Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-09-02
2001-03-20
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C526S348000, C526S352000, C526S351000
Reexamination Certificate
active
06204335
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions having particular utility in the production of film. More particularly, the present invention relates to compositions comprising a blend of a linear ultra low density polyethylene (LULDPE) and a propylene polymer, having particular utility in the production of film, especially stretch wrap cling film.
BACKGROUND OF THE INVENTION
Blown film is preferable over cast film where high strength films are required. Linear low density polyethylene (LLDPE) and linear ultra low density polyethylene (LULDPE) are the most suitable for blown stretch film. However, for commercial applications, in the stretch wrapping industry, neither blown LLDPE nor blown LULDPE film has enough peel cling strength when stretched to 200 percent elongation, the commercially acceptable amount of stretching commonly required in stretch wrapping processes. Propylene polymer cling additives have been blended with LLDPE to provide monolayer blown stretch wrap film having commercially adequate cling at 200 percent elongation. The term “commercially adequate cling” is hereinafter defined as a peel cling strength of at least 100 g/2.54 cm, for convenience and clarity.
Multilayer blown stretch film is more versatile than monolayer film for many purposes. In an A/B/A or A/N/B/C type multilayer film, the core layer is typically about 80 weight percent of the film, with each of the two skin layers making up about 10 weight percent of the film.
Blown LLDPE and LULDPE have been found to be inadequate skin layers in multilayer stretch wrap film. They do not provide enough peel cling strength when the multilayer film is stretched to 200 percent elongation. Propylene polymer cling additives have been blended with LLDPE for use in multilayer blown stretch film. However, LLDPE skin layers require a relatively high concentration of propylene polymer cling additive to be effective.
In light of the above, it would be desirable to provide a new blown film composition suitable for use in making both monolayer blown stretch cling film and multilayer blown stretch cling film. It would be further desirable if a stretched multilayer film comprising a skin layer formed from such new composition would provide adequate cling.
SUMMARY OF THE INVENTION
The present invention relates to a composition of matter which comprises a blend of about 80 to about 99 weight percent based on the composition of a linear ultra low density polyethylene having a density of less than about 0.916 g/cm
3
, and about 1 to about 20 weight percent based on the composition of a propylene polymer comprising 0 to about 40 weight percent based on the copolymer of olefin comonomer units having 2 to 10 carbon atoms and from about 60 to about 100 weight percent propylene, based on the copolymer, said propylene polymer having a Brookfield Thermosel viscosity of about 1 to about 30,000 mPa·s at 190° C. and a needle penetration hardness of about 5 to about 300 dmm at 23° C.
DETAILED DESCRIPTION OF THE INVENTION
The applicant was surprised to find that particular propylene polymers can be usefully blended with LULDPE to form a composition useful in making both monolayer and multilayer blown stretch cling film and cast film. Film formed from the LULDPE composition of the present invention provides unexpectedly effective cling when used as a skin layer of a multilayer stretch cling film.
The composition of the present invention comprises about 80 to about 99 weight percent LULDPE component based on the composition, and about 1 to about 20 weight percent propylene polymer based upon the total weight of the composition. More particularly, the present composition comprises LULDPE having a density of less than about 0.916 g/cm
3
, and about 1 to about 20 weight percent propylene polymer containing 0 to about 40 weight percent olefin comonomer units having 2 to 10 carbon atoms. The propylene polymer has a Brookfield Thermosel viscosity of about 1 to about 30,000 mPa·s at 190° C., and a needle penetration of about 5 to about 300 dmm at 23° C.
LULDPE has excellent direction (MD) elongation, good tear resistance, good tensile strength, and good puncture resistance. LULDPE is a copolymer of ethylene and an alpha olefin comonomer, with density of less than about 0.916 g/cm
3
, preferably from about 0.88 to about 0.916 g/cm
3
, more preferably about 0.9 to about 0.914 g/cm
3
. LULDPE has a melt index (MI) of about 0.4 to about 8 g/10 min., preferably about 0.5 to about 4 g/10 min. The LULDPE used is more preferably an ethylene-octene or ethylene-hexene LULDPE copolymer. A minor amount of other film-forming polyolefins such as LDPE, LLDPE, polypropylene, and ethylene vinyl acetate copolymer (EVA) may also be present in the film-forming component. The present composition comprises preferably about 85 to about 99 weight percent LULDPE, and from about 1 to about 15 weight percent propylene polymer, based on the composition.
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 LULDPE component of the composition may be prepared readily by any conventional technique known in the art.
The present propylene polymer comprises 0 to about 40 weight percent C2 to C10 olefin comonomer unit content and from about 60 to about 100 weight percent propylene, based upon the total propylene polymer. The propylene polymer preferably comprises 0 to about 25 weight percent comonomer unit content, and from about 75 to about 100 weight percent propylene, based upon the polymer, more preferably 0 to about 20 weight percent comonomer unit content and from about 80 to about 100 weight percent propylene. The olefin comonomer units are preferably ethylene units.
A particularly surprising aspect of the present invention is the broad range of molecular weights and hardness levels possible for a suitable propylene polymer. The molecular weight is evidenced by the viscosity at 190° C., determined by the Brookfield Thermosel viscosity method. The viscosity range of the propylene polymer of the present invention is from about 1 to about 30,000 mPa·s, at 190° C. The viscosity is preferably from about 1 to about 15,000 mPa·s, at 190° C., more preferably from about 1 to about 7,000 mPa·s, at 190° C. with about 1 to about 5,000 mPa·s, at 190° C. being most preferred. A composition comprising a propylene polymer having a viscosity of from about 1 to about 2,000 mPa·s at 190° C. is most suitable for use in producing blown film.
The propylene polymer of the present invention can contain a measurable amount of crystallinity, more than 1 weight percent by a hexane extraction method such as ASTM D5227, or can be totally amorphous. The propylene polymer has a needle penetration range of about 5 to about 300 dmm, determined by ASTM (test method modified to 23°, instead of 25° C.). The propylene polymer preferably has a needle penetration of about 5 to about 200 dmm at 23° C., with about 5 to about 100 dmm at 23° C. being more preferable.
The propylene polymer component of the composition utilized herein may be produced by a process disclosed in Canadian Patent 1,296,484, entitled “Process for the Direct Synthesis of Highly Amorphous Propylene Homopolymers and Propylene-Ethylene Copolymers.” Some of the propylene copolymer components within the scope of the present invention may also be purchased from Eastman Chemical Company, Kingsport, Tenn. under the Eastman Chemical Company Trademark, EASTOFLEX.
The exact amounts of the LULDPE component and the propylene polymer component of the compositions herein are determined by the application for
Choi Ling-Siu
Eastman Chemical Company
Gwinnell Harry J.
Wood Jonathan D.
Wu David W.
LandOfFree
Compositions of linear ultra low density polyethylene and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Compositions of linear ultra low density polyethylene and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compositions of linear ultra low density polyethylene and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2471768