US 2013/0323477 A1
Method for manufacturing a decorated glass sheet
AGC Glass Europe
This patent presents a process for producing decorated glass with a functional coating of a metal or metal oxide to give properties such as low-emissivity, solar protection (reduction of heat exchange) or electric conductivity or physical protection and enhanced toughness. The process may be applied to the production of a number of articles such as shelves, kitchen appliance doors and refrigerated counters, table tops, partitions, lighting, shop windows and automotive glass. Dimensioning of the glass is not necessary at the outset of the process, so several parts can be produced simultaneously: the glass can thus be cut to size at the end of the process. Both PLF (full width: 6000 mm x 3210 mm) and DLF (half width: 3210 mm x 2250/2200 mm) sheet may be processed. The glass is first decorated by a printing process such as ink jet printing and after drying, is coated by a magnetron cathodic sputtering process to give the desired functionality.
The enamel-based decorative inks consist of vitreous substances such as silica, feldspar, kaolin and metal oxides. Such inks are available from Dip-Tech Digital Printing Technologies Ltd. The drying process after printing must remove the vast majority of the ink solvent so that outgassing does not occur during the subsequent vapour deposition coating process. Inks mainly have a boiling point below 300C, and drying time is related to the thickness of the glass (40 to 90 seconds per mm thickness of glass). A drying time of 320 seconds at 150C is typically adequate.
The functional coating is subsequently applied by a magnetron cathodic sputtering process. This is a form of ionised vapour deposition in which films are deposited from atoms and ions in precise ratios. Specific ionic compositions will thus determine the functionality of the coating. An example coating is a low-emissivity, solar shield, which may also be electrically conductive and can be based on one or more doped oxides such as tin-doped indium oxide or aluminium or gallium-doped zinc oxide. Low emissivity or solar shield coatings may also be based on a silver layer with a dielectric layer on either side of it. Following deposition of the functional coating, the coated glass is fired at 670 to 700C in a sintering or fritting process, during which toughening of the glass may occur and the glass may be bent in order to shape it.
While the image is designed to be viewed through the glass with the functional coating behind it, in some instances it is helpful to deposit a base or barrier layer (up to 30 nm thickness) of silicon oxide for example, prior to printing the decorative image. This will enhance adhesion of the image and will also prevent migration of silver through the enamel-based decoration. Alternatively, the ink formulation itself may contain elements that prevent such diffusion of silver.