Abstract:
A method produces a control element having a touch-enabled surface, in which a paste-like material is applied on a carrier plate. At least one raised structure element is formed by the paste-like material on the carrier plate. For this purpose, a stencil having inherent stiffness is arranged above the carrier plate and the paste-like material is pushed through at least one recess in the stencil.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to International Application No. PCT/EP2014/000843 filed on Mar. 28, 2014 and German Application No. 10 2013 006 069.9 filed on Apr. 8, 2013, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The invention relates to a method for producing a control element having a touch-sensitive zone, in which method a paste-like material is applied to a carrier plate. Furthermore, the invention relates to a control element, in particular for a motor vehicle. 
     Control elements with touch-sensitive zones are being increasingly used in motor vehicles for inputting user instructions, for example for actuating functional units such as Infotainment systems. 
     EP 1 352 384 B1 describes the manufacture of a touch screen in which a resistance layer is applied to a carrier plate made of glass. The application of a pattern of conductive edge electrodes and of conductor tracks to the resistance layer is carried out by a screen printing method in which a silver frit composition is printed onto the resistance layer. 
     US 2002/0197455 A1 also describes the application of electrodes to an insulation layer of a touch screen. Here, the insulation layer covers a resistance layer which is arranged on a glass substrate, and the electrodes are formed on the insulation layer by a screen printing method. 
     US 2010/0200539 A1 describes a method for producing a touch screen in which a layer of indium-tin-oxide is arranged on a plastics substrate. Etching paste is applied to this oxide layer. The oxide layer is removed from the places provided with the etching paste by increasing the temperature, and in this way the plastic substrate is exposed. 
     DE 10 2006 021 270 A1 describes the printing of operator controlled symbols onto an acrylic screen by screen printing. 
     WO 2007/017485 A2 describes a touch screen in which a layer of organic light-emitting diodes is applied by a printing method to electrodes which are arranged on a substrate. 
     SUMMARY 
     One possible object is to provide a method of the type mentioned at the beginning and a control element which can be obtained by the method, with which method particularly well defined structural elements can be formed or are present on the carrier plate. 
     The inventors propose a method in which at least one raised structural element is formed on the carrier plate by the paste-like material. This is done firstly by arranging an inherently rigid stencil over the carrier plate. The paste-like material is then pressed through at least one cutout in the stencil. The contour of the cutout therefore predetermines the contour of the structural element corresponding to the cutout. A clean, defined edge of the structural element is also predefined here by the edge of the cutout. 
     In addition it is advantageous that the cutout in the stencil is free of any threads, fibers, or loops, such as are present when a screen printing method is applied. If, in fact, the paste-like material is pressed through fabric regions which are permeable to this material in the screen printing method, the paste-like material which is then applied to the carrier plate has a certain degree of unevenness, corrugations and frayed edges. In particular, the threads of the fabric or screen are apparent on the surface of the structural element, and accordingly the structural element which is produced by a screen printing method has an irregular surface. 
     In contrast, by using the inherently rigid stencil with the at least one cutout a particularly clean and good definition of the structural elements can be achieved, since there are in fact no threads or the like present in the region of the cutouts in the stencil. In addition, a particularly viscous and firm paste-like material can be used, since it is no longer necessary for the paste to disperse after the removal of a screen which is used in a screen printing method. 
     As result of the fact that the raised structural elements on the carrier plate have clean edges and a defined height, they are particularly visually attractive. In addition, a desired shape of the respective structural element can be made available through the selection of a respective shape of the cutout. In addition to the use of the structural elements on the carrier plate as design elements, haptic landscapes can also be formed, as well as structures which can be felt with a person&#39;s finger, by the raised structural elements. 
     If the paste-like material contains color pigments, a particularly high level of flexibility can also be produced when selecting the color of the raised structural elements. 
     In one advantageous refinement, the paste-like material is applied to the at least one cutout in the stencil in such a way that a height of the at least one structural element corresponds to a thickness of the stencil. The height of the structural elements can therefore be set in a targeted fashion both by the selection of the consistency of the paste-like material as well as by the thickness of the stencil, which thickness is, if appropriate, locally different. This makes it possible, in particular, to form structural elements of a comparatively large height on the carrier plate, which structural elements can then be perceived haptically particularly well. 
     If it was desired to make available structural elements with a particularly large height by a screen printing method, this would require the use of a fabric with particularly thick threads. These relatively thick threads would then, however, become particularly apparent in the structural element. In contrast, by sensing the cutout in the inherently rigid stencil with the paste-like material a corresponding structural element with a correspondingly large height can be made available which is free of any irregularities owing to threads or the like becoming apparent. 
     It has also proven advantageous if a ceramic material is applied as paste-like material to the carrier plate. The structural elements which are then formed from the ceramic material are in fact particularly abrasion-proof and scratch-proof, with the result that they have a particularly high level of robustness and long service life. 
     It has also proven advantageous if the paste-like material is connected by heating to the carrier plate. This permits a particularly intimate and at the same time stable connection of the structural elements to the carrier plate, which therefore does not weaken the structure of the carrier plate. 
     In particular, if a ceramic material is applied as paste-like material to the carrier plate it is favorable to form the carrier plate—or at least the surface thereof—from a glass, since ceramic structural elements can be connected particularly well to the glass by heating. 
     It has also proven advantages if a sensing aid for a user of the control element is made available by the at least one raised structural element. The provision of such sensing aids or orientation aids on the carrier plate—for example in the form of webs, curves or the like—permits the user to carry out operator control actions reliably on the control element without the user having to direct his gaze onto the touch-sensitive zone of the control element. This is advantageous in particular if the control element is used in a motor vehicle, since the user, for example, the driver of the motor vehicle, then does not need to avert his gaze from the events on the road. Instead, he can find the areas of the control element which he wishes to touch in order to perform operator control actions by the sensing aids. 
     In another advantageous refinement, the inherently rigid stencil is formed by a piece of sheet metal. In such a piece of sheet metal it is in fact possible to make available in a particularly easy and clean way cutouts or holes which predefine the shape of the raised structural elements to be formed. This is favorable for predefining correspondingly cleanly defined structural elements by the cutouts. 
     The at least one cutout in the piece of sheet metal can be produced, in particular, by laser cutting and/or by punching. With such cutting methods it is, in fact, possible to make available particularly clean and straight edges of the cutouts, which in turn give rise to correspondingly well defined and straight edges of the structural elements. 
     The inventors also propose a control element, in particular, for a motor vehicle. The proposed control element comprises a carrier plate and has a touch-sensitive zone. At least one raised structural element is formed on the carrier plate, said raised structural element being produced by pressing a paste-like material through at least one cutout in an inherently rigid stencil. The at least one raised structural element is so particularly well defined and does not have any unevennesses, corrugations, frayed edges or the like but instead has a particularly level surface and particularly sharply defined contours. This makes the raised structural elements particularly well suited to making available sensing aids or orientation aids for a user of the control element. 
     The control element can be embodied, in particular, as a touchpad or as a touch screen by which functional units of the motor vehicle can be actuated. 
     The advantages and preferred embodiments which are described for the proposed method also apply to the proposed control element, and vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  shows a method which is known from the related art and in which a printing ink is applied to a print medium by screen printing; 
         FIG. 2  is a schematic enlarged illustration of a structural element which is obtained by the screen printing method according to  FIG. 1  and is then located on the print medium; 
         FIG. 3  shows the application of structural elements, formed from a ceramic paste, to a glass surface of a control element which is shown in  FIG. 5 , wherein a perforated stencil made of a piece of sheet metal is used; 
         FIG. 4  is a schematic enlarged illustration of one of the structural elements which are obtained by the method according to  FIG. 3  and are then located on the glass surface; and 
         FIG. 5  shows the control element which has a surface made of glass and onto which the structural elements made of ceramic are applied by the method illustrated with reference to  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     The screen printing method which is known from the related art, and by which printing ink  10  can be applied to a print medium  12 , will now be illustrated with reference to  FIG. 1 . 
     In the screen printing method, a screen  14  is used which comprises a frame  16  over which a fabric is stretched. The individual threads  18  of the fabric are illustrated schematically in  FIG. 1 . The fabric is coated with a material, for example a photopolymer, and then exposed in areas  20  in which color is not be applied to the print medium  12 . The photopolymer which is not set is washed out at the other locations  22 . In the screen  14 , the areas  20  of the fabric which are impermeable to printing ink  10  then alternate with the locations  22  in the fabric at which the printing ink  10  can be pressed through the screen  14 . 
     The printing ink  10  is pressed through the fabric using a doctor blade  24  at these locations  22 , and said printing ink  10  passes onto the print medium  12  (cf. the middle figure in  FIG. 1 ). Subsequently, the printing ink  10  disperses in the region of the locations  22  on the print medium  12  and forms structures  26  in which the threads  18  of the fabric are apparent. 
     Correspondingly, the structures  26  on the print medium  12  have unevennesses, corrugations or restrictions  28  at the locations at which the threads  18  of the screen  14  are located during the application of the printing ink  10  to the print medium  12  (cf.  FIG. 2 ). 
     The irregular shape of the structures  26  which can be obtained by the screen printing method is undesirable. Therefore, another method is used here in order to form raised structural elements, for example in the form of webs  32  or curves  34  on a control element such as for example a touch pad  30  (cf.  FIG. 5 ). 
     A tampon printing method, in which the paste-like material to be transferred is firstly arranged on a die and then transferred to the carrier to be printed on, is in fact also unsuitable for applying raised structural elements, which can serve as sensing aids, to a surface  38  of the touch pad  30 . The quantity of ink or paste which can be applied in this way is in fact not sufficient to form raised structures which can be used as sensing aids. 
     The touch pad  30  has a carrier plate  36  which is made of glass and on the surface  38  of the which the webs  32  and curves  34  are formed (cf.  FIG. 5 ). The procedure during the formation of these structural elements is illustrated with reference to  FIG. 3 . 
     A stencil  42  which is secured in a frame  40  is arranged over the carrier plate  36 . The inherently rigid stencil  42  is formed from a piece of sheet metal in which cutouts  44  in the form of holes or slits or the like are provided. The cutouts  44  are located at the locations at which the webs  32  and curves  34  are to be arranged on the carrier plate  36 . A ceramic paste  48  is then pressed through the cutouts  44  in the stencil  42  with a doctor blade  46  or similar tool (cf. the middle illustration in  FIG. 3 ). The portion of the ceramic paste  48  which is pressed through the respective cutouts  44  forms the raised structural elements, for example in the form of the webs  32  or curves  34  on the surface  38  of the carrier plate  36  (cf. the middle and lower illustrations in  FIG. 3 ). 
     The cutouts  44  in the piece of sheet metal of the stencil  42  can be lasered or punched. As a result of the fact that there are no threads whatsoever of a fabric or the like in the region of the cutouts  44 , there are also no threads apparent in the webs  32  or curves  34 . A defined height of the webs  32  or curves  34  can also be predefined by predefining the thickness of the piece of sheet metal of the stencil  42 . 
       FIG. 4  is a schematic view of one of the webs  32 . This web  32  has clean edges  48  and a smooth level surface  50 . 
     After the webs  32  and curves  34  have been applied to the surface  38  of the carried plate  36  by the method illustrated in  FIG. 3 , the carrier plate  36  is burned. As a result, the ceramic webs  32  and/or curves  34  become connected to the carrier plate  36  which is formed from glass. 
     Different structural elements, inter alia also a plurality of letters, can be formed on the surface  38  of the carrier plate  36  by the method illustrated in  FIG. 3 . However, the structural elements on the touch pad  30  serve as sensing aids or orientation aids which can be sensed haptically. A user of the touch pad  30  can therefore feel different control areas  52 ,  56 ,  60  on the touch pad  30  without having to direct his gaze onto the surface  38 . For example radio stations can be selected by the control areas  52  or control panels which are delimited from one another here by the straight webs  32  which are parallel to one another and arranged on an upper edge  54  of the touch pad  30 . However, depending on the operating state of the touch pad  30  any further or different functions can be stored in these control areas  52  of the touch pad  30 . 
     Further control areas  56  at lateral edges of the touch pad  30  are delimited here by the curves  34 , and these control areas  56  can be assigned to different functions. A further control area  60  can be felt here by the user by another of the webs  32  at a lower edge  58  of the touch pad  30 . 
     The structural elements which are shown here by way of example in the form of the webs  32  and the curves  34  can also be provided at other locations on the touch pad  30  and can have shapes which differ from the shapes shown by way of example in  FIG. 5 . 
     The carrier plate  36  is formed here from a glass, but the structural elements made of ceramic can also be applied by the method illustrated with reference to  FIG. 3  to a carrier plate  36  which has merely a surface made of glass. The height of the structural elements which serve as sensing aids can also be set here by the consistency of the ceramic paste  48 , which can be comparatively viscous, and the thickness of the piece of sheet metal of the stencil  42 . 
     The ceramic paste  48  can also be embodied as a colored paste-like material in order to form correspondingly colored structural elements on the surface  38  of the carrier plate  36 . 
     The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  69 USPQ2d 1865 (Fed. Cir. 2004).