Screen-printing screen and process for obtaining glazings equipped with electrically conductive patterns

1. A process for obtaining a glazing coated on one of its faces with electrically conductive patterns located in at least one lateral portion and in a central portion of the glazing, said electrically conductive patterns comprising electrically conductive tracks of thickness e 1 located in the or each lateral portion and electrically conductive tracks of thickness e 2 located in the central portion, the thickness e 1 being larger than the thickness e 2 , said patterns furthermore comprising, in the central portion, at least one thick electrically conductive pattern, said process comprising screen printing said electrically conductive patterns in a single pass, by way of the following steps:

positioning a screen-printing screen facing a glass sheet, the screen-printing screen including a main mask possessing a central portion and at least one lateral portion, an aperture size of the main mask being larger in said at least one lateral portion than in said central portion, said screen screen-printing furthermore including, in at least one zone located in said central portion, at least one secondary mask fastened to a face of said main mask, said at least one zone forming a double-mask zone, an aperture size of the or each secondary mask being larger than the aperture size of the main mask in said central portion, a mesh of the main mask extending in a first direction in a surface of said main mask and a mesh of the at least one secondary mask extending in a second direction in a surface of said at least one secondary mask, said first direction making with said second direction an angle α comprised between 1 and 89°, said screen-printing screen being placed so that the central and lateral portions and of the screen-printing screen are in correspondence with the portions of the glass sheet that are intended to become the central and lateral portions of the glazing, respectively, and so that the or each double-mask zone is in correspondence with a zone of the glass sheet that is intended to be coated with a thick electrically conductive pattern; then

depositing an electrically conductive paste on the screen-printing screen.

2. The process as claimed in claim 1 , wherein the screen-printing screen is obtained by a method comprising the following steps:

a) coating a photocrosslinkable emulsion onto at least one portion of a surface of the main mask; then

b) applying, on one face of the main mask, in the or each zone intended to become a double-mask zone, a secondary mask to the still-wet photocrosslinkable emulsion, in order to form said at least one double-mask zone; then

c) drying the screen; then

d) exposing the screen in order to crosslink the photocrosslinkable emulsion in preset zones; then

e) washing and drying the screen.

3. The process as claimed in claim 2 , wherein the or each secondary mask is cut beforehand using a cutting die from a mask of larger dimensions.

4. The process as claimed in claim 2 , comprising, between steps c) and d), the following steps:

b′) coating the screen with additional photocrosslinkable emulsion in the double-mask zone; then

c′) drying the screen.

5. The process as claimed in claim 2 , wherein the photocrosslinkable emulsion is coated onto the entirety of the surface of the main mask.

6. The process as claimed in claim 1 , wherein the screen-printing screen is placed so that the or each secondary mask is turned toward the glass sheet.

7. The process as claimed in claim 1 , wherein the electrically conductive paste is a silver-containing paste.

8. The process as claimed in claim 7 , wherein the silver-containing electrically conductive paste comprises, in the wet state, at most 75% by weight silver.

9. The process as claimed in claim 1 , wherein the at least one secondary mask is fastened to the face of the main mask by (a) coating a photocrosslinkable emulsion on at least a portion of the face of the main mask and (b) cross-linking the photocrosslinkable emulsion.

10. The process as claimed in claim 9 , wherein the photocrosslinkable emulsion is coated onto the entirety of the surface of the main mask.

11. The process as claimed in claim 1 , wherein the electrically conductive paste is deposited on the screen-printing screen using a squeegee.

12. The process as claimed in claim 1 , wherein the angle α is comprised between 15 and 80°.

13. The process as claimed in claim 12 , wherein the angle α is comprised between 15 and 60°.

14. The process as claimed in claim 13 , wherein the angle α is comprised between 15 and 50°.

15. The process as claimed in claim 14 , wherein the angle α is comprised between 15 and 35°.

16. The process as claimed in claim 1 , wherein the main mask is such that a number of wires per cm in the central portion is higher than a number of wires per cm in the at least one lateral portion, and a diameter of the wires in the central portion is smaller than a diameter of the wires in the at least one lateral portion.

17. The process as claimed in claim 1 , wherein a number of wires per cm of the at least one secondary mask is lower than a number of wires per cm of the main mask in the central portion and a diameter of the wires of the secondary mask is larger than a diameter of the wires of the main mask in the central portion.

18. The process as claimed in claim 1 , wherein some of the apertures of the screen-printing screen are blocked with a resin obtained by exposing a photocrosslinkable emulsion, said at least one secondary mask being fastened to a face of said main mask using said resin.

19. The process as claimed in claim 1 , wherein the thickness e 1 is comprised between 8 and 15 μm, and the thickness e 2 is comprised between 2 and 5 μm.

20. The process as claimed in claim 1 , wherein the glazing is a motor-vehicle rear windshield, the electrically conductive patterns being antennas, bus bars and/or heating wires, and the at least one thick electrically conductive pattern being a soldering zone for antenna connection.