JPS6111187B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cushioning plastic film. More specifically, the present invention relates to a method for producing a plastic film having crepe-like wrinkles and significantly improved mechanical and thermal cushioning properties.

A first object of the present invention is to provide a method of manufacturing a plastic film for use in cushioning packaging, which is useful for protecting contents from impact forces, and can be manufactured at low cost.

A second object of the present invention is to provide a method for producing a plastic film with excellent heat insulation and heat retention properties.

In recent years, foamed polystyrene sheets, foamed polyethylene sheets, etc. have been developed for uses such as cushioning packaging materials and insulation materials. Widely used in applications that require heat insulation. However, all of these known foamed plastic sheets have a structure that contains air bubbles inside the sheet, so the sheet itself is bulky.
When used in packaging, there are drawbacks such as the appearance after packaging is not necessarily desirable, and there is also the drawback that the foam sheet must be made thicker in order to improve its heat insulation properties.

In addition to foam sheets as cushioning packaging sheets,
It consists of a laminated structure of two sheets, and by vacuum forming the entire surface of the sheet with a fine concave shape on one side and heat sealing the top surface with the other sheet, the concave shape is formed. Seats with a structure in which air is trapped inside the cavity of the seat are widely used.

However, this sheet has the disadvantage that the manufacturing process is complicated and the price of the sheet is high.
Another drawback is that the sheet becomes bulky.

Paper, cloth, etc. have traditionally been used for cushioning packaging, but paper and cloth cannot always provide sufficient cushioning properties.

In view of the current situation, the present inventors have developed a plastic film that can be made through a simple manufacturing process, can be used for cushioning packaging, heat insulation, etc., and has an excellent texture. As a result of various studies, we found that some or all of the bubbles in the foamed resin layer burst, forming a network structure, when the foamed resin layer was manufactured using a two-layer coextrusion inflation method of a foamed resin layer and a non-foamed resin layer. They discovered that when a laminated film is reheated and shrunk, the film forms a crepe-like structure, and further research led to the completion of the present invention.

The method for producing a cushioning plastic film of the present invention consists of at least two layers, a foamed resin layer and a non-foamed resin layer, and the foamed resin layer is the outermost layer, and the cells in the foamed resin layer are flattened by stretching orientation. Further, the laminated plastic film in which some or all of the bubbles have ruptured and the foamed resin layer forms a network structure is heated and shrunk to form wrinkles over the entire surface of the film. It is characterized by increasing the apparent bulk of.

The laminated plastic film is preferably produced by a coextrusion biaxial stretching method, particularly a coextrusion inflation method. When the laminated plastic film is manufactured by the inflation method, when the laminated tube in a molten state is extruded from a cylindrical lamination die and exits from the die lip, each bubble increases in the foamed resin layer. At the same time, the tube is expanded due to the pressure difference between the inside and outside of the tube, and is also stretched in the drawing direction to burst some or all of the cells in the foamed resin layer, thereby forming a foamed resin layer adjacent to the non-foamed resin layer. to form a network structure.

In this case, each cell in the foamed resin layer is sufficiently stretched to make it flat, and then some or all of the cells are ruptured. In known foam sheets, which are aggregates of microscopic bubbles that have not burst, even if they are reheated and shrunk, wrinkles are not sufficiently generated, and uniform wrinkles are observed over the entire surface of the sheet. I can't.

When manufacturing a laminated plastic film by the inflation method, in order to make the mesh size sufficiently large, it is desirable to reach a blow ratio of 3 or more and to make the take-up ratio similarly high. In order to produce a film with a large heat shrinkage rate and a high wrinkle forming ability by the air-cooled inflation method, it is preferable that the final blow ratio is 4 or more and the take-off ratio is 4 or more.

The main components of the foamed resin layer are polypropylene, low density polyethylene, high density polyethylene, ethylene-vinyl acetate copolymer resin, ionomer resin,
Styrene resin and the like are preferred. The foaming method for the foamed resin layer is not particularly limited, but preferred chemical foaming agents include sodium bicarbonate, azodicarbonamide, p-toluenesulfonyl semicarbazide, and trihydrazinotriazine.

The foaming agent is preferably contained in the resin composition in an amount of 0.1 to 2% by weight. Ordinary foaming agent turned into resin pellets
After adding about 0.3 to 1% and dry blending,
Preferably, it is charged into the hopper of an extruder. In addition, a high-concentration blowing agent is added to the resin and pre-kneaded in an extruder to produce a masterbatch, which is mixed with regular resin pellets during film production and used in the extruder of the coextrusion and stretching equipment for film production. It may be supplied.

The non-foamed resin layer is made of polypropylene, low-density polyethylene, high-density polyethylene, ionomer resin, ethylene-vinyl acetate copolymer resin, polybutadiene resin, vinyl chloride resin, etc., and polyethylene, polypropylene, etc. are particularly preferred.

The laminated plastic film, in which the foamed resin layer formed by the coextrusion stretching method forms a network structure, is heated again to shrink, resulting in uneven heat shrinkage between the foamed resin layer and the non-foamed resin layer. The key point of the method for producing a cushioning plastic film of the present invention is to form wrinkles and increase the apparent bulk of the film.

The thickness of the non-foamed resin layer of this laminated plastic film is preferably about 5μ to 100μ, and the thickness of the foamed resin layer is preferably about 20μ to 300μ in terms of the height of the unevenness of the network structure. The network structure of the foamed resin layer of the film preferably has an average diameter of about 1 mm to 10 mm along the film surface.

When a film having such a network structure is manufactured by a method such as a coextrusion inflation method, a heat-shrinkable film can be obtained. Therefore, when this film is reheated, shrinkage gradually occurs within the film plane, and the film area becomes smaller. In known plastic films, the area of the film decreases due to heat shrinkage, and the thickness of the film increases accordingly, but no particularly noticeable wrinkles are observed.

However, when a laminated plastic film in which the foamed resin layer forms a network structure is reheated to cause shrinkage, the heat shrinkability of the network-shaped foamed resin layer and the flat non-foamed resin layer adjacent to it change. Because of the difference in heat shrinkability, uniform shrinkage does not occur while the film is in a flat state, and clear wrinkles are formed over the entire surface of the film. The appearance of wrinkles increases the apparent bulk of the film, giving the film significant mechanical and thermal cushioning properties.

When the foamed resin layer thermally shrinks to a greater extent than the non-foamed resin layer, the inner flat portion of the film surrounded by the mesh swells in the vertical direction from the mesh surface, creating significant unevenness over the entire surface of the film. In this case, since the structure, shape, dimensions, etc. of the mesh are irregular for each mesh unit, the unevenness caused by thermal contraction is also irregular in size and shape when viewed individually.

However, if the heat treatment temperature of the film is kept constant, the film as a whole will have wrinkles with a uniform texture over the entire surface, making it possible to produce a film with uniform bulk and high cushioning properties.

The heating temperature of the film to generate wrinkles varies depending on the type of resin in the foamed resin layer and non-foamed resin layer and the stretching conditions of the film, but it is desirable to heat the film to at least the stretching temperature of the film. .

By the method of the present invention, a bulky and highly cushioning film with an apparent thickness of approximately 1 mm to 10 mm can be produced from a laminated film having a flat network structure with a thickness of approximately 100 μm.

Furthermore, by overlapping two or more films having such a structure, the cushioning properties are significantly improved.

When manufacturing a cushioning film, it is preferable that the periphery of the original laminated plastic film is not fixed, but is heated and shrunk in a relaxed state.
If the periphery of the film is tightly fixed to cause sufficient heat shrinkage, the film will shrink while remaining flat, and the wrinkles necessary for cushioning properties will not be sufficiently generated.

By heating the film while loosening it appropriately, it is possible to produce a cushioning film in which wrinkles are sufficiently generated and the film as a whole is less warped or twisted.

The heating temperature of the raw film to form wrinkles due to shrinkage is not particularly limited, but wrinkles will be sufficiently generated if the raw film is shrunk in a temperature range equivalent to the heat shrinkage temperature of a plastic film manufactured by a conventional method. Naturally, the outer circumferential dimension of the film with wrinkles and increased bulk is 5% to 50% of the original film dimension.
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Although the film produced by the method of the present invention is a thin plastic film, it has rich cushioning properties due to the apparent bulk caused by wrinkles, and is used for cushioning packaging and interior decoration of confectionery boxes. Alternatively, it can be used for exterior packaging, and even for individual packaging of easily damaged contents.

This film also has thermal buffering properties and can be used for various purposes as insulation and heat retention.

Since this film also has excellent sound insulation properties, it is also effective to use it as a sound insulation material by stacking multiple layers of this film.

Examples will be described below.

Example The foamed resin layer contains 1.0 parts by weight of azodicarbonamide as a foaming agent for 100 parts by weight of copolymerized polypropylene resin (Sumitomo Noblen, manufactured by Sumitomo Chemical Co., Ltd.)
A laminated plastic film was produced by a coextrusion inflation method, and the non-foamed resin layer was made of a low-density polyethylene resin (Sumikasen, manufactured by Sumitomo Chemical Co., Ltd.). Most of the bubbles in the foamed resin layer of this film had burst, and the foamed resin layer had formed an uneven network structure. The thickness of the non-foamed resin layer of this film was 50μ, the height of the unevenness of the network of the foamed resin layer was about 100μ on average, and the apparent thickness of the entire film including the two layers was about 150μ. . The mesh cells had a diameter of about 1 mm to 3 mm along the film surface. Each mesh cell has a relatively circular shape, and outside the period of each mesh, 10mm
A high-order network structure was formed by repeating high-density areas and low-density areas of the foamed resin layer at a period of 30 mm.

The film was passed through an infrared heating tunnel with its periphery loosened, and heated to a maximum temperature of about 120°C, allowing the film to freely shrink. Due to this shrinkage, uniform wrinkles were formed over the entire surface of the film. The height of the unevenness due to wrinkles was about 5 mm on average, and the period of the unevenness was about 10 mm to 15 mm.

This film has good cushioning properties and a texture similar to paper. When this was used for packaging articles, the impact resistance of the contents was significantly increased.

Furthermore, when this film was wrapped twice around a glass top, the lower part of the glass top filled with boiling water could be held in the hand for a long time, confirming that this film had excellent heat insulation and heat retention properties. .

Claims (1)

[Claims] 1 Consisting of at least two layers, a foamed resin layer and a non-foamed resin layer, the foamed resin layer is the outermost layer, and the cells in the foamed resin layer become flattened due to stretching orientation, and some or all of the cells burst. A laminated plastic film in which a foamed resin layer forms a network structure is heated and shrunk to form wrinkles over the entire surface of the film, thereby increasing the apparent bulk of the film. A method for producing a cushioning plastic film.