"A watertight composite support for bituminous membranes with limited thickness and weight and a process for the production thereof

* * * DESCRIPTION

The present invention relates to a composite product, which is intrinsically watertight and is adapted to form a support for bituminous membranes with limited thickness and weight, and to a process for the production thereof. In the normal state of the art, the non- woven fabrics used as supports for bituminous membranes are permeable to water and thus require considerable thicknesses and amounts of modified bitumen to ensure the required level of watertightness.

The bituminous membranes are made by impregnating the support weaves, among which the polyester non- woven fabrics, in blends of molten bituminous mixture, so as to obtain rolls displaying a height in the range between 50 cm and 150 cm, a length in the range between 2 m and 30 m and a weight even higher than 5 kg/m ² after cooling.

Most part of the mass of the final product consists of modified bitumen, as the weaves have an effect for limited grammages varying on the average from 100 g/m ² to 300 g/m ² .

As bitumen is derived from crude oil, it is limited both by the exhaustibility of the resources of the source material and therefore by the expectable increase in costs, and by the incidental increase in costs due to the international political instabilities. This implies a restriction for the spreading of the bituminous membranes, especially in the countries which have no natural oil resources.

It is the object of the present invention to provide a cost-effective alternative, thus allowing a considerable reduction of the amounts of bituminous mixture used in the manufacture of watertight supports.

According to the present invention, such an object is achieved by

means of a composite support for bituminous membranes, including a first and a second layer of non-woven fabric, characterised in that it further includes a continuous watertight membrane, with limited thickness, is resistant to high temperatures, which is interposed between said non-woven layers.

As the composite support according to the invention is intrinsically watertight, it allows to reduce the mass and the thickness of bitumen without compromising the performance of the product in terms of water tightness.

A possible practical embodiment of the composite support according to the present invention will now be described by way of example, together with the process for the production thereof, with reference to the accompanying drawings, in which: figure 1 is a perspective view of a composite support according to the invention, which is shown partially open; figure 2 is a cross section view of the support in figure 1; figure 3 is a diagrammatic illustrative representation of the process for the production of the support in figures 1 and 2.

Figures 1 and 2 show a composite support 10, which includes a first layer 1 of non- woven fabric, a second layer 2 of non- woven fabric and an intermediate layer 3 of watertight material, consisting of a continuous membrane with a limited thickness, interposed between the layers 1 and 2 of non- woven fabric. The latter serve as a support and mechanical protection for the above mentioned membrane.

The membrane 3 is formed by an extruded film made of a polymer which has a high resistance to heat and is totally watertight: typically PET, with a limited thickness, on the order of 20 μ.

The layers of non-woven fabric 1 and 2 are also made of low grammage, typically 50 g/m ² , polyester and are needlepunched and impregnated with appropriate resins. As well as exerting a mechanical protection effect on the intermediate membrane 3, the two layers 1 and 2 also provide the product with a very good size stability, thus being

reinforced in turn with high toughness and modulus longitudinal filaments 9, for instance made of glass, as described in Italian patent No. 1237149, or with inorganic or polymeric material meshes.

As may be noted in figures 1 and 2, the membrane 3 has a shorter length than that of the two layers 1 and 2 (a difference indicated by the letter

(a) in the section of figure 2). In this manner, during the bitumen impregnation process, the required gripping points between the two layers 1 and 2 at the side ends will be generated for the whole length of the rolls.

These gripping points are generated by the penetration of the bituminous mixture into the parts of non- woven fabric which are not involved by the polymer membrane 3.

The absence of the watertight membrane in the outer side strips of the roll does not compromise the performance of the product as far as the water tightness is concerned, as these areas are overlapped during the application step, thus conferring continuity to the watertightness given by the polymer film.

With reference to figure 3 the process for the production of a product according to the present invention is now described.

The product is produced by gluing by means of adhesives Al, A2 which are resistant to high temperatures (> 160 ⁰ C), typically having a polyurethane base but possibly also having a different base, of the polymer membrane 3 to each of the layers of non- woven fabric 1 and 2. After the application of the adhesive, the three layers 1 , 2 and 3 are compressed in a calender 4 which ensures the elimination of possible air bubbles, the uniform distribution of the adhesive and the perfect adhesion of the layers.

The production process provides that the three components 1, 2 and 3 are unwound from respective rolls 5, 6 and 7 and that the final composite product 10 is finally wound to form a single roll 8.

It should be noted that the combination between the layers 1 , 2 and 3 may occur by means of other thermal and/or mechanical systems such as ultrasound bindings etc.

The coupling of the polymer membrane 3 to the non- woven layers 1 and 2 may in turn occur in a single step or in multiple sequential steps.