FR2665605A1 - HEATING GLAZING AND PROCESS FOR OBTAINING THE SAME. - Google Patents

Abstract

The invention relates to a heated glazing comprising a glass sheet provided on one of its faces with resistance bands formed of an electrically conductive composition resulting from the baking of a suspension in an organic binder of metallic silver and of a frit to low melting point and collector bands formed from the same electrically conductive composition. According to the invention, windows are formed in the collecting bands, and closed by pellets made of an electrically conductive composition having a greater silver content than the resistance bands and the collecting bands and having a dimension slightly greater than that of the bands. windows so as to form overlap zones, the current supply lugs being welded to said pellets.

Description

I 1

HEATED GLAZING

  The invention relates to a screen printed electrical network for heated glazing, in particular for a rear window.

  rière of a motor vehicle More specifically, the invention relates to a glazing unit fitted with all of its conductive strips, that is to say strips forming the actual heating network and collector strips for- intended to be connected by welding to the current leads supplied by the current source of the vehicle. 20 To produce a glazing with a heating network ensuring the functions of defrosting and demisting, it is known for example from patent FR-B-1 464 585 to deposit on the surface of a glass sheet a series of narrow resistance bands of an electrically conductive composition. These resistance bands are serigraphed on the glass sheet before bending, so that the firing of the electroconductive composition takes place during the heating preceding the bending and / or tempering operation of the glazing The electroconductive composition is made of a pasty suspension, in an organic binder, of metallic silver and a frit, that is to say a glass with a low melting point The resistance bands forming the network are relatively thin so as not to impede visibility through the glazing and lead to collecting strips wider, located near the edges of the glazing These collector tapes are made of a composition identical to that of the resistance tapes and are deposited in the same way and preferably at the same time as these The current leads

  2 - are then welded to these collector strips.

  The first heating glazings thus produced included very conductive resistance bands, of a particularly high metallic silver content, with a view to a high heating capacity; therefore, the electrical power dissipated by the heating network was

  it is also very high. However, such high dissipated powers are not well suited to small-displacement motor vehicles whose electrical power of

  serve is relatively low This is all the more so since motor vehicles are today equipped with a whole

  series of electrical equipment which means that the maximum power capable of being dissipated at a given time is often less than the theoretical capacity required for simultaneous operation of all the electrical equipment of the vehicle. Consequently, there is a growing demand -

  The health of heated glazing dissipating lower powers, which, except for reducing the size of the heating circuit, requires the use of electroconductive compositions having relatively lower silver contents. Concretely, whereas in recent years the

  heating networks were made from pasta with a silver content of around 75% or more, the market is now moving towards products made with pasta with a silver content of at least 71%.

  In practice, this reduction in the silver content poses a problem of compatibility with the solder of the

  welding, in other words welding does not hold well To remedy welding faults, current industrial practice30 is to place at the places provided for welding a pellet made of a paste with a high silver content, this

  cond deposit being done for example by screen printing or brush and covering an area of the order of 1-4 cm 2. The authors of the present invention have however

  observed that this solution is far from always giving its-

  satisfaction, short circuits occurring fairly frequently

  only By examining the defective glazing we do not cons-

  Tate no problem at the weld On the other hand, it appears that the pellet itself does not always adhere 3 - correct way to the collector strip This phenomenon was

  totally unexpected given the great similarity between the different silver-based compositions which suggested a good bond between the two layers (the only difference being ultimately the silver-sintered ratio) Furthermore, it should be noted that this phenomenon besides his ca-

  The unpredictable character exhibited the defect of being hardly easy to be observed given the small thickness of the layers in question. The aim of the present invention is to propose a more satisfactory solution to this technical problem of the

  connection to the vehicle power source of low silver screen printing networks. This problem is solved according to the invention by a vi-

  heating trage comprising a glass sheet provided on one of its faces with resistance bands formed of an electroconductive composition resulting from the baking of a suspension in an organic metallic silver binder and of a low point frit fusion and of collector strips 20 formed of the same electroconductive composition, windows being according to the invention closed by pellets made of an electroconductive composition having a greater silver content than that of the composition forming the resistance bands and25 the collector strips and having a dimension slightly greater than that of the windows so as to form overlap zones, the current supply terminals being welded to said pellets. The glazing according to the invention is thus presented with collector strips with "holes" and pellets whose silver content is most adequate for perfect welding of the current supply terminals The window formed in the collector strip allows the pellet to be in direct contact with the substrate and not superadded35 as before The substrate is here either glass or an enameled layer previously deposited on the glass and used for example to mask the glue used during the installation of the glazing In all in the cases, the connection between the substrate and the pellet is ensured by the frit so

  4 - that there is no risk of the pellets peeling off.

  Such glazing can for example be obtained simply by modifying the screen printing frame used for the deposition

  of the heating network so as to provide windows which are subsequently covered by the deposited pellets, either by a new screen printing passage or quite simply

  with the brush. In a typical case, the silver content of the composition forming the bands of the heating network is lower.

  greater than or equal to 71%, while for the pellets a silver content greater than 75% or even 80% is expected

  which is very favorable to the quality of the weld, the small size of the pellets allowing the use of rich pastes without however resulting in a significant increase in the cost of the glazing.

  An important point of the invention is, as indicated above, the direct bond on the substrate of the pas-

  tille, so that the overlap zones between the pellets and the collector strips are fixed over time with respect to the surface of the glass sheet It can certainly happen as with glazing according to the art that the pellet made of a paste with a high silver content does not adhere correctly to the collecting strip at the level of the covering zone, but the pellet being anchored to the substrate the covering zone is always well presented, so that generally conduction is ensured simply because of the close proximity of the two layers. In a more particularly preferred variant of the invention, the patch is placed under the collecting strip at the level of the overlap zone. In fact, the collecting strip has its low silver content compensated by a

  higher frit content During baking, the collecting strip will therefore diffuse very easily towards the glass of which it is very close due to its composition. On the other hand, this diffusion is less for the pellet depleted in sinter. Tests have shown that a dough having a te-

  In this way, 75% silver diffuses twice less than a 71% paste. In these circumstances, if the collecting strip covers the pellet, its tendency to diffuse towards the glass will lead to the formation of an interpenetration layer having an average silver content guarantees perfect conduction, while leaving the pellet available for soldering current leads.

5 In the latter case, it is preferably necessary to proceed in order to obtain the glazing according to the invention to a screen printing in two stages with in a first step the deposition exclusively of the pellets and in a second step the deposition of the conductive strips heating network and collector strips, the frame used having windows of adequate size in places already provided with a patch. -6-

Claims (4)

  1 Heated glazing comprising a sheet of glass provided on one side with resistance bands formed of an electrically conductive composition resulting from the baking of a suspension in an organic binder of metallic silver and a frit low melting point and collector strips formed of the same electrically conductive composition, characterized by windows formed in said collector strips, these windows being closed 10 by pellets made of an electrically conductive composition having a higher silver content than   that of the composition forming the resistance bands and the collector bands and having a dimension slightly greater than that of the windows so as to form overlap zones, the current supply terminals being welded to said pellets.   2 heating glazing according to claim 1, characterized in that the silver content of the composition   forming the resistance bands and the collector bands 20 is less than or equal to 71% and in that the silver content of the composition forming the pellets is greater   greater than or equal to 75%. 3 heated glazing according to claim 1 or 2, characterized in that at the overlap area   the pellet is placed under the collecting strip.   4 A method of obtaining a heated glazing according to claim 3, according to which is carried out in a first step a screen printing of the pellets and in a second step the deposition of resistance bands and bands collectors.