Microwave heat generating film, microwave heat generating package, and method of manufacturing microwave heat generating film

Abstract

To provide a microwave heat generating film having high vapor permeability, capable of providing vapor holes even when a moisture content in a container is large, without causing a short circuit.MEANS FOR SOLVING THE PROBLEM: A microwave heating film has: a low resistance layer having a resistance value of 1 Ω or more and 250 Ω or less; and a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, wherein at least a part of the low resistance layer and at least a part of the high resistance layer are laminated.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a microwave heating film, a microwave heating package, and a method for producing a microwave heating film. [Background technology]

[0002] A package containing food ingredients may be heated and cooked in a microwave oven while the food ingredients are sealed inside. Therefore, by using a microwave heating composition containing a microwave heating material that generates heat by microwaves in the package, steam from the food ingredients heated by microwaves can be released from the package, allowing the package to exhibit vapor permeability. Means for allowing steam to escape from the package include, for example, providing holes in the heat-sealed portion or in the top of the package.

[0003] One method for creating an opening in the heat seal portion or the upper part of the package is to provide a coating layer that generates heat when exposed to microwaves on a film-like microwave heating package that covers the container; when microwaves are irradiated onto the coating layer, the coating layer heats up, melting part of the microwave heating package to form an opening and allow steam to escape (see, for example, Patent Document 1).

[0004] Conventional microwave heating technology has been disclosed that provides only a single microwave heating layer, but this has the problem that depending on the amount of food, most of the microwaves are absorbed by the food, reducing the amount of microwaves irradiated to the microwave heating layer, and therefore no steam holes can be provided. Furthermore, a technique for improving vapor permeability by laminating different conductive materials has been disclosed (see, for example, Patent Document 2). However, depending on the resistance value of the conductive material, there is a risk of a short circuit and a fire, posing safety issues. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment of the present invention is to provide a microwave heating film having high vapor permeability that can provide vapor holes even when there is a large amount of moisture in the container without causing a short circuit. [Means for solving the problem]

[0006] The microwave heating film according to one embodiment of the present invention is a low resistance layer having a resistance value of 1 Ω or more and 250 Ω or less; a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, At least a part of the low resistance layer and at least a part of the high resistance layer are laminated. Effect of the Invention

[0007] An embodiment of the present invention can provide a microwave heating film having high vapor permeability that can provide vapor holes even when the water content in a container is high, without causing a short circuit. [Brief description of the drawings]

[0008] [Figure 1A] 1 is a schematic cross-sectional view showing an example of a microwave heating film according to one embodiment of the present invention. [Figure 1B] FIG. 2 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. [Figure 1C] FIG. 2 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. [Figure 2A] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 2B] FIG. 2 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. [Figure 2C] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Diagram 3]4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 4] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Diagram 5] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 6] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 7] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 8] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 9] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 10] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 11] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 12] 4 is a schematic cross-sectional view showing another example of a microwave heating film according to one embodiment of the present invention. FIG. [Figure 13A] 1 is a schematic diagram showing an example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. [Figure 13B] 1 is a schematic diagram showing an example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. [Figure 14A] 4 is a schematic diagram showing another example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. FIG. [Figure 14B] 1 is a schematic diagram showing an example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. [Figure 15A] 4 is a schematic diagram showing another example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. FIG. [Figure 15B] 1 is a schematic diagram showing an example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. [Figure 16A] 4 is a schematic diagram showing another example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. FIG. [Figure 16B] 1 is a schematic diagram showing an example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. [Figure 17A] 4 is a schematic diagram showing another example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. FIG. [Figure 17B] 1 is a schematic diagram showing an example of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention, viewed from above. [Figure 18] FIG. 1 is a perspective view showing an example of a microwave heating package according to one embodiment of the present invention. [Figure 19] 1 is a schematic diagram showing the shape of a microwave heating layer in a microwave heating film according to Production Example 10, as viewed from above. FIG.

[0009] Hereinafter, embodiments of the present invention will be described in detail. In this specification, unless otherwise specified, the numerical range indicated by "to" means that the numerical range includes the numerical range before and after the range as the lower limit and upper limit. In the present invention, "vaporizing" means that steam escape holes (sometimes referred to as "vapor passage holes" in this specification) are formed.

[0010] <Microwave heating film> A microwave heating film according to one embodiment of the present invention will be described. The microwave heating film has a substrate and a microwave heating layer consisting of a low resistance layer and a high resistance layer, and may further have a sealant, an adhesive layer, a printing ink layer, an anchor coat layer, an overcoat layer, and other layers as necessary.

[0011] 1 to 12 are cross-sectional side views showing an example of a microwave heating film according to one embodiment of the present invention.

[0012] 1A, the microwave heating film 100A has a base material 10 and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is provided such that the base material 10, the high resistance layer 1, and the low resistance layer 2 are laminated in this order, with the entire high resistance layer 1 being in contact with the base material 10. In addition, the entire high resistance layer 1 and the entire low resistance layer 2 are laminated.

[0013] 1B, the microwave heating film 100B has a substrate 10 and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is partially laminated in this order of the substrate 10, the high resistance layer 1, and the low resistance layer 2, such that the entire high resistance layer 1 is in contact with the substrate 10 and a part of the low resistance layer 2 is in contact with the substrate 10. Also, a part of the high resistance layer 1 and a part of the low resistance layer 2 are laminated.

[0014] 1C, the microwave heating film 100C has a base material 10 and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is provided by laminating the base material 10, the high resistance layer 1, and the low resistance layer 2 in this order, so that the entire high resistance layer 1 is in contact with the base material 10. In addition, a part of the high resistance layer 1 and the entire low resistance layer 2 are laminated.

[0015] 2A, the microwave heating film 101A has a base material 10 and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is provided such that the base material 10, the low resistance layer 2, and the high resistance layer 1 are laminated in this order, with the entire low resistance layer 2 being in contact with the base material 10. In addition, the entire high resistance layer 1 and the entire low resistance layer 2 are laminated.

[0016] 2B, the microwave heating film 101B has a base material 10 and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is partially laminated in the order of the base material 10, the low resistance layer 2, and the high resistance layer 1, with the entire low resistance layer 2 in contact with the base material 10 and part of the high resistance layer 1 in contact with the base material 10. Also, part of the high resistance layer 1 and part of the low resistance layer 2 are laminated.

[0017] 2C, the microwave heating film 101C has a base material 10 and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is laminated in the order of the base material 10, the low resistance layer 2, and the high resistance layer 1, with the entire low resistance layer 2 being in contact with the base material 10. Also, the entire high resistance layer 1 and a part of the low resistance layer 2 are laminated.

[0018] As shown in FIG. 3, the microwave heating film 102 has a substrate 11 having sealing properties and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is laminated in the order of substrate 11 having sealing properties, high resistance layer 1, and low resistance layer 2, with the entire high resistance layer 1 being in contact with substrate 11 having sealing properties.

[0019] As shown in FIG. 4, the microwave heating film 103 has a base material 11 having sealing properties, and a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and is laminated in the order of the base material 11 having sealing properties, the low resistance layer 2, and the high resistance layer 1, with the entire low resistance layer 2 being in contact with the base material 11 having sealing properties.

[0020] As shown in FIG. 5, the microwave heating film 104 has a substrate 10, a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and a sealant 12, and is laminated in the order of sealant 12, low resistance layer 2, high resistance layer 1, and substrate 10, with the entire high resistance layer 1 being in contact with substrate 10.

[0021] As shown in FIG. 6, the microwave heating film 105 has a substrate 10, a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and a sealant 12, and is laminated in the order of sealant 12, high resistance layer 1, low resistance layer 2, and substrate 10, with the entire low resistance layer 2 being in contact with substrate 10.

[0022] As shown in FIG. 7, the microwave heating film 106 has a substrate 10, a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and a sealant 12, and is laminated in the order of sealant 12, substrate 10, low resistance layer 2, and high resistance layer 1, with the entire low resistance layer 2 being in contact with the substrate 10.

[0023] As shown in FIG. 8, the microwave heating film 107 has a substrate 10, a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and a sealant 12, and is laminated in the order of sealant 12, substrate 10, high resistance layer 1, and low resistance layer 2, with the entire high resistance layer 1 being in contact with substrate 10.

[0024] As shown in Figure 9, the microwave heating film 108 has a substrate 10, a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and a sealant 12, and is laminated in the order of the low resistance layer 2, the high resistance layer 1, the sealant 12, and the substrate 10, with the entire high resistance layer 1 being in contact with the sealant 12.

[0025] As shown in FIG. 10, the microwave heating film 109 has a substrate 10, a microwave heating layer 3 consisting of a high resistance layer 1 and a low resistance layer 2, and a sealant 12, and is laminated in the order of the high resistance layer 1, the low resistance layer 2, the sealant 12, and the substrate 10, with the entire low resistance layer 2 being in contact with the sealant 12.

[0026] As shown in FIG. 11, the microwave heating film 110 has a base material 10 and a microwave heating layer 3 formed by laminating a low resistance layer 2, a high resistance layer 1 and a low resistance layer 2 in that order, with the base material 10, the low resistance layer 2, the high resistance layer 1 and the low resistance layer 2 being laminated in that order, with the entire low resistance layer 2 being in contact with the base material 10.

[0027] As shown in FIG. 12, the microwave heating film 111 has a base material 10 and a microwave heating layer 3 formed by laminating a high resistance layer 1, a low resistance layer 2, and a high resistance layer 1 in that order, with the base material 10, the high resistance layer 1, the low resistance layer 2, and the high resistance layer 1 being laminated in that order, with the entire high resistance layer 1 being in contact with the base material 10.

[0028] [Microwave heating layer] The microwave heating layer is composed of a low resistance layer that absorbs microwave energy and converts it into eddy currents, and a high resistance layer that uses the eddy currents converted in the low resistance layer to convert it into Joule heat. Microwaves are radio waves with a frequency between 300 MHz and 300 GHz. The low resistance layer and the high resistance layer may be provided as one layer each as shown in FIGS. 1A to 10, or a plurality of layers may be laminated as shown in FIGS.

[0029] 13A to 17B are schematic plan views showing examples of the shape of a microwave heating layer in a microwave heating film according to one embodiment of the present invention.

[0030] 13A and 13B, the microwave heating layer 3 is made up of a plurality (six) of high resistance layers 1 and low resistance layers 2 which are partially overlapped in plan view. Note that Fig. 13A and Fig. 13B are in a front-back relationship, and the same is true for Figs. 14A to 17B.

[0031] In the embodiment shown in Figures 14A and 14B, the microwave heating layer 3 is made up of multiple (3) separate high-resistance layers 1 and multiple (2) separate low-resistance layers 2 which partially overlap each other in a planar view.

[0032] In the embodiment shown in FIGS. 15A and 15B, the microwave heating layer 3 includes a high resistance layer 1 and a plurality (two) of separate low resistance layers 2 which partially overlap each other in plan view.

[0033] In the embodiment shown in Figures 16A and 16B, the microwave heating layer 3 is made up of multiple (2) separate high-resistance layers 1 and multiple (2) separate low-resistance layers 2 which partially overlap each other in a planar view.

[0034] In the embodiment shown in Figures 17A and 17B, the microwave heating layer 3 is made up of multiple (7) separate high-resistance layers 1 and multiple (2) separate low-resistance layers 2 which partially overlap each other in a planar view.

[0035] The number of low resistance layers is not particularly limited and can be appropriately selected depending on the purpose. For example, there may be one as shown in FIGS. 13A and 13B, or there may be two or more as shown in FIGS. 14A to 17B.

[0036] The number of high resistance layers is not particularly limited and can be appropriately selected depending on the purpose. For example, there may be one as shown in FIGS. 15A and 15B, or there may be two or more as shown in FIGS. 13A to 17B.

[0037] The shapes of the high resistance layer 1 and the low resistance layer 2 in the microwave heating layer 3 are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polygonal, circular, elliptical, and wavy shapes.

[0038] In the microwave heating layer 3, the area ratio (A / B) between the area (A) of each low resistance layer 2 in a plan view and the area (B) of each high resistance layer 1 in a plan view is preferably 1.0 or more and 10.0 or less. When the area ratio (A / B) is 1.0 or more, it is possible to prevent the molten film from falling. Also, when the area ratio (A / B) is 10.0 or less, it is possible to prevent the film from burning due to the eddy current generated in the low resistance layer moving excessively to the high resistance layer. Here, conventionally, there has been a problem that the molten film falls into the container due to the excessive opening of the vapor passage holes depending on the coating shape of the microwave heating layer on the microwave heating film. In addition, conventional microwave heating films have a problem of discoloration due to scorching caused by the microwave heating layer. Therefore, in one embodiment of the present invention, by setting the area ratio (A / B) to 1.0 or more and 10.0 or less, it is possible to prevent the molten film from falling into the container and also to prevent discoloration due to scorching caused by the microwave heating layer.

[0039] [Low resistance layer] The low resistance layer is a layer that absorbs microwave energy and converts it into eddy currents. The low resistance layer contains a conductive material and, if necessary, further contains other components.

[0040] The resistance value of the low resistance layer may be lower than the resistance value of the high resistance layer described later, but is preferably 1Ω or more and 250Ω or less, and more preferably 1Ω or more and 100Ω or less. If the resistance value of the low resistance layer is 1Ω or more, the generation of excessive eddy currents in the low resistance layer can be suppressed, thereby preventing a short circuit in the microwave heating film. If the resistance value of the low resistance layer is 250Ω or less, microwaves can be sufficiently absorbed, and eddy currents necessary for heat generation in the high resistance layer can be generated.

[0041] When the resistance value of the low resistance layer is 1 Ω or more and 250 Ω or less, and further, the area ratio (A / B) is 1.0 or more and 10.0 or less, it is possible to prevent a short circuit of the microwave heating film, generate an eddy current necessary for heat generation in the high resistance layer, prevent the molten film from falling, and prevent the film from burning.

[0042] The method for measuring the resistance value is not particularly limited and can be appropriately selected depending on the purpose. For example, the resistance value can be measured using a two-terminal resistance meter (tester) or a four-terminal resistance meter.

[0043] (Conductive materials) The conductive material is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include nonmetallic inorganic materials such as carbon black and graphite, metals such as gold, silver, copper, aluminum, zinc, tin, and iron, alloys or metal oxides thereof, and organic materials such as thiophene, aniline, and pyrrole. Among these, metals, alloys, and metal oxides are preferred from the viewpoint of conductivity, and metals are more preferred. Furthermore, among metals, gold, silver, and copper are preferred.

[0044] The conductive material is preferably in particulate form, since this can prevent short circuits caused by excessive current flow. In addition, the conductive material in particulate form can be easily made into an ink.

[0045] The length-average diameter in the number-based distribution of the conductive material is not particularly limited and can be appropriately selected according to the purpose, but is preferably 10 μm or less. When the length-average diameter in the number-based distribution is 10 μm or less, it becomes easy to control the resistance value of the low resistance layer to an appropriate value. In addition, the number of interparticle points required for the development of conductivity increases, and the required conductivity can be obtained.

[0046] The method for measuring the length-average diameter in the number-based distribution is not particularly limited and can be appropriately selected depending on the purpose. For example, the length-average diameter can be determined from the shape of the conductive material observed from a cross section of the low-resistance layer. The cross section can be observed, for example, by preparing a sample by a conventional method and measuring the same with a transmission electron microscope (TEM). The measured length-average diameter in the number-based distribution of the conductive material observed using the TEM is substantially the same as the measured length-average diameter in the number-based distribution of the conductive material in the composition for forming a low-resistance layer used to form the low-resistance layer, so the particle size distribution of the conductive material after formation of the low-resistance layer can be set by the particle size distribution of the conductive material in the composition for forming a low-resistance layer. The length-average diameter in the volume-based distribution of the conductive material in the composition for forming a low-resistance layer can be measured, for example, by a laser diffusion method using an LA-960 manufactured by Horiba, Ltd.

[0047] The content of the conductive material is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 50% by mass or more and 99% by mass or less with respect to the low resistance layer. When the content of the conductive material is 50% by mass or more, microwaves can be sufficiently absorbed, so that eddy currents necessary for heat generation can be generated in the high resistance layer. When the content of the conductive material is 99% by mass or less, the generation of excessive eddy currents in the low resistance layer can be suppressed, thereby preventing short circuits in the microwave heating film.

[0048] (Other Ingredients) The other components are not particularly limited and may be appropriately selected depending on the purpose. Examples of the other components include resins, coloring materials, waxes, pigment dispersants, and crosslinking agents.

[0049] The resin is not particularly limited as long as it does not inhibit microwave absorption, and can be appropriately selected depending on the purpose such as the substrate, application, and configuration, and examples thereof include shellacs, rosins, nitrocellulose, celluloses, rubbers, polyamide resins, vinyl chloride-vinyl acetate copolymers, polyester resins, polyvinylidene chloride resins, ketone resins, butyral resins, chlorinated polypropylene resins, chlorinated polyethylene resins, chlorinated ethylene vinyl acetate resins, ethylene vinyl acetate resins, acrylic resins, urethane resins, casein, alkyd resins, polyvinyl alcohol resins, ethylene-vinyl alcohol resins, vinyl chloride resins, etc. Among these, acrylic resins, urethane resins, vinyl chloride resins, and rubbers are preferred from the viewpoint of adhesion to the substrate.

[0050] The coloring material is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include pigments, dyes, mixtures thereof, etc. Among these, pigments are preferred from the viewpoint of durability.

[0051] The pigment is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include inorganic pigments such as titanium oxide, red iron oxide, barium sulfate, calcium carbonate, silica, zinc oxide, zinc sulfide, mica, talc, pearl, aluminum, and carbon black, organic pigments such as phthalocyanine-based, insoluble azo-based, condensed azo-based, dioxazine-based, anthraquinone-based, quinacridone-based, perylene-based, perinone-based, and thioindigo-based pigments, as well as various other fluorescent pigments, metal powder pigments, and extender pigments. These may be used alone or in combination of two or more.

[0052] The dye is preferably one that dissolves or disperses in a solvent, and one or more types may be used in combination. Since the dye can contain a coloring material, it is very useful in terms of color variation and design.

[0053] The pigment dispersant is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include anionic surfactants, cationic surfactants, nonionic surfactants, etc. These may be used alone or in combination of two or more kinds.

[0054] The crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include hydrazides, isocyanates, epoxy systems, carbodiimides, silane coupling systems, oxazolines, aziridines, imines, metal chelates, glyoxals, and methylols. These may be used alone or in combination of two or more. Among these, isocyanates, carbodiimides, epoxy systems, and aziridines are preferred.

[0055] [High resistance layer] The high resistance layer is a layer that utilizes the eddy current converted in the low resistance layer to convert it into Joule heat. The resistance value of the high resistance layer may be any value higher than the resistance value of the low resistance layer, and is preferably more than 250 Ω. The resistance value can be measured using the same method as that for the resistance value of the low resistance layer. The high-resistance layer contains a conductive material and a resin, and further contains other components as necessary.

[0056] (Conductive materials) The conductive material is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include non-metallic inorganic materials such as carbon black and graphite, metals such as gold, silver, copper, aluminum, zinc, tin, and iron, alloys thereof or oxides of these metals, and organic materials such as thiophenes, anilines, and pyrroles. Among these, from the viewpoint of resistance value, non-metallic inorganic materials or organic materials are preferred, organic materials are more preferred, and thiophenes are particularly preferred. Among the thiophene-based materials, PEDOT is preferred from the viewpoint of electrical conductivity.

[0057] The conductive material is preferably in the form of particles or in a dissolved state.

[0058] The length-average diameter in the number-based distribution of the conductive material is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.01 μm or more. When the length-average diameter in the number-based distribution is 0.01 μm or more, it becomes easy to control the resistance value of the high-resistance layer to an appropriate value. The method for measuring the length-average diameter in the number-based distribution is not particularly limited and can be appropriately selected depending on the purpose. For example, the length-average diameter can be measured by the same method as that for the conductive material contained in the low-resistance layer.

[0059] The content of the conductive material is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 5% by mass or more relative to the high resistance layer. When the content of the conductive material is 5% by mass or more, the heat generation required for melting the film can be exhibited.

[0060] (Other Ingredients) The other components are not particularly limited and can be appropriately selected depending on the purpose. Examples of the other components include dopants, resins, coloring materials, solvents, waxes, pigment dispersants, and crosslinking agents.

[0061] There are no particular limitations on the dopant that can be used as long as it has a structure that acts as an acceptor that easily accepts electrons or a donor that easily gives electrons to the conductive material.

[0062] At least a part of the functional group of the dopant is doped into the conductive material and contributes to the development of the conductivity of the conductive material. Examples of the functional group of the dopant include a carboxyl group, a hydroxyl group, a mercapto group, an amino group, a sulfino group, and a sulfonium group.

[0063] At least a part of the functional groups of the dopant is doped into the conductive material and contributes to the development of the conductivity of the conductive material. Examples of the functional groups of the dopant include a carboxyl group, a hydroxyl group, a mercapto group, an amino group, a sulfino group, and a sulfonium group.

[0064] The dopant having a carboxyl group is preferably a carboxylic acid aromatic compound or a carboxylic acid condensed ring aromatic compound having an aromatic ring or a condensed ring aromatic compound in the molecule, which has many resonance structures and suppresses hydrolysis reactions. By using the carboxylic acid aromatic compound or the carboxylic acid condensed ring aromatic compound, a high resistance layer with enhanced water resistance can be obtained.

[0065] The carboxylic acid aromatic compound and the carboxylic acid condensed ring aromatic compound are not particularly limited and can be appropriately selected depending on the purpose. For example, carboxylic acid aromatic compounds such as ortho-phthalic acid, hemimellitic acid, trimesic acid, mellophanic acid, benzenepentacarboxylic acid, and mellitic acid, derivatives of carboxylic acid aromatic compounds such as 4-sulfophthalic acid, and condensed carboxylic acid aromatic compounds in which naphthalene is replaced by only carboxylic acid, such as 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic anhydride, can be used. Examples of such compounds include carboxylic acid aromatic condensation compounds and derivatives thereof, such as 4-chloro-1,8-naphthalenedicarboxylic anhydride, 4-sulfo-1,8-naphthalenedicarboxylic anhydride, and naphthalene-1,4,5,8-tetracarboxylic acid, and derivatives thereof; compounds having an anthracene ring, such as 2,3-anthracenedicarboxylic anhydride; carboxylated polycyclic aromatic hydrocarbons, such as naphthacene, pentacene, benzopyrene, benzopyrene, chrysene, pyrene, triphenylene, corannulene, coronene, and ovalene, and derivatives thereof.

[0066] The dopant having a hydroxyl group is not particularly limited and can be appropriately selected depending on the purpose. Examples of the dopant include salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 4-hydroxyphthalic acid, 3-hydroxyphthalic anhydride, 3,6-dihydroxyphthalic acid, phenolsulfonic acid, 3-hydroxy-2,7-naphthalenedicarboxylic acid, and derivatives thereof.

[0067] The dopant having a mercapto group is not particularly limited and can be appropriately selected depending on the purpose. Examples of the dopant include thioglycolic acid, mercaptosuccinic acid, 2-mercaptobutyric acid, 4-mercaptobutyric acid, 2-mercaptoethanol, 2-mercaptobenzoic acid, 3-mercaptobenzoic acid, 4-mercaptobenzoic acid, o-aminothiophenol, m-aminothiophenol, p-aminothiophenol, 2-hydroxythiophenol, 3-hydroxythiophenol, 4-hydroxythiophenol, and derivatives thereof.

[0068] The dopant having an amino group is not particularly limited and can be appropriately selected depending on the purpose. Examples of the dopant having an amino group include aminomethanesulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, 2-amino-5-naphthol-7-sulfonic acid, 3-aminopropanesulfonic acid, N-cyclohexyl-3-aminopropanesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, 4-amino-2-chlorotoluene-5-sulfonic acid, 4-amino-3-methylbenzene-1-sulfonic acid, 4-amino-5-methoxy-2-methylbenzenesulfonic acid, 2-amino-5-methylbenzene-1-sulfonic acid, 4-amino-2-methylbenzene-1-sulfonic acid, 5-amino-2-methylbenzene-1-sulfonic acid, 4-amino-3-methylbenzene-1-sulfonic acid, polyacrylic acid, polymethacrylic acid, polymaleic acid, and other polycarboxylic acids, and derivatives thereof.

[0069] The dopant having a sulfino group is not particularly limited and can be appropriately selected depending on the purpose. Examples of the dopant include methanesulfinic acid, ethanesulfinic acid, isopropylsulfinic acid, benzenesulfinic acid, p-toluenesulfinic acid, cyclopropanesulfinic acid, derivatives of p-chlorobenzenesulfinic acid, hydroxymethanesulfinic acid, L-cysteinesulfinic acid, 2-aminoethanesulfinic acid, and derivatives thereof.

[0070] The dopant having a sulfonium group is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include low molecular weight sulfonic acid or a salt thereof, and a sulfonic acid group-containing acidic polymer or a salt thereof.

[0071] The low molecular weight sulfonic acid is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include alkylsulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid, anthraquinonesulfonic acid, camphorsulfonic acids, derivatives thereof, etc. Among these, low molecular weight organic acids having a molecular weight of 1000 or less are preferred.

[0072] The alkylsulfonic acid is not particularly limited and can be appropriately selected depending on the purpose. Examples of the alkylsulfonic acid include derivatives of 2-acrylamido-2-methylpropanesulfonic acid and derivatives of dodecylbenzenesulfonic acid.

[0073] The benzenesulfonic acid is not particularly limited and can be appropriately selected depending on the purpose. Examples of the benzenesulfonic acid include derivatives of toluenesulfonic acid, styrenesulfonic acid, and derivatives thereof.

[0074] The naphthalenesulfonic acid is not particularly limited and can be appropriately selected depending on the purpose. Examples of the naphthalenesulfonic acid include derivatives of 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 1,3-naphthalenedisulfonic acid, 1,3,6-naphthalenetrisulfonic acid, and 6-ethyl-1-naphthalenesulfonic acid.

[0075] The anthraquinone sulfonic acid is not particularly limited and can be appropriately selected depending on the purpose. Examples of the anthraquinone sulfonic acid include derivatives of anthraquinone-1-sulfonic acid, anthraquinone-2-sulfonic acid, anthraquinone-2,6-disulfonic acid, and 2-methylanthraquinone-6-sulfonic acid.

[0076] Camphorsulfonic acid is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include (+)-10-camphorsulfonic acid, derivatives of (-)-10-camphorsulfonic acid, etc. Camphorsulfonic acid may be a racemate.

[0077] Among these, benzenesulfonic acid, toluenesulfonic acid, and naphthalenesulfonic acid are preferred. These may be used alone or in combination of two or more.

[0078] When the low molecular weight sulfonic acid is an alkylsulfonic acid, benzenesulfonic acid, naphthalenesulfonic acid, anthraquinonesulfonic acid, camphorsulfonic acid, or a derivative thereof, the low molecular weight organic acid may be a salt thereof, such as an ammonium salt or a sodium salt thereof.

[0079] The acidic polymer of the sulfonic acid group-containing acidic polymer is not particularly limited and can be appropriately selected according to the purpose, and examples thereof include polycarboxylic acids such as polyacrylic acid, polymethacrylic acid, and polymaleic acid, polysulfonic acids such as polyvinyl sulfonic acid and polystyrene sulfonic acid (PSS), and copolymers having these structural units. These may be used alone or in combination of two or more. Among these, polystyrene sulfonic acid (PSS) is preferred.

[0080] The weight average molecular weight (Mw) of the acidic polymer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably from 2,000 to 500,000, more preferably from 10,000 to 200,000.

[0081] The total content of the dopant is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 20 parts by mass or more and 3,000 parts by mass or less, and more preferably 30 parts by mass or more and 1,000 parts by mass or less, relative to 100 parts by mass of the conductive material.

[0082] The dopants may be used alone or in combination of two or more.

[0083] (resin) The resin is not particularly limited as long as it does not inhibit heat generation, and can be appropriately selected according to the purpose such as the substrate, application, and configuration, and examples thereof include shellacs, rosins, nitrocellulose, celluloses, rubbers, polyamide resins, vinyl chloride-vinyl acetate copolymers, polyester resins, polyvinylidene chloride resins, ketone resins, butyral resins, chlorinated polypropylene resins, chlorinated polyethylene resins, chlorinated ethylene vinyl acetate resins, ethylene vinyl acetate resins, acrylic resins, urethane resins, casein, alkyd resins, polyvinyl alcohol resins, ethylene-vinyl alcohol resins, vinyl chloride resins, etc. Among these, acrylic resins, urethane resins, vinyl chloride resins, and rubbers are preferred from the viewpoint of adhesion to the substrate.

[0084] The coloring material may be a pigment, a dye, or a mixture thereof. Among these, pigments are preferred from the viewpoint of durability.

[0085] Examples of pigments include inorganic pigments such as titanium oxide, red iron oxide, barium sulfate, calcium carbonate, silica, zinc oxide, zinc sulfide, mica, talc, pearl, aluminum, and carbon black, and organic pigments such as phthalocyanine-based, insoluble azo-based, condensed azo-based, dioxazine-based, anthraquinone-based, quinacridone-based, perylene-based, perinone-based, and thioindigo-based pigments, as well as various other fluorescent pigments, metal powder pigments, and extender pigments. These pigments may be used alone or in combination of two or more.

[0086] The dye is preferably one that dissolves or disperses in a solvent, and one or more types may be used in combination. Since the dye can contain a coloring material, it is very useful in terms of color variation and design.

[0087] The pigment dispersant is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include anionic surfactants, cationic surfactants, nonionic surfactants, etc. These may be used alone or in combination of two or more kinds.

[0088] The crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include hydrazide-based, isocyanate-based, epoxy-based, carbodiimide-based, silane coupling-based, oxazoline-based, aziridine-based, imine-based, metal chelate-based, glyoxal-based, and methylol-based agents. These may be used alone or in combination of two or more. Among these, isocyanate-based, carbodiimide-based, epoxy-based, and aziridine-based agents are preferred.

[0089] [Base material] The substrate is not particularly limited and can be appropriately selected depending on the purpose. Examples of the substrate include paper, plastic film or sheet, and laminates of these that have been given sealing properties. The plastic film or sheet is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate, polystyrene films, alcohol-based films such as ethylene-vinyl alcohol and polyvinyl alcohol, polyamide films or barrier polyamide films with a barrier layer disposed between them, cellophane, moisture-proof cellophane, transparent vapor-deposited polyester films or transparent vapor-deposited polyamide films in which a vapor-deposited layer of alumina, silica, or the like is provided on a PET film or polyamide film, and various coating films coated with polyvinylidene chloride resin, polyvinyl alcohol resin, polyacrylic acid resin, easy-adhesive resin, etc. These may be stretched or unstretched, and one or more types may be laminated. As the plastic film or sheet, an appropriate one can be selected in consideration of mechanical strength, dimensional stability, and the like.

[0090] The surfaces of the substrate on which the low resistance layer and the high resistance layer are formed may be subjected to corona treatment, low temperature plasma treatment, flame treatment, solvent treatment, coating treatment, etc. in order to improve the adhesion of the microwave heat generating composition.

[0091] Furthermore, the substrate may be a laminate of a thermoplastic resin or the like by a method such as dry lamination, non-solvent lamination, or extrusion lamination, or a method of bonding via an adhesive, or may be an appropriate combination of these. It may also be a uniaxially stretched film, an easy-to-cut film, a stretch film, or a shrink film.

[0092] The substrate may be a laminate having a sealability. Examples of a method for providing the sealability include lamination of a known sealant film or sheet, resin coating by extrusion lamination, etc., and a layer having a sealability provided by such a method is also called a sealant.

[0093] The substrate may be scratched in advance.

[0094] The thickness of the substrate is not particularly limited as long as it does not interfere with printability, winding suitability, etc., and can be appropriately selected depending on the purpose, but is preferably 5 μm or more and 300 μm or less, and more preferably 6 μm or more and 250 μm or less.

[0095] [Sealant] The sealant is preferably a layer containing a resin having sealing properties, and examples of resins that can be used include polyethylene resins such as LDPE, LLDPE, HDPE, and metallocene polyethylene, polypropylene resins, ethylene-vinyl acetate copolymers, ionomer resins, ethylene-acrylic acid copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl methacrylate copolymers, ethylene-propylene copolymers, methylpentene polymers, acid-modified polyolefin resins obtained by modifying polyethylene or polypropylene with maleic acid, fumaric acid, or the like, and thermoplastic resins such as polystyrene resins. These resins may be used alone or in combination.

[0096] A film containing these resins or a laminate in which a plurality of films are laminated may be formed by lamination using a dry lamination method, a wet lamination method, a non-solvent lamination method, a thermal lamination method, or the like, resin coating using extrusion lamination processing, coating with a heat sealing agent, or bonding via a hot melt adhesive, etc. Furthermore, the film or laminate containing these resins does not necessarily have to be formed on the entire surface, and may be formed only on the portion to be sealed.

[0097] Examples of the film include polyolefin films such as polyethylene, polypropylene, a mixed resin of polyethylene and polypropylene, an ethylene-vinyl acetate copolymer resin, an ethylene-(meth)acrylic acid copolymer resin, an ethylene-methyl (meth)acrylate copolymer resin, an ethylene-ethyl (meth)acrylate copolymer resin, and an ethylene-vinyl alcohol copolymer resin.

[0098] Examples of resins that can be used for resin coating by extrusion lamination or hot melt adhesives include thermoplastic resins such as polyethylene resins such as LDPE, LLDPE, and HDPE, polypropylene resins, ethylene-vinyl acetate copolymers, ionomer resins, ethylene-acrylic acid copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl methacrylate copolymers, ethylene-propylene copolymers, methylpentene polymers, acid-modified polyolefin resins obtained by modifying polyethylene or polypropylene with maleic acid, fumaric acid, or the like, and polystyrene resins. These resins may be used alone or in combination of two or more.

[0099] The thickness of the sealant is not particularly limited, but from the viewpoints of sealing property, cost, and productivity, it is preferable that the thickness be 2 μm to 200 μm for a film, 1 μm to 100 μm for a resin coating by extrusion lamination, 0.1 μm to 10 μm for a coating of a heat sealing agent, and 1 μm to 50 μm for a coating of a hot melt adhesive.

[0100] [Adhesive layer] The adhesive layer can be provided, for example, between a substrate and another substrate, or between a substrate and a sealant. The adhesive layer is a layer formed to bond two layers together using an adhesive or pressure-sensitive adhesive (including wax and hot melt) that has adhesive or tackiness.

[0101] Examples of the resin forming the adhesive layer include the above-mentioned resin having sealing properties used in forming the sealant, urethane resin, butadiene resin, polyethyleneimine resin, isocyanate resin, chelate, etc. In addition, a commercially available adhesive can be used as the resin forming the adhesive layer. Furthermore, the adhesive may be a one-liquid type adhesive in which the base agent and the curing agent are mixed, or a two-liquid type adhesive in which the base agent and the curing agent are separate. When the resin forming the adhesive layer is a two-liquid type adhesive, the mixing ratio of the base agent and the curing agent is appropriately adjusted and mixed for use.

[0102] [Printing ink layer] For the printing ink layer, a normal printing ink can be used, and can be appropriately selected depending on the substrate. From the viewpoint of printability and versatility, the printing ink is preferably a gravure ink such as a urethane resin, a vinyl chloride-vinyl acetate copolymer resin, nitrocellulose, a polyamide resin, an acrylic resin, a chlorinated polypropylene resin, or a polyester resin. These resins may be one type or a combination of two or more types of gravure ink. In addition, when two or more colors of gravure ink are used, they do not need to be inks of the same resin system, and inks of different resin systems can be used appropriately.

[0103] [Anchor coat layer] The anchor coat layer may be transparent, or may be formed using an anchor coat agent containing a coloring material, so that various color variations and color designs can be obtained. The anchor coat layer may be provided between the substrate and the microwave heating layer.

[0104] [Overcoat layer] The overcoat layer can be formed using an overcoat agent, an overcoat varnish, an overprint varnish, or the like.

[0105] [Other layers] Examples of other layers include OPP film, ONY film, PET film, EVOH film, PVA film, cellophane film, barrier nylon film, oriented polyethylene film, (modified) polyacrylic acid coated film, PVA coated film, transparent vapor deposition films in which inorganic oxides such as aluminum oxide and silicon oxide are vapor deposited on a substrate such as a biaxially oriented polyethylene terephthalate film, transparent barrier films (K-coats) in which a base film such as OPP, ONY, PET, or cellophane is coated with PVDC (polyvinylidene chloride), and barrier films in which an ethylene-vinyl alcohol copolymer resin is sandwiched between OPP films or NY films and laminated. It is preferable to provide these films on the other side of the microwave heating layer.

[0106] <Method of manufacturing microwave heating film> The microwave heating film of one embodiment of the present invention comprises a process for forming a low resistance layer having a resistance value of 1 Ω or more and 250 Ω or less (hereinafter sometimes referred to as a "low resistance layer forming process"), and a process for forming a high resistance layer having a resistance value higher than the resistance value of the low resistance layer (hereinafter sometimes referred to as a "high resistance layer forming process"), and further comprises other processes as necessary.

[0107] The high-resistance layer forming step and the low-resistance layer forming step can be appropriately selected from methods such as coating a composition for forming a high-resistance layer or a composition for forming a low-resistance layer on at least one of the substrates, vapor deposition of a conductive material, plating, etc. Among these, coating, particularly printing, is preferred. The printing process is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include silk screen printing, gravure printing, offset printing, flexographic printing, roller coater, brush coating, spraying, knife jet coater, inkjet, etc. Among these, in view of high quality and productivity, gravure printing, flexographic printing, inkjet and silk screen printing are preferred, and gravure printing is more preferred. Furthermore, as the gravure printing method, a gravure printing method using a multicolor gravure printer is preferable, which allows the low resistance layer and the high resistance layer to be overprinted and provided in multiple locations, making it easy to control the openability and heat generation of the steam escape hole.

[0108] [[Composition for forming low resistance layer]] The composition for forming a low resistance layer contains a conductive material and a solvent, and further contains other components as necessary. The conductive material and other components contained in the composition for forming a low resistance layer include the same materials as those contained in the above-mentioned low resistance layer.

[0109] The solvent is not particularly limited as long as it dissolves or disperses the components constituting the composition for forming a low resistance layer and maintains fluidity, and can be appropriately selected depending on the purpose. Examples of the solvent include commonly used organic solvents and water.

[0110] The organic solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as hexane, cyclohexane, methylcyclohexane and ethylcyclohexane; alcohol solvents such as methanol, ethanol, isopropyl alcohol (IPA), normal propyl alcohol, 1-butanol, 2-butanol, isobutanol and tert-butanol; ester solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec-butyl acetate and tert-butyl acetate; ketone solvents such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone and cyclohexanone; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene Examples of the esters include glycol ether solvents such as glycol dimethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether, and esterified products thereof. As the esterified products, acetates are mainly selected, for example, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate. These may be used alone or in combination of two or more. Among these, from the viewpoint of printability and versatility, toluene, ethyl acetate, isopropyl alcohol, methyl ethyl ketone, ethanol, and water are preferred.

[0111] [[Composition for forming high resistance layer]] The composition for forming a high-resistance layer contains a conductive material and a solvent, and further contains other components as necessary. The conductive material and other components contained in the composition for forming a high-resistance layer include the same materials as those contained in the high-resistance layer described above.

[0112] The solvent is not particularly limited as long as it can hold the conductive material in a dissolved and dispersed state, and can be appropriately selected depending on the purpose, and examples thereof include aprotic nonpolar solvents such as protic polar solvents such as water, methanol, ethanol, propanol, acetic acid, etc. These may be used alone or in combination of two or more.

[0113] It is preferable that the solvent contains a high boiling point solvent having a temperature of 100° C. or higher and 350° C. or lower.

[0114] The high-boiling point solvent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include ethylene glycol, diethylene glycol, diethylene glycol monobutyl ether, dibutylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, DMSO, formamide, glycerin, propylene glycol, 1,3-butanediol, dipropylene glycol, etc. Among these, ethylene glycol, diethylene glycol, DMSO, glycerin, propylene glycol, 1,3-butanediol, and dipropylene glycol are preferred.

[0115] The amount of the high boiling point solvent added is preferably 0.1% by mass or more and 50% by mass or less in the composition for forming a high resistance layer. By adding 0.1% by mass or more, the film-forming property can be improved. By adding 50% by mass or less, both drying property and film-forming property can be achieved.

[0116] In addition, a lamination method (overprinting of a low resistance layer forming composition and a high resistance layer forming composition) may be used to prepare a substrate having one or more laminated layers, and then a low resistance layer and a high resistance layer may be formed on one main surface of the substrate by various printing methods. After a low resistance layer and a high resistance layer are formed on one main surface of the substrate by various printing methods, another substrate may be formed on the other main surface of the substrate by the lamination method described above. In addition, a low resistance layer and a high resistance layer may be formed on both sides of the substrate.

[0117] When an overcoat layer is provided on the low resistance layer and the high resistance layer, the overcoat layer can be formed using an overcoat agent, overcoat varnish, overprint varnish, or the like.

[0118] In the microwave heat generating film according to one embodiment, the printing process in which the low resistance layer, the high resistance layer, the printing ink layer, and the anchor coat layer are formed may be a gravure printing method using one or more units of a multi-color gravure printer. This allows the low resistance layer, the high resistance layer, the printing ink layer, the anchor coat layer, etc. to be continuously formed on the substrate in-line, and the microwave heat generating film can be easily manufactured in a series of steps (one pass) at low cost. In addition, the openability and heat generation of the steam escape hole can be easily controlled. When continuous in-line formation is not possible due to constraints such as the specifications of the gravure printer, the printing environment, and the equipment, the formation may be performed offline (outline).

[0119] Furthermore, in the case of a printing process using a gravure printing method, when a low resistance layer and a high resistance layer are formed, if a dot area rate of 100% results in excessive heat generation, or depending on the required degree of openability of the steam escape opening, the openability and heat generation can be easily controlled by lowering the dot area rate, adjusting the plate depth, or adjusting the dilution rate.

[0120] The low resistance layer and the high resistance layer may be formed only in the area where the opening is desired, or may be formed on the entire surface. Also, different coating patterns such as designs or motifs may be formed depending on the shape of the steam escape opening and the required degree of openability.

[0121] In addition, the printing process is preferably a gravure printing method in which one or more colors of gravure ink are formed, and a printed ink layer can be formed arbitrarily, such as on the opposite sides of the low-resistance layer and the high-resistance layer, between the substrate and the low-resistance layer and the high-resistance layer, or between the low-resistance layer and the high-resistance layer and the anchor coat layer.

[0122] Furthermore, the printing process is preferably a gravure printing method using a multi-color gravure printer. The low resistance layer and the high resistance layer are almost uncolored and transparent, so that the formation of the printing ink layer can be simultaneously provided in-line without interfering with other information such as a pattern, and various color variations and color designs can be obtained. For example, the design of the package can be added, and the purchase appeal effect can be enhanced, information on the opening location, opening method, and warning can be displayed, and information such as the company name, logo, product name, character, contents, ingredient display, application method, campaign announcement, how to eat or use, date, place of origin, and winning lottery can be added.

[0123] The method may also include a forming process in which an intermediate layer, an anchor coat layer, an overcoat layer, etc. are formed. These layers are not particularly limited as long as they are formed by known processes such as lamination or coating.

[0124] Each composition, such as a low resistance composition, a high resistance composition, a printing ink, and an anchor coating agent, can be produced by a known method by uniformly dissolving or dispersing a conductive organic compound, a resin, a pigment, a sealing resin, various additives, etc. in a solvent. For dissolving or dispersing, various stirrers or dispersers such as a dissolver, a roll mill, a ball mill, a bead mill, a sand mill, an attritor, a paint shaker, an agitator, a Henschel mixer, a colloid mill, a pearl mill, an ultrasonic homogenizer, a wet jet mill, a kneader, and a homomixer can be used. These devices may be used alone or in combination of two or more. When air bubbles or coarse particles are contained in each composition, they are preferably removed using a known filter, centrifuge, etc., since they deteriorate the printability and the quality of the printed matter.

[0125] The viscosity of each of the above compositions is not particularly limited as long as it does not interfere with printing. In consideration of the manufacturability and handling of each composition, it is preferable that the viscosity is 10 mPa·s to 1000 mPa·s at 25°C. Furthermore, for gravure printing inks, it is more preferable that the viscosity is 10 mPa·s to 500 mPa·s.

[0126] The viscosity can be measured using a commercially available viscometer such as a Brookfield viscometer.

[0127] The microwave heat generating film according to one embodiment includes a low resistance layer and a high resistance layer, and the low resistance layer and the high resistance layer include the low resistance composition and the high resistance composition according to the above-mentioned embodiment. In the microwave heat generating film according to one embodiment, the microwave heat generating layer generates heat by irradiation with microwaves, and when the low resistance layer and the high resistance layer are overlapped on the heat seal part, an opening part can be formed from the heat seal part by shrinking the film. In addition, when the low resistance layer and the high resistance layer are provided in the center part of the microwave heat generating film, an opening part can be easily formed from the center part by breaking the microwave heat generating film. Therefore, the microwave heat generating film according to one embodiment can exhibit high vapor permeability that can provide a vapor hole without causing a short circuit even when a large amount of food is sealed in a container, and can prevent the film from falling into the container even if a vapor hole is provided.

[0128] Since the microwave heating film according to one embodiment has the above-mentioned properties, it can be suitably used as a microwave heating film for packaging, and can be particularly effectively used as a microwave heating film for packaging that allows steam to escape.

[0129] <Microwave heating packaging> A microwave heating package according to one embodiment of the present invention has at least the microwave heating film according to one embodiment of the present invention described above, and if necessary, further has a container or film for receiving the contents of the package.

[0130] The microwave heating package may be in any form that microwave heating films are generally used in. The microwave heating package may be a two-sided seal, three-sided seal, four-sided seal, pillow seal, standing pouch, envelope seal, gusset, melt-cut seal, tube, caramel package, overhold, fin seal, bun package, twist, rocket, Tetra Pak (registered trademark), gable top, brick, shibori, cup, tray, bottle, brick, container, box, case, food box, cover, lid, cap, lid material, label, sheet, etc.

[0131] The method for producing a microwave heating package preferably includes a forming step of forming the package using a microwave heating film.

[0132] In the forming step, the microwave heat generating film may be formed into a package. One microwave heat generating film may be folded back and both ends sealed to form a bag. Alternatively, two microwave heat generating films may be stacked facing each other and both ends sealed to form a bag.

[0133] In addition, the forming step may involve covering the container with a microwave heating film and forming it into a package.

[0134] The forming process may use a method used in forming general packaging bodies such as two-sided seal, three-sided seal, four-sided seal, pillow seal, standing pouch, envelope sealing, gusset, melt-cut seal, tube, caramel packaging, overhold, fin seal, bun packaging, twist, rocket, Tetra Pak (registered trademark), gable top, brick, shibori, cup, tray, bottle, brick, container, box, case, food box, cover, lid, cap, lid material, label, sheet, etc.

[0135] An example of the configuration of a microwave heating package according to one embodiment is shown in FIG.

[0136] FIG. 18 shows an example of a microwave heat generating package 200 using the microwave heat generating film 100 according to one embodiment. The microwave heat generating package 200 is a packaging container in which a microwave heat generating film 100 and a container 202 are heat sealed at a heat seal portion 201, and is an oblique view in which the microwave heat generating film 100 is arranged so that the low resistance layer 1 and the high resistance layer 2 are positioned so that they are not aligned perpendicularly to the heat seal portion 201 in a plan view. In FIG. 18, the container 202 has a rectangular parallelepiped shape, but the shape may be changed to any shape, such as a cylinder, a cube, or a triangular prism, depending on the contents and design.

[0137] The microwave heat generating package according to one embodiment includes a high resistance layer and a low resistance layer, and the high resistance layer and the low resistance layer include the high resistance composition and the low resistance composition according to the above-mentioned embodiment. In the microwave heat generating package according to one embodiment, the high resistance layer and the low resistance layer generate heat by irradiation of microwaves during heating, and when the high resistance layer and the low resistance layer are overlapped on the heat seal part, an opening part is easily formed from the heat seal part by shrinking of the film. In addition, when the high resistance layer and the low resistance layer are provided in the center part of the microwave heat generating film, an opening part is easily formed from the center part by breaking the microwave heat generating film. Therefore, the microwave heat generating film according to one embodiment can exhibit high vapor permeability that can provide a vapor passage hole without causing a short circuit even when a large amount of food is sealed in the container, and can prevent the film from falling into the container even if a vapor passage hole is provided.

[0138] The microwave heat generating package according to one embodiment can exhibit high heat generating capacity even when a large amount of food is contained therein, and therefore can be suitably used, for example, as a package in which holes are formed by microwave irradiation. The microwave heat generating package according to one embodiment can also be suitably used, for example, as a cooking sheet in which food is browned by microwave irradiation.

[0139] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. EXAMPLES

[0140] The embodiments will be described in more detail below with reference to examples and comparative examples, but the embodiments are not limited to these examples and comparative examples.

[0141] <Production of composition for forming high resistance layer> A composition for forming a high resistance layer was obtained by mixing 10 parts by mass of a PEDOT:PSS solution (S-300, manufactured by Agfa Materials Japan) as a conductive material and 2 parts by mass of ethanol.

[0142] <Production of composition for forming low resistance layer> [Composition 1 for forming low resistance layer] A low resistance layer forming composition 1 was obtained by mixing 90 parts by mass of copper powder (CuC-40, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) as a conductive material, 5 parts by mass of polyester resin (GK-810, manufactured by Toyobo Co., Ltd.), and 20 parts by mass of MEK.

[0143] [Composition 2 for forming low resistance layer] A low resistance layer forming composition 2 was obtained by mixing 90 parts by mass of silver powder (Ag-HWQ, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) as a conductive material, 5 parts by mass of polyester resin (GK-810, manufactured by Toyobo Co., Ltd.), and 20 parts by mass of MEK.

[0144] [Composition 3 for forming low resistance layer] A low resistance layer forming composition 3 was obtained by mixing 90 parts by mass of copper powder (SF-Cu, manufactured by Nippon Atomize Kako Co., Ltd.) as a conductive material, 5 parts by mass of polyester resin (GK-810, manufactured by Toyobo Co., Ltd.), and 20 parts by mass of MEK.

[0145] [Composition 4 for forming low resistance layer] A low resistance layer forming composition 4 was obtained by mixing 90 parts by mass of copper powder (EFC-09LML, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) as a conductive material, 5 parts by mass of polyester resin (GK-810, manufactured by Toyobo Co., Ltd.), and 20 parts by mass of MEK.

[0146] [Composition 5 for forming low resistance layer] A low resistance layer forming composition 5 was obtained by mixing 90 parts by mass of copper powder (CuMA-C08JF, manufactured by Mitsui Mining & Smelting Co., Ltd.) as a conductive material, 5 parts by mass of polyester resin (GK-810, manufactured by Toyobo Co., Ltd.) and 20 parts by mass of MEK.

[0147] [Composition 6 for forming low resistance layer] A low resistance layer forming composition 6 was obtained by mixing 90 parts by mass of aluminum flakes (MS630, manufactured by Toyo Aluminum Co., Ltd.) as a conductive material, 5 parts by mass of polyester resin (GK-810, manufactured by Toyobo Co., Ltd.), and 20 parts by mass of MEK.

[0148] <Production of microwave heating film> [Production Example 1] Composition 1 for forming a low resistance layer was applied onto the sealant using a gravure printer so as to obtain the coating shape shown in FIG. 13a, and dried at 90° C. for 5 minutes to form a low resistance layer. Next, a composition for forming a high-resistance layer was applied onto the sealant using a gravure printer so as to obtain the coating shape shown in FIG. 13a, and dried at 90° C. for 5 minutes to form a high-resistance layer. Next, the film was stored at 25° C. for 24 hours to prepare microwave heat generating film 1. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 1.1. In addition, the length average diameter in the number-based distribution of the low resistance layers and the resistance values ​​of the low resistance layers and high resistance layers in the obtained microwave heating film 1 were measured using the method described below.The length average diameter in the number-based distribution of the low resistance layers was 0.4 μm, the resistance value of the low resistance layers was 21 Ω, and the resistance value of the high resistance layers was 2,500 Ω. The physical properties of the microwave heating film 1 are shown in Table 1.

[0149] <Length-average diameter in number-based distribution of low-resistivity layers> The length-average diameter in the number-based distribution of the low-resistance layer was determined from the grain morphology observed from a cross-section of the low-resistance layer in the microwave heating film 1. For the cross-section observation, a sample was prepared by a conventional method, a cross-sectional TEM photograph was taken with a transmission electron microscope (TEM, JEM-210, manufactured by JEOL Ltd.), five conductive materials were measured, and the average value of the diameters was taken as the length-average diameter in the number-based distribution of the conductive material.

[0150] <Resistance value of low resistance layer> The resistance value of the low resistance layer was determined by measuring the surface resistance of the low resistance layer of the microwave heating film three times using a tester (Custom Digital Multimeter CDM-2000D), and taking the average value as the resistance value of the low resistance layer.

[0151] <Resistance value of high resistance layer> The resistance value of the high resistance layer was determined by measuring the surface resistance of the high resistance layer of the microwave heating film three times using a tester (Custom Digital Multimeter CDM-2000D), and taking the average value as the resistance value of the high resistance layer.

[0152] [Production Example 2] A microwave heat generating film 2 was obtained in the same manner as in Production Example 1, except that the low resistance layer forming composition 1 in Production Example 1 was changed to a low resistance layer forming composition 2. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 1.1. In addition, using a method similar to that used in Manufacturing Example 1, the length average diameter in the number-based distribution of the low resistance layers and the resistance values ​​of the low resistance layers and high resistance layers were measured.The length average diameter in the number-based distribution of the low resistance layers was 1.5 μm, the resistance value of the low resistance layers was 2 Ω, and the resistance value of the high resistance layers was 2,500 Ω. The physical properties of the microwave heating film 2 are shown in Table 1.

[0153] [Production Example 3] A microwave heat generating film 3 was obtained in the same manner as in Production Example 1, except that the composition 1 for forming a low resistance layer in Production Example 1 was changed to the composition 3 for forming a low resistance layer. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 1.1. In addition, using a method similar to that used in Manufacturing Example 1, the length average diameter in the number-based distribution of the low resistance layer and the resistance values ​​of the low resistance layer and high resistance layer were measured.The length average diameter in the number-based distribution of the low resistance layer was 11 μm, the resistance value of the low resistance layer was 242 Ω, and the resistance value of the high resistance layer was 2,500 Ω. The physical properties of the microwave heating film 3 are shown in Table 1.

[0154] [Production Example 4] A microwave heating film 4 was obtained by the same manufacturing method as in Manufacturing Example 1, except that the coating shape shown in Figure 13A in Manufacturing Example 1 was changed to the coating shape shown in Figure 14A and the low resistance layer forming composition 1 was changed to the low resistance layer forming composition 4. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 2.5. In addition, using a method similar to that used in Production Example 1, the length average diameter in the number-based distribution of the low resistance layer and the resistance values ​​of the low resistance layer and high resistance layer were measured.The length average diameter in the number-based distribution of the low resistance layer was 1.3 μm, the resistance value of the low resistance layer was 143 Ω, and the resistance value of the high resistance layer was 2,500 Ω. The physical properties of the microwave heating film 4 are shown in Table 1.

[0155] [Production Example 5] A microwave heating film 5 was obtained in the same manner as in Production Example 1, except that the coating shape shown in FIG. 13A in Production Example 1 was changed to the coating shape shown in FIG. 15A. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 10.0. In addition, using a method similar to that used in Production Example 1, the length average diameter in the number-based distribution of the low resistance layer and the resistance values ​​of the low resistance layer and high resistance layer were measured.The length average diameter in the number-based distribution of the low resistance layer was 0.4 μm, the resistance value of the low resistance layer was 21 Ω, and the resistance value of the high resistance layer was 2,500 Ω. The physical properties of the microwave heating film 5 are shown in Table 1.

[0156] [Production Example 6] A microwave heating film 6 was obtained in the same manner as in Production Example 1, except that the low resistance layer in Production Example 1 was formed by depositing silver in the coating shape shown in Figure 13A using a vacuum deposition apparatus (SPF-210H manufactured by Nichiden Anelva). The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 1.1. In addition, using a method similar to that used in Production Example 1, the length average diameter in the number-based distribution of the low resistance layer and the resistance values ​​of the low resistance layer and high resistance layer were measured.The length average diameter in the number-based distribution of the low resistance layer was below the measurement limit, the resistance value of the low resistance layer was 0.04 Ω, and the resistance value of the high resistance layer was 2,500 Ω. The physical properties of the microwave heating film 6 are shown in Table 1.

[0157] [Production Example 7] A microwave heating film 7 was obtained in the same manner as in Production Example 1, except that the composition 1 for forming a low resistance layer in Production Example 1 was changed to the composition 5 for forming a low resistance layer. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 1.1. In addition, using a method similar to that used in Manufacturing Example 1, the length average diameter in the number-based distribution of the low resistance layers and the resistance values ​​of the low resistance layers and high resistance layers were measured.The length average diameter in the number-based distribution of the low resistance layers was 12 μm, the resistance value of the low resistance layers was 300 Ω, and the resistance value of the high resistance layers was 2,500 Ω. The physical properties of the microwave heating film 7 are shown in Table 1.

[0158] [Production Example 8] A microwave heat generating film 8 was obtained in the same manner as in Production Example 1, except that the composition for forming a high resistance layer in Production Example 1 was changed to the composition 1 for forming a low resistance layer. In addition, when the length average diameter in the number-based distribution of the low resistance layers and the resistance value of the low resistance layers were measured using a method similar to that used in Production Example 1, the length average diameter in the number-based distribution of the low resistance layers was 0.4 μm, and the resistance value of the low resistance layers was 21 Ω. The physical properties of the microwave heating film 8 are shown in Table 1.

[0159] [Production Example 9] A microwave heat generating film 9 was obtained in the same manner as in Production Example 1, except that the low resistance layer forming composition 1 in Production Example 1 was changed to a high resistance layer forming composition. Furthermore, when the resistance value of the high resistance layer was measured in the same manner as in Production Example 1, the resistance value of the high resistance layer was 2,500 Ω. The physical properties of the microwave heating film 9 are shown in Table 1.

[0160] [Production Example 10] A microwave heating film 10 was obtained in the same manner as in Production Example 1, except that the coating shape shown in FIG. 13A in Production Example 1 was changed to the coating shape shown in FIG. 19A. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 0.8. In addition, using a method similar to that used in Manufacturing Example 1, the length average diameter in the number-based distribution of the low resistance layer and the resistance values ​​of the low resistance layer and high resistance layer were measured.The length average diameter in the number-based distribution of the low resistance layer was 0.4 μm, the resistance value of the low resistance layer was 21 Ω, and the resistance value of the high resistance layer was 2,500 Ω. The physical properties of the microwave heating film 10 are shown in Table 1.

[0161] [Production Example 11] A microwave heat generating film 11 was obtained in the same manner as in Production Example 1, except that the composition 1 for forming a low resistance layer in Production Example 1 was changed to the composition 6 for forming a low resistance layer. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 1.1. The physical properties of the microwave heating film 11 are shown in Table 1.

[0162] [Production Example 12] A microwave heating film 12 was obtained in the same manner as in Production Example 1, except that the coating shape shown in FIG. 13A in Production Example 1 was changed to the coating shape shown in FIG. 15A. The area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view was 20.0. In addition, using a method similar to that used in Production Example 1, the length average diameter in the number-based distribution of the low resistance layer and the resistance values ​​of the low resistance layer and high resistance layer were measured.The length average diameter in the number-based distribution of the low resistance layer was 0.4 μm, the resistance value of the low resistance layer was 21 Ω, and the resistance value of the high resistance layer was 2,500 Ω. The physical properties of the microwave heating film 12 are shown in Table 1.

[0163] <Production of evaluation samples> 300 g of water-soaked Kimtowel (manufactured by Nippon Paper Crecia Co., Ltd.) was placed in a PP container, and the PP container and each of the microwave heating films obtained in Production Examples 1 to 12 were heat-sealed at 180°C for 1 second to obtain each evaluation sample.

[0164] [Table 1]

[0165] The microwave heating films obtained in each production example were evaluated for "vapor permeability," "dropping of molten film," "burning of film," and "short circuiting."

[0166] [Vaporability] The evaluation sample was heated in a microwave oven (IMB-T174-5-W, manufactured by Iris Ohyama) at 500 W for 120 seconds. The "vaporability" was evaluated based on the area of ​​the vapor holes formed after heating, according to the following evaluation criteria. The evaluation results are shown in Table 2. (Evaluation Criteria) ◎: Steam hole is 2.0mm 2 End ○: Steam hole is 2.0mm 2 less than ×: No steaming

[0167] [Molten film falling] The evaluation sample was heated in a microwave oven (RE-7500, manufactured by Sharp Corporation) at 1,600 W for 60 seconds, and the presence or absence of molten film fragments falling from the microwave heating film into the container was visually observed, and the "falling of molten film" was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2. (Evaluation Criteria) ○: No falling of melted film fragments ×: Melted film fragments fell

[0168] [Film burnt] The evaluation sample was heated in a microwave oven (RE-7500, manufactured by Sharp Corporation) at 1,600 W for 60 seconds, after which the microwave heating film was visually inspected for discoloration due to scorching caused by the microwave heating layer, and the "film scorching" was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2. (Evaluation Criteria) 〇: No discoloration due to burning on the film ×: The film has discoloration due to burning.

[0169] [Short circuit] The evaluation sample was heated in a microwave oven (RE-7500 manufactured by Sharp Corporation) at 1,600 W for 60 seconds, and the occurrence of short circuits was visually observed and evaluated for "short circuit properties" based on the following evaluation criteria. The evaluation results are shown in Table 2. (Evaluation Criteria) ○: No short circuit occurs ×: Sparks occurred due to a short circuit.

[0170] [Table 2]

[0171] The aspects of the embodiment of the present invention are as follows, for example. <1> a low resistance layer having a resistance value of 1 Ω or more and 250 Ω or less; a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, A microwave heating film, comprising at least a portion of the low resistance layer and at least a portion of the high resistance layer laminated together. <2> an area ratio (A / B) of an area (A) of the low resistance layer in a planar view to an area (B) of the high resistance layer in a planar view is 1.0 or more and 10.0 or less; <1> The microwave heating film according to claim 1. <3> The resistance value of the low resistance layer is 1 Ω or more and 150 Ω or less. <1> from <2> The microwave heating film according to any one of claims 1 to 5. <4> the low resistance layer comprises a conductive material, The conductive material has a length average diameter of 10.0 μm or less in a number-based distribution. <1> from <3> The microwave heating film according to any one of claims 1 to 5. <5> The above <1> from <4> A microwave heating package comprising the microwave heating film according to any one of claims 1 to 4. <6> forming a low resistance layer having a resistance value of 1 Ω or more and 250 Ω or less on at least one of the substrates; forming a high resistance layer having a resistance value higher than the resistance value of the low resistance layer on at least one of the base materials; A method for producing a microwave heating film, comprising laminating at least a portion of the low resistance layer and at least a portion of the high resistance layer. <7> an area ratio (A / B) of an area (A) of the low resistance layer in a planar view to an area (B) of the high resistance layer in a planar view is 1.0 or more and 10.0 or less; <6> A method for producing the microwave heating film according to claim 1. <8> A low resistance layer; a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, At least a part of the low resistance layer and at least a part of the high resistance layer are laminated together, A microwave heating film, characterized in that the area ratio (A / B) of the area (A) of the low resistance layer in a planar view to the area (B) of the high resistance layer in a planar view is 1.0 or more and 10.0 or less. [Explanation of symbols]

[0172] 1 High resistance layer 2 Low resistance layer 3. Microwave heating layer 10 Base material 11. Substrate with sealing properties 12. Sealant 100~111 Microwave heating film 200 Microwave heating packaging 201 Heat seal section 202 Container [Prior art documents] [Patent documents]

[0173] [Patent Document 1] Patent No. 6713797 [Patent Document 2] JP 2021-039944 A

Claims

1. A low resistance layer having a resistance value of 1 Ω or more and 250 Ω or less; a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, A microwave heating film, comprising at least a portion of the low resistance layer and at least a portion of the high resistance layer laminated together.

2. 2. The microwave heating film according to claim 1, wherein an area ratio (A / B) of an area (A) of the low resistance layer in a planar view to an area (B) of the high resistance layer in a planar view is 1.0 or more and 10.0 or less.

3. The microwave heating film according to claim 1 , wherein the low resistance layer has a resistance value of 1 Ω or more and 150 Ω or less.

4. the low resistance layer comprises a conductive material, The microwave heating film according to claim 1 , wherein the conductive material has a length-average diameter of 10.0 μm or less in a number-based distribution.

5. A microwave heating package comprising the microwave heating film according to claim 1 .

6. forming a low resistance layer having a resistance value of 1 Ω or more and 250 Ω or less on at least one of the substrates; forming a high resistance layer having a resistance value higher than the resistance value of the low resistance layer on at least one of the base materials; A method for producing a microwave heating film, comprising laminating at least a portion of the low resistance layer and at least a portion of the high resistance layer.

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