Laminated glass panel having ir radioation reflecting properties

The present invention relates to laminated glass reflecting infrared rays.

It is a glass pane reflecting infrared radiation consisting of two sheets of glass, a transparent support layer made of tear-resistant polymer sandwiched between these two sheets of glass and provided with a surface coating that reflects infrared rays and from two adhesive layers by means of which the covering layer is connected to two sheets of glass.

Laminated glass panes of this type are known, for example, from German Patent Nos. 23 44 616 and European Application Nos. 0371 949 and 0391 165. They are particularly suitable for cars as heat protection glass. The support layer for the infrared reflecting surface covering can generally be made of material differences, such as, for example, polyester, polycarbonate, cellulose acetate, acrylate or polyvinyl chloride. Supporting layers made of polyethylene terephthalate (PET) have proven particularly suitable for this purpose. The infrared reflecting surface coating can also be of essentially different types. Multiple layers containing one or more thin silver layers are commonly used as actually functional layers sandwiched between metal and / or dielectric layers, these layers being preferably applied by magnetic field supported cathodic sputtering.

For the production of laminated glass panes, the support layers provided with a surface coating are joined to two sheets of glass by means of two thermoplastic adhesive layers using a conventional laminated glass process, with polyvinyl butyral usually being used as thermoplastic adhesive layers. The thermoplastic polyvinyl butyral layers are preferably joined in advance to the coated carrier layer to form a laminate, but the different layers can of course also be separately

183 440 prepared and joined together only during the production of laminated glass pane to form one laminated package. In the actual joining process, air is removed from the stack of layers first and then combined together by pressing in an autoclave, using heat and pressure, typically at 120 ° to 150 ° C and 784.532 kPa to 1470.997 kPa.

Laminated glass panes of this type, when subjected to accidental side lighting, often present a troublesome optical phenomenon such that the infrared reflecting surface does not give the impression of uniform reflection, but exhibits a shrinkage effect or even a hammer effect. This effect is well known and also described in the literature. It is also known that the hammer effect is apparently the result of shrinkage operations of the support layer and / or thermoplastic adhesive layers during heating in the joining process.

To reduce this annoying optical effect, US Pat. No. 4,456,736 proposes layers having only a very low degree of shrinkage.

European Patent Application Publication No. 0371 949 proposes that the above-mentioned effect be balanced by a surface coating reflecting infrared rays so modified that the reflection in the visible spectral range is limited to at most 2%, and preferably to less than 0.7%. The layer modification due to shrinkage obviously remains as such, but the shrinkage effect is no longer perceived by the eye to a degree that distorts vision.

Also in order to avoid this optically annoying effect, European Patent Publication No. 0544 717 proposes the use of special adhesive layers. According to this proposal, polyvinyl butyral layers are used as adhesive layers, with these layers having a defined wavy pattern with a small surface area on the face in contact with the infrared reflecting covering.

Each known solution to avoid the abovementioned annoying optical effect has certain disadvantages and the problem of the hammer effect in laminated glass panes in this category has not yet been satisfactorily resolved even when implementing these proposals.

The object of the present invention is therefore to construct a laminated glass pane of the type initially defined in which the optically annoying phenomenon caused by the shrinkage of the polymer layer disposed by silicate glass sheets can be prevented by using relatively simple means.

Laminated glass reflecting infrared rays consisting of two sheets of glass, a transparent support layer made of a tear-resistant polymer sandwiched between two sheets of glass and provided with a surface layer reflecting infrared rays and two adhesive layers by means of which the coated support layer is connected to two sheets glass is marked according to the invention here, that the at least one adhesive layer connecting the carrier layer to the glass sheet is at most 50 pm thick.

Preferably the adhesive layer has a thickness of 1 to 30 μ, and more preferably 5 to 10 pm.

Preferably, the second adhesive layer is 0.3 to 0.8 mm thick.

Preferably, the adhesive layers are made of a thermoplastic polymer, such as polyvinyl butyral or polyurethane.

Preferably, the support layer is made of polyethylene terephthalate. Preferably, the infrared reflecting layer is a multiple layer applied by means of a cathodic sputtering process and comprising at least one silver layer as a functional layer.

It has been discovered and confirmed experimentally that these optically observed troublesome phenomena are completely or at least largely avoided if the coated carrier layer is glued relatively firmly with at least one side to the glass sheet by means of a very thin adhesive layer. In this way, the support layer cannot deform or shrink further because it is prevented by firmly bonding with one of the two

183 440 sheets of glass. It is irrelevant here whether shrinking operations, which are also, according to our experience, responsible for the hammer effect take place primarily in the supporting layer itself provided with a covering or in adhesive layers. It is of course known in the case of polyvinyl butyral layers that these layers are often subject to internal stress and that they relax and deform under the influence of heat. Therefore, it is not possible that the shrinkage operations responsible for this effect take place primarily in the polyvinyl butyral layers and are transferred from there to the support layer. The resulting interference effects are also avoided by using the means of the present invention.

In known laminated glass panes of this type, in each of the two adhesive layers, polyvinyl butyral layers, commonly used for the production of laminated glass panes, are used in commercially available thicknesses of 0.38 mm. It has been pointed out that the objective set out in this invention is to be achieved if only one of the two adhesive layers is constructed as very thin, and the remaining adhesive layer will use commercially available adhesive film. In particular, a 0.76 mm thick polyvinyl butyral layer can be used as the second adhesive layer. The total polyvinyl butyral layer thickness of 0.76 mm is, for example, used for biomechanical reasons in the windshields of vehicles.

In principle, any of the known materials used in adhesive layers of normal laminated glass are suitable for both a very thin adhesive layer and also for the remaining adhesive layer. In particular, proven materials such as thermoplastic polyvinyl butyral and thermoplastic polyurethanes can be used for this purpose. In any case, thermoplastic materials should be used so that the normal production process can be adapted without modification.

In a further preferred embodiment of the invention, the thickness of the thin adhesive layer is 1 to 30 pm. Under these conditions, particularly good attachment of the carrier layer to the glass layer is achieved.

The subject of the invention is presented in an exemplary embodiment of the drawing, which shows in partial cross-section a laminated glass pane according to the invention. Details that are not important and generally known for carrying out the invention, such as, for example, the special structure of the infrared reflecting layer, the arrangement of the binding coatings, the composition of the support layer, the means for preventing corrosion of the infrared reflecting layer at its edges, are not described because they constitute a state technology.

The insulated glass pane contains two sheets of 1.2 glass each, e.g. 3 mm thick, supporting layer 4, provided with an infrared reflecting surface layer 3, a thin adhesive layer 5 and a relatively thick adhesive layer 6 that bind layer 4 to two sheets of glass. The support layer 4 is, for example, an approximately 50 m thick layer made of polyethylene terephthalate. The support layer 4 is provided on one face with a multiple layer reflecting infrared rays, the actual functional layer inside the multiple layer being silver. The adhesive layer 5 connecting the carrier layer 4 to the glass sheet 1 is made of thermoplastic polyvinyl butyral and has a thickness of 10 pm. The adhesive layer 6 on the other side of the support layer 4 is 760 m thick and is also made of polyvinyl butyral. Covering the support layer 4 was done by laminating a 0.76 mm thick polyvinyl butyral layer in the previous operation and covering the second frontal face with a 10 pm adhesive layer. Two sheets of 1.2 glass are connected by the laminate thus formed in an autoclave at a temperature of 140 ° C and a pressure limit of 1176,798 kPa.

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