Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-09-23
2001-02-27
Thibodeau, Paul (Department: 1773)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S177000, C525S210000, C525S211000, C525S240000, C526S348100, C526S943000, C425S035000, C425SDIG121
Reexamination Certificate
active
06194501
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyolefin film for use in shrink wrapping. More particularly, the present invention is concerned with a film for use in shrink wrapping, which is formed from a material of specified &agr;-olefin/aromatic vinyl compound random copolymer and which has excellent low-temperature shrinkability.
BACKGROUND OF THE INVENTION
Wrapping, in sealed fashion, industrial goods, daily needs, provisions and other items with the use of the property of shrinking, when heated, of a biaxially oriented film of thermoplastic resin, generally known as shrink wrapping, is now widely performed. For example, low density polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride and polyesters are commonly used as materials of the above film for shrink wrapping. However, all the films prepared from these materials do not necessarily exhibit highly satisfactory performance as shrink wrapping films.
For example, a film of low density polyethylene is available at low cost and has high impact strength, so that it is suitable for industrial wrapping. However, the transparency and gloss thereof are not so good and the film has an optimum shrink temperature being 20 to 50° C. higher than that of a soft vinyl chloride film (hereinafter referred to as “PVC film”). Further, the surface hardness thereof is so low that, when goods are piled one upon another, the low density polyethylene film is likely to have flaw and the appearance of wrapped goods is likely to be deteriorated. Therefore, the low density polyethylene film is not suitable for commercial wrapping. On the other hand, the PVC film has such an excellent transparency that the beauty of wrapped goods is enhanced to thereby increase the value thereof. Further, the PVC film has an optimum shrink temperature which is low and broad. Therefore, the performance of the PVC film is one most suited for commercial wrapping. However, the PVC film cannot be used in industrial wrapping because its impact strength, especially, impact strength at low temperature is poor.
Moreover, this film involves various problems such as a problem of food hygiene attributed to a plasticizer contained in the film, a migration of the plasticizer to the wrapped goods, a tendency for film blocking and a difficulty in disposal of the film after use. Thus, substituting polyolefin films therefor is now being studied. Although the polyolefin films are characterized by having high transparency and gloss, possessing nerve and exhibiting high shrinkage stress, they have drawbacks in that their impact strength is low and their optimum shrink temperature is high and narrow. Therefore, a method of lowering the optimum shrink temperature by copolymerizing propylene with a small amount of ethylene has been proposed. However, when the ethylene content is increased, the propylene/ethylene copolymer films tend to stick to each other to thereby suffer from blocking. Further, ethylene is heterogeneously incorporated in the polymer, so that there occur problems such that the transparency of the film is deteriorated. Therefore, the ethylene content of the propylene/ethylene copolymer which can be used in shrink wrapping is generally limited to a maximum of 10 mol %. Although significantly lower than that of a polypropylene film, the optimum shrink temperature of the propylene/ethylene copolymer film with the above ethylene content is still about 20 to 50° C. higher than that of a polyethylene film.
OBJECT OF THE INVENTION
The present invention has been made in view of the above prior art and it is an object of the present invention to provide a shrink film which can suitably be used in not only commercial wrapping but also industrial wrapping. Specifically, the first object of the present invention is to provide an olefin copolymer shrink film which is excellent in low temperature heat shrinkability, has high transparency and is free from blocking problem. The second object of the present invention is to provide an olefin copolymer shrink film which is excellent in tensile strength, tear strength, impact strength and low temperature impact strength.
SUMMARY OF THE INVENTION
The olefin copolymer shrink film of the present invention comprises an &agr;-olefin/aromatic vinyl compound random copolymer, the &agr;-olefin/aromatic vinyl compound random copolymer comprising:
99.9 to 58 mol % of structural units derived from ethylene,
0 to 30 mol % of structural units derived from an &agr;-olefin having 3 to 20 carbon atoms provided that the total of the structural units derived from ethylene and the structural units derived from an &agr;-olefin having 3 to 20 carbon atoms ranges from 99.9 to 88 mol %, and
0.1 to 12 mol % of structural units derived from an aromatic vinyl compound;
the &agr;-olefin/aromatic vinyl compound random copolymer having an intrinsic viscosity [&eegr;], as measured in decalin at 135° C., of 0.1 to 10 dl/g and having a melting point, as measured by a differential scanning calorimeter, of 60 to 125° C.,
the olefin copolymer shrink film being oriented in at least one direction.
In the olefin copolymer shrink film of the present invention, a tackifier may be blended in an amount of 1 to 50 parts by weight per 100 parts by weight of the &agr;-olefin/aromatic vinyl compound random copolymer.
The olefin copolymer shrink film of the present invention is preferably oriented biaxially. This olefin copolymer shrink film preferably has a thermal shrinkage factor of at least 20% at 100° C.
DETAILED DESCRIPTION OF THE INVENTION
The olefin copolymer shrink film of the present invention will be described in detail below.
The olefin copolymer shrink film of the present invention comprises an &agr;-olefin/aromatic vinyl compound random copolymer obtained from ethylene and an aromatic vinyl compound optionally together with an &agr;-olefin having 3 to 20 carbon atoms. This olefin copolymer shrink film is one oriented in at least one direction.
&agr;-Olefin/aromatic Vinyl Compound Random Copolymer
The &agr;-olefin/aromatic vinyl compound random copolymer for use in the present invention is a random copolymer of ethylene and an aromatic vinyl compound (ethylene/aromatic vinyl compound random copolymer) or a random copolymer of ethylene, an &agr;-olefin having 3 to 20 carbon atoms and an aromatic vinyl compound (ethylene/&agr;-olefin/aromatic vinyl compound random copolymer).
The ethylene/aromatic vinyl compound random copolymer comprises 99.9 to 88 mol %, preferably, 99 to 90 mol % of structural units derived from ethylene and 0.1 to 12 mol %, preferably, 1 to 10 mol % of structural units derived from an aromatic vinyl compound.
Examples of suitable aromatic vinyl compounds include styrene; mono or polyalkylstyrenes such as o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene and p-ethylstyrene; functional group containing styrene derivatives such as methoxystyrene, ethoxystyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylbenzyl acetate, hydroxystyrene, o-chlorostyrene, p-chlorostyrene and divinylbenzene; 3-phenylpropylene, 4-phenylbutene and &agr;-methylstyrene. Of these, styrene and 4-methoxystyrene are preferred.
In the copolymerization of the ethylene/aromatic vinyl compound random copolymer, an &agr;-olefin may be used in addition to the ethylene and aromatic vinyl compound. Examples of suitable &agr;-olefins include &agr;-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene and 1-eicodecene. Of these, 1-butene, 1-pentene, 1-hexene and 1-octene are preferred. The above &agr;-olefins can be used either individually or in combination.
The ethylene/&agr;-olefin/aromatic vinyl compound random copolymer comprises 99.9 to 58 mol % of structural units derived from ethylene, 0 to 30 mol % of structural units derived from an &agr
Morizono Kenichi
Okada Keiji
Takimoto Kazuyuki
Mitsui Chemicals Inc
Tarazano D. Lawrence
Thibodeau Paul
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