SCREEN-PRINTING SCREEN AND PROCESS FOR OBTAINING GLAZINGS EQUIPPED WITH ELECTRICALLY CONDUCTIVE PATTERNS

Abstract

A screen-printing screen for printing electrically conductive patterns on glass sheets, includes a main mask, the aperture size of the main mask being larger in a lateral portion than in the central portion, the screen furthermore including, in at least one double-mask zone, located in the central portion, at least one secondary mask fastened to a face of the main mask, the aperture size of the or each secondary mask being larger than the aperture size of the main mask in the central portion, and the mesh of the or each secondary mask making, with the mesh of the main mask, an angle α comprised between 1 and 89°.

Claims

1. A screen-printing screen for printing electrically conductive patterns on glass sheets, comprising 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 furthermore comprising, 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, and a mesh of the or each secondary mask making, with a mesh of the main mask, an angle α comprised between 1 and 89°.

2. The screen as claimed in claim 1, wherein the angle α is comprised between 15 and 35°.

3. The screen 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.

4. The screen 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.

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

6. A process for obtaining a screen-printing screen as claimed in claim 1, 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.

7. The process as claimed in claim 6, wherein the or each secondary mask is cut beforehand using a cutting die from a mask of larger dimensions.

8. The process as claimed in claim 6, 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.

9. 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 e1 located in the or each lateral portion and electrically conductive tracks of thickness e2 located in the central portion, the thickness e1 being larger than the thickness e2, 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 as claimed in claim 1 facing a glass sheet, said screen being placed so that the central and lateral portions and of the 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 is on the screen-printing screen in particular using a squeegee.

10. The process as claimed in claim 9, wherein the screen is placed so that the or each secondary mask is turned toward the glass sheet.

11. The process as claimed in claim 17, wherein the silver-containing electrically conductive paste comprises, in the wet state, at most 75% by weight silver.

12. A glazing coated on one of its faces with electrically conductive patterns obtained by screen printing and 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 e1 located in the or each lateral portion and electrically conductive tracks of thickness e2 located in the central portion, the thickness e1 being larger than the thickness e2, said electrically conductive patterns furthermore comprising, in the central portion, at least one thick electrically conductive pattern, the thickness e3 of which is at least 8 μm, and is larger than the thickness e2.

13. The glazing as claimed in claim 12, wherein the thickness e3 is at most 12 μm.

14. The glazing as claimed in claim 12, wherein the thickness e1 is comprised between 8 and 15 μm, and the thickness e2 is comprised between 2 and 5 μm.

15. The glazing as claimed in claim 12, wherein the glazing is a motor-vehicle rear windshield, the electrically conductive patterns being antennas, bus bars and/or heating wires, and the or each thick electrically conductive pattern being a soldering zone for antenna connection.

16. The process as claimed in claim 6, wherein the photocrosslinkable emulsion is coated onto the entirety of the surface of the main mask.

17. The process as claimed in claim 9, wherein the electrically conductive paste is a silver-containing paste.

18. The process as claimed in claim 12, wherein the electrically conductive patterns are silver-containing patterns.

19. The process as claimed in claim 12, wherein the thickness e3 is comprised between 8 and 15 μm.

Description

[0058] The invention will be better understood in light of the following example embodiments, which are illustrated by FIGS. 1 and 2.

[0059] FIG. 1 shows a screen-printing screen according to the invention.

[0060] FIG. 2 shows a glazing according to the invention.

[0061] In FIG. 1, the screen 1 comprises a variable-aperture-size main mask 2 allowing electrically conductive patterns of various thicknesses to be obtained on one and the same glass sheet using a single cloth. This main mask is of rectangular shape and comprises a central portion A the perpendicular bisector of the short sides of which corresponds to the perpendicular bisector Y of the long sides of the main mask 2. By way of example, the cloth of the main mask 2 in the central portion A comprises 90 wires per cm, each of the wires having a diameter of 48 μm.

[0062] The main mask 2 also comprises two lateral portions C, which portions are rectangular and placed symmetrically with respect to the perpendicular bisector Y, on either side of the latter. The cloth in the portions C comprises for example 48 wires per cm, each of the wires having a diameter of 80 μm.

[0063] The portions B shown in FIG. 1 correspond to transitional zones between the portion A and the portions C.

[0064] The screen 1 also comprises, in the central portion A, and fastened to the main mask 2 by virtue of the photocrosslinkable emulsion, a secondary mask 3, here of ellipsoidal shape. The double-mask zone located in this position is intended to print a thicker soldering zone. The cloth of the secondary mask 3 for example comprises 55 wires per cm, each of the wires having a diameter of 64 μm. The apertures of the secondary mask make an angle for example of 22° with the apertures of the main mask. To achieve this, the secondary mask was cut from a rectangular source mask using an ellipsoidal cutting die, the major axis of the ellipse making an angle of 22° with the long side of the source mask.

[0065] FIG. 2 shows a glazing 4 according to the present invention. In this figure, the screen-printing screen 1 and its various constituent portions have been represented by dashed lines in order to clearly show the correspondence between, on the one hand, the elements of the glazing and, on the other hand, the elements of the screen-printing screen that allowed the glazing to be obtained.

[0066] The glazing 4 comprises, just like the screen 1, a central portion A and two lateral portions C corresponding to the central and lateral portions of the screen 1, respectively. Electrically conductive patterns 5, 6, 7 and 8 have been printed in these portions A and C, and more precisely a network of horizontal and vertical heating wires 5, which are connected to bus bars 6 in the lateral portions C, an antenna 8 and a soldering zone for an antenna button 7.

[0067] These wires and bus bars were printed using the process of the invention, by screen printing a silver-containing paste on the glass sheet, the thickness after baking being in the example 3 μm for the wires 5 and antenna 8 in the central portion A and 10 μm for the bus bars 6 in the lateral portion C. In the central portion A, in the double-mask zone 3, the soldering zone 7, which is electrically connected to the antenna 8, was also printed in the same screen-printing pass. This soldering zone 7 is an electrically conductive pattern that is thicker than the wires 5 or the antenna 8, its thickness being comprised between 8 and 15 μm, and typically being about 10 μm.

[0068] In a first comparative example the same screen-printing step was carried out using a screen not comprising a double-mask zone. In a second comparative example, the screen printing was carried out using a screen comprising a double-mask zone, the angle α between the two masks however being 0°. In both cases, the soldering zone 7 was observed not to have the desired thickness after baking, the obtained thickness being only about 3 μm.