Patent Publication Number: US-2010110712-A1

Title: Light lens for car interior lighting device

Description:
PRIORITY INFORMATION 
     This application claims priority to Japanese Patent Application No. 2008-281415 filed on Oct. 31, 2008, which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure of a light lens used for a car interior lighting device. 
     2. Description of the Related Art 
     A car interior lighting device for illuminating the interior of a car is provided on the ceiling of the car. Some of such car interior lighting devices employ a touch switch as a light switch in order to easily light up the interior of the car when it is dark. The touch switch is used to turn a light source for illumination on and off by sensing changes in capacitance between an electrode and the human body. For example, a conventional car interior lighting device, such as the one disclosed in JP 2007-230450 A, adopts a configuration in which a transparent electrode is formed on an inner surface of a light lens by, for example, printing and painting, and the lighting device can be turned on and off by touching the design surface side of the light lens. 
     Such a transparent electrode has been made of indium oxide such as ITO. However, because indium oxide is expensive and there are issues regarding its exhaustion, a conductive polymer or the like which does not employ indium oxide has started to be used as a substitute material, as disclosed in JP 2007-134293 A. 
     However, the substitute material for indium oxide such as the conductive polymer is a colored transparent material having a lower light transmission rate than indium oxide. Therefore, when it is used as the material for an electrode to be attached to a light transmissive device such as the light lens, the amount of light transmitted through the electrode portion is reduced and the presence of the electrode may be too visible. Specifically, when two transparent electrodes are arranged inside a single light lens in the car interior lighting device so that different light sources are turned on between the driver side and the passenger side, a certain distance is provided between the electrodes in order to avoid erroneous operation. This causes problems that the presence of the electrodes becomes too visible, resulting in poor appearance. 
     Accordingly, a purpose of the present invention is to achieve a uniform light transmission rate over the light lens in the car interior lighting device. 
     SUMMARY OF THE INVENTION 
     A light lens used for a car interior lighting device has a transparent light lens body, a colored transparent conductive coating film located on a light source side of the light lens to detect the capacitance, and an insulative coating film having almost the same color and transmission rate as the conductive coating film and located on the periphery of the conductive coating film, and the light lens transmits light from the light resource and illuminates the car interior. 
     In the light lens according to the present invention, it is also preferable to locate the insulative coating film on the periphery of the conductive coating film with fine gaps in between, locate a transparent sheet, on which the conductive coating film and the insulative coating film are formed, on the light source side of the light lens body, and divide the conductive coating film and locate the divided conductive coating films in a plurality of positions on the light source side of the light lens, while locating the insulative coating between the divided conductive coating films. 
     The present invention has an advantage of achieving a uniform light transmission rate over the light lens in the car interior lighting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a car interior lighting device according to an embodiment of the present invention; 
         FIG. 2  is a cross-section showing the car interior lighting device according to the embodiment of the present invention; 
         FIG. 3  is a circuit diagram showing a control circuit of the car interior lighting device according to the embodiment of the present invention; 
         FIG. 4  is a plane view showing electrodes composed of conductive coating films formed on a light lens of the car interior lighting device, and an insulative coating film formed on a gap between the electrodes and on the periphery of the electrodes. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described hereinafter with reference to the drawings. As shown in  FIG. 1 , a car interior lighting device according to the present embodiment has a case  11  on the ceiling side of a car and a design cover  12  attached to the case  11 . The surface of the design cover  12  is refereed to as a design surface  13  and is attached toward the car interior side. A light lens  14  and a change box  7  are attached to the design surface  13  of the design cover  12 . 
     As shown in  FIG. 2 , an electric circuit board  15  is attached to the bottom portion of the case  11 , and bulbs  16 a and  16   b  as light sources for illumination are attached to the electric circuit board  15 . The bulb  16   a  is a bulb for illuminating the driver side while the bulb  16   b  is a bulb for illuminating the passenger side. A frame of the design cover  12  is fitted into a frame projecting along the circumference of the case  11  so that the case  11  and the design cover  12  are integrally provided. 
     The design cover  12  has the design surface  13  which is formed on the car interior side so as to match the car interior decoration. Further, a light lens  14  is attached to substantially the same plane as the design surface  13  of the design cover  12 . The light lens  14  is configured to transmit the lights from the bulbs  16   a  and  16   b  therethrough and guides the light to the driver side and the passenger side, respectively. Electrodes  21   a  and  21   b  for detecting the capacitance are formed on the light lens on its surface on the bulbs  16   a  and  16   b  side. 
     As shown in  FIG. 3 , the electrodes  21   a  and  21   b  are both connected to a control unit  30 . The control unit  30  detects changes in stray capacitance between the electrode  21   a  or the electrode  21   b  and the human body, and determines if there is contact between them. When the control unit  30  determines that there is contact, the control unit  30  outputs a predetermined output. The outputs from the control unit  30  are connected to gates of bulb drive transistors  32   a  and  32   b  for driving the bulbs  16   a  and  16   b , respectively. The anode sides of the bulb drive transistors  32   a  and  32   b  are connected to a power supply  36  via the bulbs  16   a  and  16   b , respectively, while the cathode sides are connected to an earth terminal. By switching currents to the gates of the bulb drive transistors  32   a  and  32   b  on and off using signals from the control unit  30 , the currents from the power supply  36  to the bulbs  16   a  and  16   b  are switched on and off. With such a configuration of the control unit  30 , the configuration in which the bulb  16   a  on the driver side is turned on when the driver touches the driver-side surface of the light lens  14 , while the bulb  16   b  on the passenger side is turned on when the passenger touches the passenger-side surface of the light lens  14 , is achieved. As shown in  FIG. 2 , the electrodes  21   a  and  21   b  are formed on the light lens on its surface on the bulbs  16   a  and  16   b  side with a gap in between, in order to prevent the passenger side bulb  16   b  from being turned on when the driver side surface is touched. 
       FIG. 4  is a plane view showing the surface of the light lens  14  on which the electrodes  21   a  and  21   b  are formed. As shown in  FIG. 4 , the light lens  14  has a transparent rectangular light lens body  14   a  fitted into the design surface  13  and a projecting portion  18  connected to the electric circuit board  15 . The electrode  21   a  of the light lens  14  corresponding to the driver side bulb  16   a  is provided on the light lens body  14   a  at a region for illuminating the driver side, while the electrode corresponding to the passenger side bulb  16   b  is provided on the light lens body  14   a  at a region for illuminating the passenger side. A gap  23  is provided between the electrodes  21   a  and  21   b . The electrodes  21   a  and  21   b  are conductive coating films that are formed by applying a conductive coating material on the bulb side surface of the light lens body  14   a  using screen printing. This conductive coating film is composed of, for example, conductive polymers having a light transmission rate of approximately 50% to 80% and a transparent color such as blue. Conductive polymers include, for example, polyolefin polymers, and, among polyolefin polymers, polyethylenedioxythiophene is preferable in terms of transparency and conductivity. The gap  23  is provided between the electrodes  21   a  and  21   b  in order to avoid erroneous operation. Further, because the passenger rarely touches the periphery  22  of the light lens  14   a  when turning the car interior lighting device  10  on and off, the electrodes  21   a  and  21   b  composed of the conductive coating films are not provided on the periphery  22 . 
     As shown in  FIG. 4 , an insulative coating film is formed on a periphery  22  of the electrodes  21   a  and  21   b  and on the gap  23  between the electrodes  21   a  and  21   b . In other words, the insulative coating film is formed on almost the entire lens except for the portions of the bulb side surface on which the electrodes  21   a  and  21   b  are formed. Like the conductive coating films constituting the electrodes  21   a  and  21   b , this insulative coating film is formed using screen printing and has the same color and transmission rate as the conductive coating films constituting the electrodes  21   a  and  21   b . After an ink for printing the insulative coating film is used to print the insulative coating film on a transparent plate at a position adjacent to the conductive coating films, the color and the transmission rate of the ink is measured using, for example, a transmissometer, a luxmeter, or a chromameter, and the ink is adjusted so that the color and the transmission rate of the insulative coating film become approximately the same as those of the conductive coating films. Further, because the insulative coating film is formed using screen printing like the conductive coating films constituting the electrodes  21   a  and  21   b , the film thickness of the insulative coating film is approximately the same as the conductive coating film. An ink of vinyl, epoxy, polyester, acrylic, urethane, polyolefin, or the like may be used for the insulative coating film. 
     As shown in  FIG. 4 , fine gaps d are provided between the electrodes  21   a  and  21   b  composed of the conductive coating films and the periphery  22 , and between the electrodes  21   a  and  21   b  and the gap  23 . These fine gaps d are provided on the grounds that, if the conductive coating material and the insulative coating material are overlapped with each other, the transmission rate of the light passing through that overlapped portion drops significantly, and the overlapped portion becomes too visible as a line when the bulb of the car interior lighting device is turned on, resulting in poor appearance. 
     The operation of the car interior lighting device  10  having the light lens  14  configured as above will be described. When the driver or the passenger touches the surface of the light lens  14 , the bulb  16   a  or  16   b  is turned on according to the touched position, and light from the bulb  16   a  or  16   b  passes through the electrode  21   a  or  21   b  and further passes through the transparent light lens body  14   a  to illuminate the car interior. Here, the light emitted from the bulb  16   a  and  16   b  passes through the colored transparent conductive coating films constituting the electrodes  21   a  and  21   b , respectively. The conductive coating films have a light transmission rate of approximately 50 to 80% and a transparent color such as blue. As such, the light passing through the electrodes  21   a  and  21   b  is projected on the car interior as bluish light due to the color of the conductive coating film. Similarly, the light emitted from the bulbs  16   a  and  16   b  passes through the insulative coating film on the periphery  22  of the light lens body  14   a  and on the gap  23  between the electrodes  21   a  and  21   b  to be projected on the car interior. The periphery  22  and the gap  23  have the same color and light transmission rate as the electrodes  21   a  and  21   b . For example, when the conductive coating films constituting the electrodes  21   a  and  21   b  are transparent blue, the insulative coating film formed on the periphery  22  and the gap  23  is also transparent blue, and the light passing through the insulative coating film also has the same color and luminance as the light passing through the conductive coating films. As such, the light passing through the conductive coating films constituting the electrodes  21   a  and  21   b  has the same color and luminance as the light passing through the insulative coating film formed on the periphery  22  and the gap  23 . As such, when the car interior lighting device  10  is turned on, the light projected through the conductive coating films constituting the electrodes  21   a  and  21   b  and the insulative coating film has the same characteristics. It is therefore possible to prevent the electrodes  21   a  and  21   b  from being highly visible from the design side of the light lens  14 , thereby improving the appearance of the light lens  14 . 
     Further, the fine gaps d are provided between the conductive coating films constituting the electrodes  21   a  and  21   b  and the insulative coating film formed on the periphery  22  and the gap  23 . Because these gaps prevent the conductive coating films and the insulative coating film from overlapping with each other, it is possible to avoid the problem that an overlapped portion becomes darker in color and the circumference of the conductive coating films being distinguished from the design surface side of the light lens  14 . For example, when this fine gap is made smaller than or equal to approximately 0.2 mm, it is possible to prevent the light passing through a portion that is not the conductive coating film or the insulative conductive coating film from being distinguished from the design surface side of the light lens  14  because of the diffusion effect of the light lens body  14   a.    
     As described above, because the car interior lighting device  10  can achieve substantial uniformity of the color and the light transmission rate of the light over the entire surface of the light lens  14 , it is possible to prevent the existence of the electrodes  21   a  and  21   b  from being recognized from the design surface side of the light lens  14  and to achieve an advantage of maintaining the appearance of the light lens  14  even when the conductive coating films are composed of the conductive polymer which is the substitute material for indium oxide. 
     Although in the above-described embodiment the conductive coating films constituting the electrodes  21   a  and  21   b  have been formed on the bulb side surface of the transparent light lens body  14   a  using screen printing, and the insulative coating film has been also formed on the periphery  22  of the light lens body  14   a  using screen printing, it is also possible to form the conductive coating films constituting the electrodes  21   a  and  21   b  on a transparent sheet using, for example, screen printing, painting, coating, and inkjet printing, and form the insulative coating film having the same color and transmission rate as the conductive coating films on the periphery  22  of the sheet using the same method as the conductive coating film, and then attach the sheet on the bulb side surface of the light lens body  14   a . Further, it is also possible to print only the conductive coating film on the sheet and print the insulative coating film directly on the lens at the periphery of a position where the sheet is to be located, while conversely, it is also possible to print only the conductive coating film on the lens and print and locate the insulative coating film on the sheet. 
     Further although the present embodiment has described that the light lens body  14   a  has the configuration in which the two electrodes  21   a  and  21   b  are located separately and the gap  23  is provided therebetween, it is also possible to adopt a configuration in which the conductive coating film constituting one electrode is formed on the light lens body  14   a  and the insulative coating film having the same color and transmission rate as the conductive coating film is formed on the periphery  22  of the electrode, or a configuration in which the number of the electrodes is not limited to two and may be more than three and the insulative coating film is formed on the gaps  23  between the respective electrodes and on the periphery  22  of the electrodes.