Microwave heating film, and method for manufacturing microwave heating film

Abstract

This invention relates to microwave heating films and methods for manufacturing microwave heating films. The objective of this invention is to provide a microwave heating film that has stable vapor permeability and prevents the film from falling off after vapor permeation. The microwave heating film of this invention comprises: a first resin film; at least one microwave receiving layer disposed on the first resin film; and one or more heating layers at least in contact with the microwave receiving layer. The microwave receiving layer contains at least metal particles, and the resistivity of the microwave receiving layer is 7.0 × 10⁻⁶. ‑5 The resistivity of the heating layer is 1.6 × 10⁻⁶ Ω•m or less. ‑5 Ω•m~8.0×10 ‑3 Ω•m.

Description

Technical Field

[0001] This invention relates to microwave heating films and methods for manufacturing microwave heating films. Background Technology

[0002] Sometimes, food is sealed in packaging and then heated in a microwave oven. Therefore, when the packaging is equipped with a structure to allow steam to escape from the inside, steam from the microwave-heated food material escapes from the packaging, thus making the packaging permeable to steam.

[0003] As a method to release vapor from the inside of the packaging, for example, methods such as providing an opening in the heat-sealed part or the top of the packaging can be cited.

[0004] As a method of providing an opening in the heat-sealed part or the upper part of the packaging body, one example is a method of providing a coating layer that utilizes microwave heating on a film-like microwave-heated packaging body covering the container. A microwave-heated packaging body is disclosed in which, when irradiated with microwaves, the coating layer heats up, causing a part of the microwave-heated packaging body to melt and form an opening through which vapor is released (for example, see Patent Document 1).

[0005] In addition, a microwave processing packaging body is disclosed, wherein the heating part has a first layer containing carbon black and a second layer overlapping the first layer and containing vapor-deposited aluminum sheets (for example, see Patent Document 2).

[0006] [Existing Technical Documents]

[0007] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent No. 6713797

[0009] [Patent Document 2] Japanese Patent Application Publication No. 2021-039944 Summary of the Invention

[0010] The purpose of one aspect of the present invention is to provide a microwave heating film that has stable vapor permeability and can prevent the film from falling off after vapor permeation.

[0011] As a means to solve the above-mentioned problems, one aspect of the present invention relates to a microwave heating film comprising:

[0012] First resin film;

[0013] At least one microwave receiving layer (also called a "microwave receiving layer") is provided on the first resin film; and

[0014] At least one or more heating layers are in contact with the microwave receiving layer.

[0015] The microwave receiving layer contains at least metal particles.

[0016] The resistivity of the microwave receiving layer is 7.0 × 10⁻⁶. -5 Ω·m or less,

[0017] The resistivity of the heating layer is 1.6 × 10⁻⁶. -5 Ω•m~8.0×10 -3 Ω•m.

[0018] The effects of the present invention are explained below:

[0019] According to one aspect of the present invention, a microwave heating film can be provided that has stable vapor permeability and can prevent the film from falling off after vapor permeation. Attached Figure Description

[0020] Figure 1 This is a schematic side view of a container containing a microwave heating film and food according to an embodiment of the present invention.

[0021] Figure 2A This is a schematic cross-sectional view of a microwave heating film according to one embodiment of the present invention.

[0022] Figure 2B This is a schematic cross-sectional view of a microwave heating film according to another embodiment of the present invention.

[0023] Figure 3 This is a schematic top view of a microwave heating film according to one embodiment of the present invention.

[0024] Figure 4A This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in the microwave heating film according to an embodiment of the present invention.

[0025] Figure 4B This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in a microwave heating film according to another embodiment of the present invention.

[0026] Figure 4C This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in a microwave heating film according to another embodiment of the present invention.

[0027] Figure 4D This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in a microwave heating film according to another embodiment of the present invention.

[0028] Figure 5 This is a schematic side view of a container containing a microwave heating film and food according to an embodiment of the present invention.

[0029] Figure 6AThis is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in the microwave heating film according to an embodiment of the present invention used in the examples and comparative examples.

[0030] Figure 6B This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in the microwave heating film according to an embodiment of the present invention used in the examples and comparative examples.

[0031] Figure 6C This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in the microwave heating film according to an embodiment of the present invention used in the examples and comparative examples.

[0032] Figure 6D This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer and the heating layer in the microwave heating film according to an embodiment of the present invention used in the examples and comparative examples.

[0033] Figure 7 This is a schematic side view showing the food adhesion state in Comparative Example 4, Example 9, and Example 10. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below.

[0035] In this invention, "steam permeation" refers to the formation of a steam port (also referred to in this specification as "steam permeation port", "steam passage port", "steam permeation hole", "steam release hole", "steam opening", etc.).

[0036] In the past, convenience stores and supermarkets sold heat-treated foods, which required airtight packaging for long-term preservation. One method of sealing was to place the food in a plastic container such as PP and heat-seal it with a top sealing film. However, if the food is heated in a microwave oven, moisture is released from the food. As a result, the internal pressure increases due to the sealed environment, leading to problems such as container deformation and breakage.

[0037] Therefore, in one embodiment of the present invention, a method is proposed to utilize the energy of microwaves from a microwave oven to convert the energy into heat and form a steam permeation port in the top sealing film. When microwaves are applied to the microwave receiving layer, a current flows around the microwave receiving layer, and a portion of this current flows through the heating layer in contact with the microwave receiving layer. As a result, Joule heating occurs in the resistive heating layer (if the resistance is R and the current is I, then it is equivalent to R×I). 2As heat is generated, the resin film or similar material in contact with the heating layer softens and shrinks due to heat transfer, forming pores that become steam permeation ports. Here, to ensure current flows through the heating layer and generates heat, the resistivity is preferably within an appropriate range. For the heating layer to form pores, it needs to directly or indirectly (e.g., through the design of a printed layer) contact the film for heat transfer.

[0038] On the other hand, when manufacturing the film according to one embodiment of the present invention, since the microwave receiving layer and the heating layer are formed separately, relative positional misalignment sometimes occurs, for example, in gravure printing. Therefore, since the microwave receiving layer and the heating layer must be in contact, this can be avoided by having an overlapping portion between the microwave receiving layer and the heating layer. The amount of the overlapping portion is preferably about 1 to 2 mm. Current can easily flow in the microwave receiving layer and heat dissipation also occurs in the overlapping portion, so no holes are formed.

[0039] In the case of forming a steam permeation port in this manner, in order to reliably ensure steam permeability, it is preferable to receive large microwaves and convert them into heat energy. However, sometimes the membrane is damaged and falls onto the food due to the large amount of heat applied to it. In particular, it is necessary to avoid the fragments falling when the food is used.

[0040] Microwaves generated in a microwave oven are electromagnetic fields. When these fields irradiate a microwave receiving layer containing metal particles, current flows through the layer based on its area. This current then flows through the heating layer adjacent to the receiving layer, generating heat due to resistance. By reducing the resistivity of the microwave receiving layer, temperature rise can be prevented, suppressing resin film deformation. By maintaining the resistivity of the heating layer within a specified range, current flows stably, enabling stable heating. This allows for the stable formation of a vapor permeation port, preventing burns caused by container deformation or breakage. Localized heating of the resin film controls the size of the vapor permeation port, thus both preventing leakage and ensuring its proper function.

[0041] Because of concerns about the impact of food contact with the microwave receiving layer and heating layer on the human body, a film is used to laminate the microwave receiving layer and heating layer, preventing them from contacting food or the human body. This can suppress damage during transportation, the effects of impact, and layer damage caused by the adhesion of solvents such as water and alcohol, and ensure stable steam permeation.

[0042] In another embodiment of the present invention, after heating food in a microwave oven, the microwave heating film needs to be removed from the food container for consumption. However, by using a film with an easy-peeling treatment on the surface in contact with the container as one of the heat seals, both sealing and easy removal can be achieved.

[0043] Due to vibrations during transport of containers containing food and boiling during microwave heating, the food adheres to the microwave heating film. When steam passes through, the food burns, glows, and produces odors caused by heating. In addition, because the food obstructs steam passage, a steam outlet cannot be formed, causing the internal pressure to rise, which can lead to container deformation and breakage.

[0044] By making food water-repellent and oil-repellent so that it does not adhere to the microwave heating film, even if the food comes into contact with the film, it can fall off. Therefore, by performing water-repellent and oil-repellent processing on the food side of the microwave heating film, the adhesion of food can be inhibited, thereby improving the above-mentioned problems.

[0045] When food is placed in a container and heat-sealed to the container with a top sealing film for sale, water may adhere to the top sealing film during storage in refrigerators or freezers, or during customer handling. In the development of this invention, it has been clarified that when microwave heating is performed with water adhering to the microwave receiving layer through the film, excessive current flows through the microwave receiving layer, causing sparks and damage. This damage also affects the resin film, and the microwave receiving layer can fall onto the food through the steam permeator. Methods to suppress this situation have been studied, and it has been found that increasing the thickness of the microwave receiving layer and reducing the resin ratio can suppress this problem by reducing the area formed by the microwave receiving layer. However, increasing the film thickness is difficult in production; reducing the resin ratio makes it impossible to ensure adhesion to the resin film; and reducing the area prevents sufficient microwave reception and the formation of the steam permeator.

[0046] During the research of this invention, it was determined that if If the value is too small, breakage will occur. This is not determined by setting individual parameters, but rather by setting a value that satisfies α ≥ 1.8 × 10⁻⁶ within a range that ensures steam permeability. -4 The D, R, and S components can thus address issues such as suppressing container deformation and burns caused by container breakage, thereby resolving the problem of falling debris.

[0047] When water adheres to the microwave receiving layer via a membrane, and the microwave receiving layer is damaged by microwave oven heating, even if the area enclosed by the microwave receiving layer is the same, the larger the area of ​​the microwave receiving layer, the more likely the membrane will be damaged and fragments will fall off. To reduce the area enclosed by the microwave receiving layer, a hollow structure can be used to form the microwave receiving layer, which maintains vapor permeability and reduces the amount of fragments falling off.

[0048] In addition, costs can be reduced by decreasing the area formed.

[0049] The area of ​​a shape consisting of 9 mm × 20 mm within a rectangle is 180 mm². 2However, in a hollow structure, when the frame width W is 2 mm, the area is 100 mm². 2 The area is 54 mm² at 1 mm. 2 This can reduce and significantly suppress the amount of debris falling. If the frame width is too small, there is a risk that it cannot be formed during gravure printing due to printing fly-white. Therefore, it is preferable to have a width of 1 mm or more.

[0050] If the microwave heating film is heated by a microwave oven, current flows around the microwave receiving layer. In areas without a heating layer, no current flows. Therefore, if the microwave receiving layers without a heating layer are placed close together, they risk breakage due to sparks, creating a risk of falling fragments. Therefore, it is preferable to arrange the microwave receiving layers non-adjacent. In the case of adjacent arrangements, the distance between the microwave receiving layers without a heating layer should preferably be at least twice the distance between the microwave receiving layers with heating layers.

[0051] Depending on the type of resin membrane used, issues such as luminescence, odor, and debris falling after the vapor permeation port is identified. It can be determined whether the problem occurs based on the arc resistance value of the resin membrane.

[0052] It is believed that if the microwave heating film is heated by a microwave oven, current flows around the microwave receiving layer. This creates a vapor permeation port, which interrupts the metal of the microwave receiving layer, generating an electric arc. This causes the aforementioned problems in resin films that cannot withstand electric arcs. In the food industry, it is necessary to avoid the risks of luminescence, odors, and falling debris. Using resin films with high arc resistance can suppress these problems.

[0053] Even with materials that are highly resistant to electric arcs, resin membranes containing benzene rings have a particularly strong odor after forming a vapor permeation port, making them unsuitable for food use. However, by using microwave resin membranes that do not contain materials with benzene rings, the odor problem can be suppressed.

[0054] If a design printing layer is formed in the part forming the steam passage, the temperature of the heating layer will rise due to microwave heating. However, due to the material of the design printing layer, there is a risk that the steam passage may be damaged due to container deformation or container breakage, or that fragments of the design printing layer in the steam passage may fall onto the food. However, according to the structure of the present invention, the design impact can be minimized and this risk can be suppressed.

[0055] In order to suppress the damage to the microwave receiving layer caused by water adhering to the membrane and reduce the resin component ratio, the adhesion to the resin membrane 1 may become lower. Therefore, by forming a designed printed layer between the resin membrane 1 and the microwave receiving layer, the adhesion can be improved.

[0056] In the production of microwave heating films, each layer is formed by gravure printing and then wound using rollers. However, there is a risk that the printed surface may peel off due to pressure from the opposite side of the film (adhesion). This risk can be suppressed by the present invention.

[0057] Microwave heating film

[0058] This invention describes a microwave heating film according to one embodiment.

[0059] The microwave heating film includes a film substrate, a microwave receiving layer, and a heating layer. It may further include sealing materials, adhesive layers, printing ink layers, anchoring coatings, outer coatings, and other layers as needed.

[0060] As an existing microwave heating technology, a technique with only a single heating layer has been disclosed. However, depending on the amount of food, most of the microwaves are absorbed by the food, resulting in less microwaves reaching the heating layer. Therefore, there is a problem that steam permeation holes cannot be set.

[0061] Depending on the resistance value of the conductive material, a short circuit may occur, potentially leading to a fire, posing a safety concern.

[0062] In addition, when heating and cooking food sealed inside in a microwave oven, the packaging containing the food must ensure safety for the human body during heating (inhibiting container deformation and breakage), maintain stable vapor permeability, and prevent debris from falling onto the food.

[0063] Regarding the size of the steam permeable opening, one issue is that if the size is too small, steam cannot be fully discharged, leading to container deformation; if the size is too large, liquid food may leak out (if a container containing food is placed in the bag and tilted after steam has passed through, the food will leak and soil the bag). To maintain stable steam permeability, it is necessary to control the size of the steam permeable opening. A preferred steam permeable opening area is 0.2 mm². 2 ~20mm 2 .

[0064] Figure 1 This is a side view showing an example of a microwave heating film according to an embodiment of the present invention.

[0065] like Figure 1 As shown, the microwave heating film of the present invention is attached to the flange of a container containing food to seal it.

[0066] Figure 2A This is a schematic cross-sectional view of a microwave heating film according to one embodiment of the present invention. Figure 3 This is a schematic top view of a microwave heating film according to one embodiment of the present invention.

[0067] like Figure 2A and Figure 3As shown, the microwave heating film 10 has a film substrate 1, a heating layer 2, a microwave receiving layer 3, a printing layer 4, and an outer coating layer 8. The microwave heating film 10 of one embodiment of the present invention is formed by heating. Figure 2A The steam inlet 6 is shown. Figure 2A In this process, any one of the following processes can be performed on the surface of the membrane substrate 1 where the microwave receiving layer and the heating layer are not formed: heat sealing, water repellency, and oil repellency.

[0068] Figure 2B This is a schematic cross-sectional view of a microwave heating film according to another embodiment of the present invention. Figure 2B As shown, the microwave heating film 10 further comprises a second resin film 7. Figure 2B In the microwave heating film shown, in the second resin film 7, any one of the following processes can be performed on the opposite side to the surface facing the microwave receiving layer 3 and the heating layer 2 formed on the first resin film 1: heat sealing, water repellency, and oil repellency.

[0069] Figure 4A This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer 3 and the heating layer 2 in a microwave heating film according to an embodiment of the present invention. Figure 4A As shown, the microwave heating film 10 has the following structure: microwave receiving layers 3, which are rectangular in shape and have long sides a and short sides b, are adjacent to each other with their short sides facing each other. Specifically, the short sides b of the first microwave receiving layer 3A and the second microwave receiving layer 3B are arranged to face each other, and the two heating layers 2 on each short side b are connected.

[0070] Figure 4B This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer 3 and the heating layer 2 in a microwave heating film according to another embodiment of the present invention. Figure 4B The microwave heating film shown is in Figure 4A In the microwave heating film shown, the microwave receiving layer 3 has a hollow structure. For example... Figure 4B As shown, the hollow structure refers to a rectangular microwave receiver 3 consisting only of sides of width W, with no microwave receiver layer formed inside the layer when viewed from above.

[0071] Figure 4C This is a schematic cross-sectional view showing the shape and size of the microwave receiving layer 3 and the heating layer 2 in a microwave heating film according to another embodiment of the present invention. Figure 4C The microwave heating film shown is in Figure 4A The microwave heating film shown further includes a third microwave receiving layer 3C, with the short side b of the second microwave receiving layer 3B and the short side b of the third microwave receiving layer 3C arranged opposite to each other and connected by two heating layers 2 on each short side b.

[0072] Figure 4DThis is a schematic cross-sectional view showing the shape and size of the microwave receiving layer 3 and the heating layer 2 in a microwave heating film according to another embodiment of the present invention. Figure 4D The microwave heating film shown is in Figure 4A The microwave heating film shown further includes a third microwave receiving layer 3C and a fourth microwave receiving layer 3D. The long side a of the first microwave receiving layer 3A and the long side a of the third microwave receiving layer 3C are arranged opposite each other at a distance U. Additionally, the long sides a of the second microwave receiving layer 3B and the fourth microwave receiving layer 3D are also arranged opposite each other at a distance U. Here, the distance U is more than twice the distance V between the short side b of the first microwave receiving layer 3A and the short side b of the second microwave receiving layer.

[0073] In addition, Figure 4D In another embodiment of the present invention shown, a fourth microwave receiving layer 3D is provided, but the fourth microwave receiving layer 3D may not be provided.

[0074] [Heating Layer]

[0075] The heating layer is composed of a layer that converts eddy currents, which are converted from microwaves by the receiving layer, into Joule heat. Microwaves are defined as radio waves with frequencies above 300 MHz and below 300 GHz.

[0076] [Microwave Received Layer]

[0077] A microwave receiving layer is a layer that absorbs microwave energy and converts it into eddy currents. The microwave receiving layer contains conductive materials and, if necessary, other components.

[0078] The resistivity of the microwave receiver layer is 7.0 × 10⁻⁶. -5 Below Ω·m. The resistivity of the microwave receiving layer is preferably even lower, preferably 7.0 × 10⁻⁶. -6 Below Ω·m. It can prevent film deformation, damage (cracking, etc.) of the microwave receiving layer, and the fall of the molten film caused by heating due to excess current in the microwave receiving layer.

[0079] There are no particular restrictions on the method for measuring resistance. It can be selected appropriately according to the purpose. For example, a two-terminal resistance meter (tester) or a four-terminal resistance meter can be used for measurement.

[0080] (Conductive material of microwave receiving layer)

[0081] There are no particular limitations on the conductive material; it can be appropriately selected according to the purpose. Examples include non-metallic inorganic materials such as carbon black and graphite, metals such as gold, silver, copper, aluminum, zinc, tin, and iron, alloys or oxides of these metals, and organic materials such as thiophene-based, aniline-based, and pyrrole-based materials. From the viewpoint of conductivity, metals, alloys, and metal oxides are preferred, with metals being more preferred. Furthermore, among metals, gold, silver, and copper are preferred.

[0082] From the viewpoint of preventing short circuits caused by excessive current flow, a particulate shape is preferred for the conductive material. Furthermore, making the conductive material particulate facilitates its graphitization.

[0083] The average diameter of the length in the reference distribution of the conductive material is not particularly limited and can be appropriately selected according to the purpose, but is preferably 10 μm or less. If the average diameter of the length in the reference distribution is 10 μm or less, it is easier to control the resistance value of the microwave receiving layer to an appropriate value. In addition, the number of interparticle contact points required to exhibit conductivity increases, and the desired conductivity can be obtained.

[0084] There are no particular limitations on the method for determining the average diameter of the length in the aforementioned reference distribution. It can be appropriately selected according to the purpose. For example, it can be determined by the shape of the conductive material observed from the cross-section of the microwave receiving layer.

[0085] As for the observation of the above-mentioned cross section, for example, the sample can be prepared by conventional methods and measured using a transmission electron microscope (TEM).

[0086] Since the measured value of the length-average diameter in the reference distribution of the number of conductive materials observed using the above-mentioned TEM is substantially consistent with the measured value of the length-average diameter in the reference distribution of the number of conductive materials in the microwave receiver layer forming composition, the particle size distribution of the conductive material after the microwave receiver layer is formed can be set according to the particle size distribution of the conductive material in the microwave receiver layer forming composition.

[0087] It should be noted that the length-average diameter in the volume reference distribution of the conductive material in the above-mentioned microwave receiving layer formation composition can be measured, for example, using LA-960 manufactured by Horiba Production based on laser diffusion.

[0088] There are no particular restrictions on the content of the conductive material, which can be appropriately selected according to the purpose, but it is preferably 50% by mass or more and 99% by mass or less relative to the microwave receiving layer. If the content of the conductive material is 50% by mass or more, microwaves can be absorbed sufficiently, thus generating the eddy currents required for heating in the heating layer. If the content of the conductive material is 99% by mass or less, short circuits in the microwave heating film can be prevented by suppressing the generation of excessive eddy currents in the microwave receiving layer.

[0089] (Other ingredients)

[0090] Other components are not particularly restricted and can be selected appropriately according to the purpose. Examples include resins, colorants, waxes, pigment dispersants, and crosslinking agents.

[0091] As for the resin, there are no particular limitations as long as it does not impair microwave absorption, and it can be appropriately selected according to the membrane substrate, application, structure, and other purposes. Examples of resins include shellac, rosin, nitrocellulose, cellulose, rubber, polyamide resin, vinyl chloride-vinyl acetate copolymer, polyester resin, polyvinylidene chloride resin, ketone resin, butyral resin, chlorinated polypropylene resin, chlorinated polyethylene resin, vinyl chloride-vinyl acetate resin, ethylene-vinyl acetate resin, acrylic resin, polyurethane resin, casein, alkyd resin, polyvinyl alcohol resin, ethylene-vinyl alcohol resin, and vinyl chloride resin. From the viewpoint of adhesion to the membrane substrate, acrylic resin, polyurethane resin, vinyl chloride resin, and rubber are preferred.

[0092] There are no particular restrictions on colorants; they can be selected appropriately depending on the purpose. Examples include pigments, dyes, and mixtures thereof. Among these, pigments are preferred from a durability point of view.

[0093] As pigments, there are no particular restrictions; appropriate selection can be made according to the intended purpose. Examples include inorganic pigments such as titanium dioxide, iron oxide red, barium sulfate, calcium carbonate, silicon dioxide, zinc oxide, zinc sulfide, mica, talc, pearl, aluminum, and carbon black; organic pigments such as phthalocyanine pigments, insoluble azo pigments, condensed azo pigments, dioxazine pigments, anthraquinone pigments, quinacridone pigments, perylene pigments, violet ketone pigments, and thioindigo pigments; and various other fluorescent pigments, metallic powder pigments, and extender pigments. These can be used alone or in combination of two or more.

[0094] As dyes, they are preferably dissolved or dispersed in a solvent, and one or more dyes can be used in combination. Because dyes can contain colorants, they are very useful in terms of color variation and design.

[0095] There are no particular limitations on the use of surfactants as pigment dispersants; they can be selected appropriately depending on the purpose. Examples include anionic surfactants, cationic surfactants, and nonionic surfactants. These can be used alone or in combination of two or more.

[0096] There are no particular limitations on the crosslinking agent; it can be appropriately selected according to the purpose. Examples include hydrazide-based, isocyanate-based, epoxy-based, carbodiimide-based, silane coupling agents, oxazoline-based, aziridine-based, imine-based, metal chelating agents, glyoxal-based, and hydroxymethyl-based agents. These can be used alone or in combination of two or more. Among these, isocyanate-based, carbodiimide-based, epoxy-based, and aziridine-based agents are preferred.

[0097] [Heating Layer]

[0098] The heating layer is a layer that converts eddy currents generated by the microwave receiving layer into Joule heat. The resistance value of the heating layer can be any value higher than that of the microwave receiving layer, but is preferably greater than 250 Ω. The resistance value can be measured using the same method as for the microwave receiving layer.

[0099] The heating layer comprises conductive materials and resin, and may further contain other components as needed. The heating layer is conductive by including conductive materials.

[0100] The resistivity of the heating layer is 1.6 × 10⁻⁶ -5 Ω·m or more and 8.0×10 -3 Below Ω·m. The resistivity through the heating layer is 1.6 × 10⁻⁶. -5 Ω·m or more and 8.0×10 -3 Below Ω·m, it can prevent film deformation, damage (such as cracking) of the microwave receiving layer, and the fall of the molten film caused by heating due to excessive current in the microwave receiving layer.

[0101] (Conductive materials)

[0102] There are no particular limitations on the conductive material; it can be appropriately selected according to the purpose. Examples include non-metallic inorganic materials such as carbon black and graphite, metals such as gold, silver, copper, aluminum, zinc, tin, and iron, alloys or oxides of these metals, and organic materials such as thiophene-based, aniline-based, and pyrrole-based materials. From the viewpoint of electrical resistance, non-metallic inorganic materials or organic materials are preferred, organic materials are more preferred, and thiophene-based materials are particularly preferred.

[0103] From the perspective of electrical conductivity, PEDOT is preferred among thiophene-based materials.

[0104] The preferred shape for conductive materials is granular or in a dissolved state.

[0105] The average diameter of the length in the reference distribution of the conductive material is not particularly limited and can be appropriately selected according to the purpose. However, it is preferred to be 0.01 μm or more. If the average diameter of the length in the reference distribution is 0.01 μm or more, it is easier to control the resistance value of the heating layer to an appropriate value.

[0106] There are no particular limitations on the method used to measure the length-average diameter in a number reference distribution, and it can be appropriately selected according to the purpose. For example, it can be measured using the same method as the conductive material contained in the microwave receiver layer.

[0107] There are no particular restrictions on the content of the conductive material, and it can be appropriately selected according to the purpose, but it is preferably 5% by mass or more relative to the heating layer. If the content of the conductive material is 5% by mass or more, it can exert the heating properties necessary for film melting.

[0108] (Other ingredients)

[0109] Other components are not particularly restricted and can be selected appropriately according to the purpose. Examples include dopants, resins, colorants, solvents, waxes, pigment dispersants, crosslinking agents, etc.

[0110] As a usable dopant, it can be used without particular restrictions as long as it has a structure that makes it an acceptor of electrons or a donor of electrons relative to the conductive material.

[0111] At least a portion of the functional groups of a dopant are incorporated into a conductive material to enhance its conductivity. Examples of functional groups that can be incorporated into a dopant include carboxyl, hydroxyl, mercapto, amino, sulfinyl, and sulfonyl groups.

[0112] Dopants containing carboxyl groups are preferably aromatic compounds with numerous intramolecular resonance structures that inhibit hydrolysis reactions, such as aromatic rings, fused rings, and aromatic compounds with fused rings of carboxylic acids. By using aromatic compounds with carboxylic acids and aromatic compounds with fused rings of carboxylic acids, a heating layer with enhanced water resistance can be obtained.

[0113] There are no particular limitations on the types of carboxylic acid aromatic compounds and fused-ring carboxylic acid aromatic compounds; appropriate selection can be made according to the purpose. For example, carboxylic acid aromatic compounds such as phthalic acid, triphenylcarboxylic acid, trimesic acid, trimesic acid, trimesic acid, phenylpentacarboxylic acid, and hexacarboxylic acid, or derivatives of carboxylic acid aromatic compounds such as 4-sulfophthalic acid, and derivatives of 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic anhydride, etc., can be used where only the carboxylic acid replaces the naphthalene. The obtained carboxylic acid aromatic fused-ring compounds and their derivatives, such as 4-chloro-1,8-naphthalenedicarboxylic anhydride, 4-sulfon-1,8-naphthalenedicarboxylic anhydride, naphthalene-1,4,5,8-tetracarboxylic acid and their derivatives, compounds with anthracene rings such as 2,3-anthracite anhydride, compounds obtained by carboxylating polycyclic aromatic hydrocarbons such as tetraphenyl, pentaphenyl, benzo[a]pyrene, pyrene, triphenylene, cyclohexene, cyclohexene and cyclohexene, and their derivatives, etc.

[0114] As dopants containing hydroxyl groups, there are no particular restrictions, and appropriate selections can be made according to the purpose. Examples 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 their derivatives.

[0115] There are no particular restrictions on dopants containing thiol groups; they can be selected appropriately according to the purpose. Examples include thioglycolic acid, thiosuccinic 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 their derivatives.

[0116] There are no particular restrictions on dopants containing amino groups, and appropriate selections can be made according to the purpose. Examples 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-tolyl-1-sulfonic acid, 4-amino-5-methoxy-2-methylbenzenesulfonic acid, 2-amino-5-tolyl-1-sulfonic acid, 4-amino-2-tolyl-1-sulfonic acid, 5-amino-2-tolyl-1-sulfonic acid, 4-amino-3-tolyl-1-sulfonic acid, polyacrylic acid, polymethacrylic acid, polymaleic acid, and other polycarboxylic acids and their derivatives.

[0117] There are no particular restrictions on the dopant containing sulfinic groups, and appropriate selection can be made according to the purpose. Examples include methyl sulfinic acid, ethyl sulfinic acid, isopropyl sulfinic acid, benzene sulfinic acid, p-toluene sulfinic acid, cyclopropane sulfinic acid, p-chlorobenzene sulfinic acid derivatives, hydroxymethane sulfinic acid, L-cysteine ​​sulfinic acid, 2-aminoethane sulfinic acid, and their derivatives.

[0118] There are no particular restrictions on the dopant with a sulfonate group; it can be selected appropriately according to the purpose. Examples include low molecular weight sulfonic acids or their salts, or acidic polymers containing sulfonic acid groups or their salts.

[0119] There are no particular restrictions on low-molecular-weight sulfonic acids; they can be selected appropriately according to the purpose. Examples include alkyl sulfonic acids, benzene sulfonic acids, naphthalene sulfonic acids, anthraquinone sulfonic acids, camphor sulfonic acids, and their derivatives. Among them, low-molecular-weight organic acids with a molecular weight of less than 1000 are preferred.

[0120] As an alkyl sulfonic acid, there are no particular restrictions, and it can be selected appropriately according to the purpose. For example, 2-acrylamido-2-methylpropanesulfonic acid derivatives and dodecylbenzenesulfonic acid derivatives can be listed.

[0121] There are no particular restrictions on benzenesulfonic acid; it can be selected appropriately according to the purpose. For example, toluenesulfonic acid derivatives, styrenesulfonic acid, and their derivatives can be listed.

[0122] There are no particular restrictions on naphthalene sulfonic acid; it can be selected appropriately according to the purpose. For example, 1-naphthalene sulfonic acid, 2-naphthalene sulfonic acid, 1,3-naphthalenedisulfonic acid, 1,3,6-naphthalenetrisulfonic acid, and 6-ethyl-1-naphthalene sulfonic acid derivatives can be listed.

[0123] There are no particular restrictions on anthraquinone sulfonic acids; they can be selected appropriately according to the purpose. Examples include anthraquinone-1-sulfonic acid, anthraquinone-2-sulfonic acid, anthraquinone-2,6-disulfonic acid, and 2-methylanthraquinone-6-sulfonic acid derivatives.

[0124] There are no particular restrictions on the type of camphor sulfonic acid used; it can be selected appropriately according to the purpose. For example, (+)-10-camphor sulfonic acid and (-)-10-camphor sulfonic acid derivatives can be listed. In addition, camphor sulfonic acid can be a racemic mixture.

[0125] Among them, benzenesulfonic acid, toluenesulfonic acid, and naphthalenesulfonic acid are preferred. These can be used alone or in combination of two or more.

[0126] When the low-molecular-weight sulfonic acid is an alkyl sulfonic acid, benzene sulfonic acid, naphthalene sulfonic acid, anthraquinone sulfonic acid, camphor sulfonic acid, or a derivative thereof, it can also be a low-molecular-weight organic acid salt. Examples of low-molecular-weight organic acid salts include their ammonium salts and sodium salts.

[0127] There are no particular limitations on the acidic polymer compounds containing sulfonic acid groups; appropriate selection can be made according to the purpose. Examples include polycarboxylic acids such as polyacrylic acid, polymethacrylic acid, and polymaleic acid; polysulfonic acids such as polyethylene sulfonic acid and polystyrene sulfonic acid (PSS); and copolymers having these structural units. These can be used alone or in combination of two or more. Among them, polystyrene sulfonic acid (PSS) is preferred.

[0128] There are no particular limitations on the weight-average molecular weight (Mw) of the acidic polymer compound, and it can be appropriately selected according to 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.

[0129] There is no particular limitation on the total content of the dopant, which can be appropriately selected according to the purpose. However, this 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, relative to 100 parts by mass of conductive material.

[0130] In addition, a single dopant can be used alone, or two or more can be used in combination.

[0131] (resin)

[0132] As for the resin, there are no particular limitations as long as it does not impede heat generation; it can be appropriately selected based on the membrane substrate, application, structure, and other objectives. Examples of resins include shellac, rosin, nitrocellulose, cellulose, rubber, polyamide resin, vinyl chloride-vinyl acetate copolymer, polyester resin, polyvinylidene chloride resin, ketone resin, butyral resin, chlorinated polypropylene resin, chlorinated polyethylene resin, vinyl chloride-vinyl acetate resin, ethylene-vinyl acetate resin, acrylic resin, polyurethane resin, casein, alkyd resin, polyvinyl alcohol resin, ethylene-vinyl alcohol resin, and vinyl chloride resin. From the viewpoint of adhesion to the membrane substrate, acrylic resin, polyurethane resin, vinyl chloride resin, and rubber are preferred.

[0133] There are no particular restrictions on colorants; they can be selected appropriately depending on the purpose. Examples include pigments, dyes, and mixtures thereof. Among these, pigments are preferred from a durability point of view.

[0134] As pigments, there are no particular restrictions; appropriate selection can be made according to the intended purpose. Examples include inorganic pigments such as titanium dioxide, iron oxide red, barium sulfate, calcium carbonate, silicon dioxide, zinc oxide, zinc sulfide, mica, talc, pearl, aluminum, and carbon black; organic pigments such as phthalocyanine pigments, insoluble azo pigments, condensed azo pigments, dioxazine pigments, anthraquinone pigments, quinacridone pigments, perylene pigments, violet ketone pigments, and thioindigo pigments; and various other fluorescent pigments, metallic powder pigments, and extender pigments. These can be used alone or in combination of two or more.

[0135] As dyes, they are preferably dissolved or dispersed in a solvent, and one or more dyes can be used in combination. Because dyes can contain colorants, they are very useful in terms of color variation and design.

[0136] There are no particular limitations on the use of surfactants as pigment dispersants; they can be selected appropriately depending on the purpose. Examples include anionic surfactants, cationic surfactants, and nonionic surfactants. These can be used alone or in combination of two or more.

[0137] There are no particular limitations on the crosslinking agent; it can be appropriately selected according to the purpose. Examples include hydrazide-based, isocyanate-based, epoxy-based, carbodiimide-based, silane coupling agents, oxazoline-based, aziridine-based, imine-based, metal chelating agents, glyoxal-based, and hydroxymethyl-based agents. These can be used alone or in combination of two or more. Among these, isocyanate-based, carbodiimide-based, epoxy-based, and aziridine-based agents are preferred.

[0138] [Resin film substrate]

[0139] There are no particular limitations on the resin film substrate; it can be appropriately selected according to the purpose. For example, paper, plastic film, or sheet, as well as laminates that impart sealing properties to them, can be listed.

[0140] There are no particular restrictions on the type of plastic film or sheet; appropriate selection can be made according to the purpose. Examples include polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate; alcohol films such as polystyrene, ethylene-vinyl alcohol, and polyvinyl alcohol; polyamide films or barrier polyamide films with an intermediate barrier layer; cellophane and moisture-proof cellophane; transparent vapor-deposited polyester films or transparent vapor-deposited polyamide films with alumina, silica, or other vapor-deposited layers on PET or polyamide films; and various coated films coated with polyvinylidene chloride resin, polyvinyl alcohol resin, polyacrylic acid resin, easy-to-adhere resin, etc. These can be stretched or unstretched, and can be one or more layers stacked together.

[0141] When selecting materials for plastic films or sheets, factors such as mechanical strength and dimensional stability can be considered.

[0142] To prevent damage to the resin film substrate caused by current from the microwave receiving layer, a resin film with high arc resistance is preferred. Additionally, if the resin film substrate contains benzene rings, odor may sometimes be generated due to resin film damage; this should be avoided.

[0143] To improve the adhesion of the microwave heating composition, the microwave receiving layer and heating layer in the film substrate can be formed by corona treatment, low-temperature plasma treatment, flame treatment, solvent treatment, coating treatment, etc.

[0144] Furthermore, the substrate can be obtained by laminating thermoplastic resins using methods such as dry lamination, solvent-free lamination, extrusion lamination, or bonding with adhesives, or by appropriately combining the above methods. Uniaxial stretch films, easy-to-cut films, stretch films, and shrink films can also be used.

[0145] Alternatively, a laminate with sealing properties can be used as the membrane substrate. Methods for imparting sealing properties include lamination of known sealing films or sheets, and resin coating through extrusion lamination. Layers that impart sealing properties through these methods are called sealing materials.

[0146] Alternatively, the membrane substrate can be pre-scratched.

[0147] The thickness of the film substrate is not particularly limited as long as it does not impair printability, rollability, etc., and can be appropriately selected according to the purpose. However, the thickness is preferably 5 μm or more and 300 μm or less, and more preferably 6 μm or more and 250 μm or less.

[0148] [Sealing material]

[0149] The sealing material is preferably a layer containing a sealing resin. Examples of usable resins include, for instance, polyethylene resins such as LDPE, LLDPE, HDPE, and metallocene polyethylene; polypropylene resins; ethylene-vinyl acetate copolymers; ionomer resins; ethylene-acrylic acid copolymers; ethylene-ethyl acrylate copolymers; ethylene-methyl acrylate copolymers; ethylene-methacrylic acid copolymers; ethylene-methyl methacrylate copolymers; ethylene-propylene copolymers; methylpentene polymers; acid-modified polyolefin resins made by modifying polyethylene or polypropylene with maleic acid, fumaric acid, etc.; and thermoplastic resins such as polystyrene resin. These resins can be used alone or in combination of two or more.

[0150] Films containing these resins, or laminates containing multiple films, can be formed, for example, by lamination using dry lamination, wet lamination, solvent-free lamination, hot lamination, etc.; by resin coating using extrusion lamination; by coating using heat-sealing materials; or by bonding using hot melt adhesives (hereinafter sometimes referred to as "heat sealing"). Furthermore, films and laminates containing these resins do not necessarily need to be formed on the entire surface; they can be formed only on the sealed portion.

[0151] Examples of membranes include polyethylene, polypropylene, mixed resins of polyethylene and polypropylene, ethylene-vinyl acetate copolymer resin, ethylene-(meth)acrylic acid copolymer resin, ethylene-(meth)acrylic acid methyl acrylate copolymer resin, ethylene-(meth)acrylic acid ethyl acrylate copolymer resin, ethylene-vinyl alcohol copolymer resin, and other polyolefin membranes.

[0152] Resins that can be used for extrusion lamination or as hot melt adhesives include, for example, polyethylene resins such as LDPE, LLDPE, and HDPE; polypropylene resins; ethylene-vinyl acetate copolymers; ionomer resins; ethylene-acrylic acid copolymers; ethylene-ethyl acrylate copolymers; ethylene-methyl acrylate copolymers; ethylene-methacrylic acid copolymers; ethylene-methyl methacrylate copolymers; ethylene-propylene copolymers; methylpentene polymers; acid-modified polyolefin resins made by modifying polyethylene or polypropylene with maleic acid, fumaric acid, etc.; and thermoplastic resins such as polystyrene resins. These resins can be used alone or in combination of two or more.

[0153] There is no particular limitation on the thickness of the sealing material. However, from the viewpoints of sealing performance, cost, and productivity, it is preferable that the film thickness is 2μm to 200μm, the resin coating thickness processed by extrusion lamination is 1μm to 100μm, the coating thickness with heat-sealing material is 0.1μm to 10μm, and the coating thickness with hot melt adhesive is 1μm to 50μm.

[0154] [Adhesive layer]

[0155] For example, an adhesive layer can be provided between the membrane substrate and other membrane substrates, or between the membrane substrate and the sealing material. An adhesive layer is a layer formed by bonding two layers together using an adhesive or tackifier (including wax and hot melt adhesive) that has adhesive or tack properties.

[0156] Examples of resins that form the adhesive layer include sealing resins such as polyurethane resin, butadiene resin, polyethyleneimine resin, isocyanate resin, and chelates, which are used to form the aforementioned sealing materials. Alternatively, commercially available adhesives can be used as the resin forming the adhesive layer. Furthermore, the resin can be a one-component adhesive consisting of a base agent and a curing agent, or a two-component adhesive where the base agent and curing agent are separate. When the resin forming the adhesive layer is a two-component adhesive, the base agent and curing agent are mixed and used after adjusting the mixing ratio to an appropriate level.

[0157] [Printing Ink Layer]

[0158] As the printing ink layer, conventional printing inks can be used, and the appropriate ink can be selected according to the substrate. From the viewpoint of printability and versatility, gravure printing inks made of polyurethane resin, vinyl chloride-vinyl acetate copolymer resin, nitrocellulose, polyamide resin, acrylic resin, polyvinyl chloride resin, polyester resin, etc., are preferred. Gravure printing inks can be made from one of these resins or from a combination of two or more. Furthermore, when using two or more color gravure printing inks, it is not necessary to use inks made from the same resin; gravure inks made from different resins can be used appropriately.

[0159] [Anchoring Coating]

[0160] The anchoring coating can be transparent or formed using an anchoring agent containing coloring materials, thus allowing for a wider range of color variations and designs. The anchoring coating can be applied between the membrane substrate and the heating layer.

[0161] [Outer Coating]

[0162] The outer coating is the layer formed on the outermost surface of the microwave heating film. It can be formed using coating agents, varnishes, or clear topcoats.

[0163] [Other layers]

[0164] Other layers may include OPP film, ONY film, PET film, EVOH film, PVA film, celluloid film, barrier nylon film, stretched polyethylene film, (modified) polyacrylic acid coating, PVA coating, transparent vapor-deposited film formed by vapor-depositing inorganic oxides such as aluminum oxide and silicon oxide on substrates such as biaxially stretched polyethylene terephthalate film, transparent barrier film (K coating) formed by coating polyvinylidene chloride (PVDC) on substrate films such as OPP, ONY, PET, and celluloid, and barrier film formed by laminating OPP film or NY film with ethylene-vinyl alcohol copolymer resin sandwiched between them. It is preferable to place these films on the other side of the microwave heating layer.

[0165] To prevent damage to the resin film substrate caused by current from the microwave receiving layer, a resin film with high arc resistance is preferred. Additionally, if the resin film substrate contains benzene rings, odor may sometimes be generated due to resin film damage; this should be avoided.

[0166] <Method for Manufacturing Microwave Heating Film>

[0167] One embodiment of the present invention relates to a method for manufacturing a microwave heating film, comprising:

[0168] The process of forming at least one microwave receiving layer for receiving microwaves on the first resin film (hereinafter, sometimes referred to as the "microwave receiving layer forming process").

[0169] The process of forming one or more conductive heating layers in a manner that overlaps with the microwave receiving layer (hereinafter, sometimes referred to as the "heating layer forming process");

[0170] The microwave receiving layer contains at least metal particles;

[0171] The process of laminating the surface of the first resin film having the microwave receiving layer and the heating layer with at least other second resin films using an adhesive; and

[0172] Then, other processes as needed.

[0173] The heating layer formation process and the microwave receiving layer formation process can be appropriately selected from methods such as coating a heating layer forming composition or a microwave receiving layer forming composition on at least one side of the film substrate, vapor-depositing a conductive material, or performing an electroplating process. Among these, coating is preferred, and printing is particularly preferred.

[0174] As a printing process, there are no particular restrictions, and the appropriate method can be selected according to the purpose. For example, screen printing, gravure printing, offset printing, flexographic printing, roller coating, brush coating, spray coating, squeegee coating, and inkjet printing can be listed. Among these, from the perspective of high quality and high productivity, gravure printing, flexographic printing, inkjet printing, and screen printing are preferred, with gravure printing being more preferred. As for gravure printing, the gravure printing method using a multi-color gravure printing machine is even more preferred. As a gravure printing method, it is even more preferred to use a multi-color gravure printing machine. Therefore, it is possible to overlay the microwave receiving layer and the heating layer, and it can be installed in multiple locations. Thus, it is easy to control the opening and sealing of the steam vent and the heating performance.

[0175] [Composition for forming microwave receiving layer]

[0176] The composition for forming a microwave receiving layer includes a conductive material and a solvent, and may also include other components as needed. Examples of conductive materials and other components included in the composition for forming a microwave receiving layer include materials identical to those included in the microwave receiving layer described above.

[0177] As a solvent, there are no particular limitations as long as it can dissolve or disperse the components of the composition constituting the microwave receiving layer while maintaining fluidity; it can be appropriately selected according to the purpose. Commonly used solvents include organic solvents and water.

[0178] There are no particular restrictions on organic solvents; they can be selected appropriately according to the purpose. Examples of organic solvents include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as hexane, cyclohexane, methylcyclohexane, and ethylcyclohexane; alcohol solvents such as methanol, ethanol, isopropanol (IPA), n-propanol, 1-butanol, 2-butanol, isobutanol, and tert-butanol; ester solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec-butyl acetate, and tert-butyl acetate; ketone solvents such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, and cyclohexanone; and glycol ether solvents and their esterifications 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, and propylene glycol monobutyl ether. As esters, acetate esters are primarily chosen, such as 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 can be used alone or in combination of two or more. From the viewpoint of printability and versatility, toluene, ethyl acetate, isopropanol, methyl ethyl ketone, ethanol, and water are preferred.

[0179] [[Composition for forming heating layer]]

[0180] The composition for forming the heating layer includes a conductive material and a solvent, and may also include other components as needed. Examples of conductive materials and other components included in the composition for forming the heating layer are materials identical to those included in the heating layer described above.

[0181] There are no particular restrictions on the solvent, as long as it can dissolve the conductive material and maintain it in a dispersed state. It can be appropriately selected according to the purpose. Examples of solvents include protic polar solvents such as water, methanol, ethanol, propanol, and acetic acid, as well as aprotic nonpolar solvents. These can be used alone or in combination of two or more.

[0182] The solvent preferably contains a high-boiling-point solvent with a temperature above 100°C and below 350°C.

[0183] There are no particular limitations on high-boiling-point solvents; they can be selected appropriately depending on the purpose. Examples include ethylene glycol, diethylene glycol, diethylene glycol monobutyl ether, dibutyl glycol monoethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, DMSO, formamide, glycerol, propylene glycol, 1,3-butanediol, and dipropylene glycol. Among these, ethylene glycol, diethylene glycol, DMSO, glycerol, propylene glycol, 1,3-butanediol, and dipropylene glycol are preferred.

[0184] The amount of high-boiling-point solvent added to the composition for forming the heating layer is preferably 0.1% by mass or more and 50% by mass or less. By adding 0.1% by mass or more, film-forming properties can be improved. Furthermore, by adding 50% by mass or less, both drying properties and film-forming properties can be balanced.

[0185] Alternatively, after fabricating one or more membrane substrates using a lamination method (overlapping printing of a microwave receiving layer composition and a heating layer composition), a microwave receiving layer and a heating layer can be formed on one main surface of the membrane substrate using various printing methods. After forming the microwave receiving layer and heating layer on one main surface of the membrane substrate using various printing methods, another membrane substrate can be formed on the other main surface of the membrane substrate using the aforementioned lamination method. Alternatively, a microwave receiving layer and a heating layer can be formed on both sides of the membrane substrate.

[0186] When an outer coating is applied to the microwave receiving layer and the heating layer, an outer coating can be formed using an external coating agent, an external coating varnish, a topcoat varnish, etc.

[0187] In one embodiment of the microwave heating film, the printing process for forming the microwave receiving layer, the heating layer, the printed ink layer, and the anchoring coating can be performed using gravure printing with one or more multi-color gravure printing presses. Therefore, the microwave receiving layer, the heating layer, the printed ink layer, and the anchoring coating can be continuously formed on a substrate in a single production line, enabling easy and low-cost manufacturing of the microwave heating film in a single, continuous process. Furthermore, the opening and closing of the steam vent and the heating process are easily controlled. Even when it is difficult to continuously form these layers on a production line due to limitations in gravure printing press specifications, printing environment, equipment, etc., offline formation is also possible.

[0188] In addition, when forming a microwave receiving layer and a heating layer in the printing process of gravure printing, the heating becomes too large at 100% dot area ratio, or when the requirement for the openability of the steam vent changes, the openability and heating can be easily controlled by reducing the area ratio, adjusting the plate depth, and adjusting the dilution rate.

[0189] The microwave receiving layer and heating layer only need to be formed in the desired opening area, or they can be formed on the entire surface. In addition, different coating patterns, designs, and textures can be formed according to the shape of the steam passage opening and the degree of openability requirements.

[0190] Furthermore, the printing process preferably employs gravure printing, which forms one or more colors of gravure ink. In this method, printing ink layers can be formed as needed, on the opposite side of the microwave receiving layer and the heating layer, between the film substrate and the microwave receiving layer and the heating layer, and between the microwave receiving layer and the heating layer and the anchoring coating.

[0191] Furthermore, the printing process preferably utilizes gravure printing using a multi-color gravure printing press. Because the microwave receiving layer and heating layer are transparent and almost entirely uncolored, the ink layers can be simultaneously applied online without compromising other information such as the pattern, allowing for a wide range of color variations and designs. For example, this can be applied to packaging designs to enhance purchasing appeal, indicate the opening location, opening method, or other attention-grabbing information, or include company names, logos, product names, characteristics, contents, ingredient lists, registration methods, promotional information, consumption or usage instructions, dates, country of origin, prize information, etc.

[0192] Additionally, it may include forming processes for intermediate layers, anchoring coatings, and outer coatings. There are no particular limitations as long as these layers can be formed through known forming processes such as lamination and coating.

[0193] Low-resistance compositions, high-resistance compositions, printing inks, anchoring coatings, and other compositions can be manufactured by uniformly dissolving or dispersing conductive organic compounds, resins, pigments, sealing resins, and various additives in a solvent using known methods. Dissolution or dispersion can be performed using various mixers or dispersers such as dissolvers, roller mills, ball mills, bead mills, sand mills, grinders, paint shakers, agitators, Henschel mixers, colloid mills, bead mills, ultrasonic homogenizers, wet jet mills, kneaders, and homogenizing mixers. These devices can be used individually or in combination of two or more. When the compositions contain air bubbles or coarse particles, these particles can reduce printability and print quality; therefore, it is preferable to use known filters, centrifuges, or similar equipment to remove air bubbles and coarse particles.

[0194] The viscosity of the above-mentioned compositions is not particularly limited as long as it does not affect printing. However, considering the manufacturing adaptability and processability of each composition, a viscosity of 10 mPa·s to 1000 mPa·s at 25°C is preferred. Furthermore, the viscosity of the ink for gravure printing is more preferably 10 mPa·s to 500 mPa·s.

[0195] It should be noted that viscosity can be measured using a commercially available viscometer (such as a Brookfield viscometer).

[0196] According to one embodiment, a microwave heating film includes a microwave receiving layer and a heating layer, wherein the microwave receiving layer and the heating layer comprise a low-resistance composition and a high-resistance composition according to the above embodiment. In the microwave heating film according to one embodiment, heat is generated in the heating layer when microwaves are irradiated. Due to the heating of the microwave receiving layer and the heating layer, the substrate is locally heated, and an opening can be easily formed from the center of the microwave heating film by means of rupture. Therefore, the microwave heating film according to one embodiment can maintain high vapor permeability without short-circuiting even when a large amount of food is sealed in a container, and the presence of vapor permeability holes also prevents the film from falling into the container.

[0197] One embodiment of the microwave heating film has the above-mentioned characteristics and is suitable for use as a microwave heating film for packaging. In particular, it can be effectively used as a microwave heating film for vapor release packaging.

[0198] Microwave heating packaging

[0199] A microwave heating package according to one embodiment includes at least a microwave heating film according to the above embodiment, and may further include a container or film for holding the contents of the package, if necessary.

[0200] Microwave-heated packaging can be any form that commonly uses microwave-heated film. Examples of microwave-heated packaging forms include: double-sided seal, three-sided seal, four-sided seal, pillow seal, stand-up pouch, sealed envelope, lining, fusible seal, tube, caramel packaging, outer packaging, wing-sealed packaging, bean curd packaging, twisted packaging, rocket packaging, Tetra Pak (registered trademark), lids, brick boxes, shrink wrap, cups, trays, bottles, brick boxes, containers, boxes, cartons, food containers, covers, caps, lid materials, labels, sheets, etc.

[0201] The preferred method for manufacturing microwave-heated packaging includes a forming process that uses a microwave-heated film to form the packaging.

[0202] In the forming process, microwave heating film can be formed into a packaging body. A single piece of microwave heating film can be folded back and sealed at both ends to form a bag. Alternatively, two pieces of microwave heating film can be overlapped facing each other and sealed at both ends to form a bag.

[0203] In addition, during the forming process, microwave heating film can be used to cover the container, thereby forming the packaging.

[0204] As a forming process, common packaging forming methods can be used, such as double-sided sealing, three-sided sealing, four-sided sealing, pillow sealing, stand-up pouches, envelope pasting, lining, fusible seal, tubes, caramel packaging, outer packaging, wing-sealed packaging, bean curd packaging, twisted packaging, rocket packaging, Tetra Pak (registered trademark), caps, brick boxes, shrink wrap, cups, trays, bottles, brick boxes, containers, boxes, cartons, food containers, covers, lids, caps, cover materials, labels, sheets, etc.

[0205] Figure 1 This is a diagram showing the structure of a microwave heating package according to one embodiment.

[0206] Figure 1 This diagram illustrates an example of a microwave-heated packaging body using a microwave-heating film according to one embodiment. The microwave-heated packaging body is a packaging container in which the microwave-heating film and the container are heat-sealed at a heat-sealing section. For example... Figure 1 As shown, the microwave heating film is configured such that the microwave receiving layer and the heating layer are positioned in a plan view not perpendicularly aligned with the heat-sealed portion.

[0207] A microwave-heated packaging body according to one embodiment includes a heating layer and a microwave-receiving layer, comprising a high-resistance composition and a low-resistance composition according to the above embodiment. In the microwave-heated packaging body according to one embodiment, during heating, the heating layer and the microwave-receiving layer heat up by microwave irradiation. When the heating layer and the microwave-receiving layer are overlapped at the heat-sealed portion, an opening is easily formed from the heat-sealed portion due to film shrinkage. Furthermore, when the heating layer and the microwave-receiving layer are disposed at the center of the microwave-heated film, an opening is easily formed from the center due to the breakage of the microwave-heated film. Therefore, the microwave-heated film according to one embodiment can maintain high vapor permeability even when a large volume of food is sealed in a container without short-circuiting, and the presence of vapor permeability holes also prevents the film from falling into the container.

[0208] According to one embodiment, the microwave heating film can exert high heating capacity even when a large volume of food is sealed in a container. For example, it can be suitable for use in packaging materials where permeable holes are formed by microwave irradiation. Furthermore, one embodiment of the microwave heating packaging material can be suitable for use as a cooking sheet for creating charred marks on food by microwave irradiation.

[0209] The embodiments described above are merely examples and are not limited to the aforementioned embodiments. The embodiments described can be implemented in various other ways, and various combinations, omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, and within the scope of the claims and their equivalents.

[0210] [Example]

[0211] The invention is described in more detail below with reference to embodiments and comparative examples. However, the invention is not limited to these embodiments and comparative examples.

[0212] <Preparation of the composition for forming the heating layer>

[0213] Ten parts by mass of a PEDOT:PSS solution (S-300, manufactured by Agfa Materials, Japan) used as a conductive material were mixed with two parts by mass of ethanol to obtain a composition for forming a heating layer. Ethylene glycol was added to the obtained composition for forming the heating layer at a wet ratio ranging from 0.1% to 10% to adjust the resistivity of the heating layer.

[0214] (Examples 1-4 and Comparative Example 1)

[0215] <Preparation of Compositions for Microwave Receiving Layer Formation>

[0216] Compared to Dotite (manufactured by Fujikura Chemicals), a silver particle powder ink composed of silver particles, resin material, and butyl acetate solvent, which serves as the conductive material, a microwave receiving layer forming composition was obtained, with a constant butyl acetate solvent and a resin ratio R (volume ratio of resin / (metal particles + resin)) of 29.5%. In the silver particle powder ink, the metal particles and resin, as solid components, were adjusted to a weight ratio of 62%. To make the resistivity of the microwave receiving layer variable, the composition for forming the microwave receiving layer was vibrated using ultrasound to change the agglomeration state, thereby controlling the resistivity change after coating.

[0217] <Preparation of the composition for forming the outer coating>

[0218] 15 parts by weight of AD393 (manufactured by Toyo Morton Co., Ltd., main component polyurethane), 1 part by weight of CAT-EP1 (curing agent manufactured by Toyo Morton Co., Ltd.), and 17 parts by weight of ethanol were mixed to obtain a composition for forming an outer coating.

[0219] <Preparation of Microwave Heating Film>

[0220] The microwave receiving layer composition and the heating layer composition are printed using a gravure printing press to form... Figure 4AThe microwave receiving layer and heating layer are coated onto an OPP substrate in the manner shown in the coating diagram, forming a gravure printing plate. The film thicknesses of the microwave receiving layer and the heating layer are 1.2 μm and 0.16 μm, respectively. Then, WET liquid is coated onto the substrate by gravure printing, and dried at 90°C for 1 minute to achieve the desired film thickness. It should be noted that the composition for forming the microwave receiving layer and the composition for forming the heating layer are vibrated with ultrasound to change their coagulation state, thereby controlling the change in resistivity after coating.

[0221] Simultaneously, a coating shape of 40 mm × 20 mm was formed, and the resistivity of the microwave receiving layer and the heating layer was measured. The resistivity at this time is shown in Table 1.

[0222] like Figure 2A As shown, on an OPP substrate having a microwave receiving layer and a heating layer, an outer coating of 2 μm is formed using an outer coating forming composition, dried at 90°C for 1 minute, and then cured at 40°C for 48 hours.

[0223] like Figure 1 As shown, the above film was attached to a container containing 300 ml of water instead of food using double-sided tape, and the sides were sealed with transparent tape to make a test sample.

[0224] The prepared test samples were heated in a microwave oven at 600W for 4 minutes. The deformation of the microwave receiving layer (including the periphery), damage to the microwave receiving layer (such as cracking), steam permeability under boiling water conditions, and the falling of fragments were visually confirmed. The results are shown in Table 1.

[0225] (Membrane deformation / damage to the microwave receiving layer)

[0226] [Evaluation Criteria]

[0227] ○: The membrane is not deformed (deformation cannot be confirmed visually).

[0228] △: The membrane is slightly deformed

[0229] ×: Membrane deformation or damage to the microwave receiving layer

[0230] (Vapor permeability)

[0231] [Evaluation Criteria]

[0232] ○: When the steam generated by the boiling water inside the container is discharged from the steam outlet, the container hardly deforms and the steam will not leak from the side sealed with transparent tape.

[0233] △: The container is deformed, but steam does not leak from the side.

[0234] ×: The container is severely deformed, and steam is leaking from the side.

[0235] (The falling fragments)

[0236] [Evaluation Criteria]

[0237] ○: It does not produce any of the following during heating: smoke, light, burning, or odor.

[0238] ×: Any of the following can be produced during heating: smoke, light, burning, or odor.

[0239] Table 1 shows that the resistivity of the microwave receiver layer exceeds 7.0 × 10⁻⁶. -5 At Ω·m, membrane deformation occurs, and fragments fall off.

[0240] [Table 1]

[0241]

[0242] (Examples 4-6 and Comparative Examples 2-3)

[0243] Similar to the layer composition in Example 1, the amount of ethylene glycol solvent added to the composition for forming the heating layer was controlled and varied to change the resistivity after coating, thereby achieving the desired effect. Figure 4A The coating pattern shown is achieved by using a gravure printing press to form a microwave receiving layer and a heating layer on an OPP substrate, creating a gravure printing plate. The film thicknesses of the microwave receiving layer and the heating layer are 1.2 μm and 0.16 μm, respectively. Then, WET liquid is coated onto the substrate by gravure printing, and the film is dried at 90°C for 1 minute to achieve the desired film thickness.

[0244] Simultaneously, a coating shape of 40 mm × 20 mm was formed, and the resistivity of the microwave receiving layer and the heating layer was measured. The results are shown in Table 2.

[0245] like Figure 2A As shown, on an OPP substrate having a microwave receiving layer and a heating layer, an outer coating of 2 μm is formed using an outer coating forming composition, dried at 90°C for 1 minute, and then cured at 40°C for 48 hours.

[0246] like Figure 1 As shown, the above film was attached to a container containing 300 ml of water instead of food using double-sided tape, and the sides were sealed with transparent tape to make a test sample.

[0247] The prepared test samples were heated in a microwave oven at 600W for 4 minutes, and the steam permeability under boiling conditions was visually confirmed using the same method as in Example 1. The results are shown in Table 2.

[0248] The results in Table 2 show that the resistivity of the heating layer deviates from 1.6 × 10⁻⁶. -5Ω·m~8.0×10 -3 At Ω·m, vapor permeability decreases.

[0249] [Table 2]

[0250]

[0251] Example 7

[0252] Similar to Example 1, to become Figure 4A The coating pattern shown is used to form a microwave receiving layer and a heating layer on an OPP substrate with film thicknesses of 1.2 μm and 0.16 μm, respectively, using a gravure printing machine, and then dried at 90°C for 1 minute.

[0253] like Figure 2A As shown, an outer coating of 2 μm was formed on an OPP substrate having a microwave receiving layer and a heating layer, using an outer coating forming composition. After drying at 90°C for 1 minute, the OPP substrate was placed on the substrate as a second resin film and laminated. The film was then cured at 40°C for 48 hours to produce the film of Example 7.

[0254] For Examples 1 and 7, a scratch test at 3H was performed on both sides according to JIS K 5600-5-4:1999, using the "scratch hardness (pencil method)". Then, as... Figure 1 As shown, the above film was attached to a container containing 300 ml of water instead of food using double-sided tape, and the sides were sealed with transparent tape to make a test sample.

[0255] The prepared test samples were heated in a microwave oven at 600W for 4 minutes to evaluate the luminescence and breakage of the microwave receiver layer during vapor transmission. The vapor transmission and fragment fall were visually evaluated while the water was boiling. The results are shown in Table 3.

[0256] Through lamination, strength that can withstand the hardness of a pencil can be ensured.

[0257] [Table 3]

[0258]

[0259] (Example 8)

[0260] Instead of the OPP substrate used as the lamination substrate in Example 7, an easy-peel substrate (Toray Industries 9501K2) was attached as the second resin film to produce the film of Example 8.

[0261] The quality of maintaining vapor permeability was confirmed, enabling attachment to containers and membrane peeling.

[0262] (Examples 9-10, Comparative Example 4)

[0263] To become Figure 4B The coating pattern shown is achieved by using a gravure printing machine to form a microwave receiving layer and a heating layer on an OPP substrate with film thicknesses of 1.2 μm and 0.16 μm, and then drying at 90°C for 1 minute.

[0264] like Figure 2B As shown, on an OPP substrate having a microwave receiving layer and a heating layer, a 2μm adhesive layer is formed using an adhesive layer forming composition. After drying at 90°C for 1 minute, an easy-peel substrate (Toray Industries 9501K2) is laminated as a second resin film and cured at 40°C for 48 hours.

[0265] like Figure 7 As shown, heat the above membrane in a container containing food and attach it to the container. Vibrate the food up and down 10 times to flip it over, and restore it to its original position after 10 seconds.

[0266] The membrane without water / oil repellency treatment on the easily peelable substrate was used as Comparative Example 4; the membrane with water / oil repellency treatment so that the water contact angle was 140 degrees and the rapeseed oil contact angle was 110 degrees was used as Example 9; and the membrane with water contact angle was 160 degrees and the rapeseed oil contact angle was 130 degrees was used as Example 10.

[0267] The contact angle is determined by dropping water or rapeseed oil from a nozzle onto the surface of a resin film in the direction of the food, taking a picture with a camera, and calculating the contact angle from the shape of the droplets.

[0268] like Figure 7 As shown, for Comparative Examples 4, 9, and 10, the ingredients were cooked in clear broth with parsley and mackerel sauce, and microwaved at 600W for 4 minutes. Container deformation and the presence of burnt steam and odors were confirmed by visual inspection, smell, and the appearance of falling debris. The results are shown in Table 4. In the confirmed items, even if only one item has a problem, it is judged as "×".

[0269] If food adheres to the membrane at the steam permeation point, it will cause burning and odor in the steam permeation area. By treating with water and oil, the amount of food adhering to the membrane is reduced, thereby improving the situation. The contact angle of water should be 140 degrees or more and the contact angle of rapeseed oil should be 110 degrees or more. Preferably, the contact angle of water should be 160 degrees or more and the contact angle of rapeseed oil should be 130 degrees or more.

[0270] [Table 4]

[0271]

[0272] (Examples 11-14, Comparative Examples 5-8)

[0273] In the microwave receiving layer, a heating layer forming composition with the resin ratio R (volume ratio of resin / (metal particles + resin)) changed as shown in Table 5 was used, and the composition was modified by gravure printing. Figure 4B The various coating shapes and film thicknesses shown in figures a and b are formed on an OPP substrate using a gravure printing press. In the silver particle powder ink, the metal particles and resin, as solid components, are adjusted at a weight ratio of 62%. Furthermore, even in the heat-generating layer, the film thickness is adjusted to 0.16 μm using a gravure printing press, formed on the OPP substrate, and dried at 90°C for 1 minute.

[0274] On an OPP substrate having a microwave receiving layer and a heating layer, a 2μm adhesive layer is formed using an adhesive layer forming composition. After drying at 90°C for 1 minute, an easy-peel substrate (Toray Industries 9501K2) is laminated as a second resin film and cured at 40°C for 48 hours.

[0275] for Figure 4B The shape shown is altered by changing the film thickness D of the microwave receiving layer, the resin ratio R, and the area S surrounded by each microwave receiving layer. Figure 4B Calculate the relation (1) for a×b): The results are shown in Table 5.

[0276] In such Figure 4C To arrange the three cases in that way, there must exist α1 and α2 that are equivalent to a1 and a2 respectively, and both satisfy 1.8 × 10 -4 That's all. The same applies to situations involving more than four arrangements.

[0277] like Figure 1 As shown, the membrane was heated in a container with 300 ml of water added instead of food ingredients and then attached to the container. It was microwaved for 4 minutes at 600W. The steam permeability was visually confirmed while the water was boiling. The results are shown in Table 5. A steam permeability of "0" means that the container does not deform even when the water inside the container boils and steam is released.

[0278] Next, as Figure 5 As shown, water to a height of 2 mm was placed on the microwave heating film, and 300 ml of water was added to replace the food. The film was microwaved for 4 minutes at a setting of 600W. The damage to the microwave receiving layer was visually confirmed, and the fragments were visually confirmed to fall. The results are shown in Table 5.

[0279] If the parameter α is 1.8 × 10 -4 The above can balance steam permeability and metal breakage.

[0280] [Table 5]

[0281]

[0282] (Examples 15-16, Comparative Example 9)

[0283] for Figure 4A and Figure 4B The shapes shown (W=2 mm, 1 mm, V=1 mm) are formed on the OPP substrate using a gravure printing machine with film thicknesses of 1.2 μm and 0.16 μm, respectively, to create a microwave receiving layer and a heating layer. The layers are then dried at 90°C for 1 minute.

[0284] On an OPP substrate having a microwave receiving layer and a heating layer, a 2μm adhesive layer is formed using an adhesive layer forming composition. After drying at 90°C for 1 minute, an easy-peel substrate (Toray Industries 9501K2) is laminated as a second resin film and cured at 40°C for 48 hours.

[0285] like Figure 1 As shown, the membrane was heated in a container with 300 ml of water added instead of food ingredients and then attached to the container. It was microwaved for 4 minutes at 600W. The steam permeability was visually confirmed while the water was boiling. The results are shown in Table 5. A steam permeability of "0" means that the container does not deform even when the water inside the container boils and steam is released.

[0286] Next, as Figure 5 As shown, water to a height of 2 mm was placed on the microwave heating film, and 300 ml of water was added to replace the food. The film was microwaved for 4 minutes at a setting of 600W. The results of visually inspecting the microwave receiving layer, the damage to the film nearby, and confirming the falling of fragments are shown in Table 6.

[0287] All three conditions result in metal breakage, but by designing it as a hollow shape, the area of ​​breakage is reduced, preventing membrane damage and minimizing the amount of fragments falling onto the food. This also helps reduce costs.

[0288] [Table 6]

[0289]

[0290] (Examples 17-18, Comparative Examples 11-13)

[0291] for Figures 6A to 6D The microwave receiving layer and heating layer were formed on the OPP substrate using a gravure printing machine with film thicknesses of 1.2 μm and 0.16 μm, respectively, and then dried at 90°C for 1 minute.

[0292] On an OPP substrate having a microwave receiving layer and a heating layer, a 2μm adhesive layer is formed using an adhesive layer forming composition. After drying at 90°C for 1 minute, an easy-peel substrate (Toray Industries 9501K2) is laminated as a second resin film and cured at 40°C for 48 hours.

[0293] exist Figure 1 The membrane was heated in a container with 50 ml of water added instead of food ingredients and then attached to the container. It was then microwaved for 30 seconds at 600W. The microwave receiving layer was visually inspected for damage. The evaluation was performed 6 times. If no damage was found in any of the 6 microwave receiving layers, it was judged as "0"; if all 6 were damaged, it was judged as "×"; and if damage occurred 1 to 5 times, it was judged as "△".

[0294] exist Figure 6C and Figure 6D In the middle, the part enclosed by a circle is the damaged area.

[0295] Next, in Figure 1 The membrane was heated in a container with 300 ml of water added instead of ingredients and then attached to the container. It was microwaved for 4 minutes at 600W. The results were shown in Table 7 by visually observing the steam permeability and confirming the falling of fragments while the water was boiling.

[0296] Configuring the microwave trusted layer online Figure 6A , Figure 6B In the middle, it can be confirmed that no damage occurred to the microwave receiver layer, but... Figure 6C , Figure 6D In this case, if U is too close, the microwave receiving layer will be damaged. Therefore, the microwave receiving layers should not be placed near each other outside the edges where the heating layers meet. Here, U is the distance between the long sides of adjacent microwave receiving layers.

[0297] In vapor permeability, Figure 6C , Figure 6D In the case where U is 2 mm, a steam permeation port cannot be formed in the central part, and is set as △. That is, it is preferable that U is more than twice V.

[0298] [Table 7]

[0299]

[0300] (Example 19, Comparative Examples 14-15)

[0301] Compared to Example 11, a sample was prepared by changing the first resin film to a material with different arc resistance. Figure 3Add 300 ml of water to the sample instead of the ingredients, and microwave for 4 minutes at 600W. Visually inspect the luminescence and smoke generation during microwave heating in the steam-permeable section (including the falling of fragments). Arc resistance was measured according to JIS C 2135 and JIS K6911. The evaluation results are shown in Table 8.

[0302] It can be seen that when the material has an arc resistance of more than 120 seconds, it does not produce light or smoke.

[0303] [Table 8]

[0304]

[0305] Compared to Example 11, a sample was prepared by changing the first resin film to a material with different arc resistance. Figure 3 Add 300 ml of water to the food instead of the ingredients, and microwave for 4 minutes at 600W. Observe the aroma produced and the fragments falling after microwave heating by observing the steam passing through the steam passage. The aroma confirmation results are shown in Table 9.

[0306] It can be seen that the presence or absence of benzene rings in the material of the first resin film determines whether an odor is produced.

[0307] [Table 9]

[0308]

[0309] (Example 20, Comparative Example 16)

[0310] for Figure 4B The shapes shown were formed on an OPP substrate using a gravure printing press, with film thicknesses of approximately 1 μm, 1.2 μm, and 0.16 μm, respectively. A printing layer, a microwave receiving layer, and a heating layer were formed on the OPP substrate, and the film was dried at 90°C for 1 minute. At this time, films with and without a printing layer were produced in the vapor transmission section; Example 20 had no printing layer, while Comparative Example 16 had a printing layer.

[0311] On an OPP substrate having a microwave receiving layer and a heating layer, a 2μm adhesive layer is formed using an adhesive layer forming composition. After drying at 90°C for 1 minute, an easy-peel substrate (Toray Industries 9501K2) is laminated as a second resin film and cured at 40°C for 48 hours.

[0312] like Figure 1 As shown, the membrane was heated in a container with 300 ml of water added instead of food and then attached to the container. It was microwaved for 4 minutes at 600W. The steam permeability and fragments falling were visually confirmed while the water was boiling. The results are shown in Table 10.

[0313] It can be seen that if a printed layer exists in the steam permeation section, fragments will fall and metal will break.

[0314] [Table 10]

[0315]

[0316] (Example 21, Comparative Example 17)

[0317] for Figure 4B The shapes shown were formed on an OPP substrate using a gravure printing press, with film thicknesses of approximately 1 μm, 1.2 μm, and 0.16 μm, respectively, by gravure printing. The resulting film was then dried at 90°C for 1 minute. At this point, films with and without a printed layer were produced; Example 21 had a printed layer, while Comparative Example 17 had no printed layer.

[0318] For Example 21 and Comparative Example 17, roll-shaped film samples were prepared with or without a printed layer under the microwave receiving layer, and left for 3 days to confirm whether adhesion caused by bonding occurred. The results are shown in Table 11.

[0319] Then, on the OPP substrate with the microwave receiving layer and the heating layer formed, a 2μm adhesive layer is formed using an adhesive layer forming composition. After drying at 90°C for 1 minute, an easy-to-peel substrate (Toray Industries 9501K2) as the second resin film is laminated and cured at 40°C for 48 hours.

[0320] like Figure 1 As shown, the membrane was heated in a container with 300 ml of water added instead of food and then attached to the container. It was microwaved for 4 minutes at 600W. The steam permeability was visually confirmed while the water was boiling. The results are shown in Table 11.

[0321] If vapor permeability is maintained, adhesion can be prevented when there is a printed layer below the microwave receiving layer, thus improving the situation.

[0322] If a printed layer exists in the steam permeation section, it can be known that metal breakage occurs under all three conditions, including when the fragment falls.

[0323] [Table 11]

[0324]

[0325] Examples of various embodiments of the present invention are as follows:

[0326] <1>

[0327] A microwave heating film, characterized in that:

[0328] The microwave heating film includes:

[0329] First resin film;

[0330] At least one microwave receiving layer is provided on the first resin film; and

[0331] At least one or more heating layers are in contact with the microwave receiving layer.

[0332] The microwave receiving layer contains at least metal particles.

[0333] The resistivity of the microwave receiving layer is 7.0 × 10⁻⁶. -5 Ω·m or less,

[0334] The resistivity of the heating layer is 1.6 × 10⁻⁶. -5 Ω•m~8.0×10 -3 Ω•m.

[0335] <2>

[0336] According to the microwave heating film described in <1> above, its characteristics are as follows:

[0337] A second resin film is present on the microwave receiving layer and the heating layer.

[0338] <3>

[0339] According to the microwave heating film described in <2> above, its characteristics are as follows:

[0340] In the second resin film, any one of the following processes is performed on the surface opposite to the surface of the microwave receiving layer and the heating layer formed on the first resin film: heat sealing, water repellency, and oil repellency.

[0341] <4>

[0342] The microwave heating film according to <1> or <2> above is characterized in that:

[0343] The first resin film is subjected to any one of the following processes: heat sealing, water repellency, and oil repellency.

[0344] <5>

[0345] According to the microwave heating film described in <4> above, its characteristics are as follows:

[0346] Satisfy any of the following:

[0347] In the aforementioned water-repellent processing, the contact angle with water is 140 degrees or more; and

[0348] In the oil-repellent process, the contact angle with rapeseed oil is 110 degrees or more.

[0349] <6>

[0350] The microwave heating film according to <1> or <2> above is characterized in that:

[0351] The microwave receiving layer is a mixture of metal particles and resin. When the film thickness of the microwave receiving layer is set as D, the resin ratio (i.e., the volume ratio of resin / (metal particles + resin)) is set as R, and the area surrounded by each microwave receiving layer is set as S, α, expressed by the following formula (1), is 1.8 × 10⁻⁶. -4 above:

[0352] [Formula 1]

[0353] Equation (1).

[0354] <7>

[0355] The microwave heating film according to <1> or <2> above is characterized in that:

[0356] The microwave receiving layer has a hollow structure.

[0357] <8>

[0358] The microwave heating film according to <1> or <2> above is characterized in that:

[0359] It has a first microwave receiving layer and a second microwave receiving layer, and its shape is rectangular;

[0360] The short sides of the first microwave receiving layer and the short sides of the second microwave receiving layer are configured opposite to each other and are connected by a heating layer.

[0361] <9>

[0362] According to the microwave heating film described in <8> above, its characteristics are as follows:

[0363] It further includes a third microwave receiving layer, which is rectangular in shape;

[0364] The long side of the third microwave receiving layer is configured to be opposite the long side of the first microwave receiving layer or the long side of the second microwave receiving layer at a distance U;

[0365] The short sides of the first microwave receiving layer and the short sides of the second microwave receiving layer are configured relative to each other at a distance V;

[0366] The distance U is more than twice the distance V.

[0367] <10>

[0368] According to the microwave heating film described in <2> above, its characteristics are as follows:

[0369] The arc resistance of the first resin film and the second resin film is more than 120 seconds.

[0370] <11>

[0371] According to the microwave heating film described in <2> above, its characteristics are as follows:

[0372] The first resin film and the second resin film contain resin;

[0373] The resin does not have benzene rings.

[0374] <12>

[0375] A method for manufacturing a microwave heating film, characterized in that:

[0376] The method for manufacturing the microwave heating film includes:

[0377] The process of forming at least a microwave receiving layer on the first resin film; and

[0378] The process of forming one or more heating layers on the first resin film in a manner that is in contact with the microwave receiving layer.

[0379] The microwave receiving layer contains at least metal particles.

[0380] The resistivity of the microwave receiving layer is 7.0 × 10⁻⁶. -5 Below Ω·m,

[0381] The resistivity of the heating layer is 1.6 × 10⁻⁶. -5 Ω·m~8.0×10 -3 Ω·m.

[0382] <13>

[0383] The method for manufacturing the microwave heating film according to <12> above is characterized in that:

[0384] The process includes forming a printed layer on the first resin film;

[0385] The printed layer, the microwave receiving layer, and the heating layer are sequentially formed on the first resin film;

[0386] The printed layer is not formed at the portion where the microwave receiving layer and the heating layer are in contact.

[0387] The above embodiments are illustrative and do not limit the invention. Therefore, many additional modifications and variations are possible based on the above teachings. For example, within the scope of the invention, elements and / or features of different illustrative embodiments can be combined with and / or substituted for each other.

Claims

1. A microwave heating film, characterized in that... : The microwave heating film includes: First resin film; At least one microwave receiving layer is provided on the first resin film; and At least one or more heating layers are in contact with the microwave receiving layer. The microwave receiving layer contains at least metal particles. The resistivity of the microwave receiving layer is 7.0 × 10⁻⁶. -5 Ω·m or less, The resistivity of the heating layer is 1.6 × 10⁻⁶. -5 Ω•m~8.0×10 -3 Ω•m.

2. The microwave heating film according to claim 1, characterized in that... : A second resin film is present on the microwave receiving layer and the heating layer.

3. The microwave heating film according to claim 2, characterized in that... : In the second resin film, any one of the following processes is performed on the surface opposite to the surface of the microwave receiving layer and the heating layer formed on the first resin film: heat sealing, water repellency, and oil repellency.

4. The microwave heating film according to claim 1 or 2, characterized in that... : The first resin film is subjected to any one of the following processes: heat sealing, water repellency, and oil repellency.

5. The microwave heating film according to claim 4, characterized in that... : Satisfy any of the following: In the aforementioned water-repellent processing, the contact angle with water is 140 degrees or more; and In the oil-repellent process, the contact angle with rapeseed oil is 110 degrees or more.

6. The microwave heating film according to claim 1 or 2, characterized in that... : The microwave receiving layer is a mixture of metal particles and resin. When the film thickness of the microwave receiving layer is set as D, the resin ratio (i.e., the volume ratio of resin / (metal particles + resin)) is set as R, and the area surrounded by each microwave receiving layer is set as S, α, expressed by the following formula (1), is 1.8 × 10⁻⁶. -4 above: [Formula 1] Equation (1).

7. The microwave heating film according to claim 1 or 2, characterized in that... : The microwave receiving layer has a hollow structure.

8. The microwave heating film according to claim 1 or 2, characterized in that... : It has a first microwave receiving layer and a second microwave receiving layer, and its shape is rectangular; The short sides of the first microwave receiving layer and the short sides of the second microwave receiving layer are configured opposite to each other and are connected by a heating layer.

9. The microwave heating film according to claim 8, characterized in that... : It further includes a third microwave receiving layer, which is rectangular in shape; The long side of the third microwave receiving layer is configured to be opposite the long side of the first microwave receiving layer or the long side of the second microwave receiving layer at a distance U; The short sides of the first microwave receiving layer and the short sides of the second microwave receiving layer are configured relative to each other at a distance V; The distance U is more than twice the distance V.

10. The microwave heating film according to claim 2, characterized in that... : The arc resistance of the first resin film and the second resin film is more than 120 seconds.

11. The microwave heating film according to claim 2, characterized in that... : The first resin film and the second resin film contain resin; The resin does not have benzene rings.

12. A method for manufacturing a microwave heating film, characterized in that... : The method for manufacturing the microwave heating film includes: The process of forming at least a microwave receiving layer on the first resin film; and The process of forming one or more heating layers on the first resin film in a manner that is in contact with the microwave receiving layer. The microwave receiving layer contains at least metal particles. The resistivity of the microwave receiving layer is 7.0 × 10⁻⁶. -5 Below Ω·m, The resistivity of the heating layer is 1.6 × 10⁻⁶. -5 Ω·m~8.0×10 -3 Ω·m.

13. The method for manufacturing the microwave heating film according to claim 12, characterized in that... : The process includes forming a printed layer on the first resin film; The printed layer, the microwave receiving layer, and the heating layer are sequentially formed on the first resin film; The printed layer is not formed at the portion where the microwave receiving layer and the heating layer are in contact.

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