Microwave packaging

Abstract

To provide a packaging material for a microwave oven, which can maintain decoration with metallic luster of high glossiness even after a heat sterilization treatment and, moreover, does not generate a spark when heated in a microwave oven.SOLUTION: The packaging material 1 for a microwave oven of the present invention comprises a laminate film having a substrate film 10 and a sealant film 11, with a metal-deposited film 15, formed of tin or indium, arranged between the sealant film and the substrate film, where a total light transmittance of the metal-deposited metal film is 28.0% to 76.0% after a heat sterilization treatment, and luster by the metal-deposited metal film is visually recognized through the substrate film.SELECTED DRAWING: Figure 1

Description

[[Technical Field]]

[0001] The present invention relates to a packaging material for microwave ovens that is decorated with metallic luster. [[Background Art]]

[0002] In packaging materials, decoration with high-brightness metallic luster is sometimes applied to create a sense of luxury and gorgeousness for the packaged goods. As such a decoration method, it is common practice to form a deposited metal film of aluminum or other metals. However, when a deposited metal film of aluminum or other metals is formed on a packaging material for microwave ovens, sparks are generated by microwave irradiation during heating in the microwave oven, which may cause accidents such as failure of the microwave oven or fire. For this reason, packaging materials having a deposited metal film of aluminum or other metals cannot practically be used as packaging materials for microwave ovens.

[0003] In order to solve such problems, a packaging material for microwave ovens provided with decoration having metallic luster by forming a glossy print layer containing specific metal scales has been proposed (see Patent Document 1). However, such packaging materials for microwave ovens have a problem that sufficient specular reflection cannot be obtained in the glossy print layer, and therefore it is difficult to provide decoration with metallic luster of high glossiness.

[0004] On the other hand, as a packaging material suitable for microwave ovens and having light-shielding properties and gas barrier properties, there has been proposed a packaging material obtained by sequentially laminating a base film, a transparent ceramic deposited layer, a transparent coat layer, an information display printing layer, a white ink layer, an insulating deposited layer made of tin, and a sealant layer (see Patent Document 2). According to this packaging material, no sparks are generated even when the insulating deposited layer made of tin is irradiated with microwaves, and therefore, accidents such as microwave oven failure or fire caused by sparks can be prevented when heating with a microwave oven. However, in such packaging materials, a light-shielding white ink layer is formed between the base film and the insulating vapor-deposited layer made of tin. Therefore, the gloss from the insulating vapor-deposited layer cannot be used as decoration, and consequently, it is difficult to apply decoration with a highly glossy metallic sheen. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-51992 [Patent Document 2] Japanese Patent Publication No. 2003-340965 [Overview of the project] [Problems that the invention aims to solve]

[0006] To solve the above-mentioned problems, the inventors have proposed a microwave-safe packaging material having a metallic luster that gives the packaging material a glossy appearance, by forming a metal vapor-deposited film of tin or indium on the outer surface that is visible from the outside (Japanese Patent Application No. 2021-72986). However, we discovered a new problem: when pouches using this type of microwave-safe packaging material are filled and sealed, and then subjected to heat sterilization treatment such as boiling or retort processing, the metal vapor-deposited film may become transparent, making it impossible to maintain the desired metallic luster.

[0007] The present invention has been made based on the circumstances described above, and its purpose is to provide a microwave-safe packaging material that can maintain a highly glossy metallic luster even after heat sterilization, and moreover, does not generate sparks when heated in a microwave oven. [Means for solving the problem]

[0008] The microwave packaging material of the present invention consists of a laminated film having a base film and a sealant film. A metal vapor-deposited film made of tin or indium is provided between the sealant film and the substrate film. The total light transmittance of the metal vapor-deposited film is, Boil at 100°C for 90 minutes. After heat sterilization treatment 56.1% or more It is 76.0% or less. The gloss of the metal vapor-deposited film is characterized in that it is visible through the substrate film.

[0009] In the microwave packaging material of the present invention, the light transmittance of the metal vapor-deposited film at wavelengths of 330 nm to 340 nm after heat sterilization treatment by boiling at 100°C for 90 minutes is 55.3% or more It is preferable that the percentage be 60.1% or less.

[0010] The microwave packaging material of the present invention consists of a laminated film having a base film and a sealant film. A metal vapor-deposited film made of tin or indium is provided between the sealant film and the substrate film. The total light transmittance of the metal vapor-deposited film is, 18.8% or more It is 22.8% or less. The gloss of the metal vapor-deposited film is characterized in that it is visible through the substrate film.

[0011] In the microwave packaging material of the present invention, the light transmittance of the metal vapor-deposited film at wavelengths of 330 nm to 340 nm is 17.0% It is preferable that the percentage is 27.1% or less.

[0012] In the microwave packaging material of the present invention, an information display printing layer is provided between the base film and the metal vapor deposition film. The information display printing layer may have a transparent layer portion formed by transparent ink.

[0013] In the microwave packaging material of the present invention, it is preferable that the transparent layer portion is formed of transparent yellow ink. Furthermore, the yellow pigment contained in the transparent yellow ink is an insoluble azo pigment. and Condensed azo pigments at least one of theit is preferable.

[0015] Further, in the microwave packaging material of the present invention, it is preferable that an intermediate resin layer is provided between the base film and the sealant film, and the metal vapor deposition film is formed on the intermediate resin layer. Further, it is preferable that the metal vapor deposition film is formed on a surface of the intermediate resin layer on the base film side. Further, it is preferable that the intermediate resin layer has transparency, and the metal vapor deposition film is formed on a surface of the intermediate resin layer on the sealant film side.

[0016] Further, it is preferable that an opaque print layer is formed between the sealant film and the metal vapor deposition film. Further, Between the substrate film and the metal vapor-deposited film, there is an information display printing layer, and the information display printing layer has a transparent layer portion formed of transparent ink. an opaque print layer is formed on a surface of the intermediate resin layer on the sealant film side, and the information display print layer is formed on a surface of the metal vapor deposition film on the base film side, it is preferable that an adhesive layer is respectively formed between the information display print layer and the base film, and between the opaque print layer and the sealant film. Further, Between the substrate film and the metal vapor-deposited film, there is an information display printing layer, and the information display printing layer has a transparent layer portion formed of transparent ink. an opaque print layer is formed on a surface of the metal vapor deposition film on the sealant film side, and the information display print layer is formed on a surface of the intermediate resin layer on the base film side, it is preferable that an adhesive layer is respectively formed between the information display print layer and the base film, and between the opaque print layer and the sealant film. Effects of the Invention

[0017] According to the present invention, a metal vapor deposition film is formed between a sealant film and a base film, and the gloss of the metal vapor deposition film is visible from the outer surface through the base film, so decoration with high-gloss metallic luster can be provided. Furthermore, since the total light transmittance of the metal vapor deposition film after heat sterilization treatment is 76.0% or less, the abundance of defective portions in the metal vapor deposition film is sufficiently low, which suppresses the transparency of the metal vapor deposition film caused by steam attacking the defective portions during heat sterilization treatment. In addition, since the total light transmittance is 28.0% or more, the metal vapor deposition film can obtain a glossiness with sufficient specular reflection and exhibit the desired metallic luster. Therefore, even after heat sterilization treatments such as boiling and retorting, the decoration with the desired metallic luster can be maintained. Further, since the metal vapor deposition film is made of tin or indium, no spark is generated when heated in a microwave oven, and thus a packaging material for microwave ovens that is suitable for use in microwave ovens can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] [Figure 1] It is an explanatory cross-sectional view showing the configuration of the packaging material for microwave ovens according to the first embodiment of the present invention. [Figure 2] It is an explanatory cross-sectional view showing the configuration of the packaging material for microwave ovens according to the second embodiment of the present invention. [Figure 3] It is an explanatory cross-sectional view showing the configuration of the packaging material for microwave ovens according to the third embodiment of the present invention. [Figure 4] It is an explanatory cross-sectional view showing the configuration of the packaging material for microwave ovens according to the fourth embodiment of the present invention. [Figure 5] It is an explanatory cross-sectional view showing the configuration of the packaging material for microwave ovens according to the fifth embodiment of the present invention. [Figure 6] It is an explanatory cross-sectional view showing an example of the manufacturing process of the packaging material for microwave ovens according to the fifth embodiment of the present invention. [Figure 7] It is an explanatory cross-sectional view showing the configuration of the packaging material for microwave ovens according to the sixth embodiment of the present invention. [Figure 8]This is an explanatory cross-sectional view showing an example of the manufacturing process for microwave packaging material according to the sixth embodiment of the present invention. [Modes for carrying out the invention]

[0019] The embodiments of the microwave packaging material of the present invention will be described in detail below. [First Embodiment] Figure 1 is an explanatory cross-sectional view showing the configuration of a microwave oven packaging material according to a first embodiment of the present invention. This microwave oven packaging material 1 is composed of a laminated film having a base film 10 and a sealant film 11.

[0020] An intermediate resin layer 16 is interposed between the base film 10 and the sealant film 11. A metal vapor-deposited film 15 is integrally formed by vapor deposition of metal onto the surface of the intermediate resin layer 16 facing the base film 10, thereby positioning the metal vapor-deposited film 15 between the base film 10 and the intermediate resin layer 16. Furthermore, an information display printing layer 12, which constitutes the decoration of the microwave packaging material 1, is formed between the base film 10 and the metal vapor-deposited film 15. This information display printing layer 12 has a transparent layer portion 13 made of transparent ink and an opaque layer portion 14 made of achromatic ink such as white or black, or chromatic opaque ink. The information display printing layer 12 is integrally formed by printing on the back surface of the base film 10 with transparent ink and opaque ink. The gloss of the metal vapor-deposited film 15 is visible from the outside (upper side in Figure 1) through the transparent layer portion 13 of the transparent ink of the information display printing layer 12 and the base film 10. The area of ​​the metal vapor-deposited film 15 covering the opaque layer portion 14 of the information display printing layer 12 is not visible from the outside.

[0021] Furthermore, the information display printing layer 12 and the metal vapor deposition film 15 are integrally bonded by an adhesive layer 17, and the sealant film 11 and the intermediate resin layer 16 are integrally bonded by an adhesive layer 18.

[0022] Since the base film 10 is usually the basic material for packaging materials, it is preferable that it is made of a synthetic resin that has excellent mechanical, physical, chemical, and other properties, and is particularly strong, tough, and heat resistant. Specific examples of the base film 10 include resin films made of tough resins such as polyester resins, polyamide resins, polyaramid resins, polyolefin resins such as polyethylene or polypropylene, polystyrene resins, polyacrylic or methacrylic resins, polycarbonate resins, polyacetal resins, fluororesins, polyacrylonitrile resins, polyvinyl alcohol resins, and others. Among these, resin films such as polyester resins like polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), and polyamide resins (Ny) are preferred. Alternatively, co-extruded films with layer configurations such as PET / Ny, PET / Ny / PET, PET / Ny / PBT, PET / PBT / PET, PBT / Ny, and PBT / Ny / PBT may also be used.

[0023] Furthermore, the above-mentioned resin film can be used as a base film 10 either in its unstretched state or after being uniaxially or biaxially stretched. Furthermore, the base film 10 can be a single layer of the above-mentioned resin film, or two or more layers of the same film can be used. Furthermore, the thickness of the base film 10 varies depending on the material of the base film 10 and the required strength, but is usually 1 to 70 μm, preferably 9 to 25 μm.

[0024] As the sealant film 11, a resin can be used that does not affect the contents and can melt and fuse with each other by heat. Specific examples of resins constituting the sealant film 11 include polyolefin resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, and ethylene-propylene copolymer.

[0025] As the sealant film 11, a film made of the above-mentioned resin can be used as a single layer, or by laminating two or more types of films. The thickness of the sealant film 11 is not particularly limited as long as the required strength is obtained, but is usually 20 to 200 μm, preferably 30 to 150 μm.

[0026] The hue of the transparent ink forming the transparent layer portion 13 in the information display printing layer 12 is selected according to the desired metallic luster color for the decoration. For example, if the desired color for the decoration is gold, transparent yellow ink is used, and if the desired color for the decoration is silver, transparent colorless ink is used.

[0027] When using transparent yellow ink, the yellow pigments contained in the transparent yellow ink include soluble azo pigments, insoluble azo pigments (monoazo yellow, disazo yellow), condensed azo pigments, and polycyclic pigments. Among these, insoluble azo pigments and condensed azo pigments are preferred because they have high resistance and can be used to create decorations that approximate the hue of gold.

[0028] In each of the transparent and opaque inks forming the information display printing layer 12, urethane-based, acrylic-based, nitrocellulose-based, rubber-based, vinyl chloride-based, and the like can be used as the binder resin. In addition, each of the transparent and opaque inks may contain additives such as plasticizers, desiccants, and stabilizers, in addition to various pigments and binder resins.

[0029] As a printing method for forming the information display printing layer 12, well-known printing methods such as offset printing, gravure printing, and screen printing can be used. Furthermore, the thickness of the information display printing layer 12 is typically 0.5 to 5 μm, preferably 1 to 3 μm.

[0030] The resin constituting the intermediate resin layer 16 is not particularly limited, but a resin having excellent mechanical, physical, chemical, and other properties is preferred, and in particular, a resin that is strong, tough, and heat resistant is preferred. Specific examples of such resins include polyamide resins, polyester resins, polyaramid resins, polyolefin resins such as polyethylene or polypropylene, polystyrene resins, polyacrylic or methacrylic resins, polycarbonate resins, polyacetal resins, fluorine resins, polyacrylonitrile resins, and polyvinyl alcohol resins. Among these, polyester resins such as polyamide resins, polyethylene terephthalate (PET), and polybutylene terephthalate (PBT) are preferred. The thickness of the intermediate resin layer 16 is typically 1 to 70 μm, preferably 9 to 25 μm.

[0031] The metal vapor-deposited film 15 is composed of tin or indium. The thickness of the metal vapor-deposited film 15 is, for example, 5 to 80 nm, preferably 10 to 60 nm. If the thickness of the metal vapor-deposited film 15 is too small, it may be difficult to apply a highly glossy metallic luster decoration. On the other hand, if the thickness of the metal vapor-deposited film 15 is too large, sparks may be generated when heated in a microwave oven due to the irradiation of microwaves. Furthermore, the surface resistivity of the metal vapor-deposited film 15 is 3-8 × 10⁻⁶. 12 It is preferable that the ratio is Ω / □, and more preferably 30 to 6 × 10 12 It is Ω / □.

[0032] Furthermore, the metal vapor-deposited film 15 preferably has a total light transmittance of 28.0% to 76.0% after heat sterilization treatment such as boiling or retorting, more preferably 30% to 60%, and particularly preferably 35% to 50%. The lower the total light transmittance of the metal vapor-deposited film 15, i.e., the greater its thickness, the lower the degree of defects in the metal vapor-deposited film 15 can be, thus preventing the metal vapor-deposited film 15 from becoming transparent due to heat sterilization. However, if the total light transmittance is excessively low, the surface becomes predominantly diffuse reflection rather than specular reflection, resulting in a loss of metallic luster and a dull, whitish appearance. In the present invention, by keeping the total light transmittance of the metal vapor-deposited film 15 within the above range after heat sterilization, the transparency of the metal vapor-deposited film 15 is suppressed and the desired metallic luster can be achieved, thus maintaining the desired metallic luster even after heat sterilization. If the total light transmittance of the metal vapor-deposited film 15 after heat sterilization exceeds 76.0%, the metal vapor-deposited film 15 will not have sufficient thickness, resulting in many defects. When steam from the heat sterilization process attacks these defects, the metal vapor-deposited film 15 becomes transparent, making it difficult to apply the desired metallic luster decoration. Furthermore, if the total light transmittance is less than 28.0%, the metal vapor-deposited film 15 is too thick, and sufficient specular reflection cannot be obtained, making it impossible to achieve a metallic luster decoration with a lustrous appearance. In addition, when heated in a microwave oven, microwave irradiation may cause welding, and if the total light transmittance is extremely low, sparks may be generated when heated in a microwave oven.

[0033] Heat sterilization treatment includes, but is not limited to, retort processing which enables distribution at room temperature, and heat treatment at 120°C for less than 4 minutes which enables chilled distribution, and refers to various known heat sterilization treatments. Retort processing refers to pressurized heating treatment. For example, it involves heating a product filled in a heat-resistant container with steam or hot water at around 110°C to 130°C for several tens of minutes while pressurizing the product to prevent the container from being damaged by the internal pressure of the product as the temperature rises, so that the F0 value is 3.1 or higher, which is equivalent to at least 120°C for 4 minutes. Chilled heat sterilization, on the other hand, refers to heat treatments such as boiling at 90°C for 10 minutes or more, which is commonly used.

[0034] The total light transmittance of the metal vapor-deposited film 15 after heat sterilization is the same as the total light transmittance of the intermediate resin layer 16 on which the metal vapor-deposited film 15 is integrally formed. The intermediate resin layer 16 on which the metal vapor-deposited film 15 is integrally formed can be obtained by removing other unnecessary films from the microwave packaging material 1 after heat sterilization. The total light transmittance of the intermediate resin layer 16 is approximately 88-90%, and the total light transmittance does not change within the range of the type and thickness of the intermediate resin layer 16 as described above. Here, the total light transmittance of the intermediate resin layer 16 on which the metal vapor-deposited film 15 is integrally formed was measured in accordance with JIS K7361-1.

[0035] Furthermore, the metal vapor-deposited film 15 preferably has a light transmittance of 330 nm to 340 nm (hereinafter also referred to as "ultraviolet transmittance") of 34.0% to 60.1% after heat sterilization treatment such as boiling or retort processing, more preferably 37.0% to 55.0%, and particularly preferably 40.0% to 54.0%. Since the ultraviolet transmittance of the metal vapor-deposited film 15 after heat sterilization is within the above range, the transparency of the metal vapor-deposited film 15 is suppressed and the desired metallic luster can be exhibited. Therefore, even if heat sterilization treatment such as boiling or retort processing is performed, the desired metallic luster decoration can be maintained. If the ultraviolet transmittance of the metal vapor-deposited film 15 after heat sterilization exceeds 60.1%, the metal vapor-deposited film 15 will not have sufficient thickness, resulting in many defects. As a result of the steam from the heat sterilization process attacking these defects, the metal vapor-deposited film 15 may become transparent, making it difficult to apply the desired metallic luster decoration. Furthermore, if the ultraviolet transmittance is less than 34.0%, the thickness of the metal vapor-deposited film 15 is too large, and sufficient specular reflection cannot be obtained, making it impossible to achieve a metallic luster decoration with a lustrous appearance. In addition, when heated in a microwave oven, welding may occur due to irradiation with microwaves, and if the ultraviolet transmittance is extremely low, sparks may be generated when heated in a microwave oven.

[0036] The ultraviolet transmittance of the metal vapor-deposited film 15 after heat sterilization is the same as the ultraviolet transmittance of the intermediate resin layer 16 on which the metal vapor-deposited film 15 is integrally formed. Note that the ultraviolet transmittance remains unchanged within the range of the type and thickness of the intermediate resin layer 16 described above. Here, the ultraviolet transmittance of the intermediate resin layer 16 on which the metal vapor-deposited film 15 is integrally formed was calculated by measuring the light transmission of the intermediate resin layer 16 on which the metal vapor-deposited film 15 is integrated using a UV-Vis-Infrared spectrophotometer "V-770" (manufactured by JASCO Corporation) with a measurement interval of 1 nm, and averaging the data obtained at each point.

[0037] Furthermore, the metal vapor-deposited film 15 preferably has an unheated total light transmittance of 7.7% to 22.8%, more preferably 10.0% to 20.0%, and particularly preferably 12.0% to 18.0%. Since the total light transmittance of the metal vapor-deposited film 15 that has not undergone heat sterilization treatment is within the above range, the transparency of the metal vapor-deposited film 15 is suppressed and the desired metallic luster can be exhibited. Therefore, even when heat sterilization treatment such as boiling or retort treatment is performed, the desired metallic luster decoration can be maintained. If the total light transmittance of the metal vapor-deposited film 15 that has not undergone heat sterilization treatment exceeds 22.8%, the metal vapor-deposited film 15 will not have sufficient thickness and will have many defects. When heat sterilization treatment is performed, the steam from the heat sterilization treatment will attack these defects, which may result in the metal vapor-deposited film 15 becoming transparent, making it difficult to maintain the desired metallic luster decoration. Furthermore, if the total light transmittance is less than 7.7%, the thickness of the metal vapor-deposited film 15 is too large, and sufficient specular reflection cannot be obtained from the metal vapor-deposited film 15, making it impossible to achieve a metallic luster decoration with a lustrous appearance. In addition, when heated in a microwave oven, welding may occur due to irradiation with microwaves, and if the ultraviolet transmittance is extremely low, sparks may be generated when heated in a microwave oven.

[0038] The total light transmittance of the metal vapor-deposited film 15 that has not undergone heat sterilization treatment can be measured in the same manner as the method for measuring the total light transmittance of the metal vapor-deposited film 15 after heat sterilization treatment, except that the target is the microwave oven packaging material 1 before heat sterilization treatment.

[0039] Furthermore, the metal vapor-deposited film 15, before heat sterilization, preferably has a light transmittance (ultraviolet transmittance) of 10.5% to 27.1% at wavelengths of 330 nm to 340 nm, more preferably 11.0% to 18.0%, and particularly preferably 12.0% to 16.0%. Since the ultraviolet transmittance of the metal vapor-deposited film 15 that has not undergone heat sterilization treatment is within the above range, the transparency of the metal vapor-deposited film 15 is suppressed and the desired metallic luster can be exhibited. Therefore, even when heat sterilization treatment such as boiling or retort processing is performed, the desired metallic luster decoration can be maintained. If the ultraviolet transmittance of the metal vapor-deposited film 15 that has not undergone heat sterilization treatment exceeds 27.1%, the metal vapor-deposited film 15 will not have sufficient thickness, resulting in many defects. When heat sterilization treatment is applied, the steam from the heat sterilization treatment will attack these defects, potentially causing the metal vapor-deposited film 15 to become transparent, making it difficult to apply the desired metallic luster decoration. Furthermore, if the total light transmittance is less than 10.5%, the thickness of the metal vapor-deposited film 15 is too large, and sufficient specular reflection cannot be obtained, making it impossible to achieve a metallic luster decoration with a lustrous appearance. In addition, when heated in a microwave oven, welding may occur due to irradiation with microwaves, and if the ultraviolet transmittance is extremely low, sparks may be generated when heated in a microwave oven.

[0040] The ultraviolet transmittance of a metal vapor-deposited film that has not undergone heat sterilization treatment can be measured in the same manner as the measurement method for the ultraviolet transmittance of a metal vapor-deposited film 15 after heat sterilization treatment, except that the target is microwave packaging material 1 before heat sterilization treatment.

[0041] As a deposition method for forming the metal vapor-deposited film 15, physical deposition methods such as vacuum deposition, sputtering, and ion plating, or chemical deposition methods can be appropriately selected and used. As a heating method during deposition, resistance heating, induction heating, electron beam heating, etc., can be used. Furthermore, as a reaction gas, oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, etc. may be introduced, or reactive deposition using means such as ozone addition or ion assistance may be used.

[0042] As the adhesives constituting the adhesive layers 17 and 18, two-component curing urethane adhesives used in dry lamination, polyester urethane adhesives, polyester urethane adhesives, acrylic adhesives, polyester adhesives, polyamide adhesives, etc., can be used.

[0043] [Second Embodiment] Figure 2 is an explanatory cross-sectional view showing the configuration of a microwave oven packaging material according to a second embodiment of the present invention. In this microwave oven packaging material 1 according to the second embodiment, the metal vapor-deposited film 15 is integrally formed by vapor deposition of metal onto the surface of the intermediate resin layer 16 on the sealant film 11 side, thereby positioning the metal vapor-deposited film 15 between the sealant film 11 and the intermediate resin layer 16. The intermediate resin layer 16 is also made transparent. The other configurations of the microwave oven packaging material 1 according to the second embodiment are the same as those of the microwave oven packaging material 1 according to the first embodiment.

[0044] According to the microwave packaging material 1 of the first and second embodiments described above, a metal vapor-deposited film 15 is formed between the sealant film 11 and the information display printing layer 12. The gloss of this metal vapor-deposited film 15 is visible through the transparent layer portion 13 formed on the information display printing layer 12 and the base film 10, so that a highly glossy metallic luster can be applied as decoration. Moreover, since the metal vapor-deposited film 15 is made of tin or indium, no sparks are generated when heated in a microwave oven, and therefore, a microwave packaging material 1 suitable for microwave ovens is obtained.

[0045] [Third Embodiment] Figure 3 is an explanatory cross-sectional view showing the configuration of a microwave oven packaging material according to a third embodiment of the present invention. In this microwave oven packaging material 1 according to the third embodiment, an opaque printing layer 19 is formed between the sealant film 11 and the metal vapor-deposited film 15. Specifically, the metal vapor-deposited film 15 is formed on the surface of the intermediate resin layer 16 on the base film 10 side, the opaque printing layer 19 is formed on the surface of the intermediate resin layer 16 on the sealant film 11 side, and an adhesive layer 18 is formed between the opaque printing layer 19 and the sealant film 11. The other configurations of the microwave oven packaging material 1 according to the third embodiment are the same as those of the microwave oven packaging material 1 according to the first embodiment. As described above, the interposition of the opaque printing layer 19 between the sealant film 11 and the metal vapor-deposited film 15 prevents the contents of the microwave packaging material 1 from being visible from the outside when the bag is formed, and allows for the display of information from the information display printing layer 12 on the outer side of the metal vapor-deposited film 15 with high precision. In the absence of the opaque printing layer 19, the contents would be visible from the outside through the transparent layer portion 13 of the information display printing layer 12.

[0046] The opaque printing layer 19 is formed by printing opaque ink onto the surface of the intermediate resin layer 16 on the sealant film 11 side. The color of the opaque ink is not particularly limited, but it is preferable to use white ink, gray ink using white ink, etc. The opaque printing layer 19 can be, for example, a solid white printing layer. As a printing method for forming the opaque printing layer 19, well-known printing methods such as offset printing, gravure printing, and screen printing can be used. Furthermore, the thickness of the opaque printing layer 19 is typically 1 to 10 μm, preferably 1 to 3 μm.

[0047] [Fourth Embodiment] Figure 4 is an explanatory cross-sectional view showing the configuration of a microwave oven packaging material according to the fourth embodiment of the present invention. In this microwave oven packaging material 1 according to the fourth embodiment, an opaque printing layer 19 is formed between the sealant film 11 and the metal vapor-deposited film 15. Specifically, the metal vapor-deposited film 15 is formed on the surface of the intermediate resin layer 16 on the sealant film 11 side, and an opaque printing layer 19 similar to that of the microwave oven packaging material 1 according to the third embodiment is formed on the surface of the metal vapor-deposited film 15 on the sealant film 11 side, and an adhesive layer 18 is formed between the opaque printing layer 19 and the sealant film 11. The other configurations of the microwave oven packaging material 1 according to the fourth embodiment are the same as those of the microwave oven packaging material 1 according to the first embodiment.

[0048] According to the microwave packaging material 1 of the third and fourth embodiments described above, the same effects as the microwave packaging material 1 of the first and second embodiments can be obtained. Furthermore, since an opaque printing layer 19 is formed between the sealant film 11 and the metal vapor deposition film 15, it is possible to prevent the contents from being visible.

[0049] [Fifth Embodiment] Figure 5 is an explanatory cross-sectional view showing the configuration of a microwave oven packaging material according to a fifth embodiment of the present invention. In this microwave oven packaging material 1 according to the fifth embodiment, a metal vapor-deposited film 15 is formed on the surface of the intermediate resin layer 16 on the base film 10 side, and an information display printing layer 12 is formed on the surface of the metal vapor-deposited film 15 on the base film 10 side. On the other hand, an opaque printing layer 19 similar to that of the microwave oven packaging material 1 according to the third embodiment is formed on the surface of the intermediate resin layer 16 on the sealant film 11 side. Furthermore, the base film 10 and the information display printing layer 12 are integrally bonded by an adhesive layer 17, and the sealant film 11 and the opaque printing layer 19 are integrally bonded by an adhesive layer 18. The other configurations of the microwave oven packaging material 1 according to the fifth embodiment are the same as those of the microwave oven packaging material 1 according to the first embodiment.

[0050] The microwave packaging material 1 shown in Figure 5 can be manufactured as follows. First, as shown in Figure 6(a), a first intermediate 2 is produced by depositing tin or indium onto one surface of the intermediate resin layer 16, thereby forming a metal vapor-deposited film 15 on one surface of the intermediate resin layer 16. Next, by double-sided printing on the first intermediate 2 using a double-sided printing machine, as shown in Figure 6(b), an information display printing layer 12 consisting of a transparent layer portion 13 and an opaque layer portion 14 is formed on the surface of the metal vapor-deposited film 15, and an opaque printing layer 19 is formed on the other surface of the intermediate resin layer 16. This produces a second intermediate 3 in which the opaque printing layer 19, intermediate resin layer 16, metal vapor-deposited film 15, and information display printing layer 12 are laminated in this order. Then, for example, by a dry lamination method, a base film 10 is laminated onto the surface of the information display printing layer 12 in the second intermediate 3 via an adhesive layer 17, and a sealant film 11 is laminated onto the surface of the opaque printing layer 19 via an adhesive layer 18, thereby obtaining the microwave oven packaging material 1 shown in Figure 5.

[0051] [Sixth Embodiment] Figure 7 is an explanatory cross-sectional view showing the configuration of a microwave oven packaging material according to the sixth embodiment of the present invention. In this microwave oven packaging material 1 according to the sixth embodiment, a metal vapor-deposited film 15 is formed on the surface of the intermediate resin layer 16 on the sealant film 11 side, and an opaque printing layer 19, similar to that of the microwave oven packaging material 1 according to the third embodiment, is formed on the surface of the metal vapor-deposited film 15 on the sealant film 11 side. On the other hand, an information display printing layer 12 is formed on the surface of the intermediate resin layer 16 on the base film 10 side. Furthermore, the base film 10 and the information display printing layer 12 are integrally bonded by an adhesive layer 17, and the sealant film 11 and the opaque printing layer 19 are integrally bonded by an adhesive layer 18. The other configurations of the microwave oven packaging material 1 according to the sixth embodiment are the same as those of the microwave oven packaging material 1 according to the first embodiment.

[0052] The microwave packaging material 1 shown in Figure 7 can be manufactured as follows. First, as shown in Figure 8(a), a first intermediate 2 is prepared by depositing tin or indium onto one surface of the intermediate resin layer 16, thereby forming a metal vapor-deposited film 15 on one surface of the intermediate resin layer 16. Next, by double-sided printing on the first intermediate 2 using a double-sided printing machine, an opaque printing layer 19 is formed on the surface of the metal vapor-deposited film 15, as shown in Figure 8(b), and an information display printing layer 12 consisting of a transparent layer portion 13 and an opaque layer portion 14 is formed on the other surface of the intermediate resin layer 16. This prepares a second intermediate 3 in which the opaque printing layer 19, the metal vapor-deposited film 15, the intermediate resin layer 16, and the information display printing layer 12 are laminated in this order. Then, for example, by a dry lamination method, a base film 10 is laminated onto the surface of the information display printing layer 12 in the second intermediate 3 via an adhesive layer 17, and a sealant film 11 is laminated onto the surface of the opaque printing layer 19 via an adhesive layer 18, thereby obtaining the microwave oven packaging material 1 shown in Figure 7.

[0053] According to the microwave packaging material 1 of the fifth and sixth embodiments, the same effects as the microwave packaging material 1 of the third and fourth embodiments can be obtained. Furthermore, since both the information display printing layer 12 and the opaque printing layer 19 can be formed in a single process by using a double-sided printing machine, productivity can be improved. [Examples]

[0054] The present invention will be described below in the form of specific embodiments, but the present invention is not limited to these embodiments.

[0055] [Example 1 of microwave packaging material production] An intermediate laminated film was prepared by dry laminating a 12 μm thick polyethylene terephthalate film (base film) printed with transparent yellow ink (urethane-based gravure ink for reverse printing) by gravure printing, and a 12 μm thick tin-deposited polyethylene terephthalate film [A] (ester film manufactured by Toyobo Co., Ltd.) with tin deposited by vacuum deposition, using a polyurethane adhesive so that the transparent yellow ink side and the tin-deposited side overlap. Furthermore, a laminated film was prepared by dry laminating a 60 μm thick polypropylene film, which will serve as a sealant film, onto the surface of the tin-deposited polyethylene terephthalate film in this intermediate laminated film using a polyurethane adhesive and dry lamination method. The resulting laminated film was cured by storing it in a constant temperature chamber at 35°C for 5 days to obtain microwave packaging material [1]. The tin-coated polyethylene terephthalate film [A] has a total light transmittance of 26.4% and a light transmittance (ultraviolet light transmittance) of 30.6% at wavelengths of 330nm to 340nm before heat sterilization treatment. Furthermore, the total light transmittance of the single intermediate resin layer obtained by removing the tin-deposited film from the tin-deposited polyethylene terephthalate film [A] was 88%.

[0056] [Examples of microwaveable packaging materials 2-7] In Example 1 of the preparation of microwave packaging materials, microwave packaging materials [2] to [7] were obtained in the same manner, except that instead of tin-deposited polyethylene terephthalate film [A], tin-deposited polyethylene terephthalate films with different tin-deposited film thicknesses were used so that the total light transmittance and ultraviolet transmittance in an untreated state were the values ​​shown in Table 1. Microwave packaging materials [2] 〔3〕 Examples 1 to 2000 of the present invention 2 And, Microwave packaging materials [4] to [5] are examples 1 to 2. Microwave packaging materials [1], [6], and [7] are comparative examples 1 to 3.

[0057] (Preparation of packaging bags and packaging bodies) For each of the microwaveable packaging materials [1] to [7], flat pouch packaging bags [1] to [7] with a height of 170 mm and a width of 130 mm were prepared by heat sealing the sealant film sides together. Then, 180 g of water was filled into each of the flat pouch packaging bags [1] to [7], heat-sealed to create packaging bodies [1] to [7], respectively. The total light transmittance and ultraviolet transmittance of the tin-deposited polyethylene terephthalate film of the microwaveable packaging materials [1] to [7] that make up each package [1] to [7] after boiling were measured. The results are shown in Table 1.

[0058] [Table 1]

[0059] [evaluation] The following evaluations were performed on each package. The results are shown in Table 1. (Evaluation of metallic luster before and after boiling) The appearance of the transparent layer formed by the transparent yellow ink in each package was observed before and after boiling. (Evaluation of microwave heating) Each package was heated in a 1700W microwave for 50 seconds, and then its appearance was observed.

[0060] [Evaluation Results] (Evaluation of metallic luster before and after boiling) Example 1~ 2 In all cases, the packages obtained from the packaging materials related to the above showed a specular gloss before and after boiling. On the other hand, in the case of the packages obtained from the packaging material related to Comparative Example 1, which had high total light transmittance and ultraviolet transmittance, it was confirmed that the specular gloss that was present before boiling was lost after boiling due to transparency. In addition, the packages obtained from the packaging material related to Comparative Example 2, which had slightly lower total light transmittance and ultraviolet transmittance, had a slight white cloudiness before boiling, but after boiling... atIt was confirmed that a specular gloss could be obtained. Furthermore, the packaging obtained from the packaging material of Comparative Example 3, which had low total light transmittance and ultraviolet transmittance, was cloudy white and showed no gloss before and after boiling. (Evaluation of microwave heating) Example 1~ 2 In the packaging obtained from the packaging material related to Comparative Example 1, no defects such as welding or sparking were observed in the packaging. On the other hand, in the packaging obtained from the packaging material related to Comparative Examples 2 and 3, which had low total light transmittance and ultraviolet transmittance, welding and sparking were confirmed to occur. [Explanation of Symbols]

[0061] 1. Packaging material for microwave ovens 2. First intermediate 3. Second intermediate 10. Base film 11. Sealant film 12 Information display printing layer 13 Transparent layer part 14 Opaque layer part 15 Metal vapor deposition film 16 Intermediate resin layer 17,18 Adhesive layer 19 Opaque printing layer

Claims

1. It consists of a laminated film having a base film and a sealant film, A metal vapor-deposited film made of tin or indium is provided between the sealant film and the substrate film. The total light transmittance of the metal vapor-deposited film is 56.1% or more and 76.0% or less after heat sterilization treatment by boiling at 100°C for 90 minutes. A microwave-safe packaging material characterized in that the gloss of the metal vapor-deposited film is visible through the base film.

2. The microwave packaging material according to claim 1, characterized in that the light transmittance of the metal vapor-deposited film at wavelengths of 330 nm to 340 nm after heat sterilization by boiling at 100°C for 90 minutes is 55.3% or more and 60.1% or less.

3. It consists of a laminated film having a base film and a sealant film, A metal vapor-deposited film made of tin or indium is provided between the sealant film and the substrate film. The total light transmittance of the metal vapor-deposited film is 18.8% or more and 22.8% or less. A microwave-safe packaging material characterized in that the gloss of the metal vapor-deposited film is visible through the base film.

4. The microwave packaging material according to claim 3, characterized in that the light transmittance of the metal vapor-deposited film at wavelengths of 330 nm to 340 nm is 17.0% or more and 27.1% or less.

5. Between the substrate film and the metal vapor-deposited film, there is an information display printing layer. The microwave packaging material according to any one of claims 1 to 4, characterized in that the information display printing layer has a transparent layer portion formed of transparent ink.

6. The microwave packaging material according to claim 5, characterized in that the transparent layer portion is formed of transparent yellow ink.

7. The microwave packaging material according to claim 6, characterized in that the yellow pigment contained in the transparent yellow ink is at least one of an insoluble azo pigment and a condensed azo pigment.

8. The microwave packaging material according to any one of claims 1 to 7, wherein an intermediate resin layer is provided between the base film and the sealant film, and the metal vapor deposition film is formed on the intermediate resin layer.

9. The microwave packaging material according to claim 8, characterized in that the metal vapor deposition film is formed on the surface of the intermediate resin layer on the base film side.

10. The microwave packaging material according to claim 9, characterized in that the intermediate resin layer is transparent, and the metal vapor deposition film is formed on the surface of the intermediate resin layer on the sealant film side.

11. The microwave packaging material according to any one of claims 1 to 10, characterized in that an opaque printing layer is formed between the sealant film and the metal vapor deposition film.

12. Between the base film and the metal vapor-deposited film, there is an information display printing layer, The information display printing layer has a transparent layer portion formed by transparent ink, An opaque printing layer is formed on the sealant film side surface of the intermediate resin layer, and the information display printing layer is formed on the substrate film side surface of the metal vapor deposition film. The microwave packaging material according to claim 9, characterized in that an adhesive layer is formed between the information display printing layer and the base film, and between the opaque printing layer and the sealant film.

13. Between the base film and the metal vapor-deposited film, there is an information display printing layer, The information display printing layer has a transparent layer portion formed by transparent ink, An opaque printing layer is formed on the sealant film side surface of the metal vapor-deposited film, and the information display printing layer is formed on the substrate film side surface of the intermediate resin layer. The microwave packaging material according to claim 10, characterized in that an adhesive layer is formed between the information display printing layer and the base film, and between the opaque printing layer and the sealant film.

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