Shrinkable, stretchable multi-layered film

Details Shrinkable, stretchable multi-layered film Shrinkable, stretchable multi-layered film

1992-07-13

1994-04-05

Buffalow, Edith

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

428349, 428516, 428520, 428518, 428910, B32B 702

Patent

active

053003535

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

The present invention relates to a multi-layered film (oriented and imparted with high strength) for use mainly in a wrapping material field, and its modified film (orientation degree control by heat treatment, crosslink by energy beam or other chemical treatment). More specifically, it relates to an at least monoaxially stretched/oriented, high-strength, multi-layered film excellent in heat resistance, shrinkability and stretchability, which has a layer constitution of at least five layers comprising at least one base layer (SBC layer) mainly containing a specific mixed composition to improve the stretchability, at least one core layer (H layer) composed mainly of at least one hard polymer selected from crystalline polypropylene, crystalline polybutene-1 and crystalline poly-4-methylpentene-1, the core layer being to improve the elastic modulus and heat resistance of the film at least one auxiliary layer (R layer) for the purpose of further synergistically improving the strength of the film, and surface layers (S layers) to improve the optical properties, anti-fogging property and sealability of the film surface.
The film of the present invention can be used not only for shrink wrapping, stretch wrapping and stretch-shrink wrapping but also for skin pack wrapping, tight-contact household wrap, nonshrink wrapping, soft deep-drawn wrapping and the like.


TECHNICAL BACKGROUND

In film wrapping, a variety of wrapping methods taking advantage of the film properties are used. For example, many methods are used such as a method of sealing in a bag form, a method of wrapping by twisting a film, a method of wrapping by heat shrinking (to be referred to as a "shrink method" hereinafter), a tight-contact wrap method typified by Saran Wrap.RTM. (made by Asahi Chemical Industry Co., Ltd.), a stretch wrap method and a skin pack method. Each wrapping method is required to have its own wrapping properties, and in a practical sense, film materials, composition, form and properties are selected suitably for each wrapping method.
Of the above methods, the shrink method uses the heat shrinkability of a preliminarily stretched and oriented film. In this method, an article to be wrapped is preliminarily loosely wrapped by a film, for example, an article is wrapped by sealing, and then the film is allowed to shrink by heating it with hot air, infrared rays, hot water or other heating medium to bring the film into tight contact with the content contained therein. The characteristics of this wrapping are that the appearance of the wrapped article is esthetically good, that the commercial value is improved, that the content quality can be visually and tangibly recognized while the article is kept in a hygienic wrapping, that even an irregularly-formed article and even a plurality of articles can be tightly fixed or wrapped in one wrapping, and that the protection performance for the content against vibration and impact is excellent. Further, as compared with a stretch wrapping method which is popular nowadays in supermarkets and will be described later, the above shrink method characteristically permits an increase in wrapping speed. The shrink method also permits the wrapping of an irregularly formed article which cannot be wrapped esthetically by a stretch wrapping and of an article without any container such as a tray. Moreover, the shrink method characteristically permits the wrapping of various articles more tightly. However, on the other hand, the shrink method has defects in that the film is required to be sufficiently heated until the film becomes shrunken. This would result in the likelihood that the sealing portion would break and that the film would deteriorate after being shrunk (strength and optical properties). On the other hand, conventional shrink films have low stretchability, and would break if stretched, to any large extent. Some conventional shrink films cannot simply be stretched due to too strong of a stress caused by the stretching. Further, these films have almost no self-

REFERENCES:
patent: 4619859 (1986-10-01), Yoshimura

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