GB2237583A

GB2237583A - Fibre reinforced thermoplastic composites

Info

Publication number: GB2237583A
Application number: GB8921844A
Authority: GB
Inventors: Peter David Jackson; Richard Graham Walker
Original assignee: PLASTIC DEVELOPMENTS Ltd
Current assignee: PLASTIC DEVELOPMENTS Ltd
Priority date: 1989-09-27
Filing date: 1989-09-27
Publication date: 1991-05-08
Also published as: GB8921844D0

Abstract

A prepreg consisting solely of thermoplastic binding fibres and reinforcing fibres is moulded to form composites. Preferably the reinforcing fibres are of carbon and form one or more unidirectional arrays or woven or knitted fabrics. The thermoplastic fibres may be polyether ketone or polyether sulphone applied to one or both faces of the reinforcing fibres. <IMAGE>

Description

A NOVEL PROCESS FOR THE PRODUCTION OF FIBRE REINFORCED THERMOPLASTIC COMPOSITES.

In the production of fibre reinforced plastics from thermoset resins, it is common to produce an intermediate process material known as a prepreg. Prepregs are reinforcement fabrics or unidirectional materials which have been pre-impregnated with resin dried and frequently partially cured to render them stable and easy to handle sufficiently flexible to enable them to subsequently rolled, unrolled cut and handled at ambient temperatures or with slight warming 30-50 c.

In the subsequent manufacture of composite structures such materials are cut into the required shapes placed in a mould and subjected to heat and pressure which causes the resin to melt, flow and subsequently cure.

This type of process is not feasible with thermoplastic resins as the pre-impregnated sheet would have the final properties as no cure cycle is required the material would therefore be stiff and extremely difficult to process.

Currently there are three methods of overcoming this problem. The first is associated with random fibre reinforced materials were a sheet is made from a mixture of the reinforcing fibres and fibres formed from the required thermoplastic resin matrix, the material is subsequently cut into the required shape and hot-press moulded. This method is limited to random fibre orientated materials.

The second method known as "Film Stacking" is applicable were preferred fibre orientation is required, this technique involves the production of a stack of alternately layers of a woven or knitted reinforcement on a film of the required thermoplastic matrix. These once again are hot press moulded.

The third method is to manufacture fabrics from yarns which are blends of the required reinforcement fibre and the desired thermoplastic material. These processes are expensive and unlikely to achieve popularity especially with the cheaper reinforcement fibres such as glass.

None of the aforementioned processes allows the production of components from layers of purely unidirection reinforcing fibres. The nearest approach would be to use woven or knitted so called unidirectional materials werein a warp of the reinforcing filaments is held by weft threads or knitted stiches of a foreign fibre.

This type of construction however does not allow the development of the full mechanical properties of the reinforcing fibres because of crimp inserted by the wearing process and stress raising caused by knitting threads or weft threads.

If thermoplastic composites are to achieve any sucess especially in the aerospace industry it is essential that processes equivalent to the unidirectional prepreg - and subsequent hot press moulding be developed.

The present invention provides a novel method of producing fibre reinforced thermoplastic composite components were all or part of the layers of the laminate are composed of unidirectional continuous filaments reinforcing fibres and the engineering thermoplastic resin matrix alone and containing no foreign support fibres or binders.

The essence of the invention is a novel process for the combining of the two components of the composite structure, the unidirectional reinforcing fibres and the engineering thermoplastic matrix. The process must corporate two essential stages. The first one being a step whereby the unidirectional reinforcement fibres are brought together to form an even gap free sheet of the required weight per square metre and a stage where the sheet of reinforcement fibres is combined with the required engineering thermoplastic polymer in such a manner has not to disturb the formation of the sheet of fibres but is still flexible enough to conform to the mould shapes in subsequent processing but without disturbing the alignment and distributor of the fibres and without introduction of a further component such as a foreign polymer binder.

Many process exist were fibres or fabrics are binded by using low melting polymers or adhesives an in process reinforcement fibres are held together by a network of low melting point fibrils such as the process described in European Patent Application 863025466 but the process as described in the invention such low melting polymer fibres, binders or adhesives would seriously interfere with the binding of the desired engineering thermoplastic polymer matrix to the required reinforcing fibres. The presence of such materials and the interference with binding would cause subsequent laminate failure often with disastrous consequences. It is this different and novel approach to the method of combining the reinforcement fibres and the resin matrix which is the basis of our invention.

The present invention provides a novel method of producing advanced fibre reinforced composites from unidirection reinforcements and advanced engineering thermoplastics, and no other foreign materials or fibres.

The required thermoplastic resin matrix material is formed into a flexible web of fine fibres and then thermally bonded onto the sheet of required fibres, this operation may be carried out by either preforming the web or as in the preferred method by direct deposition of the fibrous resin matrix at its melt temperature by one or more spray deposition. The amount of fibrous resin matrix applied to one or both faces of the is such that when the sheet is subsequently hot press moulded a component of the required fibre volume fraction is obtained.

The process is not limited to purely unidirectional materials but can incorporate woven, knitted, or random fibre mats.

The invention then allows for the reinforcements and thermoplastic resin matrix to pass to a preforming zone the sheet which at this stage is drapable and conforms to any required shape is easily preformed.

The materials then pass through a heated forming die or heated forming rollers creating a continuously formed reinforced thermoplastic profile, similar to those produced in thermoset resins by the pultrusin process such a process would be called pulforming.

The assembly of reinforcements and thermoplastic resin could also be rolled up whilst still in the flexible stage and be subsequently further processed by cutting shaping and hot press moulded.

Methods of manufacturing components according to the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagramatic illustration of a method of making a continuous profile from unidirectional reinforcements and a thermoplastic resin matrix.

Figure 2 is a diagramatic illustration of a method of collecting the drapable and flexible assembly of component materials to enable subsequent batch production of components to take place.

Figure 3 is a diagramatic illustration of batch method of manufacturing components from pre-assembled materials.

The method of production is shown is Figure 1. A unidirectional assembly of reinforcing fibres 10 is made by leading rovings 11 from a creel 12 through a reed 13 the thermoplastic resin matrix being applied in fibrous form 14a and 14b by spray heads 15a and 15b. The material then passes through a consolidating section 16 followed by a preforming section 17 were the material is preformed into the required shape 18 which then passes into a heated die 19 the finished component profile 20 is pulled through a cooling tank 21 by pullers 22a and 22b or alternatively as illustrated in figure 2 the consolidated materials may be formed into a roll 21 after the consolidation section to await further batch processing.

Figure 3 illustrates a process wereby components may be manufactured from materials processed on a machine as illustrated in figure 2. A lay-up of materials is placed into the bottom half or a heated mould 32 the top of the mould 33 is closed and heat and pressure are applied to form the component.

Typical laminates and components made according to the invention are as follows: - EXAMPLE 1 A flat planer laminate is manufactured from 66 ends of 400 tex carbon fibre roving evenly distributed over a width of 150 mm to give a tape of 175 grams per square metre into which is sprayed 67. 5 grams per square metre to each face of polyethersulphane fibres and subsequently consolidated and then hot press moulded into a flat laminate of 50% by volume carbon fibre.

EXAMPLE 2 A U shaped laminate is manufactured from a 150 mm wide tape of 300 grams per metre squared woven roving into which is sprayed 51.5 grams per square metre per face of polyetheretherketone this is then consolidated, preformed into a U cross section and subsequently hot pressed moulded in a die to give a U shaped section of 60% glass fibre by volume.

The invention is not limited to the afore-mentioned examples, any reinforcing fibre could be used as could any thermoplastic resin matrix, the quantities and arrangement of the reinforcing fibres and amounts of thermoplastic resin being determined by the final moulded laminate properties required.

The idea here is to combine the assembly of reinforcement fibres with the required amount of thermoplastic resin matrix without the presence of foreign binders or fibres in such a manner that they are flexible and drapable and easily preformed into any required shape and be subsequently hot press moulded or die moulded.

Claims

1. A novel process for the production of fibre reinforced thermoplastic composite components, that contains no foreign binders or fibres, and is composed solely of the required thermoplastic resin matrix and the required reinforcing fibres.

2. A process according to claim 1 in which the required thermoplastic resin matrix is applied to the reinforcing fibres in form of a random fibrous web prior to consolidation and hot press moulding.

3. A process according to claim 1 in which said thermoplastic resin matrix is applied to one face of the reinforcing fibres.

4. A process according to claim 1 in which said thermoplastic resin matrix is applied to both faces of the reinforcing fibres.

5. A process according to claim 1-4 in having said thermoplastic resin matrix between two layers of reinforcing fibres.

6. A process according to claim 5 in which at least one of the said layers of reinforcing fibres is unidirectional.

7. A process according to claim 5 in which both said layers of reinforcing fibres are unidirectional with different orientations.

8. A process according to any one of claims 1-7 comprising a randomly orientated chopped strand mat.

9. A process according to any one of claims 1-7 comprising a knitted or a woven reinforcement.

10. A process according to claims 1-9 in which the applied thermoplastic matrix in fibres form is polyethersulphane or polyetheretherkertine or any suitable thermoplastic resin matrix.

11. A process as hereinbefore described with reference to the accompanying drawings.

12. A process for the manufacture of fibre reinforced thermoplastic composites incorporating the application of the applied resin matrix in fibrous form.

13. A method according to claims 1-12 for the production of advanced fibre reinforced thermoplastic composites.

14. A process as hereinbefore described which may be a continuous process.