FR3045134A1 - OPTICAL PART THERMOPLASTIC MATERIAL THERMAL CONDUCTOR - Google Patents

Abstract

The invention relates to an optical part (6) for a light module (2), especially a motor vehicle, comprising: a body (64) made of thermoplastic material; a reflective surface (62, 63) on the body; remarkable in that the thermoplastic material is a thermal conductive material with a thermal conductivity greater than 1 W / mK. The invention also relates to a light module (2) for a signaling and / or lighting device for a motor vehicle, comprising such an optical part (6). The invention also relates to a method of manufacturing the optical part (6).

Description

The invention relates to the field of light signaling and / or lighting, in particular for motor vehicles.

The published patent document FR 2 987 102 A1 discloses a motor vehicle headlight part, comprising a reflective surface for reflecting rays coming from the sun when the vehicle is parked outside in an orientation favorable to the penetration of the sun's rays. . Indeed, in certain configurations where the vehicle is oriented towards the sun and where it is relatively low in the sky, especially just above the horizon line, the sunlight can penetrate the projector and, via its optical system, to concentrate in a zone of the projector and to cause an increase of temperature likely to degrade the zone in question when this one, in particular when it is in plastic material. Or the use of plastic material for optical parts is advantageous from a production cost point of view, especially when it comes to parts with complex shapes. This teaching provides as a solution to this problem of "burning" by the sun's rays to have a reflective coating on the area in question so as to reflect the solar rays converging towards said area.

This solution is interesting in that it allows the use of plastics for parts subject to the phenomenon of "burning" by the sun's rays. However, depending on the configuration of the projector, the orientation of the vehicle and the position of the sun, the room or the plastic parts subject to this phenomenon are likely to heat up due to a partial and unavoidable absorption of the rays. solar. It is then necessary to provide a plastic material of the thermosetting type resistant to such heating. However, the use of thermosetting plastic materials requires, after molding, certain operations for improving the outer surface of the parts, such as deburring at the joint plane of the mold and / or varnishing. These operations are however expensive and potentially incompatible with the desired design. The object of the invention is to propose a solution that overcomes the above-mentioned problem, in particular a solution that makes it possible to produce an optical part that is compatible with the phenomenon of "burning" by solar rays, and this in an economical manner. The subject of the invention is an optical part for a light device, in particular a motor vehicle, comprising: a body made of thermoplastic material; a reflective surface on the body; remarkable in that the thermoplastic material is a thermal conductive material with a thermal conductivity greater than 1 W / mK.

According to an advantageous embodiment of the invention, the thermal conductivity of the thermal conductive material is greater than 5 W / mK, preferentially 10 W / mK.

According to an advantageous embodiment of the invention, the thermal conductive material comprises a thermoplastic matrix and a filler comprising graphite, carbon fibers and / or boron nitride. The charge can be in the form of fibers.

According to an advantageous embodiment of the invention, the proportion by weight of the filler with respect to the thermal conductive material is between 10% and 50%, preferably between 15% and 40%.

According to an advantageous embodiment of the invention, the thermoplastic matrix is one of the following materials: polycarbonate, polyethylene, polypropylene, acrylic, vinyl, polyamide and polybutylene terephthalate.

According to an advantageous embodiment of the invention, the reflecting surface has a reflection coefficient greater than 80%, preferably 85%.

According to an advantageous embodiment of the invention, the reflecting surface comprises a metal coating applied directly to the thermally conductive thermoplastic material. The metal coating may comprise aluminum and / or silver.

According to an advantageous embodiment of the invention, the thermally conductive thermoplastic material has an outer surface under the metal coating having a roughness Ra of less than 50 nm.

According to an advantageous embodiment of the invention, the roughness Ra less than 50 nm of the outer surface of the thermally conductive thermoplastic material is obtained by plastic injection into a mold according to a technology comprising heating and cooling said mold. Heating the mold means heating other than that naturally caused by the injection of the hot plastic material. Cooling the mold means cooling other than natural cooling after injection of the plastic material. It is therefore forced heating and cooling. The subject of the invention is also a light module for a signaling and / or lighting device for a motor vehicle, comprising: a light source capable of emitting light rays; an optical system adapted to deflect the light rays to form a light beam, said system comprising an optical piece with a reflecting surface; remarkable in that the optical part is according to the invention.

According to an advantageous embodiment of the invention, the reflecting surface of the optical part is a first reflecting surface configured to receive sun rays, said optical part comprising a second reflecting surface participating in the formation of the light beam. The two reflecting surfaces are advantageously non-coplanar and may form a relative average angle of inclination greater than 20 °, preferably 30 °, more preferably 50 °.

According to an advantageous embodiment of the invention, the optical part comprises a cutting edge of the beam, located between the first and second reflecting surfaces. The invention also relates to a method for manufacturing an optical part comprising the following steps: molding the part by plastic injection into a mold; and applying a reflective coating to form a reflective surface on the molding; remarkable in that the optical part is according to the invention and in that the molding step comprises heating, preferably by means of water vapor circulating in the mold channels and / or by induction, a portion of mold corresponding to the reflecting surface, and before the injection of the plastic material.

According to an advantageous embodiment of the invention, the molding step furthermore comprises cooling, preferably by means of water circulating in the mold channels, of the mold portion corresponding to the reflecting surface, and this after injection of the plastic material.

The measurements of the invention are interesting in that they make it possible to economically produce an optical part of a light module, subject to heating, in particular due to the phenomenon of "burning" by the sun's rays. Other features and advantages of the present invention will be better understood with the aid of the description and the drawings, among which: FIG. 1 is a representation of a lighting module for a motor vehicle headlamp, the module being in conformity with to the invention; FIG. 2 is a schematic representation of the operating principle of the module of FIG. 1 and illustrating the phenomenon of "burning" by the solar rays; - Figure 3 is a perspective representation of an optical part of the module of Figures 1 and 2, according to the invention.

FIG. 1 illustrates a lighting module for a motor vehicle headlamp. The module 2 illustrated in FIG. 1 is a double module, that is to say comprising two essentially identical submodules arranged side by side. However, it is understood that this module can be a simple module, a triple module, or more.

Module 2 comprises two light sources that are not visible in FIG. 1. These sources may be of the electroluminescence diode type. Each of these sources is covered by a first reflector 4 in the form of a half-shell. These reflectors may comprise reflecting surfaces of revolution with an elliptical profile. Each of these reflecting surfaces then comprises a first focus corresponding to the location of the light source and a second focus located at the edge 61 of the support piece 6. A second reflector 8 is arranged so as to reflect the rays thus produced. a light beam. The reflecting surface of this second reflector 8 is advantageously of parabolic profile with a focus corresponding to the second focus of the reflecting surface of the first reflector 4.

The edge 61 forms a cutting edge in that part of the rays emitted by the light source and reflected by the reflector 4 are reflected by the reflective surface located upstream, along the optical path, of the cutting edge 61. These reflections have the effect of "cutting" horizontally the beam produced in that these rays, if they were not reflected near the cutting edge, would be reflected by the second reflector 8 to form an upper portion of the beam. By being reflected at the cutoff edge 61, these rays are returned to an upper portion of the second reflector 8, to then form a lower portion of the beam and thus achieve a "cut" of said beam. The optical principle which has just been described is in itself well known to those skilled in the art.

FIG. 2 schematically illustrates the operating principle of the module of FIG. 1 as well as that of the phenomenon of "burning" by the solar rays. This figure corresponds to a longitudinal sectional view of one of the sub-modules of the double module of FIG.

We can observe the path of a ray, shown in dashed line, emitted by the light source 3, reflected by the first reflector 4, passing in front of the cutoff edge 61, and then reflected by the second reflector 8 to form the beam. 'lighting.

FIG. 2 also shows the ray paths emitted by the sun 10, shown in solid lines, in the direction of the module 2. These radii are inclined upwards with respect to the optical axis of the module corresponding essentially to the axis of the illumination beam, this axis corresponding substantially to the horizontal in Figure 2. These solar rays therefore meet the reflective surface of the reflector 8 with different angles of incidence, in this case larger than those of the rays emitted by the light source 3 and reflected by this same surface in order to form the illumination beam. The solar rays are then reflected and converge towards the zone 63 of the optical part 6, which does not participate in the formation of the illumination beam. This zone 63 is a reflecting surface so as to reflect a majority of the sun rays that converge there. The reflection ratio of the surface is advantageously greater than or equal to 90%. Due to the imperfect nature of this surface, a portion of the beam, in this case between 0% and 10%, is absorbed by the reflecting surface 63. The latter therefore undergoes heating. For this purpose, the part 6 is made of thermoplastic material having a thermal conduction greater than or equal to 1 W / mK, preferably greater than or equal to 5 W / mK, more preferably still greater than or equal to 10 W / mK. Such thermal conductivity can be achieved with a thermoplastic matrix by adding a filler comprising graphite and / or boron nitride. Such materials are also commercially available, in particular from Cool Polymers, under the trade name CoolPoly® of the E series and the D series. Their thermal conductivity ranges from 1 W / mK to 100 W / mK.

The thermoplastic matrix may comprise one or more of the following materials: polycarbonate, polyethylene, polypropylene, acrylic, vinyl, polyamide and polybutylene terephthalate.

The charge can be in the form of particles, granules or fibers. It has a mass proportion relative to the final material which is between 10% and 50%, preferably between 15% and 40%.

A reinforcement, such as glass fibers, may be present. A release agent may also be present, in this case to a lesser extent, for example less than 5%, preferably less than 2% by weight.

The thermal conductive material can be used in granular form and injected into a shaping mold. For this purpose, the plastic injection can use the technology "Heat & Cool ". This technology consists in preheating the mold before injecting the plastic material and then cooling the mold, with the aim of obtaining a particularly smooth surface. The preheating of the mold can be achieved by the circulation of water vapor through channels located near the mold portion forming the surface in question and / or by induction in areas located near the mold portion in question, and this before the injection of the plastic material. This can then flow more easily, thanks to a lower viscosity, along the portion of the mold forming the surface in question of the piece.

Cooling can be achieved by flowing a fluid, such as water, through the channels in question. The forced cooling, after injection of the plastic material, makes it possible to preserve the smooth surface state achieved by the injection of the plastic material along the preheated mold. This results in a surface condition having a very low Ra roughness, in this case less than 25 nm.

The optical part 6 comprises a second reflecting surface 62 arranged directly upstream (following the path of rays emitted by the light source) of the cutting edge 61. With reference to the description above of FIG. 1, this surface serves to reflect a portion of the rays from the light source, so as to "cut" substantially horizontally the light beam.

The optical part 6 can be made by the above-mentioned method in order to have a particularly low roughness on the zones 62 and 63. These surfaces can then be covered with a metal coating applied directly on the part, in order to achieve the reflective surfaces. .

FIG. 3 illustrates in perspective the optical part 6, in this case for one of the two submodules of the module of FIG. 1, it being understood that the optical part in question can be split to form one for the double module.

With reference to FIG. 3, the optical part 6 comprises a body 64 made of thermally conductive thermoplastic material, preferably by means of the abovementioned injection method, and a reflective coating 65. A first zone corresponding to that in which the solar rays converge in In the case of unfavorable exposure as shown in FIG. 2, the reflective surface 63 is formed. Similarly, the region along the upstream (along the ray path) of the cutoff edge 61 forms the reflecting surface 62.

The body 64, by virtue of its thermal conductivity, can then diffuse the heat received from the sun's rays towards the rest of its extent, in this case towards the part supporting the second reflecting surface 62. The body thus serves as a reservoir and diffuser for heat, which will prevent it from reaching critical temperatures, such as from 100 ° C. The optical part 6 may further comprise cooling fins, advantageously on its face opposite to that comprising the first and / or second reflecting surfaces.

The first and second reflective surfaces 63 and 62 may be made with the same coating, preferably during the same operation. They can also be made separately, possibly with different coatings. The reflection rate of the first surface 63 may be less than 95%, preferably between 85 and 90%, in order to absorb a portion of the sunlight. This avoids reflecting all or almost all (given the inevitable imperfection of a highly reflective surface) to the second reflector. The second surface 62 advantageously has a higher reflection ratio, such as greater than or equal to 95%.

In the embodiment which has just been described, the optical device comprises two reflectors, one of ellipsoidal profile and the other of parabolic profile, and the optical part comprises a cutting edge. However, it is understood that the invention also applies to other optical configurations, such as in particular a configuration comprising a single reflector and a lens, for example a plano-convex lens. In this case, the optical part may comprise a somewhat different configuration, such as in particular a variation of angle between the first and the second surface which is larger, such as between 60 ° and 120 °.

Claims (14)

claims 1. Optical part (6) for a light module (2), especially a motor vehicle, comprising: - a body (64) of thermoplastic material; - a reflective surface (62, 63) on the body; characterized in that the thermoplastic material is a thermal conductive material with a thermal conductivity greater than 1 W / mK. 2. Optical part (6) according to claim 1, characterized in that the thermal conductivity of the thermal conductive material is greater than 5 W / mK, preferably 10 W / mK. 3. Optical part (6) according to one of claims 1 and 2, characterized in that the thermal conductive material comprises a thermoplastic matrix and a filler comprising graphite, carbon fibers and / or boron nitride. 4. Optical part (6) according to claim 3, characterized in that the proportion by weight of the charge relative to the thermal conductive material is between 10% and 50%, preferably between 15% and 40%. 5. Optical part (6) according to one of claims 3 and 4, characterized in that the thermoplastic matrix is one of the following materials: polycarbonate, polyethylene, polypropylene, acrylic, vinyl, polyamide and polybutylene terephthalate. 6. Optical part (6) according to one of claims 1 to 5, characterized in that the reflecting surface (62, 63) has a reflection coefficient greater than 80%, preferably 85%. 7. Optical member (6) according to one of claims 1 to 5, characterized in that the reflecting surface (62, 63) comprises a metal coating applied directly to the thermally conductive thermoplastic material. 8. Optical part (6) according to claim 7, characterized in that the thermally conductive thermoplastic material has an outer surface under the metal coating having a roughness Ra less than 50 nm. 9. Optical part (6) according to claim 8, characterized in that the roughness Ra less than 50nm of the outer surface of the thermally conductive thermoplastic material is obtained by plastic injection in a mold according to a technology comprising heating and cooling said mold . 10. Light module (2) for a signaling and / or lighting device for a motor vehicle, comprising: - a light source (3) capable of emitting light rays; - an optical system (4, 6, 8) adapted to deflect the light rays to form a light beam, said system comprising an optical part (6) with a reflective surface (62, 63); characterized in that the optical part is according to one of claims 1 to 9. Light module (2) according to claim 10, characterized in that the reflecting surface of the optical part (6) is a first reflecting surface (63) configured to receive sun rays, said optical part (6) comprising a second reflecting surface (62) participating in the formation of the light beam. 12. Light module (2) according to claim 11, characterized in that the optical part (6) comprises a cutting edge (61) of the beam, located between the first and second reflecting surfaces (63, 62). 13. A method of manufacturing an optical part (6) comprising the following steps: - molding the piece (64) by plastic injection into a mold; and - applying a reflective coating to form a reflective surface (63, 62) on the molding (64); characterized in that the optical part (6) is according to one of claims 1 to 9 and in that the molding step comprises heating, preferably by means of water vapor flowing in channels of the mold and / or by induction, a mold portion corresponding to the reflecting surface, and before the injection of the plastic material. 14. The manufacturing method according to claim 13, characterized in that the molding step further comprises cooling, preferably by means of water circulating in the mold channels, of the mold portion corresponding to the reflecting surface. after the injection of the plastic material.