Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1985-05-13
1988-05-10
Anderson, Philip
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
264 453, 264 50, 264 53, 264 54, 264101, 264DIG5, 4283066, 521 51, 521 78, 521138, 521182, B29C 6722, B29C 3912, C08J 904
Patent
active
047434171
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for the manufacture of a product comprising foamed plastic material in first and second layers. The second layer is connected to the first layer and has a higher density than the first layer.
PRIOR ART
It is usual in the manufacture of foamed plastic products to utilize some form of foaming agent which is dissolved in the base material or is added to it immediately before the foaming process is to commence. As an example of a chemical foaming agent sulphonyl hydrazides may be mentioned. The foaming process can also be brought about by the use of physical agents in the form of a volatile gas such as a chlorofluorocarbon as represented by the FREONS, for example, FREON 11, which is dissolved in (that is to say, forms part of a single-phase system with) the base material. A familiar example of the last-mentioned method is provided by the manufacture of rigid polyurethane foam. The use of carbon dioxide as a foaming agent has also been disclosed.
Activation of the foaming agent in question, for example by means of catalysts, heat and/or a vacuum, will cause the agent to generate gas, resulting in the formation of bubbles which are apparent in the finished product. The familiar methods used until now for the manufacture of foamed plastic products nevertheless call for the use of a comparatively large quantity of foaming agent of up to 10 percent by weight or more. The use of such a large quantity of foaming additives will result in various manufacturing problems such as, for example, problems associated with curing and storage which, when viewed as a whole, complicate the manufacturing process and impair the product. Furthermore, the choice of base materials and the range of possible variations in the production conditions such as, for example, the variations in temperature, are restricted to a certain extent, which has a negative effect on the result.
DESCRIPTION OF THE INVENTION
Technical Problem
A goal which is associated with foamed plastic products is for manufacturing processes to be available which provide the conditions necessary for a major reduction to be achieved in the quantity of the foaming additives used. Said additives have tendencies to disturb the curing processes and cause cracks. Demands on durable and cheap products are available as well.
Further goals are to be able to allot, if necessary, the different layers of the product different thicknesses by a simple control procedure and to be able to provide the product with exactly positioned reinforcements, if necessary.
The present invention proposes a method for the manufacture of a product having a foamed plastic material which will resolve, among other matters, the problem outlined above on the basis of the usage of unsaturated polyester and the discovery that considerably increased foaming effect can be achieved from the use of a foaming agent at a high degree of low pressure, with a vacuum of 60-95% (0.05-0.4 bar) being envisaged in this case. The essential characteristics of the new method are, among other factors, that inside a first zone, which is at a first pressure, the aforementioned foaming agent is mixed with or dissolved in a curing agent-compatible unsaturated polyester. A second feature of the invention comprises the usage of a second zone in the form of a negative pressure chamber which is at that high degree of negative pressure of 60-95% (0.05-0.4 bar) vacuum. The last mentioned pressure is quite below the first pressure. Said chamber contains an open or exposed mold on which the mixture of foaming agent and polyester is sprayed. In order to attain the first layer, polyester mixed with a first amount of foaming agent is sprayed on the whole or parts of the mode under said low pressure. The foaming effect is initiated by means of a curing agent, initiators, and/or said negative pressures, and the foaming agent causes a powerful foaming effect in which bubbles are created and/or expanded in the sprayed polyester. In order to form the second layer, polyester ha
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Anderson Philip
Rovac Technology, Inc.
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