GB2232414A

GB2232414A - Preparing decorated toughened glass article

Info

Publication number: GB2232414A
Application number: GB8905505A
Authority: GB
Inventors: Leslie Ralph Easton
Original assignee: STAINED GLASS SYSTEMS Ltd
Current assignee: STAINED GLASS SYSTEMS Ltd
Priority date: 1989-03-10
Filing date: 1989-03-10
Publication date: 1990-12-12
Anticipated expiration: 2009-03-10
Also published as: GB2232414B; GB8905505D0

Abstract

A method for producing a toughened glass article with an applied design in coloured enamels includes the steps of applying the design to the glass article as a water-slide transfer 10 comprising coloured glass frits in a printing medium. The article 17 is then subjected to a preliminary heat-treatment cycle in a first furnace 18 sufficient to burn off the printing medium but insufficient to fuse the coloured glass frits. The article is then subjected to a glass-toughening cycle in a second furnace 19 in which the glass frits are fused. <IMAGE>

Description

METHOD FOR PRODUCING COLOURED DESIGNS ON GLASS The present invention relates to a method of making a toughened glass article to which a design in coloured enamels is applied. The invention is concerned particularly, but not exclusively with a method for producing a stained glass effect on toughened sheet glass such as might be used for glass doors or windows.

Various techniques have been used for producing a coloured effect on glass to simulate stained glass windows. For certain applications it is desirable, if not mandatory, that the glass used should be toughened. It has not however been possible hitherto to provide a design on toughened glass that is durable and simple to apply.

In our earlier U.K. patent specification GB-A-2174383, we describe a method for producing a toughened glass article with an applied design in coloured enamels includes the steps of applying a water-slide transfer to the glass article, the transfer co.mprising a design in vitrious coloured enamels, and subjecting the glass panel with the applied design to a glass-toughening heat treatment cycle. Typically the toughening treatment cycle involved heating the glass panel to 620 -670 C and rapidly cooling with blasts of cold air in a cycle of about 3 minutes duration. We also described a process in which the transfer design is fused to the glass panel in a preliminary heat treatment cycle prior to the toughening cycle.The preliminary heat treatment cycle was typically for a period of 25 minutes to 1 hours at a temperature of between 5900-6O00C. The duration of the toughening cycle is much shorter and the cooling more rapid than for the preliminary cycle.

With this process, we found that coloured designs can be produced without fizzle or blistering provided suitable enamels are used. By testing commercially available enamels it has been found a range of colours that can be used to produce satisfactory results.

The present invention is a modification of our earlier process.

According to the present invention there is provided a method for producing a toughened glass article with an applied design in coloured enamels including the steps of applying the design to the glass article in the form of coloured glass frits in a printing medium, subjecting the article to a preliminary heat-treatment cycle sufficient to burn off the printing medium but insufficient to fuse the coloured glass frits, and then subjecting the glass article to a glass-toughening heat-treatment cycle.

We have found that by using this process satisfactory results can be obtained using any enamel that is compatible with the glass toughening cycle, that is it will fuse at the toughening temperature.

The design can be applied to the article in the form of a transfer or by direct printing onto the glass. Both transparent and opaque colours may be used. In the preliminary heat treament cycle the glass may reach a temperature of 400-450 C.

We have found that with this process better firing occurs with less imperfections. Because the preliminary heat treatment can be shorter than with the cycle in our earlier patent specification, there is less likelihood of dust or other foreign matter settling on the glass during firing. Typically the preliminary heat-treatment cycle will last 5 to 10 minutes.

The process will work with water based and other types of enamel colours. If a cover coat is used the preliminary heat treatment cycle should be high enough and long enough to burn off the cover coat and the printing medium. A temperature of 4500 and a time of 5 to 10 minutes should normally be sufficient.

The heat treatments may be performed in two separate furnaces or it may be carried out in one furnace with the temperature of the furnace being raised to take the glass from the preliminary heat treatment cycle to the toughening cycle.

It is not essential for the glass to be allowed to cool down before passing into the toughening cycle.

Besides enabling a wider range of enamels and hence colours to be used the method of the present invention has the advantage that the glass does not soften during the preliminary heat treatment cycle and there is therefore less tendency for the glass to distort.

Further details, features and advantages of the invention will be apparent from the following description with reference to the accompanying drawings; in which Figure 1 shows a diagrannatic perspective view (not to scale) of a water slide transfer that may be used in the method of the invention; and Figure 2 shows a schematic view of a glass view of a glass panel being heat treated in accordance with the invention.

The coloured design may be applied to the glass article by direct screen printing onto the glass in the method of the present invention. However, in the preferred method, the design is applied as a water-slide transfer, as in our earlier applications. Fig. 1 shows an example of a water-slide transfer 10. The transer 10 bearing a multi-coloured design is prepared as follows. The design is printed on the gummed side 11 of a sheet of gummed paper 12 using a screen printing technique. The areas 13, 14, 15 of different colours are printed successively in separate stages using different screens to build up the complete design. To produce a good stained-glass effect transparent vitrious enamels are used for the coloured areas 13 and 14 although opaque vitrious enamels may be used for divisions 15 between the colours and for lines of detail.

The colours are made up of lead-bearing glass frits mixed with metallic oxides to give the colour and carried in a printing medium. The glass frits are made from a mixture of lead oxide, boric acid and silica which is fused together and then quenched in water and then dried. The frit is then ground with the metallic oxide to provide the desired colour and mixed with just enough medium to enable it to be printed. The medium is burnt off during the heat treatment and the less medium that has to be burnt off the better the results. The printing medium may be cellulose or resinous and serve to bind the colours together.

After the colours have been printed on the gummed paper, the coloured areas are covered with an acrylic resin 16 cover coat to protect the transfer and hold it together during the transfer process.

When it is desired to apply the transfer to a glass article such as, for example, a 4mm thick, clear float-glass door panel, the transfer is soaked in clean water until loose, lifted from the gummed paper and applied to the flat surface of the glass. Alternatively obscured glass of different thickness may be used.

After drying for 4 to 6 hours at room temperature the glass panel 17 with the applied transfer 10 is passed through a preliminary heat treatment furnace 18. The glass enters the furnace and is heated to a temperature of 4000-4500C. The glass passes back and forth within the furnace until it reaches the desired temperature. During this period all the acrylic resin covercoat and the printing medium are burnt off in the oxidising atmosphere of the furnace. By using as little medium as possible the risk of the burning resin disturbing the glass frits is minirnised. The temperature of the oven is not however sufficient to melt the glass frits and metal oxides. The panel remains in the furnace 18 for 5 to 10 minutes until all the cover coat and medium have been burnt off.

When the glass panel emerges from the furnace it is then passed to a toughening heat treatment furnace 19. The glass is heated rapidly to a temperature of 6200-6700C in the heat toughening furnace. The glass passes back and forth within the furnace 19 until the desired temperature is reached. The glass frits and metallic oxides melt on the surface of the glass panel to form areas of transparent colour that are fused to the surface of the glass. The glass panel remains in the furnace 19 for 2 to 3 minutes.

When the glass panel emerges from the furnace 19 it is blasted with cold air from jets 20 to cause rapid cooling of the surface of the glass and consequent toughening of the glass panel 17.

The resulting product is a glass panel which is toughened and has the appearance of stained glass.

We have found that provided the enamels are compatible with the glass toughening cycle in that they fuse at the temperature of the toughening furnace, satisfactory results can be obtained using any type or colour of enamel without frizzle. It is therefore not necessary to carry out preliminary tests to determine which enamels are suitable as in the method of our previous patent.

Claims

1. A method for producing a toughened glass article with an applied design in coloured enamels including the steps of applying the design to the glass article in the form of coloured glass frits in a printing medium, subjecting the article to a preliminary heat-treatment cycle sufficient to burn off the printing medium but insufficient to fuse the coloured glass frits, and then subjecting the glass to a glass-toughening heat-treatment cycle.

2. A method according to claim 1 in which the toughening cycle is practiced by heating the glass article to a temperature in the range of 6000C to 6700C and then cooling the article with blasts of cold air.

3. A method according to claim 1 ro 2 in which the toughening cycle is completed in less than 3 minutes.

4. A method according to claim 1, 2 or 3 in which the prelniinary heat-treatment cycle is at a temperature of less than 4500C.

5. A method according to claim 1,2,3 or 4 in which the preliminary heat-treatment cycle is of 5 to 10 minutes duration.

6. A method according to claim 1,2,3,4 or 5 in which the design is applied to the glass article as a water-slide transfer.

7. A method according to claim 6 in which the water-slide transfer comprises a sheet of gummed paper on which the design is printed.

8. A method according to claim 1,6 or 7 in which the design is of the water-slide transfer has a cover coat and the cover coat is burnt off during the preliminary heat treatment cycle.

9. A method according to any of the preceding claims in which the printing medium is a cellulose or resinous, or water based medium.

10. A method according to any of the preceding claims in which the article is a glass panel.

11. A method according to any of the preceding claims in which the design is a sulti-colour design.

12. A method according to any of the preceding claims in which the glass reaches a temperatre of between 4000C and 4500C in the preliminary heat-treatment cycle.

13. A method according to claim 1 in which the design is applied to the glass by direct printing.

14. A method substantially as hereinbefore described with reference to the accompanying drawings.