EP3785489A1

EP3785489A1 - Method for printing a structured silver coating having improved current-carrying capacity

Info

Publication number: EP3785489A1
Application number: EP19714224.3A
Authority: EP
Inventors: Klaus WEISSBORN
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2018-04-25
Filing date: 2019-04-04
Publication date: 2021-03-03
Anticipated expiration: 2039-04-04
Also published as: EP3785489B1; MA52345A; WO2019206592A1; US20210053376A1; CN110637503B; CN110637503A

Abstract

The invention relates to a method for producing a silver coating on a glass panel (16), wherein the silver coating comprises at least one bus bar (1) and/or at least one solder contact surface, wherein the method comprises the steps of printing the silver coating onto the glass panel (16) by means of screenprinting with a printing pattern having printing and non-printing regions, and baking the printed silver coating, wherein the (printing region 12) of the printing pattern for the bus bar and/or the printing region of the printing pattern for the solder contact surface is at least partly provided with a dot matrix (14) or a line matrix (20). By means of the method according to the invention, higher printing thicknesses of the bus bars and/or solder contact surfaces can be achieved as compared with conventional methods without the use of a dot matrix.

Description

Process for printing a structured silver coating with improved

ampacity

The invention relates to a method for producing a silver coating on a glass screen by screen printing and the glass sheet produced by the method, which is preferably a heatable vehicle window.

To produce heatable vehicle windows, glass panes are provided with busbars and heating conductors. The busbars have solder contact surfaces for the power connection. If required, solder contact surfaces for the connection of antennas or alarm loops can be applied to glass panes. Bus bars, heating elements and solder contact surfaces are applied to the glass pane in the form of electrically conductive layers, usually silver layers. A common method for applying the silver coating to the glass sheet is screen printing with a silver paste as printing ink.

The thickness or height of the print can be determined in screen printing by the type of fabric or the thread thickness of the fabric and the layer thickness of the coating of the screen. With larger structures such as a busbar, this only applies to the edge of the busbar with respect to the coating of the screen, but the effect is not effective in the middle area of the busbar.

This problem in screen printing of larger structures such as busbars results from the formation of so-called pressure shoulders on the template edge, which usually have a maximum width of 1 mm (see Fig. 1). Therefore, there is a relatively large amount of material of the printing paste in the edge regions of the busbar to be formed, while in the middle of the busbar only small amounts of material are printed. As a result, only relatively small heights or thicknesses are achieved for the busbar.

For many applications, however, it is desirable to print busbars having a greater thickness than is possible with the simple screen printing. A higher thickness causes a reduction of the electrical resistance, whereby the current carrying capacity of the bus bars is increased and the temperature development is reduced when passing current. A bigger one Height or thickness of the busbar may also be advantageous to reduce the width of the busbar with constant current carrying capacity (current carrying capacity).

An increased thickness of the printed structure may also be advantageous in solder contact surfaces, since this increases the strength and robustness against aging of the solder joint with connection elements soldered thereto, in particular if lead-free connection elements are used.

To increase the print thickness of the silver coating, a double silver print with intermediate drying step is conceivable. However, this complicates the process and increases the processing time. Further, an increased print thickness is usually not required in all areas of the silver coating or is not possible at all because of process tolerances, resulting in unnecessary material consumption or requiring different templates for the two printing operations.

According to the state of the art, if the print thickness is insufficient, additional solder pads or flat wires are applied to better distribute the current. This, however, incurs additional costs.

The print thickness can also be adjusted by increasing the silver content in the silver paste. The maximum possible content of silver in the printing paste is limited.

Furthermore, there are special, known to the expert as Vario-silk, threads for the printing screens in use, which use different thread diameters for a vertically limited area. This also allows different pressure to be generated for vertically delimited areas. Here, however, it is limited both in terms of the different pressure, as well as the positioning of the areas with increased thickness.

DE 41 1 1625 C2 describes a soldering area for busbars of heatable car windows, which is applied with a conductive silver paste by means of screen printing and is designed as a family of positive and negative lines in the longitudinal direction of the busbar.

EP 046531 A1 relates to a heatable glass pane with electrical heating conductors, which has white busbars applied by screen printing, along two arranged parallel edges and partially covered with a colored layer. For this purpose, the busbar can be coated with a series of black stripes that leave white areas free. The blackening process is carried out by applying a new black enamel layer.

No. 5,264,263 A describes a heatable glass pane with electrical heating conductors which has light-colored busbars applied by screen printing. The light colored busbars are partly with a dark enamel coating. e.g. in the form of a series of black stripes, covered. By modifying the pattern of the enamel coating, it is possible to control the heating of the glass sheet.

EP17480341 A1 describes a glass plate with printed conductive elements, wherein the glass plate along the periphery is provided with a dark ceramic print on which busbars are applied by screen printing. The busbars have recesses in which the ceramic pressure is exposed. In the recesses, a plurality of small dots of the material of the busbar can be printed together with the busbar.

The object of the invention is to provide a method for forming busbars and / or solder pads on a glass sheet by means of a silver coating which allows for an increased print thickness of the busbars and / or solder pads compared to the print thicknesses obtainable with screen printing methods of the prior art. It is intended to achieve a more uniform distribution of the printed printing paste over the width of the busbar or the soldering surfaces for the soldering contact, in particular a more uniform distribution of the printing paste should be made possible.

The method should be easy to carry out and in particular require no additional work steps. In addition, it should be possible to apply an increased thickness only in certain selected areas of the busbar, for example in the area of the soldering surfaces.

The object according to the invention could be achieved by using a dot matrix or line grid in the printing areas of the print original for the busbar and / or the soldering surfaces.

The object is therefore achieved according to the invention by a method according to claim 1 and a glass pane obtainable by the method according to claim 15. Preferred embodiments of the invention are evident from the dependent claims.

The method according to the invention enables a higher printing thickness by modifying the master in order to overcome the technical problems described above. In the printing area in which the print original is executed at least partially with the dot matrix or line screen and the screen is optionally coated higher in the area, the print area is printed with a higher color volume per area than in a print area without a partially coated dot pattern or line grid.

By using the dot matrix or line screen in the printing area according to the invention, e.g. a wet pressure thickness which is 5 to 100 mhh thicker than the wet film thickness, which is obtained by the same method, but without the use of the dot grid or line grid. Accordingly, a higher layer thickness is obtained even after baking. With the naked eye, the wet layer is further distributed evenly over the entire width of the busbar or the solder pad. Only when magnified with a magnifying glass or microscope are several small surveys in the printed image detectable.

The greater thickness causes a reduction in resistance, thereby increasing the current carrying capacity of the bus bars and reducing the temperature evolution when current is passed, particularly at critical points such as the solder pads, e.g. the solder pads of the busbar. The higher thickness can also be used to reduce the width of the busbar while maintaining the current carrying capacity. In the case of the solder contact surfaces, the greater thickness leads to an increased strength of the solder connection with connecting elements soldered thereto, in particular if lead-free connection elements are used.

Accordingly, the invention relates to a method of producing a silver coating on a glass sheet, the silver coating comprising at least one bus bar and / or at least one solder pad, the method comprising the steps of printing the silver coating on the glass sheet by screen printing with a master and non-printing areas and the baking of the printed silver coating, wherein the printing area of the printing template for the busbar and / or the printing area of the Print template for the solder contact surface is at least partially provided with a dot matrix or line grid.

For a person skilled in the art it was surprising and unexpected that a higher thickness of the printing area can be achieved with such a structuring of the printing area. Since pressure-free areas are also created when structuring the printing area, the skilled person would expect a lower material application and a reduced current carrying capacity. The inventors have been able to show that with the printing method according to the invention, by targeted structuring of the printing area, a greater printing height and an improvement of the current carrying capacity can be achieved.

In the following, the invention will be explained in detail.

Hereinafter, the terms "left / right" and "up / down" refer to the installation position of the glass sheet in a vehicle. The direction from "top" to "bottom" is then the longitudinal direction and the direction from "left" to "right" is the transverse direction. As "top" while the adjacent in the installed position in a motor vehicle, the roof edge of the body pane edge is called. "Down", however, describes the windscreen at a motor edge and a rear window for tailgate opening facing disc edge. "Left" and "right" in a windshield, the A-pillar of the body adjacent disc edges, while the "left" and "right" The edge of the window of a rear window is adjacent to the C pillar or D pillar of the vehicle body.

The terms "solder contact surface" and "solder surface" are used synonymously below. At the solder contact surface, a solder contact can be soldered to the glass, wherein the solder contact is a connection element.

The silver coating on the glass pane comprises at least one bus bar and / or at least one solder contact surface. The silver coating preferably comprises at least one busbar and optionally at least one solder contact surface for an alarm loop and / or at least one solder contact surface for an antenna. The silver coating particularly preferably comprises at least one bus bar and a plurality of heating conductors and optionally at least one solder contact surface for an alarm loop and / or at least one solder contact surface for an antenna. Busbars are understood to mean electrically conductive strips which are positioned on the glass pane. The busbar is also referred to as a busbar. Usually, two longitudinal busbars are applied in the region of the right and / or left side edge of the glass pane, which can also extend into the areas of the lower and upper side edges. Also possible are two transversely extending busbars in the region of the lower and / or upper side edge of the glass pane. The silver coating therefore preferably comprises two busbars. There are also embodiments in which not a busbar is applied in the region of the side edge of the glass pane, but two or more separate busbars. In this case there are more than two busbars.

If the silver coating comprises at least one busbar, typically at least two busbars, the silver coating usually also forms a plurality of heating conductors positioned between the busbars, usually across it.

Solder contact surfaces for the busbar are usually also formed on the busbars with the coating. At these solder pads, connection elements can be attached or soldered, can be mounted via the supply lines for the power connection. The current is highest in the area of the solder contact surfaces of the busbar, but with a good design, the thermal power is provided by the heating surface to be cleared (heating conductor) and the busbar and the soldering contact remain as cold as possible.

Alternatively or additionally, at least one solder contact surface, which is not provided for the busbar, may be formed by the coating. The solder contact surface may e.g. a solder pad for an alarm loop or a solder pad for an antenna. At these solder pads solder contacts or connection elements can be attached or soldered, can be mounted on the elements of the antenna or the alarm loop.

An alarm loop typically includes an electrically conductive pressure or wire. The alarm loop receives a continuous quiescent current in the activated state, which is interrupted when the disc breaks and triggers an alarm. Such alarm loops are described, for example, in WO 2013/156184 A1. The busbar may have a constant width over the length. Usually, however, the busbar has an irregular geometry, the width being different at different locations. In a preferred embodiment, the bus bar has a maximum width in the range of 9 to 30 mm, preferably 9 to 16 mm.

The solder pads can e.g. have a rectangular, oval or circular geometry. The solder pads can e.g. have a largest dimension in the range of 4 to 24 mm. The largest dimension in the circle is the diameter and in a rectangle the diagonal.

The method according to the invention comprises the step of printing the silver coating on the glass pane by screen printing with a printing original having printing and non-printing areas. The screen printing is carried out in particular with a silver paste or conductive silver paste as printing ink.

The artwork is a screen stretched in a frame and has non-printing areas in which the screen is provided with a coating, also referred to as a stencil, and printing areas in which the screen is clear without coating. Through the stencil, the screen is impermeable to ink at all non-printing areas, permeable to color at the printing areas. The frame is usually a metal frame, common are e.g. Steel frame or aluminum frame, aluminum frames are preferred.

The screen is usually a fabric of plastic threads or metal threads. The threads are e.g. of polyamide, polyester, carbon fiber or stainless steel, in particular fabrics of polyester threads are preferred. The thread diameter of the fabric, in particular the polyester fabric, may e.g. suitably in the range of 30 to 150 microns, preferably 77 to 120 microns, and the screen denier of the fabric may e.g. in the range of 43 to 180 threads per cm, preferably 77 to 150 threads per cm.

At the non-print areas of the artwork is the stencil, which is a barrier or coating that is on or in the screen and makes the artwork color impermeable at the locations that are not intended to print. Common for the production of the template are the direct method (direct template) and the indirect method (indirect template), whereby the direct method is preferred. In the case of the direct template, the tissue is treated with a photosensitive layer coated, exposed and developed. The template is made directly on the fabric. In the first method, the template is first created on a carrier and then transferred to the screen. The other steps to make the template are analog.

In general, the stencil is formed by a photomechanical process. For this purpose, the screen or a support is coated with a photosensitive composition, also referred to as emulsion, or a photosensitive film is applied to the screen or the support. Subsequently, the desired pattern of opaque areas and translucent areas, for. B. by means of a slide projection or a master copy or in the CTS process ("Computer to acreen"), imaged on the resulting photosensitive layer and exposed the layer with UV light. In the translucent areas, the layer is cured by the UV light and forms the stencil or non-printing area. In the opaque areas, the layer is not cured and may subsequently be washed out, thereby forming the print areas of uncoated fabric. In the indirect method, the stencil formed is then transferred to the screen.

The print template created so far corresponds to the print template normally used. According to the invention, however, it is essential to the invention that in addition the printing region of the printing original for the busbar and / or the printing region of the printing original for the soldering contact surface is at least partially provided with a dot matrix or a line screen. The dot grid or dot pattern represents an array of multiple rows of juxtaposed dots. The line grid or line pattern represents an array of multiple parallel lines (parallel lines of lines). The embodiment with a dot matrix is preferred because the construction of a dot matrix in the embodiment is simpler and as a result the lower susceptibility to errors in the printing process has been found.

The points of the dot matrix or the lines of the line grid are formed like the template from a barrier layer on or in the screen by a photomechanical process. It is understood that the points of the dot grid and the lines of the line grid are expediently formed together with the template, as described above. For this purpose, for the image of the desired pattern on the photosensitive coating, for. B. by means of slide projection, CTS-method or master copy, to additionally include the corresponding pattern for the dot matrix or the line grid.

In the embodiment with the dot matrix, the points may have any geometry. It can be e.g. to rectangular, square, elliptical or circular points, with circular points are preferred.

It should be noted that the areas of the printed pattern designated as "dots" are those areas which are initially coating-free in the printing process and in which no silver print is applied, while the area surrounding these dots is provided with silver printing according to the invention. This printed area of the solder contact area is connected in an electrically conductive manner to the remaining area of the associated busbar. Typically this is done by continuous silver printing between these areas by printing with a common stencil. If the structured printing area is designed in the form of lines instead of a dot pattern, this results in coating-free lines that are arranged alternately with the printed lines. The lines applied by means of silver print run essentially parallel to one another and parallel to the coating-free lines located therebetween. Preferably, the structured printing area is dimensioned such that the structuring (dots or lines) is too small for an exact printing result. The ink thus runs into the initially coating-free areas. According to the usual printing process known in the art, such bleeding of the ink would be undesirable and a rejection criterion for the resulting product. Accordingly, it was surprising and unexpected to those skilled in the art that a substantial improvement in the printing result and in the printing height can be achieved by intentionally causing it.

The dimensions of the points of the dot matrix are below the resolution, preferably just below the resolution, the print template, ie the limit printable Punktfeinheiten, which is particularly dependent on the thread diameter and thread pitch of the screen fabric. When printing, therefore, the ink below the dots runs into each other and the dot matrix is not visible in the printed coating. The area under the dot pattern will appear to the human eye as fully printed. First with a microscope or in cross-section smaller mountain and valley areas can be determined (see Fig. 2).

The points of the dot matrix preferably have a diameter in the range of 0.10 mm to 0.3 mm, more preferably 0.16 to 0.2 mm. This applies to circular points. Unless they are non-circular points, these ranges apply to the largest dimension of the points. The points of the dot matrix may be the same or different sizes, but are preferably of the same size.

The distance between the points of the dot matrix from each other, ie. the distance of the centers of adjacent points is preferably in the range of 1 D to 3 D, preferably 1, 75 D to 2.25 D, particularly preferably 1, 9 D to 2, 1 D, where D is the dot diameter or the largest dimension of Point is. This means e.g. at a dot diameter of 0.2 mm a distance of 0.3 to 0.5 mm, preferably 0.35 to 0.45 mm and particularly preferably 0.38 to 0.42 mm.

In the alternative embodiment with the line grid, the line grid is formed by mutually parallel lines or straight lines. The dimensions of the lines of the line grid are below the resolution, preferably just below the resolution, the print template, ie the limit of printable Linienfeinheiten, which is particularly dependent on the thread diameter and thread pitch of the screen fabric. When printing, therefore, the ink below the lines runs into each other and the line grid is not visible in the printed coating. The area under the line pattern will appear to the human eye as fully printed. Only with a microscope or in cross-section smaller mountain and valley areas can be determined.

The lines of the line grid preferably have a line width in the range of 0.1 mm to 0.4 mm. The lines of the line grid may have the same or different widths, but are preferably of equal width. The distance from adjacent lines of the line grid is z. B. in the range of 0, 1 mm to 0.4 mm. The distance refers to the distance of the central axis in the longitudinal direction of a line to the central axis of the adjacent line. The spacing of the lines of the line grid from one another is preferably in the range from 0.7 B to 2.5 B, preferably 0.8 B to 2.2 B, more preferably 0.8 B to 1.2 B, where B is the line width of the line is. Here, the layer thickness of the template and the layer thickness of the points of the dot pattern and the layer thickness of the lines of the line screen are understood to be the total thickness of the coating in the area of the template or in the area of the points grid or in the area of the lines of the line grid.

The layer thickness of the points of the dot matrix and the lines of the line grid can be z. B. in the range of 10 to 100 mhi, preferably in the range of 1 0 to 80 mhi and more preferably in the range of 1 0 to 30 mhi lie.

The layer thickness of the template and the layer thickness of the points of the dot grid or the lines of the line grid can be the same or different. In a preferred embodiment, the layer thickness of the points of the dot grid or of the lines of the line grid is higher than the layer thickness of the template. An increased layer thickness of the points of the dot matrix or of the lines of the line grid can also be used to increase the layer thickness of the busbar at the points of the dot matrix or line screen. This can be achieved by partial post-coating of the areas in which the dot matrix or line screen has been applied. That after the coating of the non-printing areas and the areas of the dots of the dot matrix or the areas of the lines of the line grid, the coating process is repeated, but only in the area of the dot matrix or line screen.

In a preferred embodiment, a partial subsequent coating in the region of the dot matrix or line screen is thus carried out in the production of the printing original after coating the screen in the non-printing areas and in the region of the dot matrix or line screen, in order to increase the layer thickness of the dots or lines in comparison to the layer thickness to get the template. The layer thickness of the points or lines can z. B. in the range of 1, 5 times to 2.5 times the layer thickness of the template.

The print area of the print template for the busbar can, if it is to be provided with a dot matrix or a ruler, partially or completely be provided with the dot grid or line grid, the print area is preferably partially provided with the dot grid or line grid. For example, 1 to 100%, preferably 5 to 1 00%, particularly preferably 1 5 to 75%, of the print area area of the print original for the busbar may be provided with the dot matrix or line screen. If the busbar has wider and narrower sections, it is generally sufficient if the busbar is printed thicker in the broader sections, in particular in the sections of maximum width, so that only the designated print areas of the print template are provided with the dot screen or line screen can be.

In a preferred embodiment, the printing area of the printing template for the busbar is partially provided with the dot matrix or the line screen and the printing area provided with the dot matrix or line screen is arranged at the locations of the soldering contact area or surfaces of the busbar. As explained above, the highest current results at these points, so that a thicker busbar at these points can effectively contribute to a better current distribution.

Provided that it is to be provided with a dot grid or line grid, the print area area of the print master for the solder contact area can be partially or completely provided with the dot grid or line grid, wherein the print area area is preferably partially provided with the dot grid or line grid. It can e.g. 1 to 100%, preferably 5 to 100%, preferably 15 to 75%, of the print area area of the print original for the busbar be provided with the dot matrix or the line grid.

By using the dot matrix grid or the line grid for the print areas of the solder pad print template, a more robust solder pad can be obtained. This has the advantage that the functions of the solder contact surface, such as the stability of the adhesion to a connection element, can be achieved even with a smaller layer thickness. At the same time a higher thickness of the silver is achieved in comparison to the otherwise same screen printing, but without dot matrix or line grid, whereby the strength of the solder joint is improved with it soldered connection elements, especially for lead-free connection elements.

Providing the print area area of the print template for the solder contact area with the dot matrix or line grid is particularly suitable for solder contact areas for an antenna, solder contact areas for an alarm loop and for solder contact areas of busbars located in the area of the lower or upper side edge of the glass pane. Providing the print area area of the print template for the solder contact area with the dot matrix or line grid is particularly suitable for Solder pads that are not positioned in the area of the right or left side edge of the glass.

For screen printing, the created print template is used with at least one dot screen or a line screen in a partial area of the print area as described above. Otherwise, the screen printing is done as known in the art.

The artwork is positioned on the glass. The ink is applied to the top of the artwork and evenly distributed. The ink is then doctored through the meshes of the screen in the printing areas onto the glass with a squeegee. In general, the glass sheet has contact with the wire only in the immediate print zone by doctoring. By a higher distance, the so-called jump, the glass pane separates more easily from the screen after the printing phase.

The printing ink used is a silver paste or conductive silver paste. Usual commercial products can be used. Silver pastes or conductive silver pastes usually contain high levels of silver or silver alloy, e.g. B. 30 to 88 wt .-%, as a powder or flakes, organic binders, organic solvents and optionally further additives.

At the points where the corresponding print area of the artwork has a dot screen or a line screen, a thicker and more uniform layer thickness of the bus bar is achieved compared to screen printing which does not use a dot screen or line screen but is otherwise the same.

The height of the printed busbar prior to burn-in is at the locations printed with the dot-matrix or line-screen printed area of the master, e.g. 25 to 1 00 mhh, preferably 30 to 80 mpΊ. The height refers to the thickness before firing, ie. on the wet layer thickness.

Depending on the silver paste or conductive silver paste used, the screen printing may be followed by a drying process which, if appropriate, may also take place at an elevated temperature.

The method of the invention further comprises the step of baking the printed silver coating. Stoving temperature and duration depend on the type of silver paste used. The baking can z. B. at a Temperature in the range of 400 to 700 ° C take place. The duration of the heat treatment can, for. B. 5 s to 200 s.

The glass sheet can, as usual, be of inorganic glass, in particular silicate glass. Examples are soda lime glass, borosilicate glass, aluminosilicate glass or quartz glass. The glass sheet is preferably a single-pane safety glass or a laminated glass.

The glass pane may have a coating in one or more edge regions, preferably all edge regions, preferably a coating with a ceramic color, such as a black ceramic color. Those skilled in the art are familiar with such opaque coatings in the edge region of vehicle glazings under the term black printing. A coating of the side edges with ceramic paint is used for. As to mask adhesions that are used when mounting a glass to a vehicle. The busbars of the silver coating are preferably printed on this coating, in particular on the ceramic paint coating.

The glass pane provided with the silver coating is preferably a heatable glass pane, particularly preferably a heatable vehicle window, in particular a rear window.

The invention also relates to a glass panel with a silver coating comprising at least one bus bar and / or at least one solder contact surface, which is obtainable according to the inventive method described above. The product features disclosed in the description of the method are fully applicable to the glass sheet according to the invention and should not be repeated at this point. Conversely, the features disclosed in the description of the product also apply to the inventive method.

The glass pane according to the invention comprises at least one bus bar and / or the solder contact surface with printed silver coating, which is at least partially provided with a dot matrix or a line grid, wherein the layer thickness of the printed silver coating in the region of the dots of the dot grid or the lines of the line grid is less than the layer thickness in the pressure area of the dot matrix or line grid surrounding the dots or lines. The size dimensions of the points of the dot matrix and the lines of the line grid are below the resolution of the human Eye, but are detected by microscopic examination in a simple manner on the product. The structuring of the silver print of the glass sheet according to the invention is achieved by the use of the method according to the invention. A particular advantage of the glass pane according to the invention is, as described for the method according to the invention, the greater current carrying capacity in the region of the dot matrix.

In a preferred embodiment of the glass pane according to the invention, the layer thickness of the printed silver coating in the area of the dot grid or lines of the line grid is in the range of 10 to 30 mhh and the layer thickness of the printed silver coating in the area of the dot grid or line grid surrounding the dots or lines in the range of 30 to 80 mpΊ. The layer thickness in the region of the dots or lines is chosen to be smaller than the layer thickness in the pressure region surrounding the dots or lines. This ratio has proven to be particularly advantageous in terms of optimizing the current carrying capacity while minimizing the use of materials. The layer thicknesses mentioned relate to the wet layer thickness.

The invention will be explained in more detail below by means of non-limiting embodiments with reference to the accompanying drawings.

I show this:

1 shows schematically a cross section of a busbar 1 in front of the

Baking, which has been printed in the prior art on a surface 4 of a glass sheet (not shown). In this screen printing according to the prior art, no dot matrix and no line grid in the printing area of the artwork is available. It shows clear pressure shoulders 3 at the edges, while in the middle only a little material is applied. Overall, a very uneven distribution of the printing material across the width of the busbar 2.

2 shows schematically a cross section of a busbar 1 in front of the

Baking, which was printed by the method according to the invention with a dot matrix on a surface 4 of a glass sheet (not shown). In this bus bar printed in accordance with the invention, there are no distinct print shoulders which is distribution of the print material across the width of the bus bar 2 Even in the middle of the busbar below the areas of the points of the grid points 7. The division into hatched and white areas of the busbar is intended only to clarify the areas that when printing under a dot (hatched) or not under a point (white ). Both in the hatched and in the white areas is the printed material. When viewed under the microscope, several small protrusions 3 are observed, which occur at the locations corresponding to the pressure ranges between the individual halftone dots.

Fig. 3: schematically a plan view of a section of the printing original with

Screen dots 6 for the printing area of the busbar according to FIG. 2 with the uncoated screen surfaces 8 and the dots 6 (coated screen). Since the dot size is below the triggering capability of the artwork, the silver paste passes into each other when printed below the dots. The gaps 15 between the points lead to the small pressure shoulders 3 shown in FIG.

Fig. 4 schematically shows a plan view of a larger section of the

Printing area of the printing original 5 with halftone dots according to FIG. 3. The screen of the printing original can e.g. a polyester screen. The black areas 8 represent the open meshes of the screen and the white areas represent the coated areas of the dot matrix and the dots 6, respectively. The layer thickness of the dots may e.g. in the range of 10 to 80 mhh. The diameter of the dots is 0.2 mm. The distance 9 between adjacent points is 0.4 mm, both between the adjacent points within a row, and between the adjacent points of different rows.

Fig. 5 schematically shows a plan view of an even larger section of the

This section shows a part of the template 11 (non-printing area, screen coated over the entire area) as well as a part of the printing area for a busbar 12 and heating conductors 13 departing therefrom. The pressure region of the busbar has a dot matrix in a subregion 14. In particular, the dot matrix shown in area 14 is not shown to scale for practical reasons. If scaled down, the points would be much smaller.

Fig. 6 shows schematically a glass pane 16 according to the invention

Single pane safety glass or laminated safety glass with one

Silver coating comprising bus bars 1 and heating conductor 17. The glass sheet is provided on the side edges with a coating of black ceramic paint 18, on which the bus bars 1 were printed. The silver coating was printed by screen printing with a silver paste on the glass sheet with a printing original as shown in FIGS. 3 to 5. The regions 19 of the busbars 1 correspond to the dot-matrix-provided pressure-area surfaces 14 of the printing original in accordance with FIG. 5. The regions 19 can serve as the solder-contact surface of the busbar, in order there

Solder connection elements. A cross section of the busbar 1 in the region 19 is shown in FIG. The printed silver coating is then baked by heat treatment.

7 schematically shows a plan view of a section of a printing area of a printing original 5, in which the printing area according to the alternative embodiment is provided in part with a line grid 20. The black areas 8 represent the open meshes of the screen and the white areas represent the coated areas of the line grid 20 and the lines 21, respectively. The layer thickness of the lines may be in the range of 10 to 80 mhh, for example. The line width can be in the range of 0.1 mm to 0.4 mm. The distance between adjacent lines may be, for example, 0.1 mm to 0.4 mm. The detail shown of a print area of a print copy corresponds approximately to the detail of a print copy for a busbar shown in FIG. 4, except that instead of a dot raster there is a line raster. LIST OF REFERENCE NUMBERS

1 busbar (silver print)

2 width of the busbar

3 pressure shoulder

4 glass surface of the glass pane

5 artwork

6 grid point (coated screen)

7 area below grid point

8 uncoated screen surface

9 vertical point distance

1 0 horizontal point distance

1 1 coated screen mesh (template)

12 uncoated screen mesh for busbar

1 3 uncoated screen mesh for heating conductors

14 Pressure area of the screen with dot matrix

1 5 Pressure range between grid point

1 6 glass pane

1 7 heating conductor

1 8 Coating with ceramic paint

1 9 area of busbar printed with dot matrix

20 Pressure area of the screen with line grid

21 grid line (coated screen)

Claims

claims

1 . A method of forming a silver coating on a glass sheet (1 6), the silver coating comprising at least one bus bar (1) and / or at least one solder bump, the method comprising the steps of printing the silver coating on the glass sheet by screen printing with a print and non-print areas comprising printing template and the baking of the printed silver coating, characterized in that the printing region (12) of the printing template for the busbar and / or the printing region of the artwork for the Lötkontaktfläche is at least partially provided with a dot matrix (14) or a line grid (20) ,

2. The method of claim 1, wherein the silver coating comprises at least one busbar (1) and a plurality of heating conductors (17) and optionally at least one Lötkontaktfläche for an alarm loop and / or an antenna.

3. The method of claim 1 or 2, wherein the bus bar (1) has a maximum width in the range of 9 to 30 mm.

4. The method according to any one of claims 1 to 3, wherein the height of the printed busbar (1) and / or the printed solder pad before burning at the locations that are printed with the dot matrix or the line screen printing range of the artwork in the range from 25 to 1 00 mhh, preferably from 30 to 80 mhh.

5. The method according to any one of claims 1 to 4, wherein the points (6) of the dot matrix (14) have a diameter in the range of 0, 14 mm to 0.22 mm, preferably 0, 16 to 0.2 mm, and / / or wherein the lines (21) of the line grid (20) have a width in the range of 0, 1 mm to 0.4 mm.

6. The method according to any one of claims 1 to 5, wherein the distance of adjacent points (6) of the dot matrix (14) in the range of 1, 5 D to 2.5 D, preferably 1, 75 D to 2.25 D, particularly preferred 1, 9 D to 2, 1 D, where D is the dot diameter.

7. The method according to any one of claims 1 to 6, wherein the layer thickness of the points (6) of the dot matrix (14) or the lines (21) of the line grid (20) in the range of 1 0 to 80 mhh, preferably in the range of 1 0th to 30 mhh, lies.

8. The method according to any one of claims 1 to 7, wherein 1 to 100%, preferably 5 to 1 00%, more preferably 15 to 75%, the pressure area surface of the artwork for the bus bar with the dot matrix (14) or the line grid (20) provided is and / or 1 to 1 00%, preferably 5 to 1 00%, more preferably 15 to 75%, the pressure range surface of the artwork for the Lötkontaktfläche with the dot matrix (14) or the line grid (20) is provided.

9. The method according to any one of claims 1 to 8, wherein the printing area of the printing template for the busbar is partially provided with the dot matrix (14) or the line grid (20) and the print area provided with the dot matrix (14) or the line grid (20) in the vicinity of solder contact surfaces of the busbar (1) is arranged.

A method according to any one of claims 1 to 9, wherein the glass sheet (16) is a toughened safety glass or a laminated glass sheet.

1 1. Method according to any one of claims 1 to 10, wherein the glass sheet (16) has a coating in one or more edge regions, preferably a coating with a ceramic paint (18), and the busbar (1) is printed on the coating.

12. The method according to any of claims 1 to 1 1, wherein the glass pane (16) provided with the silver coating is a heatable glass pane, preferably a heatable vehicle pane.

A method according to any one of claims 1 to 12, wherein in the manufacture of the artwork after coating the screen in the

In the area of the dot matrix or of the line grid, a partial subsequent coating in the area of the dot matrix or the line screen is carried out in order to obtain an increased layer thickness of the dots or lines.

14. The method according to any one of claims 1 to 1 3, wherein the dimensions of the dots of the dot matrix below the resolution of the Print template lie or the dimensions of the lines of the line grid are below the resolution of the artwork.

A glass panel having a silver coating comprising at least one bus bar (1) and / or at least one solder pad, obtainable by a method according to any one of claims 1 to 14, wherein the bus bar

(1) and / or the solder contact surface comprises a printed silver coating which is at least partially provided with a dot matrix (14) or a line grid (20) and the layer thickness of the printed silver coating in the region of the points (6) of the dot matrix (14) or the Lines (21) of the line grid (20) is less than the layer thickness of the printed silver coating in the region of the dot matrix (14) or line grid (20) surrounding the points (6) or lines (21).