Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1992-07-24
1994-04-19
Welsh, Maurice J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 51, C08G 1814
Patent
active
053045815
DESCRIPTION:
BRIEF SUMMARY
The instant invention relates to a novel process for molding articles of microcellular elastomeric polyurethane (hereinbelow indicated, for the sake of brevity, simply as M.E.P.). More particularly, the instant invention relates to a particularly flexible process for molding a microcellular elastomeric polyurethane.
It is an object of the instant invention to provide a molding process which allows one to make a wide range--from the point of view of the physico-mechanical characteristics--of M.E.P. articles without the need for changing or substituting the starting materials.
Another object of the instant invention is that of providing a process for making M.E.P.s particularly suitable for said molding process, in which starting materials are employed having a well defined composition.
A further object of the instant invention is that of providing a process for molding M.E.P. articles wherein the reaction for producing the polyurethane is driven in a step preceding the molding of the article in order to form bases with a controlled and stable structure.
A further object yet of the instant invention is that of providing a process for molding M.E.P. articles which allows one to make M.E.P.s having different physico-mechanical characteristics, only by means of cross-linking agents.
Another important object of the instant invention is to provide a process for molding M.E.P. articles which can be automated by means of a processor.
These objects and others yet will be more clearly illustrated by the description hereinbelow.
As it is known, M.E.P. is generally made by reacting stoichiometric quantities of a polyol and of a prepolymer.
Practically, said reagents are taken from tanks and conveyed to the mixing heads by means of dosing pumps. The blending takes place as a result of the rapid increase of the flow speed of the materials introduced into the head, where they flow into one only zone of relatively limited dimensions so that there is a very high probability that the molecules of both of the reagents and of the catalyst may interact thereby producing a reaction product that is sufficiently homogeneous notwithstanding the very high reaction speed. However, for economic reasons, very short withdrawal times are demanded in the industrial process, and, hence, it is necessary to use considerable quantities of catalysts which, by remaining within the finished article, cause the deterioration of the latter's physico-mechanical characteristics.
Furthermore, since the polyols used for making M.E.P. do not consist of single components but instead of mixtures of different components, some of which are hardly or not at all soluble, this gives rise to the drawback of having to subject the polyol mixtures to homongenization before use. These polyol mixtures must also be constantly stirred during their use.
A further inconvenience of the state of the art processes lies in the fact that the quantity of reagents to be stocked for the molding process must not only be proportional to the quantity to be worked, but also to the type of article to be made. This necessitates the interruption of the production to allow for changing or modifying one or both reagents (polyol, isocyanate) and/or the catalyst. These changes and/or modifications, besides lowering productivity, cause the loss of starting materials and involve the use of solvents for washing the tanks and equipment. Last but not least, said changes and/or modifications almost always demand the re-adjustment of the operating conditions of the plant with the consequent problems of adjusting the production to the market requirements.
Evident are the shortcomings of the state of the art processes from what has briefly been described hereinabove.
Consequently, the object of the instant invention is that of providing a process for molding M.E.P. articles, that does not present the shortcomings of the processes known from the state of the art. It has now been found that when using strictly defined compounds (hereinafter called quasi-polyurethanes or, in short: Q-PUR), as the sta
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patent: 4686242 (1987-08-01), Turner et al.
patent: 4791148 (1988-12-01), Riley et al.
Scarnato Elio
Spagnoli Maurizio
C.O.I.M. Chimica Organica Industriale Milanese S.p.A.
Welsh Maurice J.
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