Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-09-17
2001-07-17
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S103000, C156S104000, C156S106000, C156S286000
Reexamination Certificate
active
06261398
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is a national phase of PCT/EP98/01347 filed Mar. 7, 1998 and based upon German National Application 1 9711 459.8 of Mar. 19, 1997 under the International Convention.
FIELD OF THE INVENTION
The present invention relates to a process for producing a bent laminated safety glass sheet or pane from a first curved glass sheet, a first bonding layer, a thermoplastic carrier foil provided with a thin layer system, a second bonding layer as well as a second bent glass sheet conforming to the first bent glass sheet.
BACKGROUND OF THE INVENTION
Laminated safety glass sheets of the aforedescribed construction are increasingly used as sunscreens, especially for motor vehicles. For this purpose, the thin layer system on the carrier foil typically consists of up to three noble metal layers, preferably of a silver basis, which are embedded in dielectric layers (U.S. Pat. No. 4,799,745). Through the use of a thermoplastic foil as a carrier system, it can be insured that the carrier foil can match the curvature the glass sheets in the course of the heat treatment required for bonding them together. The matching deformation of the carrier foil is supported in that biaxially stretched thermo-plastic carrier foils are used. In connection with the selection of suitable carrier foils reference may be had to, for example, EP 0 077 672 B2 and EP 0 457 209 A2. Especially well suited for bent laminated safety glass sheets are the biaxially stretched carrier foils which are the subject of the older PCT application EP 96-04018 (WO97/10099, Flachglas Automotive GmbH). The two laminate layers serve for adhesive bonding of the carrier foil with the glass sheets and impart safety glass characteristics to the laminate.
For the production of laminated safety glass sheets of the afore-described construction, it has already been proposed to provide a foil prelaminate from the first bonding layer, the carrier foil provided with the thin layer system and the second bonding layer, in which the foils are pressed together, degassed and are prebonded with the use of heat (EP 0 535 128 B1). The thus formed foil laminate with air evacuated from between layers is laid between the two glass sheets, whereupon the laminate of the glass sheets and prefoil laminate is subjected to a degassing process as well as to a prebonding process. Finally, the laminate is finish bonded at increased temperature and higher pressure to the laminated safety glass. This process has been found to be suitable for slightly curved glass sheets. With greater bends, especially complex bends, when this process is carried out in practice, there can be wrinkle formations above all in the edge regions in the carrier foil which have been termed edge corrugations. To overcome this problem various approaches have already been proposed in which a prelamination of at least one bonding layer and the carrier foil is suitably preformed in a special apparatus (WO 94/04 357). Such a process is expensive and requires for each sheet type, a specially prefabricated form.
Tolerance-caused deviation in the glass sheets from the intended shape can give rise in the previously known process, apart from matching defects which influence the optical characteristics of the finished laminated safety glass sheet, to bond defects between the glass sheets and the foil prelaminate.
OBJECTS OF THE INVENTION
It is an object of the invention basically, to provide an improved fabrication process for laminated safety glass sheets of the aforedescribed construction which is better able to avoid the development of wrinkles in the carrier foil during fabrication and which enables especially the production of complexly bent laminated safety glass sheets without wrinkle formation especially in the sight regions of the sheet. Another object is to make bonded laminated safety glass sheets which, to the greatest possible extent are free from such undesired deformations as have in the past caused the optical defects which have their origins in the carrier foil provided with the thin layer system, above all in reflected as well as in transmitted light.
SUMMARY OF THE INVENTION
A process for producing a bent laminated safety glass pane from a first bent glass sheet, a first bonding layer, a thermoplastic carrier foil provided with a thin layer system, a second bonding layer as well as a second bent glass sheet matching the first bent sheet can be made by the following sequence of steps:
(a) a foil prelaminate, comprised of the first bonding layer and the carrier foil are placed with the bonding layer side against the first glass sheet,
(b) a cover sheet, bent to match the first glass sheet, is placed on the foil prelaminate,
(c) the glass-foil stack formed from the first glass sheet and the foil prelaminate is degassed and prebonded through the use of heat and pressure,
(d) the cover sheet is removed,
(e) the second bonding layer and the second glass sheet are applied to the prebonded glass-foil stack,
(f) the thus formed laminate is degassed and prebonded with the use of heat and pressure, and
(g) the prebonded laminate is finally bonded through the application of pressure and heat to a laminated safety glass pane.
The invention resides in the surprising discovery that with the aid of a multistage prebonding and final bonding process a cover sheet is applied to an initially prebonded prelaminate of a first bent glass sheet, a first bonding layer and a carrier foil, on the carrier foil to which the cover sheet is applied, before the second bonding layer and the second glass sheet initially prebonded with the prelaminate are provided and then the entire laminate is finally bonded so that detrimental wrinke formation of the carrier foil is avoided in a reliable manner. The invention is suitable most especially for the production of complexly bent motor vehicle laminated safety glass panes with a transverse bend of 10 mm or more. The transverse bend (height) which can be measured in the region of the transverse central axis as a standard, is normally the symmetry axis for windshields or rear vehicle windows.
It is indeed possible to work with bonding layers formed in situ from bonding materials applied in a flowable state to one of the glass sheets or the carrier foils, for example, with cast resins or with bonding materials which are solubilized in suitable solvents and brought into a liquid state. The bonding layers coming within the realm of the invention however are preferably bonding foils which are preferably rendered grainy superficially and are of the usual thicknesses, i.e. typically 0.38 or 0.76 mm as are known for use as materials in laminated glass production.
The carrier foils used preferably here are such as those described in PCT application EP 96/04018. The invention is not however, limited to them. The criteria for the material and thickness selection for a carrier foil in combination with the present invention are its compatibility with the bonding layers and use in the prebonding and final bonding processes as well as its suitability from the point of view of thermal shrinkage characteristics such that a wrinkle-free matching deformation of the carrier foil can take place in the course of producing the laminated safety glass sheet. For this purpose, biaxially stretched carrier foils are basically indeed preferred. However, within the framework of the invention depending upon the curvature of the glass panes in individual cases, nonstretched carrier foils or carrier foils which have only been weakly stretched can be used. This can be the case especially when process step (c) is carried out at relatively high temperatures. The carrier foils must have sufficient light permeability for the respective purpose and must be suitable as carriers for the thin layer system and have good adhesion to the bonding layers on both sides.
Preferably, in accordance with the process of the invention, a foil prelaminate is used in which the thin layer system of the carrier foil adjoins the first bonding layer. The thin layer system is protected
Ball Michael W.
Dubno Herbert
Haran John T.
Pilkington Automotive Deutschland GmbH
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