Reinforced polymer articles

Abstract: A moulding process comprising contacting an aqueous slurry of reinforcing fibres and an alternating copolymer CO and an olefinically unsaturated compound with the outer surface of a rotating wheel which operates under vacuum and which is provided with inwardly or outwardly projecting moulds, and removing water from material deposited on or in the moulds.

Description: This invention is concerned with a process for producing reinforced polymer articles starting from an aqueous dispersion of a particulate thermoplastic polymer and reinforcing fibres having a minimum length of 2 mm. It is known to produce fibre reinforced polymer articles of manufacture by various methods, e.g. melt-extrusion of a fibre-containing polymer composition to form sheet, film, slabs, tubes, piping, profiles etc., calendering of similar compositions to form sheet or film, injection-moulding, blow-moulding and compression-moulding of similar compositions to form moulded objects, particularly those having a reduced wall-thickness, e.g. cups, bottles and other containers. Such techniques present no particular problems provided staple fibres of relatively short length, i.e. having a length of less than 2 mm, are employed. With longer fibres very few of the above techniques are to date practised on a truly commercial scale since there are very restricted possibilities for achieving the desired degree of homogeneity in the mixture of fibre and polymer at the moment the very moulding or shaping is about to be effected. Since the reinforcing effect is a function of fibre length, there exists a general incentive to employ longer fibres, e.g. having a length of at least 5 mm. It has been proposed to solve the problem related to the processing of long reinforcing fibres in thermoplastics by a completely different technology which is a paper-making process based upon using a thermoplastic polymer in particulate form e.g. a powder or granules, ground down to a very small particle size, as binder for the fibres. Thus, a paper is produced when the fibres are cellulose fibres, or a paper-like material or synthetic paper can be produced from metal fibres, glass fibres, carbon fibres, nylon fibres, polyaramid fibres, etc. The commercial development of this different technology basically hinges around the use of olefin polymers, e.g. polyethylene, polypropylene or polybutene as the binding polymer. (c.f. EP-A-6930, EP-A-100720, EP-A-180863 and FR-A-2530724.) The binding performance of such polyolefins is however rather poor, most likely due to their outspoken hydrophobic properties. Because of this it is necessary to use various surfactants, detergents or flocculating agents in order to improve wettability performance. These auxiliary agents may even have to be employed at different stages of the paper-making process, which significantly complicates the technology. There is thus a need to find a simplified process. It will be clear that the paper-making process when employed to thermoplastic polymer binders leads to flat sheet, just as in the case of paper. A separate moulding operation is required to produce articles like egg-boxes, food trays, cups, bowls and other containers. Unexpectedly, it has now been found that another thermoplastic polymer has a very attractive wettability and that there is no strict need to employ the auxiliary agents referred to hereinabove. This polymer is an alternating copolymer of carbon monoxide and an olefinically unsaturated compound, provided its Limiting Viscosity Number is within the range of from 0.5 to 10 dl.g⁻¹. In addition the process of this invention obviates the need for a post-moulding operation. Therefore, the present invention is concerned with a process for producing a fibre reinforced polymer article, comprising contacting an aqueous suspension of 1) 60 to 80 %wt, based on the weight of solid material, of reinforcing fibres having a length of at least 3 mm, and 2) 20 to 40 %wt of a particulate alternating copolymer of carbon monoxide and an olefinically unsaturated compound having a Limiting Viscosity Number, determined in m-cresol at 60 °C, of from 0.5 to 10 dl.g⁻¹, with the outer surface of a rotating wheel having an internal vacuum and which wheel is provided with inwardly or outwardly projecting moulds which mould surfaces are provided with material that is permeable to water, removing water from the material deposited in or on the moulds by the internal vacuum and an at least partial drying operation involving heating the deposited material and removing the self-supporting moulded article from the rotating wheel. The particle size of the copolymer in the suspension should be such that adequate handling of the product is obtained. Both the presence of particles which are too small or too large for this purpose is to be avoided. Particle sizes of up to 0.5 mm are preferred. Preferred fibre lengths are from 3 to 9 mm. Alternating copolymers of olefinically unsaturated compounds and carbon monoxide are known per se. They can be produced with a catalytic copolymerization process disclosed for example in EP-A 121965, and EP-A 181014. The term "copolymer" as used in this specification includes terpolymers of an olefinically unsaturated compound, e.g. ethylene carbon monoxide and another olefinically unsaturated compound such as styrene, norbornene, propylene, butene-1, decene, vinylacetate, etc. The term "alternating" as used herein defines those copolymers having the general formula -[-A - CO-] n -, in which units -A- are derived from the olefinically unsaturated compound, e.g. -CH₂-CH₂-in a copolymer of ethylene and carbon monoxide. Preferred melting points are from 210 to 260 °C. Preferred limiting viscosity numbers are from 0.8 to 4.0 dl.g⁻¹. In a terpolymer some of the units -A-are replaced by a unit of another olefinically unsaturated compound. Such substitution effects a lowering of the melting point of the carbon monoxide copolymer, preferred terpolymers are those of ethylene, propylene and carbon monoxide having a melting point in the range of from 215 to 240 °C. Preferred copolymers are copolymers of ethylene and carbon monoxide. The implementation of the process of this invention presents no problems to those familiar with paper-making technology. A homogeneous suspension in water of reinforcing fibres and polymer particles is prepared, which as in the case of paper-making has a low solids content, preferably within the range of from 0.05 to 15 %wt. The rotating wheel is dipped into the suspension at its lower part and the internal vacuum of the machinery ensures that the moulds provided on the surface of the wheel are covered with a deposit of polymer/fibre mass. The second function of the vacuum is to ensure drainage of water from the deposited layer, this drainage may be combined with simultaneous or subsequent drying of the wet deposit, usually this will be done by heating, for example with infra-red heating sources or by blowing hot air. The mould surfaces on the wheel are provided with material that is permeable to water, this permeability not being so large that the maintenance of the internal sub-atmospheric pressure would be impossible. A dense wire mesh or a few layers of woven cloth are examples of eligible mould materials. The dewatering and drying should be continued long enough to ensure the self-supporting character of the moulded articles at the moment they are removed from the wheel, e.g. by peeling-off or by the action of a hydraulically driven piston. The moulded articles can be subjected to operations ensuring increased dimensional stability such as further hot air-drying or drying by microwave or radiofrequency heating. Before or after such post-heating the articles may be subjected to trimming or to stamping operations to create a further detailed appearance. The rotating wheel does not necessarily have a circular outer surface, other forms, e.g. a polygonal, e.g. hexa- or octagonal, cross-section is also feasible. The reinforced copolymer compositions used in this invention may further comprise various additives such as fillers, colourants, plasticizers, thermostabilizers or antioxidants. Other polymeric constituents may be incorporated as well, for example polyethylene or polypropylene and it is also possible to use hybrids as reinforcing fibres. Preferred reinforcing fibres are those selected from the group consisting of glass fibres, hydrophylic silane coated glass fibres, carbon fibres, polypropylene fibres, high molecular weight, gel-spun polyethylene fibres, nylon (polyamide) fibres and polyaramide fibres. EXAMPLE A powder of an ethylene/propylene/carbon monoxide terpolymer, with a crystalline melting point of 222 °C and a Limiting Viscosity Number of 1.76 dl.g⁻¹ (determined in m-cresol at 60 °C), was stirred to a dense suspension in demineralized water not containing any surfactant or flocculant. Then polyaramide or glass fibres were added, all fibres had a length of 6 mm. The fibres were defibrillated by continuous, vigorous stirring of the suspension having a solids content of 1.5 g.l⁻¹ . Then, a rotating wheel of hexagonal cross-section was dipped at its lower part into the suspension. Each surface of the wheel was provided with a mould for a food-tray, 22 cm long, 12 cm wide and 1.5 cm deep. The wheel was allowed to make 35 complete revolutions, under the action of an internal vacuum each time each mould passed the suspension a thin layer of deposit in the mould was formed, thus creating, layer by layer, adequate thickness. Then the wheel was lifted from the suspension, drainage was continued but now combined with blowing of hot air to effect complete drying. The articles were removed from the moulds and were all of acceptable self-supporting strength, wall thickness was 0.3 cm.

Claims: A process for producing a fibre reinforced polymer article, comprising contacting an.aqueous suspension of 1) 60 to 80 %wt, based on the weight of solid material, of reinforcing fibres having a length of at least 3 mm, and 2) 20 to 40 %wt of a particulate alternating copolymer of carbon monoxide and an olefinically unsaturated compound having a Limiting Viscosity Number, determined in m-cresol at 60 °C, of from 0.5 to 10 dl.g⁻¹, with the outer surface of a rotating wheel having an internal vacuum and which wheel is provided with inwardly or outwardly projecting moulds which mould surfaces are provided with material that is permeable to water, removing water from the material deposited in or on the moulds by the internal vacuum and an at least partial drying operation involving heating the deposited material and removing the self-supporting moulded article from the rotating wheel. A process as claimed in claim 1, in which the polymer is a copolymer of carbon monoxide and ethylene. A process as claimed in claim 1, in which the polymer is a copolymer of carbon monoxide, ethylene and propylene. A process as claimed in claim 1, in which the polymer has a Limiting Viscosity Number of from 0.8 to 4.0 dl.g⁻¹. A process as claimed in claim 1, in which the copolymer has a melting point of from 210 to 260 °C. A process as claimed in claim 1, in which the suspension comprises reinforcing fibres selected from glass fibres, hydrophylic silane coated glass fibres, carbon fibres, polypropylene fibres, high molecular weight, gel-spun polyethylene fibres, nylon (polyamide) fibres and polyaramide fibres. A process as claimed in any one of claims 1 to 6, in which the moulded article is subjected to a final drying step involving radiofrequency or microwave heating.

Inventors: DANFORTH RICHARD LOUIS, GERGEN WILLIAM PETER, NEATE JOHN AUBREY, DANFORTH, RICHARD LOUIS, GERGEN, WILLIAM PETER, NEATE, JOHN AUBREY
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1989
Main classification: C08J5
IPC codes: C08G67, D21H13, C08J5, D21H17, D21H15, B29C41, B29B11, B29B13, C08J3, D21H27, B29C70