Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1987-09-08
1988-04-26
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521143, 521144, C08V 900
Patent
active
047405295
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a foamed shrinkable film with superior heat resistance which is suitable for use as, for example, shrink labels of glass containers of, for example, soft drinks. More particularly, the present invention relates to a heat resistant foamed shrinkable film comprising a composition of (i) an ethylene-propylene block copolymer and (ii) an ethylene-propylene random copolymer and having a foam ratio of 3.0 or less. The film has not only a heat resistance able to withstand 30 minutes heating at 120.degree. C. for sterilization, but also a heat shrinkage property of 30% or more at a temperature of 140.degree. C.
2. Background Art
A conventional heat shrinkable film normally begins to shrink at a temperature of 80.degree. C. to 100.degree. C. and displays a large shrinkage of 30% or more at a temperature of approximately 120.degree. C. to 130.degree. C. However, such a film cannot withstand the high temperatures used for such as retort sterilization, since the material generally used as the film material is polyvinyl chloride (PVC), polystyrene (PS), low density polyethylene (LDPE), and other resins which melt at a temperature of 120.degree. C. or more.
On the other hand, a heat shrinkable film comprised of polypropylene, which has an excellent heat resistance, is in general use, but this film must be treated at a high temperature of 150.degree. C. or more to obtain a heat shrinkage of 30% or more. Further, the film is made of polypropylene resin alone (not a composition), and thus a problem arises in that it has a poor buffering ability and heat resistance. In particular, there is a demand for films which can be shrunk and used as a label for bottles or special containers, and which have heat resistance, buffering ability, and heat insulation properties.
As is well known, shrink labels are comprised of heat shrinkable resin films with a foam ratio of approximately 2 to 3, and, for example, the product name, vendor, is printed on one surface thereof. The film is rolled into a tube, the glass container inserted therethrough, and heat applied to shrink the label and thus closely adhere it to the glass container.
This shrink label has a mechanical buffering effect and heat retention and heat insulation properties, since it is a foamed film, and in particular, is suitable as a packaging material for glass containers containing carbonated beverages and other soft drinks.
However, when such foamed shrinkable films are used for shrink labels, to obtain a sufficient buffering effect and heat retention and insulation, it is necessary to increase the foam ratio. If the foam ratio is increased, however, the surface of the film has a large surface roughness, resulting in a rough surface and a reduction of the print finish, particularly the clarity thereof, thus degrading the aesthetic appearance. Conversely, if the foam ratio is made smaller, to increase the printability, a disadvantage arises in that an insufficient buffering effect and heat retention and insulation are obtained.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is to eliminate the problems in the prior art mentioned above and provide a heat resistant shrinkable film which not only has a heat resistance sufficient to withstand heating for sterilization but also has an excellent buffering effect, and further, a large heat shrinkage of 30% or more at a temperature of 140.degree. C.
Another object of the present invention is to provide a foamed heat shrinkable film having a superior buffering ability and heat retention and insulation, and a superior printability.
According to the present invention, there is provided a heat resistant shrinkable film comprising a composition of (i) 50% to 90% by weight of an ethylene-propylene block copolymer with an ethylene content of 3% to 20% by weight and (ii) 50% to 10% by weight of an ethylene-propylene random copolymer with an ethylene content of 2% to 15% by weight and having a foam ratio of 3.0 or less.
Further, according to the pr
REFERENCES:
patent: 3974237 (1976-08-01), Brumbaugh et al.
patent: 4467061 (1984-08-01), Yamamoto et al.
patent: 4510031 (1985-04-01), Matsumura et al.
patent: 4510292 (1985-04-01), Chiba et al.
patent: 4568608 (1986-02-01), Kuwabara et al.
Hashimoto Akihiro
Okubo Takuo
Shishido Kihachi
Taka Toshio
Yoneda Kazuo
Foelak Morton
Showa Denko Kabushiki Kaisha
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