Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1982-03-30
1985-03-12
Anderson, Philip
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
15624411, 156324, 264 461, 264 464, 264 53, 264257, 264259, 264265, 264DIG64, 264DIG5, 425113, 425127, 425817R, 4283044, 428419, 521 79, B32B 520, B32B 3120, B29D 2700
Patent
active
045043388
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
TECHNICAL FIELD
The invention concerns methods for producing foamed thermoplastics materials and articles.
BACKGROUND ART
The consistent production of foamed thermoplastics materials (for example foamed polyethersulphone--hereinafter referred to as P.E.S.--polysulphone, polycarbonates and the like aromatic polymers) present several problems. One great problem is the production of a suitable preliminary material, precursor or pre-form for the foaming process.
In general a foamed thermoplastics material is formed by heating a pre-form or precursor material leading to a substantial expansion in its volume, and a substantial decrease in its density. To produce consistently high quality foamed thermoplastics material it is necessary that the pre-form material contains no large, visible, random, irregular holes which would lead to irregularities in the size and structure of the cells of the finished, foamed material. Such holes are hereafter referred to as `voids`.
The known techniques for producing pre-form materials essentially comprise soaking granules of a thermoplastics material to be foamed in a solvent for a considerable period of time (say 170 to 350 hours) and then heating the resultant gel to produce a foam of expanded material with a density substantially less than that of the original thermoplastics material. For example when foaming P.E.S. having an original density of approximately 1370 kgs/m.sup.3, steeping granules of P.E.S. in acetone and heating produces an expanded, foamed material with a density of approximately 100 kgs/m.sup.3.
The main problem with this method is that air becomes trapped in the gel pre-form material and causes irregularities in the size and structure of the cells in the finished product; the size of holes produced is usually so large that the material is of little use in applications requiring a uniform and readily reproducible product.
It is known that if the gel pre-form is allowed to dry for a considerable period of time (two to three months) after steeping, it is possible to produce a finished article having smaller and more regular cells. However large irregular `voids` still occur in such materials.
DISCLOSURE OF INVENTION
According to one aspect the invention provides a method of producing foamed thermoplastics materials in which the thermoplastics material is mixed with a solvent and the resultant gel is compressed to form a pre-form material which is then heated.
Fillers, reinforcing fibres of glass, carbon and the like, and/or colourants may also be added.
Chemical blowing or foaming agents may be incorporated in the compression stage. These agents do not generate gas until the pre-forms are heated.
The pre-form material produced may be expanded in a mould containing layers of continuous reinforcement material e.g. glass--or carbon-fibre reinforced materials. A random array of reinforcing fibres may be added to the thermoplastics material during its production to increase its structural stability.
Compression of the thermoplastics/solvent mix may be achieved by making use of a press or a two or three roll compounding mill (for one-off pre-form production), or of an extruder/die combination (for continuous pre-form production).
Other aspects of the invention provide foamed thermoplastics materials formed in accordance with the above methods and articles made thereof.
Experiments we have performed and which exemplify methods embodying the invention will now be described briefly.
The experiments we carried out make use of polyethersulphone (P.E.S.), (a thermoplastics material of the general formula: ##STR1## of the three following commercially available grades:
PES 200P (with a reduced viscosity of 0.39-0.43)
PES 300P (with a reduced viscosity of 0.46-0.50)
PES 500P (with a reduced viscosity of 0.34-0.38) C. Other grades and copolymers of the above may be used.
Similar results can be expected from polysulphone (of the general formula: ##STR2## and having a normal glass transition temperature of approximately 174.degree. C., or with polycarbonate
REFERENCES:
patent: 2714076 (1955-07-01), Seckel
patent: 4179540 (1979-12-01), Smarook
Anderson Philip
H. R. Smith (Technical Development) Limited
Schaffer Murray
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