Abstract:
In a case of curing and bonding a liquid crystal display panel (LCD) and a translucent substrate by using an optical adhesive, in order to reduce bonding fluctuations occurring in the vicinity of a light shielding portion provided on a periphery of the translucent substrate, enhance mechanical bonding strength, and prevent deterioration of image quality, which arises from curing variations of the optical adhesive, there is provided a display device including: a display panel including a display surface; a translucent substrate opposed to the display surface; a light shielding portion provided on a periphery of a display surface side of the translucent substrate, for shielding light; and a light reflecting portion provided on a display surface side of the light shielding portion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a display device using a display panel. In particular, the present invention relates to a display device having a structure in which a translucent substrate including a light shielding portion formed on a periphery of a display surface side is bonded to a display panel. 
         [0003]    2. Description of the Related Art 
         [0004]    A liquid crystal display device (LC display device) is used in various devices such as a cellular phone, a personal digital assistant (PDA), an electronic dictionary, a car navigation system, and a music player.  FIGS. 6A and 6B  illustrate a conventionally-known liquid crystal display device.  FIG. 6A  is a plan view and  FIG. 6B  is a longitudinal sectional view. As illustrated in  FIGS. 6A and 6B , the liquid crystal display device includes a liquid crystal display panel (LCD)  62  and a translucent substrate  68  thereabove, which serves as a front plate. In the LCD  62 , a liquid crystal layer is sandwiched between two glass substrates, and polarizing plates are bonded to outer surfaces of the two glass substrates. The translucent substrate  68  is entirely transparent, and a black light shielding portion  74  shields light of an outer peripheral portion of the LCD  62  and defines a display region of the LCD  62 . The light shielding portion  74  is provided in order that an image beyond the display region may not be viewed by a user and that design aesthetics of a display portion may be improved. 
         [0005]    In such a display device as described above, a glass substrate forming the translucent substrate  68  or the LCD  62  is made thinner as the various devices become thinner (for example, thickness of 0.20 mm to 0.25 mm). Further, there are increasing demands for narrowing a gap between the LCD and the translucent substrate (for example, gap equal to or smaller than 0.2 mm). 
         [0006]    However, along with the achievement of the thinner liquid crystal display devices, the LCD  62  has become more fragile due to dropping of portable devices onto which the liquid crystal display device is mounted or due to objects fallen onto a display surface of the LCD  62 . In addition, there has been a risk that, when an air space is interposed between the LCD  62  and the translucent substrate  68 , light may be reflected on the display surface of the LCD  62  or a lower surface of the translucent substrate  68 , and hence the display surface becomes dark due to this reflection loss. 
         [0007]    For example, JP 09-274536 A discloses the method of filling a gap between the LCD  62  and the translucent substrate  68  with a transparent adhesive.  FIG. 7  is a longitudinal sectional view illustrating an end portion of the conventionally-known liquid crystal display device. A liquid crystal display device  60  has the structure in which the gap between the LCD  62  and the translucent substrate  68  which serves as the front plate is filled with a transparent adhesive  76 . In the LCD  62 , a thin film transistor (TFT) substrate  92  onto which TFTs are mounted and a color filter substrate  96  including color filters  79 R,  79 G, and  79 B formed therein are bonded to each other through a sealing agent  94 , and a liquid crystal layer  90  is sandwiched between both the substrates. A transparent electrode is formed on a liquid crystal layer  90  side of the color filter substrate  96 . A black matrix  78  is provided in the color filter substrate  96 . Polarizing plates  65  and  67  are bonded to outer surfaces of the TFT substrate  92  and the color filter substrate  96 , respectively. With this structure, the LCD  62  and the translucent substrate  68  are integrated with each other through the transparent adhesive  76 , whereby shock resistance can be increased. Further, with the use of the transparent adhesive  76  having a refractive index which is approximate to that of the translucent substrate  68  or the polarizing plate  65  ( 67 ), the reflection loss generated at an interface between the polarizing plate  67  and the transparent adhesive  76  or between the translucent substrate  68  and the transparent adhesive  76  may be reduced. 
         [0008]    As the transparent adhesive  76 , an optical adhesive of a photo curable type, which is cured by light such as ultraviolet rays or visible light, is mainly used. A heat curing adhesive which is cured by heat may be used, but is difficult to use because, for example, liquid crystals or polarizing plates are deteriorated when the heat curing adhesive is exposed to a high temperature equal to or higher than 100 degrees, or shelf life of the adhesive is short. 
         [0009]    On the other hand, a photo-curable adhesive is convenient, for example, it can be bonded under environment of room temperature. A step of curing the photo-curable adhesive as described above includes a first step of filling the gap between the LCD  62  and the translucent substrate  68  with an transparent adhesive  76  and then irradiating the transparent adhesive  76  with light such as ultraviolet rays from a translucent substrate  68  side, and a second step of irradiating the transparent adhesive  76  with light from a lateral side of the LCD  62 . Specifically, in the first step, light A 1  is emitted from the translucent substrate  68  side to cure the translucent adhesive  76  which is positioned at a translucent portion of the translucent substrate  68 . However, the transparent adhesive  76  positioned under the black light shielding portion  74  is shaded, which causes insufficient curing thereof. For this reason, in the second step, light A 2  is emitted from the lateral side of the LCD  62 . As a result, the transparent adhesive  76  positioned under the light shielding portion  74  is cured. 
         [0010]    However, in the liquid crystal display device described above, the gap between the LCD  62  and the translucent substrate  68  is small, and therefore the light A 2  is unlikely to penetrate therethrough. In addition, light absorption in the light shielding portion  74  of the translucent substrate  68  is large, and the light A 2  is propagated while being repeatedly reflected on the light shielding portion  74  to be attenuated, which involves a risk that the transparent adhesive  76  positioned in the vicinity of the light shielding portion  74  may be insufficiently cured. 
         [0011]    Further, the LCD  62  is also provided with the black matrix  78  so as to be opposed to the light shielding portion  74  of the translucent substrate  68 . For this reason, light is also absorbed in the black matrix  78 , whereby the light A 2  is further attenuated. As a result, an uncured portion of the transparent adhesive  76  is left in a lower region of the light shielding portion  74 . 
         [0012]    When an uncured portion is left in the transparent adhesive  76 , sufficient bonding strength cannot be obtained in the vicinity of the LCD  62  and the light shielding portion  74  of the translucent substrate  68 , which involves a risk that mechanical strength such as strength against falling may be impaired. 
         [0013]    Further, in the transparent adhesive  76 , a volume of the adhesive itself contracts during curing. When an uncured portion is left in the transparent adhesive  76 , an amount of the volume contraction is small in the vicinity of the light shielding portion  74 . Therefore, there is a risk that a thickness of the transparent adhesive  76  may become uneven and the LCD  62  to which the translucent substrate  68  is bonded may be deformed, which is specifically described with reference to  FIG. 8 .  FIG. 8  is an explanatory view of the conventionally-known liquid crystal display device, in which an upper stage is a plan view thereof, a middle stage is a longitudinal sectional view thereof, and a lower stage illustrates a gap between the TFT substrate  92  and the color filter substrate  96 . As illustrated in  FIG. 8 , the light shielding portion  74  for shielding light is provided on a periphery of the translucent substrate  68 . The translucent substrate  68  serving as a front plate and the LCD  62  are bonded to each other through the transparent adhesive  76 . In the LCD  62 , the TFT substrate  92  and the color filter substrate  96  are opposed to each other through the sealing agent  94  or a spacer member  98 , and the liquid crystal layer  90  is formed therebetween. When an uncured portion is left in the transparent adhesive  76  positioned under the light shielding portion  74 , an amount of the volume contraction becomes small in the vicinity of the light shielding portion  74  and becomes large in the display region. As a result, the TFT substrate  92  and the color filter substrate  96  are deformed to thereby cause fluctuations of a gap (cell gap) between the TFT substrate  92  and the color filter substrate  96 . Hence, there is a fear of deterioration of image quality in the display surface, such as display fluctuation. Particularly, a thickness of a substrate forming the LCD  62  is conventionally set to about 0.5 mm, whereas, in recent years, the thickness has been set to 0.2 mm to 0.25 mm by abrasion and thinning through etching or polishing. Accordingly, the LCD  62  is particularly likely to be affected by unevenness of the volume contraction. 
         [0014]    In response thereto, the film thickness of the light shielding portion  74  may be reduced to thereby reduce optical density and enhance transmittance from the translucent substrate side, or the light shielding portion may be configured to be a half mirror. However, when a black concentration is reduced, the end portion of the LCD  62  may be viewed from thereabove or light emitted from a backlight may be leaked from therebelow upwardly, which results in poor design aesthetics. Accordingly, the black concentration of the light shielding portion  74  is preferred to be high. 
       SUMMARY OF THE INVENTION 
       [0015]    Under the above-mentioned circumstances, an object of the present invention is, in a case of bonding a translucent substrate and a liquid crystal display panel (LCD) to each other through an optical adhesive, to reduce bonding fluctuations occurring in the vicinity of a light shielding portion provided on a periphery of the translucent substrate, enhance mechanical bonding strength, and prevent deterioration of image quality, which arises from curing variations of the optical adhesive. 
         [0016]    In order to achieve the above-mentioned object, a display device according to the present invention includes: a display panel including a display surface for displaying an image; a translucent substrate opposed to the display surface; and a black light shielding portion disposed on a periphery of a display surface side of the translucent substrate, for shielding light, in which the display panel and the translucent substrate are integrally bonded to each other through a photo-curable translucent adhesive. Further, in the display device, a light reflecting portion having high reflectance of light is disposed on the display surface side of the light shielding portion. 
         [0017]    Further, in the display device, a second light shielding portion having light shielding property is provided on a periphery of the display panel, and a second light reflecting portion having high reflectance of light is provided on the display surface side of the second light shielding portion. 
         [0018]    Further, the second light reflecting portion is provided beyond a viewing range of a user from the display surface side. 
         [0019]    According to the present invention, the mechanical bonding strength can be enhanced and the deterioration of image quality, which arises from curing variations of the optical adhesive, can be prevented. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0020]    In the accompanying drawings: 
           [0021]      FIG. 1  is a front view illustrating a liquid crystal display device according to a first embodiment of the present invention; 
           [0022]      FIG. 2  is a longitudinal sectional view illustrating the liquid crystal display device according to the first embodiment of the present invention; 
           [0023]      FIG. 3  is a longitudinal sectional view illustrating an end portion of the liquid crystal display device according to the first embodiment of the present invention; 
           [0024]      FIG. 4A  is a sectional view illustrating the liquid crystal display device according to the first embodiment of the present invention; 
           [0025]      FIG. 4B  is a sectional view illustrating a conventional liquid crystal display device; 
           [0026]      FIG. 5A  is a sectional view illustrating the liquid crystal display device according to the first embodiment of the present invention; 
           [0027]      FIG. 5B  is a sectional view illustrating the conventional liquid crystal display device; 
           [0028]      FIG. 6A  is a plan view illustrating the conventional liquid crystal display device; 
           [0029]      FIG. 6B  is a longitudinal sectional view illustrating the conventional liquid crystal display device; 
           [0030]      FIG. 7  is a longitudinal sectional view illustrating an end portion of the conventional liquid crystal display device; and 
           [0031]      FIG. 8  is an explanatory view including a sectional view of the conventional liquid crystal display device and illustrating a substrate gap. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    In the present invention, a display device includes a display panel and a translucent substrate for transmitting light. The display panel has a display surface on which an image is displayed. The translucent substrate is provided so as to be opposed to the display surface. A light shielding portion for intercepting light is provided on a periphery of the translucent substrate. A photo-curable translucent adhesive exists between the display panel and the translucent substrate in order to integrally bond to each other. A light reflecting portion is provided on a display surface side of the light shielding portion. With this structure, the translucent adhesive of the light shielding portion is brought into contact with the light reflecting portion. Accordingly, light for curing the translucent adhesive is prevented from being absorbed in the light shielding portion, and hence an uncured portion of the translucent adhesive can be reduced in the light shielding portion. 
         [0033]    Further, a second light shielding portion having light shielding property is provided also on a periphery of the display panel, and a second light reflecting portion is provided on the display surface side of the second light shielding portion so as to be opposed to the light shielding portion of the translucent substrate. With this structure, the translucent adhesive of the light shielding portion is sandwiched between the reflecting portion and the second reflecting portion. Accordingly, the light for curing the translucent adhesive is propagated between the light reflecting portion and the second light reflecting portion, whereby an uncured portion of the translucent adhesive can be reduced in the light shielding portion. 
         [0034]    Here, the second light reflecting portion is formed so as to be shaded by the light shielding portion and cannot be seen when the second light reflecting portion is observed from the display surface side. 
         [0035]    With reference to  FIGS. 1 to 5B , a description is made on the display device according to the present invention. Note that, in this embodiment, a liquid crystal display device  10  is adapted as an example of the display device. 
         [0036]      FIG. 1  is a front view illustrating the liquid crystal display device  10  according to a first embodiment of the present invention. As illustrated in  FIG. 1 , the liquid crystal display device  10  has a configuration in which a cover plate  18  is arranged on an liquid crystal display panel (LCD)  12 . The cover plate  18  has a center portion, i.e., translucent region, through which light is transmitted, and a peripheral portion, i.e., light shielding region, in which light is intercepted. From the translucent region, a user views an image displayed by the LCD  12 . The user cannot view a portion shaded by the light shielding region. 
         [0037]      FIG. 2  illustrates a cross section structure taken along a line Y of  FIG. 1 . As illustrated in  FIG. 2 , the liquid crystal display device  10  includes the LCD  12 , the cover plate  18 , a driver IC  20 , a flexible printed circuit board (FPC)  22 , and a backlight unit  24 . 
         [0038]    The LCD  12  has a thin plate-like shape. The LCD  12  includes a display surface  12   a  on which an image is displayed according to a signal from the driver IC  20 . The LCD  12  includes a thin film transistor (TFT) substrate  30 , a color filter substrate  28 , and polarizing plates  14  and  16 . The polarizing plate  14 , the color filter substrate  28 , the TFT substrate  30 , and the polarizing plate  16  are configured to be laminated in the stated order. The LCD  12  is bonded to the cover plate  18  on the display surface  12   a  thereof through an optical adhesive  26 . The two polarizing plates  14  and  16  are arranged so as to sandwich the TFT substrate  30  and the color filter substrate  28 . Those polarizing plates  14  and  16  transmit light traveling in a specific polarization direction. Further, an upper surface of the polarizing plate  14  becomes the display surface  12   a.  With reference to  FIG. 3 , the LCD  12  is described later in more detail. 
         [0039]    The cover plate  18  has a thin plate-like shape. The cover plate  18  is a plate for covering the LCD  12  from the display surface  12   a  side. The cover plate  18  has the center portion, i.e., translucent region, and the peripheral portion (outer periphery), i.e., light shielding region. The cover plate  18  is bonded to the LCD  12  on the display surface  12   a  side thereof through the optical adhesive  26 . With reference to  FIG. 3 , the cover plate  18  is described later in more detail. 
         [0040]    The driver IC  20  controls the LCD  12  and the like. The FPC  22  is a board for supplying a signal to the driver IC  20 . The backlight unit  24  emits light from a back surface side of the LCD  12 . 
         [0041]      FIG. 3  is a longitudinal sectional view illustrating a part of the liquid crystal display device  10  taken along a line X of  FIG. 1 . As illustrated in  FIG. 3 , the cover plate  18  includes a translucent plate  32  provided with a light shielding portion  34  and a reflecting portion  36 . The translucent plate  32  has a thin plate-like shape. Owing to its light transmission property, the translucent plate  32  makes an image of the LCD  12  viewable and downwardly transmits light from thereabove, such as ultraviolet rays. 
         [0042]    The light shielding portion  34  is provided on the display surface  12   a  side of the translucent plate  32 . Further, the light shielding portion  34  surrounds an outer periphery of the translucent plate  32  and prevents an outside of a display region B of an image from being viewed. In this embodiment, as the light shielding portion  34 , black ink that intercepts light is formed by printing (black painting), but the light shielding portion  34  is not limited thereto. The light shielding portion  34  may be, for example, a black resin having light shielding property or metal formed by sputtering. 
         [0043]    The reflecting portion  36  is provided on the display surface  12   a  side of the light shielding portion  34 . The reflecting portion  36  has a high reflectance of light. In this embodiment, as the reflecting portion  36 , a pigment having high light reflection property is used, but the reflecting portion  36  is not limited thereto. The reflecting portion  36  may be, for example, a white pigment. Further, in a case where the light shielding portion  34  is the metal described above, a metal material such as aluminum or chrome is subjected to sputtering and patterning to thereby obtain an arbitrary shape. Further, the reflecting portion  36  is provided on the display surface  12   a  side of the light shielding portion  34  and thus is not viewed. 
         [0044]      FIG. 4A  is a longitudinal sectional view illustrating an end portion of the cover plate  18  of the liquid crystal display device  10  according to the first embodiment of the present invention, and  FIG. 4B  is a longitudinal sectional view illustrating an end portion of a cover plate  68  of a conventional liquid crystal display device. Conventionally, the cover plate  68  has a structure in which only a black light shielding portion  74  is provided on a display surface side of a translucent plate  72 . In this embodiment, the cover plate  18  has a structure in which the light shielding portion  34  and the reflecting portion  36  are laminated in the stated order on the display surface side of the translucent plate  32 . For that reason, as illustrated in  FIG. 3 , light A 2  emitted from a lateral side of the LCD  12  is propagated while being repeatedly reflected not on the light shielding portion  34  but on the reflecting portion  36 . Accordingly, attenuation of the light A 2  can be suppressed and the optical adhesive  26  is sufficiently cured in the vicinity of the light shielding portion  34 . 
         [0045]    The color filter substrate  28  has a structure in which a black matrix  50  and color filters  52 R,  52 G, and  52 B respectively having three colors of red, green, and blue are manufactured on a color filter side glass  56 . 
         [0046]    The black matrix  50  is a second light shielding portion for shielding light. The black matrix  50  is also provided among the respective color filters  52 R,  52 G, and  52 B and in an outside of the display region B, and shields unnecessary light. In this embodiment, as the black matrix  50 , a chromium oxide or the like is used, but the black matrix  50  is not limited thereto. The black matrix  50  may be made of, for example, a resin. 
         [0047]    Further, a second reflecting portion  54  is provided to an end portion of the color filter side glass  56 . The second reflecting portion  54  is arranged outside of the display region B on a cover plate  18  side of the black matrix  50 . The second reflecting portion  54  is provided so as to be opposed to the light shielding portion  34  of the cover plate  18  through the optical adhesive  26 . The second reflecting portion  54  is provided outside of a user&#39;s viewing range C and cannot be viewed. Further, the second reflecting portion  54  has a high reflectance of light. In  FIG. 3 , the second reflecting portion  54  is provided between the color filter side glass  56  and the black matrix  50 . In this embodiment, as the second reflecting portion  54 , a metal material such as chrome is used, but the second reflecting portion  54  is not limited thereto. Another metal material such as aluminum may be used. Further, a pigment having high light reflection property or a white pigment may be used. 
         [0048]    As illustrated in  FIG. 3 , an over coat  48  is formed on surfaces of the black matrix  50  and the color filters  52 R,  52 G, and  52 B. The color filter substrate  28  thus formed and the TFT substrate  30  are opposed to each other and bonded through a sealing agent  44 , to thereby provide a liquid crystal layer  46  between those two substrates. 
         [0049]      FIG. 5A  is a longitudinal sectional view illustrating an end portion of the LCD  12  of the liquid crystal display device  10  according to the first embodiment of the present invention, and  FIG. 5B  is a longitudinal sectional view illustrating an end portion of an LCD  62  of the conventional liquid crystal display device. Conventionally, the LCD  62  has a structure in which only a black matrix  78  serving as a second light shielding portion is provided. In this embodiment, the LCD  12  has a structure in which the second reflecting portion  54  is provided on a translucent plate  32  side of the black matrix  50 . In  FIG. 5A , the second reflecting portion  54  is formed between the black matrix  50  and the color filter side glass  56 . For that reason, as illustrated in  FIG. 3 , the light A 2  emitted from the lateral side of the LCD  12  is propagated while being repeatedly reflected not on the black matrix  50  but between the second reflecting portion  54  and the reflecting portion  36 . Accordingly, the attenuation of the light A 2  can be suppressed and the optical adhesive  26  is sufficiently cured in the vicinity of the light shielding portion  34 . 
         [0050]    As described above, the reflecting portion having a high reflectance of light is provided on the display surface side of the light shielding portion. Further, the second reflecting portion having a high reflectance of light is provided on the display surface side of the second light shielding portion which is provided on the periphery of the LCD. Hence, in a case where the translucent substrate is bonded through the optical adhesive, propagation efficiency of the light emitted from the lateral side of the LCD can be enhanced by reflection of the reflecting portion and the second reflecting portion. Accordingly, a crosslinking reaction in the vicinity of the light shielding portion provided on the periphery of the LCD is promoted and the translucent substrate can be bonded stably. As a result, a mechanical bonding strength is enhanced and deterioration of an image, which is derived from curing variations of the optical adhesive, can be prevented. 
         [0051]    Further, the second reflecting portion is provided outside the user&#39;s viewing range from the display surface side. Accordingly, the second reflecting portion cannot be viewed by the user, which prevents loss of visibility. 
         [0052]    Note that, in the embodiment described above, the LCD having the TFT structure is adapted, but the present invention is not limited thereto. For example, the present invention may be applicable to another display panel such as an LCD having a structure other than the TFT structure, or an organic EL panel.