EGLASSTREK – INT. PATENT APPLICATION (PCT) SPOUT FOR LCD FLOAT®

Substrate glass for flat panel displays should fulfil higher standards as far as optical quality goes in comparison to window glass. This kind of substrate glass should not have any bubbles or cords which reduce the optical quality of a flat screen.  

Due to its different composition compared to window glass, it is required that the temperature of LCD substrate glass must be at about 1.400°C just before it reaches the floatbath so that a sufficient viscosity is achieved. These higher temperatures also mean a higher risk of cords forming caused by temperature inhomogeneities and due to evaporation of the gaseous components.

This problem is solved by using grain stabilised platinum alloys pipes to transport the molten LCD substrate glass from preparation (Spout) area to the floatbath. This platinum metal spout widens in the direction of flow like a funnel and can be directly heated by electrical current passing through it. A circular shaped inlet with a diameter of 50 to 500 mm and a rectangular shaped outlet make up the spout, whereby the longer rectangular shaped side runs horizontally. The height (H) of the outlet can measure 30 mm or more. The length of the preparation area measures 100 to 2.000 mm. The spout of grain stabilised platinum and/or platinum alloy has a wall thickness (t) of 5 mm or less.

The height for the molten glass outlet is calculated by dividing the height (H) by the wall thickness (t) and is between 5,0 and 600. Further the height (H) of the rectangular outlet is characterised by the fact that (H) is between 2% and 90% of the maximum diameter of the circular shaped inlet.

Preferably the current flanges are placed not only at the end wall, but also at the opposite side walls of the funnel shaped extension. Thus the current sources can be regulated appropriately allowing for heat regulation in accordance with the temperature of the molten glass and the resulting pull.

The diagram shows the spout from the top with the individual current flanges. Furthermore, the corresponding high current sources that regulate the current through the walls of the spout are also shown. The diagram also depicts schematically the lines of electric flux and flow of currents that develop in the spout walls when current between the flanges is turned on.

By means of this innovative measure the temperature of the glass is kept constant and the molten glass is simultaneously sealed off from the surrounding air. As a result, no evaporation of individual components in the composition of the glass occurs and the glass remains very homogeneous which allows for a high standard of optical quality.