JPS6333273A - Sealing vessel - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sealed container in which the container body is heat-sealed with a lid so that the container can be easily opened after the contents have been heated in a microwave oven.

(Prior art) A sealed container (hereinafter referred to as a heat-sealed sealed container) is made by heat-sealing a container body filled with contents such as food with a lid made of a laminate made of a silastic film or the like. , the type that is subjected to retort sterilization has a peel strength of the heat seal part (hereinafter referred to as heat seal strength) of 2-3 kg/1.5 cn+ or more (Ministry of Health and Welfare Notification No. 17 Whistle 3 (4) "Heat seal strength"). This is legally regulated. If the heat seal strength is weak, the heat seal part may peel off due to the high temperature and inner layer pressure during retort sterilization processing, or pinholes may be formed in the heat seal part that penetrate inside and outside, impairing the sealing performance1. This is because it may cause hygiene problems.

The above type of sealed container (hereinafter referred to as a high heat-sealing strength sealed container) has a high heat-sealing strength that makes it impossible to peel off the heat-sealed part when opening the container. There was a problem in that unless the incisions were made with a knife or the like, it would take a lot of effort. Recently, microwave ovens have become popular in households, but in the case of the above-mentioned type of sealed container, the above-mentioned problem still remains even after the contents are heated in the microwave oven.

On the other hand, the above legal regulations do not apply to heat seal sealed containers that are not subjected to retort sterilization (hereinafter referred to as low heat seal strength sealed containers), so the heat seal strength of low heat seal strength sealed containers is 2.3
kl? / Lower than 1.5α, and is set as high as possible within the range where it is possible to grasp the tab by hand and pull it off. In this case, it is relatively easy to peel off after the peeling has started, but there is a problem in that a relatively large force is required for the initial peeling, making the initial peeling difficult. This problem still remains even after heating the contents in the microwave.

(Problems to be Solved by the Invention) An object of the present invention is to provide a sealed container with high heat-seal strength that can be easily opened by peeling off the heat-sealed portion after heating in a microwave oven.

Another object of the present invention is to provide a sealed container with a low heat-seal strength that allows easy initial peeling of the heat-sealed portion after heating in a microwave oven.

(Means for Solving the Problems) The sealed container of the present invention is a sealed container in which a container body is heat-sealed with a lid, and a portion of the inner layer of the lid that corresponds to the heat-sealed portion extends over the entire circumference. or locally made of a foamable heat-sealing resin, and the lid or container body is placed in contact with or facing a layer of the foamable heat-sealable resin, and heated in a high-frequency electric field to form the foamable resin. It is characterized by a heat-generating layer that can be foamed with heat-sealable resin.

Examples of the container body include those made of thermoplastic only, or those made of paper or glass that have a heat-sealable resin layer at least at the opening to be heat-sealed. The lid is mainly made of a thermoplastic film, but this film is coated with a non-conductive inorganic coating (e.g. silicon oxide, aluminum oxide, etc.) by vapor phase plating.
It may also be formed of magnesium fluoride (having barrier properties).

In the case of a sealed container with high heat-sealing strength, the thermoplastic plastic that forms the heat-sealing resin layer of the container body (hereinafter referred to as the first plastic) is the thermoplastic that is the base material of the foamable heat-sealing resin of the lid. It is desirable that the material is the same as the plastic (hereinafter referred to as second plastic) (for example, a combination of low-density polyethylene and low-density polyethylene) or of the same type (for example, a combination of low-density polyethylene and medium-density polyethylene).

In the case of a low heat seal strength sealed container, the first plastic is of a different type than the second plastic (for example, a combination of polyethylene/polypropylene blend and polyethylene).
It is desirable that

The foamable heat-sealing resin is made of a thermoplastic resin containing a foaming agent, and it is desirable that the foaming temperature of the foaming agent is higher than the heat-sealing temperature. This is to prevent loss of heat-sealing strength due to foaming during heat-sealing.

A heat-generating layer that heats up in a high-frequency electric field refers to a heat-sealing layer that heats up in a high-frequency electric field due to resistance loss, magnetic loss, discharge, etc., preferably before the contents reach a predetermined heating temperature. A layer that rises in temperature, preferably rapidly, to a temperature higher than the foaming temperature of the foam.

In the case of a sealed container with high heat-sealing strength, it is desirable that the entire circumference of the inner layer of the lid portion corresponding to the heat-sealing portion is made of foamable heat-sealable resin. On the other hand, in the case of a sealed container with low heat-sealing strength, only the portion of the inner layer of the lid portion corresponding to the heat-sealing portion, which faces the tab, may be made of foamable heat-sealable resin.

(Function) When the sealed container of the present invention filled with the contents is placed in a microwave oven and the microwave oven is energized, the contents are heated by high-frequency dielectric heating. At the same time, the heat generation layer is heated to melt and foam the foamable heat-sealable resin layer that is in contact with or faces the heat generation layer, preferably before the contents reach a predetermined temperature.

Although the internal pressure of the container increases due to the water vapor generated by heating the contents, the water vapor escapes through the molten heat-sealed portion, thereby preventing the lid portion or the container body from bursting due to the increased internal pressure. When the microwave oven is turned off and the sealed container is taken out from the microwave oven, the foamed resin is rapidly cooled and solidified, forming a foamed resin layer around the entire circumference of the heat-sealed portion or locally. . This foamed resin layer is fragile and can be easily peeled off.

(Example) In FIGS. 1 and 2, 1 is a sealed container, 2 is a container body, 3 is a lid, and 4 is a content such as food. The container body 2 is formed by thermoforming a low density polyethylene sheet. The lid part 3 has an outer layer 3a made of a biaxially stretched polyethylene terephthalate film (thickness is, for example, 12 μm).
, and a low-density polyethylene film (thickness e.g. 6
The inner layer 3b (0 μm) is punched out from a laminate film which is laminated with an adhesive layer (not shown) interposed therebetween. The thermoplastic plastic forming the outer layer 3a preferably has a higher melting point than that of the inner layer 3b.

The lid part 3 is heat-sealed to the flange part 2a of the container body 2 to form a heat-sealed part 5, and the sealed container 1 is a sealed container with high heat-sealing strength. The portion 3bl of the inner layer 3b that corresponds to the heat-sealed portion 5, that is, the portion 3bl that follows the heat seal portion 5, is
The entire circumference contains a foaming agent and is made of a foamable heat-sealable resin 6 based on low-density polyethylene. As a foaming agent, those whose foaming temperature in the resin is higher than the heat sealing temperature (approximately 150°C in the case of low-density polyethylene) are heavy, such as azodicarboxylic acid amide (foaming temperature: 160 to 200°C).

The amount added is preferably, for example, 1 to 10 parts per 100 parts of the resin. Note that when the resin forming the heat-sealed portion is polypropylene, barium azodicarboxylate (foaming temperature 250° C.), for example, is preferably used as the foaming agent.

In contact with the layer of foamable heat-sealable resin 6, the outer layer 3a
On the side, a heat-generating layer 7 that heats up in a high-frequency electric field to foam the foamable heat-sealing resin 6 is disposed on the heat-sealing portion 5.
It is attached along the entire circumference. The ring-shaped heating layer 7 is
In the case of this embodiment, the heat generating layer 7 is heated to a temperature higher than the foaming temperature due to the resistance loss based on the induced current circulating in the metal foil in the high-frequency electric field. Preferably, the temperature increases rapidly.

The heat generating layer 7 is a conductive film formed by a vapor phase plating method such as a vacuum evaporation method, a conductive film containing conductive powder such as metal powder or carpin powder, a polar comb such as nitrile butyl rubber, or a magnetic powder such as ferrite. (generates heat due to magnetic loss).

FIG. 3 shows the state when the sealed container 1 is placed in a microwave oven, the contents 4 are heated to a predetermined temperature, and then taken out from the microwave oven. Heat-sealed portion 5 that increases the heat of the heat-generating layer 7
The foamable heat-sealable resin 6 is foamed and then solidified to form a foamed resin layer 6'. Since the foamed resin layer 6' is fragile, by pulling up the tab 3X of the lid part 3, the foamed resin layer 6',
It can be easily opened by tearing it.

FIG. 4 shows that the heat generating layer 7 is attached along the entire circumference near the upper surface of the flange portion 2a of the container body 2, that is, facing the 60 layers of foamable heat-sealable resin.
The main parts of the same sealed container 11 are shown. FIG. 5 shows the state after the sealed container 11 is taken out of the microwave oven, where the layer of foamable heat-sealable resin 6 becomes a fragile foamed resin layer 6', and the upper part of the flange portion 2a becomes a heat-generating layer. 7 is partially deformed due to melting when heated.

In the sealed container 21 shown in FIGS. 6 and 7, the container body 22 is formed by thermoforming a polypropylene sheet. The lid portion 23 includes an outer layer 23a made of a biaxially stretched polyethylene terephthalate film (thickness: 12 μm, for example), an intermediate layer 23b1 made of an unstretched polyzolopylene film (thickness: 50 μm, for example), and an ethylene-globylene copolymer blend film ( For example, the thickness is 40
It is formed from a laminate film having an inner layer 23e made of .mu.m). The intermediate layer 23b and the inner layer 23c are formed into a film by a co-melt extrusion method, and this co-extruded film is laminated to the film forming the outer layer 23a via an acid-modified polypropylene layer (not shown) to form the above-mentioned laminate film. is formed.

The above ethylene/propylene copolymer blend has, for example, an ethylene content of 5 mol, a melting point of 154°C, and a density of 0.90.
fj/cm3, MI 25g/10min ethylene-propylene random copolymer 60% by weight, melting point 109°C,
It is a blend of 40% by weight of low density polyethylene with a density of 0.915 g/cm3 and a M of 112 g/10 min.

The portion of the inner layer 23C that extends in the machine direction, ie, the extrusion direction, through the tab 23x contains a foaming agent (for example, 5.0 parts of azodicardate/Sium per 100 parts of resin) and is foamable and heat-sealable. It is a layer of a synthetic resin 26.

The container body 22 is sealed by heat-sealing the lid portion 23 to the flange portion 22a to form a heat-sealed portion 25. The heat-sealing strength of the heat-sealing part 25 is in the case of the resin composition exemplified above, and the heat-sealing conditions are 11,200°C x 2 seconds, and the pressing force is 2 kg/cm.
”, 1.21 kg/l, 5 m, and the heat seal part 2 can be relatively easily removed by hand, except when initially opened.
5 can be torn off.

A ring-shaped metal foil layer 27 (for example, 20μ thick
m iron foil) is attached. The portion 27a of the metal foil layer 27 facing the knob tab 23x has a relatively narrow width (for example, a width of 1
．． 0 mm), and the other portion 27b is relatively wide, so that when the sealed container 21 is placed in a high-frequency electric field, the resistance loss due to the induced current circulating in the metal foil layer 27 is reduced by the narrow portion. 27a, so that the narrow portion 27a is heated particularly high, and the foamable heat-sealing resin 26 that is in contact therewith is foamed. That is, the narrow portion 27a becomes a heat generating layer. A conductive coating layer may be provided instead of the metal foil layer 27. Further, the heat generating layer may be composed of a magnetic coating layer or a conductive (aluminum, tin oxide, etc.) vapor deposited layer (which heats up due to discharge).

Figure 8 shows the sealed container 21 placed in the microwave and the contents 4.
27) When taken out of the microwave oven after being heated, only the layer of the foamable heat-sealable resin 26 of the heat-sealable portion 25 facing the tab 23x is foamed. The foamed resin layer 26' is large.

Therefore, initial opening can be easily performed.

(Effects of the Invention) Even in the case of a sealed container with high heat-sealing strength, the sealed container of the present invention can be obtained by forming a layer of foamable heat-sealing resin preferably along the entire circumference of the heat-sealing part. This has the effect that the package can be easily opened by peeling off the heat-sealed portion after heating in a microwave oven.

Furthermore, in the case of a sealed container with low heat-seal strength, the sealed container of the present invention is preferably provided with a layer of foamable heat-sealable resin locally along a portion of the heat-sealed portion facing the tab. This has the effect that the initial peeling off of the heat-sealed portion after heating in a microwave oven can be easily performed.

[Brief explanation of the drawing]

Fig. 1 is a plan view of a sealed container according to the first embodiment of the present invention, Fig. 2 is a vertical sectional view taken along the line The second part of the sealed container shown in Figure 1
FIG. 4 is a longitudinal sectional view of a main part of the sealed container according to the second embodiment of the present invention, and FIG. 5 is a longitudinal sectional view of the sealed container shown in FIG. Main part longitudinal sectional view, No. 6
The figure is a plan view of a sealed container according to a third embodiment of the present invention, FIG. 7 is a vertical sectional view taken along the line ■-■ in FIG. 6, and FIG. FIG. 7 is a vertical cross-sectional view of the sealed container shown in FIG. 7, corresponding to FIG. 1.11.21... Sealed container, 2, 22... Container body, 3, 23... Lid, 3b, 23c... Inner layer,
5゜25... Heat sealing part, 6.26... Foaming o heat sealing resin, 7.27a... Heat generating layer. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) In a sealed container in which the container body is heat-sealed with a lid, the portion of the inner layer of the lid that corresponds to the heat-sealed portion is made of foamable heat-sealable resin over the entire circumference or locally. , on the lid or container body,
Opposite or facing the foamable heat-sealable resin layer,
1. A sealed container comprising a heat generating layer capable of foaming the foamable heat-sealable resin by increasing the temperature in a high-frequency electric field.