Description

The present invention relates to an adhesive tape, comprising an adhesive layer applied on a carrier layer.

Adhesive tapes of this type are generally known.

In the building trade, adhesive tapes are widely used, inter alia when carrying out outdoor painting and plasterwork to cover edges, for fixing masking paper or masking film in window frames, door openings, etc., and for many other purposes. In particular when sticking down masking paper or masking film in window or door frames, adhesive tapes of this type must have good adhesive force, must stick well to dusty and otherwise contaminated surfaces, and must be removable after having been stuck for a prolonged period, without leaving behind residues of adhesive. When adhesive tapes of this type are used for outdoor applications, the effect of solar radiation constitutes a significant problem, because the adhesive used is sensitive to UN radiation (UN = ultraviolet) and IR radiation (IR = infra-red). UV radiation and IR radiation increase the rate of oxidation of natural rubber, a raw material frequently used for adhesive, and attack the adhesive, so that residues of adhesive remain behind when the adhesive tape is removed after having been stuck for a prolonged period.

Over the years, many solutions have been proposed for rendering adhesive tape able to withstand UV radiation and IR radiation. In this context, the solution is mainly sought in the adhesive used. In the case of adhesives based on natural rubber, for example, so-called antioxidants and/or UV stabilisers are added. Another approach is the use of a type of adhesive based on a different raw material, for example acrylatc; however, this approach is particularly suitable for the application of relatively thin layers of adhesive. Such solutions are frequently expensive and make the adhesive tape less suitable for the envisaged application.

The aim of the present invention is to provide a UV- and IR-resistant adhesive tape which has universal use, can have a high adhesive force, is removable, after prolonged exposure to UV and IR radiation, without leaving residues of adhesive, is resistant to water and chemicals, is easy to tear and has good dimensional stability. This aim is achieved according to the invention in that the carrier layer is

provided with a light-coloured layer and a dark-coloured layer, wherein said light- coloured layer and dark-coloured layer completely overlap one another and extend over the entire carrier layer, and wherein the dark-coloured layer is arranged between the light-coloured layer and the layer of adhesive. With this arrangement, the two coloured layers cover the adhesive layer and protect it against outside influences when the adhesive tape is stuck to any surface. In this case, the light-coloured layer reflects a substantial proportion of the IR and UV radiation, whilst the dark-coloured layer absorbs UV radiation which the light-coloured layer has allowed to pass through. Penetration of UV and IR radiation as far as the adhesive layer is thus impeded. In this context, the light-coloured layer is preferably essentially white, since white reflects UV and IR radiation to an optimum extent. The dark-coloured layer is preferably essentially black, since black absorbs UV radiation very well. The dark-coloured layer is preferably arranged between the light-coloured layer and the layer of adhesive. This is highly advantageous, since it frequently arises, especially in the case of outdoor plasterwork, that small pieces of adhesive tape remain behind in the plasterwork or paintwork. If the light-coloured layer in such cases is located on the outermost, surface side of the adhesive tape, these small pieces are less noticeable.

For optimum scattering, that is to say the ability to diffuse and to reflect light, the light-coloured layer is preferably arranged as the top layer, i.e. the layer located uppermost on the outside.

According to the invention it is particularly highly advantageous if the pigment in the light-coloured layer comprises a zinc oxide and/or titanium dioxide, such as a form of rutile, for example rutile titanium dioxide. Rutile titanium dioxide in particular provides a very high scattering capacity for radiation from the visible part of the spectrum, whilst it absorbs UV radiation to a high degree and reflects most of the IR radiation. UV radiation which nevertheless has penetrated through the light-coloured layer is virtually completely absorbed in the dark-coloured layer.

In particular when the light-coloured layer is the top layer, it can be advantageous to incorporate so-called UV stabilisers and/or so-called UV absorbers in the light— coloured layer. This is because the heat generated by the action of the UV absorbers and/or UV stabilisers is then as far as possible dissipated into the surroundings and thus kept away from the adhesive layer.

So that UV radiation which still penetrates as far as the adhesive layer is rendered

harmless, it is, according to the invention, further advantageous if UV absorbers and/or UV stabilisers are also added to the adhesive layer.

Light and dark-coloured layers of this type can be used with virtually all adhesive tapes known from the prior art, as a result of which these adhesive tapes become even more UV- and IR-resistant, if they were already UV- and IR-resistant.

So that adhesive tapes of this type provide good adhesion to virtually all substrates, it is, according to the invention, advantageous if: the adhesive force on stainless steel determined in accordance with the "PSTC-1" test is at least 500 g per 25 mm tape width, and preferably more than 700, such as 800 g per 25 mm tape width; the adhesive layer is thick, preferably 50 to 60 μm (measured in accordance with PSTC-33); and the amount of adhesive applied is large, preferably at least 150 gram/m ² .

According to an inexpensive embodiment, with the aid of calendering, a coarse- mesh fabric is particularly suitable for the application of a thick layer of adhesive.

In this context, coarse mesh is understood to mean a fabric which has a warp every 25 mm plus a weft every 25 mm of at least 25 threads. However, very good results are obtained according to the invention with a warp every 25 mm plus a weft every 25 mm of 50 to 150, for example 80, threads. For good adhesive properties, the thickness of the adhesive layer of the adhesive tape according to the invention will in general be at least 70 μm.

For good dimensional stability and tearability of the adhesive tape, it is advantageous, according to the invention, if the elongation at break measured in accordance with PSTC-31 is less than 20 %. According to an advantageous embodiment, a coarse-mesh fabric is particularly suitable for this purpose.

The adhesive layer of an adhesive tape according to the invention preferably comprises an adhesive based on rubber, such as natural rubber, and the adhesive is preferably of the so-called dry type. Such adhesives based on rubber are relatively inexpensive, can be applied in a relatively thick layer and have good adhesive properties on diverse substrates.

Such adhesive tapes according to the invention can be manufactured in accordance with methods known per se from the prior art. For example by calendering, optionally in combination with coating of the adhesive and/or top layer.

In the case of calendering, a fabric which constitutes the carrier layer is provided on one side with a sheet or foil and at the same time is provided on the other side with adhesive. During this operation, said adhesive penetrates [into the meshes of the fabric, as a result of which the sheet or foil is stuck firmly onto the carrier layer, i.e. forms an integral whole. By now taking a co-extruded laminate containing a light-coloured and dark-coloured layer as the sheet or foil, an adhesive tape according to the invention is obtained in a simple manner. However, the sheet or foil can also be of a dark colour, in which case the light top layer can be applied by coating.

Adhesive tapes are also often produced by coating the coarse-mesh fabric on one side with a coating layer, such as polyethylene or another plastic, and on the other side with an adhesive, by means of calendering. Using a method of this type for the production of adhesive tape, an adhesive tape according to the invention can be obtained by first applying a dark-coloured layer and then a light-coloured layer to that side of the carrier layer which is opposite the adhesive layer. The adhesive can also be applied by coating (application of adhesive by the so-called wet method), especially in the case of fine-mesh fabrics.

The invention will be explained in more detail below with reference to a figure. This figure shows, highly diagrammatically, an adhesive tape according to the invention. The adhesive tape is made up of a carrier layer 1, which on one side is provided with an adhesive layer 4 containing adhesive and on the other side is provided with a first layer 2 and a second layer 3. With this arrangement, the first layer 2 is a dark- coloured, preferably black, layer, and the second layer 3 is a light-coloured, preferably white, layer.

The white top layer 3 scatters a large proportion of the visible radiation and IR radiation incident from above and absorbs UV radiation. The remaining IR radiation is absorbed. The UV radiation which is still transmitted is, however, largely absorbed by the dark-coloured, black layer 2, so that this radiation likewise does not reach the adhesive layer 4.

It will be apparent that numerous variants of the present invention are conceivable. It is conceivable that the carrier layer itself is made up of a dark and a light layer, so that the layer indicated by 1 in the figure can, as it were, be dispensed with.

It will be apparent that virtually any adhesive tape known from the prior art can be provided with a dark- and a light-coloured layer, so that, therefore, virtually any

adhesive tape known from the prior art can be converted to an adhesive tape according to the invention.