Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-01-26
2001-04-03
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S425600, C428S426000, C428S427000, C428S428000
Reexamination Certificate
active
06210805
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a glass plate provided with a conductive layer, which has a conductive layer formed on a glass plate of e.g. a rear window of an automobile to prevent fogging of such a rear window, a method for its production, a conductive paste which forms a glass exudate coating layer by firing, and a window for an automobile wherein the glass plate provided with a conductive layer is used.
2. Discussion of Background
To prevent fogging of a glass plate used for a rear window of an automobile, a plurality of conductive strips for heating and common power source lines (bus bars) connected to both ends of the conductive strips, are printed and fired on the glass plate. Metallic terminals for lead wires are attached to the bus bars by soldering. A voltage is applied across the metallic terminals to let the conductive strips generate heat so that the surface temperature of the glass plate is maintained at a level higher than the dew point, whereby fogging of the glass plate can be prevented.
The conductive strips are formed on the glass plate by printing a conductive paste on the glass plate and then firing it. In the case of a glass plate for an automobile, the width of such conductive strips is usually at most 1 mm and about 0.4 mm at the center portion of the glass plate, in order to secure the visibility.
Such a conductive paste is prepared usually by mixing a conductive material powder such as a silver powder, a low melting point glass powder, an organic varnish and in some cases, an inorganic refractory filler powder. When the printed conductive paste is fired, the conductive material powder such as a silver powder will be sintered to form a conductive layer. The surface of the conductive layer facing the substrate, is baked to the substrate by low melting point glass formed by melting of the low melting point glass powder. Here, the substrate means the glass plate or a ceramic color layer formed on the glass plate surface.
In recent years, along with the diversification of automobile designs, it is desired to make the rear window or the like provided with conductive strips slidable. If such a rear window or the like provided with conductive strips is made slidable, the conductive layer of the conductive strips is likely to be abraded due to friction between the rear window and the rubber packing, which takes place during the sliding operation. This is likely since the hardness of the conductive layer exposed on the surface of the conductive strips is small.
As a method for preventing such abrasion of the conductive layer, there has been known (1) a method wherein a dense and highly hard copper-nickel layer is formed by electroplating treatment on the surface of the conductive strips printed and fired on the glass plate, or (2) a method wherein a conductive paste to form conductive strips is coated with a predetermined width, then a glass paste is coated with a width wider than the above width, followed by heating for baking to form a glass layer on the surface of the conductive strips (JP-A-50-15514).
These conventional methods involve many process steps and accordingly have had problems such that the operation efficiency tends to be poor, and the cost tends to be high. Further, in the method (2), overflow of the glass layer beyond the conductive strips tends to be substantial, whereby a see-through image is likely to be deformed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a glass plate provided with a conductive layer, a method for its production, a conductive paste for forming a glass exudate coating layer by firing and a window for an automobile wherein the glass plate provided with a conductive layer is used, which overcome the above problems.
The present invention provides a glass plate provided with a conductive layer, which comprises a glass plate, a conductive layer baked to the glass plate and containing a conductive material as the main component, and a glass exudate coating layer formed to substantially cover the conductive layer and containing low melting point glass as the main component.
Further, the present invention provides a method for producing a glass plate provided with a conductive layer, which comprises printing on a glass plate a conductive paste comprising at least from 50 to 90 wt % of a conductive material powder and from 10 to 50 wt % of a low melting point glass powder, as inorganic components, followed by firing.
The present also provides a conductive paste to be printed on a glass plate and fired to produce a glass plate provided with a conductive layer, whereby a glass exudate coating layer is formed by exudation to the conductive layer surface of low melting point glass formed by melting of a low melting point glass powder contained in the conductive paste at the time of the firing.
Still further, the present invention provides a window for an automobile, wherein the above glass plate provided with a conductive layer is used as a sliding window glass plate for the automobile.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the present invention, the conductive material is one which imparts a desired electrical conductivity to the conductive layer. As the conductive material, silver, gold, platinum, a silver-platinum alloy, a silver-palladium alloy, a silver-rhodium alloy or rhodium oxide may, for example, be used. It is preferred to use silver for such reasons that the electroconductivity is high, it is readily available, and the price is low.
In the present invention, the conductive layer contains a conductive material as the main component, and its content is usually at least 50 wt %.
In the present invention, the conductive layer surface means the surface on the side not baked to the substrate (the glass plate or a ceramic color layer formed on the glass plate surface).
In the present invention, the conductive layer is one baked to the glass plate, or to the ceramic color layer formed on the glass plate surface. In the following description, reference is made to a case where the conductive layer is baked to a glass plate.
In the present invention, the low melting point glass is glass which starts to be softened and flow at a temperature lower than the softening point (about 730° C.) of soda lime glass which is commonly used as a glass plate.
In the present invention, the glass exudate coating layer is one formed by exudation to the conductive layer surface of low melting point glass formed by melting of a low melting point glass powder contained in the conductive paste, at the time of firing, and it contains a low melting point glass as the main component. The content is usually at least 50 wt %. The glass exudate coating layer may contain an inorganic refractory filler in addition to the low melting point glass. In such a case, the glass exudate coating layer is a layer wherein the total amount of the low melting point glass and the inorganic refractory filler is at least 50 wt %.
The detailed mechanism of exudation of the low melting point glass to the conductive layer surface is not clearly understood. However, it is considered that at the time of the firing, the conductive material powder contained in the conductive paste is densified, whereby the low melting point glass is extruded or squeezed out to the conductive layer surface.
In the present invention, each of the low melting point glass and the inorganic refractory filler has a hardness higher than the conductive layer. Accordingly, the abrasion resistance of the conductive layer can be improved by covering the conductive layer with the glass exudate coating layer containing the low melting point glass, or the low melting point glass and the inorganic refractory filler.
When a metallic power supply terminal for a lead wire is to be electrically connected to the conductive layer by soldering or the like, the conductive layer will be provided with a portion to be connected with such a power supply terminal. Such a portion may be formed, for example, by 1) removing the gl
Asahi Glass Company Ltd.
Lam Cathy
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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