Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Patent
1989-12-18
1991-07-30
Lorin, Hubert C.
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
264171, 26421122, 26421123, 264108, B29B 1508
Patent
active
050358480
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the processing of liquids containing aggregates of discrete filaments for the purpose of ensuring separation of the filaments from each other. The invention relates more particularly, although not exclusively, to the separation of such filaments in liquid (e.g. molten) polymer or resin flows prior to further processing of such flows to produce a coherent or semi-coherent structure of the filaments within the polymer or resin which is subsequently formed into solid artefacts.
It has long been recognised that the addition of glass, or other strong fibres, to a thermoplastic or thermoset polymer in a suitable fashion, usually brings increased stiffness or strength, or both, to the material processed into its final form. In the case of thermoplastics the glass fibres have until recently been quite short, often in the range 0.3 to 1 mm, and compositions have been processed in the same ways, for example by extrusion or injection moulding, as apply to thermoplastics on their own. The result of such processing is that by and large the fibres are disposed in the resulting solid artefact in ways which reflect the adventitious actions of the flow of the thermoplastic during the shaping process. It follows that the fibres will not in general be disposed so as to maximise their beneficial effect.
In the case of thermoset compositions, reinforcing fibres may be short, of the order 0.3 to 1 mm as in reaction injection moulding, with the same disadvantage described for thermoplastic materials, or they may be long discrete fibre rovings (typically 25 mm or longer) or as in filament winding, continuous through a considerable portion of the structure. If long discrete fibres are used, they are usually either constructed into a loose woven mat prior to contacting the resin, or scattered in a random, overlapping fashion on to a layer of resin with further resin placed on top.
In all cases with thermosets a degree of beneficial organisation of the fibres is obtained separately from the processes of resin flow and shaping to final artefact form.
This organisation into a more-or-less organised structure is a major reason why fibre-resin reinforced thermoset compositions show much greater strength and stiffness than do compositions based on short fibres which cannot be formed into such structures at the fibre loadings generally used. As will readily be appreciated, however, the advantage of the long-fibre method referred to carries with it a processing disadvantage by comparison with its short-fibre competitor, in that generally a good deal of semi-manual or mechanical intervention is required to achieve the desired organisation or disposition of the fibres.
Recently it has become clear that it is possible to create three dimensional network structures within a liquid by perturbing in a controlled, sequential manner, the liquid flow relative to its predominant direction provided the product of volume concentration and aspect ratio (1/d) of the fibre elements present in the flow exceeds a minimum value. In practice the criterion is met by fibre elements in the form of monofilaments of 5 to 15 mm long at volume concentrations of a few percent upwards. Such a process is disclosed in PCT/GB 87/00883 filed Dec. 7, 1987. In particular it is possible to obtain such network structures with thermoplastic and thermoset resins and to substantially preserve their structures during shaping of the thermoplastic or thermosets into their final solid state forms.
The fibres may be provided by polymer granules with a high loading (e.g. 20-50% by volume of the granules) of glass, carbon or metal fibres which have become available for use in extrusion or moulding. The fibres in the granules are typically in the form of a tow or roving of discrete filaments having a typical length of 5 to 15 mm and diameter of 2-20 microns Each granule may contain several (e.g. 2 to 4) lengths of the tow or roving each of which may contain 1000 to 5000 of the filaments. Such granules the `fibre granules`) may be admixed wi
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Lorin Hubert C.
Prosyma Research Limited
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