Laminated glass with infrared radiation reflecting properties

p0001The present invention relates to a laminated glazing reflecting infrared radiation consists of two glass sheets, a transparent support film in the tensile strength polymer disposed between the two glass sheets and provided with a surface layer reflecting infrared radiation, and two adhesive layers, by means of which the coated film is joined to two glass sheets.

p0002laminated glazing of this type are for example known from DE 2344616 A1, EP 0371949 A1 and EP 0391165 A2. They are particularly suitable as insulating glazing for automobiles. The carrier film for the surface layer that reflects infrared radiation may in principle be made of different materials, such as for example polyester, polycarbonate, cellulose acetate, acrylate or vinyl chloride. Supporting film of polyethylene terephthalate (PET) have proved particularly suitable for this purpose. The surface layer reflects infrared radiation can also in principle be formed in different ways. generally used usually multiple layers comprising one or more thin layers of silver as functional layers themselves, which are embedded between metal layers and / or dielectric, these layers are deposited preferably assisted by the sputtering process magnetic field.

p0003For the manufacture of laminated glazing, the support film provided with the surface layer are united by means of two thermoplastic adhesive layers to the two glass sheets following the processes customarily used for laminated glazing, films being polyvinyl butyral generally used as thermoplastic adhesive layers. Thermoplastic polyvinyl butyral film are advantageously previously joined to the carrier coated film to form a laminate, but the different films can of course also be prepared separately and the pack of layers may be only in the manufacture of the laminated glazing . During the union or assembly process itself, the package of layers is first freed from air therein and is then compressed in an autoclave under heat and pressure, usually under a know temperature of 120 to 150 ° C and a pressure of 8-15 atm.

p0004laminated glazing of this type have often, if oblique incidence of light, an optically disturbing aspect of the fact that the surface infrared reflective thinking does not appear uniformly flat, but is a withdrawal effect or as an effect hammering. This effect is known and is also described in the literature. It is also known that this hammering effect depends obviously on a process of removing the carrier film and / or thermoplastic adhesive films while warming during the union or assembly process.

p0005To avoid this optically disturbing effect, the use of carrier films which present only a very small degree of shrinkage is proposed in US-PS 4,456,736.

p0006It is proposed in EP 0371949 A1 to counter the effect mentioned by modifying the surface layer reflects infrared radiation so that the reflection is limited in the visible spectrum to 2% or better within 0.7%. The modification of the layer caused by the withdrawal remain in this case certainly fully present, but the removing effect will no longer be visible in a disturbing measure for the eye.

p0007Also to avoid this optically disturbing effect, EP 0544717 B1 proposes the use of special adhesive layers. Under this proposal, will be used as adhesive layers of polyvinyl butyral films which, on the face adjacent to the layer reflecting infrared radiation, have a low surface waviness defined.

p0008The proposals known to prevent the optically disturbing effect mentioned above each have specific disadvantages, and the problem of hammering effect in the case of laminated panes of the specified type has also not been resolved until now satisfactorily in the case of the implementation of these known proposals.

p0009The invention therefore aims to provide a laminated glazing of the type mentioned in the preamble so that optically disturbing effects caused by removal of a polymeric layer disposed between the silicate glass sheets are avoided using relatively simple measures.

p0010According to the invention, this object is achieved in that at least one of the adhesive layers has a maximum thickness of about 50 microns.

p0011It has been found and confirmed by tests that the optically disturbing effects observed may be completely or at least largely avoided when the coated film support is glued on one side at least relatively securely to a glass sheet with the aid of a very thin adhesive layer. In this way, the support film may not deform or retract since this is prevented by the strong union with one of the two glass sheets. The fact that the withdrawal process, which are responsible following the global experience of the hammering effect, taking place mainly in the same film holder provided with the layer or in the adhesive layers plays in which case no role. It is known in particular, precisely in the case of polyvinyl butyral film, these films are still subjected to internal stresses and they relax and deform under the effect of heat. It is therefore not excluded that the withdrawal process responsible for the effect mainly take place in the polyvinyl butyral layers and are there transferred to the support film. The disturbing effects caused in this way are also avoided by the measures of the invention.

p0012In the case of laminated glazing known of the specified type are used for the two adhesive layers each time the polyvinylbutyral films used generally for the manufacture of laminated panes, with the usual thickness of 0.38 mm. It turned out that the purpose according to the invention is also achieved when only one of the two adhesive layers is in an extremely thin form, and when a film thickness of conventional adhesive is used for the other layer glue. For the other adhesive layer, mention may in particular also use a polyvinyl butyral film 0.76 mm thick. A total thickness of the polyvinyl butyral layer of 0.76 mm is required, for example, in the case of windscreens, for biomechanical reasons.

p0013In principle all materials known as adhesive layers in the case of a normal laminated glazing can be taken into account for the extremely thin layer of adhesive and the other adhesive layer. In particular, materials such as thermoplastic proven polyvinyl butyrals and thermoplastic polyurethanes can be used for this purpose. In all cases, use of thermoplastic materials so that the usual manufacturing process can be taken over unchanged.

p0014In an advantageous development of the invention, the thickness of the thin adhesive layer is from 1 to 30 microns, or more preferably 5 to 10 .mu.m. Under these conditions, a particularly good fixing of the carrier film to a glass sheet is obtained.

p0015An embodiment of the invention will be described in more detail below with reference to the accompanying drawing.

p0016The drawing shows a fragmentary sectional view representation of a laminated glazing constituted according to the invention. The characteristics, which are not important to the embodiment of the invention and are generally known, such as the special constitution of the layer reflecting infrared radiation, the provision of adhesive layers, the composition of the carrier film, measures to prevent corrosion at the edge of the layer reflecting infrared radiation, etc., are not described as they are part of the known art.

p0017The laminated glazing comprises two glass sheets 1, 2, for example float glass each 3 mm thick, the carrier film 4 provided with the surface layer 3 reflecting the infrared radiation, the thin adhesive layer 5 and a layer relatively thick adhesive 6, which join the film 4 to two glass sheets. The carrier film 4 is a film for example of about 50 .mu.m thick polyethylene terephthalate. The carrier film 4 is provided on one side of a multiple layer that reflects infrared radiation, the actual functional layer within the multi-layer being formed of silver. The adhesive layer 5 combining the carrier film 4 to the glass sheet 1 is made of thermoplastic polyvinylbutyral and has a thickness of 10 .mu.m. The adhesive layer 6 on the other side of the carrier film 4 has a thickness of 760 .mu.m and is also made of thermoplastic polyvinylbutyral. The supporting film 4 coated was laminated with a film of 0.76 mm thick polyvinyl butyral in a previous working step and was coated on the other side with an adhesive film of 10 .mu.m of thickness. The two glass sheets 1, 2 are joined to each other using the laminate prepared in this manner in an autoclave at a temperature of 140 ° C and 12 atm. overpressure.