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US 5,294,398 AGranted
Low temperature heat shrinkable film and process for producing the same
AssigneeShowa Denko K.K.
InventorsToshio Taka, Kihachi Shishido, Takuo Ohkubo
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AssigneeShowa Denko K.K.
InventorsToshio Taka, Kihachi Shishido, Takuo Ohkubo
Estimating the term…
The present invention provides a low temperature heat shrinkable film comprising a linear low density polyethylene resin having a short branched chain and a density of 0.935 g/cm.sup.3, and whose film properties are such that the haze value is 5% or less, the heat shrinkages at 90.degree. C. in the M and T directions are 30% or more and 5% or less, respectively , and the shrinkage stress at 90.degree. C. in the M direction is 300 g/mm.sup.2 or more. This transparent film having an excellent low temperature heat shrinkability can be produced by drawing a film of the above-mentioned polyethylene resin between two rolls having a diameter of 200 mm or less at an air gap of 10 mm or less at a draw ratio of 3.0 to 6.0. Further, an inflation film having a multilayer structure can be obtained by press bonding or press bonding and drawing a plurality of films comprising the above-mentioned polyethylene resin. This laminate film has an excellent transparency and strength, and has a uniform film thickness.
A process for producing a low temperature heat shrinkage film, comprising:
Dependencies are inferred from the claim text.
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From the US filing history. Foreign family members aren’t listed.
Manufacture of articles or shaped materials containing macromolecular substances: manufacture of films or sheets
Of plates or sheets: using multilayered plates or sheets
Uniaxial, e.g. oblique: parallel with the direction of feed
Shaping by liberation of internal stresses; Making preforms having internal stresses; Apparatus therefor: characterised by the choice of material
Term ended 15 Mar 2011 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
The present invention relates a low temperature heat shrinkable film and a process for producing the same. More specifically, the present invention relates to a low temperature heat shrinkable film which has high heat shrinkability at low temperature and high shrinkage stress and which has a remarkably excellent transparency as compared with conventional shrink films, and process for producing such a film. Moreover, the present invention relates to an inflation film consisting of a multilayer structure of a single resin.
Conventionally, there have been used low temperature heat shrinkable films exhibiting a low temperature shrinkability at 90.degree. to 100.degree. C. of 30 to 50% which are obtained by drawing a low density polyethylene resin (LDPE) having a long branched chain usually called high-pressure polyethylene, or a blend of the low density polyethylene resin with an ethylene-vinyl acetate copolymer, a butene type rubber or the like at a draw ratio of 1.5 to 3.0.
However, these films are disadvantageous in that, because the LDPE having a number of long branched chains has a remarkably inferior stretchability, it can be drawn only at a low draw ratio and it cannot be uniformly drawn, with the result that unevenness in drawing is generated in the resultant film and unevenness in thickness or jetting are generated in the film due to the internal strain remaining in the film. Therefore, there are serious problems with regard to the productivity of these films. Further, these films have another disadvantage in that they cannot exhibit a display effect to a sufficient degree because the haze value indicative of the transparency of the film, which is a very important factor in a packaging film, is 5% or more, typically about 10%.
The present invention will now be explained by examples and comparative examples. It is to be understood that these examples by no means limit the scope of the present invention. In the examples and comparative examples, the used physical properties were determined by the following methods.
1) Haze value (%): ASTMD-1003
2) Impact strength (kg/mm): pendulum type, impactor=1 inch hemisphere