TECHNICAL FIELD The present invention relates to a method of manufacturing fiber-reinforced plastics material.

BACKGROUND ART

Fiber-reinforced plastics materials can be produced by both wet and dry forming methods. In a wet forming method, the fiber web is produced by blending a water dispersion of reinforcing fibers and particle-form plastics material and by filtering the water out. In a dry method, a web of the reinforcing fibers is formed and onto the web a powdery plastics matrix is dosed. When the web, after it has been formed, is heated the plastics melts to an extent and is bound to the reinforcing fibers. However, the use of the fiber-reinforced materials produced in this way has been limited by the fact that they are too thick and heavy for many purposes.

The object of the present invention is to provide very thin and light but strong fiber-reinforced plastics materials.

Bound non-woven fiber mats have been produced by forming a web of fibers, for example glass fibers, and impregnating it with a binding agent. The binding agent has been sprayed onto the fiber web, or a foam has been produced of the binding agent solution or suspension which has been applied onto the fiber mat to be impregnated. After that, a bound mat has been produced by curing the binding agent by heat. Mats of this kind can be used for example as a coating, facing or insulation materials.

DISCLOSURE OF INVENTION

The method of the present invention can be used for producing thin mouldable coating materials, such as the

coating used in the ceiling of a car for example, the strength of which material is, however, remarkably better than the strenght of conventional fiber mats. Because the material is thin also costs are reduced.

BEST MODE FOR CARRYING OUT THE INVENTION

In the method of the present invention, a frothed water dispersion of a binding agent is applied onto a reinforcing fiber web, which is preferably prebound, the coated fiber web is dried, heated and pressed in order to produce a fiber-reinforced plastics material; and a characteristic feature of the method is that said foam contains a powdery thermoplastic matrix.

The fiber web is preferably a fiber glass mat prebound by a thermoplastic latex. Besides glass fiber, the mat can contain also, or alternatively, other reinforcing fibers such as carbon fiber or aramid fiber. The initial surface weight of the fiber mat is 10 - 100 g m ^-2 .

The foam is preferably formed of a binding agent which is a water soluble thermoplastic latex. For example polyvinyl acetate, ethylvinyl acetate, acrylic and corresponding materials are suitable.

Many thermoplastic materials such as polyethylene, polypropylene and corresponding agents, are suitable to be used as the matrix powder.

The matrix powder is added to the water solution of the latex and the mixture is frothed by mixing air into the dispersion. The foam is generated by methods known per se, for example mechanically. The foam is pumped onto the fiber web on a wire and applied by methods know per se, for example by a scraper knife, to form a layer of the desired thickness. Foam can be applied on one or both sides of the mat. The coated fiber mat is dried and heated for example in an infrared oven and pressed in a nip which

gives the desired thickness and appearance depending on the surface pattern of the rolls.

The dispersion of the binding agent to be frothed and the matrix powder preferably contains auxiliary frothing agent and foam stabilizing agent in order to produce a foam of the desired type. The density of the foam is preferably 0.05 - 0.3 kg dm ^-3 .

Depending on the density, the foam can be either stable or non-stable. The more stable the foam is the more of it remains on the surface of the mat. Thus, a stable foam gives the fiber mat an appearance of expanded plastics. A non-stable foam and thus also the matrix powder particles mostly penetrate into the fiber web whereby a thinner surface layer but a stronger matrix is produces than with a stable foam.

The method of the present invention provides for production of thin but strong fiber-reinforced plastics materials with a surface weight of 20 - 150 g m ^-2 .

EXAMPLE

50 % by weight of polypropylene powder and auxiliary foaming agent were added to a water solution of polyvinyl acetate latex. The dispersion was frothed by mechanically mixing air with it. The density of the foam was 0.3 kg m ^~3 . The foam was pumped onto a glass fiber felt having a surface weight of 50 g m ^~2 and applied by means of a scraper on both sides of the felt to form a 0.6 mm thick layer. The coated fiber mat was dried and heated to 150 °C and pressed between rolls to achieve the desired thickness and surface. The produced fiber-reinforced plastics material had a thickness of approx. 0.2 mm, a surface weight of 150 g m ^~2 and a tensile modulus of 50 N mm ^-2 .