Abstract:
This antenna ( 10 ) has an underlying print layer ( 2 ) which is upon the surface of a material ( 1 ) to be printed in a predetermined antenna pattern, and an electro-less plating layer ( 3 ) applied to the surface of the underlying print layer ( 2 ). The underlying print layer ( 2 ) is formed from an ink ( 2   a ) and a metallic powder ( 2   b ). A portion of the particles of the metallic powder ( 2   b ) are entrained within the ink layer in which the ink ( 2   a ) has been printed in a substantially uniform thickness. Some particles which are of large particle size project from the ink layer, and a portion of the ink ( 2   a ) covering the projecting portions is removed.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to antennas, communication devices, and antenna manufacturing methods. In particular, the invention relates to an antenna disposed on a face material, a communication device having a face material on which the antenna is disposed, and a method for manufacturing the antennas. 
       BACKGROUND ART 
       [0002]    In various communication devices including mobile phones and personal computers capable of wireless transmission and reception, there have hitherto been demands for antennas which can operate at a wide range of frequencies and save space. In order to meet such demands, the inventor of the present invention has disclosed an invention directed to printing of antennas to housings of communication devices (see, for example, Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2008-283587 (pp. 5-6,  FIG. 4 ) 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    The invention disclosed in Patent Literature 1 has met the demands with a technique in which a workpiece (for example, an exterior face of a mobile phone or the like) is printed with a conductive ink to form an antenna pattern, and the formed pattern is coated with an electroless plating and an electrolytic plating, and further the plated pattern is covered with a decorative coating. 
         [0005]    However, the technique involves the need of providing contacts for energization on the workpieces. Thus, the production of contacts as well as preparing jigs for ensuring energization need extra efforts and result in a decrease in working efficiency, making it difficult to save production costs. Further, because the areas for the contacts formed for energization are not plated, there is a risk that corrosion (oxidation) occurs from these unplated portions. Thus, there have been demands on further saving of production costs as well as on the stabilization of quality for a long term. 
         [0006]    Further, conductive inks contain large amounts of metal particles. Thus, the adhesion between a conductive ink layer and an electroless plating layer is not always sufficiently strong. Thus, there have been some concerns about reliability of the design of appearance and of the durability during long use. Thus, higher adhesion for improving reliability has been demanded. 
         [0007]    In order to meet these demands, the invention provides antennas which are obtainable by simple work but have improved reliability of quality, as well as communication devices having the antennas, and methods for manufacturing the antennas. 
       Solution to Problem 
       [0008]    (1) An antenna according to the present invention includes a base print, layer printed in a predetermined antenna pattern on a workpiece, and an electroless plating layer disposed on the surface of the base print layer, 
         [0009]    the base print layer being formed of an ink containing a plurality of metal particles having a predetermined particle diameter distribution, 
         [0010]    some of particles of the metal particles are buried in an ink layer forming the base print layer, some of the particles of the metal particles are protrudent from the ink layer forming the base print layer, and part of the ink covering the protrudent portions having been removed. 
         [0011]    (2) In (1), the metal particles may be contained in the ink with a proportion by volume of 30 to 70%. 
         [0012]    (3) In (1) or (2), the electroless plating layer may be formed of Cu, and an electroless Ni plating layer may be disposed on a surface of the electroless Cu plating layer. 
         [0013]    (4) in (3), an electroless Au plating layer may be disposed on a surface of the electroless Ni plating layer. 
         [0014]    (5) in any of (1) to (4), the metal particles may be any of Cu, Ni, Fe, Mg, Pd, Ag, Au and C, or may be an alloy of any of Cu, Ni, Fe, Mg, Pd, Ag and Au, 
         [0015]    the particle diameters of approximately 95% of the metal particles may be distributed in the range from 0.04 to 50 μm, and the particle diameters of approximately 40% of the metal particles may be distributed in the range from 5 to 30 μm. 
         [0016]    (6) A communication device according to the present invention includes the antenna of any of (1) to (5). 
         [0017]    (7) An antenna manufacturing method according to the present invention includes a printing step of forming a base print layer in a predetermined antenna pattern on a surface of a workpiece with an ink containing a plurality of metal particles having a predetermined particle diameter distribution; 
         [0018]    an ink removing step of removing, from those of the metal particles being protrudent from an ink layer forming the base print layer, part of the ink covering the portions protrudent from the ink layer; and 
         [0019]    an electroless plating step of forming an electroless plating layer on a surface of the base print layer. 
       Advantageous Effects of Invention 
       [0020]    (i) In the antennas of the invention, an electroless plating layer is disposed on a surface of a base print layer formed of an ink containing metal particles. Thus, the invention eliminates the needs of forming contacts for energization, or preparing jigs for ensuring energization, thereby allowing for the work to be completed simply and quickly. Consequently, production costs can be saved. Further, the absence of contacts eliminates partially unplated areas and thus eliminates the risk of the occurrence of local corrosion (oxidation). 
         [0021]    Furthermore, some of the particles of the metal particles are buried in the ink layer (some of small particles are exposed on the surface of the ink layer), some of the particles of the metal particles are protrudent from the ink layer, and the protrudent portions are partially cleared of the ink (some of large particles are not cleared of the ink at their protrudent portions). With this configuration, the ink layer achieves good adhesion with respect to the electroless plating layer, thus improving reliability of the design of appearance and of the durability during long use. 
         [0022]    The term “insulating”, when used for the “ink” or the “base print layer”, does not mean that the material does not conduct electricity at all (the electrical resistance is substantially infinite), but indicates that the material has higher electrical resistance compared to that of the metal particles. That is, this term may be otherwise read as hardly conductive or being high in electrical resistance. 
         [0023]    (ii) The communication devices of the invention have the antennas, and therefore the costs of manufacturing thereof can be saved and reliability of the design of appearance and of the durability during long use can be improved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is a sectional view schematically illustrating an antenna and an enlarged sectional view schematically illustrating a portion (base print layer) of the antenna according to Embodiment 1 of the invention, 
           [0025]      FIG. 2  is distribution graphs illustrating examples of an integral particle size distribution (sedimentation method) and a differential particle size distribution (sedimentation method) of metal particles. 
           [0026]      FIG. 3  is a sectional view schematically illustrating an antenna according to Embodiment 2 of the invention. 
           [0027]      FIG. 4  is perspective views schematically illustrating a mobile phone and a personal computer for explaining communication devices according to Embodiment 3 of the invention. 
           [0028]      FIG. 5  is a flow chart illustrating an antenna manufacturing method according to Embodiment 4 of the invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     Antennas  
       [0029]      FIG. 1  illustrates an antenna according to Embodiment 1 of the invention.  FIG. 1(   a ) is a schematic sectional view, and  FIG. 1(   b ) is an enlarged sectional view schematically illustrating a portion (base print layer).  FIG. 2(   a ) is a distribution graph illustrating an example of an integral particle size distribution (sedimentation method) of metal particles, and  FIG. 2(   b ) is a distribution graph illustrating an example of a differential particle size distribution (sedimentation method) of metal particles. 
         [0030]    In  FIG. 1(   a ), an antenna  10  has a base print layer  2  printed in a predetermined antenna pattern on a surface of a workpiece  1 , and an electroless plating layer  3  disposed on the surface of the base print layer  2 . 
         [0031]    The antenna pattern is variable in accordance with the desired performance of the antenna as well as the shape (such as the size) of the workpiece. The linewidth of the antenna pattern (the same as the linewidth of the base print layer  2  and the linewidth of the electroless plating layer  3 ) is not limited. 
         [0032]    The term “surface” is not limited literally to the meaning of front surface, but includes back surface, front side, backside, and any corners or edges connecting these faces. 
         [0033]    In  FIG. 1(   b ), the base print layer  2  is formed of an ink  2   a  and metal particles  2   b.  The ink  2   a  has been printed with a substantially uniform thickness (for example, about 7 μm) to form an ink layer (marked with diagonal lines), in which some of the metal particles  2   b  (particles having a smaller particle diameter than the thickness of the ink layer) are buried. Even when the particles have a smaller particle diameter than the thickness of the ink layer, some of such particles are partially exposed on the surface of the ink layer (see  FIG. 1(   b )). 
         [0034]    Further, some of the metal particles  2   b  (mainly particles having a particle diameter larger than the thickness of the ink layer) are protrudent from the ink layer, and the protrudent portions are partially cleared of the ink  2   a.  Some protrudent portions of the metal particles  2   b  are not cleared of the ink (not shown in the figure). 
         [0035]    For example, referring to  FIGS. 2(   a ) and  2 ( b ), the particle diameters of approximately 95% of the metal particles  2   b  are distributed in the range from 0.04 to 50 μm, and the particle diameters of approximately 40% of the metal particles are distributed in the range from 5 to 30 μm. The metal particles  2   b  include coarse particles having a particle diameter of 20 μm or more, as well as fine particles having a particle diameter of 0.4 μm or less. 
         [0036]    The metal particles  2   b  may be contained with a proportion by volume of 30 to 70%, and preferably 40 to 60% relative to the ink  2   a.  Accordingly, the base print layer  2  has greater electrical resistance than the electrical resistance of the metal particles  2   b  and thus may be deemed as insulating. 
         [0037]    Further, because the ink  2   a  covering the portions of larger particles of the metal particles  2   a  that protrude from the ink layer has been partially removed as described above, electroless plating takes place slowly and good adhesion is obtained between the base print layer  2  and the electroless plating layer  3 . Consequently, reliability of the design of appearance and of the durability during long use may be improved. 
         [0038]    The electroless plating layer  3  is formed of Cu or Ni with a thickness of 7 to 15 μm, and has a linewidth substantially the same as the linewidth of the base print layer  2 , thus achieving functions as an antenna. 
         [0039]    The material (metal) forming the electroless plating layer  3  is not limited to Cu or Ni, and may be any of appropriate materials. 
         [0040]    An electroless Au (gold) plating layer may be additionally formed on the surface of the electroless plating layer  3 . 
         [0041]    The material (metal) of the metal particles  2   b  is not limited, and may be any of Cu, Ni, Fe, Mg, Pd, Ag, Au, and C, or may be an alloy of any of Cu, Ni, Fe, Mg, Pd, Ag, and Au. The particle size (particle diameter) distributions are not limited to the exemplary distributions illustrated in  FIG. 2 . 
       Embodiment 2 
     Antennas  
       [0042]      FIG. 3  is a sectional view schematically illustrating an antenna according to Embodiment 2 of the invention. Members that are identical with or correspond to the members in Embodiment 1 are assigned with the same reference signs and part of the explanations of such members may be omitted. 
         [0043]    In  FIG. 3 , an antenna  20  has a base print layer  2  printed in a predetermined antenna pattern on a surface of a workpiece  1 , an electroless plating layer  3  disposed on the surface of the base print layer  2 , a covering face  4  covering the surface of the electroless plating layer  3 , a supplementary coating layer  5  covering the surface of the workpiece  1  except the region covered with the base print layer  2 , and a decorative coating layer  6  covering the covering face  4  and the supplementary coating layer  5 . 
         [0044]    The covering face  4  is a film that is formed from an ink containing 5 to 30% (preferably 10%) of silicone oil. This face is dry, and exhibits so-called repellency and “repels” the supplementary coating layer  5 . 
         [0045]    The supplementary coating layer  5  is repelled by the dry covering face  4  and is prevented from attaching to the surface of the covering face  4 . Therefore, the supplementary coating layer  5  is formed by being printed or applied so as to fill the workpiece  1  except the antenna pattern (the covering face  4 ). The supplementary coaling layer  5  is formed such that the surface thereof is of the same level as the surface of the covering face  4  to give a uniform surface (without unevenness) on which the decorative coating layer  6  is to be disposed; in view of this, the material thereof is not limited as long as the supplementary coating layer  5  exhibits good adhesion with respect to the workpiece surface  1  and the decorative coating layer  6 . 
         [0046]    The decorative coating layer  6  is a covering of a very thin coating agent on the covering face  4  and the supplementary coating layer  5 . A single layer or a stack of layers is disposed in accordance with, for example, designing demands. Before the decorative coating layer  6  is disposed, the surface of the covering face  4  is activated by forming fine unevenness on the surface by chemical or physical means in order to give wettability to the surface of the covering face  4 . 
         [0047]    This configuration can render the antenna pattern (the same as the electroless plating layer  3 ) invisible. Thus, even when the antenna  20  is provided on an exterior surface of a device such as a communication device, the aesthetic appearance of the device such as a communication device is not deteriorated. Further, appropriate selection of the decorative coating layers  6  is possible to allow for an enhancement of design properties. 
       Embodiment 3 
     Communication Devices  
       [0048]      FIG. 4  illustrates communication devices according to Embodiment 3 of the invention.  FIG. 4(   a ) is a perspective view schematically illustrating a mobile phone, and  FIG. 4(   b ) is a partially transparent perspective view schematically illustrating a personal computer (hereinafter, referred to as “computer”). 
         [0049]    In  FIG. 4(   a ), a mobile phone  100  has antennas  10   a,    10   b  provided on an inner face (or a back surface)  112  of a body case  110 . The inner face  112  is to be covered with a member such as a liquid crystal display or a keyboard (not shown), and therefore the antennas  10   a,    10   b  are not visible from outside. 
         [0050]    The antenna  10   a  and the antenna  10   b  are the same as the antennas  10  described in Embodiment 1 and have the effects described hereinabove. Thus, the mobile phone  100  achieves improved reliability of durability during long use. 
         [0051]    The antenna  10   a  and the antenna  10   b  are switched in accordance with sending and receiving frequencies. The mobile phone  100  is not limited to the configuration having the antennas  10   a,    10   b,  and may have one of these antennas or a third antenna  10 , or may have an antenna  20  on the exterior face of the body case  110 . 
         [0052]    In  FIG. 4(   b ), a computer  200  has an antenna  20  provided on an exterior face (or a front surface)  211  of a lid  210 . A decorative coating layer  6  of the antenna  20  covers not only the top of the antenna  20  but also the entirety of the exterior face  211 . 
         [0053]    This configuration renders the antenna pattern (the same as an electroless plating layer  3 ) invisible. Thus, design properties can be enhanced while ensuring the communication functions of the antenna  20  without deteriorations in the aesthetic appearance of the computer  200 . 
         [0054]    The computer  200  is not limited to the configuration having the antenna  20 , and may have a plurality of the antennas  20  or may have an antenna  10  in an inner face (or a back surface) together with the antenna  20  or in place of the antenna  20 . 
       Embodiment 4 
     Antenna Manufacturing Methods  
       [0055]      FIG. 5  is a flow chart illustrating an antenna manufacturing method according to Embodiment 4 of the invention. Members or sections that are identical with or correspond to the members or sections in Embodiment 1 are assigned with the same reference signs and part of the explanations of such members or sections may be omitted. 
         [0056]    In  FIG. 5 , an antenna manufacturing method  400  includes a printing step (S 1 ) in which a base print layer  2  is formed in a predetermined antenna pattern on a surface of a workpiece  1  with an ink  2   a  containing a plurality of metal particles  2   b  having a predetermined particle diameter distribution; 
         [0057]    an ink removing step (S 2 ) in which, among the metal particles  2   b,  those metal particles  2   b  protrudent from an ink layer forming the base print layer  2  (marked with diagonal lines in  FIG. 1(   b )) are cleared of part of the ink  2   a  covering the portions protrudent from the ink layer; and 
         [0058]    an electroless plating step (S 3 ) in which an electroless plating layer  3  is formed on the surface of the base print layer  2 . 
         [0059]    According to the antenna manufacturing method  400  having this configuration, the antennas  10  described in Embodiment 1 can be obtained through simple work with simple equipment (which does not require any energization devices and jigs or tools for holding contacts). 
       INDUSTRIAL APPLICABILITY 
       [0060]    According to the present invention, the configurations (shapes, sizes) of antenna patterns are not limited. Thus, the antennas and the antenna manufacturing methods of the invention can be used widely as or to produce communication sections of various apparatuses that send or receive signals wirelessly at various frequencies. Further, the inventive devices can be used widely as various communication devices including computers and mobile phones. 
       REFERENCE SIGNS LIST 
       [0061]      1  workpiece  2  base print layer  2   a  ink  2   b  metal particles  3  electroless plating layer  4  covering face  5  supplementary coating layer  6  decorative coating layer  10  antenna (Embodiment 1)  20  antenna (Embodiment 2)  100  mobile phone (Embodiment 3)  110  body case  112  inner face  200  computer (Embodiment 3)  210  lid  211  exterior face  400  antenna manufacturing method (Embodiment 4)