EP4179853A1

EP4179853A1 - Method for manufacturing an electrically conductive device made of lignocellulosic material

Info

Publication number: EP4179853A1
Application number: EP21746516.0A
Authority: EP
Inventors: Sébastien PATOUR; Timothée BOITOUZET
Original assignee: Woodoo SAS
Current assignee: Woodoo SAS
Priority date: 2020-07-08
Filing date: 2021-07-06
Publication date: 2023-05-17
Also published as: JP2023532773A; TW202219991A; FR3112449B1; WO2022008831A1; FR3112449A1; CA3183801A1; US20230140418A1; CN115812343A

Abstract

A method for the production of an electrically conductive device made of lignocellulosic material comprises the following steps: - impregnating (S10) the lignocellulosic material with at least one filling compound so as to produce a composite substrate; and - depositing (S12) at least one conductive layer on at least one surface of the composite substrate so as to produce an electrically conductive device. Use of an electrically conductive device thus produced, particularly as a tactile interface.

Description

Method for manufacturing an electrically conductive device in lignocellulosic material

The present invention relates to a method of manufacturing an electrically conductive device made of lignocellulosic material.

It also relates to an electrically conductive device made of lignocellulosic material obtained by such a process.

The field of connected objects, the Internet of Things (loT or Internet of Things in Anglo-Saxon terminology), home automation and smart surfaces (smart surface) and the proliferation of display and control screens are multiplying today. today the need for interactivity thanks to electronic functions directly integrated into the objects.

Payment cards, with or without contact, access control badges, cards with certificate of authenticity are also used more and more often in everyday life.

In particular, touch interfaces to control the operation of a device are used today in a wide variety of fields: transport (automotive, nautical, aeronautical), building, packaging, access security or even furniture.

To date, touch interfaces are often made from a glass or silica substrate on which a plastic film is deposited and glued, generally a thin layer of PET (PolyEthylene Terephthalate), bearing a printed circuit, for example made of ITO (Indium Tin Oxide). Capacitive touch interfaces are thus offered.

However, these touch interfaces are thick, heavy and fragile, and dimensionally limited to flat, two-dimensional applications.

Their manufacture also requires deposition of ITO at high temperature, in a controlled environment, generating a high energy expenditure, which makes their manufacturing process more expensive and complex. These manufacturing processes also have a high carbon footprint. Alternatives to glass substrates have been proposed, such as plastic substrates allowing the development of flexible screens. However, the ITO deposition temperature is limited on such plastic substrates, which reduces the electrical and optical performance of these structures.

Also known in document WO 2019/055680 is a tactile interface developed using a non-polymeric substrate, such as paper, textile, ceramic, wood or foam. Electrical conductive tracks are deposited directly on the substrate, by printing a conductive ink or via a hydrography transfer technique, well suited to three-dimensional substrates.

However, the quality of the deposition of an electrically conductive coating is highly dependent on the nature of the substrate and the surface that receives it. The electrical operation of the conductive circuit thus produced is also influenced by the nature of the substrate and its dielectric qualities.

The purpose of the present invention is to propose an alternative to existing solutions, by simplifying the manufacture of an electrically conductive device whatever its final form, and while ensuring a good quality of electrical conduction of the device thus obtained.

According to a first aspect, the present invention relates to a method of manufacturing an electrically conductive device made of lignocellulosic material.

According to the invention, the manufacturing process comprises the following steps:

- impregnation of the lignocellulosic material with at least one filler compound so as to produce a composite substrate; and

- deposition of at least one conductive layer on at least one surface of the composite substrate so as to produce the electrically conductive device.

Such a process thus makes it possible to deposit an electrically conductive coating directly on a lignocellulosic substrate, in contact with the surface of the cellulosic substrate, in order to add an electrical and/or electronic function to the device thus manufactured. The use of an intermediate plastic film, glued to the substrate, is thus unnecessary. The functionalization of ligno-cellulosic substrate without having to bond with an adhesive a plastic film incorporating printed electronics, allows iso-functionality to reduce the number of parts to be implemented, to simplify assembly and to reduce manufacturing costs.

In addition, such a process makes it possible to use a lignocellulosic material, derived from biomass with a favorable carbon balance, in order to produce intelligent, interactive and three-dimensional parts and surfaces.

The impregnation of the lignocellulosic substrate with a filling compound makes it possible to dimensionally stabilize the lignocellulosic substrate, improving the final structure of the electrically conductive device.

In addition, the impregnation makes it possible to homogenize the surface state of the composite substrate brought to receive the deposition of at least one conductive layer. The surface of the composite substrate can be controlled and has less asperities or hollows thanks to the impregnation with a filling compound.

The substrate of lignocellulosic material, such as raw wood, thus has a lower roughness after impregnation, improving the quality of the deposition of the conductive layer, and thus the conductive properties of the latter during use of the device. electrically conductive thus obtained. The low roughness of the composite substrate improves the adhesion of the conductive layer and its conductivity.

It is thus possible to deposit a network of electronic components or to transform the impregnated lignocellulosic substrate into a semiconductor element. The electrically conductive device can in particular form a two-dimensional or three-dimensional control interface.

According to an advantageous characteristic of the invention, the composite substrate comprises a fraction of a filling compound of between 30% and 80% by mass relative to the total mass of said substrate.

The filling compound makes it possible to improve the dielectric qualities of the lignocellulosic substrate. By replacing hearts in the lignocellulosic substrate pores and air pockets, the filling compound increases the electrical insulation properties of the composite substrate.

In practice, the filling compound is an impregnating polymer, and for example a thermoplastic polymer, of the acrylic type.

A polymer is well suited to modifying and controlling the dielectric properties of the composite substrate thus produced.

In addition, a thermoplastic polymer is well suited to the subsequent shaping of the composite substrate, in particular by hot forming, such as by thermoforming or thermocompression.

According to an advantageous characteristic of the invention, the ligno-cellulose material is wood comprising lignin and a network of cellulose and hemicellulose, the wood being at least partially delignified.

The at least partial removal of the lignin makes it possible to optimize the optical properties of the composite substrate. Since lignin is degraded under the effect of ultraviolet radiation, once at least part of the lignin is removed, the composite substrate is more resistant to natural degradation and ultraviolet aging.

The removal of the lignin coupled with the impregnation of the filling compound makes the composite substrate less sensitive to variations in humidity and changes in temperature.

These properties are important for optimum operation of the electrically conductive device, and in particular for the stability of the dielectric properties of the composite substrate. The electrically conductive device thus obtained can thus be used in different environments, both indoors and outdoors, while guaranteeing proper electrical operation.

In a practical embodiment, the composite substrate comprises at least one flat face, a conductive track being deposited on the surface of said at least one flat face.

The deposition of a conductive layer can be carried out by screen printing a conductive track on the surface of the composite substrate, screen printing being well suited to mass production. Screen printing is well suited to the deposition of a conductive ink in particular. A technique for depositing an ink conductive inkjet can also be used for small series production.

Thanks to the surface condition improved by the impregnation of the lignocellulosic substrate, a screen printing technique can be implemented satisfactorily, with good adhesion of the conductive layer thus deposited and good electrical continuity. Deposition by screen printing or by conductive ink jet makes it possible to implement a step of depositing a conductive layer at room temperature. It makes it possible to obtain an electronic circuit printed on the composite substrate.

The deposition of the conductive layer at room temperature makes it possible to avoid the use of high temperature necessary for the deposition of ITO.

In an improved embodiment, the manufacturing method further comprises a step of baking the conductive track, optionally followed by a step of shaping the composite substrate so as to produce an electrically conductive device in three dimensions.

Baking the conductive track removes solvents and volatile compounds from the conductive track deposited on the composite substrate.

It is thus possible to use a conductive ink which must be baked after deposition. It can be used in applications in which the composite substrate must be patterned to obtain a three-dimensional electrically conductive device. Baking conductive ink further improves its electrical conductivity properties.

The shaping step makes it possible, when it implements a hot forming of the composite substrate, to improve the electrical conductivity properties of the conductive ink thanks to a second curing of the conductive ink.

In one embodiment, the filling compound is a resin loaded with metal particles, the manufacturing process further comprising a step of activating the metal particles by laser or ultraviolet beam before the deposition step.

It is thus possible to etch tracks by locally activating the resin charged with metallic particles, which then makes it possible to produce the deposition of a conductive layer by immersing the composite substrate in one or more baths of metals in suspension.

A metallization of the tracks activated locally on the composite substrate is thus obtained, the metal in suspension adhering to the activated metal particles.

Such a manufacturing method is well suited to the production of an electrically conductive device in three dimensions.

In practice, the manufacturing process may include a step of shaping the composite substrate after the impregnation step and before the deposition step.

The conductive layer is thus directly applied to one or more three-dimensional surfaces of the composite substrate, after thermoforming or thermocompression for example.

In a practical embodiment, the composite substrate is a plate comprising two opposite faces, the manufacturing method comprising a step of depositing at least one conductive layer on at least one surface of one of the two faces of the plate.

The method thus makes it possible to functionalize a plate by providing a conductive element on one of the two faces, such as an electrode or a mesh of conductive wires for example, thus transforming the plate into a tactile control interface, from the detection of a touch on the opposite side. It is thus possible to obtain a tactile control interface, with capacitive or resistive detection technology.

In practice, the thickness of the plate is less than 10 mm.

By limiting the thickness of the composite substrate, it is possible to use the electrically conductive device as a coating or as a control interface placed on an electronic object.

Advantageously, the composite substrate is translucent or transparent, the light transmission coefficient of the translucent substrate being at least equal to 3%.

The translucency of the composite substrate makes it possible to use it in association with a light device, such as a display screen or an indicator. LED type light (Light Emitting Diode). The transmission of the light beam and therefore of information is made possible.

Preferably, the conductive layer comprises a transparent conductive ink.

The use of a transparent conductive ink, in combination with the translucency or transparency of the composite substrate, makes it possible to use the composite substrate as an interface above a display screen for example.

In practice, the refractive index of the filling compound is between 1.35 and 1.70.

The optical index of the filling compound is thus close to that of the cellulose of the ligno-cellulosic material.

Indeed, in order to obtain a composite substrate that is at least translucent, it is important that the refractive index of the filling compound be close to that of the lignocellulosic substrate after at least partial delignification.

Thus, once the filler compound has polymerized, it has substantially the same optical density as that of the cellulose present in the substrate.

The refractive index of cellulose being close to 1.47, the choice of a filling compound having a refractive index included in a range of 1.35 to 1.70, makes it possible to have refractive indices close to one of the other. The light can thus pass through the composite substrate substantially without being deflected.

According to a second aspect, the present invention relates to an electrically conductive device made of lignocellulosic material obtained by the manufacturing process according to the invention.

This electrically conductive device has characteristics and advantages similar to those previously described in relation to the method.

In practice, the device electrically constitutes a control interface for an electronic object, a payment card, an access control badge, a sensor, a transistor, a resistor, an energy-generating device or an electrical conductor. Such an electrically conductive device forms, for example, an automobile, nautical or aeronautical part, or an element or accessory in the field of building, packaging or furniture.

Other features and advantages of the invention will appear further in the description below.

In the accompanying drawings, given by way of non-limiting examples:

- Figure 1 is a block diagram illustrating an embodiment of the method of manufacturing an electrically conductive device according to the invention;

- Figure 2a is a front view of an antenna made according to one embodiment of the method of manufacturing an electrically conductive device of the invention;

- Figure 2b is an exploded perspective view of the antenna of Figure 2a;

- Figure 3a illustrates a first step in the production of a touch interface in lignocellulosic material according to an embodiment of the method for manufacturing an electrically conductive device of the invention; and

- Figure 3b illustrates a second stage of production of a touch interface in lignocellulosic material of Figure 3a.

We will first describe with reference to Figure 1 an example of a method of manufacturing an electrically conductive device in lignocellulosic material.

The ligno-cellulose material is for example wood comprising lignin and a network of cellulose and hemicellulose.

By way of example, different species of wood such as beech, oak, walnut, poplar, maple, ash, or a softwood can be used.

The manufacturing process can use a raw lignocellulosic material, or a partially or totally delignified one.

By way of non-limiting example, the fraction of lignin removed from the raw ligno-cellulosic material can be between 40% and 90% by weight of the lignin initially present in the raw ligno-cellulosic material. The at least partial delignification of the lignocellulosic material makes it possible to obtain a piece of wood that is at least translucent, or even transparent.

Furthermore, since lignin is degraded by ultraviolet rays during the use of a part made of ligno-cellulosic material, the at least partial delignification of the ligno-cellulosic material makes it possible to obtain a part that is more resistant to degradation under the effect light or ultraviolet.

In the embodiment described below, the manufacturing process is implemented from a plate of lignocellulosic material. Of course, the manufacturing process can be implemented on any type of shape, in two or three dimensions.

The manufacturing process firstly comprises a step S10 of impregnation of the lignocellulosic material with at least one filler compound so as to produce a composite substrate.

The impregnation step S10 implements a filling compound suitable for impregnating to the heart, in the thickness, the lignocellulosic material.

The filling compound is thus suitable for filling the interstices and voids present naturally in the raw ligno-cellulosic material and/or created by the at least partial delignification of the ligno-cellulosic material.

The filling compound can be an impregnating polymer, an elastomer, a silica derivative or any type of impregnating compound.

By way of example, the impregnating polymer can be a thermoplastic polymer of the acrylic type.

Alternatively, the impregnating polymer can be a thermosetting resin.

The filler compound can be petro-based or bio-based.

A process for impregnating a lignocellulosic material is known to those skilled in the art and is described in particular in documents WO 2017/098149 and WO 2019/155159.

The impregnation process makes it possible to obtain a full impregnation of the filling compound in the structure of the ligno-cellulosic material, in order to mechanically reinforce and sheath the cellulose fibers of the wood. The impregnation step S10 comprises a step of filling with a compound for filling the plate of lignocellulosic material and a finishing step by polymerization and/or crosslinking of the filling compound. Multiple examples of the delignification and impregnation process are described in detail in document WO 2017/098149, the content of which is incorporated by reference into the present description.

In particular, the extraction of the lignin can be implemented by soaking and washing, optionally coupled in the same step, of the plate of lignocellulosic material in a solution allowing at least partial dissolution of the lignin.

Document WO 2019/155159 gives multiple examples of filler compounds, and proportions used depending on the nature of the wood used.

In particular, the filling compound can be a resin doped with conductive particles in order to modify and control the conductivity of the composite substrate thus produced.

It is thus possible, by modifying the percentage of conductive particles in the filling compound, to control the dielectric qualities of a composite substrate obtained from a ligno-cellulosic material. In particular, unlike a raw ligno-cellulosic material, the composite substrate thus obtained has a stable electrical conductivity value, well suited to its use both indoors and outdoors.

When the filling compound is a polymer, the finishing step has the effect of completely polymerizing or cross-linking the filling compound and thus ensuring good physico-chemical stability of the composite substrate for its subsequent use.

In general, the fraction of the filler compound in the composite substrate thus obtained is between 30% and 80% by mass relative to the total mass of the composite substrate.

The composite substrate thus obtained can then optionally be shaped during an initial shaping step S11, for example by hot forming. The initial shaping step S11 can be implemented by various hot forming techniques, and in particular by thermocompression or vacuum thermoforming.

In a non-limiting manner, hot forming can implement industrial processes used to produce composite parts, after resin transfer molding (RTM or Resin Transfer Molding) or high pressure resin transfer molding (HP-RTM or High Pressure Resin Transfer Moulding).

The hot forming processes can implement thermo molding (RIM or Reaction Injection Molding), compression molding, or even a sheet molding technique (SMC or Sheet Molding Compound).

In principle, thermoforming implements a step of heating the composite substrate obtained at the end of the impregnation step S10, then a step of heating the thermocompression mould.

The temperatures used for heating the composite substrate and the mold depend on the glass transition temperature of the impregnating polymer.

Thus, the heating temperatures of the composite substrate and of the thermoforming mold must be sufficient to fluidify the impregnation polymer, and allow the shaping of the composite substrate, while maintaining a viscosity to this impregnation polymer in order to maintain the structure and maintenance of the composite substrate.

Thus, when the composite substrate obtained at the end of the impregnation step S10 is a plate, the initial shaping step S11 makes it possible, for example, to curve this plate along one or more directions in space so as to to obtain a piece of cylindrical, frustoconical, hemispherical shape or any type of shape with double curvature or left surface.

At the end of the impregnation step S10 or the initial shaping step S11, the manufacturing method comprises a step S12 of depositing at least one conductive layer on at least one surface of the composite substrate of so as to produce an electrically conductive device. The deposition step S12 is implemented after the composite substrate has cooled after the impregnation step S10 or optionally after cooling after the initial shaping step S11.

The deposition step S12 can implement different techniques for depositing a conductive layer on a support.

By way of non-limiting examples, the deposition step S12 can be carried out using a screen printing technique. Screen printing is well suited to depositing a conductive track on the surface of a flat face of the composite substrate. The conductive track can be produced for example by means of a conductive ink.

Traditionally, stencils or masks are used and interposed between a conductive ink and the composite substrate.

Once the mask is deposited on the composite substrate, a liquid ink is deposited on the mask and spread over the surface using a scraper.

The use of a mask or stencil makes it possible to obtain a wide variety of designs, lines or conductive tracks on the composite substrate.

A layer of conductive ink thus deposited by screen printing is particularly well suited to large production volumes.

Of course, several layers of conductive ink can be deposited on the surface of the composite substrate, by interposing between the conductive layers an insulating layer such as an insulating plastic film or a layer of electrically insulating ink.

Alternatively, a conductive ink jet deposition technique can be implemented, in particular for production in smaller series.

If the composite substrate has a three-dimensional shape, and in particular the conductive layer is not deposited on a flat surface, various graphic printing methods on a non-flat surface can be implemented during the deposition step. S12.

In particular, hydrographic printing can be used. A hydrographic film is printed with a graphic before being deposited on the surface of water from a pond. Since this hydrographic film is water soluble, it dissolves by applying an activating solution in water.

The composite substrate being soaked in the water of the basin, the surface tension of the water makes it possible to deposit the graphic of the hydrographic film on one or more faces of the composite substrate.

According to another embodiment, the filling compound used in the impregnation step S10 can be a resin loaded with metal particles.

The manufacturing process then includes a step S13 for activating the metal particles, for example by laser or ultraviolet beam, before the deposition step S12.

The laser or ultraviolet beam thus makes it possible to etch tracks or different lines on the composite substrate impregnated with a resin loaded with metal particles or an organometallic additive.

The material is thus activated locally, the laser or ultraviolet beam tearing off the metallic elements present in the filled resin.

The composite substrate is then immersed during the deposition step S12 in a bath and a deposition of a metallized conductive layer is obtained by electrolysis on the zones thus activated.

This deposition technique is conventionally used in plastronics, to produce plastic parts incorporating electronic functions.

It is particularly well suited to the implementation of the manufacturing method on a composite substrate of lignocellulosic material in three dimensions.

These different techniques for depositing a conductive layer are well known in the prior art and do not need to be described in more detail here.

Furthermore, the examples above are not limiting and other techniques such as techniques of transfer by pressure, under the action of heat or of humidification of the composite substrate could also be implemented. A photolithography process could also be implemented during the deposition step S12, making it possible to transfer an image to the composite substrate, whatever its shape in two or three dimensions.

The manufacturing method then optionally includes a step S14 of baking the conductive layer thus deposited.

The baking step S14 makes it possible to remove the solvents and the volatile compounds from a conductive ink, and thus to improve the electrical conductivity of the conductive ink deposited.

The temperatures implemented during the firing step S14 are typically below 180° C. in order to avoid any risk of burning the composite substrate made of ligno-cellulosic material.

Depending on the type of inks or conductive tracks produced, the temperatures are typically between 100°C and 150°C.

By way of non-limiting example, the cooking step S14 can be implemented at a temperature of 130°C.

During the baking step S14, the composite substrate on which the conductive layer is deposited is placed in an oven at a regulated temperature for a predetermined duration.

Alternatively, the cooking step S14 can use the combined implementation of pressure and heat. Thus, two heating plates can be pressed against surfaces of the composite substrate. Alternatively, rotating cylinders (rolling machine) can be used to apply a pressure force on the composite substrate on which the conductive layer is deposited.

In a continuous industrial manufacturing process, when the composite substrate is in the form of a plate, it can advantageously pass through a rolling mill heated during the baking step S14.

More generally, the baking step S14 makes it possible to bake the conductive ink by implementing heating, optionally combined with pressurizing the surface on which the conductive ink has been deposited. Optionally, the cooking step S14 can be implemented in two parts: first of all, a pre-cooking or a drying of the ink can be implemented, at a temperature of the order of 50 °C. The ink thus deposited changes from the liquid state to the solid state, facilitating the manipulation or transport of the composite substrate during the manufacturing process of the non-conductive electrical device.

An effective baking step, at a higher temperature between 100°C and 150°C, can then be implemented in order to remove the solvents and volatile compounds from the conductive ink and thus obtain the conductivity properties. electricity of this ink.

Finally, the manufacturing process may optionally include, after the deposition step S12 or the firing step S14, a final shaping step S15 of the composite substrate.

This final shaping step S15 may be similar to the initial shaping step S11.

The final shaping step S15 can thus be implemented, as described previously, by thermoforming or thermocompression techniques.

This new rise in temperature of the composite substrate during the final shaping step S15 makes it possible to heat the composite substrate on which the conductive layer has been deposited once again, and thus to optionally carry out a second firing of the conductive layer after cooking step S14.

The use of a thermoformable ink, with the composite substrate itself thermoformable, makes it possible to model electrically functional surfaces in three dimensions. The hot forming of the composite substrate implemented during the final shaping step S15 will act as a second curing of the conductive ink, which will further improve these electrical conductivity properties.

The manufacturing process described above thus makes it possible to obtain an electrically conductive device from a composite substrate made of lignocellulosic material. The functionalization of the composite substrate is obtained by depositing at least one conductive layer, in direct contact with the surface of the composite substrate, without requiring the use of an adhesive and of a plastic film incorporating printed electronics.

The manufacturing process thus implemented is simple and inexpensive, limiting the number of parts required and the assembly steps for the production of an electrically conductive device.

The technique of depositing one or more layers of conductive ink at room temperature on a ligno-cellulosic material impregnated with a filling compound makes it possible to produce a wide variety of electrically conductive devices.

In particular, when the composite substrate is a plate comprising two opposite faces, the manufacturing method may include a step S12 of depositing one or more conductive layers on at least one surface of the opposite faces of the plate.

It is thus possible to produce various electrically conductive elements on one of the faces of the plate.

There will thus be described, in relation to FIGS. 2a and 2b, an example of implementation of the manufacturing method, making it possible to produce an antenna on a composite substrate in the form of a plate.

In this embodiment, the composite substrate is a plate 20 comprising two opposite faces 20a and 20b. The manufacturing process includes a step of depositing a conductive layer on the flat surface of a face 20a of the plate 20.

In this exemplary embodiment, the manufacturing process comprises two successive deposition steps S12: a first deposition step S12 makes it possible to deposit, for example by screen printing a conductive ink, a first conductive track 21 .

An insulator 22, made for example by screen printing an electrically insulating ink, is placed on the first conductive track 21. The insulator 22 makes it possible to separate the different conductive layers made on the same face 20a of the plate 20. A second deposition step S12 is then implemented to produce a second conductive track 23.

The second conductive track 23 is made in a spiral shape so as to form an antenna. The second conductive track 23 is electrically connected to the first conductive track 21 .

An electronic component 24 can also be mounted on the surface, such as a CMS (surface mounted device) component. The electronic component 24 can thus be welded for example to two pads 23a, 23b of the second conductive track 23. The electronic component 24 can be a memory.

The electrically conductive device thus takes the form of a card of the identity card, access control badge or payment card type. The thickness of the plate 20 can be less than 10 mm, and for example between 0.1 and 3 mm, or between 1 and 3 mm.

The manufacturing process thus makes it possible to functionalize one of the two faces 20a of the plate 20.

The radiofrequency antenna thus produced can operate according to different types of well-known communication protocols such as RFID, Bluetooth, Wifi, NFC (Near Field Communication).

Of course, the embodiment of Figures 2a and 2b is not limiting.

One of the faces 20a of the plate 20 could also be functionalized by the deposition, by screen printing for example, of a trace of electrodes forming for example a resistive or capacitive sensor.

The composite substrate in impregnated lignocellulosic material being dielectric, the second face 20b of the plate 20 thus has a tactile function, making it possible to act through the plate 20 on the sensor produced on the first face 20a of the plate 20.

It is thus possible to produce a control interface for an electronic object. The composite substrate 20 can then preferably be translucent, the light transmission coefficient of the composite substrate 20 being equal to at least 3%. It is thus possible, through the composite substrate 20, to display a light signal emitted by an electronic object controlled by the control interface.

More generally, the deposition of a conductive layer makes it possible to produce a circuit or conductive tracks on which one or more SMD or through-hole components can be soldered.

It is also possible to deposit a conductive ink loaded with carbon, giving the conductive ink a resistive character.

During the circulation of a current in a track made with such a conductive ink, a heating element is obtained, which can be thermoregulated.

It is thus possible to produce an electrically conductive device forming a resistor, or an energy-generating device or even a simple electrical conductor.

We will now describe with reference to Figures 3a and 3b another example of implementation of the manufacturing method for producing a touch interface in lignocellulosic material 30.

As illustrated in FIG. 3a, using a conductive ink, deposited for example by screen printing, a network of conductive tracks 31 in a matrix is produced on one face 32a of a composite substrate 32 made of ligno-cellulosic material impregnated with an impregnating polymer.

The touch sensor thus produced may be resistive or capacitive in nature.

As illustrated in FIG. 3b, the composite substrate 32, after deposition of a conductive layer, can be shaped, for example by thermoforming, to form an electrically conductive device in three dimensions.

In the example illustrated, the electrically conductive device is thus hot-formed to form a surface, with two radii of curvature, such as a portion of a sphere.

Of course, any type of left surfaces with two radii of curvature could be hot formed. As described previously, it is thus possible to produce a tactile interface 30, in two or three dimensions, thanks to the dielectric composite substrate.

The lignocellulosic material is preferably at least partially delignified and the refractive index of the filling compound is between 1.35 and 1.70.

A refractive index of the filling compound close to that of cellulose, of the order of 1.47, is chosen.

Thus, the light coming from an electronic object or from a screen placed under the touch interface 30 is little or not deviated, improving the light rendering for the user.

The delignification of the composite substrate 32 allows light to pass without diffraction of the light ray.

Preferably, when the touch interface 30 is intended to be used to control an electronic object or a display screen, it is advantageous to use a transparent conductive ink in combination with the translucent or transparent composite substrate.

In addition, a touch interface can be obtained by coupling several plates of ligno-cellulosic material in such a way that the overall touch interface can have a thickness greater than 10 mm.

This type of touch interface is well suited to protect fragile or sensitive electronic objects, and can for example be used in applications where traditionally armored glass is required.

It will be noted that in the exemplary embodiments illustrated in FIGS. 2a, 2b, 3a and 3b, only one of the faces 20a, 32a of the composite substrate 20, 32 is functionalized using the deposition of a conductive layer. The other face 20b, 32b of the electrically conductive device thus forms an appearance face, and in particular has a rendering and the appearance of a ligno-cellulosic material, with the characteristics and the grain of the wood used to manufacture the composite substrate. .

It is thus possible to form appearance parts in various fields, and in particular an automobile, nautical or aeronautical part, or even a element or accessory in the field of building, packaging or furniture.

Furthermore, it is possible to produce an object in lignocellulosic material to which it is desired to confer a tactile detection function directly integrated into the object.

For example, the casing of a mobile telephone can be made from an electrically conductive device as described previously making it possible to functionalize the rear face of the mobile telephone, opposite the screen on the front.

By way of example, the manufacturing process also makes it possible to produce an electrically conductive device that can be used as a communicating watch strap or as a watch case.

An electrically conductive device made of lignocellulosic material can also be used for sports equipment such as skis, or consumer products (glasses, telephone covers).

The electrically conductive device made of lignocellulosic material can also be an element of furniture, and for example an office table with an integrated touch screen, or a door with a touch detection device.

Such an electrically conductive device can also be used in a passenger compartment (dashboard, door element) in the automotive, nautical or aeronautical field.

It will be noted that the electrically conductive device made of lignocellulosic material more generally makes it possible to replace all the types of interfaces today made from plastic or glass but which have the disadvantage of being fragile or thick and heavy and of have a harmful ecological impact on the environment because it is petro-sourced.

Of course, the embodiments described above are in no way limiting.

In particular, the composite substrate can have a highly variable 2D or 3D shape, making it possible to produce objects with complex geometries, of the skew surface or hyperbolic paraboloid type. In addition, the deposition of a conductive layer can be carried out on several faces of the composite substrate.

Claims

1 . Process for manufacturing an electrically conductive device in lignocellulosic material, characterized in that it comprises the following steps:

- impregnation (S10) of said lignocellulosic material with at least one filler compound so as to produce a composite substrate; and

- deposition (S12) of at least one conductive layer on at least one surface of said composite substrate so as to produce said electrically conductive device.

2. Manufacturing process according to claim 1, characterized in that said composite substrate comprises a fraction of a filling compound of between 30% and 80% by mass relative to the total mass of said substrate.

3. Manufacturing process according to claim 2, characterized in that said filling compound is an impregnating polymer, and for example a thermoplastic polymer of the acrylic type.

4. Manufacturing process according to one of claims 1 to 3, characterized in that said ligno-cellulose material is wood comprising lignin and a network of cellulose and hemicellulose, said wood being at least partially delignified.

5. Manufacturing process according to one of claims 1 to 4, characterized in that said composite substrate comprises at least one flat face, a conductive track being deposited on the surface of said at least one flat face.

6. Manufacturing process according to claim 5, characterized in that it further comprises a baking step (S14) of said conductive track, optionally followed by a shaping step (S15) of said composite substrate so as to produce a three-dimensional electrically conductive device.

7. Manufacturing process according to one of claims 1 to 6, characterized in that said filling compound is a resin charged with metallic particles, said manufacturing process further comprising a step of activating (S13) the metallic particles by laser or ultraviolet beam before said deposition step (S12).

8. Manufacturing process according to one of claims 1 to 7, characterized in that it further comprises a shaping step (S11) of said composite substrate after said impregnation step (S10) and before said step deposit (S12).

9. Manufacturing process according to one of claims 1 to 8, characterized in that said composite substrate is a plate having two opposite faces, said manufacturing process comprising a step of depositing (S12) at least one conductive layer on at least one surface of one of said two faces of said plate.

10. Manufacturing process according to claim 9, characterized in that the thickness of said plate is less than 10 mm.

11 . Manufacturing process according to one of Claims 1 to 10, characterized in that the said composite substrate is translucent or transparent, the light transmission coefficient of the said translucent substrate being at least equal to 3%.

12. Manufacturing process according to one of claims 1 to 11, characterized in that the refractive index of the filling compound is between 1.35 and 1.70.

13. Manufacturing process according to one of claims 1 to 12, characterized in that said at least one conductive layer comprises a transparent conductive ink.

14. Electrically conductive device made of lignocellulosic material, characterized in that it is obtained by said manufacturing method according to one of claims 1 to 13.

15. Electrically conductive device according to claim 14, characterized in that said device constitutes a control interface for an electronic object, a payment card, an access control badge, a sensor, a transistor, a resistor, an energy-generating device or an electrical conductor.

16. Electrically conductive device according to one of claims 14 or 15, characterized in that it forms an automotive, nautical or aeronautical part, or an element or accessory in the field of building, packaging or furniture.