COMPOSITE PANE FOR A HEAD-UP DISPLAY WITH AN ELECTRICALLY CONDUCTIVE COATING AND AN ANTI-REFLECTIVE COATING

Abstract

A composite pane for a head-up display with an upper edge, a lower edge, and an HUD region, including an outer pane and an inner pane, which are joined to one another via a thermoplastic intermediate layer, and a transparent, electrically conductive coating on the surface of the inner pane facing the intermediate layer or within the intermediate layer, wherein the intermediate layer is formed by at least one ply of thermoplastic material, which is arranged between the electrically conductive coating and the outer pane, wherein the thickness of the ply of thermoplastic material is variable with a wedge angle over its vertical course between the lower edge and the upper edge at least in the HUD region, and wherein an anti-reflective coating is applied on the surface of the inner pane facing away from the intermediate layer.

Claims

1. A composite pane for a head-up display with an upper edge, a lower edge, and an HUD region, comprising an outer pane and an inner pane, which are joined to one another by a thermoplastic intermediate layer, and a transparent, electrically conductive coating on a surface of the inner pane facing the intermediate layer or within the intermediate layer, wherein the intermediate layer is formed by at least one ply of thermoplastic material, which is arranged between the electrically conductive coating and the outer pane, wherein a thickness of the ply of thermoplastic material is variable with a wedge angle over its vertical course between the lower edge and the upper edge at least in the HUD region, and wherein an anti-reflective coating is applied on the surface of the inner pane facing away from the intermediate layer.

2. The composite pane according to claim 1, wherein the wedge angle is suitable for superimposing the reflections at the electrically conductive coating and at the exterior-side surface of the outer pane or for at least reducing the distance between them.

3. The composite pane according to claim 1, wherein the electrically conductive coating includes at least two electrically conductive layers, which are arranged between two dielectric layers or layer sequences.

4. The composite pane according to claim 1, wherein the anti-reflective coating is formed from alternatingly arranged layers with different refractive indices.

5. A projection arrangement for a head-up display, at least comprising a composite pane according to claim 1, and a projector that is aimed at the HUD region.

6. The projection arrangement according to claim 5, wherein the light of the projector has at least one p-polarised component, and wherein the composite pane has, in the spectral range from 400 nm to 650 nm, only a single local reflection maximum for p-polarised light, which is in the range from 510 nm to 550 nm.

7. The projection arrangement according to claim 6, wherein, in the spectral range from 400 nm to 650 nm, the difference between the reflectance of a local reflection maximum and he a minimally occurring reflectance for p-polarised light is at most 10%.

8. The projection arrangement according to claim 6, wherein the reflectance for s-polarised light in the spectral range from 450 nm to 600 nm is substantially constant such that a difference between the maximally occurring reflectance and a mean as well as a difference between a minimally occurring reflectance and the mean are at most 5%.

9. The projection arrangement according to claim 5, wherein the proportion of p-polarised light in the total light of the projector is from 20% to 80%.

10. The projection arrangement according to claim 5, wherein the electrically conductive coating includes at least four electrically conductive layers, which are in each case arranged between two dielectric layers or layer sequences.

11. The projection arrangement according to claim 10, wherein the electrically conductive layers are based on silver and have, in each case, a layer thickness from 5 to 15 nm, wherein a total layer thickness of all electrically conductive layers is from 20 nm to 50 nm.

12. The projection arrangement according to claim 10, wherein each dielectric layer sequence includes an anti-reflective layer, and wherein the anti-reflective layer below the first electrically conductive layer has a thickness from 15 nm to 25 nm, the anti-reflective layer between the first and the second electrically conductive layer has a thickness from 25 to 35 nm, the anti-reflective layer between the second and the third electrically conductive layer has a thickness from 45 nm to 55 nm, the anti-reflective layer between the third and the fourth electrically conductive layer has a thickness from 15 nm to 25 nm, and the anti-reflective layer above the fourth electrically conductive layer has a thickness from 8 nm to 18 nm.

13. The projection arrangement according to claim 10, wherein all anti-reflective layers that are arranged between two electrically conductive layers are divided into a dielectric layer having a refractive index smaller than 2.1, and an optically high refractive layer having a refractive index greater than or equal to 2.1.

14. The projection arrangement according to claim 5, wherein the anti-reflective coating includes the following layers, starting from the inner pane: a high refractive layer based on silicon nitride with a thickness from 15 nm to 25 nm, a low refractive layer based on silicon dioxide with a thickness from 15 nm to 25 nm, a high refractive layer based on silicon nitride with a thickness from 90 nm to 110 nm, a low refractive layer based on silicon dioxide with a thickness from 80 nm to 100 nm.

15. A method comprising utilizing a composite pane according to claim 1, in a motor vehicle as a windshield that serves as a projection surface of a head-up display.

16. The composite pane according to claim 3, wherein the electrically conductive coating includes at least four electrically conductive layers, which are in each case arranged between two dielectric layers or layer sequences.

17. The projection arrangement according to claim 7, wherein the difference between the reflectance of the local reflection maximum and the minimally occurring reflectance for p-polarised light is at most 8%.

18. The projection arrangement according to claim 8, wherein the difference between the maximally occurring reflectance and the mean as well as the difference between the minimally occurring reflectance and the mean are at most 1%.

19. The projection arrangement according to claim 9, wherein the proportion of p-polarised light in the total light of the projector is from 50% to 80%.

20. The projection arrangement according to claim 13, wherein the dielectric layer is based on silicon nitride, and the optically high refractive layer is based on a mixed silicon/metal nitride.

Description

[0100] 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.

[0101] They depict:

[0102] FIG. 1 a cross-section through a composite pane according to the invention,

[0103] FIG. 2 the composite pane of FIG. 1 as part of an HUD projection arrangement,

[0104] FIG. 3 a plan view of the composite pane of FIGS. 1 and 2,

[0105] FIG. 4 a cross-section through a preferred electrically conductive coating,

[0106] FIG. 5 a cross-section through a preferred anti-reflective coating,

[0107] FIG. 6 reflection spectra of a composite pane with an electrically conductive coating according to FIG. 4 and a composite pane with a prior art electrically conductive coating.

[0108] FIG. 1 depicts an embodiment of a composite pane 10 according to the invention that is provided as 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 by a thermoplastic intermediate layer 3. In the installed position, the outer pane 1 faces the outside environment; the inner pane 2, the vehicle interior. The outer pane 1 has an exterior-side surface I that faces the outside environment in the installed position and an interior-side surface II that faces the interior in the installed position. Likewise, the inner pane 2 has an exterior-side surface III that faces the outside environment in the installed position and an interior-side surface IV that faces the interior in the installed position. The lower edge U of the composite pane 10 is arranged downward in the direction of the engine of the passenger car; its upper edge O, upward in the direction of the roof.

[0109] The outer pane 1 and the inner pane 2 are made, for example, of soda lime glass. The outer pane 1 has, for example, a thickness of 2.1 mm; the inner pane 2, a thickness of 1.6 mm. The intermediate layer 3 is made of a single ply 3a of thermoplastic material, for example, of a PVB film with a thickness of 0.76 mm (measured at the lower edge U). The intermediate layer 3 is wedge like with a wedge angle such that the thickness of the intermediate layer 3 and, thus, of the entire composite pane 10 increases from bottom to top.

[0110] The composite pane 10 also includes an electrically conductive coating 20 that is applied on the exterior-side surface III of the inner pane 2 and is provided, for example, as an IR-reflecting coating or as a heatable coating. The composite pane also includes an anti-reflective coating 30 that is applied on the interior-side surface IV of the inner pane 2.

[0111] FIG. 2 depicts a projection arrangement according to the invention for an HUD. The projection arrangement includes, in addition to the composite pane 10 of FIG. 1, a projector 4 that is aimed at a region B of the composite pane 10. In the region B, usually referred to as the HUD region, the projector 4 can generate images that are 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 eye box E.

[0112] In generic projection arrangements, the light of the projector 4 is partially reflected in each case at the interior-side surface IV of the inner pane 1 (primary reflection) and at the exterior-side surface I of the outer pane 1 (secondary reflection). In a prior art composite pane 10, the two reflections result in two HUD projections offset relative to one another (a primary image and a so-called ghost image), which is distracting for the viewer 5. By means of the anti-reflective coating 30, the reflection at the interior-side surface IV of the inner pane 1 is drastically reduced. As for the glass surfaces, only the exterior-side surface I of the outer pane 1 contributes to the HUD image generated. There is either no perceivable ghost image or only a barely perceivable ghost image due to the two external glass surfaces I, IV.

[0113] However, the electrically conductive coating 20 on the exterior-side surface II of the inner pane 2 constitutes a further reflection surface for the light of the projector 4. In prior art composite panes with parallel surfaces, this would also result in a ghost image. In order to avoid or at least to reduce this, the intermediate layer 3 is wedge-like. The thickness of the intermediate layer 3 increases continuously over its vertical course from the lower edge U to the upper edge O. For the sake of simplicity, in the figures, the increase in thickness is depicted linearly, but can also have more complex profiles. The wedge angle describes the angle between the two surfaces of the intermediate layer and is, for example, about 0.5 mrad. Due to the wedge-like intermediate layer, which results in an angled arrangement of the two reflection surfaces I, 20, the primary image and the ghost image are ideally superimposed exactly, but, at least the distance between them is reduced.

[0114] FIG. 3 depicts a plan view of the composite pane 10 of FIG. 1. The upper edge O, the lower edge U, and the HUD region B are discernible.

[0115] The light of the projector 4 comprises a mixture of s-polarised and p-polarised components. Since the projector 4 irradiates the composite pane 10 with an angle of incidence of about 65, which is close to Brewster's angle, the s-polarised light components are predominately reflected by the surfaces of the composite pane 10. The electrically conductive coating 20 is, on the other hand, optimized for the reflection of the p-polarised light components. A viewer 5 with polarisation-selective sunglasses that allow only p-polarised light to pass can, consequently, perceive the HUD projection. With prior art projection arrangements that operate only with s-polarised light, this is not the case. A viewer 5 without sunglasses sees the sum of s-polarised and p-polarised light such that the intensity of the HUD projection is not reduced for him.

[0116] The coating 20 is in particular optimised for the reflection of p-polarised light, if it has only a single local reflection maximum for p-polarised light in the spectral range from 400 nm to 650 nm, which is in the range from 510 nm to 550 nm.

[0117] FIG. 4 depicts the layer sequence of an embodiment of the electrically conductive coating 20 that is optimised for the reflection of p-polarised light. The coating 20 contains four electrically conductive layers 21 (21.1, 21.2, 21.3, 21.4). Each electrically conductive layer 21 is in each case arranged between two of a total of five anti-reflective layers 22 (22.1, 22.2, 22.3, 22.4, 22.5). The anti-reflective layers 22.2, 22.3, 22.4 that are arranged between two electrically conductive layers 21 are in each case subdivided into a dielectric layer 22a (22a.2, 22a.3, 22a.4) and an optically high refractive layer 22b (22b.2, 22b.3, 22b.4). The coating 20 also contains three smoothing layers 23 (23.2, 23.3, 23.4), four first matching layers 24 (24.1, 24.2, 24.3, 24.4), four second matching layers 25 (25.2, 25.3, 25.4, 25.5), and four blocking layers 26 (26.1, 26.2, 26.3, 26.4).

[0118] The layer sequence can be seen schematically in the figure. The layer sequence of a composite pane 10 with the coating 20 on the exterior-side surface III of the inner pane 2 is also presented, together with the materials and layer thicknesses of the individual layers, in Table 1 (Example). Table 1 also depicts the layer sequence of an electrically conductive coating, as it is currently already in use (Comparative Example). It can be seen that the preferred reflection properties of the coating 20 were achieved by suitable optimisation of the layer thicknesses of the individual layers.

[0119] FIG. 5 depicts the layer sequence of an anti-reflective coating 30, comprising two high refractive layers 31 (31.1, 31.2) and two low refractive layers 32 (32.1, 32.2). The layer sequence can be seen schematically in the figure. The layer sequence of a composite pane 10 according to the invention with the electrically conductive coating 20 on the exterior-side surface III of the inner pane 2 and the anti-reflective coating 30 on the interior-side surface IV of the inner pane 2 is also shown in Table 2, together with the materials and layer thicknesses of the individual layers. The anti-reflective coating 30 is adjusted such that it does not substantially shift the reflection spectrum of the composite pane 10 for p-polarised light such that the preferred properties with regard to p-polarised light are still retained.

TABLE-US-00001 TABLE 1 Layer Thickness Material Reference Character Example Comparative Example Glass 1 .sup.2.1 mm .sup.2.1 mm PVB 3 0.76 mm 0.76 mm SiZrN 20 22.5 12.3 nm 25.2 nm ZnO 25.5 10.0 nm 10.0 nm NiCr 26.4 0.2 nm 0.2 nm Ag 21.4 5.3 nm 14.1 nm ZnO 24.4 10.0 nm 10.0 nm SnZnO:Sb 23.4 7.0 nm 7.0 nm SiZrN 22b.4 22.4 15.0 22.9 nm SiN 22a.4 5.2 nm 29.8 nm ZnO 25.4 10.0 nm 10.0 nm NiCr 26.3 0.2 nm 0.2 nm Ag 21.3 9.6 nm 14.2 nm ZnO 24.3 10.0 nm 10.0 nm SnZnO:Sb 23.3 7.0 nm 7.0 nm SiZrN 22b.3 22.3 15.0 nm 20.1 nm SiN 22a.3 35.1 nm 29.6 nm ZnO 25.3 10.0 nm 10.0 nm NiCr 26.2 0.2 nm 0.2 nm Ag 21.2 12.4 nm 17.1 nm ZnO 24.2 10.0 nm 10.0 nm SnZnO:Sb 23.2 7.0 nm 7.0 nm SiZrN 22b.2 22.2 15.0 nm 19.4 nm SiN 22a.2 15.5 nm 34.1 nm ZnO 25.2 10.0 nm 10.0 nm NiCr 26.1 0.2 nm 0.2 nm Ag 21.1 9.5 nm 11.7 nm ZnO 24.1 10.0 nm 10.0 nm SiN 22.1 21.2 nm 28.8 nm Glass 2 .sup.1.6 mm 1.6 nm

TABLE-US-00002 TABLE 2 Material Reference Character Layer Thickness SiO 30 32.2 92.7 nm SiN 31.2 102.2 nm SiO 32.1 20.5 nm SiN 31.1 19.9 nm Glass 2 1.6 mm 20 (See Table 1) PVB 3 0.76 mm Glass 1 2.1 mm

[0120] FIG. 6 depicts the reflection spectrum of a composite pane 10 with a prior art conductive coating 20 per the Comparative Example and a preferred conductive coating 20 per the Example (cf. Table 1) for p-polarised light (Part a) and for s-polarised light (Part b). The spectra were measured on the interior-side at an angle of incidence of 65, thus simulating the reflection behaviour for the HUD projector.

[0121] The prior art coating per the Comparative Example, as it has been used to date, has, in the spectral range from 400 nm to 650 nm for p-polarised light, two local reflection maxima: at 476 nm and at 600 nm. The difference between the reflectance of the local reflection maximum and the minimally occurring reflectance for p-polarised light in the spectral range from 400 nm to 650 nm is significantly more than 10%.

[0122] In contrast, the preferred coating per the Example has, in the spectral range from 400 nm to 650 nm for p-polarised light, only a single local reflection maximum. The local reflection maximum is situated at 516 nm, i.e., in the green spectral range, for which the human eye is particularly sensitive. The difference between the reflectance of the local reflection maximum and the minimally occurring reflectance for p-polarised light in the spectral range from 400 nm to 650 nm is only 6.7%.

[0123] For s-polarised light as well, the reflection spectrum of the preferred coating is significantly flatter than that of the prior art coating in the spectral range from 450 nm to 600 nm. The difference between the maximally occurring reflectance and the mean is 0.4%; the difference between the minimally occurring reflectance and the mean is 0.3%.

[0124] By means of the preferred embodiment of the coating of the Example, an HUD image with neutral colouration is generated. In addition, the relative proportions of s-polarised and p-polarised light can be freely selected without being associated with a colour shift or other undesirable effects. The light components are thus adjustable according to the requirements of the individual case, without imposing limits on the person skilled in the art due to the coating. A ratio can be set such that optimum intensity of the HUD projection is achieved for drivers with and without polarisation-selective sunglasses.

[0125] Table 3 presents the total reflectance with various polarisation proportions of the projector light, on the one hand, for a prior art composite pane (coating 20 as specified in Table 1 under Comparative Example, no anti-reflective coating 30), on the other, for a composite pane according to the invention (coating 20 as specified in Table 1 under Example, structure with anti-reflective coating 30 as specified in Table 2). It is clear to see that the reflectance for p-polarised light (perceived by a viewer with polarisation-selective sunglasses) is significantly increased at any polarisation ratio. The reflectance for s- and p-polarised light (perceived by a viewer without polarisation-selective sunglasses) is also increased starting at a p-polarisation proportion of 50%. Overall, a more intense image results.

TABLE-US-00003 TABLE 3 Light Components Total Reflectance/% of the Projector Comparative Light Example Example p s s + p p s + p p 0 100 33.1 0 26.4 0.0 10 90 30.5 0.7 25.4 1.6 20 80 27.9 1.4 24.4 3.3 30 70 25.3 2.1 23.4 4.9 40 60 22.7 2.8 22.4 6.6 50 50 20.1 3.5 21.4 8.2 60 40 17.4 4.2 20.4 9.8 70 30 14.8 4.9 19.4 11.5 80 20 12.2 5.6 18.4 13.1 90 10 9.6 6.3 17.4 14.8 100 0 7.0 7.0 16.4 16.4

List of Reference Characters:

[0126] (10) composite pane

[0127] (1) outer pane

[0128] (2) inner pane

[0129] (3) thermoplastic intermediate layer

[0130] (3a) ply of thermoplastic material of the intermediate layer

[0131] (4) projector

[0132] (5) viewer/vehicle driver

[0133] (20) electrically conductive coating

[0134] (21) electrically conductive layer

[0135] (21.1), (21.2), (21.3), (21.4) 1., 2., 3., 4. electrically conductive layer

[0136] (22) anti-reflective layer

[0137] (22.1), (22.2), (22.3), (22.4), (22.5) 1., 2., 3., 4., 5. anti-reflective layer

[0138] (22a) dielectric layer of the anti-reflective layer 4

[0139] (22a.2), (22a.3), (22a.4) 1., 2., 3. dielectric layer

[0140] (22b) optically high refractive layer of the anti-reflective layer 4

[0141] (22b.2), (22b.3), (22b.4) 1., 2., 3. optically high refractive layer

[0142] (23) smoothing layer

[0143] (23.2), (23.3), (23.4) 1., 2., 3. smoothing layer

[0144] (24) first matching layer

[0145] (24.1), (24.2), (24.3), (24.4) 1., 2., 3., 4. first matching layer

[0146] (25) second matching layer

[0147] (25.2), (25.3), (25.4), (25.5) 1., 2., 3., 4. second matching layer

[0148] (26) blocking layer

[0149] (26.1), (26.2), (26.3), (26.4) 1., 2., 3., 4. blocking layer

[0150] (30) anti-reflective coating

[0151] (31) high refractive layer of the anti-reflective coating 30

[0152] (31.1), (31.2) 1., 2. high refractive layer

[0153] (32) low refractive layer of the anti-reflective coating 30

[0154] (32.1), (32.2) 1., 2. low refractive layer

[0155] (O) upper edge of the composite pane 10

[0156] (U) lower edge of the composite pane 10

[0157] (B) HUD region of the composite pane 10

[0158] (E) eye box

[0159] (I) exterior-side surface of the outer pane 1, facing away from the intermediate layer 3

[0160] (II) interior-side surface of the outer pane 1, facing the intermediate layer 3

[0161] (III) exterior-side surface of the inner pane 2, facing the intermediate layer 3

[0162] (IV) interior-side surface of the inner pane 2, facing away from the intermediate layer 3

[0163] wedge angle