COMPOSITE PANE FOR A HEAD-UP DISPLAY COMPRISING A HEATABLE SENSOR REGION

Abstract

A composite pane with an HUD region and a sensor region is provided with an electrically conductive coating that reflects the p-polarized radiation of the HUD projector. The electrically conductive coating has precisely one electrically conductive layer based on silver, below which a lower dielectric layer or layer sequence with a refractive index of at least 1.9 is arranged and above which an upper dielectric layer or layer sequence with a refractive index of at least 1.9 is arranged. The ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is at least 1.7. A busbar provided for connection to a voltage source is arranged on both sides of the sensor region and is connected to the coating such that a current path for a heating current is formed between the busbars.

Claims

1. A composite pane for a head-up display (HUD) with a heatable sensor region, comprising: an outer pane with an exterior-side surface and an interior-side surface, an inner pane with an exterior-side surface and an interior-side surface, wherein the interior-side surface of the outer pane is joined to the exterior-side surface of the inner pane via a thermoplastic intermediate layer, an electrically conductive coating on the interior-side surface of the outer pane, on the exterior-side surface of the inner pane, or within the intermediate layer, wherein the composite pane has an HUD region that is provided for irradiation by an HUD projector with p-polarized radiation, and has a sensor region that is provided for transmission of electromagnetic radiation for a sensor directed toward the interior-side surface of the inner pane, and wherein the electrically conductive coating is suitable for reflecting adapted to reflect the radiation of the HUD projector, the electrically conductive coating has precisely one electrically conductive layer based on silver, a lower dielectric layer or lower dielectric layer sequence, whose refractive index is at least 1.9, is arranged below the electrically conductive layer, an upper dielectric layer or upper dielectric layer sequence, whose refractive index is at least 1.9, is arranged above the electrically conductive layer, a ratio of an optical thickness of the upper dielectric layer or upper dielectric layer sequence to an optical thickness of the lower dielectric layer or lower dielectric layer sequence is at least 1.7, and wherein a busbar provided for connection to a voltage source is arranged in each case on both sides of the sensor region and is connected to the electrically conductive coating such that a current path for a heating current is formed between the busbars, with said current path running across the sensor region.

2. The composite pane according to claim 1, that has light transmittance of at least 70% at an angle of incidence of 0? and light transmittance of at least 50% at an angle of incidence of 73.5?.

3. The composite pane according to claim 1, wherein a ratio of a transmittance of p-polarized light to a transmittance of s-polarized light at an angle of incidence of 70? is at least 1.20.

4. The composite pane according to claim 1, which has, in a spectral range from 400 nm to 680 nm, an averaged reflectance for p-polarized radiation of at least 10%, wherein a difference between a maximally occurring reflectance and a mean value of the reflectance as well as a difference between a minimally occurring reflectance and the mean value of the reflectance for p-polarized radiation is at most 3%.

5. The composite pane according to claim 1, which has an upper edge, a lower edge, and two side edges extending therebetween, wherein one busbar is arranged between the sensor region and one side edge of the two side edges and the other busbar is arranged between the sensor region and the other side edge of the two side edges.

6. The composite pane according to claim 1, wherein a heated region of the electrically conductive coating arranged between the busbars has an area of 20 cm.sup.2 to 100 cm.sup.2, while a majority of the composite pane is not heated by the electrically conductive coating.

7. The composite pane according to claim 1, wherein a region of the electrically conductive coating that contains the busbars and the sensor region situated therebetween is electrically isolated from the surrounding electrically conductive coating by an insulation line.

8. The composite pane according to claim 1, wherein the electrically conductive layer has a geometric thickness of 8 nm to 14 nm.

9. The composite pane according to claim 1, wherein the optical thickness of the upper dielectric layer or upper dielectric layer sequence is from 100 nm to 200 nm, and the optical thickness of the lower dielectric layer or lower dielectric layer sequence is from 50 nm to 100 nm.

10. The composite pane according to claim 1, wherein the upper dielectric layer or upper dielectric layer sequence and the lower dielectric layer or lower dielectric layer sequence, independently of one another, have, in each case: an anti-reflection layer based on silicon nitride, optionally, a matching layer based on zinc oxide, and optionally, a refractive-index-enhancing layer based on a mixed silicon-metal nitride.

11. The composite pane according to claim 1, wherein the outer pane and the inner pane are made of clear soda lime glass.

12. The composite pane according to claim 1, which is a vehicle windshield, wherein the sensor region is arranged outside and the HUD region is arranged at least partially within the field of vision B or I according to ECE-R43, wherein the field of vision B or I is not heated by the electrically conductive coating.

13. A projection assembly for a head-up display (HUD), at least comprising: a composite pane according to claim 1, a sensor attached to the interior-side surface of the inner pane and directed toward the sensor region, and an HUD projector, which is directed toward the HUD region and whose radiation is p-polarized.

14. The projection assembly according to claim 13, wherein the sensor is an IR sensor, a light sensor, a UV sensor, a camera, a radar system, or a lidar system.

15. The projection assembly according to claim 13, wherein the radiation of the projector strikes the windshield at an angle of incidence of 60? to 70?.

16. The composite pane according to claim 8, wherein the electrically conductive layer has a geometric thickness of 10 nm to 12 nm.

17. The composite pane according to claim 8, wherein the electrically conductive layer has a geometric thickness of 10 nm to 11 nm.

18. The composite pane according to claim 9, wherein the optical thickness of the upper dielectric layer or upper dielectric layer sequence is from 130 nm to 170 nm, and the optical thickness of the lower dielectric layer or lower dielectric layer sequence is from 60 nm to 90 nm.

Description

[0096] In the following, the invention is explained in detail with reference to drawings and exemplary embodiments. The drawings are schematic representations and are not true to scale. The drawings in no way restrict the invention.

[0097] They depict:

[0098] FIG. 1 a plan view of a composite pane according to the invention,

[0099] FIG. 2 a cross-section through the composite pane of FIG. 1,

[0100] FIG. 3 a first cross-section through the composite pane of FIG. 1 as part of a projection assembly according to the invention,

[0101] FIG. 4 a second cross-section through the composite pane of FIG. 1 as part of a projection assembly according to the invention,

[0102] FIG. 5 a schematic side view of a projection assembly according to the invention,

[0103] FIG. 6 a cross-section through an embodiment of the reflection coating according to the invention on an inner pane,

[0104] FIG. 7 reflection spectra of composite panes for p-polarized radiation in accordance with Examples 1 and 2 and Comparative Example 1,

[0105] FIG. 8 reflection spectra of composite panes for p-polarized radiation in accordance with Example 3 and Comparative Example 2, and

[0106] FIG. 9 reflection spectra of composite panes for p-polarized radiation in accordance with Examples 4 and 5 and Comparative Examples 3 and 4.

[0107] FIG. 10 reflection spectra of composite panes for p-polarized radiation in accordance with Example 6 and Comparative Example 5,

[0108] FIG. 11 plan views of the heatable sensor region of four embodiments of the composite pane according to the invention.

[0109] FIG. 1 and FIG. 2 depict in each case a detail of a composite pane 10 according to the invention. The composite pane 10 is the windshield of a passenger car. The composite pane 10 is constructed from an outer pane 1 and an inner pane 2 that are joined to one another via a thermoplastic intermediate layer 3. Its lower edge U is arranged downward in the direction of the engine of the passenger car; its upper edge O, upward in the direction of the roof. Two side edges S1, S2 extend between the upper edge O and the lower edge U.

[0110] In the installed position, the outer pane 1 faces the external surroundings; the inner pane 2, the vehicle interior. The outer pane 1 has an exterior-side surface I that, in the installed position, faces the external surroundings, and an interior-side surface II that, in the installed position, faces the interior. Likewise, the inner pane 2 has an exterior-side surface III that, in the installed position, faces the external surroundings, and an interior-side surface IV that, in the installed position, faces the interior. The outer pane 1 and the inner pane 2 are made, for example, of clear soda lime glass. The outer pane has, for example, a thickness of 2.1 mm; the inner pane 2, a thickness of 1.6 mm or 2.1 mm. The intermediate layer 3 is made, for example, of a PVB film with a thickness of 0.76 mm. The PVB film has a substantially constant thickness, apart from any surface roughness common in the artit is not implemented as a so-called wedge film.

[0111] The composite pane 10 has an HUD region B, which is arranged at least partially in the central field of vision (field of vision B per ECE-R43) of the composite pane 10. The HUD region B is intended to be irradiated by an HUD projector to generate an HUD image, which is perceived by a viewer (vehicle driver) as virtual images on the side of the composite pane 10 facing away from him.

[0112] The composite pane 10 also has a sensor region S. The sensor region S is arranged outside the central field of vision (field of vision B per ECE-R43), namely between this central field of vision and the upper edge O. The composite pane 10 is intended to be equipped with a sensor that is arranged in the interior relative to the sensor region S and is associated therewith in such a way that electromagnetic radiation passing through the sensor region S can be detected by the sensor.

[0113] The exterior-side surface III of the inner pane 2 is provided with an electrically conductive coating 20 according to the invention. The electrically conductive coating 20 serves, on the one hand, as a reflection surface for the radiation of the HUD projector, which is p-polarized in order to avoid reflections on the external surfaces I, IV facing away from the intermediate layer. Consequently, the electrically conductive coating 20 can also be referred to as a reflection coating. The electrically conductive coating 20 is compatible with typical sensors for passenger cars such that it does not have to be removed in the sensor region S, but covers it as well. There, on the other hand, it is provided to heat the sensor region S. For this purpose, the electrically conductive coating 20 is electrically conductively connected on both sides of the sensor region S to two busbars 7.1, 7.2. The busbars 7.1, 7.2 are arranged laterally relative to the sensor region S, with the first busbar 7.1 arranged between the sensor region S and the first side edge S1 of the composite pane 10 and the second busbar 7.2 arranged between the sensor region S and the second side edge S2. The busbars 7.1, 7.2 are implemented, for example, in the form of a screen print that contains glass frits and silver particles and is printed on the electrically conductive coating 20. Alternatively, metallic foils, for example, tinned-copper foils can be used as busbars 7.1, 7.2, which are placed on the electrically conductive coating 20 and optionally soldered to it. The busbars 7.1, 7.2 are intended to be connected to a voltage source (in particular the on-board voltage of the passenger car) such that a current path for a heating current is formed, which runs across the sensor region S between the busbars 7.1, 7.2. For this, each of the busbars 7.1, 7.2 is contacted with a flat conductor (not shown) that extends beyond the upper edge O of the composite pane 10 and can be connected to cables for connection to the voltage source.

[0114] FIG. 3 and FIG. 4 depict in each case a cross-section through the composite pane 10 of FIGS. 1 and 2 as part of a projection assembly according to the invention. The cross-section of FIG. 3 extends through the HUD region B; the cross-section of FIG. 4, through the sensor region S. The electrically conductive coating 20 is not shown for the sake of simplicity.

[0115] The projection assembly comprises the composite pane 10 and an HUD projector 4 that is directed at the HUD region B of the composite pane 10 (FIG. 3). There, the radiation of the HUD projector 4 is reflected by the electrically conductive coating 20 such that an HUD image is generated, which is perceived by a viewer 5 (vehicle driver) as virtual images on the side of the composite pane 10 facing away from him, if his eyes are situated within the so-called eyebox E. The radiation of the HUD projector 4 is p-polarized, in particular substantially purely p-polarized. Since the HUD projector 4 irradiates the composite pane 10 at an angle of incidence near Brewster's angle (not depicted realistically in the schematic drawing), the radiation of the projector 4 is only insignificantly reflected at the external surfaces I, IV of the composite pane 10. In contrast, the reflection coating 20 according to the invention is optimized for reflection of p-polarized radiation. It serves as a reflection surface for the radiation of the HUD projector 4 for generating the HUD projection.

[0116] Arranged in the interior relative to the sensor region S is a sensor 6 that can detect electromagnetic radiation (for example, light, IR-radiation, or radar radiation) passing through the sensor region S from outside (FIG. 4). The sensor 6 is, arranged for example, in a housing (not shown), which is attached, for example, is glued, to the interior-side surface IV of the inner pane 2. The sensor 6 is directed forward (relative to the direction of travel) substantially horizontally through the composite pane 10.

[0117] FIG. 5 illustrates some angles that occur in the projection assembly according to the invention. The composite pane 10 is a windshield that is installed in the vehicle with an installation angle de. The installation angle de is measured relative to the vertical and is, by way of example, 65?. The angle of incidence as with which radiation passing horizontally through the composite pane 10 from outside, which is then detected by the sensor 6, strikes the exterior-side surface I of the composite pane 10, is dependent on the installation angle ?.sub.E. The angle of incidence ?.sub.S is the angle of the exterior-side surface normal of the exterior-side surface I of the outer pane 1 relative to the horizontal. Based on simple geometry, it follows that the angle of incidence ?.sub.S corresponds to the installation angle ?.sub.E (at least in the simplified case of a flat composite pane 10 that is shown). The radiation of the HUD projector 4 strikes the composite pane 10 at an angle of incidence ?.sub.H, which is, by way of example, 65?. The angle of incidence is the angle between the projector radiation and the interior-side surface normal of the interior-side surface IV of the inner pane in the geometric center of the HUD region B.

[0118] In contrast to the simplified representation in the figure, real windshields are not flat, but curved. This results in location-dependency of the angles shown. The angle of incidence ?.sub.S used for the quantitative characterization is measured in the geometric center of the sensor region S; the angle of incidence ?.sub.H in the geometric center of the HUD region B.

[0119] FIG. 6 depicts the layer sequence of an embodiment of the electrically conductive coating 20 (reflection coating 20) according to the invention. The reflection coating 20 is a stack of thin layers. The reflection coating 20 includes an electrically conductive layer 21 based on silver. A metallic blocking layer 24 is arranged directly above the electrically conductive layer 21. Above that, an upper dielectric layer sequence is arranged, consisting, from bottom to top, of an upper matching layer 23b, an upper refractive-index-enhancing layer 23c, and an upper anti-reflection layer 23a. Arranged below the electrically conductive layer 21 is a lower dielectric layer sequence, consisting, from top to bottom, of a lower matching layer 22b, a lower refractive-index-enhancing layer 22c, and a lower anti-reflection layer 22a.

[0120] The layer structure shown is intended only as an example. The dielectric layer sequences can also include more or fewer layers, provided at least one dielectric layer is present above and below the conductive layer 21. The dielectric layer sequences also do not have to be symmetrical. Exemplary materials and layer thicknesses can be found in the following Examples.

[0121] The layer sequences of a composite pane 10 with the reflection coating 20 on the exterior-side surface III of the inner pane 2 in accordance with Examples 1 through 5 according to the invention, together with the materials and geometric layer thicknesses of the individual layers are presented in Table 1. Independent of one another, the dielectric layers can be doped, for example, with boron or aluminum.

TABLE-US-00001 TABLE 1 Layer Thickness Reference Example Example Example Example Example Material Character 1 2 3 4 5 Soda lime 1 2.1 mm 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass PVB 3 0.76 mm 0.76 mm 0.76 mm 0.76 mm 0.76 mm SiN 20 23a 70 nm 70 nm 60 nm 60 nm 50 nm SiZrN 23c 10 nm ZnO 23b 10 nm 10 nm 10 nm NiCr 24 0.3 nm 0.3 nm 0.3 nm 0.3 nm 0.3 nm Ag 21 11 nm 12 nm 12 nm 11 nm 14 nm ZnO 22b 10 nm 10 nm 10 nm SiZrN 22c 10 nm SiN 22a 30 nm 35 nm 25 nm 20 nm 25 nm Soda lime 2 2.1 mm 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass

[0122] For comparison, Comparative Examples 1 through 4, which do not conform to the features according to the invention, were investigated. Their layer sequences are shown in Table 2.

TABLE-US-00002 TABLE 2 Layer Thickness Reference Comparative Comparative Comparative Comparative Material Character Example 1 Example 2 Example 3 Example 4 Soda lime 1 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass PVB 3 0.76 mm 0.76 mm 0.76 mm 0.76 mm SiN 20 23a 50 nm 35 nm 30 nm 40 nm SiZrN 23c 10 nm 10 nm ZnO 23b 10 nm 10 nm 10 nm NiCr 24 0.3 nm 0.3 nm 0.3 nm 0.3 nm Ag 21 12 nm 13 nm 13 nm 13 nm ZnO 22b 10 nm 10 nm 10 nm SiZrN 22c 10 nm 10 nm SiN 22a 50 nm 35 nm 50 nm 40 nm Soda lime 2 2.1 mm 2.1 mm 2.1 mm 2.1 mm glass

[0123] The Examples and the Comparative Examples differ primarily in the ratio of the optical thickness of the upper dielectric layer sequence to the optical thickness of the lower dielectric layer sequence. The optical thickness is in each case the product of the geometric thickness and the refractive index (SiN: 2.0; SiZrN: 2.2, ZnO: 2.0) shown in Tables 1 and 2. The optical thicknesses and their ratio are summarized in Table 3. The ratio o describes the ratio of the optical thickness of the upper dielectric layer 23a or layer sequence 23a, 23b, optionally 23c to the optical thickness of the lower dielectric layer 22a or layer sequence 22a, 22b, optionally 22c.

TABLE-US-00003 TABLE 3 Optical Thickness of the Optical Thickness of Upper Dielectric Layer the Lower Dielectric Sequence Layer Sequence Ratio ? Example 1 140 60 2.33 Example 2 140 70 2.00 Example 3 140 70 2.00 Example 4 162 82 1.98 Example 5 120 70 1.71 Example 6 130 72 1.8 Comparative 100 100 1.00 Example 1 Comparative 90 90 1.00 Example 2 Comparative 102 142 0.72 Example 3 Comparative 122 122 1.00 Example 4

[0124] FIG. 7, FIG. 8, and FIG. 9 depict reflection spectra of composite panes 10 as in FIG. 2, in each case with a layer structure in accordance with Examples 1 through 5 according to the invention of Table 1 and in accordance with Comparative Examples 1 through 4 of Table 2. The reflection spectra were recorded with a light source that emits p-polarized radiation of uniform intensity in the spectral range observed, when irradiated via the inner pane 2 (so-called interior-side reflection) at an angle of incidence of 65? relative to the interior-side surface normal. The reflection measurement is thus approximated to the situation in the projection assembly. For better clarity, the Examples and Comparative Examples that have a similar layer structure are summarized in each case. In FIG. 7, Examples 1 and 2 and Comparative Example 1 are shown, having, in each case, only dielectric anti-reflection layers 22a, 23a. FIG. 8 shows Examples 3 and 5 and Comparative Example 2, having in each case dielectric anti-reflection layers 22a, 23a, and matching layeren 22b, 23b. FIG. 9 shows Example 4 and Comparative Examples 3 and 4, having in each case dielectric anti-reflection layers 22a, 23a, matching layers 22b, 23b, and refractive-index-enhancing layers 22c, 23c.

[0125] From the graphic representation of the spectra, it is already apparent that the Examples according to the invention with the ratio according to the invention of the optical thicknesses of the upper and lower dielectric layer or layer sequence result in a substantially smoother spectrum in the spectral range of interest from 400 nm to 680 nm. This ensures a more color-neutral display of the HUD projection. In addition, the general color impression of the pane is improved.

[0126] The averaged reflectance for p-polarized radiation as well as the differences of the maximum and minimum values relative to the reflectance of Examples 1 through 5 are summarized in Table 4; the corresponding values for the Comparative Examples 1 through 4, in Table 5. Also, the standard deviation of the reflection spectrum is indicated in each case. The analyses refer in each case to the spectral range from 400 nm to 680 nm.

TABLE-US-00004 TABLE 4 Example Example Example Example Example Example 1 2 3 4 5 6 Averaged reflectance 17.6% 19.9% 20.2% 16.6% 23.8% 12.7% for p-polarized radiation, 400 nm-680 nm difference between the 1.8% 1.7% 2.0% 1.1% 2.6% 1.4% maximally occurring reflectance and the mean difference between the 1.1% 0.7% 1.5% 0.9% 1.2% 0.7% minimally occurring reflectance and the mean Standard deviation, 0.55% 0.48% 0.60% 0.27% 1.08% 0.65% 400 nm-680 nm

TABLE-US-00005 TABLE 5 Comp. Comp. Comp. Comp. Comp. Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 Averaged reflectance 17.6% 19.8% 23.1% 22.0% 2.0% for p-polarized radiation, 400 nm-680 nm difference between the 4.2% 3.6% 5.1% 5.8% 0.1% maximally occurring reflectance and the mean difference between the 1.4% 1.6% 2.2% 2.3% 0.7% minimally occurring reflectance and the mean Standard deviation. 1.49% 1.11% 2.52% 2.70% 0.16% 400 nm-680 nm

[0127] Although relatively high average reflection values can also be achieved in the Comparative Examples, the spectra in the relevant spectral range from 400 nm to 680 nm are subject to strong fluctuations, which can lead to undesirable color shifts in the HUD image and to a poorer color impression of the pane for the viewer. In contrast, the ratio of the optical thicknesses of the lower and upper dielectric layer/layer sequence of the examples according to the invention results in a significant smoothing of the reflection spectrum, which leads to a more color-neutral reproduction of the projector image and a more color-neutral overall impression.

[0128] Table 6 shows the layer sequence of a composite pane 10 with the reflection coating 20 on the exterior-side surface III of the inner pane 2 according to another Example 6 according to the invention, together with the materials and geometric layer thicknesses of the individual layers. The dielectric layers can, independently of one another, be doped, for example, with boron or aluminum.

TABLE-US-00006 TABLE 6 Reference Layer Thickness Material Character Example 6 Soda lime glass 1 2.1 mm PVB 3 0.76 mm SiN 20 23a 55 nm SiZrN 23c ZnO 23b 10 nm NiCr 24 0.3 nm Ag 21 10 nm ZnO 22b 10 nm SiZrN 22c 10 nm SiN 22a 15 nm Soda lime glass 2 1.6 mm

[0129] The outer pane 1 and the inner pane 2 of Example 6 were again made of clear soda lime glass. Comparative Example 5 was investigated for comparison. Comparative Example 5 had no electrically conductive coating 20; the thicknesses of the outer pane 1 and of the inner pane 2 corresponded to those of Example 6. In contrast, the outer pane 1 was made of green-colored soda lime glass, while the inner pane 2 was made of clear soda lime glass.

[0130] Table 7 compares transmittance values at different radiation angles (relative to the exterior-side surface normals) of Examples and Comparative Examples with one another. The transmittance values were measured with illuminant A, the angle listed indicates the angle of incidence.

[0131] All panes have light transmittance greater than 70% at an angle of incidence of 0? such that they can be used as a windshield.

[0132] The comparison of Examples 1 through 6 further shows that the thinner the silver layer, the higher the light transmittance at angles of incidence greater than 0?. This is advantageous in terms of the functionality of the sensor.

[0133] At an angle of incidence of 0? (the light strikes the composite pane 10 perpendicularly), the transmittance of Example 6 and of Comparative Example 5 is comparable. However, as the angle of incidence increases, the transmittance of Example 6 is significantly higher. Since the radiation detected by the sensor 6 passes through the composite pane 10 at an angle that is typically in the range of the specified values, the detection efficiency of Example 6 is significantly higher.

[0134] The polarization ratio, defined as the ratio of the transmittance of p-polarized radiation TL(p-pol) to the transmittance of s-polarized radiation TL(s-pol), measured here at an angle of incidence of 70?, is also compared. It can be seen that the Examples according to the invention tend to have a significantly higher polarization ratio than the Comparative Examples, such that s-polarized reflections, for example, from a wet road, have a less interfering effect on the sensor 6. In particular, when comparing Example 6 to Comparative Examples 1 and 5, which have essentially the same light transmittance (0?), the advantageous influence of the layer structure according to the invention on the polarization ratio can be seen.

TABLE-US-00007 TABLE 7 TL A (0?) TL A (60?) TL A (70?) TL A (73.5?) [00001]$\frac{\mathrm{TL}\left(p-\mathrm{pol}\right)}{\mathrm{TL}\left(s-\mathrm{pol}\right)}\left(70?\right)$ Example 1 73.5% 68.1% 59.2% 53.7% 1.68 Example 2 72.6% 67.2% 58.3% 52.9% 1.64 Example 3 71.9% 66.7% 58.0% 52.6% 1.64 Example 4 73.9% 68.7% 59.7% 54.1% 1.66 Example 5 71.2% 65.0% 56.2% 51.0% 1.56 Example 6 80.0% 73.4% 63.1% 56.9% 1.67 Comparative 80.1% 72.6% 62.0% 55.8% 1.58 Example 1 Comparative 78.5% 70.3% 60.0% 54.1% 1.56 Example 2 Comparative 73.2% 68.3% 59.0% 53.4% 1.56 Example 3 Comparative 74.2% 69.4% 59.8% 54.1% 1.54 Example 4 Comparative 80.1% 71.3% 60.4% 53.9% 1.49 Example 5

[0135] FIG. 10 shows reflectance spectra of Example 6 per Table 6 and Comparative Example 5. The reflectance spectra were recorded under the same conditions as the reflectance spectra of FIG. 7 through 9. Since Comparative Example 5 had no reflection coating 20, no satisfactory reflectance for p-polarized radiation occurs, as expected. In contrast, good values are obtained with Example 6. The quantitative analyses of the reflectance spectra are indicated In Tables 4 and 5; the optical thicknesses of Example 6, in Table 3.

[0136] FIG. 11 depicts various embodiments of the heatable sensor region S of the composite pane according to the invention. In the embodiment of FIG. 11a, the busbars 7.1, 7.2 are connected to the region of the coating 20 that is to be heated and contains the sensor region S, without said region being isolated from the surrounding coating. When a voltage is applied to the busbars 7.1, 7.2, a heating current flows through the region of the coating 20 between them such that the sensor window S is heated.

[0137] In the embodiment of FIG. 11b, a region of the coating 20 that contains the sensor region S is materially separated from the surrounding regions of the coating 20 by an insulation line 8 and is, consequently, electrically insulated. The insulation line 8 is implemented as a circumferential line that encloses, for example, a rectangular shape. The region (heating region) delimited by the insulation line 8 is completely surrounded by other regions of the coating 20. The busbars 7.1, 7.2 are arranged completely within the heating region. As a result of the insulation lines 8, the heating current is limited to the region intended for heating; outward radiation of the heating current can be prevented. The insulation line 8 is, for example, produced by laser decoating.

[0138] FIG. 11c shows another embodiment of the separation of the heating region by insulation lines 8. A region of the coating 20 that contains the busbars 7.1, 7.2 and the sensor window S is isolated from the surrounding regions of the coating 20 by a first (outer) insulation line 8. The beginning and the end of this first insulation line 8 are located at the edge of the coating 20. This separated, for example, rectangular, region is adjacent said edge of the coating 20, which coincides, in the representation, with the upper edge O of the composite pane; whereas, in reality, there is often an uncoated edge region such that the insulation line 8 does not extend all the way to the upper edge O but only up to this edge of the coating 20 facing it. This embodiment has the advantage that the busbars 7.1, 7.2 can extend all the way to or close to to the upper edge O of the composite pane, which is advantageous in terms of their electrical connection. Between the busbars, a further region of the coating 20 adjacent the edge is excluded from the heating region by a second (inner) insulation line 8. The beginning and the end of this second insulation line 8 are located at the edge of the coating 20. Starting from the edge of the coating 20, the two insulation lines have in each case two end sections that extend parallel to the busbars 7.1, 7.2 and a middle section therebetween that runs substantially parallel to the current path. The actual heating region is then delimited on the one hand by the busbars 7.1, 7.2; on the other, by the middle sections of the insulation lines 8.

[0139] The separation of the heating region from the surrounding coating 20 is realized in FIG. 11d in a manner similar to that in FIG. 11c with two insulation lines 8. A further insulation line 9 runs through the heating region substantially parallel to the desired current direction. The flow of current can be selectively directed by the insulation line 9. This is, in particular, advantageous when the busbars 7.1, 7.2, as in the case shown, do not run parallel to one another, such that the distance between them and, consequently, the electrical resistance between them is not constant. By directing a current path using the insulation line 9, it can be ensured that the entire sensor region S is heated as uniformly as possible. Instead of just one, there can be multiple insulation lines 9.

LIST OF REFERENCE CHARACTERS

[0140] (10) composite pane [0141] (1) outer pane [0142] (2) inner pane [0143] (3) thermoplastic intermediate layer [0144] (4) projector [0145] (5) viewer/vehicle driver [0146] (6) sensor [0147] (7.1) first busbar [0148] (7.2) second busbar [0149] (8) insulation line for delimiting the heated coating 20 in the sensor region S from the surrounding coating 20 [0150] (9) insulation line for guiding the current path within the sensor region S [0151] (20) electrically conductive coating/reflection coating [0152] (21) electrically conductive layer [0153] (22a) first lower dielectric layer/anti-reflection layer [0154] (22b) second lower dielectric layer/matching layer [0155] (22c) third lower dielectric layer/refractive-index-enhancing layer [0156] (23a) first upper dielectric layer/anti-reflection layer [0157] (23b) second upper dielectric layer/matching layer [0158] (23c) third upper dielectric layer/refractive-index-enhancing layer [0159] (24) metallic blocking layer [0160] (O) upper edge of the composite pane 10 [0161] (U) lower edge of the composite pane 10 [0162] (S1) first side edge of the composite pane 10 [0163] (S2) second side edge of the composite pane 10 [0164] (B) HUD region of the composite pane 10 [0165] (E) eyebox [0166] (S) sensor region of the composite pane 10 [0167] (I) exterior-side surface of the outer pane 1 [0168] (II) interior-side surface of the outer pane 1 [0169] (III) exterior-side surface of the inner pane 2 [0170] (IV) interior-side surface of the inner pane 2 [0171] (?.sub.E) installation angle of the composite pane 10 relative to vertical [0172] (?.sub.S) angle of incidence of the radiation detected by the sensor 6 [0173] (?.sub.H) angle of incidence of the HUD projector 4