JP2005338160A - Polarizing plate and liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate which does not require time and labor for joining a holding plate and a polarizer, is low in cost and excellent in light transmission and heat dissipation, and a liquid crystal projector using the same.
A liquid crystal projector (1) includes an illumination optical system (100), a color light separation optical system (200) that separates illumination light emitted from the illumination optical system (100) into three colors of different wavelength ranges, and modulates each color beam. Liquid crystal panels 400R, 400G, and 400B, a prism 500 that combines the modulated color beams, and a projection lens unit 12 that magnifies and projects the combined beam. Incident-side polarizing plates 260R, 260G, and 260B are made of a sintered substrate of translucent ceramics (translucent yttrium, aluminum, garnet (YAG)) having an isotropic crystal structure without optical anisotropy. A polarizer is bonded to the surface of the plate.
[Selection] Figure 1

Description

  The present invention relates to a polarizing plate and a liquid crystal projector used in a liquid crystal projector that projects and displays an image on a liquid crystal panel.

  Conventionally, as an image display device for presentation or home theater use, it is composed of a liquid crystal panel having a light modulation action and a light source lamp for irradiating light to the liquid crystal panel, and the light modulated by the liquid crystal panel is enlarged and projected on the screen. Liquid crystal projectors that display images are widely known. In such a liquid crystal projector, a light source lamp that emits intense light has been used to cope with downsizing, high definition, and high brightness.

  Such a liquid crystal projector usually has polarizing plates on the light incident surface side and the light exit surface side of the liquid crystal panel. The polarizing plate has a function of transmitting only the light component in the polarization axis direction and blocking other light components. Therefore, heat is generated when light other than the light component in the polarization axis direction is blocked. If the temperature of the polarizing plate rises due to this heat generation, the polarizing plate itself will be distorted and deteriorated, and light that should be blocked will be transmitted or light that should not be blocked will be blocked and projected onto the screen. There is a problem that the sharpness of the image to be lost is lost. In addition, the liquid crystal panel is also vulnerable to heat, and the characteristics are hindered at high temperatures.

  In order to cope with such heat, a polarizing plate has been proposed in which a polarizer is bonded to the surface of a holding plate made of a sapphire substrate (see, for example, Patent Document 1).

Japanese Patent No. 3443549

  However, although the polarizing plate of the above-mentioned Patent Document 1 can obtain a sufficient heat dissipation effect by using a sapphire substrate as a holding plate to which a polarizer is bonded, a shaving process after generating a single crystal sapphire substrate. During the (polishing step), it is necessary to polish while repeating the measurement of the tilt angle of the C axis by X-ray diffraction or the like, and at the time of joining the holding plate and the polarizer, the transmission polarization axis of the polarizer and the holding plate (sapphire substrate) ) And the C-axis need to be precisely controlled.

  Accordingly, the present invention provides a polarizing plate that does not require time and effort to join the holding plate and the polarizer, is low in cost, and is excellent in light transmission and heat dissipation, and a liquid crystal projector using the polarizing plate. Objective.

  In order to solve the above problems, the polarizing plate of the present invention is characterized in that a polarizing body is bonded to the surface of a holding plate made of a transparent ceramic having an isotropic crystal structure.

  According to this configuration, the holding plate is made of a transparent ceramic having an isotropic crystal structure (equiaxial crystal system), so that when the holding plate and the polarizer are bonded, Thus, it is possible to provide a polarizing plate which does not require time and effort to match the polarization axis with that of the holding plate, is low in cost, and has excellent light transmittance and heat dissipation.

  The polarizing plate of the present invention is characterized in that the translucent ceramic is made of a polycrystalline sintered body.

  According to this configuration, when the holding plate is formed of a polycrystalline sintered body substrate having an isotropic crystal structure, the polarization axis of the polarizing body and the polarization of the holding plate are bonded when the holding plate and the polarizing body are joined. It is possible to provide a polarizing plate that does not require the effort to align the axes, is low in cost, and is excellent in light transmittance and heat dissipation. Moreover, since it is a sintered body, it can be manufactured in a shorter time than a single crystal, and the manufacturing time of the polarizing plate can be shortened.

  The polarizing plate of the present invention is characterized in that the polycrystalline sintered body is made of polycrystalline transparent yttrium aluminum garnet ceramics.

  According to this configuration, when the holding plate is formed of a polycrystalline transparent yttrium aluminum garnet ceramic substrate having an isotropic crystal structure, the polarizing axis of the polarizing body and the holding plate are joined when the holding plate and the polarizing body are joined. Therefore, it is possible to provide a polarizing plate which is low in cost and excellent in light transmittance and heat dissipation. Furthermore, heat dissipation suitable for the use of a liquid crystal projector can be obtained.

  The polarizing plate of the present invention is characterized in that the polycrystalline sintered body is made of polycrystalline transparent spinel.

  According to this configuration, since the holding plate is formed of a polycrystalline spinel substrate having an isotropic crystal structure, the polarization axis of the polarizer and the polarization axis of the holding plate are set at the time of joining the holding plate and the polarizer. It is possible to provide a polarizing plate that does not require labor for matching, is low in cost, and is excellent in light transmittance and heat dissipation. Furthermore, heat dissipation suitable for the use of a liquid crystal projector can be obtained.

  The electro-optical unit of the present invention includes an electro-optical device that modulates according to image information, a polarizing plate in which a polarizer is bonded to the surface of a holding plate, and the electro-optical device and the polarizing plate facing each other. An electro-optical unit including a holding body that holds the polarizing plate on at least one of a light incident surface side and a light emission surface side of the electro-optical device, and the electro-optical device. It is characterized by being held with an interval of 0.1 to 10 mm.

  According to this configuration, the light transmission and the heat dissipation are excellent, and dust or the like does not adhere to the surface of the electro-optical device. An electro-optic unit that is difficult to focus by being away from the display surface and prevents the quality of the projected image from being impaired can be obtained. The distance between the polarizing plate and the electro-optical device is preferably 0.1 to 10 mm, and more preferably 0.5 to 5 mm. If the distance between the polarizing plate and the electro-optical device is narrower than 0.1 mm, the heat accumulated between the two becomes difficult to dissipate sufficiently, and as a result, the electro-optical device is likely to be thermally deformed. If the interval is larger than 10 mm, the thickness of the electro-optical unit increases, so that it takes up space, and downsizing cannot be realized. Moreover, since the holding body is a sintered body, it can be manufactured in a shorter time than a single crystal and the manufacturing time of the polarizing plate can be shortened.

  The liquid crystal projector of the present invention projects an illumination optical system that emits illumination light, an electro-optical device that modulates light from the illumination optical system according to image information, and a modulated light beam obtained by the electro-optical device. A projection optical system, and at least one of a light incident surface side and a light emission surface side of the electro-optical device is provided with a gap of 0.1 to 10 mm from the electro-optical device. It is characterized by having prepared.

  According to this configuration, the holding plate is provided with the polarizing plate formed of the translucent ceramic substrate on at least one of the light incident surface side and the light emitting surface side of the electro-optical device, thereby transmitting light. In addition, it is possible to provide a liquid crystal projector with a clear image projected on a screen, with excellent properties and heat dissipation, while suppressing a decrease in contrast of modulated light (image light) emitted from an electro-optical device. The distance between the polarizing plate and the electro-optical device is preferably 0.1 to 10 mm, and more preferably 0.5 to 5 mm. If the distance between the polarizing plate and the electro-optical device is narrower than 0.1 mm, the heat accumulated between the two becomes difficult to dissipate sufficiently, and as a result, the electro-optical device is likely to be thermally deformed. If the interval is larger than 10 mm, the thickness of the electro-optical unit increases, so that it takes up space, and downsizing cannot be realized. Moreover, since the holding body is a sintered body, it can be manufactured in a shorter time than a single crystal and the manufacturing time of the polarizing plate can be shortened.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing a liquid crystal projector to which the present invention is applied, and FIG. 2 is an explanatory view of a polarizing plate of the present invention.

First, the configuration of the liquid crystal projector 1 will be described with reference to FIG.
In FIG. 1, a liquid crystal projector 1 modulates an illumination optical system 100, a color light separation optical system 200 that separates illumination light emitted from the illumination optical system 100 into three colors of light of different wavelength ranges, and each color beam. Liquid crystal panels 400R, 400G, and 400B as electro-optical devices, a prism (dichroic prism) 500 as a color combining optical system for combining modulated color light beams, and a projection optical system for enlarging and projecting the combined light beams A projection lens unit 12 is provided.

  In addition, a light modulation system 300 that guides the blue light beam B out of the color light beams separated by the color light separation optical system 200 to the liquid crystal panel 400B is provided. Further, incident side polarizing plates 260R, 260G, and 260B and emission side polarizing plates 270R, 270G, and 270B are provided on the light incident surface side and the light emitting surface side of the liquid crystal panels 400R, 400G, and 400B.

  The illumination optical system 100 includes a reflection mirror 101 that bends the optical axis 1a of light emitted from the light source lamp unit 11 at a right angle toward the front of the apparatus, and a uniform illumination optical element that is orthogonal to the front and rear with the reflection mirror 101 interposed therebetween. Integrator lenses 102 and 103. The light source lamp unit 11 is a high-intensity lamp light source such as a metal halide lamp, a xenon lamp, or a mercury lamp.

  The integrator lenses 102 and 103 have a plurality of rectangular lenses arranged in a matrix, and the integrator lens 102 divides the luminous flux of the emitted light emitted from the light source lamp unit 11 into a plurality of partial luminous fluxes. The partial light beam is condensed near the integrator lens 103. The integrator lens 103 has a function of superimposing the partial light beams emitted from the integrator lens 102 on the liquid crystal panels 400R, 400G, and 400B.

  The color light separation optical system 200 includes a blue-green reflection dichroic mirror 201, a green reflection dichroic mirror 202, and a reflection mirror 203. First, in the blue-green reflecting dichroic mirror 201, the red light beam R included in the light beam W among the light beams W that have passed through the uniform illumination optical element (integrator lenses 102 and 103) is transmitted, and the blue light beam B and the green light beam G are perpendicular to each other. Reflect on. The reflected blue light beam B and green light beam G are directed toward the green reflecting dichroic mirror 202.

  The red light beam R that has passed through the blue-green reflecting dichroic mirror 201 is reflected at a right angle by the rear reflecting mirror 203 and is emitted from the emitting portion 204 of the red light beam R to the prism 500 side. Next, out of the blue light beam B and the green light beam G reflected by the blue-green reflecting dichroic mirror 201, only the green light beam G is reflected at a right angle by the green reflecting dichroic mirror 202, and the prism from the green light beam G emitting part 205 is reflected. Injected on the 500 side. The blue light beam B that has passed through the green reflecting dichroic mirror 202 is emitted from the emission unit 205 of the blue light beam B to the light modulation system 300 side. The distances from the illumination optical system 100 configured in this way to the emission portions 204, 205, and 206 of the light beams of the respective colors are set to be equal.

  Condensing lenses 251 and 252 are arranged on the exit side of the emission portions 204 and 205 of the red light beam R and the green light beam G in the color light separation optical system, respectively. Therefore, the red light beam R and the green light beam G emitted from each emitting part are incident on these condenser lenses 251 and 252 and are collimated.

  The paralleled red light beam R and green light beam G are aligned in the polarization direction by the incident-side polarizing plates 260R and 260G (only the light component in the same direction as the polarization axis is transmitted). The light beams transmitted through the incident-side polarizing plates 260R and 260G are incident on the liquid crystal panels 400R and 400G and modulated, and image information corresponding to each color light is added. That is, the liquid crystal panels 400R and 400G are switching-controlled by an image signal corresponding to image information by a driving means (not shown), and thereby each color light passing therethrough is modulated. Known means can be used as such driving means.

  On the other hand, the blue light beam B is incident on the corresponding liquid crystal panel 400B through the light modulation system 300 and further aligned in the polarization direction by the incident side polarizing plate 260B, and modulated in accordance with the image information in the liquid crystal panel 400B. Applied. As the liquid crystal panels 400R, 400G, 400B, for example, those using polysilicon TFTs as switching elements can be employed. The incident-side polarizing plates 260R, 260G, and 260B are set from the liquid crystal panels 400R, 400G, and 400B with an interval of, for example, 0.1 to 10 mm.

  The light modulation system 300 includes a condenser lens 301, an incident-side reflection mirror 302, an emission-side reflection mirror 303, an intermediate lens 304 disposed between these reflection mirrors, and a collector disposed on the front side of the liquid crystal panel 400B. And an optical lens 305. The blue light beam B has the longest optical path length of each color light beam, that is, the distance from the light source lamp unit 11 to each liquid crystal panel. Therefore, the light quantity loss of the luminous flux is the largest, but the light quantity loss can be suppressed by interposing the light modulation system 300. When the light modulation system 300 is not provided in the path of the blue light beam B, the illumination area of the liquid crystal panel 400B illuminated by the blue light beam B is larger than the illumination area of the liquid crystal panel illuminated by other color light beams, Lighting efficiency decreases.

  Each color beam modulated through the liquid crystal panels 400R, 400G, and 400B is incident on the exit-side polarizing plates 270R, 270G, and 270B. The polarization axes of the exit-side polarizing plates 270R, 270G, and 270B are set to be the same as the predetermined polarization direction of the linearly polarized light that is modulated and incident, and the transparent adhesive is directly applied to the surface of each incident surface of the prism 500. A polarizing body is pasted using. The light transmitted through the emission side polarizing plates 270R, 270G, and 270B enters the prism 500 and is combined.

  The prism 500 includes an R light reflecting dichroic surface 501 that reflects R light and a B light reflecting dichroic surface 502 that reflects B light. The R-light reflecting dichroic surface 501 and the B-light reflecting dichroic surface 502 are formed in a substantially X shape at the interface of four right-angle prisms with a dielectric multilayer film that reflects R light and a dielectric multilayer film that reflects B light. It is provided by forming. The two dichroic surfaces 501 and 502 combine the three colors of converted light to form light representing a color image.

  Then, the color image synthesized by the prism 500 is enlarged and projected onto the projection surface of the screen 13 at a predetermined position via the projection lens unit 12.

  Next, the polarizing plate will be described with reference to FIG. FIG. 4A is a schematic plan view of the incident side polarizing plate, and FIG. 4B is a schematic sectional view of the incident side polarizing plate.

  In addition, the polarizing plate shown in FIG. 2 is explanatory drawing of incident side polarizing plate 260R, 260G, 260B. The exit side polarizing plates 270R, 270G, and 270B provided on the light exit surface side of the liquid crystal panels 400R, 400G, and 400B transmit most of the incident modulated light, but on the light entrance surface side of the liquid crystal panels 400R, 400G, and 400B. The incident-side polarizing plates 260R, 260G, and 260B that are provided generate a large amount of heat (temperature rise) in order to block part of the incident linearly polarized light. In the present embodiment, in order to reduce this temperature rise, the holding plate is applied only to the incident side polarizing plates 260R, 260G, and 260B having a large temperature rise. Note that the heat conductivity of the heat radiating plate (holding plate) that can ensure the heat radiating property necessary for the liquid crystal projector needs to be about 5.0 W / mK or more. The transmittance of the polarizing plate is generally as low as about 40%.

  The incident-side polarizing plates 260R, 260G, and 260B are made of light-transmitting ceramic polycrystalline transparent yttrium, aluminum, isotropic (no anisotropy or cubic) crystal structure (equal axis system). It is composed of a holding plate MB made of garnet ceramics (hereinafter referred to as YAG) and a polarizer PO. The polarizer PO is transparently bonded to the surface of the holding plate MB, such as a silicon-based adhesive or an acrylic adhesive. Bonding (bonding) is performed so that bubbles are not generated by an agent (not shown). Since the holding plate MB and the polarizer PO are formed corresponding to the effective display areas of the liquid crystal panels 400R, 400G, and 400B having a substantially rectangular shape, both have a substantially rectangular shape.

  Polarizer PO is made by adsorbing and dispersing iodine in polyvinyl alcohol (PVA) to form a film, and then stretching the film in a certain direction. Acetate cellulose film is applied to both sides of the stretched film. It is a polarizer laminated with an adhesive.

  In the polarizing plate configured as described above, since the holding plate MB is formed of YAG having an isotropic crystal structure (isometric crystal system), the polarizing plate is predetermined without taking time and effort to control the polarization axis. Can be processed into a shape. The polarizer PO is bonded to the holding plate MB in such a manner that the transmission polarization axis ax of the polarizer PO is bonded in the direction along the side s1, for example, of the two sides s1 and s2 orthogonal to the holding plate MB. ing.

  At the time of this bonding, since the holding plate MB is formed of YAG having an isotropic crystal structure, it is not necessary to align the optical axes of the holding plate MB and the polarizer PO. Further, since the holding plate MB is formed of YAG that is colorless and transparent (in the wavelength band of visible light), it can be used as a holding plate for any polarizing plate of R, G, and B colors. A description of YAG forming the holding plate MB will be given later.

  The polarizing plates 260R, 260G, and 260B on which the holding plate MB and the polarizer PO are bonded are arranged on the incident side of the corresponding liquid crystal panels 400, 400G, and 400B with the polarizer PO on the liquid crystal panel side. It is set with an interval of 1-5 mm. In addition, the change of polarization characteristics can be suppressed as much as possible by disposing the polarizer PO of the incident side polarizing plate on the side of each liquid crystal panel.

  The incident-side polarizing plates 260R, 260G, and 260B configured as described above can conduct heat generated by absorption of light that could not be transmitted through the polarizer PO to the holding plate MB, and can efficiently dissipate the heat. By maintaining the characteristics of the plate and the liquid crystal panel, it is possible to obtain a projected image without uneven illuminance. In addition, by configuring the holding plate MB constituting the incident side polarizing plates 260R, 260G, and 260B with YAG, the polarizing plates for the liquid crystal projector (holding plate MB) are inferior to sapphire on the surfaces of the liquid crystal panels 400R, 400G, and 400B. ), Sufficient temperature lowering effect (heat dissipation) was obtained.

  Next, the polycrystalline yttrium aluminum garnet (YAG) used for the holding plate of the present invention will be described.

YAG is produced by weighing Al (NH ₄ ) · (SO ₄ ) ₃ and YCl ₃ at a predetermined molar ratio, ball milling, and pre-baking at 1200 ° C. for 3 hours in air, with an average particle size of 1 μm or less The raw material powder of yttrium, aluminum and garnet is obtained. Prior to the preliminary firing, a predetermined weight of a fluorine compound LiF is added as a firing aid and mixed uniformly.

The material is not limited to Al (NH ₄ ) · (SO ₄ ) ₃ and YCl ₃ , but any Al or Y hydroxide, carbonate, or any other substance that is thermally decomposed at 500 to 1300 ° C. and converted to YAG, Any material can be used. Although the calcination atmosphere is arbitrary, an oxygen-containing atmosphere such as air or oxygen is preferable.

Further, the sintering aid may be in addition to LiF, may be used _{NaF, MgF 2, NH 4 F} , any fluorine raw material such as tetrafluoroethylene resin. A preferable addition amount is set to 100 to 4000 wtppm with respect to the total weight of YAG after calcination in terms of F ions. When the addition amount of F ions is insufficient, the sinterability at the time of subsequent sintering is lowered, and when it is excessive, a heterogeneous phase is precipitated at the time of sintering, and the transparency is lowered.

  Then, after pulverizing the YAG powder of the presintered product, it is granulated into a 100 mesh pass, poured into a gypsum mold (slip casting method), and molded into a predetermined shape. In this molding, since the YAG does not have polarization anisotropy, the holding plate MB can be formed of a sintered body. Therefore, the predetermined shape (out-plane shape) can be the outer shape of the completed holding plate MB. .

  Next, the molded YAG is sintered in an oxygen-free atmosphere such as in vacuum, hydrogen, Ar, or He. A transparent sintered body cannot be obtained in air or oxygen. Sintering is performed in two stages, primary firing and secondary sintering. In the primary firing, YAG is sintered to some extent and the activity of YAG particles is suppressed, and abnormal growth of YAG particles in the sintering (secondary firing). To prevent. When abnormal growth of YAG particles occurs, the sintered body becomes opaque.

  The primary firing temperature is set to a maximum temperature of 1300 to 1550 ° C. Below this temperature, the sintered body is not sufficiently densified, and above this, opacification occurs due to abnormal growth of YAG particles. The primary firing and the secondary sintering are preferably performed continuously, and the rate of temperature rise during that is preferably 120 ° C./hour or less. When the heating rate is increased, uniform grain growth cannot be obtained and the transparency is lowered. The secondary sintering temperature is set to a maximum temperature of 1650 to 1900 ° C. If the temperature is lower than 1650 ° C, the sintering is insufficient and the transparency is lowered, and if it exceeds 1900 ° C, melting and evaporation of YAG become remarkable.

  Thereafter, the sintered body is lapped using diamond abrasive grains or the like, thereby completing a substrate (holding plate) made of polycrystalline transparent yttrium / aluminum / garnet ceramics (YAG ceramics) excellent in light transmittance.

Table 1 shows a comparison of the characteristic values of YAG and other transparent materials such as quartz glass (SiO ₂ ), sapphire, and quartz.

表１に示すように、多結晶透明イットリウム・アルミニウム・ガーネットセラミックス（ＹＡＧ）は、熱伝導率（１４．０Ｗ／ｍＫ）はサファイア（４２．０Ｗ／ｍＫ）に比べて劣るが、石英ガラス（１．３０Ｗ／ｍＫ）や水晶（６．２〜１０．４Ｗ／ｍＫ）に比べて優れており、液晶プロジェクタ用の偏光板（保持板ＭＢ）として用いるのには充分な放熱性を有する。また、透過率も他と比べて遜色がなく高く、偏光板として用いるのに適した特性を有している。さらに、高強度であるため、他の材料（石英ガラスや水晶）と比較して薄く設計することも可能である。

As shown in Table 1, polycrystalline transparent yttrium / aluminum / garnet ceramics (YAG) has a thermal conductivity (14.0 W / mK) inferior to sapphire (42.0 W / mK), but quartz glass (1 .30 W / mK) and quartz (6.2 to 10.4 W / mK), and has sufficient heat dissipation to be used as a polarizing plate (holding plate MB) for a liquid crystal projector. Further, the transmittance is not inferior to that of others, and has characteristics suitable for use as a polarizing plate. Furthermore, since it has high strength, it can be designed to be thinner than other materials (quartz glass or quartz).

  And, by forming the holding plate MB constituting each incident side polarizing plate 260R, 260G, 260B with YAG, it is inferior to sapphire in terms of heat dissipation, but YAG is not anisotropic (no optical rotation with respect to polarized light). Thus, it is not necessary to match the polarization axis of the polarizer PO and the polarization axis of the holder plate MB when the holder plate MB and the polarizer PO are joined. Moreover, since sapphire has a crystal structure with optical anisotropy, it must be manufactured as a single crystal. On the other hand, because YAG has a crystal structure without optical anisotropy, a holding plate can be formed of a sintered body. Thus, it is possible to obtain a polarizing plate that is superior in cost compared to the case of using sapphire, or the liquid crystal projector 1 using this polarizing plate.

  Further, if the substrate material constituting the holding plate MB is a single crystal, it is necessary to grow it into an ingot over several weeks to several months. On the other hand, since YAG can be provided as a sintered body, the holding plate MB can be manufactured in a few days. Furthermore, if it is a single crystal, it takes time and cost to process the ingot, etc., but since YAG is a sintered body, it can be formed into a desired shape at the time of forming, and the processing time and cost can be reduced.

  Also, among ceramics that are generally said to have good thermal conductivity (heat dissipation), YAG, which has a crystal structure with no optical anisotropy and relatively good thermal conductivity, is adopted. Sufficient heat dissipation is obtained.

The present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.
(Modification 1)

In the above embodiment, the case where the holding plate MB is formed from polycrystalline transparent yttrium aluminum garnet (YAG) as a translucent ceramic is described, but it is formed from polycrystalline transparent spinel (MgAl ₂ O ₄ ). Even in this case, the same effect as YAG can be obtained. Polycrystalline transparent spinel, also called spinel, is excellent in light transmission and thermal conductivity.

  The polycrystalline transparent spinel is produced by a solid phase reaction in which alumina and magnesia powder raw materials are heated to 1000 to 1400 ° C. At this time, since the volume expansion is about 8%, the formed spinel is finely pulverized, formed into a predetermined shape as a raw material spinel powder, and then sintered again. Table 2 shows the characteristic values of such a polycrystalline transparent spinel.

表２に示すように、多結晶透明スピネルは、熱伝導率はサファイアに比べて劣るが、石英ガラスや水晶に比べて優れており（表１の比較表を参照）、液晶プロジェクタ用の偏光板（保持板ＭＢ）として用いるのには充分な放熱性を有する。また、透過率（光学透過率）も他と比べて遜色がなく高く、偏光板として用いるのに適した特性を有している。

As shown in Table 2, the polycrystalline transparent spinel is inferior to sapphire in thermal conductivity, but superior to quartz glass or quartz (see the comparison table in Table 1), and is a polarizing plate for a liquid crystal projector. It has sufficient heat dissipation to be used as (holding plate MB). Further, the transmittance (optical transmittance) is not inferior to that of others and has characteristics suitable for use as a polarizing plate.

(Modification 2)
In the embodiment, only the incident-side polarizing plates 260R, 260G, and 260B have a configuration in which the polarizer PO is attached to the surface of the holding plate MB formed of translucent ceramics (polycrystalline YAG or polycrystalline spinel). However, similarly, the emission-side polarizing plates 270R, 270G, and 270B may have a configuration in which the polarizing body PO is attached to the surface of the holding plate MB formed of a translucent ceramic. Also in this case, it is preferable to set each exit-side polarizing plate at an interval of 1 to 5 mm from the liquid crystal panels 400R, 400G, and 400B. Thereby, it becomes possible to radiate heat more efficiently.

Further, only the exit side polarizing plates 270R, 270G, and 270B may be polarizing plates configured by the holding plate MB and the polarizing body PO formed of translucent ceramics. In this case, the polarization axis of each exit-side polarizing plate is set to be the same as the predetermined polarization direction of the linearly polarized light that is modulated and incident, and the corresponding liquid crystal panel has, for example, a light incident surface. Just paste.
(Modification 3)

  In the embodiment, the incident-side polarizing plate 260 (260R, 260G, 260B) and the emission-side polarizing plate 270 (270R, 270G, 270B) are used as the light incident surface side and the light emitting surface of the liquid crystal panel 400 (400R, 400G, 400B). As described in the case of the individual arrangement on the side, an electro-optical unit having an integrated configuration in which at least one of the incident-side polarizing plate 260 and the emission-side polarizing plate 270 is held opposite to the liquid crystal panel 400 with a space therebetween. It is good. This embodiment will be described with reference to a schematic cross-sectional view of the electro-optic unit shown in FIG.

  In the electro-optical unit 20, the liquid crystal panel 400 and the incident-side polarizing plate 260 are held opposite to each other with a spacing i of, for example, 0.1 to 10 mm in a rectangular cylindrical holder 21. The holding body 21 is made of a highly heat conductive material such as aluminum, and is configured to cover the outer peripheral surface of the space i between the liquid crystal panel 400 and the incident side polarizing plate 260.

  The electro-optic unit 20 configured in this way is excellent in light transmission and heat dissipation, and can prevent dust from adhering to the surface of the liquid crystal panel to enlarge the display. Further, even when dust or the like adheres to the surface of the polarizing plate 260, it is difficult to focus because the dust is away from the display surface of the liquid crystal panel 400, and it is possible to prevent the quality of the projected image from being impaired. In this embodiment, the case of the electro-optic unit 20 that holds the incident-side polarizing plate 260 oppositely on one side (light incident side) of the liquid crystal panel 400 has been described, but both surfaces (light incident side and light emitting side) of the liquid crystal panel 400 are described. The structure which arrange | positions a polarizing plate may be sufficient.

(Modification 4)
The translucent ceramic having an optically anisotropic (isotropic) crystal structure is not limited to a polycrystal (sintered body) and may be formed of a single crystal. For example, the polarizing plate holding plate can be formed of single crystal YAG or single crystal spinel. In this case, it is not necessary to consider the direction of the polarization axis of the polarizer when the holding plate is bonded to the polarizer as long as the holding plate is made of a single crystal translucent ceramic and has an optically anisotropic crystal structure. .

(Modification 5)
In the embodiment, the temperature rise of the polarizing plate is reduced by sticking the polarizer PO to the surface of the holding plate MB made of translucent ceramics. In addition, the polarizing plate is forcibly cooled. A cooling device such as a cooling fan may be used. By using the cooling device, the temperature rise of the polarizing plate can be considerably reduced.

(Modification 6)
In the embodiment, the polarizing plate holding plate MB may be provided with an antireflection film for preventing reflection of light at the interface on one surface (light incident surface) or both surfaces. By applying the antireflection film, the light transmittance of the holding plate MB can be further increased.

(Modification 7)
In the embodiment, the case of a transmissive liquid crystal projector using a so-called transmissive liquid crystal panel in which light is transmitted through a liquid crystal panel as a light modulation unit has been described. However, a so-called reflective liquid crystal in which the liquid crystal panel reflects light. A reflective liquid crystal projector using a panel may be used. When the present invention is applied to a reflective liquid crystal projector, substantially the same effect as that of a transmissive liquid crystal projector can be obtained.

(Modification 8)
In the above embodiment, a sintered body of YAG, which is a kind of synthetic garnet (equal axis system), is used as the holding plate of the polarizing plate. ) A sintered body of Y ₃ (AlGa) ₂ (AlGaO ₄ ) ₃ can also be employed.

(Modification 9)
The translucent ceramic sintered body having an isotropic (equal axis) crystal structure used as a holding plate is not limited to being colorless and transparent. For example, it may be colored and transparent. In this case, it is impossible to use a substrate common to all three colors of RGB as the holding plate, but if the transmittance in the wavelength band of the visible light wavelength band (one color of RGB) is sufficiently high. In addition, it can be used as the holding plate in a polarizing plate dedicated to the color.

FIG. 3 is an explanatory diagram showing a liquid crystal projector to which the present invention is applied. (A) is a schematic plan view of a polarizing plate, (b) is a schematic sectional drawing of a polarizing plate. FIG. 3 is a schematic sectional view of an electro-optic unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal projector, 11 ... Light source lamp unit, 12 ... Projection lens unit as projection optical system, 13 ... Screen, 20 ... Optical unit, 21 ... Holding body, 100 ... Illumination optical system, 200 ... Color light separation optical system, 260R , 260G, 260B... Entrance side polarizing plate as a polarizing plate, 270R, 270G, 270B... Exit side polarizing plate, 300... Light modulation system, 400. Panel, 500 ... Prism, MB ... Holding plate constituting polarizing plate, PO ... Polarizing body constituting polarizing plate.

Claims (6)

  A polarizing plate characterized in that a polarizer is bonded to the surface of a holding plate made of a substrate formed of a translucent ceramic having an isotropic crystal structure. The polarizing plate according to claim 1,
A polarizing plate, wherein the translucent ceramic is made of a polycrystalline sintered body. The polarizing plate according to claim 2,
The polarizing plate, wherein the polycrystalline sintered body is made of polycrystalline transparent yttrium aluminum garnet ceramics. The polarizing plate according to claim 2,
A polarizing plate, wherein the polycrystalline sintered body is made of polycrystalline transparent spinel. An electro-optical device comprising: an electro-optical device that modulates according to image information; a polarizing plate having a polarizing body bonded to the surface of a holding plate; and a holding body that holds the electro-optical device and the polarizing plate facing each other. A unit,
On at least one of the light incident surface side and the light exit surface side of the electro-optical device,
An electro-optic unit that holds the polarizing plate according to claim 1 at a distance of 0.1 to 10 mm from the electro-optic device. An illumination optical system that emits illumination light;
An electro-optical device that modulates light from the illumination optical system according to image information;
A projection optical system that projects the modulated light beam obtained by the electro-optical device, and at least one of the light incident surface side and the light exit surface side of the electro-optical device,
A liquid crystal projector comprising the polarizing plate according to claim 1 and the electro-optical device at a distance of 0.1 to 10 mm.

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