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
2002-11-12
2004-10-12
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...
C525S333700, C525S333800, C524S394000, C524S230000, C524S451000
Reexamination Certificate
active
06803421
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to filled propylene polymer blend compositions suitable for injection molding comprising a propylene-ethylene impact copolymer and an ethylene plastomer having melt flow rate greater than 10. The blends, and particularly visbroken blends, exhibit high flow and provide a desirable balance of impact properties and dimensional stability.
DESCRIPTION OF THE PRIOR ART
Two phase propylene copolymer resins comprised of an intimate mixture of a continuous phase of crystalline propylene homopolymer and dispersed rubbery phase of ethylene-propylene copolymer are well known and widely used for numerous applications. While these so-called impact polypropylene products can be produced by melt compounding the individual polymer components, existing multi-reactor technology makes it possible to directly produce these products. This is conveniently accomplished by polymerizing propylene in a first reactor and discharging the polypropylene homopolymer from the first reactor into a secondary reactor where propylene and ethylene are copolymerized in the presence of the homopolymer. Gas-phase polymerizations of this type are described in the article by Ross, et al. al., “An Improved Gas-Phase Polypropylene Process.”
Ind. Eng. Chem. Prod. Res. Dev
. 1985, 24, pp. 149-154. This gas-phase technology has been extended to products containing significantly higher rubber/elastomer contents which are referred to as in-situ thermoplastic polyolefins (TPOs).
The high rubber content PP-EPR materials produced by these in-reactor processes are increasingly being used by the automotive industry for the manufacture of injection molded large parts such as bumpers, body side mouldings and the like. Primary requirements for materials used for these applications are good impact and high dimensional stability, i.e., low coefficient of linear thermal expansion (CLTE). The need for bumper materials having reduced expansion or “O-gap” and the ability to significantly improve the expansion coefficient using mineral fillers is discussed by E. Seitl, et al.,
Kunstoffe Plast Europe
, August 1994, pp. 50-53. The reference further notes that the expansion coefficient also influences the shrinkage. Shrinkage is an important consideration in the injection molding process since tools/molds are designed for a certain shrink requirement.
Ethylene-olefin elastomeric copolymers (plastomers) are known to be useful modifiers for polypropylene impact copolymers. The addition of plastomers makes it possible to obtain blends with enhanced properties, such as improved low temperature ductility. This latter feature is important since most manufacturer specifications now also have ductile-brittle failure mode requirements in addition to low temperature (−30° C. or −40° C.) impact requirements. For high flow injection molding polypropylene compositions there also are certain melt flow rate (MFR) requirements if acceptable fabrication is to be achieved.
U.S. Pat. No. 6,399,707 discloses polypropylene impact copolymer blends with low melt index (MI) plastomers, i.e., plastomers with MIs from 0.8 to 10 g/10 min and, more preferably, 0.8 to 3.5 g/10 min. The reference points out that while higher MFR (>15 g/10 min) materials are desirable for injection molding, it is difficult to achieve the low temperature ductility and impact properties required by the automotive industry with such high MFR resins. For this reason resin blends having MRFs less than 15 g/10 min are used.
It would be highly advantageous if polypropylene impact copolymer/plastomer blends having higher MFRs with acceptable impact and low temperature ductility were available. These and other benefits are achieved with the improved compositions of the invention which are described in detail to follow.
SUMMARY OF THE INVENTION
The present invention provides propylene polymer compositions suitable for injection molding. More specifically, the compositions are blends of ethylene-propylene impact copolymers, ethylene-olefin plastomers and mineral fillers. They are characterized by having high flow and a desirable balance of impact and dimensional properties.
The compositions are blends comprised of 45 to 90 weight percent (wt. %), based on the total composition, propylene-ethylene copolymer comprised of crystalline and amorphous phases, said copolymer having an ethylene content from 5 to 25 wt. % and MFR from 10 to 60 g/10 min; 5 to 35 wt. %, based on the total composition, ethylene-C
4-8
&agr;-olefin plastomer, said plastomer having a density less than 0.92 g/cm
3
and MI from 12 to 50 g/10 min; and 5 to 40 wt. %, based on the total composition, mineral filler. MFRs of the compositions will range from 20 to 60 g/10 min and, more preferably, are from 25 to 50 g/10 min. In one highly useful embodiment of the invention, the above-described MFRs are achieved by visbreaking lower MFR blends of the components. Typically blends which are visbroken have initial MFRs less than 20 g/10 min. Visbreaking is particularly advantageous when MFRs of the initial blend are 15 g/10 min or less.
Preferably the improved compositions of the invention are talc-filled and contain 0.01 to 1 wt. % blending aid. Ethylene-octene-1 copolymers having densities from 0.86 to 0.90 g/cm
3
and MIs from 20 to 40 g/10 min are particularly useful plastomers for the inventive blends.
DETAILED DESCRIPTION
The propylene polymer compositions of the invention are high flow blends of impact copolymer, plastomer and filler useful for injection molding applications. The high flow compositions are particularly suitable for the manufacture of injection molded parts which require high impact, low temperature ductility and dimensional stability, such as exterior automobile components. It is generally recognized that attempting to increase flow rates of injection molding blend resins by using higher MFR propylene impact copolymers adversely affects impact resistance. On the other hand, if the amount of plastomer is increased to compensate for the impact loss, the flow rate is adversely affected.
By high flow is meant compositions, having MFRs 20 g/10 min or greater, most commonly, from 20 to 60 g/10 min. Resins having MFRs in the range 20 to 60 g/10 min are, from the standpoint of fabrication, considered to be highly suitable for use in injection molding equipment. MFRs referred to herein are determined in accordance with ASTM D 1238 at 230° C. and 2.16 Kg load. In those instances where the MI is specified, the MI is determined using test method ASTM D 1238 at 190° C. and 2.16 Kg load.
From the standpoint of product performance for the above-referenced automotive applications, impact properties and the ability to control expansion and contraction of the parts during production and end use are paramount. For obvious reasons performance criteria include impact strength requirements. In recent years, however, cold impact resistance of the material determined using an instrumented impact test and the type of failure mode (brittle-ductile) have become increasingly important material performance specifications for manufacturers. These test procedures will be described in more detail to follow.
Dimensional stability, as referred to herein, relates to both the expansion/contraction characteristics of the material after it is molded and the shrink characteristics of the material during fabrication. The former is determined by measuring the coefficient of linear thermal expansion in accordance with ASTM test method E 831. Shrinkage is determined by observing the difference in size of a molded plaque from the mold dimensions after the plaque has been allowed to stand, typically for 24 hours.
The ability to balance all of the aforementioned properties of an injection molding resin to achieve the optimal balance of properties, i.e. optimize each of the properties without unduly sacrificing the performance of any one property, is highly desirable. Furthermore, the ability to vary individual properties by judicious modification of the injection molding resin composition is equa
Baracka Gerald A.
Equister Chemicals, LP
Heidrich William A.
Lee Rip A
Wu David W.
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