OPTICAL ELEMENT FOR A MOTOR VEHICLE

Abstract

An optical element, which is transparent, for a motor vehicle, including at least one transparent first layer containing a polymer material and at least one second layer including at least silicon, titanium and oxygen. The optical element has a surface roughness defined by a mean square deviation Rq greater than or equal to 20 nm.

Claims

1. Optical element for a motor vehicle, comprising at least one transparent first layer containing a polymer material, and at least one second layer comprising at least silicon, titanium and oxygen, wherein the optical element has a surface roughness defined by a mean square deviation Rq greater than or equal to 20 nm.

2. Optical element according to claim 1, wherein the second layer also comprises at least one dopant chosen from the chemical elements of the Periodic Table of Elements which have an atomic size ranging from 1 to 4 .

3. Optical element according to claim 1, wherein the optical element has a roughness defined by a mean square deviation of at least 50 nm.

4. Optical element according to claim 1, wherein the second layer of the optical element comprises: one or more silicon-oxygen (SiO) group(s), and one or more titanium-oxygen (TiO) group(s).

5. Optical element according to claim 4, wherein the second layer also comprises one or more silicon-oxygen-hydrogen (SiOH) group(s).

6. Optical element according to claim 2, wherein the second layer comprises from 0.0001% to 10% by weight of dopant, relative to the total weight of the second layer.

7. Optical element according to claim 1, wherein the transparent first layer comprises at least 50% by weight of polymer material, relative to the total weight of the first layer.

8. Optical element according to claim 1, wherein the transparent first layer and/or the second layer comprising silicon, oxygen and titanium is an etched layer.

9. Optical element according to claim 1, wherein the optical element also comprises a transparent layer of polyorganosiloxane.

10. Optical element according to claim 9, wherein the transparent layer of polyorganosiloxane is positioned between the transparent first layer and the second layer comprising silicon, oxygen and titanium.

11. Motor vehicle luminous device comprising an optical element according to claim 1.

12. Process for manufacturing an optical element according to claim 1, wherein the process for manufacturing an optical element comprises, starting from the transparent first layer, at least the following steps: an oxidative etching step, and a step of depositing the second layer comprising silicon, oxygen and titanium.

13. Process according to claim 12, wherein the etching step and the step of depositing the second layer are carried out according to one of the following two alternatives A) or B): A) etching, by oxidative etching, the transparent first layer, and depositing the second layer comprising silicon, oxygen and titanium, on the transparent first layer etched in the preceding step, or B) depositing the second layer comprising silicon, oxygen and titanium, on the transparent first layer, and etching, by oxidative etching, the second layer comprising silicon, oxygen and titanium, deposited in the preceding step.

14. Process according to claim 12, wherein the oxidative etching step is carried out by dry etching.

15. Process according to claim 12, wherein the process also comprises a step of hydroxylation of the second layer comprising silicon, oxygen and titanium.

16. Optical element according to claim 2, wherein the optical element has a roughness defined by a mean square deviation of at least 50 nm.

17. Optical element according to claim 2, wherein the second layer of the optical element comprises: one or more silicon-oxygen (SiO) group(s), and one or more titanium-oxygen (TiO) group(s).

18. Optical element according to claim 3, wherein the second layer comprises from 0.0001% to 10% by weight of dopant, relative to the total weight of the second layer.

19. Optical element according to claim 2, wherein the transparent first layer comprises at least 50% by weight of polymer material, relative to the total weight of the first layer.

20. Optical element according to claim 2, wherein the transparent first layer and/or the second layer comprising silicon, oxygen and titanium is an etched layer.

Description

[0159] Other features and advantages of the present invention will emerge in the light of the description of non-limiting examples given only by way of non-limiting illustration, with reference to the appended FIG. 1.

[0160] FIG. 1 is a diagrammatic representation of examples of roughness of the optical element of the invention.

[0161] In the interests of clarity, only the elements essential for understanding the invention have been diagrammatically represented in this FIG. 1, which is not to scale.

[0162] In particular, in FIG. 1, several forms of crenellations are represented. The crenellations may be of the sinusoidal type having a height h.sub.1 or h.sub.2 and a pitch p.sub.1 or p.sub.2; of triangular type having a height h.sub.4 and a pitch p.sub.4; or of truncated pyramid type having a height h.sub.3 or h.sub.5 and a pitch p.sub.3 or p.sub.5.

EXAMPLE

Manufacture of an Optical Element in Accordance with the Invention

[0163] 1. Step of Etching the Transparent First Layer

[0164] The support used as transparent first layer is a transparent polycarbonate (PC), sold by the company Kudeb under the reference Makrolon AL 2447. This support is in the shape of a rectangular plate with the following dimensions: 100 mm long, 100 mm wide and 2.5 mm thick.

[0165] The step of oxidative etching by atmospheric plasma oxidation is carried out on the transparent first layer.

[0166] The etching step is carried out on the support as described above by means of an atmospheric-pressure plasma torch comprising an internal electrode connected to a variable-frequency high-voltage generator and a nozzle for transferring the plasma to the support.

[0167] The ionization gas is dioxygen. The gas flow rate is 50 litres per minute. The frequency of the generator is set at 25 kHz, the applied voltage is set at 400 volts, the nozzle/source-to-support distance is 6 mm and the speed at which the nozzle moves relative to the support is 10 metres per minute.

[0168] An etched polycarbonate transparent first layer is thus obtained.

[0169] 2. Step of Depositing the Second Layer Comprising Silicon, Oxygen and Titanium and a Dopant

[0170] The step of depositing the second layer comprising silicon, oxygen, titanium and nitrogen as dopant, by means of an atmospheric plasma torch, is then carried out.

[0171] The following compounds are used to prepare the transparent second layer: [0172] PR1: TEOS sold by the company Sigma Aldrich under the reference 86578 purity99% (CAS No. 78-10-4); [0173] PR2: TIPP sold by the company Sigma Aldrich under the reference 87560 purity97% (CAS No. 546-68-9); and [0174] the nitrogen used as carrier gas, ionization gas and dopant: sold by the company Air Liquide under the reference Alphagaz 1 Azote (CAS No. 7727-37-9).

[0175] The TEOS/TIPP weight ratio is 80/20.

[0176] A generator supplies an internal electrode with a voltage ranging from 200 to 450 volts and a current ranging from 10 to 30 amps (frequency of 20-25 kHz).

[0177] The flow rate of the TEOS precursor PR1 is 8 l.sub.s/min and the flow rate of the TIPP precursor PR2 is 2 l.sub.s/min, and the flow rate of dopant gas (N.sub.2) ranges from 10 to 30 l.sub.s/min.

[0178] The frequency of the generator is set at 20 kHz, the applied voltage is set at 350 volts, the nozzle/source-to-support distance is 15 mm and the speed at which the nozzle moves relative to the support is 100 metres per minute. The temperature of the carrier gas is 200 C.

[0179] An optical element according to the invention comprising an etched polycarbonate transparent first layer covered with a second layer of silicon, titanium, oxygen and nitrogen is thus obtained.

[0180] The second layer has a thickness of approximately 20 nm.

[0181] This second layer is characterized by SEM/EDS (Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy). It comprises a structure of core/shell type, in which at least one SiO.sub.2 particle is covered with a shell of TiO.sub.2-xN.sub.x nanoparticles distributed at the surface of said SiO.sub.2 particle.

[0182] 3. Step of Hydroxylation of the Second Layer

[0183] The support is then subjected to a hydroxylation step by means of an atmospheric plasma torch. The ionization gas is a mixture of dinitrogen and dioxygen in a 4/1 volume ratio. The gas flow rate is 50 litres per minute. The generator frequency is set at 22 kHz, the applied voltage is set at 300 volts, the nozzle/source-to-support distance is 10 mm and the speed at which the nozzle moves relative to the support is 30 metres per minute.

[0184] 4. Step of Plasma Treatment, in the Presence of Helium, of the Second Layer

[0185] The support is then subjected to a plasma treatment in the presence of helium. A generator supplies an internal electrode with a voltage of 300 volts, a current of 20 amps and a frequency of 25 kHz. The helium flow rate is from 20 to 50 l.sub.s/min. The nozzle/source-to-support distance is 15 mm.

[0186] 5. Characterization of the Optical Element in Accordance with the Invention

[0187] 5. a. Characterization of the Anti-fogging Properties

[0188] The anti-fogging properties were characterized by means of a test in which the optical element is exposed to water vapour by exposing it above a water bath heated to and maintained at a temperature of 78 C. (10 C.). The optical element is positioned 20 cm above the level of the water until saturation of the exposed surface (runoff of the condensed water).

[0189] The optical element remains perfectly transparent to the eye. No loss of transmission was observed on the surface of the optical element, which makes it possible to show its anti-fogging properties.

[0190] 5. b. Characterization of the Photocatalytic Properties

[0191] The photocatalytic activity is measured by exposing the surface of the optical element, as obtained above, to strictly visible light (400 nm800 nm).

[0192] To do this, the optical element is placed in Petri dishes containing a solution of methylene blue (organic coloured indicator). The Petri dishes are then placed in an opaque chamber with an opening in its upper part made with a visible-bandpass filter (400 nm<<800 nm) above which is switched on a halogen lamp.

[0193] A decolouration of the methylene blue solution is visually observed in less than 30 minutes, which shows the photocatalytic effect in the visible range of the optical element in accordance with the invention.

[0194] 5. c. Effect of Texturing/roughness

[0195] The roughness of the transparent polycarbonate (PC) support as described above (transparent first layer) was measured by means of an atomic force microscope.

[0196] Said support has a mean square deviation Rq of approximately 19.1 nm.

[0197] By comparison, the optical element as obtained at the end of step 2 described above has a mean square deviation Rq of approximately 65.2 nm.

[0198] The water contact angle is measured by means of a Krss DSA 25 contact angle analyser according to the ASTM D 724-99 standard.

[0199] Said support has a water contact angle of 10, while the contact angle of the optical element is less than 5.

[0200] The support and the optical element are then stored at 23 C. without protection. After 28 days, said support has a water contact angle of 20, while the contact angle of the optical element is 11.

[0201] This makes it possible to show that the optical element of the invention has a superhydrophilicity which is maintained over time.