Thermoplastic polyurethane copolymer molding compositions
View Patent ↗Compositions for forming molded articles, particularly, shells for automotive applications are made up of melt blends of an aliphatic thermoplastic urethane elastomer and one or more polyolefin-based modifiers. These compositions may be blended to form a powder, pellets, microspheres or minibeads which may then be cast to form air bag door and instrument panel cover skins which may meet automotive deployment and weathering requirements.
1. A molding composition consisting of a compatible blend of
a) from 5 to 95 wt. % of an aliphatic thermoplastic polyurethane comprising the reaction product of
(i) a polyol component comprising at least one polyether polyol having a molecular weight of from 1000 to 10,000 Da and an unsaturation level less than or equal to 0.04 meq/g,
(ii) an isocyanate component comprising at least one aliphatic organic diisocyanate,
(iii) a chain extender,
(iv) optionally, a UV stabilizing agent,
(v) optionally, an antioxidant,
(vi) optionally, a pigment, and
(vii) a catalyst which promotes urethane formation,
b) from 5 to 95 wt. % of a polyolefin-based modifier selected from the group consisting of a vulcanized terpolymer of ethylene/propylene/diene dispersed in polypropylene, a vulcanized terpolymer of ethylene/propylene/diene dispersed in polyethylene, a styrenic block copolymer with a hydrogenated midblock of styrene-ethylene/butylene-styrene (SEBS), a styrenic block copolymer with a hydrogenated midblock of styrene ethylene/propylene-styrene (SEPS), a block copolymer of styrene butadiene-styrene (SBS), a block copolymer of styrene-isoprene-styrene (SIS), and an ethylene-octene copolymer,
c) optionally, a UV stabilizing agent,
d) optionally, an antioxidant,
e) optionally, a pigment,
f) optionally, a mold release agent, and
g) optionally, an ethylene/methacrylic acid copolymer in which the methacrylic acid groups have been partially neutralized.
2. The composition of claim 1 in which the modifier b) has a shear viscosity of approximately 900 at a shear rate of 250 sec −1 which drops to approximately 150 at 2100 sec −1 .
3. The composition of claim 1 in which the polyther polyol in a)(i) has an unsaturation level of less than 0.02 meq/g.
4. The composition of claim 1 in which the aliphatic diisocyanate is selected from the group consisting of hexamethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and isophorone diisocyanate.
5. The composition of claim 1 in which the chain extender is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, 1,4-butane diol, pentane diol, 3-methylpentane-1,5-diol, 1,6-hexane diol, hydroquinone bis(2-hydroxyethyl) ether, 1,4-cyclohexanedimethanol, neopentyl glycol, and hydrogenated bisphenol A.
6. The composition of claim 1 in which a portion of the ethylene/methacrylic acid copolymer is neutralized with a metal ion.
7. The composition of claim 1 in which modifier b) is a vulcanized terpolymer of ethylene, propylene, and diene dispersed in a polyolefin.
8. The composition of claim 1 in which a) is produced from a mixture comprising from 40 to 70 wt. %, based on total weight of the thermoplastic composition, of the polyol component.
9. The composition of claim 1 in which a) and b), and optionally, c), d), e) f), or g) are melt blended.
10. The composition of claim 1 comprising:
a) 45-90 wt. % of aliphatic thermoplastic polyurethane;
b) 5-45 wt. % of polyolefin-based modifier; and
e) 5-10 wt. % color concentrate,
with the total amount of a), b) and e) being equal to 100 wt. %.
11. The composition of claim 1 comprising:
a) 45-90 wt. % of aliphatic thermoplastic polyurethane;
b) 5-45 wt. % of polyolefin-based modifier and up to 10 wt. % ionomer; and
e) 5-10 wt. % color concentrate,
with the total amount of a), b) and e) being equal to 100 wt. %.
12. The composition of claim 1 in which the ratio of a) to b) by weight is greater than or equal to 1:1.
13. The composition of claim 1 in which the modifier b) is selected from linear triblock copolymers of styrene, ethylene, and butylene, hydrogenated styrene-ethylene-butylene-styrene, hydrogenated styrene-ethylene-propylene-styrene, styrene copolymerized in midblock, or unsaturated styrene copolymerized in midblock.
14. A thermoplastic polyurethane produced from only the composition of claim 1 , characterized by a DE less than or equal to 3 after exposure to 1993 kiloJoules/m 2 of Xenon arc.
15. A thermoplastic polyurethane produced from only the composition of claim 1 , characterized by elongation at break after heat aging of at least 100% after 500 hours at 120° C.
16. A thermoplastic polyurethane produced from only the composition of claim 1 , characterized by elongation at break before heat aging of from 300 to 600%.
17. A slush castable powder, pellet, microsphere, or minibead consisting of the composition of claim 1 .
18. A thermoformed sheet produced from only the composition of claim 1 .
19. A process for producing a slush castable powder comprising cryogenically grinding a melt blended extrudate comprising the composition of claim 1 .
20. A process for producing slush castable microspheres comprising melt blending the composition of claim 1 in an extruder, passing the melt blended composition through a die, and cutting the composition exiting the die.
21. A process for producing slush castable powder comprising underwater grinding of a melt blended extrudate comprising the composition of claim 1 .
22. A process for the production of a single layer cast shell, comprising:
a) applying only the composition of claim 1 to a mold surface;
b) heating the mold surface to cause the applied composition to melt;
c) allowing the melt to flow over the mold surface; and
d) allowing the melt to cool.
23. A molded article produced by the process of claim 22 .
24. A process for the production of a dual layer coast shell, comprising:
a) applying only the composition of claim 1 to a mold as an outer layer;
b) applying an inner layer comprising another composition to the outer layer; and
c) molding the inner and outer layers in a manner such that the inner and outer layers harden and bond together.
25. The process of claim 24 in which the inner layer composition is a polyurethane produced from an aromatic polyisocyanate.
26. The process of claim 24 in which the inner layer composition has a melt flow comparable to that of the composition of claim 1 used as the outer layer.
27. A molded article produced by the process of claim 26 .
28. A molded article in the form of a skin, cover or shell produced by the process of claim 26 .
29. A process for the production of an article, comprising injection molding only the composition of claim 1 .
30. An injection molded article produced by the process of claim 29 .