Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Patent
1997-04-21
2000-02-22
Davis, Jenna
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
156242, 156252, 428220, 4282954, B32B 310, B32B 3124
Patent
active
060277866
DESCRIPTION:
BRIEF SUMMARY
This invention relates to improved composite materials with improved mouldability and methods for making them, and more particularly to the improvement of composite materials which can be shaped by rapid thermo-forming from semi-finished materials such as sheet, rod and tube.
It is common practice to reinforce materials by incorporating in them a reinforcing material in the form of lengths of fibre or continuous filament. Further, to increase the effect of such reinforcement, it is common to align the reinforcing fibres or filaments so that they give the composite an extra improvement in a selected direction, substantially in the direction of the alignment. Moreover, if highly reinforced materials are required, a high degree of alignment is a necessary condition for achieving the desired level of fibre content, which normally involves using the reinforcement in continuous form.
If attempts are made to form deeply drawn three-dimensional articles from composite materials which are reinforced with continuous filaments, severe fibre disturbance and even breakage can occur because of the minimal extensibility in the direction of the reinforcement.
This problem can be potentially overcome if the continuous filaments are replaced by discontinuous fibres, but there are problems in aligning discontinuous fibres to the high level which can be achieved when continuous filaments are used.
One method is disclosed in GB. Patent No. 1,389,539, where chopped fibres are dispersed in a viscous medium such as glycerol and subsequently aligned by subjecting the medium to convergent laminar flow conditions prior to depositing the fibres on a suitable filter bed. Another method is disclosed in U.S. Pat. Nos. 4,552,805 and 4,759,985 where a tow of reinforcing filaments is converted into a cohesive sliver of stretch-broken fibres which can subsequently be collimated and impregnated. However, in both cases there is some loss of control over fibre alignment, and this can limit the level of fibre volume fraction and material properties which can be achieved.
Also, in the case of GB. Patent No. 1,389,539 there is only mention of relatively short discontinuous fibres, i.e. 3 mm, which yield products with inferior impact properties, whilst in the case U.S. Pat. Nos. 4,552,805 and 4,759,985 the degree of control over fibre length is restricted to the natural fibre length distributions which results from the stretch-breaking process.
The principal object of the present invention is to overcome these problems and to provide a method for making composite materials with discontinuous fibre reinforcement which are equivalent in fibre alignment and fibre volume fraction to those based on continuous filament reinforcement.
We have now found that the problems can be overcome by making the composite first with the long continuous filaments and appropriately aligning these, and then--once these filaments are secured in the matrix material--treating this composite so that the length of the filaments can be broken down (severed) in a controlled manner in situ to whatever shorter lengths are desired for further use. This retains the alignment of the fibres to a degree which cannot be attained reliably if the manufacture of the composite starts with the task of embedding short fibres into the matrix material.
Thus according to our invention we provide a method for the manufacture of a composite material of improved mouldability, which comprises subjecting a composite material containing aligned fibre reinforcing material of long length ("continuous filament") embedded within a matrix material to a treatment with means which form discontinuities in the said continuous filaments so that they can be severed into shorter lengths in a controlled and pre-determined manner without unduly affecting the matrix material within which the said continuous filaments are embedded.
This allows the alignment to be achieved most easily, using known methods and materials, and for this to be maintained as the length of the continuous filament is reduced.
The starting m
REFERENCES:
patent: 4990207 (1991-02-01), Sakai et al.
patent: 5047281 (1991-09-01), Betz et al.
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