JPH11297116A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of uneven brightness in a liquid crystal display panel caused by heat generation of a fluorescent tube in the case of having an edge back light. SOLUTION: A radiating sheet 22 is stored in a groove 21 formed on a surface of a resin case 1 in a pressure contact state to a inner surface of a shield case 2. Accordingly, heat conducted from a fluorescent tube 8 to a bottom part of the groove 21 of the resin case 1 is rapidly conducted through the radiating sheet 22 to the shield case 2 so as to be difficult to conduct to an end surface 4a of a liquid crystal display panel 4. Furthermore, because the tube center of the fluorescent tube 8 is disposed in an opposite side of the liquid crystal panel 4 on a basis of a central normal line 5b of an end surface 5a of a light guide plate 5 in its thickness direction, heat from the fluorescent tube 8 is more difficult to conduct to the liquid crystal display panel 4. A reflective surface of a reflecting sheet 6 facing to the light guide plane 5 has a light- absorbing pattern corresponding to uneven brightness caused by heat generation of the fluorescent tube 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having an edge light type backlight.

[0002]

2. Description of the Related Art Some liquid crystal display devices have an edge light type backlight provided on the back surface of a liquid crystal display panel. 8 shows a plan view of an example of such a conventional liquid crystal display device with a part cut away, FIG. 9 shows a plan view of an arrangement relationship between a liquid crystal display panel and a fluorescent tube, and FIG.
1 is a sectional view taken along line XX of FIG. This liquid crystal display device has a structure in which an edge light type backlight 3 and a liquid crystal display panel 4 are housed in this order between a lower resin case 1 and an upper shield case 2. Among them, the backlight 3 includes a light guide plate 5 having, for example, irregularities on the back surface and a light emission surface on the front surface, a reflection sheet 6 provided on the back surface of the light guide plate 5, and a diffusion sheet provided on the front surface of the light guide plate 5. Sheet 7 and predetermined two end faces 5 of light guide plate 5
a (the upper end face and the right end face in FIG. 8).
A fluorescent lamp (tubular light source) 8 having a U-shape and a reflector 9 provided so as to cover the outer peripheral surface of the fluorescent tube 8. The liquid crystal display panel 4 has a structure in which liquid crystal (not shown) is sealed between two glass substrates 11 and 12, and polarizing plates 13 and 14 are provided on the front surface of the glass substrate 11 and the back surface of the glass substrate 12, respectively. Has become. A display window 16 is provided in a portion of the shield case 2 corresponding to a display area 15 indicated by a dashed line of the liquid crystal display panel 4. The light emitted from the L-shaped fluorescent tube 8 and the light reflected by the reflector 9 are incident on two predetermined end faces 5 a of the light guide plate 5,
While propagating in the light guide plate 5 toward the opposite end surface, the light is reflected by the irregularities formed on the back surface and emitted to the front surface side, and the emitted light is diffused by the diffusion sheet 7 to form a surface light source. The converted light is applied to the back surface of the liquid crystal display panel 4. The reflection sheet 6 is provided to reflect the light emitted to the back surface while propagating in the light guide plate 5 and re-enter the light guide plate 5.

[0003]

By the way, in such a conventional liquid crystal display device, as shown in FIG. 10, in order to make the direct light from the fluorescent tube 8 efficiently enter the end face 5a of the light guide plate 5, it is necessary to use the same. The fluorescent tube 8 is positioned directly in front of the end surface 5a, that is, a tube axial center line 8a extending in a direction perpendicular to the plane of the drawing of the fluorescent tube 8 (hereinafter referred to as a tube center line) 8a is a normal to the center in the thickness direction of the end surface 5a of the light guide plate 5. 5b.
For this reason, the fluorescent tube 8 is in close proximity to two predetermined end faces 4a (the upper end face and the right end face in FIGS. 3 and 4) of the liquid crystal display panel 4 only with the resin case 1 interposed therebetween. It will be located. On the other hand, since the fluorescent tube 8 generates heat when turned on, this heat is generated via the resin case 1 near the fluorescent tube 8 through the predetermined two end faces 4 of the liquid crystal display panel 4.
a, and the temperature of the liquid crystal at the end face 4a is higher than at the other portions. When the temperature of the liquid crystal increases, the refractive index anisotropy Δn of the liquid crystal decreases, and the light transmittance of the liquid crystal increases. As a result, in the display area 15 of the liquid crystal display panel 4, there is a problem that the luminance is relatively high in the area indicated by hatching (hatching) in FIG.
However, in this case, the uneven brightness area indicated by hatching in FIG. 11 indicates not only the uneven brightness due to an increase in the liquid crystal temperature but also a pair of long sides of the liquid crystal display panel 4 (an upper side and a lower side in FIG. 11). This is a region that also includes luminance unevenness caused by gap unevenness that is likely to occur. It is an object of the present invention to prevent luminance unevenness due to heat generation of a light source in a liquid crystal display panel.

[0004]

In order to solve the above-mentioned problems, the invention according to the first aspect of the present invention is to provide a liquid crystal display panel having at least a heat generated by a tubular light source on a surface of a reflection sheet provided on a back surface of a light guide plate. A light absorption pattern for adjusting brightness is provided according to the distribution of occurrence of uneven brightness. According to the first aspect of the present invention, the unevenness in brightness of the liquid crystal display panel caused by at least heat generation of the tubular light source is provided by the light absorption pattern for adjusting brightness provided on the surface of the reflection sheet provided on the back surface of the light guide plate. Therefore, it is possible to prevent the liquid crystal display panel from generating uneven brightness due to the heat generated by the tubular light source. According to a second aspect of the present invention, an elastically deformable heat radiation sheet is interposed between at least a portion of the tubular light source that generates a large amount of heat and the shield case. According to the second aspect of the present invention, the heat of at least a portion of the tubular light source having a large amount of heat is quickly transmitted to the shield case via the heat radiation sheet, so that the heat is not easily transmitted to the liquid crystal display panel. Therefore, it is possible to prevent the liquid crystal display panel from having uneven brightness due to heat generated by the tubular light source. According to a fourth aspect of the present invention, the center of at least a part of the tube of the tubular light source is arranged on the opposite side to the arrangement position of the liquid crystal display panel with respect to the normal to the center in the thickness direction of the end surface of the light guide plate. is there. According to the fourth aspect of the present invention, the center of at least a part of the tube of the tubular light source is arranged on the opposite side to the arrangement position of the liquid crystal display panel with respect to the normal to the center in the thickness direction of the end surface of the light guide plate. As a result, the heat of the tubular light source can be made less likely to be conducted to the liquid crystal display panel, and therefore, it is possible to prevent the liquid crystal display panel from having uneven brightness due to the heat generated by the tubular light source.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a liquid crystal display device according to a first embodiment of the present invention will be described. The basic configuration is the same as that of the prior art shown in FIGS.
The description will be made with reference to these figures as appropriate. The first embodiment differs from the conventional case shown in FIGS. 8 to 10 in that the reflection sheet 6 provided on the back surface of the light guide plate 5 has the structure shown in FIG.

As shown in FIG. 1, on the surface of the reflection sheet 6, the heat generated by the L-shaped fluorescent tube 8 and the unevenness of the gap between the pair of long sides of the liquid crystal display panel 4 cause the unevenness of the liquid crystal display panel 4. Two types of light absorption patterns 6a and 6b for luminance adjustment are provided by printing so as to eliminate luminance unevenness. In this case, the main body of the reflection sheet 6 may be any one of a white resin sheet, a mirror-like sheet obtained by evaporating silver or the like on the surface of the resin sheet, and a mirror-finished sheet metal or the like. The two types of light absorption patterns 6a and 6b correspond to the state of occurrence of luminance unevenness indicated by oblique lines (hatching) in FIG. In this case, the light absorption patterns 6a provided on the upper end and the lower end of the surface of the reflection sheet 6 (that is, the ends corresponding to the pair of long sides of the liquid crystal display panel 4 shown in FIG. 11) have a gray solid shape. It has become. Each light absorption pattern 6a at the upper end and the lower end of the surface of the reflection sheet 6
The light absorption pattern 6b provided inside and at the right end has gray dots. These dots may be uniform or may be changed according to the state of occurrence of uneven brightness of the liquid crystal display panel 4. In addition, the width of the light absorption pattern 6b forming region in the portions corresponding to both ends and the bent portion of the fluorescent tube 8 is larger by a predetermined size than the width of the light absorption pattern 6b forming region in the other portions. I have.

Next, the reason why the light absorption pattern 6a is made gray and the light absorption pattern 6b is made gray and the reason why the width of the region where the light absorption pattern 6b is formed is changed will be described. As described above, the area indicated by the diagonal lines (hatched area) in FIG. 11 is not only the area where the uneven brightness caused by the heat generation of the tubular light source 8 but also the liquid crystal display panel 4.
Are regions including a region where luminance unevenness occurs due to gap unevenness in the pair of long side portions. Therefore, the light absorption patterns 6a,
6b, and only the light absorption pattern 6b is provided in a region corresponding only to a region where luminance unevenness caused by heat generation of the tubular light source 8 occurs. In addition, when a countermeasure for eliminating the gap unevenness at the pair of long sides of the liquid crystal display panel 4 is taken, the light absorption pattern 6a at the lower side in the figure where the occurrence of luminance unevenness due to heat generation of the tubular light source 8 is small. One or both of 6b can be omitted. Further, since the amount of heat generated at both end portions and the bent portions of the L-shaped fluorescent tube 8 is larger than that of the other portions, the width of the light absorption pattern 6b forming region is made different in order to cope with this. .

In this liquid crystal display device, the light guide plate 5
The two types of light absorption patterns 6a and 6b for brightness adjustment provided on the front surface of the reflection sheet 6 provided on the back surface of
It is possible to eliminate the uneven brightness of the liquid crystal display panel 4 due to the heat generation of the fluorescent tube 8 and the uneven gap at the pair of long sides of the liquid crystal display panel 4. That is, when the reflection sheet 6 is a conventional simple reflection sheet (for example, a white resin sheet), the light transmittance of the display area 15 of the liquid crystal display panel 4 in the cross section along the line YY in FIG. As shown in FIG. 2 (A), both sides are higher than the center. On the other hand, the luminance distribution of the reflected light when uniformly radiated on the reflective sheet 6 shown in FIG. 1 is lower on both sides than at the center, as shown in FIG. 2B. Therefore, the brightness distribution on the display surface of the liquid crystal display device provided with the reflection sheet 6 shown in FIG. 1 is the same as the light transmittance of the liquid crystal shown in FIG.
2C, and is uniformed as shown in FIG. 2C. As a result, it is possible to prevent the liquid crystal display panel 4 from generating heat due to the fluorescent tubes 8 and uneven brightness due to gap unevenness at a pair of long sides of the liquid crystal display panel 4.
As a result, the display quality can be improved.

In the first embodiment, the case where the light absorption patterns 6a and 6b are printed on the surface of the reflection sheet 6 has been described. However, the present invention is not limited to this. For example, the light absorption patterns 6a and 6b may be printed on a transparent sheet different from the reflection sheet 6, and both may be attached to each other, or both may be simply overlapped. Also, the light absorbing patterns 6a, 6b
An opening corresponding to the light-absorbing patterns 6a and 6b may be formed on the rear surface of the reflection sheet 6, for example, the resin case 1 shown in FIG. The color of the light absorption patterns 6a and 6b is not limited to gray, but may be black or color, or may be a plurality of colors. Furthermore, the light absorption pattern may be only dots or only solids.

Next, FIG. 3 is a plan view of a liquid crystal display device according to a second embodiment of the present invention, in which a part of a main portion is cut away, and FIG. 4 is a cross-sectional view taken along line XX. Things. In these figures, the same reference numerals are given to the same parts as those in FIGS. 8 and 10, and the description thereof will be omitted as appropriate. In this liquid crystal display device, a predetermined area around the portion where the liquid crystal display panel 4 is stored on the surface of the resin case 1
A groove 21 is provided in a portion corresponding to the position where the V-shaped fluorescent tube 8 is disposed, and a heat radiation sheet 22 made of a silicone sheet or the like having good heat conduction and elastic deformation is accommodated in the groove 21. The surface of the heat radiation sheet 22 is pressed against the inner surface of the shield case 2. In this case, the reflection sheet 6 is integrated with the reflector 9.

When the heat radiation sheet 22 is formed of a silicone sheet, for example, as shown in FIG. 5, a relatively soft and thick silicone rubber layer 22b is provided on the back surface of a relatively hard and thin silicone resin layer 22a. It is desirable to have a structure. In this way, even when the overall thickness of the heat dissipation sheet 22 is reduced to, for example, about 1.5 mm, the silicone rubber layer 22 is relatively soft when the heat dissipation sheet 22 is attached by being pulled into the groove 21 while being attached.
b) a relatively hard silicone resin layer 2 that changes in length and thickness
2a can be prevented, and has excellent thermal conductivity and improves workability in mounting.

In this liquid crystal display device, the fluorescent tube 8
The heat conducted to the bottom of the groove 21 of the resin case 1 is quickly conducted to the sheet metal shield case 2 via the heat dissipation sheet 22 and is quickly dissipated from the sheet metal shield case 2 into the air. Therefore, conduction of heat generated by the fluorescent tube 8 to the end face 4 a of the liquid crystal display panel 4 can be significantly suppressed. For this reason, it is possible to suppress the occurrence of luminance unevenness in the liquid crystal display panel 4 due to the heat generated by the fluorescent tubes 8, thereby improving the display quality.
Further, since the heat radiating sheet 22 interposed between the resin case 1 and the shield case 2 can be elastically deformed, it also has a function as a cushion material for eliminating rattling between the resin case 1 and the shield case 2. doing. The position of the heat radiating sheet 22 may be limited to a portion where the calorific value of the fluorescent tube 8 is large, that is, a portion corresponding to both ends and the bent portion of the fluorescent tube 8.

FIG. 6 is a sectional view showing a main part of a liquid crystal display device according to a third embodiment of the present invention.
In this figure, parts having the same names as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In this embodiment, as in the first embodiment shown in FIG. 1, a reflection sheet having a light absorption pattern formed so as to eliminate at least luminance unevenness caused by heat generation of the fluorescent tube 8 is used as the reflection sheet 6. Is used. In this liquid crystal display device, the tube center line 8a of the fluorescent tube 8 is aligned with the end surface 5a of the light guide plate 5.
The liquid crystal display panel 4 is disposed on the opposite side of the liquid crystal display panel 4 with respect to the normal 5b at the center in the thickness direction. in this case,
The distance d between the normal 5b at the center in the thickness direction of the end face 5a of the light guide plate 5 and the tube center line 8a of the fluorescent tube 8 is about 80 to 90% of the tube diameter of the fluorescent tube 8, and as an example, End face 5 of light plate 5
a has a thickness of 3 mm, and the fluorescent tube 8 has a diameter of 2.2 to 2.4 m.
m, it is about 2 mm. A line 8 connecting the center of the fluorescent tube 8 and the center in the thickness direction of the end face 5 a of the light guide plate 5.
b and the normal 5b at the center of the end face 5a of the light guide plate 5 in the thickness direction are within 40 ° in order to prevent the light emitted from the fluorescent tube 8 from being reflected by the end face 5a of the light guide plate 5. It is preferable that

As described above, in this liquid crystal display device, the tube center line 8a of the fluorescent tube 8 is aligned with the arrangement position of the liquid crystal display panel 4 with respect to the normal 5b at the center in the thickness direction of the end surface 5a of the light guide plate 5. Are shifted to the opposite side, a relatively large space is formed between the fluorescent tube 8 and the bottom of the resin case 1, and this space forms a kind of heat insulating layer. Therefore, according to this embodiment, the heat generated by the fluorescent tube 8 is less likely to be transmitted to the resin case 1 by the large space heat insulation layer as described above, and the heat transmitted to the resin case 1 is quickly transmitted to the heat radiation sheet 22. Since the heat can be dissipated into the outside atmosphere, the heat generated by the fluorescent tube 8 can be made more difficult to be transmitted to the liquid crystal display panel 4. As a result, the occurrence of luminance unevenness due to the heat generated by the fluorescent tubes 8 in the liquid crystal display panel 4 is further suppressed, and the display quality can be further improved.

In the third embodiment, the cross section of the reflector 9 covering the outer peripheral surface of the fluorescent tube 8 is substantially U-shaped. However, as in the fourth embodiment of the present invention shown in FIG. The reflector 9 covering the upper half of the tube 8 is brought into contact with the bottom inner surface of the groove 21 of the resin case 1 to form a relatively large space between the reflector 9 covering the upper half of the fluorescent tube 8 and the fluorescent tube 8. You may make it.

In the third and fourth embodiments, L
The tube center line 8a of the V-shaped fluorescent tube 8 is entirely
Although the case where it is arranged below b has been described, it is not limited to this. For example, the tube center lines 8a at both ends of the L-shaped fluorescent tube 8 are arranged below a predetermined normal line 5b, and the tube center lines 8a of the bent portions are located at the same positions as the conventional case shown in FIG. Alternatively, the tube center line 8a of the bent portion of the L-shaped fluorescent tube 8 may be arranged below a predetermined normal line 5b, and the tube center lines at both ends may be arranged. 8a may be arranged at the same position as the conventional case shown in FIG.

Further, it goes without saying that the reflection sheet 6 in the second embodiment may be a reflection sheet 6 on which the light absorption pattern shown in FIG. 1 is formed. Further, the heat dissipation sheet 22 of the second embodiment or the like may be provided in the first embodiment. That is, a configuration for preventing the brightness unevenness of the liquid crystal display panel 4 due to the heat generated by the fluorescent tube 8, a configuration for forming a light absorption pattern on the reflection sheet 6, a configuration for interposing the heat radiation sheet 22, and a position of the fluorescent tube 8. In the direction away from the liquid crystal display panel 4,
Each configuration may be used alone.
One configuration may be used in combination, or all three configurations may be employed. Further, the shape of the fluorescent tube is not limited to the L shape, and may be a straight shape or a U shape. The number of fluorescent tubes may be two, that is, an L-shape and a straight line, or may be three, which are linear.

[0018]

As described above, according to the first aspect of the present invention, at least the light source of the tubular light source is formed by the brightness adjusting light absorption pattern provided on the surface of the reflection sheet provided on the back surface of the light guide plate. Since unevenness in brightness of the liquid crystal display panel due to heat generation can be eliminated, unevenness in brightness due to heat generation of the tubular light source can be prevented from occurring in the liquid crystal display panel, thereby improving display quality. . According to the second aspect of the invention, the heat of at least the portion of the tubular light source that generates a relatively large amount of heat is quickly transmitted to the shield case via the heat radiation sheet, is radiated to the outside air, and is transmitted to the liquid crystal display panel. Since it is possible to make it difficult, it is possible to significantly suppress the occurrence of luminance unevenness due to the heat generated by the tubular light source in the liquid crystal display panel, and to improve the display quality. According to the fourth aspect of the present invention, the center of at least a part of the tube of the tubular light source is arranged on the side opposite to the arrangement position of the liquid crystal display panel with respect to the normal to the center in the thickness direction of the end surface of the light guide plate. Therefore, it is possible to make it difficult for the heat of the tubular light source to be conducted to the liquid crystal display panel, and therefore, it is possible to significantly suppress the occurrence of luminance unevenness due to the heat generated by the tubular light source in the liquid crystal display panel, thereby improving the display quality. can do.

[Brief description of the drawings]

FIG. 1 is a plan view of a reflection sheet provided on a back surface of a light guide plate of a backlight of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a view for explaining luminance characteristics of a liquid crystal display device including the reflection sheet shown in FIG.

FIG. 3 is a plan view of a main part of a liquid crystal display device according to a second embodiment of the invention, in which a part of the main part is cut away.

FIG. 4 is a sectional view taken along line XX of FIG. 3;

FIG. 5 is a cross-sectional view of an example of a heat dissipation sheet according to a second embodiment.

FIG. 6 is a sectional view of a main part of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 7 is a sectional view of a main part of a liquid crystal display device according to a fourth embodiment of the present invention.

FIG. 8 is a plan view in which a part of an example of a conventional liquid crystal display device is cut away.

FIG. 9 is a plan view showing an arrangement relationship between a liquid crystal display panel and a fluorescent tube in FIG. 8;

FIG. 10 is a sectional view taken along the line XX of FIG. 8;

FIG. 11 is a plan view illustrating a problem of a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resin case 2 Shield case 3 Backlight 4 Liquid crystal display panel 5 Light guide plate 6 Reflection sheet 6a, 6b Light absorption pattern 7 Diffusion sheet 8 Fluorescent tube 9 Reflector 22 Heat dissipation sheet

Claims (7)

[Claims] 1. A liquid crystal display device in which an edge light type backlight is provided on a back surface of a liquid crystal display panel.
The backlight includes at least a light guide plate having a light emission surface, a tubular light source provided on an end surface of the light guide plate, and a reflection sheet provided on a back surface of the light guide plate. A liquid crystal display characterized in that a light absorption pattern for luminance adjustment is provided on a surface according to at least a distribution state of luminance unevenness caused by heat generation of the tubular light source among luminance unevenness generated in the liquid crystal display panel. apparatus. 2. A liquid crystal display device in which a liquid crystal display panel and an edge light type backlight are housed in a shield case, wherein the backlight has at least a light guide plate having a light exit surface, and an end face of the light guide plate. A liquid crystal display device, comprising: a tubular light source provided in the first case; and a heat dissipating sheet that can be elastically deformed is interposed between at least a portion of the tubular light source that generates a relatively large amount of heat and the shield case. 3. The liquid crystal display device according to claim 2, wherein the heat radiation sheet is made of a silicone sheet. 4. A liquid crystal display device in which an edge light type backlight is provided on a back surface of a liquid crystal display panel,
The backlight includes at least a light guide plate whose surface is a light emission surface, and a tubular light source provided on an end surface of the light guide plate, and a tube center of at least a part of the tubular light source, an end surface of the light guide plate. A liquid crystal display device, wherein the liquid crystal display device is disposed on a side opposite to a position where the liquid crystal display panel is disposed with reference to a normal line at a center in a thickness direction of the liquid crystal display panel. 5. The invention according to claim 4, wherein the distance between the center of at least a part of the tube of the tubular light source and the normal to the center in the thickness direction of the end surface of the light guide plate is smaller than the tube diameter of the tubular light source. A liquid crystal display device characterized by being about 80 to 90%. 6. The invention according to claim 4, wherein
The angle between a line connecting the center of the tube of at least a part of the tubular light source and the center in the thickness direction of the end face of the light guide plate and the normal to the center in the thickness direction of the end face of the light guide plate is within 40 °. Characteristic liquid crystal display device. 7. A liquid crystal display device in which a liquid crystal display panel and an edge light type backlight are housed in a shield case, wherein the backlight has at least a light guide plate having a light exit surface, and an end surface of the light guide plate. And a reflection sheet provided on the back surface of the light guide plate, and the surface of the reflection sheet has at least a portion of luminance unevenness generated in the liquid crystal display panel caused by heat generation of the tubular light source. A light absorption pattern for luminance adjustment is provided in accordance with the occurrence distribution state of the luminance unevenness, and an elastically deformable heat radiation sheet is interposed between at least a portion of the tubular light source having a relatively large amount of heat generation and the shield case. The center of at least a part of the tube of the tubular light source is opposite to the position of the liquid crystal display panel with respect to the normal to the center in the thickness direction of the end surface of the light guide plate. A liquid crystal display device characterized by being disposed on the side.