JP2001290120A - Projection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that decrease in the reproducibility for luminance or display irregularity occurs even when intense light from a light source is supplied in a projection type liquid crystal display device, to prevent decrease in the display quality of a projected image due to dust or the like, and to always maintain the display characteristics and the display quality to the original optimum state. SOLUTION: The coefficient of linear expansion of a first dust-proof glass 2 and a second dust proof glass 3 is specified to <=1.0×10-6/ deg.C so that even when heat is accumulated in a light-transmitting member or a transparent substrate by supplying intense light from a light source, generation of double refraction due to the heat can be prevented. Or, by specifying the photoelastic constant of the glass to <=1.0×10-12/Pa, generation of double refraction can be prevented even when heat is accumulated in the light-transmitting member or the transparent substrate by supplying intense light from the light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-panel type liquid crystal panel using one liquid crystal panel or a three-panel type liquid crystal display device using three liquid crystal panels, one for each color light.

[0002]

2. Description of the Related Art In general, a projection type liquid crystal display device includes a liquid crystal panel, polarizing plates disposed on both front and rear main surfaces thereof, and a projection optical system such as a projection lens for enlarging light transmitted therethrough and projecting the light on a screen. And is attracting attention as a display device capable of displaying a large screen with a relatively small liquid crystal panel. The projection type liquid crystal display device uses a single liquid crystal panel and realizes color display using a color filter or the like, and a single liquid crystal display device, and three liquid crystal panels corresponding to each color light such as R, G, and B. A color display is realized by combining light transmitted through the liquid crystal panels with an optical system using a panel.
A plate type is proposed.

In such a projection type liquid crystal display device, it is generally desirable to increase the amount of light or the light intensity supplied from the light source in order to realize an image display with higher brightness and easier viewing. Often.

[0004]

By the way, in the above-mentioned projection type liquid crystal display device, generally, when dust or the like adheres to the vicinity of the surface of the liquid crystal panel, it is enlarged by a projection lens or the like and projected on a screen. There is a problem that the display quality is significantly reduced.

[0005] Therefore, a transparent member such as a borosilicate glass plate is arranged at least in the image display area on the front and back sides of the liquid crystal panel so as to defocus dust or the like so that it does not stand out in the projected image. A method of doing so has been proposed. It is considered that such a transparent member having a plate thickness determined in consideration of the depth of field (depth of focus) of the projection optical system is preferable.

However, in the projection type liquid crystal display device, it is generally desirable to increase the amount of light or the light intensity supplied from the light source as described above. Temperature rises, and internal stress such as so-called thermal stress occurs,
Birefringence occurs in the light transmitted through the transparent member. For this reason, there is a problem that the contrast characteristics of the projected image and the uniformity of the display within the screen are reduced.

That is, the display characteristics of the liquid crystal panel, including the contrast characteristics, are generally originally set so as to be optimized by the combination of the polarizing plate and the liquid crystal panel. However, if the above-described birefringence occurs in a transparent member or the like provided between such a polarizing plate and a liquid crystal panel, the birefringence phase difference (retardation;
Due to the retardation, the optical rotation characteristics of the transmitted light deviate from the optimal conditions. As a result, for example, in a normally white mode liquid crystal panel, there is a problem that the luminance level of the black display shifts in a direction to increase, and the contrast characteristic is reduced, and the display quality is remarkably deteriorated. Alternatively, in a normally black mode liquid crystal panel, there is a problem in that the luminance level of white display shifts in a direction of lowering, and the contrast characteristic is reduced, and the display quality is significantly deteriorated.

In particular, when the transparent member is attached between the polarizing plate and the liquid crystal panel, the light absorbed by the polarizing plate becomes heat, and the heat generates internal stress in the transparent member. There is a problem that the brightness level of the central portion having the highest light density or heat storage density is different from the brightness level of the peripheral portion having the lowest light density, resulting in a decrease in brightness reproducibility, uneven brightness and unevenness of contrast characteristics in the screen. .

For example, in a normally black mode liquid crystal panel, a phenomenon occurs in which the central portion becomes brighter than the original display image. Conversely, in a normally white mode liquid crystal panel, a phenomenon occurs in which the central portion is darker than the original luminance of the display screen. As a result, in any of the modes, there is a problem that the luminance reproducibility of the projected image is reduced, the contrast characteristics in the screen are varied, and the luminance is uneven.

As a technique for solving the problem of the deterioration of the display characteristics caused by the irradiation of the strong light from the light source, it has been proposed to cool the liquid crystal panel and its periphery by using a forced air cooling device or the like.

However, in order to achieve a higher brightness of the projected image, it is desired to irradiate a stronger light source light. However, a cooling effect against the heat storage caused by such a strong light source light is desired. It tends to be inadequate. In addition, in order to obtain a sufficient cooling effect, it is necessary to use a more powerful forced air cooling device or the like, but noise or heat generated by a motor or the like for driving a cooling fan or the like increases, The improvement of the cooling effect is already near the limit in practice.

Further, when a strong cooling air is blown to obtain a strong cooling effect, dust is charged due to friction of the air at the time of the blowing and the likelihood of adhering to the surface of a liquid crystal panel or a polarizing plate is high. May be. In addition, since the flow velocity distribution near the surface of the object is generally 0, it is practically difficult to blow off the dust once adhered to the surface by the cooling wind.

Alternatively, a cooling technique other than the forced air cooling apparatus can be considered, but it is extremely difficult to cool the liquid crystal panel or the polarizing plate without optically blocking the surface. For example, in the case of a water-cooling device, it is difficult to prevent light from being transmitted through the display area of the liquid crystal panel, and its structure is extremely complicated, which is not practical. Therefore, there is no practical cooling technology other than the forced air cooling device.

As described above, even if a forced air cooling device or the like is used, it is difficult to solve the above-described problem of deterioration in luminance reproducibility and display unevenness due to heat storage due to the supply of strong light source light. there were. Further, there is a problem that it is difficult to solve the deterioration of display quality due to dust or the like adhering to the surface of the liquid crystal panel.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to solve the problems of reduced luminance reproducibility and display unevenness even when strong light source light is supplied, and to reduce the problem of dust and the like. An object of the present invention is to provide a projection-type liquid crystal display device that can always maintain the display characteristics and the display quality at the original optimum settings by eliminating the deterioration of the display quality of the projected image.

[0016]

A projection type liquid crystal display device according to the present invention comprises a liquid crystal panel having pixels disposed in a display area, a light source for emitting light toward the liquid crystal panel, and a light source for emitting light from the light source. A projection optical system for projecting light transmitted through the liquid crystal panel onto a screen, wherein at least one or both of the front and rear surfaces of the liquid crystal panel have a linear expansion coefficient. 1.
A light transmitting member made of a material of 0 × 10 ⁻⁶ / ° C. or less and having a thickness determined according to the depth of field of the projection optical system is arranged at least in the display area.

According to the projection type liquid crystal display device of the present invention, there is provided a liquid crystal panel having pixels disposed in a display area, a light source for emitting light toward the liquid crystal panel, and a light emitted from the light source and transmitted through the liquid crystal panel. A projection optical system for projecting the generated light onto a screen, wherein the photoelastic constant is 1.0 × 10 ^{−12 on} at least one or both of the front and back surfaces of the liquid crystal panel. / Pa or less, and a light transmitting member having a thickness determined according to the depth of field of the projection optical system is disposed at least in the display area.

The projection type liquid crystal display device according to the present invention comprises a liquid crystal display.
Having a liquid crystal layer and two transparent substrates sandwiching the liquid crystal layer.
The liquid crystal panel on which
And a liquid crystal emitted from the light source
Projection optics that project light transmitted through the panel onto the screen
Projection type liquid crystal display device having a transparent
At least one or both of the substrates are
Tensile coefficient is 1.0 × 10 ^-6/ ° C or lower and projection optics
From a light transmitting material with a thickness determined according to the depth of field of the system
It becomes.

A projection type liquid crystal display device according to the present invention comprises a liquid crystal panel having a liquid crystal layer and two transparent substrates sandwiching the liquid crystal layer, in which pixels are arranged, and a light beam directed toward the liquid crystal panel. , And a projection optical system that projects light emitted from the light source and transmitted through the liquid crystal panel onto a screen, wherein at least one of the two transparent substrates is used. One or both
It is made of a light transmitting material having a photoelastic constant of 1.0 × 10 ⁻¹² / Pa or less and having a plate thickness determined according to the depth of field of the projection optical system.

In the projection type liquid crystal display device according to the present invention, the thickness of the light transmitting member or the transparent substrate is set in consideration of the depth of field of the projection optical system. More specifically, the thickness of the light transmitting member or the transparent substrate is set so that even if dust or the like adheres to the light transmitting member or the transparent substrate, it is defocused in the projected image. This makes it possible to prevent the display quality of the projected image from deteriorating even if dust or the like adheres.

In addition, since the light transmitting member or the transparent substrate has a linear expansion coefficient of 1.0 × 10 ⁻⁶ / ° C. or less, the light transmitting member or the transparent substrate is supplied by supplying strong light from a light source. Even if a heat storage phenomenon occurs, it is possible to prevent the occurrence of birefringence due to the phenomenon. Alternatively, the photoelastic constant of the light transmitting member or the transparent substrate is 1.0 × 10 ⁻¹² / P
Since it is set to a or less, even if a heat storage phenomenon occurs in the light transmitting member or the transparent substrate by supplying strong light from the light source,
It is possible to prevent the occurrence of birefringence due to this.

The plate thickness effective for defocusing the dust as described above and preventing the occurrence of birefringence is determined by the linear expansion coefficient or the photoelastic constant, the size of the dust to be attached, the depth of field of the projection optical system, and the like. Although it is determined by taking into account the above, it is desirable to set the range from 0.5 mm to 4.5 mm as a practically effective range.

Further, by making the light transmitting member adhered to the liquid crystal panel so as to be in close contact with the liquid crystal panel, the heat generated by the supply of the strong light source light can be dispersed not only in the liquid crystal panel but also in the light transmitting member. It is possible to suppress the temperature rise of the liquid crystal panel and the light transmitting member.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment)

FIG. 1 shows an example of a schematic configuration of a projection type liquid crystal display device according to a first embodiment of the present invention. This projection type liquid crystal display device is a single-panel type projection type liquid crystal display device, and includes a liquid crystal panel 1, a first dustproof glass (light transmitting member) 2, and a second dustproof glass 3 (light transmitting member). , Incident-side polarizing plate 4, emission-side polarizing plate 5, light source 6
, Condenser lens 7, and projection lens system 8 (projection optical system)
And a forced air cooling fan device 10 in its main part.

The light source 6 supplies light from the light source to the liquid crystal panel 1 through the condenser lens 7, and is generally set to emit strong light from the light source in order to obtain a high-luminance projected image. is there.

Although the detailed internal structure of the liquid crystal panel 1 is omitted, a TN (twisted nematic) liquid crystal layer, a pixel electrode sandwiching the TN type liquid crystal layer and a liquid crystal applied voltage are switched. TFT element (Thin Fil
m Transistor), a transparent substrate on which the surrounding area is sealed, a sealing material for sealing the periphery, and a color filter for coloring transmitted light for each pixel in its main part. It is. The position where each pixel of the liquid crystal panel 1 is formed is the imaging plane (focal position) of the projection lens system 8. The liquid crystal panel 1 is a so-called TN
It goes without saying that various types of devices such as an STN type simple matrix liquid crystal panel 1 can be applied in addition to the TFT type liquid crystal panel 1.

The incident side polarizing plate 4 is attached to the glass plate 11 as a support and is installed on the light incident surface side of the liquid crystal panel 1. Only the component in the direction is transmitted and incident on the liquid crystal panel 1. Needless to say, a phase difference compensating plate or the like may be further provided together with the incident-side polarizing plate 4 in order to compensate for so-called retardation or the like generated in the light path.

The first dustproof glass 2 is attached (attached) to the surface of the liquid crystal panel 1 on the light incident side. Further, the second dustproof glass 3 is attached to the surface of the liquid crystal panel 1 on the side from which light is emitted. This first
The dust-proof glass 2 and the second dust-proof glass 3 are exposed to dust and the like floating in the air on the exposed surface opposite to the surface attached to the liquid crystal panel 1. Also,
To avoid prominent image formation in the projected image,
It is provided to defocus the dust and the like.
These plate thicknesses are determined according to the depth of field of the projection lens system 8 and the size of the dust, but are generally the average of the depth of field and the size of the dust of the projection lens system 8 which are generally used. The thickness is set in the range of 1 mm to 4 mm as a plate thickness capable of defocusing such dust based on the values. Furthermore, the first dustproof glass 2
And the second dustproof glass 3 has a linear expansion coefficient of 1.0 × 1.
Glass plate of 0 ^-6 / ° C or less, or a photoelastic constant of 1.0 ×
It is made of a glass plate of 10 ⁻¹² / Pa.

The exit-side polarizing plate 5 is attached so as to be in close contact with the second dust-proof glass 3 and absorbs light that has passed through the liquid crystal panel 1 without being rotated. For example, in a pixel displaying black, almost all light transmitted through the liquid crystal layer without being rotated is absorbed by the output-side polarizing plate 5. The light absorbed at this time is converted into heat energy, and the emission-side polarizing plate 5, the liquid crystal panel 1, the second dustproof glass 3,
Spread to. Similarly, in the incident-side polarizing plate 4, the component of the light absorbed without passing through the incident-side polarizing plate 4 is:
The energy changes into heat energy and diffuses into the incident side polarizing plate 4, the liquid crystal panel 1, and the first dustproof glass 2. These heat energies increase the temperatures of the output side polarizing plate 5, the input side polarizing plate 4, the liquid crystal panel 1, the first dustproof glass 2, the second dustproof glass 3, and the like.

In order to prevent the heat generated as described above from being stored in the liquid crystal panel 1 or the like, the forced air cooling fan device 10 air-cools them with cooling air. It goes without saying that the forced air-cooling fan device 10 may be a centrifugal fan or an axial fan fan. In any case, this forced air cooling fan device 10
In order to prevent the optical characteristics of the liquid crystal layer of the liquid crystal panel 1 from changing so as to adversely affect the projected image, the liquid crystal panel 1 is set to be air-cooled to prevent heat storage. It is set so that electric or mechanical noise caused by a motor for rotating the fan or fluid noise such as wind noise does not occur practically.

Next, regarding the operation of the projection type liquid crystal display device according to the first embodiment, in particular, the operation of defocusing so that dust is not formed on the projected image and the occurrence of birefringence due to heat storage are not generated. The outline of the operation will be described mainly.

Liquid crystal panel 1 in projection type liquid crystal display device
When light is supplied from the light source 6, the temperature of the polarizing plate or the like near the room becomes the indoor temperature (the temperature in a state where the light is not supplied).
Increases by 10 to 45 ° C. The fact that such a rise in temperature causes internal stress, called so-called thermal stress, to occur in a glass plate such as borosilicate glass, which causes birefringence in light transmitted through the glass plate. The inventors have confirmed by various experiments and their analysis.

The birefringence δ due to internal stress in such a dust-proof glass such as a glass plate can be expressed by the following equation. That is,

Δ = (2π / λ) × B × (σ 1 −σ 2) × t

Here, λ is the wavelength of light (light source light) supplied from the light source 6, B is the photoelastic constant of the transparent substrate, σ1 is the internal stress in the direction of the absorption axis of the polarizing plate in the dustproof glass, and σ2 is the stress in the dustproof glass. The internal stress in the polarization axis direction of the polarizing plate, t, is the thickness of the dust-proof glass.

In the above equation, it can be seen that the birefringence δ can be reduced by reducing the plate thickness t of the conventional dustproof glass, but if it is too thin, dust adhering to the surface as dustproof glass is projected. The function of deviating from the depth of field of the lens system 8 (defocusing function) becomes insufficient, and a projected image of dust is formed in an image projected on the screen 9 or the like, and the display quality of the projected image is reduced. Will be reduced.

Alternatively, the thickness t of the dust-proof glass is reduced, and the dust-proof glass is set apart from the surface of the liquid crystal panel 1 by at least a distance at which a practical defocusing action can be obtained. It is also conceivable to seal the periphery of the gap between them so that dust and the like do not enter.

However, if such a gap is provided, the heat conductivity is reduced in the gap to prevent heat from being dissipated from the liquid crystal panel 1, or the air sealed in the gap stores heat. As a result, the temperature of the liquid crystal panel 1 may further increase. When the temperature of the liquid crystal panel 1 itself rises in this way, the optical characteristics of the liquid crystal layer change, resulting in luminance characteristics and contrast characteristics different from the original settings.
Eventually, display quality will be degraded.

Alternatively, it has been considered that a birefringence δ generated in response to a specific temperature rise is predicted in advance, and a phase difference compensating plate or the like for compensating the birefringence δ is arranged in advance. In general, the degree of rise in temperature and the occurrence of birefringence δ due to the temperature rise in a projection type liquid crystal display device vary variously depending on the duration of use of the projection type liquid crystal display device and the outside air temperature. Even if a phase difference compensating plate or the like for compensating the refraction δ is fixedly provided, since the actually generated birefringence δ changes every moment, it is not always possible to effectively compensate for the phase difference.
Rather, display characteristics may vary over time.

As a result of examining these various points, the present inventors set the thickness of the dust-proof glass to a thickness that would provide a practically sufficient defocusing effect, and set the temperature to be lower than room temperature. It is preferable to find such a condition that even if the temperature rises to 10 to 45 ° C. or higher, only a small birefringence of practically no problem occurs, and to form the dust-proof glass with a material satisfying such a condition. Was concluded. And actually, a projection type liquid crystal display device using the dust-proof glass of such a setting was manufactured, and an experiment of supplying a strong light source light capable of obtaining a projection image with sufficiently high brightness was tried. It has been confirmed that the display characteristics can be favorably maintained under such a condition that a temperature rise is likely to occur.

More specifically, the first dustproof glass 2 and
And the thickness t of the second dust-proof glass 3 is set to 1.0 mm to 4.0 m.
m, and the material is photoelastic constant 1.0 ×
10 ^-12 / Pa or less or a coefficient of linear expansion of 1.0 × 10^-6
Made of borosilicate glass with a material of less than / ° C
Was preferred.

In other words, in the above equation, if the photoelastic constant B (or the coefficient of linear expansion) is set to 0, the birefringence δ is set to 0 regardless of the plate thickness t. be able to. However, in practice, a transparent member made of a material having a photoelastic constant B or a linear expansion coefficient of 0 cannot be practically provided. Therefore, first, the plate thickness at which a practically sufficient defocusing effect is obtained is set to t = 1.0 to 4.0 mm, and the birefringence δ is adjusted to the display quality of the projected image in accordance with the plate thickness. On the other hand, a range of a preferable value of the photoelastic constant or the linear expansion coefficient which can be maintained at a low value which does not adversely affect practical use was examined. As a result, the photoelastic constant was 1.0 × 10 ⁻¹² / Pa or less or the linear expansion coefficient was 1.0.
It was confirmed that the temperature should be set at × 10 ⁻⁶ / ° C. or less.

FIG. 2 shows an image actually projected by a projection type liquid crystal display device using the first dustproof glass 2 and the second dustproof glass 3 satisfying the above conditions of the plate thickness and the photoelastic constant. 7 is a graph showing an experimental result of a change in luminance (illuminance) of black display over time when is displayed. In the experiment whose results are shown in FIG. 2, the first dust-proof glass 2 and the second dust-proof glass 3 have a plate thickness t = 3.
A borosilicate glass having a setting of 3 mm, a photoelastic constant B = 0.43 × 10 ⁻¹² / Pa, and a coefficient of linear expansion α = 12.4 × 10 ⁻⁶ / ° C. was used. In this case, the photoelastic constant B satisfies the condition of the above preferable value.

FIG. 3 shows a projection type liquid crystal display device using the first dustproof glass 2 and the second dustproof glass 3 satisfying the above conditions of the plate thickness and the linear expansion coefficient. 9 is a graph showing an experimental result of a change in luminance (illuminance) of black display over time when an image is displayed. In the experiment whose results are shown in FIG. 3, the first dust-proof glass 2 and the second dust-proof glass 3 have a thickness t =
3.3 mm, photoelastic constant B = 3.5 × 10 ⁻¹² / Pa,
A borosilicate glass having a linear expansion coefficient α = 0.7 × 10 ⁻⁶ / ° C. was used. In this case, the linear expansion coefficient α satisfies the condition of the above preferable value.

In FIGS. 2 and 3, the luminance level at the center of the projection screen is indicated by a circle, and the luminance level at the periphery is indicated by a triangle.

As is apparent from FIGS. 2 and 3, in each case, it was confirmed that the luminance level was maintained substantially constant in both the central portion and the peripheral portion even after the elapse of time. .

On the other hand, as a comparative example, the plate thickness was t
= 3.3 mm, but the photoelastic constant B = 4.0 × 10
The first dustproof glass 2 and the second dustproof according to the present invention described above were prepared by replacing the conventional dustproof glass made of borosilicate glass having a setting of ⁻¹² / Pa and a coefficient of linear expansion α = 3.3 × 10 ⁻⁶ / ° C. An experiment was performed under the same conditions as above, using the glass 3 instead of the glass 3. As a result, as shown in FIG. 5, it was confirmed that the luminance level particularly at the center of the screen significantly changed with the lapse of time from the start of the display, and the display quality was significantly reduced. In the peripheral area, a change of about several percent to 10 percent was observed. At this time, the temperature measured on the surface of the dust-proof glass is shown in FIG.
It was found that both the central part and the peripheral part of the dust-proof glass had a temperature rise of about 10% with the passage of time.

As described above, as compared with the case of the projection type liquid crystal panel 1 using the conventional dustproof glass, the projection type liquid crystal display device according to the present embodiment shows that the photoelastic constant B or the linear expansion coefficient α By setting the thickness t as described above, birefringence occurs in the first dustproof glass 2 and the second dustproof glass 3 even when the temperature rises due to the supply of the strong light source light. It has been confirmed that it is possible to eliminate the occurrence of deterioration in brightness characteristics and contrast characteristics of a projected image, uneven display, and changes in display characteristics over time, and the like.

Further, since the first dust-proof glass 2 and the second dust-proof glass 3 are stuck together on the main surface (front surface or back surface) of the liquid crystal panel 1, strong light source light is supplied and Even if most of the heat is changed to heat energy, the heat energy is not stored in the liquid crystal panel 1, but the first dustproof glass 2 having a large plate thickness t = 1.0 to 4.0 mm and a large heat capacity. And the second dustproof glass 3. Furthermore, it is possible to prevent the temperature of the liquid crystal panel 1 itself or the liquid crystal panel 1 to which it is attached from rising by dissipating heat to the outside from the side surfaces and the like of the first dustproof glass 2 and the second dustproof glass 3. it can. As a result, it is possible to prevent a change in optical rotation characteristics due to a change in temperature of the liquid crystal panel 1.

(Second Embodiment)

FIG. 4 shows an example of a schematic configuration of a projection type liquid crystal display device according to a second embodiment of the present invention.

The projection type liquid crystal display device according to the second embodiment includes a total of three liquid crystal panels 1 ', one for each color light, and passes through the three liquid crystal panels 1'. This is a three-panel projection type liquid crystal display device including a cross prism 12 for synthesizing light provided with image components for each color.

The main part of the projection type liquid crystal display device according to the second embodiment is different from the projection type liquid crystal display device according to the first embodiment in that the liquid crystal panel 1
'Is a color filter omitted,
Different color light is supplied to each of the liquid crystal panels 1 ′, and the light transmitted through the three liquid crystal panels 1 ′ is transmitted to the cross prism 12.
And projecting toward the screen 9. The incident-side polarizing plates 4'a, 4'b, 4'c and the outgoing-side polarizing plates 5'a, 5'b, 5'c are first dustproof glasses 2'a, 2'b, 2'c. And the second dustproof glass 3 '
a, 3'b, 3'c and the liquid crystal panels 1'a, 1'b, 1 '
c at a position away from the support plate 11′a,
It is supported by 11'b, 11'c. The other configuration is the same as that of the first embodiment.

In such a three-panel projection liquid crystal display device, unlike the single-panel projection liquid crystal display device described in the first embodiment, the incident side polarizing plates 4'a, 4'b, 4
'C and the first dust-proof glasses 2'a, 2'b, 2'c resulting from the absorption of light by the exit-side polarizing plates 5'a, 5'b, 5'c.
And the second dust-proof glass 3'a, 3'b, 3'c itself is unlikely to raise the temperature and accumulate heat. For example, when the liquid crystal panels 1'a, 1'b, 1'c are of the TFT type. For example, the liquid crystal panels 1'a, 1'b, 1
'C accumulates heat, and the heat is applied to the first dustproof glass 2'a, 2'b, 2'c or the second dustproof glass 3
'A, 3'b, and 3'c also propagate to increase the temperature. In the case of irradiating extremely strong light source light, the first dustproof glass 2′a, 2′b, 2′c
Also, a part of the light from the light source is converted into heat and stored in the second dustproof glass 3'a, 3'b, 3'c itself. Therefore, even in the case of such a three-panel projection type liquid crystal display device, the first dust-proof glass 2 ′ due to the strong light source light supply.
a, 2'b, 2'c and the second dustproof glass 3'a, 3 '
Birefringence may occur in b and 3'c.

Therefore, even in the case of such a three-panel projection type liquid crystal display device, the first dustproof glasses 2'a, 2'b,
By setting the 2'c and the second dustproof glasses 3'a, 3'b, 3'c to the same settings as in the first embodiment, the first dustproof glasses 2'a, 2'b , 2′c and the second dust-proof glass 3′a, 3′b, 3′c can be prevented from causing birefringence, which leads to a decrease in the luminance characteristic and a decrease in the contrast characteristic of the projected image, Alternatively, display unevenness and a change in display characteristics over time can be eliminated.

The thickness of the dust-proof glass is not only capable of achieving the above-mentioned defocusing effect, but also has a birefringence in consideration of the above-described setting of the photoelastic constant or the linear expansion coefficient. As a result of studying a practical minimum value and a maximum value that can suppress the occurrence, the thickness t may be set in the range of 0.5 mm to 4.5 mm, and the intensity of light from the light source is further increased. If there is room to cope with the case where the temperature or room temperature rises or the size of the dust is further increased, as described above, the plate thickness t
= 1.0 mm to 4.0 mm has been confirmed by various experiments and the like.

Further, in the above embodiment, the dust-proof glass is used by bonding it to the transparent substrate of the liquid crystal panel. However, the transparent substrate itself of the liquid crystal panel has the above characteristics such as the plate thickness and the photoelastic constant. A provided dustproof glass may be used. Employing such a configuration is preferable because the structure of the projection type liquid crystal display device can be simplified.

Further, in the above embodiment, the dust-proof glass is attached to the surface of the liquid crystal panel so as to be in close contact therewith. However, the dust-proof glass is not necessarily limited to just being in close contact with the liquid crystal panel. May be arranged at intervals. However, in such a case, it may be difficult to disperse heat from the liquid crystal panel to the dust-proof glass. Therefore, it may be necessary to take measures to radiate heat from the liquid crystal panel. However, when such measures are possible, or when the heat storage of such a degree does not significantly change the characteristics of the liquid crystal panel, the dustproof glass should be placed away from the surface of the liquid crystal panel in this way, It is also possible to set the dustproof glass as thin as possible, such as 1.0 mm, while ensuring effective defocusing, so that it can be used up to the upper limit of the allowable range of photoelastic constant and linear expansion coefficient. It is.

In the above embodiment, the case where borosilicate glass is used as the dust-proof glass has been described. However, it goes without saying that the light-transmitting member is not limited to the dust-proof glass made of such a glass material. In addition, a quartz plate, an artificial quartz plate, or the like can be used as long as it satisfies the above conditions of the photoelastic constant or the coefficient of linear expansion.

Further, it goes without saying that the liquid crystal panel is not limited to only the TN type TFT liquid crystal panel as described above. In addition, various types (structures and display methods) such as a liquid crystal panel using a ferroelectric liquid crystal can be applied.

[0063]

As described above, claims 1 to 1
According to the projection type liquid crystal display device described in any one of the above items, the light transmitting member or the transparent substrate is set to have such a thickness that even if dust or the like adheres, it is defocused in the projected image. By this, it is possible to eliminate the deterioration of the display quality of the projected image due to the attachment of dust and the like, and to display the birefringence generated on the light transmitting member or the transparent substrate even when strong light is supplied from the light source. The display characteristics and the display quality can be always maintained at the original optimum settings by suppressing the display characteristics to such an adverse effect.

According to the projection type liquid crystal display device of the present invention, since the transparent substrate constituting a part of the liquid crystal panel is made of the above-mentioned light transmitting member, the above-mentioned light is transmitted. The same effect as the transmissive member can be obtained, and the structure of the projection type liquid crystal display device can be simplified.

Further, according to the projection type liquid crystal display device of the third or sixth aspect, the light transmission member is stuck to the liquid crystal panel so as to be in close contact with the liquid crystal panel, and the heat generated by the supply of the strong light source light is provided. Is dispersed not only in the liquid crystal panel but also in the light transmitting member, in addition to the above-described effects, the temperature rise of the liquid crystal panel and the light transmitting member can be suppressed, and the birefringence due to heat storage can be further reduced. The effect that the generation | occurrence | production of can be prevented is produced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a projection type liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an experimental result of a change in luminance of black display over time when a projected image is displayed by a projection-type liquid crystal display device using dustproof glass satisfying a condition of a photoelastic constant B.

FIG. 3 is a diagram showing an experimental result of a change in luminance of black display over time when a projection image is displayed by a projection type liquid crystal display device using dustproof glass satisfying a condition of a linear expansion coefficient α.

FIG. 4 is a diagram illustrating a schematic configuration of a projection type liquid crystal display device according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating, as a comparative example, an experimental result of a change in luminance of black display over time when a projected image is displayed by a conventional projection-type liquid crystal display device using dustproof glass.

FIG. 6 is a diagram illustrating a change in temperature of the surface of the dust-proof glass over time when a projection image is displayed by the projection-type liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel, 2 ... 1st dust-proof glass, 3 ... 2nd dust-proof glass, 4 ... Incident side polarizing plate, 5 ... Exit side polarizing plate, 6 ...
Light source, 7: condenser lens, 8: projection lens system, 10: forced air cooling fan device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H088 EA12 FA01 HA16 HA18 MA04 MA20 5G435 AA00 AA11 AA12 BB12 BB17 CC09 CC12 DD02 DD04 DD05 GG01 GG02 GG03 GG44 GG46 HH02 LL15

Claims (10)

[Claims] 1. A liquid crystal panel having pixels disposed in a display area, a light source for emitting light toward the liquid crystal panel, and a light emitted from the light source and transmitted through the liquid crystal panel is projected on a screen. A projection optical system comprising: a liquid crystal panel having a linear expansion coefficient of 1.0 × 10 ^-6 /
A projection type liquid crystal display device, wherein a light transmitting member made of a material having a temperature equal to or lower than 0 ° C. and having a thickness determined according to a depth of field of the projection optical system is arranged at least in the display area. 2. The projection type liquid crystal display device according to claim 1, wherein said light transmitting member has a plate thickness of 0.5 mm to 4.5 mm. 3. The projection type liquid crystal display device according to claim 1, wherein said light transmitting member is attached to said liquid crystal panel. 4. A liquid crystal panel having pixels arranged in a display area, a light source for emitting light toward the liquid crystal panel, and a light emitted from the light source and transmitted through the liquid crystal panel is projected on a screen. A projection optical system, wherein a photoelastic constant is 1.0 × 10 ^{−12 on} at least one or both of a front surface and a back surface of the liquid crystal panel.
/ Pa or less, and a light transmitting member having a thickness determined according to the depth of field of the projection optical system is arranged at least in the display area. 5. The projection type liquid crystal display device according to claim 4, wherein the light transmitting member has a plate thickness of 0.5 mm to 4.5 mm. 6. The projection type liquid crystal display device according to claim 4, wherein said light transmitting member is attached to said liquid crystal panel. 7. A liquid crystal panel having a liquid crystal layer and two transparent substrates sandwiching the liquid crystal layer and having pixels disposed thereon,
A projection-type liquid crystal display device comprising: a light source that emits light toward the liquid crystal panel; and a projection optical system that projects light emitted from the light source and transmitted through the liquid crystal panel onto a screen. At least one or both of the transparent substrates have a linear expansion coefficient of 1.0 × 10 ⁻⁶ / ° C. or less and a plate thickness determined according to the depth of field of the projection optical system. A projection type liquid crystal display device comprising a material. 8. A transparent substrate comprising the light transmitting material,
8. The projection type liquid crystal display device according to claim 7, wherein the projection type liquid crystal display device has a plate thickness of 0.5 mm to 4.5 mm. 9. A liquid crystal panel including a liquid crystal layer and two transparent substrates sandwiching the liquid crystal layer and having pixels disposed thereon,
A projection-type liquid crystal display device, comprising: a light source that emits light toward the liquid crystal panel; and a projection optical system that projects light emitted from the light source and transmitted through the liquid crystal panel onto a screen. At least one or both of the transparent substrates have a photoelastic constant of 1.0 × 10 ⁻¹² / Pa or less and a light transmission having a thickness determined according to the depth of field of the projection optical system. A projection type liquid crystal display device comprising a material. 10. A transparent substrate comprising the light transmitting material,
10. The projection type liquid crystal display device according to claim 9, having a plate thickness of 0.5 mm to 4.5 mm.