JPS5933305B2 - Packaging film that provides an easy-to-open heat seal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a packaging film that provides an easy-open heat seal.

The film of the present invention can be sealed in a liquid-filled state when packaging and heat-sealing an article, and after sealing, the package can be sterilized with hot water, and furthermore, it is easy to open. Polystyrene resins are generally transparent, have good moldability, and are inexpensive, so they are useful as materials for containers for various articles, especially processed foods, and containers manufactured by injection molding, blow molding, film vacuum forming, etc. is widely used.

However, polystyrene has poor compatibility with other resins, so the only way to seal the containers made from this is by completely fusing similar materials together, or by using a hot melt or hot tracker. .

A completely fused seal allows the contents to be sterilized by immersing the container in hot water, which is advantageous in terms of improving the shelf life of the food; however, when attempting to remove the contents, the lid must be removed. I have to cut it open.

This requires a knife or the like, which is not only troublesome but also dangerous, and there is a risk that the contents may splatter when the package is opened. On the other hand, when adhesives such as hot melt or hot glue are used, opening is easy, but the seal is not heat resistant and cannot be sterilized with hot water after filling.

Therefore, when used for food packaging, it cannot be distributed at room temperature and must be distributed in a tilted state. Furthermore, there is a risk of low-temperature embrittlement in the materials used in hot melts, and the possibility of seal failure due to impact at low temperatures must also be taken into consideration. For this reason, there has been a need for a packaging film made of polystyrene resin that allows the contents to be sterilized with hot water after sealing, and that provides a heat seal that is easy to open.

In order to meet these demands, the present inventors pursued a means to control the degree of fusion when heat-sealing polystyrene resin, and to achieve easy opening while maintaining hot water resistance. As a result, polystyrene resin The present invention was achieved by discovering that a material rubber-modified with PROTSUCK SBR exhibits these characteristics. The packaging film that provides easy-to-open heat sealing of the present invention is the above-mentioned PROTSU SBR.
A heat-sealing layer made of rubber-modified polystyrene, sandwiched with a buffer layer made of a flexible plastic material, and laminated with a reinforcing layer made of a strong plastic material or metal foil. It is.

The rubber-modified polystyrene mentioned above is
A product manufactured by the method described in Japanese Patent No. 32773 is used.

The process consists of melt mixing 50 to 95 parts by weight of polystyrene and 5 to 5 parts by weight of PROC SBR in the presence of an organic substance that dissolves or swells PROC SBR. Protsuk SBR contains 10 to 50% by weight of styrene.
, preferably 20-45% by weight and butadiene or isoprene 90-50% by weight, preferably 80-55% by weight? Preferably, the copolymer has the structure s-B-S (where S represents a styrene polymer protester, and B represents a butadiene or isoprene polymer protease, respectively). has been done. Regarding the degree of rubber modification of polystyrene, when it is used as a material for the packaging film of the present invention, approximately the same ratio as described above is suitable.

That is, the rubber content in the rubber-modified polystyrene is 5% by weight.
Otherwise, the deformation effect will be insufficient and an easy-to-open heat seal will not be obtained. On the other hand, if the rubber content reaches 50% by weight, the rubber content will be excessive and will cause blocking and the characteristics of polystyrene resin. is lost. The effect of rubber modification also varies depending on the proportion of "B", that is, butadiene or isoprene polymer block, in the rubber, but a suitable polystyrene/block SBR ratio is 90 to 60/
It is within the range of 10-40. The above-mentioned prior art method for producing rubber-modified polystyrene is an invention made with the intention of providing a polystyrene material that can produce molded products with excellent transparency, and is disclosed in Japanese Patent Publication No. 52-32773. There is no mention of heat sealing properties.

As for the reason why such materials can be easily opened and heat-sealed, the present inventors have found that the B polymer block portion in the block copolymer rubber acts as an inhibitor against fusion, and the heat-seal strength is moderately increased. It is interpreted as weakening the The heat-sealing rubber-modified polystyrene layer described above is laminated with a reinforcing layer of tough plastic material or metal foil, with a buffer layer of flexible plastic material sandwiched between the two.

The reinforcing layer compensates for the disadvantage that rubber-modified polystyrene is somewhat hard and easily breaks when used as a single-layer film, and examples of specific plastic materials include stretched polyethylene terephthalate, nylon, or polypropylene.

If the material is to be drawn and used, unstretched nylon or polypropylene would be appropriate. Aluminum foil can be said to be a practical metal foil. The buffer layer functions to improve the contact of the laminated film and ensure uniformity of heat sealing, and this effect is particularly effective when the film of the present invention is used as a lid material for a container body made by injection molding or the like. has great significance.

Typical materials include polyethylene, polypropylene, and ethylene monovinyl acetate copolymer. The thicknesses of the above three layers can be chosen arbitrarily, but the most common combinations will be found within the ranges below.

Lamination of the three layers can be carried out according to conventional techniques using conventional laminating equipment.

As long as the layer of rubber-modified polystyrene for heat sealing is exposed on one side, one or more layers of another material may be added between each layer or on top of the reinforcing layer as desired. There is no problem even if it is laminated. Further, appropriate printing may be applied to the front or back surface of the reinforcing layer prior to lamination or after lamination. Polystyrene rubber-modified with PROTSUBR can be heat-sealed to the same material or to other styrenic resins, such as GP polystyrene, Hl polystyrene, etc., and the seal is easy to open.

Therefore, the packaging film of the present invention can be used by itself to form a packaging bag, or can be used in combination with other styrene resin container parts.

A preferred example of the latter is one in which the film of the present invention is combined as a lid material with a cup-shaped container body made by injection molding of GP polystyrene, and this is a representative example of the use of the pool t of the present invention. This can be said to be a perfect example. Heat sealing of the packaging film of the present invention can be carried out in the same manner as conventional equipment, using existing equipment such as widely used simple sealers, filling and sealing machines, and tray sealers.

Seal conditions such as temperature and pressure should be determined based on the materials used and the strength required of the seal. Appropriate sealing strength varies depending on the case, but generally speaking, the minimum adhesive strength is 500 to 7009/15m77 as measured by the method specified in JISP8ll3! Up to 1000~12009/15m7! within the range of t. The sealing temperature that provides such strength is usually 170~
The temperature is around 200°C, especially around 180-190°C. The packaging film of the present invention can be heat-sealed as described above, and unlike hot-melt adhesives, this seal can withstand the temperature of hot water and has no risk of low-temperature embrittlement.

To open the package, there is no need for a knife because it is not a completely fused seal, and it can be easily opened by simply applying an appropriate amount of force to the seal and pulling it apart. Therefore, it can be used to manufacture all kinds of packaging containers that require easy-opening properties, but is especially suitable for foods that are heat sterilized after filling, such as jelly, pudding, jam, yokan, kuzu mochi, pickles, tofu, mochi, etc. It is of great significance when used as a material for containers. Example 80 parts by weight of polystyrene G-15 (product of Nippon Steel Chemical Industry Co., Ltd.), which is GP polystyrene, and 40% styrene.
20 parts by weight of Tabprene (manufactured by Asahi Kasei Kogyo Co., Ltd.), which is an S-B-S type SBR, was kneaded with 4 parts by weight of butyl stearate and extruded through a T-die to form a film with a thickness of 80 μm.

This film was laminated with a reinforcing layer of polyethylene terephthalate having a thickness of 12μ with a buffer layer of polyethylene having a thickness of 25μ sandwiched therebetween to produce a packaging film according to the present invention.

On the other hand, another styrenic resin film was made by laminating a 60 μm thick film of HI polystyrene Haren (product of Toyo Kagaku Co., Ltd.) with the same polyethylene terephthalate film as above.

These two types of films were heat-sealed at various temperatures between 100 and 240°C, immersed in hot water at 80°C for 30 minutes, and then their adhesive strength was measured according to the method specified in JISP8ll3.

As a result, the easy-open heat seal strength is approximately 900 to 12
It was found that the suitable temperature for sealing was in the range of about 170 to 200°C, which gave 0.009/15 mm. A flower cup container body made by injection molding of GP polystyrene is filled with molten Japanese parsley using a filling and sealing machine, and the above three-layer packaging film of the present invention is supplied as a lid, and while squeezing the overflow, I heat sealed it in a liquid-filled state, trimmed it, and cut it out.

After sterilization in hot water and cooling, the lid of this packaged jelly could be easily peeled off.

Claims (1)

[Scope of Claims] 1 Polystyrene that has been rubber-modified by blending block SBR, and the rubber modification is carried out by melt-mixing the block SBR in the presence of an organic substance that dissolves or swells the block SBR. layer for heat sealing,
A packaging film that provides an easy-to-open heat seal, consisting of a buffer layer made of a flexible plastic material and laminated with a reinforcing layer made of a strong plastic material or metal foil. 2. The rubber-modified polystyrene forming the layer for heat sealing contains 95 to 50 parts by weight of polystyrene, preferably 90 to 60 parts by weight, 10 to 50 parts by weight of styrene,
Preferably, 5 to 50 parts by weight, preferably 10 to 40 parts by weight of block SBR, which is a block copolymer of 20 to 45 weight % and butadiene or isoprene 90 to 50 weight %, preferably 80 to 55 weight %, are blended. The packaging film according to claim 1. 3. The packaging film of claim 1, wherein the flexible plastic material forming the buffer layer is selected from polyethylene, polypropylene and ethylene-vinyl acetate copolymers. 4. The packaging film according to claim 1, wherein the tough plastic material forming the reinforcing layer is stretched or unstretched polyethylene terephthalate, nylon, or polypropylene. 5. The packaging film according to claim 1, wherein the reinforcing layer has a desired print.