Reflector element and a method for manufacturing same

Abstract

A reflector element and a method for manufacturing a reflector element are disclosed. In an embodiment the reflector element includes a plastic substrate and a silver layer arranged on the plastic substrate. The reflector element further includes a first barrier layer arranged on the silver layer, wherein the barrier layer has an at least 15 nm-thick oxide layer and a second barrier layer arranged on the first barrier layer, wherein the barrier layer includes siloxane, and wherein a thickness of the second barrier layer is at least 250 nm and at most 450 nm.

Claims

1. A reflector element comprising: a plastic substrate; a silver layer arranged on the plastic substrate; a first barrier layer arranged on the silver layer, wherein the first barrier layer comprises an at least 15 nm-thick oxide layer; and a second barrier layer arranged on the first barrier layer, wherein the second barrier layer comprises siloxane, and wherein a thickness of the second barrier layer is at least 250 nm and at most 450 nm, wherein an integral IR absorption of the second barrier layer in a wave number range from 850 cm.sup.1 to 950 cm.sup.1 is less than 65% of the integral IR absorption in the wave number range from 1000 cm.sup.1 to 1100 cm.sup.1.

2. The reflector element according to claim 1, wherein the second barrier layer is a top layer of the reflector element.

3. The reflector element according to claim 1, wherein the first barrier layer comprises aluminum oxide, silicon oxide, titanium oxide or yttrium oxide.

4. The reflector element according to claim 1, wherein the first barrier layer has a thickness between 15 nm and 150 nm.

5. The reflector element according to claim 1, further comprising a metallic intermediate layer arranged between the plastic substrate and the silver layer.

6. The reflector element according to claim 5, wherein the metallic intermediate layer comprises Cr, Cu, Ni or Ti.

7. The reflector element according to claim 1, wherein the reflector element has an average reflectivity R.sub.blue in a wavelength range from 420 nm to 480 nm, and an average reflectivity R.sub.vis in an wavelength range from 420 nm to 760 nm, wherein R.sub.vis-blue=R.sub.visR.sub.blue1.5%.

8. A method for manufacturing a reflector element, the method comprising: applying a silver layer on a plastic substrate; applying a first barrier layer on the silver layer, wherein the first barrier layer is applied by a PVD method, wherein the first barrier layer comprises an at least 15 nm-thick oxide layer; and applying a second barrier layer on the first barrier layer, wherein the second barrier layer is applied by a CVD method, wherein the second barrier layer comprises siloxane, and wherein the second barrier layer has a thickness of at least 250 nm and of at most 450 nm, wherein an integral IR absorption of the second barrier layer in a wave number range from 850 cm.sup.1 to 950 cm.sup.1 is less than 65% of the integral IR absorption in the wave number range from 1000 cm.sup.1 to 1100 cm.sup.1.

9. The method according to claim 8, wherein the second barrier layer is an outermost layer of the reflector element.

10. The method according to claim 8, wherein the first barrier layer is applied by a sputtering method.

11. The method according to claim 8, wherein the first barrier layer comprises an oxide of at least one of Al, Si, Ti or Y.

12. The method according to claim 8, wherein the second barrier layer is formed by plasma polymerization of a silicon organic compound.

13. The method according to claim 12, wherein the silicon organic compound is hexamethyldisiloxane (HMDSO) or tetramethyldisiloxane (TMDSO).

14. A reflector element comprising: a plastic substrate; a silver layer arranged on the plastic substrate; a first barrier layer arranged on the silver layer, wherein the first barrier layer comprises an at least 15 nm-thick oxide layer; and a second barrier layer arranged on the first barrier layer, wherein the second barrier layer comprises siloxane, and wherein a thickness of the second barrier layer is at least 250 nm and at most 450 nm, wherein the reflector element has an average reflectivity R.sub.blue in a wavelength range from 420 nm to 480 nm, and an average reflectivity R.sub.vis in an wavelength range from 420 nm to 760 nm, wherein R.sub.vis-blue=R.sub.blue1.5%.

15. The reflector element according to claim 14, wherein the second barrier layer is a top layer of the reflector element.

16. The reflector element according to claim 14, wherein the first barrier layer comprises aluminum oxide.

17. The reflector element according to claim 14, wherein the first barrier layer comprises silicon oxide, titanium oxide or yttrium oxide.

18. The reflector element according to claim 14, wherein the first barrier layer has a thickness between 15 nm and 150 nm.

19. The reflector element according to claim 14, further comprising a metallic intermediate layer arranged between the plastic substrate and the silver layer.

20. The reflector element according to claim 19, wherein the metallic intermediate layer comprises Cr, Cu, Ni or Ti.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail below on the basis of exemplary embodiments and in connection with the FIGS. 1 to 5, of which:

(2) FIG. 1 shows a schematic illustration of a cross section through a reflector element according to an exemplary embodiment;

(3) FIGS. 2 to 4 show a graphic illustration of FTIR absorption spectra of three different exemplary embodiments of the reflector element; and

(4) FIG. 5 shows a graphic illustration of the difference between the medium reflectivity in the entire visual spectral range and the reflectivity in the blue spectral range as a function of the quotient of the FTIR absorption in the wave number range 850 cm.sup.1 . . . 950 cm.sup.1 and the FTIR absorption in the wave number range 1000 cm.sup.1 . . . 1100 cm.sup.1.

(5) The illustrated components and the size ratios of the components with respect to one another are not to be considered true to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(6) The reflector element 6 which is illustrated schematically in cross section in FIG. 1 is formed by a sequence of layers applied to a substrate 1. For the sake of simplification, the substrate 1 is illustrated here as a planar substrate. In the case of the reflector element 6, the substrate 1 can, however, be, in particular, a curved substrate. The substrate can be manufactured, for example, by means of a shaping method such as injection molding or deep drawing and can have any desired three-dimensional shape. In particular, the substrate 1 can have an at least partially curved surface shape which is provided for an optical application. The surface roughness of the substrate 1 is advantageously less than 15 nm, particularly preferably less than 5 nm.

(7) The material of the substrate 1 is preferably a plastic, in particular a thermoplast or a duroplast. The substrate 1 can contain, in particular, PC (polycarbonate), PMMA (polymethylmethacrylate) or PBT (polybutylene terephthalate). The plastic can, if appropriate, have an additive added to it such as, for example, ABS (acrylonitrile-butadiene-styrene). Furthermore, it is possible for pigments such as, for example, TiO.sub.2 particles to be added to the plastic in order, for example, to influence the color impression or the thermal conductivity of the substrate material.

(8) In the exemplary embodiment, an intermediate layer 2 is arranged between the substrate 1 and a silver layer 3 which is arranged over the latter and functions as a reflector layer. The intermediate layer 2 can have, in particular, the function of an adhesion promoting layer and is preferably a metallic layer which has or is composed of, in particular, chromium, copper, titanium or nickel. Chromium or copper is particularly preferably used. The intermediate layer 2 can advantageously also contribute to the smoothing of the substrate surface and/or act as a diffusion barrier for substances which could diffuse out of the substrate (for example, small quantities of water and/or oxygen) in the direction of the silver layer 3. The intermediate layer is preferably 15 nm to 75 nm, for example, 30 nm thick. The intermediate layer can be applied, for example, by sputtering.

(9) The silver layer 3 which acts as a reflector layer is approximately 100 nm to 200 nm, preferably 150 nm to 200 nm, thick. The silver layer 3 is preferably applied by sputtering. By using silver as a material for the reflector layer, particularly high reflection is advantageously achieved in the visible spectral range.

(10) In order to protect the silver layer 3 against environmental influences, in particular temperature change loading and moisture, a combination of a first barrier layer 4 and a second barrier layer 5 is arranged in the reflector element 6. The first barrier layer 4 is advantageously an oxide layer which is, for example, between 15 nm and 150 nm thick. With respect to the optical properties, it is advantageous if the first barrier layer 4 is less than 60 nm, for example, between 40 nm and 60 nm thick. Preferred materials for the first barrier layer 4 are SiO.sub.2 and Al.sub.2O.sub.3. The first barrier layer 4 is applied, for example, by reactive sputtering.

(11) In order to achieve the desired long-term stability, a second barrier layer 5 is arranged over the first barrier layer 4 in the reflector element 6. The second barrier layer 5 can be manufactured, in particular, by plasma-enhanced chemical vapor deposition (PEVCD). The second barrier layer 5 is preferably a siloxane layer which is applied, in particular, by plasma polymerization of HMDSO (hexamethyldisiloxane) or TMDSO (tetramethyldisiloxane) or mixtures thereof or of other silicon organic compounds.

(12) It is particularly advantageous for the long-term stability, on the one hand, and the optical properties, on the other, if the thickness of the second barrier layer 5 is between inclusively 250 nm and inclusively 450 nm. Given a thickness of preferably at least 250 nm, a particularly good barrier effect against the diffusion of water and gas is achieved. Furthermore, a thickness of at most 450 nm is advantageous in order, in particular, to keep the absorption of the second barrier layer 5 low. When there is a relatively large layer thickness of 450 nm, in particular the absorption at short wavelengths would increase significantly and therefore reduce the optical transparency for blue light. As a result of increased absorption at short wavelengths, in particular in the region of the blue light, a yellow color impression of the reflected radiation could therefore occur if an excessive layer thickness of the second barrier layer 5 were selected.

(13) The second barrier layer 5 is preferably the outermost layer on the side of the reflector element 6 which faces away from the substrate. This is therefore advantageous because the abovementioned absorption effects which could occur when an excessively thick second barrier layer 5 is applied would occur, in particular when further layers are applied to the second barrier layer 5.

(14) Furthermore, it is advantageous that the second barrier layer 5 is the outermost layer because in this way hydrophobic surface properties can be achieved. The use of a siloxane layer for the second barrier layer 5 has, inter alia, the advantage that this material has hydrophobic surface properties. The molecules of the siloxane layer have a stable SiOSi structure on which approximately 1.5 methyl groups are bound per Si atom on statistical average. The presence of these groups brings about the hydrophobic properties of the surface. If the second barrier layer 5 in the form of a siloxane layer is the outermost layer of the reflector element 6, the surface of the reflector element therefore acts in an advantageously water repellant fashion.

(15) The quality of the second barrier layer 5 can be adjusted by means of the process control of the plasma polymerization with respect to monomer composition, plasma power, addition of O.sub.2 and temperature profile of the substrate and can be characterized with respect to the structure composition by, inter alia, the FTIR absorption spectrum. The process conditions permit the adjustment of various properties of the siloxane layer, in particular the barrier effect with respect to the diffusion of water and gas, the optical transparency in the blue color (yellow coloring), the mechanical properties or the surface energy for adjusting a hydrophobic surface characteristic.

(16) The outermost siloxane layer is, in particular, elastic and is distinguished by a strongly polymer-like structure which is distinguished in the FTIR spectrum by broad, strongly pronounced absorption in the range from 3000 cm.sup.1 to 3600 cm.sup.1, a strong SiO band at about 1100 cm.sup.1 and high absorption levels in the range between the SiO band (1100 cm.sup.1) and 600 cm.sup.1, in particular in the range between 850 cm.sup.1 and 950 cm.sup.1 as a result of high portions of Si(CH.sub.3) molecular bonds. The deposition conditions of the siloxane layer are preferably adapted by the process control in such a way that the broadband FTIR absorption in the wave number range from 600 to 1000 cm.sup.1 is reduced. It is apparent that in this way the barrier properties and the transmission in the blue spectral range are improved, wherein the elasticity of the siloxane layer is retained in order to achieve the long-term stability.

(17) The FTIR absorption spectra of three exemplary embodiments of the reflector element 6 are illustrated in FIGS. 2, 3 and 4. The reflector element 6 with the FTIR absorption spectrum according to FIG. 2 has a substrate 1 composed of polycarbonate, a metallic intermediate layer composed of Cu with a thickness of approximately 30 nm, a reflective silver layer 3 with a thickness of approximately 150 nm to 220 nm, a first barrier layer 4 composed of SiO.sub.2 with a thickness of approximately 90 nm and a second barrier layer 5 composed of siloxane with a thickness of approximately 310 nm.

(18) The manufacture of the siloxane layer occurred in the exemplary embodiment after the coating of a reflector substrate body 1 with Cu, Ag and SiO.sub.2 in a plasma polymerization coating system (Nano type from Diener electronics). A gas distributor system is provided here in a planar coating electrode of the substrate arranged in an insulated fashion over the mass electrode, at a distance of 75 mm from the substrate. The system has an electrode surface of 100100 mm and an effective plasma power of 280 W at the operating frequency of 13.56 MHz. In a first step, pre-treatment took place for 1 minute by plasma formation in the argon plasma with 280 W RF power at an overall pressure of p=0.2 mbar in the plasma system. This was followed by a coating period of 5 minutes, wherein HMDSO was let in with a flow rate of 10 sccm, and a further 4 minutes of coating method in which both HMDSO with a flow rate of 10 sccm and O.sub.2 with a flow rate of 40 sccm were let in. During the coating steps, the overall pressure in the plasma system continued to be p=0.2 mbar.

(19) A further exemplary embodiment whose FTIR absorption spectrum is illustrated in FIG. 3 differs from the exemplary embodiment in FIG. 2 in that chromium instead of copper was used for the material of the metallic intermediate layer 2.

(20) The further exemplary embodiment whose FTIR absorption spectrum is illustrated in FIG. 4 differs from the two previous exemplary embodiments in that no metallic intermediate layer has been arranged between the substrate 1 and the silver layer 3. Furthermore, the exemplary embodiment in FIG. 4 differs from the previous exemplary embodiments in that the first barrier layer 4 has Al.sub.2O.sub.3 instead of SiO.sub.2.

(21) It is apparent that in various exemplary embodiments of reflector elements differences in the FTIR absorption spectra occur as a function of the layer materials, layer thicknesses and growth conditions used.

(22) In this context, a relationship was established between the FTIR absorption properties and the optical properties. The integral FTIR absorption of the OSiO bond in the range from 1100 cm.sup.1 to 1000 cm.sup.1 can be placed in a relationship with the absorption in the range from 950 cm.sup.1 to 850 cm.sup.1 in which the absorption of integrated SiCH.sub.3 and SiO groups with little cross-linking occurs. This ratio A(850 cm.sup.1 . . . 950 cm.sup.1)/A(1000 cm.sup.1 . . . 1100 cm.sup.1)/shows a correlation with the difference R.sub.vis-blue=R.sub.vis(420 nm-760 nm)R.sub.blue (420 nm480 nm) between the reflectivity R.sub.vis which is averaged over the visual spectral range from 420 nm to 760 nm and the reflectivity R.sub.blue which is averaged over the blue spectral range from 420 nm to 480 nm.

(23) This correlation is illustrated in FIG. 5. If the FTIR absorption ratio is below 65%, the reduction of the blue reflectivity with respect to the average visual reflectivity is less than 1.5%. If the FTIR absorption ratio is greater than 75%, the reduction of the blue reflectivity with respect to the visual reflectivity is above 2%. In this case, the reflected light exhibits increased yellow coloring. In order to avoid such yellow coloring, the layer thicknesses, materials and growth conditions are therefore adjusted in such a way that the FTIR absorption ratio is less than 65%.

(24) The invention is not limited by the description on the basis of the exemplary embodiments. Instead, the invention comprises any new feature as well as any combination of features, which includes, in particular, any combination of features in the patent claims even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.