Polymers, and novel compositions and films therefrom

Details Polymers, and novel compositions and films therefrom Polymers, and novel compositions and films therefrom

2000-08-10

2003-02-04

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...

C526S348000, C526S352000, C526S351000, C525S236000, C525S240000, C053S441000

Reexamination Certificate

active

06515093

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to novel polymers and use thereof in compositions having particular utility in the production of film. More particularly, the present invention relates to novel propylene copolymers and compositions comprising a blend of an ethylene polymer and the novel propylene polymers having particular utility in the production of film, especially stretch wrap cling film.
BACKGROUND OF THE INVENTION
Blown stretch wrap film generally has higher tensile strength than cast film. Linear low density polyethylene (“LLDPE”) is much more useful than low density polyethylene (“LDPE”) as the film-forming component of blown stretch wrap films. However, a cling additive must be blended with LLDPE since LLDPE film does not exhibit a high level of cling when stretched in the typical usage to about 200 percent elongation. The film made from the composition of the present invention generally also has an unwinding noise not greater than the unwinding noise of the neat ethylenic polymer. This is important in light of the OSHA noise workplace restrictions.
June 1992 U.S. Research Disclosure 33875 discloses that a polyolefin having a Brookfield Thermosel Viscosity of about 6,000 mPa·s at 190° C., and a needle penetration hardness of about 35 dmm and a polyolefin having a Brookfield Thermosel viscosity of 2300 mPa·s at 190° C. and a needle penetration hardness of 20 dmm are useful in cast and blown LLDPE and LDPE film. The applicant has found that blown polyethylene based stretch cling films containing these polyolefins have little or no peel cling strength at 200 percent elongation. The applicant has previously disclosed a very low viscosity partially crystalline propylene-ethylene cling additive for EVA, LDPE, and LLDPE stretch film composition. The disclosed propylene-ethylene cling additive comprises a partially crystalline propylene-ethylene copolymer having 10 to 40 weight percent ethylene units, within the viscosity range of 1 to 2,000 mPa·s at 190° C. The known propylene-ethylene copolymer cling additive has a needle penetration hardness less than about 150 dmm at 23° C. The film composition disclosed therein is more useful for film blowing than are film compositions made with the above higher viscosity polyolefins. However, the previously disclosed blown film has a peel cling strength that is lower than cast films containing the above higher viscosity polyolefin cling additives.
In light of the above, it would be desirable to have a polyethylene-based film having the combination of excellent blown film properties as well as relatively high peel cling strength.
SUMMARY OF THE INVENTION
The present invention relates to novel propylene copolymers described hereinafter and to a composition of matter which comprises about 85 to about 99 weight percent based on the composition of an ethylenic component selected from the group consisting of low density polyethylene, linear low density polyethylene, ethylene vinyl acetate copolymer and mixtures thereof, and about 1 to about 15 weight percent based on the composition of a novel propylene copolymer comprising from about 60 to about 80 weight percent propylene, based on the copolymer, and from about 20 to about 40 weight percent olefin comonomer units having 2 to 10 carbon atoms, based on the copolymer, wherein said propylene copolymer has a Brookfield Thermosel viscosity of about 1 to about 2,000 mPa·s at 190° C. and a needle penetration of greater than about 150 to about 300 dmm, determined according to ASTM at 23° C. Novel films are produced from the novel compositions.
DETAILED DESCRIPTION OF THE INVENTION
The applicant has unexpectedly found that, within the viscosity range of about 1 to about 2,000 mPa·s at 190° C., a propylene-ethylene copolymer, having a needle penetration hardness of greater than from about 150 to about 300 dmm, is useful in stretch cling film compositions based on LDPE, LLDPE, or EVA. The composition of the present invention provides a blown stretch cling film having a good balance between maximizing peel cling strength and acceptably low high-speed unwinding noise.
It was surprising to find that the stretch cling film composition of the present invention provides a film having excellent peel cling when stretched to about 200 percent elongation, yet also having good blown film properties such as lower haze, higher gloss, and improved puncture penetration.
The composition of the present invention comprises from about 85 to about 99 weight percent based on the composition, of an ethylenic component selected from the group of ethylene polymers consisting of low density polyethylene (“LDPE”), linear low density polyethylene (“LLDPE”), ethylene vinyl acetate (“EVA”), and mixtures thereof, and about 1 to about 15 weight percent based on the composition, of a propylene copolymer comprising from about 60 to about 80 weight percent propylene, based on the copolymer, and from about 20 to about 40 weight percent based on the copolymers, of olefin comonomer units having 2 to 10 carbon atoms. The propylene copolymer has a Brookfield Thermosel viscosity of about 1 to about 2,000 mPa·s at 190° C., and a needle penetration of greater than about 150 to about 300 dmm, at 23° C.
The ethylene containing polymeric component is a homopolymer of ethylene or a copolymer of ethylene with a comonomer copolymerizable therewith. More particularly, the ethylene containing polymeric component is selected from a homopolymer of ethylene, an ethylene alpha olefin copolymer, an ethylene vinyl acetate copolymer, and mixtures thereof, wherein the ethylene containing polymeric component has a density no greater than 0.94 g/cc. The ethylene containing polymeric component preferably has a density of from about 0.88 to about 0.93 g/cc, and more preferably from about 0.89 to about 0.92 g/cc.
The alpha olefin comonomer of the ethylene alpha olefin copolymer preferably has from 3 to 20 carbon atoms per molecule and is present in an amount of from about 2 to about 20 weight percent based on the ethylene alpha olefin copolymer. Examples of the alpha olefin comonomer include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-dodecene, a terpolymer of ethylene, a terpolymer of 1-butene, a terpolymer of 1-hexene, and mixtures and derivatives thereof. In a preferred embodiment, the alpha olefin is selected from 1-butene, 1-hexene and 1-octene.
The ethylene containing polymeric component may be prepared readily by any conventional technique known in the art.
Stretch wrap film made from blown film processes is generally stronger than film made from casting. Since LDPE and EVA are not as strong as LLDPE films, the preferred ethylenic component of the present invention is LLDPE. LLDPE has excellent machine direction (MD) elongation, good tear resistance, good tensile strength, and good puncture resistance. LLDPE is a copolymer of ethylene and an alpha olefin, with density of from about 0.88 to about 0.94 g/cm
3
and a melt index of about 0.4 to 8 g/10 min. The LLDPE used is more preferably an ethylene-octene or ethylene-hexene LLDPE copolymer. The presence of up to about 20 weight percent LDPE, along with the LLDPE, improves processability, bubble stability, and optical properties.
The ethylenic containing polymeric component comprises from about 85 to about 99 weight percent of the present composition and the propylene copolymer comprises from about 1 to about 15 weight percent of the composition. More preferably, the composition comprises about 90 to about 99 weight percent ethylenic polymer, and from about 1 to about 10 weight percent propylene polymer, based on the composition.
The novel propylene copolymers, of the present invention are very low molecular weight copolymers, comprising from about 60 to about 80 percent by weight propylene, based on the copolymer, and from about 20 to about 40 weight percent based on the copolymer, of C2 to C10 alpha olefin comonomer unit content. The propylene copolymer preferably has about 20 to about 35 weight percent olefin comonomer unit content and from about

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