PRODUCTION OF LAMINATES

Abstract: A method of making thermoplastics material fibres reinforced laminates includes the steps or arranging one or more layers of fibers reinforcement impregnated with the thermoplastics material in register with and between sheets of another material to form a stack, passing the stack to a tool having platens at least one of which is movable relative to the other, and operating the tool to compress the stack and form a laminate. The stack is passed to the tool in steps substantially less than the length of the tool so that each area of the stack is subjected to repeated compressions by the tool in passing therethrough. The laminate may be made continuously, the impregnated fibres reinforcement and outer sheets being continuously aligned and passed to the tool. The thermoplastics material is said to be one or more of polysulphone, polyethersulphone, polyetheretherketone and a polyamide. The outer sheets are preferably metal. In one embodiment (Figures 1 and 2) the outer sheets are removed from the laminate after passing through the tool; and may (Figure 2) be endless stainless steel bands. In this embodiment the surfaces of the outer sheets which contact the impregnated fibres reinforcement are coated with a release agent before they passed to the tool. In another embodiment the outer sheets are bonded to and form part of the laminate, preferably having their surfaces which contact the fibres reinforcement coated with an adhesive (e.g. a solution of the polymer impregnant for the fibers reinforcement in a suitable solvent) before they are brought to the tool. Apparatus for making the laminates is described.

Description: PRODUCTION OF LAMINATES DESCRIPTION The invention concerns the production of laminates, in particular the continuous production of laminates from fibres reinforced thermoplastics materials. Throughout this specification the term laminate is intended to encompass a structure formed by consolidating (usually by application of heat and pressure) one or more layers of fibres reinforced material impregnated with one or a mixture of thermoplastics materials to form the laminate of desired shape. The polymers may have fillers or other additives added to them to give desired strength and/or visual characteristics to the final laminate. The laminate may have additional outer (or inner) layers of other materials for decorative and/or functional purposes. The production of laminates is well known and normally when making continuous lengths of them the heating and compression of the impregnated fibres reinforcement is effected by passing the impregnated fibres reinforcement through one or more pairs of heated compression rollers. In this way the polymer material is forced into the interstices of the fibres reinforcement, is cured and a laminate of the desired form produced. One difficulty with this technique for producing laminates is in controlling the consistency of the final product. - It has been found that laminates produced by passing thermoplastics impregnated fibres reinforcement through compression rollers may be formed with "Dry * ' areas - that is to say areas in which the polymer has not thoroughly wetted the the fibres reinforcement. This problem appears to be particularly associated with the use of compression rollers and in attempts to overcome it another method of continuously forming laminates has been proposed. This other proposal makes use of a compression tool having a pair of platens through which the thermoplastics material impregnated fibres reinforcement is passed in steps - the tool being operated between step movements of the impregnated fibres reinforcement to compress it and form the laminate. This proposal overcomes the noted difficulty found with the use of compression rollers, however, the laminates produced are imperfect (at least visually) as they come from the tool with a series of lines extending across their widths corresponding to and caused by the edges of the platens of the tool. In attempts to overcome this is has been suggested that the impregnated fibres reinforcement be moved through the compression tool in small steps and that each area of the impregnated fibres reinforcement be ^ subjected to multiple compressions within the tool. This has been only partially successful in eliminating the visual imperfections in the final laminate and has done nothing for (or even exacerbated) another problem found when producing laminates, namely the sticking of the thermoplastics impregnant to the surfaces of the tool (compression rollers or platens) used; which leads to difficulty in controlling the pressure applied to the laminate within the tool and consistency of the final product. To prevent this happening it has been suggested that the surfaces of the tool contacting the impregnated fibres reinforcement in the tool be coated with a release agent (e.g. P.T.F.E.) which acts to inhibit adhesion of the polymer in the impregnated fibres reinforcement to the surfaces of the tool. However, even with this safeguard the polymer material can still adhere to the surfaces of the tool with the effect that the laminates produced are imperfect and with the result that the process must be stopped so that he tool can be broken down, cleaned, re-coated with the release agent and reassembled to enable laminate production to continue. Such a procedure is expensive in terms of both labour and lost laminate production. One object of this invention is the provision of a method of making thermoplastics material impregnated fibres reinforced laminates which overcomes or at least alleviates the noted problems of the methods proposed to date. In the production of certain articles there is need to coat a laminate with metal. For example, printed circuit boards are produced by coating a flat laminate with a conductive metal layer which is thereafter treated, e.g. photo etched, to produce the desired electrical interconnections on the faσe(s) of the laminate to which the active elements of the circuit are. connected. The usual method of forming such a metal coated laminate is to take * a formed laminate and then apply the metal coating to- it (by depositing or simply sticking the metal layer onto the laminate). This process is time consuming and prone to difficulties in ensuring the metal layer is of consistent thickness and/or adequately fixed onto the face(s) of the laminate Another object of this invention is the provision of a method for producing of laminates coated with metal layers which overcomes the noted difficulties of the known processes. In accordance with one aspect of the invention there is provided a method of making thermoplastics material fibres reinforced laminates including the steps of arranging one or more layers of fibres reinforcement impregnated with the thermoplastics material in register with and between outer sheets of another material to form a stack, passing the stack to a tool having platens at least one of which is movable relative to the other, and operating the tool to compress the stack and form a laminate. The outer sheets may be of any material which is relatively strong and has good thermal conductivity, ferrous or non-ferrous metals may be used for these sheets as well other materials such as silicone rubber, or cloth impregnated with P.T.F.E or silicone rubber. Preferably, the stack is passed through the tool in steps the extent of each of which is substantially less than the length of the tool so that each area of the stack is repeatedly compressed in passing through the tool. With advantage the impregnated fibres reinforcement and said outer sheets are continuously aligned and passed to the tool such that the laminate is formed continuously. The thermoplastics material is preferably one or more of polysulphone, polyethersulphone, a polyamide and polyetheretherketone. The outer sheets are preferably of metal. In one preferred embodiment the outer sheets are removed from the laminate after passing through the tool; and may comprise endless stainless steel bands arranged to run through the tool in register with the polymer impregnated fibre reinforcement. In this embodiment the surfaces of the outer sheets which contact the impregnated fibres reinforcement are coated with a release agent before they are brought into contact with the impregnated fibres reinforcement. In a another embodiment the outer sheets are bonded to and form part of the laminate as the laminate is formed in the tool; preferably having their surfaces which contact the impregnated fibres reinforcement coated with an adhesive before they are brought into contact with the fibres reinforcement. The adhesive may comprise a solution of the polymer impregnant for the fibres reinforcement in a suitable solvent. In a second aspect the invention provides a laminate made by the method noted above. In a third aspect the invention provides apparatus making laminates in accordance with the method noted above. Embodiments of the invention will now be described with reference to the accompanying drawings, in which:- Figure 1 , shows diagrammatiσally at A an arrangement for use in the method of the invention, and at B a view drawn on the line B-B of Figure 1A, Figure 2, diagrammatically shows a platen of a tool shown in Figure 1 illustrating the preferred temperature gradient thereacross in use. Figure 3 diagramatically illustrates a modified form of the arrangement shown in Figure 1 , and Figure 4 schematically illustrates an electro-hydraulic drive system for the arrangements of Figure 1 or Figure 2. Figure 1 shows an arrangement for use in one method of the invention and which will be described in the manufacture of a simple laminate, e.g. a laminate not having outer surfaces of a material different from the material forming the main body of the laminate. The arrangement includes a tool with upper and lower platens, 12 and 14 respectively, one of which is movable relative to the other to compress impregnated fibre reinforcement fed therebetween. In the embodiment illustrated platen 12 is movable (as indicated by arrow A), over a relatively short distance (typically 0.06" - 1.5mm) relative to the platen 14 which fixedly mounted on a base 16. One or more layers of fibres reinforcement 18 impregnated with a thermoplastics material is fed through the tool, in the direction indicated by the arrow M, in relatively small steps (e.g. as little as 0.10" - 2.5mm) and is compressed by repeated operation of the tool. The impregnated fibres reinforcement comprises any suitable thermoplastics material reinforced with fibres, e.g. polyethersulphone reinforced with glass or carbon fibres. The impregnated fibres reinforcement is drawn through the tool by means of hydraulically powered drive rollers 17 which pinch the laminate emerging from the tool and the laminate is wound onto a take-up roller 19 located at the end of the tool as shown. Two metal outer sheets 20 which are slightly wider than the impregnated fibres reinforcement 16 are passed to the tool in register with the impregnated fibre reinforcement 16 as shown, one sheet lying above and the other beneath the the impregnated fibre reinforcement 16. The sheets 20 are taken from rollers 22 as shown and their centre lines aligned with the centre line of the impregnated fibres reinforcement as they are carried into the tool. Prior to their being aligned with the impregnated fibres reinforcement the surfaces of the sheets 20 which will contact the impregnated fibres reinforcement are coated with a suitable release agent (such as P.T.F.E.) from spray nozzles 24 as shown. Immediately before the stack is passed to " the tool it is preferably run between two pairs of pinch rollers 25 arranged to bear on the edges of it. The rollers 25 are heated sufficiently for the impregnated fibres reinforcement to become attached to the outer sheets 20 along the edges of the stack so that the fibres reinforcement and outer sheets 20 move through the tool as one and the need for additional guiding and/or locating means for controlling the relative positions of the parts of the stack as it moves through the tool is removed. As noted above the stack is drawn through the tool by the drive rollers 17 and after passing through these rollers the edges of the outer sheets 20 are cut off by cutters 26 and the remaining parts of those sheets are stripped away from the laminate 28 which has been formed and wound onto hydraulically driven take-up rollers 30 as shown. The operation of the drive rollers 17, the take-up rollers 19 and the take-up rollers 30 is controlled so that each step of the movement of the impregnated fibres reinforcement and sheets 20 through the tool is significantly smaller than the extent of the platens 12 and 14 in the direction of motion of the impregnated fibres reinforcement. Thus for a 5.platen 12 which is 30" (0.75m) long the typical length of each step by which the impregnated fibres reinforcement is moved would be 3" (7.5cm) so that each area of the fibres reinforcement would be subjected to 10 separate compressions by the platen as it moves through the tool. 0 As can been seen particularly from Figure 1B, the platens 12 and 14 are shaped such that the moving platen 12 has a raised centre section 32 which is received within a complementary shaped recess 34 of the fixed platen 14. One or both of the platens 12 and 14 are 5 differentially heated (and possibly also cooled) to give a preferred temperature gradient along the length of the tool substantially as shown in Figure 2. In Figure 2A the platen is shown schematically at 36 and at 38 and 40. are indicated suitable means (e.g. ducts for heating liquids or gases, 0 electrical heating wires) by means of which the platen is heated (and also possibly cooled) so that the temperature along its length follows the curve shown in Figure 2B. The temperatures maintained in the platen will depend upon both the -particular polymer (or mixture of polymers) used to 5 impregnate the fibres reinforcement and upon the thickness of the laminate being produced. When using, for example, polyethersulphone impregnated glass fibres the temperature along the length of the tool will fall by approximately 25°C, typically 325°C to 300°C or 300°C to 275°C depending 0 upon the thickness of the laminate to be produced. The length of the platens (and in particular the length of the moving platen 12) is significantly greater than the width of the impregnated fibres reinforcement fed to the tool - typically the length of the operative part of 5 the tool is at least three times the width of the impregnated fibres reinforcement fed to the tool. Thus for a laminate approximately 10" (25cm) wide the preferred length of the platen 12 would be 30" (0.75m). The movement of the platen 12 is over a small distance and it therefore may be moved at a wide range of speeds ranging from relatively low speeds of, say, three or four strokes per minute to relatively high speeds of up to 300 strokes per minute depending upon the impregnated fibres reinforcement being processed. The range of pressures applied to the impregnated fibres reinforcement in the tool is also dependent upon the impregnated fibres reinforcement being processed but it will be appreciated that, particularly with the relatively high speeds which can be used the pressures needed may be relatively low ( e.g. as low as 0.5 Tons per square inch - 2 40 Kg/cm ) whilst still obtaining a high quality finished laminate product. The outer sheets 20 may be of any suitable ferrous or non-ferrous metal of any suitable thickness e.g. aluminium foil of thickness 0.002"-0.010 π (0.05 - 0.25mm) - may be advantageously used. If it is desired to produce metal coated laminates, in substance the same arrangement as that described above is used. However, the arrangement is modified in the following ways:- the sheets 20 are of the metal with which it is desired to coat the laminate (when making printed circuit boards, copper, silver or gold foils of thicknesses of .002" - 0.05mm may be used); the nozzles 24 are omitted or arranged to spray the sheets 20 with a solution of the thermoplastics material impregnating the fibres reinforcement; the take-up rollers 30 are removed and the metal coated laminate drawn from the tool by the drive rollers 17 or a tractor to a position at which it is cut to desired lengths (rather than being wound on a take-up roller) . Additionally the cutters 26 may be removed or be arranged to cut through both the outer sheets and the formed laminate 28 to provide a clean, cut edge to the metal coated laminate. If a solution of • the thermoplastics material impregnant is sprayed onto the outer sheets the solvent used is one which will be fully evaporated and driven-off at the operational temperature in the tool; e.g. if polyethersulphone is being used a suitable solvent would be dichloroethane. Figure 3 illustrates a modified form of the tool shown in Figure 1 and parts shown in it which are the same as parts shown in Figure 1 are given the same reference numerals. In the arrangement of Figure 3 the outer sheets 20 have been replaced by two endless stainless steel bands 42 arranged to run round hydraulically driven rollers 44 and idler rollers 46 as shown. The drive rollers 17 have been replaced by a hydraulically driven tractor 48 which acts to drawn the formed laminate 28 through the tool. The thickness of the stainless steel bands is selected in .dependence upon the polymer and fibres reinforcement being processed and normally lies in the range 0.01" - 0.02" (0.025 -0.050mm). As with the arrangement already described the bands are carried into and run through the tool in register with the impregnated fibres reinforcement and are stripped from the formed laminate 28 once they have passed through the tool. It will be appreciated that the arrangement shown in Figure 3 has particular advantage in providing that the metal sheets which pass through the tool are not destroyed (cut) once they have passed through it and are re-usable. With the arrangement of Figure 3 the chance of the thermoplastics impregnant ahering to the stainless steel bands is low as they are continuously being coated with a release agent (such as P.T.F.E.) from the nozzles 24, if it is thought necessary, however, means may be provided to continuously clean the bands of any polymer which could adhere to them. Such means may comprise, for example, a pair of blades or brushes arranged to contact and wipe the surfaces of the bands 42 in their run between the driven rollers 44 and the idler rollers 46. Apparatus for driving the tool and other parts of the arrangement shown in Figures 1, 2 and 3 in the formation of a laminate (with or without a metal coating) will now be described with reference to Figure 4 which illustrates, highly diagra atiσally, a typical electro-hydraulic drive system for the arrangement. The drive system includes a reservoir 50 for hydraulic fluid from which the hydraulic fluid is passed by a pump 52 to a mechanical two way valve 54. In one position (the position shown) of the valve 54 the hydraulic fluid is passed to a valve 56 driven between two end positions by operation of two solenoids 58 and 60. Operation of the solenoids is effected by a controller 100. When solenoid 58 is operated to move valve 56 to its rightmost position (as viewed in the Figure) the pressurised hydraulic fluid drives a. piston 62 in cylinder 64 to carry the moving platen 66 toward the other, fixed, platen (not shown). A pressure sensor 68 is arranged to output to an electrical controller 100 a signal indicating when a desired (pre-set) pressure in the hydraulic system has been reached and platen 66 is applying the desired pressure to the impregnated fibres reinforcement in the tool. Controller 100 is arranged to then operate the solenoid 60 to move the valve 56 to its leftmost position (as viewed in the Figure) releasing the pressure on piston 62 and allowing the moving platen 66 to be moved away from the fixed platen. The controller 100 may be arranged to effect this release of pressure applied to the piston 62 immediately the pre-set pressure has been reached or after maintaining the pressure for a pre-set time period during which time the valve 56 is moved by solenoid 60 from its rightmost position to a central position - that shown in the Figure for the duration of the delay and then moved to its leftmost position. In the particular arrangement shown in the Figure 4 the movement of the valve 56 to its leftmost position acts to couple the pressurised hydraulic fluid to a second piston 70 arranged to drive platen 66 away from the fixed platen. When platen 66 has moved sufficient distance away from the fixed platen a limit switch 72 is tripped which signals to controller 100 that the platen 66 has moved the desired distance. The controller 100 then operates solenoid 60 to drive the valve 56 from its rightmost position and release the pressure on piston 70 and so stop further movement of platen 66. Controller 100 then causes the take-up rollers 18 and 30 (or driven roller 44 and tractor 48) to move by a small amount such that the outer sheets and impregnated fibres reinforcement is advanced through the tool by a pre¬ set desired amount. Thereafter solenoid 58 is energised to restart the noted cycle of operations once again. Controller 100 may also be arranged to control operation of the cutters 26 (if - ' they are provided). When valve 54 is in the position other than that shown (i.e manually moved leftwardly a viewed in the Figure from the position shown) pressurised hydraulic fluid may be applied to the tool 10 via a manually operable valve 74 to cause the tool to operate in the usual fashion. As already noted movement of the moving platen is over a small distance and it may be moved at relatively high speeds enabling relatively low pressures to be used - e.g. in the range of 0.5 to 2 Tons p.s.i. (40 - 120 Kg/cm ) whilst still obtaining a high quality finished laminate product. With the method described laminates of good structural integrity and high quality surface finishes are obtained. It is thought that the high quality of the laminates produced by the method of the invention is achieved specifically by the sheets 20 (or bands 42) which are used. These sheets act; firstly, to seal the impregnated fibres reinforcement as it is carried through the tool (thus aiding the wetting of the fibres reinforcement with the polymer impregnant), secondly to contain the loading of the platens on the impregnated fibres reinforcement,. and thirdly to transmit heat from the tool to the impregnated fibres reinforcement more effectively than has until now been the case. It will also be appreciated that in the described arrangements for making un-coated laminates it is provided that the impregnated fibres reinforcement contact outer sheets (or stainless steel bands) so that the tool surfaces do not come into contact with the polymer impregnant and cannot therefore become fouled by that polymer. The embodiments further provide that the outer sheets (or bands) are coated with a release agent as they are passed to the tool so that the metal surfaces contacting the impregnated fibres reinforcement will not lift polymer from the fibres reinforcement reducing the visual or strength characteristics of the laminate as it is made. It will be appreciated that the sheets - 20 (and bands 42) although specifically described as being of metal need not be of metal and that other materials which are relatively strong and have good thermal conductivity could be used. It is envisaged that such other sheets might be of silicone rubber, or cloth impregnated with P.T.F.Ξ or silicone rubber. If appropriate alternative materials are used the need to coat the sheets with a release agent before passing them to the tool will be reduced. It will further be seen that the arrangement described with reference to Figure 4 is merely one way of ensuring that the arrangements described with reference to Figures 1 and 2 are operated in accordance with the method of the invention. The specific method of driving the movable platen (i.e using two pistons to drive it) may be modified; e.g. a single, reciprocating piston may be used to drive the movable piston both toward and away from the fixed platen. It is envisaged that each of the platens could be movable, and that any suitable (e.g. electro-mechanical, pneumatic) method of driving the tool may be used. It is possible to make more complex shaped laminates with the method of the invention either by reheating and post forming flat laminates made in accordance with the methods described above or by feeding the sandwiched impregnated fibres reinforcement to pairs of shaped platens directly forming impregnated fibres reinforcement laminates of any desired shape. Other more complex shapes may also be made by processes making use of the method of the invention e.g. impregnated fibres reinforcement "wrapped" in the outer sheets may be wound on a mandrel or other former to provide a helically wound reinforced precursor which is then passed to the arrangement described above. The arrangements described above may be used in combination with one another and with other standard laminate production techniques (e.g. to produce a laminate coated on one side only with a metal layer) without departing from the invention.

Claims: CLAIMS 1. A method of making thermoplastics material fibres reinforced laminates including the steps of arranging one or more layers of fibres reinforcement impregnated with the thermoplastics material in register with and between outer sheets of another material to form a stack, passing the stack to a tool having platens at least one of which is movable relative to the other, and operating the tool to compress the stack and form a laminate. 2. A method as claimed in Claim 1 , wherein the stack is passed to the tool in steps the extent of each of which is substantially less than the length of the tool so that each area of the stack is subjected to repeated compressions by the tool in passing therethrough. 3. A method as claimed in Claim 1 or Claim 2, wherein the impregnated fibres reinforcement and said outher sheets are continuously aligned and passed to the tool such that the laminate is formed continuously. 4. A method as claimed in any one of the preceding claims, wherein the thermoplastics material is one of polysulphone, polyethersulphone, polyetheretherketone and a polyamide. ' 5. A method as claimed in any one of the preceding claims, wherein the outer sheets are of metal. 6. A method as claimed in any one of the preceding claims, wherein the outer sheets are removed from the laminate after passing through the tool. 7. A method as claimed in Claim 5, wherein the outer sheets comprise endless bands arranged to run through the tool in register with the polymer impregnated fibre reinforcemen . 8. A method as claimed in Claim 7, wherein the endless bands are of stainless steel. 9. A method as claimed in any one of the preceding claims, wherein the surfaces of the outer sheets which contact the impregnated fibres reinforcement are coated with a release agent before they are brought into contact with the impregnated fibres reinforcement. 10. A method as claimed in any one of claims 1 to 5, wherein the outer sheets are bonded to and form part of the laminate as the laminate is formed in the tool. 11. A method as claimed Claim 10, wherein the surfaces of the outer sheets which contact the impregnated fibres reinforcement are coated with an adhesive before they are brought into contact with the impregnated fibres reinforcement. 12. A method as claimed in Claim 11, wherein the adhesive is a solution of the polymer impregnant for the fibres reinforcement in a suitable solvent. 13. A method as claimed in Claim 1 and substantially as herein described with reference to the accompanying drawings. 14. A laminate made by the method of any one of -the preceding claims. 16. Apparatus for making laminates substantially as herein " described with reference to Figures 1 , 2 and 4 or Figures 2, 3 and 4 of the accompanying drawings.

Inventors: ASHTON JOHN WILLIAM, ASHTON, JOHN, WILLIAM
Applicants: SMITH TECH DEV H R, H R SMITH (TECHNICAL DEVELOPMENTS) LIMITED
Application year: 1986
Main classification: B29C67
IPC codes: B29C43, B29C70