Cast stretch film of interpolymer compositions

Details Cast stretch film of interpolymer compositions Cast stretch film of interpolymer compositions

2002-07-22

2004-11-02

Lipman, Bernard (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, C526S348100, C526S348200, C526S348600, C526S943000

Reexamination Certificate

active

06812289

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
Cast stretch films are high clarity films utilized to protect and unitize manufactured goods or items for transport and storage. Such films with commercial applicability have been produced from ethylene polymers and copolymers. It is highly desirable for such polymers to have excellent processability, i.e., they can be processed into cast stretch film at a faster throughput rate with lower energy requirements and with reduced melt flow perturbations. This has previously required the use of ethylene/&agr;-olefin copolymers with a high shear rate response (where shear response is defined as the high load melt index divided by the melt index of the polymer). It is known to those skilled in the art, that, for such polymers, high melt flow ratio (MFR) values are indicative of a relatively broad molecular weight distribution. Typical Ziegler catalyzed linear low density polyethylene has been used in this application because of its relatively broad molecular weight distribution.
While it is important that polymers used for cast stretch film applications process easily, it is also highly desirable for such films to exhibit high impact strength and on-pallet puncture. For traditional Ziegler Natta catalyzed linear ethylene/&agr;-olefin polymers, increasing impact and puncture strength is often accomplished by narrowing the molecular weight distribution and/or increasing the molecular weight.
U.S. Pat. Nos. 5,231,151 and 5,487,938 (Spencer et al.) teach that linear low density polyethylene (LLDPE) which has a high density fraction, as measured by ATREF, of higher than 17% and a molecular weight distribution (MWD) of less than about 3.6, are particularly effective in making cast films used in pallet wrapping applications.
U.S. Pat. No. 4,243,619 (Fraser et al.) describes a process for making film from a narrow molecular weight distribution polymer compositions which are ethylene/&agr;-olefin copolymers prepared by a Ziegler catalyst useful for stretch film applications and exhibiting good optical and mechanical properties.
U.S. Pat. No. 5,175,049 (Huff et al.) describes the composition of a wrap-packaging cling film which is a film laminate comprising at least two layers. The outer layer comprises a very low density ethylene/&agr;-olefin copolymer (LVLDPE) and at least one of the layers comprises a linear low density ethylene/&agr;-olefin copolymer (LLDPE). These compositions exhibited differential cling properties suitable for wrap packaging.
It is also well known that narrow molecular weight distribution linear polymers possess low melt elasticity causing problems in melt fabrication. Such polymers also experience significant surface melt fracture at relatively low extrusion rates thereby processing unacceptably and causing surface irregularities in the finished product. These irregularities can present difficulties in, for instance, electronic reading of bar codes on packaged material. Thus there remains a difficulty in producing resins which are able to exhibit good processability, while exhibiting improved, on-pallet puncture, dart impact and stretchability and yielding film with few surface irregularities.
The relatively recent introduction of metallocene-based catalysts for ethylene/&agr;-olefin copolymerization has resulted in the production of new ethylene interpolymers. The term “interpolymer” is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes copolymers, terpolymers, etc.
These metallocene catalysts include the bis(cyclopentadienyl)-catalyst systems and the mono(cyclopentadienyl) Constrained Geometry catalyst systems. Such constrained geometry metal complexes and methods for their preparation are disclosed in U.S. application Ser. No. 545,403, filed Jul. 3, 1990 (EP-A-416,815); U.S. application Ser. No. 547,718, filed Jul. 3, 1990 (EP-A-468,651); U.S. application Ser. No. 702,475, filed May 20, 1991 (EP-A-514,828); U.S. application Ser. No. 876,268, filed May 1, 1992, (EP-A-520,732); U.S. application Ser. No. 8,003, filed Jan. 21, 1993 (WO93/19104); U.S. application Ser. No. 08/241,523, (WO95/00526); as well as U.S. Pat. Nos. 5,055,438, 5,057,475, 5,096,867, 5,064,802, and 5,132,380.
In EP-A 418,044, published Mar. 20, 1991 (equivalent to U.S. Ser. No. 07/758,654) and in U.S. Ser. No. 07/758,660 certain cationic derivatives of the foregoing constrained geometry catalysts that are highly useful as olefin polymerization catalysts are disclosed and claimed. In U.S. Ser. No. 720,041, filed Jun. 24, 1991, certain reaction products of the foregoing constrained geometry catalysts with various boranes are disclosed and a method for their preparation taught and claimed. In U.S. Pat. No. 5,453,410 combinations of cationic constrained geometry catalysts with an alumoxane were disclosed as suitable olefin polymerization catalysts. For the teachings contained therein, the aforementioned pending United States Patent applications, issued United States Patents and published European Patent Applications are herein incorporated in their entirety by reference thereto.
The use of metallocene catalyst systems have generated new interpolymers and new requirements for compositions containing these materials. Such polymers are known as homogeneous interpolymers and are characterized by their narrower molecular weight and composition distributions (defined as the weight percent of the polymer molecules having a comonomer content within 50 percent of the median total molar comonomer content) relative to, for example, traditional Ziegler catalyzed heterogeneous polyolefin polymers. Generally blown and cast film made with such polymers are tougher and have better optical properties and heat sealability than film made with Ziegler Natta catalyzed LLDPE. It is known that metallocene LLDPE (see “EXCEED™ mLLDPE Hexene Copolymers—Structure/Property Relationships” by B. C. Trudell and G. D. Malpass Jr,) offer significant advantages over Ziegler Natta produced LLDPE's in cast film for pallet wrap applications, particularly improved on-pallet puncture resistance. Such metallocene LLDPE's however have a significantly poorer processability on the extruder than Ziegler Natta products. The metallocene LLDPE's known as EXCEED™ (Trademark of Exxon Chemical) have Composition Distribution Branch Index (CBDI) values higher than 65% (see “EXCEED™ mLLDPE Hexene Copolymers—Structure/Property Relationships” by B. C. Trudell and G. D. Malpass Jr.). Ziegler Natta produced materials have broader composition distributions and have values lower than 65%.
The substantially linear ethylene/&agr;-olefin polymers described in U.S. Pat. No. 5,272,236 (Lai et al.) are also metallocene based homogeneous polymers, as the comonomer is randomly distributed within a given interpolymer molecule and wherein substantially all of the interpolymer molecules have the same ethylene/comonomer ratio within that interpolymer. Such polymers are unique however due to their excellent processability and unique rheological properties and high melt elasticity and resistance to melt fracture. These polymers can be successfully prepared in a continuous polymerization process using the constrained geometry metallocene catalyst systems.
Recent work has examined the properties of blends of metallocene-catalyzed LLDPE and High pressure LDPE or Ziegler catalyzed LLDPE. Such blends typically seek to balance the processability of Ziegler LLDPE with the improved physical properties of metallocene based polymers. Additionally, such blends may lower the cost of production compared to pure metallocene-based polymers due to the higher costs associated with the new and complex metallocene catalyst systems relative to the well-established Ziegler catalyst systems.
Research Disclosure No. 310163 (Anonymous) teaches that blends of Ziegler Natta- and metallocene-catalyzed ethylene copolymers when fabricated into cast films have improved optical, toughness, heat sealability,

Affiliated with

Also associated with

Rating

Cast stretch film of interpolymer compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Cast stretch film of interpolymer compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cast stretch film of interpolymer compositions will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3361879