Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1998-08-21
2001-10-30
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S170000, C521S174000, C528S059000, C528S065000, C528S066000, C568S025000, C568S026000, C568S330000, C568S359000
Reexamination Certificate
active
06310114
ABSTRACT:
The present invention relates to a process for producing compact and preferably cellular polyurethane elastomers, hereinafter also abbreviated to PU elastomers, by reacting
a) polyhydroxyl compounds having molecular weights of from 800 to 6000 and, if desired,
b) chain extenders and/or crosslinkers having molecular weights of up to 800 with
c) naphthylene 1,5-diisocyanate and at least one additional aromatic diisocyanate selected from the group consisting of tolylene diisocyanate, diphenylmethane diisocyanate, 3,3′-dimethylbiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and phenylene diisocyanate, and/or aliphatic diisocyanate having from 4 to 12 carbon atoms an d/or cycloaliphatic diisocyanate having from 6 to 18 carbon atoms, where the formative components (a), (c) and, if used, (b) are preferably reacted by the prepolymer method,
in the absence or preferably in the presence of
d) catalysts,
e) water-containing blowing agents and
f) additives,
and isocyanate prepolymers suitable for this purpose, preferably those based on diphenylmethane 4,4′-diisocyanate (MDI) and naphthylene 1,5-diisocyanate (NDI).
The microcellular PU elastomers display excellent static and dynamic properties. Owing to their specific damping characteristics and long-term use properties, they are used, in particular, in vibration- and shock-damping systems.
The production of compact or cellular, eg. microcellular, PU elastomers has been known for a long time from numerous patent and literature publications.
Their industrial importance depends on the combination of good mechanical properties with the advantages of inexpensive processing methods. The use of various chemical formative components in different mixing ratios enables the production of thermoplastically processible or crosslinked, compact or cellular PU elastomers which display a wide variety of processing properties and mechanical properties. An overview of PU elastomers, their properties and uses is given, for example, in Kunststoff-Handbuch, volume 7, Polyurethane, 1st edition, 1966, edited by Dr. R. Vieweg and Dr. A. Höchtlen, 2nd edition, 1983, edited by Dr. G. Oertel, and 3rd edition, 1993, edited by Prof. Dr. G. W. Becker and Prof. Dr. D. Braun, (Carl-Hanser-Verlag, Munich, Vienna).
In comparison with the types of rubber which can be used in a similar manner, microcellular PU elastomers have significantly better damping properties together with an excellent volume compressibility, so that they are used as constituents of vibration- and shock-damping systems, particularly in the automobile industry. For producing microcellular PU elastomers, reaction products of 1,5-NDI and poly(ethylene glycol adipate) having a molecular weight of 2000, which are reacted in the form of an isocyanate prepolymer with an activator-containing, aqueous solution of a fatty acid sulfonate, have proven useful. (Kunststoff-Handbuch, volume 7, Polyurethane, 1st edition, pp. 270ff.)
Since such base formulations give microcellular PU elastomers having very good damping characteristics and static and dynamic performance parameters, the prior art discloses only a few efforts aimed at replacing the 1,5-NDI responsible for the good elastomer properties, despite its difficult handling because of its high melting point, by more easily handled and less costly diisocyanates, since this results in significant mechanical property losses. Characteristic property differences between PU elastomers based on 1,5-NDI and those based on 4,4′-MDI are given for compact PU elastomers in general and microcellular PU elastomers in particular in Journal of Elastomers and Plastics, Vol. 21, (1989), pages 100 to 121. Significant disadvantages described for a microcellular PU elastomer based on 4,4′-MDI are a distinctly higher degree of damping with increased material heating and significantly increased consolidation under dynamic loading, which finally lead to more rapid material wear compared with PU elastomers based on 1,5-NDI.
Despite these obvious disadvantages, attempts have been made in the production of microcellular PU elastomers to replace the 1,5-NDI by the lower-melting and less costly 4,4′-MDI. However, these attempts have been restricted to the use of new starting components, in particular relatively high molecular weight polyhydroxyl compounds, by means of which certain mechanical properties of the microcellular PU elastomer are improved.
EP-A-0 496 204 (U.S. Pat. No. 5,173,518) describes a process for producing cellular PU elastomers using polyether polycarbonate diols containing polyoxytetramethylene glycol radicals having a mean molecular weight of from 150 to 500 in condensed-in form, as relatively high molecular weight polyhydroxyl compounds. This improves the mechanical properties, in particular the elongation at break, even at relatively low temperatures. However, no improvement is found in the static compressive sets in accordance with DIN 53 572 at 70° C., which are known to correlate with the dynamic consolidation values. Even when using 1,5-NDI as polyisocyanate, only average static compressive sets are obtained.
EP-B-0 243 832 (U.S. Pat. No. 4,798,851), which describes the use of pseudoprepolymers based on 4,4′-MDI, inter alia in combination with water as blowing agent, for producing elastic, compact or cellular PU or PU-polyurea moldings, teaches the use of a hydroxyl-containing polycondensate of a short-chain polyoxytetramethylene glycol and an aliphatic dicarboxylic acid as relatively high molecular weight polyhydroxyl compound with the object of the invention being to obtain a polyhydroxyl compound containing ester groups which can readily be metered by means of pumping for producing cellular or compact PU elastomers having improved mechanical and hydrolytic properties. Information about degrees of compressive set on static or dynamic loading, by means of which vibration-resistant materials are usually characterized, is not disclosed.
DE-A-36 13 961 (U.S. Pat. No. 4,647,596) describes a microcellular PU elastomer based on 4,4′-MDI which, owing to a defined composition of the relatively high molecular weight polyhydroxy compounds, consisting of a copolymer of polytetrahydrofuran and &egr;-caprolactone, has mechanical properties which are a favorable compromise between static strength and dynamic stressability. Despite the use of expensive feedstocks for producing the polyhydroxyl compounds, the performance gain achieved thereby appears to be relatively small when the test values “product durability, flexural strength by the De Mattia method and compressive set at 50% compression” are examined. For example, the measured values for the compressive set, which are directly related to the practically important dynamic consolidation, show only slight improvements when using the teachings of that invention.
In addition, the test criteria “product durability and flexural strength by the De Mattia method” used appear to be insufficiently suitable for a realistic evaluation of the dynamic properties, since, in the case of partial property improvements, they are not able to satisfactorily show up the actual property differences between polyurethane elastomers based on 4,4′-MDI and 1,5-NDI. Thus, the example based on 1,5-NDI displays no qualitatively higher level of properties than the examples based on 4,4′-MDI.
The stepwise production of PU elastomers is also known. According to DE-A-25 47 864 (U.S. Pat. No. 4,191,818), a heat-resistant PU elastomer can be produced by reacting an essentially linear relatively high molecular weight dihydroxy compound with a deficiency of diisocyanate to give an adduct containing terminal hydroxyl groups and subsequently reacting this adduct with a symmetric aromatic diisocyanate in excess and alkanediols or di(alkylene glycol) terephthalates as chain extenders. If cellular PU elastomers are to be produced by this method, water can also be used as chain extender, possibly in combination with alkanediols and/or di(alkylene glycol) terephthalates.
Cellular PU elastomers can also be pr
Bollmann Heinz
Genz Manfred
Haselhorst Walter
Hellmann Gerhard
Jeschke Torsten
BASF - Aktiengesellschaft
Borrego Fernando A.
Cooney Jr. John M.
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