Microwave shielding and food containers

Abstract

The present invention aims to provide a microwave shield that can partially irradiate an object with microwaves. [Solution] The present invention comprises a microwave shielding body 10 in which a heat-shielding film 11, a water-containing layer 12, and a surface substrate 13 are laminated in this order, wherein the water-containing layer 12 is a polymer layer capable of supporting water, and water is supported in a range of 30% to 60% by mass when the total mass of the water-containing layer 12 is 100% by mass, and a handle portion 14 is located at one of the periphery locations.

Description

Technical Field

[0001] The present invention relates to a microwave shield and a food container provided with the same.

Background Art

[0002] When purchasing boxed lunches at stores that sell foods such as convenience stores, they are often heated in a microwave oven either at the store or after being taken home and then eaten. Among these boxed lunches, there are packages that contain ingredients such as grains, vegetables, and pickled vegetables, as well as seasonings, etc., sorted and placed in plastic containers. It is important to place the container containing these various ingredients and packaging materials inside a microwave oven, irradiate it with microwaves, and heat it to a preferred temperature in order to eat the boxed lunches deliciously.

[0003] Generally, when heating boxed lunches in a microwave oven, the main adjustments are the irradiation time and the amount of irradiation energy of the microwaves for heating the food. At the same time, it is difficult to make adjustments such as changing the heating temperature for each food (for each part) being heated. However, even if the containers of boxed lunches receive the same amount of microwaves, there are ingredients such as pickled vegetables that become too hot compared to grains and, in some cases, dry out and have a poor texture. Also, the center part of ingredients such as hamburgers is difficult to be warmed by microwaves compared to grains, etc. When warming a hamburger to an appropriate temperature, the grains and pickled vegetables are overheated, and there is a problem that the texture of the pickled vegetables, etc. is significantly reduced. Furthermore, due to its sealed structure, when the package containing seasonings, etc. receives too much heat, it may expand and cause a crack in a part of the package, and there is a risk that the seasonings will scatter inside the boxed lunch container. Therefore, there has been a consideration to introduce a special structure on the container side of boxed lunches to block a part of the microwaves irradiated from the microwave oven before they reach the food, so that only some of the ingredients and seasonings are not overheated according to the type of ingredients and the type of contents.

[0004] For example, a tray has been proposed for microwave heating that has a first integrated compartment and a second integrated compartment separated by a part of the side wall or a bottom wall that protrudes upward, and one of the compartments includes a microwave energy entry adjustment structure (see Patent Document 1). Furthermore, a microwave-safe container and packaging, and a partially non-heating cooking method using the same, have been proposed, which consists of a microwave-shielding container body having a bottom wall and peripheral walls rising from its periphery, and a microwave-transparent inner tray, with the inner tray supported near the opening of the container body (see Patent Document 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2013-516216 [Patent Document 2] Japanese Patent Publication No. 2005-263319 [Overview of the project] [Problems that the invention aims to solve]

[0006] The microwave heating tray described in Patent Document 1 employs foil, microwave absorbing material, microwave transmitting material, microwave reflecting material, and combinations thereof as a microwave energy limiting structure. Specifically, aluminum foil is used as the foil described in Patent Document 1. The microwave shielding material described in Patent Document 2 employs a synthetic resin sheet equipped with an aluminum metal foil or a metal vapor-deposited film. However, even synthetic resin sheets equipped with aluminum metal foil or a metal vapor-deposited film can easily generate sparks in the metal foil or film when placed in a microwave oven and exposed to microwaves. Depending on the nature of the sparks, there is a risk that the resin adjacent to the metal foil or film may burn, which is a problem that prevents practical application at present. Therefore, there is a need for the introduction of a safe microwave shielding structure that does not generate sparks when microwaves are irradiated into a microwave oven.

[0007] Electromagnetic waves with wavelengths of 1 to 1000 mm are called microwaves, and their frequencies range from 500 MHz to 500 GHz. Of these, microwaves in the 2450 MHz band, as defined by the Radio Law, are used in home and commercial microwave ovens. Water, which efficiently absorbs microwave power in this frequency band, is instantly heated as its molecular motion becomes more active upon microwave irradiation. However, ceramic materials such as glass, which have low absorption efficiency for microwave power in this frequency band, transmit microwaves. Therefore, even if only a ceramic container is placed in a microwave oven, the container itself will not be heated. In contrast, when microwaves in the aforementioned frequency range are irradiated onto metal foil or metal vapor-deposited film, the irradiated microwaves are diffusely reflected inside the microwave oven, and free electrons are emitted by the current generated on the metal surface. The diffusely reflected microwaves and the free electrons emitted from the metal surface degrade the magnetron that generates microwaves in the microwave oven, leading to a problem of microwave oven malfunction. Therefore, although metal foils and metal vapor-deposited films have a microwave shielding effect, they cannot be used as microwave shielding materials for microwave ovens due to the aforementioned problem of spark generation.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a microwave shield capable of partially irradiating an object with microwaves, and a food container equipped with the same. [Means for solving the problem]

[0009] The present invention has the following configuration. [1] The present invention comprises a heat-shielding film, a water-containing layer, and a surface substrate laminated in this order, wherein the water-containing layer has water supported on a water-bearing polymer layer in a range of 30% to 60% by mass when the total mass of the water-containing layer is 100% by mass, and has a handle at one of its periphery locations. [2] The surface substrate is the microwave shield described in [1] above, having fine pores or valves. [3] The knob portion is provided by the microwave shield described in [1] above, wherein the heat-shielding film protrudes from the outer circumference of the microwave shield. [4] The microwave shield described in [1] above, wherein the water-containing layer is made of at least one aqueous gel selected from the group consisting of polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, polyurethane, silicone, vinyl acetate copolymer, and maleic anhydride copolymer, and the thickness of the water-containing layer is 100 μm or more and 10 mm or less. [5] The heat-shielding film is a microwave shield described in [1] above, which consists of a polyethylene terephthalate film, a polypropylene film, a polycarbonate film, and a polyimide film having a thermal conductivity of 0.12 to 0.6 W / (m·K). [6] The microwave shield described in [1] above, wherein the surface substrate is made of polyethylene terephthalate film or polyethylene terephthalate nonwoven fabric. [7] Another invention is a food container comprising a container, a lid, and a microwave shielding body as described in any of [1] to [6] above. [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain a microwave shield capable of partially irradiating an object with microwaves, and a food container equipped with the same. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing one embodiment of the microwave shielding body of the present invention. [Figure 2] This is a plan view of one embodiment of the microwave shielding body of the present invention. [Figure 3] This is a cross-sectional view showing another embodiment of the microwave shielding body of the present invention. [Figure 4] This is a schematic cross-sectional view of a bento box using a microwave shield according to one embodiment. [Modes for carrying out the invention]

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Microwave shielding body] FIG. 1 is a cross-sectional view of the microwave shielding body 10 of the present embodiment. FIG. 2 is a plan view of the microwave shielding body 10 of the present embodiment. As shown in FIG. 1, the microwave shielding body 10 is formed by laminating a heat insulating film 11, a water-containing layer 12, and a surface base material 13 in this order. The water-containing layer 12 carries water in the range of 30% by mass or more and 60% by mass or less when the total mass of the water-containing layer 12 is 100% by mass in a polymer layer capable of carrying water. And, as shown in FIG. 2, the microwave shielding body 10 has a knob portion 14 at any location on the periphery.

[0013] (Heat insulating film) The heat insulating film 11 is preferably made of a resin film having a low thermal conductivity, high heat resistance, and low water permeability. Such a resin film is preferably made of a PET (polyethylene terephthalate) film, a polypropylene (PP) film, a PET film having pores, a foamed PET film, a polycarbonate (PC) film, a polyimide (PI) film, a polyester non-woven fabric, or the like.

[0014] PET has a melting point of 260 ° C, an actual use temperature (the upper limit temperature at which the sheet shape is maintained (the same hereinafter)) of about 200 ° C, and a thermal conductivity of 0.14 W / (m·K). PP has a melting point of 160 ° C, an actual use temperature of about 120 ° C, and a thermal conductivity of 0.12 W / (m·K). PC has a melting point of 150 ° C, an actual use temperature of 120 to 130 ° C, and a thermal conductivity of 0.19 W / (m·K). PI has an actual use temperature of about 400 ° C and a thermal conductivity of 0.29 W / (m·K). The resin having a low thermal conductivity as the resin constituting the heat insulating film 11 means a resin having a thermal conductivity of 0.6 W / (m·K) or less. The resin having high heat resistance as the resin constituting the heat insulating film 11 means a resin having an actual use temperature of 120 ° C or higher. Thermal conductivity can be measured using the AI ​​Phase Mobile 1u (manufactured by AI Phase Co., Ltd.) in a standard environmental test chamber (23°C, 50% RH). The sample size is set to 50mm x 50mm, with a sample thickness of 50μm.

[0015] As shown in Figure 3, if the heat-shielding film 31 is made of resin, it may have fine holes or valves 31a to release the heat and water vapor generated when heated. The range and position of the formation of the fine holes or valves are not limited, and they may be formed locally or over the entire surface, as long as heat and water vapor can be released smoothly to the outside. It is preferable that the fine holes or valves be provided over almost the entire surface of the surface substrate 13 in order to release heat and water vapor. The number of fine holes or valves is not particularly limited, and many may be formed. It is preferable that the fine holes or valves be provided over almost the entire surface of the surface substrate 13. In this case, the water vapor permeability of the heat-shielding film 31 is 5 g / m². 2 ·day · atm or more 10000g / m 2 It is preferable that it is less than or equal to day·atm. Fine holes can be formed by conventionally known methods such as porosizing, punching, and laser drilling. Fine valves can also be formed, for example, by cutting into the heat-shielding film 31 with a punching blade. The shape of the fine valves can vary and may be C-shaped, U-shaped, tongue-shaped, etc. The configuration shown in Figure 3 consists of a heat-shielding film 31, a water-containing layer 32, and a surface substrate 33, with the heat-shielding film 31 having a handle portion 34.

[0016] (water-containing layer) The water-containing layer 12 is composed of an aqueous gel, which is a layer in which water is supported on a polymer layer capable of supporting water. When the total mass of the water-containing layer is considered to be 100% by mass, the water content is in the range of 30% to 60% by mass. The above amount of water supported in the water-containing layer 12 makes it possible to provide a microwave shielding body 10 that has excellent moldability and can suppress excessive heating by microwaves. As the polymer species used to constitute the aqueous gel, any polymer capable of supporting water may be used, such as polyacrylic acid (PAAc), polyvinyl alcohol (PVA), polyvinylpyrrolidone, polyurethane, silicone, vinyl acetate copolymer, maleic anhydride copolymer, etc. In addition, the water-containing layer 12 may contain small amounts of preservatives, fragrances, pigments (organic dyes), antioxidants, and other components.

[0017] The thickness of the water-containing layer 12 is preferably 100 μm or more and 10 mm or less, more preferably 200 μm or more and 5 mm or less, even more preferably 500 μm or more and 3 mm or less, and even more preferably 2 mm or more and 3 mm or less. The water-containing layer 12 preferably has exposed peripheral sides to allow water vapor generated by heating to escape.

[0018] (Surface base material) The surface substrate 13 is preferably made of a material with high heat resistance, and a print-receiving layer may be separately provided on the surface of the surface substrate 13. Examples of resin films constituting the surface substrate 13 include PET film, PP film, PC film, PI film, etc., and the surface substrate 13 can also be made of a nonwoven or woven fabric such as PET, PP, or cellulose. If a print-receiving layer is provided, printing on the print-receiving layer can improve the aesthetic appearance of the microwave shielding body 10.

[0019] When a resin film such as a PET film is used as the surface substrate 13, it is preferable to have fine pores or valves to release the heat and water vapor generated when the water-containing layer 12 is heated. The range and position of formation of the fine pores or valves are not limited, and they may be formed locally or over the entire surface, as long as heat and water vapor can be released smoothly to the outside. It is preferable to provide the fine pores or valves over almost the entire surface of the surface substrate 13 in order to release heat and water vapor. The number of fine pores or valves is not particularly limited, and many may be formed. It is preferable to provide the fine pores or valves over almost the entire surface of the surface substrate 13. In this case, the water vapor permeability of the surface substrate 13 is 5 g / m². 2·day · atm or more 10000g / m 2 It is preferable that it is less than or equal to day·atm.

[0020] The thickness of the surface substrate 13 is preferably 10 μm or more and 200 μm or less, and more preferably 15 μm or more and 75 μm or less.

[0021] (Snack section) The microwave shielding body 10 has a handle 14 to facilitate handling, as the microwave heats up the water in the water-containing layer 12, causing the microwave shielding body 10 to become hot. In this embodiment, the knob portion 14 is formed by molding the heat-shielding film 11 so as to protrude from the outer circumference of the microwave shield 10. In this embodiment, it is provided on one short side of the rectangular microwave shield 10, but it may be provided anywhere on the periphery of the microwave shield 10. For example, it may be provided on one long side of the rectangular microwave shield 10, on two opposing sides, or along the entire periphery of the microwave shield 10. If it is provided along the entire periphery, it can be easily formed by using a heat-shielding film 11 that is larger than the outer diameter of the microwave shield 10. The shape of the knob portion 14 is not limited to a rectangular shape; in addition, its outer shape may be composed of curves such as a semicircular or semi-elliptical shape. Furthermore, the knob portion 14 may be provided separately from the heat-shielding film 11 or the surface substrate 13, for example, by adhering an adhesive label to the microwave shielding body 10. In this embodiment, the knob portion 14 has been described as being provided on the heat-shielding film 11, but it may also be provided on the surface substrate 13.

[0022] Since the microwave shield 10 has a handle at one of its periphery locations, even if the water-containing layer of the microwave shield becomes hot after heating and the entire microwave shield 10 becomes hot, the microwave shield can be easily removed by pinching the handle.

[0023] [Food containers] The food container of the present invention comprises a container, a lid, and a microwave shield. Such a food container can be used as a container for bento boxes. For example, the container can hold ingredients that are more prone to changes in taste compared to other ingredients, such as fruits and raw vegetables, ingredients that are more easily heated than other ingredients and are more likely to be overheated (hereinafter abbreviated as "unheated ingredients," but this does not mean that they should not be heated at all, but rather that the degree of heating should be kept relatively low), and ingredients such as cooked grains and prepared foods (hereinafter abbreviated as "heated ingredients," but that refers to ingredients that should be kept relatively high). The food container of the present invention can be used for room temperature foods, refrigerated foods, and frozen foods. Even if the container contains ingredients that require different levels of heating, by covering the ingredients that do not need to be heated as much as other ingredients with a microwave shield, the ingredients can be consumed at a preferred temperature.

[0024] [How to use] The following describes one embodiment in which a food container equipped with the microwave shielding body 10 of the present invention is used in a bento box. Figure 4 shows a cross-sectional view in which the microwave shielding body 10 of this embodiment is used in a bento box. The bento box 20 contains, in a container 21, non-heated ingredients 23 such as fruits and raw vegetables, which are ingredients whose taste is more likely to change compared to other ingredients, and which are more easily heated and more likely to be overheated compared to other ingredients, as well as heated ingredients 24 such as cooked grains and side dishes. When heating the bento box 20 in a microwave oven, the microwave shielding body 10 is placed on top of the lid 22 above the non-heated food items 23 contained in the container 21, and on the bottom of the container 21. The microwave shield 10 may be additionally positioned to cover the side wall of the container 21 on the side where the food to be heated 24 is located. Alternatively, the microwave shield 10 may be positioned only on the top of the container 21.

[0025] When the microwave shielding body 10 is placed on the lid 22 of the container 21, it is preferable to position it so that the heat-shielding film 11 faces the lid 22. Furthermore, when the microwave shielding body 10 is placed below the container 21, it is preferable to arrange them in the following order from the container 21 side: the heat-shielding film 11, the water-containing layer 12, and the surface substrate 13.

[0026] When microwaves from a microwave oven are shone onto the bento box 20, the microwaves that reach the microwave shield 10 vibrate the water molecules in the water-containing layer 12, heating the water. Heating the water consumes some of the microwave energy, reducing the amount of microwaves that reach the uncooked food 23. When the uncooked food 23, sandwiched between microwave shields 10, is heated in a microwave oven in its container, it receives less microwave radiation than other food items not covered by microwave shields 10, thus preventing overheating. As a result, the uncooked food 23 is not overheated and remains at a moderate temperature, while the heated food 24 can be consumed warm.

[0027] [Method for manufacturing microwave shielding material] An aqueous gel, which will become a water-containing layer 12, is applied to the surface of the surface substrate 13 described above, to a predetermined water content and film thickness. There are no particular restrictions on the application method, but conventionally known application methods can be used, such as methods using application equipment such as knife coaters, roll coaters, roll knife coaters, gravure coaters, variogravure coaters, air knife coaters, bar coaters, die coaters, and curtain coaters. Subsequently, the heat-shielding film 11 is bonded to the side of the water-containing layer 12 opposite to the surface substrate 13 to produce a microwave shield 10. One process for cutting the microwave shielding body 10 to the desired size is to form notches at predetermined locations in the cross-sectional direction of the microwave shielding body 10. The notches can be formed using a Thomson blade, a Pinnacle® blade, a die-cutting roll, etc. After that, any unnecessary parts that are not used as microwave shielding are removed by scraping. [Explanation of symbols]

[0028] 10, 30 Microwave shielding 11, 31 Heat-shielding film 12, 32 water-containing layer 13, 33 Surface base material 14, 34 Knob section 20 Bento 21 Container 22 Lid 23 Unheated foods 24 Heating ingredients 31a Fine holes or valves

Claims

1. The heat-shielding film, water-containing layer, and surface substrate are laminated in this order. The water-containing layer has water supported on a water-supporting polymer layer in a range of 30% to 60% by mass, where the total mass of the water-containing layer is 100% by mass. A microwave shield having a handle at one of its periphery locations.

2. The microwave shielding body according to claim 1, wherein the surface substrate has fine pores or valves.

3. The microwave shielding body according to claim 1, wherein the knob portion is provided such that the heat-shielding film protrudes from the outer circumference of the microwave shielding body.

4. The microwave shielding body according to claim 1, wherein the water-containing layer is made of at least one aqueous gel selected from the group consisting of polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, polyurethane, silicone, vinyl acetate copolymer, and maleic anhydride copolymer, and the thickness of the water-containing layer is 100 μm or more and 10 mm or less.

5. The microwave shielding body according to claim 1, wherein the heat-shielding film is made of any one of polyethylene terephthalate film, polypropylene film, polycarbonate film, and polyimide film having a thermal conductivity of 0.12 to 0.6 W / (m·K).

6. The microwave shielding body according to claim 1, wherein the surface substrate is a polyethylene terephthalate film or a polyethylene terephthalate nonwoven fabric.

7. A food container comprising a container, a lid, and a microwave shielding body according to any one of claims 1 to 6.

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