Reflector element for motor vehicle lighting device

Abstract

The invention relates to a reflector element (100) for a motor vehicle lighting device, comprising at least: - a substrate (1); - a mirror layer (2) arranged on the substrate (1), the mirror layer having aluminum or silver; - a protective layer (3) arranged on the mirror layer (2), the protective layer having siloxane; and - a cover layer (4) arranged on the protective layer (3), the cover layer having a transition metal oxide, wherein the protective layer (3) and the cover layer (4) each have a layer thickness (D3, D4) of 10 nm to 100 nm.

Description

Technical Field

[0001] The present invention relates to a reflector element for a motor vehicle lighting device and a method for manufacturing the motor vehicle lighting device. Background Technology

[0002] Existing reflector elements for automotive lighting typically have a substrate made of plastic, on which a thin mirror layer made of aluminum is deposited. For corrosion protection, a transparent protective layer, usually made of plasma polymer, is typically disposed on the mirror layer. Such reflector elements have a reflectivity of approximately 85% in the visible spectrum.

[0003] To achieve high luminous efficiency, for example, in automotive lighting equipment including multi-reflector designs, it is known to apply a dichroic auxiliary layer to the specular layer, which increases reflectivity through interference effects. However, commonly used dichroic auxiliary layers disadvantageously lack corrosion protection, and the typically required high layer thickness leads to long deposition times, which can be accompanied by undesirable and intense heating of the substrate, potentially causing damage or at least discoloration.

[0004] As an alternative to aluminum protective layers, silver coatings are known in the prior art, characterized by high reflectivity in the visible spectrum. Disadvantageously, silver coatings exhibit particularly low corrosion resistance, especially in the presence of sulfur compounds. Therefore, protective layers with large thicknesses are used in the prior art, thereby degrading the reflective properties of the reflective element. In particular, the reflectivity of silver drops sharply in the blue range, resulting in a yellowish appearance to the silver mirror layer itself, which is further enhanced by the thick protective layer.

[0005] DE 10 2015 102 870 A1 discloses a reflector element comprising a plastic substrate, a silver layer, a first barrier layer disposed on the silver layer consisting of an oxide layer at least 15 nm thick, and a second barrier layer disposed on the first barrier layer having a siloxane content, wherein the thickness of the second barrier layer is at least 250 nm and at most 450 nm. The use of a second barrier layer several hundred nanometers thick disadvantageously results in long process times when manufacturing such a reflector element. Furthermore, the presence of such a thick monolayer undesirably enhances the angular dependence of reflectivity. Summary of the Invention

[0006] Therefore, the objective of this invention is to provide a reflector element for motor vehicle lighting equipment that overcomes the disadvantages of the prior art reflector elements mentioned above and has high reflectivity across the entire visible spectrum while exhibiting high corrosion resistance.

[0007] This task is solved by a reflector element.

[0008] This invention includes the following technical teachings, namely, that the reflector element comprises at least:

[0009] - Matrix;

[0010] - A mirror layer disposed on a substrate, the mirror layer being made of aluminum or silver;

[0011] - A protective layer disposed on the mirror layer, the protective layer having a siloxane; and

[0012] - A cover layer disposed on the protective layer, the cover layer having a transition metal oxide.

[0013] The protective layer and the cover layer each have a thickness of 10 nanometers to 100 nanometers.

[0014] The present invention arises from the concept of compensating for the deterioration of reflective properties caused by the protective layer made of silicone organic compounds required for corrosion protection by applying a capping layer made of transition metal oxides as an optical enhancement layer on the protective layer. Surprisingly, and unlike layer structures known in the prior art, the present invention constitutes a single layer of protective and capping layers less than 100 nm thick. The reflector element according to the invention thus possesses sufficient corrosion resistance and long-term durability for practical operation, and regarding functional optical properties, it is characterized by improved reflectivity compared to a simple metal layer, while optimizing the neutral tone of the appearance. Due to the small layer thickness according to the invention, an extremely short deposition time is required when manufacturing the reflector element according to the invention, thereby minimizing the heat input to the typically heat-sensitive substrate.

[0015] In an advantageous embodiment of the reflector element according to the invention, the capping layer has a binary transition metal oxide having a high refractive index in the visible spectrum, particularly a refractive index greater than 2. For example, titanium dioxide or zirconium dioxide constitutes a suitable transition metal oxide. Due to the high refractive index, the capping layer can be constructed thinly, i.e., particularly thinner than 100 nm, while still providing sufficient optical enhancement for the reflectivity of the reflector element according to the invention.

[0016] For example, the mirror layer is made of aluminum and the cover layer is made of titanium dioxide, wherein the protective layer has a thickness of 70 nm to 80 nm, preferably 75 nm, and the cover layer has a thickness of 50 nm to 60 nm, preferably 55 nm. In another embodiment, the mirror layer is made of silver and the cover layer is made of titanium dioxide, wherein the protective layer has a thickness of 45 nm to 55 nm, preferably 50 nm, and the cover layer has a thickness of 45 nm to 55 nm, preferably 50 nm. The outstanding reflective properties of these embodiments are further illustrated below with reference to the accompanying drawings.

[0017] The reflector element according to the invention preferably has a neutral-toned appearance, wherein the white light reflected by the reflector element along the normal direction is characterized in the CIELAB color space by having chromatic coordinates with values ​​less than 2, preferably zero. The CIELAB color space is standardized in EN ISO 11664-4. The three-dimensional CIELAB color space is defined by a color plane formed by chromatic coordinates a* and b* and a luminance value L* perpendicular to said color plane. If both chromatic coordinates a* and b* are equally zero, then an absolute neutral tone exists. The reflector element according to the invention is particularly configured such that the inherent yellowish tint in the reflection of white light on pure silver is compensated by a coordinated combination of the protective layer and the overlay layer.

[0018] Further advantageously, the reflector element according to the invention has a maximum reflectance of 95° to 99° in the visible spectrum. That is, in addition to improving the neutral tone, the effect of the layer stack applied according to the invention is particularly that the reflectance of the reflector element according to the invention is significantly improved relative to a simple metallic mirror layer.

[0019] For example, the substrate of the reflector element according to the invention is made of plastic, and in particular of polycarbonate, polyetherimide, or, for example, a bulk molding compound coated with a primer. These materials are suitable for use in reflector elements of motor vehicle lighting equipment due to their thermomechanical properties, their processability, and their economic viability.

[0020] Furthermore, the reflector element according to the invention may have, for example, an optional intermediate layer having a layer thickness of less than 50 nm, disposed between the substrate and the mirror layer. Depending on the material used for the substrate, the intermediate layer serves as an adhesion promoter layer between the substrate and the mirror layer and / or as a diffusion barrier to protect the mirror layer from substances, such as water or oxygen, that leak from the substrate.

[0021] The present invention further relates to a method for manufacturing a reflector element for a motor vehicle lighting device according to one of the embodiments mentioned above, wherein the mirror layer and the capping layer are deposited by means of sputtering, also known as cathode sputtering, and the protective layer is deposited by means of plasma-assisted chemical vapor deposition. The protective layer is preferably formed by plasma polymerization of hexamethyldisiloxane (HMDSO). The mirror layer is preferably deposited by DC voltage sputtering and the capping layer is deposited by AC voltage sputtering, preferably at a mid-frequency sputtering frequency in the range of, for example, 20 kHz to 70 kHz. Attached Figure Description

[0022] Next, other measures to improve the invention will be further described with reference to the accompanying drawings and the description of preferred embodiments. In the drawings:

[0023] Figure 1 A schematic cross-sectional partial view of a reflector element according to the present invention is shown;

[0024] Figure 2a The spectral reflectance of the Al-based layer stack is shown;

[0025] Figure 2b The spectral reflectance of the Ag-based layer stack is shown;

[0026] Figure 3a The angle-dependent spectral reflectance of the Al-based layer stack is shown; and

[0027] Figure 3b The angle-dependent spectral reflectance of the Ag-based layer stack is shown. Detailed Implementation

[0028] Figure 1 A schematic cross-sectional view of a section of a reflector element 100 according to the invention is shown, the reflector element having a substrate 1 together with a thin stack of functional layers 2-5 applied thereon. The substrate 1 is preferably made of plastic.

[0029] The mirror layer 2 is made of silver, which, compared to aluminum which is more commonly used in the prior art, is characterized by its higher reflectivity in the visible spectrum. Depending on the surface shape of the substrate, i.e., the surfaces of the substrate 1 and the intermediate layer 5, and the deposition conditions, the thickness D2 of the mirror layer 2 is preferably chosen such that the surface of the mirror layer has the lowest possible roughness, i.e., the highest possible mirror effect. The layer thickness D2 is typically 50 nm to 150 nm in this case.

[0030] Optionally, an intermediate layer 5 deposited prior to the deposition of the mirror layer 2 on the substrate may be made of, for example, an HMDSO-based plasma polymer or sputtered titanium. Depending on the material and surface characteristics of the substrate 1, the intermediate layer 5 may function as an adhesion promoter for the mirror layer 2 and / or constitute a diffusion barrier against substances, such as water molecules or oxygen, that may leak from the substrate 1 and cause damage to the mirror layer 2.

[0031] A protective layer 3, deposited particularly by plasma polymerization using HMDSO, is formed on the mirror layer 2. This protective layer serves as corrosion protection. The thickness D3 of the protective layer 3 is less than 100 nm according to the invention. A capping layer 4 deposited on the protective layer 3 is made of a high-refractive-index material, preferably a binary transition metal oxide having a refractive index greater than 2 in the visible spectrum, and also has a small layer thickness D4 of less than 100 nm according to the invention.

[0032] Figure 2a and Figure 2b The experimentally determined spectral reflectance of aluminum-based or silver-based layer stacks in the visible spectrum, i.e., at light wavelengths between 400 nm and 750 nm, is shown in contrast to a simple mirror layer (Al or Ag), a mirror layer including a protective layer made of a siloxane plasma polymer, and a mirror layer including a protective layer made of a siloxane plasma polymer and a capping layer made of titanium dioxide (TiO2). The thickness of each layer is given in the legend of the figures and, as set according to the present invention, is less than 100 nm.

[0033] The comparison of simple metallic layers reveals the inherently higher reflectivity of silver compared to aluminum. Except for the blue wavelengths below 450 nm, a simple mirror layer made of silver exhibits a reflectivity greater than 95%, thus demonstrating its particular suitability for use in reflective elements. The decrease in reflectivity in the blue region results in a yellowish tint to the appearance of the silver layer. The protective layer's effect is to reduce reflectivity across the entire spectral range shown, particularly in the blue region, thereby adversely further enhancing its yellowish tint in combination with silver. The layer stack, including the final capping layer made of titanium dioxide, is characterized by a significant increase in reflectivity, justifying its designation as an optical enhancement layer. Despite the presence of a protective layer made of plasma polymer, this results in an average reflectivity above 95% in the visible spectrum in the case of the silver-based layer stack. Here, the presence of the overlay layer also advantageously leads to a certain redistribution of spectral weights from red to blue, which causes a correction of the yellowish appearance, so that the reflector element according to the invention, including such a layer stack, has a neutral-toned appearance, wherein the white light reflected along the normal direction in the CIELAB color space is characterized by a color coordinate of less than 2.

[0034] Figure 3a and Figure 3b The simulations show the angle-dependent spectral reflectance in the visible spectrum of stacked aluminum-plasma polymer-titanium dioxide or silver-plasma polymer-titanium dioxide layers, with single-layer thicknesses of 10 nm and 100 nm, respectively, within the range set according to the present invention. The reflectance is shown under light incident at an angle of 0° to (locally) the surface along the normal direction, i.e., perpendicularly, and under grazing light incident at an angle of 80°. In both stacked layers, the reflectance under grazing incident light is characterized by a minimum value in the light wavelength range around 500 nm, which corresponds to a change in color appearance relative to normal incident light under white light illumination. However, it should be emphasized that the average reflectance at a flat viewing angle of 80° is only slightly less than the average reflectance along the normal direction. This constitutes another advantage of the reflector element according to the invention having a layer thickness of less than 100 nm, because, in contrast, in reflector elements known in the art that include a plasma polymer protective layer with a higher layer thickness, especially greater than 250 nm, there is a significant and stronger decrease in reflectivity at a flat viewing angle. Figure 3a and 3b The comparison further demonstrates the advantage of the silver-based layer stack over the aluminum-based layer stack in terms of the angular correlation of reflectivity. This is because silver's reflectivity inherently has a smaller correlation with the polarization of incident light.

[0035] The present invention is not limited in its implementation to the preferred embodiments described above. Instead, various variations are conceivable, which in principle also use the solutions shown in different types of implementations. All features and / or advantages derived from the specification or drawings, including structural details, spatial arrangements, and method steps, are important to the present invention not only in themselves but also in different combinations.

[0036] List of reference numerals

[0037] 100 reflector elements

[0038] 1 matrix

[0039] 2 mirror layers

[0040] 3 protective layers

[0041] 4 covering layers

[0042] 5 intermediate layers

[0043] Thickness of layers D2, D3, and D4

Claims

1. A reflector element (100) for a motor vehicle lighting device, said reflector element comprising at least: - Matrix (1); - A mirror layer (2) disposed on a substrate (1), the mirror layer having aluminum or silver; - A protective layer (3) disposed on the mirror layer (2), the protective layer having a siloxane; and - A cover layer (4) disposed on the protective layer (3), the cover layer having a transition metal oxide, The protective layer (3) and the cover layer (4) have a thickness of 10 nm to 100 nm, respectively.

2. The reflector element (100) according to claim 1, characterized in that, The capping layer (4) has a binary transition metal oxide with a refractive index greater than 2 in the visible spectrum.

3. The reflector element (100) according to claim 1 or 2, characterized in that, The mirror layer (2) has aluminum and the cover layer (4) has titanium dioxide, wherein the protective layer (3) has a layer thickness of 70 nm to 80 nm and the cover layer (4) has a layer thickness of 50 nm to 60 nm.

4. The reflector element (100) according to claim 3, characterized in that, The protective layer (3) has a layer thickness of 75 nm, and the cover layer (4) has a layer thickness of 55 nm.

5. The reflector element (100) according to claim 1 or 2, characterized in that, The mirror layer (2) has silver and the cover layer (4) has titanium dioxide, wherein the protective layer (3) has a layer thickness of 45 nm to 55 nm and the cover layer (4) has a layer thickness of 45 nm to 55 nm.

6. The reflector element (100) according to claim 5, characterized in that, The protective layer (3) has a layer thickness of 50 nm, and the cover layer (4) has a layer thickness of 50 nm.

7. The reflector element (100) according to claim 1 or 2, characterized in that, The reflector element (100) has a neutral-toned appearance, wherein the white light reflected by the reflector element (100) along the normal direction is characterized in the CIELAB color space by having a color coordinate with a value less than 2.

8. The reflector element (100) according to claim 7, characterized in that, The color coordinates have a value of zero.

9. The reflector element (100) according to claim 1 or 2, characterized in that, The mirror layer (2) is silver, and the reflector element (100) has a maximum reflectivity of 95% to 99% in the visible spectrum.

10. The reflector element (100) according to claim 1 or 2, characterized in that, The substrate (1) is made of plastic.

11. The reflector element (100) according to claim 10, characterized in that, The matrix (1) has polycarbonate, polyetherimide or bulk molding compound.

12. The reflector element (100) according to claim 1 or 2, characterized in that, The reflector element (100) has an intermediate layer (5) disposed between the substrate (1) and the mirror layer (2).

13. A method for manufacturing a reflector element (100) for a motor vehicle lighting device according to any one of claims 1 to 12, characterized in that, The mirror layer (2) and the capping layer (4) are deposited by sputtering, and the protective layer (3) is deposited by plasma-assisted chemical vapor deposition.

14. The method according to claim 13, characterized in that, The mirror layer (2) is deposited by DC voltage sputtering, and the capping layer (4) is deposited by AC voltage sputtering.

15. The method according to claim 14, characterized in that, The capping layer (4) is deposited using mid-frequency sputtering.

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