Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1998-04-06
2001-07-31
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C525S240000, C428S516000, C428S523000, C428S910000, C428S349000
Reexamination Certificate
active
06268062
ABSTRACT:
This invention relates to novel compositions comprised of blends or mixtures of propylene polymers prepared by use of different types of catalysts. Specifically it relates to blends of propylene polymers prepared using a Ziegler-Natta catalyst and propylene polymers prepared using a metallocene catalyst.
BACKGROUND OF THE INVENTION
In recent years, vast quantities of propylene polymers have been prepared via the well known Ziegler-Natta catalyst system. This catalyst consists essentially of the reaction product of titanium halide, typically TiCl
4
, with an alkyl aluminum compound, typically an alkyl aluminum sesquichloride. This is an extremely effective catalyst for preparing highly crystalline polymers and in its various forms, has become the industry standard.
More recently, much work has been done to develop new catalyst systems, one result of which has been the discovery of metallocene catalyst systems. Metallocene catalysts are defined as bridged bis dicyclopentadienyl or bis indenyl Group 4,5 or 6 transition metal dihalide derivatives. Specific metallocene catalysts known to be useful for producing polypropylene are discussed, inter alia, in EPA 485,820; 485,821; 485,822; 485,823; 518,092 and 519,237 and in U.S. Pat. Nos. 5,145,819 and 5,296,434. Other references that discuss the metallocene catalyzed process include EPA 351,932 and U.S. Pat. Nos. 5,055,438; 5,234,800; 5,272,016; 5,272,236 and 5,278,272. All of the cited documents are incorporated hereinto by reference.
The polymers resulting from metallocene catalysis are said to be of extremely uniform steric structure. Depending on the specific metallocene employed, the polymer can be of an a syndiotactic structure wherein the pendant methyl groups on the polymer chain are located on alternating carbon atoms and are alternately oriented above and below the plane of the chain. With another metallocene, the polymer can be of an isotactic structure wherein all of the pendant methyl groups are still located on alternate carbon atoms, but they are disposed predominantly on the same side of the chain.
In addition to the high degree of stereoregularity of the polymer chains, there is a very high degree of uniformity of molecular weight among the polymer chains, i.e., the molecular weight distribution is narrower than that found in conventional isotactic polypropylene. Thus, whereas a conventional polypropylene has a polydispersity (i.e. the ratio of weight average molecular weight to number average molecular weight) on the order of about 7, a metallocene catalyzed polypropylene prepared by the same manufacturer has a polydispersity on the order of about 3. Likewise, in the manufacture of copolymers or terpolymers, the metallocene catalyst leads to a more even distribution of the comonomer or comonomers throughout the product. Yet another good feature of the metallocene polymers is that they have a lower concentration of low molecular weight, xylene soluble materials.
The narrower molecular weight distribution of the metallocene catalyzed homopolypropylene and copolymer and the more even distribution of the comonomer in the copolymer lead to greater uniformity of the properties of the product whether it be the homopolymer or the coploymer. Thus, the metallocene catalyzed products exhibit a sharper melting point and a more uniform intrinsic viscosity throughout the product. These property improvements translate into improved flow properties and thus to improved processing during film extrusion and drawing. Processing is thus significantly facilitated.
However, in attempting to manufacture oriented packaging films with the metallocene catalyzed polypropylene in conventional processes and equipment, it has been found that the cast films exhibit very poor optical properties. Specifically, the films cast preparatory to drawing to effect orientation are extremely hazy, bordering on being translucent. In addition, they have a rough, sand paper-like surface. Drawn films prepared from these polymers are also found to exhibit a high degree of haze, making them unsuitable for high quality packaging applications.
It is an objective of this invention to provide a polymer composition containing metallocene catalyzed polypropylene that can be employed in the manufacture of polypropylene film. It is a further objective of the invention to provide superior polypropylene films comprising metallocene catalyzed polypropylene, which films exhibit a combination of improved properties as compared with polypropylene films heretofore known to the art.
BRIEF DESCRIPTION OF THE INVENTION
The invention to be described hereinafter is afilm forming composition comprising a blend comprised of about 10 to 90 percent by weight, based on the total weight of its polypropylene component, of a polypropylene prepared by use of a Ziegler-Natta catalyst and about 90 to 10 percent of a polypropylene prepared by use of a metallocene catalyst. The blends preferably comprise about 25 to 75 percent Ziegler-Natta catalyzed polypropylene and 75 to 25 percent of the metallocene catalyzed polypropylene. Most preferred are blends comprised of about 40 to 60 percent by weight Ziegler-Natta catalyzed polypropylene and 60 to 40 percent by weight metallocene catalyzed polypropylene.
The invention also includes biaxially oriented films prepared from a blend comprised of about 10 to 90 percent by weight, based on the total weight of the polymeric components, of a polypropylene prepared by use of a Ziegler-Natta catalyst and about 90 to 10 percent of a polypropylene prepared by use of a metallocene catalyst. More preferably, the films are prepared with a blend comprised of 25 to 75 percent Ziegler-Natta catalyzed polypropylene and 75 to 25 percent metallocene catalyzed polypropylene. Most preferably, the films are prepared with a blend comprised of 40 to 60 percent Ziegler-Natta catalyzed polypropylene and 60 to 40 percent metallocene catalyzed polypropylene.
The polypropylene blends according to the invention and the films prepared therewith can also contain up to about 30%, preferably up to about 20% and most preferably up to about 10% by weight of a low molecular weight hydrocarbon resin, based on the total weight of the polypropylene blend and the resin.
DETAILED DESCRIPTION OF THE INVENTION
When reference is made herein to polypropylene, it is intended to indicate a crystalline propylene homopolymer or a copolymer of propylene with another &agr;-olefin having about 2 to 5 carbon atoms in an amount insufficient to have a significant effect on the crystallinity of the polypropylene. Typically, this is ethylene in an amount up to about 6% by weight. This will be the case either with reference to polypropylene prepared with metallocene catalyst (sometimes referred to as “metallocene polypropylene” or as “metallocene polymer”) or to the polypropylene prepared with a Ziegler-Natta catalyst (sometimes referred to as “Ziegler polypropylene” or “Ziegler polymer”). The polypropylene employed is preferably the homopolymer.
Suitable Ziegler polypropylenes are the commercially available isotactic polypropylenes having a melt flow rate between about 2 and 10 gm/10 min at 230° C. and 2.16 Kg. load and a DSC melting point of about 160 to 166° C. One polypropylene that can be used is the isotactic homopolymer having a melt flow rate of about 3.5 dg/min at 230° C. and 2.16 Kg. load, available from Aristech Chemical Corporation, Pittsburgh, Pa. Suitable polypropylenes are also available from Montell, Inc. Wilmington, Del., Exxon Chemical Company, Baytown, Tex. and Fina Oil and Chemical Co., Deer Park, Tex.
The metallocene polypropylene employed in the manufacture of the films of this invention can be either an isotactic or a syndiotactic polymer. The preferred polymer is the isotactic species because this species has a higher melting point and accordingly, can be employed in higher temperature environments than can the syndiotactic species. A preferred isotactic metallocene polypropylene is a homopolymer having a melt flow rate between about 1 and 10 and more preferably, between about 1 and 5
Applied Extrusion Technologies, Inc.
Caesar Rivise Bernstein Cohen & Pokotilow Ltd.
Tarazano D. Lawrence
Thibodeau Paul
LandOfFree
Polypropylene blends and films prepared therewith does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polypropylene blends and films prepared therewith, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polypropylene blends and films prepared therewith will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2461217