Intrinsic low friction polyoxymethylene
View Patent ↗A tribologically modified polyoxymethylene polymer composition is disclosed. The polyoxymethylene polymer composition is comprised of a polyoxymethylene polymer and at least one tribological modifier. The tribological modifier may comprise at least one tribological modifier comprising an ultra-high molecular weight silicone having a kinematic viscosity of greater than 100,000 mm 2 s −1 . The composition may exhibit a dynamic coefficient of friction against a counter-material of from about 0.01 to about 0.15. The polyoxymethylene polymer compositions provide polymer articles with improved tribological properties and mechanical properties.
1. A polyoxymethylene polymer composition, the polyoxymethylene polymer composition comprising
a polyoxymethylene copolymer combined with a nucleant, the nucleant comprising an oxymethylene terpolymer, and
at least one tribological modifier comprising an ultra-high molecular weight silicone having a kinematic viscosity at 40° C. of greater than 100,000 mm 2 s −1 ,
wherein the polymer composition is substantially free of silicone oil, and
wherein the polymer composition has a dynamic coefficient of friction against a counter-material of from about 0.01 to about 0.15, the dynamic coefficient of friction being tested according to VDA Test 230-206 using ball-on-plate configuration with a load of 12.5 N, a sliding speed of 8 mm/s and a test duration of 8 minutes, and wherein the counter material is a polyester surface, a steel surface, or a polypropylene surface.
2. The polymer composition of claim 1 , wherein the nucleant is present in the composition in an amount from about 0.01% by weight to about 2% by weight.
3. The polymer composition of claim 1 , wherein the polyoxymethylene copolymer contains comonomer units in an amount from about 0.5 mol % to about 5 mol %.
4. The polymer composition of claim 1 , wherein the polyoxymethylene copolymer has a melt flow index of greater than about 5 g/10 min.
5. The polymer composition of claim 1 , wherein the ultra-high molecular weight silicone is present in an amount of from about 0.1 to about 10 wt. %.
6. The polymer composition of claim 1 , wherein the tribological modifier further comprises a hexagonal boron nitride in an amount of from about 0.1 to about 5 wt. %.
7. The polymer composition of claim 6 , wherein the hexagonal boron nitride has a particle size of less than 10 μm.
8. The polymer composition of claim 1 , wherein the tribological modifier further comprises polytetrafluoroethylene in an amount of from about 0.1 to about 50 wt. %.
9. The polymer composition claim 1 , wherein the composition further comprises a polyethylene wax in an amount of from about 0.1 to about 5 wt. %, an amide wax in an amount of from about 0.1 to about 5 wt. %, or a combination thereof.
10. The polymer composition of claim 1 , wherein the composition further comprises calcium carbonate particles, ultrahigh molecular weight polyethylene, stearyl stearate, an aliphatic ester wax composed of a fatty acid and of a monohydric alcohol, a graft copolymer comprising a polyethylene or polypropylene graft base grafted with an acrylonitrile or with a styrene/acrylonitrile copolymer, or a combination thereof.
11. The polymer composition of claim 1 , wherein the counter-material is the polyester surface, the polyester surface comprising a polyethylene terephthalate surface.
12. The polymer composition of claim 1 , wherein the composition has a dynamic coefficient of friction against the counter-material of from about 0.05 to less than 0.09.
13. The polymer composition of claim 1 , wherein the composition has a modulus of elasticity measured according to ISO Test No. 527 of at least about 2000 MPa.
14. The polymer composition of claim 1 , wherein the composition is substantially free of a reinforcing fiber.
15. A polymer article made from the composition of claim 1 , the polymer article comprising a gear, a lever, a cam, a roller, a sliding element, a pulley, a latch, a claw, a wiper arm, a conveyor component, a medical inhaler, or a medical injector.
16. A polymer article comprising a polyoxymethylene polymer composition as defined in claim 1 .
17. The polymer article of claim 16 , wherein the polymer article has a surface roughness determined according to DIN 4768 of greater than about 0.1 μm and less than about 30 μm.
18. A polyoxymethylene polymer composition, the polyoxymethylene polymer composition comprising
a polyoxymethylene copolymer having a melt flow index of less than about 50 g/10 min, and
at least one tribological modifier comprising an ultra-high molecular weight silicone having a kinematic viscosity at 40° C. of greater than 100,000 mm 2 s −1 ,
wherein the polymer composition is substantially free of silicone oil, and
wherein the polymer composition has a dynamic coefficient of friction against a counter-material of from about 0.01 to about 0.15, the dynamic coefficient of friction being tested according VDA Test 230-206 using a ball-on-plate configuration with a load of 12.5 N sliding seed of 8 mm/s and a test duration of 8 minutes, and wherein the counter material is a polyester surface, a steel surface, or a polypropylene surface.
19. The polymer composition of claim 18 , wherein the composition further contains a nucleant comprising an oxymethylene terpolymer.
20. The polymer composition of claim 18 , wherein the nucleant is present in the composition in an amount from about 0.01% by weight to about 2% by weight.
21. The polymer composition of claim 18 , wherein the polyoxymethylene copolymer contains comonomer units in an amount from about 0.5 mol % to about 5 mol %.
22. The polymer composition of claim 18 , wherein the polyoxymethylene copolymer has a melt flow index of greater than about 5 g/10 min.
23. The polymer composition of claim 18 , wherein the ultra-high molecular weight silicone is present in an amount of from about 0.1 to about 10 wt. %.
24. The polymer composition of claim 18 , wherein the tribological modifier further comprises a hexagonal boron nitride in an amount of from about 0.1 to about 5 wt. %.
25. The polymer composition of claim 18 , wherein the tribological modifier further comprises polytetrafluoroethylene in an amount of from about 0.1 to about 50 wt. %.
26. The polymer composition claim 18 , wherein the composition further comprises a polyethylene wax in an amount of from about 0.1 to about 5 wt. %, an amide wax in an amount of from about 0.1 to about 5 wt. %, or a combination thereof.
27. The polymer composition of claim 18 , wherein the composition further comprises calcium carbonate particles, ultrahigh molecular weight polyethylene, stearyl stearate, an aliphatic ester wax composed of a fatty acid and of a monohydric alcohol, a graft copolymer comprising a polyethylene or polypropylene graft base grafted with an acrylonitrile or with a styrene/acrylonitrile copolymer, or a combination thereof.
28. The polymer composition of claim 18 , wherein the counter-material is the polyester surface, the polyester surface comprising a polyethylene terephthalate surface.
29. The polymer composition of claim 18 , wherein the composition has a modulus of elasticity measured according to ISO Test No. 527 of at least about 2000 MPa.
30. The polymer composition of claim 18 , wherein the composition is substantially free of a reinforcing fiber.
31. A polymer article made from the composition of claim 18 , the polymer article comprising a gear, a lever, a cam, a roller, a sliding element, a pulley, a latch, a claw, a wiper arm, a conveyor component, a medical inhaler, or a medical injector.
32. A polyoxymethylene polymer composition, the polyoxymethylene polymer composition comprising
a polyoxymethylene copolymer having a melt flow index of less than about 50 g/10 min, and
at least one tribological modifier comprising an ultra-high molecular weight silicone having a kinematic viscosity at 40° C. of greater than 100,000 mm 2 s −1 ,
reinforcing fibers present in the composition in an amount of at least 10% by weight up to 50% by weight; and
polytetrafluoroethylene in an amount from 0.1% to 50% by weight.