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
2001-09-27
2003-07-01
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...
C525S232000, C525S191000
Reexamination Certificate
active
06586531
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a polyolefin masterbatch which can be used to prepare a polyolefin composition suitable for injection molding into relatively large articles. More particularly, the polyolefin composition can be injection molded into large objects which exhibit improved surface properties, particularly with respect to reduction of tiger striping.
Polypropylene and thermoplastic polyolefins have enjoyed wide commercial acceptance because of their outstanding cost/performance characteristics. For example, these polymers are used in molded-in color applications because of their good weatherability.
Polypropylene and thermoplastic polyolefins are generally injection molded into desired articles. Relatively large parts, such as automobile bumpers and fascia, offer particularly challenging problems such as cold flow and tiger striping. “Cold flow” occurs when the molten polymer being injected into a mold begins to cool and solidify before the mold is completely filled with the polymer. “Tiger striping” refers to color and gloss variations on the surface of an injection molded article, which occur because of unstable mold filling properties of the molten polymer as it is being injected into the mold and formed into the desired shape.
The art has made various proposals to improve the physical characteristics of injection molded articles. Thus, Mizutani et al., “Flow Mark Reduction of Metallic Colored PP,”
SAE
2000
World Congress
(2000) discloses that the use of a low molecular weight polypropylene matrix having a broad molecular weight distribution improves the surface aesthetics of injection molded parts.
U.S. Pat. No. 5,055,528 discloses a sequential polymerization process for producing a propylene block copolymer having a melt flow rate of at least 10 g/min. and which is said to possess good flowability, moldability and impact strength.
U.S. Pat. No. 6,048,942 proposes a thermoplastic olefin composition useful for making molded articles having high surface gloss and mar resistance which contains (1) a propylene homopolymer, copolymer or terpolymer, (2) either a low molecular weight ethylene copolymer rubber, an elastomeric copolymer of ethylene and a C
3
-C
8
&agr;-olefin made with a metallocene catalyst, or a mixture of the two, and (3) a lubricant.
Japanese Patent Publication No. 9-227,735 discloses a propylene-based resin composition said to be suitable for injection molding products having good appearance and difficult to notice flow marks. The composition contains specified amounts of a propylene-based copolymer and either an ethlene-based copolymer or a styrene-based block copolymer, optionally together with an inorganic filler and/or a nucleating agent.
An object of the present invention is to provide a polyolefin composition which can be injection molded into large articles which exhibit a good balance of physical properties and minimal tiger striping.
Another object of the present invention is to provide a convenient method for preparing this polyolefin composition based on a masterbatch composition.
A feature of the masterbatch composition of the present invention is a crystalline polypropylene component which has a bimodal molecular weight distribution. Another feature of the masterbatch composition is a xylene-soluble ethylene copolymer component having a high intrinsic viscosity of 4 to 9 dl/g at room temperature.
A feature of the polyolefin composition of the present invention is the presence of a crystalline polypropylene component which has a bimodal molecular weight distribution and at least 3 weight percent of a xylene-soluble ethylene copolymer component having a high intrinsic viscosity of 4 to 9 dl/g at room temperature.
An advantage of the masterbatch composition is its ability to be formulated with a broad molecular weight olefin matrix to form a polyolefin composition having high melt fluidity which can be injection molded into large articles such as automobile bumpers which exhibit a good balance of physical properties and reduced flow marks such as tiger striping.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to a masterbatch composition, containing (percent by weight):
A) 20%-90% of a crystalline polypropylene component containing from 25% to 75% of a fraction A
I
having a melt flow rate MFR
I
of from 0.5 to 10 g/10 min., and from 75% to 25% of a fraction A
II
having a melt flow rate MFR
II
such that a ratio MFR
II
/MFR
I
is from 30 to 2000; and wherein fractions A
I
and A
II
are independently selected from the group consisting of a propylene homopolymer, a random copolymer of propylene containing up to 8% of ethylene, and a random copolymer of propylene containing up to 8% of at least one C
4
-C
10
&agr;-olefin; and
B) 10%-80% of a copolymer component of ethylene and at least one C
3
-C
10
&agr;-olefin, the copolymer containing from 10 to 70% of ethylene, and optionally minor amounts of a diene, said copolymer being soluble in xylene at room temperature, and having an intrinsic viscosity [&eegr;] of from 4 to 9 dl/g.
In another aspect, the present invention relates to a polyolefin composition suitable for injection molding, containing (all percentages by weight of the total composition):
A) from 0.1 to 50% of a masterbatch composition comprising
i) 20%-90% of a crystalline polypropylene component containing from 25% to 75% of a fraction A
I
having a melt flow rate MFR
I
of from 0.5 to 10 g/10 min., and from 75% to 25% of a fraction A
II
having a melt flow rate MFR
I
such that a ratio MFR
II
/MFR
I
is from 30 to 2000; and wherein fractions A
I
and A
II
are independently selected from the group consisting of a propylene homopolymer, a random copolymer of propylene containing up to 8% of ethylene, and a random copolymer of propylene containing up to 8% of at least one C
4
-C
10
&agr;-olefin; and
ii) 10%-80% of a copolymer component of ethylene and at least one C
3
-C
10
&agr;-olefin, the copolymer containing from 10 to 70% of ethylene, and optionally minor amounts of a diene, said copolymer being soluble in xylene at room temperature, and having an intrinsic viscosity [&eegr;] of from 4 to 9 dl/g; and
B) from 50% to 99.1% of a crystalline propylene homopolymer having an isotactic index greater than 80 or a crystalline random copolymer of propylene and an olefin selected from the group consisting of ethylene and C
4
-C
10
&agr;-olefins, provided that when the olefin is ethylene, the maximum polymerized ethylene content is 10% by weight, and when the olefin is a C
4
-C
10
&agr;-olefin, the maximum content thereof is 20% by weight, the copolymer having an isotactic index greater than 85.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The masterbatch composition contains at least two components: a crystalline polypropylene component and a copolymer component. The crystalline polypropylene component is present in an amount ranging from 20 to 90%, preferably 30 to 80%, most preferably 50 to 80% of the total weight of the masterbatch composition. Conversely, the copolymer component is present in an amount of from 80 to 10%, preferably 70 to 20%, most preferably 50 to 20% of the total weight of the masterbatch composition, with the sum of the percentage amounts of the individual components of the masterbatch composition equal to 100 percent.
The fractions A
I
and A
II
which form the crystalline polypropylene component can each be a propylene homopolymer, a random copolymer of propylene containing up to 8%, preferably 0.2 to 5% of ethylene, or a random copolymer of propylene containing up to 8%, preferably 1 to 8%, of at least one C
4
-C
10
&agr;-olefin which conforms to the formula CH
2
═CHR, wherein R is a linear or branched alkyl C
1-8
radical or an aryl radical such as phenyl. Illustrative C
4
-C
10
&agr;-olefins include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene, with 1-butene being particularly preferred.
Fractions A
I
and A
II
differ from one another in their molecular weight distribution, as described by melt flow rate
Minowa Kazuhiko
Nakajima Takeshi
Pelliconi Anteo
Takenouchi Hiroshi
Washiyama Junichiro
Basell Poliolefine Italia S.p.A.
Nutter Nathan M.
Tran Thao
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