Thermoplastic elastomeric blends

Details Thermoplastic elastomeric blends Thermoplastic elastomeric blends

1997-10-07

2001-04-17

Mulcahy, Peter D. (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...

Reexamination Certificate

active

06218470

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a thermoplastic elastomeric blend composition comprising an elastomer block copolymer and an ethylene/&agr;-olefin interpolymer, and to fabricated articles made therefrom.
BACKGROUND OF THE INVENTION
Elastomer block copolymers of polystyrene and rubber are widely used in the industry, frequently for impact modification of thermoplastic resins and engineering thermoplastics or for compatibilization of different types of resins. The class of elastomer saturated rubber block copolymers, such as examplified by styrene-ethylene/butene-styrene block copolymers (S-EB-S), however, is expensive to produce. These materials are used when high performance and/or clarity or transparency are required. Blends of polymer components not readily miscible with these block copolymers, such as conventional polyethylenes, can exhibit inferior mechanical properties, especially failure properties and poorer ductility related properties, such as tensile elongation at rupture.
It would be desirable to provide lower cost blends of these block copolymers by adding a polymeric component that does not significantly decrease the required performance properties. It would be further desirable to provide blends of these block copolymers and a polymeric component thereby maintaining or improving the performance of these block copolymers while providing transparent blends. It would also be desirable to improve U.V. stability and abrasion resistance of these block copolymers.
SUMMARY OF THE INVENTION
According to the present invention there is provided a thermoplastic elastomeric blend composition comprising:
A) from 99 to 1 weight percent of an elastomer block copolymer comprising at least one segment of a styrenic polymer and at least one segment of an elastomeric saturated olefin polymer; and
B) from 1 to 99 weight percent of a substantially linear ethylene/&agr;-olefin interpolymer, wherein the substantially linear ethylene/&agr;-olefin interpolymer is characterized as having:
a) a melt flow ratio, I
10
/I
2
, ≧5.63,
b) a molecular weight distribution, M
w
/M
n
, defined by the equation: M
w
/M
n
≦(I
10
/I
2
)−4.63,
c) a density from 0.85 to 0.90 g/cm
3
, and
d) a critical shear rate at onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear ethylene/&agr;-olefin interpolymer having about the same I
2
and M
w
/M
n
.
According to another aspect, the present invention provides a thermoplastic elastomeric blend composition comprising:
A) from 99 to 1 weight percent of an elastomer block copolymer comprising at least one segment of a styrenic polymer and at least one segment of an elastomeric saturated olefin polymer; and
B) from 1 to 99 weight percent of a substantially linear ethylene/&agr;-olefin interpolymer, wherein the substantially linear ethylene/&agr;-olefin interpolymer is characterized as having:
a) a melt flow ratio, I
10
/I
2
, ≧5.63,
b) a molecular weight distribution, M
w
/M
n
, defined by the equation: M
w
/M
n
≦(I
10
/I
2
)−4.63,
c) a density from 0.85 to 0.90 g/cm
3
, and
d) a processing index less than or equal to about 70 percent of the PI of a linear ethylene/&agr;-olefin interpolymer having about the same I
2
and M
w
/M
n
.
According to a further aspect, there is provided a thermoplastic elastomeric blend composition comprising:
A) from 99 to 1 weight percent of an elastomer block copolymer comprising at least one segment of a styrenic polymer and at least one segment of an elastomeric saturated olefin polymer; and
B) from 1 to 99 weight percent of a substantially linear ethylene/&agr;-olefin interpolymer, wherein the substantially linear ethylene/&agr;-olefin interpolymer is characterized as having:
a) a melt flow ratio, I
10
/I
2
, ≧5.63,
b) a density from 0.85 to 0.90 g/cm
3
, and
c) a molecular weight distribution, M
w
/M
n
, from about 1.5 to about 2.5.
According to another aspect, the present invention provides a thermoplastic elastomeric blend composition comprising:
A) from 99 to 1 weight percent of an elastomer block copolymer comprising at least one segment of a styrenic polymer and at least one segment of an elastomeric saturated olefin polymer; and
B) from 1 to 99 weight percent of at least one homogeneously branched linear ethylene/&agr;-olefin interpolymer, wherein the &agr;-olefin is a C
3
-C
20
&agr;-olefin and having a density of 0.85 to 0.90 g/cm
3
.
In yet another aspect the present invention provides a fabricated article made from such a thermoplastic elastomeric blend composition.
Both the substantially linear and the homogeneously branched linear ethylene/&agr;-olefin interpolymers are ethylene/&agr;-olefin interpolymers having a short chain branching distribution index (SCBDI) greater than about 30 percent. Both the substantially linear and linear interpolymers have a single melting point, as opposed to traditional Ziegler polymerized polymers having two or more melting points (determined using differential scanning calorimetry (DSC)).
DETAILED DESCRIPTION OF THE INVENTION
The term “interpolymer” is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer.
The term “homogeneously branched linear ethylene/&agr;-olefin interpolymers” means that the olefin polymer does not have long chain branching and wherein the short chain branches derived from the comonomer polymerized into the interpolymer are homogeneously distributed both within the same and between different polymer chains. That is, the linear ethylene/&agr;-olefin interpolymer has an absence of long chain branching, as for example the linear low density polyethylene polymers or linear high density polyethylene polymers made using uniform branching (i.e., homogeneously branched) distribution polymerization processes (e.g., U.S. Pat. No. 3,645,992 (Elston), the disclosure of which is incorporated herein by reference) and wherein the comonomer is randomly distributed within a given interpolymer molecule and wherein substantially all of the interpolymer molecules have substantially the same ethylene/comonomer ratio within that interpolymer. The term “homogeneously branched linear ethylene/&agr;-olefin interpolymers” does not refer to high pressure branched polyethylene which is known to those skilled in the art to have numerous long chain branches nor to the traditional heterogeneously branched linear low density polyethylene. Typically, the homogeneously branched linear ethylene/&agr;-olefin interpolymer is an ethylene/&agr;-olefin interpolymer, wherein the &agr;-olefin is at least one C
3
-C
20
&agr;-olefin (e.g., propene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like), preferably wherein at least one of the &agr;-olefins is 1-octene. Most preferably, the ethylene/&agr;-olefin interpolymer is a copolymer of ethylene and a C
5
-C
20
&agr;-olefin, especially an ethylene/1-octene copolymer.
The substantially linear ethylene/&agr;-olefin interpolymers of the present invention are not in the same class as traditional linear ethylene/&agr;-olefin interpolymers (e.g., heterogeneously branched linear low density polyethylene, linear high density polyethylene, or homogeneously branched linear polyethylene), nor are they in the same class as traditional highly branched low density polyethylene. The substantially linear olefin interpolymers useful in this invention have excellent processability, even though they have relatively narrow molecular weight distributions. Surprisingly, the melt flow ratio (I
10
/I
2
) of the substantially linear olefin interpolymers can be varied essentially independently of the polydispersity index i.e., molecular weight distribution (M
w
/M
n
)). This is contrasted with conventional heterogeneously or homogeneously branched linear polyethylene resins having rheological properties such that as the polydispersity index increases, the I
10
/I
2
value also increases.
The term “substantially linear” ethylene/&agr;-olefin interpolymers means that the pol

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