Microwave heatable film, microwave heatable package, and method for producing microwave heatable film

Abstract

A microwave heatable film including a low resistance layer (2) having a resistance value of 1 Ohm or more and 250 Ohm or less, and a high resistance layer (1) having a resistance value higher than the resistance value of the low resistance layer, in which at least a part of the low resistance layer and at least a part of the high resistance layer are laminated together.

Description

MICROWAVE HEATABLE FILM, MICROWAVE HEATABLE PACKAGE, AND METHOD FOR PRODUCING MICROWAVE HEATABLE FILM [Technical Field]

[0001] The present disclosure relates to a microwave heatable film, a microwave heatable package, and a method for producing a microwave heatable film.[Background Art]

[0002] [Background Art]A package storing a food material is sometimes heated and cooked in a microwave oven while the food material is sealed inside the package. Thus, when a means for causing steam to be released from the inside of the package is provided in the package, the steam from the food material heated by microwaves is released from the package, allowing the package to exhibit steam permeability.Examples of a means for releasing the steam from the inside of the package include a method of providing an opening in a heat-sealing portion or an upper part of the package.Regarding the method of providing an opening in a heat- sealing portion or an upper part of the package, a method is provided which provides a coating layer that generates heat by microwaves on a film-like microwave heatable package that covers the container. A microwave heatable package is disclosed in which the coating layer is heated when irradiated with microwaves, causing a part of the microwave heatable package to melt and form an opening through which the steam is released (e.g., see PTL 1).A conventional microwave heating technology is disclosed in which only a single microwave heatable layer is provided. However, depending on the amount of the food material, most of the microwaves are absorbed by the food material, thereby reducing the amount of microwaves irradiated to the microwave heatable layer, resulting in a problem of not being able to provide the steam opening.Further, a technology for improving steam permeability by laminating different conductive materials has been disclosed (e.g., see PTL 2).However, depending on the resistance value of the conductive material, there is a risk of a short circuit and fire, posing a safety issue.[Citation List][Patent Literature]

[0003] [PTL 1]Japanese Patent No. 6713797[PTL 2]Japanese Unexamined Patent Application Publication No. 2021-039944[Summary of Invention][Technical Problem]

[0004] An object of the present disclosure is to provide a microwave heatable film having high steam permeability, which can provide a steam opening even when the water content in a container is high without causing a short circuit.[Solution to Problem]

[0005] A microwave heatable film according to one embodiment of the present disclosure includes a low resistance layer having a resistance value of 1 or more and 250 or less, and a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, and at least a part of the low resistance layer and at least a part of the high resistance layer are laminated together.[Advantageous Effects of Invention]

[0006] One embodiment of the present disclosure can provide a microwave heatable film having high steam permeability, which can provide a steam opening even when the water content in the container is high without causing a short circuit.[Brief Description of Drawings]

[0007] A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings.[FIG. 1A]FIG. 1A is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. IB]FIG. IB is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 1C]FIG. 1C is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 2A]FIG. 2A is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 2B]FIG. 2B is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 2C]FIG. 2C is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 3]FIG. 3 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 4]FIG. 4 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 5]FIG. 5 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 6]FIG. 6 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 7]FIG. 7 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 8]FIG. 8 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 9]FIG. 9 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 10]FIG. 10 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 11]FIG. 11 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 12]FIG. 12 is a schematic cross-sectional view of a microwave heatable film according to one embodiment of the present disclosure.[FIG. 13 A]FIG. 13 A is a schematic plan view seen from above, of the shape of a microwave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 13B]FIG. 13B is a schematic plan view seen from above, of the shape of the microwave heatable layer in a microwave heatable film according to one embodiment of the present disclosure.[FIG. 14A]FIG. 14A is a schematic plan view seen from above, of the shape of a micro wave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 14B]FIG. 14B is a schematic plan view seen from above, of the shape of the micro wave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 15 A]FIG. 15A is a schematic plan view seen from above, of the shape of a microwave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 15B]FIG. 15B is a schematic plan view seen from above, of the shape of the micro wave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 16 A]FIG. 16A is a schematic plan view seen from above, of the shape of a micro wave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 16B]FIG. 16B is a schematic plan view seen from above, of the shape of the micro wave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 17A]FIG. 17 A is a schematic plan view seen from above, of the shape of a micro wave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 17B]FIG. 17B is a schematic plan view seen from above, of the shape of the micro wave heatable layer in a microwave heatable film according to one embodiment of the present disclosure. [FIG. 18]FIG. 18 is a perspective view of a micro wave heatable package according to one embodiment of the present disclosure.[FIG. 19]FIG. 19 is a schematic plan view seen from above, of the shape of the microwave heatable layer in the micro wave heatable film according to Production example 10.The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views. [Description of Embodiments]

[0008] In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific elementincludes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0009] Hereinafter, embodiments of the present disclosure are described in detail. Note that, in the present specification, a numerical range “X to Y” means a range of values including X as a lower limit and Y as an upper limit, unless otherwise specified.In the present disclosure, the term “releasing steam” means that a steam-releasing opening (in the present specification, also referred to as a “steam opening”) is formed.

[0010] <Microwave heatable film>A microwave heatable film according to one embodiment of the present disclosure is described.The microwave heatable film includes a microwave heatable layer including a low resistance layer and a high resistance layer, and may further include a base material, a sealant, an adhesive layer, a printing ink layer, an anchor coat layer, an overcoat layer, and other layers, as necessary.

[0011] FIG. 1 to FIG. 12 are cross-sectional views seen from one side, each showing a microwave heatable film according to one embodiment of the present disclosure.

[0012] As illustrated in FIG. 1A, a microwave heatable film 100A includes a base material 10 and a micro wave heatable layer 3 including a high resistance layer 1 and a low resistance layer 2. In the micro wave heatable film 100A, the base material 10, the high resistance layer 1, and the low resistance layer 2 are laminated in this order such that the entirety of the high resistance layer 1 is in contact with the base material 10. Further, the entirety of the high resistance layer 1 and the entirety of the low resistance layer 2 are laminated together.

[0013] As illustrated in FIG. IB, a microwave heatable film 100B includes the base material 10 and the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2. In the microwave heatable film 100B, the base material 10, the high resistance layer 1, and the low resistance layer 2 are partially laminated in this order such that the entirety of the high resistance layer 1 is in contact with the base material 10 and a part of the low resistance layer 2 is in contact with the base material 10. Further, a part of the high resistance layer 1 and a part of the low resistance layer 2 are laminated together.

[0014] As illustrated in FIG. 1C, a microwave heatable film 100C includes the base material 10 and the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2. In the micro wave heatable film 100C, the base material 10, the high resistance layer 1, and the low resistance layer 2 are laminated in this order such that the entirety of the high resistance layer 1 is in contact with the base material 10. Further, a part of the high resistance layer 1 and the entirety of the low resistance layer 2 are laminated together.

[0015] As illustrated in FIG. 2A, a microwave heatable film 101A includes the base material 10 and the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2. In the microwave heatable film 101A, the base material 10, the low resistance layer 2, and the high resistance layer 1 are laminated in this order such that the entirety of the low resistance layer 2 is in contact with the base material 10. Further, the entirety of the high resistance layer 1 and the entirety of the low resistance layer 2 are laminated together.

[0016] As illustrated in FIG. 2B, a microwave heatable film 101B includes the base material 10 and the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2. In the microwave heatable film 101B, the base material 10, the low resistance layer 2, and the high resistance layer 1 are partially laminated in this order such that the entirety of the low resistance layer 2 is in contact with the base material 10 and a part of the high resistance layer 1 is in contact with the base material 10. Further, a part of the high resistance layer 1 and a part of the low resistance layer 2 are laminated together.

[0017] As illustrated in FIG. 2C, a microwave heatable film 101C includes the base material 10 and the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2. In the microwave heatable film 101C, the base material 10, the low resistance layer 2, and the high resistance layer 1 are laminated in this order such that the entirety of the low resistance layer 2 is in contact with the base material 10. Further, the entirety of the high resistance layer 1 and a part of the low resistance layer 2 are laminated together.

[0018] As illustrated in FIG. 3, a microwave heatable film 102 includes a base material 11 with sealing properties and the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2. In the microwave heatable film 102, the base material 11 with sealing properties, the high resistance layer 1, and the low resistance layer 2 are laminated in this order such that the entirety of the high resistance layer 1 is in contact with the base material 11 with sealing properties.

[0019] As illustrated in FIG. 4, a microwave heatable film 103 includes the base material 11 with sealing properties and the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2. In the microwave heatable film 103, the base material 11 withsealing properties, the low resistance layer 2, and the high resistance layer 1 are laminated in this order such that the entirety of the low resistance layer 2 is in contact with the base material 11 with sealing properties.

[0020] As illustrated in FIG. 5, a microwave heatable film 104 includes the base material 10, the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2, and a sealant 12. In the microwave heatable film 104, the sealant 12, the low resistance layer 2, the high resistance layer 1, and the base material 10 are laminated in this order such that the entirety of the high resistance layer 1 is in contact with the base material 10.

[0021] As illustrated in FIG. 6, a microwave heatable film 105 includes the base material 10, the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2, and the sealant 12. In the microwave heatable film 105, the sealant 12, the high resistance layer 1, the low resistance layer 2, and the base material 10 are laminated in this order such that the entirety of the low resistance layer 2 is in contact with the base material 10.

[0022] As illustrated in FIG. 7, a microwave heatable film 106 includes the base material 10, the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2, and the sealant 12. In the microwave heatable film 106, the sealant 12, the base material 10, the low resistance layer 2, and the high resistance layer 1 are laminated in this order such that the entirety of the low resistance layer 2 is in contact with the base material 10.

[0023] As illustrated in FIG. 8, a microwave heatable film 107 includes the base material 10, the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2, and the sealant 12. In the microwave heatable film 107, the sealant 12, the base material 10, the high resistance layer 1, and the low resistance layer 2 are laminated in this order such that the entirety of the high resistance layer 1 is in contact with the base material 10.

[0024] As illustrated in FIG. 9, a microwave heatable film 108 includes the base material 10, the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2, and the sealant 12. In the microwave heatable film 108, the low resistance layer 2, the high resistance layer 1, the sealant 12, and the base material 10 are laminated in this order such that the entirety of the high resistance layer 1 is in contact with the sealant 12.

[0025] As illustrated in FIG. 10, a microwave heatable film 109 includes the base material 10, the microwave heatable layer 3 including the high resistance layer 1 and the low resistance layer 2, and the sealant 12. In the microwave heatable film 109, the high resistance layer 1, the low resistance layer 2, the sealant 12, and the base material 10 are laminated in this order such that the entirety of the low resistance layer 2 is in contact with the sealant 12.

[0026] As illustrated in FIG. 11, a microwave heatable film 110 includes the base material 10 and the microwave heatable layer 3 formed by laminating the low resistance layer 2, the high resistance layer 1, and the low resistance layer 2 in this order. In the micro wave heatable film110, the base material 10, the low resistance layer 2, the high resistance layer 1, and the low resistance layer 2 are laminated in this order such that the entirety of the low resistance layer 2 is in contact with the base material 10.

[0027] As illustrated in FIG. 12, a microwave heatable film 111 includes the base material 10 and the microwave heatable layer 3 formed by laminating the high resistance layer 1, the low resistance layer 2, and the high resistance layer 1 in this order. In the microwave heatable film111, the base material 10, the high resistance layer 1, the low resistance layer 2, and the high resistance layer 1 are laminated in this order such that the entirety of the high resistance layer 1 is in contact with the base material 10.

[0028] [Microwave heatable layer]The microwave heatable layer includes the low resistance layer that absorbs microwave energy and converts it into an eddy current, and the high resistance layer that converts the eddy current converted in the low resistance layer into Joule heat.Microwaves are radio waves with a frequency of 300 MHz or higher and 300 GHz or lower. Each of the low resistance layer and the high resistance layer may be provided as one layer as illustrated in FIG. 1 A to FIG. 10, or may be a plurality of layers laminated as illustrated in FIG. 11 and FIG. 12.

[0029] FIG. 13A to FIG. 17B are schematic plan views of the microwave heatable layers in the microwave heatable film according to one embodiment of the present disclosure.

[0030] In the embodiment illustrated in FIG. 13 A and FIG. 13B, the microwave heatable layer 3 is configured such that the high resistance layer 1, which is provided in a plurality of pieces (i.e., six pieces), and the low resistance layer 2 are partially overlapped in a plan view. Note that FIG. 13 A and FIG. 13B show opposite sides of the same microwave heatable layer 3, and the same applies to FIGS. 14A to 17B.

[0031] In the embodiment illustrated in FIG. 14A and FIG. 14B, the microwave heatable layer 3 is configured such that the high resistance layer 1, which is provided in a plurality of pieces (i.e., three pieces), and the low resistance layer 2, which is provided in a plurality of pieces (i.e., two pieces), are partially overlapped in a plan view.

[0032] In the embodiment illustrated in FIG. 15A and FIG. 15B, the microwave heatable layer 3 is configured such that the high resistance layer 1 and the low resistance layer 2, which is provided in a plurality of pieces (i.e., two pieces), are partially overlapped in a plan view.

[0033] In the embodiment illustrated in FIG. 16A and FIG. 16B, the microwave heatable layer 3 is configured such that the high resistance layer 1, which is provided in a plurality of pieces (i.e., two pieces), and the low resistance layer 2, which is provided in a plurality of pieces (i.e., two pieces), are partially overlapped in a plan view.

[0034] In the embodiment illustrated in FIG. 17A and FIG. 17B, the microwave heatable layer 3 is configured such that the high resistance layer 1, which is provided in a plurality of pieces (i.e., seven pieces), and the low resistance layer 2, which is provided in a plurality of pieces (i.e., two pieces), are partially overlapped in a plan view.

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

[0036] The number of the high resistance layer is not particularly limited and can be appropriately selected depending on the purpose. For example, there may be one high resistance layer as illustrated in FIG. 15A and FIG. 15B, or there may be two or more high resistance layers as illustrated in FIG. 13A to FIG. 14B and FIG. 16A to FIG. 17B.

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

[0038] In the micro wave heatable layer 3, an area ratio (A / B) of an area (A) of each low resistance layer 2 in a plan view with respect to an 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, the melted film can be prevented from falling. Further, when the area ratio (A / B) is 10.0 or less, film burning can be prevented which is caused by the eddy current generated in the low resistance layer and is moved excessively to the high resistance layer.Conventionally, there is a problem in that, depending on the coating shape of the microwave heatable layer on the microwave heatable film, the steam opening is opened too wide, causing the melted film to fall into the container. Further, a conventional microwave heatable film has a problem of discoloration due to burning caused by the microwave heatable layer. Regarding these problems, one embodiment of the present disclosure sets the area ratio (A / B) to be 1.0or more and 10.0 or less to prevent the melted film from falling into the container and prevent discoloration due to burning caused by the microwave heatable layer.

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

[0040] The resistance value of the low resistance layer is lower than the resistance value of the high resistance layer described below. However, the resistance value is preferably I Q or more and 250 or less, more preferably 1 or more and 150 Q or less, and much more preferably 1 or more and 100 or less. When the resistance value of the low resistance layer is 1 or more, the excessive generation of the eddy current in the low resistance layer can be prevented, and a short circuit in the microwave heatable film can be prevented. Further, when the resistance value of the low resistance layer is 250 or less, microwaves can be sufficiently absorbed, and the eddy current can be generated which is required for heat generation in the high resistance layer.

[0041] When the resistance value of the low resistance layer is 1 or more and 250 or less, and the area ratio (A / B) is 1.0 or more and 10.0 or less, a short circuit in the microwave heatable film can be prevented, thereby preventing the melted film from falling and the film from burning, while generating the eddy current necessary for heat generation in the high resistance layer.

[0042] A 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 material)The conductive material is not particularly limited and can be appropriately selected depending on the purpose. Examples of the conductive material include a non-metallic inorganic material such as carbon black or graphite, a metal such as gold, silver, copper, aluminum, zinc, tin, or iron, an alloy or an oxide of these metals, and an organic material such as a thiophene-based material, an aniline-based material, or a pyrrole-based material. Of these, from the viewpoint of electrical conductivity, a metal, an alloy, and a metal oxide are preferable, and a metal is more preferable. Further, among metals, gold, silver, and copper are preferable.

[0044] The conductive material is preferably in the form of particles, as such a shape can prevent a short circuit caused by excessive current flow. Further, the conductive material in the particle form can be easily turned into ink.

[0045] 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. However, it is preferably 10pm or less. When the length-average diameter in the number-based distribution is 10 pm or less, it becomes easy to control the resistance value of the low resistance layer to an appropriate value. Further, the number of interparticle contacts necessary for electrical conductivity increases, and the required electrical conductivity can be obtained.

[0046] A 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, it can be determined from the shape of the conductive material observed in the cross section of the low resistance layer.The cross section can be observed, for example, by preparing a sample by a conventional method and using a transmission electron microscope (TEM) for the measurement.A measurement value of the length average diameter in the number-based distribution of the conductive material obtained by the observation using the TEM and a measurement value of the length average diameter in the number-based distribution of the conductive material of a low resistance layer forming composition used to form the low resistance layer are substantially consistent, thus the particle size distribution of the conductive material after the low resistance layer is formed can be set by the particle size distribution of the conductive material in the low resistance layer forming composition.Note that the length-average diameter in the volume -based distribution of the conductive material in the low resistance layer forming composition can be measured, for example, by a laser diffusion method using LA-960 manufactured by Horiba, Ltd. or the like.

[0047] The content of the conductive material in the low resistance layer is not particularly limited and can be appropriately selected depending on the purpose. However, the content of the conductive material in the low resistance layer is preferably 50% by mass or more and 99% by mass or less. When the content of the conductive material is 50% by mass or more, microwaves can be sufficiently absorbed, and the eddy current required for heat generation in the high resistance layer can be generated. When the content of the conductive material is 99% by mass or less, the excessive generation of the eddy current in the low resistance layer can be prevented, and a short circuit in the microwave heatable film can be prevented.

[0048] (Other components)Other components are not particularly limited and can be appropriately selected depending on the purpose. Examples of other components include a resin, a coloring material, a wax, a pigment dispersant, and a crosslinking agent.

[0049] There are no particular limitations on the resin as long as it does not impair microwave absorption, and it can be appropriately selected depending on the purpose such as the base material, application, and configuration. Examples of the resin include a shellac, a rosin, nitrocellulose, cellulose, a rubber, a polyamide resin, a vinyl chloride- vinyl acetate copolymer, a polyester resin, a polyvinylidene chloride resin, a ketone resin, a butyral resin, a chlorinated polypropylene resin, a chlorinated polyethylene resin, a chlorinated ethylene vinyl acetate resin, an ethylene vinyl acetate resin, an acrylic resin, a urethane resin, casein, an alkyd resin, a polyvinyl alcohol resin, an ethylene-vinyl alcohol resin, and a vinyl chloride resin. Of these, from the viewpoint of adhesion to the base material, an acrylic resin, a urethane resin, a vinyl chloride resin, and a rubber are preferable.

[0050] The coloring material is not particularly limited and can be appropriately selected depending on the purpose. Examples of the coloring material include a pigment, a dye, and a mixture thereof. Of these, a pigment is preferable from the viewpoint of durability.

[0051] The pigment is not particularly limited and can be appropriately selected depending on the purpose. Examples of the pigment include an inorganic pigment such as titanium oxide, red iron oxide, barium sulfate, calcium carbonate, silica, zinc oxide, zinc sulfide, mica, talc, pearl, aluminum, or carbon black, an organic pigment such as a phthalocyanine-based pigment, an insoluble azo-based pigment, a condensed azo-based pigment, a dioxazine-based pigment, an anthraquinone-based pigment, a quinacridone -based pigment, a perylene-based pigment, a perinone-based pigment, or a thioindigo-based pigment, and 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 dissolved or dispersed in a solvent, and one or more kinds of dyes may be used in combination. Since the dye can include a coloring material, the dye is extremely useful in terms of color variations and design.

[0053] The pigment dispersant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the pigment dispersant include an anionic surfactant, a cationic surfactant, and a nonionic surfactant. These may be used alone or in combination of two or more.

[0054] The crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the crosslinking agent include a hydrazide-based agent, an isocyanate-based agent, an epoxy-based agent, a carbodiimide-based agent, a silane coupling agent, an oxazoline-based agent, an aziridine-based agent, an imine-based agent, a metal chelating agent, a glyoxal-based agent, and a methylol-based agent. These may be used alone or in combination of two or more. Of these, an isocyanate-based agent, a carbodiimide -based agent, an epoxy-based agent, and an aziridine -based agent are preferable.

[0055] [High resistance layer]The high resistance layer is a layer that utilizes the eddy current converted in the low resistance layer and 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. However, it is preferably more than 250 Q. The resistance value can be measured with the same method as for the resistance value of the low resistance layer.The high resistance layer includes a conductive material and a resin, and further includes other components as necessary.

[0056] (Conductive material)The conductive material is not particularly limited and can be appropriately selected depending on the purpose. Examples of the conductive material include a non-metallic inorganic material such as carbon black or graphite, a metal such as gold, silver, copper, aluminum, zinc, tin, or iron, an alloy or an oxide of these metals, and an organic material such as a thiophene-based material, an aniline-based material, or a pyrrole-based material. Of these, from the viewpoint of the resistance value, a non-metallic inorganic material or an organic material is preferable, an organic material is more preferable, and a thiophene-based material is particularly preferable.Among the thiophene-based materials, PEDOT is preferable 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. However, it is preferably 0.01 pm or more. When the length-average diameter in the number-based distribution is 0.01 pm or more, it becomes easy to control the resistance value of the high resistance layer to an appropriate value.A 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,it can be measured with the same method as for the conductive material included in the low resistance layer.

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

[0060] (Other components)Other components are not particularly limited and can be appropriately selected depending on the purpose. Examples of other components include a dopant, a resin, a coloring material, a solvent, a wax, a pigment dispersant, and a crosslinking agent.

[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 an electron from the conductive material or a donor that easily gives an electron to the conductive material.

[0062] At least a part of the functional groups included in the dopant that is doped into the conductive material contributes to the development of the electrical conductivity of the conductive material.

[0063] Examples of the functional group included in 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, in the molecule, an aromatic ring or a condensed aromatic ring, which has many resonance structures and prevents a hydrolysis reaction. The use of the carboxylic acid aromatic compound or the carboxylic acid condensed- ring aromatic compound can provide the high resistance layer with improved water resistance.

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

[0066] The dopant having a hydroxyl group is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof 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 a derivative thereof.

[0067] The dopant having a mercapto group is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof 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 a derivative thereof.

[0068] The dopant having an amino group is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof 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-l-sulfonic acid, 4-amino- 5-methoxy-2-methylbenzenesulfonic acid, 2-amino-5-methylbenzene-l-sulfonic acid, 4- amino-2-methylbenzene-l -sulfonic acid, 5-amino-2-methylbenzene-l -sulfonic acid, 4-amino-3-methylbenzene-l-sulfonic acid, a poly carboxy lie acid such as a poly(acrylic acid), a poly(methacrylic acid), or a poly(maleic acid), and a derivative thereof.

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

[0070] The dopant having a sulfonium group is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a 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. Examples thereof include an alkyl sulfonic acid, a benzene sulfonic acid, a naphthalene sulfonic acid, an anthraquinone sulfonic acid, a camphorsulfonic acid, and a derivative thereof. Of these, a low molecular weight organic acid having a molecular weight of 1000 or less is preferable.

[0072] The alkyl sulfonic acid is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a derivative of 2-acrylamido-2- methylpropanesulfonic acid and a derivative of dodecylbenzenesulfonic acid.

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

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

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

[0076] The camphorsulfonic acid is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a derivative of (+)-10-camphorsulfonic acid and (-)-lO-camphorsulfonic acid. Further, the camphorsulfonic acid may be in the form of a racemate.

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

[0078] When a low molecular weight sulfonic acid is a low molecular weight organic acid such as an alkyl sulfonic acid, a benzenesulfonic acid, a naphthalenesulfonic acid, an anthraquinonesulfonic acid, a camphorsulfonic acid, or a derivative thereof, it may be a salt ofthe low molecular weight organic acid. Examples of the salt of the low molecular weight organic acid include an ammonium salt and a sodium salt of the low molecular weight organic acid.

[0079] The acidic polymer of the sulfonic acid group-containing acidic polymer is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a polycarboxylic acid such as a poly(acrylic acid), a poly(methacrylic acid), or a poly(maleic acid), a polysulfonic acid such as polyvinyl sulfonic acid or polystyrene sulfonic acid (PSS), and a copolymer containing these structural units. These may be used alone or in combination of two or more. Of these, polystyrene sulfonic acid (PSS) is preferable.

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

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

[0082] Further, the dopant may be used alone or in combination of two or more.

[0083] (Resin)There are no particular limitations on the resin as long as it does not inhibit heat generation, and it can be appropriately selected according to the purpose such as the base material, application, and configuration. However, examples of the resin include a shellac, a rosin, nitrocellulose, cellulose, a rubber, a polyamide resin, a vinyl chloride- vinyl acetate copolymer, a polyester resin, a polyvinylidene chloride resin, a ketone resin, a butyral resin, a chlorinated polypropylene resin, a chlorinated polyethylene resin, a chlorinated ethylene vinyl acetate resin, an ethylene vinyl acetate resin, an acrylic resin, a urethane resin, casein, an alkyd resin, a polyvinyl alcohol resin, an ethylene-vinyl alcohol resin, and a vinyl chloride resin. Of these, from the viewpoint of adhesion to the base material, an acrylic resin, a urethane resin, a vinyl chloride resin, and a rubber are preferable.

[0084] The coloring material can include a pigment, a dye, or a mixture thereof. Of these, a pigment is preferable from the viewpoint of durability.

[0085] Examples of the pigment include an inorganic pigment such as titanium oxide, red iron oxide, barium sulfate, calcium carbonate, silica, zinc oxide, zinc sulfide, mica, talc, pearl, aluminum, or carbon black, an organic pigment such as a phthalocyanine-based pigment, an insoluble azo-based pigment, a condensed azo-based pigment, a dioxazine-based pigment, an anthraquinone-based pigment, a quinacridone -based pigment, a perylene-based pigment, a perinone-based pigment, or a thioindigo-based pigment, and 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 dissolved or dispersed in a solvent, and one or more kinds of dyes may be used in combination. Since the dye can include a coloring material, the dye is extremely useful in terms of color variations and design.

[0087] The pigment dispersant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the pigment dispersant include an anionic surfactant, a cationic surfactant, and a nonionic surfactant. These may be used alone or in combination of two or more.

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

[0089] [Base material]The base material is not particularly limited and can be appropriately selected depending on the purpose. Examples of the base material include a paper, a plastic film or sheet, and a laminate of these materials with sealing properties.The plastic film or sheet is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a polyester film such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), a polyolefin film such as polyethylene, polypropylene, or ethylene- vinyl acetate, a polystyrene film, an alcohol-based film such as ethylene- vinyl alcohol or polyvinyl alcohol, a polyamide film or a barrier polyamide film having a barrier layer disposed therebetween, cellophane, moisture-proof cellophane, a transparent vapor-deposited polyester film or a transparent vapor-deposited polyamide film, obtained by providing a vapor-deposited layer of alumina, silica, or the like on a PET film or a polyamide film, and various coating films coated with a polyvinylidenechloride resin, a polyvinyl alcohol resin, a polyacrylic acid resin, an easy-adhesive resin, or the like. These may be either stretched or unstretched, and may be laminated either alone or in combination of two or more.The plastic film or sheet can be appropriately selected taking into consideration mechanical strength, dimensional stability, and the like.

[0090] The surface of the base material on which the low resistance layer and the high resistance layer are formed may be subjected to a corona treatment, a low temperature plasma treatment, a flame treatment, a solvent treatment, a coating treatment, or the like to improve the adhesion of the microwave heatable composition.

[0091] Further, the base material may be obtained by laminating thermoplastic resins or the like using a method such as dry lamination, non-solvent lamination, or extrusion lamination, a method such as adhesive-mediated bonding, or a method in which these methods are appropriately combined. A uniaxially stretched film, an easy-to-cut film, a stretch film, or a shrink film may also be used for the base material.

[0092] Further, as the base material, a laminate with sealing properties may be used. Examples of a method for imparting sealing properties include bonding with a known sealant film or sheet and resin coating through extrusion lamination processing. A layer imparted with sealing properties by these methods is referred to as a sealant.

[0093] Further, the base material may be subjected to scratching processing in advance.

[0094] The thickness of the base material is not particularly limited as long as it does not interfere with printability, winding suitability, and the like, and can be appropriately selected according to the purpose. However, the thickness is preferably 5 pm or more and 300 pm or less, more preferably 6 pm or more and 250 pm or less.

[0095] [Sealant]The sealant is preferably a layer including a resin with sealing properties. Examples of the resin which can be used include a thermoplastic resin such as a polyethylene resin such as LDPE, LLDPE, HDPE, or metallocene polyethylene, a polypropylene resin, an ethylene- vinyl acetate copolymer, an ionomer resin, an ethylene-acrylic acid copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, an ethylene-methacrylic acid copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-propylene copolymer, a methylpentene polymer, an acid-modified polyolefin resin made by modifying polyethylene or polypropylene with maleic acid, fumaric acid, or the like, or a polystyrene resin. These resins may be used alone or in combination of two or more.

[0096] A film, a laminate obtained by laminating multiple films, or the like including these resins may be formed by, for example, lamination using a dry lamination method, a wet lamination method, a non-solvent lamination method, a thermal lamination method, or the like, resin coating by extrusion lamination processing, coating with a heat sealant, or bonding through a hot melt adhesive or the like. Further, the film, the laminate, or the like including these resins does not necessarily need to be formed on the entire surface, and may be formed only on a part to be sealed.

[0097] Examples of the film include a polyolefin film made from 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, an ethylene-vinyl alcohol copolymer resin, or the like.

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

[0099] The thickness of the sealant is not particularly limited. However, from the viewpoint of sealing properties, costs, and productivity, it is preferable that the thickness is 2 pm to 200 pm for the fdm, 1 pm to 100 pm for the resin coating by extrusion lamination processing, 0.1 pm to 10 pm for the coating with the heat sealant, and 1 pm to 50 pm for the coating by the hot melt adhesive.

[0100] [Adhesive layer]An adhesive layer can be provided, for example, between the base material and another base material or between the base material and the sealant. The adhesive layer is a layer formed for bonding two layers together using an adhesive or a tackifier (including wax and hot melt) that has adhesiveness or tackiness.

[0101] Examples of a resin for forming the adhesive layer include a resin with sealing properties used for forming the sealant described above, a urethane resin, a butadiene resin, apolyethyleneimine resin, an isocyanate resin, and a chelate. Further, a commercially available adhesive can be used as the resin for forming the adhesive layer. Further, the resin may be a one-component adhesive in which a base agent and a curing agent are mixed or a two- component adhesive in which a baes agent and a curing agent are separated. If the resin for forming the adhesive layer is the two-component adhesive, the base agent and the curing agent are adjusted at an appropriate mixing ratio and then mixed and used.

[0102] [Printing ink layer]As the printing ink layer, a conventional printing ink can be used and can be selected as appropriate depending on the base material. From the viewpoint of printability and versatility, the printing ink is preferably a gravure ink made from a urethane resin, a vinyl chloride- vinyl acetate copolymer resin, nitrified cotton, a polyamide resin, an acrylic resin, a chlorinated polypropylene resin, a polyester resin, or the like. The gravure ink may be made from one type of these resins or a combination of two or more types. Further, when two or more color gravure inks are used, the gravure inks do not need to be made from the same resin, and the gravure inks made from different resins can be used as appropriate.

[0103] [Anchor coat layer]The anchor coat layer may be transparent, or may be formed using an anchor coat agent including a coloring material, to obtain many color variations and color designs. The anchor coat layer may be provided between the base material and the microwave heatable layer.

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

[0105] [Other layers]Examples of other layers include an OPP film, an ONY film, a PET film, an EVOH film, a PVA film, a cellophane film, a barrier nylon film, a stretched polyethylene film, a (modified) polyacrylic acid coated film, a PVA coated film, a transparent vapor-deposited film in which an inorganic oxide such as aluminum oxide or silicon oxide is vapor-deposited onto a base material such as a biaxially stretched polyethylene terephthalate film, a transparent barrier film (K-coating) in which a base film such as OPP, ONY, PET, or cellophane is coated with polyvinylidene chloride (PVDC), and a barrier film in which an ethylene-vinyl alcohol copolymer resin is laminated so as to be sandwiched between OPP films or NY films. These films are preferably provided on the other side of the microwave heatable layer.

[0106] <Method for producing microwave heatable film>The microwave heatable film according to one embodiment of the present disclosure includes a step of forming a low resistance layer having a resistance value of 1 or more and 250 or less (hereinafter, sometimes referred to as a “low resistance layer forming step”), and a step of 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 step”), and further includes other steps 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 of a high resistance layer forming composition or a low resistance layer forming composition onto at least one surface of the base material, vapor deposition or plating of the conductive material, and the like. Of these, coating, particularly printing, is preferable.The printing step is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a screen printing method, a gravure printing method, an offset printing method, a flexographic printing method, a roller coating method, a brush coating method, a spray method, a knife jet coater method, and an inkjet method. Of these, due to the high quality and productivity, a gravure printing method, a flexographic printing method, an inkjet method, and a screen printing method are preferable, with a gravure printing method being more preferable.Further, as a gravure printing method, a gravure printing method using a multi-color gravure printing machine is preferable. This allows the low resistance layer and the high resistance layer to be overprinted and provided in multiple locations, making it easy to control openability of the steam-releasing opening and heat generation.

[0108] [Low resistance layer forming composition]]The low resistance layer forming composition includes a conductive material and a solvent, and further includes other components as necessary.The conductive material and other components included in the low resistance layer forming composition include the same materials as those included in the low resistance layer described above.

[0109] The solvent is not particularly limited as long as it can maintain the fluidity by dissolving or dispersing the components constituting the low resistance layer forming composition, and can be appropriately selected depending on the purpose. Examples of the solvent include a commonly used organic solvent 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 an aromatic hydrocarbon solvent such as toluene or xylene, an aliphatic hydrocarbon solvent such as hexane, cyclohexane,methylcyclohexane, or ethylcyclohexane, an alcohol solvent such as methanol, ethanol, isopropyl alcohol (IPA), n-propyl alcohol, 1 -butanol, 2-butanol, isobutanol, or tert-butanol, an ester solvent such as ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec -butyl acetate, or tert-butyl acetate, a ketone solvent such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, or cyclohexanone, and a glycol ether solvent such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, or propylene glycol monobutyl ether, and an esterification product thereof. As for the esterification product, an acetate was primarily selected. Examples thereof include 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. Of these, from the viewpoints of printability and versatility, toluene, ethyl acetate, isopropyl alcohol, methyl ethyl ketone, ethanol, and water are preferable.

[0111] [High resistance layer forming composition]]The high resistance layer forming composition includes a conductive material and a solvent, and further includes other components as necessary.The conductive material and other components included in the high resistance layer forming composition include the same materials as those included in the high resistance layer described above.

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

[0113] It is preferable that the solvent includes a high boiling point solvent 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. 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, and dipropylene glycol. Among these, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether are preferable. Of these, ethylene glycol,diethylene glycol, DMSO, glycerin, propylene glycol, 1,3-butanediol, and dipropylene glycol are preferable.

[0115] The amount of the high boiling point solvent added to the high resistance layer forming composition is preferably 0.1% by mass or more and 50% by mass or less. When the added amount is 0.1 mass % or more, the film-forming properties can be improved. Further, when the added amount is 50% by mass or less, both drying properties and film-forming properties can be achieved.

[0116] Further, after the base material in which one or more types of compositions are laminated using a lamination method (overprinting of the low resistance layer forming composition and the high resistance layer forming composition) is produced, the low resistance layer and the high resistance layer may be formed on one main surface of the base material by various printing methods. After the low resistance layer and the high resistance layer are formed on one main surface of the base material by various printing methods, another base material may be formed on the other main surface of the base material by the lamination method described above. Further, the low resistance layer and the high resistance layer may be formed on both surfaces of the base material.

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

[0118] Regarding the microwave heatable film according to one embodiment, the printing step in which the low resistance layer and the high resistance layer, the printing ink layer, and the anchor coat layer are formed may be performed with a gravure printing method using one or more units of the multi-color gravure printing machine. This allows the low resistance layer and the high resistance layer, the printing ink layer, an anchor coat layer, and the like to be continuously formed on the base material in-line, making it possible to easily produce the microwave heatable film at low cost in a single pass. Further, it becomes easy to control openability of the steam-releasing opening and heat generation. If the continuous in-line formation is not possible due to a constraint in a specification of the gravure printing machine, a printing environment, a facility, or the like, offline (out-line) formation may be used.

[0119] Further, when the low resistance layer and the high resistance layer are formed in the printing step using the gravure printing method, when 100% dot coverage generates too much heat, the area ratio can be reduced, the plate depth can be adjusted, and the dilution rate can be adjusted, depending on the requirement for openability of the steam-releasing opening, making it easy to control openability and heat generation.

[0120] The low resistance layer and the high resistance layer need to be formed only in a part where the opening is to be desirably formed, or may be formed on the entire surface. Further, a coating pattern different in design, motif, or the like may be formed depending on the shape and the requirement of openability of the steam-releasing opening.

[0121] Further, the printing step is preferably performed by the gravure printing method that forms one or more colors of gravure inks. In this step, the printing ink layer can be formed as desired on the opposite surfaces of the low resistance layer and the high resistance layer, between the base material, and the low resistance layer and the high resistance layer, between the low resistance layer and the high resistance layer, and the anchor coat layer, or the like.

[0122] Further, the printing step is preferably performed with the gravure printing method using a multi-color gravure printing machine. Since the low resistance layer and the high resistance layer are transparent with almost no coloration, when the printing ink layer is formed, the low resistance layer and the high resistance layer can be provided inline simultaneously with the printing ink layer without interfering with other pieces of information such as a pattern, making it possible to obtain many color variations and color designs. For example, a package design or the like can be provided to improve a purchasing appeal effect, display information on where to open the package, how to open the package, or a warning, notify a company name, a logo, a product name, a character, a content, an ingredient fact, an application method, or a campaign, and provide information on how to eat or use, date, a place of origin, a winning lottery ticket, or the like.

[0123] Further, a formation step of forming an intermediate layer, the anchor coat layer, the overcoat layer, or the like may be included. These layers are not particularly limited as long as they can be formed using a known formation step such as bonding or coating.

[0124] Each composition such as the low resistance composition, the high resistance composition, a printing ink, or an anchor coat agent can be produced by a known method by uniformly dissolving or dispersing a conductive organic compound, a resin, a pigment, a resin with sealing properties, various additives, and the like in a solvent. Dissolution or dispersion can be performed by using 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 homo-mixer. These devices may be used alone or in combination of two or more. When an air bubble or a coarse particle is included in each composition, it is preferably removed by using a known filter, centrifuge, or the like to prevent deterioration in printability and print quality.The viscosity of each of the above compositions is not particularly limited as long as printing is not affected. Considering production suitability, handling, and the like of each composition, the viscosity is preferably 10 mPa-s to 1000 mPa- s at 25°C. Further, the viscosity of an ink for gravure printing is more preferably 10 mPa-s to 500 mPa-s.

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

[0127] The microwave heatable film according to one embodiment includes the low resistance layer and the high resistance layer, and the low resistance layer and the high resistance layer include the low resistance composition and the high resistance composition, respectively, according to one embodiment described above. In the microwave heatable film according to one embodiment, the microwave heatable layer generates heat when irradiated with microwaves. Thus, when the low resistance layer and the high resistance layer are overlapped in a heat-sealing portion, the film shrinks to form an opening in the heat-sealing portion. Further, when the low resistance layer and the high resistance layer are provided in the center of the microwave heatable film, the opening can be easily formed by breakage in the center of the microwave heatable film. Thus, the microwave heatable film according to one embodiment can exhibit high steam permeability by providing the steam opening without causing a short circuit even when a large amount of food material is sealed in a container, and can prevent the film from falling into the container even when the steam opening is provided.

[0128] The microwave heatable film according to one embodiment having the above-mentioned characteristics can be suitably used as a microwave heatable film for package. In particular, the microwave heatable film can be effectively used as a microwave heatable film for steamreleasing package.

[0129] <Microwave heatable package>A microwave heatable package according to one embodiment of the present disclosure includes at least the microwave heatable film according to one embodiment of the present disclosure described above, and further includes a container or a film for storing the content of the package as necessary.

[0130] The microwave heatable package may be in any form in which the microwave heatable film is commonly used. The microwave heatable package may be in a form of two-sided sealing, three-sided sealing, four-sided sealing, pillow sealing, a standing pouch, envelope pasting, gazette packaging, melt-cut sealing, a tube, caramel wrapping, over-folded wrapping, fin seal wrapping, bun wrapping, twist wrapping, rocket wrapping, Tetra Pak (registered trademark), a Gable top carton, a brick carton, deep drawing packaging, a cup, a tray, a bottle, a brickcarton, a container, a box, a case, a food container, a cover, a lid, a cap, a lid material, a label, a sheet, or the like.

[0131] A method for producing the microwave heatable package preferably includes a formation step of forming a package using the microwave heatable film.

[0132] In the formation step, the microwave heatable film may be formed into a package. One piece of microwave heatable film may be folded back and sealed at both ends to form a bag.Further, two pieces of microwave heatable films may be stacked to face each other and sealed at both ends to form a bag.

[0133] Further, in the formation step, the microwave heatable film may be used to cover a container, thereby forming a package.

[0134] The formation step may use a general method for forming a package, such as two-sided sealing, three-sided sealing, four-sided sealing, pillow sealing, a standing pouch, envelope pasting, gazette packaging, melt-cut sealing, a tube, caramel wrapping, over-folded wrapping, fin seal wrapping, bun wrapping, twist wrapping, rocket wrapping, Tetra Pak (registered trademark), a Gable top carton, a brick carton, deep drawing packaging, a cup, a tray, a bottle, a brick carton, a container, a box, a case, a food container, a cover, a lid, a cap, a lid material, a label, a sheet, or the like.

[0135] The configuration of a microwave heatable package according to one embodiment is illustrated in FIG. 18.

[0136] FIG. 18 is a diagram illustrating a microwave heatable package 200 using a microwave heatable film 100 according to one embodiment.The microwave heatable package 200 is a packaging container in which the microwave heatable film 100 and a container 202 are heat-sealed in a heat-sealing portion 201. FIG. 18 is a perspective diagram of the microwave heatable package 200 in which the microwave heatable film 100 is disposed such that the low resistance layer 1 and the high resistance layer 2 are positioned so as not to be vertically aligned with the heat-sealing portion 201 in a plan view.In FIG. 18, the container 202 has a rectangular parallelepiped shape. However, the shape can be changed to any shape such as a cylindrical shape, a cubic shape, or a triangular prism shape depending on the content and design.

[0137] The microwave heatable package according to one embodiment includes the high resistance layer and the low resistance layer, and the high resistance layer and the low resistance layerinclude the high resistance composition and the low resistance composition, respectively, according to one embodiment described above. In the microwave heatable package according to one embodiment, heat is generated in the high resistance layer and the low resistance layer upon microwave irradiation during heating. When the high resistance layer and the low resistance layer are laminated in the heat- sealing portion, an opening is easily formed in the heat- sealing portion through shrinkage of the film. Further, when the high resistance layer and the low resistance layer are provided in a center portion of the microwave heatable film, an opening is easily formed in the center portion through breakage of the microwave heatable film. Thus, the microwave heatable film according to one embodiment can exhibit high steam permeability by providing the steam opening without causing a short circuit even when a large amount of food material is sealed in a container, and can prevent the film from falling into the container even when the steam opening is provided.

[0138] The microwave heatable package according to one embodiment can generate high heat even when it contains a large amount of food material. Thus, for example, the microwave heatable package can be suitably used as a package or the like in which a through-hole is formed by microwave irradiation. Further, the microwave heatable package according to one embodiment can be suitably used, for example, as a cooking sheet for browning a food material by microwave irradiation, or the like.

[0139] As described above, the embodiments have been described, but the embodiments are presented as examples, and the present invention is not limited to the embodiments described above. The embodiments described above can be implemented in various other forms, and various combinations, omissions, substitutions, changes, and the like can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the invention described in the claims and equivalents thereof.[Examples]

[0140] Hereinafter, the embodiments are described in more detail with reference to Examples and Comparative examples. However, the embodiments are not limited to these Examples and Comparative examples.

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

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

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

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

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

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

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

[0148] Production of microwave heatable film>[Production example 1]The low resistance layer forming composition 1 was applied onto a sealant using a gravure printing machine so as to obtain the coating shape illustrated in FIG. 13a, and dried at 90°C for 5 minutes to form a low resistance layer.Next, the high resistance layer forming composition was applied onto the sealant using the gravure printing machine so as to obtain the coating shape illustrated in FIG. 13a, and dried at 90° C for 5 minutes to form a high resistance layer.Next, the resulting product was stored under the condition of 25 °C for 24 hours to produce a microwave heatable film 1.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 1.1.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer in the obtained microwave heatable film 1 were measured by the methods described below. As a result, the length average diameter in the number-based distribution of the low resistance layer was 0.4 pm, the resistance value of the low resistance layer was 21 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 1 are presented in Table 1.

[0149] < Length average diameter in number-based distribution of low resistance layer>The length- average diameter in the number-based distribution of the low resistance layer was obtained from the particle shape observed in the cross section of the low resistance layer in the microwave heatable film 1. For the cross-sectional observation, a sample was prepared by a conventional method, and a transmission electron microscope (TEM, JEM-210, manufactured by JEOL Ltd.) was used to take a cross-sectional TEM photograph. Five conductive materials were measured, and the average value of the diameter 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 value of the low resistance layer of the microwave heatable film three times using a tester (Custom corp., digital multimeter CDM-2000D), and the average value of three measurements was taken 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 value of the high resistance layer of the microwave heatable film three times using the tester (Custom corp., digital multimeter CDM-2000D), and the average value of three measurements was used as the resistance value of the high resistance layer.

[0152] [Production example 2]A microwave heatable film 2 was obtained with the same production method as in Production example 1, except that the low resistance layer forming composition 1 in Production example 1 was changed to the low resistance layer forming composition 2.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 1.1.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the number-based distribution of the low resistance layer was 1.5 pm, the resistance value of the low resistance layer was 2 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 2 are presented in Table 1.

[0153] [Production example 3]A microwave heatable film 3 was obtained with the same production method as in Production example 1, except that the low resistance layer forming composition 1 in Production example 1 was changed to the low resistance layer forming composition 3.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 1.1.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the number-based distribution of the low resistance layer was 11 pm, the resistance value of the low resistance layer was 242 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 3 are presented in Table 1.

[0154] [Production example 4]A microwave heatable film 4 was obtained with the same production method as in Production example 1, except that the coating shape illustrated in FIG. 13A in Production example 1 was changed to the coating shape illustrated in FIG. 14A and that the low resistance layer forming composition 1 was changed to the low resistance layer forming composition 4.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 2.5.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the number-based distribution of the low resistance layer was 1.3 pm, theresistance value of the low resistance layer was 143 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 4 are presented in Table 1.

[0155] [Production example 5]A microwave heatable film 5 was obtained with the same production method as in Production example 1, except that the coating shape illustrated in FIG. 13A in Production example 1 was changed to the coating shape illustrated in FIG. 15 A.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 10.0.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the number-based distribution of the low resistance layer was 0.4 pm, the resistance value of the low resistance layer was 21 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 5 are presented in Table 1.

[0156] [Production example 6]A microwave heatable film 6 was obtained with the same production method as in Production example 1, except that the low resistance layer in Production example 1 was formed by depositing silver into the coating shape illustrated in FIG. 13 A using a vacuum deposition apparatus (SPF-210H manufactured NEC Anelva Corp).Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 1.1.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length-average diameter in the number-based distribution of the low resistance layer was the measurement limit value or below, the resistance value of the low resistance layer was 0.04 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 6 are presented in Table 1.

[0157] [Production example 7]A microwave heatable film 7 was obtained with the same production method as in Production example 1, except the low resistance layer forming composition 1 in Production example 1 was changed to the low resistance layer forming composition 5.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 1.1.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the number-based distribution of the low resistance layer was 12 pm, the resistance value of the low resistance layer was 300 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 7 are presented in Table 1.

[0158] [Production example 8]A microwave heatable film 8 was obtained with the same production method as in Production example 1, except the high resistance layer forming composition in Production example 1 was changed to the low resistance layer forming composition 1.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance value of the low resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the numberbased distribution of the low resistance layer was 0.4 pm, and the resistance value of the low resistance layer was 21 .The physical property values of the microwave heatable film 8 are presented in Table 1.

[0159] [Production example 9]A microwave heatable film 9 was obtained with the same production method as in Production example 1, except the low resistance layer forming composition 1 in Production example 1 was changed to the high resistance layer forming composition.Further, the resistance value of the high resistance layer was measured with the same method as in Production example 1. As a result, the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 9 are presented in Table 1.

[0160] [Production example 10]A microwave heatable film 10 was obtained with the same production method as in Production example 1, except that the coating shape illustrated in FIG. 13 A in Production example 1 was changed to the coating shape illustrated in FIG. 19A.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 0.8.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the number-based distribution of the low resistance layer was 0.4 pm, theresistance value of the low resistance layer was 21 Q, and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 10 are presented in Table 1.

[0161] [Production example 11]A microwave heatable film 11 was obtained with the same production method as in Production example 1, except that the low resistance layer forming composition 1 in Production example 1 was changed to the low resistance layer forming composition 6. Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 1.1.The physical property values of the microwave heatable film 11 are presented in Table 1.

[0162] [Production example 12]A microwave heatable film 12 was obtained with the same production method as in Production example 1, except that the coating shape illustrated in FIG. 13 A in Production example 1 was changed to the coating shape illustrated in FIG. 15 A.Note that the area ratio (A / B) of the area (A) of the low resistance layer in a plan view with respect to the area (B) of the high resistance layer in a plan view was 20.0.Further, the length average diameter in the number-based distribution of the low resistance layer and the resistance values of the low resistance layer and the high resistance layer were measured with the same methods as in Production example 1. As a result, the length average diameter in the number-based distribution of the low resistance layer was 0.4 pm, the resistance value of the low resistance layer was 21 , and the resistance value of the high resistance layer was 2,500 .The physical property values of the microwave heatable film 12 are presented in Table 1.

[0163] Production of evaluation sample>Three hundred grams of water-soaked KIMWIPES (manufactured by Nippon Paper Crecia Co., Ltd.) was placed in a PP container, and the PP container and each of the microwave heatable films obtained in Production examples 1 to 12 were heat-sealed under the condition of 180°C for 1 second to obtain each evaluation sample.

[0164] [Table 1]

[0165] The micro wave heatable film obtained in each Production example was evaluated for “steam permeability”, “falling of melted film”, “film burning”, and “short circuit”.

[0166] [Steam permeability]The evaluation sample was heated in a microwave oven (IMB-T174-5-W manufactured by Iris Ohyama Inc.) at 500 W for 120 seconds. The “steam permeability” was evaluated based on the area of the steam opening formed after heating according to the following evaluation criteria. The evaluation results are presented in Table 2.(Evaluation criteria)Good: steam opening of 2 mm2or moreFair: steam opening of less than 2 mm2Poor: no steaming permeability

[0167] [Falling of melted film]The evaluation sample was heated in a microwave oven (RE-7500 manufactured by Sharp Corp.) at 1,600 W for 60 seconds, and the presence or absence of a falling fragment of the melted film derived from the microwave heatable film in the container was visually observed, and the “falling of melted film” was evaluated according to the following evaluation criteria. The evaluation results are presented in Table 2.(Evaluation criteria)Good: no falling of melted film fragmentPoor: falling of melted film fragment

[0168] [Film burning]The evaluation sample was heated in the microwave oven (RE-7500, manufactured by Sharp Corp.) at 1,600 W for 60 seconds. Then, the microwave heatable film was visually examined for discoloration due to burning caused by the microwave heatable layer, and the “Film burning” was evaluated according to the following evaluation criteria. The evaluation results are presented in Table 2.(Evaluation criteria)Good: no discoloration on film due to burningPoor: discoloration on film due to burning

[0169] [Short circuit]The evaluation sample was heated in the microwave oven (RE-7500 manufactured by Sharp Corp.) at 1,600 W for 60 seconds, and the occurrence of a short circuit was visually observed, and the “short circuit” was evaluated according to the following evaluation criteria. The evaluation results are presented in Table 2.(Evaluation criteria)Good: no short circuitPoor: spark due to short circuit

[0170] [Table 2]

[0171] Note that, for example, aspects of the present disclosure are as follows.<Aspect 1> A microwave heatable film including: a low resistance layer having a resistance value of 1 and more and 250 or less; and a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, in which at least a part of the low resistance layer and at least a part of the high resistance layer are laminated together.< Aspect 2> The microwave heatable film according to the < Aspect 1>, in which an area ratio (A / B) of an area (A) of the low resistance layer in a plan view with respect to an area (B) of the high resistance layer in a plan view is 1.0 or more and 10.0 or less.< Aspect 3> The microwave heatable film according to any one of the < Aspect 1> and <Aspect 2>, in which the resistance value of the low resistance layer is 1 or more and 150 or less.<Aspect 4> The microwave heatable film according to any one of the <Aspect 1> to <Aspect 3>, in which the low resistance layer includes a conductive material, the conductive material having a length average diameter in a number-based distribution of 10.0 pm or less.< Aspect 5> A microwave heatable package including the microwave heatable film according to any one of the < Aspect 1> to <Aspect 4>.<Aspect 6> A method for producing a microwave heatable film, the method including: forming a low resistance layer having a resistance value of 1 and more and 250 or less on at least one surface of a base material; and forming a high resistance layer having a resistance value higher than the resistance value of the low resistance layer on the at least one surface of the base material, in which at least a part of the low resistance layer and at least a part of the high resistance layer are laminated together.< Aspect 7 > The method for producing the microwave heatable film according to the < Aspect 6>, in which an area ratio (A / B) of an area (A) of the low resistance layer in a plan view with respect to an area (B) of the high resistance layer in a plan view is 1.0 or more and 10.0 or less.< Aspect 8> A microwave heatable film, including: a low resistance layer; and a high resistance layer having a resistance value higher than the resistance value of the low resistance layer, in which: at least a part of the low resistance layer and at least a part of the high resistance layer are laminated together; and an area ratio (A / B) of an area (A) of the low resistance layer in a plan view with respect to an area (B) of the high resistance layer in a plan view is 1.0 or more and 10.0 or less.

[0172] The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and / or features of different illustrative embodiments may be combined with each other and / or substituted for each other within the scope of the present invention.

[0173] This patent application is based on and claims priority to Japanese Patent Application No. 2023-156614, filed on September 22, 2023, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.[Reference Signs List]

[0174] 1 High resistance layer2 Low resistance layerMicrowave heatable layer Base material Base material with sealing properties Sealant 0 to 111 Microwave heatable film 0 Microwave heatable package 1 Heat-sealing portion 2 Container

Claims

[CLAIMS]

1. A micro wave heatable film comprising: a low resistance layer having a resistance value of 1 and more and 250 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 together.

2. The micro wave heatable film according to claim 1, wherein an area ratio (A / B) of an area (A) of the low resistance layer in a plan view with respect to an area (B) of the high resistance layer in the plan view is 1.0 or more and 10.0 or less.

3. The microwave heatable film according to any one of claims 1 and 2, wherein the resistance value of the low resistance layer is 1 or more and 150 or less.

4. The micro wave heatable film according to any one of claims 1 to 3, wherein the low resistance layer includes a conductive material, the conductive material having a length average diameter in a number-based distribution of 10.0 pm or less.

5. A microwave heatable package comprising the microwave heatable film according to any one of claims 1 to 4.

6. A method for producing a micro wave heatable film, the method comprising: forming a low resistance layer having a resistance value of 1 and more and 250 or less on at least one surface of a base material; and forming a high resistance layer having a resistance value higher than the resistance value of the low resistance layer on the at least one surface of the base material, wherein at least a part of the low resistance layer and at least a part of the high resistance layer are laminated together.

Images