Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-01-11
2001-03-06
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...
C521S131000, C521S172000, C521S173000, C521S174000, C528S044000, C528S060000, C528S065000, C528S085000
Reexamination Certificate
active
06197839
ABSTRACT:
The present invention relates to a process for preparing compact and preferably cellular polyurethane elastomers, hereinafter also abbreviated as PU elastomers.
The preparation of compact or cellular, eg. microcellular, PU elastomers has long been known from numerous patent and literature publications.
Their industrial importance is based on the combination of good mechanical properties with the advantages of the inexpensive processing methods. The use of different types of chemical formative components in different ratios makes it possible to prepare thermoplastically processable or crosslinked, compact or cellular PU elastomers which differ widely in respect of their processability and their mechanical properties. An overview of PU elastomers, their properties and applications 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. G. W. Becker and Prof. D. Braun, (Carl-Hanser-Verlag, Munich, Vienna).
Compared with the types of rubber which can be used in a similar manner, microcellular PU elastomers have significantly improved damping properties and an excellent volume compressibility so that they are used as constituents of vibration- and shock-damping systems, in particular in the automobile industry. For preparing microcellular PU elastomers, reaction products of 1,5-NDI and poly(ethylene glycol adipate) having a molecular weight of 2,000 which are reacted in the form of an isocyanate prepolymer with an activator-containing, aqueous solution of a fatty acid sulfonate have been found to be useful. (Kunststoff-Handbuch, Volume 7, Polyurethane, 1st edition, pages 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 to replace the 1,5-NDI responsible for the good elastomeric properties, despite the fact that it is more difficult to handle because of its high melting point, by more readily handleable and less expensive diisocyanates since this leads to significantly poorer mechanical properties.
Characteristic property differences between compact PU elastomers in general and microcellular PU elastomers in particular based on 1,5-NDI and 4,4′-MDI are presented in Journal of Elastomers and Plastics, Vol. 21, (1989), pages 100 to 121. Important disadvantages given for a microcellular PU elastomer based on 4,4′-MDI are a significantly higher degree of damping with increased material heating and significantly increased consolidation values under dynamic loading which finally lead to a more rapid material wear in comparison with PU elastomers based on 1,5-NDI.
Despite these known disadvantages, attempts have been made in the preparation of microcellular PU elastomers to replace the 1,5-NDI by the lower-melting and less expensive 4,4′-MDI. However, these attempts have been restricted to the use of new starting components, in particular relatively high molecular weight polyhydroxyl compounds, the use of which improves certain mechanical properties of the microcellular PU elastomers.
EP-A-0 496 204 (U.S. Pat. No. 5,173,518) describes a process for preparing cellular PU elastomers using polyether polycarbonate diols containing polyoxytetramethylene glycol groups 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, there is no noticeable improvement 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 in the presence or absence of 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 purpose of obtaining a polyhydroxyl compound containing ester groups which is readily able to be metered by means of pumping for cellular or compact PU elastomers having improved mechanical and hydrolytic properties. Details of degrees of permanent deformation under static or dynamic loading, by means of which vibration-resistant materials are customarily characterized, are 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 polyhydroxyl compounds comprising a copolymer of polytetrahydrofuran and &egr;-caprolactone, has mechanical properties which represent a favorable compromise between static strength and dynamic stressability. Despite the use of expensive starting materials for preparing the polyhydroxyl compounds, the resulting performance improvement in terms of the test values “product durability, flexural strength by the De Mattia method and permanent deformation at 50% compression” is only relatively small. For example, the measured values for the compressive set which are directly related to the practically important parameter of dynamic consolidation are improved only slightly by applying the teachings of the invention.
In addition, the test criteria used, viz. “product durability and flexural strength by the De Mattia method”, do not appear to be sufficiently suitable for an assessment of the dynamic properties which is close to practice, 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 shows no better level of properties than the examples based on 4,4′-MDI.
The stagewise preparation 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 prepared by reacting an essentially linear relatively high molecular weight dihydroxy compound with a deficiency of diisocyanate to give an adduct having 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 prepared by this method, water, if desired in combination with alkanediols and/or di(alkylene glycol) terephthalates, can also be used as chain extenders.
Cellular PU elastomers can also be prepared by the process described in DE-A-2 940 856 (U.S. Pat. No. 4,334,033). According to this process, the relatively high molecular weight polyhydroxyl compounds and, if desired, chain extenders are reacted with an organic diisocyanate in a ratio of OH to NCO groups of from 1.2:1 to 2:1 to give a hydroxyl-containing prepolymer. This is divided in a weight ratio of about 80-20:20-80 into components (I) and (II); the component (I) is reacted with 1,5-NDI in a ratio of OH:NCO groups of 1:2.5-12 to give an NDI-polyurethane adduct containing NCO groups and the component (II) is combined with chain extenders, water and additives to form a mixture (II). The NDI-polyurethane adduct and the mixture (II) are finally reacted to give a compact or cellular PU elastomer. This process enables the formative components to be metered exactly and mixed rapidly and intensively. The PU elastomers are homogeneous and have uniform mechanical properties over the entire molding.
It is an object of the present invention to provide a process for preparing compact or preferably microcellular PU elastomers in which the expensive 1,5-NDI can be replaced at least partially by more readily handleab
Bollmann Heinz
Bruns Ute
Genz Manfred
Haselhorst Walter
Hellmann Gerhard
BASF - Aktiengesellschaft
Borrego Fernando A.
Cooney Jr. John M.
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