Microcellular polyurethane elastomer containing urea groups

Details Microcellular polyurethane elastomer containing urea groups Microcellular polyurethane elastomer containing urea groups

1998-10-07

2000-03-14

Cooney, Jr., John M.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

521170, 521172, 521174, C08G 1804

Patent

active

060373830

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a microcellular polyurethane elastomer containing urea groups which is based essentially on diphenylmethane 4,4'-diisocyanate (4,4'-MDI) as isocyanate component and has improved static and dynamic properties. The invention also relates to a process for preparing such a microcellular polyurethane elastomer and to its use for producing damping elements.


PRIOR ART

The preparation of cellular polyurethane elastomers, their use and their mechanical and chemical performance parameters are comprehensively described in Kunststoffhandbuch, Volume VII, Polyurethanes, 1966, 1983 and 1993 by R. Vieweg and A. Hochtlen or G. Oertel (Carl Hanser Verlag, Munich). Essentially, in comparison with rubber types used in a similar way, microcellular polyurethane elastomers have significantly improved damping properties with excellent volume compressibility, as a result of which they are favored as constituents of vibration- and shock-damping systems, particularly in the automobile sector.
The most typical example of a microcellular polurethane elastomer for the above application is probably the reaction product of naphthylene 1,5-diisocyanate (NDI) and polyethylene glycol adipate having a mean molecular weight of about 2000 g/mol, which is reacted as NCO prepolymer with an activator-containing 50% strength aqueous solution of a fatty acid sulfonate. Although the performance level of this basic formulation has not hitherto been equalled in respect of its damping characteristics and other static and dynamic performance parameters, the literature does disclose a few efforts made to replace the NDI responsible for the excellent elastomeric properties by the far cheaper and significantly easier-to-handle 4,4'-MDI as isocyanate component, with distinct property losses being reckoned with. Characteristic differences in performance values between NDI-based and 4,4'-MDI-based compact polyurethane elastomers in general and microcellular formulations in particular are given by E. C. Prolingheuer, J. J. Lindsay and H. Kleimann in Journal of Elastomers and Plastics, Vol. 21, April 1980. Important disadvantages of a microcellular polyurethane elastomer based on 4,4'-MDI are here given as a significantly higher degree of damping with greater material heating and significantly increased consolidation values under dynamic loading, which lead to more rapid material wear compared with NDI.
Despite these obvious disadvantages, it is known from the literature, as already mentioned above, that attempts have been made to use 4,4'-MDI in place of NDI as isocyanate component in microcellular polyurethane elastomers. However, these experiments have been restricted to the use of new raw material components, in particular relatively high molecular weight polyhydroxyl compounds, by means of which certain property advantages of the resulting microcellular polyurethane elastomer are to be achieved.
Thus, EP-A-0496204 describes a process for preparing cellular polyurethane elastomers using polyether carbonate diols containing polyoxytetramethylene glycol units having a number-average molecular weight M.sub.n of from 150 to 500 g/mol as oligomeric polyhydroxyl compound. This is supposed to improve the mechanical properties, in particular the extension at break, even at relatively low temperatures. An improvement according to the invention in the static compressive sets in accordance with DIN 53 572, 70.degree. C., which are known to correlate with the dynamic consolidation values, cannot be found. Even when using NDI and an aqueous foaming component as described in the original preparation instructions (cf. Kunststoffhandbuch, Volume VII, Polyurethane, 1966, 1983 and 1993), only average static compressive sets are obtained.
EP-A-0243832, which likewise claims the use of 4,4'-MDI, inter alia in combination with water as blowing agent, for preparing microcellular polyurethane elastomers, encompasses as significant inventive concepts the use of a hydroxyl-containing polycondensate of a short-chain polyox

REFERENCES:
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patent: 5585413 (1996-12-01), Nagashima
patent: 5698608 (1997-12-01), Nagashima
Journal of Elastomers and Plastics, vol. 21--Apr. 1980, E. C. Proungheuer, J.J. Lindsey & H. Kleimann.
Kautschuk & Gummi, Kunstoffe 35. Jahrgang, Nr. Jul. 1982. Th. Timm.

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