JP2003294949A - Optical element, method for manufacturing the same and color liquid crystal projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing beamsplitter, a polarizing plate and the like for a color liquid crystal projector, any one of which has satisfactory brightness and durability. <P>SOLUTION: Light transmissive magnesia ceramics having ≥78% transmittance of linear light having 600 nm wavelength at 4 mm thickness is used for the polarizing beamsplitter 4 made of magnesia, polarizing plates 7R, 7G and 7B with magnesia substrates and the like which are used for the color liquid crystal projector. The magnesia ceramics contains alumina and silicon oxide so that sum total content of alumina and silicon oxide is ≤2,000 ppm by weight and 6*alumina + silicon oxide is ≥250 ppm by weight. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia optical element used in a color liquid crystal projector, and more particularly to a magnesia polarization beam splitter, a polarizing plate, a retardation plate and the like. The present invention also relates to a method for manufacturing such an optical element and a color liquid crystal projector in which the optical element is arranged.

[0002]

2. Description of the Related Art In a color liquid crystal projector, light is absorbed because a polarizing plate is used in its liquid crystal image forming section, and an image having a small area of 1 to 6 inches is enlarged to several tens to several hundreds of inches. This reduces the brightness. Therefore, a high-luminance light source is used, but there is a strong demand for improving the brightness of the projector, and as a result, the intensity of the light source used is becoming higher and higher.

Generally, in a color liquid crystal projector, a polarization beam splitter is used between a light source and a liquid crystal panel. The polarizing beam splitter is an optical component that splits natural light into polarized light that is orthogonal to each other and rotates one polarized light in the other polarized light direction to improve brightness. For the polarization beam splitter, ordinary amorphous glass such as BK-7 glass or white plate glass is used as a glass material.

[0004]

However, due to the recent demand for higher brightness, smaller size and lighter weight of the color liquid crystal projector, the intensity of the light source to be used becomes stronger and moreover, the optical parts are made smaller, so that the durability is improved. There is a demand for a polarizing beam splitter, a polarizing plate, and a color liquid crystal projector that have both the lightness and the brightness of the projected image.

In general, when a polarization beam splitter is used in a color liquid crystal projector, light from a light source is first condensed into a band shape at an equal pitch by an integrator lens. The thus focused and amplified light alternately enters the strip-shaped pattern of the polarization beam splitter, and is internally divided into polarized lights orthogonal to each other. here,
In order to increase the polarization conversion efficiency of the polarization beam splitter, the optical design is made so that the light is focused on the pattern of the polarization beam splitter alternately and in a band shape at the center of the pattern. Therefore, the unevenness of the illuminance and the unevenness of the temperature in the plane of the polarization beam splitter are large, and the deterioration occurs from the highest part of the illuminance and the temperature.

This kind of problem is solved by using a glass material having a higher thermal conductivity than glass. Industrially applicable materials having high thermal conductivity include crystalline sapphire and YAG ceramics. However, these crystals are extremely hard and are not suitable for the glass material of the polarization beam splitter which requires complicated processing.

In the case of a polarizing plate, sapphire is a glass material (substrate)
However, since sapphire has a high hardness, it is difficult to polish it, and since it is an axial crystal (trigonal crystal), if the glass material is cut out with a slight inclination from the crystal axis, the image will be blurred. On the other hand, the inventor has noticed that magnesia has a high light-transmitting property because its crystal is a cubic system and that it is a ceramic, so that it is not necessary to pay attention to axis alignment. Furthermore, considering the heat load on the polarizing plate of the color liquid crystal projector, if the thermal conductivity of sapphire is 1, then YA
We paid attention to the high thermal conductivity of magnesia, with G ceramics being 0.5 and magnesia being 2. The thermal conductivity of sapphire is 23 (W / mK) and that of YAG ceramics is 12 (W / mK).
K), magnesia 55 (W / mK) and optical glass 7 (W / mK).

Color liquid crystal projectors include R, G,
Three polarizing plates of B are required, but the blue polarizing plate has reached the limit in terms of heat load even with sapphire, and in consideration of future high brightness, it has high translucency and high durability. Material is needed. Such a situation is the same as in a retardation plate such as a half-wave plate or a quarter-wave plate, and a retardation plate having high translucency and high thermal conductivity is required.

[0009]

The inventors of the present invention have conducted various studies to solve the above-mentioned problems, and as a result, have found that magnesia having a thermal conductivity higher than that of glass and a Vickers hardness of about 400, which is close to that of glass, is used. By using it as a glass material for optical elements such as a polarizing beam splitter, a polarizing plate, and a retardation plate, the surface temperature of the glass material can be lowered and the in-plane temperature can be made uniform, so that it has a long life and is inexpensive. The present invention has been completed by finding out that such an optical element can be obtained.

The optical element for a color liquid crystal projector of the present invention has a linear light transmittance of 7 mm at a thickness of 4 mm at a wavelength of 600 nm.
8% or more of translucent magnesia ceramics is used as a glass material (Claim 1). When the optical element of the present invention is used in a polarizing beam splitter for a color liquid crystal projector, for example, a color liquid crystal projector with an output of about 1000 ANSI lumens can achieve durability of about 5000 hours and linear light transmittances of 76% and 78%. Then, there is a great difference in durability as shown in the examples. Wavelength 600 here
It is preferable that the linear light transmittance in nm is 83% or more at a thickness of 4 mm, because the durability is further increased, and the wavelength of 60 is particularly preferable.
The linear light transmittance at 0 nm is 84% or more at a thickness of 4 mm, and most preferably 85% or more under the same conditions. The same applies to the case of a polarizing plate or a retardation plate, and the higher the linear light transmittance, the more preferable. The linear light transmittance at a wavelength of 600 nm is at least 78% or more, preferably 83% or more at a thickness of 4 mm, and particularly preferably. Is 84% or more, and most preferably 85% or more. The theoretical linear light transmittance of sapphire is 85.4%
Therefore, if the transmittance of magnesia ceramics is 84% or more, it is comparable in brightness to sapphire. If magnesia ceramics is used as the glass material,
It has advantages such as easy polishing, no axis alignment, and high thermal conductivity. In the following, the transmittance means the linear light transmittance at a wavelength of 600 nm and a thickness of 4 mm.

Preferably, the magnesia ceramic has a total content of Al ₂ O ₃ and SiO ₂ of 2000 wtppm or less and 6 * Al ₂ O ₃ + SiO ₂ of 250 wtppm or more (preferably 3 wt% or more).
(More than 00 wtppm) (Claim 2). Al ₂ O ₃ and SiO ₂ significantly improve the linear light transmittance of magnesia ceramics, and since Al ₂ O ₃ is about 6 times more effective than SiO ₂ in the low concentration region, 6 * Al ₂ O ₃ + SiO ₂ 2
50wtppm or more (preferably 300wtppm or more), Al
The sum of 6 times the ₂ O ₃ concentration and the SiO ₂ concentration is set to 250 wtppm or more. The impurity level of Al ₂ O ₃ is 10 wtppm or less, and the impurity level of SiO ₂ is 30 wtppm or less.

The magnesia ceramics can be easily polished by double-sided lapping and double-sided polishing and do not require axial alignment at the time of cutting. Since they are cubic crystals, they have a high light transmittance as a ceramic and a bright image can be obtained. And because it has high light transmittance and high thermal conductivity, it also has high heat resistance, and when used for optical elements such as polarization beam splitters, polarizing plates, and phase difference plates, it prevents temperature rise of the optical elements and is highly durable. The element can be obtained, and a uniform image can be projected (claims 3 to 5).

In the method for producing an optical element such as a polarizing beam splitter or a polarizing plate of the present invention, a molded body is formed by using a magnesia raw material powder obtained by heat-treating basic magnesium carbonate containing Al ₂ O ₃ or SiO ₂ and a binder. After manufacturing and removing the binder by heat treatment, sintering is performed at 1250 ° C. or more and 1500 ° C. or less in a hydrogen atmosphere or a vacuum,
Further, by HIP treatment (high temperature isotropic pressure pressurization), a translucent magnesia ceramic having a linear light transmittance at a wavelength of 600 nm of 78% or more at a thickness of 4 mm is obtained, which is used as a glass material (claim 6). . Preferably, the magnesia raw material powder contains Al ₂ O ₃ and SiO ₂ in a total content of 2000 wtppm or less and 6 * Al ₂ O ₃ + SiO ₂ of 250 wtppm or more (claim 7).

The present invention also resides in a color liquid crystal projector using the optical element according to any one of claims 1 to 5 (claim 8). More preferably, the polarizing beam splitter of claim 3, the polarizing plate of claim 4, or the retardation plate of claim 5 is used.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Since magnesia is excellent in electric insulation and thermal conductivity, it is used as an insulator of a sheath heater in the form of electro-fused magnesia, but the melting point of magnesia is as high as 2800 ° C. In the process of producing fused magnesia, large crystals are rarely obtained to some extent, and up to now, no large-scale single crystal growing technique that can be industrially applied has been found.

On the other hand, the method of powder manufacturing technology and ceramics manufacturing technology is disclosed in Japanese Patent Laid-Open No. 153798/1975.
And Japanese Patent Application Laid-Open No. 51-47911, the transparent ceramics applicable to optics have been manufactured. The magnesia ceramics used in the present invention is a plate-shaped translucent magnesia ceramics.

The linear light transmittance of the translucent magnesia ceramics is important for use in an optical element. When the linear light transmittance is low, the incident light is scattered and the amount of transmitted light is reduced and the efficiency of conversion into vertical polarized light or horizontal polarized light is reduced. Further, light absorption occurs inside the ceramic, and the surface temperature of the glass material rises. For these reasons, the transmissive magnesia ceramics has a linear light transmittance of 60 nm.
At 4 nm thickness at 0 nm, 78% or more, preferably 83
% Or more, particularly preferably 84% or more, and most preferably 85% or more. The theoretical transmittance is 86%.

The retardation film used in the magnesia optical element may be a 1/2 wavelength film, for example, WBR-90PCAR or WBR-90PC (CL) AR manufactured by Polatechno.
WBR-90 series such as (1/2 wavelength film for broadband)
and so on. Note that "WBR-90PCAR" and the like are trade names, and the 1/2 wavelength film and the like are sometimes called 1/2 wavelength plate and the like. An AR (antireflection) layer may be provided on the surface of the magnesia polarization beam splitter of the present invention. For example, a vapor deposition film or a sputtering film of silicon dioxide, titanium oxide or the like is used, and a fluorine-based substance is thinly applied. Can also be formed.

The size of the optical element of the present invention may be any desired size, for example, one side or diameter is 5 to 300 mm, preferably about 20 to 200 mm, and its shape is rectangular, square, circular, etc., with no particular limitation. No, but usually rectangular.
Its thickness is generally about 0.3 to 10 mm, preferably about 0.5 to 5 mm. In the case of a polarization beam splitter, the thickness is, for example, 0.5 to 10 mm, preferably about 1 to 5 mm.

One aspect of the polarization beam splitter of the present invention is that a polarization separation film is vapor-deposited and multi-coated on one surface of a magnesia substrate obtained by polishing a plate-shaped light-transmitting magnesia ceramics, and a desired number of them are adhered to each other. The one cut out in the direction of 45 degrees is used as a glass material, and the ½ wavelength film is attached at an equal pitch. By doing so, due to the high thermal conductivity of the magnesia substrate,
Even when exposed to high brightness, high temperature or uneven high temperature,
Uniformization of temperature occurs, causing a significant temperature drop in the highest temperature part, improving the durability of the attached 1/2 wavelength film,
It is possible to prevent yellowing and peeling of the joint portion of the glass material. Further, in order to further improve the light transmittance of the single plate, it is preferable to provide an AR (antireflection) layer on one or both of the magnesia surface and the pitch surface of the ½ wavelength film.

In order to manufacture the polarization beam splitter of the present invention, first, for example, the slow axis or the fast axis of a retardation film such as a ½ wavelength film is measured, and one side is set as a desired axis angle. Transparent adhesion (adhesion) to a magnesia substrate that has a size and is cut into a rectangular shape and is prepared as a glass material and arranged at an equal pitch.
The agent may be applied, and then the retardation film may be attached to this application surface. Alternatively, a transparent adhesive (adhesive) agent may be applied to the retardation film, and then the magnesia substrate may be attached to the applied surface. The adhesive (adhesive) used here is preferably, for example, an acrylic ester type. The size of the ½ wavelength film may be a desired size, for example, one side is 1 to 300 m.
m, preferably about 3 to 150 mm, and the shape thereof is not particularly limited and may be rectangular, square, etc., but generally rectangular is preferable. Its thickness is 0.1-1 mm, preferably 0.1-
About 0.3mm is good.

Further, in order to manufacture a glass material used for the polarization beam splitter, a desired number of magnesia substrates whose surface is precisely polished so as to have a uniform thickness are prepared from a plate of translucent magnesia ceramics. prepare. This thickness may be a desired thickness, for example, 0.3 to 10 mm, preferably 0.5 to 5 mm. A polarization separation film is formed on one surface of this magnesia substrate by vapor deposition multi-coating, and a desired number of sheets are stacked and bonded. As the adhesive (adhesive) agent used here, for example, either an ultraviolet curable adhesive or a thermosetting adhesive can be used.

The adhered product is accurately cut in the direction of 45 degrees and surface-polished so as to have a uniform thickness. This thickness is generally the same as the pitch width of the polarization beam splitter, for example, one pitch is 0.5 to 10 mm,
It is preferably about 1 to 5 mm. This magnesia is cut into a desired size to obtain a glass material used in the present invention.
This size may be a desired size, for example, one side is 5 to 3
The length is about 00 mm, preferably about 20 to 200 mm, and the shape thereof is not particularly limited and may be rectangular, square, etc., but generally rectangular is preferable.

In the color liquid crystal projector of the present invention,
The above-mentioned polarized beam splitter made of magnesia is used and is usually arranged between the light source and the incident side polarization plate. If a reflective liquid crystal panel is used, it should be placed at the optimum position for each system.

In the color liquid crystal projector of the present invention,
For example, an ultraviolet cut filter and a multi-lens are sequentially provided immediately after the light source, and then the above-mentioned magnesia polarization beam splitter is arranged. With the multi lens,
At every other pitch of the polarizing beam splitter, the light is focused, and the luminous flux density in this part is extremely high, and the temperature is also high. When the polarizing beam splitter made of magnesia of the present invention is arranged here, the glass material is magnesia, so that the thermal conductivity is high, the heat is dispersed to the surroundings to lower the temperature of the high temperature portion, and the 1/2 wavelength film of the polarizing beam splitter is provided. It is possible to reduce the load on the joint and the joint and improve the durability.

Preferably, the glass material of the polarizing plate is claim 4.
The magnesia ceramics are used as in. Here, the light-incident-side polarization plate is exposed to intense light and rises in temperature during use of the liquid crystal projector. When the liquid crystal cell and the light-incident-side polarization plate are in close contact with each other like a normal liquid crystal display element, the heat of the light-incidence-side polarization plate is transferred to the liquid crystal cell, and the liquid crystal in the liquid crystal cell is at the NI point (liquid crystal phase Beyond the phase change temperature of the isotropic phase), the display will not be possible. In order to avoid this, it is preferable to dispose the liquid crystal cell and the light incident side polarization plate apart from each other, and to circulate air or gas by a cooling fan or the like, or to prevent overheating of the liquid crystal cell by liquid cooling such as water cooling.

As the glass material of the retardation plate, it is preferable to use magnesia ceramics,
The retardation plate includes a half-wave plate and a quarter-wave plate.
By doing so, since the magnesia ceramics has a high light transmittance and a high thermal conductivity, a bright and highly durable phase difference plate can be obtained.

Also, the polarization beam splitter is exposed to strong light while using the liquid crystal projector and its temperature rises, the deterioration of the polarization beam splitter progresses, and the brightness of the projected image decreases and a defect occurs. In order to avoid this, air or gas is circulated around the polarization beam splitter by a cooling fan or the like to prevent the polarization beam splitter from overheating. A water cooling method is also used as a method for preventing overheating.

As an example of the color liquid crystal projector of the present invention, light emitted from a light source such as a metal halide lamp passes through an ultraviolet ray cut filter and a polarization beam splitter, and then is reflected by three dichroic mirrors.
The light is divided into light of three primary colors (red), G (green), and B (blue), and passes through the respective polarizing plates to be irradiated on the liquid crystal display panel. The light of the three primary colors that has passed through the liquid crystal display panel passes through the polarizing plate on the emission side, is condensed by the dichroic prism, and then is enlarged by the projection lens and projected on the screen.

[0030]

Example Preparation of translucent magnesia ceramics Translucent magnesia ceramics were prepared by the following method. The purity of magnesium chloride as a raw material is 99.99% or more. Al element or Si element is added to a 0.4 (mol / l) aqueous solution of magnesium chloride in the form of an aluminum chloride solution or a sodium silicate solution, and this is added to 0.4 (mol / l).
/ l) was reacted with a sodium carbonate solution to obtain magnesium carbonate (MgCO ₃ .3H ₂ O). The obtained precipitate was washed by filtration, and the pH was adjusted to 9.7 with carbon dioxide. Further, the precipitate was aged at 35 ° C. for 24 hours to obtain basic magnesium carbonate (4MgCO ₃ .Mg (OH) ₂ .5H ₂ O). Impurities in the raw materials and sodium in sodium silicate are lost in the process of filtration and washing, and most of the impurities remaining in basic magnesium carbonate are Al ₂ O ₃ or SiO ₂ and these are intentionally added. If not, the impurity level is 10wtppm each
And below 30 wtppm.

The obtained basic magnesium carbonate was added to 110
After drying at 0 ° C., it was heat-treated at 900 ° C. for 18 hours in an oxygen atmosphere to obtain a light-transmitting magnesia ceramic raw material powder. The content of Al ₂ O ₃ and SiO ₂ was measured for this raw material powder. A peptizer (for example, Floren G-700 manufactured by Kyoeisha Chemical Co., Ltd.) was added to 200 g of the obtained magnesia raw material powder.
6g, "Floren G" is a trade name), 4g of methylcellulose as a binder, 120g of ethanol are added,
The mixture was mixed for 5 hours using a nylon pot and a nylon ball to obtain an alcohol slurry. This slurry was poured into a water-permeable resin mold to obtain a 100 mm × 100 mm × 7 mm molded body.

This molded body was heated at 10 ° C./hr in an oxygen stream and degreased at 1000 ° C. for 20 hours. Sintering in hydrogen atmosphere or vacuum (vacuum degree is 0.1 Pa or less)
At 1250 ° C to 1500 ° C (primary sintering),
HIP treatment was carried out at a pressure of 10 ⁸ Pa (generally 3 × 10 ⁷ Pa or higher) in a high-purity argon gas atmosphere at 1300 ° C. to 1550 ° C. for 4 hours. Both surfaces of the obtained sintered body were mirror-polished using diamond slurry, and the linear light transmittance was measured with a spectrophotometer. Linear light transmittance of the obtained translucent magnesia ceramics (4 m at 600 nm)
The relationship between m thickness) and manufacturing conditions is shown in Table 1 as Test Examples 1 to 9. The particle size of the translucent magnesia is 10 to 20 μm and the structure is uniform, and the Al ₂ O ₃ content (impurity) is 3 wtppm, Si
O ₂ content (added as sodium silicate) is 600wtppm
Met.

[0033]

[Table 1] Sintering conditions for translucent magnesia ceramics Primary sintering temperature HIP temperature after primary sintering (° C) After HIP (° C x hour) Density of compact (%) Linear light transmittance (%) Test example 1 1250 × 1 92.5 1350 75.5 Test Example 2 1300 × 1 93.8 1400 76.0 Test Example 3 1350 × 1 94.9 1450 78.0 Test Example 4 1400 × 1 96.3 1500 83.0 Test Example 5 1450 × 1 97.8 1550 84.0 Test Example 6 1475 × 1 99.0 1550 84.5 Test Example 7 1475 × 1 99.0 1600 85.0 Test Example 8 1500 × 1 99.1 1600 85 .3 Test Example 9 1500 × 1 99.1 1625 85.4

Under the conditions of Test Example 5, the Al ₂ O ₃ content was ₃ wtppm.
The magnesia ceramics were prepared in the same manner as in Test Example 5 except that the content of SiO ₂ was changed. Table 2 shows the relationship between the SiO ₂ content and the linear light transmittance at a wavelength of 600 nm and a thickness of 4 mm.

[0035]

Table 2 SiO ₂ concentration (wtppm) 100 300 600 2000 Linear light transmittance (%) 45.0 84.0 84.0 82.0

Under the conditions of Test Example 5, the SiO ₂ content was 30 wtpp.
Magnesia ceramics were prepared in the same manner as in Test Example 5 except that the content of Al ₂ O ₃ was changed while the content was fixed to m. Al ₂ O ₃
Table 3 shows the relationship between the content and the linear light transmittance at a wavelength of 600 nm and a thickness of 4 mm.

[0037]

[Table 3] Al ₂ O ₃ concentration (wtppm) 10 50 2000 Linear light transmittance (%) 45.0 84.0 82.0

From Tables 2 and 3, in order to obtain magnesia ceramics having a linear light transmittance of 78% or more, Al ₂ O ₃ or SiO ₂ is used.
₂ is required, Al ₂ O ₃ in the low concentration range effectively improves the light transmittance than SiO _2, it can be seen the effect of Al ₂ O ₃ is about 6 times the effect of SiO _2. Further, when the Al ₂ O ₃ content or the SiO ₂ content is about 5000 wtppm, Al ₂ O ₃ or SiO ₂ which cannot be solid-dissolved precipitates at the grain boundaries, and the linear light transmittance is remarkably reduced, and it is processed as a glass material. The average grain size increased to such an extent that the strength of the ceramics decreased. Therefore, the total content of Al ₂ O ₃ and SiO ₂ is 2000 wtppm or less.

Structure of Polarizing Beam Splitter (Example
1) Fig. 1 shows an example of the magnesia polarization beam splitter 4. Here, the joint portion 41 of FIG. 1 is a portion where substrates are adhered to each other, and the attaching portion 42 is a portion where a ½ wavelength film is attached to the substrates. From a plate of translucent magnesia ceramics, the desired number of magnesia substrates whose surface has been accurately polished to a thickness of 2.8 mm (= 2√2: one pitch is 4.0 mm) , Prepared. The translucent magnesia ceramics substrate (Test Example 7) used had a linear light transmittance of 85.0% at a thickness of 4 mm. A polarization separation film was formed on one surface of this magnesia substrate by vapor deposition multi-coating, 17 sheets were stacked and adhered by an ultraviolet curable adhesive. Cut this bonded piece exactly in the direction of 45 degrees, grind the surface to a thickness of 4 mm, and cut it vertically 6
It was cut out to a size of 8.8 mm and a width of 66.8 mm. Also, a polycarbonate-based half-wave film W having an adhesive layer on one surface
BR-90PC (manufactured by Polatechno Co., Ltd. "WBR-90P
"C" is the product name), and the length is 68.8 mm and the width is 4.
Exactly cut to a size of 0 mm. Eight cut pieces
The adhesive surface of the / 2 wavelength film is attached to the magnesia glass material sticking portion 4
It was adhered exactly as in No. 2 and AR processing (antireflection processing) was applied to both surfaces thereof to obtain a polarizing beam splitter 4 made of magnesia.

Structure of Polarizing Beam Splitter (Example
2) Using the magnesia ceramics prepared in Test Example 7, after forming and adhering the polarization separation film and before attaching the half-wavelength film, the light transmittance of 68.8 mm in length, 66.8 mm in width, and 4 mm in thickness. Both surfaces of the magnesia ceramics glass material were subjected to AR processing. Further, a polycarbonate-based half-wave film WBR-90PCAR (surface AR having an adhesive layer on one surface thereof)
Processed product, made by Polatechno Co., "WBR-90PCA
"R" is the product name), and the length is 68.8 mm and width is 4.0
Exactly cut out to the size of mm. 1 of 8 cut out
The pressure-sensitive adhesive surface of the two-wavelength film is attached to the sticking portion 42 of the magnesia glass material.
And affixed exactly to obtain a polarized beam splitter made of magnesia. The other points are exactly the same as in the first embodiment.

Change of glass material As a translucent magnesia ceramic, linear light transmittance at a wavelength of 600 nm is 76% at 4 mm thickness (Test Example 2), 78%.
Three types of polarizing beam splitters were produced in the same manner as in Example 1 except that those used in (Test Example 3) and 84% (Test Example 5) were used.

Color Liquid Crystal Projector A color liquid crystal projector using the polarizing beam splitter made of magnesia obtained by the method of Example 1 is shown in FIG.
Shown in. In this example, a polarizing plate with a glass plate in which a polarizing plate with a ½ wavelength film is attached to a normal glass plate is used as an incident side polarizing plate, the polarizing plate surface is arranged on the liquid crystal side, and the polarizing plate with a sapphire substrate is a liquid crystal cell. Is arranged on the emission side of. The visible light emitted from the light source (metal halide lamp) 1 is UV
After passing through the / IR cut filter 2, most of the natural light is efficiently converted into polarized light in a fixed direction by the integrator lens 3 and the polarization beam splitter 4, and then red (R) is separated by the first color separation dichroic mirror 5. Is
Then, the second color separation dichroic mirror 5 separates them into green (G) and blue (B) to obtain three primary colors. R, G,
The respective light beams of B are incident on the blue incident side polarizing plate 7B, the red incident side polarizing plate 7R, and the green incident side polarizing plate 7G, and only the light beams of polarized light in a certain direction are incident on the TFT liquid crystal cell 8.
In addition, 6 is a mirror. The polarized light that has passed through the liquid crystal cell 8 is incident on the blue emitting side polarizing plate 9B, the red emitting side polarizing plate 9R, and the green emitting side polarizing plate 9G. The polarized light that has passed through the emission side polarization plates 9B and 9R is directly incident on the cross prism 11 with the dichroic mirror for combining, and the emission side polarization plate 9G for green.
The light beam that has passed through passes through the ½ wavelength film 10 and is incident on the cross prism 11 with a dichroic mirror for color synthesis. Then, the polarized light that has passed through the cross prism 11 and is synthesized is passed through the projection lens 12 and the screen 13
Projected on.

Durability A polarizing beam splitter using ordinary glass as a glass material and four types of polarizing beam splitters (linear light transmittance of 76%, 78%, 84%, 85%) using translucent magnesia ceramics were used. Then, the color liquid crystal projector shown in FIG. 2 was produced. The output (brightness) of each liquid crystal projector was about 1000 ANSI lumens. Further, these five projectors were continuously operated at 40 ° C. for 5000 hours at the same time, and the change of the polarization beam splitter 4 was confirmed. In the normal glass polarization beam splitter and the magnesia polarization beam splitter having a linear light transmittance of 76%, the half-wavelength film was burnt and the joint was yellowed. On the other hand, wavelength 600nm
In the case of the three types of magnesia-made polarization beam splitters having a linear light transmittance of 4 mm thickness of 78% or more, there was no change.

Further, the same operation was continued for 10,000 hours, and the change in the polarization beam splitter 4 was confirmed. The linear light transmittance at a wavelength of 600 nm was 78% at a thickness of 4 mm.
In the polarized beam splitter manufactured by Magnesia, the half-wavelength film was burnt and the joint part was yellowed. On the contrary,
There was no change in the magnesia polarization beam splitter having a linear light transmittance of 84% or more. As described above, the wavelength 6
By using a magnesia polarization beam splitter with a linear light transmittance of 00 nm of 4 mm and a thickness of 78% or more,
By using a magnesia polarization beam splitter with a linear light transmittance of 84% or more, it is possible to prevent the half-wavelength film from burning and the yellowing and peeling of the joint during 5000 hours of continuous operation. It is possible to prevent burning of the 1/2 wavelength film and yellowing or peeling of the joint, and to display a bright, high-contrast and excellent uniformity image for a long time,
A color liquid crystal projector was obtained.

Preparation of Polarizing Plate Under the conditions corresponding to Test Example 7 in Table 1, the linear light transmittance (60
An 85% magnesia ceramics plate (4 mm thick at 0 nm) was prepared. Al ₂ O ₃ content (impurity level) is 3 wtppm, SiO ₂
The content was 600 wtppm. This magnesia ceramic is cut into a length of 27 mm, a width of 33 mm, and a thickness of 0.5 mm, both sides are mirror-polished, and one side is AR (antireflection).
processed. Next, an organic polarizing film (one side may be AR-processed, in which case the AR-processed surface is not the adhesive surface)
Is attached to the surface of the magnesia ceramic on the side not subjected to the AR processing with an acrylic ester adhesive.

FIG. 3 shows the structure of the obtained polarizing plate 20. Reference numeral 22 is the above-mentioned magnesia ceramic glass material, 23 is an antireflection coating layer, and 24 is a polarizing film. In this way, three types of magnesia polarizing plates for blue, green and red were obtained and used for both the incident side polarizing plates 7R-7B and the emitting side polarizing plates 9R-9B of FIG. The 1/2 wavelength film was attached to the cross prism 11 side with the dichroic mirror.

For comparison, the glass material was changed from magnesia to BK.
The same polarizing plate (Comparative Example 1) except that the glass was changed to -7 glass,
A similar polarizing plate (Comparative Example 2) was prepared except that the glass material was YAG ceramics, and a similar polarizing plate (Comparative Example 3) was prepared except that the glass material was sapphire. These were used for the incident side and emission side polarizing plates (R, G, B) of FIG. 2 to prepare four types of color liquid crystal projectors. The output (brightness) of each projector was about 1000 ANSI lumens. After these four color liquid crystal projectors were continuously operated in an environment of 40 ° C. for 10,000 hours, the surface temperatures of the blue and green polarizing plates having a large heat load were measured. The results are shown in Table 4.

[0048]

[Table 4] Polarizing plate surface temperature sample after use for 10,000 hours Surface temperature (° C) 7B 9B 7G 9G Example 3 (magnesia) 48 55 40 57 Comparative Example 1 (glass) 65 76 56 78 78 Comparative Example 2 ( YAG) 56 66 47 69 Comparative Example 3 (sapphire) 52 61 44 64

As described above, the surface temperature of the polarizing plate can be kept low by using a magnesia substrate, which has a high thermal conductivity and a high light-transmitting property, and thus generates little heat, so that a uniform image can be maintained for a long time. A polarizing plate was obtained. The linear light transmittance of the magnesia ceramics is at least 78% or more, preferably 83% under the condition of wavelength of 600 nm and thickness of 4 mm.
% Or more, particularly preferably 84% or more, most preferably 8%
5% or more. In order to improve the linear light transmittance of magnesia ceramics, the total content of Al ₂ O ₃ and SiO ₂ is 2000 wtppm or less, and 6 * Al ₂ O ₃ + SiO ₂ is 250 wtpp.
It is contained so as to be m or more (preferably 300 wtppm or more).

As in the case of the polarizing plate, a half-wave plate or a 1-wave plate is used.
It is preferable to use magnesia ceramics also for the glass material of the retardation plate such as the / 4 wavelength plate. In the case of a retarder,
The linear light transmittance of the glass material magnesia ceramics is at least 78% or more, preferably 83% or more, particularly preferably 84% or more, most preferably 85% or more under the condition of a wavelength of 600 nm and a thickness of 4 mm. In addition, in order to improve the linear light transmittance, magnesia ceramics as a glass material has a total content of Al ₂ O ₃ and SiO ₂ of 2000 wtppm or less and 6 * Al ₂ O ₃ + SiO ₂ of 250 wtppm or more (preferably 3 wt% or more).
(00 wtppm or more).

In the production of the retardation plate, both surfaces of the magnesia ceramic are mirror-polished, for example, an antireflection coating layer is provided on one surface, and a ½ wavelength film or a ¼ wavelength film is attached to the other surface with a transparent adhesive. wear. The half-wave film and the quarter-wave film are, for example, uniaxially stretched films of polyvinyl alcohol, polycarbonate, etc. to have anisotropy, and depending on the degree of stretching and additives, for red, blue, Providing types such as for green,
Different retardation values are used. And 1
The / 2 wavelength film and the 1/4 wavelength film are cut so that the fast axis and the slow axis are oriented in a predetermined direction, and attached to a magnesia glass material with a transparent adhesive such as an acrylate ester or polyvinyl alcohol . By doing so, since the linear light transmittance of the glass material is high and the thermal conductivity is high, the half-wavelength film and the quarter-wavelength film are not burnt or yellowed and have a high durability of the half-wavelength. Since a plate or the like can be obtained and the light source can be brightened, a high-brightness color liquid crystal splitter can be obtained. Also, since the glass material is equiaxed magnesia ceramics, there is no need to align the axes.

[0052]

By using the optical element of the present invention, it is possible to obtain a color liquid crystal projector having excellent brightness and durability and capable of stably displaying an excellent image for a long time.
By using the polarizing beam splitter of the present invention, an image having higher contrast and excellent uniformity can be stably displayed for a long time. When the polarizing plate and the retardation plate of the present invention are used, the ceramic is bright enough to be comparable to sapphire,
Axis alignment is not required, and since the temperature rise is small, deterioration of the polarizing layer and the half-wavelength film can be prevented, and a high-intensity color image can be displayed stably for a long time.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a polarization beam splitter of an example.

FIG. 2 is a diagram showing a structure of a color liquid crystal projector using the polarization beam splitter of the embodiment.

FIG. 3 is a sectional view of a polarizing plate of an example.

[Explanation of symbols]

1 Light Source (Metal Halide Lamp) 2 UV / IR Cut Filter 3 Integrator Lens 4 Polarization Beam Splitter 41 Joining Section 42 Attachment Section 5 Color Separation Dichroic Mirror 6 Mirror 7R Red Incident Side Polarizer 7G Green Incident Side Polarizer 7B Blue Incident side polarizing plate 8 TFT liquid crystal cell 9R Red emitting side polarizing plate 9G Green emitting side polarizing plate 9B Blue emitting side polarizing plate 10 1/2 wavelength film 11 Cross prism with dichroic mirror for color synthesis 12 Projection lens 13 Screen 20 Polarizing plate 22 Magnesia ceramics glass material 23 Antireflection coating layer 24 Polarizing film

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H049 BA02 BA05 BA06 BA42 BA43                       BB03 BB42 BB51 BC10 BC13                       BC14 BC22                 2H088 EA12 HA15 HA20                 2H091 FA10X FA11X FB06 FC22                 2K103 AA01 AA05 AA11 AA16 AB04                       BC11 BC15 BC16 CA26 DA01                       DA11

Claims (8)

[Claims] 1. An optical element for a color liquid crystal projector, comprising a translucent magnesia ceramic as a glass material having a linear light transmittance at a wavelength of 600 nm of 4% and a thickness of 78% or more. 2. The magnesia ceramics is Al ₂ O ₃
And SiO ₂ with a total content of 2000 wtppm or less, 6 * Al ₂
The optical element according to claim 1, wherein O ₃ + SiO ₂ is contained in an amount of 250 wtppm or more. 3. The optical element according to claim 2, wherein the optical element is a polarization beam splitter. 4. The optical element according to claim 2, wherein the optical element is a polarizing plate. 5. The optical element according to claim 2, wherein the optical element is a retardation plate. 6. A molded body is prepared using a magnesia raw material powder obtained by heat-treating basic magnesium carbonate containing Al ₂ O ₃ or SiO ₂ and a binder, and the binder is removed by heat treatment, and then, in a hydrogen atmosphere or In vacuum 1
Wavelength 600nm obtained by sintering at 250 ℃ or more and 1500 ℃ or less and further HIP treatment (high temperature isotropic pressure)
A method for manufacturing an optical element for a color liquid crystal projector, which uses a translucent magnesia ceramic having a linear light transmittance of 4 mm thickness of 78% or more as a glass material. 7. The magnesia raw material powder contains Al ₂ O ₃ and S.
When the total content of iO ₂ is 2000 wtppm or less, 6 * Al ₂ O ₃
7. The method for manufacturing an optical element according to claim 6, wherein the content of + SiO ₂ is 250 wtppm or more. 8. A color liquid crystal projector using the optical element according to claim 1.