Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-05-23
2002-03-05
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C524S556000
Reexamination Certificate
active
06353067
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a stretch film (cling film) for packaging food and other items and a method for manufacturing the same.
The stretch wrap film material utilized to prepackage various kinds of food such as fruit and vegetables, fresh fish, meat, delicatessen, etc. by stretch wrapping the item to be packaged either directly or after placing the item on a light weight tray made of plastic, etc. used to be produced mainly from poly(vinyl chloride). Poly(vinyl chloride) film, however, would pose problems associated with environmental pollution and sanitary and health hazards. It is under said circumstance that polyolefin resins such as polyethylene, ethylene 1-butene copolymer, ethylene vinyl acetate copolymer have come to be used as raw materials for the stretch wrap film in these years.
Nonetheless, problems that ensued from the diversion from poly(vinyl chloride) to polyolefin were such that films produced from polyethylene and ethylene 1-butene copolymer are relatively hard, and hence not readily stretched and that ethylene vinyl acetate copolymer film is susceptible to breakage after the wrapping operation. Accordingly, there has been proposed a stretch wrap film material obtained by laminating a ethylene vinyl acetate copolymer layer onto both sides of a 1-butene-based resin layer (Japanese Laid-open Patent Application No. 1986 (Sho 61)-89040). Although the aforesaid problem associated with relatively high hardness and low stretchability of the film was thereby resolved, there still remained unresolved such further problem that the film gives only a narrow latitude of compatibility with the automatic wrapping machine. Another drawback was that sagging tends to occur when the item to be wrapped was loaded on the film.
For the purpose of remedying said shortcomings, there was proposed a film produced from a resin obtained by mixing ethylene (meth)acrylic acid (meth) acrylic ester copolymer with ethylene (meth)acrylic acid copolymer (Japanese Laid-open Patent Application No. 1994 (Hei 6)-322192). Nevertheless, said film did not give a satisfactory stress at elongation, etc., and hence, there still remained a need for such film that will have a further satisfactory compatibility with the automatic wrapping machine. Moreover, said film had the demerit of affording only a low productivity inherent to the blown (inflation) film extrusion system by which said film can be obtained.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a polyolefin stretch film which possesses (a) a large elongation, cut property of traverse direction, adherence/conformance property (cling property), elastic recovery after distention by fingertips, etc., which are essential properties required of the stretch wrap film material to be used on the automatic wrapping machine, (b) a good balance between the stress at 100% elongation in the longitudinal direction and the stress at 100% elongation in the transverse direction, (c) the ability to accomplish wrinkle-free packaging, and (d) an excellent productivity; and to provide a process for manufacturing such film.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
According to the present invention, the polyolefin stretch film of the present invention is produced from a resin composition comprising a polyolefin resin either consisting entirely of ethylene (meth)acrylic acid copolymer or ethylene (meth)acrylic acid (meth)acrylic ester terpolymer or consisting of a mixture of both, as a base resin and being, insofar as necessary, compounded with an anti-fogging agent and a tackifier, which is characterized in that the stress at 100% elongation in the longitudinal direction (the machine direction) is 12-30 MPa and the stress at 100% elongation in the transverse direction (the cross direction) is 5-11 MPa.
A preferred embodiment of the present invention is a polyolefin stretch film produced from a resin composition comprising 100 parts by weight of said polyolefin resin, 0.5-12 parts by weight of a tackifier and 1-5 parts by weight of an anti-fogging agent.
The preferred polyolefin stretch film of the present invention comprises a film produced from said resin composition by the extrusion film forming technique employing a straight manifold die. Furthermore, the preferred polyolefin stretch film of the present invention also comprises a film produced from said resin composition by the extrusion film forming technique employing a straight manifold die which has undergone an orientation preventing treatment.
The process for manufacturing the polyolefin stretch film of the present invention comprises carrying out an orientation preventing treatment in the course of producing a film by the extrusion film forming technique employing a straight manifold die from a resin composition comprising a polyolefin resin either consisting entirely of ethylene (meth)acrylic acid copolymer or ethylene (meth)acrylic acid (meth)acrylic ester terpolymer or consisting of a mixture of both, as a base resin and being, insofar as necessary, compounded with an anti-fogging agent and a tackifier either during the film forming step or after the film has been formed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the polyolefin stretch film of the present invention, a detailed description is given in the following as for the polyolefin resin composition constituting such film, the process for manufacturing the film and the stretch film thereby obtained.
The resin composition from which the film was produced of the present invention is comprising a polyolef in resin either consisting entirely of ethylene (meth)acrylic acid copolymer or ethylene (meth)acrylic acid (meth)acrylic ester terpolymer or consisting of a mixture of both, as a base resin and being, insofar as necessary, compounded with an anti-fogging agent and a tackifier.
The ethylene (meth)acrylic acid copolymer is manufactured by copolymerizing ethylene with methacrylic acid or copolymerizing ethylene with acrylic acid by the well-known radical polymerization process, etc., and the ratio of the structural unit component (hereinafter referred to simply as “component”) derived from (meth)acrylic acid is preferably 3-20 mole %. When the ratio of (meth)acrylic acid component declines to an excessively low level deviating from said range, the flexibility and the elastic recovery after distention by fingertips of the obtained film tend to prove insufficient. On the contrary, when the ratio of (meth)acrylic acid component exceeds said range, the cut property of traverse direction of the obtained film often turns out to be insufficient.
The melt flow rate of ethylene (meth)acrylic acid copolymer (as determined in accordance with ASTM D1238 at a temperature of 190° C.) is generally 0.5-30 g/10 min.
The ethylene (meth)acrylic acid (meth)acrylic ester terpolymer is obtained by either copolymerizing ethylene with acrylic acid and (meth)acrylic ester or copolymerizing ethylene with acrylic acid and (meth)acrylic ester by the well-known radical polymerization process, etc.
The (meth)acrylic ester in this case is represented by acrylic ester or methacrylic ester whose alcohol residue is a hydrocarbon having 1-8 carbon atoms. As examples of such (meth)acrylic ester, there can be cited methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, isobutyl methacrylate, etc. Among the above-exemplified ester, the preferred ones are acrylic ester or methacrylic ester whose alcohol residue is a hydrocarbon having 4-6 carbon atoms.
A preferred ethylene (meth)acrylic acid (meth)acrylic ester terpolymer contains 3-20 mole % or preferably 5-15 mole % of a component derived from (meth)acrylic acid and 0.3-20 mole %, or preferably 0.7-15 mole %, or more preferably 1.0-15 mole % of a component derived from (meth)acrylic ester. In particular, an ethylene (meth)acrylic acid (meth)acrylic ester terpolymer containing 2 or less mole %, or preferably 0.3-2 mol
Ishii Toshiyuki
Itoh Toshiki
Kameyama Masao
Michl Paul R.
Mitsui Chemicals Inc.
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