Microwave-safe food packaging bags

Abstract

To prevent a bag body from bursting when a food inside is heated in a microwave oven.SOLUTION: In a food packaging bag for microwave oven, by bending a lamination film of two or more layers having at least a heat-resistant base layer P2 and a sealant layer P1 into a cylindrical shape with the center of a backlining part of a bag body as a butt sealed part 1, there are provided a heat seal part between the films facing each other at the butt sealed part and the heat seal part between the films facing each other at both open ends 4, 4 of the cylinder, and the heat seal part is sealed after storing a food inside. A foaming ink layer 5 containing thermal expansion microcapsules foamed by heat during heat sealing so as to traverse from an inside to an outside of the packaging bag in a specific region of the heat seal part is provided on a base layer side of the sealant layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a packaging bag made of plastic film, and more particularly to a microwave-safe packaging bag for food that is used when distributing food that can be heated in a microwave oven in a packaging bag. [Background technology]

[0002] Packaged foods are known in which food is placed in a microwave-safe plastic bag, which is then sealed and distributed in that sealed state. In this case, consumers who purchase the food heat the food in a microwave oven without opening the sealed bag. As a result, the internal pressure of the bag increases due to water vapor evaporated from the food and the thermal expansion of the air inside the bag, causing the bag to expand and eventually burst, posing a risk of accidents in which food and other items are scattered throughout the microwave.

[0003] In order to prevent this type of accident, an invention has been proposed in which a valve is attached to the packaging bag in advance to release the pressure generated by the heating (Patent Document 1), and an invention in which the heat seal strength of part of the heat-sealed joint of the packaging body is weakened to make it easier to peel off due to the increase in internal pressure caused by water vapor evaporated by heating, and pressure is released by steaming through this point (Patent Document 2). [Patent Document 1] Patent No. 3006528 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-025848 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] However, the former known invention has a problem in that the manufacturing cost of the packaging bag increases due to the labor, process and material costs required for attaching the valve body.

[0005] On the other hand, in the latter known invention, it is difficult to set the heat seal strength, and if the internal pressure rises suddenly due to reasons such as high output from the microwave oven's magnetron or high moisture content in the food, there is a risk that other parts will peel off at the same time and the package will be destroyed before the pressure relief provided by the weak heat seal can function.

[0006] Furthermore, if the material is suddenly peeled off and steamed, there is a risk of a popping sound being generated.

[0007] 4 Microwave-safe food packaging bags have the problem that they cannot be made without using easy-peel film or specially shaped seal bars. When using easy-peel film, there are drawbacks such as difficulty in controlling the seal strength due to variations in the quality of the easy-peel film, which weakens the seal strength on the easy-peel side and makes the bag more likely to tear.

[0008] On the other hand, when using a specially shaped seal bar, a unique seal bar must be made for each bag size, which means the seal must protrude from the inside of the bag, which inevitably creates the problem of the seal easily retracting when external pressure is applied. [Means for solving the problem]

[0009] The present invention was created with the objective of providing a microwave-safe food packaging bag that solves the above-mentioned problems.

[0010] That is, the microwave-safe packaging bag for food of the present invention is a bag made by folding a laminated film of two or more layers, which has at least a heat-resistant base layer and a sealant layer, into a tubular shape with the center of the back sealing part of the bag body as a seam, thereby providing a heat-seal part between opposing films at the seam and a heat-seal part between opposing films at both open ends of the tube, and the heat-seal part is sealed after food is placed inside. In a specific area of ​​the heat seal part, a foaming ink layer containing thermally expandable microcapsules that expand due to the heat generated during heat sealing is applied across the packaging bag from the inside to the outside. When measuring Elmendorf tear strength (based on JIS K7128), the film has tear strength of MD 1.2 (N) or less and TD 2.7 (N) or less when MD and TD are 30μ, MD 1.5 (N) or less and TD 3.1 (N) or less when MD and TD are 40μ, and MD 2.1 (N) or less and TD 3.7 or less when MD and TD are 50μ, and is provided on the base layer side of a sealant layer using a film with a dart impact strength (based on JIS K7124) of 3.5 (J) or less.

[0011] In addition, the invention described in claim 2 is characterized in that, in the microwave-safe packaging bag for food, the foamed ink layer is arranged in a specific area of ​​the heat-seal portion between the opposing films at both open ends of the tube, crossing from the inside to the outside of the packaging bag.

[0012] Furthermore, the invention described in claim 3 is characterized in that, in the microwave-safe packaging bag for food, the foamed ink layer is arranged in a specific area of ​​the heat-seal portion between the opposing films at the folding point, so as to cross from the inside to the outside of the packaging bag.

[0013] Furthermore, the invention described in claim 4 is characterized in that, in the microwave-safe packaging bag for food, the microcapsule-containing foaming ink layer foams to 20 to 100 μm at temperatures of approximately 100°C for 30 to 60 seconds, 150°C for 1 second, and 160°C for 0.5 seconds.

[0014] The invention described in claim 5 is characterized in that in the microwave-safe food packaging bag, the microcapsule-containing foamed ink layer is provided by gravure printing.

[0015] The invention described in claim 6 is characterized in that in the microwave-safe food packaging bag, a brittle film that is easily torn is used as the sealant layer. [Effects of the Invention]

[0016] The thermally expandable microcapsules contained in the foaming ink layer foam due to the heat generated during heat sealing, which inhibits lamination at that point.

[0017] Therefore, in the microwave-compatible packaging bag for food of the present invention, a foaming ink layer that foams with the heat of the heat seal is partially provided in the heat seal portion between the opposing films at the joint where pressure is applied when heating in a microwave oven, and in the heat seal portion between the opposing films at both open ends of the tube.This partially weakens the interlayer strength of the laminated film, allowing steam that generates internal pressure to escape from there.This allows steam to escape from a designated location before internal pressure is generated that would cause the heat seal portion to peel off, preventing irregular ruptures.

[0018] In this case, the layer for weakening the interlayer strength is applied by printing as a foaming ink layer, so microwave-safe packaging bags for food can be manufactured at low cost without the need for special separate parts or cutting processes. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a perspective view of the back seal side of a microwave-safe food packaging bag according to the present invention. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. 10 is a cross-sectional view of the open end of the tube that constitutes the bag. [Figure 5] Same as above, a schematic diagram showing the steaming process. [Figure 6] Same as above, a schematic diagram showing the steaming process. [Figure 7] FIG. 10 is a cross-sectional view of the open end of the tube in a different embodiment. [Figure 8] FIG. 10 is a perspective view of the spine adhesive side of a different embodiment of the same. [Figure 9] FIG. 10 is a cross-sectional view of a joining portion of a different embodiment of the present invention. [Figure 10]FIG. 10 is a cross-sectional view of a joining portion of a different embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0020] Specific embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a perspective view showing a pouch body P of the present invention, a microwave-safe packaging bag for food, in the state before opening. This pouch body P is based on a known pouch body constructed by folding a plastic film into a cylindrical shape with a seam 1 in the center of the back sealing part S of the pouch body, and then bonding together the seam and the inner surfaces of the open ends 4, 4 of the tube (see Figures 2 and 3).

[0021] The plastic film that makes up the bag body P is made of a laminated film of two or more layers having at least a heat-resistant base layer and a sealant layer, and has heat-sealed sections between opposing films at the joint 1 and between opposing films at both open ends of the tube, and the heat-sealed sections are sealed after food F is placed inside.

[0022] FIG. 4 shows an example of lamination of plastic films constituting the bag body P, in which a two-layer structure is used in which a sealant layer P1 is laminated on a heat-resistant base material layer P2.

[0023] Examples of the film that constitutes the base material layer P2 include OPP, PET, and ONY, and examples of the film that constitutes the sealant layer P1 include CPP and LL.

[0024] It is also possible to use a brittle film that is easily torn as the sealant layer.

[0025] In the drawing, reference numeral 5 denotes a foamed ink layer, which is the gist of the present invention, and here it is provided so as to cross from the inside to the outside of the packaging bag in a specific region of the heat-sealed portion between the opposing films at both opening ends 4, 4 of the tube (see FIG. 4). More specifically, the foamed ink layer 5 is provided near the center of the opening end 4, on the base layer P2 side of the sealant layer P1 that constitutes the film on the opposite side to the spine bonding portion.

[0026] The foaming ink layer 5 is an ink containing thermally expandable microcapsules that expand due to the heat generated during heat sealing. For example, microcapsules based on a thermoplastic resin such as vinyl chloride resin, ethylene vinyl acetate resin, or acrylic resin may contain aliphatic hydrocarbons such as isobutane, butane, isopentane, or n-pentane (a specific product is LG-MC Bubble Agent E, manufactured by Tokyo Ink Co., Ltd.). Here, we use an ink that expands to 20 to 100 μm at temperatures of approximately 100°C for 30 to 60 seconds, 150°C for 1 second, and 160°C for 0.5 seconds.

[0027] The foamed ink layer 5 is placed across the heat seal portion of the top and bottom of the opposing films at both open ends 4, 4 of the tube, from the inside to the outside of the packaging bag, and based on the results of the following experiment, it is desirable that the width of the layer be 15.4% to 23.0% of the top and bottom seal width.

[0028] The experiment was carried out on a bag containing Chinese buns, measuring 130mm wide x 170mm long, with the foamed ink layer placed in the center of the 130mm wide top and bottom seal. The results are shown below, where the width of the foamed ink layer was varied within the range of 20mm to 40mm. 20mm → 15.4% of the top and bottom seal width. The result was an explosion. 30mm → 23.0% of the top and bottom seal width. The bag was successfully steamed without exploding. 40mm → 30.7% of the top and bottom seal width. The bag was successfully steamed without exploding.

[0029] Figure 7 shows a different example of lamination of plastic films that make up the bag body P, in which a three-layer structure is used, with heat-resistant base layers P2 and P3 and a sealant layer P1 laminated thereon. Here, the foamed ink layer 5 is provided near the center of the opening edge 4, on the base layer P2 side of the sealant layer P1 that makes up the film on the side opposite the back adhesive portion.

[0030] Examples of films that can be used to form the base layer P2 include OPP, PET, and ONY; examples of films that can be used to form the base layer P3 include OPP, PET, and ONY; and examples of films that can be used to form the sealant layer P1 include CPP and LL.

[0031] In the above process, the foamed ink layer 5 is applied by gravure printing. In addition, although not shown, printing for whitening or design is performed between the layers.

[0032] 5 and 6 are schematic diagrams showing the operation of the present invention, i.e., the steaming process. When food F sealed in a packaging bag P is heated in a microwave oven, water vapor evaporates, and the resulting pressure and the thermal expansion of the air increase the internal pressure of the packaging bag, causing it to expand and burst. However, the sealant edge breaks at the foaming ink area located at the three-point intersection X, allowing steam to escape between the layers and preventing bursting.

[0033] Table 1 shows the laminated structure of the plastic film that constitutes the bag body, and the seal strength, lamination strength, and steam permeability results for each structure. [Table 1]

[0034] As a result of experiments, the inventors of the present application have found that a film constituting the sealant layer P1 on which the foamed ink layer 5 is provided, which has tear strength in Elmendorf tear strength measurement (in accordance with JIS K7128) of MD 1.2 (N) or less and TD 2.7 (N) or less when MD and TD are 30μ, MD 1.5 (N) or less and TD 3.1 (N) or less when MD and TD are 40μ, and MD 2.1 (N) or less and TD 3.7 or less when MD and TD are 50μ, and which has a dart impact strength (in accordance with JIS K7124) of 3.5 (J) or less, is suitable for achieving the effect of the present invention of realizing vapor permeability and not producing popping sounds.

[0035] Table 2 shows the tear strength and impact strength of commercially available films from various manufacturers. [Table 2]

[0036] As a result of experiments, the inventors of the present invention have found the following. By arranging the foaming ink in a way that stops it midway through the bottom seal (so that it does not enter the contents side), steam can be released only from the top seal. If the top seal is 10 mm and the base seal is 10 mm, the side from which steam escapes can be controlled by placing the foaming ink only within the width of the base seal, for example, only about 5 mm. Although regular LL sealant film can be used for steaming, the popping noise it makes during steaming can be a concern. In the test, Skyfilm's Easy-to-Tear LL (product name: KF601C) was used, and the popping sound during steaming became unnoticeable. A test was conducted using a general-purpose CPP as a sealant film, but it did not go well as the package was opened from the back sticker. The cause is thought to be that the sealant was thin at 18μ and was of general-purpose grade, so it did not have enough sealing strength or heat resistance, causing the bag to burst before the laminate layers broke due to the rise in internal pressure. With the OPP / / LL structure, OPP is brittle and it is difficult to achieve laminate strength, so although steam escapes from the foamed ink area, it splits sideways during steaming, so it is difficult to say that steam escapes properly.

[0037] Figure 8 shows another embodiment of the microwave-safe packaging pouch for food according to the present invention. In this embodiment, foamed ink layer 5 is provided across the packaging pouch from the inside to the outside in a specific region of the heat-sealed portion between opposing films at seam 1. More specifically, foamed ink layer 5 is provided near the center of seam 1, on the base layer P2 side of sealant layer P1 (see Figure 9).

[0038] FIG. 9 shows an example of lamination of two layers of plastic film constituting the bag body P, and FIG. 10 shows an example of lamination of two layers. [Explanation of symbols]

[0039] P bag body S Back adhesive part P1 sealant layer P2 base material layer P3 base material layer 1. Prayer point 4 Open End 5 Foamed ink layer F Food

Claims

1. A microwave-safe food packaging bag is made by folding a laminated film of two or more layers, which has at least a heat-resistant base layer and a sealant layer, into a cylindrical shape with the center of the back sealing part of the bag body as a gable part, thereby providing heat seal parts between opposing films at the gable part and heat seal parts between opposing films at both open ends of the tube, and sealing the heat seal parts after placing food inside. In a specific area of ​​the heat seal part, a foaming ink layer containing thermally expandable microcapsules that expand due to the heat at the time of heat sealing is applied across the packaging bag from the inside to the outside. In the Elmendorf tear strength measurement (based on JIS K7128), when the MD and TD are 30μ, the tear strength is MD 1.2 (N) or less and TD 2.7 (N) or less, when the MD and TD are 40μ, the tear strength is MD 1.5 (N) or less and TD 3.1 (N) or less, when the MD and TD are 40μ, and when the MD and TD are 50μ, the tear strength is MD 2.1 (N) or less and TD 3.7 or less, and the dart impact strength (based on JIS K7124) is 3.0 (J) or less. A microwave-safe packaging bag for food, characterized in that it is provided on the base layer side.

2. 2. The microwave-safe packaging bag for food according to claim 1, wherein the foamed ink layer is provided across the packaging bag from the inside to the outside in a specific region of the heat-sealed portion between the opposing films at both open ends of the tube.

3. 2. The microwave-safe packaging bag for food according to claim 1, wherein the foamed ink layer is provided across the packaging bag from the inside to the outside in a specific region of the heat seal portion between the opposing films at the joining portion.

4. 4. The microwave-safe packaging bag for food according to claim 1, 2 or 3, wherein the microcapsule-containing foamed ink layer foams to a thickness of 20 to 100 μm at temperatures of about 100° C. for 30 to 60 seconds, 150° C. for 1 second, and 160° C. for 0.5 seconds.

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