JPH1179260A - Packaging material which can release internal pressure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable internal pressure to be released at the time of heating by a microwave oven or the like by providing a breaking layer of specific thickness and relatively weak fracture strength on a heat seal layer, fusing this to a part of a base material or the heat seal layer, and providing an internal pressure release port reaching the breaking layer. SOLUTION: In the packaging material 1 comprising a heat seal layer 3 laminated on a heat-resistant material 2, an internal opening port 4 with an end opened on an external face of the base material 2 and the other end reaching at least the heat seal layer 3 is provided, and a braking layer with a fusing interface approximately coinciding with an end of the internal opening port 4 and made of thermoplastic synthetic resin having relatively weak fracture strength as thick as 5 to 30 μm is provided on the heat seal layer 3. The heat seal layer 3 may comprise an external breaking layer and an internal resin layer fused thereto, while the internal pressure opening port 4 may be from the base material 2 through the internal resin layer. The external breaking layer is preferably formed of one of low density polyethylene, ethylene-vinyl acetate copolymer, ionomer or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packaging material capable of automatically releasing internal pressure when a package is heated by a microwave oven or the like.

[0002]

2. Description of the Related Art If a frozen or refrigerated food is heated in a microwave oven in a sealed package, the moisture contained in the food becomes steam and the internal pressure rises sharply, eventually causing the package to burst. Therefore, take out the food from the package, transfer it to another heat-resistant container, wrap it with wrap film,
Heated with lid. This is a laborious operation that lacks convenience.

Therefore, a method has been considered in which the package is formed of a heat-resistant film or sheet, and the package is cut with scissors or the like during heating to provide an opening. However, this is not only troublesome, but sometimes there are no tools like scissors nearby. On the other hand, a part of the package is opened in advance in the manufacturing stage, but the sealing property is impaired, and the contents to be packaged are limited. Therefore, there is a method in which the internal pressure release port provided in advance is sealed with a label, and the label is peeled off during heating to open the release port. However, this also has a problem that an extra step of sealing with a label is added.

For this reason, a portion having a weak adhesive strength is provided in the heat-sealed portion of the package, or a superposing tape having a weak adhesive strength and easily separated into two is inserted, and the internal pressure is increased by heating. In some cases, when the adhesive strength is weakened, a portion having a weak adhesive strength is automatically peeled off to form an opening to release the internal pressure. However, even if it is partial, uniform and strong sealing properties cannot be expected because the heat-sealed portion has a portion with low adhesive strength, and a pouch such as a bag is formed in advance, and the contents are added thereto. It is necessary to take the process of filling,
It is not suitable for pillow packaging in which packaging and filling are performed simultaneously and continuously. In addition, there is a problem that the method of inserting the tape is structurally complicated and leads to an increase in cost.

[0005] In addition, there is also known a material obtained by laminating a low melting point resin film as a heat sealing material on a base material provided with a ventilation hole to form a cover material, and heat sealing the container. When the low-melting-point resin film reaches the melting point by heating, it is liquefied and pushed up to the air hole by the internal pressure, so that a penetrated air hole is formed. However, when the low melting point film is melted, there is a problem that the sealing strength is weakened and the sealing property is impaired. In addition, since the low-melting point film is located on the innermost layer that directly touches the contents, when this layer is melted, it becomes sticky and adheres to the contents. The taste may be impaired.

Further, in any of the internal pressure releasing methods described above, there is a problem that it is very difficult to control the heating temperature when releasing the internal pressure.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to heat a food in a microwave oven while wrapping the food, thereby preventing rupture or scattering of the content, easily controlling the internal pressure release temperature, and unsealing the content. An object of the present invention is to provide a packaging material that can be completely airtightly packed without any parts, can be used in any of pillow packaging and pouch packaging, and has high productivity and low cost.

[0008]

In order to solve the above-mentioned problems, the present invention relates to a packaging material in which a heat-sealing layer is laminated on a heat-resistant base material, one end of which is open to the outer surface of the base material and the other end is at least. Providing an internal pressure release port reaching the heat seal layer,
The heat-sealing layer is provided with a breakable layer made of a thermoplastic synthetic resin having a relatively weak rupture strength with a fusion interface almost coincident with the other end of the internal pressure release port and a thickness up to the outer surface of 5 μm to 30 μm. Features.

[0009] The heat seal layer may include an outer surface breakable layer and an inner resin layer fused thereto, and the internal pressure release port may be penetrated from the base material to the inner resin layer.

[0010] The outer surface breaking layer may be made of low density polyethylene,
Linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-acrylic acid copolymer,
It is preferably formed by any of the ionomers.

Preferably, the inner resin layer is formed of a thermoplastic synthetic resin of the same quality as the outer fracture layer.

The internal pressure release port comprises a cut or a small hole.

[0013]

The rupture layer is made of a resin layer having relatively low rupture strength and is fused to the base material or a part of the heat seal layer except for the internal pressure release port. The corresponding rupture layer ruptures due to an increase in internal pressure.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example in which the heat seal layer itself is a breakable layer. As shown in the figure, a packaging material 1 includes a heat-resistant base material 2 and a heat-sealing layer 3.
The internal pressure release port 4 penetrating through is provided. The internal pressure release port 4 has a linear "-" shaped cut 4 as shown in FIG.
In addition to a, "+", "x", "U" shaped cut 4
b, 4c, 4d, or the small hole 4e. The shape of the small hole 4e is not limited to the illustrated circle, but may be a polygon or other irregular shapes. The size of the cut or small hole is not particularly limited, but the length of the cut is about 1 to 15 mm and the long diameter of the small hole is 2 mm.
About 5 mm. Of course, a plurality may be provided.

As the heat-resistant base material 2, a heat-resistant synthetic resin film is generally used. For use in a microwave oven, particularly high heat resistance is not required, and biaxially oriented polypropylene, A simple substance or a composite of oriented high-density polyethylene, biaxially oriented polyester, biaxially oriented polyamide or the like is used. In addition, paper or metal foil may be used, and in this case, it is necessary to form a composite for the reasons described below. Of course, a printing layer can be provided.

The heat sealing layer 3 as the breaking layer is
First, it must be capable of being fused to the base material 2. Here, the term "fusion" means that the heat seal layer 3 (breaking layer) has compatibility with each other, has a property of homogenizing each other at the bonding interface, has a very large adhesive strength at the bonding interface, and 2 means strongly supported. Second, it must break relatively easily under internal pressure. Examples of such a synthetic resin include low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-acrylic acid copolymer, and ionomer, and have a thickness of 5 μm to 30 μm.
m. Of course, it is necessary to avoid damage due to the impact during handling in the distribution process and so on.
m or more is necessary, and if it exceeds 30 μm, breakage due to an increase in internal pressure becomes difficult. Such a heat seal layer 3 is
It is formed by ordinary roll coating, extrusion coating, heat lamination, or the like, and requires a resin layer that can be fused to the surface of the substrate 2 facing the heat seal layer 3. As such a resin, the same resin as that of the heat seal layer 3 is selected. Of course, the resin may not be the same as long as the resin can be fused.

Incidentally, in order to enhance the sealing performance of a package such as a container or a bag, it is necessary to increase the sealing strength between the lid and the container flange, for example. For that purpose, the thickness of the heat sealing layer must be secured to a certain degree or more. On the other hand, in order to easily release the internal pressure, it is necessary to weaken the breaking strength, that is, to make the heat seal layer as thin as possible. Thus, obtaining the required seal strength and the appropriate breaking strength are contradictory concepts. Therefore,
As shown in FIG. 3, an inner resin layer 31 of the heat seal layer 3 is provided on the inner surface of the base material 2 via a dry lamination adhesive such as a two-component curable urethane resin or an anchor coat layer 21. An internal pressure release port 4 is provided in this laminate. Then, the outer surface break layer 32 is formed on the inner surface resin layer 31.
Is provided. The layers 31 and 32 are made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-acrylic acid copolymer, ionomer, or the like. It does not have to be. The thickness of the inner resin layer 31 is sufficient if the outer fracture layer 32 can be held to the base material 2 with sufficient adhesive strength, and 5 μm to 40 μm is sufficient. Further, the thickness of the outer surface break layer 32 is about 5 to 30 μm as described above. In addition, it is a matter of course that the base material 2 and the inner resin layer 31 may be directly laminated in addition to being laminated with another adhesive.

As described above, by forming the heat seal layer 3 as the two layers of the inner resin layer 31 and the outer rupture layer 32, a sufficient thickness can be secured, while the internal pressure release port 4
Since the rupture layer 32 has reached the thin rupture layer 32 and the rupture layer 32 is fused to the inner resin layer 31, the rupture layer 32 is easily broken by an increase in internal pressure. That is, the heat seal layer 3
By appropriately selecting the thicknesses of the inner resin layer 31 and the outer rupture layer 32 in a layer structure, it is possible to control the seal strength and the rupture strength in a well-balanced manner.

Examples will be described below.

[0021]

Example 1 12 μm as heat-resistant plastic film
A polyester film (E5101 manufactured by Toyobo Co., Ltd.) is coated with a two-liquid reaction type urethane anchor coat (Takelac A3210 manufactured by Takeda Pharmaceutical Co., Ltd.), and a low-density polyethylene (Sumikasen L-705 manufactured by Sumitomo Chemical Co., Ltd.) is coated thereon.
Was extruded to form a long sheet. This was aged in an atmosphere of 40 ° C. for 24 hours, and then cut endlessly at intervals of about 50 mm with a rotary blade, and the same kind of polyethylene was extrusion-coated by 8 to 10 μm. The packaging material was used to wrap a frozen Shumai placed on a polypropylene tray in a bag and heated with a 500 W microwave oven. In about 50 seconds, the package swelled and the vapor escaped from the cut, and did not burst.

The shape of the cut is "-", "+",
"X", and the length of each side is 3 mm,
Three types of 5 mm and 10 mm were prepared.

[0023]

Example 2 The same packaging material as in Example 1 was prepared, and
200 g of water was sealed in a flat bag having a size of 50 × 180 mm and a seal width of 10 mm and a four-side seal. In the longitudinal center of the flat bag,
Three types of bags provided with "-"-shaped cuts (through only the base material) having a length of 3 mm, 5 mm, and 10 mm were prepared. When these were naturally dropped on a concrete floor ten times from a place having a height of 1 m, no water leaked from any of the bags.

When these bags were placed on a ceramic dish and heated in a microwave oven of 500 W, steam was blown out of the cut in about 60 seconds.

[0025]

Embodiment 3 15 μm as heat resistant plastic film
Biaxially stretched nylon film (Unitika ONS) and 3
A linear low-density polyethylene film of 0 μm (Rix L6102 manufactured by Toyobo Co., Ltd.) was laminated with a two-liquid reaction type urethane dry lamination adhesive to form a long sheet. After this was aged for 48 hours in an atmosphere of 40 ° C., endless cuts were made at intervals of about 50 mm with a rotary blade.
5 μm linear low-density polyethylene (Ultzex 1500C manufactured by Mitsui Petrochemical) was extrusion coated. The packaging material was used to wrap a frozen shoe mai placed on a polypropylene tray in a bag shape and heat it with a 500 W microwave oven. About 60
In seconds, the package swelled and steam escaped from the cut, and did not burst.

The shape of the cut was "-" and the length was 5 mm or 10 mm.

[0027]

Example 4 A two-liquid reaction type urethane adhesive (Takeda Pharmaceutical Takelac A-31) comprising a polyester film of 25 μm (E5101 manufactured by Toyobo Co., Ltd.) and a low-density polyethylene film of 40 μm (S-203 manufactured by Aicello Chemicals).
0) to form a laminated long sheet. After this was aged, "-" cuts were made with a die-cut roll, and low-density polyethylene (Sumikasen L-705, manufactured by Sumitomo Chemical Co., Ltd.) was extruded thereon to a thickness of 15 μm to form a cover material. The cuts were cut so that three cuts were made at a length of 15 mm and arranged at a pitch of 50 mm.

A polyethylene container (made by Idemitsu Petrochemical Co., Magic Top) was covered with absorbent cotton, impregnated with 50 g of water, and sealed with the lid so that the cut lined up at the center. The container was heated in a household 500 W microwave for 2 minutes. About 1 minute after the heating, the lid material swelled, and then the steam escaped from the cut, and continued to emit while expanding.

[0029]

According to the present invention, as described above, the heat-seal layer is provided with a break layer having a relatively small break strength having a specific thickness, and is fused to a part of the base material or the heat-seal layer.
By providing an internal pressure release port that reaches this break layer,
It is possible to release the internal pressure when heating with a microwave oven or the like, so that not only can the cost be reduced significantly, but also pillow packaging and the like, and the temperature or pressure of the internal pressure release can be easily controlled simultaneously with the sealing performance. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a packaging material of the present invention.

FIG. 2 is a plan view showing the shape of an internal pressure release port according to the first embodiment;

FIG. 3 is a sectional view showing another example of a packaging material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Packaging material 2 Heat resistant base material 3 Heat seal layer 4 Internal pressure release port 4a, 4b, 4c, 4d Cut 4e Small hole 21 Anchor coat layer 31 Inner resin layer 32 Outer fracture layer

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshiyuki Ota 3-6-1-8 Kutaro-cho, Chuo-ku, Osaka City Inside Toyo Aluminum Co., Ltd. (72) Inventor Mamoru Kamata 3-6-68 Kutaro-cho, Chuo-ku, Osaka City No. Toyo Aluminum Co., Ltd.

Claims (5)

[Claims] 1. A packaging material in which a heat seal layer is laminated on a heat-resistant base material, wherein one end is opened to the outer surface of the base material and the other end is provided with an internal pressure release port reaching at least the heat seal layer. The fusion interface almost coincides with the other end of the opening,
A wrapping material capable of releasing internal pressure, wherein a breakable layer having a thickness up to an outer surface of 5 to 30 μm is provided on the heat seal layer. 2. The heat seal layer is composed of an outer surface fracture layer and an inner resin layer fused to the outer surface fracture layer, and the internal pressure release port extends from the substrate to almost the outer surface fracture layer. The packaging material according to claim 1, wherein the internal pressure can be released. 3. The method according to claim 1, wherein the breaking layer comprises a low-density polyethylene, a linear low-density polyethylene, an ethylene-vinyl acetate copolymer, a polypropylene, an ethylene-acrylic acid copolymer,
3. The method of claim 1, wherein the ionomer comprises one of the following:
4. A packaging material capable of releasing internal pressure according to item 1. 4. The method according to claim 1, wherein the inner resin layer is any one of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-acrylic acid copolymer, and ionomer. Or the packaging material capable of releasing internal pressure according to 2. 5. The packaging material capable of releasing internal pressure according to claim 1, wherein the internal pressure release port comprises a cut or a small hole.