Food packaging bag suitable for microwave
The laminated film packaging bag with an acrylic bead ink layer addresses manufacturing cost and seal strength issues, ensuring safe and cost-effective pressure relief during microwave heating.
Patent Information
- Application Number
- JP2024080721
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-17
- Publication Date
- 2025-11-28
AI Technical Summary
Existing microwave-safe food packaging bags face issues such as increased manufacturing costs due to labor and material requirements for pressure relief valves, difficulty in controlling seal strength, and risks of sudden tearing or popping sounds during microwave heating.
A microwave-safe packaging bag made of laminated film with a heat-resistant base layer and sealant layer, featuring an acrylic bead ink layer applied across specific heat-sealed portions to reduce interlayer strength, allowing steam to escape and prevent bursting.
The solution effectively manages internal pressure during microwave heating without additional parts or complex processes, preventing bag rupture and reducing manufacturing costs while minimizing popping sounds.
Smart Images
Figure 2025174378000001_ABST
Abstract
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 inside 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, 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. 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] 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 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 acrylic bead ink layer is arranged in a specific area of the heat seal portion between the opposing films at the joint, 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 food packaging bag, the acrylic bead ink layer is provided by gravure printing.
[0014] The invention described in claim 5 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]
[0015] In acrylic bead ink, the large particle size of the acrylic beads, which are made of a different resin system, mixed with the urethane ink inhibits 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 evaporated 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.
[0016] Therefore, in the microwave-compatible packaging bag for food of the present invention, an acrylic bead ink layer is partially provided on the heat-sealed portion between the opposing films at the joint where pressure is applied during microwave heating, and on the heat-sealed portion between the opposing films at both open ends of the tube, which allows steam that generates internal pressure to escape from these portions.This allows steam to escape from the specified location before internal pressure is generated that would cause the heat-sealed portion to peel off, preventing irregular ruptures.
[0017] In this case, the layer for weakening the interlayer strength is applied by printing as an acrylic bead ink layer, so microwave-safe packaging bags for food can be manufactured at low cost without requiring any special separate parts or cutting processes. [Brief explanation of the drawings]
[0018] [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
[0019] 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).
[0020] 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.
[0021] FIG. 4 shows an example of lamination of plastic films constituting the bag body P, which has a two-layer structure in which a sealant layer P1 is laminated on a heat-resistant base material layer P2.
[0022] 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.
[0023] It is also possible to use a brittle film that is easily torn as the sealant layer.
[0024] In the drawing, reference numeral 5 denotes an acrylic bead 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 seal part 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 opposite side to the back adhesive part.
[0025] The acrylic bead ink layer 5 in the present invention is Ink binder: urethane Matting agent: acrylic resin Matting agent particle size: approx. 20μ 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 between the ink layers, which have weak interlayer strength.
[0026] The acrylic bead 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.
[0027] 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 seal. Below are the results of changing the width of the acrylic bead ink layer 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.
[0028] 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 on top. Here, the acrylic bead 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.
[0029] 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.
[0030] In the above process, the acrylic bead ink layer 5 is applied by gravure printing. In addition, although not shown, printing for whitening or design is performed between the layers.
[0031] 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. The resulting pressure and the thermal expansion of the air increase the internal pressure of the packaging bag, causing it to swell and burst. However, the sealant edge breaks at the acrylic bead ink area located at the three-point intersection X, allowing steam to escape between the layers and preventing bursting.
[0032] 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]
[0033] 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 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.
[0034] Table 2 shows the tear strength and impact strength of commercially available films from various manufacturers. [Table 2]
[0035] 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 midway through the bottom seal (and 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 acrylic bead 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 strong lamination, so although steam escapes from the acrylic bead ink area, it splits sideways during steaming, so it is difficult to say that steam escapes properly.
[0036] Figure 8 shows another embodiment of the microwave-safe packaging bag for food according to 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-sealed portion 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).
[0037] 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]
[0038] 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 Acrylic bead 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-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.
2. The microwave-safe packaging bag for food according to claim 1, wherein the acrylic bead 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 both open ends of the tube.
3. 2. The microwave-safe packaging bag for food according to claim 1, wherein the acrylic bead 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 joint.
4. 5. The microwave-safe packaging bag for food according to claim 1, 2, 3 or 4, wherein the acrylic bead ink layer is provided by gravure printing.
5. 5. The microwave-safe packaging bag for food according to claim 1, 2, 3 or 4, wherein the sealant layer is a brittle film that is easily torn.