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
1997-11-26
2001-11-13
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...
C525S242000, C525S320000, C526S161000, C526S348600, C526S352000, C526S943000, C502S152000
Reexamination Certificate
active
06316549
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions comprising specific ethylene/&agr;-olefin polymer blends. The polymer blends preferably comprise:
(A) at least one homogeneously branched substantially linear ethylene/&agr;-olefin interpolymer having specific processing characteristics, blended together with
(B) a heterogeneously branched ethylene polymer.
Such compositions are particularly useful in film applications (e.g., high strength thin gauge packaging film or heat sealable packaging film).
BACKGROUND OF THE INVENTION
Thin film products fabricated from linear low density polyethylene (LLDPE) and/or high density polyethylene (HDPE) are widely used for packaging applications such as merchandise bags, grocery sacks, and industrial liners. For these applications, films with high tensile strength, as well as high impact strength, are desired because film producers can down gauge their film products and still retain packaging performance.
Previous attempts were made to optimize film tensile strength and yield strength by blending various heterogeneous polymers together on theoretical basis. While such blends exhibited a synergistic response to increase the film yield strength, the film impact strength followed the rule of mixing, often resulting in a “destructive synergism” (i.e., the film impact strength was actually lower than film made from one of the two components used to make the blend).
For example, it is known that while improved modulus linear polyethylene resin can be produced by blending high density polyethylene with a very low density polyethylene (VLDPE), the impact strength of the resin blend follows the rule of mixing.
There is a continuing need to develop polymers which can be formed into fabricated articles (e.g., film) having these combinations of properties (e.g., improved modulus, yield strength, impact strength and tear strength). The need is especially great for polymers which can be made into film which can also be down gauged without loss of strength properties, resulting in savings for film manufacturers and consumers, as well as protecting the environment by source reduction.
Surprisingly, we have now discovered that film can have synergistically enhanced physical properties, when the film is made from a blend of at least one homogeneously branched ethylene/&agr;-olefin interpolymer and a heterogeneously branched ethylene/&agr;-olefin interpolymer.
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Chum Pak-Wing Steve
Knight George W.
Lai Shih-Yaw
Markovich Ronald P.
Harlan R.
The Dow Chemical Company
Wu David W.
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