JPH02268932A - Heat sealing method for sealed can - Google Patents

Abstract

PURPOSE:To improve a sealing strength by using a combined sheet of a synthetic resin and aluminum foil as a material for cover and heat-sealing on a can body of the shape that the upper part of can barrel is inclined inward. CONSTITUTION:The upper part of can barrel metallic or plastic can is inclined inward. It is desirable that the length of the inclined face is above about 5mm. It is desirable that the inclined angle theta is 5 deg.-10 deg.. As the material for cover, the combined sheet of a thermo plastic resin and the aluminum foil is previously formed by matching itself to the shape of the sealing part of can and a heat sealing is performed with a sealing head after the can to be sealed is covered with it. The heat-sealing strength is very high in comparison with a conventional sealed can by heat-sealing. The can has easy-peel ability and is safe owing to the combined material of aluminum foil even when the can is opened.

Description

Detailed Description of the Invention [Industrial Application Field J] The present invention relates to a heat sealing method for packaging sealed cans for products such as seaweed, tea, instant coffee, etc. that require packaging that does not come in contact with moisture or oxygen. This invention relates to a heat sealing method for sealed cans that can withstand internal pressure fluctuations and have easy beer properties.

[Conventional technology] Conventionally 1. Metal cans, etc., have been used to preserve foods for long periods of time. In this case, the common sealing method is to double-seal the can body and lid. This canned food can withstand long-term storage and has excellent oxygen barrier properties, but a can opener is required to open it, which can sometimes be a problem.

As a countermeasure to this problem, canned goods with pull-top lids that have an easy-to-open function have been developed. To open this can, you can open the mouth to a predetermined size by pulling your finger and hand, but there is a problem that the scored edge of the lid can injure your hand when doing so. safe and
There was a desire to develop a can with good sealing properties.

On the other hand, there are also packaging containers on the market in which a composite material of aluminum foil and plastic is heat-sealed to the can as a lid material. In this case, an oxygen absorber or dehumidifier is placed inside the container to maintain the quality of the contents. Alternatively, the air in these packaging containers is often replaced with nitrogen gas, etc. Due to the reduced pressure inside the container, or due to temperature changes or differences in internal and external pressure when taken to high altitudes, heat sealing may occur. Although it is easy to tear and has excellent lightness and easy-to-be-sealed packaging as a simple sealed package, the sealing performance is still insufficient and there are still points to be improved.

[Problem to be Solved by the Invention J] The present invention is a simple sealed package made by heat-sealing an aluminum foil composite material, but it is not suitable for use in a reduced pressure state containing an oxygen absorber or dehumidifier, or in a large temperature rise or in a high place. The present invention relates to a heat-sealing method for cans that is lightweight and easy to brew by heat-sealing, which prevents the seal from breaking due to the pressure difference between the inside and outside of the container when the can is brought to the store.

[Means for solving the problem J The upper part of the can sealed by the conventional heat sealing method is
As shown in the figure, there is a can top at the top of the upright can body, and an aluminum foil composite lid is heat-sealed to this, but the radius of the sealed top part is small.
Therefore, the area to be heat-sealed had to be small. For this reason, when a pressure difference occurs between the inside of the can and the outside world, the seal part is naturally pulled inward, but because the seal area is small, this resistance is small (and the rate of leakage naturally has to be high). .

The present inventors have conducted various studies to improve this drawback and have completed the present invention.

That is, the present invention uses a composite sheet made of a synthetic resin film and aluminum foil as a 1M material, and is a method of heat-sealing a can body with the upper part of the can body inclined inward.In particular, the composite sheet is used as a lid material. A method of sealing cans that involves pre-shaping the top and body of the can to be sealed, and crimping this to the can body with a seal head that has the same shape as the radius of the can top and the slope of the can body. This is a heat sealing method.

The composite sheet is two-wheel stretched film/aluminum r?, which is used as a normal lid material. 3/ It may be an adhesive resin, and in some cases, paper may be laminated on the surface to improve printability, or aluminum foil may be made into two or more layers, a synthetic resin film may be sandwiched between them, or aluminum foil may be used. It is possible to laminate a two-wheeled stretched film between the adhesive resins, and it may be selected as appropriate depending on the purpose and use.

As the biaxially stretched film, polyester, polypolypropylene, polyamide, etc. can be used, and polyester is particularly well-balanced in terms of strength, price, heat resistance, etc. There is no need to limit the thickness of the film used, but
Approximately 6 to 35 μm is reasonable.

Since aluminum foil only needs to be bent when heat-sealing, one layer is considered sufficient since pinholes are unlikely to occur due to heat-sealing, but laminating two layers can further prevent pinholes and reduce costs. This will be decided based on the balance between the amount and the nature of the contents.

As the adhesive resin, a resin with good adhesion to metal must be selected. In this case, it is more preferable to pre-treat the adhesive surface of the can with a silane coupling agent, a titanium coupling agent, etc.

As adhesive resins, thermoplastic resins such as polyethylene, polyolefins such as polypropylene, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers,
So-called hot melt such as ethylene-acrylic acid copolymer, chlorinated polypropylene, non-grade copolymerized nylon, saturated amorphous polyester, etc., or a mixture thereof, or a resin layer such as polyethylene between it and aluminum foil can be used. Sandwich and stack. The thickness is 10 to 200 μm, preferably 50 μm to 80 μm, excluding the aluminum foil.

Such a composite sheet is formed in advance to match the shape of the sealing part of the can, and after covering the can to be sealed,
Heat sealing is performed using a seal head.

On the other hand, for cans made of metal or plastic, the upper part of the can body is slanted inward, and the tip of the can body is either a can top with a small 7-hole or a cut-off can (no need to process the cross section). ).

The length of this slope varies depending on the size of the can, contents to be packaged, reduced pressure or expected differential pressure, but is usually 3 mm.
By changing the structure of the can, which only needs to be 1 to 2 mm, the sealing surface can be changed from just the can top to a part of the can body. Since the seal area can be increased all at once from 3 mm or more to 10 to 15 mm depending on the size of the can, the seal strength can be significantly increased.

In this case, since the inclination angle θ (FIG. 2 (4)) is also related to the volume of the can, it is sufficient if it is about 1° to 20″, preferably about 5″ to IO°. Furthermore, if the sealed portion is slightly recessed, the sealed portion will not protrude from the surface of the can, which will prevent it from getting caught and peeled off during work such as stacking.

In this way, since the top part is made slightly smaller than the bottom part of the cans, when stacking cans, the seaming part of the can bottom part fits into the sloping part, so cans can be stacked more stably than conventional cans.

Furthermore, this inclination prevents the trouble of the can being stuck to the seal head during the heat-sealing process and preventing the sealing of the next can, making it possible to speed up the heat-sealing process, which is effective in mass production. There is.

As described above, according to the present invention, packaging that can completely block the effects of moisture, oxygen, light, etc. is possible even by using an inexpensive aluminum foil composite material.

Hereinafter, a more specific explanation will be given with reference to Examples.

[Example J As a lid material, an aluminum foil composite material of 70 μm of biaxially oriented polyethylene terephthalate and 1 layer of vinyl acetate copolymer was used, and a first plate with an inclination angle of 7°, a slope length of 5 mm, and a diameter of 75 mm was used.
It was attached to an epoxy resin coated can as shown in the figure.

Heat sealing conditions are 200℃, '70Kg/can, 1, 5
Seconds.

In this case, we covered the can body with a lid that had been molded in advance to match the shape of the seal part and performed heat sealing, but we were able to completely eliminate the idle time of the seal head.
There were also no seal failures.

Under exactly the same conditions as this, a normal 75m
The adhesive was bonded to a mφ epoxy resin coated can, and the strength of the heat seal was compared.

At this time, a can got stuck to the seal head twice during one day's operation, causing problems in the process.

The results are shown in Table 1.

Table 1 Sealing performance after heat sealing When the lids were peeled off by hand, both had good easy beer properties, although there was a difference in strength.

By making the concavity of the seal head slightly larger than the radius of the can top, we were able to eliminate the problem of the can sticking to the seal head, but we observed a decrease in adhesive strength.

[Effects] When employing the method of heat sealing a sealed can according to the present invention.

ii1 The material used is an aluminum foil composite material, which can reduce costs.

(ii) It has easy beer properties and is safe even when opened because it is made of aluminum foil composite material.

(iii) Barrier properties against light, gas, etc. are the same as all-metal cans.

(iv l The heat sealing strength is much higher than that of conventional heat seal sealed cans. (Leaks do not occur even when the pressure is reduced.) fVl When heat sealing, the can does not stick to the seal head, so the seal There are fewer problems in the process.

(vi) Since the lid material is molded in advance to match the can body, there are fewer mistakes in heat sealing and fewer troubles.

This is a layered method and can provide a sealed can that can be used for packaging a wide variety of products.

[Brief explanation of drawings]

FIG. 1 shows four embodiments of the present invention. Figure 2 (1) shows the heat sealing situation of the present invention. (2) shows the situation of positive pressure inside the can, and (3) shows the situation of reduced pressure inside the can.
(4) indicates the inclination angle of the upper part of the can body, respectively. Figure 3 shows the conventional heat sealing situation, positive pressure inside the can, and reduced pressure inside the can.

Claims (2)

[Claims] (1) A method for heat-sealing a sealed can, which is characterized by using a composite sheet made of a synthetic resin film and aluminum foil as a lid material and heat-sealing the top of the can body to a can body having an inwardly inclined shape. (2) Claim No. 1, wherein the composite sheet made of synthetic resin film and aluminum foil used as the lid material is pre-formed to match the shape of the seal head, which has a shape that follows the can top and can body. Heat-sealing method for sealed cans in Section 1.