Thermoplastic polymer compositions having low friction resistance
A polymer composition comprises a thermoplastic polymer (A) and a copolymer (B). The thermoplastic polymer (A) is selected from a polyacetal and a polyolefin. The copolymer (B) is of a polysiloxane (B1) and an olefin polymer (B2). The copolymer (B) is a branched block copolymer and is free of any siloxane homopolymer. The copolymer (B) is useful as a friction reducing additive in the polymer composition.
1. A polymer composition comprising:
a thermoplastic polymer (A) selected from a polyacetal and a polyolefin; and
a copolymer (B) of a polysiloxane (B1) and an olefin polymer (B2);
wherein the copolymer (B) is a branched block copolymer having a zero shear viscosity of 50,000 to 8,000,000 Pa·s at 190° C.;
and wherein the polymer composition is free of any siloxane homopolymer.
2. The polymer composition according to claim 1 , wherein the olefin polymer (B2) is a copolymer of at least 50% by weight ethylene with up to 50% of an acrylate or methacrylate ester.
3. The polymer composition according to claim 2 , wherein the thermoplastic polymer (A) is polyoxymethylene.
4. The polymer composition according to claim 2 , wherein the olefin polymer (B2) is a copolymer of 95-60% by weight ethylene with 5-40% methyl methacrylate.
5. The polymer composition according to claim 1 , wherein the olefin polymer (B2) is polyethylene.
6. The polymer composition according to claim 1 , wherein the branched block copolymer (B) is a copolymer of 20-80% by weight polysiloxane (B1) and 80-20% olefin polymer (B2).
7. A process for the production of a thermoplastic polymer composition of reduced coefficient of friction, said process comprising the steps of:
(i) melt kneading a polysiloxane (B1) containing ethylenically unsaturated groups with an olefin polymer (B2) under process conditions at which all the polysiloxane (B1) is reacted with the olefin polymer (B2) to produce a branched block copolymer (B) which is free of any siloxane homopolymer; and
(ii) blending a thermoplastic polymer (A) with the branched block copolymer (B) produced in step (i) to produce the thermoplastic polymer composition.
8. The process according to claim 7 , wherein the polysiloxane (B1) and the olefin polymer (B2) are melt kneaded in an extruder at a temperature in the range of 150° C. to 240° C.
9. The process according to claim 8 , wherein the extruder is a biaxial or multiaxial extruder.
10. The process according to claim 7 , wherein the polysiloxane (B1) contains at least 3 vinyl groups per molecule.
11. The process according to claim 7 , wherein the thermoplastic polymer (A) and the branched block copolymer (B) are blended in an extruder.
12. The process according claim 7 , wherein the thermoplastic polymer (A) and the branched block copolymer (B) are blended by mixing in an injection press.
13. The process according to claim 7 , wherein the thermoplastic polymer (A) is polyoxymethylene or an oxymethylene copolymer.
14. The process according to claim 7 , wherein the thermoplastic polymer (A) is a polyolefin.
15. A process of improving a thermoplastic polymer (A), said process comprising the step of:
adding a solid copolymer (B) to the thermoplastic polymer (A);
wherein the thermoplastic polymer (A) is selected from a polyacetal and a polyolefin; and
wherein the copolymer (B) is a branched block copolymer of a polysiloxane (B1) and an olefin polymer (B2), and wherein the copolymer (B) has a zero shear viscosity of 50,000 to 8,000,000 Pa·s at 190° C.; and
wherein the process is free of any siloxane homopolymer.
16. The process according to claim 15 , wherein addition of the solid copolymer (B) improves the slidability and/or reduces the coefficient of friction and/or improves the wear resistance of the thermoplastic polymer (A).