JP3979106B2 - LCD projector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal projector that projects an image on a liquid crystal display element, and more particularly to a technique for efficiently radiating heat with respect to a polarizing film that becomes high temperature as the image becomes brighter.
[0002]
[Prior 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 bonded to a transparent substrate with an adhesive material in order to prevent deformation when absorbing heat from the light source and generating heat. Hereinafter, a polarizing film bonded to the transparent substrate is referred to as a polarizing plate.
[0003]
Recently, as this transparent substrate, for example, as disclosed in Japanese Patent No. 3091183, sapphire has been used paying attention to the characteristic of high thermal conductivity. At this time, as described in the 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]
[Problems to be solved by the invention]
Sapphire used as a material for the transparent substrate is very expensive compared to glass or the like. The transparent substrate is required to have high planar accuracy in order not to cause distortion in the image. However, since sapphire has high hardness, workability is poor and the polishing cost is higher than that of glass or the like.
[0005]
An object of the present invention is to solve the above-described problems and provide a liquid crystal projector using a member having good workability and high thermal conductivity as a transparent substrate of the polarizing film.
[0006]
[Means for solving the problems]
As a polarizing plate, a polarizing element is bonded to a quartz substrate having a plate thickness of 0.3 mm or more and 1.0 mm or less, and its optical axis is configured to be parallel or orthogonal to incident polarized light. With this configuration, compared to the case of using a sapphire substrate, it is possible to improve the workability and reduce the cost of the substrate with the same heat dissipation effect.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0008]
1 and 2 are diagrams showing an embodiment of the present invention. FIG. 1 shows a configuration of a polarizing plate according to the present invention disposed before and after a transmissive liquid crystal display element, and FIG. 2 uses the polarizing plate. 1 shows the configuration of a transmissive liquid crystal projector. In FIG. 1 and FIG. 2, the same parts are indicated by the same reference numerals.
[0009]
The present invention is characterized in that in a liquid crystal projector using polarized light, quartz is used as a material for a holder of a polarizing element disposed on an optical path from a light source to a projection lens.
[0010]
Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 2, the light beam emitted from the light source 1 enters the first lens array 6. The first lens array 6 divides an incident light beam into a plurality of light beams by a plurality of lens cells arranged in a matrix and efficiently guides the light 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 form the shape of the lens cell of the first lens array 6 corresponding to each of the constituting lens cells, as a transmissive liquid crystal. Projecting to the display elements 20R, 20G, and 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. The projected images of the lens cells of the first lens array 6 are converted into liquid crystal display elements 20R, 20 by the condenser lens 9, condenser lenses 10R, 10G, 10B, the first relay lens 17, and the second relay lens 18, respectively. Overlay on 20G and 20B. Reference numerals 14, 15, and 16 denote reflection mirrors.
[0011]
In the process, white light emitted from the light source 1 is separated into three primary colors of red (R), green (G), and blue (B) by the dichroic mirrors 12 and 13, and the corresponding liquid crystal display elements 20R, 20R, 20G and 20B are irradiated. 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.
[0012]
Each of the liquid crystal display elements 20R, 20G, and 20B includes incident-side polarizing plates 4R, 4G, and 4B on the incident side, and outgoing-side polarizing plates 5R, 5G, and 5B on the outgoing side, and allows light in a predetermined polarization direction to pass therethrough. ing. Then, light intensity modulation is performed to change the density for each pixel by controlling the amount of light transmitted through the liquid crystal display element by a video signal driving circuit (not shown).
[0013]
The images on the liquid crystal display elements 20R, 20G, and 20B formed by the light intensity modulation are color-synthesized by the color synthesizing prism 11, and further projected onto the screen 19 by the projection lens 3 to obtain a large screen image. be able to.
[0014]
The first relay lens 17 and the second relay lens 18 indicate that the optical path length from the light source 1 to the liquid crystal display element surface of the liquid crystal display element 20B is longer than the liquid crystal display elements 20R and 20G. It is a supplement.
[0015]
In addition, the condenser lenses 10R, 10G, and 10B suppress the spread of the light beam after passing through the liquid crystal display elements 20R, 20G, and 20B, and the projection lens 3 realizes efficient projection.
[0016]
The cooling fan 26 absorbs part of the irradiation light from the light source 1 by, for example, the incident side polarizing plates 4R, 4G, 4B, the outgoing side polarizing plates 5R, 5G, 5B, the liquid crystal display elements 20R, 20G, 20B, and the like. The generated heat is blown through an air flow (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.
[0017]
The liquid crystal projector configured as described above is required to be particularly small and to obtain a bright image. Therefore, the liquid crystal display element has been miniaturized and the efficiency of the light source has been improved. It is planned. Accordingly, light concentrates on the downsized liquid crystal display element, and the temperature rises due to heat generation due to light absorption. In addition, the temperature rises due to heat generated by light absorption even in a polarizing plate of approximately the same size as the liquid crystal display elements disposed before and after 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. In particular, the heat dissipation effect is further enhanced and the temperature rise is improved in the polarizing plate.
[0018]
FIG. 1 shows in detail the incident side polarizing plate, the outgoing side polarizing plate, and the transmissive liquid crystal display element. 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 includes a polarizing film 41 and a quartz substrate 42, and the emitting side polarizing plate 5 includes a polarizing film 51 and a quartz substrate 52.
[0019]
If 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 passes through the quartz substrate 42. Then, the light enters the polarizing film 41 with the vertical direction as the transmission axis. At this time, in order to prevent the crystal axis of the crystal substrate 42 from affecting the polarization, 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 a direction orthogonal thereto. is there. When this crystal axis angle is deviated, the linearly polarized light is largely changed to elliptically polarized light, and the amount of light absorbed by the polarizing film 41 increases, resulting in a loss of light quantity and an increase in heat generation.
[0020]
FIG. 3 shows an actual measurement value of the loss light quantity with respect to the crystal axis angle deviation. In FIG. 3, the horizontal axis is the crystal axis angle deviation, and the vertical axis is the amount of light loss generated in the polarizing film. From measured values, it is known that light absorption increases by about 0.5% when the shaft angle deviates by ± 1 °, and light absorption increases by about 2% when the shaft angle deviates by ± 2 °. Is preferably within ± 2 °. When the crystal axis angle deviation exceeds ± 2 °, the amount of lost light increases rapidly. Increasing the amount of lost light causes a decrease in brightness.
[0021]
In general, in the manufacturing process of the liquid crystal projector shown in FIG. 2, in the optical system from the illumination optical system excluding the light source 1 to the projection lens 3, the brightness management is managed at about 10% with respect to a predetermined value. . Of these, the luminance varies by about 5% for dichroic mirrors and by about 7 to 8% for liquid crystal display elements, and also by several percent for other optical lenses. The total luminance fluctuation is set to be within 10%. Therefore, ± 2 ° of the crystal axis angle deviation of the quartz substrate that makes the light absorption amount about 2% can be regarded as an allowable upper limit value.
[0022]
Next, the light passing through the transmission axis of the polarizing film 41 is changed in the polarization direction according to the gradation of the video signal (not shown) by the liquid crystal display element 20, enters the polarizing film 51, and enters the polarizing film 51. The polarized light component parallel to the transmission axis of the light passes through the polarizing film 51, but the other components are absorbed by the polarizing film 51.
[0023]
Since the polarizing films 41 and 51 generate heat by absorbing polarized components other than the transmission axis, the temperature rise due to heat generation is suppressed by air-cooling the surfaces of the polarizing films 41 and 51 and the surfaces of the quartz substrates 42 and 52. The reason why high thermal conductivity is required for the quartz substrates 42 and 52 is to improve the heat radiation effect from the surfaces of the quartz substrates 42 and 52.
[0024]
Fig. 4 shows the measured temperature of a polarizing film with a liquid crystal projector when glass, quartz and sapphire are used for the transparent substrate of the polarizing film. The horizontal axis indicates the thickness of the transparent substrate, and the vertical axis indicates the polarizing film temperature. ing. The conditions for temperature measurement are as follows.
[0025]
Ambient temperature is Ta25 ° C., light source is 155 W ultra high pressure mercury lamp, transmissive liquid crystal display element is 0.7 inch, polarizing film size is 21.5 mm × 18.0 mm, transparent substrate size is 23.5 mm × 20. At 0 mm, the measurement location is the G input side polarizing plate.
[0026]
As is clear from FIG. 4, since the thermal conductivity of the substrate improves as the plate thickness decreases, the temperature of the polarizing film decreases. The thermal conductivity is 5.4 (W / mK) for quartz and 42 (W / mK) for sapphire versus 0.55 to 0.75 (W / mK) for glass. Although quartz is inferior to sapphire in terms of thermal conductivity, the temperature reduction effect (approximately 10 ° C.) on glass when used as a polarizing plate substrate has been sufficiently confirmed. The difference in temperature between using a quartz substrate and using a sapphire substrate decreases as the plate thickness decreases, and is substantially the same at 0.3 mm or less. In order to make the temperature difference between the case of using a quartz substrate and the case of using a sapphire substrate 2 ° C. or less, the plate thickness should be 1 mm or less.
[0027]
In general, it is desirable to use a polarizing film at 70 ° C. or less from the viewpoint of service life and color unevenness (luminance unevenness) due to thermal deformation. Assuming that the temperature of the polarizing film is 70 ° C. at 35 ° C. which is an allowable upper limit temperature of the ambient temperature, the temperature of the polarizing film is 60 ° C. when the ambient temperature is 25 ° C. In the measured value in FIG. 4 where the ambient temperature is 25 ° C., when the thickness of the substrate is 1.0 mm, the sapphire substrate is about 57 ° C. and the quartz substrate is about 59 ° C. Not desirable.
[0028]
When quartz is used for the transparent substrate, it can be easily processed even if the plate thickness is 0.3 mm, but 0.3 mm or more is desirable in consideration of the breaking strength of the substrate.
[0029]
Since the price of quartz is about 1/3 of the price of sapphire, the configuration according to the present invention as described in FIG. 3 is adopted, and a quartz substrate is used in comparison with a conventional sapphire substrate. There is an effect that significant cost reduction can be realized while ensuring a reduction in temperature.
[0030]
Further, since quartz is cheaper than the price of sapphire, it is possible to increase the external size of the quartz substrate. Even if the size is about twice, it is cheaper than the price of sapphire, so when it is made about twice the size of sapphire with crystal, the temperature can be lowered further than that of sapphire of the size of 1 times.
[0031]
FIG. 5 is a conceptual diagram for explaining image distortion due to planar accuracy of the transparent substrate of the polarizing plate. In FIG. 5, 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 denotes an example of a distorted image projected on the screen 19.
[0032]
When an image like the image example 24 is formed by the transmissive liquid crystal display elements 20R, 20G, and 20B, the image examples 24 of RGB usually overlap each other and a white image having the same shape as the image example 24 is formed on the screen 19. Is done. However, when the plane accuracy of the transparent substrate of the polarizing plate disposed before and after the liquid crystal display element is low, a phenomenon in which RGB three-color images do not overlap occurs due to the lens effect of the transparent substrate. For example, when only the output side polarizing plate 5G has low plane accuracy, the image formed on the screen 19 looks like the image example 25 distorted only for G, and the image does not overlap in the peripheral portion, and the white color is Coloring occurs without becoming a pixel shift. Since this lens effect is proportional to the refractive index, the above phenomenon can be reduced more than the sapphire (refractive index of about 1.78) by using crystal (refractive index of about 1.55) for the transparent substrate.
[0033]
Furthermore, when compared with Mohs hardness, the sapphire is 9, whereas the crystal is 7. The lower the Mohs hardness, the better the workability, so it is clear that quartz is easier to process than sapphire. Using sapphire makes it easier to ensure the flatness of the transparent substrate and reduces processing costs. be able to. Generally, when processing sapphire so as to satisfy the above planar accuracy, it is desirable to make the plate thickness 0.5 mm or more, but when using quartz, processing is easy even with 0.3 mm. . However, when considering the breaking strength of the transparent substrate, it is desirable that the thickness be 0.3 mm or more.
[0034]
In the above description, a three-plate type liquid crystal projector using three liquid crystal display elements shown in FIG. 2 is described as an embodiment of the liquid crystal projector. However, the present invention is not limited to this. A single-plate type liquid crystal projector using one sheet may be used.
[0035]
In the above description, it has been described that 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. It is obvious that the present invention can also be applied to two opposing transparent substrates that sandwich the liquid crystal of the element therebetween.
[0036]
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 align the polarization direction or to reduce an undesired polarization direction component. Examples of use include, for example, Japanese Patent Application Laid-Open Nos. 2001-215491 and 10-312034. In these reflection type liquid crystal projectors, it is also clear that a quartz substrate can be applied as a transparent substrate of a polarizing plate.
[0037]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a liquid crystal projector using a quartz 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 a polarizing plate can be made substantially equivalent to the case where sapphire is used for a transparent substrate, and cost reduction can be realized. In addition, the flatness of the transparent substrate can be ensured from the ease of processing of quartz, and image distortion due to flatness can be reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a polarizing plate according to the present invention.
FIG. 2 is a configuration diagram of a transmissive liquid crystal projector using a polarizing plate according to the present invention.
FIG. 3 is a measurement diagram showing a loss light amount with respect to a crystal axis angle shift.
FIG. 4 is a measurement diagram showing the polarizing film temperature when glass, quartz and sapphire are used for the transparent substrate of the polarizing film.
FIG. 5 is a conceptual diagram for explaining image distortion due to planar accuracy of a transparent substrate of a polarizing filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Light source, 20 ... Liquid crystal display element, 3 ... Projection lens, 4 ... Incident side polarizing plate, 5 ... Outgoing side polarizing plate, 6 ... 1st lens array, 7 * .. Second lens array, 8... Polarization conversion element, 9... Condensing lens, 10 .. Condenser lens, 11... Color synthesis prism, 12 ... Dichroic mirror, 13. Dichroic mirror, 14, 15, 16 ... reflective mirror, 17, 18 ... relay lens, 19 ... screen, 21 ... optical path, 24 ... on the liquid crystal display element 20 Example of normal image formed, 25 ... Example of distorted image projected on screen 19, 26 ... Cooling fan, 27 ... Channel, 41, 51 ... Polarizing film, 42, 52: A quartz substrate.

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, a color separation unit that separates white light into three colors of red, green, and blue, and a video signal of each color A liquid crystal display element having a projection unit for projecting the optical image and a liquid crystal display element that converts the optical image according to
The polarizing plate disposed on at least one of the incident side and the emission side of the liquid crystal display element includes a crystal substrate and a polarizing element, and the crystal substrate and the polarizing element are bonded to each other,
The thickness of the quartz substrate is 0.3 mm or more and 1.0 mm or less ,
The liquid crystal projector , wherein an angle formed by the optical axis of the quartz substrate and the absorption axis of the polarizing element is either 90 ± 2 ° or 0 ± 2 ° .

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