EP4103422A1

EP4103422A1 - Production of plastic touch controls using laser-etched conductive layers

Info

Publication number: EP4103422A1
Application number: EP21723906.0A
Authority: EP
Inventors: Roberto DEIANA
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-02-10
Filing date: 2021-04-08
Publication date: 2022-12-21
Also published as: WO2021161295A1; WO2021161295A4

Abstract

A method for manufacturing touch controls (100) provided with surface symbols (105) backlit by light guide (109) is disclosed. Said touch controls (100) are used to detect the interaction between a finger (102) and the magnetic field (103) generated by conductive traces (104). In particular, a process is disclosed for making said conductive traces (104) and said light guide (109), so that they are free from dispersive phenomena and adapted to the typical aesthetic requirements for this type of products, namely an embossed surface finish or a smooth surface finish. The process comprises a combination between a layer of conductive coating (108) and a layer of insulating coating (107), said layers being applied to the inner surface, i.e., opposite the physical interaction area, of a transparent plastic support (101), said inner surface, generally the lower surface, being therefore in raw plastic material or already treated with decorative coatings.

Description

Production of plastic touch controls using laser-etched conductive layers

Technical field

The invention relates to the industrial production of touch type control elements obtained by laser- etched conductive coating applied to plastics, preferably but not necessarily transparent. More precisely, the proposed invention relates to a process of layering and the subsequent laser-etching of conductive and non-conductive coatings, said coatings being progressively applied to a plastic surface and being processed with laser to obtain conductive traces used to operate a touch control. The proposed solution primarily concerns the industrial manufacture of said touch control elements from the electronic point of view, but also concerns the fulfilment of functional and/or decorative requirements, such as the integration of light guides for backlighting, the presence of surface finishes with tactile effect, and additional aesthetic aspects, such as the shine and colouring of the visible surfaces of said touch control elements. Background art

Recent years have witnessed a growing demand for control interfaces that are increasingly function-rich, and, which, above all, must feature new ways of providing inputs, such as voice commands, gesture commands and tactile commands. The latter technology and the related market demand have increased along with the dissemination of native touch devices, such as Smartphones, tablets, PCs etc. This has also affected traditional controls and interfaces (mechanical, electromechanical, electronic, pneumatic, etc.) that have been progressively revised and modernised according to touch optics.

In this technological and market context, the sector of touch controls realised on plastic, glass or ceramic supports has been emerging; the use of such controls has been steadily increasing and finds use in kitchen appliances, operating machines and, particularly, the automotive sector, as for example in Patent US 2014/327951 A1 (DE WIND DARRYL P DE WIND P [US] ET AL, 6 November 2014. The implementation and integration of touch controls in these markets requires a dual approach both of a functional technical nature and of a qualitative aesthetic nature: it is necessary to create new control systems that combine and meet at once the design requirements (for example, to have attractive and modern shiny seamless surfaces) with the demands for innovation (to provide sensitive surfaces to enable new modes of Man Machine Interaction, so- called “Smart Touch”), and, finally, to ensure that the components meet quality and reliability standards and are suitable for and industrial applications. Compared to switches or other conventional physical controls, plastic touch control elements have the advantage of being able to operate reliably even in unfavourable environments, for example in the presence of aggressive gases or when constantly exposed to humidity. To deal with these environmental situations, traditional controls need to be sealed in a complicated manner and this is a possible cause of defects, in addition to resulting in a significant increase in costs.

In addition, compared to traditional control elements, such as push-button panels and the like, touch controls usually save considerable space because they integrate into spaces that are normally unusable and, sometimes, even conceal the visible symbols.

Despite these excellent application premises and the fact techniques to integrate plastic touch controls have been in use, there are still considerable problems for these control systems: in terms of reliability, costs, aesthetics and functional performance.

Materials such as glass, ceramics, transparent plastic (e.g., PC polycarbonate or PMMA poly(methyl methacrylate), can be used as a substrate for making such touch-type control elements. From an industrial point of view, these products are manufactured, for example, using the so-called “In Mold Layer” (IML) process, by which a film printed with the symbols of the control elements to be made is injected from behind or overmoulded on specific types of plastic. The drawback of the IML process is the relatively high scrap rate, which makes it very expensive in terms of costs. Furthermore, the defect of a scrap piece can only be ascertained when the piece is finished, and is not visible during preliminary phases, when any economic damage could be mitigated. Another disadvantage of said IML process is that it only allows manufacturing essentially flat and regular components, and, in any case, those without curvatures or complex surfaces. Finally, this method can be justified for very high quantities of parts because the film used to make them must be printed in large quantities to be economically viable.

According to a more economical and alternative method to the aforementioned IML process it is possible to manufacture the plastic moulded part by injection moulding. This technique requires transparent plastics to be applied from the front or the back by printing or coating processes. Under these conditions, the process involves the use of fade-resistant lacquers and any symbols to be illuminated are laser-etched or, alternatively, printed. With regard to the electronic and circuit aspects in this type of touch controls, the electromagnetic fields are obtained by traces of metal conductors made on or inside translucent sheets or laminae. Said sheets are glued inside the components by machining from the inside. From the application point of view, said sheets are secured to the plastic so that the conductive traces are positioned at and around the dedicated control areas, said areas being characterised by the decoration of the symbols of the different control elements and, said symbols being typically back-lit.

In the devices thus made, the electromagnetic field is generated by an electric current flowing through the conductive traces and is subject to interference, or by touching with a finger the front of the plastic touch control. Interference due to physical interaction with said finger may be detected by measuring the corresponding electrical signal, and said signal may be converted with appropriate conversion, analysis and control software and used to drive a switching process. However, the controls obtained by the aforementioned systems are subject to a significant technical problem inherent in the stability and repeatability of said electrical signal, with negative consequences on the reliability and quality of the transduction of the commands imparted by touch. In fact, in order to function correctly, it is required that the signal detected is always likely to have the same intensity in the face of the same interaction, in order to distinguish with certainty and precision whether the modification of the electromagnetic field is certainly and uniquely attributable to and associated with a voluntary physical interaction.

The great practical problem of the techniques currently used is that air can accumulate over time between the sheet containing the conductive traces and the plastic, thus partially loosening the connection. This air, acting as an insulator, attenuates the detected signal power and, as a consequence, may alter or even impede the operation of the touch control element.

In addition to this crucial reliability problem, a further constructive problem is noted: the metal traces of the conductive films must be electrically brought into contact with signal acquisition lines and with the control electronics; this is usually done by thermal processes. By means of said processes a PCB (printed circuit board) positioned behind and at the film is connected; said PCB housing the control electronics and typically a fluoroscopic lighting unit often consisting of LEDs. Unfortunately, these thermal processes have additional negative consequences, since the connections with said film are subject to ageing and can reasonably break during the useful life of the control element, thus preventing the connection between the conduction traces and the underlying PCB.

As an alternative to this approach, if the geometry of the component allows it, it is also possible to apply conductive interconnections to the PCB; this allows eliminating the aforementioned conductive film and the PCB is then glued directly to the plastic of the component by means of a foam used as spacer. Unfortunately, this alternative solution also presents problems of correct and stable reception of the signal, and, in particular, problems of signal acquisition following the alteration of the magnetic field caused by the touch of the finger. It is known that the aforementioned foam also releases gas over time, and also in this case, as in the aforementioned procedure, the intensity of the magnetic field detected can be affected by said interference, with obviously negative consequences in terms of correct acquisition and operation of the command or touch control implemented.

In conclusion, and in addition to the aforementioned technical vulnerabilities, it is pointed out and, would be useful to reiterate, that both methods for generating the aforementioned conductive fields are very expensive, since it is necessary to create a separate film or a “tailored” PCB for each type of component. And this is extremely difficult because, even functionally, similar components may require further customisation: for example, think of markets outside Europe, where different symbols or characters are usually used for the same controls. From the production point of view, these peculiarities imply the creation of a functionally identical, though concretely and practically, different control component, since it is independent or provided with a different type of conductive sheet and dedicated PCB. All this is extremely expensive and disadvantageous to produce small quantities of pieces.

In conclusion, the use of conductive sheets, flat cables, or copper tracks performs the conductive function, but, at the same time, requires a further assembly, gluing or bonding phase; said processing would increase not only the complexity and cost of the process, but potentially decrease the reliability of the components due to problems related to the use of, additional widths, trapped air, decay of the adhesives over time, etc.

To avoid the use of the aforementioned conductive sheets, flat cables, or copper tracks, solutions based on conductive traces applied directly on the support and made by conductive coatings or by deposition methods of conductive material functionally equivalent to conductive coatings have been proposed. Said coatings are obtained by integrating micro-particles in the mixture, which, in most cases, are based on silver, copper or nickel and can guarantee good adherence to almost all plastic materials. Thanks to conductive coatings, it is therefore possible to create conductive traces directly on plastic, which are useful for implementing a circuit, as in the case of Patent US2017/031480 A1 (GABRIEL ANNELIE [DE] ET AL) 2 February 2017. According to a typical method of making conductive traces, the conductive coating is applied to the plastic material, for example, by means of an airbrush, and subsequently selectively removed so as to create suitable conductive traces. These controls made with conductive coatings still present numerous problems; for example, in the automotive field, said problems are attributable to the coexistence of the conductive coating with additional paints used to decorate and protect said plastic controls; there could also be problems related to laser machining applied to obtain said conductive traces. An initial significant issue concerns the fact that conductive coating tends to transfer its properties or part thereof to a large number of decorative/protective coatings, even if these normally do not serve as conductors and are insulating. This makes the functional compatibility between conductive and decorative coatings applied on the same touch components difficult for the necessary and equally important aesthetic or protection purposes. The diffusion of conductive elements to adjacent coatings can in fact cause dangerous circuit anomalies with uncontrolled current leakage and serious alterations, or even interruptions of the electromagnetic field that underlies the touch control.

Another issue what limits the application of conductive coatings in the realisation of touch controls is the presence of problems of aesthetic nature caused by the introduction of conductive coatings in the common decoration or surface finishing processes of said components. Said components, and especially those intended for the automotive market, provide for the use of additional lacquers to obtain particular colours rather than particular shine or opacity effects; said additional lacquers are also submitted to laser-etching, for example, to draw the symbols relating to the different controls implemented rather than to create light guides that are useful for the backlighting of said controls, and, finally, to obtain particular surface effects. It follows that the laser-etching of the conductive traces and the related energy supply can interfere with the other coatings applied and be a source of aesthetic defects. In particular, the laser-etching of conductive traces can interfere with plastic and decorative paints and negatively affect the sharpness of the control symbols, their backlighting and the surface finish of the components.

Disclosure of the Invention

To overcome the aforementioned limits of the interfaces with plastic “touch” controls and to improve performance in terms of cost, construction quality, methodological standardisation, and to combine the technical requirements with the equally necessary and important demands for yield and aesthetic pleasantness, we want to propose a method to build touch control elements based on conductive coating, said conductive coating being integrated with additional decorative and insulating paints according to appropriate layers. Said coating being used for the construction of conductive tracks and consequent I/O transmission and control systems.

The main objective of the proposed method is therefore to overcome the current solutions (flat cable, copper tracks, etc.) by applying conductive coating to the plastic material, which is subsequently laser-etched o obtain conductive traces useful for generating the electromagnetic field underlying the operation of a touch type control. Said integration of conductive traces directly on the plastic would bring many advantages, such as functional reliability, permanent, robust and durable grip on the plastic surface; this, in turn, would eliminate the classic problems due to gluing or assemblies (air formation, glue deterioration, detachments, poor repeatability of signals etc.).

A further objective of the proposed patent is to provide a solution to overcome interference between conductive coating and other coatings commonly used to decorate and protect touch controls, in particular, to eliminate unpleasant aesthetic consequences that the laser-etching of a conductive coating can have on visible parts, such as symbols and their backlighting. In addition, the proposed method is intended to overcome functional problems related to the undesirable diffusion of conductive particles from the conductive coating layer to adjacent layers.

A further objective of the proposed invention is to make the process of making conductive traces cheaper, both on a small and large scale, by allowing the integration and assimilation of the prototype phase and production phase, by decreasing the number of processes currently required and by zeroing production equipment that is considered ancillary to the application and masking of said coating, and, finally, by excluding the assembly phase between prefabricated circuits and touch infrastructure. In addition, we want to propose a reduction in the number of contacts and connection elements with the circuits connected to the control elements, and to prepare a manufacturing process that allows them to be thinner and possibly allows the elimination of connection cables, in that they would be replaced by optical fibres, where geometry allows it.

A further object of the invention is to provide a method for making conductive traces on surfaces with complex geometries and with inclination changes, angles and other complexity factors.

Finally, the objective of the proposed invention is to improve the electromagnetic aspects and performance of the conductive tracks or to implement the antenna functions with thin layers; said aspects, for example, can be used to implement more complex functions on a touch control, such as, for example, keyboard short cuts that to date can only be implemented on relatively flat surfaces, and with considerable manufacturing and reliability problems.

The achievement of the aforementioned objectives is achieved by the combined application of a layer of conductive coating and a layer of insulating coating applied to the inner surface of the plastic material; said layers are integrated with additional coating layers for decorative and protective use according to an appropriate arrangement adaptable to the required aesthetic requirements; said layers (conductive, insulating and decorative) are subsequently processed with laser techniques to obtain the conductive traces, symbols and light guides for the backlighting of the controls. The invention makes it possible to use the same laser machine for a triple purpose, namely: to create the symbols, to create the light guides useful for backlighting the controls and, above all, to create the conductive tracks of the touch control by selectively removing the applied conductive coating. The conductive traces obtained on plastic material are designed and laser- etched to obtain a circuit functionally equivalent to that of touch type controls with copper tracks commonly used in the electronics industry. Going into more detail, the proposed invention requires a layer of insulating coating (both electromagnetic insulation and optical/light insulation) to be interposed between the conductive coating and the adjacent layers (plastic and/or decorative coatings). Said interposition is adaptable to different aesthetic and functional requirements of the control element (surface finish, shine and colour). The insulating layer prevents adjacent layers from becoming partially conductive by diffusion, thus allowing perfectly functioning conductive traces to be made. Further, said insulating layer is characterised by pigments of suitable colour to absorb and screen any selective laser; this process prevents undesirable effects due to energy contributions that improperly propagate to the adjacent layers, as well as aesthetic or functional damage. Once stratification is applied, conductive traces are obtained within the conductive coating layer by a laser set to selectively remove excess conductive coating and without affecting the underlying insulating coating layer.

Brief Description of the Attached Drawings

Further characteristics and advantages of the proposed technical solution will become more evident in the attached 3 drawings, in which: Fig.l and Fig. 2 represent the operation of a traditional touch control;

Fig. 3 and Fig. 4 represent a touch control made according to the proposed solution and characterised by a raised surface finish;

Fig. 5 and Fig. 6 represent a touch control made according to the proposed solution and characterised by a smooth surface finish.

Best mode for carrying out the invention

The present invention consists of a method of making a touch control by laser-etched conductive layers and its integration, mainly but not necessarily, to thermoplastic materials; said method being based on the appropriate overlapping of conductive layers and on the creation of conductive traces obtained by selective laser removal.

More precisely, the proposed procedure includes a layering layout of coatings (conductive, insulating and decorative/protective), and a series of machining processes with laser machines that allow to create touch type control elements; said elements being free from causes of degradation and poor signal acquisition/interpretation, and said process allowing to combine technical reliability requirements with aesthetic needs, both being important and necessary for this type of interfaces. To date, there are two main types of aesthetic/ functional finishes required by manufacturers and, particularly, by the automotive market, which is one of the markets in which the use of touch controls is particularly growing:

0 Touch-type controls with embossed surface finish (from now on CASE A); said finish being obtained by applying a coating that can be laser-etched on the upper surface of the plastic components; said coating being subsequently partially removed with a laser to obtain the corresponding surface symbol. This machining allows to have in the vicinity of said surface symbol a relief sensitive to the user’s touch when the upper surface of the control is touched (sensitivity to the touch). Looking at the surface of the touch-type controls made with this technique, it is therefore possible to see in relief the reference to the shape of the surface symbol relative to the control that can be activated. This type of finish is often associated with a backlight by means of a light guide through the laser-etched symbol and increases the visibility of the interaction/touch point.

• Touch-type controls with smooth surface finish (henceforth CASE B): according to said finish, it is expected that the entire surface of the touch control or the panel provided with touch interaction elements be completely smooth to the touch, without any apparent perception of areas dedicated to the control (keys, interaction id points, symbols, etc.). In this particularly minimalist version, the upper surface of the panel and of the interaction zones is therefore uniform and features a usually shiny and homogeneous appearance, and the interaction zones of the controls are identifiable only by an appropriate backlight that makes the corresponding symbols visible.

The proposed patent allows solving technical problems mentioned in the previous paragraph by means of a process to create the magnetic excitation circuit of a touch control using traces of conductive coating, said conductive traces being free of dispersive phenomena and adapted to the aforementioned aesthetic requirements (CASE A and CASE B).

The founding core of the invention is the combination between a layer of conductive coating and a layer of insulating coating, said layers being applied on the inner surface (i.e., opposite to the physical interaction area) of the plastic component, and said inner surface (generally the lower surface) being thus of rough plastic material or already treated with decorative coatings.

The rear application of a conductive coating with the interposition of an insulating layer makes it possible to laser safely on both opaque and transparent plastic, and also allows the application of additional aesthetic finishes that, thanks to the presence of the insulating coating layer, can be safely interposed (without altering aesthetics and conductive properties) between the pair of conductive and insulating layers and the internal surface of the support.

The application behind the aforementioned layers finally allows creating a circuit of conductive traces protected from external agents and from standard wear, scratches or incidental damage etc. It should be noted that the following description is based on the realisation of a touch type electronic control made on a transparent plastic substrate, assuming the predominant use that is currently made in these embodiments (e.g., polycarbonate), but the process of the proposed patent will be easily extended, through knowledge in the common availability of a person skilled in the art, to alternative materials, such as transparent glass, ceramics and even non-transparent plastic materials without departing from the scope of the proposed invention.

With reference to the accompanying drawings and, particularly to Fig. 1, it represents the operating principle of a touch control (100) made on a transparent plastic support (101). Said touch control (100) electronically detects the interference/interaction between a finger (102) and the magnetic field (103) generated by an electric current flowing along conductive traces (104) positioned on said transparent plastic support (101).

With reference to Fig. 2, it represents the same simplified diagram as Fig.l, updated according to a possible real implementation and with an exploded view. According to said implementation, the conductive traces (104) form an excitation circuit centred below and at the portion of the transparent plastic support (101) housing the surface symbol (105) of the control, and which is physically employed by the users to operate it. This is to ensure that the electromagnetic field generated by the current passing through said tracks (104) corresponds to the physical interaction zone of the touch control (100).

Referring to Figs .3, 4, 5, 6, they represent the stratification system of conductive, insulating and decorative coatings pursuant to the invention proposed in the two variants and used to meet the main functional aesthetic requirements already mentioned (case A and B).

With reference to said drawings and, in particular Fig. 3 and Fig. 4, they represent the layered structure of said touch control (100) relating to case A, that is, with a raised surface finish. This structure comprises: · A layer of decorative coating (106) resistant to light and applied to the top of the transparent plastic support (101). Said decorative coating (106) is applied by transfer processes such as buffering, PVD (Physical Vapour Deposition), sublimation or coating. Light sealing for this type of decorative coating is achieved through high pigmentation of the lacquer and by employing light-shielding pigments, e.g., carbon black or metal pigments. In the case of automotive applications, the decorative coating used must adhere to the specifications of the product field, such as the Volkswagen TL226 standard. Depending on the scope of use, decorative coatings (106) characterised by high hydrolysis resistance and with a thickness between 15 - 40 microns is preferable.

• A layer of insulating paint (107); said insulating coating must be suitable for laser-etching and applied inside the transparent plastic support (101). Said coating layer (107) must be preferably beige or of similar neutral colour. The insulating coating (107) thus applied prevents the decorative coating (106) from becoming contaminated by conductive material, as well as the unwanted propagation of light sources and, in particular, subsequent laser processes applied from below (and more precisely in the next conductive layer) from penetrating further into the transparent plastic support (101), thus creating imperfections on said structural material and, especially, on the upper decorative coating (106). Said insulating coating (107) can be applied by transfer or coating process and the thickness of said coating layer (107) must be reasonably between 15 - 40 microns.

• A layer of conductive coating (108). Said conductive layer (107) must have a conductivity less than 10 k ohm with characteristics such that it can be laser-etched without residues and with sharp contours and specific geometries. Said conductive layer (108) can be applied by printing or coating techniques and the thickness provided for said conductive coating layer (108) is 15-50 microns.

Compared to this standard stratification, it should be noted that it is possible to obtain a layer of conductive material functionally equivalent to that proposed with conductive coating (108) by using deposition processes such as, for example, PVD consisting of evaporated metals. Said solution is alternative and even preferable if conductive traces with antenna function are to be made. In this case, processes specific to PVD, such as sputtering, will be used. The metals that can be used with this technique will generally be copper, aluminium, zinc, stainless steel, chromium or metals with excellent conductivity, such as gold, platinum or silver. The thickness of the conductive layer made with these alternative application techniques to the conductive coating (108) will be within the nanometre range.

Finally, since metals are used in the conductive layer, the stratification described above may include an additional layer of anti-corrosion protective coating, depending on the type of environment where the touch control 100 is to be used.

According to the proposed invention and its application to the aforementioned case A, the laminated coatings as previously described are subsequently laser-processed. Said processes are employed to selectively remove portions of the applied coating layers and obtain the functional elements of the touch control (100), such as conductive traces (104) that generate the magnetic field (103), surface symbols (105), and light guides (109) that allow backlighting at the surface symbol (105). Said method comprises:

• Realisation of light guides (109) and the corresponding surface symbol (105): said elements are obtained by laser, by removing portions of the conductive coating layer (108) and the following layers (107) and (106), so as to allow the passage of light between the layers and further obtain surface symbolism (105). This processing is achieved by lasering with intensity such as to selectively penetrate the layers and, in particular, by crossing the support/substrate by allowing intra-material lasering; such techniques allow lasering together the conductive layer (108), the light guide (109) and the surface symbol (105) with a single, possibly progressive, removal through all the applied layering, including plastic support, starting from the conductive paint (108) up to the decorative paint surface layer (106). More precisely, the laser removes the conductive coating layer (108) and the adjacent layer of insulating coating (107); it subsequently crosses the transparent plastic substrate (101) and finally removes the decorative coating layer (106), thus allowing the creation of surface symbols (105); said surface symbols (105) can be lit by means of the light guide (109) obtained by progressively removing the layers (108) and (107) below. It should be noted that the laser removal described above is preferable but subject to modifications by a person skilled in the art, said modifications relating, for example, to the progressive order of laser removal and its application from below rather than from above. In particular glyphs, symbols, conductive traces and other laser machining will not be applicable from below as in the example provided, but, thanks to the patented layering, they can be modulated, distributed and oriented according to methodological necessity and convenience.

• Realisation of conductive traces (104): by means of a laser, portions of conductive coating (108) are removed so as to form conductive traces (104); said traces will reproduce the excitation circuit of the touch control (100) and will then be obtained under and near the surface symbols (105) obtained with the laser process described above. The portion of conductive coating (108) remaining after etching of the conductive traces (104) is retained and constitutes a screen (110). More precisely, said screen (110) is formed by the remaining part of conductive coating (108) external to the obtained conductive traces (104); said screen (110) during the operation of the touch control (100) is not powered but passively employed as a protection against external electromagnetic interference. The screen (110) promotes precise, circumscribed and localised generation of the magnetic field (103) near the conductive tracks (104) and the surface symbol (105), thereby increasing the sensitivity and precision of the touch control (100).

During the realisation of the conductive traces (104) the intensity of the laser beam is set at a lower intensity adequate to remove the single layer without compromising the integrity of the adjacent layers and without leaving processing residues. To create said conductive traces (104), the conductive coating layer (108) is laser-etched up to the insulating coating layer (107), said insulating layer has as an anticipated function of both electrical and luminous insulation, and also allowing the application without interference of further aesthetic finishes, colours etc. The conductive traces (104) obtained by this process of deep extrusion of the conductive coating (108) may have a width ranging from 0.1 mm to several mm. With reference to the accompanying drawings and, particularly, to Fig. 5 and Fig. 6, they represent the layered structure of said touch control (100) relative to case B, i.e., with a smooth surface finish. Said method comprises:

• A layer of decorative coating (106); said coating is fade-resistant and applied to the lower surface of the transparent plastic support (101) by a transfer process, such as padding, printing, painting or PVD. Said coating is characterised by a high pigmentation with pigments that absorb light, e.g., carbon black or metal pigments, and are in compliance with the specifications of the product field. The thickness of this layer (106) typically ranges between 15 and 40 microns.

• An insulating coating layer (107) is applied on the decorative coating layer (106). Said layer of insulating coating (107) is preferably beige or a similar neutral colour. This colouring is normally used to provide visual feedback during processing, but, in this case, has a much more important purpose, namely to “brake” the laser intensity thanks to its colour spectrum. In particular, it allows limiting the propagation of the laser beam to the adjacent layer of decorative coating (106). Additionally, the insulating coating (107) allows solving a compatibility problem between conductive coatings and many decorative coatings, by allowing the aforementioned problem of unwanted conduction between adjacent coating layers to be solved, and a plurality of decorative coatings (106) to be applied to the transparent plastic support (101) without limitations of type or chemical characteristics. Finally, the pigmentation of the insulating coating layer (107) performs an insulating function also from an optical point of view, because it prevents subsequent laser processes required for creating conductive traces (104) in the underlying conductive coating layer (108) from propagating to adjacent layers, and, above all, from propagating to the decorative coating layer (106), which would make edges of the conductive traces (104) visible on the front of the control (100), with evident aesthetic damage. Said insulating coating (107) will be applied by transfer or coating process, and the thickness must be reasonably between 15 and 40 microns.

• A layer of conductive coating (108). Said conductive layer must be characterised by a conductivity of less than 10 k ohm and can be laser-etched with sharp contours and specific geometries. This conductive layer (108) is applicable by printing or coating processes and techniques, and characterised by a typical thickness of 15-50 microns. If particularly high conductivities are required, e.g., to obtain antennas, the conductive layer (108) will be obtained by deposition processes, such as so-called PVD processes and, in particular, the sputter - PVD process will be applicable. The metals usable to make the conductive coating layer (108) will generally be copper, aluminium, zinc, stainless steel or chromium, but other metals with good conductivity such as gold, platinum or silver may also be used. The thickness of the conductive paint layer (108) containing the aforementioned metals will be in the range of nanometres, up to about 10 nanometres.

• An (additional) layer of UV protective coating (111), preferably but not necessarily, of a glossy or translucent black type; said protective coating layer (111) is applied above the transparent plastic support (101) and used not only as protection against scratches and other mechanical damage, but also as an aesthetic finish to achieve the so-called concealed effects. The possible glossy or translucent black colour of said UV protective coating (111) makes it possible to obtain a surface symbol (105) that is visible to the naked eye only when a backlight is applied to the light guide (109). Alternatively, this UV protective coating (111) may be transparent and used to obtain scratch protection.

The stratification described above represents a preferred model of implementation, but may include an additional layer of anti-corrosion protective coating, said additional layer being added below to protect the metals included in the conductive coating layer (108), or, alternatively, to the conductive layer deposited by the aforementioned PVD processes. According to the invention proposed and applied to the aforementioned case B, the laminated coatings as previously described are subsequently processed by lasering. Said laser machining is used to selectively remove portions of the layers and obtain the functional elements of the touch control (100), such as the traces of conductors (104) that generate the magnetic field (103), the surface symbol (105) and the light guides (109) used for the backlighting of said surface symbol (105). Said laser machining comprises: · Realisation of the light guide (109) corresponding to the surface symbol (105): similarly to the aforementioned case A, the proposed procedure involves a step to remove all the layers of coating under the position of the surface symbol (105). The light guide (109) is made by progressive laser removal of the conductive layer (108), the insulating coating layer (107) and the decorative coating layer (106); said processing is carried out with high intensity lasers.

• Realisation of the conductive traces (104): by means of a laser, portions of conductive coating (108) are selectively removed near the previously obtained surface symbols (105). To perform this operation, the intensity of the laser beam is set to a lower value, so that the conductive coating layer (108) remains free of residues. The conductive traces (104) are obtained by laser that selectively removes the conductive coating (108) up to the insulating coating layer (107). The conductive traces (104) obtained will typically have a width ranging from 0.1 mm to several mm.

In this application too, the portion of conductive coating (108) remaining after obtaining said conductive traces (104) constitutes a screen (110). Both in case A and in case B described above, the touch controls thus carried out (both in case A and in case B) can be backlit by means of the light guide (109).

Industrial Applicability

The industrial production process of a touch control (100) according to the proposed invention benefits from eliminating the use of classical conductive film and the direct generation of the magnetic field (103) by laser-etching the conductive traces (104). This aspect, together with the fact that all the conductive and non-conductive coating layers adhere directly and firmly to the structural layer makes it possible to implement a stable and reliable automated manufacturing process. Thanks to the adhesion of the conductive coating (108) to the inner portion of the transparent plastic support (101), it is possible to obtain damage protection and a higher signal strength, or vice versa, to use lower feed strengths since, as is known, the signal strength decreases exponentially with distance from the substrate (104). All the aforementioned aspects benefit from greater reliability and durability of the components. In addition, and always from the point of view of industrial manufacturing, the presence of the aforementioned screens (110), in addition to raising the functional quality standard, allows, in an equally important manner, to reduce the amount of conductive coating (108) to be removed, thus saving time, speeding up processing processes and reducing industrial complexity. From an industrial point of view, the described process is not limited to flat surfaces; on the contrary, it is possible to create complex three-dimensional components directly without the development and manufacture of custom-made components, instead adapting the process and the relative use of laser machines in a flexible and economical way, even for small quantities of products. Thanks to these flexible machining processes, a change in conductive geometries and touch functionalities does not necessarily involve the creation of a new component because only the laser parameters must be changed.

The backlighting of the components manufactured according to the invention may be carried out using conventional PCBs or, alternatively to said PCBs, the lighting guides may be injected using the injection moulding process. In the case of aesthetic finishing of case A), the light source for the light guide (109) may be injected into the control component (100) prior to coating. Alternatively, the light may be introduced with cross-cutting solutions to be then redirected into the surface symbols (105) by means of micromanaged mirrors, prisms or standard light guiding methods.

Finally, additional electronic components necessary for the operation of the touch control (100) may be glued directly to the conductive layer (108), or anchored by ultrasonic welding processes. This allows completing eliminating the PCBs and making the touch control (100) very thin.

If it is desired to carry out touch controls manufactured according to the same stratification as in the proposed patent, but with PCB-free fibre optic technology, it will be necessary to replace the decorative coating layer (104) with a suitably modified coating layer to allow the touch control (100) to be further inserted into an injection moulding tool, which will allow printing the fibre optic separately. In this case, said decorative coating (104) must be replaced with a combined thermoplastic component, such that it can permanently adhere to the light guide in the further injection moulding process.

In industrial manufacturing, the connection between the contact points of the conductive layer (108) and the remote electronic unit to be controlled with the touch control (100) can normally be made by means of a cable for contact point. Said contact should be preferably obtained using a conductive silicone bearing or a conductive adhesive.

Alternatively to this method, the contact may be made by ultrasonic welding. Alternatively, a Can Bus device may be used for data transmission.

If touch controls are to be used in the automotive field, which is reasonably but not necessarily one of the best areas of use for the proposed solution, the coating layers and, in particular, the conductive coating (108) must meet the automotive specifications, and, in particular, those concerning hydrolysis resistance and a condensation water test, as well as a climate change test, as described in standard automotive specifications, such as VW TL 226.

A possible implementation of the conductive coating (108) according to the invention is obtained by a cross-linked organic compound combined with a hardener, in order to form a durable three- dimensional molecule; said conductive coating (108) includes: 10 - 40 wt % of a bisphenol A type epoxy resin with free OH groups 12-30 wt % conductive pigment 1-5 wt % of a dispersant 1-2% surface-treated smoked silica 1-2% of a wetting agent of the substrate a mixture of low, medium and high boiling solvents 1-2 wt % soot

Preferably, a poly-isocyanate with 3 groups of isocyanates, a so-called trimmer, is used as a hardener alternatively, it can be cross-linked with polyfunctional amines.

The degree of cross-linking will be selected stoichiometrically at 100-130%. The conductive pigments preferably employed are: Carbon, graphite and other pigments with a metallic charge and having a high conductivity can be used as a conductive pigment. Conductivity is obtained by a high concentration of pigment volume, with the individual surfaces in contact. Since the conductive pigments mentioned above all have a strong intrinsic colour, it may be problematic in some design applications. In this case nano-metal particles will preferably be used because the particle size of 1 to 100 nanometres makes the metals largely transparent. This also allows to increase conductivity enormously, up to 10 - 1000 Ohm/cm.

Claims

1) Method for the manufacture of touch controls (100) with embossed or smooth surface finish; said controls being provided with rear surface symbols (105) illuminable by light guide (109); said touch controls being employed to detect the interaction between a finger (102) and the magnetic field (103) generated by conductive traces (104); said conductive traces (104) and said light guide (109) being obtained by lasering coating layers applied to the inner surface of said transparent plastic support (101); said method for the manufacture of touch controls (100) comprising the following steps:

• application of a layer of decorative coating (106) to the outer surface of said transparent plastic support (101) in the case of touch controls (100) with embossed surface finish, or to the lower surface of said transparent plastic support (101) in the case of touch controls (100) with smooth surface finish;

• application of an insulating coating layer (107) to the inner side of the transparent plastic support (101) processed according to point a); said insulating coating layer (107) being employed to prevent the diffusion of light and conductive material to adjacent layers;

• application of a conductive coating layer (108) to said insulating coating layer (107);

• realisation of said light guide (109) by laser removal of portions of said coating layers (108), (107) and (106); said portions being located below said surface symbol (105);

• realisation of said conductive traces (104) and screens (110) by laser removal of portions of said conductive coating layer (108); said traces (104) and said screens (110) are used to generate said magnetic field (103) at said surface symbol (105).

2) Method according to claim 1, wherein said touch controls (100) in the case of a smooth surface finish are further treated with a layer of scratch-resistant UV protective coating (111) applied to the upper surface of said transparent plastic support (101).

3) Method according to claims 1 and 2, wherein said scratch-resistant UV paint layer (111) is characterised by a glossy or translucent black colour; said layer (111) being used to partially obscure said light guide (109) thus making said surface symbol (105) retractable. 4) The method according to the preceding claims, wherein said coating layers (106), (107), (108) and (111) are applied by a printing, buffering, coating or PVD process.

5) Touch-type control (100) with illuminable surface symbols (105) obtained according to the method of the preceding claims, wherein said layer of conductive coating (108) is obtained by an organic compound cross-linked with a hardener; said compound being characterised by a three-dimensional molecule comprising:

• 10 - 40% by weight of a bisphenol A type epoxy resin with free OH groups;

• 12-30 wt % conductive pigment; · 1-5 wt % of a dispersant;

• 1-2% surface-treated smoked silica;

• 1-2% of a substrate wetting agent;

• a mixture of low, medium and high boiling solvents;

• 1-2 wt % soot.

6) The backlit touch control (100) obtained according to claim 5, wherein said conductive pigment consists of carbon particles, graphite or, alternatively, other high conductive metals with a particle size of between 1 and 100 nanometres. 7) The backlit touch control (100) obtained according to claim 4, wherein said hardener consists of a polyisocyanate with 3 groups of isocyanates or polyfunctional amines;both with 100-130% stoichiometrically selected cross-linking.