Propylene impact copolymers

Details Propylene impact copolymers Propylene impact copolymers

2000-03-24

2002-05-07

Nutter, Nathan M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S240000

Reexamination Certificate

active

06384142

ABSTRACT:

FIELD
This invention relates to propylene impact copolymer compositions. In particular, these unique and improved compositions can be produced using metallocene catalysts in commercial-scale processes.
BACKGROUND
Propylene impact copolymers are commonly used in a variety of applications where strength and impact resistance are desired such as molded and extruded automobile parts, household appliances, luggage and furniture. Propylene homopolymers are often unsuitable for such applications because they are too brittle and have low impact resistance particularly at low temperature, whereas propylene impact copolymers are specifically engineered for applications such as these.
A typical propylene impact copolymer contains two phases or components, a homopolymer component and a copolymer component. These two components are usually produced in a sequential polymerization process wherein the homopolymer produced in a first reactor is transferred to a second reactor where copolymer is produced and incorporated within the matrix of the homopolymer component. The copolymer component has rubbery characteristics and provides the desired impact resistance, whereas the homopolymer component provides overall stiffness.
Many process variables influence the resulting impact copolymer and these have been extensively studied and manipulated to obtain various desired effects. For example U.S. Pat. No. 5,166,268 describes a “cold forming” process for producing propylene impact copolymers where finished articles are fabricated at temperatures below the melting point of the preform material, in this case, the propylene impact copolymer. The patented process uses a propylene impact copolymer comprised of either a homopolymer or crystalline copolymer matrix (first component) and at least ten percent by weight of an “interpolymer” of ethylene and a small amount of propylene (the second component). Adding comonomer to the first component lowers its stiffness. The ethylene/propylene copolymer second component enables the finished, cold-formed article to better maintain its shape.
U.S. Pat. No. 5,258,464 describes propylene impact copolymers with improved resistance to “stress whitening.” Stress whitening refers to the appearance of white spots at points of impact or other stress. These otherwise conventional propylene impact copolymers have first and second components characterized by a numerical ratio of the second component intrinsic viscosity to the first component intrinsic viscosity which is near unity.
In U.S. Pat. No. 5,362,782, nucleating agent is added to propylene impact copolymers having a numerical ratio of the intrinsic viscosity of the copolymer rubber phase (second component) to the intrinsic viscosity of the homopolymer phase (first component) which is near unity, and an ethylene content of the copolymer phase in the range of 38% to 60% by weight. These propylene impact copolymers are described as producing articles having good clarity as well as impact strength and resistance to stress whitening. The nucleating agents increase stiffness and impact strength.
U.S. Pat. No. 5,250,631 describes a propylene impact copolymer having a homopolypropylene first component and an ethylene/butene/propylene terpolymer second component. Again, the goal is to obtain high impact strength coupled with resistance to stress whitening.
Propylene impact copolymers are also used to produce films as described in U.S. Pat. No. 5,948,839. The impact copolymer described in this patent contains a conventional first component and 25 to 45 weight percent ethylene/propylene second component having from 55 to 65 weight percent ethylene. This impact copolymer composition has a melt flow of from 7 to 60 dg/min. Such films are used in articles such as diapers.
Recently, efforts have been made to prepare propylene impact copolymers using the newly developed metallocene catalysis technology in order to capitalize on the inherent benefits such catalysts provide. It is well known that homopolymers prepared with such “single-site” catalysts have narrow molecular weight distributions, and low extractables and a variety of other favorable properties associated therewith. Metallocene catalyzed copolymers have narrow composition distributions in addition to narrow molecular weight distribution and low extractables.
Unfortunately, known metallocenes are not able to provide copolymer components with high enough molecular weight under commercially relevant process conditions. The resulting propylene impact copolymers have poor impact strength compared to their conventionally catalyzed counterparts.
U.S. Pat. No. 5,990,242 approaches this problem by using an ethylene/butene (or higher &agr;-olefin) copolymer second component, rather than a propylene copolymer, prepared using a hafnocene type metallocene. Such hafnium metallocenes in general are known for producing relatively higher molecular weight polymers; however, their activities are much lower than the more commonly used zirconocenes. In any event, the second component molecular weights and intrinsic viscosities are lower than desired for good impact strength.
The present inventors have discovered new propylene impact copolymer compositions having the benefits of metallocene catalyzed polymers in addition to properties needed for high impact strength. Importantly, these polymers can be economically produced using commercial-scale processes.
SUMMARY
The present invention provides reactor produced propylene impact copolymer compositions comprising:
(a) From about 40% to about 95% by weight Component A based on the total weight of the impact copolymer, Component A comprising propylene homopolymer or copolymer wherein the copolymer comprises 10% or less by weight ethylene, butene, hexene or octene comonomer;
(b) From about 5% to about 60% by weight Component B based on the total weight of the impact copolymer, Component B comprising propylene copolymer wherein the copolymer comprises from about 20% to about 70% by weight ethylene, butene, hexene and/or octene comonomer, and from about 80% to about 30% by weight propylene, wherein Component B:
(i) has a weight average molecular weight of at least 100,000;
(ii) a composition distribution of greater than 60%; and
(iii) an intrinsic viscosity of greater than 1.00 dl/g.
This invention also provides a process for producing propylene impact copolymer in a multiple stage process wherein Component A comprising propylene homopolymer or copolymer wherein the copolymer comprises 10% or less by weight ethylene, butene, hexene or octene comonomer is produced in a primary stage and Component B is produced in a subsequent stage, Component B comprising propylene copolymer wherein the copolymer comprises from about 20% to about 70% by weight ethylene, butene, hexene and/or octene comonomer, and from about 80% to about 30% by weight propylene, wherein at least one of Components A and/or B are polymerized using a metallocene selected from the group consisting of: rac-dimethylsiladiyl(2-iPr,4-phenylindenyl)
2
zirconium dichloride; rac-dimethylsiladiyl(2-iPr,4-[1-naphthyl]indenyl)
2
zirconium dichloride; rac-dimethylsiladiyl(2-iPr,4-[3,5-dimethylphenyl]indenyl)
2
zirconium dichloride; rac-dimethylsiladiyl(2-iPr,4-[ortho-methyl-phenyl]indenyl)
2
zirconium dichloride; and rac-diphenylsiladiyl(2-methyl-4-[1-naphthyl]indenyl)
2
zirconium dichloride.
DESCRIPTION
The propylene impact copolymers (“ICPs”) of this invention comprise at least two major components, Component A and Component B. Component A is preferably an isotactic propylene homopolymer, though small amounts of a comonomer may be used to obtain particular properties. Typically such copolymers of Component A contain 10% by weight or less, preferably less than 6% by weight or less, comonomer such as ethylene, butene, hexene or octene. Most preferably less than 4% by weight ethylene is used. The end result is usually a product with lower stiffness but with some gain in impact strength compared to homopolymer Component A.
As used herein Component A refers genera

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