Food containers

Abstract

The present invention provides a thin plastic food container that can be heated by induction heating. [Solution] The above problem is solved by a food container having a bottom made of a synthetic resin sheet and side walls protruding from the edge of the bottom made of a synthetic resin sheet, wherein a metal layer is laminated on the bottom. In this container, the metal layer provided on the bottom is heated by electromagnetic induction, and the food placed inside the container is heated by the heat of the metal layer.

Description

Technical Field

[0001] The present invention relates to a food container.

Background Art

[0002] As shown in Patent Document 1, a disposable container made of aluminum foil and composed of a bottom wall, side walls rising from the periphery of the bottom wall, a flange provided at the upper end opening of the side walls, and a rim provided on the outer periphery of the flange is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A container made of aluminum foil as in Patent Document 1 can generate heat by induction heating of the aluminum constituting the container. A container made of aluminum foil can heat food placed in the container with an electromagnetic cooker such as an IH (Induction Heating) stove, but it is easily damaged by physical impact. For example, when it comes into contact with a sharp object such as a corner of a table, perforation is likely to occur, and even if it does not perforate, the area where the object hits is likely to be deeply dented. Also, when cooking is performed with food placed in the container, since aluminum has a relatively high thermal conductivity, the entire container is heated. When there is soup in the container, at the inner wall of the container near the interface between the liquid and the gas or at the part where the liquid has splashed and adhered, the liquid may vaporize and the components contained in the liquid may burn onto the container.

[0005] As other containers, plastic containers formed from synthetic resin sheets are known. In a plastic container, a method of heating food by irradiating the food with microwaves in a state where food is placed in the container is taken.

[0006] In induction heating, the magnetic field generated by the alternating current flowing through a coil is used to create eddy currents within a conductor such as a metal. Then, the Joule heat (resistive heat) generated as the eddy currents flow through the metal causes the dielectric to self-heat. Applying a magnetic field to a plastic container does not generate eddy currents, so plastic containers cannot be heated with an induction cooker.

[0007] The present invention aims to provide a plastic food container that can be heated by induction heating. [Means for solving the problem]

[0008] The above problems are solved by a food container having a bottom made of a synthetic resin sheet and side walls protruding from the edge of the bottom made of a synthetic resin sheet, wherein a metal layer is laminated on the bottom (hereinafter sometimes simply referred to as "container"). In this container, the metal layer provided on the bottom is heated by electromagnetic induction, and the food placed inside the container can be heated by the heat of the metal layer.

[0009] In the above-mentioned container, it is preferable that the metal layer is laminated on a substantially flat portion formed on the bottom, which is made of a synthetic resin sheet. With this configuration, for example, it is possible to prevent air bubbles from remaining at the bottom and to prevent scorching at the interface between the gas contained in the air bubbles and the liquid.

[0010] In the aforementioned container, the metal layer is a metal sheet, and the metal sheet can be laminated on the upper surface of a protrusion formed on the bottom, which is made of a synthetic resin sheet. This configuration makes it easier to heat-weld the synthetic resin sheet and the metal sheet that make up the bottom.

[0011] In the aforementioned container, it is preferable to have a support portion that forms a food support surface above the substantially flat portion. For example, when solid food is placed in the container and the container is heated, the metal layer and the food can be separated. This prevents overheating of the food and prevents the food from burning.

[0012] In the aforementioned container, the metal layer may not be laminated to a height of at least half the height of the side wall. This configuration prevents excessive heat generation in the side wall of the container, making it easier to touch the side wall of the container by hand, for example.

[0013] In the aforementioned container, the metal layer is a metal sheet, and the metal sheet and the synthetic resin sheet at the bottom can be fixed together by heat fusion or adhesive. Alternatively, it is possible to pre-bond the metal sheet to the inner surface of the mold using an injection molding insert method, and then inject synthetic resin into the mold space to form the container. Injection molding also involves fusing molten resin to the metal sheet and is therefore included in the heat fusion method.

[0014] In the aforementioned container, the metal layer can be laminated on the inside bottom of the food container. With this configuration, the heat from the metal layer can be transferred more directly to the food placed in the container.

[0015] In the aforementioned container, the metal layer may mainly contain one or more metals such as aluminum, stainless steel, copper, silver, and gold. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a thin plastic food container that can be heated by induction heating. [Brief explanation of the drawing]

[0017] [Figure 1] This is a plan view showing one embodiment of a food container. [Figure 2]It is an end view of the AA' part in FIG. 1, and the lower part is an enlarged view at a scale of 1 / 1. [Figure 3] It is an end view of the BB' part in FIG. 1, and the lower part is a partial enlarged view. [Figure 4] It is an end view of the CC' part in FIG. 1. [Figure 5] It is a perspective view of the food container in FIG. 1. [Figure 6] It is a plan view of the food container according to the second embodiment. [Figure 7] It is a perspective view of the food container in FIG. 6. [Figure 8] It is a plan view showing the state where a metal layer is laminated on the food container in FIG. 6. [Figure 9] It is an end view showing the structure of the central part of the food container in FIG. 6 on which a metal layer is laminated. In order to represent the concavo-convex shape of the central part, the concavities and convexities are exaggeratedly shown. [Figure 10] It is a plan view of the food container according to the third embodiment. [Figure 11] It is a plan view showing the state where a metal layer is laminated on the food container in FIG. 10. [Figure 12] It is an end view showing the structure of the central part of the food container in FIG. 11 on which a metal layer is laminated. In order to represent the concavo-convex shape of the central part, the concavities and convexities are exaggeratedly shown. [Figure 13] It is a plan view of the food container according to the fourth embodiment in which a metal layer is laminated on the entire bottom surface. [Figure 14] It is an end view of the BB' part in FIG. 13, and the lower part is a partial enlarged view. [Figure 15] It is an explanatory view showing the state of heat-welding a metal sheet, which is an example of a metal layer, to the food container. [Figure 16] It is an explanatory view showing the state of manufacturing a food container by insert molding with a metal sheet, which is an example of a metal layer, placed in a mold.

Mode for Carrying Out the Invention

[0018] The following describes embodiments of the food container of the present invention. The embodiments shown below are merely limited examples of embodiments of the present invention, and the technical scope of the present invention is not limited to the embodiments described herein.

[0019] [First Embodiment] Figures 1 to 4 show examples of food containers for solid foods.

[0020] The food container (hereinafter sometimes simply referred to as "container") 1a of this embodiment has a bottom portion 11a made of a synthetic resin sheet and a side wall portion 12 protruding from the edge of the bottom portion 11a, which is also made of a synthetic resin sheet. A metal layer 13a is laminated on the bottom portion 11a. In Figures 2 to 4, the metal layer 13a is shown by a thick line (the same applies to the second, third, and fourth embodiments).

[0021] As shown in Figure 2, the side wall portion 12 protrudes diagonally upward from the edge of the bottom portion 11a radially outward from the bottom portion. The side wall portion 12 is a plate-like structure made of a synthetic resin sheet and forms a substantially circular peripheral wall surrounding the bottom portion 11a. In this specification, the term "subject to" is used to indicate that the shape may not be precise due to molding errors and the bending of the synthetic resin sheet, and also to take into account rounded edges, etc.

[0022] As shown in Figures 3 and 5, the side wall portion 12 has multiple grooves 122 that protrude radially outward from the side wall surface 121 towards the bottom. The grooves 122 have a groove shape with a substantially arc-shaped cross-section. Multiple grooves 122 are arranged so as to extend radially from the center of the bottom portion 11a. The grooves 122 function as reinforcing ribs for the container 1a.

[0023] The bottom portion 11a is a plate-like structure made of a synthetic resin sheet continuous with the side wall portion 12, and constitutes the surface on which food is placed. As shown in Figures 3 and 5, the bottom portion 11a has multiple grooves 132 that protrude downward from the substantially flat bottom surface 131, which is continuous with the side wall surface 121. The grooves 132 have a groove shape with a substantially arc-shaped cross-section and are continuous with the grooves 132 of the side wall portion 12. Multiple grooves 132 are arranged so as to extend radially from the center of the bottom portion 11a. The grooves 132 function as reinforcing ribs for the container 1a.

[0024] A flat portion 133 made of a synthetic resin sheet is provided in the center of the bottom portion 11a. As the name suggests, the flat portion 133 is a substantially flat surface made of a synthetic resin sheet. The flat portion 133 and the bottom surface 131 and groove 132 are separated by a support portion 134. The support portion 134 is composed of an annular protrusion having a substantially flat upper surface. As shown in Figure 3, the groove 132 of the bottom portion 11a and the flat portion 133 of the bottom portion 11a are located at approximately the same height, so that when the container is placed on a horizontal surface, for example, the horizontal surface, the flat portion 133, and the groove 132 are in contact. In Figure 3, only the groove 132 is shown in terms of depth. As shown in Figure 3, the bottom surface 131 of the bottom portion 11a is located above the flat portion 133 and groove 132, and the support portion 134 protrudes upward so that its upper surface is higher than the bottom surface 131.

[0025] A flange portion 14 is provided at the upper end of the side wall portion 12, along the edge of the opening of the container 1a. As shown in Figures 2, 4, and 5, the flange portion 14 has a plate-shaped first portion 141 extending laterally, a plate-shaped second portion 142 extending upward from the end of the first portion 141, a plate-shaped third portion 143 extending laterally from the end of the second portion, a plate-shaped fourth portion 144 extending downward from the end of the third portion 143, a plate-shaped fifth portion 145 extending substantially laterally from the end of the fourth portion 144, a plate-shaped sixth portion 146 extending downward from the fifth portion 145, and a seventh portion 147 extending laterally from the sixth portion 146. The first part 141, the second part 142, the third part 143, the fourth part 144, the fifth part 145, the sixth part 146, or the seventh part 147 is a plate made of synthetic resin sheet. The flange part 14 functions as a reinforcing part to prevent the container 1a from easily bending. The third part 143 of the flange part 14 is substantially rectangular in plan view. The housing part, which is made up of the side wall part 12 and the bottom part 11a, is substantially circular in plan view. The corners of the substantially rectangular part are rounded in an arc shape, and a recessed hole 148 is provided in the fifth part 145. The recessed hole 148 is a non-penetrating hole recessed below the container 1a, which is substantially triangular in shape with its corners rounded in an arc shape in plan view, and functions as a reinforcing rib to prevent the container 1a from easily bending. Furthermore, as shown in the lower part of Figure 2, the flange portion 14 has a portion where the fourth portion 144 and the sixth portion 146, which form a roughly circular frame in plan view, are continuous without going through the fifth portion 145. The third portion 143 becomes the upper end of the container.

[0026] [Second Embodiment] Figures 6 to 8 show a food container 1b according to the second embodiment. In container 1b, the shape of the central part of the bottom 11b differs from that of container 1a. Regarding container 1b, the parts that are common with container 1a will not be explained.

[0027] The bottom 11b of the container 1b is provided with a projection 23b which includes a plurality of ridges 21 extending radially from the center of the bottom 11b, and a plurality of annular portions 22b of different diameters arranged concentrically from the center of the bottom 11b of the container 1b. The plurality of annular portions 22b are provided with a plurality of ridges 2 1 The protruding portion 21 is positioned to be enclosed on the outside. 1 is It includes a first protruding portion and a second protruding portion that is shorter in length than the first protruding portion and is positioned between the first protruding portions. The protruding portion 21 and the annular portion 22b are made of synthetic resin sheet.

[0028] In container 1b, metal layers 13b are laminated so as to be in contact with the upper surfaces of multiple annular sections 22b and multiple protruding sections 21. The position of the upper surface of the annular section 22b or the upper surface of the multiple protruding sections 21 is lower than the height of the upper surface of the support section 134. The support section 134 supports the solid food so that the metal layers 13b fixed to the upper surface of the annular section 22b or the multiple protruding sections 21 do not come into direct contact with the solid food.

[0029] It is preferable that the metal layer 13b be a metal sheet. When heat-pressing the metal sheet and the synthetic resin sheet that constitutes the bottom 11b, applying pressure to the upper surface of the protrusion 23b, such as the ridge portion 21 or the annular portion 22b, and the metal sheet reduces the area over which pressure is applied compared to applying pressure to the entire flat portion, allowing greater pressure to be applied to the upper surface of the protrusion 23b. This reduces welding defects when heat-pressing the metal sheet and the synthetic resin sheet that constitutes the bottom, and improves the yield of the container.

[0030] As shown in Figures 6 and 9, the multiple annular portions 22b have directions that intersect the direction in which the protrusions constituting the annular portions 22b extend. In other words This creates a ventilation hole 221b that penetrates the rib in the lateral direction. The gas that expands due to the heat generated by the metal layer escapes through the ventilation hole 221b from the space surrounded by the metal layer 13b, the bottom 11b, and the annular portion 22b to the outside of the space.

[0031] [Third Embodiment] Figures 10 to 12 show a food container 1b according to the third embodiment. The shape of the bottom 11b of container 1b differs from that of container 1a. Parts of container 1b that are common to container 1a will not be described.

[0032] The bottom 11c of the container 1c is provided with multiple annular sections 22c of different diameters arranged concentrically from the center of the bottom 11c, and the radially extending protrusions described above are not provided. The multiple annular sections 22c are provided with the ventilation holes 221 described above. b A ventilation hole 221c similar to that is provided. A metal layer 13c is laminated on the upper surface of the multiple annular portions 22c. Preferably, the metal layer 13c is a metal sheet. Greater pressure can be applied to the upper surface of the protrusion 23c formed by the annular portions 22c during heat sealing. As described above, yield can be improved.

[0033] The upper surface of the annular portion 22c is lower than the height of the support portion 134. The support portion 134 supports the solid food so that it does not come into direct contact with the metal layer 13c laminated on the upper surface of the annular portion 22c.

[0034] [Fourth Embodiment]

[0035] Figures 13 and 14 show a food container 1d according to the fourth embodiment. The container 1d has a bottom portion 11d made of a synthetic resin sheet and a side wall portion 12d that protrudes from the edge of the bottom portion 11d, which is also made of a synthetic resin sheet. A metal layer 13d is laminated on the bottom portion 11d.

[0036] The side wall portion 12d protrudes diagonally upward from the edge of the bottom portion 11d radially outward from the bottom portion. The side wall portion 12d is a plate-like structure made of a synthetic resin sheet and forms a substantially circular peripheral wall surrounding the bottom portion 11d. The side wall portion has a substantially flat peripheral surface. The bottom portion 11d is a substantially flat surface made of a synthetic resin sheet and is circular in plan view. The metal layer 13d is laminated over the entire bottom portion 11d but not on the side wall portion 12d.

[0037] A flange portion 14d is provided at the upper end of the side wall portion 12d, along the edge of the opening of the container 1d. As shown in Figure 14, the flange portion 14d has a plate-shaped first portion 141d extending laterally, and a plate-shaped second portion 142d extending downward from the end of the first portion 141d. The first portion 141d or the second portion 142d is plate-shaped and made of a synthetic resin sheet. The flange portion 14d functions as a reinforcing rib to reinforce the container 1d so that it does not easily bend.

[0038] Each of the containers 1, 1b, 1c, or 1d can heat solid or liquid food by heating the metal layer through electromagnetic induction using an induction cooker while the food is placed inside.

[0039] In containers 1a, 1b, or 1c equipped with a support portion 134, the solid food is supported on the upper surface of the support portion 134 so that the metal layer 13a, 13b, or 13c does not come into direct contact with the solid food. This prevents the metal layer 13a, 13b, or 13c from sticking to the solid food, and prevents burnt residue from oil or other components dripping from the solid food from adhering to the metal layer 13a, 13b, or 13c. Note that containers 1a, 1b, or 1c are not exclusively for solid foods and may also be used for liquid foods.

[0040] In containers 1a or 1d, where a metal layer 13a or 13d is laminated on a nearly flat surface, when liquid food is placed in container 1a or 1d, the metal layer 13a or 13d is nearly flat, making it difficult for air bubbles to be trapped on the surface of the metal layer. When the metal layer 13a or 13d is heated by electromagnetic induction, scorching is less likely to occur at the interface between the liquid and gas in the air bubbles. Even in containers such as container 1b or 1c, which have protrusions 23b or 23c at the bottom, when metal sheets are laminated by adhesion or heat welding, the metal sheets are slightly indented but are still nearly flat, making scorching relatively less likely at the interface between the liquid and gas in the air bubbles. Note that containers 1a or 1d are not exclusively for liquid food, but may also be used for solid food.

[0041] In containers equipped with a metal layer, it is preferable that the metal layer is not laminated to a height of at least half or more of the height of the side wall. More preferably, it is preferable that the layer is not laminated to at least one-third of the height, and even more preferably, the metal layer is not laminated to the side wall. By reducing the area on the side wall where the metal layer is provided, or by not providing a metal layer at all, the temperature of the side wall when the metal layer is heated by electromagnetic induction can be lowered. Even if the metal layer covers the entire side wall, it will be insulated to some extent by the synthetic resin sheet.

[0042] In containers equipped with a metal layer, it is preferable that the metal layer be laminated on the inside bottom of the food container. By providing the metal layer on the inside, the food placed inside the container can be heated more efficiently by the metal layer, and when the container is touched from the outside, it is insulated by the synthetic resin sheet, making burns less likely.

[0043] The food placed inside the container is not particularly limited. Examples of applicable foods are listed below. Examples of solid foods include okonomiyaki, gyoza, shumai, hamburgers, or steak. Solid foods are defined as foods that have a fixed shape. Examples of liquid foods include soups used in hot pot dishes such as samgyetang, hot pot, or yosenabe. Other applicable foods include combinations of solid and liquid foods. Examples of combinations of solid and liquid foods include the aforementioned hot pot dishes, noodle dishes such as ramen, udon, or pasta, or rice bowl dishes such as gyudon, oyakodon, and katsudon. Furthermore, other applicable foods include fresh foods such as vegetables, meat, and fish. The food placed inside the container may contain oils and fats.

[0044] The thickness of the synthetic resin sheet is not particularly limited, but can be, for example, 0.1 to 4.2 mm, 0.1 to 3.4 mm, or 0.1 to 1.0 mm. The synthetic resin sheet includes not only thin sheets but also thick sheets. The container can be molded by vacuum forming using a mold, or by insert molding by injection as described later.

[0045] The synthetic resin sheet can preferably use a thermoplastic resin with a heat resistance temperature of 120°C or higher. It is preferable that the synthetic resin sheet uses polypropylene or crystalline polyethylene terephthalate (CPET), which have excellent heat resistance, as its main component. The synthetic resin sheet may also contain fillers such as calcium carbonate and other trace amounts of additives. It is preferable that the proportion of fillers and additives in the total mass of the composition constituting the synthetic resin sheet be less than 50% by mass.

[0046] The metal layer is composed of a metal that generates heat through electromagnetic induction and has low biotoxicity. Examples of metals that make up the metal layer include those mainly containing one or more metals such as aluminum, stainless steel, copper, silver, and gold. It is preferable to use metals with a metal content of 99% or more for the metal layer, and medical-grade metals can be suitably used.

[0047] The shape of the metal layer can be various shapes in plan view, such as circular, square, trapezoidal, or triangular. A circular shape can improve the heating efficiency of food. The thickness of the metal layer can be 7 μm to 1 mm. Preferably, the thickness of the metal layer is 20 μm or less in order to reduce the mass of the container. Preferably, the area of ​​the metal layer in plan view is large enough to accommodate a circle with a diameter of 90 mm or more. The upper limit of the size of the circle can be changed according to the container, for example, it can be 300 mm or less.

[0048] The metal layer can be laminated to a synthetic resin sheet, for example, by metal vapor deposition, welding of the metal sheet, or adhesion of the metal sheet. To weld the metal layer to the synthetic resin sheet, for example, as shown in Figure 15, the container 1d is fixed to the jig 81, the metal sheet constituting the metal layer 13d is placed on the bottom 11d of the container, and the heated pressing part 82 is pressed onto the metal layer 13d to heat-weld the metal layer 13d to the bottom 11d of the container. In the example in Figure 15, the container 1d was used as an example, but heat welding can be performed in the same manner on containers 1a, 1b, or 1c.

[0049] As shown in Figure 16, the metal layer can also be laminated onto the synthetic resin sheet by insert molding using injection molding. Specifically, the metal layer 13d is pre-placed in the space inside the die 83, which has a shape corresponding to the container, at a position corresponding to the bottom of the container. Then, molten thermoplastic resin is filled into the die containing the metal layer 13d, and the container 1d with the metal layer 13d laminated is obtained by demolding. In the example in Figure 16, container 1d is used as an example, but containers 1a, 1b, or 1c can be heat-welded in the same manner. The arrows in Figure 16 indicate the direction in which the synthetic resin is filled.

[0050] Food containers may be disposable or designed to be washable and reusable. The thickness of the synthetic resin sheet can be adjusted depending on the application. If the container is to be used repeatedly, the thickness of the synthetic resin sheet should be increased.

[0051] [Differentiation] The food storage compartment can be of various shapes in plan view, such as circular, square, trapezoidal, or triangular. Making the food storage compartment circular in plan view can improve the heating efficiency of the food. The shape of the flange in plan view can be changed according to the shape of the edge of the opening that stores the food. Furthermore, the food storage compartment, which consists of a bottom and side walls surrounding the bottom, may be a single unit as in the above embodiments, or it may be multiple units, and can be changed according to the food being stored. The number of metal layers may also be single or multiple.

[0052] A food container only needs to have side walls and a bottom. The side walls may have reinforcing protrusions or recesses to increase the rigidity of the container, or they may be substantially flat. The bottom may also have reinforcing protrusions or recesses, or projections for laminating metal layers, or it may be substantially flat. When projections for laminating metal layers are provided, the configuration of the projections is not limited to the examples above.

[0053] The side walls should be shaped in a way that prevents food placed inside the container from spilling out. The shape of the side walls is not limited to a roughly circular shape in plan view; they can be various shapes such as circles, squares, trapezoids, or triangles. A circular shape can improve the heating efficiency of the food.

[0054] A metal layer is provided at the bottom to generate heat through electromagnetic induction. The heat generated by the metal layer can heat the food placed in the container. The synthetic resin sheet that makes up the container does not generate heat through electromagnetic induction, and its thermal conductivity is lower than that of the metal. This makes it less likely for users to get burned if they touch the container.

[0055] Containers made of aluminum foil are susceptible to punctures when they come into contact with sharp objects, such as the corner of a desk, or to significant dents when dropped. The container of the present invention, being made of a synthetic resin sheet, is less prone to punctures and dents from external forces and is therefore less susceptible to damage. Furthermore, when food is heated inside a container made of aluminum foil, the entire container heats up, and touching it can cause burns. The container of the present invention, being made of a synthetic resin sheet, has superior heat insulation compared to aluminum foil and is less likely to cause burns when touched.

[0056] In containers made of aluminum foil, if a liquid is placed inside, the liquid may vaporize and burn onto the inner wall of the container near the interface between the liquid and gas, or on areas where the liquid has splashed and adhered. Containers made of synthetic resin sheets are less prone to this type of burning.

[0057] Food containers may be used with or without lids. [Examples]

[0058] [Example 1] A container with the same shape as shown in Figure 1 was filled with water, and the container was placed on an induction cooktop (Ishizaki Electric Works, round IH cooktop SICH-W1400) to heat the water by electromagnetic induction. The heat was set to the maximum power (P6 mode, 1400W). The amount of water added was set to 1 / 3 of the height of the side wall.

[0059] The container according to Example 1 has a synthetic resin sheet with a thickness of 0.6 mm, a bottom diameter of 185 mm, and a vertical height of 34 mm from the bottom to the top of the side wall, excluding the flange. Multiple grooves with a depth of 1.5 mm are formed in the side wall and bottom. An aluminum foil with a thickness of 17 μm and a diameter of 120 mm is fixed to the flat bottom of the container by heat welding. The synthetic resin sheet mainly contains polypropylene and has a heat resistance temperature of 120°C or higher.

[0060] The water boiled approximately 100 seconds after heating began. The temperature of the water in the container was over 95°C near the center. The temperature of the container's side wall was approximately 85°C outside the area in contact with the water. The temperature of the container's side wall above the interface between the water and gas, i.e., the area not in contact with water, was 40°C. The temperatures of each part were measured using an infrared radiation thermometer with a laser marker (A&D Company, Limited AD-5611A). No melting or deformation of the container due to heating was observed.

[0061] [Example 2] Except for changing the container to a circular container in plan view, having the same shape as in Figures 13 and 14, and changing the liquid poured into the container to kimchi hot pot soup (straight kimchi hot pot soup base, Mizkan Co., Ltd.), the liquid was heated in the same manner as in Example 1. In Example 2, to improve the rigidity of the container, protrusions with a height of 1 mm were formed on the side wall along the vertical direction of the side wall at intervals of 20 mm. The amount of liquid poured in was set to 1 / 3 of the height of the side wall. At the bottom of the container, a 17 μm thick aluminum foil was fixed by heat welding to cover the entire bottom surface.

[0062] The container according to Example 2 had a synthetic resin sheet with a thickness of 0.4 μm, a base diameter of 130 mm, and a vertical height of 38 mm from the bottom to the top of the side wall. The synthetic resin sheet mainly contained polypropylene.

[0063] The kimchi soup boiled approximately 80 seconds after heating began. The temperature of the kimchi soup in the container was over 95°C near the center. The temperature of the side wall of the container was approximately 85°C outside the area in contact with the water contents. The temperature of the side wall of the container was 40°C above the interface between the kimchi soup and the gas, i.e., the area not in contact with the kimchi soup. The temperatures of each part were measured using an infrared radiation thermometer with a laser marker (A&D Company, Limited AD-5611A). No melting or deformation of the container due to heating was observed. Furthermore, no scorching occurred at the interface between the soup and the atmosphere. No scorching due to the adhesion of air bubbles to the bottom of the container was observed.

[0064] [Example 3] Except for changing the container to a rectangular container from a planar perspective and changing the liquid poured into the container to sundubu soup (Marudai Foods Co., Ltd.), the liquid was heated in the same manner as in Example 1. In Example 3, to improve the rigidity of the container, protrusions with a height of 1 mm were formed on the side wall along the vertical direction of the side wall at intervals of 20 mm. The amount of liquid poured in was set to 1 / 3 of the height of the side wall. A 17 μm thick aluminum foil was fixed to the bottom of the container by heat welding so as to cover the entire bottom surface. No melting or deformation of the tray due to heating was observed.

[0065] The container according to Example 3 has a synthetic resin sheet with a thickness of 0.7 mm, a base with dimensions of 60 mm in length and 180 mm in width, and a vertical height of 38 mm from the bottom to the top of the side wall. The synthetic resin sheet mainly contains polypropylene and has a heat resistance temperature of 120°C or higher.

[0066] The sundubu soup boiled approximately 100 seconds after heating began. The temperature of the sundubu soup in the container was over 95°C near the center. The temperature of the side wall of the container was approximately 85°C outside the area in contact with the water contents. The temperature of the side wall of the container was 40°C above the interface between the sundubu soup and the gas, i.e., the area not in contact with the sundubu soup. The temperatures of each part were measured using an infrared radiation thermometer with a laser marker (A&D Company, Limited AD-5611A). No melting or deformation of the tray due to heating was observed. In addition, no scorching occurred at the interface between the soup and the atmosphere.

[0067] [Example 4] The only difference was that the liquid added to the container was changed to pork bone broth (Tomita Chinese Noodles Rich Pork Bone Seafood Hot Pot Soup, Mizkan Co., Ltd.), and the pork bone broth was heated in the same manner as in Example 2.

[0068] The pork bone broth boiled approximately 70 seconds after heating began. The temperature of the pork bone broth in the container was over 95°C near the center. The temperature of the side wall of the container was approximately 85°C outside the area in contact with the water contents. The temperature of the side wall of the container was 40°C above the interface between the pork bone broth and the gas, i.e., the area not in contact with the pork bone broth. The temperatures of each part were measured using an infrared radiation thermometer with a laser marker (A&D Company, Limited AD-5611A). No melting or deformation of the tray due to heating was observed. Furthermore, no scorching occurred at the interface between the soup and the atmosphere. No scorching due to the adhesion of air bubbles to the bottom of the container was observed. [Explanation of Symbols]

[0069] 1a Food containers 1b Food containers 1c food container 1d food container 11a bottom 12a bottom 13a bottom 14a bottom 12 Side wall section 12d Side wall part 13a metal layer 13b Metal layer 13c metal layer 13d metal layer 133 Roughly flat area 23b Protrusion 23c protrusion 134 Support part

Claims

1. A food container having a bottom made of synthetic resin sheet and side walls protruding from the edge of the bottom made of synthetic resin sheet, The bottom of the container has a protrusion that is made up of an annular section. A food container wherein a metal sheet is laminated on the upper surface of the protrusions constituting the annular portion of the bottom so as to cover the protrusions constituting the annular portion, and ventilation holes are provided in the protrusions constituting the annular portion that penetrate the protrusions in the lateral direction.

2. The food container is the food container according to claim 1, wherein the metal sheet generates heat by electromagnetic induction.

3. The shape is such that the metal sheet is laminated on the upper surface of the protruding portion formed on the bottom, which is made of a synthetic resin sheet, The food container according to claim 1, wherein the protruding portion is enclosed within the annular portion and has a shape that is not continuous with the annular portion.

4. The food container according to claim 1, further comprising a support portion that forms a food support surface above the upper surface of the aforementioned protrusion.

5. The food container according to claim 1 or 2, wherein the metal sheet is not laminated to a height of at least half the height of the side wall portion.

6. The food container according to claim 1 or 2, wherein the metal sheet and the bottom synthetic resin sheet are fixed together by heat fusion or adhesive.

7. The food container according to claim 1 or 2, wherein the metal sheet is laminated on the inside bottom of the food container.

8. The food container according to claim 1 or 2, wherein the metal sheet mainly contains one or more metals: aluminum, stainless steel, copper, silver, and gold.

Images