JP2025174378A - Microwave-safe food packaging bags - Google Patents

Abstract

To prevent a bag from bursting when food inside is heated in a microwave oven.
[Solution] A two or more layer laminated film having at least a heat-resistant base layer P2 and a sealant layer P1 is folded into a cylindrical shape with a seam 1 at the center of the back adhesive of the bag body, to provide a heat seal section between opposing films at the seam 1 and heat seal sections between opposing films at both open ends 4, 4 of the tube, and in this microwave-safe packaging bag for food, the heat seal section is sealed after food is placed inside. In this bag, an acrylic bead ink layer 5, which contains acrylic beads with a particle size of approximately 20μ and a particle size distribution of 5 to 40μ in urethane ink, is provided on the base layer side of the sealant layer in a specific area of the heat seal section, so as to cross from the inside to the outside of the packaging bag.
[Selected Figure] Figure 1

Description

This invention relates to a packaging bag made of plastic film, and more specifically to a microwave-safe packaging bag for food that is used when distributing food that can be heated in a microwave oven.

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

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 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 due to the increase in internal pressure caused by water vapor evaporated by heating, and pressure is released by steaming through this weakened part (Patent Document 2).
Patent No. 3006528 Japanese Patent Application Laid-Open No. 2000-025848

However, the former known invention had the problem of increasing the manufacturing costs of the packaging bag due to the labor, process, and material costs required to attach the valve.

On the other hand, with the latter known invention, it is difficult to set the heat seal strength, and if the internal pressure rises suddenly due to factors 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, causing the package to break before the weak heat seal can release pressure.

In addition, if the material suddenly peeled off and steamed, there was a risk of a popping sound being generated.

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.

On the other hand, when using a specially shaped seal bar, a custom 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.

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

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 heat seal parts between opposing films at the seam and heat seal parts between opposing films at both open ends of the tube, and the heat seal parts are sealed after food is placed inside the microwave-safe packaging bag for food,
In a specific area of the heat-sealed portion, an acrylic bead ink layer containing acrylic beads with a particle size of approximately 20 μm and a particle size distribution of 5 to 40 μm in urethane ink is applied across the packaging bag from the inside to the outside.
The sealant layer is characterized by being provided on the base layer side of a sealant layer using a film having an Elmendorf tear strength (based on JIS K7128) of 1.2 (N) or less in MD and 2.7 (N) or less in TD when the MD and TD are 30μ, 1.5 (N) or less in MD and 3.1 (N) or less when the MD and TD are 40μ, and 2.1 (N) or less in TD and 3.7 or less when the MD and TD are 50μ, and having a dart impact strength (based on JIS K7124) of 3.5 (J) or less.

Furthermore, the invention described in claim 2 is characterized in that, in the microwave-safe packaging bag for food, the acrylic bead ink layer is provided across the packaging bag from the inside to the outside in a specific area of the heat-sealed portion between the opposing films at both open ends of the tube.

Furthermore, the invention described in claim 3 is characterized in that, in the microwave-safe packaging bag for food, the acrylic bead ink layer is provided across a specific area of the heat seal portion between the opposing films at the joint, from the inside to the outside of the packaging bag.

Furthermore, the invention described in claim 4 is characterized in that, in the microwave-safe food packaging bag, the acrylic bead ink layer is formed by gravure printing.

Furthermore, the invention described in claim 5 is characterized in that, in the microwave-safe food packaging bag, a brittle, easily tearable film is used as the sealant layer.

In acrylic bead ink, the inclusion of large acrylic beads, which are made of a different resin system, within the urethane ink prevents the formation of a smooth ink film and reduces the cohesive strength of the ink. As a result, when the internal pressure of the packaging bag increases due to water vapor evaporating from the food when heated, or the thermal expansion of the air inside the packaging bag, the steam escapes between the ink layers, which have weak interlayer strength.

The microwave-safe food packaging bag of the present invention has an acrylic bead ink layer partially applied to the heat-sealed areas between the opposing films at the joints, which are areas that are subject to pressure during microwave heating, and to the heat-sealed areas between the opposing films at both open ends of the tube. This allows steam that generates internal pressure to escape from these areas, allowing steam to escape from designated locations before internal pressure builds up that would cause the heat-sealed areas to peel, preventing irregular ruptures.

In this case, the layer used to weaken the interlayer strength is applied by printing as an acrylic bead ink layer, so microwave-safe food packaging bags can be manufactured at low cost without the need for special separate components or cutting processes.

1 is a perspective view of the back seal side of a microwave-safe food packaging bag according to the present invention. FIG. FIG. FIG. 10 is a cross-sectional view of the open end of the tube that constitutes the bag. Same as above, a schematic diagram showing the steaming process. Same as above, a schematic diagram showing the steaming process. FIG. 10 is a cross-sectional view of the open end of the tube in a different embodiment. FIG. 10 is a perspective view of the spine adhesive side of a different embodiment of the same. FIG. 10 is a cross-sectional view of a joining portion of a different embodiment of the present invention. FIG. 10 is a cross-sectional view of a joining portion of a different embodiment of the present invention.

Specific embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 is a perspective view showing a pouch body P of the present invention, a microwave-safe food packaging bag, before it is opened. 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 at the center of the back seam 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).

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

Figure 4 shows an example of the plastic film lamination that makes up the bag body P, which has a two-layer structure in which a sealant layer P1 is laminated onto a heat-resistant base layer P2.

Examples of films that may form the base layer P2 include OPP, PET, and ONY, while examples of films that may form the sealant layer P1 include CPP and LL.

In addition, a brittle film that is easily torn may also be used as the sealant layer.

The reference numeral 5 in the figure denotes the acrylic bead ink layer that is the gist of the present invention. In this case, it 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 both opening ends 4, 4 of the tube (see Figure 4). More specifically, the acrylic bead 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 side opposite the back adhesive portion.

The acrylic bead ink layer 5 in the present invention is
Ink binder: urethane Matting agent: acrylic resin Matting agent particle size: approx. 20 μ
Particle size distribution: 5 to 40 μ (20 μ is the volume zone)
The inclusion of large acrylic beads, which are made of a different resin system, in the urethane ink prevents the formation of a smooth ink film and reduces the ink's cohesive strength. As a result, when the internal pressure of the packaging bag increases due to water vapor evaporated from the food when heated or the thermal expansion of the air inside the packaging bag, the steam escapes through the ink, which has weak interlayer strength.

The acrylic bead ink layer 5 is applied across the heat seal area at 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. Based on the results of the following experiment, it is desirable for the width of the layer to be 15.4% to 23.0% of the top and bottom seal width.

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

Figure 7 shows a different example of the plastic film layer that makes up the bag body P. In this case, a three-layer structure is used, with heat-resistant base layers P2 and P3 laminated to a sealant layer P1. Here, the acrylic bead ink layer 5 is located 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.

Examples of films that may constitute the base layer P2 include OPP, PET, and ONY; examples of films that may constitute the base layer P3 include OPP, PET, and ONY; and examples of films that may constitute the sealant layer P1 include CPP and LL.

The acrylic bead ink layer 5 is applied by gravure printing. Also, although not shown, printing is applied between layers for whitening and design.

Figures 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. This pressure, along with the thermal expansion of the air, increases the internal pressure of the packaging bag, causing it to expand and burst. However, the acrylic bead ink area located at the three-point intersection X cuts the edges of the sealant, allowing steam to escape between the layers and preventing bursting.

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 in each case.

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

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

As a result of experiments, the inventors of the present invention have found the following.
- By arranging the acrylic bead ink in a way that stops it halfway through the base seal (not entering the contents side), it is possible to allow steam to escape 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 acrylic bead ink only within the seal width of the base seal, for example, only about 5 mm.
・General LL sealant film can be used for steaming, but the popping noise it makes during steaming is a concern.
In the test, Skyfilm's Easy-to-Tear LL (product name: KF601C) was used, and the popping sound during steaming became unnoticeable.
- Tests were conducted using general-purpose CPP as a sealant film, but this 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 acrylic bead ink area, it splits sideways during steaming, so it is difficult to say that steam is escaping properly.

Figure 8 shows a different embodiment of the microwave-safe packaging bag for food of the present invention. In this embodiment, the acrylic bead ink layer 5 is provided across the packaging bag from the inside to the outside in a specific region of the heat seal between the opposing films at the seam 1. More specifically, the acrylic bead ink layer 5 is provided near the center of the seam 1, on the base layer P2 side of the sealant layer P1 (see Figure 9).

Figure 9 shows an example of a two-layer laminate of plastic film that makes up the bag body P, and Figure 10 shows an example of a two-layer laminate.

P: Bag body S: Back adhesive part P1: Sealant layer P2: Base layer P3: Base layer 1: Joint part 4: Opening edge 5: Acrylic bead ink layer F: Food

Claims (5)

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-sealed portion, an acrylic bead ink layer containing acrylic beads with a particle size of approximately 20 μm and a particle size distribution of 5 to 40 μm in urethane ink is applied across the packaging bag from the inside to the outside.
A microwave-safe packaging bag for food characterized in that, in an Elmendorf tear strength measurement (based on JIS K7128), the tear strength is MD 1.2 (N) or less and TD 2.7 (N) or less when the MD and TD are 30μ, MD 1.5 (N) or less and TD 3.1 (N) or less when the MD and TD are 40μ, and MD 2.1 (N) or less and TD 3.7 or less when the MD and TD are 50μ, and the sealant layer is made of a film having a dart impact strength (based on JIS K7124) of 3.5 (J) or less, and is provided on the base layer side. The microwave-safe packaging bag for food according to claim 1, wherein the acrylic bead ink layer is applied across the packaging bag from the inside to the outside in a specific area of the heat seal portion between the opposing films at both open ends of the tube. The microwave-safe packaging bag for food according to claim 1, wherein the acrylic bead ink layer is provided across a specific area of the heat seal between the opposing films at the joint, from the inside to the outside of the packaging bag. A microwave-safe food packaging bag according to claim 1, 2, 3, or 4, in which the acrylic bead ink layer is applied by gravure printing. A microwave-safe food packaging bag according to claim 1, 2, 3, or 4, in which an easily tearable, brittle film is used as the sealant layer.