METHOD OF MAKING LAMINATED REINFORCED THERMOPLASTIC SHEETS AND ARTICLES MADE THEREFROM

Abstract: A method of making laminated reinforced thermoplastic sheets which includes preparing first and second porous sheets each comprising 20% to 60% by weight of reinforcing fibres having a high modulus of elasticity as herein defined and 40% to 80% by weight of a thermoplastics material differing from the thermoplastic material in the other sheet and applying heat and pressure to cause the sheets to consolidate and adhere together to form a laminate.

Description: This invention relates to a method of making reinforced thermoplastic laminates from thermoplastic sheets which may be different or incompatible, and to articles made therefrom. In the Applicants' European Patent Application No. 85300032.1 (Publication No. 0 148 761) a method of making fibre reinforced plastics material sheet is described. It has been found that sheets of this type embodying different kinds of thermoplastic material which will not readily bond together and are difficult to laminate if they have been consolidated. It has now been discovered however that it is possible to make such a laminate if the starting sheets are unconsolidated as described in European Patent Application No. 85300031.3 (Publication No. 0 148 760) or have been expanded from a consolidated state as described in the Applicants' European Patent Application No. 85300034.7 (Publication No. 0 148 763). The subject matter disclosed in the above three European Patent Applications is incorporated by reference herein. According to the present invention therefore a method of making laminated reinforced thermoplastic sheets includes preparing first and second porous sheets each comprising 20% to 60% by weight of single discrete reinforcing fibres between about 7 and about 50 mm long and having a high modulus of elasticity higher than 10,000 Mega Pascals and 40% to 80% by weight of a thermoplastics material differing from and incompatible with the thermoplastic material in the other sheet and applying heat and pressure to cause the sheets to consolidate and adhere together to form a laminate. The porosity content of the sheet may be inherent in the unconsolidated state of the starting sheet to be generated by expanding a consolidated sheet. Preferably a substantial proportion of the fibres are 13 microns or less in diameter. Where the fibres are required to confer structural strength in the laminate, the discrete glass fibres should not be shorter than about 7 millimetres or of a diameter greater than 13 microns, since such fibres which are longer do not adequately reinforce the plastics matrix and fibres which are of greater diameter do not efficiently reinforce the matrix. Single fibres of other materials having a reinforcement efficiency at least as high as glass fibres may, alternatively, be used. At least one sheet can be unconsolidated and at least one sheet can be expanded by the application of heat after consolidation. Again the sheets may be first consolidated and then expanded by the application of heat prior to laminating. In an alternative method the unconsolidated sheets can be formed and dried together prior to laminating. The thermoplastic materials may for example be of polyethylene, polypropylene, polystyrene, acrilonitrystyrenebutadiene, polyethyleneterephthalate, polybutyleneterephthalate or polyvinylchloride, both plasticised and unplasticised or alloys or blends of these materials with each other or other polymeric materials. Other suitable thermoplastics include polyphenylene ether or polycarbonates or polyestercarbonates or thermoplastic polyesters or polyetherimides or acrylonitrile - butylacrylate - styrene polymers or amorphous nylon or polyarylene ether ketone or alloys or blends of these materials with each other or other polymeric materials. The invention can be performed in many ways and some embodiments will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 shows a method of joining sheets into a laminate which only provides very poor adhesion; Figure 2 shows a method of producing a laminate according to the present invention; Figure 3 shows an alternative method; Figure 4 shows another alternative method; and, Figure 5 shows a method of manufacturing an article utilizing the laminate made according to the invention. In the following examples porous sheets A and B were made to a total weight of 2,000 g/m² each according to the method set forth in European Patent Application No. 85300032.1 (Publication No. 0 148 761), each sheet containing 25% by weight of glass fibres (11 µm diameter, by 13 mm long) but idspersed in a different thermoplastic. Sheet A, as shown in the drawings, was made with polypropylene, grade GY545M, made by I.C.I. Limited, and Sheet B was made with XENOY, a thermoplastic alloy of polycarbonate and polybutyleneterephthalate made by G.E. Plastics Inc. Laminates were made up in four different ways as shown in the accompanying drawings. The adhesion between the plies was assessed subjectively by cutting a strip 15 mm wide by 200 mm long, and twisting its ends in the opposite directions, until either delamination, or a transverse break occurred. Example 1 (Control) As shown in Figure 1, unconsolidated dry sheets A and B made as described in European Patent Application No. 85300031.3 (Publication No. 0 148 760), were individually hot pressed respectively at 190°C and 260°C and cooled to produce cold consolidated sheets 1 and 2. The cold consolidated sheets A and B were then hot pressed together in a press 3 at 14 bar (200 lbs per sq. inch), the temperatures of the press platens in contact with the sheets being respectively 170°C and 250°C. The resulting laminate 4 was cooled and when tested was found to have very poor adhesion between the component sheets. Example 2 As shown in Figure 2, the sheets A and B which had previously been consolidated, were heated and expanded in the manner described in European Patent Application No. 85300034.7 (Publication No. 0 148 763) so that they became permeable as indicated by reference numerals 5 and 6. The expanded sheets were placed together in a press 3 where they were subjected to a pressure of 14 bar (200 lbs per sq. inch) at a temperature of 90°C. The resulting laminate was cooled and the adhesion between the component sheets was found to be better than in the method described with regard to Figure 1. Example 3 As shown in Figure 3, unconsolidated sheets A and B of the kind used at the start of Example 1 were placed together in press 3 where they were subjected to a pressure of 14 bar (200 lbs per sq. inch) with the press platens at a temperature of 170°C and 250°C respectively. The resulting laminate was allowed to cool and it was found that there was very good adhesion between the component sheets. Example 4 As shown in Figure 4, unconsolidated dry sheets A and B of the kind used in Example 1, were formed and dried together prior to being placed in the hot press, where they were subjected to the same treatment as in Example 3. Very good adhesion between the component sheets was achieved. Example 5 Figure 5 shows a method of manufacturing an article out of a laminate 8 made according to the method of Example 3. The laminate 8 is placed in a suitable heated forming tool 9 in a press 10, the two platens of which are heated at 90°C, and subjected to a pressure of 14 bar (200 lbs per sq. inch) to produce a moulded article 11. Depending upon the materials used, the finish of the laminate or moulding can be varied. Thus, if the sheet A has a relatively low glass fibre content, of for example 25%, the lower surface 12 of the manufactured article will be formed with a fairly smooth finish. On the other hand, a high glass fibre content, of for example 60%, will result in a porous surface providing a key for a surfacing layer subsequently applied. The invention therefore provides a technique for producing a moulded article from a laminate which may, for example, a heat resisting ply on one side and an easily mouldable ply on the other made from a cheaper thermoplastic. It will be appreciated that the invention also extends to the formation of laminates having more than two plies. For example, a three ply laminate could be provided having a core layer of fibre reinforced polypropylene and surfacing layers of fibre reinforced nylon. In the following Examples a 22 centimetre diameter disc of a glass mat/polypropylene laminate having a weight of 4000 grams per sq. metre and a glass fibre content of 40%, sold under the trade name AZDEL, was heated to 205°C for seven and a half minutes in an oven and laminated in a dish shaped mould at 140 bar (2000 pounds per sq. inch) to the material specified. Example 6 The second component of the laminate comprised a porous unconsolidated sheet like material having a weight of 3000 grams per sq. metre and made as described in European Patent Application No. 85300031.3 (Publication No. 0 148 760) from 30% glass fibres 12 millimetres long and 11 microns in diameter and 70% Nylon 6 powder sold under the trade name MARANYL 236R by ICI Ltd. The resulting laminate when cooled exhibited good adhesion between the plies. Example 7 The second component of the laminate was essentially the same as that of Example 6, except that the thermoplastic content comprised 70% of a thermoplastic alloy of polycarbonate and polybutyleneterephthalate sold under the trade mark VALOX by G.E. Plastics Inc. The resulting laminate, when cooled, exhibited good adhesion between the plies.

Claims: A method of making laminated reinforced thermoplastic sheets which includes preparing first and second porous sheets each comprising 20% to 60% by weight of single discrete reinforcing fibres between about 7 and about 50 mm long and having a high modulus of elasticity higher than 10,000 Mega Pascals and 40% to 80% by weight of a thermoplastics material differing from and incompatible with the thermoplastic material in the other sheet and applying heat and pressure to cause the sheets to consolidate and adhere together to form a laminate. A method as claimed in Claim 1, in which at least one sheet is unconsolidated. A method as claimed in Claim 1, in which at least one sheet is expanded by the application of heat after consolidation. A method as claimed in any one of Claims 1 to 3, in which a substantial proportion of the fibres are 13 microns or less in diameter. A method as claimed in any one of Claims 1 to 4, in which the sheets are first consolidated, then expanded by the application of heat prior to laminating. A method as claimed in Claim 1, in which both sheets are unconsolidated. A method as claimed in Claim 6, in which the sheets are formed and dried together. A method as claimed in any one of the preceding Claims, in which the thermoplastic materials are polyethylene, polypropylene, polystyrene, acrilonitrystyrenebutadiene, polyethyleneterephthalate, polybutyleneterephthalate, or polyvinylchloride, both plasticised and unplasticised or alloys or blends of these materials with each other or other polymeric materials. A method as claimed in any one of the preceding Claims 1 to 7, in which the thermoplastic materials are polyphenylene ether or polycarbonates or polyestercarbonates or thermoplastic polyesters or polyetherimides or acrylonitrile - butyacrylate - styrene polymers or amorphous nylon or polyarylene ether ketone or alloys or blends of these materials with each other or other polymeric materials.

Inventors: BIGGS, IAN STEDMAN, RADVAN, BRONISLAW
Applicants: THE WIGGINS TEAPE GROUP LIMITED
Application year: 1987
Main classification: B29C67
IPC codes: B29C43, B32B27, B29C70, B32B5, B29K105