JP2003228058A - Liquid crystal projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain cooling effect on a polarizing plate substrate, used for a liquid crystal projector, by the use of a member with good heat conductivity, to improve the machinability, and to reduce the cost. <P>SOLUTION: A crystal substrate of 0.3 to 1.0 mm in plate thickness on which a deflecting element is stuck is used as a polarizing plate substrate. By using the polarizing plate substrate of this constitution, plane precision is more easily obtained than using a sapphire substrate with high hardness while the same cooling effect with the use of a conventional sapphire substrate is held to lower the cost compared with the case when an expensive sapphire substrate is used. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector for projecting an image on a liquid crystal display device, and more particularly to a technique for efficiently radiating heat to a polarizing film which becomes hot with the increase in brightness of the image. is there.

[0002]

2. Description of the Related Art In an optical system of a projector using a liquid crystal display element, at least one liquid crystal display element and a pair of polarizing films before and after the liquid crystal display element are used. This polarizing film has high heat shrinkability, and is generally used by being attached to a transparent substrate with an adhesive in order to prevent deformation when absorbing light from a light source and generating heat. The one obtained by laminating a polarizing film on this transparent substrate is hereinafter referred to as a polarizing plate.

Recently, sapphire has been used as the transparent substrate because of its high thermal conductivity, as disclosed in, for example, Japanese Patent Publication No. 3091183. At this time, as described in the above-mentioned patent publication, the optical axis of the sapphire is made parallel or orthogonal to the incident polarized light so as not to affect the polarized light incident on the transparent substrate.

[0004]

Sapphire used as a material for the transparent substrate is much more expensive than glass or the like. Further, the transparent substrate is required to have high plane accuracy in order to prevent distortion of an image, but sapphire has a high hardness and thus has poor workability, and a polishing cost is higher than that of glass or the like.

The object of the present invention is to solve the above problems,
Another object of the present invention is to provide a liquid crystal projector using a member having good workability and high thermal conductivity as the transparent substrate of the polarizing film.

[0006]

[Means for Solving the Problems] As a polarizing plate, the plate thickness is 0.3.
A polarizing element is attached to a crystal substrate having a size of not less than 1.0 mm and not more than 1.0 mm, and its optical axis is configured to be parallel or orthogonal to the incident polarized light. With this configuration, as compared with the case where a sapphire substrate is used, it is possible to improve the workability of the substrate and reduce the cost with the same heat radiation effect.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

1 and 2 are views showing an embodiment of the present invention. FIG. 1 shows the constitution of a polarizing plate according to the present invention arranged before and after a transmissive liquid crystal display element, and FIG. 1 shows a configuration of a transmissive liquid crystal projector using a plate. Note that FIG.
In FIG. 2, the same parts are designated by the same reference numerals.

The present invention is characterized in that, in a liquid crystal projector utilizing polarized light, quartz is used as a material for the holder of the polarizing element arranged on the optical path from the light source to the projection lens.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 2, the light flux emitted from the light source 1 enters the first lens array 6. First lens array 6
Is configured to divide the incident light flux into a plurality of light fluxes by a plurality of lens cells arranged in a matrix and efficiently guide the light flux so as to pass through the second lens array 7 and the polarization conversion element 8. Similar to the first lens array, the second lens array 7 having a plurality of lens cells arranged in a matrix has a configuration in which the shape of the lens cells of the first lens array 6 corresponding to each of the constituent lens cells is a transmissive liquid crystal. Display elements 20R, 20
Project to G, 20B side. At this time, the polarization conversion element 8 aligns the light flux from the second lens array 7 in a predetermined polarization direction. Then, the projected images of the respective lens cells of the first lens array 6 are collected by the condenser lens 9 and the condenser lens 10.
Each of the liquid crystal display elements 20R, 20G, 2 by the R, 10G, 10B, the first relay lens 17, and the second relay lens 18.
Overlay on 0B. Incidentally, reference numerals 14, 15 and 16 are reflection mirrors.

In the process, dichroic mirrors-12 and
13, the white light emitted from the light source 1 is red (R),
It is separated into three primary colors of green (G) and blue (B), and the corresponding liquid crystal display elements 20R, 20G, and 20B are irradiated respectively. Here, the dichroic mirror-12 has a red reflection / green / blue transmission characteristic, and the dichroic mirror-13 has a green reflection / blue transmission characteristic.

Each of the liquid crystal display elements 20R, 20G and 20B is provided with incident side polarization plates 4R, 4G and 4B on the incident side and emission side polarization plates 5R, 5G and 5B on the emission side, and allows light of a predetermined polarization direction to pass therethrough. It is like this. Then, a video signal drive circuit (not shown) controls the amount of light transmitted through the liquid crystal display element to perform light intensity modulation for changing the light and shade of each pixel.

Liquid crystal display element 20 formed by light intensity modulation
The images on R, 20G, and 20B are color-synthesized by the color synthesizing prism 11, and are further projected onto the screen 19 by the projection lens 3 to obtain a large screen image.

The first relay lens 17 and the second relay lens 17
The lens 18 supplements that the optical path length of the liquid crystal display element 20B from the light source 1 to the liquid crystal display element surface is longer than that of the liquid crystal display elements 20R and 20G.

The condenser lenses 10R, 10G,
Reference numeral 10B suppresses the spread of light rays after passing through the liquid crystal display elements 20R, 20G, 20B, and realizes efficient projection by the projection lens 3.

The cooling fan 26 is, for example, an incident side polarization plate 4R, 4G, 4B, an emission side polarization plate 5R, 5G, 5B, a liquid crystal display element 20R, 20G, 20B, etc. The heat generated by the absorption is blown by a flow of air (wind) through a cooling duct (not shown) to form a flow path 27 to the polarizing plate and the liquid crystal display element for cooling.

The liquid crystal projector configured as described above is required to be particularly small in size and to obtain a bright image. Therefore, the liquid crystal display element is downsized and the efficiency of the light source is also improved. , High brightness is achieved. Along with this, light is concentrated on the miniaturized liquid crystal display element, and the temperature rises due to heat generation due to light absorption. In addition, the temperature rises due to the heat generated by the light absorption even with the polarizing plates disposed in front of and behind the liquid crystal display element and having substantially the same size as the liquid crystal display element. Therefore, the heat dissipation effect of the polarizing plate is enhanced and the temperature rise is prevented by cooling with a cooling fan or the like, and in particular, in the polarizing plate, the heat dissipation effect is further enhanced and the temperature rise is improved.

FIG. 1 shows the incident side polarization plate, the emission side polarization plate, and the transmission type liquid crystal display device in detail. In FIG. 1, 41 and 51 are polarizing films, and 42 and 52 are crystal substrates which are transparent substrates to which the polarizing films 41 and 51 are attached. The incident side polarizing plate 4 is a polarizing film 4
1 and a crystal substrate 42, and the emission side polarization plate 5 is composed of a polarizing film 51 and a crystal substrate 52.

Assuming that the polarization direction of the linearly polarized light converted by the polarization conversion element 8 is the XX ′ direction (hereinafter referred to as the vertical direction) parallel to the paper surface orthogonal to the optical path 21, this linearly polarized light is the crystal substrate 42. To enter the polarizing film 41 having the transmission axis in the vertical direction. At this time, in order to prevent the crystal axis of the crystal substrate 42 from affecting the polarized light, the crystal axis of the crystal substrate 42 needs to be in the same vertical direction as the transmission axis of the polarizing film 41 or in the direction orthogonal thereto. is there. When the crystal axis angle is deviated, the linearly polarized light is largely changed to the elliptically polarized light, and the light absorption amount in the polarizing film 41 increases, so that the loss of the light amount and the increase of the heat generation amount occur.

FIG. 3 shows measured values of the amount of light loss with respect to the crystal axis angle deviation. In FIG. 3, the horizontal axis represents the crystal axis angle deviation, and the vertical axis represents the amount of light lost in the polarizing film. If the axis angle deviates ± 1 ° from the measured value, the amount of light absorption will be about 0.
It is known that the light absorption amount increases by about 2% when the axis angle deviates by 5% and ± 2 °, and the axial angle tolerance is preferably within ± 2 °. When the crystal axis angle deviation exceeds ± 2 °, the amount of light loss increases rapidly. An increase in the amount of light loss causes a decrease in brightness.

Generally, in the manufacturing process of the liquid crystal projector shown in FIG. 2, from the illumination optical system excluding the light source 1 to the projection lens 3
In the optical system up to, the brightness control manages the decrease in brightness at about 10% with respect to a predetermined value. Of these, the dichroic mirror changes the brightness by about 5%, and the liquid crystal display device changes the brightness by about 7 to 8%, and the other plural optical lenses also change by several%. The brightness variation of the total is controlled to be within 10%. Therefore,
The crystal axis angle deviation of ± 2 ° of the above-mentioned crystal substrate that makes the light absorption amount about 2% can be regarded as an allowable upper limit value.

Next, the light passing through the transmission axis of the polarizing film 41 has its polarization direction changed by the liquid crystal display element 20 according to the gradation of a video signal (not shown), and enters the polarizing film 51. A polarization component parallel to the transmission axis of the polarizing film 51 passes through the polarizing film 51, but the other components are absorbed by the polarizing film 51.

Since the polarizing films 41 and 51 absorb the polarized component other than the transmission axis to generate heat, the polarizing film 41 is used.
By cooling the surfaces of and 51 and the surfaces of the quartz substrates 42 and 52 with air, the temperature rise due to heat generation is suppressed.
The crystal substrates 42 and 52 are required to have high thermal conductivity in order to improve the heat radiation effect from the surfaces of the crystal substrates 42 and 52.

FIG. 4 shows the temperature of the polarizing film measured by a liquid crystal projector when glass, quartz and sapphire are used as the transparent substrate of the polarizing film. The horizontal axis represents the thickness of the transparent substrate and the vertical axis represents the polarizing film. Shows the temperature. The conditions for temperature measurement are as follows.

Ambient temperature is Ta 25 ° C., light source is ultra high pressure mercury lamp of 155 W specification, transmission type liquid crystal display element is 0.7 inch, and size of polarizing film is 21.5 mm × 18.
0 mm, transparent substrate size is 23.5 mm x 20.0 m
In m, the measurement location is the G input side polarization plate.

As is clear from FIG. 4, in all three types, the thinner the plate thickness, the higher the thermal conductivity of the substrate, so the temperature of the polarizing film becomes lower. The thermal conductivity of glass is 0.55
Quartz is 5.4 (W / mK) for 0.75 (W / mK)
K) and sapphire are 42 (W / mK). Quartz is inferior in thermal conductivity to sapphire, but when used as a polarizing plate substrate, it has a temperature reducing effect on glass (about 10%).
(° C) was fully confirmed. The temperature difference between the case of using the quartz substrate and the case of using the sapphire substrate was smaller as the plate thickness was thinner, and was almost the same at 0.3 mm or less. In order to keep the temperature difference between the case of using the crystal substrate and the case of using the sapphire substrate at 2 ° C. or less, the plate thickness may be set at 1 mm or less.

Generally, it is desirable that the polarizing film is used at 70 ° C. or lower in terms of service life and color unevenness (luminance unevenness) due to thermal deformation. 35 ° C, which is the maximum allowable ambient temperature
When the temperature of the polarizing film is 70 ° C., the temperature of the polarizing film is 60 ° C. when the ambient temperature is 25 ° C. which is the room temperature. In the measurement value of FIG. 4 where the ambient temperature is 25 ° C., when the thickness of the substrate is 1.0 mm, the sapphire substrate has a temperature of about 57 ° C.
The temperature of the quartz substrate is about 59 ° C., and a temperature difference beyond this is undesirable from the viewpoint of performance.

When quartz is used for the transparent substrate, the plate thickness is 0.
Although it can be easily processed with a thickness of 3 mm, it is preferably 0.3 mm or more in consideration of the breaking strength of the substrate.

The price of crystal is about 1 compared to the price of sapphire.
/ 3, the structure according to the present invention as described in FIG. 3 is used, and the crystal substrate is used as compared with the conventional sapphire substrate, so that the temperature reduction substantially equal to that of the sapphire substrate is ensured and the cost is significantly increased. There is an effect that can be achieved down.

Further, since the crystal is cheaper than the price of sapphire, it is possible to increase the outer size of the crystal substrate. Even if the size is about twice the size, it is cheaper than the price of sapphire. Therefore, if the size of the crystal is about twice that of sapphire, it is possible to further lower the temperature than the size of sapphire.

FIG. 5 is a conceptual diagram for explaining image distortion due to plane accuracy of the transparent substrate of the polarizing plate. In FIG. 5, reference numeral 24 is a normal image example formed on the liquid crystal display elements 20R, 20G, and 20B by the liquid crystal projector shown in FIG. Reference numeral 25 shows an example of a distorted image projected on the screen 19.

Transmissive liquid crystal display elements 20R, 20G, 20
When an image like the image example 24 is formed in B, the image examples 24 of RGB are usually overlapped with each other, and a white image having the same shape as the image example 24 is formed on the screen 19.
However, when the plane accuracy of the transparent substrates of the polarizing plates disposed in front of and behind the liquid crystal display element is low, the phenomenon that the images of the three colors RGB do not overlap due to the lens effect of the transparent substrate occurs. For example, when the plane accuracy of only the exit-side polarizing plate 5G is low, the image formed on the screen 19 is as in the image example 25 in which only G is distorted, and the images do not overlap with each other in the peripheral portion and are white. Coloring occurs without becoming
It becomes a pixel shift. Since this lens effect is proportional to the refractive index, it is possible to reduce the above-mentioned phenomenon as compared with sapphire (refractive index of about 1.78) by using crystal (refractive index of about 1.55) for the transparent substrate.

Further, in comparison with Mohs hardness, sapphire is 9, whereas quartz is 7. Since the lower the Mohs hardness, the better the workability, it is clear that quartz is easier to process than sapphire, and using crystal rather than sapphire makes it easier to secure the flatness of the transparent substrate and reduces the processing cost. be able to. Generally, when processing sapphire so as to satisfy the above-mentioned plane accuracy, it is desirable to set the plate thickness to 0.5 mm or more, but when using quartz, the processing is easy even at 0.3 mm. . However, considering the breaking strength of the transparent substrate, it is desirable that the thickness is 0.3 mm or more.

In the above, three liquid crystal display elements shown in FIG. 2 are used as an embodiment of the liquid crystal projector.
Although the plate type liquid crystal projector has been described, the present invention is not limited to this and may be, for example, a single plate type liquid crystal projector using one liquid crystal display element.

In the above description, quartz is used instead of sapphire for the transparent substrate of the polarizing plate disposed before and after the transmissive liquid crystal display element, but the application is not limited to this. For example, it is obvious that the present invention can be applied to two opposing transparent substrates with the liquid crystal of the liquid crystal display element sandwiched therebetween.

Further, not only in the transmission type liquid crystal projector but also in the reflection type liquid crystal projector, a polarizing plate is used in order to make the polarization directions uniform or to reduce undesired polarization direction components. As a usage example, for example, JP 2001
-215491 and Japanese Patent Laid-Open No. 10-312034. It is also clear that a quartz substrate can be used as the transparent substrate of the polarizing plate in these reflective liquid crystal projectors.

[0037]

As described above, according to the present invention, it is possible to provide a liquid crystal projector using a crystal substrate, which is a member having good workability and high thermal conductivity, as a transparent substrate constituting a polarizing plate. Thereby, the temperature rise of the polarizing film of the polarizing plate can be made almost equal to that when sapphire is used for the transparent substrate, and the cost can be reduced.
Further, the flatness of the transparent substrate can be ensured due to the ease of processing the crystal, and the image distortion due to the flatness can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a polarizing plate according to the present invention.

FIG. 2 is a configuration diagram of a transmission type liquid crystal projector using a polarizing plate according to the present invention.

FIG. 3 is a measurement diagram showing the amount of light loss with respect to crystal axis angle deviation.

FIG. 4 is a measurement diagram showing the temperature of a polarizing film when glass, crystal and sapphire are used as the transparent substrate of the polarizing film.

FIG. 5 is a conceptual diagram for explaining image distortion due to plane accuracy of a transparent substrate of a polarization filter.

[Explanation of Codes] 1 ... Light source, 20 ... Liquid crystal display element, 3 ... Projection lens,
4 ... Incident side polarization plate, 5 ... Emission side polarization plate, 6 ... First lens array, 7 ... Second lens array, 8 ... Polarization conversion element, 9 ... Condensing Lens, 10 ... Condenser lens, 11
... Color synthesis prism, 12 ... Dichroic mirror, 1
3 ... Dichroic mirror, 14, 15, 16 ... Reflective mirror, 17, 18 ... Relay lens, 19 ... Screen
, 21 ... Optical path, 24 ... Normal image example formed on the liquid crystal display element 20, 25 ... Distorted image example projected on the screen 19, 26 ... Cooling fan, 27 ... Channel, 41, 51 ... Polarizing film, 42, 52 ... Quartz substrate.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 5/74 H04N 5/74 A (72) Inventor Eiji Yamaguchi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Incorporated company Hitachi, Ltd. Digital Media System Division (72) Inventor Nobuyuki Honda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa F-Term (Reference), Hitachi Ltd. Digital Media System Division (reference) 2H049 BA02 BB22 BC10 BC22 2H088 EA13 EA14 EA68 HA01 HA13 HA18 HA21 HA24 HA25 KA01 MA01 MA20 2H091 FA08X FA08Z FA14Z FA26X FA26Z FA29Z FA41Z FD07 GA01 KA10 LA04 5C058 BA23 BA35 EA01 EA02 EA11 EA14 EA26

Claims (3)

[Claims] 1. A light source unit that emits white light, a polarization conversion element that converts light emitted from the light source unit into linearly polarized light, and a color separation unit that separates white light into three colors of red, green, and blue. A liquid crystal projector having a liquid crystal display element for converting an optical image according to a video signal of each color and a projection unit for projecting the optical image, wherein at least one of an incident side and an emission side of the liquid crystal display element A liquid crystal projector having a structure in which a crystal substrate and a polarizing element are bonded together as a polarizing plate. 2. The thickness of the quartz substrate is 0.3 mm or more 1.
The liquid crystal projector according to claim 1, wherein the thickness is 0 mm or less. 3. The angle between the optical axis of the quartz substrate and the absorption axis of the polarizing element is either 90 ± 2 ° or 0 ± 2 °. The liquid crystal projector according to Crab.