Biaxially stretched polyethylene film

Details Biaxially stretched polyethylene film Biaxially stretched polyethylene film

1991-03-27

1994-04-26

Buffalow, Edith

Stock material or miscellaneous articles

Structurally defined web or sheet

Physical dimension specified

428516, 428910, B32B 2708

Patent

active

053065492

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to packaging materials. More particularly, the present invention relates to a polyethylene film for packaging prepared from a specific ethylene copolymer as a main component, which has a little variation in thickness, and a single layer or multi-layer biaxially stretched polyethylene film which is caused oriented by stretching under specific conditions, which is excellent in stretchability, shrinkability and restoration from deformation; and a preparation process thereof.
2. Background Art
As a conventional heat shrinkable polyethylene film, there have been known films prepared by tubular biaxial stretching and applicable to shrink packaging at a low temperature lower than a melting point, which have been found out by the present inventors, and put on the market.
Further, the present inventors have found out heat shrinkable polyethylene films improved in stability of a stretched tube and uniformity of stretching by specifying polyethylene copolymers (Japanese unexamined Patent Publication No. 62-201229).
On the other hand, recently, as a film for packaging foods such as meats, sea foods, vegetables, fruits and daily dishes, stretchable films have been increased with the increase of the number and expansion of the scale of supermarkets and convenience stores.
Heretofore, as a heat stretchable film, a film prepared from a plasticized polyvinyl chloride as a raw material has been most widely used, since the film has excellent properties such as excellent transparency and tackiness. The film is, however, disadvantageous in safety, health or environmental pollution. For instance, it is easy to cause the loss of weight or the deterioration of a package object to be packaged because of a large amount of steam permeating through the film, or it is easy to contaminate the a packaged object with the plasticizer which results from the use of a large amount of the plasticizer. In addition, harmful hydrogen chloride gas is generated during the production of the film, melt-cutting of the film in the packaging production process, destruction of the film by fire, and the like.
Therefore, films which can be substitued for the plasticized polyvinyl chloride film have been actively developed in an ethylene resin such as polyethylene or ethylene-vinyl acetate copolymer, a polybutadiene resin, and the like.
Although the films obtained by this invention are improved in stability of the stretched tube and uniformity of stretching and show the effect for improving the thickness variation, films having a less variation in thickness have been desired from the viewpoints of suitability for packaging machine and printability.
Although the polyethylene or polybutadiene resin films as mentioned above have no disadvantages regarding safety, health and the environmental pollution, they are not fully satisfactory as a stretchable film. For instance, a non-stretched low density polyethylene film causes a necking phenomenon where the stretched film has stretched parts and non-stretched parts. Thus the film thickness remarkably varies upon stretching for stretch packaging and the elastic restoration is small, thereby resulting in unacceptable packaged objects. Further, the film strength is poor and the transparency is unsatisfactory. So, in order to improve the strength of the film or give the heat shrinkability to the film, it has been attempted that the film be given a high orientation by biaxial stretching. However, low density polyethylene has technical difficulties such that the film is broken during the processing, therefore, its preparation method is the so-called inflation method. Thus, since the obtained film is not given effective molecular orientation, it is inadequate in strength and shows a heat shrinkability only at high temperatures close to its melting point.
Also, it has been tried to market films prepared from a crystalline 1,2-polybutadiene or ethylene-vinyl acetate copolymer as a main component, to which an antifogging agent or a tackifier are added. However, s

REFERENCES:
patent: 4801652 (1989-01-01), Mizutani et al.
patent: 4837262 (1989-06-01), Jeon et al.

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