Liquid crystal display having a frame which does not transmit light source heat to the display

A liquid crystal display device is provided with a heat releasing means. The heat releasing means is constructed such that a frame for fixing a liquid crystal display board to an illuminating device has a cutout formed in a position corresponding to a light source in order to expose a holding member of the light source for releasing heat. Alternatively, the heat releasing means is constructed by providing a metallic plate in a portion corresponding to the light source. With these means, it is possible to prevent local rise of temperature in the edge portion of the liquid crystal board.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a liquid crystal display device to be used 
to realize slim type, i.e., lap-top type and/or notebook type personal 
computers, word processors etc and relates, in particular, to a liquid 
crystal display device which can provide an uniform display screen and 
improve quality of display. 
(2) Description of the Prior Art 
FIGS. 1 and 2 show an example of conventional back light type liquid 
crystal display device, which includes a liquid crystal display board X, a 
back light type illuminator Y, a light source 1 such as of a cold cathode 
fluorescent tube (CCFT), a light-introducing plate 2 made of a light 
transmissive material, a plastic chassis 3 and plastic holding members 4a 
and 4b for holding light source 1. All these elements are formed into a 
square unit and enclosed by a frame 5 (metallic bezel) made of a metal. 
The illuminator used here is called a back light illuminator of side light 
type, and in allowably the device to be slim. 
Meanwhile, in the prior art liquid crystal display, the liquid crystal 
display board X (liquid crystal panel) and the light source 1 (CCFT, etc.) 
are enclosed together by the frame 5 (metallic bezel), and no 
heat-separating measure is provided between the liquid crystal display 
board X and the illuminator Y. Therefore, heat generated while the light 
source 1 is being turned on, is transmitted through the frame 5 to the 
liquid crystal display board X, and/or the heat is confined inside the 
frame 5 to raise the temperature of the liquid crystal display board X. 
Liquid crystal display board X by nature is affected by a slight 
temperature variation to change its threshold voltage for display. 
Accordingly, when a temperature difference is generated between the near 
area and the distant area from the light source 1 of the liquid crystal 
display board X, this would bring about unevenness in display density and 
deteriorate quality of display. 
There are some proposals in which the influence of heat radiated from the 
liquid crystal display device is considered. For example, Japanese Utility 
Model Application Laid-Open Sho 64 No. 10,780 discloses a back lighting 
equipment for a liquid crystal display device comprising a light source 
and a reflecting plate wherein heat releasing holes are provided in the 
reflecting plate and at least one part of the heat releasing holes is 
covered by a ventilative sheet having a similar color to that of the 
reflecting plate. On the other hand, Japanese Utility Model Application 
Laid-Open Sho 64 No. 26,775 proposes a liquid crystal module structure 
comprising a liquid crystal panel and an illuminator disposed in the 
backside of the panel, wherein holes or space is provided in the upper 
screen portion of the illuminator. Nevertheless, either of these proposals 
uses a direct illuminating type back lighting device, which is different 
from the side-light type device shown in FIGS. 1 and 2. More clearly, a 
direct illuminating type device is constructed such that an illuminating 
light source is disposed on the back side of the liquid crystal panel to 
directly illuminate the liquid crystal panel with the help of a reflecting 
plate and/or condenser plate. Accordingly, in a device of this type, the 
temperature of the liquid crystal panel is liable to rise and it is 
difficult to make the entire device slim. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a liquid 
crystal display device which is capable of preventing heat generated from 
a light source from being transmitted to a liquid crystal display board, 
and which can improve the liquid crystal display board in display quality. 
The above object of the present invention can be achieved by the following 
features. 
A first aspect of the present invention lies in that a liquid crystal 
display device comprises: a liquid crystal display board; an illuminating 
device for illuminating the liquid crystal display board from the back 
side thereof; and a frame for fixing the liquid crystal display board in 
front of the illuminating device, and the illuminating device comprises a 
light-introducing plate disposed on the backside of liquid crystal display 
board in parallel therewith, a light source disposed adjacent to an end 
face of the light-introducing plate, a holding member for holding the 
light source and light-introducing plate, and in that the holding member 
is made of a material that blocks light, and the frame has a cutout formed 
in a position corresponding to the light source in order to expose the 
holding member outside for releasing heat. 
In accordance with a second aspect of the present invention, a liquid 
crystal display device comprises: a liquid crystal display board; an 
illuminating device for illuminating the liquid crystal display board from 
the back side thereof; and a frame for fixing the liquid crystal display 
board in front of the illuminating device, and the illuminating device 
comprises a light-introducing plate disposed on the backside of liquid 
crystal display board in parallel therewith, a light source disposed 
adjacent to an end face of the light-introducing plate, a holding member 
for holding the light source and light-introducing plate, and the liquid 
crystal display device is characterized in that the frame has a cutout 
formed in a position corresponding to the light source for releasing heat 
and a metallic plate having a high heat conductivity is provided in the 
cutout without keeping in contact with the frame. 
In accordance with a third aspect of the present invention, a liquid 
crystal display device comprises: a liquid crystal display board; an 
illuminating device for illuminating the liquid crystal display board from 
the back side thereof; and a frame for fixing the liquid crystal display 
board to a display window in front of the illuminating device, and the 
illuminating device comprising a light-introducing plate disposed on the 
backside of liquid crystal display board in parallel therewith, a light 
source disposed adjacent to an end face of the light-introducing plate, a 
holding member for holding the light source and light-introducing plate, 
and the liquid crystal display device is characterized in that the frame 
is disposed inwardly of the display window while keeping away from the 
holding member, and a metallic plate for releasing heat is provided on the 
surface of the holding member while the metallic plate is disposed without 
keeping in contact with the frame. 
With the configurations described above, heat generated from the light 
source for illumination when it is activated, is dissipated via the cutout 
and/or the metallic plate to the air. Accordingly, the heat in the frame 
for fixing the liquid crystal display board can be lowered so that the 
temperature of the liquid crystal display board can be reduced in the 
vicinity of the light source. Accordingly it is possible to prevent the 
occurrence of unevenness in display density on the liquid crystal board.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will hereinafter be described in detail referring to 
embodiments. 
First Embodiment 
A liquid crystal display device in accordance with a first embodiment of 
the present invention is, as shown in FIGS. 3 and 4, of an edge-light 
type, and includes a liquid crystal display board 8 (liquid crystal 
panel), an illuminating device 9 for illuminating the liquid crystal 
display board 8 from the back side thereof, and a frame 10 (metallic 
bezel) for fixing the liquid crystal display board 8 in front of 
illuminating device 9. 
The illuminating device 9 is composed of a light-introducing plate 11 
disposed on the backside of liquid crystal display board 8 in parallel 
therewith, a light source 12 disposed adjacent to an end face of the 
light-introducing plate 11, a holding member 13 (plastic chassis) for 
holding the light source 12 and light-introducing plate 11. 
The holding member 13 is made of a material that blocks light. The frame 10 
has a cutout 15 formed in a position corresponding to the light source 12 
in order to release heat. 
As shown in FIG. 3, the light-introducing plate 11 is a flat plate made of 
acrylic resin with about 2.0 mm in thickness and having larger length and 
width than those of a display area L1 of the liquid crystal display board 
8. 
The light source 12 may use a straight tube type cold cathode fluorescent 
tube (CCFT) that is constructed by a luminous element such as filament or 
the like and an enclosing tube thereof and has a diameter of 4.1 mm, a 
length of 164 mm and a consumption power of 2.0 W, as an example. 
The holding member 13 comprises a front holding portion 13a supporting the 
light source 12 from the front and a rear holding portion 13b supporting 
the light source 12 from the back side. Both holding portions 13a and 13b 
are made of a material that blocks light and has a low heat-conductivity 
such as polycarbonate, ABS resin and etc., and are hermetically put 
together, with screws fixed at periphery outside where the light source 12 
occupies in order to prevent leaking of light from the light source 12. Of 
the two, the front holding portion 13a is provided over the 
light-introducing plate 11 but only in a limited region on the side of 
light source 12. On the other hand, the rear holding portion 13b is 
disposed entirely over the backside of the light-introducing plate 11 and 
also serves as a reflection sheet for returning light emitted backward 
from the inside of the light-introducing plate 11 thereinto. 
The frame 10 is made from a galvanized sheet iron or the like and provided 
with a display window 14 having a rectangular shape as shown in FIGS. 3 to 
5. The edge portion of the frame 10 on the side of the light source 12 is 
formed into L-shape in section so as to cover the front side of the front 
holding portion 13a and the side end of both holding portions 13a and 13b. 
A cutout 15 for releasing heat by exposing the holding member 13 is formed 
on the frame 10 in a position corresponding to the light source 12. The 
width W1 of the cutout 15 is preferably set two times greater than the 
diameter (4.1 mm) of the light source in view of the heat distribution 
created inside the holding member 13. 
The other edges of the frame 10 than that on the side of the light source 
12 are formed so as to cover the end faces of the light-introducing plate 
11 to thereby prevent the ingress of scattering light from the outside. 
The outside edges of the frame 10 except that on the side of light source 
12 are preferably provided with clamping claws (not shown) capable of 
being bent onto the back side of the rear holding portion 13b so as to 
prevent the illuminating device from falling out. 
In thus constructed liquid crystal display device, light emitted from the 
light source 12 is incident on the end face of the light-introducing plate 
11 to enter the inside thereof. The thus proceeding light is reflected on 
the rear holding portion 13b so as to illuminate the rear side of the 
liquid crystal display device 8. 
In this while, heat generated from the light source 12 causes the 
temperature of the holding member 13 to rise. In the present embodiment, 
however, since the cutout 15 is formed on the frame 10 in the portion 
corresponding to the light source 12 as shown in FIG. 3, the heat from the 
light source 12 is not confined inside the frame 10, but will be mostly 
released through the cutout 15 into the air. Accordingly, the temperature 
of the holding member 13 falls, which means that the liquid crystal 
display device 8 decreases in temperature in the vicinity of the holding 
member 13. As a result, temperature variation in the liquid crystal 
display device 8 can be reduced so as to prevent the occurrence of 
unevenness in display density and therefore to be able to improve quality 
of display. 
Specifically, as to the device of the present invention and the prior art 
apparatus shown in FIGS. 1 and 2, measurement of surface temperature of 
the liquid crystal display board 8 was made at two points A and B shown in 
FIG. 5 and defined as follows: 
Point A is a point that lies in a central portion apart from the light 
source 12 and has a relatively low temperature. 
Point B is a point that lies in a corner adjacent to the light source 12 
for liquid crystal display board 8 and has the highest temperature on the 
plate. 
Each measurement of surface temperature of the liquid crystal display board 
8 was taken after the light source 12 had been on for one hour. The result 
is shown in Table 1. As apparent from Table 1, variation of the 
temperature of the present embodiment was improved noticeably as compared 
to that in the prior art. The quality of display was improved such that no 
unevenness in display density could be found by the visual observation. 
In this connection, if the cutout 15 is formed in the frame 10, there could 
be a fear that light emitted from the light source 12 might dissipate 
through the cutout 15, but no light loss will occur and almost all light 
can be lead into the light-introducing plate 11 because the holding member 
13 has a light-blocking property as mentioned above. Accordingly, 
brightness on the illuminated surface can be prevented from deteriorating. 
TABLE 1 
______________________________________ 
Temperature 
Temperature 
Variation 
Current at central at edge in 
through portion A portion B temperature 
tube (mA) (.degree.C.) 
(.degree.C.) 
(.degree.C.) 
______________________________________ 
CEx. 5.0 28.4 31.7 3.3 
Ex. 1 
5.0 26.6 29.3 2.7 
CEx. 6.8 28.3 32.6 4.3 
Ex. 1 
6.8 27.5 31.0 3.5 
______________________________________ 
CEx.: Conventional example, 
Ex: Example of the present invention 
Second Embodiment 
A liquid crystal display device in accordance with a second embodiment of 
the present invention is, as shown in FIGS. 6 and 7, includes a liquid 
crystal display board 8, an illuminating device 9 for illuminating the 
liquid crystal display board 8 from the back side thereof, and a frame 10 
for fixing the liquid crystal display board 8 in front of illuminating 
device 9. The illuminating device 9 is composed of a light-introducing 
plate 11 disposed on the backside of liquid crystal display board 8 in 
parallel therewith, a light source 12 disposed adjacent to an end face of 
the light-introducing plate 11, a holding member 13 for holding the light 
source 12 and light-introducing plate 11. 
A cutout 15 for releasing heat is formed on the frame 10 in a position 
corresponding to the light source 12. In addition, a metallic plate 16 
having a high heat-conductivity is provided in the cutout 15 with keeping 
space from, or not in contact with the frame 10. In one word, the 
configuration is similar to that of the first embodiment in that the 
cutout 15 is formed in the frame 10 in the position corresponding to the 
light source 12, but is different in that the metallic plate 16 having a 
high heat-conductivity is provided in the cutout 15 as is shown in FIGS. 6 
and 7. 
The metallic plate 16 is formed with a typical aluminum plate having an 
elongate rectangular shape, and intimately attached to the holding member 
13 that is exposed in the cutout 15 using an adhesive or any other 
attaching means. This metallic plate 16 is kept away from the frame 10 in 
order to establish adiabatic property from the frame 10. The other 
configurations are the same with those of the first embodiment. 
In this arrangement, heat from the light source 12 is absorbed by the 
metallic plate 16 through the holding member 13. This metallic plate 16 is 
located in the cutout 15 and is exposed outside, so that almost all the 
absorbed heat will be released into the air. Accordingly, the temperature 
of the holding member 13 falls. 
Here, since the frame 10 is kept away from the metallic plate 16, the 
temperature of the frame 10 does not rise as high as that of the metallic 
plate 16, but is kept as low as that of the holding member 13 having a 
relatively low temperature. Accordingly, the temperature of the liquid 
crystal display device 8 in the vicinity of the holding member 13 falls 
relatively as compared to the metallic plate 16. As a result, temperature 
variation in the liquid crystal display device 8 can be reduced so as to 
prevent the occurrence of unevenness in display density and therefore to 
be able to improve quality of display. 
Specifically, as to the device of the present invention and the prior art 
apparatus shown in FIGS. 1 and 2, measurement of surface temperature of 
the liquid crystal display board 8 was made at two points A and B shown in 
FIG. 5 and defined as in the description of the first embodiment. 
Each measurement of surface temperature of the liquid crystal display board 
8 was taken after the light source 12 had been on for one hour. The result 
is shown in Table 2. As apparent from Table 2, variation of the 
temperature of the present embodiment was improved noticeably as compared 
to that in the prior art. The quality of display was improved such that no 
unevenness in display density could be found by the visual observation. 
TABLE 2 
______________________________________ 
Temperature 
Temperature 
Variation 
Current at central at edge in 
through portion A portion B temperature 
tube (mA) (.degree.C.) 
(.degree.C.) 
(.degree.C.) 
______________________________________ 
CEx. 5.0 28.4 31.7 3.3 
Ex. 2 
5.0 28.9 30.5 1.6 
CEx. 6.8 28.3 32.6 4.3 
Ex. 2 
6.8 29.2 31.5 2.3 
______________________________________ 
CEx.: Conventional example, 
Ex: Example of the present invention 
Third Embodiment 
A liquid crystal display device in accordance with a third embodiment of 
the present invention is, as shown in FIGS. 8 and 9, includes a liquid 
crystal display board 8, an illuminating device 9 for illuminating the 
liquid crystal display board 8 from the back side thereof, and a frame 10 
for fixing the liquid crystal display board 8 to a display window 14 in 
front of illuminating device 9. The illuminating device 9 is composed of a 
light-introducing plate 11 disposed on the backside of liquid crystal 
display board 8 in parallel therewith, a light source 12 disposed adjacent 
to an end face of the light-introducing plate 11, a holding member 13 for 
holding the light source 12 and light-introducing plate 11. The frame 10 
is disposed inwardly of the display window 14 while keeping away from the 
holding member 13. Provided on a surface of the holding member 13 is a 
metallic plate 16 for releasing heat, which is not in contact with the 
frame 10. Again, the metallic plate 16 for releasing heat is made of the 
same material as used in the second embodiment such as aluminum, etc., and 
is disposed on the surface of the holding member 13, more clearly, the 
front face, side end and rear face of the holding member 13. The metallic 
plate 16 is kept away from the frame 10 so as not to exchange heat with 
the frame 10. 
In this arrangement, the heat from the light source 12 is absorbed by the 
metallic plate 16 through the holding member 13. This metallic plate 16 is 
exposed outside, so that almost all the absorbed heat will be released 
into the air. 
Accordingly, as the temperature of the holding member 13 falls, the 
temperature of the liquid crystal display device 8 in the vicinity of the 
holding member 13 falls. As a result, temperature variation in the liquid 
crystal display device 8 can be reduced so as to prevent the occurrence of 
unevenness in display density and therefore to be able to improve quality 
of display. 
Specifically, as to the device of the present invention and the prior art 
apparatus shown in FIGS. 1 and 2, measurement of surface temperature of 
the liquid crystal display board 8 was made at two points A and B shown in 
FIG. 5 and defined as in the description of the first embodiment. 
Each measurement of surface temperature of the liquid crystal display board 
8 was taken after the light source 12 had been on for one hour. The result 
is shown in Table 3. As apparent from Table 3, variation of the 
temperature of the present embodiment was improved noticeably as compared 
to that in the prior art. The quality of display was improved such that no 
unevenness in display density could be found by the visual observation. 
TABLE 3 
______________________________________ 
Temperature 
Temperature 
Variation 
Current at central at edge in 
through portion A portion B temperature 
tube (mA) (.degree.C.) 
(.degree.C.) 
(.degree.C.) 
______________________________________ 
CEx. 5.0 28.4 31.7 3.3 
Ex. 2 
5.0 29.0 30.2 1.2 
CEx. 6.8 28.3 32.6 4.3 
Ex. 2 
6.8 28.6 30.5 1.9 
______________________________________ 
CEx.: Conventional example, 
Ex: Example of the present invention 
It should be understood that the present invention is not limited to the 
above embodiments, and various changes and modifications can be added to 
the above embodiment within the scope of the present invention. 
For example, although the light source 12 is disposed on one side end of 
the light-introducing plate 11 in the above embodiments, a pair of light 
sources can be provided on both side ends, respectively. 
As has been apparent from the description heretofore, according to one 
aspect of the present invention, since the cutout is formed in the frame 
in a portion corresponding to the light source so as to expose the holding 
member outside, it is possible to release the heat from the light source 
outside via the cutout. 
In accordance with another aspect of the present invention, there is 
provided a metallic plate for absorbing and releasing the heat from the 
light source, it is possible to cause the temperature of the holding 
member to fall. In this case, the metallic plate is kept away from the 
frame, so that the heat discharged from the metallic plate can be 
prevented from being transmitted to the liquid crystal display board. 
From the above, it is possible to markedly reduce heat-conductance between 
the liquid crystal display board and the light source by establishing 
heat-separation therebetween. Consequently, the present invention exhibits 
an advantage that unevenness in display density on the liquid crystal 
display board can be diminished.