Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2000-04-28
2001-07-17
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S331110, C264S338000
Reexamination Certificate
active
06261503
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the protection of flexible bi-constituent silicone membranes, more particularly flexible self-demoulding silicone membranes, particularly in the case of use in moulding by resin transfer.
A bi-constituent silicone has the following general formula when it is obtained by poly addition:
Resin transfer moulding consists in preparing forms having confronting surfaces generating a volume of the shape of the piece to be made, placing on the walls of this volume a flexible silicone membrane to permit demoulding the finished piece, and injecting into the space delimited by said membrane, resin and its polymerization catalyst. The mould walls can be heated so as better to control the polymerization reaction.
This process is widely used in the automotive industry and in the field of sports and leisure. This process permits obtaining better technical performances, reducing the production cycles.
Initially used only for small-size pieces, this process tends to be more widespread and to find applications including the production of structures of large size, as in the aeronautical field.
Moreover, the injected resins are of the phenolic type and have particularly interesting advantages in this aeronautical field, because they are self-extinguishing and the fumes given off, of small volume, are not harmful.
Each resin is sold with its catalyst and there is more particularly known one among others which contains paratoluene sulfonic acid.
This catalyst is well known for this property as to certain resins but it has on the other hand drawbacks as to health, because it is an irritating acid but above all it can become noxious at the temperatures at which it is used, in addition to being costly.
The flexible self-demoulding silicone membrane itself has numerous qualities which are essential for the good practice of the process. There is no machining, it is easy to demould because one need only pull on the membrane to peel it relative to the piece, and the surface condition of the obtained piece is excellent.
On the other hand, this membrane has an important drawback: in contact with the resin, and more particularly the phenol groups, the membrane corrodes. This corrosion has the effect of degrading the condition of the surface and this phenomenon becomes progressively more marked upon successive uses.
This premature aging causes the membrane to lose all its demoulding qualities and accordingly leads to a decrease of the quality of the surface condition of the piece. This fact requires the user to replace the membrane frequently, which replacement decreases the profitability of the process of resin transfer moulding.
SUMMARY OF THE INVENTION
The object of the invention is to provide a process for the production of a piece with a self-demoulding silicone membrane permitting avoiding premature degradation and thereby increasing the potential for use. This process must permit preserving the demoulding qualities, the good condition of the surface of the produced piece, which two generally go together, while avoiding substantially increasing the thicknesses.
To this end, the invention relates to a process for the production of a resin piece particularly by moulding with the aid of a self-demoulding silicone membrane, at least one of said resins comprising groups susceptible to have damaging action on said membrane, particularly corrosion, which process is characterized in that the time of polymerization of said resin is reduced such that it polymerizes rapidly after its introduction into the mould to block the action of said groups.
In the case of at least one resin comprising phenol groups, the catalyst is selected from the family of sulfonic acids and is methane sulfonic acid.
The quantity of catalyst used is of the order of one part by weight per 100 parts by weight of resin.
The solvent used is aqueous and the working temperature is below 95° C.
REFERENCES:
patent: 4200706 (1980-04-01), Starks
patent: 4270964 (1981-06-01), Flaskett
patent: 4740535 (1988-04-01), Iyer et al.
patent: 5243015 (1993-09-01), Hutchings et al.
patent: 5344909 (1994-09-01), Hutchings et al.
patent: 384 800 A1 (1990-08-01), None
Abstract of Japan 57-72750 (May 7, 1982).*
Abstract of Japan 59-172541 (Sep. 29, 1984).
Aumont Christophe
Fournier Alain
Aerospatiale Matra Airbus
Tentoni Leo B.
Young & Thompson
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