FR3138680A1 - Optical element for optical module of a motor vehicle - Google Patents

Abstract

TITLE: Optical element for optical module of a motor vehicle Optical element (1) for an optical module (5) of a motor vehicle comprising a central plate (10) arranged between a first side plate (20) and a second side plate (30), characterized in that it comprises at minus a layer of glue (41) disposed between the first side plate (20) and the central plate (10). Figure for abstract: figure 10

Description

Optical element for an optical module of a motor vehicle Technical field of the invention

The invention relates to an optical element for an optical module of a motor vehicle. It also relates to an optical module comprising such an optical element. Finally, it relates to a method for manufacturing such an optical element for an optical module of a motor vehicle.

State of the prior art

An optical module used in a lighting device of a motor vehicle generally comprises a light source and an optical element that transmits the light emitted by the light source according to predefined lighting characteristics. A known optical element comprises a central glass plate, covered on either side by two layers of transparent resin, which form two side plates of the optical element. One face of the central plate comprises an optical mask forming a pattern corresponding to a desired lighting. Each resin layer is respectively molded and hardened on each of the two faces of the central plate, using a mold formed by a lithography process. The mold is made of a resin that is exposed to light radiation after having been covered with a partially transparent mask having gray levels. The gray levels correspond to the shapes of the patterns desired on the side plates. The lighter the gray, the more light radiation penetrates inside the resin of the mold, the darker it is, the less it penetrates. Thus, the resin is more or less impacted by the light radiation, which allows hard areas and fragile areas to be created over a variable depth, the latter being then removed to reveal the desired shapes. This process makes it possible to form a repetition of identical patterns of very small dimensions on the outer face of the resin layers, that is to say the face opposite the glass of the central plate. Each pattern has a dimension less than or equal to 0.1 mm. Each pattern of the resin behaves like an independent optical cell, capable of transmitting light according to the desired properties, and will also be called an optical pattern for this purpose. This transmission of light generates a particular aesthetic lighting effect linked to the shape of the resin patterns.

Such an optical element of the state of the art has the first drawback of a high manufacturing cost, in particular due to the process used, in particular lithography. On the other hand, such a process is limited in the shapes that can be produced, and consequently in the possible lighting aesthetics. Indeed, the dimensions of the optical patterns formed on the outer surface of the resin are necessarily very small, and the resulting aesthetic lighting effects are substantially always the same. In other words, it is not possible to choose aesthetic lighting effects that are far from those already known, which represents a second drawback of this solution of the state of the art.

Presentation of the invention

A first object of the invention is to propose a solution for an optical module for a motor vehicle making it possible to reduce the cost of the state of the art.

A second object of the invention is to propose a solution for an optical module for a motor vehicle making it possible to offer varied and attractive lighting aesthetics.

For this purpose, the invention relates to an optical element for an optical module of a motor vehicle comprising a central plate arranged between a first side plate and a second side plate, characterized in that it comprises at least one layer of glue arranged between the first side plate and the central plate.

The optical element may include another layer of glue disposed between the second side plate and the central plate.

The first side plate and/or the second side plate may be made of a plastic material, such as polymethyl methacrylate (PMMA), polycarbonate (PC), a cycloolefin copolymer (COC), or a cycloolefin polymer (COP).

At least one of the first side plate and the second side plate may be made of a material at least partially transparent to crosslinking radiation of a glue layer of the optical element, so as to allow crosslinking of the glue by radiation passing therethrough during manufacture of the optical element.

The central plate and at least one of the first side plate and the second side plate may be made of a material resistant to a heat treatment temperature of a glue layer of the optical element, so as to allow the glue to harden by heat treatment during manufacture of the optical element.

The at least one layer of glue can have a thickness of between 100 and 300 µm.

The at least one layer of adhesive may extend over the entire surface of a surface of the central plate, at the interface between the central plate and the first side plate or the second side plate, or extend over only a portion of this surface.

The at least one layer of glue can be in an epoxy resin based material.

The optical element may include at least one of the first side plate and the second side plate having optical patterns larger than 1 mm on its outer surface.

The central plate may be made of plastic or glass, particularly of the Flint glass type. It may include an optical mask on at least one surface.

The invention also relates to an optical module, comprising a light source, and characterized in that it comprises an optical element according to the invention intended to be traversed by the light emitted by said light source.

The invention also relates to a method of manufacturing an optical element according to the invention.

The invention also relates to a method of manufacturing an optical element for an optical module of a motor vehicle, characterized in that it comprises a step consisting of manufacturing by molding, in particular by injection, at least one side plate, and a step consisting of assembling by gluing said at least one side plate on a central plate of the optical element.

The step of assembling by gluing said at least one side plate on the central plate of the optical element may comprise a step of crosslinking at least one layer of glue by crosslinking radiation or a step of hardening at least one layer of glue by heat treatment.

Presentation of figures

These objects, characteristics and advantages of the present invention will be explained in detail in the following description of a particular embodiment made without limitation in relation to the attached figures among which:

Figures 1 to 10 represent the different steps of the manufacturing process of an optical element according to one embodiment of the invention.

There schematically represents an optical module according to one embodiment of the invention.

Detailed description

According to the invention, an optical element also comprises three superimposed plates, as in the prior art. However, according to the concept of the invention, at least one side plate is manufactured independently, in particular by molding, before being associated with a central plate by bonding. This approach has the advantage of greatly simplifying the manufacturing process, since said side plate is manufactured in a much simpler manner, without lithography technique. In addition, this manufacturing reduces the geometric constraints on this side plate, which can have shapes very far removed from existing plates, thus producing all kinds of lighting aesthetics that did not exist. By this concept, the invention thus meets the two objects mentioned above. As a remark, advantageously, the two side plates will be manufactured independently and then bonded to the central plate.

The invention will be described in detail by means of a method of manufacturing such an optical element according to an embodiment of the invention.

There thus illustrates a first step of the manufacturing method, which consists in preparing a central plate 10 of the optical element, by the formation E1 of an optical mask 18 on at least one of its two faces 11, 12. Such an optical mask can be formed by any known means, for example by depositing a coating that is not transparent to the light used in an optical module. Such a coating can for example be deposited by a vapor deposition technique, known by the English acronym PVD, optionally followed by laser retouching. Alternatively, it can be deposited by a lithography technique. The mask can comprise a metallic material, in particular aluminum or chrome. This mask is intended to allow incident light to pass only according to a predefined pattern, in a known manner. For this, the optical mask can be made of an opaque material, comprising at least one at least partially transparent opening, the contours of which correspond to the shape of the light pattern that it is desired to project. The central plate can be made of glass or plastic material, as will be detailed later.

There represents a second step of the manufacturing method, which consists in preparing a first side plate 20. This is a step consisting in manufacturing the first side plate 20 by molding E2. Preferably, this step comprises injecting a plastic material into a mold. Alternatively, this step comprises casting molding, which consists in filling a mold to the desired shape with a liquid material, which gradually solidifies inside the mold. More generally, any manufacturing method by molding can be used. The mold, not shown, is such that it forms a first flat inner face 21 of this first side plate 20, intended for attachment to the first face 11 of the central plate 10, and a second opposite outer face 22, which comprises optical patterns, which will be specified later.

There represents a third step consisting of depositing E3 a layer of glue 41 on the first surface 11 of the central plate 10, using an applicator 40. This glue can be based on epoxy resin.

There represents a fourth step consisting of assembling E4 the first side plate 20 and the central plate 10, at the level of the first glued surface 11 of the central plate 10. The pressure exerted between the two plates 10, 20 during this assembly makes it possible to distribute the glue over substantially the entire first surface 11 of the central plate 10, and therefore also over the entire interior surface 21 of the first side plate 20.

There illustrates the result obtained at the end of this fourth step. This results in an intermediate layer of glue 41 between the central plate 10 and the first side plate 20. This bonding step thus makes it possible to assemble the two plates 10, 20 while avoiding any presence of air between the two plates, which would be detrimental to the optical performance of the optical element.

As a note, when a side plate is formed according to the technique described above of the prior art, it is deposited in liquid form on the surface of the central plate, and has intrinsic adhesive properties which allow it to adhere automatically to the central plate after hardening, without the presence of a separate glue. This technique of the prior art is more expensive, but has the advantage that the technical problem of the quality of the interface between the two plates does not arise, in particular with regard to the potential presence of air. With the manufacturing method according to the invention, the great simplification makes it possible to significantly reduce the overall cost, but there is however a new technical problem during assembly, to obtain an interface of acceptable quality between the two plates.

There represents a fifth step of the manufacturing method, which consists in hardening E5 the glue. According to this embodiment, this hardening is obtained by crosslinking from ultraviolet radiation by a tool 45. In this embodiment, the radiation is applied through the central plate 10. The latter is then in a material at least partially transparent to the crosslinking radiation, this transparency being sufficient to achieve crosslinking of the glue and an acceptable resulting bonding. Alternatively, this radiation could be carried out through the first side plate 20, in which case it would be in a material at least partially transparent to the crosslinking radiation. The assembly of the two plates 10, 20 is therefore finalized at the end of this fifth step. All of the steps E3 to E5 represented by FIGS. 3 to 6 therefore form a step of bonding the first side plate 20 to the central plate 10.

Figures 7 to 10 describe steps E6 to E9 of the manufacturing method for obtaining the bonding of a second side plate 30 on the second surface 12 of the central plate 10. These steps E6 to E9 are respectively substantially identical to the steps E2 to E5 described previously. The last step of the bonding consists in hardening E9 the layer of glue 42 arranged between the inner surface 32 of the second side plate 30 and the second surface 12 of the central plate 10. As a note, for this crosslinking step, at least the second side plate 30 or the assembly of the central plate 10 and the first side plate 20 is at least partially transparent to the crosslinking radiation. The radiation is then applied either through the second side plate 30 if the latter is at least partially transparent to the crosslinking radiation, or through the assembly of the central plate 10 and the first side plate 20 if the latter is at least partially transparent to the crosslinking radiation. If these three elements are all transparent to said radiation, then it can be applied indifferently through one or more of these elements.

There represents the finalized optical element 1.

The invention is naturally not limited to the described embodiment of the manufacturing method.

For example, the hardening of the glue could be achieved by heat treatment. In this variant, the materials of the plates are chosen so as to withstand the heat treatment temperature. This temperature can be greater than or equal to 90°C.

On the other hand, the assembly has been described in two successive phases to respectively glue separately each side plate 20, 30 on the central plate 10. Alternatively, these two side plates 20, 30 could be glued simultaneously on the central plate 10.

The invention also relates to an optical element 1 as such, in particular obtained by the manufacturing method described above.

The optical element 1 therefore comprises a central plate 10, positioned between two side plates 20, 30. Each assembly of two plates is obtained by a respective layer of glue 41, 42. This layer of glue 41, 42 advantageously extends over the entire surface at the interface between the two plates to be bonded. Alternatively, it could extend over only one part. In particular, it can be present on a central part only. Laterally, any configuration making it possible to guarantee the seal between the bonded plates will then be implemented. In all cases, the layer of glue can have a thickness of between 100 and 300 µm.

In addition, another important advantage of the invention, in addition to the simplification of the manufacturing process, is to make it possible to manufacture a side plate having optical pattern shapes, which cannot be produced using the prior art technique. In particular, patterns of much larger dimensions are possible, such as patterns of dimensions greater than 1 mm. Preferably, these patterns will be of dimensions less than 10 mm, or even less than 5 mm.

These optical patterns can be defined by a regular mesh produced at the level of the external surface 22, 31 of one or both side plates 20, 30 of the optical element 1. The aforementioned pattern dimension then corresponds in such a diagram to the pitch of these patterns, or to the smallest pitch of these patterns if they are distributed regularly in two directions.

These optical patterns may also have an identifiable base, such as a circular or rectangular or polygonal base. In this case, the aforementioned dimension corresponds to the smallest side of the base, or to the diameter of this base. If the patterns have a more complex shape, the aforementioned dimension may correspond to the diameter of the circle in which their base is inscribed. Any more complex geometry may be envisaged, such as the presence of irregular patterns and/or the presence of optical patterns of different size and/or shape on the external surface of an external plate.

As mentioned above, the optical patterns formed on the surface of a side plate make it possible to induce a particular optical effect. Indeed, each pattern behaves like an independent optical cell. The combination of the optical patterns thus generates its own lighting aesthetic. According to the invention, it is possible to easily define, and at low cost, a large number of possibilities of optical patterns. The invention thus has the advantage of making it possible to achieve a large number of lighting aesthetics.

As an additional remark, in addition to the dimension of the patterns mentioned above, the invention also makes it possible to define various shapes, any relief on the surface of a side plate, in particular convex shapes, for example spherical.

The central plate can be made of glass, preferably Flint glass.

The side plates are preferably made of a plastic material, otherwise known as resin. For example, the plastic material may be polymethyl methacrylate (PMMA), polycarbonate (PC), a cycloolefin copolymer (COC), or a cycloolefin polymer (COP)

As is apparent from the preceding description, the materials of the three plates of the optical element 1 are chosen for their optical property, with respect to the light source used in an optical module 5. In addition, they have optical properties that are compatible with each other. Optionally, they may include an optical property that is compatible with a glue crosslinking technique, as detailed previously. They may also have particular mechanical properties, and in particular resistance to a certain high temperature, in particular to the temperature used during hardening of the glue by heat treatment.

The invention is not limited to the embodiment described. For example, as a variant, only a first side plate 20 could be manufactured independently and glued to the central plate 10 according to the invention. In this variant, the second side plate 30 could be formed differently, for example according to the method of the prior art.

The invention also relates to an optical module 5, represented by the , which comprises a light source 2 and an optical element 1 as described above. The light source 2 thus transmits light rays 7, which pass through the optical element 1 to exit according to the optical mask 18 present on the central plate 10, and according to the optical patterns and more generally the optical properties of the optical element 1. As a reminder, each optical pattern forms an optical entity as such, which emits light rays 8 towards the outside.

The optical module 5 is thus suitable for any use in a lighting device for a motor vehicle.

Claims (10)

Optical element (1) for an optical module (5) of a motor vehicle comprising a central plate (10) arranged between a first side plate (20) and a second side plate (30), characterized in that it comprises at least one layer of glue (41) arranged between the first side plate (20) and the central plate (10). Optical element (1) according to the preceding claim, characterized in that it comprises another layer of glue (42) arranged between the second side plate (30) and the central plate (10). Optical element (1) according to one of the preceding claims, characterized in that the first side plate (20) and/or the second side plate (30) is made of plastic material, such as polymethyl methacrylate (PMMA), polycarbonate (PC), a cycloolefin copolymer (COC), or a cycloolefin polymer (COP). Optical element (1) according to one of the preceding claims, characterized in that at least one of the first side plate (20) and the second side plate (30) is made of a material at least partially transparent to a crosslinking radiation of an adhesive layer (41, 42) of the optical element (1), so as to allow the crosslinking of the adhesive by radiation passing through it during the manufacture of the optical element (1), and/or in that the central plate (10) and at least one of the first side plate (20) and the second side plate (30) are made of a material resistant to a heat treatment temperature of an adhesive layer (41, 42) of the optical element (1), so as to allow the hardening of the adhesive by a heat treatment during the manufacture of the optical element (1). Optical element (1) according to one of the preceding claims, characterized in that the at least one adhesive layer (41, 42) has a thickness of between 100 and 300 µm and/or in that the at least one adhesive layer (41, 42) extends over the entire surface of a surface (11, 12) of the central plate (10), at the interface between the central plate (10) and the first side plate (20) or the second side plate (30), or extends over only a part of this surface, and/or in that the at least one adhesive layer (41, 42) is in an epoxy resin-based material. Optical element (1) according to one of the preceding claims, characterized in that it comprises at least one of the first side plate (20) and the second side plate (30) having optical patterns of dimensions greater than 1 mm on its external surface (22, 31). Optical element (1) according to one of the preceding claims, characterized in that the central plate (10) is made of plastic material or glass, in particular of the Flint glass type, and/or in that the central plate (10) comprises an optical mask (18) on at least one surface (11). Optical module (5), comprising a light source (2), and characterized in that it comprises an optical element (1) according to one of the preceding claims intended to be traversed by the light emitted by said light source (2). Method for manufacturing an optical element (1) for an optical module (5) of a motor vehicle, characterized in that it comprises a step consisting of manufacturing by molding (E2), in particular by injection, at least one side plate (20, 30), and a step consisting of assembling by gluing (E3, E4, E5; E7, E8, E9) said at least one side plate (20, 30) on a central plate (10) of the optical element. Method for manufacturing an optical element (1) according to the preceding claim, characterized in that the step of assembling by gluing (E3, E4, E5; E7, E8, E9) said at least one side plate (20, 30) on the central plate (10) of the optical element (1) comprises a step of crosslinking at least one layer of glue (41, 42) by crosslinking radiation or a step of hardening at least one layer of glue (41, 42) by heat treatment.