PANE HAVING AN ELECTRIC HEATING LAYER

Abstract

A pane having an electric heating layer is described, including at least: a first pane having a first surface; at least one electric heating layer that is applied to at least part of the surface and has an uncoated zone; at least two busbars, provided for connection to a voltage source, which are connected to the electric heating layer such that a current path for a heating current is formed between the busbars; and at least one separating line which electrically subdivides the electric layer into at least two segments. At least one segment is arranged in the form of a strip around the uncoated zone such that the current path for the heating current is at least partially guided around the uncoated zone.

Claims

1. A pane having an electric heating layer, comprising: a first pane having a surface; at least one electric heating layer that is applied at least on part of the surface and includes an uncoated zone; at least two busbars provided for connection to a voltage source, the at least two busbars being connected to the electric heating layer such that a current path for a heating current is formed between the at least two busbars; and at least one separating line that electrically subdivides the at least one electric heating layer into at least two segments, wherein at least one segment of the at least two segments is arranged in strip form around the uncoated zone such that the current path for the heating current is guided at least partially around the uncoated zone.

2. The pane according to claim 1, wherein the electric heating layer has at least two separating lines, which form segments that are arranged at least partially in strip form around the uncoated zone.

3. The pane according to claim 1, wherein the electric heating layer has four to thirty separating lines, which form segments that are arranged at least partially in strip form around the uncoated zone.

4. The pane according to claim 1, wherein a width of each separating line is from 30 m to 200 m.

5. The pane according to claim 1, wherein a width of each separating line is from 70 m to 140 m.

6. The pane according to claim 1, wherein at least one of a width of each segment between the uncoated zone and a nearest separating line and a width between two adjacent separating lines is from 1 cm to 15 cm.

7. The pane according to claim 1, wherein the area of the uncoated zone is from 0.5 dm.sup.2 to 15 dm.sup.2.

8. The pane according to claim 1, wherein an average length of each segment deviates by less than 25% from a mean of the average length of each segment.

9. The pane according to claim 1, wherein an average length of each segment deviates from 0% to 5% from a mean of the average length of each segment.

10. The pane according to claim 1, wherein a third busbar is arranged in electrical contact with a first busbar or a second busbar, wherein the third busbar is in electrical contact with at least one segment.

11. The pane according to claim 1, wherein a third busbar is arranged in electrical contact with a first busbar or a second busbar, wherein the third busbar is in electrical contact with all segments.

12. The pane according to claim 1, wherein a low-impedance bridge, which reduces an electrical resistance along the current path, is arranged in at least one segment.

13. The pane according to claim 12, wherein at least one of the at least two busbars and the low-impedance bridge is implemented as fired printing paste.

14. The pane according to claim 13, wherein the fired printing paste contains at least one of metallic particles, metal particles, and carbon particles.

15. The pane according to claim 13, wherein the fired printing paste has a specific resistance from 0.8 ohm.Math.cm to 7.0 ohm.Math.cm.

16. The pane according to claim 1, wherein the surface of the first pane is areally bonded to a second pane via a thermoplastic intermediate layer.

17. The pane according to claim 16, wherein at least one of the first pane and the second pane contains flat glass, float glass, quartz glass, borosilicate glass, soda lime glass, or a polymer.

18. The pane according to claim 1, wherein the electric heating layer is a transparent, electrically conductive coating.

19. The pane according to claim 18, wherein the electric heating layer has a sheet resistance from 0.4 ohm/square to 10 ohm/square.

20. The pane according to claim 19, wherein the electric heating layer contains silver, indium tin oxide, fluorine-doped tin oxide, or aluminum-doped zinc oxide.

21. A method for producing a pane having an electric heating layer, comprising: applying an electric heating layer having an uncoated zone onto a surface of a pane; connecting at least two busbars to the electric heating layer, the at least two busbars being configured for connection to a votage source such that a current path for a heating current is formed between the busbars; and introducing least one separating line that electrically subdivides the electric heating layer into at least two segments, wherein at least one segment is arranged in strip form around the uncoated zone such that the current path for the heating current is guided at least partially around the uncoated zone.

22. The method according to claim 21, wherein introducing at least one separating line includes laser patterning.

23. A method of using a pane having an electric heating layer, comprising: providing the pane having an electric heating layer of claim 1; and installing the pane in a means of transportation for travel on land, in the air, or on water.

24. The method according to claim 23, wherein installing the the pane includes providing the pane in at least one of a windshield, a rear window, a side window, and a roof pane of a motor vehicle.

25. A method of using a pane having an electric heating layer, comprising: providing the pane having an electric heating layer of claim 1; and installing the pane as a functional individual piece or as a built-in component in furniture, a device, or a building.

26. The pane of claim 1, further comprising: a pluralty of additional busbars, wherein each of the plurality of additional busbars in contact between one of the first busbar and second busbar and a segment of the at least two segments, such that each additional busbar is each in contact with only one of the at least two segments and no two additional busbars are in contact with the same segment of the at least two segements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] The invention is explained in detail in the following with reference to drawings and exemplary embodiments. The drawings are a schematic representation and not true to scale. The drawings in no way restrict the invention.

[0083] They depict:

[0084] FIG. 1A a plan view of an embodiment of the pane according to the invention having an electric heating layer,

[0085] FIG. 1B a cross-sectional view along the section line A-A through the pane of FIG. 1A,

[0086] FIG. 1C an enlarged view of a detail of FIG. 1A,

[0087] FIG. 2A a plan view of a pane according to the prior art as a comparative example,

[0088] FIG. 2B simulation of the heating power distribution of the comparative example of FIG. 2A,

[0089] FIG. 2C simulation of the temperature distribution of the comparative example of FIG. 2A,

[0090] FIG. 3A a plan view of another embodiment of the pane according to the invention,

[0091] FIG. 3B simulation of the heating power distribution of the pane according to the invention of FIG. 3A,

[0092] FIG. 3C simulation of the temperature distribution of the pane according to the invention of FIG. 3A,

[0093] FIG. 4 a plan view of another embodiment of the pane according to the invention,

[0094] FIG. 5 a plan view of another embodiment of the pane according to the invention, and

[0095] FIG. 6 a detailed flowchart of an embodiment of the method according to the invention.

DETAILED DESCRIPTION

[0096] FIG. 1A depicts a plan view of an exemplary embodiment of a pane 100 according to the invention having an electric heating layer. FIG. 1B depicts a cross-section through the pane 100 according to the invention of FIG. 1A along the section line A-A. The pane 100 comprises a first pane 1 and a second pane 2, which are bonded to each other via a thermoplastic intermediate layer 4. The pane 100 is, for example, a motor vehicle window and in particular the windshield of an automobile. The first pane 1 is, for example, intended to face the interior in the installed position. The first pane 1 and the second pane 2 are made of soda lime glass. The thickness of the first pane 1 is, for example, 1.6 mm and the thickness of the second pane 2 is 2.1 mm. The thermoplastic intermediate layer 4 is made of polyvinyl butyral (PVB) and has a thickness of 0.76 mm. An electric heating layer 3 made of an electrically conductive coating is applied on the interior-side surface III of the first pane 1. The electric heating layer 3 is a layer system that contains, for example, three electrically conductive silver layers that are separated from each other by dielectric layers. When a current flows through the electric heating layer 3, it is heated due to its electrical resistance and Joule heat development. The electric heating layer 3 can, consequently, be used for active heating of the pane 100.

[0097] The electric heating layer 3 extends, for example, over the entire surface III of the first pane 1 minus a circumferential frame-shaped uncoated region with a width of 8 mm. The uncoated region is used for the electrical insulation between the current-carrying electric heating layer 3 and the motor vehicle body. The uncoated region is hermetically sealed by gluing to the intermediate layer 4 to protect the electric heating layer 3 against damage and corrosion.

[0098] For electrical contacting, in each case, a first busbar 5.1 is arranged in the lower edge region; and another, second busbar 5.2 is arranged in the upper edge region on the electric heating layer 3. The busbars 5.1, 5.2 contain, for example, silver particles and were applied by screen printing and then fired. The length of the busbars 5.1, 5.2 corresponds to approximately the dimension of the electric heating layer 3.

[0099] When an electric voltage is applied to the busbars 5.1 and 5.2, a uniform current flows through the electric heating layer 3 between the busbars 5.1, 5.2. A feed line 7 is arranged approximately centrally on each busbar 5.1, 5.2. The feed line 7 is a foil conductor known per se. The feed line 7 is electrically conductively connected to the busbar 5.1, 5.2 via a contact surface, for example, by means of a soldering compound, an electrically conductive adhesive, or by simple placement and application of pressure inside the pane 100. The foil conductor contains, for example, a tinned copper foil with a width of 10 mm and a thickness of 0.3 mm. The busbars 5.1, 5.2 are connected via the electrical feed lines 7 via connecting cable 13 to a voltage source 14, which provides a customary onboard voltage for motor vehicles, preferably from 12 V to 15 V and, for example, roughly 14 V. Alternatively, the voltage source 14 can even have higher voltages, for example, from 35 V to 45 V, and in particular 42 V.

[0100] A third busbar 5.3 in the shape of a semicircular line that is electrically conductively connected to the second busbar 5.2 is arranged, for example, on the upper edge of the pane 100. Alternatively, the third busbar 5.3 can be implemented with a rectangular, triangular, trapezoidal, or other shape. The third busbar 5.3 has, for example, a width of 10 mm.

[0101] An uncoated zone 8 is arranged in the upper region of the pane 100 roughly centrally relative to the width of the pane. The uncoated zone 8 has no electrically conductive material of the electric heating layer 3. The uncoated zone 8 is, for example, completely surrounded by the electric heating layer 3. Alternatively, the uncoated zone 8 can be arranged at the edge of the electric heating layer 3. The area of the uncoated zone 8 is, for example, 1.5 dm.sup.2. The length of the uncoated zone 8 is, for example, 18 cm. Here, the term length means the dimension in the direction that runs in the direction of the current path through the pane, i.e., in the direction of the shortest connecting line between the busbars 5.1, 5.2. In the example of the motor vehicle window of FIG. 1, the length of the uncoated zone 8 is arranged in the vertical direction and the width in the horizontal direction, parallel to the busbars 5.1, 5.2. The uncoated zone 8 is adjacent the busbar 5.3 on its upper end.

[0102] The busbars 5.1, 5.2, 5.3 have, in the example depicted, a constant thickness of, for example, roughly 10 m and a constant specific resistance of, for example, 2.3 ohm.Math.cm.

[0103] The electric heating layer 3 has four separating lines 9.1, 9.1, 9.2, 9.2, which are arranged, for example, in mirror symmetry to the uncoated zone 8. In the region of the separating lines 9.1, 9.1, 9.2, 9.2, the electric heating layer 3 is electrically interrupted. The separating lines 9.1, 9.1, 9.2, 9.2 are arranged in strip form around the uncoated zone 8 and form segments 10.1, 10.1, 10.2, 10.2, 10.3, 10.3 in the electric heating layer 3. The current paths 11 are guided around the uncoated zone 8 by the segments 10.1, 10.1, 10.2, 10.2 in the electric heating layer 3. In particular, the current paths 11 in the segments 10.1, 10.1 are guided in the immediate vicinity of the uncoated zone 8 into the region 12 below the uncoated zone 8. In this region 12, only a small heating power would be obtained in an electric heating layer 3 according to the prior art without separating lines (cf. heating power distribution according to the prior art in FIG. 2B).

[0104] FIG. 1B schematically depicts a cross-section through the pane 100 according to the invention along the section line A-A. The separating lines 9.1, 9.1, 9.2, and 9.2 have a width d.sub.1, d.sub.1, d.sub.2, and d.sub.2 of, for example, 100 m and are, for example, introduced into the electric heating layer 3 by laser patterning. Separating lines 9.1, 9.1, 9.2, 9.2 with such a small width are hardly perceptible optically and only disrupt vision through the pane 100 a little, which is of particular importance for driving safety especially for use in motor vehicles.

[0105] By means of an opaque ink layer known per se as a masking print, the region of the third busbar 5.3 can be prevented from being visible to an observer. The masking print (not shown here) can be applied, for example, on the interior-side surface II of the second pane 2 in the form of a frame.

[0106] A contact strip (not shown here) can be arranged between the feed line 7 and the busbar 5.1, 5.2. The contact strip is used for simple connection of the busbar 5.1, 5.2 to an external feed line 7 and is, for example, arranged orthogonal to the feed line 7 and in the long direction 6 of the busbar 5.1, 5.2. The contact strip advantageously increases the current-carrying capacity of the busbar 5.1, 5.2. Thus, the passage of the electrical current from the busbar 5.1, 5.2 to the feed line 7 is distributed over a larger area and local overheating, so-called hotspots, is prevented. The contact strip is in contact, for example, over its entire surface with the busbar 5.1, 5.2. The contact strip is, for example, during production of the pane 100 placed on the busbar 5.1, 5.2 and is durably stably fixed by the thermoplastic layer 4 on the busbar 5.1, 5.2. The contact strip is made, for example, of copper and has a thickness of 100 m, a width of 8 mm, and a length of 5 cm. The contact strip and the busbar 5.1, 5.2 are preferably in direct contact. Thus, the electrical connection is not made via a soldering compound or an electrically conductive adhesive. Thus, the production process of the pane 100 is significantly simplified. In addition, the risk of damage to the busbar 5.1, 5.2, as it exists, for example, in the case of soldering or with stressing a soldered joint, can be avoided.

[0107] FIG. 10 depicts an enlarged view of a detail in the region of the uncoated zone 8 and of the separating lines 9.1, 9.2 that are arranged on the left side of the uncoated zone 8. The segment 10.2 between the separating lines 9.1 and 9.2 is, for example, represented by hatching. All separating lines 9.1, 9.2 terminate at the line 6 below the uncoated region 8. Furthermore, the average length L.sub.1 of the segment 10.1 and the average length L.sub.2 of the segment 10.2 are shown. The average length L.sub.1 is, for example, 25 cm. The average length L.sub.2 is, for example, 28 cm. In an advantageous embodiment of the invention, the average lengths L.sub.1 and L.sub.2 are implemented roughly the same. The average length L of a segment 10.1, 10.2 is generally determined by the curvature of the separating lines and thus by the curvature of the segment as well as by the position of the upper busbar 5.2 and possibly of the third busbar 5.3. An optimal average length L of the segment 10.1, 10.2 for homogeneous heating power distribution can be determined in simple experiments and simulations.

[0108] FIG. 2A depicts a pane 100 according to the prior art. The pane 100 comprises a first pane 1 and a second pane 2, which are bonded to each other via a thermoplastic intermediate layer 4. The pane 100 is, for example, a motor vehicle window and, in particular, the windshield of an automobile. The first pane 1 is, for example, intended to face the interior in the installed position. The first pane 1 and the second pane 2 are made of soda lime glass. The thickness of the first pane 1 is, for example, 1.6 mm and the thickness of the second pane 2 is 2.1 mm. The thermoplastic intermediate layer 4 is made of polyvinyl butyral (PVB) and has a thickness of 0.76 mm. An electric heating layer 3 made of an electrically conductive coating, which corresponds in structure to the electric heating layer 3 of FIG. 1A, is applied on the interior-side surface III of the first pane 1. In contrast to FIG. 1A, the busbar 5.1 arranged on the lower edge of the pane 100 has two feed lines 7.1, 7.2. The busbars 5.1, 5.2 have in each case a constant thickness of, for example, 10 m and a constant specific resistance of, for example, 2.3 ohm.Math.cm. Moreover, the pane 100 according to the prior art differs from the pane 100 according to the invention of FIG. 1A in that no separating lines are incorporated into the electric heating layer 3.

[0109] The area of the electric heating layer 3 is roughly 0.98 m.sup.2. The electric heating layer 3 has an uncoated region 8 in the upper third of the pane and roughly centrally relative to the width of the pane. The uncoated region 8 has, for example, a maximum width of 21 cm, a maximum length of 24 cm, and a total area of 400 cm.sup.2.

[0110] The pane has a busbar 5.2 on the upper edge. The current is fed into the busbar 5.2 through a feed line 7, identified by an arrow. The current flows through the electric heating layer 3 into a busbar 5.1 that is arranged in the lower region of the pane 100. The busbar 5.1 is connected on its right and its left end, respectively, to a feed line 7.1, 7.2. The busbars 5.1, 5.2 have, for example, a width of 16 mm and a thickness of 10 m. The electric heating layer 3 has, for example, a sheet resistance of 0.9 ohm/square. For a finite element simulation, a voltage of 14 V between the lower feed lines 7.1 and 7.2 and the upper feed line 7 and an ambient temperature of 22 C. were assumed. Moreover, a heating time of 12 minutes was assumed in the simulation.

[0111] FIG. 2B depicts the simulation of the heating power distribution of the pane 100 according to the prior art of FIG. 2A without separating lines in the electric heating layer 3. The electric output of the pane is 318 W.

[0112] FIG. 2C depicts the simulation of the temperature distribution of the comparative example according to the prior art of FIG. 2A. The maximum temperature T.sub.max on the pane 100 is 50.7 C., the average temperature T.sub.mitt in the region 12 below the uncoated zone 8 is 26.2 C.

[0113] FIG. 3A depicts a plan view of another embodiment of a pane 100 according to the invention. The first pane 1, the second pane 2, the electric heating layer 3, the thermoplastic intermediate layer 4, and the external feed lines 7, 7.1, 7.2 are configured as in FIG. 2A. The electric heating layer 3 has an uncoated zone 8, which corresponds to that of FIG. 2A. A third busbar 5.3 is arranged in the upper region of the pane 100. Moreover, the electric heating layer 3 has in each case eight separating lines 9.1-9.8, 9.1-9.8 on both sides of the uncoated zone 8. By means of the separating lines 9.1-9.8, 9.1-9.8, eight segments 10.1-10.8, 10.1-10.8 are formed on each of the two sides of the uncoated zone 8, through which the current path is guided from the busbar 5.2 or the third busbar 5.3 into the region below the uncoated zone 8. As the following simulations demonstrate, homogenization of the heating power distribution and of the temperature distribution of the pane 100 according to the invention can thus be obtained. The separating lines 9 are preferably introduced into the electric heating layer 3 by laser patterning. The width of the individual separating lines 9 is, for example, 100 m, as a result of which the view through the pane 100 is only minimally affected.

[0114] FIG. 3B depicts the simulation of the heating power distribution of the pane 100 according to the invention of FIG. 3A. The electrical output of the pane is 312 W.

[0115] FIG. 3C depicts the simulation of the temperature distribution of the pane 100 according to the invention of FIG. 3A. The maximum temperature T.sub.max on the pane 100 is 54.2 C.; the average temperature T.sub.mitt in the region 12 below the uncoated zone 8 is 32.2 C.

[0116] Table 1 again summarizes the simulation results.

TABLE-US-00001 TABLE 1 Average Heating output temperature T.sub.mitt in in the region the region 12 below Heating 12 below the the coating-free output uncoated zone 8 zone 8 distribution Comparative <150 W/m.sup.2 26.2 C. Poor example of FIG. 2A (prior art) Pane 100 >300 W/m.sup.2 32.2 C. Good according to the invention of FIG. 3A

[0117] The pane 100 according to the invention of FIG. 3A shows clearly improved heating properties compared to the pane 100 according to the prior art of the comparative example of FIG. 2A. In particular, in the region 12 below the uncoated zone 8, the pane according to the prior art has only a heating power of <150 W/m.sup.2 and an average temperature of roughly 26.2 C. The inhomogeneity of the heating power distribution results in an only unsatisfactory defrosting and defogging function of the pane 100. In the central field of vision in the region 12 below the uncoated zone 8, the heating properties do not suffice to ensure a problem-free view through the pane 100 in winter weather conditions.

[0118] The pane 100 according to the invention of FIG. 3A has improved heating properties in the critical region 12 below the uncoated zone 8. Thus, simulations yielded a heating power of more than 300 W/m.sup.2 and heating to an average temperature of roughly 32.2 C. under the simulation conditions. The view through the pane is negatively affected only minimally because of the low width of the separating lines and satisfies the requirements for motor vehicle glazing.

[0119] This result was unexpected and surprising for the person skilled in the art.

[0120] FIG. 4 depicts a plan view of a detail of another embodiment of a pane 100 according to the invention. The first pane 1 with the electric heating layer 3, the second pane 2, the thermoplastic intermediate layer 4, and the external feed lines 7, 7.1, 7.2 are configured as in FIG. 3A. The electric heating layer 3 has an uncoated zone 8 and separating lines 9.1-9.4, 9.1-9.4, which subdivide the electric heating layer 3 into a plurality of segments 10.1-10.4, 10.1-10.4. The segments 10.1-10.4, 10.1-10.4 are arranged in strip form on the sides of the uncoated zone 8. Moreover, each segment 10.1-10.4, 10.1-10.4 has another busbar 5.3-5.6, 5.3-5.6. Each busbar 5.3-5.6, 5.3-5.6 is electrically conductively connected directly to the busbar 5.2.

[0121] Due to the curvature of the segments 10.1-10.4, 10.1-10.4, the current path 11 is lengthened through the respective segment 10.1-10.4, 10.1-10.4; and due to the constant specific sheet resistance of the electric heating layer 3, the ohmic resistance through the segment 10.1-10.4, 10.1-10.4 is increased. This would result in an inhomogeneous heating power distribution compared to the current paths outside the segments 10.1-10.4, 10.1-10.4 formed by the separating lines 9.1-9.4, 9.1-9.4. By a shortening of the length of the current path 11 through the segment 10.1-10.4, 10.1-10.4 by means of another busbar 5.3-5.6, 5.3-5.6 through which the current is fed into the segment 10.1-10.4, 10.1-10.4, further homogenization of the heating power distribution and of the temperature distribution of the electrically heated pane 100 can be obtained. The length of the of the busbar 5.3-5.6, 5.3-5.6 and its dimensions, such as thickness and width, can be determined in simple experiments and simulations. In the example depicted, the busbars 5.4-5.6, 5.4-5.6 are configured in zigzag form, with the busbars 5.4, 5.4 configured thicker than the busbars 5.5, 5.5, and these, in turn, thicker than the busbars 5.6, 5.6. The busbars 5.4, 5.4 have, as a result, lower resistance than the busbars 5.5, 5.5 and these, in turn, a lower resistance than the busbars 5.6, 5.6.

[0122] FIG. 5 depicts a plan view of another embodiment of a pane 100 according to the invention. The first pane 1 with the electric heating layer 3 and the external feed lines 7, 7.1, 7.2 are configured as in FIG. 4. The electric heating layer 3 has an uncoated zone 8 and separating lines 9.1-9.4, 9.1-9.4, which subdivide the electric heating layer 3 into a plurality of segments 10.1-10.4, 10.1-10.4. The segments 10.1-10.4, 10.1-10.4 are arranged in strip form on the sides of the uncoated zone 8. The segments 10.4 and 10.4, which are arranged farthest from the uncoated zone 8, have, in each case, a third busbar 5.3 and 5.3, which is electrically conductively connected directly to the busbar 5.2. Moreover, the other inward-positioned segments 10.1-10.3, 10.1-10.3 have, in each case, a low-impedance bridge 15.4-15.6, 15.4-15.6, which lowers the electrical resistance of the current path through the respective segment. The low-impedance bridges 15.4-15.6, 15.4-15.6 are made, for example, from the material of the busbar 5.2 and have an electrical resistance with lower impedance than that of the electric heating layer 3. The low impedance bridges 15.4-15.6, 15.4-15.6 are not connected electrically conductively directly to the busbar 5.2, but are electrically conductively connected over their full length to to the electric heating layer 3.

[0123] Due to the curvature of the segments 10.1-10.4, 10.1-10.4, the current path 11 is lengthened through the respective segment 10.1-10.4, 10.1-10.4; and due to the constant specific sheet resistance of the electric heating layer 3, the ohmic resistance through the segment 10.1-10.4, 10.1-10.4 is increased. This would result in an inhomogeneous heating power distribution compared to the current paths outside the segments 10.1-10.4, 10.1-10.4 formed by the separating lines 9.1-9.4, 9.1-9.4. By a shortening of the length of the current path through the low impedance bridges 15.4-15.6, 15.4-15.6, further homogenization of the heating power distribution and of the temperature distribution of the electrically heated pane 100 can be obtained. The length of the low impedance bridges 15.4-15.6, 15.4-15.6 and their optimum electrical resistance can be determined in simple experiments and simulations.

[0124] FIG. 6 depicts a flowchart of an exemplary embodiment of the method according to the invention for producing an electrically heatable pane 100.

[0125] It was possible to demonstrate that panes 100 according to the invention with separating lines present clearly improved heating properties, improved homogeneity of the heating power distribution, and a more uniform temperature distribution at relatively high temperatures in particularly important sections of the pane. At the same time, the view through the pane 100 is negatively affected only minimally by the separating lines according to the invention.

[0126] This result was unexpected and surprising for the person skilled in the art.

TABLE-US-00002 List of Reference Characters: (1) first pane (2) second pane (3) electric heating layer, (4) thermoplastic intermediate layer (5.1), (5.2), (5.3), (5.4), (5.5) busbar (5.1), (5.2), (5.3), (5.4), (5.5) busbar (6) line (7) feed line (8) uncoated zone (9.1), (9.2), (9.3), (9.4), (9.5), separating line (9.6), (9.7), (9.8) (9.1), (9.2), (9.3), (9.4), (9.5), separating line (9.6), (9.7), (9.8) (10.1), (10.2), (10.3), (10.4), segment (10.5), (10.6), (10.7), (10.8) (10.1), (10.2), (10.3), (10.4), segment (10.5), (10.6), (10.7), (10.8) (11) current path (12) region (13) connecting cable (14) voltage source (15.4), (15.5), (15.6), (15.4), low-impedance bridge (15.5), (15.6) (100) pane (II) surface of the second pane 2 (III) surface of the first pane 1 b, b.sub.1, b.sub.2 width of the segment 10, 10.1, 10.2 d, d.sub.1, d.sub.2 width of the separating line 9 L, L.sub.1, L.sub.2 length of the segment 10, 10.1, 10.2 A-A section line