Multilayer reflective module, and associated manufacturing method

Abstract

The present invention relates to a multilayer reflective module (1) for an automotive component, comprising a first substrate (2), forming a base, and a reflective multilayer stack (3) comprising at least one metal mirror (4), at least one intermediate layer (5) on said at least one metal mirror (4), said intermediate layer (5) forming a Fabry-Pérot cavity generating a light beam (200') reflected by said metal mirror (4), said stack (3) being configured to receive an incident light beam (200) and to reflect the reflected light beam (200') having a determined wavelength. The module also comprises at least one scattering coating layer (7) deposited covering said stack (3), configured to scatter at least said reflected light beam, and comprising a material in the form of beads (70) of microscopic sizes dispersed within a polymer matrix (71), said beads (70) giving said material the ability to scatter at least the beam reflected by said metal mirror (4). The invention also relates to an automotive component (100) with such a module (1), and to a method for manufacturing said module (1).

Description

MULTILAYER REFLECTIVE MODULE AND ASSOCIATED MANUFACTURING PROCESS

[0001] The present invention relates to the field of reflective multilayer modules. The invention finds particularly advantageous application in the field of exterior or interior trim, or even in the signaling of motor vehicles, in particular for vehicle body parts, especially front parts, or for the interior passenger compartment of such vehicles. State of the art

[0002] Currently, it is common practice to display a design or visual element on a vehicle part, either for decoration or for signaling purposes, such as headlight lenses. This is generally achieved using modules equipped with light sources that display and illuminate such a design, both day and night. To limit the power consumption of these modules, more energy-efficient solutions are being explored, utilizing the properties of ambient light, at least during the day.

[0003] To this end, there are multilayer reflective modules, hereinafter referred to as "modules," configured to reflect a portion of the visible spectrum and thus emit a specific color. Modules exploiting the Fabry-Pérot cavity effect are particularly well-known. In a Fabry-Pérot cavity, a reflected color called "structural color" appears when light is confined within a nanometric cavity delimited by two substantially parallel surfaces: a lower, reflective surface and an upper, semi-reflective surface to allow the passage of an incident light beam and a light beam reflected by the lower reflective layer.

[0004] Such modules comprise a substrate on which a stack is formed, including at least one reflective mirror layer and a Fabry-Pérot absorber layer, for example, a conductive polymer layer. The thickness of the absorber layer determines the wavelengths of the reflected light beam that will emerge from the polymer layer through interference. These specific wavelengths correspond to a color in the visible spectrum and reach the eyes of an observer.

[0005] Furthermore, to enhance the external aesthetic appearance, particularly regarding gloss and reflectivity, and also for protection, a coating is applied. This coating is often reflective and comprises metallic materials, indium- or aluminum-based. Historically, parts with a glossy, aesthetically pleasing finish were commonly referred to as "chromes," in reference to the process of coating a metal part, for example, through chrome plating.

[0006] The evolution of automotive parts manufacturing has led to the use of plastic and composite materials, particularly for exterior trim components. Techniques for depositing metallic coatings onto such plastic or composite parts have led to the use of other metals, especially indium, which exhibits a silver-like luster and reflective properties that produce a mirrored or polished appearance (i.e., a reflective optical surface). Furthermore, indium offers the advantage of high corrosion resistance.

[0007] However, such covering materials generate a reflection that is essentially specular in nature, meaning that the reflected radiation spreads substantially in one and the same direction, like a mirror.

[0008] One problem therefore lies in the fact that, depending on the observer's angle of view, the reflected radiation in a specular manner modifies the visual perception of said observer, impacting the color and intensity of the color thus reflected.

[0009] In particular, depending on the observer's viewing angle, which can change as the vehicle moves or the observer's position changes, the radiation's path passes through the conductive polymer layer and is reflected at varying relative thicknesses. This results in a difference in perception for the observer, altering the color and intensity of the perceived radiation.

[0010] In addition, a surface with a high reflectivity index is likely to induce glare, which is particularly harmful to drivers of other motor vehicles.

[0011] An object of the present invention is therefore to propose a solution improving a reflective multilayer module compared to existing solutions, and in particular to make it compatible with an application in automotive parts.

[0012] To achieve this, such a module incorporates a diffusing coating layer over the multilayer stack, generating diffusion of light radiation reflected by the underlying layers of the module, but potentially also of incident radiation. Specifically, this diffusing coating layer comprises a compound with light-diffusing characteristics, incorporating a dispersion of microscopically sized beads (or "microbeads") into its material. This compound also exhibits characteristics that allow the passage of incident radiation to the lower layers of the stack thus coated.

[0013] With the incorporation of microbeads in the overlay coating layer, the module offers a wider field of vision, while retaining intensity and colorimetry characteristics thanks to the disordered arrangement of microstructures which refract light to give it a diffusive appearance.

[0014] The other objects, features, and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated.

[0015] To achieve this objective, according to a first aspect, a multilayer reflective module is planned for an automotive part, the module comprising: - a first substrate, forming a base, - a reflective multilayer stack positioned on the first substrate and comprising: i) at least one metallic mirror, ii) at least one intermediate layer on said at least one metallic mirror, said intermediate layer forming a Fabry-Pérot type cavity generating a light beam reflected by said metallic mirror, said stack being configured to receive an incident light beam as well as to reflect the reflected light beam having a determined wavelength; - at least one diffusing coating layer deposited over said stack, configured to diffuse at least said reflected light beam;characterized in that said at least one diffusing coating layer comprises a material in the form of microscopically sized beads dispersed within a polymer matrix, said beads conferring to said material at least a diffusion of the beam reflected by said metallic mirror.

[0016] According to additional, non-limiting characteristics, said microscopic beads comprise a diameter between 2 microns and 10 microns, preferably a diameter of about 2 microns.

[0017] According to one embodiment, the concentration of microscopic beads within the polymer matrix is ​​between 2% and 10% by weight of the beads relative to the weight of said polymer matrix, preferably 2% by weight of the beads relative to the weight of said polymer matrix.

[0018] According to one embodiment, the microscopic beads have a refractive index between 1.4 and 1.5.

[0019] According to one embodiment, said microscopic beads are based on a compound chosen from: - polymethylsilsesquioxane (PMSQ), - polymethyl methacrylate (PMMA), - polybutyl methacrylate (PBMA).

[0020] According to one embodiment, the polymer matrix material has a refractive index between 1.5 and 1.6.

[0021] According to one embodiment, the polymer matrix of said material of said at least one diffusing coating layer is based on a compound selected from: - polymethyl methacrylate (PMMA) or a derivative, - polycarbonate (PC) or a derivative, - polystyrene (PS) or a derivative, - polyamide (PA) or a derivative, - polyvinyl chloride (PVC) or a derivative.

[0022] According to one embodiment, the material of said at least one diffusing coating layer comprises a thickness of between 5 microns and 20 microns, preferably between 5 microns and 10 microns.

[0023] According to one embodiment, said at least intermediate layer comprises: - an organic material selected from polymethyl methacrylate (PMMA) or a derivative, polybutyl methacrylate (PBMA) or a derivative, polycarbonate (PC) or a derivative, polyvinyl acetate (PVA) or a derivative, poly(3,4-ethylenedioxythiophene) (PEDOT) or a derivative composed such as PEDOT:PSS with poly(styrene sulfonate) or such as PEDOT:Tos with a toluene sulfonate derivative; or - an inorganic material selected from a silicon oxide or a derivative such as silicon dioxide (SiO2), an aluminium oxide or a derivative such as alumina or aluminium oxide (Al2O3), a titanium oxide or a derivative such as titanium dioxide (TiO2), an indium tin oxide (ITO for "indium tin oxide").

[0024] According to one embodiment, the first substrate comprises - a flexible material selected from polyethylene terephthalate (PET) or a derivative, polymethyl methacrylate (PMMA) or a derivative, polycarbonate (PC) or a derivative, polydimethyl esiloxane (PDMS) or a derivative; or - a material selected from glass, a silicon wafer, or a polymer with a thickness of less than 1 millimeter (mm).

[0025] According to one embodiment, the metallic mirror comprises, from said first substrate to the diffusing coating layer, - an aluminium (Al) layer, in particular with a thickness of 70 nanometres (nm), - a chromium (Cr) layer, in particular with a thickness of 5 nanometres (nm), - a gold (Au) layer, in particular with a thickness of 3 to 7 nanometres (nm).

[0026] According to one embodiment, the stacking further comprises, above said at least one intermediate layer, iii) a metallic layer.

[0027] According to one embodiment, the metallic layer comprises, from said first substrate to the diffusing coating layer, - a layer of gold (Au), in particular with a thickness of 3 nanometers (nm), - a layer of chromium (Cr), in particular with a thickness of 3 nanometers (nm).

[0028] The invention also relates to a part of a motor vehicle comprising a reflective module according to the first aspect.

[0029] According to a second aspect, the invention relates to a method for manufacturing the reflective module according to the first aspect, comprising at least the following steps: - a supply of a first substrate, - the successive depositions of the layers of the reflective multilayer stack, - the covering of said stack by said at least one diffusing coating layer, characterized in that said at least one diffusing coating layer is made - by dissolving the polymer matrix with a solvent, preferably an organic solvent, then - by dispersing microscopic beads within the dissolution of the polymer matrix and said solvent: and in that - the covering is carried out by a coating operation by centrifugation (spin-coating) or by spreading (bar-coating).

[0030] According to one embodiment, the solvent is chosen from: - toluene, - anisole, - chloroform, preferably toluene. Presentation of the drawings

[0031] Other features and advantages of the invention will become apparent from the following detailed description of non-limiting embodiments of the invention, with reference to the accompanying figures, in which:

[0032] schematically represents a view of a reflective module according to a preferred embodiment, in particular provided below with a metallic mirror and above with a metallic layer covered by a diffusing coating layer, showing, on the left, the diffraction of incident light radiation through the diffusing coating layer, as well as its diffusion by the diffusing coating layer and, on the right, the reflection of the incident light radiation diffracted and diffused by the metallic layer as well as the diffusion of the radiation thus reflected by the diffusing coating layer;

[0033] schematically represents a view similar to the one, showing, on the left, the diffraction of the incident light radiation diffracted and scattered through the metallic layer and, on the right, the reflection by the metallic mirror of the incident light radiation diffracted and scattered, which is again diffracted and scattered through the diffusing coating layer; schematically represents a view of a reflective module according to another embodiment, in particular lacking a metallic layer at the top, showing, on the left, the diffraction of incident light radiation through the diffusing coating layer, as well as its scattering by the diffusing coating layer and, on the right, the reflection by the metallic mirror of the incident light radiation diffracted and scattered, which is again diffracted and scattered through the diffusing coating layer.

[0034] schematically represents a cross-sectional view of the preferred embodiment of the, showing in particular the superposition of the different layers of a multilayer reflective module;

[0035] schematically represents a cross-sectional view of the embodiment of the, showing in particular the superposition of the different layers of a multi-layer reflective module;

[0036] schematically represents a principle view in perspective of an example of a rear bumper type automotive part, equipped with a multi-layer reflective module, highlighting in magnification according to a vertical cross section a multi-layer reflective module covered with a diffusing coating layer. Detailed description

[0037] Before beginning a detailed review of embodiments of the invention, definitions of certain terms in the context of the present invention are set forth below.

[0038] A substrate or layer "based" on species A is understood to be a substrate or layer comprising only that species A, or that species A and possibly other species.

[0039] Several embodiments of the invention implementing successive steps of the manufacturing process are described below. Unless explicitly stated, the adjective "successive" does not necessarily imply, although this is generally preferred, that the steps follow each other immediately; intermediate steps may separate them.

[0040] Furthermore, the term "step" refers to the completion of a part of the process, and can designate a set of sub-steps.

[0041] Furthermore, the term "step" does not necessarily imply that the actions carried out during a step are simultaneous or immediately successive. Some actions in a first step may be followed by actions related to a different step, and other actions from the first step may be repeated later. Thus, the term "step" does not necessarily refer to unitary actions that are inseparable in time and in the sequence of phases of the process.

[0042] The thickness of a layer or substrate is measured along a direction perpendicular to the surface at which that layer or substrate has its maximum extent. The thickness is thus measured along a direction perpendicular to the principal faces of the substrate on which the different layers rest.

[0043] The terms "on", "overcome", "cover", "underlying", "opposite" and their equivalents do not necessarily mean "in contact with".

[0044] Thus, for example, the depositing, transferring, gluing, assembling or applying a first layer on a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.

[0045] The term "solid" used to describe the connection between two parts means that the two parts are linked / fixed to each other, in all degrees of freedom, unless explicitly specified otherwise.

[0046] Terms such as "longitudinal," "transverse," "upper," and "lower" should be interpreted relatively in relation to the position of the reflective module elements once assembled, with the direction normal to the principal extension plane of the stacking layers being considered the vertical direction. A lateral or transverse dimension is understood as a dimension in a plane parallel to or coinciding with the principal extension plane of the stacking layers.

[0047] By "juxtaposed" elements we mean here that these elements are arranged side by side according to their main extension plane or arranged one above the other according to the direction of stacking, this direction being perpendicular to the main extension plane.

[0048] By "in contact", we mean that a thin interface may exist, for example caused by manufacturing variability.

[0049] A parameter that is "approximately equal to / greater than / less than" a given value means that the parameter is equal to / greater than / less than the given value, within ±10% of that value. A parameter that is "approximately between" two given values ​​means that the parameter is at least equal to the smaller of the two given values, within ±10% of that value, and at most equal to the larger of the two given values, within ±10% of that value.

[0050] By "nanometric", and more specifically "nanometric thickness", we mean a dimension, more specifically a thickness, greater than or equal to 1 nm (nanometer) and strictly less than 1 μm (micrometer or micron).

[0051] The term "nanotheres" refers to holes or a network of holes, or even nanocavities, with dimensions on the order of nanometers. Nanoholes are created in a substrate using specific techniques, such as colloidal lithography or electron beam lithography ("e-beam lithography").

[0052] By "visible spectrum" or "visible range", we mean the range of wavelengths between 400 and 800 nm. By refractive index, we mean a dimensionless quantity, characteristic of a medium, describing the behavior of light in said medium and measured by a refractometer, in particular an Abbe refractometer, or by an optical ellipsometry technique, in particular by means of a spectroscopic ellipsometer.

[0053] The multi-layer reflective module 1 is now described according to several embodiment examples.

[0054] Regarding the reflective module 1, or simply "module 1".

[0055] Such a module 1 is specifically dedicated to an automotive part 100, or "part 100".

[0056] According to one aspect of the invention, the reflective module 1 is intended to be integrated into the materials composing a part 100 of a motor vehicle. Such a part 100 can be of any type, interior or exterior, preferably dedicated to a bodywork or exterior trim part for said motor vehicle.

[0057] Lamontre gives an example of a part 100 located at the rear of the motor vehicle, in the form of a shield or rear bumper. Other locations can be considered with the corresponding parts, front or at the front, laterally or on the sides, or even above or below the motor vehicle, such as a front or front-facing shield, bodywork or exterior trim parts, such as a trim strip or grille, a headlight or taillight, or even a side mirror.

[0058] Further on, said module 1 includes a first substrate 10, or "substrate 10", forming a base, namely that a face located above or on the outside allows to receive other layer(s) of said module 1.

[0059] In addition, such a substrate 2 may comprise several superimposed layers, including at least one lower layer, enabling in particular the stiffening of the module 1, and an upper layer provided with the upper or outer face.

[0060] According to one embodiment, the substrate material 2 is provided to be flexible, i.e., it is supple or semi-rigid, or has resilience or elasticity allowing its deformation, in particular its bending, from an initial position and its return to the initial position without being chosen. According to different embodiments, the substrate material 2 is chosen from polyethylene terephthalate (PET) or a derivative, polymethyl methacrylate or polymethyl methacrylate (PMMA) or a derivative, polycarbonate (PC) or a derivative, polydimethyl esiloxane (PDMS) or a derivative. According to different embodiments, the superimposed layers of the substrate material 2 can be chosen from a combination of the aforementioned materials for substrate 10. According to other embodiments, the substrate material 2 is chosen from glass, a silicon wafer, or a polymer with a thickness of less than 1 millimeter (mm).

[0061] Advantageously, module 1 also includes a reflective multilayer stack of 3, or "stack of 3". Such a stack of 3 is positioned on the first substrate, specifically on the top or outer layer.

[0062] Further on, this stacking 3 comprises a superposition of several layers. Such a stacking 3 is configured to receive an incident 200 beam of light, or "incident 200 beam," and to reflect, by the Fabry-Pérot effect, a reflected 200' beam of light, or "reflected 200' beam." It is therefore understood that the wavelength spectrum of the reflected 200' beam is reduced compared to the spectrum of the incident 200 beam.

[0063] To enable this reflection, the multilayer stack 3 first includes at least one metallic mirror 4, or "mirror 4". In particular, said mirror 4 is located on the first substrate 10, directly on its upper or outer face. In one embodiment, the mirror 4 comprises several layers, from said first substrate 2 to a diffusing coating layer 7, namely from bottom to top or from the inside to the outside. In particular, said mirror 4 comprises an aluminum (Al) layer 40, notably with a thickness of 40 of 70 nanometers (nm). The mirror also includes, preferably at the top, a 41 layer of chromium (Cr). Such a 41 layer of chromium can have a thickness of 41 of 5 nanometers (nm). Mirror 4 also includes, preferably at the top, a layer 42 of gold (Au), notably with a thickness of 42 from 3 to 7 nanometers (nm). Examples of thicknesses of 40 ,d41 , d 42 The corresponding layers 40, 41, 42 are visible in figures 4 and 5. It should be noted that said mirror 4 may include additional layers, preferably of metallic material.

[0064] Further on, the stack 3 includes at least one intermediate layer 5 on said at least one metallic mirror 4. This intermediate layer 5 forms a cavity or a Fabry-Pérot type absorber generating a light beam reflected by said metallic mirror 4.

[0065] Preferably, such an intermediate layer 5 may have a thickness d5 between 50 and 300 nanometers (nm). According to different embodiments, said at least intermediate layer 5 comprises an organic material selected from polymethyl methacrylate (PMMA) or a derivative, polybutyl methacrylate or polybutyl methacrylate (PBMA) or a derivative, polycarbonate (PC) or a derivative, polyvinyl acetate (PVA) or a derivative, poly(3,4-ethylenedioxythiophene) (PEDOT) or a derivative compound such as PEDOT:PSS with poly(styrene sulfonate) or such as PEDOT:Tos with a toluene sulfonate derivative.Alternatively, according to various embodiments, said at least intermediate layer 5 comprises an inorganic material selected from a silicon oxide or a derivative such as silicon dioxide (SiO2), an aluminium oxide or a derivative such as alumina or aluminium oxide (Al2O3), a titanium oxide or a derivative such as titanium dioxide (TiO2), an indium tin oxide (ITO for "indium tin oxide").

[0066] According to a preferred embodiment, the stack 3 comprises, directly overlying the intermediate layer 5, the diffusing coating layer 7. Such a configuration of the stack 3 is particularly visible in Figures 1 and 2, as well as in the figure. According to another embodiment, the stack 3 further comprises, above said at least one intermediate layer 5, a metallic layer 6. In particular, such a metallic layer 6 is provided to be semi-reflective, allowing the incident radiation 200 to pass through it partially in one direction, as well as in the opposite direction, radiation reflected by the mirror 4.

[0067] According to one embodiment, the metallic layer 6 comprises, from said first substrate 2 to the diffusing coating layer 7, namely from bottom to top or from the inside to the outside, a layer 60 of gold (Au), in particular of a thickness of 60of 3 nanometers (nm). The metallic layer 6 also includes a chromium (Cr) layer 61, notably with a thickness of 61 of 3 nanometers (nm). This chromium layer 61 is therefore located on the gold layer 60. Such a 3-layer stacking configuration is notably visible in Figures 3 and 5, with examples of thicknesses of 60 ,d 61 corresponding layers 60,61. It should be noted that said metallic layer 6 may include additional layers, preferably made of metallic material.

[0068] It should be noted that the small thicknesses of layers 40,41,42 of mirror 4, as well as of layers 60,61 of the upper metallic layer 6, ensure an absorption of 200,200' light radiation and are suitable to generate the Fabry-Pérot effect.

[0069] Thus, said stack 3 is configured to receive an incident light beam as well as to reflect a reflected light beam having a determined wavelength.

[0070] According to the invention, the module 1 comprises at least one diffusing coating layer 7, or "diffusion layer 7," deposited over said stack 3. This diffusion layer 7 is configured to diffuse at least said reflected light beam 200'. Relatedly, said diffusion layer 7 also diffuses at least a portion of the incident light beam 200'. Advantageously, said at least one diffusing coating layer 7 comprises a material in the form of microscopic beads 70 dispersed within a polymer matrix 71. It is said beads 70 (or microbeads) that impart to said material at least diffusion of the beam 200' reflected by said metallic mirror 4, as well as related diffusion of the incident beam 200'.

[0071] According to one embodiment, said microscopic beads 70 have a diameter between 2 microns and 10 microns (or micrometers), preferably a diameter of about 2 microns. Several different diameters of beads 70 can be combined. Such a diameter allows for a balanced distribution of the beads 70 within the polymer matrix material 71. It should be noted that, with a diameter of 2 µm, the scattering of light by the beads 70 encapsulated in the polymer matrix 71 can occur approximately at an angle of plus or minus 30 degrees to the normal. With a diameter of 10 µm, the scattering of light by the beads 70 encapsulated in the polymer matrix 71 can occur approximately at an angle of plus or minus 60 degrees to the normal.By varying the diameter of the 70 balls, it is therefore possible to act on the perception of an observer, in particular on his perception of the light diffused by the material, depending on his angle of vision relative to the normal to the surface of said material.

[0072] According to one embodiment, the concentration of microscopic beads 70 within the polymer matrix 71 is between 2% and 10% by weight of the beads 70 relative to the weight of said polymer matrix 71, preferably 2% by weight of the beads 70 relative to the weight of said polymer matrix 71.

[0073] According to one embodiment, the 70 microscopic beads have a refractive index between 1.4 and 1.5.

[0074] According to one embodiment, said microscopic beads 70 are based on a compound selected from: - polymethylsilsesquioxane (PMSQ), - polymethyl methacrylate (PMMA), - polybutyl methacrylate (PBMA). Such materials ensure refraction, in the aforementioned ranges, as well as good combination with the polymer matrix material 71.

[0075] Accordingly, in one embodiment, the polymer matrix 71 of said material of said at least one diffusing coating layer 7 is based on a compound selected from: - polymethyl methacrylate (PMMA) or a derivative, - polycarbonate (PC) or a derivative, - polystyrene (PS) or a derivative, - polyamide (PA) or a derivative, - polyvinyl chloride (PVC) or a derivative. Such materials ensure good dispersion of the beads 70 within the polymer matrix 71.

[0076] According to one embodiment, the material of said at least one diffusing coating layer 7 comprises a thickness d7 of between 5 microns and 20 microns, preferably between 5 microns and 10 microns. Such a thickness d7 is suitable for the diffusion of 200,200' radiation.

[0077] According to one embodiment, the polymer matrix material 71 has a refractive index between 1.5 and 1.6.

[0078] As mentioned previously, the invention also relates to a motor vehicle part 100 comprising a multilayer reflective module 1 according to one or / and the other of the embodiments described previously.

[0079] According to another aspect, the invention relates to a method of manufacturing the multilayer reflective module 1 according to one and / or the other of the aforementioned embodiments.

[0080] To achieve this, the manufacturing process includes at least the following steps. First, the process involves supplying the first substrate, in particular in the form of one or more layers. Then, the process involves the successive deposition of the layers of the reflective multilayer stack.

[0081] In particular, the process includes the production of the mirror 4, by successive deposits, from the substrate 2, namely from bottom to top or from inside to outside, of the aluminum layer 40, then the chromium layer 41, then the gold layer 42. Next, the process includes the deposition of the intermediate layer 5 on the mirror 4, in particular on its gold layer 42.

[0082] According to the corresponding embodiment, the process includes the production of the metallic layer 6, on top of the intermediate layer 5. In particular, the process provides for successive deposits of the gold layer 60 and then the chrome layer 61.

[0083] As an example of a manufacturing process for the stack 3, on a first flexible or rigid substrate 2, a 70nm thick layer 40 of aluminum is deposited, followed by a 7nm thick layer 41 of chromium and then a 5nm thick layer 42 of gold, through PVD (physical vapor deposition) evaporation operations. Next, the intermediate layer 5 is deposited by spin-coating or bar-coating for polymeric materials to form a transparent cavity, or by PVD evaporation to form inorganic cavities. Then, depending on the corresponding embodiment, the metallic layer 6 is deposited on top by successive depositions of the 3nm thick gold layer 60 and the 3nm thick chromium layer 61, by PVD evaporation.

[0084] Advantageously, the process involves coating said stack 3 with said at least one diffusing coating layer 7. To this end, said at least one diffusing coating layer 7 is produced by dissolving the polymer matrix 71 with a solvent, in particular an organic solvent. In one embodiment, the solvent is chosen from toluene, anisole, or chloroform, preferably toluene. In particular, toluene improves dissolution and makes it possible to obtain the thicknesses targeted during the coating operation, in particular by spin-coating, namely a thickness of 4 to 7 microns (or micrometers µm).

[0085] Next, a dispersion of the microscopic beads 70 within the dissolution of the polymer matrix 71 and said solvent.

[0086] As an example, one manufacturing protocol involves placing the respective quantities of diffusive beads 70 and the polymer matrix 71 in powdered PMMA form in a container. The polymer matrix 71 is dissolved by adding an organic solvent to obtain a polymer concentration of between 10% and 14% by mass in the solution and 2% by mass of diffusive beads 70. The resulting solution is heated, with stirring, for several hours to facilitate dissolution. In particular, the heating temperature can be around 50°C for a low-volatility solvent, for a duration of between 5 and 24 hours. Once dispersion has occurred, a coating operation is carried out to form the diffusion layer 7. This coating is achieved by spin-coating or bar-coating.

[0087] As an example of a spin-coating protocol, also known as centrifugal coating, the material is accelerated to a speed of 500 rpm (revolutions per minute) to obtain a significant thickness of thin film, with a rotation time of 120 s (seconds) to allow maximum solvent evaporation.

Claims

Multilayer reflective module (1) for an automotive part, the module (1) comprising: - a first substrate (2), forming a base, - a multilayer reflective stack (3) positioned on the first substrate (2) and comprising: i) at least one metallic mirror (4), ii) at least one intermediate layer (5) on said at least one metallic mirror (4), said intermediate layer (5) forming a Fabry-Pérot type cavity generating a light beam (200') reflected by said metallic mirror (4), said stack (3) being configured to receive an incident light beam (200) as well as to reflect the reflected light beam (200') having a determined wavelength; - at least one diffusing coating layer (7) deposited over said stack (3), configured to diffuse at least said reflected light beam;characterized in that said at least one diffusing coating layer (7) comprises a material in the form of microscopically sized beads (70) dispersed within a polymer matrix (71), said beads (70) conferring to said material at least a diffusion of the beam reflected by said metallic mirror (4). Module (1) according to the preceding claim, characterized in that said microscopic beads (70) comprise a diameter between 2 microns and 10 microns, preferably a diameter of about 2 microns. Module (1) according to any one of the preceding claims, characterized in that the concentration of microscopic beads (70) within the polymer matrix (71) is between 2% and 10% by weight of the beads (70) relative to the weight of said polymer matrix (71), preferably 2% by weight of the beads (70) relative to the weight of said polymer matrix (71). Module (1) according to any one of the preceding claims, characterized in that the microscopic beads (70) have a refractive index between 1.4 and 1.

5. Module (1) according to any one of the preceding claims, characterized in that said microscopic beads (70) are based on a compound selected from: - polymethylsilsesquioxane (PMSQ), - polymethyl methacrylate (PMMA), - polybutyl methacrylate (PBMA). Module (1) according to any one of the preceding claims, characterized in that the polymer matrix material (71) has a refractive index between 1.5 and 1.

6. Module (1) according to any one of the preceding claims, characterized in that the polymer matrix of said material of said at least one diffusing coating layer is based on a compound selected from: - polymethyl methacrylate (PMMA) or a derivative, - polycarbonate (PC) or a derivative, - polystyrene (PS) or a derivative, - polyamide (PA) or a derivative, - polyvinyl chloride (PVC) or a derivative. Module (1) according to any one of the preceding claims, characterized in that the material of said at least one diffusing coating layer (7) comprises a thickness of between 5 microns and 20 microns, preferably between 5 microns and 10 microns. Module (1) according to any one of the preceding claims, characterized in that said at least intermediate layer (5) comprises: - an organic material selected from polymethyl methacrylate (PMMA) or a derivative, polybutyl methacrylate (PBMA) or a derivative, polycarbonate (PC) or a derivative, polyvinyl acetate (PVA) or a derivative, poly(3,4-ethylenedioxythiophene) (PEDOT) or a derivative composed such as PEDOT:PSS with poly(styrene sulfonate) or such as PEDOT:Tos with a toluene sulfonate derivative; or - an inorganic material selected from a silicon oxide or a derivative such as silicon dioxide (SiO2), an aluminium oxide or a derivative such as alumina or aluminium oxide (Al2O3), a titanium oxide or a derivative such as titanium dioxide (TiO2), an indium tin oxide (ITO for "indium tin oxide"). Module (1) according to any one of the preceding claims, characterized in that the first substrate (2) comprises - a flexible material selected from polyethylene terephthalate (PET) or a derivative, polymethyl methacrylate (PMMA) or a derivative, polycarbonate (PC) or a derivative, polydimethyl esiloxane (PDMS) or a derivative; or - a material selected from glass, a silicon wafer, or a polymer of a thickness of less than 1 millimeter (mm). Module (1) according to any one of the preceding claims, characterized in that the metallic mirror (4) comprises, from said first substrate to the diffusing coating layer, a layer (40) of aluminum (Al), in particular of a thickness (d 40 ) of 70 nanometers (nm), - a 41-layer of chromium (Cr), notably of a thickness (d 41 ) of 5 nanometers (nm), - a 42-layer of gold (Au), notably of a thickness (d 42 ) from 3 to 7 nanometers (nm). Module (1) according to any one of the preceding claims, characterized in that the stack (3) further comprises, above said at least one intermediate layer, iii) a metallic layer (6). Module (1) according to the preceding claim, characterized in that the metallic layer (6) comprises, from said first substrate (2) to the diffusing coating layer (7), a layer (60) of gold (Au), in particular of a thickness (d 60 ) of 3 nanometers (nm),- a layer (61) of chromium (Cr), in particular of a thickness (d 61 ) of 3 nanometers (nm). Motor vehicle part (100) comprising a multilayer reflective module (1) according to any one of claims 1 to 13. A method for manufacturing the multilayer reflective module (1) according to any one of claims 1 to 13, characterized in that it comprises at least the following steps: - a supply of a first substrate (2), - the successive deposition of the layers of the multilayer reflective stack (3), - the coating of said stack (3) by said at least one layer (7) of diffusing coating, characterized in that said at least one layer (7) of diffusing coating is carried out - by dissolving the polymer matrix (71) with a solvent, preferably an organic solvent, then - by dispersing microscopic beads (70) within the dissolution of the polymer matrix (71) and said solvent: and in that - the coating is carried out by a coating operation by centrifugation (spin-coating) or by spreading (bar-coating). Manufacturing process according to the preceding claim, characterized in that the solvent is chosen from: - toluene, - anisole, - chloroform, preferably toluene.

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