This invention relates to the welding of different plastics materials. It was specifically devised with reference to the welding of polymethylmethacrylate to polyvinyl chloride (acrylic to PVC) .

Interior vanity mirrors for vehicles have successfully been made for a number of years from acrylic resin which is strong and durable and less hazardous in the event of an impact than conventional mirror glass. The type of acrylic used hitherto has had a relatively low temperature rating, for example below 95°C. However, standards are increasingly requiring a higher temperature rating, typically 150°C. The expression "temperature rating" refers to the working rating of the acrylic plastics.

In use, an acrylic mirror needs to be secured to a sun visor which is covered with a different plastics material, typically a flexible PVC or other plastics sheeting. There is some difficulty in welding acrylic mirrors to visor coverings since the two plastics are not very compatible. However, such welding has been possible on a commercial scale.

In recent times, there has been a tendency to use light coloured film for interior lining of vehicles, including the film used for sun visors. In order to produce a light coloured film, pigments such as titanium dioxide are used as whiteners. It has been found that the presence of pigments and fillers of this type gives a significantly worse weld performance than was achieved with darker coloured films which did not have the same quantity of these pigments and fillers. It is believed that titanium dioxide in particular reduces the amplitude of the high frequency weld signal, and hence it is difficult to produce a satisfactory weld on a production basis.

This problem is further aggravated by the need to increase the temperature rating of the acrylic resins used for mirrors.

For example a conventional acrylic resin mirror has hitherto been made of a plastics material having a working rating of less than 95°C. It is now becoming necessary to use a material having a working rating of 150°C in order to meet improving standards in the motor industry.

It has proved to be impossible using conventional production techniques to weld high temperature acrylic to visor coverings particularly where the latter contains substantial proportions of light coloured pigments.

It is an object of the present invention to provide a method of welding which overcomes or reduces these disadvantages and it is a further object of the invention to provide a welded article.

According to the first aspect of the invention there is provided a method of welding two different plastics materials having poor weld compatibility, the method comprising placing an interlayer of plastics film having good weld compatibility with each of said two different plastics between the two different plastics materials and performing a single welding operation on said two different plastics material and interlayer.

One of the plastics materials may be polyvinyl chloride (PVC) having a substantial content of opacifier or pigment. Alternatively said one material may be another type of plastics film containing a substantial content of opacifier or pigment.

The other plastics material may be polymethylmethacrylate (acrylic). The acrylic may be a high temperature rating acrylic such as a polyi ide enhanced acrylic.

The interlayer may be a low temperature rated PVC film. The PVC of the interlayer is preferably transparent and contains substantially no opacifiers or pigments.

The weld may be formed by high frequency electric welding or by ultrasonic welding.

The welding tool may incorporate a sharp edge adapted to penetrate substantially through the said one material and interlayer whereby, when the tool has been removed, a portion of the said one material and interlayer adjacent the weld may be readily manually removed.

The invention further provides an article comprising two different plastics materials having poor weld compatibility and having an interlayer of plastics film having good weld compatibility to each of said two different plastics materials, welded therebetween in a single weld. The article may comprise an assembly of pigmented opaque PVC sheet and an acrylic mirror.

The interlayer may be a low temperature rated PVC. Preferably the interlayer is a transparent PVC containing no opacifiers or pigments.

The PVC and interlayer may be welded to a front face of the mirror and the rear face of the mirror may be silvered prior to welding.

The pigmented opaque film and interlayer may cover the face of the mirror during welding and may be removed manually thereafter along a line defined by the welding tool.

An embodiment of the invention will now be described in more detail by way of example only with reference to the accompanying drawings in which

Figure 1 is a\' front elevational view partly broken away of a vehicle sunvisor embodying the invention.

Figure 2 is a sectional view on the lines 2.2 of Figure 1.

Referring firstly to Figure 1 of the drawings, a sunvisor 10 is faced with a light coloured film 11 and contains a vanity mirror 12 which is made of a high temperature rating clear acrylic plastics material and which is silvered on the rear side 13. The mirror has a peripheral wall or rim 14 having a rounded contour in accordance with our European Patent No. 0088846.

The material 11 does not have adequate compatibility with the acrylic material of the mirror 12 to permit direct welding. This is because the acrylic material is of a high temperature rating, for example comprising a polyi ide enhanced form of polymethylmethacrylate, and also because the weld amplitude in high frequency welding is greatly reduced when attempts are made to weld a light coloured film. It is believed that this is due to the presence of pigments and opacifiers, for example the use of a titanium dioxide whitener in the film.

In order to make a reliable weld between the film and the acrylic, it has been found that an interlayer 15 may be used, the interlayer comprising a transparent low temperature rating ^• PVC which is substantially devoid of pigments and opacifiers. The film 15 is of relatively low cost, since it is preferred to be thinner than the film 11 and also since it merely needs to extend across the region of the weld 16.

In a manufacturing process, the mirror 12 is firstly formed as an injection moulding in high temperature acrylic, after which the rear side 13 is metallised, for example by vacuum metallisation in generally known manner. It will be seen from Figure 2 that there is a small step 17 on each face of the mirror and it is within the area defined by this step 17 that

a weld is made.

In order to make the weld, the interlayer 15 is first placed in contact with the mirror 12 and then the opaque film layer is added so that the three are face to face. It is preferred that the film and interlayer 11 and 15 have some form of openings overlying the central portion of the mirror 12 to enable them to be removed readily after welding. A high frequency electric welding tool is applied and the weld is carried out for a suitable period at a temperature determined by experiment for the particular materials used. From Figure 2, it will be seen that the main body of the weld 18 is relatively flat and that there is also a sharp pinched portion 19 of the weld at the forward face of the mirror 12. Once the film and interlayer have been positioned, a single welding operation is carried out and, once the tool has been removed, the central portion of the film 11 and interlayer 15 is removed manually from the forward face of the mirror 12 using the openings previously referred to. Separation takes place at the sharp pinched edge portion 19 of the weld.

It has been found that a reliable weld can be achieved even using a plastics such as that marketed under the name Kamax 260 by Rohm and Haas, which is a polyimide enhanced acrylic material having a working rating of approximately 150°C. This can be welded in a single pass of the welding tool to a heavily pigmented PVC film. The resulting visor assembly has been tested at 90°C without noticeable deterioration over a period of many hours.