3.0, may be 1.5 or less, or may be 1.3 or less. From the viewpoint of ease of manufacturing, the lower limit of the color difference may be 0.1 or more, or may be 0.3 or more. When the surface 300A is viewed in plan, the coverage ratio of the electrostatic ink layer 50 to the entire region (area) to be measured for color difference may be 50 area% or more, 70 area% or more, or even 100 area%. A coverage ratio of 100 area% means that the entire region to be measured for "color difference" is covered by the electrostatic ink layer 50. A coverage ratio of 50 area% means that half of the region to be measured for "color difference" is covered by the electrostatic ink layer 50. In the laminate 300 of FIG. 1, the coverage ratio of the electrostatic ink layer 50 to the entire region (area) to be measured for "hue" is approximately 55 area%.

[0037] The reason why the color difference before and after heat sealing can be reduced is thought to be that the components contained in the adhesive layer 30 have the effect of aggregating the electrostatic ink composition of the electrostatic ink layer 50, improving the strength of the electrostatic ink layer 50 itself, and the effect of improving the adhesive strength between the electrostatic ink layer 50 and an adjacent layer. This makes it possible to prevent gaps from occurring at the interfaces between the electrostatic ink layer 50 and the adhesive layer 30 and the primer layer 40, as well as the electrostatic ink layer 50 from shifting and deforming, or from breaking. This is thought to prevent discoloration associated with the occurrence of gaps, deformation, and breakage, and to sufficiently prevent discoloration of the printed surface 52.

[0038] 2 is a cross-sectional view showing another example of a laminate. The laminate 310 of FIG. 2 differs from the laminate 300 of FIG. 1 in that one surface of the primer layer 40 is entirely covered with an electrostatic ink layer 51. That is, in the laminate 310, the coverage rate of the electrostatic ink layer 50 with respect to the entire region (area) subject to measurement of "color difference" is 100 area %. The other configurations of the laminate 310 may be the same as those of the laminate 300 of FIG. 1. The color difference at the seal portion when the laminate 310 is heat-sealed is also measured in the same manner as for the laminate 300.

[0039] 1 and 2 are made up of circular halftone dots of an electrostatic ink composition. The color density on the printing surface 52 can be adjusted by changing the size of the halftone dots.

[0040] Figure 3 is an optical microscope photograph showing an enlarged view of the heated and pressurized surface of the sealant film side of the laminate when the surface is heated and pressurized under the heat-sealing conditions described above. In Figure 3, discoloration points 55 have appeared in the halftone dots 53 (electrostatic ink layer) on the heated and pressurized surface of the laminate. These discoloration points 55 indicate that gaps have appeared at the interface between the halftone dots 53 and the adhesive layer 30, or that the halftone dots 53 have been deformed. The discoloration points 55 may be due to air bubbles at the interface.

[0041] In the laminates 300, 310, the strength of the electrostatic ink layers 50, 51 made up of halftone dots is sufficiently high, and the adhesive strength between the electrostatic ink layers 50, 51 and the adhesive layer 30 is also sufficiently high, so that discoloration points 55 as shown in Fig. 3 can be sufficiently reduced. As shown in Fig. 3, the surface 300A of the laminate 300 is observed at a magnification of 100 times using an optical microscope, and an arbitrarily selected 1 mm 2In an area of ​​1.0 mm x 1.0 mm, the number of discoloration points 20 μm or larger that occur when heated and pressurized under the heat-sealing conditions described above is preferably 10 or fewer, more preferably 6 or fewer, and even more preferably 3 or fewer. By reducing the number of discoloration points 55 in this manner, color unevenness that occurs during heat-sealing can be more effectively suppressed. The number of discoloration points 20 μm or larger is determined by drawing a circumscribing circle of the discoloration points 55 as shown in FIG. 3 and counting the points with a diameter of 20 μm or larger. In this specification, discoloration points refer to points where the shape, size, color, etc. of the halftone dots change to a degree that can be detected by visually observing a magnified image under an optical microscope (magnification: 100x) before and after heating and pressurization.

[0042] The electrostatic ink compositions constituting the electrostatic ink layers 50, 51 in the laminates 300, 310 are ink compositions used in liquid electrophotographic printing, i.e., electrostatic printing, and are printed onto substrates such as paper and plastic. The electrostatic ink composition may contain a colorant or pigment such as a dye and a resin. In addition to these, the electrostatic ink composition may also contain a carrier fluid or carrier liquid. It may also contain a charge director, a charge adjuvant, a surfactant, a viscosity modifier, an emulsifier, and other additives.

[0043] Examples of the colorant include cyan pigments, magenta pigments, yellow pigments, and black pigments. Examples of the resin include thermoplastic resins such as ethylene acrylic acid copolymers, propylene acrylic acid copolymers, ethylene methacrylic acid copolymers, propylene methacrylic acid copolymers, and ethylene vinyl acetate copolymers.

[0044] Carrier liquids include hydrocarbons, silicone oils, and vegetable oils. Hydrocarbons include aliphatic hydrocarbons, branched-chain aliphatic hydrocarbons, and aromatic hydrocarbons. The electrostatic ink composition may be substantially free of carrier liquid when printed onto a print substrate, such as a first substrate. The carrier liquid may be removed, for example, by an electrophoretic process or evaporation during printing, thereby transferring substantially only solids to the print substrate.

[0045] Charge directors serve to maintain a sufficient electrostatic charge on particles contained in the electrostatic ink composition, and include ionic compounds such as metal salts of fatty acids, metal salts of sulfosuccinates, metal salts of oxyphosphates, metal salts of alkylbenzene sulfonic acids, and metal salts of aromatic carboxylic or aromatic sulfonic acids, as well as zwitterionic and nonionic compounds such as polyoxyethylenated alkylamines, lecithin, polyvinylpyrrolidone, and organic acid esters of polyhydric alcohols.

[0046] Charge adjuvants have the effect of increasing or stabilizing the charge of particles contained in the electrostatic ink composition. Examples of charge adjuvants include barium petronate, calcium petronate, Co naphthenate, Ca naphthenate, Cu naphthenate, Mn naphthenate, Ni naphthenate, Zn naphthenate, Fe naphthenate, Ba stearate, Co stearate, Pb stearate, Zn stearate, Al stearate, Cu stearate, Fe stearate, and metal carboxylates.

[0047] The electrostatic ink composition may contain a crosslinked product crosslinked by components contained in the adhesive layer 30 and / or primer layer 40. This can sufficiently increase the strength of the electrostatic ink layer 50 itself, as well as the adhesive strength between the printing surface 52 and the electrostatic ink layer 50, and between the electrostatic ink layer 50 and the primer layer 40. In addition, during heat sealing, it is possible to prevent the dots constituting the electrostatic ink layer 50 from moving and to prevent gaps from forming at the interface between the electrostatic ink layer 50 and the adhesive layer 30. This can sufficiently prevent discoloration due to heat sealing.

[0048] The printed surface 52 of the electrostatic ink composition and the adhesive layer 30 are adhered to each other. That is, the printed surface 52 is the adhesive surface for the adhesive layer 30, and the electrostatic ink composition and the adhesive composition are in direct contact with each other. The adhesive composition contains a polyol, a polyisocyanate, and an epoxy compound. These three components are described below.

[0049] The polyol has, for example, a number-average molecular weight of 400 or more and has two or more hydroxyl groups in one molecule. The polyisocyanate has two or more isocyanate groups in one molecule. The polyol and polyisocyanate react as a base resin and a curing agent, respectively, to produce polyurethane (polyurethane adhesive). The number-average molecular weight of the polyol may be, for example, 10,000 or less.

[0050] The polyol may contain at least one selected from the group consisting of polyester polyols and polyether polyols. Among these, from the viewpoint of sufficiently increasing the adhesive strength of the adhesive layer 30 in a high-temperature environment, the polyol may contain a polyester polyol or may contain an aliphatic polyester polyol.

[0051] The polyester polyol can be obtained, for example, by a condensation reaction or transesterification reaction between a polyhydric alcohol and a polybasic acid, its alkyl ester, its acid anhydride, or its acid halide. Examples of the polyhydric alcohol include low-molecular-weight diols, low-molecular-weight triols, and low-molecular-weight polyols having four or more hydroxyl groups.

[0052] Examples of low molecular weight diols include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 3,3-dimethylolheptane, and 2-ethyl-2-butyl-1,3-propanediol.

[0053] Examples of low molecular weight triols include glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-(hydroxymethyl)pentane, and 2,2-bis(hydroxymethyl)-3-butanol.

[0054] Examples of low molecular weight polyols having four or more hydroxyl groups include tetramethylolmethane, pentaerythritol, dipentaerythritol, D-sorbitol, xylitol, D-mannitol, and D-mannite.

[0055] Examples of alkyl esters of polybasic acids include methyl esters and ethyl esters of polybasic acids. Examples of acid anhydrides include acid anhydrides derived from polybasic acids, such as oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, 2-alkyl (C12 to C18) succinic anhydride, tetrahydrophthalic anhydride, and trimellitic anhydride.

[0056] The acid halides include those derived from the above-mentioned polybasic acids, such as oxalic acid dichloride, adipic acid dichloride, and sebacic acid dichloride.

[0057] The polyether polyol may be a polyalkylene oxide. For example, it may be obtained by addition reaction of an alkylene oxide such as ethylene oxide and / or propylene oxide with a low molecular weight polyol as an initiator. Specific examples include polyethylene glycol, polypropylene glycol, and polyethylene polypropylene glycol (random or block copolymer). Other examples include polytetramethylene ether glycol obtained by ring-opening polymerization of tetrahydrofuran.

[0058] Examples of polyisocyanates include polyisocyanate monomers, polyisocyanate derivatives, and isocyanate-terminated prepolymers. The adhesive composition may contain multiple different polyisocyanates. The molar ratio (NCO / OH) of the isocyanate groups contained in the polyisocyanate to the hydroxyl groups of the polyol may be 0.5 to 10. Such an adhesive composition can form a cured product that has high adhesive strength and excellent flexibility.

[0059] Examples of the polyisocyanate monomer include aliphatic polyisocyanates, aromatic polyisocyanates, araliphatic polyisocyanates, and alicyclic polyisocyanates.

[0060] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate (tetramethylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,6-diisocyanate methylcaprate.

[0061] Examples of the aromatic aliphatic polyisocyanate include xylylene diisocyanate derivatives, such as xylylene diisocyanate (1,3-xylylene diisocyanate or 1,4-xylylene diisocyanate) (XDI), tetramethyl xylylene diisocyanate (1,3-tetramethyl xylylene diisocyanate or 1,4-tetramethyl xylylene diisocyanate) (TMXDI), ω,ω'-diisocyanato-1,4-diethylbenzene, and polyol-modified xylylene diisocyanate obtained by reacting xylylene diisocyanate with trimethylolpropane.

[0062] The content of the xylylene diisocyanate derivative relative to the entire polyisocyanate may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more, from the viewpoint of improving the reactivity with the base agent (for example, polyol). By making it 30% by mass or more, the reactivity can be further increased.

[0063] Examples of alicyclic polyisocyanates include 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, cyclohexane diisocyanate (1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorodiisocyanate) (IPDI), methylcyclohexane diisocyanate (methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate), and norbornane diisocyanate (NBDI).

[0064] Examples of polyisocyanate derivatives include polymers of the above-mentioned polyisocyanate monomers, allophanate-modified products, polyol-modified products, polyol-modified products produced by the reaction of a monomer with an alcohol, biuret-modified products, urea-modified products, oxadiazinetrione-modified products, carbodiimide-modified products, uretdione-modified products, and uretonimine-modified products.

[0065] The isocyanate-terminated prepolymer is a urethane prepolymer having at least two isocyanate groups at the molecular end. It can be obtained by subjecting at least one member selected from the group consisting of a polyisocyanate monomer, a polyisocyanate derivative, and an isocyanate-terminated prepolymer to a urethane reaction with a polyol. The molar ratio (NCO / OH) of the isocyanate groups contained in the polyisocyanate to the hydroxyl groups of the polyol may be 0.5 or more, 0.6 or more, 0.8 or more, 1 or more, or 1.5 or more. The molar ratio (NCO / OH) may be 10 or less, 5 or less, 4 or less, or 3 or less. Examples of numerical ranges for the molar ratio (NCO / OH) include 0.5 to 10, 0.5 to 5, 0.8 to 4, and 0.6 to 3.

[0066] The epoxy compound may be a compound having one or more epoxy groups in one molecule. From the viewpoint of further increasing the adhesive strength of the adhesive layer 30 in a high-temperature environment, the epoxy compound may have epoxy groups at both ends. Examples of the epoxy compound include glycidyl ether type epoxy compounds, glycidyl amine type epoxy compounds, glycidyl ester type epoxy compounds, and alicyclic epoxy compounds (alicyclic epoxy compounds).

[0067] The molecular weight of the epoxy compound may be 500 or less, 450 or less, or 400 or less. Such an epoxy compound can sufficiently penetrate into the electrostatic ink composition that constitutes the electrostatic ink layer. The lower limit of the molecular weight of the epoxy compound may be, for example, 98.

[0068] Examples of the alicyclic epoxy compound include epoxycyclohexylmethyl-epoxycyclohexanecarboxylate and bis(epoxycyclohexyl)adipate.

[0069] Examples of monofunctional alicyclic epoxy compounds having one epoxy group per molecule include 3,4-epoxycyclohexylmethyl methacrylate and 1,2-epoxy-4-vinylcyclohexane. Examples of bifunctional epoxy compounds having two epoxy groups per molecule include 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, and 4-vinylcyclohexene dioxide. Examples of epoxy compounds having one or more epoxy groups per molecule include the 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol represented by the following general formula (I):

[0070] [ka]

[0071] In the above general formula (I), n may be an integer of 1-4.

[0072] The epoxy compound preferably contains a bifunctional alicyclic epoxy compound. The bifunctionality increases the number of crosslinking points with the electrostatic ink composition and the primer resin, accelerating the curing reaction of the adhesive and facilitating curing. Furthermore, the alicyclic nature of the epoxy compound inhibits reaction with polyisocyanate due to steric hindrance. This allows for stable curing and ensures excellent adhesion at the interface between the printing surface 52 and the adhesive layer 30.

[0073] In the adhesive composition, the content of the epoxy compound per 100 parts by mass of polyol may be 3 to 25 parts by mass, 6 to 25 parts by mass, or 8 to 20 parts by mass, from the viewpoint of achieving both high adhesive strength and excellent shear suppression. If the content of the epoxy compound is too high, the excellent shear suppression tends to be impaired. That is, when the adhesive layer 30 is formed, the adhesive surface may shift or the adhesive composition may protrude. If the amount of the epoxy compound is too low, the adhesive strength under high-temperature hot water treatment conditions tends to decrease.

[0074] In the adhesive composition, the content of polyisocyanate per 100 parts by mass of polyol may be 10 to 50 parts by mass, 15 to 35 parts by mass, or 20 to 30 parts by mass, from the viewpoint of sufficiently increasing the seal strength and the adhesive strength under high-temperature hot water treatment conditions.

[0075] The molar ratio of the epoxy groups contained in the epoxy compound to the isocyanate groups contained in the polyisocyanate may be 0.5 to 10, 1.5 to 9, or 2.0 to 6.5, which allows a sufficiently high adhesive strength to be maintained under high-temperature hot water treatment conditions.

[0076] In addition to the components described above, the adhesive composition constituting the adhesive layer 30 may contain optional components such as additives. Examples of additives include antioxidants, UV absorbers, light stabilizers, fillers, silane coupling agents, epoxy resins, catalysts, coatability improvers, leveling agents, nucleating agents, lubricants, release agents, antifoaming agents, plasticizers, surfactants, pigments, dyes, organic fine particles, inorganic fine particles, antifungal agents, and flame retardants. The adhesive composition may contain a solvent such as an organic solvent.

[0077] The adhesive composition bonds the print surface 52, on which the electrostatic ink composition is printed, to the sealant film 20. An optional layer may be provided between the sealant film 20 and the adhesive layer 30. In this case, the adhesive composition bonds the print surface 52 to the optional layer. The adhesive composition forms a urethane bond by reaction with the polyol and polyisocyanate, thereby functioning as an adhesive. Even in the presence of an epoxy compound, the formation of the urethane bond proceeds smoothly, allowing the print surface 52 to be bonded to the sealant film 20 or an optional layer with sufficiently high adhesive strength.

[0078] The adhesive composition may have the function of cross-linking the electrostatic ink composition that forms the electrostatic ink layers 50 and 51 in addition to forming urethane bonds. This can improve the adhesive strength between the printed surface 52 and the sealant film 20 or any layer. Even if the ink coverage on the printed surface 52 is high, the epoxy compound can be sufficiently permeated into the electrostatic ink layer 50 formed by the electrostatic ink composition by increasing the content of the epoxy compound in the adhesive composition accordingly. The permeated epoxy compound cross-links the electrostatic ink composition, thereby increasing the strength of the electrostatic ink composition (electrostatic ink layers 50 and 51). Therefore, discoloration due to heat sealing can be suppressed even if the ink coverage on the printed surface 52 is high.

[0079] The adhesive composition maintains high adhesive strength even after heat treatment while also having an excellent pot life. This allows for excellent workability during coating and lamination processes, such as bonding a printed surface to a substrate. The adhesive composition may contain a urethane-forming polyol and polyisocyanate, and an epoxy compound, at least a portion of which may be cured to form the adhesive layer. This allows for a reduction in the number of layers constituting the laminate 300 compared to when an adhesive layer containing only polyurethane and an epoxy coating layer are separately provided. Therefore, when producing a laminate using a roll-to-roll process, for example, problems such as roll meandering after aging and wrinkling due to blocking do not occur. Furthermore, the aging process after coating can be eliminated, improving manufacturing efficiency.

[0080] In the laminates 300, 310, where the electrostatic ink layers 50, 51 and the adhesive layer 30 on the printing surface 52 are in direct contact, components such as epoxy compounds and / or polyisocyanates contained in the adhesive composition sufficiently penetrate into the electrostatic ink layers 50, 51. This crosslinks the electrostatic ink composition constituting the electrostatic ink layers 50, 51, improving the strength of the electrostatic ink composition (electrostatic ink layers 50, 51). It also improves the adhesive strength between the layers. Even if the printing surface 52 includes a plain area (transparent area) without the electrostatic ink layer 50, as shown in FIG. 1, the epoxy compounds contained in the adhesive layer can eliminate stickiness. On the other hand, if an epoxy coating layer is provided separately from the adhesive layer 30, when the printing surface 52 includes a plain area, excess epoxy compounds can be present near the plain area, making stickiness more likely. In this way, the laminate 300 can bond the printing surface 52, including the plain area without the electrostatic ink layer 50, with high adhesive strength while eliminating stickiness.

[0081] Since the laminates 300, 310 can suppress color unevenness in the printed area, they may be used as packaging materials for food, sanitary products, and the like, where appearance is important. However, the uses are not limited to these. For example, since they have excellent adhesive strength and seal strength even after high-temperature hot water treatment and retort heat treatment, they may be used as packaging materials for retort pouches, microwave-safe packaging materials, packaging materials for boiling, and packaging materials for boiling. The thickness of the laminates 300, 310 may be, for example, 15 to 200 μm or 18 to 120 μm.

[0082] The laminate according to the modified example may not have the primer layer 40, or may have a primer layer 40 on each of the opposing surfaces of the base film 10 and the sealant film 20. Furthermore, from the viewpoint of improving the gas barrier property and water vapor barrier property of the laminate 300, 310, at least one of a metal layer such as an aluminum foil and a resin layer such as a nylon film may be present between the base film 10 and the sealant film 20 and / or between the sealant film 20 and the adhesive layer 30.

[0083] Specific examples of the layer structure of the laminate are shown below. In each example, the left end is the base film 10, the right end is the sealant film 20, and the layers are laminated in order from left to right. The first adhesive layer is adhesive layer 30, and the second adhesive layer may be a conventional adhesive layer.

[0084] (1) Transparent vapor-deposited PET film / primer layer / electrostatic ink layer / first adhesive layer / nylon layer / second adhesive layer / CPP film (non-oriented polypropylene film) (2) PET film / primer layer / electrostatic ink layer / first adhesive layer / aluminum layer / second adhesive layer / CPP film (non-oriented polypropylene film) (3) Nylon layer / primer layer / electrostatic ink layer / first adhesive layer / LLDPE (linear low-density polyethylene) film (4) PET film / primer layer / electrostatic ink layer / first adhesive layer / nylon layer / second adhesive layer / CPP film (5) PET film / primer layer / electrostatic ink layer / first adhesive layer / PET film (6) OPP film (biaxially oriented polypropylene film) / primer layer / electrostatic ink layer / first adhesive layer / CPP film (7) PET film / primer layer / electrostatic ink layer / first adhesive layer / LLDEP film (8) Transparent vapor-deposited PET film / primer layer / electrostatic ink layer / first adhesive layer / CPP film (9) PET film / primer layer / electrostatic ink layer / first adhesive layer / aluminum vapor deposition barrier film / LLDPE film (10) OPP film / primer layer / electrostatic ink layer / first adhesive layer / aluminum vapor deposition barrier film / second adhesive layer / CPP film (11) PET film / primer layer / electrostatic ink layer / first adhesive layer / OPP film / second adhesive layer / CPP film (12) PET film / primer layer / electrostatic ink layer / first adhesive layer / nylon layer / second adhesive layer / LLDEP film

[0085] In each of the above specific examples, a primer layer may be omitted. Also, any layer may be provided at any position. (1) and (2) are suitable packaging materials for retort pouches, (3) for boiled foods or for pizza and pet food, (4) for microwave ovens, (5) for can labels, (6) and (7) for confectioneries, noodles, and soup stock, (8) and (12) for rice crackers and cookies, (9) for supplements, pet treats, vegetable seeds, and coffee, (10) for fish food and coffee, (11) for frozen foods, and (12) for packaging with a spout. However, the applications are not limited to those described above.

[0086] A method for manufacturing a laminate according to one embodiment is described below. In this manufacturing method, a laminate 300 shown in Fig. 1 is manufactured. The manufacturing method includes the steps of forming a primer layer 40 on one surface of a substrate film 10, printing an electrostatic ink composition on the primer layer 40 to form an electrostatic ink layer 50 to obtain a printed surface 52, and bonding the printed surface 52 to one surface of a sealant film 20 using an adhesive composition.

[0087] The primer layer 40 may be formed on one side of the substrate film 10 by gravure printing. The primer layer 40 may be formed by crosslinking a resin raw material with a crosslinking agent. Crosslinking may be achieved by irradiation with ultraviolet light, heat, ionizing radiation such as an electron beam, or non-ionizing radiation such as microwave radiation. The electrostatic ink composition may be printed by electrostatic printing using a digital printer.

[0088] The adhesive composition can be used to bond the printed surface 52 to one side of the sealant film 20 by lamination. Lamination can be performed using any suitable device. The epoxy compound and / or polyisocyanate contained in the adhesive composition may penetrate into the electrostatic ink composition and primer layer 40 that make up the electrostatic ink layer 50 and undergo a cross-linking reaction with the components contained in the electrostatic ink composition and primer layer 40. This improves the strength of the electrostatic ink layer 50 and allows for the production of a laminate 300 in which the interfaces of the layers are sufficiently bonded. During lamination, at least a portion of the adhesive composition may be cured to form a cured product. In this manner, a laminate 300 can be produced that includes, in this order, the substrate film 10, the primer layer 40, the electrostatic ink layer 50, the adhesive layer 30, and the sealant film 20. The laminate 310 and the laminates according to the variations can also be produced in the same manner as the laminate 300.

[0089] The laminates 300 and 310 thus manufactured have the same configurations and properties as those described in these embodiments. The description of the laminates 300 and 310 and their modifications also applies to the description of the above-described manufacturing method embodiment.

[0090] The laminates 300 and 310 are suitable for use as packaging materials, and can be used to produce packaging bags.

[0091] FIG. 4 is a plan view showing one embodiment of a packaging bag formed using the above-described laminate. The packaging bag 100 is formed by bonding the sealant films 20 of a pair of laminates 300 (310) together. The packaging bag 100 includes a sealed portion 101 formed by bonding the peripheral edges of a pair of film-like, approximately rectangular laminates 300 (310) together, and a storage portion 102 formed between the pair of laminates 300 (310) by the sealed portion 101. That is, the side edges, bottom edge, and top edge of the packaging bag 100 are sealed by the sealed portion 101. The packaging bag 100 includes the storage portion 102 in which the packaged item (e.g., food) is stored in the non-sealed portion (sheet portion) surrounded by the sealed portion 101. The sealed portion 101 at the bottom edge may be sealed after the packaged item has been filled into the storage portion 102. The sealed portion 101 is formed by heat-sealing the sealant films 20 together.

[0092] It is not essential that the pair of packaging materials that make up the packaging bag 100 have the same layer structure, and for example, the pair of packaging materials may be composed of laminates having different layer structures.

[0093] The packaging bag 100 may be equipped with opening means 120. The opening means has a pair of easy-open processed sections 124 consisting of V-shaped notches formed in the sealed section 101 at the side edge, and a half-cut line 121 that serves as a cutting path between the pair of easy-open processed sections 124. The half-cut line 121 can be formed using a laser. The easy-open processed sections 124 are not limited to V-shaped notches, and may be U-shaped or I-shaped notches, or may be a group of scars.

[0094] The procedure for manufacturing a packaging bag 100 using the laminate 300 is described below. A pair of laminates 300 cut to a predetermined shape is prepared as packaging materials. The sealant films 20 provided on one side of each laminate 300 are placed opposite each other, and the sealant films 20 are bonded together. This forms sealed portions 101 at the top and side edges, and forms an unsealed portion surrounded by the sealed portions 101 in a U-shape. In this way, a packaging bag 110 is obtained in which only the top edge (or only the bottom edge) is unsealed, as shown in FIG. 5. In some other embodiments, the packaging bag may have some edges that are not sealed, as shown in FIG. 5.

[0095] Next, the packaged item is filled from the unsealed upper end (or lower end). After that, the stacks 300 are bonded together at the upper end (or lower end) to form a sealed portion 101 at the upper end (or lower end). In this way, a package 200 including a packaging bag 100 and a packaged item contained therein can be manufactured.

[0096] The packaging bag 100 and the packaging body 200 are manufactured using the laminate 300. This allows for sufficient suppression of discoloration in the sealed portion 101. This allows for sufficient maintenance of color uniformity, for example, when the sealed portion 101 and the non-sealed portion therein are the same color. Furthermore, the laminate 300 used as a packaging material has excellent heat resistance, and is therefore suitable for use with foods that are heated in hot water or in a microwave oven. Examples of the packaging body 200 include retort pouch packaging that is heated by boiling or in a microwave oven. The packaging bag 100 and the packaging body 200 may be manufactured using the laminate 310 or a laminate according to a variation thereof, instead of the laminate 300.

[0097] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. For example, the laminate may be a packaging film attached to the surface of a PET bottle. Furthermore, the shape of the packaging bag is not limited to a four-sided bag, and may be, for example, a two-sided bag, a three-sided bag, a two-sided bag, a two-sided bag, or a standing pouch. [Example]

[0098] The present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples.

[0099] Example 1 [Laminate fabrication] An alumina-deposited PET film (manufactured by Toppan Printing Co., Ltd., trade name: GLARHF, thickness: 12 μm) was prepared as the substrate film. An aqueous primer resin (a resin containing polyethyleneimine, manufactured by Michelman, trade name: DP050) was applied to this alumina-deposited surface to form a primer layer. The amount of aqueous polyethyleneimine applied was 0.10 to 0.18 g / m 2 The coating was applied so that

[0100] A predetermined printing was performed on the surface of the primer layer using a digital printer (HP Indigo 20000 label and packaging digital printer). The electrostatic ink composition used was an electrostatic ink composition (HP Indigo ElectroInk) containing a thermoplastic resin containing a copolymer of ethylene acrylic acid and ethylene methacrylic acid. The colors of the electrostatic ink composition used were yellow (Y), magenta (M), and cyan (C), as shown in Table 1. Several samples with different colors and ink coverages of the electrostatic ink composition were prepared. The ink coverages of each color and their total were as shown in Table 1. The ink coverages of each color were adjusted by adjusting the settings of the digital printer. As shown in Table 1, the total ink coverages were 100 to 160%.

[0101] An adhesive composition with a solids concentration of 36.5% by mass was prepared by blending an aliphatic polyester polyol (manufactured by Mitsui Chemicals, Inc., trade name: Takelac A626, hereinafter sometimes referred to as "(A)") as the base agent, a polyisocyanate (manufactured by Mitsui Chemicals, Inc., trade name: Takenate A50, hereinafter sometimes referred to as "(B)") as the curing agent, 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (hereinafter sometimes referred to as "C") as the epoxy compound, and ethyl acetate as the solvent. The structure of this epoxy compound is shown in formula (1) below. The blending ratio (by mass) of the components was (A):(B):(C) = 8:1:0.28.

[0102] The adhesive composition prepared as described above was applied to the surface printed with the electrostatic ink composition using a dry laminating device to form an adhesive layer. The amount of the adhesive composition applied was 4.0 g / m. 2 It was decided.

[0103] [ka]

[0104] A nylon film and a non-oriented polypropylene film were laminated together using a commercially available adhesive to produce a laminate. Using the dry laminating device described above, the nylon film and the adhesive layer were laminated together, with the adhesive layer on the base film facing the nylon film of the laminated film. The aging time was 40°C for 2 days.

[0105] [Heat seal and color measurement] Using a spectrophotometer (manufactured by X-rite, product name: eXact), the lightness (L * ), and Chromaticity (a * and b * ) was measured.

[0106] Thereafter, using a heat sealing device, heating and pressing were performed under heat sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds. After heating and pressing, the lightness (L * ), and Chromaticity (a * and b * The above measurements were carried out on the same surface and at the same position before and after heating and pressing. The difference in brightness (ΔL * ), and Chromaticity difference (Δa * and Δ b * The color difference (ΔE) was calculated from the above formula (A) using the above data. The results are shown in Table 1.

[0107] Examples 2 to 6 A laminate was produced in the same manner as in Example 1, except that the color and coverage of the electrostatic ink composition printed on the surface of the primer layer were changed as shown in Table 1. Heating and pressure were then applied using a heat-sealing device in the same manner as in Example 1, and the color difference (ΔE) before and after heating and pressure was determined. The results are shown in Table 1.

[0108] (Comparative Examples 1 to 6) Laminates were prepared in the same manner as in Examples 1 to 6, except that no epoxy compound (component (C)) was added when preparing the adhesive composition, and then heated and pressed using a heat-sealing device. The color difference (ΔE) before and after heating and pressing was then determined using the same method as in Examples 1 to 6. The results are shown in Table 2.

[0109] [Table 1]

[0110] [Table 2]

[0111] As shown in Tables 1 and 2, the color difference (ΔE) before and after heating and pressing was sufficiently small for the laminates of Examples 1 to 6. Thus, it was confirmed that the laminates of Examples 1 to 6 were able to sufficiently suppress discoloration caused by heating and pressing.

[0112] Example 7 A laminate was prepared in the same manner as in Example 1, except that the ink coverage of the electrostatic ink composition was set to Y: 20%, M: 20%, and C: 20%. Heating and pressing were then performed under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds. The surface before and after heating and pressing were observed under an optical microscope at 100x magnification. In a randomly selected 1.0 mm x 1.0 mm area from the observation image, the number of discoloration points (circumscribed circle diameters of 20 μm or more) caused by heating and pressing was counted. The results are shown in Table 3.

[0113] Example 8 Heating and pressing were carried out in the same manner as in Example 7, except that the heat sealing conditions were a temperature of 240°C, a pressure of 0.2 MPa, and a time of 1.5 seconds, and the number of discolored spots caused by heating and pressing was counted in the same manner as in Example 7. The results are shown in Table 3.

[0114] (Comparative Example 7) A laminate was produced in the same manner as in Comparative Example 1, except that the ink coverage rates of the electrostatic ink composition were Y: 20%, M: 20%, and C: 20%. Heat sealing was then performed under the same heat sealing conditions as in Example 7, and heating and pressure were applied. The number of discoloration points caused by heating and pressure was counted in the same manner as in Example 7. The results are shown in Table 3.

[0115] [Table 3]

[0116] Figure 6(A) is an optical microscope photograph at 100x magnification of the surface (the surface on the alumina-deposited PET film side) of the laminate of Example 7 before heating and pressurization. Figure 6(B) is an optical microscope photograph at 100x magnification of the same surface of the laminate of Example 7 after heating and pressurization. As shown in Table 3 and Figure 6, in Examples 7 and 8, almost no discoloration occurred due to heat sealing.

[0117] Fig. 7(A) is an optical microscope photograph, enlarged 100 times, showing the surface (the surface on the alumina-deposited PET film side) of the laminate of Comparative Example 7 before heating and pressurization. Fig. 7(B) is an optical microscope photograph, enlarged 100 times, showing the copper surface of the laminate of Comparative Example 7 after heating and pressurization. As shown in Table 3 and Fig. 7, in Comparative Example 7, many discolored spots occurred due to heat sealing. This confirmed the occurrence of discoloration.

[0118] The results of the above-mentioned Examples and Comparative Examples confirmed that discoloration due to heat sealing can be suppressed by using an adhesive composition containing a polyol, a polyisocyanate, and an epoxy compound. The factors that contribute to this suppression of discoloration are thought to be the improved strength of the electrostatic ink composition and the improved adhesive strength between each layer. To verify these improvements, the following experiment was conducted.

[0119] (Reference example 1) [Preparation of adhesive composition and laminate] A polyethylene terephthalate film (PET film, thickness: 12 μm) was prepared as a substrate film. The same aqueous primer resin as in Example 1 was applied to one side of this PET film to form a primer layer. The amount of aqueous polyethyleneimine applied was also the same as in Example 1.

[0120] A predetermined printing was performed on the surface of the primer layer using the digital printing machine used in Example 1. The electrostatic ink composition used was an electrostatic ink composition (HP Indigo ElectroInk) containing a thermoplastic resin containing a copolymer of ethylene acrylic acid and ethylene methacrylic acid. The colors of the electrostatic ink composition used were white (W), yellow (Y), magenta (M), and cyan (C), as shown in Table 4. Multiple samples with different colors and ink coverage rates of the electrostatic ink composition were prepared. The ink coverage rates of each color and their total were as shown in Table 4. As shown in Table 4, the total ink coverage rate was 200 to 500%.

[0121] The same adhesive composition as in Example 1 was prepared, and the adhesive composition was applied to the printed surface in the same manner as in Example 1 to form an adhesive layer. The amount of adhesive composition applied was 4.0 g / m 2 It was decided.

[0122] A laminated film having an aluminum foil (manufactured by Toyo Aluminum Co., Ltd., thickness: 7 μm), a nylon film, and an unstretched polypropylene film in this order was prepared. Using the same dry laminating device as in Example 1, the adhesive layer on the base film and the aluminum foil of the laminated film were placed facing each other, and the aluminum foil and the adhesive layer were bonded together to obtain a laminate. The curing time (aging) was 40°C for 2 days.

[0123] [Measurement of adhesive strength (room temperature)] The adhesive strength of the prepared laminate was measured in accordance with JIS K 6854-1:1999. Specifically, the prepared laminate was cut into a 15 mm width to prepare a measurement sample. After peeling between the layers at the edge of the measurement sample, the peel strength between the layers of the laminate was measured using a tensile tester at an angle of 90°, a tensile speed of 300 mm / min, and room temperature. This peel strength was defined as the adhesive strength at room temperature (20°C). The measurement results are shown in Table 4.

[0124] (Reference examples 2~6) Laminates were prepared and adhesive strengths were measured in the same manner as in Reference Example 1, except that the formulation of the adhesive composition was changed as shown in Tables 4 and 5. The measurement results are shown in Tables 4 and 5.

[0125] (Reference example 7) A two-component adhesive was prepared in which a first component consisting of an aliphatic polyester polyol (A) (manufactured by Mitsui Chemicals, Inc., product name: Takelac A626) and a second component consisting of a polyisocyanate (B) (manufactured by Mitsui Chemicals, Inc., product name: Takenate A50) and an epoxy compound (C) were housed in separate containers. The first and second components were mixed to prepare an adhesive composition having the formulation shown in Table 5. A laminate was produced in the same manner as in Reference Example 1, except that this adhesive composition was used, and the adhesive strength was measured. The measurement results are shown in Table 5.

[0126] Comparative Example 9 A laminate was produced in the same manner as in Reference Example 1, except that the epoxy compound (C) was not added when preparing the adhesive composition, and the adhesive strength was measured. The measurement results are shown in Table 5.

[0127] (Comparative Example 10) A laminate was produced in the same manner as in Reference Example 1, except that an epoxy compound of formula (1) was applied to the printed surface of the electrostatic ink composition to form an epoxy coating layer, and the adhesive composition of Comparative Example 9 was applied to this epoxy coating layer, and the adhesive strength was measured. The amount of the epoxy coating layer applied was an amount equivalent to 0.53 parts by mass in the formulation shown in Table 5. The measurement results are shown in Table 5.

[0128] [Table 4]

[0129] [Table 5]

[0130] The column [(B) / (A)] x 100 in Tables 4 and 5 shows the amount (parts by mass) of polyisocyanate blended relative to 100 parts by mass of aliphatic polyester polyol. The column [(C) / (A)] x 100 in Tables 4 and 5 shows the amount (parts by mass) of epoxy compound blended relative to 100 parts by mass of aliphatic polyester polyol. The column "Epoxy group / Isocyanate group" in Tables 4 and 5 shows the molar ratio of epoxy groups contained in epoxy compound (C) to isocyanate groups contained in polyisocyanate (B).

[0131] As shown in Tables 4 and 5, the laminates of Reference Examples 1 to 7, in which an adhesive layer containing an epoxy compound was bonded to a printed surface, were confirmed to have higher adhesive strength than the laminate of Comparative Example 9, in which an adhesive layer not containing an epoxy compound was bonded to a printed surface. Comparative Example 10 achieved relatively high adhesive strength, but the number of steps increased because an epoxy coating layer was formed in addition to the adhesive layer. It took two days for the epoxy coating layer to harden (age), reducing productivity.

[0132] In the laminate of Comparative Example 9, peeling occurred near the interface between the electrostatic ink layer and the primer layer. In the laminate of Comparative Example 10, the electrostatic ink layer underwent cohesive failure. On the other hand, in the laminates of Reference Examples 1 to 7, peeling occurred at the interface between the electrostatic ink layer and the adhesive layer, and no cohesive failure of the electrostatic ink layer was observed. This suggests that the cohesive force of the electrostatic ink layer was improved. In Reference Examples 1 to 7, the molar ratio of isocyanate groups contained in the polyisocyanate (B) to hydroxyl groups of the aliphatic polyester polyol (A) was within the range of 0.5 to 10.

[0133] Next, the adhesive strength, hot water adhesive strength, and seal strength of the laminates of Reference Example 5 and Comparative Example 10 were measured. For the measurements, samples with a total ink coverage of 500% and 200% were used. Details of the measurement procedure are as follows.

[0134] [Measurement of hot water adhesive strength] The laminates of Reference Example 5 and Comparative Example 10 were each cut to a width of 15 mm to obtain a measurement sample. After peeling between the layers at the edge of the measurement sample, the sample was immersed in hot water at 90°C and the peel strength was measured using a tensile tester. Specifically, the peel angle was free and the tensile speed was 300 mm / min. This peel strength is shown in Table 6 as the hot water adhesion strength.

[0135] [Measurement of seal strength (before heat treatment)] Using a pair of laminates from Reference Example 5, the unstretched polypropylene films were overlapped and heat-sealed to form a sealed portion. This resulted in heat welding of the unstretched polypropylene films to each other, producing a 15 mm wide measurement sample. The seal strength of the sealed portion of the produced measurement sample was measured in accordance with JIS K 7127:1999. The peel strength between the heat seals was measured using a tensile tester under the following conditions: a peel angle of 90°, a tensile speed of 300 mm / min, and room temperature (20°C). This peel strength was defined as the seal strength "before heat treatment." The measurement results are shown in Table 6. A similar measurement sample was produced using the laminate from Comparative Example 10, and similar measurements were performed. The measurement results are shown in Table 6.

[0136] [Seal strength measurement (after boiling)] The measurement samples prepared in the above "Measurement of seal strength (before heat treatment)" were heated in water at 100°C for 30 minutes. Thereafter, the seal strength was measured using the same procedure as in the above "Measurement of seal strength (without heat treatment)". The measurement results are shown in the "After boiling" column in Table 6.

[0137] [Measurement of seal strength after retort (120℃)] The measurement samples prepared in the above "Measurement of seal strength (before heat treatment)" were subjected to retort heat treatment (120°C x 30 minutes). Peel strength was measured using a tensile tester in the same manner as in "Measurement of seal strength (before heat treatment)". The measurement results are shown in the "120°C x 30 minutes" column in Table 6.

[0138] [Measurement of seal strength after retort (130℃)] The measurement samples prepared in the above "Measurement of seal strength (before heat treatment)" were subjected to retort heat treatment (130°C x 30 minutes). Peel strength was measured using a tensile tester in the same manner as in "Measurement of seal strength (without heat treatment)". The measurement results are shown in the "130°C x 30 minutes" column in Table 6.

[0139] [Table 6]

[0140] As shown in Table 6, the hot water adhesive strength of Reference Example 5 was significantly higher than that of Comparative Example 10. It was also confirmed that Reference Example 5 had better seal strength than Comparative Example 10. In particular, the seal strength of Reference Example 5 was sufficiently high even after boiling, whereas the seal strength of Comparative Example 10 decreased significantly after boiling. It was confirmed that the adhesive strength and seal strength of the laminate of Comparative Example 10 decreased significantly when heated in the presence of moisture.

[0141] (Reference example 8) [Preparation of adhesive composition and laminate] A polyethylene terephthalate film (PET film, thickness: 12 μm) was prepared as a substrate film. The same aqueous primer resin as in Example 1 was applied to one side of this PET film to form a primer layer. The amount of aqueous polyethyleneimine applied was also the same as in Example 1.

[0142] Using the digital printing machine used in Example 1, a predetermined printing was performed on the surface of the primer layer. The colors of the electrostatic ink composition used were white (W), yellow (Y), magenta (M), and cyan (C). Two ink coverage ratios were prepared: one with W 200% and the other with C 100% + M 100% + Y 100% + W 200%. In Table 7, the former is referred to as "ink coverage ratio (1)," and the latter is referred to as "ink coverage ratio (2)." In this way, two types of samples with different ink coverage ratios of the electrostatic ink composition were prepared.

[0143] The same adhesive composition as in Example 1 was prepared, and the adhesive composition was applied to the printed surface in the same manner as in Example 1 to form an adhesive layer. The amount of adhesive composition applied was 4.0 g / m 2 It was decided.

[0144] The laminated film used in Example 1 (a laminated film obtained by laminating a nylon film and an unstretched polypropylene film with a commercially available adhesive) was attached to the adhesive layer of the base film to obtain a laminate in the same manner as in Example 1. The curing time (aging) was 40°C for 2 days.

[0145] The seal strength (before heat treatment) and seal strength (after boiling) of the laminate thus obtained were measured. The measurement results are shown in Table 7. In addition, the adhesive strength (before heat treatment) and hot adhesive strength (120°C) were measured by the following procedure.

[0146] A pair of laminates from Reference Example 8 was used to heat-seal the unstretched polypropylene films so that they overlapped each other, producing a three-sided bag with a sealed section. Water was then sealed into the three-sided bag. A retort heat treatment (120°C x 30 minutes) was then performed using a retort treatment device (manufactured by Hisaka Works, Ltd.). After the retort heat treatment, the bag was cut into a 15 mm width to obtain a sample of the sealed section, and the interlayer strength between the electrostatic ink layer and the layer in contact with the electrostatic ink layer was measured. The measured peel strength is shown in the "Hot adhesive strength (120°C)" column in Table 7. Table 7 also shows the adhesive strength before the retort heat treatment.

[0147] (Reference examples 9~12) A laminate was produced in the same manner as in Reference Example 8, except that when preparing the adhesive composition, the amount of polyisocyanate (B) was changed as shown in Table 7. The produced laminate was evaluated in the same manner as in Reference Example 8. The evaluation results are shown in Table 7.

[0148] (Comparative Example 11) A laminate was produced in the same manner as in Comparative Example 9, except that lamination of the printed surface with the electrostatic ink composition was performed using a hand laminator instead of a dry laminator. The color and ink coverage of the electrostatic ink composition were as shown in Table 7. The produced laminate was evaluated in the same manner as in Reference Example 8. The evaluation results are shown in Table 7.

[0149] [Table 7]

[0150] As shown in Table 7, it was confirmed that high adhesive strength and seal strength were obtained in each Reference Example even under heated conditions. It was also confirmed that the hot adhesive strength (120°C) and seal strength (before heat treatment and after boiling) could be sufficiently increased by adjusting the blending ratio of polyisocyanate (B) to aliphatic polyester polyol (A). On the other hand, it was confirmed that in Comparative Example 11, which did not use epoxy compound (C), the adhesive strength and seal strength were significantly reduced when exposed to high-temperature hot water treatment conditions. In Reference Examples 8 to 12, the molar ratio of isocyanate groups contained in polyisocyanate (B) to hydroxyl groups contained in aliphatic polyester polyol (A) was within the range of 0.5 to 10.

[0151] (Reference examples 13~17) An adhesive composition was prepared by blending an aliphatic polyester polyol (A1) (Takelac A525, manufactured by Mitsui Chemicals, Inc.), a polyisocyanate (B1) (Takenate A52, manufactured by Mitsui Chemicals, Inc.), and 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate as the epoxy compound (C). The blending ratios were as shown in Table 8. Laminates were produced and evaluated in the same manner as in Reference Examples 8 to 12, except that such adhesive compositions were used. The evaluation results were as shown in Table 8.

[0152] (Comparative Example 12) An adhesive composition was prepared by blending an aliphatic polyester polyol (A1) (Takelac A525, manufactured by Mitsui Chemicals, Inc.) as the polyol and a polyisocyanate (B1) (Takenate A52, manufactured by Mitsui Chemicals, Inc.) in the blending ratios shown in Table 8. A laminate was produced and evaluated in the same manner as in Comparative Example 11, except that such an adhesive composition was used. The evaluation results are shown in Table 8.

[0153] [Table 8]

[0154] As shown in Table 8, it was confirmed that high adhesive strength and seal strength were obtained in each Reference Example even when the combination of aliphatic polyester polyol and polyisocyanate was changed. It was also confirmed that the hot adhesive strength (120°C) and seal strength (without heat treatment and after boiling) could be sufficiently increased by adjusting the blending ratio of polyisocyanate (B1) to aliphatic polyester polyol (A1). On the other hand, it was confirmed that in Comparative Example 12, which did not use epoxy compound (C), the adhesive strength and seal strength were significantly reduced when exposed to high-temperature hot water treatment conditions. In Reference Examples 13 to 17, the molar ratio of isocyanate groups contained in polyisocyanate (B1) to hydroxyl groups contained in aliphatic polyester polyol (A1) was within the range of 0.5 to 10. [Industrial Applicability]

[0155] According to the present disclosure, it is possible to provide a laminate that has a surface printed by a digital printer but is capable of sufficiently suppressing discoloration that occurs during heat sealing. It is also possible to provide a packaging bag and a package that have a surface printed by a digital printer but are sufficiently suppressed from discoloration. [Explanation of symbols]

[0156] 10...base film, 20...sealant film, 30...adhesive layer, 40...primer layer, 50, 51...electrostatic ink layer, 52...printed surface, 53...halftone dot, 55...discoloration point, 100...packaging bag, 101...seal portion, 102...storage portion, 110...packaging bag, 120...opening means, 121...half-cut line, 124...easy-open processing portion, 200...packaging body, 300, 310...laminate, 300A...surface.

Claims

1. A laminate comprising a substrate film, an adhesive layer, and a sealant film in this order, and a printed surface of an electrostatic ink composition adhered to the substrate film side of the adhesive layer, the adhesive layer is composed of at least one of an adhesive composition containing an aliphatic polyester polyol, a polyisocyanate, and a bifunctional alicyclic epoxy compound having epoxy groups at both ends and a molecular weight of 500 or less, and a cured product thereof; A laminate in which the color difference (ΔE) calculated by the following formula (A) on the heat-sealed printed surface, which has a coverage rate of 50 area% or more with an electrostatic ink layer composed of the electrostatic ink composition, is less than 3.0 before and after the sealant film on the heat-sealed printed surface is heated and pressurized under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds. [Equation 1] [In the above formula (A), ΔL ＊ indicates the difference in brightness before and after heating and pressing under the heat sealing conditions, and Δa ＊ and Δb ＊ indicates the difference in color before and after heating and pressing under the heat sealing conditions.]

2. The number of discoloration points having a size of 20 μm or more that are generated on the printed surface by heating and pressing under the heat sealing conditions is 1 mm ２ The laminate of claim 1, wherein the number of particles is 10 or less per one particle.

3. A laminate comprising a substrate film, an adhesive layer, and a sealant film in this order, and a printed surface of an electrostatic ink composition adhered to the substrate film side of the adhesive layer, the adhesive layer is composed of at least one of an adhesive composition containing an aliphatic polyester polyol, a polyisocyanate, and a bifunctional alicyclic epoxy compound having epoxy groups at both ends and a molecular weight of 500 or more, and a cured product thereof; When the sealant film on the printed surface, which has a coverage rate of 50 area % or more with an electrostatic ink layer constituted by the electrostatic ink composition, is heated and pressurized under heat sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds, the number of discoloration points having a size of 20 μm or more that occur on the heat-sealed printed surface is 1 mm ２ 10 or less per stack.

4. The laminate according to any one of claims 1 to 3, wherein a molar ratio of epoxy groups contained in the alicyclic epoxy compound to isocyanate groups contained in the polyisocyanate is 0.5 to 10.

5. A laminate described in any one of claims 1 to 4, wherein the alicyclic epoxy compound has penetrated into the electrostatic ink layer, crosslinking the electrostatic ink composition.

6. The laminate according to any one of claims 1 to 5, wherein the polyisocyanate comprises a xylylene diisocyanate derivative.

7. A packaging bag formed by heat-sealing the sealant films in the laminate according to any one of claims 1 to 6.

8. A package comprising the packaging bag according to claim 7 and an item to be packaged in the packaging bag.

9. a step of printing an electrostatic ink composition on one side of a substrate film to obtain a printed surface; and a step of adhering the printed surface and a substrate including a sealant film using an adhesive composition including an aliphatic polyester polyol, a polyisocyanate, and a bifunctional alicyclic epoxy compound having epoxy groups at both ends and a molecular weight of 500 or more to obtain a laminate, A method for producing a laminate, wherein the color difference (ΔE) calculated by the following formula (A) on the heat-sealed printed surface, which has a coverage rate of 50 area % or more with an electrostatic ink layer composed of the electrostatic ink composition, is less than 3.0 before and after the sealant film on the heat-sealed printed surface is heated and pressurized under heat-sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds. [Equation 2] [In the above formula (A), ΔL ＊ indicates the difference in brightness before and after heating and pressing under the heat sealing conditions, and Δa ＊ and Δb ＊ indicates the difference in color before and after heating and pressing under the heat sealing conditions.]

10. a step of printing an electrostatic ink composition on one side of a substrate film to obtain a printed surface; and a step of adhering the printed surface and a substrate including a sealant film using an adhesive composition including an aliphatic polyester polyol, a polyisocyanate, and a bifunctional alicyclic epoxy compound having epoxy groups at both ends and a molecular weight of 500 or more to obtain a laminate, When the sealant film on the printed surface, which has a coverage ratio of 50 area % or more with an electrostatic ink layer constituted by the electrostatic ink composition, is heated and pressurized under heat sealing conditions of a temperature of 220°C, a pressure of 0.2 MPa, and a time of 1.5 seconds, the number of discoloration points having a size of 20 μm or more that occur on the heat-sealed printed surface is 1 mm ２ A method for manufacturing a laminate, wherein the number of particles per unit area is 10 or less.

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