Patent Publication Number: US-7907158-B2

Title: Thermal head and printing device

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention contains subject matter related to Japanese Patent Application JP 2006-075661 filed in the Japan Patent Office on Mar. 17, 2006, the entire contents of which being incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a thermal head and a printing device for thermal-transferring a color material on an ink ribbon to a print medium. 
     2. Related Art 
     As a printing device for printing images or characters on a print medium, there is a thermal transfer printing device (hereinafter simply referred to as a printing device) which sublimates a color material forming a ink layer provided to one surface of an ink ribbon to thermal-transfer the color material to a print medium, thereby printing color images or characters. The printing device is provided with a thermal head for thermal-transferring the color material on the ink ribbon to the print medium and a platen disposed at a position facing the thermal head and for supporting the ink ribbon and the print medium. 
     In the printing device, the ink ribbon and the print medium are overlapped so that the ink ribbon faces the thermal head and the print medium faces the platen, and the ink ribbon and the print medium run between the thermal head and the platen while the platen presses the ink ribbon and the print medium against the thermal head. In this case, the printing device applies thermal energy to the ink ribbon running between the thermal head and the platen with the thermal head on the ink layer from the rear face side of the ink ribbon, and sublimates the color material with the thermal energy to thermal-transfer the color material to the print medium, thereby printing color images or characters. 
     In this thermal transfer printing device, power consumption becomes larger when printing at higher speed because the thermal head needs to be rapidly heated to a high temperature. Therefore, it is difficult particularly in home-use-printing devices to increase printing speeds while achieving lower power consumption. In order for achieving high speed printing particularly by a home-use thermal transfer printing device, it is required to improve the thermal efficiency of the thermal head to reduce power consumption. 
     As a thermal head for a thermal transfer printing device used from the past, for example, a thermal head  100  shown in  FIG. 20  can be cited. The thermal head  100  is composed of a glass layer  102  formed on a ceramic substrate  101 , and a heat generating resistor  103 , a pair of electrodes  104   a ,  104   b  for making the heat generating resistor generate heat, a protective layer  105  for protecting the heat generating resistor  103  and the electrodes  104   a ,  104   b  sequentially formed on the glass layer  102 . In the thermal head  100 , a part of the heat generating resistor  103  exposed from a gap between the pair of electrodes  104   a ,  104   b  forms a heat generating section  103   a  for generating heat. The glass layer  102  is formed to have a substantially circular arc shape in order for making the heat generating section  103   a  face the ink ribbon and the print medium. 
     Since the ceramic substrate  101  having high thermal conductivity is used in the thermal head  100 , the thermal energy generated from the heat generating section  103   a  is radiated from the glass layer  102  through the ceramic substrate  101  to rapidly lower the temperature, thus offering a preferable response. However, in the thermal head  100 , since the thermal energy in the heat generation section  103   a  is radiated to the side of the ceramic substrate  101  to easily reduce the temperature, the power consumption in raising the temperature to the sublimation point increases, thus making the thermal efficiency worse. According to the thermal head  100 , although the preferable response can be obtained, thermal efficiency is degraded, and accordingly, it is required to heat the heat generating section  103   a  for a long period of time to obtain a desired depth, which causes large power consumption and makes it difficult to improve the printing speed while achieving low power consumption. 
     In order for solving such a problem, the inventors of the present invention invented a thermal head  110  as shown in  FIG. 21 . This thermal head will be explained below as related art of the present invention, in which the thermal head  110  uses a glass layer  111  having lower thermal conductivity than the ceramic substrate instead of the ceramic substrate in order for preventing the thermal energy in thermal-transferring the color material to the print medium from being conducted to the substrate side. The thermal head  110  is composed of a heat generating resistor  112 , a pair of electrodes  113   a ,  113   b  and protective layer  114  sequentially formed on the glass layer  111  provided with a protruding section  111   a  having a substantially circular arc shape. The protruding section  111   a  of the glass layer  111  is formed like a substantially circular arc in order for making a heat generating section  112   a  of the heat generating resistor  112 , which is exposed from a gap between the pair of electrodes  113   a ,  113   b , and generating heat, face the ink ribbon and the print medium. 
     In the thermal head  110 , since the glass layer  111  having lower thermal conductivity than the ceramic substrate  101  shown in  FIG. 20  serves as the ceramic substrate  101 , it becomes difficult for the thermal energy generated from the heat generating section  112   a  to be radiated to the side of the glass layer  111 . Thus, in the thermal head  110 , the quantity of the heat conducted to the ink ribbon side can be increased, thus the temperature thereof can rapidly be raised in thermal-transferring the color material to the print medium. Therefore, it becomes possible to reduce power consumption for raising the temperature to the sublimation temperature, thus making the thermal efficiency more preferable. However, in the thermal head  110 , it becomes difficult for the thermal energy stored in the glass layer  111  to be radiated, thus the temperature of the thermal head  110  does not drop immediately because of the thermal energy stored in the glass layer  111 , which degrades the response in contrast to the case with the thermal head  100 . Thus, in the thermal head  110 , since the response is degraded even with the improved thermal efficiency, it is difficult to increase the printing speed. 
     Since it is required to improve both of the thermal efficiency, which is a downside of the thermal head  100 , and the response, which is a downside of the thermal head  110 , for achieving high speed printing of high quality images or characters with reduced power consumption in thermal transfer printing devices, the inventors of the present invention further invented a thermal head  120  as shown in  FIG. 22 . This thermal head will be explained below as further related art of the present invention, in which the thermal head  120  is composed of a heat generating resistor  122 , a pair of electrodes  123   a ,  123   b , a protective layer  124  sequentially formed on the glass layer  121  having a protruding section  121   a  formed like a substantially circular arc in order for making a heat generating section  122   a  of the heat generating resistor  122 , which is exposed from a gap between the pair of electrodes  123   a ,  123   b , face the ink ribbon and the print medium, and inside the glass layer  121 , there is formed a groove section  125  filled with air. 
     In the thermal head  120 , by providing a groove section  125  to the glass section  121 , the thermal conductivity of the groove section  125  is lowered because of the nature of air of having lower thermal conductivity than glass, thus the heat radiation to the glass layer  121  side can further suppressed than in the case with the thermal head  100  shown in  FIG. 20  using the ceramic substrate  101 . Thus, in the thermal head  120 , the amount of heat conducted to the ink ribbon side increases, and accordingly, the power consumption for raising the temperature to the sublimation temperature of the color material can be reduced when thermal-transferring the color material, thus making the thermal efficiency preferable. Further, in the thermal head  120 , since the thickness of the glass layer  121  is made thinner to reduce the heat storage capacity of the glass layer  121  by providing the groove section  125  to the glass layer  121 , the thermal energy stored in the glass layer  121  can be radiated in a shorter period of time than in the case with the thermal head  110  shown in  FIG. 21  without the groove in the glass layer  111 , thus rapidly lowering the temperature when the color material is not thermal-transferred to make the response preferable. According to these facts, in the thermal head  120 , both of the thermal efficiency and the response can be made preferable by providing the groove section  125  to the glass layer  121 . In other words, the downsides of the thermal head  100  and the thermal head  110  described above can be solved at the same time in the thermal head  120 . 
     However, even in such a thermal head  120 , it is required to further improve the thermal efficiency in order for performing high speed printing with further reduced power consumption. Further, in the thermal head  120 , the physical strength of the glass layer  121  might be lowered by providing the groove section  125  to the glass layer  121 . 
     The related art is described in JP-A-8-216443. 
     SUMMARY 
     It is therefore desirable to provide a thermal head and a printing device preferable in the thermal efficiency and the response. 
     According to an embodiment of the present invention, there is provided a thermal head including a glass layer having a protruding section formed on one surface and a concave groove section formed on the other surface facing the protruding section, a heat generation resistor provided on the protruding section, and a pair of electrodes provided to both sides of the heat generation resistor, wherein a part of the heat generation resistor exposed between the pair of electrodes is defined as a heat generation section, the protruding section has a smaller curvature radius in both sides than a curvature radius in a central portion, and a width of the groove section is one of equal to and larger than a length of the heat generation section. 
     According to an embodiment of the present invention, there is provided a printing device including a thermal head having a glass layer having a protruding section formed on one surface and a concave groove section formed on the other surface facing the protruding section, a heat generation resistor provided on the protruding section, and a pair of electrodes provided to both sides of the heat generation resistor, wherein a part of the heat generation resistor exposed between the pair of electrodes of the thermal head is defined as a heat generation section, the protruding section of the glass layer has a smaller curvature radius in both sides than a curvature radius in a central portion, and a width of the groove section is one of equal to and larger than a length of the heat generation section. 
     In embodiment of the invention, by forming the groove section in the glass layer, it becomes difficult for the heat generated by the heat generation section to radiated to the glass layer side, thus the thermal efficiency can be improved. Further, in the embodiment of the invention, the heat storage capacity of the glass layer is reduced by providing the groove section, thus the heat can easily be radiated and the response is improved. From the facts described above, thermal efficiency and response can be improved in the invention. Further, according to the embodiment of the invention, by forming the groove section to have a width equal to or larger than the length of the heat generation section, the thickness of the both ends of the heat storage section facing the heat generation section and storing the heat is made smaller, thus the heat radiation from the both ends can be suppressed to further improve the thermal efficiency. Further, in the embodiment of the invention, the thickness of the both ends of the heat storage section is made further smaller by making the curvature radius of the both sides of the protruding section smaller than the curvature radius in the central portion thereof, thus the thermal efficiency can further be improved. Thus, in the embodiments of the invention, high speed printing with low power consumption can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a printing device using a thermal head applying an embodiment of the invention. 
         FIG. 2  is a partial perspective view showing a relationship between the thermal head and a ribbon guide. 
         FIG. 3  is a perspective view of the thermal head. 
         FIG. 4  is a partial perspective view of the thermal head. 
         FIGS. 5A and 5B  are cross-sectional views of the head section, wherein  FIG. 5A  is a cross-sectional view of the whole of the head section, and  FIG. 5B  is a partial cross-sectional view enlargedly showing a leading end side of the groove section. 
         FIG. 6  is a plan view of the head section. 
         FIG. 7  is a cross-sectional view of another example of the head section. 
         FIGS. 8A and 8B  are cross-sectional views of another example of the head section, wherein  FIG. 8A  is a cross-sectional view of the whole of the head section, and  FIG. 8B  is a partial cross-sectional view enlargedly showing a protruding section. 
         FIG. 9  is a cross-sectional view showing only the glass layer of the head section shown in  FIGS. 8A and 8B . 
         FIG. 10  is a cross-sectional view of the glass layer with a protruding section having a smaller curvature radius in both sides than in a central section. 
         FIGS. 11A and 11B  are cross-sectional views of a glass layer provided with reinforcing sections. 
         FIG. 12  is a partial cross-sectional view of the glass layer shown in  FIGS. 11A and 11B . 
         FIG. 13  is a cross-sectional view showing a glass material to be the material of the glass layer. 
         FIG. 14  is a cross-sectional view showing the glass layer. 
         FIG. 15  is a cross-sectional view showing a condition in which a heat generating resistor and a pair of electrodes are patterned on the glass layer. 
         FIG. 16  is a cross-sectional view showing a condition in which a resistor protective layer is provided on the heat generating resistor and the pair of electrodes. 
         FIG. 17  is a partial cross-sectional view showing a condition in which a groove section is in a process of formation with a cutter. 
         FIG. 18  is a partial perspective view of the thermal head. 
         FIG. 19  is a cross-sectional view showing a condition in which the glass layer is adhered to a heat radiation member with an adhesive layer. 
         FIG. 20  is a cross-sectional view of a thermal head in the related art. 
         FIG. 21  is a cross-sectional view of the thermal head explained as the related art. 
         FIG. 22  is a cross-sectional view of the thermal head explained as the related art. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a thermal transfer printing device implementing a thermal head applying an embodiment of the invention will be explained in detail with reference to the accompanying drawings. 
     A thermal transfer printing device  1  (hereinafter referred to as a printing device  1 ) shown in  FIG. 1  is a dye sublimation printer for sublimating a color material of an ink ribbon to thermal-transfer the color material to a print medium, and uses a thermal head  2  applying an embodiment of the invention as a recording head. The printing device  1  applies thermal energy generated by the thermal head  2  to the ink ribbon  3 , thereby sublimating the color material of the ink ribbon  3  to thermal-transfer it to the print medium  4 , thus printing color images or characters. The printing device  1  is a home-use printing device, and is able to print on objects of, for example, a post card size as the print medium  4 . 
     The ink ribbon  3  used here is formed of a long resin film, and is housed in an ink cartridge in a condition in which a part of the ink ribbon  3  not yet used in the thermal transfer process is wound around a supply spool  3   a  while a part of the ink ribbon  3  already used in the thermal transfer process is wound around a winding spool  3   b . The ink ribbon  3  is provided with a transfer layer  3   c  repeatedly formed in a plane on one side of the long resin film, the transfer layer  3   c  being composed of an ink layer formed of a yellow color material, an ink layer formed of a magenta color material, an ink layer formed of a cyan color material, and a laminate layer formed of a laminate film to be thermal-transferred on the print medium  4  for improving stability of images or characters printed on the print medium  4 . 
     As shown in  FIG. 1 , the printing device  1  is provided with a thermal head  2 , a platen  5  disposed at a position facing the thermal head  2 , a plurality of ribbon guides  6   a ,  6   b  for guiding running of the ink ribbon  3  mounted thereon, a pinch roller  7   a  and a capstan roller  7   b  for running the print medium  4  together with the ink ribbon  3  between the thermal head  2  and the platen  5 , an ejection roller  8  for ejecting the print medium on which printing has been performed, and a feed roller  9  for carrying the print medium  4  towards the thermal head  2 . As shown in  FIG. 2 , the thermal head  2  is provided to the printing device  1  by attaching to an attachment member  10  on the side of the housing of the printing device  1  with a fixing member  11  such as a screw. 
     The ribbon guides  6   a ,  6   b  for guiding the ink ribbon  3  are disposed in front of and behind the thermal head  2 , namely, in the side from which the ink ribbon  3  enters and in the side to which the ink ribbon  3  is ejected with respect to the thermal head  2 . The ribbon guides  6   a ,  6   b  guide the ink ribbon  3  and the print medium  4  between the thermal head  2  and the platen in front of and behind the thermal head  2  so that the ink ribbon  3  and the print medium  4  overlapping each other abut on the thermal head  2  substantially perpendicular to each other, thus the thermal energy of the thermal head  2  can surely be applied to the ink ribbon  3 . 
     The ribbon guide  6   a  is disposed in the side from which the ink ribbon  3  enters with respect to the thermal head  2 . The ribbon guide  6   a  has a curved surface in the lower end surface  12 , and guides the ink ribbon  3  supplied from the supply spool  3   a  disposed upper position of the thermal head  2  to enter between the thermal head  2  and the platen  5 . 
     The ribbon guide  6   b  is disposed in the side to which the ink ribbon  3  is ejected with respect to the thermal head  2 . The ribbon guide  6   b  has a flat section  13  evenly formed on the lower end and a separation section  14  rising substantially perpendicular from the end of the flat section  13  opposite the thermal head  2  and for breaking away the ink ribbon  3  from the print medium  4 . The ribbon guide  6   b  removes the heat of the ink ribbon  3  after the thermal transfer process by the flat section  13 , and then raises the ink ribbon  3  substantially perpendicular to the print medium  4  by the separation section  14  to break away the ink ribbon  3  from the print medium  4 . The ribbon guide  6   b  is attached to the thermal head  2  with a fixing member  15  such as a screw. 
     In the printing device  1  having such a configuration, as shown in  FIG. 1 , the winding spool  3   b  is rotated in a winding direction to run the ink ribbon  3  in the winding direction, and the print medium  4  is pinched between the pinch roller  7   a  and the capstan roller  7   b  and runs in an ejection direction by rotating the capstan roller  7   b  and the ejection roller  8  in the ejection direction (the direction of arrow A in  FIG. 1 ) between the thermal head  2  and the platen  5  while pressing the platen  5  against the thermal head  2 . In a printing operation, the thermal energy is fist applied to the yellow ink layer of the ink ribbon  3  from the thermal head  2  to thermal-transfer the yellow color material to the print medium  4  running while overlapping the ink ribbon  3 . After thermal-transferring the yellow color material, in order for thermal-transferring the magenta color material to the image forming section on which images or characters are formed and the yellow color material has been thermal-transferred, the feed roller  9  is rotated towards the thermal head  2  (the direction of the arrow B in  FIG. 1 ) to back-feed the print medium  4  to the thermal head  2 , thus making the leading end of the image forming section face the thermal head  2  and the magenta ink layer of the ink ribbon  3  face the thermal head  2 . Then, similarly to the case of thermal-transferring the yellow ink layer, the thermal energy is also applied to the magenta ink layer to thermal-transfer the magenta color material to the image forming section of the print medium  4 . Regarding the cyan color material and the laminate film, they are also thermal-transferred to the image forming section similarly to the case of thermal-transferring the magenta color material, thus color images or characters are printed by sequentially thermal-transferring the cyan color material and the laminate film to the print medium  4 . 
     The thermal head  2  used for such a printing device  1  can print a framed image having margins on both edges in a direction perpendicular to the running direction of the print medium  4 , namely the width direction of the print medium  4 , and also a frameless image without the margins. The thermal head  2  has a size in a direction designated by the direction of the arrow L shown in  FIG. 3  larger than the width of the print medium  4  so that the color material can be thermal-transferred to the both edges of the print medium  4  in the width direction thereof. 
     As shown in  FIG. 3 , the thermal head  2  is provided with a head section  20  for thermal-transferring the color material of the ink ribbon  3  to the print medium  4  attached to a heat radiation member  50 . As shown in  FIGS. 4 and 5A , the head section  20  is provided with a glass layer  21 , a heat generation resistor  22  disposed on the glass layer  21 , a pair of electrodes  23   a ,  23   b  disposed on both sides of the heat generation resistor  22 , and a resistor protective layer  24  disposed on and around the periphery of the heat generation resistor  22 . In the thermal head  2 , a part of the heat generation resistor  22  exposed between the pair of electrodes  23   a ,  23   b  is defined as a heat generation section  22   a . The glass layer  21  is provided with the pair of electrodes  23   a ,  23   b , the heat generation resistor  22 , and the resistor protective layer  24  formed on the upper surface thereof, and forms a base layer of the head section  20 . 
     As shown in  FIGS. 4 and 5A , the glass layer  21  has a substantially circular arc shaped protruding section  25  on the outer surface facing the ink ribbon  3 , and a groove section  26  on the inner surface thereof. The glass layer  21  is made of glass having a softening point of, for example, 500° C. to form a substantially rectangular shape. The protruding section  25  is formed to have a substantially semicylindrical shape in a substantially central position of the glass layer  21  in the width direction along the length direction (the L direction in  FIG. 2 ) thereof. The glass layer  21  improves the contact condition of the heat generation section  22   a  disposed on the protruding section  25  with the ink ribbon  3  by providing the protruding section  25  having a substantially circular arc shape on the surface facing the ink ribbon  3 . Thus, it becomes possible that the thermal head  2  appropriately applies the heat generated by the heat generation section  22   a  of the heat generation resistor  22  to the ink ribbon  3 . 
     It should be noted that the central section  25   a  of the protruding section  25  can be substantially flat. Further, it is sufficient that the glass layer  21  is made of a material having a predetermined surface property, a thermal characteristic, and so on represented by glass, and the concept of glass here includes synthetic gems or artificial stones such as synthetic quartz, synthetic ruby, or synthetic sapphire, or high-density ceramics. 
     As shown in  FIGS. 4 and 5A , the groove section  26  provided to the inner surface of the glass layer  21  faces a line  22   b  of heat generation sections  22   a  disposed substantially linearly on the protruding section  25  in the length direction (the L direction in  FIG. 4 ) of the thermal head  2 , and is formed to have a concave shape towards the heat generation section  22   a . Further, in the glass layer  21 , a heat storage section  27  for storing the thermal energy generated by the heat generation section  22   a  is defined between the protruding section  25  and the groove section  26 . 
     In the glass layer  21 , by providing the groove section  26 , according to the nature of air of having lower thermal conductivity than glass, the thermal energy is prevented from conducted to the whole layer, and can easily be stored in the heat storage section  27  between the heat generation section  22   a  and the groove section  26 . In the glass layer  21 , since the thermal energy is prevented from being radiated to the whole of the layer by providing the groove section  26 , the thermal energy generated by the heat generation section  22   a  can be prevented from being radiated, thus the amount of heat conducted to the ink ribbon  3  can be increased. Thus, the thermal efficiency of the thermal head  2  can be improved with the glass layer  21 . Further, since in the glass layer  21 , the color material can immediately be heated to the sublimation temperature with low power consumption by the thermal energy stored in the heat storage section  27  in thermal-transferring the color material to the print medium  4 , the thermal efficiency of the thermal head  2  can be made preferable. Further, since in the glass layer  21 , the thickness of the heat storage section  27  is made thinner to reduce heat storage capacity of the heat storage section  27  by forming the groove section  26 , it becomes possible to radiate the heat in a short period of time, thus the temperature of the thermal head  2  can rapidly be lowered when the heat generation section  22   a  is not heated. According to the above, the thermal efficiency and the response of the thermal head  2  can be improved with the glass layer  21  provided with the groove section  26 . Thus, high quality images and characters can be printed at high speed with low power consumption without causing a problem such as a blur in the images and characters using the thermal head  2  offering preferable response. 
     The heat generation resistor  22  for generating thermal energy is formed on the protruding section  25  side surface of the glass layer  21 , as shown in  FIG. 5A . The heat generation resistor  22  is made of a material having high resistivity and heat resistance such as Ta—N or Ta—SiO 2 . The heat generation sections  22   a , which are each exposed between the pair of electrodes  23   a ,  23   b  of the heat generation resistor  22  and generate heat, are disposed substantially linearly on the protruding section  25 , and are each formed in a size slightly larger than a dot size to be thermal-transferred for dispersing the thermal energy and having a substantially rectangular or square shape. The heat generation resistors  22  are patterned on the glass layer  21  by a photolithography technology. 
     The pair of electrodes  23   a ,  23   b  provided to both sides of the heat generation resistor  22  supply the heat generation section  22   a  with a current from a power supply not shown in detail to make the heat generation section  22   a  generate heat. The pair of electrodes  23   a ,  23   b  are made of a material having good electrical conductivity such as aluminum, gold, or copper. As shown in  FIGS. 3 and 6 , the pair of electrodes  23   a ,  23   b  are composed of a common electrode  23   a  electrically connected to all of the heat generation sections  22   a  and an individual electrode  23   b  electrically connected individually to every heat generation section  22   a , and are disposed distant from each other across the heat generation section  22   a.    
     The common electrode  23   a  is disposed on one side opposite to a side where a power supply flexible board  80  described below is bonded thereon across the protruding section  25  of the glass layer  21 . The common electrode  23   a  is electrically connected to all of the heat generation sections  22   a , and the both ends thereof are led to the side where the power supply flexible board  80  is bonded thereon along the narrow sides of the glass layer  21  to be electrically connected to the power supply flexible board  80 . The common electrode  23   a  is connected to a rigid board  70  electrically connected to the power supply not shown via the power supply flexible board  80 , thus electrically connecting the power supply with each of the heat generation sections  22   a.    
     The individual electrode  23   b  is disposed on a side where a signal flexible board  90  described below is bonded thereon across the protruding section  25  of the glass layer  21 . The individual electrode  23   b  is provided to the heat generation section  22   a  one-on-one. The individual electrode  23   b  is electrically connected to the signal flexible board  90  connected to a control circuit for controlling the drive of the heat generation section  22   a  of the rigid board  70 . 
     The common electrode  23   a  and the individual electrode  23   b  supply the heat generation section  22   a  selected by a circuit for controlling drive of the heat generation section  22   a  with a current for a predetermined period of time, thereby making the heat generation section  22   a  generate heat to raise the temperature to a point enough for sublimating the color material to be thermal-transferred to the print medium  4 . 
     It should be noted that in the head section  20 , the heat generating resistor  22  is not necessarily required to be provided to the entire surface of the glass layer  21 , but it is possible that the heat generating resistor  22  is disposed on a part of the protruding section  25 , and the end portions of the common electrode  23   a  and the individual electrode  23   b  are formed on the heat generating resistor  22 . 
     As shown in  FIG. 4 , the resistor protective layer  24  provided as the outermost layer of the head section  20  covers the whole of the heat generation resistors  22  and the common electrodes  23   a  and the heat generation section  22   a  side end portions of the individual electrodes  23   b , and protects the heat generation sections  22   a  and the pairs of electrodes  23   a ,  23   b  disposed around the heat generation sections  22   a  from the friction and so on caused when the thermal head  2  and the ink ribbon  3  come in contact with each other. The resistor protective layer  24  is made of an inorganic material containing metal excel in mechanical characteristic such as high-strength and abrasion resistance under high temperature and in thermal characteristic such as heat resistance, thermal shock resistance, and thermal conductivity, and is made of, for example, SIALON (a trade name) including silicon (Si), aluminum (Al), oxygen (O), and nitrogen (N). 
     In the head section  20  having the configuration described above, as shown in  FIGS. 4 ,  5 A, and  5 B, the groove section  26  is formed on the inner surface of the glass layer  21  at a position corresponding to the line  22   b  of the heat generation section  22   a  formed substantially linearly in the length direction (the L direction in  FIG. 4 ) of the head section  20  so as to have a width W 1  (the distance between the intersections of extended lines the wall faces  30  and an extended line of the ceiling face  31   a  of the groove section  26 ) equal to or longer than the length L 1  of the heat generation section  22   a . In the glass layer  21 , the thermal efficiency of the thermal head  2  can further be improved by forming the groove section  26  so as to have the width W 1  equal to or larger than the length L 1  of the heat generation section  22   a.    
     In more detail, in the glass layer  21 , the thickness of the both ends of the heat storage section  27  becomes thinner by forming the groove section  26  so as to have the width W 1  equal to or larger than the length L 1  of the heat generation section  22   a  than in the case in which the groove section  26  is formed to have the width W 1  smaller than the length L 1  of the heat generation section  22   a . Thus, in the glass layer  21 , it becomes difficult to radiate the thermal energy stored in the heat storage section  27  from the both ends of the heat storage section  27  to the peripheral area, namely the peripheral section  28  of the groove section  26 . In particular, in the glass layer  21 , by forming the groove section  26  so as to have the width W 1  larger than the length of the heat generation section  22   a , the thickness of the both ends of the heat storage section  27  becomes thinner than in the case with the width W 1  equal to the length of the heat generation section  22   a , thus the heat radiation becomes more difficult. As described above, since the heat radiation to the peripheral section  28  can be suppressed in the glass layer  21 , it becomes possible to further increase the amount of heat conducted to the ink ribbon  3 , and to further improve the thermal efficiency of the thermal head  2 . 
     It should be noted that the length of the heat generation section  22   a  is, for example, 20 μm, the width of the groove section  26  is in a range of 50 μm through 700 μm, and the preferably in a range of 200 μm through 400 μm. 
     Further, as shown in  FIGS. 5A and 10 , in the glass layer  21  the protruding section  25  is formed so as to have a smaller curvature radius R 2  in the both side portions  25   b  than a curvature radius R 1  in the central portion  25   a  (R 1 &gt;R 2 ). For example, in the glass layer  21 , the curvature radius R 1  of the central portion  25   a  is set to, for example, 2.5 μm, and the curvature radius R 2  of the both side portions  25   b  is set to, for example, 1.0 μm. In the glass layer  21 , the thickness of the glass layer  21  between the both side portions  25   b  and the groove section  26  becomes smaller, namely the thickness of the both ends of the heat storage section  27  becomes smaller by forming the protruding section  25  so as to have the smaller curvature radius R 2  in the both side portions  25   b  than the curvature radius R 1  in the central portion  25   a  than in the case of forming the protruding section  25  so as to have the larger curvature radius R 2  in the both side portions  25   b  than the curvature radius R 1  in the central portion  25   a  (R 1 ≦R 2 ). Thus, since the heat storage capacity of the heat storage section  27  is further reduced, and the amount of heat radiated from the both edges to the peripheral section  28  of the groove section  26  is also further reduced, the thermal efficiency thereof can further be improved. Further, since in the glass layer  21  the width of the protruding section  25  is reduced by forming the protruding section  25  so as to have the smaller curvature radius R 2  in the both side portions  25   b  than the curvature radius R 1  in the central portion  25   a , the whole size of the layer can be reduced. 
     Further, as shown in  FIG. 5A , in the glass layer  21 , the groove section  26  is formed so that the wall faces  30  rise substantially vertically from the opposite side of the heat generation section  22   a , namely the side of the base end  29 . In the glass layer  21  having such a groove section  26 , since the pressure caused by the platen  5  pressing the thermal head  2  and acting on the both ends  29   a  of the groove section  26  on the side of the base end  29  from the side of the protruding section  25  is not concentrated in the both ends  29   a  but is dispersed in the bottom face  21   a  of the glass layer  21 , thus the physical strength against the pressure from the platen  5  is increased. Thus, in the glass layer  21  deformation or breakage of the both ends  29   a  caused by the pressure from the platen  5  can be prevented, and accordingly, deformation or breakage of the glass layer  21  can thus be prevented. 
     It should be noted that the glass layer  21  can be formed, as shown in  FIG. 7 , so that the distance between the wall faces  30  facing in the length direction of the heat generation section  22   a  is longer in the side of the base end  29  than in the side of the leading end  31 . According to such a glass layer  21 , since the distance between the wall faces  30  facing in the length direction of the heat generation section  22   a  is longer in the side of the base end  29  than in the side of the leading end  31 , in the case in which the groove section  26  is molded by the thermal press molding using a press die, for example, demolding can be made easier. Thus, the glass layer  21  can easily be formed by die-casting, thus improving the production efficiency. 
     Further, as shown in  FIGS. 5A and 5B , in the glass layer  21 , the groove section  26  is formed so that the both end corner sections  31   b  of the ceiling face  31   a  on the side of the leading end  31  of the groove section  26  are formed as substantially circular arc shapes, and a part of the ceiling face  31   a  between the both end corner sections  31   b  is substantially flat. In the glass layer  21 , by forming the both end corner sections  31   b  on the side of the leading end  31  of the groove section  26  as the substantially circular arc shapes, the pressure applied to the both end corner sections  31   b  from the protruding section  25  caused by the platen pressing the thermal head  2  is dispersed, thus the physical strength against the pressure from the platen  5  increases. Thus, in the glass layer  21 , deformation and breakage of the both end corner sections  31   b  on the side of the leading end  31  of the groove section  26  caused by the pressure from the platen  5  can be prevented. 
     It should be noted that as shown in  FIGS. 8A ,  8 B, and  9 , in the glass layer  21  of the head section  20 , the ceiling face  31   a  of the groove section  26  can be formed to have a substantially circular arc shape along the surface of central section  25   a  of the protruding section  25  so that the thickness between the ceiling face  31   a  of the leading end  31  of the groove section  26  and the surface of the central section  25   a  of the protruding section  25 , namely the thickness T 1  of the protruding section  25  becomes substantially constant, namely substantially even. As shown in  FIG. 9 , in the glass layer  21 , the ceiling face  31   a  of the groove section  26  and the central section  25   a  are formed concentrically, thus the thickness T 1  of the protruding section  25  can be made substantially even. It should be noted that the thickness T 1  of the protruding section  25  is in a range of 10 μm through 100 μm, preferably in a range of 20 μm through 40 μm, and particularly preferably, for example, 27.5 μm. In the glass layer  21 , the stress caused by the pressure from the platen  5  is prevented from being concentrated to the both end corner sections  31   b  of the groove section  26  by making the thickness T 1  of the protruding section  25  substantially even to prevent the thickness T 1  of the protruding section  25  from being unevenly distributed. Thus, in the glass layer  21 , high physical strength can be obtained even with the very small thickness T 1  of the protruding section  25 . Further, in the glass layer  21 , by making the thickness T 1  of the protruding section  25  substantially even, the thickness of the heat storage section  27  becomes substantially even, thus the thermal balance of the heat storage section  27  becomes preferable because there is no uneven distribution in the thickness of the heat storage section  27 , thereby making the thermal efficiency and response of the thermal head  2  preferable. 
     According to the thermal head  2  having such a head section  20 , it becomes difficult for the thermal energy generated by the heat generation section  22   a  to be radiated to the glass layer  21  by forming the groove section  26  to the glass layer  21 , and the heat generation section  22   a  can be heated to be the sublimation temperature of the color material with low power consumption using the heat stored in the heat storage section  27 , thus the thermal efficiency can be improved. Further, in the thermal head  2 , since the thickness of the heat storage section  27  becomes smaller to reduce the heat storage capacity by providing the groove section  26  to the glass layer  21 , heat radiation becomes easier, thus improving the response. Therefore, in the thermal head  2 , the thermal efficiency and the response can be improved by forming the groove section  26  to the glass layer  21 . 
     Further, in the thermal head  2 , by making the width W 1  of the groove section  26  of the glass layer  21  equal to or larger than the length L 1  of the heat generation section  22   a , the thickness of the both ends of the heat storage section  27  becomes smaller to make it difficult to radiate heat from the heat storage section  27 , thus the radiation of the thermal energy generated by the heat generation section  22   a  is suppressed to further improve the thermal efficiency. 
     Further, talking of the thermal efficiency, in the thermal head  2  the width of the both sides of the heat storage section  27  is narrowed by making the curvature radius R 2  of the both sides smaller than the curvature radius R 1  of the central portion  25   a  of the protruding section  25  of the glass layer  21 , thus the heat radiation from the heat storage section  27  becomes further difficult to further suppress the radiation of the thermal energy generated by the heat generation section  22   a , and the thermal efficiency can further be improved. 
     Still further, in the thermal head  2 , by making the groove section  26  of the glass layer  21  rise substantially vertically and forming the both end corner sections  31   b  on the side of the leading end  31  to have circular arc shapes as shown in  FIGS. 5A and 5B , or by forming the protruding section  25  to have the substantially even thickness T 1  as shown in  FIG. 9 , the physical strength can be increased. In the thermal head  2 , by increasing the physical strength of the glass layer  21 , deformation or breakage of the glass layer  21 , in particular deformation or breakage of the protruding section  25  having a small thickness can be prevented even if the pressure as strong as about 45 kg per unit area caused by the pressure from the platen  5  applied in performing printing is applied to the glass layer  21 . 
     As described above, according to the thermal head  2 , since the thermal efficiency and the response are preferable, and deformation and breakage of the glass layer  21  and the protruding section  25  caused by the pressure from the platen  5  can be prevented, high quality images or characters can be printed with low power consumption at high speed. Further, in the thermal head  2 , as shown in  FIG. 7 , by forming the groove section  26  so that the width between the wall faces  30  thereof is longer in the side of the base end  29  than in the side of the leading end  31 , in the case of molding the groove section  26  by the thermal press molding using a press die, for example, demolding can be made easier, thus improving the production efficiency. 
     Further, in the glass layer  21  of the head section  20 , as shown in  FIGS. 11A and 11B  and  FIG. 12 , the groove section  26  is provided to face the line  22   b  of the heat generation sections  22   a  substantially linearly arranged in parallel in the length direction (the L direction in  FIGS. 11A and 11B ) of the head section  20 , and first reinforcement sections  32  for reinforcing the strength are provided on both sides of the heat generation sections  22   a  in the arranging direction thereof. The first reinforcement sections  32  are formed by forming the glass layer  21  so as to have a larger thickness. The thickness T 2  of the first reinforcement section  32  is made larger than the thickness T 1  of the protruding section  25  (T 2 &gt;T 1 ). In the glass layer  21 , the protruding section  25  can be reinforced by providing the first reinforcement sections  32  each having a larger thickness T 2  than the thickness T 1  of the protruding section  25  on the both sides of the groove section  26  in the length direction thereof. Thus, in the glass layer  21 , the deformation or the breakage of the protruding section  25  caused by the pressure from the platen  5  can be prevented when the pressure from the platen  5  is applied to the glass layer  21 . 
     Further, as shown in  FIGS. 11A and 11B  and  FIG. 12 , besides the first reinforcement sections  32 , the glass layer  21  is further provided with second reinforcement sections  33  each formed inside the first reinforcement sections  32  so as to have a thickness gradually increases from the end portion of the protruding section  25  towards the first reinforcement section  32  including a thickness T 3 . Thus, in the glass layer  21 , the protruding section  25  is further reinforced by providing the second reinforcement sections  33  in addition to the first reinforcement sections  32 . Thus, in the glass layer  21 , the physical strength of the protruding section  25  increases, and the deformation and breakage of the protruding section  25  caused by the pressure from the platen  5  can further be prevented. 
     In the thermal head  2 , the physical strength of the glass layer  21  is improved by forming the first reinforcement sections  32  and the second reinforcement sections  33  on both sides of the heat generation sections  22   a  of the glass layer  21  in the arranging direction thereof, and even when the strong pressure caused by the pressure from the platen  5  applied thereto in printing operation is applied to the glass layer  21 , deformation and breakage of the glass layer  21 , in particular deformation and breakage of the protruding section  25  with smaller thickness can be prevented. 
     The head section  20  having the glass layer  21  can be manufactured as described below. Firstly, as shown in  FIG. 13 , a glass material  41  to be used as the material of the glass layer  21  is prepared, and then as shown in  FIG. 14 , by performing a thermal press process on the glass material  41  to mold the glass layer  21  having the protruding section  25  on the upper surface thereof. 
     Subsequently, although not shown in detail, the resistor film to form the heat generation resistor  22  is formed on the surface of the glass layer  21  provided with the protruding section  25  with a material having high resistivity and thermal resistance using a thin film forming technology such as sputtering, and further, a conductive film to form the pair of electrodes  23   a ,  23   b  is then formed with a material having good electrical conductivity such as aluminum so as to have a predetermined thickness. 
     Subsequently, as shown in  FIG. 15 , the heat generation resistor  22  and the pair of electrodes  23   a ,  23   b  are patterned using a pattern forming technology such as a photolithography process, and the heat generation section  22   a  is formed by exposing the heat generation resistor  22  between the pair of electrodes  23   a ,  23   b . The glass layer  21  is exposed in the portion where either the heat generation resistor  22  or the pair of electrodes  23   a ,  23   b  is not formed. 
     Subsequently, as shown in  FIG. 16 , the resistor protective layer  24  is formed on the heat generation resistor  22  and the pair of electrodes  23   a ,  23   b  with, for example, SIALON in a predetermined thickness using a thin film forming technology such as a sputtering process. 
     Subsequently, as shown in  FIG. 17 , the groove section  26  having a concave shape is formed on a surface opposite the surface of the glass layer  21  on which the protruding section  25  is formed, namely the surface to be located inside the thermal head  2  by, for example, cutting with a cutter  42  so as to face the line  22   b  of the heat generation sections  22   a , thus manufacturing the head section  20 . As shown in  FIG. 17 , by forming the groove section  26  with the cutter  42 , the first reinforcement sections  32  and the second reinforcement sections  33  can be provided to the glass layer  21  in a series of cutting processes. 
     It should be noted that after forming the groove section  26  by the cutting process, a hydrofluoric acid treatment can be performed on the inner surface of the groove section  26  in order for remove scratches caused on the inner surface of the groove section  26 . Further, the groove section  26  can be formed by an etching process or a thermal press process besides the machining process such as a cutting process. 
     Further, in the case of forming the groove section  26  as shown in  FIG. 7 , since the wall faces  30  broadens from the side of the leading end  31  towards the side of the base end  29 , demolding becomes easier, and accordingly, the groove  26  can be formed by the thermal press process using a press die. Still further, in the case of forming the groove section  26  by the thermal press process, it is possible to form the protruding section  25  with an upper die and to form the groove section  26  with a lower die, thus simultaneously forming the protruding section  25  and the groove section  26 . 
     Since the head section  20  is formed of the glass layer  21  as a whole without using a ceramic substrate, it becomes possible to reduce the number of component by eliminating the ceramic substrate in comparison with the thermal head  100  shown in  FIG. 20  using the ceramic substrate  101 , thus the configuration can be made simpler. Further, according to the thermal head  2 , the number of components can be reduced, and accordingly, the production efficiency can be improved. 
     As shown in  FIGS. 3 and 18 , in the thermal head  2  having the head section  20  described above, the head section  20  is disposed on the heat radiation member  50  via an adhesive layer  60 , and the head section  20  and the rigid board  70  provided with a control circuit for the head section  20  are electrically connected to each other with the power supply flexible board  80  and the signal flexible board  90 . In the thermal head  2 , the rigid board  70  is disposed on the side face of the heat radiation member  50  by bending the power supply flexible board  80  and the signal flexible board  90  towards the heat radiation member  50 . 
     The heat radiation member  50  is for efficiently radiating the thermal energy generated by the head section  20  when thermal-transferring the color material, and is made of a material having high thermal conductivity such as aluminum. As shown in  FIGS. 3 and 18 , the heat radiation member  50  is provided with an attachment protruding section  51  to which the head section  20  is attached formed on the upper surface in substantially the center in the width direction, and along the length direction (the L direction in  FIG. 18 ). Further, the heat radiation member  50  is provided with an inclined section  52  for guiding the power supply flexible board  80  and the signal flexible board  90  bending along the side surface formed at the upper end of the side surface towards which the power supply flexible board  80  and the signal flexible board  90  bend, and a first notch section  53  for positioning the rigid board  70  formed at the lower end of the inclined section  52 . Further, the heat radiation member  50  is provided with a second notch  54  formed so as to allow a semiconductor chip  91  described later provided to the signal flexible board  90  to be disposed on the side of the heat radiation member  50 . 
     As shown in  FIG. 19 , the head section  20  is attached to the attachment protruding section  51  of the heat radiation member  50  via the adhesive layer  60 . The adhesive layer  60  has thermal conductivity and is formed of an adhesive having elasticity. Since the adhesive layer  60  has thermal conductivity, it can efficiently radiate the heat generated by the head section  20  to the heat radiation member  50 . Further, since the adhesive layer  60  has elasticity, even if the head section  20  and the heat radiation member  50  expand or shrink differently because of difference in the thermal expansion coefficient, it can be prevented that the head section  20  is separated from the heat radiation member  50  when the head section  20  generates heat. The thickness of the adhesive layer  60  is, for example, about 50 μm. 
     As shown in  FIG. 19 , the adhesive layer  60  is made of resin having thermal conductivity such as thermoset liquid silicone rubber containing a filler  61  having high hardness and thermal conductivity. The filler  61  contained therein is, for example, aluminum oxide of granulated or linear shapes. The adhesive layer  60  contains the filler  61  which functions as a spacer between the head section  20  and the heat radiation member  50 , and accordingly, is not compressed by the head section  20  which is pressed by the platen  5 , thus maintaining the constant thickness so that the ends  29   a  on the side of the base end  29  of the glass layer  21  is not deformed towards the heat radiation member  50 . Thus, in the adhesive layer  60 , since the thickness can be maintained constant by the filler  61 , the pressure applied from the protruding section  25  to the both ends  29   a  on the side of the base end  29  of the groove section  26  in response to the head section  20  being pressed by the platen  5  is dispersed to the bottom face  21   a  of the glass layer  21 , and can be received by the entire bottom face  21   a  of the glass layer  21 . Further, in the adhesive layer  60 , it becomes possible to let the pressure applied from the platen  5  escape in a direction parallel to the bottom face  21   a  by the filler rotating accordingly. As described above, in the thermal head  2 , even if the strong pressure is applied to the glass layer  21  from the platen  5 , the glass layer  21  can be prevented from being deformed towards the heat radiation member  50 , thus deformation and breakage of the glass layer  21  can be prevented. 
     It should be noted that the filler  61  to be contained by the adhesive layer  60  can have a diameter equal to or greater than the thickness of the adhesive layer  60 . Since the adhesive layer  60  contains the filler  61  having the diameter equal to or larger than the thickness of the adhesive layer  60 , even if the head section  20  is pressed by the platen  5 , the adhesive layer  60  is not compressed by the head section  20  because of the filler  61 , thus the thickness thereof can be maintained constant, thereby further preventing deformation and breakage of the glass layer  21 . 
     The rigid board  70  disposed on the side surface of the heat radiation member  50  shown in  FIG. 3  is provided with power supply wiring not shown and for supplying current from the power supply to the head section  20  and the control circuit not shown, provided with a plurality of electronic components mounted thereon, and for controlling driving of the head section  20 . As shown in  FIG. 3 , flexible boards  71  to form power supply lines and signal lines are electrically connected to the rigid board  70 . The rigid board  70  is disposed in the first notch  53  on the side face of the heat radiation member  50  and is fixed to the heat radiation member  50  on the both sides with fixing members  72  such as screws. 
     As shown in  FIGS. 3 and 6 , the power supply flexible board  80  electrically connected to the rigid board  70  is electrically connected to wiring for power supply not shown of the rigid board  70  on one end thereof, and is electrically connected to the common electrodes  23   a  of the head section  20  on the other end thereof, thereby electrically connecting the common electrodes  23   a  of the head section  20  and the wiring of the rigid board  70  to each other to supply each of the heat generation sections  22   a  with the current. It should be noted that the power supply flexible board  80  can electrically be connected to the common electrodes  23   a  with a film made of an insulating resin material containing conductive particles such as an anisotropic conductive film (ACF) intervening between the power supply flexible board  80  and the common electrodes  23   a . By electrically connecting the power supply flexible board  80  and the common electrode  23   a  with the AFC, the thermal energy generated by the heat generation section  22   a  can be prevented from being radiated to the side of the power supply flexible board  80  via the common electrodes  23   a.    
     As shown in  FIGS. 3 and 6 , the signal flexible board  90  electrically connected to the control circuit of the rigid board  70  is electrically connected to the control circuit not shown of the rigid board  70  on one end thereof, and is electrically connected to the individual electrodes  23   b  of the head section  20  on the other end thereof. A plurality of signal flexible boards  90  are arranged in parallel in the length direction (the L direction in  FIG. 3 ) of the thermal head  2 . 
     As shown in  FIGS. 6 and 18 , each of the signal flexible boards  90  is provided with a semiconductor chip provided with a drive circuit for driving each of the heat generation sections  22   a  of the head section  20  disposed on one surface thereof, and is provided with connection terminals  92  for electrically connecting the semiconductor chip  91  and the each of the individual electrodes  23   b  disposed on the same surface and on the side of connection with the head section  20 . 
     The semiconductor chip  91  provided to each of the signal flexible boards  90  is, as shown in  FIG. 18 , disposed inside the signal flexible board  90 . As shown in  FIG. 6 , the semiconductor chip  91  includes a shift register  93  for converting a serial signal corresponding to the print data transmitted from the control circuit of the rigid board  70  into a parallel signal, and a switching element  94  for controlling driving of heat generation of the heat generation section  22   a . The shift register  93  converts the serial signal corresponding to the print data into a parallel signal, and latches the converted parallel signal. The switching element  94  is provided to every individual electrode  23   b  disposed to each of the heat generation sections  22   a . The parallel signal latched by the shift register  93  controls switching on/off of the switching element  94  to control the current supply and the supply time period to each of the heat generation sections  22   a , thus driving and controlling the heat generation of the heat generation sections  22   a.    
     As shown in  FIG. 6 , the connection terminals  92  are provided corresponding to each of the individual electrodes  23   b  provided one-on-one to the heat generation sections  22   a , and electrically connecting the individual electrodes  23   b  and the semiconductor chips  91  to each other. As shown in  FIG. 4 , the connection terminals  92  and the individual electrodes  23   b  are electrically connected via a film  95  made of insulation resin material containing conductive particles such as an anisotropic conductive film (ACF) held between the glass layer  21  on the side of the individual electrode  23   b  and the signal flexible board  90 . In the thermal head  2 , by connecting the individual electrodes  23   b  of the head section  20  and the connection terminals  92  of the signal flexible boards  90  with the ACF made of an insulation resin material, even if the signal flexible boards  90  are connected adjacent to the heat generation sections  22   a , the thermal energy generated by the heat generation sections  22   a  can be prevented from being radiated to the side of the signal flexible boards  90  via the individual electrodes  23   b , thus degradation of the thermal efficiency can be suppressed. Thus, in the thermal head  2 , the groove section  26  is provided to the glass layer  21  of the head section  20 , and further, the individual electrodes  23   b  and the signal flexible boards  90  are connected with the ACF, thereby further suppressing the radiation of the thermal energy of the heat generation sections  22   a , thus the thermal efficiency can further be improved. Further, in the thermal head  2 , since the thermal energy of the heat generation sections  22   a  can be prevented from being radiated to the side of the signal flexible boards  90  via the individual electrodes  23   b  by connecting them with the ACF, the semiconductor chips  91  disposed on the signal flexible boards  90  can be protected from the heat. 
     It should be noted that the electrical connection between the connection terminals  92  and the individual electrodes  23   b  can be made by electrically connecting with a material containing resin and having low thermal conductivity such as a conductive paste instead of the film  95  such as the ACF. Further, in the thermal head  2 , it can be arranged that the semiconductor chips  91  are disposed outside. 
     Still further, in the thermal head  2 , it can also be arranged that by making insulating members intermediate between the heat radiation member  50  and the rigid board  70 , the power supply flexible boards  80 , or the signal flexible boards  90 , electrical contact and mechanical contact between the heat radiation member  50  and the semiconductor chip  91 , and the rigid board  70  and the heat radiation member  50  are prevented. 
     As described above, according to the thermal head  2 , by disposing the semiconductor chips  91  having the shift register  93  for converting a serial signal into a parallel signal on the signal flexible boards  90  for electrically connecting the individual electrodes  23   b  of the head section  20  and the control circuit of the rigid board  70 , serial transmission can be used between the rigid board  70  and the signal flexible boards  90 , thus the number of electrical connection points can be reduced. 
     According to the thermal head  2  having the configuration described above, the rigid board  70  can freely be disposed around the head section  20  by connecting the head section  20  and the rigid board  70  with the power supply flexible boards  80  and signal flexible boards  90 . As shown in  FIGS. 3 and 18 , in the thermal head  2 , the semiconductor chips  91  are faced the second notch  54  of the heat radiation member  50 , and the power supply flexible boards  80  and the signal flexible boards  90  are bent along the inclined section  52  of the heat radiation member  50  so that the semiconductor chips  91  come inside, thus the rigid board  70  is positioned in the first notch  53  of the heat radiation member  50 . Thus, in the thermal head  2 , miniaturization can be achieved by disposing the rigid board  70  on the side face of the heat radiation member  50 , and accordingly, the whole printing device  1  can be downsized. Therefore, with the thermal head  2 , downsizing required to the printing device  1 , particularly to home-use printing devices can be realized. 
     Further, in the thermal head  2 , the head section  20  can simply be provided on the heat radiation member  50  via the adhesive layer  60 , the configuration can be simplified, and it can easily be manufactured, thus the production efficiency can be improved. Further, in the thermal head  2 , the semiconductor chips  91  can be protected from static electricity by disposing the semiconductor chips inside. 
     In the thermal head  2 , miniaturization is possible by disposing the semiconductor chips  91  inside, and disposing the rigid board  70  on the side face of the heat radiation member  50 , and accordingly, as shown in  FIGS. 1 and 2 , the ribbon guide  6   a  in the entrance side of the print medium  4  can be disposed closer to the thermal head  2 . Thus, the printing device  1  using the thermal head  2  can guide the ink ribbon  3  and the print medium  4  to a position immediately before entering the gap between the thermal head  2  and the platen  5 , thus it is possible to make the ink ribbon  3  and the print medium  4  appropriately enter the gap between the thermal head  2  and the platen  5 . Therefore, in the printing device  1 , since it is possible to make the ink ribbon  3  and the print medium  4  appropriately enter the gap between the thermal head  2  and the platen  5 , it becomes that the ink ribbon  3  and the print medium  4  make substantially the right angle with the thermal head  2 , thus the thermal energy of the thermal head  2  is appropriately applied to the ink ribbon  3 . Further, since the thermal head  2  can be made compact, freedom can be provided to the design of the running path of the ink ribbon  3  and the print medium  4  running near by the thermal head  2 . 
     Further, since the semiconductor chips  91  are provided on the signal flexible boards  90  in the thermal head  2 , the semiconductor chips  91  can be eliminated from the glass layer  21  of the head section  20 , thus the glass layer  21  can be made smaller, and accordingly the cost can be reduced. 
     As shown in  FIGS. 1 and 2 , when printing images or characters, the printing device  1  using the thermal head  2  described above runs the ink ribbon  3  and the print medium  4  between the thermal head  2  and the platen  5  while pressing the ink ribbon  3  and the print medium  4  against the thermal head by the platen  5 . 
     In this case, although force as strong as 45 kg per unit area is applied to the thermal head  2  from the platen  5 , by forming the groove section  26  of the glass layer  21  so as to rise substantially vertically and forming the both end corners  31   b  on the side of the leading end  31  to have circular arc shapes as described above and shown in  FIGS. 5A and 5B , by forming the protruding section  25  so as to have a substantially even thickness as shown in  FIGS. 8A and 8B , by providing the first reinforcement sections  32  and the second reinforcement sections  33  on the both ends in the length direction of the head section  20  as shown in  FIGS. 11A and 11B , or by adding filler to the adhesive layer  60  between the head section  20  and the heat radiation member  50  as shown in  FIG. 19 , the physical strength is improved, thus preventing deformation and breakage of the glass layer  21  caused by the pressure from the platen  5 . 
     Then, the color material of the ink ribbon  3  is thermal-transferred to the print medium  4  running between the thermal head  2  and the platen  5 . When performing the thermal transfer of the color material, the serial signal corresponding to the print data and transmitted to the control circuit of the rigid board  70  is converted into the parallel signal by the shift registers  93  of the semiconductor chips  91  provided to the signal flexible boards  90 , the parallel signals thus converted are latched, and the on/off time period for the switching element  94  provided for every individual electrode  23   b  are controlled with the latched parallel signals. In the thermal head  2 , when the switching element  94  is switched on, a current flows through the heat generation section  22   a  connected to the switching element  94  for a predetermined period of time, the heat generation section  22   a  generates heat, and the thermal energy thus generated is applied to the ink ribbon  3 , thus the color material is sublimated to be thermal-transferred to the print medium  4 . When the switching element  94  is switched off, the current flowing through the heat generation section  22   a  connected to the switching element stops, since the heat generation section  22   a  stops generating the heat, the thermal energy is not applied to the ink ribbon  3 , and accordingly the color material is not thermal-transferred to the print medium  4 . In the printing device  1 , the serial signal for every one line of the print data is transmitted from the control circuit of the thermal head  2  to the semiconductor chips  91  of the signal flexible boards  90 , and the yellow color material is thermal-transferred to the image forming section by repeating the operation described above. After thermal-transferring the yellow color material, the magenta and cyan color materials and the laminate film are sequentially thermal-transferred to the image forming section in the similar manner, thus a frame of image is printed. 
     When the color material of the ink ribbon  3  is thermal-transferred, since the groove section  26  having a width W 1  equal to or larger than the length L 1  of the heat generation section  22   a  is provided to the glass layer  21  of the head section  20  of the thermal head  2 , it is difficult for the thermal energy generated by the heat generation section  22   a  to be radiated to the side of the glass layer  21 , and it is also difficult for the thermal energy stored in the heat storage section  27  of the glass layer  21  to be radiated to the peripheral section  28  of the groove section  26 , thus the amount of heat to the ink ribbon  3  increases. Further, in the thermal head  2 , by forming the curvature radius R 2  of the both sides  25   b  of the protruding section  25  of the glass layer  21  smaller than the curvature radius R 1  of the central portion  25   a  thereof, it becomes further difficult for the thermal energy stored in the heat storage section  27  to be radiated to the peripheral section  28 . Thus, in the thermal head  2 , it becomes easy to raise the temperature of the heat generation section  22   a  with the thermal energy stored in the heat storage section  27  of the glass layer  21 . From the fact described above, the thermal head  2  has preferable thermal efficiency. Further, in the thermal head  2 , since the heat storage capacity of the glass layer  21  is reduced by providing the groove section  26  in the glass layer  21 , when the heat generation section  22   a  does not generate heat, the temperature drops rapidly, thus preferable response can be obtained. Thus, since the printing device  1  can obtain preferable thermal efficiency and response, it can print high quality images and characters with reduced power consumption at high speed. 
     As described above, since the thermal head  2  can be made smaller, does not cause deformation or breakage of the glass layer  21  by the pressure from the platen  5 , and has preferable thermal efficiency and response, it can print high quality images and characters with reduced power consumption at high speed even in the home-use printing device  1 . 
     It should be noted that although the thermal head  2  is exemplified in the case of printing postcards with the home-use printing device  1 , it is not limited to the home-use printing device  1 , but can be applied to a business-use printing device, the size is not particularly limited, it can also be applied to L-size photo paper or plain paper in addition to the postcards, and it can achieve high speed printing even in these cases. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.