Fastening strip and roof covering comprising such strips

Abstract

 Fastening strip for fastening a plastic film to the top surface of a layer of a bituminous material, said fastening strip comprising a fibrous layer (1) coated on one side with a material (3) capable of bind ing to the plastic film, the opposite side of the fibrous layer being covered by a metal foil (2), the free surface of the metal foil being covered by a layer (4) of a heat activatable bituminous binder.
Roof covering comprising a layer of a bituminous material and having fastened thereto a plastic film by means of a fastening strip.

Description

[0001] This invention relates to a fastening strip for fastening a plastic film to the top surface of a layer of a bituminous material, said fastening strip comprising a strip of a fibrous sheet material one side of said fibrous sheet material being coated with a layer of material capable of bonding to the plastic film.

[0002] A prior art technique for repairing a worn bituminous roof covering comprises applying one or more additional layers of a roofing felt to the top surface of the roof covering.

[0003] In recent years it has been attempted to repair such a roof covering by fastening to the top surface of the roof covering a plastic film e.g. a PVC film having a thickness of 1-2 mm.

[0004] By attempting to fasten a PVC film to the bituminous roof covering by means of a heat activatable binder e.g. a polymer-containing bitumen it has been found that the softener contained in the PVC­film tends to migrate towards the heat activatable binder and to form a fatty layer, which prevents the PVC film from securely adhering to the bituminous roof covering.

[0005] It has also been attempted to fasten a PVC film containing a softener which does not migrate to a bituminous roof covering by applying a layer of hot bitumen to the roof covering and by unrolling the PVC film on top of said layer.

[0006] Apart from the inconvenience of using hot bitumen e.g. having a temperature of about 200°C on the roof the above mentioned method suffers from the drawback that the PVC film becomes too soft to be handled.

[0007] Furthermore it has been attempted to fasten PVC film to a bituminous roof covering by means of strips of non-woven glass fibres coated on both sides with a PVC layer and to fasten such strips to the bituminous roof covering by means of mechanical fastening means such as screws and pressure distribution disks which are spaced e.g. 100 cm. Following the attachment of the strips to the bituminous layer the PVC film is unrolled across the roof and connected to the strips by heating or by swell welding i.e. by using a solvent such as tetrahydrofuran which is capable of partially dissolving both the PVC layer forming the top surface of the strips and the PVC film located on top of the strips.

[0008] The mechanical fastening means are not capable of preventing the plastic film from being torn away from the roof in case strong winds create a strong suction above the roof covering unless a large number of fastening means is employed.

[0009] Furthermore some roof covering supports are not suitable for mechanical fastening. As an example the support may comprise zones which do not offer a sufficient strength for securing a safe attachment of mechanical fastening means.

[0010] The specification of Danish patent publication No. 147.979 discloses a bituminous roof felt consisting of a thin fibrous layer, e.g. made from polyester fibres, said felt comprising a metal foil glued to one side of the felt and both sides being coated with bituminous layers. When attached to a roof surface the roof felt is caused to adhere to the roof surface all over its surface.

[0011] The object of the invention is to provide a fastening strip of the above mentioned type which provides a safe continous bond between a plastic film and a layer of a bituminous material in particular a bituminous roof covering in need of a new weather resistant surface layer.

[0012] This object is achieved with the fastening strip of the invention which is characterized in that the side of the strip which is opposite to the layer of the material capable of binding to the plastic film is covered by a metal foil, the free surface of the metal foil being coated with a layer of heat activatable bituminous binder, said heat activatable binder layer being optionally covered by a protective sheet material.

[0013] Apart from permitting a safe and simple fastening of the plastic film to a bituminous roof covering the fastening strips of the invention present the advantage that they are useful for securing the plastic film to the vertical surfaces along the perimeter of the roof and around skylights.

[0014] The metal foil of the fastening strip of the invention is preferable an aluminium foil and the thickness of the metal foil is conveniently between 3 and 150 µm.

[0015] The metal foil prevents the softener, if any, present in the plastic film from migrating towards the bituminous binder and to form a harmful separating layer.

[0016] The metal foil and the fibrous layer also serve to protect the binder layer and optionally the plastic film against thermal decompostion or softening when the heat activatable binder is heated during the application of the fastening means of the bituminous surface.

[0017] In a preferred embodiment of the fastening strips of the invention the strips are attached to the surface of the plastic film to be fastened to the bituminous layer. When fastening the film with the fastening strip attached thereto to the bituminous layer the heat activatable binder on the free surface of the fastening strip is heated to a sufficiently high temperature to ensure that the fastening strip after being forced into contact with the bituminous layer adheres thereto. The heating may be effected in a manner which is well known per se by means of a gas burner using liquified gas as fuel.

[0018] In such a case it is essential that the heat generated by the gas burner is not transmitted to the plastic film so as to make it so soft that it cannot be handled in a conventional manner. This is achieved with the fibrous layer and the metal foil which isolate the plastic film.

[0019] The fibrous layer also serves to reinforce the fastening strips.

[0020] The fibrous layer preferably consists of polyester fibres and the weight is preferably between 50 and 500 and more preferably between 150 and 350 g/m². Other types of fibrous layers e.g. a fibrous layer made from glass fibres are also suitable.

[0021] The composition of the material capable of binding to the plastic film depends on the type of the plastic film to be fastened to the bituminous layer.

[0022] When using a PVC film the material preferably consists of a PVC layer, which may be prepared from a PVC plastisol, i.e. a dispersion of PVC particles and optionally a pigment, a stabilizer, etc. in an oily liquid phase containing oil, softener etc.

[0023] A layer of this type is preferably prepared by impregnating one side of the fibrous layer with the plastisol and subsequently heating the layer thus formed to a temperature of about 180°C to cure the layer. The procedure is repeated until the desired thickness of the layer has been obtained.

[0024] The invention also relates to a roof covering comprising a layer of a bituminous material and a plastic film fastened to the top surface of the layer of bituminous material by means of the fastening strips described above.

[0025] The invention will now be described in further detail with reference to the drawing which shows a vertical sectional view of a fastening strip according to the invention and to the following example.

[0026] The fastening strip illustrated in the drawing comprises a fibrous layer 1, e.g. a layer of polyester fibres and a metal foil 2 such as an aluminium foil. The top surface of the fibrous layer 1 is coated with a binder layer 3, e.g. in the form of a cured layer of PVC plastisol.

[0027] The free surface of the metal foil 2 is coated with a layer 4 of bitumen.

Example

[0028] A strip (width 15 cm) consisting of a polyester felt of a weight of 200 g/m² and an aluminium foil of a weight of 50 g/m² was prepared as described in the example of DK patent publication No. 147.979. A layer of PVC plastisol was applied to the top surface of the strip thus formed in an amount of 500 g/m². The strip was then passed through a tunnel furnace so as to heat the plastisol layer to a temperature of about 180°C and to cure the PVC. Additional layers of PVC plastisol were applied and follwing the application of each layer the layer was cured as described above. The final product thus obtained had a weight of 1400 g/m².

[0029] A layer of adhesive bitumen was then applied to the non-coated side of the aluminium foil in an amount of 800 g/m². The adhesive bitumen used consisted of bitumen containing 10 % thermoplastic SBS rubber and 6 % resin.

[0030] Following the application of the layer of adhesive bitumen the layer was covered with a polyethylene film of a thickness of 10 µm.

[0031] Fastening strips thus prepared were used for fastening a PVC film to the top surface of a bituminous roof covering.

[0032] After cleaning and optionally applying a primer to the cleaned surface the strips were fastened to the roof covering by heating the layer of adhesive bitumen to its melting point using a gas burner. Concurrently with the heating of the adhesive bitumen the thin polyethylene film was burned off. The strips were placed parallel to each other and with a spacing of about 200 cm.

[0033] Subsequently PVC films having a width of about 2 m and a thickness of about 1,5 mm and being reinforced with polyester tissue having a weight of 10 g/m² were unrolled over the strips. The PVC film was placed in such a manner that its centre line was located above and parallel with a fastening strip. The PVC film was then connected to the strips thus applied by swell welding using tetrahydrofuran as solvent.

Claims

1. A fastening strip for fastening a plastic film to the top surface of a layer of a bituminous material said fastening strip comprising a strip of a fibrous sheet material, one side of said fibrous sheet material being coated with a layer of a material capable of binding to the plastic film, characterized in that the side of the strip which is opposite to the layer of the material capable of binding to the plastic film is covered by a metal foil the free surface of the metal foil being coated with a layer of heat activatable bituminous binder, said heat activatable binder layer being optionally covered by a protective sheet material.

2. A fastening strip as in claim 1, characterized in that the metal foil is an aluminium foil.

3. A fastening strip as in claim 1, characterized in that it is attached to the plastic film which is to be fastened to the layer of bituminous material.

4. A fastening means as in claim 1, characterized in that the fibrous layer consists of polyester fibres and has a weight of from 50 to 500 g/m².

5. A fastening means as in claim 1 for fastening a PVC film to a layer of bituminous material, characterized in that the binder is prepared from a PVC plastisol.

6. A roof covering comprising a layer of bituminous material and a plastic film fastened to the top surface of said bituminous layer by means of fastening strips comprising a fibrous layer coated on one side with a material capable of binding to the plastic film with the plastic film, characterized in that the opposite side of the fibrous layer is covered by a metal foil and that the metal foil is coated with a layer of heat activatable bituminous binder, said layer of heat activatable binder being optionally covered by a protective sheet material.

Drawing