Transparent pane having a heatable coating

Abstract

A transparent pane with a conductive coating extending at least over a part of the transparent pane surface, in particular over a visual field of the transparent pane is described. The conductive coating is electrically connected to at least two strip-shaped bus bars such that after application of a supply voltage, a current flows over a heating field formed by the conductive coating. The conductive coating has an electrical resistance such that upon application of a supply voltage in the range from more than 100 volts to 400 volts, a heating output from the heating field is in the range from 300 watt/m.sup.2 to 1000 watt/m.sup.2. The at least two strip-shaped bus bars have a maximum width of less than 5 mm and are dimensioned such that a maximum electrical power loss per unit of length is 10 watt/m. Moreover, the at least two strip-shaped bus bars have a specific resistivity ranging from 2 ohm.Math.cm to 4 ohm.Math.cm.

Claims

1. A transparent pane, comprising: a first pane having a surface; a conductive coating extending at least over a part of the surface of the first pane; and at least two strip-shaped bus bars on the first pane, wherein the conductive coating is electrically connected to the at least two strip-shaped bus bars, wherein the at least two strip-shaped bus bars are configured to receive a supply voltage from a power source and wherein after application of the supply voltage, a current flows over a heating field formed between the at least two strip-shaped bus bars, wherein the conductive coating has an electrical resistance such that upon application of the supply voltage in a range between more than 100 volts and 400 volts, a heating output from the heating field is in a range from 300 watt/m.sup.2 to 1000 watt/m.sup.2, wherein the conductive coating has an electrical resistance per surface unit in a range from more than 100 ohms/square meter to 200 ohms/square meter, wherein the at least two strip-shaped bus bars have at least in sections of the at least two strip-shaped bus bars, a maximum width of less than 5 mm and a width of the at least two strip-shaped bus bars being dimensioned such that a maximum electrical power loss per unit of length is 10 watt/m, wherein a cross-sectional area along the width and perpendicular to a length of the at least two strip-shaped bus bars is in a range from 0.01 to 1 mm.sup.2, and wherein the at least two strip-shaped bus bars having a specific resistivity in a range from 2 ohm.Math.cm to 4 ohm.Math.cm.

2. The transparent pane according to claim 1, wherein the at least two strip-shaped bus bars have at least in sections of the at least two strip-shaped bus bars, a width in a range from 1 mm to less than 5 mm.

3. The transparent pane according to claim 1, wherein the at least two strip-shaped bus bars have an electrical resistance per unit of length in a range from 0.15 ohm/m to 4 ohm/m.

4. The transparent pane according to claim 1, wherein the conductive coating has an electrical resistance such that a current flowing through the heating field has a maximum magnitude of 5 A.

5. The transparent pane according to claim 1, wherein the at least two strip-shaped bus bars are adapted to be electrically contacted in a common connector zone by connector conductors.

6. The transparent pane according to claim 1, wherein the heating field is subdivided by one or a plurality of decoated zones into a plurality of segments galvanically separated from each other, wherein the plurality of segments are serially connected to each other by the at least two strip-shaped bus bars.

7. The transparent pane according to claim 1, wherein the heating field is subdivided by one or a plurality of decoated zones into a plurality of segments galvanically connected to each other in series, wherein a current path between the at least two strip-shaped bus bars is lengthened relative to a current path without decoated zones.

8. The transparent pane according to claim 7, wherein the plurality of decoated zones is implemented as parallel lines.

9. The transparent pane according to claim 7, wherein the plurality of decoated zones form a staggered pattern, wherein zone ends of adjacent decoated zones face opposite edges of the transparent pane.

10. The transparent pane according to claim 1, wherein the at least two strip-shaped bus bars are produced by printing a metallic printing paste onto the conductive coating.

11. The transparent pane according to claim 10, wherein the at least two strip-shaped bus bars are produced by using a screen-printing method.

12. The transparent pane according to claim 1, wherein the at least two strip-shaped bus bars are produced in form of prefabricated metal strips connected to the conductive coating, the prefabricated metal strips being affixed on the conductive coating by a conductive adhesive.

13. The transparent pane according to claim 1, further comprising a second pane having a surface, wherein the first pane and the second pane are bonded to each other by a thermoplastic adhesive layer, wherein the conductive coating is situated on at least one surface of the first pane and the second pane or on a surface of a carrier disposed between the first pane and the second pane.

14. The transparent pane according to claim 1, wherein the transparent pane is implemented as a motor vehicle windshield, wherein a bus bar of the at least two strip-shaped bus bars disposed on a lower edge of the transparent pane is situated under a resting or parked position of windshield wipers provided to wipe the transparent pane.

15. The transparent pane according to claim 1, wherein the transparent pane is implemented as a motor vehicle windshield, wherein the at least two strip-shaped bus bars are disposed on a lateral edge of the first pane.

16. The transparent pane according to claim 15, wherein the at least two strip-shaped bus bars are covered by at least one opaque covering element.

17. A method comprising: using the transparent pane according to claim 1 as a functional individual piece, as a built-in part in furniture, devices, or buildings, as well as in means of transportation on land, in air, or on water.

18. The method according to claim 17, wherein the transparent pane is used as a windshield, rear window, side window, and/or glass roof in means for transportation.

19. The method according to claim 18, wherein the means for transportation is a motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now explained in detail with reference to exemplary embodiments, referring to the accompanying figures. They depict, in simplified representation, not to scale:

(2) FIG. 1-2 perspective views of exemplary embodiments of a windshield according to the invention;

(3) FIG. 3-5 sectional views of other exemplary embodiments of the windshield according to the invention;

(4) FIG. 6-9 perspective views of other exemplary embodiments of the windshield according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIGS. 1 to 5 are considered first, wherein FIGS. 1 and 2 depict, in each case, a windshield in typical installation position in a motor vehicle designated as a whole with the reference number 1, and FIGS. 3 through 5 depict sectional views of the windshields perpendicular to the plane of the pane. In these embodiments, the windshield 1 is a composite pane, whose structure is depicted in the sectional views.

(6) According to these embodiments, the windshield 1 comprises a rigid outer pane 2 and a rigid inner pane 3, both configured as individual panes and fixedly bonded to each other by a thermoplastic adhesive layer 4, here, for example, a polyvinyl butyral film (PVB), ethylene vinyl acetate film (EVA), or polyurethane film (PU). The two individual panes are the same size, have a trapezoidal curved contour, and are made, for example, from glass, being equally possibly made of a nonglass material such as plastic. For an application other than as a motor vehicle windshield 1, it would also be possible to make the two individual panes from a flexible material.

(7) The contour of the windshield 1 results from an edge of the pane 5 common to the two individual panes 2, 3. Corresponding to its trapezoidal shape, the windshield 1 has two opposing first sides 6 corresponding to the upper and lower edges of the pane and two opposing second sides 7 corresponding to the left and right (lateral) edges of the pane.

(8) As depicted in FIGS. 3 to 5, a transparent, electrically heatable, conductive heating coating 8 is deposited on the side of the inner pane 3 bonded to the adhesive layer 4. The heating coating 8 in this case is, for example, applied substantially over the entire surface of the inner pane 3, with a circumferential edge strip 9 on all sides of the inner pane 3 not coated such that a coating edge 10 of the heating coating 8 is set back inward relative to the edge of the pane 5. This effects electrical insulation of the heating coating 8 toward the outside. Moreover, the heating coating 8 is protected against moisture penetrating from the edge of the pane 5.

(9) The transparent heating coating 8 comprises, in a manner known per se, a layer sequence (not shown in detail) with at least one electrically heatable, metallic sublayer, preferably silver (Ag), and, optionally, other sublayers such as antireflection layers and blocker layers. The layer sequence advantageously has high thermal stability such that it withstands, without damage, the temperatures of typically more than 600 C. necessary for the bending of glass panes; however, layer sequences with low thermal stability can also be provided. The heating coating 8 can also be applied as a metallic individual layer. It is also conceivable to apply the heating coating 8 not directly on the inner pane 3, but, rather, to first apply it on a carrier, for example, a plastic film, which is then adhesively bonded to the outer and inner pane 2, 3. The heating coating 8 is preferably applied by sputtering or magnetron cathode sputtering.

(10) As depicted in FIGS. 1 and 2, the heating coating 8 is electrically connected, on the upper first side 6 of the windshield 1, to a strip-shaped first collecting conductor 11 (bus bar) and, on the lower first side 6 of the windshield 1, to a strip-shaped second collecting conductor 12 (bus bar). The first bus bar 11 is provided for connection to one pole and the second bus bar 12 for connection to the other pole of a voltage source (not shown). The two bus bars 11, 12 of opposite polarity serve for uniform introduction and broad distribution of the heating current in the heating coating 8, with a heatable section (heating field) of the heating coating 8 enclosed between the two bus bars 11, 12. The lower second bus bar 12 is situated near the lower edge of the pane 5, in particular under a resting or parked position of windshield wipers provided to wipe the windshield 1. Thus, the heating field extends into this region of the windshield 1 which can be adequately heated to prevent the wipers from freezing in place. Additional precautions for heating this region can be foregone. Alternatively, the lower second bus bar 12 can also be situated inside the region of the resting or parked position of the wipers in order to heat this region by means of the heat given off (power loss) by the second bus bar 12.

(11) The two bus bars 11, 12 are, in each case, electrically connected to connector conductors 15 for connection to the voltage source, which conductors are implemented here, for example, as metal strips. FIG. 1 depicts a variant in which the upper first bus bar 11 is contacted by a connector conductor 15 disposed in the upper left corner region of the windshield 1, whereas the lower second bus bar 12 is contacted by another connector conductor 15, which is disposed in the lower left corner region of the windshield 1. In contrast, FIG. 2 depicts a variant in which the upper first bus bar 11 is contacted by a connector conductor 15 disposed in the center of the windshield 1, whereas the lower second bus bar 12 is contacted by two other connector conductors 15, which are, in each case, laterally offset relative to the center of the windshield 1.

(12) Moreover, an edge region of the surface of the outer pane 2 facing the inner pane 3 is provided with an opaque color layer that forms a frame-shaped circumferential masking strip 13. The masking strip 13 is made, for example, of an electrically insulating, black-colored material, that is baked into the outer pane 2. On the one hand, the masking strip 13 prevents seeing an adhesive strand (not shown), with which the windshield 1 is glued into the vehicle body; on the other, it serves as UV protection for the adhesive material used. Moreover, the masking strip 13 defines the visual field of the windshield 1. A further function of the masking strip 13 is to conceal the two bus bars 11, 12, such that they cannot be visible from the outside. For this purpose, the masking strip 13 covers, in each case, the two bus bars 11, 12, with the masking strip 13 having a certain excess 14 or tolerance on the side facing away from the edge of the pane 5. Except for the excess 14, the visual field of the windshield 1 is congruent with the heating field situated between the two bus bars 11, 12.

(13) As already presented in the introduction, the two bus bars 11, 12 can be produced by printing, for example, in screenprinting of a metallic printing paste (for example, silver printing paste) on the heating coating 8 or through application of a prefabricated metal strip made, for example, of copper or aluminum. The connector conductors 15 can be electrically connected to the bus bars 11, 12 in a conventional manner, for example, by soldering. As depicted in FIG. 4, the connector conductors 15 can, however, also be adhesively bonded to the bus bars 11, 12 by an electrically conductive adhesive, which is implemented here, for example, in the form of an adhesive strip 16. As depicted in FIG. 5, an air- and water-tight seal, can also be implemented here, for example, as sealing strip 17. By this means, the heating coating 8 is additionally protected against moisture and premature wear.

(14) The bus bars 11, 12 preferably have an electrical resistance per unit of length in the range from 0.15 to 4/m. The specific resistivity of the two bus bars 11, 12 is, in particular for bus bars 11, 12 produced in the printing method, preferably in the range from 2 to 4 ohm.Math.cm. The width of the strip-shaped bus bars 11, 12 is, at least in one or a plurality of sections, less than 5 mm, with the width in these sections dimensioned such that the bus bars 11, 12 give off, in each case, a maximum of 10 W/m, preferably a maximum of 8 W/m, for example, 5 W/m, as power loss. Preferably, the width of the strip-shaped bus bars 11, 12 is, for this purpose, at least in sections, in each case, in the range from 1 to less than 5 mm. The thickness of the bus bars 11, 12 is preferably in the range from 5 to 25 m, more preferably in the range from 10 to 15 m. The cross-sectional area of the bus bars 11, 12 is preferably in the range from 0.01 to 1 mm.sup.2, more preferably in the range from 0.1 to 0.5 mm.

(15) For prefabricated strip-shaped bus bars 11, 12, made, for example, of copper (Cu), the thickness is preferably in the range from 30 to 150 m, more preferably in the range from 50 to 100 m. For these bus bars 11, 12, the cross-sectional area is preferably in the range from 0.05 to 0.25 mm.sup.2. The width of the strip-shaped bus bars 11, 12 is, at least in sections, less than 5 mm.

(16) Preferably, the electrical resistance of the heating coating 8 is selected such that the current flowing through the heating field 23 has a maximum magnitude of 5 A. Preferably, the electrical sheet resistance of the heating coating 8 is in the range from 5 to 200/, more preferably in the range from 10 to 80/, and, in particular, in the range from 40 to 80/. However it is also conceivable for the sheet resistance of the heating coating 8 to be in the range from more than 100 to 200/, in order to reduce the power loss of the bus bars 11, 12.

(17) Reference is now made to FIGS. 6 to 9, in which additional exemplary embodiments of the windshield 1 according to the invention are depicted. To avoid unnecessary repetition, only the differences relative to the previous embodiments are explained; otherwise, reference is made to the statements made there.

(18) FIG. 6 depicts a variant which differs from the variant depicted in FIG. 1 in that the upper first bus bar 11 is electrically connected to a connection conductor 18, which, together with the lower second bus bar 12, extends all the way to a common connector zone 19 for connection with two connector conductors 15. In the present example, the common connector zone 19 is situated in the lower left corner of the windshield 1, which enables a particularly simple electrical contacting of the two bus bars 11, 12. The connection conductor 18 is implemented here, for example, as a metal strip.

(19) FIG. 7 depicts a variant that differs from the variant depicted in FIG. 6 in that the two bus bars 11, 12 are disposed on the to lateral second sides 7 of the windshield 1. Here, the two bus bars 11, 12 are completely concealed by the circumferential masking strip 13. In addition, the right second bus bar 12 is electrically connected to a connection conductor 18, which extends, together with the left first bus bar 11 all the way to a common connector zone 19 for connection with two connector conductors 15. In the present example, the common connector zone 19 is situated in the lower left corner of the windshield 1, which enables a particularly simple electrical contacting of the two bus bars 11, 12. Here, the connection conductor 18 is implemented, for example, as a metal strip. In particular, the connection conductor 18 can be situated within the region of the resting or parked position of wipers provided to wipe the windshield 1. By means of these measures, it can be achieved that this region of the windshield 1 can be heated by the connection conductor 18, in order to prevent the wipers from freezing in place. It is possible to forego additional precautions for the heating of this region.

(20) FIG. 8 depicts another variant that differs from the variant depicted in FIG. 1 in that the heating coating 8 is subdivided by four decoated zones 20 into five segments 21 completely separated from each other galvanically. It is understood that a larger or smaller number of decoated zones 20 and, accordingly, a larger or smaller number of galvanically separated segments 21 can be provided. Here, the decoated zones 20 are, for example, implemented as parallel lines and decoated, for example, by laser ablation; here, it would also be equally possible to provide alternative methods such as chemical ablation, for example, by means of etching, or mechanical ablation, for example, by means of a grinding wheel. The decoated zones 20 subdivide the heating coating, in each case, completely into at least roughly rectangular segments 21.

(21) Here, it is essential that the electrically isolated segments 21 relative to the heating coating 8 are serially connected to each other by a plurality of first and second bus bars 11, 12. For this purpose, first and second bus bars 11, 12 are disposed on the upper and lower edge of the pane 5, with, in each case, a bus bar of one polarity, which is situated inside an individual segment 21, disposed opposite a bus bar of the other polarity, which electrically connects this segment 21 to an adjacent segment 21.

(22) In the example of FIG. 8, suppose the five segments 21 are numbered from left to right with the numbers 1 to 5. Accordingly, a first bus bar 11 is electrically connected on the upper edge of the pane 5 of the windshield 1 only to the first segment 21; another first bus bar 11, to the second and third segment 21; and yet another first bus bar 11, to the fourth and fifth segment 21. Here, the second and third segments 21, as well as the fourth and fifth segments 21 are, in each case, short-circuited by the first bus bar 11. On the other hand, a second bus bar 12 is electrically connected, on the lower edge of the pane 5 of the windshield 1, to the first and second segment 21; another second bus bar 12, to the third and fourth segment 21; as well as yet another second bus bar 12, to the fifth segment 21. Here, the first and second segments 21 as well as the third and fourth segments 21 are, in each case, short-circuited by the second bus bar 12. In the heating field of FIG. 8, the heating current must thus flow through the serially connected segments 21 one after another, by which means the effective (sheet) resistance (total resistance) of the heating coating 8 is significantly increased.

(23) The sheet resistance of the heating coating 8 is, before production of the decoated zones 20, preferably in the range from 1 to 10/ and is, in particular, preferably 4/. After production of the decoated zones 20, the total resistance of the heating coating 8 is preferably in the range from 10 to 160, more preferably in the range from 40 to 80.

(24) FIG. 9 depicts another variant, which differs from the variant depicted in FIG. 8 in that the pane 1 is a side window pane of a motor vehicle. Moreover, the heating coating 8 is partially interrupted by five decoated zones 20 and subdivided into six segments 21 galvanically connected to each other. The decoated zones 20 thus subdivide the heating coating 8, in each case, only partially, but not completely. It is understood that a larger or smaller number of decoated zones 20 and, correspondingly, a larger or smaller number of segments 21 galvanically connected to each other can be provided. The decoated zones 20 are implemented here, for example, as parallel lines.

(25) In contrast to the variant of FIG. 8, the decoated zones 20 are alternatingly set back, in each case, with a zone end 22 relative to the opposite edge of the pane 5 far enough that the heating coating 8 is not completely divided. The result is that the heating current must flow meanderingly through the segments 21 serially connected to each other, by which means the effective resistance (total resistance) of the heating coating 8 is increased.

(26) In the following Table I, exemplary values for the respective bus bars 11, 12 are indicated, with these values corresponding to a power loss of 0.05 W/cm.

(27) TABLE-US-00001 TABLE I A B C D E F G H 100 350 Ag 15 0.1305 0.0326 8.7000 2.1750 (screen print) 400 1000 Ag 15 0.0690 0.0173 4.6000 1.1500 (screen print) 400 350 Ag 15 0.0075 0.0019 0.5000 0.1250 (screen print) 100 350 Cu-strand 50 0.0735 0.0184 1.4703 0.3676 400 1000 Cu- strand 50 0.0389 0.0097 0.7774 0.1944 400 350 Cu- strand 50 0.0042 0.0011 0.0845 0.0211 A: Supply voltage [V] B: Heating output of the heating coating [W/m.sup.2] C: Bus bar-type D: Thickness of the bus bar [m] E: Minimum cross-sectional area of the bus bar (connector conductor on the end) [mm.sup.2] F: Minimum cross-sectional area of the bus bar (connector conductor in the center) [mm.sup.2] G: Width of the bus bar (connector conductor on the end) [mm] H: Width of the bus bar (connector conductor in the center) [mm]

(28) In the following Table II, exemplary values for bus bars 11, 12 implemented in the form of CU-strands are indicated.

(29) TABLE-US-00002 TABLE II A B C D E F G 1.7 50 10 15 0.034 7.65 765 1.7 100 6 15 0.0283 6.375 1062.5 A: Specific resistivity [cm] B: Thickness [m] C: Width [mm] D: Heating current [A] E: Resistance per unit of length [/m] F: Heating output (power loss) [W/m] G: Heating output (power loss) [W/m]

(30) In the following Table III, exemplary values for bus bars 11, 12 produced from a silver printing paste in the screenprinting method are indicated. The conductivity of the bus bars 11, 12 is 2.9.Math.10.sup.8 ohm.Math.m, their thickness is 15 m.

(31) TABLE-US-00003 TABLE III A B C D E F G H 350 473 400 1.18 5 3.58 0.01 0.54 350 473 100 4.73 5 0.22 0.13 8.63 377 509 100 5 5 0.19 0.15 10 1000 1350 265 5 5 0.19 0.15 10 444 600 200 3 5 0.56 0.05 3.48 A: Heating output heating coating per surface unit [W/m.sup.2] B: Heating output [W] C: Voltage [V] D: Current [A] E: Heating output per unit of length Bus bar [W/m] F: Resistance per unit of length Bus bar [ohm/m] G: Cross-section [mm.sup.2] H: Width [mm]

(32) Additional exemplary values for a transparent pane 1 are indicated in the following:

(33) Supply voltage 400 V

(34) Pane Geometry:

(35) Pane height 0.9 m

(36) Pane width 1.5 m

(37) Length of connection line 1.5 m

(38) Bus Bar (Produced in the Screenprinting Method from Silver Printing Paste):

(39) Specific resistivity 3 cm

(40) Width 0.5 mm

(41) Thickness 15 m

(42) Width extension 0.5 mm

(43) Resistance per unit of length 0.0369 /cm

(44) Resistance Bus bar+Tin solder 0.01

(45) Heating Coating

(46) Sheet resistance 202.09/

(47) Total Resistance (Sum from Both Bus Bars)

(48) Heating coating 336.82

(49) Bus bar 1.66

(50) Extension of the bus bars 5.54

(51) Contact Bus barHeating coating 0.04101

(52) Connector conductor 0.02

(53) Total resistance 344.08

(54) Heating Output

(55) Total heating output 465.0 W

(56) TABLE-US-00004 Voltage [V] Power [W] Spec. Power [W/m.sup.2] Heating coating 391.6 455.2 337.2 Bus bar 1.9 2.2 2302.2 Extension 6.4 7.5 9208.7 Contact Bus bar - 0.0 0.1 56.8 Heating coating Sum Bus bar 2.3 2359.0 Connector conductor 0.0 0.0
Hottest Parts of the Bus Bar

(57) Total current 1.2 A

(58) Max. Heating output 0.050 W/cm (9208.7 W/m.sup.2)

(59) Inhomogeneity Due to Bus Bar Resistance

(60) Heating output in heating coating without bus bar 474.98 W

(61) Heating output in heating coating with bus bar 465.74 W

(62) Inhomogeneity 1.94%

(63) Geometric Inhomogeneity

(64) Width variation 10 cm

(65) Resistance heating coating with new width 314.4

(66) Total resistance with new width 321.6

(67) Heating output of the heating coating with new width 486.2 W

(68) Inhomogeneity 6%

(69) The invention makes available a transparent pane with electrically heatable coating, to which a high supply voltage in the range from more than 100 to 400 V can be applied to obtain suitable heating output for practical applications. The width of the bus bar is, at least in one or a plurality of sections, less than 5 mm and is, moreover, dimensioned in these sections such that the maximum heating output is 10 W/m. The bus bars 11, 12 can, in particular, be disposed on the lateral edges of the pane and concealed by an opaque masking strip.

LIST OF REFERENCE CHARACTERS

(70) 1 pane 2 outer pane 3 inner pane 4 adhesive layer 5 edge of the pane 6 first side 7 second side 8 heating coating 9 edge strip 10 coating edge 11 first bus bar 12 second bus bar 13 masking strip 14 excess 15 connector conductor 16 adhesive strip 17 sealing strip 18 connection conductor 19 connector zone 20 decoated zone 21 segment 22 zone end 23 heating field