Patent Publication Number: US-2004042172-A1

Title: Electronic apparatus comprising heat generating element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-249201, filed Aug. 28, 2002, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to an electronic apparatus comprising a heat generating element, e.g. a semiconductor package.  
       [0004] 2. Description of the Related Art  
       [0005] There have been smaller functional differences among various types of electronic apparatuses such as portable computers. Users have paid more attention to outward design as well as functions in selecting an electronic apparatus. Thus, users have recently been more interested in the appearance and design of electronic apparatuses.  
       [0006] Among such electronic apparatuses are reversible temperature-sensing color changing cellular telephones published in Jpn. Pat. Appln. KOKAI Publication No. 2002-64603. One of the cellular telephones described in this publication is provided with a reversible temperature-sensing color changing layer on at least a part of its outer surface. Another cellular telephone described in this publication has a reversible thermal color changing pigment dispersed in at least a part of a plastic member constituting an outer case. These cellular telephones appear finer by thermally changing the color of their own outer surface.  
       [0007] With the former of these cellular telephones which is provided with the reversible temperature-sensing color changing layer on its outer surface, the user can directly touch the reversible temperature-sensing color changing layer. Accordingly, as this cellular telephone is repeatedly used, the reversible temperature-sensing color changing layer may be released or have its performance degraded. On the other hand, with the latter cellular telephone that has the reversible thermal color changing pigment dispersed in the plastic member, it is necessary to provide, for example, a facility that disperses the reversible thermal color changing pigment in plastics in order to manufacture this cellular telephone. Consequently, this cellular telephone requires high manufacturing costs.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008] Embodiments of the present invention are provided an electronic apparatus with color changing layer inside the display housing.  
       [0009] According to an embodiment of the present invention, an electronic apparatus has an electronic comprising: a main unit having a heat generating element; a heat receiving portion provided in the main unit and thermally connected to the heat generating element; a display unit supported to the main unit and having a display housing and a display panel provided to the display housing; a heat radiating portion provided in the display housing, to radiate heat generated by heat generating element; and a circulation path to circulate a liquid coolant between the heat receiving portion and the heat radiating portion; a light transmitting portion provided in a part of an area corresponding to the heat radiating portion of the display housing; and a color changing layer provided in a part of an area located inside the display housing and corresponding to the heat radiating portion, the color changing layer changing its own color or color tone at a temperature of the heat radiating portion.  
       [0010] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.  
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0011] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
     [0012]FIG. 1 is a perspective view of a portable computer according to a first embodiment of the present invention as viewed from its front;  
     [0013]FIG. 2 is an exploded perspective view of the portable computer according to the first embodiment of the present invention, showing the positional relationship of a cooling unit;  
     [0014]FIG. 3 is a sectional view of the portable computer according to the first embodiment of the present invention, showing the positional relationship of a cooling unit;  
     [0015]FIG. 4 is a sectional view showing that a heat receiving portion integrated with a pump is fixed to a printed circuit board via a holding member according to first embodiment of the present invention;  
     [0016]FIG. 5 is a sectional view of a heat radiating portion according to the first embodiment of the present invention;  
     [0017]FIG. 6 is a perspective view of the portable computer according to the first embodiment of the present invention as viewed from its rear;  
     [0018]FIG. 7 is a sectional view of a display unit according to the first embodiment of the present invention;  
     [0019]FIG. 8 is a perspective view of a portable computer according to a second embodiment of the present invention as viewed from its rear;  
     [0020]FIG. 9 is a sectional view of a display unit according to the second embodiment of the present invention;  
     [0021]FIG. 10 is a perspective view of a portable computer according to a third embodiment of the present invention as viewed from its rear;  
     [0022]FIG. 11 is a sectional view of a display unit according to the third embodiment of the present invention;  
     [0023]FIG. 12 is a perspective view of a portable computer according to a fourth embodiment of the present invention as viewed from its rear;  
     [0024]FIG. 13 is a sectional view of a display unit according to the fourth embodiment of the present invention;  
     [0025]FIG. 14 is a perspective view of a portable computer according to a fifth embodiment of the present invention as viewed from its rear;  
     [0026]FIG. 15 is a sectional view of a display unit according to the fifth embodiment of the present invention;  
     [0027]FIG. 16 is a perspective view of a part of a portable computer according to a sixth embodiment of the present invention as viewed from its front;  
     [0028]FIG. 17 is a sectional view of a part of a housing which is close to a palm rest according to the sixth embodiment of the present invention;  
     [0029]FIG. 18 is a perspective view of a part of a portable computer according to a seventh embodiment of the present invention as viewed from its front; and  
     [0030]FIG. 19 is a sectional view of a housing and a keyboard according to the seventh embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0031] A first embodiment of the present invention will be described below with reference to FIGS.  1  to  7 .  
     [0032]FIG. 1 discloses a portable computer  1  as an electronic apparatus. The portable computer  1  comprises a main unit  2  and a display unit  3 .  
     [0033] As shown in FIG. 1, the main unit  2  has a flat box-shaped housing  10 . The housing  10  comprises a bottom wall  10   a , a top wall  10   b , a front wall  10   c , a right and left side walls  10   d , a rear wall  10   e . The top wall  10   b  has a palm rest  11  and a keyboard mounting portion  12 . The keyboard mounting portion  12  is located behind the palm rest  11 . A keyboard  13  is mounted on the keyboard mounting portion  12 .  
     [0034] The top wall  10   b  has a display supporting portion  14  behind the keyboard mounting portion  12 . The display supporting portion  14  extends upward from a rear end of the top wall  10   b  and in a width direction of the housing  10 . The display supporting portion  14  has a pair of dimples  14   a  and  14   b . The dimples  14   a  and  14   b  are spaced from each other in the width direction of the housing  10 .  
     [0035] As shown in FIGS. 2 and 3, the display unit  3  comprises a liquid crystal display panel  20  as a display panel and a flat box-shaped display housing  21  that accommodates the liquid crystal display panel  20 . The liquid crystal display panel  20  has a screen  20   a  that displays an image on its front surface.  
     [0036] The display housing  21  comprises a mask  22  and a cover  23  (see FIG. 7). Specifically, the mask  22  has a front wall  22   a  having an opening  24  and four side walls  22   b . The cover  23  has a rear wall  23   a  and four side walls  23   b . The mask  22  and the cover  23  are combined together so that the side wall  22   b  and the side wall  23   a  are directed inward and so that the front wall  22   a  and the rear wall  23   a  are arranged opposite each other. The mask  22  and the cover  23  form the display housing  21 . The liquid crystal display panel  20  is accommodated in the display housing  21  so that its periphery is held by a rubber frame  26 . The screen  20   a  of the liquid crystal display panel  20  is exposed from the display housing  21  through the opening  24 .  
     [0037] The display housing  21  has a pair of leg portions  27   a  and  27   b  projecting from one end of it. The leg portions  27   a  and  27   b  each constitute a hollow portion and are spaced from each other in the width direction of the display housing  21 . The leg portions  27   a  and  27   b  are inserted into the dimples  14   a  and  14   b , respectively, in the display supporting portion  14 . The leg portions  27   a  and  27   b  are connected to the housing  10  via a hinge device not shown in the drawings.  
     [0038] Thus, the display unit  3  is supported to the main unit  2  so as to move rotatively between a closed position in which it is brought down to cover the keyboard  13  from above and an opened position in which it is brought up to exposed the keyboard  13  and the screen  20   a.    
     [0039] As shown in FIGS. 2 and 3, the housing  10  accommodates a printed circuit board  30 , a hard disk drive device  34 , and a battery pack  35 . The printed circuit board  30 , the hard disk drive device  34 , and the battery pack  35  are arranged on the inner surface of the bottom wall  10   a  of the housing  10 .  
     [0040] As shown in FIG. 4, a semiconductor package  31  as a heat generating element is mounted on the top surface of the printed circuit board  30 . The semiconductor package  31  constitutes a microprocessor acting as a core of the portable computer  1  and is located behind the printed circuit board  30 . The semiconductor package  31  has a base substrate  32  and an IC chip  33  arranged in a central portion of the top surface of the base substrate  32 .  
     [0041] The IC chip  33  generates a very large amount of heat because of its constantly increased processing speed and its constantly increased number of functions. Consequently, the IC chip  33  must be cooled in order to operate stably. Thus, a liquid-cooling-type cooling unit  40  is mounted on the portable computer  1  to cool the semiconductor package  31 .  
     [0042] As shown FIGS.  2  to  5 , the cooling unit  40  comprises a rotary pump  41  integrated with a heat receiving portion  41   a , a heat radiating portion  48 , and a circulation path  53 . As shown in FIG. 4, the heat receiving portion  41   a  is composed of a metal plate larger than the base substrate  32  of the semiconductor package  31  and covers the IC chip  33  from above. The IC chip  33  is thermally connected to a central portion of the bottom surface of the heat receiving portion  41   a  via conductive grease not shown in the drawings.  
     [0043] The pump  41  comprises an impeller  42  and a pump housing  43 . The impeller  42  is supported on the pump housing  43  via a flat motor  45 . The flat motor  45  rotates the impeller  42 , for example, when the portable computer  1  is powered on or when the temperature of the semiconductor package  31  reaches a predetermined temperature. The pump housing  43  has a pump chamber  44  and a refrigerant inlet  46  and a refrigerant outlet  47  both connected to the pump chamber  44 . The impeller faces the pump chamber  44 .  
     [0044] As shown in FIGS. 2 and 3, the heat radiating portion  48  is accommodated inside the display housing  21 . In the present embodiment, the heat radiating portion  48  is accommodated between the cover  23  of the display housing  21  and the liquid crystal display panel  20 . The heat radiating portion  48  is shaped like a rectangular plate having a size substantially equivalent to that of the liquid crystal display panel  20 .  
     [0045] Further, as shown in FIGS. 2, 3, and  5 , the heat radiating portion  48  comprises a first heat radiating plate  49  and a second heat radiating portion  50 . The first and second heat radiating portions  49  and  50  are composed of a highly conductive metal material and laid on top of each other. The first heat radiating portion  49  has a bulging portion  49   a  projected from it in a direction opposite to the second heat radiating plate  50 . The bulging portion  49   a  is formed to meander almost all over the surface of the first heat radiating plate. An opening end of the bulging portion  49   a  is closed by the second heat radiating portion  50 . Thus, the bulging portion  49   a  of the first heat radiating portion  49  constitutes a circulation channel  100  between the first heat radiating plate  49  and the second heat radiating plate  50 .  
     [0046] As shown in FIG. 3, the heat radiating portion  48  has a refrigerant inlet  51  and a refrigerant outlet  52 . The refrigerant inlet  51  is located at the left end (the left of FIG. 3) of the heat radiating portion  48  to connect to an upstream end of a circulation channel  100 . The refrigerant inlet  51  is located adjacent to the left leg portion  27   a . The refrigerant outlet  52  is located at the right end (the right of FIG. 3) of the heat radiating portion  48  to connect to a downstream end of the circulation channel  100 . The refrigerant outlet  52  is located adjacent to the right leg portion  27   b . Thus, the refrigerant inlet  51  and the refrigerant outlet  52  are spaced from each other in the width direction of the display housing  21 .  
     [0047] The circulation path  53  circulates a liquid refrigerant between the heat receiving portion  41   a  and the circulation channel  100  in the heat radiating portion  48 . As shown in FIGS. 2 and 3, the circulating path  53  comprises a first line  54  and a second line  55 . The first line  54  is extended between the main unit  2  and the display unit  3  to connect the refrigerant outlet  47  of the pump housing  43  to the refrigerant inlet  51  of the heat radiating portion  48 . The first line  54  is guided from the interior of the housing  10  through the inside of the display supporting portion  14  and left leg portion  27   a  to the interior of the display housing  21 . The second line  55  is extended between the main unit  2  and the display unit  3  to connect the refrigerant inlet  46  of the pump housing  43  to the refrigerant outlet  52  of the heat radiating portion  48 . The second line  55  is guided from the interior of the housing  10  through the inside of the display supporting portion  14  and right leg portion  27   b  to the interior of the display housing  21 .  
     [0048] The pump chamber  44 , the refrigerant path  100 , and the circulating path  53  are filled with a coolant as a liquid refrigerant. The coolant is, for example, an antifreeze solution consisting of an aqueous solution of ethylene glycol to which a corrosion inhibiter is added as required.  
     [0049] As shown in FIGS.  2  to  4 , the pump  41 , integrated with the heat receiving portion  41   a , is pressed against the semiconductor package  31  via a cross-shaped spring member  56  having four leg portions  56   b . That is, a central portion  56   a  of the spring member  56  is pressed against the pump  41  owing to the elasticity of the leg portion  56   b  by fixing the leg portions  56   b  of the spring member  56  to four boss portions  57  on the printed circuit board  30  using screws  58 . Accordingly, the heat radiating portion  41   a  finely contacts and is thermally connected to the IC chip  33  of the semiconductor package  31 .  
     [0050] The display housing  21  is provided with a light transmitting portion  60   a  in association with at least a part of the area corresponding to the heat radiating portion  48 , the transmitting portion  60   a  being formed of a transparent member. In the first embodiment, the cover of the display housing  21  is formed of a transparent member so that the light transmitting portion  60   a  is composed of almost all the area corresponding to the heat radiating portion  48  (see FIGS. 6 and 7).  
     [0051] Further, a reversible temperature-sensing color changing layer  61   a  is provided inside the display housing  21  in association with at least a part of the area corresponding to the heat radiating portion  48 . The reversible temperature-sensing color changing layer  61   a  reversibly changes its own color or color tone at a predetermined temperature. In the portable computer  1 , the reversible temperature-sensing color changing layer  61   a  is provided on the inner surface of the rear wall  23   a  of the cover  23  in association with almost all the area of the heat radiating portion  48 , the rear wall  23   a  constituting the light transmitting portion  60   a  (see FIGS. 6 and 7). For easy understanding, in FIG. 6, the area in which the reversible temperature-sensing color changing layer  61   a  is provided is shown with a dotted pattern. The reversible temperature-sensing color changing layer  61   a  may be provided not only on the inner surface of the rear wall  23   a  of the cover  23  but also on the inner surfaces of the four side walls  23   b.    
     [0052] The cover  23  and the reversible temperature-sensing color changing layer  61   a  may be formed, for example, in the manner described below.  
     [0053] The cover  23  is molded using a colorless and transparent acrylonitrile-butadiene-styrene copolymer resin (ABS resin). The reversible temperature-sensing color changing layer  61   a  is formed using a paint obtained by uniformly dispersing a thermal-discoloring-type reversible thermal color changing pigment that has no color at 29° C. or higher and turns black at 27° C. or lower, a thermal-discoloring-type reversible thermal color changing pigment that has no color at 35° C. or higher and turns pink at 33° C. or lower, a blue pigment, a vinyl chloride-vinyl acetate copolymer resin, an oily acrylic resin (45% of solids contents; toluene and ethyl acetate are used as a solvent), methyl isobutyl ketone, and xylene at the following ratio:  
     30:15:3:30:30:15:15  (1).  
     [0054] This paint is sprayed on the inner surface of the rear wall  23   a  of the cover  23  so that the reversible temperature-sensing color changing layer  61   a  has a thickness of 40 μm. Subsequently, the layer  61   a  is dried and hardened at 40° C. for ten minutes. Thus, the cover  23  and the reversible temperature-sensing color changing layer  61   a  are formed.  
     [0055] The reversible temperature-sensing color changing layer  61   a  thus formed turns black at 27° C. or lower, purple between 28 and 34° C., and blue at 35° C. or higher.  
     [0056] The reversible temperature-sensing color changing layer  61   a  may be formed on the inner surface of the rear wall  23   a  by forming a reversible temperature-sensing color changing layer on a transparent film consisting of a transparent resin or the like and then sticking this film to the inner surface of the rear wall  23   a  of the cover  23 .  
     [0057] With this configuration, the IC chip  33  of the semiconductor package  31  generates heat while the portable computer  1  is being operated. Heat from the IC chip  33  is transmitted to the pump housing  43  via the heat receiving portion  41   a . The pump housing  43  has the pump chamber  44  filled with the coolant. Accordingly, the coolant absorbs much of the heat transmitted to the pump housing  43 .  
     [0058] When the impeller  42  is rotated, the coolant in the pump chamber  44  is fed to the heat radiating portion  48  via the first line  54 . The coolant is then forcibly circulated between the pump chamber  44  and the circulation channel  100  in the heat radiating portion  48 .  
     [0059] Specifically, the coolant heated by heat exchange with the pump chamber  44  is fed to the heat radiating portion  48  via the first line  54 . The coolant then flows through the circulation channel  100 , bent to meander. During this flow, the heat from the IC chip absorbed by the coolant is diffused to the first and second heat radiating plates  49  and  50 . The heat is then radiated from the surfaces of the heat radiating plates  49  and  50 .  
     [0060] The coolant cooled while passing through the circulation channel  100  is returned to the pump chamber  44  through the second line  55 . The coolant absorbs heat from the IC chip  33  again while flowing through the pump chamber  44 . It is then fed to the heat radiating portion  48 . This cycle is repeated to release the heat from the IC chip  33  to the exterior of the portable computer  1  through the heat radiating portion  48  in the display housing  21 .  
     [0061] The reversible temperature-sensing color changing layer  61   a  is black at room temperature. When heat is radiated from the surfaces of the heat radiating plates  45  and  50  of the heat radiating portion  48 , this radiated heat heats the reversible temperature-sensing color changing layer  61   a . The reversible temperature-sensing color changing layer  61   a  turns purple at 28° C. or higher. Furthermore, it turns blue at 35° C. or higher. In this regard, the temperature of the reversible temperature-sensing color changing layer  61   a  is balanced at a certain point and does not increase far above 35° C.  
     [0062] Further, when the heat stops being radiated from the surfaces of the heat radiating plates  49  and  50 , the reversible temperature-sensing color changing layer  61   a  is cooled to return to the room temperature. The reversible temperature-sensing color changing layer  61   a  turns purple at 34° C. or lower. Furthermore, the reversible temperature-sensing color changing layer  61   a  turns black at 27° C. or lower. These changes in the color of the reversible temperature-sensing color changing layer  61   a  are seen from the exterior of the portable computer  1  through the light transmitting portion  60   a , i.e. the cover  23 , composed of the transparent member.  
     [0063] As described above, according to the portable computer  1 , the color or color tone of the reversible temperature-sensing color changing layer  61   a  is varied owing to changes in the temperature of the inside of the display housing  1  caused by heat radiated by the heat radiating portion  48 . These changes in the color or color tone of the reversible temperature-sensing color changing layer  61   a  are externally seen through the light transmitting portion  60   a  of the display housing  21 . Specifically, according to the portable computer  1 , after the computer  1  has been simply activated, the appearance of the display housing  21  is varied during operation without the need for the user to perform any special operations. This provides an attractive and well-designed portable computer  1 .  
     [0064] Furthermore, according to the portable computer  1 , the reversible temperature-sensing color changing layer  61   a  is provided inside the display housing  21 . Consequently, the user does not directly touch the reversible temperature-sensing color changing layer  61   a  when using or carrying the portable computer  1 . This suppresses degradations such as the release of the reversible temperature-sensing color changing layer  61   a  and the degradation of performance. Further, the computer maintains a fine appearance.  
     [0065] Moreover, in the portable computer  1 , the reversible temperature-sensing color changing layer  61   a  is provided on the housing (the inner surface of the rear wall  23   a  of the cover  23 ) by spraying a paint or sticking a film on which the reversible temperature-sensing color changing layer  61   a  is formed. This eliminates the need for a cumbersome operation of dispersing a reversible thermal color changing pigment in a plastic member when providing the reversible temperature-sensing color changing layer  61   a  on the housing  10 . It is thus possible to reduce manufacturing costs.  
     [0066] The present invention is not limited to the first embodiment. A second embodiment of the present invention will be described below with reference to FIGS. 8 and 9.  
     [0067] The second embodiment is different from the first embodiment in the area in which the light transmitting portion is provided and in the area in which the reversible temperature-sensing color changing layer is provided. The other basic arrangements of the portable computer  1  are similar to those of the first embodiment. Thus, in the second embodiment, the same components as those of the first embodiment are denoted by the same reference numerals. Their description is omitted.  
     [0068] The cover  23  of the display housing  21  is formed of, for example, a colored opaque resin. Further, an opening  25  is formed in the rear wall  23   a  of the cover  23  in association with a part of the area corresponding to the heat radiating portion  48  so that the bulging portion  49   a  on the first heat radiating plate  49  is exposed from the opening  25 . A panel-like light transmitting portion  60   b  formed of a transparent member, e.g., a colorless transparent resin or glass, is fitted into the opening  25 .  
     [0069] A reversible temperature-sensing color changing layer  61   b  is not provided all over the surface of the light transmitting portion  60   b  but on a part of it so as to show characters or a pattern. In the portable computer  1 , the reversible temperature-sensing color changing layer  61   b  is provided to show, for example, the characters “ABC”. For easy understanding, in FIG. 8, the area in which the reversible temperature-sensing color changing layer  61   b  is provided is shown with a dotted pattern.  
     [0070] The reversible temperature-sensing color changing layer  61   b  can be formed by, for example, silk screen printing or the like to print directly and then dry the inner surface of the light transmitting portion  60   b  or forming a reversible temperature-sensing color changing layer all over the surface of a transparent film consisting of a transparent resin or the like, cutting the film into the form of desired characters, and sticking the characters obtained onto the inner surface of the light transmitting portion  60   b.    
     [0071] The color or color tone of the portable computer  1  is varied owing to changes in the temperature of the inside of the display housing  1  caused by heat radiated by the heat radiating portion  48 . These changes in the color or color tone are externally seen through the light transmitting portion  60   b , formed of the transparent member. This provides a fine-appearing and well-designed portable computer  1 .  
     [0072] Further, a member may be provided between the reversible temperature-sensing color changing layer  61   b  and the heat radiating portion  48  to conceal the heat radiating portion  48  from the exterior.  
     [0073] Furthermore, the characters can be made to appear at a predetermined temperature by selecting as a paint forming the reversible temperature-sensing color changing layer  61   b , for example, a reversible temperature-sensing color changing paint that has no color at a temperature lower than the predetermined one and assumes a certain color at this predetermined temperature or higher.  
     [0074] Moreover, the characters can be made to disappear at a predetermined temperature by selecting as a paint forming the reversible temperature-sensing color changing layer  61   b , for example, a reversible temperature-sensing color changing paint that assumes a certain color at a temperature lower than the predetermined one and become colorless at this predetermined temperature or higher.  
     [0075] Now, a third embodiment of the present invention will be described with reference to FIGS. 10 and 11.  
     [0076] The third embodiment differs from the first embodiment, described above, in the area in which the light transmitting portion is provided and in the area in which the reversible temperature-sensing color changing layer is provided. The other basic arrangements of the portable computer  1  are similar to those of the first embodiment. Thus, in the third embodiment, the same components as those of the first embodiment are denoted by the same reference numerals. Their description is omitted.  
     [0077] The cover  23  of the display housing  21  is formed of, for example, a colored opaque resin. Further, the opening  25  is formed in the rear wall  23   a  of the cover  23  in association with a part of the area corresponding to the heat radiating portion  48  so that the bulging portion  49   a  on the first heat radiating plate  49  is exposed from the opening  25 . A panel-like light transmitting portion  60   c  formed of a transparent member, e.g. a colorless transparent resin or glass is fitted into the opening  25 .  
     [0078] Further, as shown in FIG. 11, a reversible temperature-sensing color changing layer  61   c  is provided on the outer surface of the circulation channel  100  formed between the bulging portion  49   a  of the first heat radiating plate  49  and the second heat radiating plate  50 , i.e., on the outer surface of the bulging portion  49   a . For easy understanding, in FIG. 10, the area in which the reversible temperature-sensing color changing layer  61   c  is provided is shown with a dotted pattern.  
     [0079] The color or color tone of the portable computer  1  is varied owing to changes in the temperature of the outer surface of the circulation channel  100  caused by heat radiated by the heat radiating portion  48 . These changes in the color or color tone are externally seen through the light transmitting portion  60   c  formed of the transparent member. This provides an attractive and well-designed portable computer  1 .  
     [0080]FIGS. 12 and 13 disclose a fourth embodiment of the present invention.  
     [0081] The fourth embodiment differs from the first embodiment, described above, in the form of the light transmitting portion and in the area in which the reversible temperature-sensing color changing layer is provided. Thus, in the fourth embodiment, the same components as those of the first embodiment are denoted by the same reference numerals. Their description is omitted.  
     [0082] The cover  23  of the display housing  21  is formed of, for example, a colored opaque resin. Further, the opening  25  is formed in the rear wall  23   a  of the cover  23  in association with a part of the area corresponding to the heat radiating portion  48  so that the bulging portion  49   a  on the first heat radiating plate  49  is exposed from the opening  25 . A light transmitting portion  60   d  is fitted into the opening  25 . The light transmitting portion  60   d  is composed of a panel formed of a colored opaque resin or the like and in which a plurality of hole portions  62  are formed. The hole portions  62  are each sized so that the user&#39;s fingers do not slip into the hole portions  62 . The opening  25  in the rear wall  23   a  of the cover  23  may be omitted with the hole portions  62  formed directly in the rear wall  23 .  
     [0083] Further, as shown in FIG. 13, the reversible temperature-sensing color changing layer  61   d  is provided on the outer surface of the circulation channel  100  formed between the bulging portion  49   a  of the first heat radiating plate  49  and the second heat radiating plate  50 , i.e., on the outer surface of the bulging portion  49   a . For easy understanding, in FIG. 12, the area in which the reversible temperature-sensing color changing layer  61   c  is provided is shown with a dotted pattern.  
     [0084] The color or color tone of the portable computer  1  is varied owing to changes in the temperature of the outer surface of the circulation channel  100  caused by heat radiated by the heat radiating portion  48 . These changes in the color or color tone are externally seen through the hole portions  62  in the light transmitting portion  60   d  formed. This provides an attractive and well-designed portable computer  1 .  
     [0085] Further, in the portable computer  1 , the hole portions  62  are each sized so that the user&#39;s fingers do not slip into the hole portions  62 . Accordingly, the user does not directly touch the reversible temperature-sensing color changing layer  61   d . This suppresses the degradation of the reversible temperature-sensing color changing layer  61   d  to keep the computer  1  appearing attractive.  
     [0086] Furthermore, according to the portable computer  1 , the plurality of hole portions  62  are located opposite the heat radiating portion  48 . Consequently, heat radiated from the surface of the heat radiating portion  48  can be efficiently radiated to the exterior of the display housing  1  through the hole portions  62 . This hinders heat from remaining between the heat radiating plate and the rear wall  23   a.    
     [0087] In the fourth embodiment, the light transmitting portion  60   d  is composed of the panel formed of a colored opaque resin or the like and in which the plurality of hole portions  62  are formed. The light transmitting portion  60   d  may be composed of a panel formed of a colorless transparent resin or the like and in which the plurality of hole portions  62  are formed. Alternatively, the light transmitting portion  60   d  may be composed of a panel formed of a colored transparent resin or the like and in which the plurality of hole portions  62  are formed. In this case, the color observed through the holes is that of the reversible temperature-sensing color changing layer  61   d , whereas the color observed in the areas other than the hole portions  62  is a mixture of the colors of the light transmitting portion  60   d  and the reversible temperature-sensing color changing layer  61   d.    
     [0088] Now, a fifth embodiment of the present invention will be described with reference to FIGS. 14 and 15.  
     [0089] The cover  23  of the display housing  21  is formed of, for example, a colored opaque resin. Further, the opening  25  is formed in the rear wall  23   a  of the cover  23  in association with a part of the area corresponding to the heat radiating portion  48  so that the bulging portion  49   a  on the first heat radiating plate  49  is exposed from the opening  25 . A panel  64  having a plurality of dimples  63  formed in its outer surface is fitted in the opening  25 . The panel  64  is formed of, for example, a colored opaque resin. The pluralities of dimples  63  are each sized so that the user&#39;s fingers do not slip into the dimples  63 . The opening  25  in the rear wall  23   a  of the cover  23  may be omitted with the dimples  63  formed directly in the rear wall  23 . The other arrangements are the same as those of the first embodiment, described above. Thus, duplicate description is omitted by using, in FIGS. 15 and 16, the same reference numerals as those in the first embodiment.  
     [0090] Further, as shown in FIGS. 14 and 15, a reversible temperature-sensing color changing layer  61   e  is provided in each of the dimples  63 . For easy understanding, in FIG. 14, the area in which the reversible temperature-sensing color changing layer  61   e  is provided is shown with a dotted pattern.  
     [0091] The color or color tone of the dimples  63  is varied owing to changes in the temperature of the display housing  21  caused by heat radiated by the heat radiating portion  48 . This provides a fine-appearing and well-designed portable computer  1 .  
     [0092] Further, in the portable computer  1 , the dimples  63  are each sized so that the user&#39;s fingers do not slip into the dimples  63 . Accordingly, the user does not directly touch the reversible temperature-sensing color changing layer  613 . This suppresses the degradation of the reversible temperature-sensing color changing layer  61   d  to keep the computer  1  appearing attractive.  
     [0093] Furthermore, according to the portable computer  1 , the plurality of dimples  63  are formed in the panel  64 , constituting a part of the cover  23  of the display housing  21 . This makes it possible to increase the surface area of the cover  23 . Thus, with the portable computer  1 , heat radiated from the surface of the heat radiating portion  48  can be efficiently radiated to the exterior of the display housing  21 . This hinders heat from remaining between the heat radiating plate and the rear wall  23   a.    
     [0094] Now, a sixth embodiment of the present invention will be described with reference to FIGS. 16 and 17.  
     [0095] In the portable computer  1 , for example, the hard disk drive device  34  is used as a heat generating element. Further, as shown in FIGS. 16 and 17, an opening  15  a size smaller than the hard disk drive device  34  is formed in the top wall  10   b  of the housing  10  in association with the hard disk drive device  34 . A panel-like light transmitting portion  60   f  formed of a transparent member, e.g. a colorless transparent resin or glass, is fitted into the opening  15 .  
     [0096] The reversible temperature-sensing color changing layer  61   f  is provided on the inside of the housing  10 , e.g. on the inner surface of the light transmitting portion  60   f , constituting a part of the housing  10 . For easy understanding, in FIG. 16, the area in which the reversible temperature-sensing color changing layer  61   f  is provided is shown with a dotted pattern. The other arrangements are the same as those of the first embodiment, described above. Accordingly, duplicate description is omitted by using, in FIGS. 16 and 17, the same reference numerals as those in the first embodiment.  
     [0097] In the portable computer  1 , the color or color tone of the reversible temperature-sensing color changing layer  61   f  is varied owing to changes in temperature caused by heat radiated by the hard disk drive device  34 . Further, changes in the color of the reversible temperature-sensing color changing layer  61   f  are externally seen through the light transmitting portion  60   f , constituting the transparent member.  
     [0098] The housing  10  appears to change partly its own color or color tone. This provides an attractive and well-designed portable computer  1 .  
     [0099] In this embodiment, the light transmitting portion  60   f  and the reversible temperature-sensing color changing layer  61   f  are provided in association with the hard disk drive device  34 . However, the light transmitting portion  60   f  and the reversible temperature-sensing color changing layer  61   f  may be provided in association with another heat generating element such as a battery or a semiconductor package.  
     [0100] Further, in the portable computer  1 , the liquid-cooling-type cooling unit  40 , shown in the first embodiment, may be replaced with, for example, an air-cooling-type cooling unit having a heat receiving portion, a heat pipe, a heat exchanging portion, and an electric fan.  
     [0101] Furthermore, if the heat radiating portion of the cooling unit is provided in the housing  10 , the light transmitting portion  60   f  and the reversible temperature-sensing color changing layer  61   f  may be provided in association with the heat radiating portion of the cooling unit.  
     [0102]FIGS. 18 and 19 disclose a seventh embodiment of the present invention.  
     [0103] In the portable computer  1 , the liquid-cooling-type cooling unit  40 , shown in the first embodiment, is replaced with, for example, an air-cooling-type cooling unit  71  having a heat receiving portion  70 . As shown in FIG. 19, the heat receiving portion  70  is composed of a metal plate larger than the base substrate  32  of the semiconductor package  31 . The heat receiving portion  70  covers the IC chip  33  from above. The heat receiving portion  70  is thermally connected to a heat sink via a heat pump not shown in the drawings. The heat sink is disposed away from the heat receiving portion  70 . Cooling winds are blown against the heat sink via the electric fan.  
     [0104] Further, in the portable computer  1 , the keyboard  13  is located above the heat receiving portion  70 . The keyboard  13  has a plurality of key tops  13   a  and a support plate  65  that supports the key tops  13   a . Those of the key tops  13   a  which are located in an area immediately above the heat receiving portion  70  are formed of a colorless transparent resin material. These key tops  13   a  formed of the colorless transparent resin material constitute a light transmitting portion  60   g . The reversible temperature-sensing color changing layer  61   g  is provided all over the inner surfaces of the transparent key tops. FIG. 18 schematically shows, by a dotted pattern, that the color of the reversible temperature-sensing color changing layer  61   g  has been changed. The other arrangements are the same as those of the first embodiment, described above. Accordingly, duplicate description is omitted by using, in FIGS. 18 and 19, the same reference numerals as those in the first embodiment.  
     [0105] With this configuration, when the semiconductor package  31  is heated, heat from the semiconductor package  31  is transmitted to the heat receiving portion  70 . When the heat from the semiconductor package  31  is transmitted to the heat transmitting section  70 , part of the heat is radiated from the surface of the heat receiving portion  70 . The radiated heat heats and changes the color of the reversible temperature-sensing color changing layer  61   g  on the key tops  13   a  located in the area corresponding to the semiconductor package  31  (see FIG. 18). Since the key tops  13   a  having the reversible temperature-sensing color changing layer  61   g  are formed of the transparent member, the density of the color or color tone of the reversible temperature-sensing color changing layer  61   g  can be seen from outside the keyboard  13 . This provides an attractive and well-designed portable computer  1 .  
     [0106] The reversible temperature-sensing color changing layer  61   g  may be provided on the outer surfaces of the key tops  13   a  located opposite the heat receiving portion  70 . This makes it possible to change the color or color tone of the key tops  13   a  located in the area corresponding to the semiconductor package  31 .  
     [0107] Further, in this embodiment, the reversible temperature-sensing color changing layer  61   g  on the key tops  13   a  is provided in association with the heat receiving portion  70 . However, if the battery or hard disk drive device, which generates heat, is arranged below the keyboard  13 , the reversible temperature-sensing color changing layer  61   g  on the key tops  13   a  may be provided in association with the battery or hard disk drive device.  
     [0108] In the first, second, third, sixth, and seventh embodiments, the light transmitting portions  60   a ,  60   b ,  60   c ,  60   f , and  60   g  are each composed of a colorless transparent member. However, the light transmitting portions  60   a ,  60   b ,  60   c ,  60   f , and  60   g  may each be composed of a colored transparent member. In this case, the externally observed color is a mixture of the colors of the light transmitting portion  60   a ,  60   b ,  60   c ,  60   f , or  60   g  and reversible temperature-sensing color changing layer  61   a ,  61   b ,  61   c ,  61   f , or  61   g.    
     [0109] Further, in the first embodiment, three colors are made to appear by using two types of reversible temperature-sensing color changing paints and one type of pigment and changing their colors in the two temperature zones, i.e. between 27 and 28° C. and between 34 and 35° C. However, it is possible to use any number of types of reversible temperature-sensing color changing paints and pigments. Furthermore, the paint forming the reversible temperature-sensing color changing layers  61   a  to  61   g  is not limited to the paint shown in the first embodiment. A wide variety of reversible temperature-sensing color changing paints can be used.  
     [0110] The electronic apparatus according to the present invention is not limited to a portable computer. The present invention is applicable to various electronic apparatuses comprising a heat generating element.  
     [0111] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.