Polyethylene useful for producing film and molded articles in a process which uses solid state stretching
Applicants have discovered that certain polyethylene (PE) homopolymers or copolymers of ethylene and C 3 to C 10 alpha-olefin monomers are more suitable for oriented processes than other polyethylene resins. In an aspect, the PE has a MFI of 0.3 g/10 min. to 5.0 g/10 min., a melting point of from 110° C. to 140° C., a density of from 0.912 g/cm 3 to 0.965 g/cm 3 (%), a haze of 10% or less, a clarity of at least 90, and a gloss of at least 60. The polyethylene is heated and formed into an article, cooled, and then the article is stretch oriented. In an embodiment, the film, tape, the melt extruded, injection blow molded, injection stretch blow molded, cast, and thermoformed articles that can be produced with this polyethylene has a thickness of 0.1 mil to 100 mils. The polyethylene exhibits excellent elasticity, toughness, stretch and optical properties for such applications.
1. A method of making an article, comprising the steps of:
providing, a resin, the resin consisting of a metallocene-catalyzed polyethylene/hexene copolymer having a melt flow index of about 0.9 g/10 min, a density of from 0.925 g/cm 3 to 0.935 g/cm 3 , and a melting point of from 110° C. to 140° C., wherein the zero shear viscosity in Pa-sec is about 2.8E+05;
heating said resin and using casting to form a cast article;
allowing the formed article to cool to a solid state;
reheating the formed article; and
orienting the article uniaxially or biaxially, thereby forming an oriented article.
2. The method of claim 1 , wherein the article is uniaxially oriented by stretching said article in a machine direction to produce a uniaxially-oriented article.
3. The method of claim 1 , wherein the article is biaxially oriented by stretching said article in a machine direction and then separately stretching said article in a transverse direction to produce a biaxially-oriented article.
4. The method of claim 1 , wherein the article is biaxially oriented by simultaneously stretching said article in a machine direction and stretching said article in a transverse direction to produce a biaxially-oriented film.
5. The method of claim 1 , wherein the article is tape.
6. The method of claim 1 , wherein the clarity of an oriented film made from the polyethylene/hexene copolymer at a stretch temperature of between 115 and 119° C. for thirty seconds is between about 97 and about 99 as measured by ASTM D1003.
7. The method of claim 1 , wherein the transmittance of an oriented film made from the polyethylene/hexene copolymer at a stretch temperature of between 115 and 119° C. for thirty seconds is between about 92 and about 93 as measured by ASTM D1003.
8. The method of claim 1 , wherein the gloss (45°) of an oriented film made from the polyethylene/hexene copolymer at a stretch temperature of about 115° C. for thirty seconds is between about 83 and 89 as measured by ASTM D2457.
9. The method of claim 1 , wherein the haze (%) of an oriented film made from the polyethylene/hexene copolymer at a stretch temperature of about 115° C. for thirty seconds is between about 2.2 and 2.6% as measured by ASTM D1003.
10. The method of claim 1 , wherein D′ (M z /M w ) of the resin is about 2.