Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By gas forming or expanding
Patent
1998-09-04
2000-10-24
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By gas forming or expanding
249135, 264299, B29C 4138, B29C 4402
Patent
active
061362387
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The application relates to an improved process for producing plastic items, in particular polyurethane moulded items, wherein a device for producing polyurethane moulded items is used in which the internal surfaces consist entirely or partly of the steel defined in more detail below.
BACKGROUND OF THE INVENTION
To produce plastic items, in particular polyurethane articles, the prior art makes use of a mould release agent which enables removal of articles from the mould. These are generally waxes, silicones or soaps, dissolved/dispersed in water and/or organic solvents. Extraordinary efforts have been made for a long time to reduce or completely eliminate the use of mould release agents. There is a number of reasons for this which are well known to a person skilled in the art: of applying the mould release agent (aerosols) such as "powerwash" or sandblasting etc.
The majority of solutions proposed hitherto have been directed to the use of so called internal mould release agents, which are incorporated into the plastic (precursor) mixture before injecting this into the mould and which produce an improved mould separation effect. In fact, some improvements have been produced with selected polyurethane plastics. A number of applications for using internal mould release agents have been disclosed. Examples of these can be found e.g. in Oertel (Publisher), Kunststoffhandbuch Volume VII, Polyurethane, published by Hanser-Verlag. Here again, the internal release agent often has to be supported by use of a small amount of external mould release agent and thus post-treatment, e.g. if the item is to be lacquered, is required. Internal mould release agents may also exude and thus reduce the long term performance. On the other hand, there are cases where no internal mould release agents can be used, for example in the case of metallic inserts which have to exhibit firm adhesion, e.g. foam-padded steering wheels.
Suggestions for improving the mould material have also been disclosed. The work of Menges et al. (Kunststofftechnik 13 (1974), No. 9/10, p. 181 et seq.), has disclosed that aluminium has substantially better release behaviour, that is less adhesion, for polythurethane than steel moulds. However aluminium moulds cannot be used for mass production because they are not sufficiently wear resistant. Ceramic moulds have also been suggested for improved separation, and siliconised, galvanised, nickel-plated, chrome-plated moulds and moulds coated with PTFE etc. have also been proposed. Moulds which have been provided with surface coatings can only be repaired, if at all, at great expense when they become damaged. None of these modifications to steel surfaces has been incorporated into an industrial scale process.
All in all there is still a high demand for polyurethane moulded items which have been produced using no mould release agents or at least very little mould release agent. Economic, ecologic and occupational hygiene reasons have been put forward as reasons for this.
SUMMARY OF THE INVENTION
The object of the present invention was to provide a process which enables improved separating behaviour for plastic parts, in particular those made from polyurethane plastics, and which permits the improved production of moulded articles.
Surprisingly, it was found that separating characteristics could be achieved which exceeded all those in previously known processes if the production of moulded articles is performed in moulds in which the internal surfaces entirely or partly consist of optionally nitrided steel with the following percentage composition. and other elements such as S, Ti, Ni, and optionally
DETAILED DESCRIPTION OF THE INVENTION
The present invention therefore provides a process for producing plastic items, characterised in that they are produced in moulds in which the internal metallic surface(s) consist of steel with the percentage composition other elements such as S, Ti, Ni, and
Polyurethane moulded items are preferably produced.
The present invention also provides a pro
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Menges et al (Kunststofftechnik 13 (month unavailable) 1974 No. 9/10 pp. 181 et seq.
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Muller Henry
Rasshofer Werner
Symannek Achim
Bayer Aktiengesellschaft
Eyl Diderico van
Gil Joseph C.
Kuhns Allan R.
Whalen Lyndanne M.
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