HK1038542A1

HK1038542A1 - Packaged food and container for packaged food

Info

Publication number: HK1038542A1
Application number: HK01109074A
Authority: HK
Inventors: 日吉祥子
Original assignee: 株式会社 Zac
Priority date: 2000-02-01
Filing date: 2001-12-27
Publication date: 2002-03-22
Also published as: US20010012530A1; EP1127810B1; EP1127810A2; CN1118424C; EP1127810A3; DE60101487T2; JP3707977B2; CN1309070A; DE60101487D1; JP2001213483A

Abstract

The present invention provides a container (1) for packaging food, in which a sheet (4) seals a vent hole (3) formed at a portion of the container (1) cannot so easily be peeled off but, when the food is heated by an microwave oven, the sheet (4) automatically comes off at the time when the food contained in the container has reached the adequately cooked state. Specifically, the present invention is produced by enclosing food, which contains water or an aqueous solution, in the container for packaging food, the container (1) for packaging food having, on one side thereof, a surface portion (2) made of plastic sheet, at least one vent hole (3), the vent hole being sealed by an adhesive hole-sealing sheet (5) whose vertical peeling strength is no less than 1N/cm in the temperature range of 40 DEG C or lower and is no higher than 0.1N/cm at the temperature range of 80 DEG C or higher.

Description

Container for packaging food

Technical Field

The present invention relates to a packaged food which is obtained by packaging a non-frozen or frozen food in a sealed container and which can be directly heat-cooked in a microwave oven. The invention also relates to a container for packaging a food product, in which the food product can be stored packaged.

Background

Packaged food products stored by packaging non-frozen food products (i.e. food products at room temperature) or frozen food products in a container are generally known. It is also known that when such packaged food products are heated in a microwave oven, the pressure within the package increases substantially, increasing the likelihood of the package exploding. Therefore, there has been proposed a process for preventing explosion, in which a plurality of holes are formed in a container for packaging food so that each hole is covered with a circular sealing member coated with an adhesive (japanese utility model No. 62-69466). Similarly, a process technique has been proposed in which a plurality of holes are formed in a container enclosing a food product, and a valve plate is attached so as to close each hole by applying a first adhesive having a low melting point corresponding to a heating temperature of the food product within a range between the periphery of the hole and the periphery of the valve plate end and a second adhesive which does not melt on both sides of the applied low-melting-point adhesive portion at the heating temperature of the food product (japanese utility model 63-156978).

These known process techniques are useful for preventing explosions during microwave oven heating. However, in these conventional techniques, there is a problem in that the holes are opened before the food is sufficiently heated, which causes uneven heating, or the holes are opened too late, causing the food to be dried or burned. These problems have not been solved. Therefore, in packaged food products that require microwave oven cooking, it is desirable to provide a sealed structure of the aperture in which the steam generated by heating the food product is maintained for a suitable period of time without allowing said steam to escape to the outside too early, and such a seal can only be released when the food product is sufficiently heated. However, it is not easy to determine the most preferred sealing conditions for the wells for each food product. Furthermore, the seal structure that is supposed to be the most preferable tends to have a complicated structure. In short, the prior art has not successfully developed an economical and practical process that meets the above-mentioned requirements.

Disclosure of Invention

In order to satisfy the above-described requirements, the present invention intends to provide an economical sealing structure in which a hole sealing layer sealing a vent hole on a container for food is automatically peeled off at the most appropriate timing when the food is cooked by heating in a microwave oven.

A first object of the present invention is to provide a packaged food in which a hole sealing layer covering a vent hole formed at a portion of a container is not easily peeled off when the container is stored at room temperature or under a frozen condition, but is automatically peeled off when the food is heated by a microwave oven substantially when the food packaged in the container has reached a sufficiently cooked state.

A second object of the present invention is to provide a container for packaging a food, which is provided with at least one ventilation hole and is used for producing a packaged food by packaging a food therein, wherein a hole sealing layer covering the ventilation hole in the container does not easily come off when the container is kept at room temperature or under a frozen condition, but the hole sealing layer automatically comes off when the food is heated by a microwave oven substantially when the food packaged in the container has reached a sufficiently cooked state. That is, a second object of the present invention is to provide a container for packaging food, which can realize the most preferable heating of food by flexibly selecting the adaptive various heating conditions of a microwave oven in terms of functions according to the packaged food.

The packaged food of the present invention which can achieve the aforementioned first object is characterized in that a food containing water or an aqueous solution is packaged in a container having a surface portion made of a plastic layer on one side thereof, at least one ventilation hole is formed near the center of the surface portion, the ventilation hole is sealed by a hole sealing layer with an adhesive, and the vertical peel strength is not less than 1N/cm in a temperature range of 40 ℃ or less and not more than 0.1N/cm in a temperature range of 80 ℃ or more.

Further, the hole sealing layer of the container for enclosing food of the present invention is preferably made of white moisture-proof paper as a base material. And preferably the vent hole formed in the container is sealed by the hole sealing layer so that the adhesive layer having a non-uniform width in the hole sealing layer covers the periphery of the vent hole.

Drawings

Fig. 1 is a sectional view showing a portion of a vent hole formed in a container cap for packaging food according to the present invention;

fig. 2 is a perspective view showing the structure of the container for enclosing food in accordance with the present invention.

Detailed Description

The packaged food product of the present invention is intended to represent a packaged food product which can be cooked by heating in a microwave oven. At least one vent hole is provided in a container enclosing a food product to prevent an explosion from occurring by releasing steam to reduce an increased pressure inside the container when the pressure increases due to an increase in air volume and generation of the steam inside the container during heating of the food product. In the present invention, the vent holes are sealed by a hole sealing layer with an adhesive thereon. That is, the present invention is achieved by utilizing and improving a general process technology.

When cooking, the food in the container must be heated sufficiently. Therefore, it is inevitable that the pressure in the container is raised to a vapor pressure corresponding to the temperature of the food, because the pressure in the container is increased when the temperature in the container is raised. In view of this, a known general technique makes the bonding strength of the hole sealing layer relatively weak, or provides a portion (vent hole peripheral portion or the like) having a relatively weak bonding strength so that the hole sealing layer is easily peeled off when the pressure in the container has become high. In other words, the conventional technique expects the pore sealing layer to operate as a pressure relief valve.

The inventors of the present invention assiduously studied the problem that it is not easy to produce a preferable cooking completion state by heating in accordance with the pressure resistance characteristics of the hole sealing layer. As a result of the research, the present inventors have found that the pressure resistance characteristics of the pore sealing layer can be changed by adjusting the adhesive strength temperature characteristics of the adhesive used to attach the pore sealing layer. The present invention has been completed based on this finding.

The container for packaging food of the present invention may have a box-like shape or a bag-like shape. That is, the shape of the container is not limited to any particular form, and any structure is acceptable as long as the container is made of a material excellent in airtightness, watertightness, oil resistance, and heat resistance, and can transmit electromagnetic waves and has appropriate mechanical strength. However, at least one side of the container must be made of a plastic layer. This surface, which is made of a plastic layer, is preferably transparent so that the contents can be seen.

As mentioned above, embodiments of the plastic used to make the container include: a single material layer or a composite material layer containing polypropylene, polyester, polysulfone, polyamide (nylon), polycarbonate or the like as a main component; and a laminate composite wherein the foregoing single material or composite layers are combined with polyacrylate, polyvinylidene chloride, polyvinyl alcohol or the like.

A vent hole is formed in the surface of the plastic layer made of the aforementioned material. The vent hole is preferably formed near the center of the container in which the food is packaged (near the center of the upper surface for a flat type container having a relatively small height compared to its length/width dimension) in terms of uniformly heating the food in the container. The holes may have any shape, such as circular, elliptical, oval or polygonal, as long as the shape is suitable for the purpose. The diameter of the hole is preferably about 5mm, but is not particularly limited.

The hole-sealing layer for sealing the ventilation hole is preferably made of a base material having excellent air-tightness, water-tightness, oil-resistance and heat-resistance, similarly to the above-described plastic layer. Examples of such base materials include layers made of polyester, polypropylene or the like, synthetic papers made of plastic and moisture-proof papers. It is preferable that the pore sealing layer itself hardly generates heat when heated by electronic microwave and also that the temperature does not rise when it absorbs infrared rays. The pore sealing layer has an aluminum deposition layer thereon so as to reflect the above-mentioned microwaves, and is colorless, and particularly, white is most preferable. The pore sealing layer may have any suitable shape, such as circular or oval. The diameter is preferably about 10mm, but is not limited to this size.

The adhesive for attaching the hole-sealing layer to the vent hole formed in the plastic layer must be an adhesive having adhesiveness with respect to the plastic layer, that is, a pressure-sensitive adhesive. Examples of such pressure-sensitive adhesives include natural rubber, synthetic rubber. Particularly preferably used is a pressure-sensitive adhesive prepared by mixing styrene butadiene type rubber (styrene-butadiene rubber) and acrylic type rubber with such a material providing tackiness as rosin type or petroleum resin type so as to have excellent pressure-sensitive characteristics and heat-sensitive characteristics.

The pressure-sensitive adhesive of the present invention as described above is required to have heat-sensitive characteristics in which the vertical peel strength is not less than 1N/cm, preferably not less than 2N/cm in the temperature range of 40 ℃ or less and the vertical peel strength is not more than 0.1N/cm in the temperature range of 80 ℃ or more. The vent holes formed in the plastic layer are sealed by applying a hole-sealing layer coated on the back with a pressure-sensitive adhesive satisfying the aforementioned conditions or characteristics, which is opened after the food packaged in the container has been completely cooked by heating.

It should be noted that the value under the aforementioned conditions is not an inherent value of the adhesive itself, since it is obtained according to a standard adhesive measurement method and the like (for example, described in JIS Z0237) practiced in the industry, but represents a heat-sensitive property of the adhesive strength of the hole sealing layer with respect to the plastic layer of the food-packaging container with one vent hole. It should be noted that this is because it is generally not known whether a pressure-sensitive adhesive satisfies the aforementioned conditions for the adhesion strength characteristics with respect to a specific polyester layer, and whether the adhesion strength characteristics conditions are satisfied with respect to a specific nylon 6 layer.

Further, said adhesive property conditions are to be applied to a container for packaging food products, designed to contain the most common food products, i.e. food products containing water or an aqueous solution in suitable proportions and suitable for heating by microwave oven. Such "most common food products" include cooked food products such as main meals, snack foods, parboiled foods, and the like. Therefore, for foods that need to be heated to a relatively high temperature of not less than 100 ℃ or foods that need to be heated only to 40 to 60 ℃, it is necessary to select a pressure-sensitive adhesive having better adhesive strength characteristics within the aforementioned range of conditions. Further, however, needless to say, foods such as dry foods or the like which are not suitable for heating by a microwave oven are in the present document

Outside the scope of the invention.

The invention will be described below in terms of preferred embodiments thereof.

In fig. 1, reference numeral 1 denotes a food container which is made by molding a polycarbonate layer. A composite layer or the like of a suitable material may be provided in the food container 1. Reference numeral 2 denotes a flexible cover made of a nylon 6 layer. The peripheral portion of the lid 2, which is designed to be bonded by melt bonding or adhesive bonding, can be fixed to the rim portion 1 of the food container 1. A circular vent hole 3 is formed near the center of the cover 2. The vent hole 3 is hermetically sealed by a circular hole sealing layer 4.

A pressure-sensitive adhesive layer 5 adhered to a nylon 6 layer is provided on the back of the pore sealing layer 4 so that an oval-shaped non-adhering portion 5' is formed substantially at the center portion of the pressure-sensitive adhesive layer 5. In the pressure-sensitive adhesive layer 5, the width of the pressure-sensitive adhesive-coated portion is made uneven. Further, the center position of the vent hole 3 does not need to coincide with the center position of the hole sealing layer 4. A slight misalignment of around 1-2mm between the central position of the vent hole 3 and the central position of the hole sealing layer 4 is relatively preferable, since such a slight deviation facilitates peeling of the hole sealing layer 4 in a reliable manner.

The pore sealing layer 4 used here is produced in such a way that: preparing synthetic paper made of polyester as a base material, having a thickness of 60 μm, and coated thereon with a white surface coating; an acrylic type pressure-sensitive adhesive a was coated on the base material so that the thickness of the adhesive a was 25 μm, thereby forming the pressure-sensitive adhesive layer 5. For comparison, a pore sealing layer 4b and a pore sealing layer 4c were produced by coating the base material with other acrylic type pressure-sensitive adhesive b or styrene butadiene type pressure-sensitive adhesive c, respectively, so that the thickness of each of the adhesive b and the adhesive c was 25 μm, and a pressure-sensitive adhesive layer was formed on each of the pore sealing layer 4b and the pore sealing layer 4c in a manner similar to the pore sealing layer 4 a.

The adhesive strength characteristics of the aforementioned pressure-sensitive adhesives a, b, and c with respect to the nylon 6 layer were measured, respectively. The results are as follows:

TABLE 1

Adhesion strength to nylon 6 layer (10)^-2N/cm)

Temperature (. degree.C.)	30	40	50	60	70	80	90
Temperature (. degree.C.)	30	40	50	60	70	80	90	Pressure-sensitive adhesive a	300	190	110	38	13	8	5
Pressure-sensitive adhesive b	220	85	43	18	9	2	-	Pressure-sensitive adhesive a	300	190	110	38	13	8	5
Pressure-sensitive adhesive b	220	85	43	18	9	2	-	Pressure-sensitive adhesive c	350	240	175	130	92	63	42

The hole sealing layers 4a, 4B and 4C, which were made by coating the base material with the pressure-sensitive adhesive a, the pressure-sensitive adhesive B and the pressure-sensitive adhesive C, respectively, were each press-adhered to the vent hole 3 of the food container lid 2 made of a nylon 6 layer so as to seal the vent hole 3 (except for the hole sealing layer, three food containers of the three adhesives used herein have substantially the same structure), thereby producing the container of the present invention enclosing the food a and the containers enclosing the foods B and C as comparative examples. Five samples were prepared for each container of packaged food products A, B and C. 210 g of the frozen shakedown was air-tightly packed in each container, and a heat cooking experiment was performed by using a microwave oven which satisfied the microwave oven output value measurement standard described in JIS Z9212. The results shown in Table 2 were obtained.

TABLE 2

Heating cooking experiment of packaged food

Food container	Time required for pore sealing layer to peel off (minutes)	Heated and cooked state of food
Food container	Time required for pore sealing layer to peel off (minutes)	Heated and cooked state of food	ABC	4.5-5.03.5-4.07.0-7.5	Uniformly and completely heating the surface of the core part which is not sufficiently heated and burning

As can be understood from the above results, the packaged food of the present invention prepared using the container for packaged food of the present invention reliably prevents the pore sealing layer thereof from peeling when the food is not sufficiently heated, when the packaged food is heated by a microwave oven. In the present invention, the pore sealing layer is peeled off only when the food reaches a proper cooking state and sufficient steam is generated, and the temperature of the vent hole portion has reached the temperature at which the pressure-sensitive adhesive is peeled off due to the steam. Therefore, the operation of the microwave oven is stopped when the steam has been sprayed, and the food is not excessively heated.

As described above, the packaged food of the present invention is produced by packaging a food with water or an aqueous solution in the container in which the food of the present invention is packaged, the container in which the food is packaged having a surface portion made of a plastic layer on one side thereof, at least one vent hole being formed near the center of the surface portion, the vent hole being sealed by an adhesive hole sealing layer, the vertical peel strength of which is not less than 1N/cm in a temperature range of 40 ℃ or less and the vertical peel strength of which is not more than 0.1N/cm in a temperature range of 80 ℃ or more. When the packaged food of the present invention is heated by a microwave oven, the pore sealing layer thereof is automatically peeled off after the food is sufficiently heated. Therefore, it is impossible to occur a case where the pore sealing layer is peeled off before insufficient heat cooking or the food is excessively heated due to too late peeling of the pore sealing layer. In other words, the present invention achieves an excellent effect and can easily obtain a properly cooked food.

Claims

1. A container for enclosing a food, said container having a surface portion made of a plastic layer, at least one vent hole being formed in said surface portion, said vent hole being sealed by an adhesive hole sealing layer having a vertical peel strength of not less than 1N/cm at a temperature range of 40 ℃ or less and a vertical peel strength of not more than 0.1N/cm at a temperature range of 80 ℃ or more.

2. A packaged food container according to claim 1 wherein at least one vent hole is formed near the center of a surface portion formed on one side of the container.

3. The packaged food container of claim 1 wherein the hole sealing layer seals the vent hole such that the adhesive layer of non-uniform width on the hole sealing layer covers the perimeter of the vent hole.

4. A packaged food container according to claim 1 wherein the hole sealing layer is formed of white moisture barrier paper as a base material.