FR3066349A1 - CONDUCTIVE COATING WITH SILVER PARTICLES FOR PROJECTOR ICE WITH DEFROSTING FUNCTION - Google Patents

Abstract

The invention relates to an ice (2) for a motor vehicle light device, with an outer face (2.1) and an inner face (2.2), comprising on a central zone of the inner face (2.2), an electrically conductive coating (4) forming a central heating zone for defrosting said ice, said coating comprising silver particles providing electrical conductivity.

Description

The invention relates to the field of lighting and light signaling, in particular for motor vehicles. More particularly, the invention relates to the realization of a defrosting function on a light device glass. The use of light emitting diode (LED) light sources is becoming more common, mainly due to better energy efficiency. This means that the light source or sources arranged in a light device produce significantly less heat in comparison with more conventional light sources such as discharge and incandescent light sources. This also means that in the event of frost forming on the ice of a headlamp equipped with LED type light source (s), the heat produced by said source or sources may not be sufficient to melt and disappear frost. It is then necessary to provide a specific deicing device.

Such a device is known per se for other applications, such as that of a windshield or of a rear window of a motor vehicle. It essentially comprises a resistive coating made up of metal wires arranged on the inner face of the glass and connectors connecting the metal wires, at their opposite ends, to a source of voltage or electric current. The circulation of electric current in the metallic wires causes heating capable of melting and disappearing the frost.

This defrosting device is not or only slightly applicable to a light device, such as a projector, since it is visible and inhomogeneous. It then negatively influences the photometry of the light device. The purpose of the invention is to overcome at least one of the drawbacks of the above-mentioned prior art. More specifically, the invention aims to provide an ice defrosting device, in particular a motor vehicle light device, which is optically more efficient. The subject of the invention is a lens for a light device for a motor vehicle, with an external face and an internal face, remarkable in that it comprises, on a central zone of the internal face, an electrically conductive coating forming a central zone of heats for defrosting said ice, said coating comprising silver particles ensuring electrical conductivity.

According to an advantageous embodiment of the invention, the coating is transparent with a transmission rate of visible and / or infrared light greater than 80%, preferably greater than 90%.

According to an advantageous embodiment of the invention, the coating extends over more than 50% of the inner face of the glass and is a resistive coating with a sheet resistance for a square of 1m by 1m between 20 and 120 Ω.

According to an advantageous embodiment of the invention, the coating has a thickness of between 0.3 μm and 10 μm.

According to an advantageous embodiment of the invention, said glass further comprises electrodes on the inner face, in electrical contact with, and at the periphery of, the central heating zone. At least two electrical connection tracks connecting to the periphery of the glass at least two electrodes can be provided.

According to an advantageous embodiment of the invention, the electrodes are formed by an ink comprising silver particles ensuring an electrical conductivity.

According to an advantageous embodiment of the invention, the silver particles comprise silver nanowires.

According to an advantageous embodiment of the invention, the silver nanowires have an average diameter greater than 50 nm and / or less than 800 nm.

According to an advantageous embodiment of the invention, the silver nanowires have an average length greater than 1 nm and / or less than 100 nm.

According to an advantageous embodiment of the invention, the ice is made of organic material, advantageously of PC or PMMA. A subject of the invention is also a light device, such as a headlamp, for a motor vehicle, comprising a housing with an opening and a glass closing said housing at the opening, remarkable in that the glass conforms to the 'invention. The invention also relates to a method for producing a defrosting function on a window of a light device for a motor vehicle; remarkable in that the glass is according to the invention, and said method comprises the following stages: deposition, on a central zone of the internal face of the glass, of a material forming the transparent and electrically conductive coating so as to form the central heating zone; polymerization and / or drying of the material forming the coating.

Advantageously, the material comprises a polymeric binder.

According to an advantageous embodiment of the invention, the deposition of the material is carried out by spraying.

According to an advantageous embodiment of the invention, the spraying of the material is carried out by means of a spray head supported by a robot.

According to an advantageous embodiment of the invention, the method comprises a preliminary step of preparation of the internal face of the ice by application to said face of a surfactant and / or by flame treatment and / or by plasma of said face.

The measures of the invention are advantageous in that they provide an ice cream with a heating zone exhibiting great transparency (expressed in particular by a transmission rate) and good electrical conductivity. The Joule effect is indeed proportional to the resistance of the heating zone and to the square of the current flowing through it. When the heating zone is supplied by a voltage source, it is then useful to provide a resistance of the heating zone sufficiently low that to circulate a current sufficient to reach the desired heating power.

The measures of the invention are also advantageous in that the electrically conductive coating based on silver has very good compatibility with electrodes also based on silver. The use of silver in the coating is also advantageous in that it reduces the formation of corrosion, and ensures better climatic resistance. Other characteristics and advantages of the present invention will be better understood with the aid of the description and the drawings, among which: - Figure 1 illustrates a motor vehicle headlamp window equipped with a de-icing device according to the invention ; - Figure 2 is an enlarged view of silver nanowires present in the electrically conductive coating on the glass of Figure 1; - Figure 3 schematically illustrates a method of depositing electrically conductive material to form the deicing device.

Figure 1 illustrates a motor vehicle headlight glass. The glass 2 consists essentially of a main element of transparent material, such as inorganic glass or even organic glass, such as in particular polycarbonate (PC). By transparent is meant that at least 80% of visible and / or infrared light is transmitted through the element. The main transparent element has an extended and preferably curved wall shape. The window 2 includes an outer face 2.1 and an inner face 2.2. The latter is intended to be directed into the interior of a projector housing. On this inner face 2.2 is deposited an electrically conductive and transparent coating 4.

Electrodes 6.1, 6.2, 6.3 and 6.4 are arranged along the ends of the extent of the coating 4, in contact with said coating. These electrodes are intended to provide an electrical supply to the electrically conductive coating so as to generate a current along and over the entire coating and, consequently, overheating of the latter and of the transparent material constituting the ice and supporting the coating. This heating makes it possible to melt a deposit of ice, frost and / or mist on the ice 2. The location of the electrodes can be chosen so as to optimize the flow of current over the extent of the electrically conductive coating 4, so as to ensure a desired heating.

The electrically transparent conductive coating 4 thus forms a heating zone.

It can be seen in Figure 1 that the upper electrode 6.1 extends along the generally horizontal upper edge of the glass 2. It is directly connected to a connector 10.1 intended to be connected to a power supply 12. The lower electrodes 6.2 and 6.3 and the side electrode 6.4 are connected, via connection tracks 8.2, 8.3 and 8.4, to a connector 10.2 intended to be connected to the electrical supply.

The electrically conductive coating 4 is produced by applying a material, on an inner face 2.2 of the crystal 2, said material comprising a polymeric binder and silver particles ensuring the electrical conductivity, followed by polymerization. The silver particles advantageously include nanowires of silver. The nanosilver wires can have an average diameter greater than 50 nm and / or less than 800 nm. They can also have an average length greater than 1 nm and / or less than 100 nm.

The material, as described above, deposited to form the electrically conductive coating 4 is commercially available from the LOCTITE ECI 5000 E & C series from the company Henkel® and also in development at the French Atomic Energy and Alternative Energies Commission (CEA).

FIG. 2 illustrates a greatly enlarged view of such a material, illustrating the silver nanotubes. The transmission is of the order of 90%, that is to say comparable to that obtained with indium tin oxide (ITO for the English name: Indium tin oxide) which is a mixture of oxide d indium (III) (ln2O3) and tin oxide (IV) (SnO2) and known to be electrically conductive and transparent. The resistance expressed for a layer forming a square of 1m by 1m is less than 100 Ohm, advantageously less than 60 Ohm, and can even be less than 20 Ohm. It is called a sheet resistance or "sheet resistance".

FIG. 3 schematically illustrates a method of depositing the electrically conductive material in order to form the heating zone 4. The deposition of the material forming the electrically conductive coating 4 can be carried out by spraying, in particular by means of a head spray 12 supported by a robot 14, sweeping the area of ice 2 to be covered with the material. This type of application is interesting in particular because of the fact that the surface of the glass to be treated is not usually flat or even left, which makes other methods such as screen printing initially suitable for flat surfaces, more difficult to implement under these conditions.

The coating has a thickness of between 0.3 µm and 10 µm.

The electrodes 6.1, 6.2, 6.3 and 6.4 and the connection tracks 8.2, 8.3 and 8.4 described above in relation to FIG. 1 can also be produced by applying a material similar or identical to that used for the electrically conductive coating 4, namely a material comprising a polymeric binder and silver particles ensuring electrical conductivity. Reference is therefore made to the above description of the material in question. The application is also followed by polymerization and / or drying. The material to be deposited may, however, differ from that used to form the heating zone 4 by having a lower resistance.

The electrodes 6.1, 6.2, 6.3 and 6.4 (Figure 1) are in direct contact with the coating 4 forming the heating zone, by superposition with said coating. Tracks 8.2, 8.3 and 8.4 provide the electrical connection between some of these electrodes 6.2, 6.3 and 6.4 and the connector 10.2. These electrodes 6.1, 6.2, 6.3 and 6.4 are formed by depositing conductive material directly on the coating 4 in question. Given the elongated and narrow nature of the electrodes and the connection tracks, the material is advantageously deposited by ink jet or microdosing (or “microdispensing” in English) in particular by means of an ink jet or microdosing head. supported by a robotic arm, as illustrated in FIG. 3. Such installations are commercially available, in particular from the company Musashi Engineering Inc.

In general, it is possible to provide a preliminary step for preparing the inner face of the ice by applying a surfactant to the face in question and / or by flame treatment and / or by plasma treatment.

In general, it is possible to provide for the deposition of an electrically insulating varnish on the inner face of the glass, after application of the material forming the heating zone and of the material forming the electrodes and possibly the electrical connection tracks. The use of a conductive ink based on silver particles has advantages in terms of performance, durability and processing. Indeed, such an ink has advantages of electrical conductivity and implementation. In addition, the silver nanotubes have great stability over time and the implementation of such still by spraying, in particular with a head of the inkjet or microdosing type on robot arm, is particularly easy on a surface similar to that of a light device glass.

Claims (15)

claims 1. Glass (2) of a light device for a motor vehicle, with an outer face (2.1) and an inner face (2.2), characterized in that it comprises, on a central zone of the inner face (2.2), a coating electrically conductive (4) forming a central heating zone for defrosting said ice, said coating comprising silver particles ensuring electrical conductivity. 2. Glass (2) according to claim 1, characterized in that the electrically conductive coating (4) is transparent with a transmission rate of visible and / or infrared light greater than 80%, preferably greater than 90%. 3. Glass (2) according to one of claims 1 and 2, characterized in that the electrically conductive coating (4) extends over more than 50% of the inner face (2.2) and is a resistive coating with a resistance sheet for a square of 1m by 1m between 20 and 120 Ω. 4. Glass (2) according to one of claims 1 to 3, characterized in that the electrically conductive coating (4) has a thickness between 0.3 pm and 10 pm. 5. Glass (2) according to one of claims 1 to 4, characterized in that said glass further comprises electrodes (6.1, 6.2, 6.3, 6.4) on the inner face (2.2), in electrical contact with , and at the periphery of, the central heating zone (4). 6. Ice (2) according to claim 5, characterized in that the electrodes (6.1, 6.2, 6.3, 6.4) are formed by an ink comprising silver particles ensuring the electrical conductivity. 7. Ice (2) according to one of claims 1 to 6, characterized in that the silver particles comprise nanowires of silver. 8. Ice (2) according to claim 7, characterized in that the silver nanowires have an average diameter greater than 50 nm and / or less than 800 nm. 9. Ice (2) according to one of claims 7 and 8, characterized in that the silver nanowires have an average length greater than 1 nm and / or less than 100 nm. 10. Ice (2) according to one of claims 1 to 9, characterized in that the ice (2) is made of PC or PMMA. 11. Luminous device, such as a headlamp, for a motor vehicle, comprising a housing with an opening and a window (2) closing said housing at the opening, characterized in that the window conforms to one of the claims 1 to 10. 12. Method for producing a defrosting function on a window (2) of a light device for a motor vehicle; characterized in that the glass (2) is according to one of claims 1 to 10, and the method comprises the following steps: - deposition, on a central area of the inner face (2.2) of the glass (2), d 'a material forming the electrically conductive transparent coating (4) so as to form the central heating zone; - polymerization and / or drying of the material forming the coating. 13. Method according to claim 12, characterized in that the deposition of the material is carried out by spraying. 14. Method according to claim 13, characterized in that the spraying of the material is carried out by means of a spray head (12) supported by a robot (14). 15. Method according to one of claims 12 to 14, characterized in that said method comprises a preliminary step of preparation of the inner face (2.2) of the ice (2) by application to said face of a surfactant and / or by flame and / or plasma treatment of said face.