PROJECTION ASSEMBLY FOR A HEAD-UP DISPLAY (HUD) WITH P-POLARIZED RADIATION

Abstract

A projection arrangement for a head-up display (HUD), includes a composite pane, including an outer pane and an inner pane, which are connected to one another via a thermoplastic intermediate layer and having an HUD region, and an HUD projector, which is directed toward the HUD region. The radiation of the projector is at least partially p-polarised, and the composite pane is provided with a reflective layer which is suitable for reflecting p-polarised radiation. The reflective layer includes precisely one electrically conductive layer based on silver, which layer is arranged in a planar manner between a first layer module and a second layer module, the first layer module is the layer module of the reflective layer closest to the HUD projector, the first layer module and the second layer module include dielectric layers or layer sequences, and the first layer module contains a layer based on a transparent conductive oxide.

Claims

1. A projection arrangement for a head-up display, at least comprising: a composite pane, comprising an outer pane and an inner pane, which are connected to one another via a thermoplastic intermediate layer and having an HUD region; and an HUD projector, which is directed toward the HUD region; wherein a radiation of the projector is at least partially p-polarised, and the composite pane is provided with a reflective layer which is suitable for reflecting p-polarised radiation; and wherein the reflective layer comprises precisely one electrically conductive layer based on silver, which electrically conductive layer is arranged in a planar manner between a first layer module and a second layer module, the first layer module is a layer module of the reflective layer closest to the HUD projector, the first layer module and the second layer module comprise dielectric layers or layer sequences, and at least the first layer module contains at least one layer based on a transparent conductive oxide.

2. The projection arrangement according to claim 1, wherein the at least one layer based on a transparent conductive oxide contains indium tin oxide (ITO), indium zinc mixed oxide (IZO), fluorine-doped tin oxide (SnO.sub.2:F), aluminium-doped zinc oxide, (ZnO:Al), gallium-doped zinc oxide (ZnO:Ga), antimony-doped tin oxide (ATO, SnO.sub.2:Sb) and/or niobium-doped titanium oxide (TiO.sub.2:Nb).

3. The projection arrangement according to claim 2, wherein the at least one layer based on a transparent conductive oxide contains indium tin oxide (ITO) and is deposited by physical vapour deposition with an oxygen content of 0% volume fraction to 5% volume fraction in the process gas.

4. The projection arrangement according to claim 1, wherein the reflective layer directly adjacent to the layer based on a transparent conductive oxide comprises at least one dielectric barrier layer that inhibits diffusion of oxygen.

5. The projection arrangement according to claim 1, wherein the first layer module comprises dielectric layers or layer sequences and a layer based on a transparent conductive oxide, and the second layer module comprises dielectric layers or layer sequences and no layers based on a transparent conductive oxide.

6. The projection arrangement according to claim 1, wherein at least the first layer module comprises dielectric layers or layer sequences and a layer based on a transparent conductive oxide, and the layer based on a transparent conductive oxide is the layer of the first layer module closest to the HUD projector.

7. The projection arrangement according to claim 1, wherein the reflective layer is arranged on a surface facing the thermoplastic intermediate layer (II, III) of the outer pane or of the inner pane or within the thermoplastic intermediate layer.

8. The projection arrangement according to claim 1, wherein a blocker layer is arranged between the electrically conductive layer and the adjacent first or second layer module with a thickness of less than 1 nm.

9. The projection arrangement according to claim 1, wherein a thickness of the electrically conductive layer is at least 12 nm and at most 25 nm.

10. The projection arrangement according to claim 1, wherein a thickness of the at least one layer based on the transparent conductive oxide is from 20 nm to 150 nm.

11. The projection arrangement according to claim 1, wherein an optical thickness of the dielectric layers or layer sequences is from 30 nm to 150 nm.

12. The projection arrangement according to claim 1, wherein the dielectric layers or layer sequences comprise one or more of the following layers: an anti-reflective layer with a refractive index of at least 1.9, a refractive-index-enhancing layer with a refractive index of at least 2.1, a matching layer.

13. The projection arrangement according to claim 1, wherein the composite pane with the reflective layer has an integrated light reflection with respect to p-polarised radiation of at least 15%, measured with a p-polarised light source of the light type A at an angle of incidence of 65 and a viewing angle of 65 to a surface normal of the surface facing away from the thermoplastic intermediate layer of the inner pane.

14. The projection arrangement according to claim 1, wherein the outer pane is tinted or coloured and has a light transmittance of at least 80%.

15. A method comprising providing a projection arrangement according to claim 1 as HUD in a vehicle on land, on water or in the air.

16. The projection arrangement according to claim 3, wherein the oxygen content is less than 1% volume fraction in the process gas.

17. The projection arrangement according to claim 10, wherein the thickness of the at least one layer based on the transparent conductive oxide is from 60 nm to 100 nm.

18. The projection arrangement according to claim 12, wherein: the anti-reflective layer is based on silicon nitride, the refractive-index-enhancing layer is based on a silicon-metal mixed nitride, the matching layer is based on zinc oxide.

19. The projection arrangement according to claim 18, wherein the refractive-index-enhancing layer is a layer of silicon-zirconium mixed nitride, silicon titanium mixed nitride or silicon hafnium mixed nitride.

20. The method according to claim 15, wherein the vehicle is a motor vehicle, a rail vehicle, an aircraft, or a ship.

Description

[0092] In the figures:

[0093] FIG. 1 shows a plan view of a composite pane of a generic projection arrangement,

[0094] FIG. 2 shows a cross-section through a generic projection arrangement,

[0095] FIG. 3 shows a cross-section through a composite pane of a projection arrangement according to the invention,

[0096] FIG. 4 shows a cross-section through an embodiment of the reflective layer according to the invention on an inner pane, and

[0097] FIG. 5 shows a diagram of the refractive indices of ITO layers as a function of the wavelength.

[0098] FIG. 1 and FIG. 2 each show a detail of a generic projection arrangement for an HUD. The projection arrangement comprises a composite pane 10, in particular the windscreen of a passenger vehicle. The projection arrangement also comprises an HUD projector 4, which is directed toward a region of the composite pane 10. In this region, which is usually referred to as HUD region B, images can be generated by the HUD projector 4, which images are perceived by a viewer 5 (vehicle driver) as virtual images on the side of the composite pane 10 facing away from him when his eyes are located within the so-called eye box E.

[0099] The laminated pane 10 is constructed from an outer pane 1 and an inner pane 2, which are connected 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 vehicle, its upper edge O is arranged at the top in the direction of the roof. In the installed position, the outer pane 1 faces the external environment; the inner pane 2 faces the vehicle interior.

[0100] FIG. 3 shows an embodiment of a composite pane 10 formed according to the invention. The outer pane 1 has an outer-side surface I which, in the installed position, faces the external environment, and an interior-side surface II which faces the interior in the installed position. Likewise, the inner pane 2 has an outer-side surface III which faces the external environment in the installed position, and an interior-side surface IV which faces the interior in the installed position. The outer pane 1 and the inner pane 2 consist, for example, of soda lime glass and have, for example, a thickness of 2.1 mm in each case. The intermediate layer 3 is formed, for example, from a PVB film with a thickness of 0.76 mm. The PVB film has a substantially constant thickness, apart from any surface roughness that is customary in the art; it is not designed as a so-called wedge film.

[0101] The outer-side surface III of the inner pane 2 is provided with a reflective layer 20 according to the invention, which is provided as a reflective surface for the projector radiation. The reflective layer 20 should also serve as a sun protection layer and reduce the energy input into the vehicle interior, which is caused in particular by the infrared radiation components of the sunlight.

[0102] According to the invention, the radiation of the projector 4 is p-polarised, in particular substantially purely p-polarised. Because the HUD projector 4 irradiates the windscreen 10 with an angle of incidence of approximately 65, which is close to the Brewster angle, the radiation of the projector is reflected only to an insignificant extent at the external surfaces I, IV of the composite pane 10. The reflective layer 20 according to the invention, on the other hand, is optimized for the reflection of p-polarised radiation. It serves as a reflective surface for the radiation of the HUD projector 4 for generating the HUD projection.

[0103] FIG. 4 shows the layer sequence of an embodiment of the reflective layer 20 according to the invention on the inner pane 2. The reflective layer 20 is a stack of thin layers. The reflective layer 20 comprises exactly one electrically conductive layer 21 based on silver. A blocker layer 24 is arranged directly above the electrically conductive layer 21. A first layer module M1 is arranged below the conductive layer 21. A second layer module M2 is arranged above the conductive layer 21 with the blocker layer 24. A barrier layer 25 is arranged below the first layer module M1, between first layer module M1 and inner pane 2 and prevents the diffusion of oxygen from the inner pane 2 into the first layer module M1.

[0104] The first layer module M1 consists of a dielectric layer sequence and a single layer 23 based on a TCO. The layer 23 improves the IR reflectivity of the composite pane 10, so that the energy input into the vehicle interior can be further reduced. Furthermore, a reflective layer 20 can be realized with the layer 23 and has excellent reflective properties with respect to the p-polarised radiation of the HUD projector 4, so that a strong intensity and colour-neutral representation of the HUD projection is ensured. These are great advantages of the reflective layer 20 according to the invention with the TCO layer 23. The layer 23 is attached directly to the barrier layer 23, i.e., provided as the lowermost layer of the first layer module M1, above which the dielectric layer sequence of the first layer module M1 follows. The dielectric layer sequence of the first layer module M1 consists from bottom to top of a refraction-index-enhancing layer 22c and a matching layer 22b.

[0105] The second layer module M2 is designed as a dielectric layer sequence, wherein the layer sequence consists from bottom to top in this order of a matching layer 22b and a refraction-index-enhancing layer 22c.

[0106] The layer sequence can be seen schematically in the figure. The layer sequence of a composite pane 10 with the reflective layer 20 on the outer-side surface III of the inner pane 2, together with the materials and layer thicknesses of the individual layers, is shown in Table 1 for four examples B1 to B5 according to the invention which differ in the individual layer thicknesses. The dielectric layers can be doped independently of one another, for example with boron or aluminium. The TCO layer 23 provided as an ITO layer is deposited with an oxygen content of approximately 0% in the process gas by means of magnetic-field-assisted cathode sputtering. The layer sequences of examples B1 to B5 are applied to the outer-side surface III of the inner pane 2. The inner pane 2 has a thickness of 2.1 mm in each case and is joined via the outer-side surface III, on which the reflective layer is located, via a PVB film with a thickness of 0.76 mm to the outer pane 1 with a thickness of 2.1 mm. The inner pane 2 and the outer pane 1 consist of soda-lime glass. Table 2 shows comparative examples V1 to V4 according to the invention, wherein a composite pane according to comparative examples has the identical basic structure to the examples according to the invention, but differs in the structure of the reflective layer.

[0107] The optical thickness of a layer results in each case as a product of the geometric thickness shown in the tables and the refractive index (SiN:2.0; SiZrN:2.2, ZnO:2.0).

TABLE-US-00001 TABLE 1 Examples according to the invention Layer thicknesses in nm Material Reference signs B1 B2 B3 B4 B5 SiN 20 M2 22a 5 5 5 SiZr 22c 31 17% SiZr 22c 30 34 36 27% SnZnO 22c 10 TiO.sub.x 22b 27 5 5 ZnO 22b 5 5 NiCrO.sub.x 24 1 1 Ag 21 13.8 15.1 14.6 15.7 15.4 ZnO M1 22b 5 5 5 5 5 SiZrN 22c 36 40 38 30 27% SiZrN 22c 37 17% SiN 22a 11 ITO 23 70 87 70 88 72 SiN 25 5 Soda- 2 2.1 mm 2.1 mm 2.1 mm 2.1 mm 2.1 mm lime glass

[0108] Comparative examples V1 to V5 are shown in Table 2. Like examples B1 to B5 according to the invention, the reflective layers of the comparative examples also comprise individual silver layers 21 and two layer modules M1, M2. Both layer modules M1, M2 are designed as dielectric layer sequences and each comprise an anti-reflective layer 22a, a refractive-index-enhancing layer 22c, and a matching layer 22b. The layer modules M1, M2 of the comparative examples do not comprise any TCO layers 23.

TABLE-US-00002 TABLE 2 Comparative examples not according to the invention Layer thicknesses in nm Material Reference signs V1 V2 V3 V4 V5 SiN 20 M2 22a 19 17 SiZr 22c 56 53 17% SiZr 22c 39 51 27% SnZnO 22c 11 TiO.sub.x 22b 7 5 ZnO 22b 5 5 5 NiCrO.sub.x 24 1 1 1 Ag 21 11.7 13.0 12.2 13.4 13.8 ZnO M1 22b 5 5 5 5 SiZrN 22c 16 13 27% SiZrN 22c 3 60 20 17% SiN 22a 24 10 2 15 17 ITO 23 SiN 25 Soda- 2 2.1 mm 2.1 mm 2.1 mm 2.1 mm 2.1 mm lime glass

[0109] Table 3 summarizes some characterising parameters of examples B1 to B5 and of comparative examples V1 to V5. Compared are: [0110] TL (A): integrated light transmittance in accordance with ISO 9050, measured with a light source of light type A [0111] TTS: total solar energy radiated in accordance with ISO 13837 [0112] R(A)p-pol: integrated light reflection with respect to p-polarised radiation, measured with a p-polarised light source of light type A at an angle of incidence of 65 and a viewing angle of 65 relative to the surface normal on the interior side [0113] a*(A)p-pol, b*(A)p-pol: colour values in the L*a*b* colour spectrum as reflection colour with respect to p-polarised radiation, measured with a p-polarised light source of light type A at an angle of incidence of 65 and a viewing angle of 65 relative to the surface normal on the interior side

[0114] The light transmittance TL (A) is a measure of the transparency of the composite pane 10, wherein values greater than 70% are desirable in particular for windscreens. The radiated solar energy TTS is a measure of the energy input into the vehicle interior and thus for the thermal comfort. R (A) p-pol is a measure of the reflectivity relative to the radiation of the HUD projector 4 and thus the intensity of the HUD projection. The colour values in the L*a*b* colour spectrum are a measure of how colour-neutral the HUD display is, wherein the values should be as close as possible to zero.

TABLE-US-00003 TABLE 3 TL(A)/% TTS/% R(A)p-pol/% a*(A)p-pol b*(A)p-pol B1 72.5 53.2 17.1 0.7 0.6 B2 72.5 52.3 17.9 0.3 0.1 B3 72.5 53.2 17.3 0.9 1.3 B4 72.5 52.1 18.7 0.6 0.4 B5 72.5 52.9 18.5 0.8 1.0 V1 72.5 59.6 17.3 1.1 1.0 V2 72.5 58.5 17.7 1.5 0.1 V3 72.5 59.2 17.1 1.2 2.2 V4 72.5 58.3 18.6 1.1 2.0 V5 72.5 56.3 19.4 2.9 0.7

[0115] From Table 3 it is clear that all examples and also the comparative example have a sufficiently high light transmittance TL (A), so that the laminated panes 10 can be used as windscreens. In contrast to the comparative example, the inventive examples have a significantly lower TTS value-due to the TCO layer 23, which is integrated in the first layer module M1, the irradiated solar energy is significantly reduced and the thermal comfort in the vehicle is increased. Surprisingly, a high degree of reflection that is comparable to the comparative example can nevertheless be achieved with respect to the p-polarised radiation of the HUD projector 4, so that the laminated panes 10 are suitable as a projection surface of a generic HUD projection arrangement.

[0116] The introduction of a TCO layer 23 made of ITO within the first layer module M1 leads to a reduction in the total solar transmittance TTS by approximately 6%. This is accompanied by a reduction in the energy transmittance (TE) by a similar amount (approximately 7%). Furthermore, the external energetic reflection increases by about 3-4%, and the external energetic absorption by about 2-3%. The increase in energetic absorption is attributable to the absorption of the ITO layer in the infrared range of the spectrum. The reflective layers with ITO have a greater energetic reflection, which is attributable to a greater thickness of the silver layers in coatings comprising an ITO layer. The inventors have found that the presence of the ITO layer and the preferred positioning of the ITO layer as the furthest inward layer within the first layer module (M1) are advantageous in order to achieve as neutral a colouring as possible even in the case of comparatively thick silver layers. This positive influence of the layer 23 on the colouring of the layers is also illustrated using a comparison of example 1 to comparative example 5. Comparative example 5 and example 1 both comprise a silver layer having a thickness of 13.8 nm, wherein comparative example 5 does not contain a TCO layer 23, and example 1 contains an ITO layer as TCO layer 23. In comparative example 5, a TTS value of 56.3% is achieved; in example 1 the TTS value is 53.2%. In comparative example 5, undesirably high colour values occur, whereas in example 1 a neutral colour results.

[0117] The use of ITO layers within the first layer module M1 thus improves the IR absorption and increases the energy absorption, which leads to a smaller total solar transmittance TTS. Furthermore, the production of reflective layers with thicker silver layers is made possible while maintaining the colour neutrality. Reflective layers with thicker silver layers in turn have a higher energetic reflection. The greater energetic absorption and reflection of the reflective layers comprising an ITO layer in module M1 both contribute to improving the total solar transmittance (TTS). The inventors have found that ITO layers in this context are particularly advantageous as layer 23, but this effect can also be achieved by means of other transparent conductive oxides.

[0118] FIG. 5 shows the refractive indices of a plurality of TCO layers 23 as a function of the wavelength. The TCO layers 23 are designed as ITO layers which are deposited by means of magnetic-field-assisted cathode sputtering. In each case no oxygen (curve ITO 0% O.sub.2), 0.7% oxygen (curve ITO 0.7% O.sub.2) and 1.5% oxygen (curve ITO 1.5% O.sub.2) was added to the process gas. The refractive indices were each determined by means of ellipsometry. TCO layers, which, at a wavelength of 550 nm, have a refractive index of from 1.6 to 2.0, preferably from 1.7 to 1.9, particularly preferably from 1.7 to 1.8, have proven to be particularly advantageous. The refractive index of the TCO layers preferably decreases continuously with increasing wavelength.

LIST OF REFERENCE SIGNS

[0119] (10) Composite pane [0120] (1) Outer pane [0121] (2) Inner pane [0122] (3) Thermoplastic intermediate layer [0123] (4) HUD projector [0124] (5) Viewer/vehicle driver [0125] (20) Reflective layer [0126] (21) Electrically conductive layer/silver layer [0127] (22a) Anti-reflective layer [0128] (22b) Matching layer [0129] (22c) Refractive-index-enhancing layer [0130] (23) Layer based on a transparent conductive oxide (TCO) [0131] (24) Blocker layer [0132] (25) Barrier layer [0133] (M1) First layer module [0134] (M2) Second layer module [0135] (O) Upper edge of the windscreen 10 [0136] (U) Lower edge of the windscreen 10 [0137] (B) HUD region of the windscreen 10 [0138] (E) Eye box [0139] (I) Outer-side surface of the outer pane 1 facing away from the intermediate layer 3 [0140] (II) Interior-side surface of the outer pane 1 facing the intermediate layer 3 [0141] (III) Outer-slide surface of the inner pane 2 facing the intermediate layer 3 [0142] (IV) Interior-side surface of the inner pane 2 facing away from the intermediate layer 3