Method for manufacturing a control panel for a motor vehicle

Abstract

A method for manufacturing a control panel for a motor vehicle, wherein a sensor film for providing a capacitive sensor function is glued to the back of a panel body made of polycarbonate, is characterized according to the invention in that a structure is introduced into the interface between the panel body made of polycarbonate and the sensor film, which forms channels for venting gases that may be produced into the outside space.

Description

The invention relates to a method for producing an operating panel for a motor vehicle, wherein a sensor film for providing a capacitive sensor function is bonded on the rear side to a panel body made of polycarbonate.Control panels or generally panels for switches in the automobile industry frequently consist of the material polycarbonate (PC). The switches are manufactured by an injection molding process. Switches in the automotive industry have changed widely over the last decade. Whereas the switches were all equipped with a switching mat before 2010 and thereby detected the triggering of the switching, more and more switches in the form of capacitively sensitive touch sensors have been implemented since 2015.In order to realize a capacitive touch sensor, regardless of whether it is the operation of an individual switching function or that of a touchscreen, a sensor film must frequently be adhesively bonded to the panel of the switch. These sensor films can be embodied as printed circuit boards, for example on polycarbonate (PC) or polyethylene terephthalate (PET), in the form of metal-filled polymers or else intrinsically conductive polymers. Alternatively, indium tin oxide films with semiconductor structures or FPC films with etched metal structures are suitable.The sensor foils are typically clamped or bonded to the aperture. Since the diaphragm consists of PC, the adhesive can be detached in the form of bubbles here by moisture inclusion. The reason here is the vapor pressure at the bond site by water vapor diffusion. This problem can be solved nowadays by special adhesives or by pretreatment of the aperture. Pretreatments are, for example, cleaning and pretreatment with chemicals, increasing / decreasing the roughness, corona or plasma treatment, primers of the PC surface, the use of adhesives with higher adhesive power to the PC, thicker adhesives, adhesives with special properties such as better liquid absorption or gas binding or gas absorption.The present invention relates both to screens which consist solely of polycarbonate and to screens in which the polycarbonate is additionally flooded with a polyurethane (PUR).As seen in FIG. 2, which shows a shutter according to the prior art, the base of the shutter is formed, for example, by a shutter body 1 made of polycarbonate. This diaphragm body 1 can be, for example, a plate with a thickness greater than 500 μm, a film with a thickness between approximately 12 μm and 500 μm or generally an object produced from polycarbonate by the injection molding process. The screen body 1 can also be additionally equipped with a decorative print 3 which shows the symbol of the screen or of the switch.In order to implement the capacitive sensor function, a sensor foil 2 is here glued on the rear side of the panel body 1. The surface facing the operator is finally flooded with a polyurethane 4.Even if the aforementioned pretreatment steps or adhesive modifications are used, bubbles B still form in the boundary layer between the aperture body 1 and the sensor film 2, which can impair the sensor function or can also detach the sensor film 2. The reason for this is a chemical reaction in the polyurethane. Isocyanates are the essential starting materials for the preparation of polyurethanes. The crosslinking reaction and the concentration of isocyanate in the aperture are time- and temperature-dependent here and thus dependent on the process parameters of the PUR flooding process and the percentage proportion of isocyanate in the process. As a result, isocyanates are always present in the system. Isocyanates form carbon dioxide in the presence of water. This reaction is temperature and moisture dependent. The carbon dioxide escapes from the diaphragm as indicated in the drawing by the double arrow D by diffusion processes. If a sensor film 2 is now bonded to the panel body 1, the adhesive can no longer hold the sensor film 2 completely on the panel body 1 despite the aforementioned pretreatment steps. Partial or complete detachment of the sensor film 2 from the screen body 1 and thus the formation of bubbles B occurs. If the adhesive force of the sensor film 2 to the screen body 1 is higher than the adhesive force of different layers within the sensor film 2, then detachment / bubble can also take place within the sensor film 2. This bubble formation is a temperature- and aging-dependent process, as a result of which the bubbles B are dynamically formed at different points and different sizes and disappear again. Bubbles B cause differences in the distance between the sensor film 2 and the operating surface, as a result of which the capacitive sensor function can be disturbed or restricted.In order to prevent this bubbling, various ways are known in the art. Thus, for example, it is possible to store the panel body 1 before the bonding to the sensor film 2 until the process of isocyanate conversion into carbon dioxide is concluded to such an extent that the additional vapor pressure caused by the carbon dioxide and other gases formed no longer leads to bubbles / detachments of the sensor film 2 from the panel body 1 or within the sensor film which are conspicuous by sensor means. The screen body 1 must be stored at room temperature for several weeks or at elevated temperature for at least several hours before the sensor film 2 can subsequently be bonded to the screen body 1.Alternatively, it is possible to prevent or at least reduce the diffusion of the carbon dioxide and / or other gases formed in the direction of the sensor film 2 by applying a diffusion-inhibiting / dense layer. Such a layer can be applied either to the decorative print 3 in contact with the polyurethane 4 or to or under any layer above, within or below the decorative print 3 or alternatively to the rear side of the panel body 1, which is in contact with the adhesive film of the sensor film 2. This layer can be applied to the decorative print 3 before flooding with the polyurethane 4, that is to say the final process during the production of the panel. This can be effected, for example, by screen printing, pad printing, PVD and CVD. Alternatively, the layer can also be applied to the finished panel before the sensor film 2 is bonded. This too can be effected, for example, by screen printing or pad printing.These known processes are, however, very expensive, since they require very long process times, and nevertheless do not necessarily lead to satisfactory results.It is an object of the invention to provide a process which avoids the disadvantages described and gives qualitatively satisfactory results with high process reliability.This object is achieved according to the invention by the combination of features of claim 1.As shown in FIG. 1, it is provided according to the invention that a structure 5 is introduced into the boundary surface between the diaphragm body 1 made of polycarbonate and the sensor film 2, which structure forms channels for discharging gases that are produced into the outer space.This measure prevents carbon dioxide, water vapor and / or other gases present or arising from accumulating in the boundary surface and forming bubbles there, but instead being able to escape into the outer space.The structure 5 provided according to the invention can be located on the surface of the trim body 1 made of polycarbonate facing the sensor film 2 and can be applied prior to the production of the trim, for example by screen printing or pad printing.The structure 5 can consist, for example, of an arrangement of parallel lines with a width of 1 mm and at a distance of 1 mm, the height of which is between 10 and 150 μm. Subsequently, the sensor foil 2 is then glued onto the structure 5.Alternatively, the structure 5 can also be introduced directly into the aperture body 1, for example by cutting tool, by means of etching, laser engraving or similar machining methods.Furthermore, the structure 5 can also be located on the sensor film 2. In this case, either the sensor film 2 itself or the adhesive film of the sensor film 2 can be correspondingly perforated, slit, milled or lasered, so that a channel structure is formed here, which can discharge gases.As a further alternative, the structure 5 can also be printed directly onto the sensor film 2, for example by screen printing or pad printing, namely under the adhesive used for the adhesive bonding of the sensor film 2 to the panel body 1.Finally, the surface facing the operator is flooded with a polyurethane 4.The methods described here for preventing the detachment of the sensor film 2 or the formation of bubbles can of course also be used with screens which are produced from polycarbonate and are not flooded with polyurethane.

Claims

Method for producing an operating panel for a motor vehicle, wherein a sensor film (2) for providing a capacitive sensor function is bonded on the rear side to a panel body (1) made of polycarbonate, characterized in that a structure (5) is introduced into the boundary surface between the panel body (1) made of polycarbonate and the sensor film (2), said structure forming channels for discharging gases that are produced into the exterior space.Method according to Claim 1, characterized in that the structure (5) is applied to the surface of the panel body (1) facing the sensor film (2) by screen printing or pad printing.Method according to Claim 1, characterized in that the structure (5) is introduced directly into the aperture body (1) by cutting tool, by means of etching, laser engraving or similar machining methods.Method according to Claim 1, characterized in that the structure (5) is applied to the sensor film (2) by screen printing or pad printing.Method according to Claim 1, characterized in that the structure (5) is introduced into the sensor film (2) or into the adhesive film of the sensor film (2).Method according to one of Claims 1 to 5, characterized in that the aperture body (1) is formed by a plate made of polycarbonate with a thickness of greater than 500 μm.Method according to one of Claims 1 to 5, characterized in that the aperture body (1) is formed by a film made of polycarbonate with a thickness of between approximately 12 μm and 500 μm.Method according to one of Claims 1 to 7, characterized in that the panel body (1) made of polycarbonate is flooded with polyurethane (4).

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