Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-09-30
2001-06-19
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S160000, C526S943000, C428S523000
Reexamination Certificate
active
06248850
ABSTRACT:
The present invention relates to a film containing an aromatic vinyl compound-&agr;-olefin random copolymer of a uniform composition having an aromatic vinyl compound content of from 1 to less than 99.9% by molar fraction and having head-to-tail chain structures comprising at least two aromatic vinyl compound units. Further, the present invention relates to a film containing an aromatic vinyl compound-ethylene random copolymer wherein the alternating structure of the aromatic vinyl compound and ethylene is in a predetermined proportion and the alternating structure is highly isotactic, and to a strength packaging film.
More particularly, the film of the present invention is preferably transparent and may have an optional physical property ranging from elastic to plastic and may have stretchability or shrinkability, by changing the content of the aromatic vinyl compound. Especially, the stretch packaging film is excellent in the self-adhesive property, mechanical strength such as tear propagation resistance, puncture resistance, breaking strength or elongation at break, elastic recovery, transparency, stretchability, tying property and oil resistance, and is thus suitable for use for stretch packaging.
Films employing so-called pseudo random styrene-ethylene copolymers having no head-to-tail styrene chain and no stereoregularity derived from styrene units, are known.
For example, U.S. Pat. No. 5,703,187 discloses a pseudo random copolymer (or interpolymer) obtained by using a so-called CGCT catalyst, and a film employing it.
WO95/32095 discloses a (multi-layered) shrinkable film employing a pseudo random copolymer obtained by using a similar CGCT catalyst.
However, these pseudo random copolymers are not fully satisfactory with respect to the mechanical properties such as breaking strength, or the chemical resistance such as solvent resistance.
Further, the copolymer obtained by using a CGCT catalyst, particularly a copolymer having a styrene content of at most 20 mol %, especially at most 10 mol %, has a drawback that it is poor in its transparency for an application as a film, since the compositional distribution of the styrene content is relatively large, and it contains a copolymer component having a styrene content substantially lower than the average styrene content.
A copolymer having a styrene content of at least 50 mol % has a glass transition point of at least 30° C. and has high transparency and high initial modulus of elasticity, and is thus useful particularly for a plastic film or a shrinkable film. However, the above-mentioned pseudo random copolymers have no head-to-tail styrene chain, and the styrene content is accordingly up to 50 mol % at the maximum, and it is impossible to obtain a copolymer having a higher styrene content.
For stretch packaging in the filed of food packaging, films of polyvinyl chloride type have been mainly used, and films of olefin type made of a low density polyethylene, an ethylene-vinyl acetate copolymer or a linear low density polyethylene, have been used in some cases, as stretch films for so-called prepackaging, for wrapping food products such as vegetables, fishes, meats or daily dishes, directly or by placing them on plastic trays or the like.
Further, in the filed of general packaging and industrial packaging, an industrial stretch film such as a stretch film for pallet wrapping, is employed whereby wrapping is carried out by using the same film as described above, i.e. by highly stretching it.
However, in recent years, with respect to a film made of polyvinyl chloride, problems have been pointed out such as elution of the plasticizer contained therein or combustion gas formed during its incineration. Accordingly, development of a film made of a non-chlorine type material is desired as a substitute for the vinyl chloride type film.
With a single layered or composite stretch film comprising a low density polyethylene or an ethylene/vinyl acetate copolymer, stretchability of about 150% is maximum. If stretched more than that, there has bene a problem that the film breaks during the stretching.
In the case of a film made of a linear low density polyethylene, after wrapping, an excessive stress is likely to be exerted to a wrapped product, whereby the wrapped product or its tray is likely to be deformed, or the strength after wrapping tends to be weak, or the film tends to undergo non-uniform stretching, so that the appearance of a commercial product after wrapping tends to be poor. To solve such problems, if the density of the linear low density polyethylene is reduced, starting material pellets or the resulting film tends to be excessively sticky, which brings about a trouble during the production or in handling of wrapped products after wrapping. A stretch film has an adhesive property as its basic function, but if the adhesive property is excessive, there will be problems such that a trouble is likely to occur during the production of a film, and the yield tends to be substantially poor.
Further, if the density of the starting material for these olefin films is reduced, or a tackier is mixed, such a material will contain a relatively large amount of a low molecular weight component, which brings about a problem from the viewpoint of food safety in the application for food packaging. Further, the olefin type stretch films tend to be poor in elastic recovery, whereby in the application for food packaging, during display of the wrapped commercial products, the films are likely to have non-recoverable dents, for example, when pressed by fingers of consumers, thus leading to a problem that the package appearance of the commercial products be impaired, or the bottom sealing property tends to be inadequate.
It is an object of the present invention to provide a transparent novel aromatic vinyl compound-&agr;-olefin random copolymer film having such drawbacks of convectional styrene-ethylene copolymer films overcome. Further, it is an object of the present invention to overcome the drawbacks of a stretch film and to provide a film which is useful for stretch packaging as being excellent in the self-adhesive property, mechanical strength such as tear propagation resistance, puncture resistance, breaking strength or elongation at break, transparency, stretchability, tying property and elastic recovery, for example, a stretch packaging film which is useful for packaging food products and which is suitable for a hand wrapper or for a stretch wrapping machine.
The present invention provides a film containing at least 5 wt % of an aromatic vinyl compound-&agr;-olefin random copolymer having an aromatic vinyl compound content of from 1 to less than 99.9% by molar fraction and having head-to-tail chain structures comprising at least two aromatic vinyl compound units. Further, the present invention provides a film, preferably a transparent film, more preferably a stretch packaging film, containing an aromatic vinyl compound-ethylene random copolymer having an alternating structure of an aromatic vinyl compound and ethylene in a predetermined proportion, wherein the alternating structure is highly isotactic.
Namely, the present invention provides a film, preferably a highly transparent film, made of a composition or a single copolymer containing at least 5 wt %, preferably at least 50 wt %, more preferably at least 80 wt %, of a novel aromatic vinyl compound-&agr;-olefin random copolymer having the following characteristics.
1) The aromatic vinyl compound content is from 1 to less than 99.9% by molar fraction.
2) It has head-to-tail chain structures comprising at least two aromatic vinyl compound units.
Further, the present invention provides a highly transparent film wherein an aromatic vinyl compound-&agr;-olefin random copolymer to be used, has the following characteristic.
3) An aromatic vinyl compound-ethylene random copolymer wherein the alternating structure index &lgr; represented by the following formula (i) of the alternating structure of an aromatic vinyl compound and ethylene represented by the following formula (1) contained in the co
Denki Kagaku Kogyo Kabushiki Kaisha
Harlan R.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wu David W.
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