Food wrapping material for microwave oven heating

Abstract

To provide a food wrapping material for microwave oven heating which selectively discharges water vapor from a first adhesive part when heating food, reduces the number of components, has a simple structure, and reduces loads on environment.SOLUTION: A food wrapping material for microwave oven heating includes a paper base material sheet, and an adhesive layer composed of a hot melt adhesive. The food wrapping material for microwave oven heating includes: a first adhesive part where a first outer edge region is bonded to a second outer edge region by an adhesive layer so that the first outer edge region faces the second outer edge region; a second adhesive part where a third outer edge region is bent, and a first part is bonded to a second part and a third part by the adhesive layer; and a third adhesive part where a fourth outer edge region is bent, and a fourth part is bonded to a fifth part and a sixth part by the adhesive layer. The length of the first adhesive part is longer than each of the length of the second adhesive part and the length of the third adhesive part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a food packaging material for heating in a microwave oven. [Background technology]

[0002] A food packaging material for microwave heating that has an internal closed space and stores food therein is known (see Patent Document 1). The food packaging material for microwave heating described in Patent Document 1 includes a first base film, a second base film, and a lid piece. In the food packaging material for microwave heating described in Patent Document 1, an opening is formed in the center of the first base film. The second base film is overlapped with the first base film in the thickness direction. The peripheral region of the second base film is adhered to the peripheral region of the first base film. Both the first base film and the second base film are made of synthetic resin. The lid piece closes the opening. The back surface of the lid piece is coated with a hot melt adhesive. A slit is formed in the lid piece. In Patent Document 1, food inside the food packaging material for microwave heating is heated using a microwave oven, and water vapor is released from the food. This fills the closed space, and the hot melt adhesive is softened by the heat of the water vapor. Furthermore, the pressure inside the closed space increases, pushing the slit open. This releases steam to the outside through the gap. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Jikko No. 59-31590 Summary of the Invention [Problem to be solved by the invention]

[0004] Food packaging for microwave heating is required to have a reduced number of parts and a simple structure.Food packaging for microwave heating is also required to reduce the burden on the environment.Food packaging for microwave heating is also required to release water vapor to the outside from the desired part when food is heated.

[0005] The present disclosure provides a food packaging material for microwave heating that selectively releases water vapor from the first adhesive portion when heating food, reduces the number of parts, has a simple configuration, and reduces the burden on the environment. [Means for solving the problem]

[0006] The food packaging for microwave heating of the present disclosure has a rectangular shape when viewed in the thickness direction. The food packaging for microwave heating is made by folding a single base sheet and bonding it with an adhesive layer, the base sheet having: a first outer edge region adjacent to and extending along a first side of the rectangle; a second outer edge region adjacent to and extending along a second side of the rectangle opposite the first side; a third outer edge region adjacent to and extending along a third side of the rectangle perpendicular to the first and second sides; and a fourth outer edge region adjacent to and extending along a fourth side of the rectangle opposite the third side. The food packaging for microwave heating has an internal closed space and contains moist food in the closed space. The food packaging for microwave heating is used to heat food in a microwave oven so that water vapor is released from the food. This food packaging material for microwave heating comprises a paper base sheet having a first main surface and a second main surface located opposite the first main surface in the thickness direction, and adhesive layers disposed on the first main surface of each of the first, second, third, and fourth outer peripheral regions, and made of a hot melt adhesive having a melting point of 50°C to 100°C. The third outer peripheral region comprises a first section including a center in a first direction along the third outer peripheral region, and a second section and a third section located on either side of the first section in the first direction. The fourth outer peripheral region comprises a fourth section including a center in the first direction, and a fifth section and a sixth section located on either side of the fourth section in the first direction and facing the second and third sections, respectively, in the thickness direction and a second direction perpendicular to the first direction. The food packaging material for microwave heating comprises: a first adhesive portion extending in a second direction, in which the first outer peripheral region is bonded to the second outer peripheral region with an adhesive layer so that the first main surface of the first outer peripheral region faces the first main surface of the second outer peripheral region; a second adhesive portion in which the third outer peripheral region is folded so that the first main surface of the first portion faces the first main surfaces of the second and third portions and the first portion is bonded to the second and third portions with an adhesive layer; and a third adhesive portion in which the fourth outer peripheral region is folded so that the first main surface of the fourth portion faces the first main surfaces of the fifth and sixth portions and the fourth portion is bonded to the fifth and sixth portions with an adhesive layer. The length of the first adhesive portion in the second direction is longer than the lengths of the second adhesive portion and the third adhesive portion in the first direction. [Effects of the Invention]

[0007] In the food packaging for microwave heating disclosed herein, water vapor is selectively released from the first adhesive portion when food is heated, reducing the number of parts, simplifying the structure, and reducing the burden on the environment. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a food packaging material for heating in a microwave oven. [Figure 2] FIG. 2 is a perspective view of the base sheet and adhesive layer before they are bonded together. [Figure 3] FIG. 3 is a plan view of the base sheet. [Figure 4] FIG. 4 is a plan view of a food packaging material for heating in a microwave oven. [Figure 5] Fig. 5 is a cross-sectional view of the food packaging material for heating in a microwave oven shown in Fig. 4. Fig. 5 is a cross-sectional view taken along line XX in Fig. 4. [Figure 6] Fig. 6 is a cross-sectional view of the food packaging material for heating in a microwave oven shown in Fig. 4. Fig. 6 is a cross-sectional view taken along line YY in Fig. 4. [Figure 7] Fig. 7 is a cross-sectional view of the food packaging material for heating in a microwave oven shown in Fig. 4. Fig. 7 is a cross-sectional view taken along line ZZ in Fig. 4. [Figure 8] FIG. 8 shows a step of forming the first adhesive portion. [Figure 9] FIG. 9 shows the process of folding parts 7 to 10. [Figure 10] Fig. 10 shows a process for heating food in a microwave oven, and is a cross-sectional view taken along line XX in Fig. 4. [Figure 11] Fig. 11 shows the process of heating food in a microwave oven, and is a cross-sectional view taken along line ZZ in Fig. 4. [Figure 12] FIG. 12 is a cross-sectional view of a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Outline of the embodiment] The food packaging for microwave heating of the present disclosure has a rectangular shape when viewed in the thickness direction. The food packaging for microwave heating is made by folding a single base sheet and bonding it with an adhesive layer, the base sheet having: a first outer edge region adjacent to and extending along a first side of the rectangle; a second outer edge region adjacent to and extending along a second side of the rectangle opposite the first side; a third outer edge region adjacent to and extending along a third side of the rectangle perpendicular to the first and second sides; and a fourth outer edge region adjacent to and extending along a fourth side of the rectangle opposite the third side. The food packaging for microwave heating has an internal closed space and contains moist food in the closed space. The food packaging for microwave heating is used to heat food in a microwave oven so that water vapor is released from the food.

[0010] The food packaging material for microwave heating comprises a paper base sheet having a first main surface and a second main surface positioned opposite the first main surface in the thickness direction, and adhesive layers arranged on the first main surface of each of the first outer edge region, the second outer edge region, the third outer edge region and the fourth outer edge region, and made of a hot melt adhesive having a melting point of 50°C or more and 100°C or less.

[0011] The third outer edge region includes a first portion including the center in a first direction along the third outer edge region, and a second portion and a third portion located on either side of the first portion in the first direction. The fourth outer edge region includes a fourth portion including the center in the first direction, and a fifth portion and a sixth portion located on either side of the fourth portion in the first direction and facing the second portion and the third portion, respectively, in a second direction perpendicular to the thickness direction and the first direction. The food packaging material for microwave heating comprises: a first adhesive portion extending in a second direction, in which the first outer peripheral region is bonded to the second outer peripheral region with an adhesive layer so that the first main surface of the first outer peripheral region faces the first main surface of the second outer peripheral region; a second adhesive portion in which the third outer peripheral region is folded so that the first main surface of the first portion faces the first main surfaces of the second and third portions and the first portion is bonded to the second and third portions with an adhesive layer; and a third adhesive portion in which the fourth outer peripheral region is folded so that the first main surface of the fourth portion faces the first main surfaces of the fifth and sixth portions and the fourth portion is bonded to the fifth and sixth portions with an adhesive layer. The length of the first adhesive portion in the second direction is longer than the lengths of the second adhesive portion and the third adhesive portion in the first direction.

[0012] When food is placed in the closed space of the food packaging for microwave heating of the present disclosure and heated in a microwave oven so that water vapor is released from the food, the water vapor is released from the food and fills the closed space, causing an increase in pressure within the closed space, which in turn applies a force to the entire food packaging for microwave heating.

[0013] In the present disclosure, the first adhesive portion is longer than the second adhesive portion and the third adhesive portion. Therefore, the degree of freedom of deformation of the first adhesive portion when a force is applied to it is greater than the degree of freedom of deformation of the second adhesive portion when a force is applied to it, and the degree of freedom of deformation of the third adhesive portion when a force is applied to it. Therefore, in the first adhesive portion, the first outer edge region peels from the second outer edge region, and water vapor is released to the outside from the peeled portion. As a result, water vapor is selectively released from the first adhesive portion when heating food.

[0014] Unlike the base sheet of Patent Document 1, which includes two films, a first base film and a second base film, the food packaging for microwave heating of the present disclosure uses a single base sheet that is folded and adhered with an adhesive layer, which reduces the number of parts and simplifies the construction.

[0015] Unlike Patent Document 1, in which the two base films are made of resin, the food packaging material for heating in a microwave oven of the present disclosure has a base sheet made of paper, which reduces the burden on the environment.

[0016] In the food packaging for microwave heating described above, the third outer peripheral region may further include a seventh section interposed midway between the second section in the first direction. The fourth outer peripheral region may further include an eighth section facing the seventh section in the second direction and interposed midway between the fifth section in the first direction. The food packaging for microwave heating may further include a first gusset section formed between the seventh section and the eighth section by folding the seventh section and adhering it with an adhesive layer, and folding the eighth section and adhering it with an adhesive layer. The food packaging for microwave heating includes a first gusset section, which allows the enclosed space to be enlarged. This increases the amount of food that can be accommodated in the enclosed space of the food packaging for microwave heating.

[0017] In the food packaging for microwave heating described above, the third outer peripheral region may further include a ninth section interposed midway between the third section in the first direction. The fourth outer peripheral region may further include a tenth section facing the ninth section in the second direction and interposed midway between the sixth section in the first direction. The food packaging for microwave heating may further include a second gusset section formed between the ninth section and the tenth section by folding the ninth section and adhering it with an adhesive layer, and folding the tenth section and adhering it with an adhesive layer. The food packaging for microwave heating includes a second gusset section, which allows the enclosed space to be enlarged. This increases the amount of food that can be accommodated in the enclosed space of the food packaging for microwave heating.

[0018] In the food packaging for heating in a microwave oven described above, the adhesive layer may be disposed over the entire first main surface. Because the adhesive layer is disposed over the entire first main surface, the food packaging for heating in a microwave oven has a simple structure.

[0019] [Specific example of embodiment] [Basic composition of food packaging material 1 for microwave heating] The basic structure of food packaging for heating in a microwave oven will be described with reference to Figures 1 and 2. Figure 1 is a perspective view of the food packaging for heating in a microwave oven. Figure 2 is a perspective view of the base sheet and adhesive layer before they are bonded together.

[0020] As shown in Figure 1, food packaging material 1 for heating in a microwave oven has an internal closed space CS and is used to store food 100 (imaginary line) in the closed space CS. As shown in Figure 2, food packaging material 1 for heating in a microwave oven is made by folding one base sheet 2 and bonding it with an adhesive layer 3 (see Figure 2).

[0021] [Base sheet 2] The base sheet 2 has a rectangular shape when viewed in the thickness direction TD. The base sheet 2 described above is before being bonded. The rectangle has a first side E1, a second side E2, a third side E3, and a fourth side E4. The second side E2 faces the first side E1. The third side E3 is perpendicular to the first side E1 and the second side E2. The fourth side E4 faces the third side E3. In this embodiment, the rectangle does not necessarily have four right angles. At least one of the four corners may have a curved shape. At least one of the four corners may be notched (chamfered).

[0022] The base sheet 2 has a first outer edge region 21, a second outer edge region 22, a third outer edge region 23, and a fourth outer edge region 24. The first outer edge region 21 is adjacent to the first side E1 and extends along the first side E1. The first outer edge region 21, the second outer edge region 22, the third outer edge region 23, and the fourth outer edge region 24 form a frame shape when viewed in the thickness direction TD (see imaginary lines). The first outer edge region 21, the second outer edge region 22, the third outer edge region 23, and the fourth outer edge region 24 are continuous in the circumferential direction of the frame. When viewed in the thickness direction TD, the first outer edge region 21 may include a portion overlapping the first side E1 or a portion separated from the first side E1. The second outer edge region 22 is adjacent to the second side E2 and extends along the second side E2. The second outer edge region 22 may include a portion overlapping with the second side E2, or a portion spaced apart from the second side E2, as viewed in the thickness direction TD. The third outer edge region 23 is adjacent to the third side E3 and extends along the third side E3. The third outer edge region 23 may include a portion overlapping with the third side E3, or a portion spaced apart from the third side E3, as viewed in the thickness direction TD. The fourth outer edge region 24 is adjacent to the fourth side E4 and extends along the fourth side E4. The fourth outer edge region 24 may include a portion overlapping with the fourth side E4, or a portion spaced apart from the fourth side E4, as viewed in the thickness direction TD.

[0023] The base sheet 2 has a first main surface 25 and a second main surface 26. The second main surface 26 is located opposite to the first main surface 25 in the thickness direction TD.

[0024] [Adhesive layer 3] The adhesive layer 3 is disposed in contact with the base sheet 2. The adhesive layer 3 is disposed on the first main surface 25 of each of the first outer peripheral region 21, the second outer peripheral region 22, the third outer peripheral region 23, and the fourth outer peripheral region 24. In this embodiment, the adhesive layer 3 is disposed over the entire first main surface 25. In other words, the adhesive layer 3 is disposed on the first main surface 25 of each of the first outer peripheral region 21, the second outer peripheral region 22, the third outer peripheral region 23, and the fourth outer peripheral region 24, and on the first main surface 25 of the region inside the first outer peripheral region 21, the second outer peripheral region 22, the third outer peripheral region 23, and the fourth outer peripheral region 24.

[0025] [Details of microwave-heated food packaging 1] The food packaging for heating in a microwave oven will be described in detail with reference to Figures 3 to 7. Figure 3 is a plan view of a base sheet. Figure 4 is a plan view of the food packaging for heating in a microwave oven. Figure 5 is a cross-sectional view of the food packaging for heating in a microwave oven shown in Figure 4. Figure 5 is a cross-sectional view taken along line XX in Figure 4. Figure 6 is a cross-sectional view of the food packaging for heating in a microwave oven shown in Figure 4. Figure 6 is a cross-sectional view taken along line YY in Figure 4. Figure 7 is a cross-sectional view of the food packaging for heating in a microwave oven shown in Figure 4. Figure 7 is a cross-sectional view taken along line ZZ in Figure 4.

[0026] Food packaging material 1 for heating in a microwave oven comprises the above-mentioned base sheet 2 and the above-mentioned adhesive layer 3 (FIG. 2).

[0027] [Base sheet 2] The base sheet 2 is made of paper. Examples of paper include fine paper and kraft paper. The thickness of the base sheet 2 is 25 μm or more and 145 μm or less. The basis weight of the base sheet 2 is 30 g / m 2 More than 100g / m 2 A printed layer (or decorative layer) (not shown) may be formed on the second main surface 26 of the base sheet 2. As shown in Fig. 3, the base sheet 2 has the first outer edge region 21, the second outer edge region 22, the third outer edge region 23, and the fourth outer edge region 24 described above.

[0028] [First outer edge region 21] The first outer edge region 21 is formed adjacent to the first side E1 from the third side E3 to the fourth side E4. The first outer edge region 21 extends in the second direction D2. The length of the first outer edge region 21 in the second direction D2 is the same as the length of the first side E1.

[0029] [Second outer edge region 22] The second outer edge region 22 is formed adjacent to the second side E2 from the third side E3 to the fourth side E4. The second outer edge region 22 extends in the second direction D2. The length of the second outer edge region 22 in the second direction D2 is the same as the length of the second side E2.

[0030] [Third outer edge region 23] The third outer edge region 23 is formed between the first outer edge region 21 and the second outer edge region 22 so as to be adjacent to the third side E3. The third outer edge region 23 extends in a first direction D1. The first direction D1 is perpendicular to the thickness direction TD and the second direction D2. In other words, the second direction D2 is perpendicular to the thickness direction TD and the first direction D1. The length of the third outer edge region 23 in the first direction D1 is shorter than the length of the third side E3. In the first direction D1, both ends of the third outer edge region 23 contact the first outer edge region 21 and the second outer edge region 22, respectively.

[0031] The third outer edge region 23 includes a first portion 231, a second portion 232, and a third portion 233. The third outer edge region 23 includes a first boundary 2311 and a second boundary 2312. The first portion 231 is an intermediate portion that includes a center 23C of the third outer edge region 23 in the first direction D1. The second portion 232 and the third portion 233 are located on either side of the first portion 231 in the first direction D1. The second portion 232 is in contact with the first portion 231. A first boundary 2311, which is the boundary between the second portion 232 and the first portion 231, is located between the second portion 232 and the first portion 231. The first boundary 2311 is aligned with the second direction D2. The first boundary 2311 is not visible in the third outer edge region 23 before being folded. The third portion 233 is in contact with the first portion 231. Between the third portion 233 and the first portion 231 is a second boundary 2312, which is a boundary between the third portion 233 and the first portion 231. The second boundary 2312 is along the second direction D2. The second boundary 2312 is not visible in the third outer edge region 23 before being folded.

[0032] [Fourth outer edge region 24] The arrangement, shape, and configuration of the fourth outer edge region 24 are similar to those of the third outer edge region 23. Specifically, the fourth outer edge region 24 includes a fourth portion 241, a fifth portion 242, and a sixth portion 243. The fourth outer edge region 24 includes a third boundary 2411 and a fourth boundary 2412. The fourth portion 241 is an intermediate portion that includes the center 24C of the fourth outer edge region 24 in the first direction D1. The fifth portion 242 and the sixth portion 243 are located on either side of the fourth portion 241 in the first direction D1. The fifth portion 242 and the sixth portion 243 face the second portion 232 and the third portion, respectively, in the second direction D2.

[0033] [Adhesive layer 3] The adhesive layer 3 is made of a hot melt adhesive. A hot melt adhesive is an adhesive that has no tack (adhesiveness) at room temperature (25°C) but becomes tacky when heated. A hot melt adhesive has a melting point of 50°C or higher and 100°C or lower. In other words, the lower limit of the melting point of a hot melt adhesive is 50°C. The upper limit of the melting point of a hot melt adhesive is 100°C. The lower limit of the melting point of a hot melt adhesive is preferably 60°C, more preferably 70°C, even more preferably 80°C, and particularly preferably 85°C. The upper limit of the melting point of a hot melt adhesive is preferably 95°C, more preferably 90°C. The melting point of a hot melt adhesive is determined by differential scanning calorimetry (DSC). If the hot melt adhesive is commercially available, the value listed in the product catalog of the commercially available product is used as the melting point of the hot melt adhesive. If the melting point of the hot melt adhesive is equal to or higher than the above-mentioned lower limit, the first adhesive portion 11, the second adhesive portion 12, and the third adhesive portion 13 can be reliably formed at room temperature (25°C) or low temperatures (-20°C or higher, -10°C or lower), and the adhesive layer 3 can be prevented from extruding at room temperature. If the melting point of the hot melt adhesive is equal to or higher than the above-mentioned lower limit, peeling of the first adhesive portion 11, the second adhesive portion 12, and the third adhesive portion 13 can be prevented at room temperature (25°C), and blocking can also be prevented. If the melting point of the hot melt adhesive is equal to or lower than the above-mentioned upper limit, the adhesive layer 3 in the first adhesive portion 11 can be reliably softened by water vapor generated when food contained in the closed space 10 is heated in a microwave oven, and the first outer peripheral region 21 in the first adhesive portion 11 can be reliably peeled from the second outer peripheral region 22. If the melting point of the hot melt adhesive is below the upper limit described above, when the adhesive layer 3 is disposed over the entire first main surface 25, water vapor generated when food contained in the closed space 10 is heated in a microwave oven can permeate (pass through) the adhesive layer 3 in areas other than the first adhesive portion 11, the second adhesive portion 12, and the third adhesive portion 13. Examples of hot melt adhesives include olefin resins, thermoplastic elastomer resins, ionomer resins, and ethylene-vinyl acetate polymer resins. Preferred examples of hot melt adhesives include ionomer resins. The thickness of the adhesive layer 3 is 1 μm or more and 25 μm or less.The ratio of the thickness of the adhesive layer 3 to the thickness of the base sheet 2 is 0.0005 or more and 1.0 or less.

[0034] [First adhesive portion 11, second adhesive portion 12, and third adhesive portion 13] As shown in FIG. 4, food packaging material 1 for heating in a microwave oven has first adhesive portion 11, second adhesive portion 12, and third adhesive portion 13.

[0035] [First adhesive part 11] As shown in FIGS. 5 and 6 , in the first adhesive portion 11, the first outer edge region 21 is adhered to the second outer edge region 22 by the adhesive layer 3 so that the first main surface 25 of the first outer edge region 21 faces the first main surface 25 of the second outer edge region 22. The first adhesive portion 11 extends in the second direction. In this embodiment, as shown in FIG. 6 , the entire first outer edge region 21 is adhered to the entire second outer edge region 22. With the first outer edge region 21 and the second outer edge region 22 facing each other, the adhesive layer 3 is heated and then allowed to cool to room temperature (25°C), thereby adhering the first outer edge region 21 to the second outer edge region 22. The heating temperature of the adhesive layer 3 is 50°C or higher and 200°C or lower.

[0036] [Second adhesive part 12] 7 , in the second adhesive portion 12, the third outer edge region 23 is folded so that the first main surface 25 of the first portion 231 faces the first main surfaces 25 of the second portion 232 and the third portion 233, and the first portion 231 is adhered to the second portion 232 and the third portion 233 by the adhesive layer 3. The third outer edge region 23 is folded with the first boundary 2311 and the second boundary 2312 each forming a mountain, and the second portion 232 and the third portion 233 are overlapped with the first portion 231. With the second portion 232 and the third portion 233 facing and overlapping the first portion 231, the adhesive layer 3 is heated and then allowed to cool, thereby adhering the first portion 231 to the second portion 232 and the third portion 233. The heating conditions for the adhesive layer 3 in the third outer peripheral region 23 are the same as the heating conditions for the adhesive layer 3 in the first outer peripheral region 21 and the second outer peripheral region 22.

[0037] [Third adhesive part 13] 4 and 6, in the third adhesive portion 13, the fourth outer edge region 24 is folded so that the first main surface 25 (see FIG. 2) of the fourth portion 241 (see FIG. 3) faces the first main surfaces 25 of the fifth portion 242 and the sixth portion 243, and the fourth portion 241 is bonded to the fifth portion 242 and the sixth portion 243 by the adhesive layer 3. The folding, bonding, and conditions (including temperature) of the third adhesive portion 13 are the same as those of the second adhesive portion 12.

[0038] [Sizes of the first adhesive portion 11, the second adhesive portion 12, and the third adhesive portion 13] As shown in FIG. 4 , the length L1 of the first adhesive portion 11 in the second direction D2 is longer than the length L2 of the second adhesive portion 12 and the length L3 of the third adhesive portion 13 in the first direction D1. The first aspect ratio, which is the ratio (L1 / L2) of the length L1 of the first adhesive portion 11 in the second direction D2 to the length L2 of the second adhesive portion 12 in the first direction D1, exceeds 1, preferably is 1.1 or greater, more preferably is 1.2 or greater, and even more preferably is 1.3 or greater. The upper limit of the first aspect ratio is not limited. The upper limit of the first aspect ratio is 10, preferably is 5, and more preferably is 3. The second aspect ratio, which is the ratio (L1 / L3) of the length L1 of the first adhesive portion 11 in the second direction D2 to the length L3 of the third adhesive portion 13 in the first direction D1, is the same as the first aspect ratio described above.

[0039] The length (width) W1 of the first adhesive portion 11 in the first direction D1 is 1 mm or more, preferably 3 mm or more, and 30 mm or less, preferably 20 mm or less. The length (width) W2 of the second adhesive portion 12 in the second direction D2 is 1 mm or more, preferably 3 mm or more, and 30 mm or less, preferably 20 mm or less. The ratio (W1 / W2) of the length (width) W1 of the first adhesive portion 11 in the first direction D1 to the length (width) W2 of the second adhesive portion 12 in the second direction D2 is 0.3 or more, preferably 0.5 or more, and 3 or less, preferably 2 or less. The length (width) W3 of the third adhesive portion 13 in the second direction D2 is the same as the length (width) W2 of the second adhesive portion 12 in the second direction D2.

[0040] [First gusset section 15 and second gusset section 16] As shown in FIG. 5, food packaging material 1 for microwave heating further includes first gusset section 15 and second gusset section 16. First gusset section 15 is formed by folding seventh section 234 and eighth section 244 shown in FIG. 3 . Second gusset section 16 is formed by folding eighth section 244 and tenth section 245. In base sheet 2 before folding, third outer peripheral region 23 further includes seventh section 234 and ninth section 235. Seventh section 234 is located midway through second section 232 in first direction D1. Ninth section 235 is located midway through third section 233 in first direction D1. In base sheet 2 before folding, fourth outer peripheral region 24 further includes eighth section 244 and tenth section 245. The eighth portion 244 faces the seventh portion 234 in the second direction D2. The eighth portion 244 is located midway between the fifth portion 242 in the first direction D1. The tenth portion 245 faces the ninth portion 235 in the second direction D2. The tenth portion 245 is located midway between the sixth portion 243 in the first direction D1.

[0041] As shown in FIG. 1 , the seventh portion 234 is folded and bonded with the adhesive layer 3, and the eighth portion 244 (see FIG. 5 ) is also folded and bonded with the adhesive layer 3, thereby forming a first gusset portion 15 between the seventh portion 234 and the eighth portion 244. The seventh portion 234 and the eighth portion 244 are each folded once or twice or more, and in this embodiment, the number of folds is preferably one. The eighth portion 244 is folded the same number of times as the seventh portion 234. The first gusset portion 15 is aligned in the second direction D2. The base sheet 2 is not bonded to the first gusset portion 15 by the adhesive layer 3.

[0042] The 9th portion 235 is folded and bonded with the adhesive layer 3 (see FIG. 7 ), and the 10th portion 245 is folded and bonded with the adhesive layer 3, thereby forming a second gusset portion 16 between the 9th portion 235 and the 10th portion 245. The 9th portion 235 and the 10th portion 245 are each folded once or twice or more, and in this embodiment, preferably once. The 10th portion 245 is folded the same number of times as the 9th portion 235. The 9th portion 235 and the 10th portion 245 may be folded the same number of times as the 7th portion 234 and the 8th portion 244, or may be folded differently. The second gusset portion 16 faces the first gusset portion 15 in the first direction D1. The second gusset portion 16 is positioned away from the first gusset portion 15 in the first direction D1. The second gusset portion 16 is aligned with the second direction D2. In the second gusset portion 16 , the base sheet 2 is not bonded by the adhesive layer 3 .

[0043] [Formation of the first adhesive portion 11 to the third adhesive portion 13, and containing and heating the food 100] A method for placing food in the closed space of a food packaging material for heating in a microwave oven will be described with reference to Figures 1, 2, and 5 to 9. Figure 8 shows the step of forming the first adhesive part. Figure 9 shows the step of folding parts 7 to 10.

[0044] As shown in FIG. 2 , first, an adhesive layer 3 is disposed on the first main surface 25 of one substrate sheet 2. To dispose the adhesive layer 3 on the first main surface 25, for example, a hot melt adhesive is applied to the first main surface 25. Specifically, an adhesive composition containing an adhesive component and a solvent is applied to the first main surface 25 to form a coating film. Examples of the solvent include water and organic solvents. Preferably, the solvent is water. In the adhesive composition, the adhesive component is dispersed in the solvent. Examples of the adhesive composition include water-dispersed adhesive compositions in which the adhesive component is dispersed in water. Commercially available adhesive compositions can be used, such as the Chemipearl series (water-dispersed adhesive composition, manufactured by Mitsui Chemicals). Preferably, an adhesive composition is Chemipearl S500 (water-dispersed adhesive composition, manufactured by Mitsui Chemicals). Next, the coating film is heated to remove the solvent (water) from the coating film. The heating temperature is 55°C or higher, preferably 60°C or higher, and 200°C or lower, preferably 180°C or lower. As a result, an adhesive layer 3 made of a hot melt adhesive is formed on the first main surface 25.

[0045] As shown in FIG. 8 , the first outer peripheral region 21 and the second outer peripheral region 22 of the base sheet 2 are then brought together to form the first adhesive portion 11. Specifically, the first main surface 25 of the first outer peripheral region 21 and the first main surface 25 of the second outer peripheral region 22 are brought together (overlapped) so that the adhesive layer 3 of the first outer peripheral region 21 and the adhesive layer 3 of the second outer peripheral region 22 are in contact with each other. Next, the first outer peripheral region 21 and the second outer peripheral region 22 are bonded together via the adhesive layer 3, for example, by heat sealing. In the heat sealing, the overlapped first outer peripheral region 21 and the second outer peripheral region 22 are heat-pressed (heated and pressurized) from both sides in the overlapping direction. The heat sealing temperature is 50°C or higher, preferably 70°C or higher, and 200°C or lower, preferably 150°C or lower. When forming the adhesive portion 13, a folded portion 221 may be formed along the third direction D3 on the edge of the second outer edge region 22 located opposite the second side E2 (see FIG. 5). The folded portion 221 is formed at the boundary between the second outer edge region 22 and the other region. The folded portion 221 is formed along the second direction D2.

[0046] 9, the seventh section 234, the ninth section 235, and the section therebetween are then folded. The eighth section 244, the tenth section 245, and the section therebetween are then folded. The above-mentioned folding and the formation of the adhesive section 13 may be performed simultaneously. Alternatively, the above-mentioned folding may be performed after the adhesive section 13 is formed.

[0047] 6 and 7, the second adhesive portion 12 is formed. The third outer edge region 23 is folded so that the first portion 231 faces the second portion 232 and the third portion 233, and the first portion 231 is adhered to the second portion 232 and the third portion 233 via the adhesive layer 3 (see FIG. 2).

[0048] Next, food 100 is placed inside food packaging 1 for heating in a microwave oven that is currently being manufactured. Food 100 is inserted into food packaging 1 for heating in a microwave oven from the side of fourth outer edge region 24, which is open.

[0049] 1 and 6, third adhesive section 13 is then formed. Fourth outer peripheral region 24 is folded so that fourth section 241 faces fifth section 242 and sixth section 243, and fourth section 241 is adhered to fifth section 242 and sixth section 243 via adhesive layer 3 (see FIG. 2). This forms a closed space CS inside food packaging material 1 for heating in a microwave oven.

[0050] A method of heating food using a microwave oven will be described with reference to Figures 10 and 11. Figure 10 shows the steps of heating food in a microwave oven. Figure 10 corresponds to a cross-sectional view taken along line XX in Figure 4. Figure 11 shows the steps of heating food in a microwave oven. Figure 11 corresponds to a cross-sectional view taken along line ZZ in Figure 4.

[0051] As shown in Figures 10 and 11, food packaging 1 for microwave heating containing food 100 is placed in microwave oven 4. Microwave oven 4 has a stage 41. Stage 41 has an upper surface 42. Upper surface 42 is aligned with the horizontal direction HD. Food packaging 1 for microwave heating is placed on stage 41 so that first adhesive portion 11 is located on the opposite side of stage 41. Specifically, food packaging 1 for microwave heating is placed on upper surface 42 of stage 41 so that first adhesive portion 11 is located at the top of food packaging 1 for microwave heating. Food 100 contains moisture. The moisture may be solid or liquid.

[0052] Next, the microwave oven is operated. The moisture contained in food 100 is heated and turns into steam (gaseous water). In other words, steam is released from food 100. The steam fills closed space CS. At this time, first gusset portion 15 and second gusset portion 16 open, as shown in FIG.

[0053] As the closed space CS fills with steam, the pressure inside the closed space CS increases. This causes a force to be applied to the entire food packaging 1 for microwave heating. In the first adhesive region 11, a force is applied that causes the first outer peripheral region 21 to peel from the second outer peripheral region 22. In the second adhesive region 12, a force is applied that causes the first portion 231 to peel from the second portion 232 and the third portion 233 in the third outer peripheral region 23. In the third adhesive region 13, a force is applied that causes the fourth portion 241 to peel from the fifth portion 242 and the sixth portion 243 in the fourth outer peripheral region 24. As the above forces are applied to the first adhesive region 11, the second adhesive region 12, and the third adhesive region 13, the heat of the steam softens the hot melt adhesive in the adhesive layer 3, reducing the cohesive strength of the hot melt adhesive.

[0054] 4 , in this embodiment, the length L1 of the first adhesive portion 11 in the second direction D2 is longer than the length L2 of the second adhesive portion 12 and the length L3 of the third adhesive portion 13 in the first direction D1. Therefore, the degree of freedom of deformation of the first adhesive portion 11 when a force is applied to the first adhesive portion 11 is higher than the degree of freedom of deformation of the second adhesive portion 12 when a force is applied to the second adhesive portion 12 and the degree of freedom of deformation of the third adhesive portion 13 when a force is applied to the third adhesive portion 13. As a result, the first outer edge region 21 of the first adhesive portion 11 peels off from the second outer edge region 22 before the above-described third outer edge region 23 of the second adhesive portion 12 and the above-described fourth outer edge region 24 of the third adhesive portion 13 peel off. In other words, water vapor is first released to the outside from the portion (gap) where the first outer edge region 21 is peeled off from the second outer edge region 22. Specifically, the peeling occurs at the center of the first adhesive region 11 in the second direction D2. This opens the closed space CS of the food packaging 1 for microwave heating, causing the pressure inside the food packaging 1 to decrease and become equal to the external pressure. This means that no force is applied to the second adhesive region 12 or the third adhesive region 13. Therefore, before the third outer edge region 23 of the second adhesive region 12 peels off and the fourth outer edge region 24 of the third adhesive region 13 peels off, the first outer edge region 21 of the first adhesive region 11 peels off from the second outer edge region 22. This means that water vapor is not released from the second adhesive region 12 or the third adhesive region 13, but is selectively released from the first adhesive region 11. Therefore, water vapor is selectively released from the first adhesive region 11 when the food 100 is heated.

[0055] [Variations] A modified example of food packaging material 1 for heating in a microwave oven will be described with reference to Figure 12. Figure 12 is a cross-sectional view of the modified example.

[0056] Food packaging material 1 for heating in a microwave oven does not have first gusset section 15 (see FIG. 5) or second gusset section 16 (see FIG. 5). In a modified example, third outer peripheral region 23 does not include seventh section 234 (see FIG. 3) or ninth section 235 (see FIG. 3). Fourth outer peripheral region 24 does not include eighth section 244 (see FIG. 3) or tenth section 245 (see FIG. 3).

[0057] Although not shown, food packaging material 1 for heating in a microwave oven may have first gusset section 15 but may not have second gusset section 16.

[0058] The adhesive layer 3 may be arranged on the first main surface 25 of each of the second outer edge region 22, the third outer edge region 23 and the fourth outer edge region 24, and may not be arranged on the first main surface 25 of the regions inside the first outer edge region 21, the second outer edge region 22, the third outer edge region 23 and the fourth outer edge region 24.

[0059] The embodiments of the present disclosure are illustrative in all respects and should not be construed as limiting in any respect. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0060] 1 Food packaging material for microwave heating, 2 Base sheet, 3 Adhesive layer, 4 Microwave oven, 10 Closed space, 11 First adhesive portion, 12 Second adhesive portion, 13 Third adhesive portion, 15 First gusset portion, 16 Second gusset portion, 21 First outer edge region, 22 Second outer edge region, 23 Third outer edge region, 23C Center, 24 Fourth outer edge region, 24C Center, 25 First main surface, 26 Second main surface, 41 Stage, 42 Top surface, 100 Food, 221 Folded portion, 231 First part, 232 Second part, 233 Third part, 234 Seventh part, 235 Ninth part, 241 Fourth part, 242 Five part, 243 Sixth part, 244 Eighth part, 245 Tenth part, 2311 First boundary, 2312 Second boundary, 2411 Third boundary, 2412 Fourth boundary, CS closed space, D1 first direction, D2 second direction, D3 third direction, E1 first edge, E2 second edge, E3 third edge, E4 fourth edge, HD horizontal direction, TD thickness direction.

Claims

1. a first outer edge region adjacent to a first side of the rectangle and extending along the first side; a second outer edge region adjacent to a second side of the rectangle opposite the first side and extending along the second side; a third outer edge region adjacent to a third side of the rectangle perpendicular to the first and second sides and extending along the third side; and a fourth outer edge region adjacent to a fourth side of the rectangle opposite the third side and extending along the fourth side; the food packaging for microwave heating is made by folding a single base sheet and bonding it with an adhesive layer; the food packaging has an internal closed space and contains moist food in the closed space; The food packaging material for microwave heating is used to heat the food in a microwave oven so that water vapor is released from the food, The food packaging material for microwave heating is The base sheet is made of paper and has a first main surface and a second main surface located opposite the first main surface in the thickness direction; the adhesive layer being disposed on the first main surface of each of the first outer peripheral region, the second outer peripheral region, the third outer peripheral region, and the fourth outer peripheral region, and being made of a hot melt adhesive having a melting point of 50°C or higher and 100°C or lower; Equipped with the third outer edge region includes a first portion including a center in a first direction along the third outer edge region, and a second portion and a third portion located on both sides of the first portion in the first direction, the fourth outer edge region includes a fourth portion including a center in the first direction, and a fifth portion and a sixth portion located on both sides of the fourth portion in the first direction and facing the second portion and the third portion, respectively, in a second direction perpendicular to the thickness direction and the first direction, The food packaging material for microwave heating is a first adhesive portion extending in the second direction, the first outer edge region being bonded to the second outer edge region by the adhesive layer such that the first main surface of the first outer edge region faces the first main surface of the second outer edge region; a second adhesive portion in which the third outer edge region is folded so that the first main surface of the first portion faces the first main surfaces of the second portion and the third portion, and the first portion is adhered to the second portion and the third portion by the adhesive layer; a third adhesive portion in which the fourth outer edge region is folded so that the first main surface of the fourth portion faces the first main surfaces of the fifth portion and the sixth portion, and the fourth portion is adhered to the fifth portion and the sixth portion by the adhesive layer; Equipped with a length of the first adhesive portion in the second direction that is longer than each of the length of the second adhesive portion and the length of the third adhesive portion in the first direction;

2. the third outer edge region further includes a seventh portion interposed midway between the second portion in the first direction, the fourth outer edge region further includes an eighth portion facing the seventh portion in the second direction and interposed between the fifth portion in the first direction, The food packaging material for microwave heating is 2. The food packaging material for microwave heating according to claim 1, further comprising a first gusset portion formed between the seventh portion and the eighth portion by folding the seventh portion and adhering it with the adhesive layer, and folding the eighth portion and adhering it with the adhesive layer.

3. the third outer edge region further includes a ninth portion interposed between the third portion in the first direction, the fourth outer edge region further includes a tenth portion facing the ninth portion in the second direction and interposed between the sixth portion in the first direction, The food packaging material for microwave heating is 3. The food packaging material for microwave heating according to claim 2, further comprising a second gusset portion formed between the ninth portion and the tenth portion by folding the ninth portion and adhering it with the adhesive layer, and folding the tenth portion and adhering it with the adhesive layer.

4. 4. The food packaging material for heating in a microwave oven according to claim 1, wherein the adhesive layer is disposed over the entire first main surface.

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