GB2429431A - Printing on glazing - Google Patents

Abstract

A method of printing a surface of a glazing, for example, an automobile backlight, comprising depositing a first ink to form a first pattern, depositing a second ink to form a second pattern, the second pattern being aligned with the first is disclosed. The print device used to deposit the ink does not contact the surface of the glazing. A separate drying stage before the second pattern can be printed is not necessary, removing the need to re-position or re-align the glazing between prints.

Description

1 2429431

GLAZING

The present invention relates to a method of printing onto a glazing, in particular, printing onto an automotive glazing.

The glazing used in automotive vehicles (termed "automotive glazing") may be printed for a variety of reasons. For example, a windscreen or backlight may be provided with an obscuration band, which appears as a black or dark-coloured band around the edge of the glass. The obscuration band covers the adhesive on the glazing, and is both aesthetic and functional. Not only is the adhesive hidden from view, but damage by UV light is also prevented.

In addition to the obscuration band, a backlight may be printed with a pattern of lines forming a heater circuit. The printed lines in the heater circuit have a conductivity chosen to produce sufficient heat when current is applied to the heater circuit in order to defrost or demist the backlight in adverse weather conditions. Antennas may also be printed on a backlight in the form of fine lines, and connected into the electrical junctions in the vehicle. In the case of heater circuits, it is also necessary to provide busbars to which the printed wires of the heater circuit are electrically connected. The busbars may also be hidden from view by the obscuration band. Typically, the heater circuit and antennas are printed using a silver-containing ink, which on firing typically turns a shade of yellow or brown when viewed from the exterior of the vehicle.

The use of a silver containing ink for printing such heater circuits has both advantages and disadvantages. One advantage is that narrow lines, for example, 0.4 mm in width, that provide sufficient conductivity to enable the heater circuit or antenna to function can be printed. I lowever, even though the lines have a small width, one disadvantage is that due to the yellow or brown appearance of the heater circuit or antenna, the light coloured lines viewed from the outside of a vehicle when the glazing is fitted is less aesthetically appealing than dark or black lines.

One solution to reduce the visibility of the heater circuit is to make the lines appear to an outside viewer as being black in colour. However, in practice, this is difficult to achieve. One method of producing black lines is to use a heavily pigmented silver- containing ink to print the heater circuit or antenna. Once fired, the ink appears to be black in colour. The disadvantage of this approach is that the amount of black pigmentation needed reduces the conductivity of the lines to below the level required for either the heating or antenna function.

A second approach is to print a series of black concealment lines and to overprint a set of heater circuit or antenna lines using an electricallyconductive silver-containing ink. Both the black concealment and conductive silver lines are printed on the inside of the backlight, resulting in a black heater circuit or antenna that appears to be black in colour when viewed from the outside of a vehicle.

A screen printing method is used to print the obscuration bands, heater circuits and antenna lines onto the backlight. Printing takes place in a temperature controlled printing room. A screen having a negative pattern of the obscuration band, heater circuit and/or antenna is placed onto the backlight. The negative is transferred to the backlight as a positive by holding the screen against the glass and applying coats of a black, nonconductive ink, using a squeegee. Once the ink has been applied to the backlight, the backlight is removed from the printing station and placed in a drying cabinet. The printed pattern is then fired, revealing the positive of the pattern of the screen printed onto the backlight.

however, in order to overprint conductive silver heater circuit or antenna lines onto the initial pattern of concealment lines, a second screen with a new negative pattern must be used. To do this, the bacidight is returned to a printing station after drying of the first pattern and before firing. Difficulties arise in the need to line up the new screen with the glazing in an exact manner in order to ensure registration of the printed pattern and the negative pattern to be overprinted. Registration marks are used as a guide to aligning the second screen with the pattern on the glazing.

With screen printing processes, only a single layer of ink can be printed in each printing pass. It is not possible to screen print an overprinted pattern (so called "wet- on-wet" printing) until the ink of the first pattern is dry. If the ink of the first pattern is not dry when overprinting takes place, the inks may mix on the surface of the glazing and/or the pattern become smudged when the pressure of the squeegee on the screen during the second print causes the screen to contact the glass and hence the ink of the first print. In order to overprint therefore, the glazing must still be removed from the printing station and dried before any further printing can occur.

Even with the use of registration marks, tolerances in the accuracy with which the concealment lines and conductive lines can be matched still exist. In the case of heater circuits, it may also be necessary to use a further print run to print the busbars to which the conductive lines are connected, giving rise to additional registration problems.

In order to accommodate these tolerances therefore, the width of the concealment lines in the initial pattern must be approximately at least twice the width of the heater circuit and/or antenna to ensure adequate coverage and concealment. Typical line widths for heater circuits are approximately in the range 0.4 - 0.6mm. Such broad lines are obvious to the viewer. A similar problem occurs on other glazings (for example, windscreens and sidelights) where overprinted patterns or images require more than one printing pass to be made.

There is therefore a need to be able to produce narrow width lines in a heater circuit or antenna printed onto a glazing, which have reduced visibility to an outside viewer, and which have sufficient conductivity to perform the function for which they are intended.

Thc present invention aims to address these problems by providing a method of printing a surface of a glazing, comprising depositing a first ink to form a first pattern, depositing a second ink to form a second pattern, where the second pattern is aligned with the first pattern, wherein the print device used to deposit the ink does not contact the surface of the glazing.

This has the advantage that as there is no contact between the print device and the surface of the glazing, there is no separate drying stage necessary before the second pattern can be printed. There arc also no issues with re-positioning or re-aligning the glazing between prints, as with screen printing methods.

The second pattern may be in registration with the first pattern, the second pattern may overlap the first pattern or the second pattern may be adjacent to the first pattern.

Preferably, the first pattern conceals the second pattern when the glazing is viewed from the exterior of a vehicle.

The first pattern may comprise concealment lines. The second pattern may comprise at least one line forming a heater circuit or an antenna. The second pattern may be deposited using a conductive ink, which may be a silver-containing ink. The concealment lines may be deposited using a black ink. At least one of the silver- containing and black ink may be UV or heat curable.

Preferably, the concealment lines have a width of less than 0.6mm. The width of the concealment lines is preferably 50% greater than that of the lines forming the heater circuit or antenna, or less, more preferably 20% greater than that of the lines forming the heater circuit or antenna, or less, and even more preferably 10% greater than that of the lines forming the heater circuit or antenna, or less. The heater circuit lines in a central region of the glazing may bc different in width to the heater circuit lines in an edge region of the glazing.

The first and second patterns may comprise logos or text. Preferably, the glazing is supported on a print table during printing, and wherein there is no relative movement of the glazing to the print table after depositing the first ink to form the first pattern and before depositing the second ink to form the second pattern.

A first print device may be used to deposit the ink forming the first pattern, and a second print device may be used to deposit the ink forming the second pattern.

Alternatively, the print device may have at least two ink containers. If two ink containers are used, the print device may be used to deposit ink to form the first pattern and to deposit ink to form the second pattern.

The print device may be an ink jet print head. Preferably, the print device is digitally controlled.

An obscuration band may be printed onto the surface of the glazing. Busbars may be printed onto the obscuration band. The glazing is preferably a bacidight.

A glazing printed in accordance with the invention is also provided.

The invention will now be described by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a schematic representation of a backlight after a first printing pass; Figure 2 is a schematic representation of a backlight after a second printing pass; Figure 3 is a schematic representation of a backlight after a third printing pass; Figure 4 is a schematic representation of a backlight after a fourth printing pass; Figure 5 is a schematic representation of a printing station in accordance with a first embodiment of the invention; Figure 6 is a schematic representation of a printing station in accordance with a second embodiment of the invention; and Figure 7 is a schematic representation of a printing station in accordance with a third embodiment of the invention.

In non-contact printing methods, a screen or other printing device, such as a roller, does not contact the surface of the object to be printed. As there is no contact with the object surface that could lead to smudging or mixing of ink, there may be, depending on the characteristics of the inks, no need to provide an intermediate drying stage when printing and overprinting multiple patterns. Such printing is typically digitally controlled, for example, ink jet printing. Lnkjet printers use either a continuous jet process or an impulse or drop-on-demand process to create droplets of ink. In continuous systems, a charged stream of ink droplets is directed at a substrate by a pair of charged plates. In an impulse or drop-on-demand- system, individual droplets are forced out of a print head, using either vibrational (piezoelectnc) or thermal (bubble jet) propulsion methods.

Digital printing may be used to print ceramic-based inks onto glass. For example, W02005/O 18941 describes a digital inkjet printer suitable for printing various designs onto glass. The printer comprises a horizontal support board, for supporting glass boards to be printed, and a print head that may be moved above the surface of the glass to deposit ink on the surface of the glass board. The head is controlled by a computer or controller. The printer also includes heaters to heat the glass surface before and/or after printing in order to provide a primary fixing stage. Once printed, the glass board must be fired at 550 C in a furnace to fully fix the ink. The ink itself then becomes integral with the surface of the glass board. A solvent flush is used, in conjunction with a wiping assembly, to clean the print head before and after a change of ink, after use, or after prolonged down-time.

A ceramic ink, as described in W02005/019360, is used to print the surface of the glass board. The ink is either solvent-based or water- based, and contains both pigment (having a particle size of less than I.2. tm) and sub-micron sized glass flit.

Water-based inks additionally contain silica nanoparticles. IJV-curable inks may also be used.

In order to print onto the glass board, it is first loaded onto the support board, either by hand or using an automated or semi-automated system. Ink is deposited onto the surface of the glass board in accordance with the signals received from the computer or controller, using a standard print head. The print head is able to move above the surface of the glass in either X-axis or Y-axis directions to create an image. The ink is injected onto the surface via a plurality of orifices, and dried using the heaters, to ensure that there is no smudging or mixing. If an image is to be printed near the edge of a fmished glass board, test marks may be used to ensure that there is no deviation of the printed image.

Digitally controlled (for example, controlled by a digital computer or controller) non- contact printing techniques may be used to print automotive glazings. In particular, a print device, such as an inkjet print head, may be used to print heater circuits and antennas (which may comprise circuits or single lines) on to backlights. For example, digital printing of automotive glass with sinterable silver pastes is disclosed in WO 2005/051856. However, as described below, the embodiments of the present invention enable the use of non-contact printing techniques to produce improved, more aesthetically appealing heater circuit and antenna patterns on automotive glazings, than presently available.

A backlight is typically formed of toughened or tempered glass, or, if it is to be laminated, annealed glass. Initially, a backlight to be printed in accordance with the present invention is loaded into a printing station, where it is supported on a print table during the printing process, with the side that will eventually form the inside of the backlight, when fitted in the vehicle, facing the print head or heads. Once the backlight is correctly positioned, the first printing pass is started. The first printing pass is used to lay down the obscuration band around the outside of the backlight.

Figure 1 is a schematic representation of the backlight 1 after the first printing pass.

The obscuration band 2 is shown in black.

Figure 2 shows a schematic representation of the backlight 1 after a second printing pass. In this second pass, concealment lines 3a-i, stretching between opposite sides of the obscuration band 2, arc printed using a non-conductive ink. These concealment lines 3 are coloured black, and will eventually hide the conductive silver lines of the heater circuit from outside view. The concealment lines are typically in the range of 0.4 - 0.6mm in width. Typically, the concealment lines have a width of 50%, preferably 20%, and more preferably 10% greater than the heater circuit lines, or less.

In a preferred embodiment, the concealment lines and heater circuit lines are of the same width, and the lines located in registration. For example, the concealment line for a 0.4mm width heater circuit line may be up to 0.2mm, preferably up to 0.08mm or more preferably 0.04mm wider than the heater circuit line. For concealment lines with a greater width than the heater circuit lines, the concealment lines may be in registration with the heater circuit lines, with an equal overlap on either side of the heater circuit lines. For example, for a heater circuit line of 0.4mm in width, the concealment lines may extend up to 0.02mm in width either side of the heater circuit line.

It is not necessary for the heater circuit lines to have the same width at every position on the backlight. Backlights are typically trapezoidal in shape, and contain regions of heating lines in the central area of the backlight and at edge regions of the backlight.

The central region of a backlight is generally rectangular in shape, whereas, for a trapezoidal backlight, the edge regions are typically triangular in shape. The heater circuit lines in the edge regions may be inclined at an angle to those in the central area. In order to ensure that the current density in the edge regions is sufficient to heat the backlight, the lines of the heater circuit in this region may have a different width to those in the central region. In particular, the width of the heater lines in the edge regions may be greater than those in the central region. The width of the concealment lines in the edge regions may also therefore be different to the width of the concealment lines in the central region. If other glazings are to be printed, for example, side lights, the widths of the heater circuit lines printed on the glazing may differ in different regions of the glazing.

Figure 3 shows a schematic representation of the backlight 1 after a third printing pass. In this pass, busbars 4a 4b (shown in white for illustration purposes), for forming an electrical connection to the printed heater circuit are printed onto the obscuration band 2. The busbars 4a 4b will be hidden from outside view once the backlight 1 is fitted in a vehicle. The busbars 4a 4b arc printed using an electrically conductive ink.

Figure 4 shows a schematic representation of the backlight I after a fourth printing pass. In the fourth printing pass, the printed wires of the heater circuit 5a-i are overprinted onto the concealment lines 3a-i, using a conductive ink, preferably a silver-containing ink. The width of the heater circuit lines 5a-i may be the same as that of the concealment lines 3a-i or narrower than that of the concealment lines. The heater circuit lines may preferably have a width of 0.25mm or less. In the case of antenna lines, the width is preferably 0.1mm or less.

In the above example, four printing passes are used to illustrate the overprinting of each pattern. however, it may be desirable to combine all four printing passes into a single printing pass, or to combine certain printing passes that require the same ink, for cxample, the first and second printing passes described above (to print an obscuration band and black concealment lines) into a single printing pass. Preferably, only two printing passes (obscuration band and concealment lines, followed by heater circuit and busbars) are made. Separate print heads may be used for each printing pass. For example, a first print head may be used to print the concealment lines, and a second print head to print the heater circuit. Preferably, the print head is an ink jet print head.

Once the printing pass or passes arc completed, the finished backlight is removed from the printing station. There has been no relative movement between the backlight and the print table between any of the printing passes. As there has been no need to align or re-align the backlight and the printing station or print head during the printing process, the registration problems inherent in screen printing or other techniques arc minimised. There is also no need to use a silver-containing ink for the heater lines with a high black pigment loading as the colour of the ink after firing is immaterial, since it will be hidden from external view by the concealment lines. The conductivity of the heater circuit printed wires is therefore not compromised. The resulting concealment lines do not suffer from the registration problems of screen printing techniques.

Once printed, the backlight is fired and bent to shape. If a laminated glazing is used, the outer pane may be fired and bent with the inner pane in the configuration in which the panes will be laminated, or with the printed pane uppermost to allow organic ink components to be driven off during firing. In the case of laminated glazings, either pane may be printed. For example, the side of the outer pane adjacent the interlayer may be printed. Alternatively, either side of the inner pane may be printed: that adjacent the interlayer or that forming the inner surface of the window when fitted in a vehicle.

In the above example, the overprinting of patterns involves ensuring that a second pattern printed is aligned with a first pattern printed. In particular, the second pattern may be in registration with the first pattern. I lowever, the second pattern printed may overlap the first pattern, or be adjacent to it, depending upon the individual design to be printed.

In order to avoid smudging or mixing of the inks during subsequent printing passes, it is necessary to ensure that the viscosity of the ink is low enough to exit the ink container and printing head. The viscosity of the ink should, however, also be such that the printed pattern dries on the surface of the glazing without smudging or running, and such that there is no loss of definition in the edge regions of the pattern printed. Suitable inks are typical of those used for printing automotive glazings. The ink may be applied either in a continuous manner, for example, as a series of printed lines or a spray, or in a discrete manner, such as in a series of dots or spots. If the ink is to be applied in a spotwise manner, the viscosity of the ink may be chosen to ensure that the discrete spots merge to form a continuous coating before drying. Once the printing is complete, the backlight may be fired to fix the ink.

Once the backlight has been printed, it may be processed further, for example, by bending. Typically, firing and bending are carried out together. If the glazing is to be processed further after printing, the dimensions of the image printed may be adjusted to take into account changes in the glazing shape once processed. For example, a pattern of obscuration and heater lines may be printed to appear curved, but once the backlight is processed, appear as a series of horizontal, parallel circuit lines.

A further advantage is that the patterns printed may be printed using different inks without moving the object to be printed between printing stations. This may be achieved either by using separate ink containers or reservoirs for each ink on a single print head, or by using several print heads, each with a single container or reservoir of ink. In each case, multiple print heads and/or ink container can be housed in a single printing station. As no intermediate drying stage is necessary, there is also no need to move the glazing from a printing station to a drying cabinet.

Figures 5, 6, and 7 show schematic diagrams of various printing head arrangements in accordance with embodiments of the invention.

Figure 5 shows a printing station having a print table 21 on which a bacldight 22 is placed. The backlight is positioned and secured with the aid of two stops 23a 23b. A first print head assembly 24a linked to a supply of black ink (not shown) is spaced a distance di from a second print head assembly 24b linked to a supply of silver containing ink (not shown). The distance d1 between the two assemblies is determined by the speed at which the two print head assemblies 24a 24b move across the backlight in the direction of arrows A (the solid arrow representing the direction of movement of the first print head assembly 24a and the dashed arrow representing the direction of movement of the second print head assembly 24b), and the time needed for the black ink to dry sufficiently that the silver ink can be overprinted with no smudging or mixing. Figure 5 depicts a stage partway through the printing process, where the obscuration band 25 and concealment lines 26 are being printed by the first print head assembly 24a, but the second print head has not yet moved into position to overprint heater circuit lines and busbars.

Figure 6 shows a printing station having a print table 31 on which a backlight 32 is placed, again, partway through a first printing pass. The backlight is positioned and secured for printing with the aid of two stops 33a 33b. A print head assembly 34 having first and second sub- assemblies 35 36 moves initially across the backlight 32 in the direction of arrow A. The first sub-assembly is linked to a supply of black ink (not shown) and the second sub-assembly is linked to a supply of silver- containing ink (also not shown). This first pass is used to print the obscuration band 37 and concealment lines 38 using the first sub-assembly 35. Once the first pass is complete, the print head assembly 34 moves in the reverse direction across the backlight 32, in the direction of arrow B to enable the printing of the heater lines and busbars (not shown) using the second sub-assembly 36. A second assembly 39, shown in dotted lines, may be used to carry either a UV or IR lamp or other heating device, to cure the ink after one or both printing passes. For example, the assembly may be passed over the backlight 32 after the first printing pass, the second printing pass or after both the first and second printing passes.

Figure 7 illustrates a printing station where the ink used is LIV cured, again, partway through a first printing pass. The printing station comprises a print table 41 on which a backlight 42 is placed, the backlight 42 being positioned and secured with the aid of two stops 43a 43b. A first and second print head assemblies 44 45, separated by a distance di, determined by the print speed and the drying time of the black ink, are used to print the obscuration band 46, concealment lines 47, heater lines and busbars (not shown) in a printing pass across the backlight 42 in the direction of A, as illustrated by the unbroken and dashed arrows. A IJV lamp 48 is then passed over the printed backlight, again in direction A, as illustrated by the dotted arrows, to cure the ink. The UV lamp is positioned a distance d2 from the second print head assembly 45.

Although the LIV lamp is shown as passing over the backlight after both print head assemblies, depending on ink characteristics, the lamp could be placed between the first and second print head assemblies 44 45, to cure the black ink. Alternatively two lamps, one passing over the backlight after each print head assembly, could be used.

Any other suitable curing or drying device, for example an IR light or a warm air supply for heat cured inks, may be used in place of the UV lamp. Typically, black inks used in printing automotive glazings are UV curable, whereas silver-containing inks require drying. I lowever, a UV-curable silver-containing ink may be used with this embodiment if desired.

Depending on the characteristics of the ink used, it may be desirable to use more than one printing pass to print the black or silver inks onto the glazing. For example, certain inks may require at least two passes to ensure sufficient ink density on the surface of the glass once fired, in order to ensure either full coverage by the concealment lines or adequate electrical conductivity. Curing of the ink may take place in between each printing pass, or once all the required printing passes have been completed.

Although the invention has been described in terms of printing a heater circuit onto a backlight, other conductive items, such as antennas may also be printed. In addition, text and logos, such as those used in identification or certification marks (known as "trade marks" within the automotive glazing industry) may be printed. Whilst it is preferable that the concealment lines be coloured black, inks of other colours may be used. Other automotive glazing products can be printed, for example, windscreens or sidelights, depending upon the pattern or effect desired.

Claims (31)

1. A method of printing a surface of a glazing, comprising depositing a first ink to form a first pattern, depositing a second ink to form a second pattern, the second pattern being aligned with the first pattern, wherein the print device used to deposit the ink does not contact the surface of the glazing.

2. The method of claim 1, wherein the second pattern is in registration with the first pattern.

3. The method of claim I, wherein the second pattern overlaps the first pattern.

4. The method of claim 1, wherein the second pattern is adjacent to the first pattern.

5. The method of claim 1, 2 or 3, wherein the first pattern conceals the second pattern when the glazing is viewed from the exterior of a vehicle.

6. The method of claim 5, wherein the first pattern comprises concealment lines.

7. The method of claim 5 or 6, wherein the second pattern comprises at least one line forming a heater circuit or an antenna.

8. The method of claim 7, wherein the second pattern is deposited using a conductive ink.

9. The method of claim 8, wherein the conductive ink is a silvercontaining ink.

10. The method of claim 6, wherein the concealment lines are deposited using a black ink.

11. The method of claim 9 or 10, wherein at least one of the silvercontaining ink and the black ink is UV or heat curable.

12. The method of any of claims 7 to 11, wherein the concealment lines have a width of less than 0.6mm.

13. The method of any of claims 7 to 12, wherein the width of the lines forming the heater circuit or antenna, are the same as or less than the width of the concealment lines.

14. The method of any of claims 7 to 12, wherein the width of the concealment lines is 50% greater than that of the lines forming the heater circuit or antenna, or less.

15. The method of any of claims 7 to 12, wherein the width of the concealment lines is 20% greater than that of the lines forming the heater circuit or antenna, or less.

16. The method of any of claims 7 to 12, wherein the width of the concealment lines is 10% greater than that of the lines forming the heater circuit or antenna, or less.

17. The method of any of claims 12 to 15, wherein the width of the lines forming the heater circuit or antenna, is less than 0.6mm.

18. The method of any of claims 7 to 17, wherein the heater circuit lines in a central region of the glazing are different in width to the heater circuit lines in an edge region of the glazing.

19. The method of claim 5, wherein the first and second patterns comprise logos or text.

20. The method of any preceding claim, wherein the glazing is supported on a print table during printing, and wherein there is no relative movement of the glazing to the print table after depositing the first ink to form the first pattern and before depositing the second ink to form the second pattern.

21. The method of any preceding claim, wherein a first print device is used to deposit the ink forming the first pattern, and a second print device is used to deposit the ink forming the second pattern.

22. The method of claim 21, wherein the print device has at least two ink containers.

23. The method of any of claims I to 21, wherein the print device is used to deposit ink to form the first pattern and to deposit ink to form the second pattern.

24. The method of any proceeding claim, wherein the print device is an ink jet print head.

The method of any preceding claim, wherein the print device is digitally controlled.

26. The method of any proceeding claim, comprising printing an obscuration band onto the surface of the glazing.

27. The method of claim 26, comprising printing busbars onto the obscuration band.

28. The method of any of claims 1 to 27, wherein the glazing is a backlight.

29. A glazing printed according to the method of any of claims 1 to 28.

30. A method of printing a surface of a glazing, substantially as herein described, and with reference to the accompanying drawings.

31. A glazing having a printed surface, substantially as herein described, and with reference to the accompanying drawings.