Liquid crystal display unit having an enclosed space between the liquid crystal cell and at least one polarizer

In a liquid crystal display unit for use in a liquid crystal projector used in a high-temperature environment, this invention is directed to provide a liquid crystal display unit which prevents deterioration of the display unit and deformation of a polarizer plate due to temperature, and has a dust-proofing effect for a liquid crystal cell. The liquid crystal display unit 1 comprises at least one liquid crystal cell 2 and at least one polarizer member 3, and further includes a frame member 5 disposed for forming a space 4 between the polarizer member 3 and the liquid crystal cell 2, a vent hole 6 formed at at least a part of the frame member 5 and a filter 7 disposed in at least a part of the vent hole 6.

TECHNICAL FIELD 
This invention relates to a structure of a liquid crystal display unit used 
in a high temperature environment, and a structure of a liquid crystal 
projector. 
BACKGROUND ART 
A typical example of a technology for effecting optical display in a high 
temperature environment using a liquid crystal cell is a liquid crystal 
projector which illuminates the back of a liquid crystal panel comprising, 
for example, a liquid crystal cell and a polarizer plate to form a 
projected image of the liquid crystal panel, and projects a magnified 
image of the liquid crystal panel by an optical system as a projection 
means. 
Hereinafter, the structure and problems with the liquid crystal projector 
ordinarily known in the art will be explained. FIG. 1 is a schematic view 
of the known liquid crystal projector described in Japanese Unexamined 
Patent Publication (Kokai) No. 4-27929, and an air inlet is shown disposed 
at a part of a housing and a dust-proofing filter 401 is added to this air 
inlet. 
In the liquid crystal projector shown in FIG. 1, since transmissivity of a 
polarizer plate 103 is low, about 60% of the light leaving illumination 
means 203, comprising light source means 201 and a condenser lens 202, is 
converted to heat at the polarizer plate 103. 
Particularly in the liquid crystal projector, exothermy in the polarizer 
plate 103 becomes extremely high because luminance of a lamp as light 
source means 201 of the illumination means is high. Accordingly, a change 
in temperature characteristics and deterioration of the liquid crystal and 
of the polarizer plate occur due to this high temperature, and a drop in 
image quality of the projected image and a reduction in the service life 
of the liquid crystal cell 108 occur due to the high temperature. 
Various technologies have been developed in the past to solve the 
temperature problems described above. 
For example, Japanese Unexamined Utility Model Publication (Kokai) No. 
2-69316 and Japanese Unexamined Patent Publication (Kokai) No. 4-27929 
described above propose a solution. However, the liquid crystal projector 
shown in FIG. 1 employs a construction wherein illumination means 203 
comprising mainly a light source lamp 201, a liquid crystal cell 108, and 
an optical system 300 comprising mainly a projection lens are accommodated 
in a casing 500 having a sealed structure and equipped with a cooling fan 
400, a polarizer plate 103 and a liquid crystal cell 108 are spaced apart 
from each other, and the cooling fan 400 cools the inside of the liquid 
crystal projector so as to cool the polarizer plate 103 as well as the 
liquid crystal cell 108 and thus to prevent deterioration of the liquid 
crystal and the polarizer plate due to the heat. 
Further, a dust-proofing filter 401 for preventing intrusion of the dust is 
disposed in front of the cooling fan 400 of the liquid crystal projector 
as shown in FIG. 1, so as to prevent deterioration of quality of the 
projected image due to the dust. 
However, it has not been possible to completely eliminate the dust that has 
entered the liquid crystal projector during the production thereof and the 
dust that unavoidably enters when the lamp as the illumination means is 
exchanged. Accordingly, the dust that has entered the liquid crystal 
projector flies up due to the air pressure of the cooling fan or to the 
vibration or drop of the projector during transportation, and adheres to 
the surface of the liquid crystal cell. When the dust adheres to the 
liquid crystal cell, even if the dust is small, it is magnified by the 
optical system as the projection lens and deteriorates the quality of the 
projected image. 
Once adhered to the surface of the liquid crystal cell, the dust cannot be 
removed easily because the the liquid crystal cell is sealed in the casing 
of the liquid crystal projector, and the liquid crystal projector cannot 
be disassembled without using a high level of skill and the jigs used by 
the manufacturer of the liquid crystal projector. Further, the liquid 
crystal cell may be damaged when removing the dust, and this damage 
results in a drop in the quality of the projected image. 
Accordingly, no means has been available for effectively preventing 
adhesion of the dust in the liquid crystal projector to the surface of the 
liquid crystal cell, or a method of easily removing the dust when the dust 
adheres to the surface of the liquid crystal cell, and users must ask the 
manufacturer to disassemble the liquid crystal display unit. Thus, not 
only the cost is high, but use of the liquid crystal projector is 
curtailed. 
On the other hand, the liquid crystal cell, too, has a problem in that its 
temperature characteristics change when the temperature rises and a drop 
in contrast occurs. This problem must be solved together with the problems 
described above. 
DISCLOSURE OF THE INVENTION 
It is an object of the present invention to provide a liquid crystal 
display unit which solves the problems in the prior art described above, 
exhibits an excellent cooling effect, and either does not allow the 
adhesion of the dust onto the surface of the liquid crystal cell or, if 
the dust does adhere, can prevent the dust from being seen in the image 
that is optically reproduced. The present invention is further directed to 
provide a liquid crystal display unit which prevents a change of contrast 
in the liquid crystal cell even when the temperature of the liquid crystal 
cell reaches a high temperature, and can always provide a high quality 
image, and furthermore, to provide a liquid crystal projector using such a 
liquid crystal display unit. 
To accomplish the objects described above, the present invention provides 
the following technical constructions. Namely, the present invention 
provides a liquid crystal display unit comprising at least one liquid 
crystal cell and at least one polarizer member, and includes a frame 
member so disposed as to define a space between the polarizer member and 
the liquid crystal cell, a vent hole formed at at least a part of the 
frame member, and a filter disposed at at least a part of the vent hole, 
and a liquid crystal projector using the liquid crystal display unit. 
The liquid crystal display unit according to the present invention will be 
explained in further detail. The liquid crystal display unit comprises, 
for example, a first polarizer member, at least one liquid crystal cell 
and a second polarizer member, and includes a frame member so disposed as 
to define a space at least between the first polarizer member and the 
liquid crystal cell or between the liquid crystal cell and the second 
polarizer member, a vent hole formed at at least a part of the frame 
member, and a filter disposed at at least a part of the vent hole. The 
liquid crystal projector uses the liquid crystal display unit having such 
a construction. 
In other words, in the liquid crystal display unit according to the present 
invention, the space between the liquid crystal cell and the polarizer 
member is covered with a dust-proofing filter; hence, it is difficult for 
dust to enter the peripheral portion of the liquid crystal cell. In the 
liquid crystal projector using the display unit according to the present 
invention, the dust is not allowed to adhere to the liquid crystal cell 
even when dust is trapped inside the projector at the time of assembly or 
at the time of exchange of the lamp. 
Even when the dust adheres to the outside surface of the polarizer member 
in the liquid crystal display unit according to the present invention, 
design is so made as to secure the space between the liquid crystal panel 
and the polarizer and to make this gap larger than the depth of focus of 
the lens constituting the optical system. According to this construction, 
even when the dust adheres to the surface of the liquid crystal cell, the 
dust is out of focus, and cannot be seen even when the projected image is 
observed. Accordingly, even when the dust adheres to the outside surface 
of the polarizer member, the influence of the dust on the quality of the 
projected image cannot be observed. As will be described later, too, the 
polarizer member can be in close contact with transparent glass. 
Accordingly, deformation of the polarizer plate due to heat can be 
prevented, and, when the polarizer plate is disposed in such a manner that 
the glass side is on the outside surface, the dust adhering to the outside 
surface of the transparent glass plate can be easily cleaned without 
damaging the polarizer plate.

BEST MODE FOR CARRYING OUT THE INVENTION 
Hereinafter, definite examples of a liquid crystal display unit according 
to the present invention and a liquid crystal projector constituted by the 
use of this liquid crystal display unit will be described in detail with 
reference to the accompanying drawings. 
FIG. 2 is a sectional view useful for explaining the basic structure of a 
liquid crystal display unit 1 according to the present invention. The 
drawing shows the liquid crystal display unit 1 which comprises at least 
one liquid crystal cell 2 and at least one polarizer member 3, and has a 
construction wherein a frame member 5 is so disposed as to define a space 
4 between the polarizer member 3 and the liquid crystal cell 2, a vent 
hole 6 is bored at at least a part of the frame member 5, and a filter 7 
is disposed at at least a part of this vent hole 6. 
The structure of the liquid crystal cell 2 used in the present invention is 
not particularly limited, and a TN type liquid crystal cell or an STN type 
liquid crystal cell, which are known in the art, can be used. In 
connection with a driving method of these liquid crystal cells, it is 
possible to employ a passive type liquid crystal cell wherein a plurality 
of electrodes are juxtaposed with one another on the surfaces of liquid 
crystal support members opposing each other, and moreorever orthogonally, 
with one another between the liquid crystal support members, or an active 
type liquid crystal cell wherein active devices each comprising a 
transistor, or the like, are individually arranged in such a manner as to 
correspond to elements of the liquid crystal cells, respectively. 
An example of the passive type liquid crystal cell which can be used in the 
present invention will be hereby explained with the sectional view of FIG. 
3. 
The passive type liquid crystal cell 100 includes a plurality of electrodes 
104, 105 which comprise a conductor film, etc., and are juxtaposed on the 
inner surfaces of substrates 101, 102 so disposed as to oppose each other 
with a predetermined gap between them, and with a suitable seal member 
103, interposed therebetween. 
In other words, a plurality of electrodes 104 each comprising a conductor 
film are juxtaposed with one another on the inner surface of the substrate 
101 and are covered with a suitable orientation film 106. 
On the other hand, a plurality of conductor films 105 are juxtaposed with 
one another on the inner surface of the other substrate 102 at right 
angles to the direction of arrangement of the electrodes 104, and are 
covered with a suitable orientation film 107. 
A suitable liquid crystal 108 is sandwiched in a space between the 
substrates 101 and 102 and a spacer 109 is mixed in this liquid crystal 
108 so as to suitably keep the gap between the substrates. 
Another structural example of the passive type liquid crystal cell is shown 
in FIG. 4. 
Fundamentally, this liquid crystal cell has exactly the same structure as 
that of the passive type liquid crystal cell 100 shown in FIG. 3, and the 
difference lies in that suitable color filters 120 are disposed on a 
conductor film 115 provided to the inside surface of the substrate 112 as 
shown in FIG. 4. 
On the other hand, an example of an active type liquid cyrstal cell is 
shown in FIG. 5. 
As shown in FIG. 5, the active type liquid crystal cell has a construction 
wherein an active device 122 comprising a transistor, or the like, is 
disposed on each of the pixel electrodes 121; hence, each pixel electrode 
is individually controlled by a signal. 
In this active type liquid crystal cell, too, the color filters can be 
used. 
On the other hand, the structure of the polarizer member 3 used in the 
present invention is not particularly limited, and a polarizer member that 
has been used ordinarily in the past can be used, too. 
The materials, thickness, etc, of the polarizer member 3 are not 
particularly limited, either. 
A polarizer member "G1220UD", a product of Nitto Denko K.K., for example, 
can be suitably used as the polarizer member 3 in the present invention. 
Next, the frame member 5 used for the liquid crystal display unit according 
to the present invention will be explained. This frame member has the 
function of forming a suitable gap at least between the liquid crystal 
cell 2 and the polarizer member 3, and its size, length, etc, are varied 
in accordance with the size of the liquid crystal display units used, 
respectively. 
In the present invention, connection between the frame member 5 and the 
liquid crystal cell 2 can be established by sandwiching a suitable liquid 
crystal cell support. 
The frame member 5 shown in FIG. 2 may be composed of a member having four 
surfaces as shown in FIG. 6(A) comprising a sheet-like member 11 so that 
the space 4 between the liquid crystal cell 2 and the polarizer member 3 
can be completely sealed, for example. In this case, the afore-mentioned 
vent hole or holes 6 are preferably bored at a suitable position or 
positions of the sheet-like member 11. 
As to the frame member 5, a member assembled by rods, thin sheets 12, etc, 
only at portions corresponding to the outer peripheral portions of the 
space 4 can be used, as shown in FIG. 6(B). 
In such a case, a suitable shield member is fitted to the peripheral 
portion of the frame member 12 so as to define a sealed space inside the 
frame assembly, and the vent hole 6 is formed at a suitable position. An 
airpermeable filter made of a non-woven fabric, a knitted fabric, or the 
like, may also be fitted as the shield member. In such a case, the vent 
hole 6 need not be disposed, in particular. 
Alternatively, as shown in FIG. 6(C), a trapezoidal frame member 5 formed 
by mutually connecting four peripheral sheet portions 13 may be used as a 
modified member of FIG. 6(A). 
In the present invention, any filter can be used as the filter disposed at 
at least a part of the vent hole so long as it has the function of easily 
passing an air stream but cutting off the dust, etc, which might cause 
problems. For example, a non-woven fabric, mesh knitted fabrics, etc, 
having a large number of voids thereinside, or a combination, may be used. 
An example of the liquid crystal display unit 1 constituted by the use of 
the frame member shown in FIG. 6(C) corresponding to the frame member 5 
shown in FIG. 2 will be explained with reference to FIG. 7. 
FIG. 7 shows an example wherein a liquid crystal projector 200 is 
constituted by the use of liquid crystal unit 1. In the drawing, a light 
source 201 constituting the afore-mentioned illumination means 203, the 
liquid crystal display unit 1 and a projection optical system 300 are 
disposed in such a manner that their optical axes are in parallel with, 
and touching, one another. The ray of light leaving the light source 201 
passes through the liquid crystal cell 2 fitted to the liquid crystal cell 
support 10 that constitutes the liquid crystal display unit 1, then passes 
through the polarizer member 3 fitted to the frame member 5 molded into a 
trapezoidal shape, passes into the optical system 300 and forms a 
projection image. 
The frame member 5 molded into the trapezoidal shape has a substantially 
prismatic shape and has a suitable opening 14 at a portion at which the 
polarizer member 3 is supported and fixed. On the other hand, a suitable 
opening 15 is bored at a substantial center of the liquid crystal cell 
support 10 so as to allow the passage of light to the liquid crystal cell 
2. 
The frame member 5 and the liquid crystal cell support 10 are fixed to each 
other by suitable connection means 16. 
The liquid crystal display unit 1 is fixed to a part of a casing 500 which 
constitutes the liquid crystal projector 200, by a suitable fixing member 
17. 
In the liquid crystal projector 200 according to the present invention, a 
suitable vent hole 401 is formed at a part of the casing 500, and 
compulsive air circulation means 401 such as a suitable fan is preferably 
disposed at this vent hole 400. 
Incidentally, reference numeral 402 denotes an exhaust port. 
In other words, when the liquid crystal display unit 1 according to the 
present invention is used inside the liquid crystal projector 200, the 
portion of the liquid crystal cell 2 is generally disposed at a position 
near the light source 201 of the liquid crystal projector 200. Therefore, 
the liquid crystal cell 2 directly receives optical energy from the light 
source 201. Since this optical energy is built up inside the liquid 
crystal cell 2, the internal temperature rises inside the liquid crystal 
cell 2. 
Accordingly, when the temperature of the liquid crystal cell 2 becomes 
high, the characteristics of the liquid crystal cell 2 deteriorate, 
depending on the temperature characteristics of the liquid crystal cell 2, 
and its contrast may drop. However, a cooling air stream is introduced 
from the vent hole 6 of the frame member 5 and cools the inside surface of 
the liquid crystal cell 2 so as to prevent the rise of the temperature of 
the liquid crystal cell 2 above a predetermined temperature. At the same 
time, when the frame member 5 seals the space between the liquid crystal 
cell 2 and the polarizer member 3 and a suitable filter 7 is disposed at 
the vent hole 6 disposed at a suitable position, the problem of intrusion 
and adhesion of the dust onto the surface of the liquid crystal cell 2, 
that has been the problem with the prior art devices, can be solved. 
The explanation given above explains the fundamental structure of the 
liquid crystal display unit 1 according to the present invention, which 
comprises one liquid crystal cell 2 and one polarizer member 3. In the 
present invention, however, a plurality of polarizer members 3 can be used 
for one liquid crystal cell 2 or a plurality of liquid crystal cells 2 can 
also be used in the present invention. 
Next, an example of the liquid crystal display unit 1 constituted by the 
use of one liquid crystal cell 2 and two polarizer members 3 in the 
present invention will be explained. 
FIG. 8 is a sectional view useful for explaining the outline of the 
construction described above. The drawing shows the liquid crystal display 
unit 1 comprising a first polarizer member 31, at least one liquid crystal 
cell 2 and a second polarizer member 3. The liquid crystal display unit 
further includes a frame member 51 or 5 for defining a space 41 or 4 at 
least between the first polarizer member 31 and the liquid crystal cell 2 
or between the liquid crystal cell 2 and the second polarizer member 3, a 
vent hole 61 or 6 disposed at at least a part of the frame member 51, 5, 
and a filter 71, 7 disposed at at least a part of the vent hole 61, 6. 
Accordingly, the construction shown in FIG. 8 illustrates only one example 
of the technical construction of the present invention. For example, one 
of the spaces 41, 4 may be omitted and the liquid crystal cell 2 and 
either one of the polarizer members 31, 3 may be directly bonded. 
In the definite embodiment of the present invention, the spaces 41, 4 
between the first polarizer member 31 and the liquid crystal cell 2 and 
between the liquid crystal cell 2 and the second polarizer member 3 may be 
the same, or may be changed, whenever necessary. 
Another definite structural example of the present invention will be 
explained with reference to FIG. 9. This drawing shows the construction 
wherein another polarizer member is so disposed on the opposite surface to 
the surface of the liquid crystal cell 2, on which the polarizer member 3 
is disposed, as to oppose the polarizer member 3, in the construction 
shown in FIG. 7. 
In other words, the frame member 51 having substantially the same structure 
as that of the frame member 5 in FIG. 7 is fitted to the liquid crystal 
cell support 10 of the liquid crystal display unit 1 in FIG. 7 on the side 
of the light source 201, and the first polarizer member 31 is disposed to 
the opening 41 of the frame member 51. 
In this embodiment, the polarizer member 3 in FIG. 7 will be called "the 
second polarizer member", and the polarizer member 31 adjacent to the 
light source 201 in this embodiment will be called the "first polarizer 
member". Further, the frame member 5 in FIG. 7 will be called the "second 
frame member", and the frame member 51 close to the light source 201 in 
this embodiment will be called the "first frame member". 
The construction in this embodiment will be explained in further detail. 
The definite example shown in FIG. 9 is fundamentally the same as the 
definite example shown in FIG. 7, and represents an example wherein the 
liquid crystal projector 200 is constituted by the use of the liquid 
crystal display unit 1. In FIG. 9, the light source 201, the liquid 
crystal display unit 1 and the projection optical system 300 are disposed 
in such a manner that their optical axes are in parallel with, and 
touching, one another. The ray of light leaving the light source 201 first 
passes through the first polarizer member 31 disposed on the first frame 
member 51 molded into a trapezoidal shape and fitted to the liquid crystal 
cell support 10 constituting the liquid crystal display unit 1, then 
passes through the liquid crystal cell 2 supported by the liquid crystal 
cell support 10, is incident into the optical system 300 and forms a 
projection image. 
The first frame member 51 molded into the trapezoidal shape has a 
substantially primsatic shape, has a suitable opening 141 at the portion 
at which the first polarizer member 31 is supported and fixed, and is 
fixed to the liquid crystal cell support 10 by suitable connection means 
161 such as, for example, screws. 
The liquid crystal display unit 1 is fixed to a part of the casing 500 
constituting the liquid crystal projector 200 by a suitable fixing member 
17. 
In the liquid crystal projector 200 according to the present invention, a 
vent hole 401 is formed at a suitable position of the casing 500, and air 
circulation means 400 such as a suitable fan, etc, is preferably provided 
at this vent hole 401. 
FIG. 10 is a perspective view showing the appearance of the construction of 
the liquid crystal display unit 1 of this embodiment of the present 
invention. The unit 1 includes connection members 16, 161 for connecting 
and integrating the constituent members of the liquid crystal display unit 
1 described above, and air is caused to flow inside the display unit 1 
having at least two openings 6, 61 formed on the side surface portions 
thereof. A fixing end portion 17 is formed at the end portion of the 
liquid crystal cell support 10 so as to fix the support 10 to the casing 
500. The display unit 1 comprises three members, that is, the first frame 
member 51, the liquid crystal cell support 10 and the second frame member 
5, and these members are molded from a resin material, for example. The 
liquid crystal cell support 10 is clamped between the first and second 
frame members 5, 51, and the connecting end portion of each frame member 
is fastened by screws as an example of the connecting members 16, 161 
described above so as to define a sealed structure. 
When the fixing member 17 of the liquid crystal cell support 10 clamped in 
the way described above is fixed by screws to the casing 500, the liquid 
crystal display unit 1 is fixed to the casing 500. The frame members 5, 51 
and the liquid crystal cell support 10 may be made of a resin, but the 
object of the present invention can also be accomplished by using other 
materials such as metal, ceramic, and so forth. 
In the definite example shown in FIG. 9, the liquid crystal cell 2 is fixed 
by a bonding member to the liquid crystal cell support 10 so that it is 
positioned substantially vertical to the direction of the optical axis. 
On the other hand, the first and second polarizer members 31 and 3 are 
bonded by a bonding material to the open end portions 14, 114 of the frame 
members 5, 51 on the opposite side to the liquid crystal cell 2. It is 
possible, for example, to use a member obtained by bonding a polarizer 
plate 53, 531 to transparent glass 52, 521, as the polarizer member 3, 31. 
Since the polarizer plate is bonded to heat-resistant glass in this case, 
deformation of the polarizer plate due to heat can be prevented. A 
double-face adhesive tape is preferably used as the bonding member for 
bonding the glass member to the polarizer plate as bonding efficiency can 
be improved in this way. 
In the definite example of the present invention described above, the 
filter 7, 71 for preventing intrusion of the dust is disposed at the 
opening 6, 61 for passing the air, disposed on the side surface of the 
prasmatic frame member 5, 51. The filter having the construction described 
above, for example, may be provided by bonding or fusion, so that the 
inside of the liquid crystal display unit 1 assumes structure sealed to 
dust. Bonding by an adhesive may be used as a method of fitting the filter 
for preventing dust entering to the frame. 
A driving circuit 600 for driving the liquid crystal cell 2 and forming a 
projection image is disposed inside the casing 500 of the liquid crystal 
projector 200, and is connected to the liquid crystal cell 2 by a thin 
flexible printed circuit (FPC) 601. A notch 54 corresponding to the 
thickness of the FPC 601 is formed in the frame member 5, 51. The filter 
of a non-woven fabric, for example, is disposed on the notch 54 and at the 
same time, wiring is made through the FPC. The frame member 5, 51 and the 
liquid crystal cell support 10 are combined and are then fixed by screws 
16, 161, as connecting means, so as to seal the liquid crystal cell 2. 
FIG. 10 shows a definite example of the sealed structure of the liquid 
crystal display unit 1 using the liquid crystal cell 2 of the present 
invention. 
In the construction of the liquid crystal projector 200 according to the 
present invention, a suction port 401 for external air and an exhaust port 
402 are formed in the casing 500 of the liquid crystal projector 200, a 
cooling fan 400 fitted to the casing 500 generates an air stream inside 
the casing 500, and the polarizer plate 3 and the liquid crystal cell 2 
are cooled by this air stream through the filters 7, 71 fitted to the 
frame members 5, 51. 
The explanation given above explains the case where the prismatic support 
frames 5, 51 are used for the structure of the liquid crystal display unit 
1 of the present invention, but their shapes are arbitrary. The 
explanation given above deals with the case where the liquid crystal 
display unit 1 comprises the prismatic frame members 5, 51 for supporting 
the polarizer members 3, 31 and the liquid crystal cell support 10 for 
supporting the liquid crystal cell 2, but other structures may of course 
be used. In short, it is possible to employ a structure wherein the first 
polarizer member, the liquid crystal cell and the second polarizer member 
are disposed in order named and with gaps between them, respectively, and 
are integrally held, and wherein the spaces 4, 41 are connected to the 
openings 6, 61 of the frame members 5, 51, capable of ventillating with 
the outside and the openings 6, 61 are covered with the dustproofing 
filters 7, 71. 
In the definite example of the invention described above, four openings 6, 
61 for ventillation, in all, are shown disposed in the liquid crystal 
display unit, but the number of openings and their sizes are not 
particularly limited. 
As another structural example of this embodiment, it is also possible to 
directly dispose the first polarizer member 31 on the surface of the 
liquid crystal cell support 10, to which the second frame member 5 is not 
bonded and which opposes the light source 201, without disposing the frame 
member 51. 
In such a definite example, the gap portion defined in the liquid crystal 
cell support 10, that is, a window 15, defines the gap between the liquid 
crystal cell 2 and the first polarizer member 31. 
In the definite example of the invention described above, only one liquid 
cell 2 is shown used, but two or more liquid crystal cells 2 can be used 
in combination. 
The reason why the present invention uses the active type liquid crystal 
cell as the liquid crystal cell 2 is because the contrast of the display 
screen of the liquid crystal display unit comprising the liquid crystal 
cell is by far better than the liquid crystal cells of other types, and an 
angle of visibility, too, is greater than in other types of liquid crystal 
cells. 
Furthermore, in the present invention, at least one of the polarizer 
members 3, 31 is preferably supported by a suitable polarizer member 
support 18 as shown in FIG. 11, and this polarizer member support 18 may 
be the frame member 5, 51 itself or may be bonded in a suitable form to 
the frame member 5, 51. 
The polarizer member 3, 31 is fixed to, and supported by, the polarizer 
member support 18 by adhesion, bonding, fixing, fitting, and other 
suitable means. 
When the polarizer plate support 18 is made of a light-transmitting 
material, this support 18 need not particularly be provided with an 
opening or a window for transmitting light at the portion corresponding to 
the opening provided to the frame member 5, 51 or to the window 14, 141, 
and it is possible to employ the structure where the polarizer member 3, 
31 is directly bonded to the polarizer member support 18. 
FIGS. 12 and 13 are sectional views useful for explaining another 
embodiment of the present invention. 
FIG. 12 shows the liquid crystal display unit 1 having a construction 
wherein the polarizer member 3 is bonded to the outside surface of the 
polarizer member support 18 by a suitable adhesive 19 so that the surface 
of the polarizer member 3 constitutes the outside surface of the liquid 
crystal display unit 1. FIG. 13 shows the liquid crystal display unit 1 
having a construction wherein the polarizer member 3 is bonded to the 
inside surface of the polarizer member support 18 by a suitable adhesive 
so that the surface of the polarizer 3 constitutes the inside surface of 
the liquid crystal display unit 1. 
Such constructions can be as such applied to the liquid crystal display 
unit 1 having the construction using the first and second polarizer 
members 3, 31 shown in FIG. 8. 
In the embodiment described above, the polarizer member support 18 is 
preferably made of glass or a heat reflective filter or a suitable plastic 
material. 
When the material constituting the polarizer member support 18 is glass in 
the present invention, this glass preferably has heat absorption property, 
and is preferably the Kind 1 IR-absorption glass as stipulated in JIS 
R3207, for example. 
In other words, in the embodiment described above, the polarizer member 3 
has a structure obtained by bonding transparent glass and the polarizer 
member so as to prevent deformation of the polarizer plate 3. 
As an example where the polarizer member 3 is bonded to the frame member 5 
as the prismatic support, FIG. 12 shows the example where the polarizer is 
so disposed as to constitute the outside surface of the liquid crystal 
display unit 1 and glass 18 is so disposed as to exist on the internal 
side of the liquid crystal display unit 1. In this case, however, there is 
the possibility that the polarizer plate 3 is damaged when the dust 
adhering to it is cleaned. Therefore, if the arrangement is made in such a 
manner that the surface of glass 18 becomes the outside surface, the dust 
adhering to the surface of glass 18 can be removed without damaging the 
polarizer plate 3, and the effect of the present invention can be further 
improved. Needless to say, the polarizer member 3 may have a structure 
obtained by closely sandwiching the polarizer plate 3 by two transparent 
glass 18 and in this case, bonding between the polarizer plate and glass 
becomes unnecessary. 
As already described, the material of the liquid crystal cell used in the 
present invention is not particularly limited but in order to obtain the 
desired performance from the liquid crystal display unit, the liquid 
crystal cell is preferably constituted by a liquid crystal the liquid 
cyrstal molecules of which have a twist angle .alpha. within the range 
described below: 
EQU 180.degree..ltoreq..alpha. 
More preferably, the twist angle .alpha. is from 240.degree. to 
270.degree.. 
As a liquid crystal cell that satisfies the condition described above, a 
super-twist nematic type (STN) liquid crystal is preferably used, for 
example. 
As also described already, it has been found that in the liquid crystal 
display unit according to the present invention, the image display 
characteristics of the liquid crystal cell 2 used for the liquid crystal 
display unit 1 are greatly affected by temperature, and when the liquid 
crystal display unit 1 is used in a high temperature as in one of the 
definite examples, there might occur a problem in that the contrast 
changes. 
Accordingly, in the present invention, this problem can be solved by using 
a member made of a light transmitting material and having opposite 
temperature characteristics to the temperature characteristics of the 
liquid crystal cell 2 as a correction member, in combination. 
In another embodiment of the liquid crystal display unit 1 of the present 
invention, the liquid crystal display unit 1 comprises at least one liquid 
crystal cell 2, at least one polarizer member 3 and at least one phase 
correction member 20 as shown in FIG. 14, wherein the phase correction 
member 20 is made of a light transmitting material having opposite 
temperature characteristics to those of the liquid crystal cell 2. 
Such a phase correction member 20 is made of a light transmitting material 
having temperature characteristics opposite to those of the liquid crystal 
cell 2. Therefore, when the temperature changes, the change of the 
characteristics on the basis of their temperature characteristics mutually 
offset, so that flat temperature characteristics can be formed. 
Accordingly, the problem that the colors of the image change at high 
temperatures can be avoided. 
Such a phase correction member 20 may be bonded to the liquid crystal cell 
2 used in the liquid crystal display unit 1 or may be so disposed as to 
oppose the liquid crystal cell 2 through a suitable gap between them. 
In other words, as shown in FIG. 14, the liquid crystal display unit 1 
according to another embodiment of the present invention comprises at 
least one liquid crystal cell 2, at least one polarizer member 3 and at 
least one phase correction member 20. This liquid crystal display unit 1 
includes the frame member 5 for defining the space at least between the 
polarizer member 3 and the liquid crystal cell 2 or between the liquid 
crystal cell 2 and the phase correction member 20 or the polarizer member 
3 and the phase correction member 20, the vent hole 6 formed at at least a 
part of the frame member 5, and the filter 7 provided to at at least a 
part of the vent hole 6, wherein the phase correction member 20 is either 
bonded to, or disposed near, the polarizer member 3 or the liquid crystal 
cell 2, or is disposed inside the space 4 defined between the polarizer 
member 3 and the liquid crystal cell 2. 
In other words, this embodiment of the present invention has a construction 
wherein the phase correction member 20 is added to the basic construction 
of the liquid crystal display unit of the invention shown in FIG. 2, and 
several forms can be conceived depending on the position of this phase 
correction member 20. 
In the embodiment shown in FIG. 14, the phase correction member 20 is 
disposed on the outside surface of the liquid crystal cell 2, that is, in 
the direction towards the light source when the liquid crystal display 
unit is assembled in the liquid crystal projector, and moreover, the 
liquid crystal cell 2 and the phase correction member 20 are bonded in 
close contact with each other. 
In the present invention, the liquid crystal cell 2 and the phase 
correction member 20 may be disposed with a predetermined gap between 
them. 
Further, the phase correction member 20 may be disposed on the surface of 
the liquid crystal cell 2 the surface of which being on the opposite to 
the polarizer member 3; or in close contact with the same surface of the 
liquid crystal cell 2 with a predetermined gap between them, and may also 
be disposed in the proximity of the polarizer member 3 or may be bonded to 
the polarizer member 3. 
In the embodiment of the present invention described above, the phase 
correction member 20 is preferably disposed on the outside surface of the 
liquid crystal cell 2 so as to prevent the adhesion of the dust on the 
surface of the liquid crystal cell 2 and to protect the surface of the 
liquid crystal cell 2 from damage. Further, when the liquid crystal cell 
is used as the liquid crystal display unit of the liquid crystal 
projector, the surface of the liquid crystal cell 2 opposing the light 
source 200 of the liquid crystal projector is preferably covered with the 
phase correction member 20. 
The surface of the phase correction member 20 is preferably cooled by 
cooling air. 
The thickness of the phase correction member 20 in the present invention is 
not particularly limited but when the liquid crystal display unit 1 is 
used as the liquid crystal display unit of the liquid crystal projector, 
the design is preferably made in such a manner that the outside surface of 
the phase correction member is outside the depth of focus of the 
projection lens of the liquid crystal projector, because, even when the 
dust adheres to the outside surface of the phase correction member 20, the 
dust is not seen on a projected image. 
Still another embodiment of the invention is shown in FIG. 15. Namely, this 
embodiment represents the liquid crystal display unit 1 which uses two 
polarizer members, and has the construction wherein the first polarizer 
member 31, at least one phase correction member 20, at least one liquid 
crystal cell 2 and the second polarizer member 3 are disposed in order 
named along the optical axis. The display unit 1 further includes the 
frame member 5, 51 for defining the space 4, 41 at least between the 
second polarizer member 3 and the liquid crystal cell 2 or between the 
liquid crystal cell 2 and the phase correction member 20 or between the 
phase correction member 20 and the first polarizer member 31, the vent 
hole 6, 61 formed at at least a part of the frame member 5, 51 and the 
filter 7, 71 disposed at at least a part of the vent hole 6, 61. 
As a preferred embodiment of this embodiment, the filter 71 is disposed at 
the vent hole 61 of the space 41 and cooling air is caused to flow into 
this space 41. 
According to such a construction, dust is prevented from adhering to the 
liquid crystal cell 2, the surface of the liquid crystal cell 2 can be 
protected from damage, and a temperature rise in the liquid crystal cell 2 
can be effectively prevented. 
Still another embodiment of the invention described above is shown in FIG. 
16. Namely, this embodiment employs a construction wherein the filter 71 
is not provided to the vent hole 61 formed in the frame member 51 for 
defining the space 41 between the first polarizer member 31 and the phase 
correction member 20 as shown in the drawing. As described above, when 
design is made in such a manner that the outside surface of the phase 
correction member 20 exists outside the depth of focus of the projection 
lens of the liquid crystal projector, the dust cannot be seen on the 
projected image even if the dust adheres to the outside surface of the 
phase correction member 20. Accordingly, the filter becomes unnecessary, 
and the cooling effect of the liquid crystal cell 2 can be improved. 
FIG. 17 shows still another embodiment of the liquid crystal display unit 1 
of the invention described above. This embodiment comprises the liquid 
crystal display unit 1 comprising the first polarizer member 31, at least 
one liquid crystal cell 2, at least one phase correction member 20, and 
the second polarizer member 3, which are disposed in the order given along 
the optical axis. The display unit 1 further includes the frame member 5, 
51 for defining the space 4, 41 at least between the first polarizer 
member 3 and the liquid crystal cell 2 or between the liquid crystal cell 
2 and the phase correction member 20 or between the phase correction 
member 20 and the second polarizer member 3, the vent hole 6, 61 formed at 
at least a part of the frame member 5, 51 and the filter 7, 71 disposed at 
at least a part of the vent hole 6, 61. 
This embodiment is mainly directed to effect color correction of the liquid 
crystal cell 2, and can further compensate for the temperature 
characteristics of the liquid crystal cell 2. Furthermore, the filter 71 
must be disposed at the vent hole 61 of the frame member 51 constituting 
the space 41. 
FIG. 18 shows still another embodiment of the liquid crystal display unit 1 
of the invention described above. The liquid crystal unit 1 comprises the 
first polarizer member 31, at least one liquid crystal cell 2, the second 
polarizer member 3 and at least two phase correction members 20, 21. The 
first phase correction member 20 is interposed between the first polarizer 
member 31 and the liquid crystal cell 2 and the second phase correction 
member 21 is interposed between the liquid crystal cell 2 and the second 
polarizer member 3. The liquid crystal display unit 1 further includes the 
frame members 5, 51, for defining the space 4, 41, at least between the 
first polarizer member 31 and the first phase correction member 20 or 
between the first phase correction member and the liquid crystal cell 2, 
or between the liquid crystal cell 2 and the second phase correction 
member 21, or between the second phase correction member 21 and the second 
polarizer member 3, the vent hole 6, 61 formed at at least a part of the 
frame member 5, 51 and the filter 7, 71 provided at at least a part of the 
vent hole 6, 61. 
The connection method between the polarizer members, the liquid crystal 
cell and the phase correction members, the connection method between these 
members and the frame member, etc, are the same as the connection methods 
used in the foregoing embodiments. 
In the embodiment shown in FIG. 18, in particular, a method shown in FIG. 
19 can be used as the bonding method between the liquid crystal cell 2 and 
the two phase correction members 20, 21. 
In other words, the liquid crystal cell 2 is fitted and fixed to the 
opening of the liquid crystal cell support 10 and the window 15, and the 
first and second phase correction members 20, 21 are arranged and fixed to 
both surface of the liquid crystal cell support 10 in such a manner as to 
cover the window 15. In this way, the space 4, 41 between the liquid 
crystal cell 2 and the phase correction member 20, 21 can be set to a 
predetermined gap. 
The phase correction member 20 used in the present invention preferably has 
opposite the temperature characteristics to the liquid crystal cell 2 
used, as already described, and the effect is shown in FIG. 20. 
FIG. 20 is a graph showing the temperature characteristics of TN and STN 
liquid crystal cells as the typical liquid crystal cells used in the 
present invention in terms of the change of a ratio of a threshold voltage 
V.sub.th (25.degree. C.) at 25.degree. C. to a threshold voltage V.sub.th 
with a temperature change, that is, V.sub.th /V.sub.th (25.degree. C.), 
with respect to an ambient temperature. 
The temperature characteristics of the TN and STN type liquid crystal cells 
exhibit negative characteristics to the temperature rise. Accordingly, the 
temperature characteristics of the TN or STN type liquid crystal cell can 
be flattened as represented by symbol HC by constituting the phase 
correction member 20 by a material having positive temperature 
characteristics as represented by dotted line HB and combining it with the 
TN or STN type liquid crystal cell. 
Ideally, the phase correction member 20 must be designed so that the graph 
becomes the dashed line graph H0 which exhibits constant characteristics 
irrespective of the temperature as shown in FIG. 20. 
The construction of the liquid crystal display unit using the phase 
correction member 20 according to the present invention can be used in 
combination with all the constructions not using the phase correction 
member. 
The phase correction member 20 may be constituted by a liquid crystal cell 
having a phase correction function in the same way as the one used as the 
liquid crystal cell 2, and may also be constituted by a film having a 
phase correction function. 
When the liquid crystal cell type member is used as the phase correction 
member 20 in the present invention, a liquid crystal cell made of the same 
material as the liquid crystal cell used as the driving liquid crystal 
cell 2 of the liquid crystal display unit is preferably used, and in such 
a case, electrodes similar to those of the driving liquid crystal cell 2 
of the liquid crystal display unit need not be provided, but the 
orientation of this liquid crystal is preferably opposite to the 
orientation of the driving liquid crystal cell 2. 
When a member consisting of a film is used as the phase correction member 
20 in the present invention, "NRZ440" produced by Nitto Denko K.K., for 
example, can be suitably used. 
Furthermore, when the liquid crystal cell unit 1 constituted by the use of 
such a phase correction member 20 according to the present invention is 
used for the liquid crystal projector, it is preferred that the phase 
correction member 20 be disposed on the light input side and the liquid 
crystal cell 2, on the light output side. 
In the present invention, an opposite construction to the above, that is, a 
construction wherein the phase correction member 20 is disposed on the 
light output side and the liquid crystal cell is disposed, on the light 
input side, can also be used in the liquid crystal display unit comprising 
the liquid crystal display unit 1 and the light source 201 and using the 
phase correction member 20 described above. 
Further, it is possible in the present invention to constitute the liquid 
crystal projector using the liquid crystal display unit 1 constituted by 
the use of the phase correction member 20 described above. As a definite 
structural example, the liquid crystal projector comprises an illumination 
device 203 comprising an illumination optical system including at least 
the light source 201 and the condenser lens 202, the projection optical 
system 300 and the liquid crystal display unit 1 described above. More 
definitely, as shown in FIG. 18, the first polarizer member 31 in the 
liquid crystal display unit is preferably disposed at the light source 
side and in another embodiment, the first polarizer member 31 or the first 
phase correction member 20 in the liquid crystal display unit are both 
preferably disposed at the light source side relative to the liquid 
crystal cell 2. 
The fan 400 is provided to the liquid crystal display unit 1 so as to 
generate an air stream in the same way as in the foregoing embodiments. 
In the embodiment described above, too, the heat absorption filter may be 
disposed between the illumination device and the liquid crystal display 
unit in the same way as in the embodiment using the liquid crystal display 
unit not using the phase correction member, and this heat absorption 
filter may, of course, be interposed between the illumination optical 
system and the liquid crystal display unit. 
The foregoing embodiments illustrate the liquid crystal display unit 1 
using only one liquid crystal cell 2 or the liquid crystal projector 200 
using such a liquid crystal display unit 1. However, when an RGB color 
separation/synthesis system must be employed for a color display, or the 
like, the liquid crystal display unit or the liquid crystal projector must 
obviously be constituted by the use of at least three liquid crystal 
cells. 
In such a case, two or more, or a plurality of liquid cells, are used to 
constitute one liquid crystal display unit, and such a unit is 
incorporated on the basis of the present invention. By the way, the 
positional relationship between the polarizer member and the liquid 
crystal cell may be sufficient when they oppose each other on the optical 
axis. Accordingly, when the optical axis is refracted by a reflecting 
mirror, or the like, the positional relationship between the polarizer 
member and the liquid crystal cell need not always be parallel to each 
other. 
EFFECT OF THE INVENTION 
As described above, since the present invention employs a sealed 
construction to prevent the accumulation of dust on the liquid crystal 
cell, the dust does not adhere to the liquid crystal cell and the image of 
the dust is not projected by the projection lens as the optical system and 
does not deteriorate the quality of the projected image. Further, it is 
only on the outside surface of the polarizer member inside the liquid 
crystal projector that the dust adheres inside the liquid crystal 
projector, and the dust adhering to the polarizer member is outside the 
depth of focus of the projection lens. Accordingly, the dust does not 
appear on the projected image, and the quality of the projected image is 
not deteriorated. Further, after-care against the dust is not necessary 
and a high quality projected image can be obtained. Since the liquid 
crystal cell has a sealed structure, seal of the casing need not be as 
strict as has been necessary in the prior art apparatuses. When the casing 
is opened and closed for exchanging the lamp as the illumination means, a 
high level of skill and jigs produced by the manufacturer are not 
necessary, so that inspection and maintenance becomes easier. 
Since the liquid crystal display unit according to the present invention 
uses the phase correction member, it is possible to eliminate the problems 
such as pixel quality and contrast changes with the temperature change 
where the display quality becomes ineferior due to a change in the colors.