JPH04355427A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To prevent thermal deterioration of a polarizing plate to be used for a liquid crystal projector. CONSTITUTION:An output light beam from a light source 10 is separated by a dichroic mirror to green G, blue B, and red R. Each light beam of green G, blue B, and red R gets into a dye-based polarizing plate 22G, 22B, 22R through a capacitor lens 20, so a beam of polerized light in a predetermined direction is radiated to a liquid crystal panel 24G, 24B, 24R. The light beam passing through the liquid crystal panel 24G, 24B, 24R becomes a visible information by an iodine-based polarizing plate 26G, 26B, 26R. Because the dye-based polarizing plate is used for the polarizing plate closer to the light source 10, deterioration of the polarizing plate by the heat-radiation and high-output light of the light source can be prevented. In addition, becuase the iodine-based polarizing plate is used for the other polarizing plate, total optical performance is not deteriorated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector for projecting image information from a liquid crystal panel onto a large screen.

0002

2. Description of the Related Art A conventional liquid crystal projector will be explained with reference to FIG. The illustrated liquid crystal projector with a single-plate optical system includes a light source (60), a reflector (62), and a first polarizing plate (6
4), a liquid crystal panel (66), a second polarizing plate (68), and a projection lens (70). Metal halide lamps are often used as the light source (60) in terms of color temperature and longevity. This metal halide lamp obtains various light emitting characteristics by adding metal vapor in the form of a metal halide in the discharge arc of mercury vapor, and can emit light close to natural light.

[0003] First and second polarizing plates (64) (68)
One is an iodine-based polarizing plate that has a polarizing function by dyeing a PVA film with an iodine solution, stretching it in a certain direction, and arranging the PVA molecules and polyiodine in the stretching direction, and the other is an iodine-based polarizing plate that has a polarizing function by dyeing a PVA film with an iodine solution and stretching it in a certain direction. Dye-based polarizing plates have been provided that have a polarizing function by uniaxially stretching the dye molecules and arranging the dye molecules together with the PVA molecules in the stretching direction, but generally, iodine-based polarizing plates Iodine-based polarizing plates are mainly used in liquid crystal projectors because they have superior optical performance and can provide a high contrast ratio.

[0004] This first polarizing plate (64) is a light source (60).
The light ray from the
6). The second polarizing plate (68) allows only the light beams polarized in a certain direction to pass through the liquid crystal panel (66).

[0005] When image information is input to the liquid crystal panel (66), the local orientation of the liquid crystal of the liquid crystal panel (66) changes in accordance with the image information, and the liquid crystal that is incident on the liquid crystal panel (66) changes. Change the plane of polarization of a beam of light. Therefore, the local orientation change of the liquid crystal of the liquid crystal panel (66) is obtained from the second polarizing plate (68) as visible information, and is projected onto the screen via the projection lens (70).

[0006]

[Problems to be Solved by the Invention] FIG. 3 shows the initial and 70
The parallel and orthogonal transmittance of the iodine-based polarizing plate after storage at ℃ for 200 hours is shown. As shown in the figure, the orthogonal transmittance of an iodine-based polarizing plate is at a wavelength of 600 nm due to the sublimation property of iodine molecules.
It gets bigger than that. For this reason, it is used in poor environments,
Although expensive, dye-based polarizing plates are used as polarizing plates for automotive LCD devices that require reliability, and low-cost polarizing plates are used for LCD projectors that require high resolution and brightness. Iodine-based polarizing plates, which have good initial optical properties, are mainly used.

However, as the screens of liquid crystal projectors become larger and brighter, the deterioration of the polarizing plates of liquid crystal projectors due to heat generation has become an important issue. In addition, the tendency for optical properties to deteriorate is particularly noticeable on the long wavelength side, and as the polarizing plate deteriorates, the color tone of the projected image changes (particularly red color disappears).

[0008]

[Means for Solving the Problems] The present invention has been made by focusing on the fact that the polarizing plate placed behind the liquid crystal panel has less heat generation and deterioration. A dye-based polarizing plate with excellent heat resistance is used for the polarizing plate placed behind the LCD panel at the expense of optical performance, and a polarizing plate placed behind the liquid crystal panel and used in a relatively good environment has good optical performance. The main feature is the use of an iodine-based polarizing plate with excellent properties.

[0009]

[Operation] Since a dye-based polarizing plate is used only for the polarizing plate placed close to the light source, the problem of heat generation is solved, and if the thermal deterioration of the iodine-based polarizing plate is taken into consideration, the overall optical performance is sufficient. performance can be achieved.

0010

Embodiment An embodiment of the present invention will be described with reference to FIG. The output light from a light source (10) using a metal halide lamp is filtered by a cold mirror reflector (12) and an ultraviolet cut filter (14) to cut infrared rays and ultraviolet rays, and then converted to green (G) by a first dichroic mirror (16). is separated and blue (B) is separated by the second dichroic mirror (18).
is separated into three primary colors.

Green (G), blue (B), and red (R) light rays are incident on dye-based polarizing plates (22G), (22B), and (22R), respectively, via a condenser lens (20). , a liquid crystal panel (24
G), (24B), and (24R). The liquid crystal panels (24G), (24B), and (24R) are driven by green (G), blue (B), and red (R) color signals, and change the polarization direction of transmitted light according to the color signal level. Therefore, iodine-based polarizing plates (26G), (26B), (2
The amount of light transmitted through 6R) is green (G), blue (B), and red (R).
This corresponds to the signal level of each color. In this optical system, dye-based polarizing plates (22G), (22B), (22
R), LCD panel (24G), (24B), (24R)
, and iodine-based polarizing plates (26G), (26B), (2
6R) have the same function.

Next, an iodine-based polarizing plate (26G), (26
B), green (G), blue (B), red (26R) transmitted through
R) are sequentially combined by a third dichroic mirror (28) and a fourth dichroic mirror (30), and projected onto a screen (not shown) via a projection lens (32).

FIG. 2 shows polarizing plates (22G), (22B), (
22R) and polarizing plates (26G), (26B), (26R)
2 shows the parallel spectral characteristics and orthogonal spectral characteristics of a conventional example using an iodine-based polarizing plate, and the broken line shows the characteristics after 200 hours at 70° C. In addition, Figure 3 shows the initial state, 70°C, and 200°C when all dye-based polarizing plates are used.
The optical properties after time storage are shown, and Figure 4 shows the polarizing plate (22G).
, (22B) and (22R) using dye-based polarizing plates,
The optical properties are shown initially and after storage at 70° C. for 200 hours when iodine-based polarizing plates are used as polarizing plates (26G), (26B), and (26R). The horizontal axis of the figure is the wavelength (unit: n
m), and the vertical axis is the transmittance (unit: %).

As is clear from the comparison of FIGS. 2 to 4, the liquid crystal projector of the present invention whose optical characteristics are shown in FIG. is obtained. In addition, although the initial optical characteristics are inferior to those when iodine-based polarizing plates are used for all polarizing plates, considering that the orthogonal transmittance of iodine-based polarizing plates changes greatly in the wavelength region of 600 nm or more, the conventional It has better optical characteristics than a liquid crystal projector. Although the mirror sequential arrangement type liquid crystal projector has been described as an embodiment, the present invention is also applicable to a prism type liquid crystal projector.

[0015]

Effects of the Invention In the present invention, a dye-based polarizing plate is used only as a polarizing plate that is placed close to the light source (10), absorbs half of the incident light as thermal energy, and generates heat. Since an iodine-based polarizing plate with excellent optical properties is used as the polarizing plate in which heat generation is hardly a problem, the problems of optical performance, reliability, and cost can be solved at the same time. In particular, by adopting the three-color separation method, the amount of light incident on the iodine-based polarizing plates (26G), (26B), and (26R) is reduced, so that the problem of thermal deterioration becomes slight.

[0016]

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an optical characteristic diagram of a conventional liquid crystal projector using an iodine-based polarizing plate.

FIG. 3 is an optical characteristic diagram of a liquid crystal projector using a dye-based polarizing plate.

FIG. 4 is an optical characteristic diagram of an example of the present invention.

FIG. 5 is a block diagram of a conventional liquid crystal projector.

[Explanation of symbols]

10 Light source 12 Cold mirror reflector 14 Ultraviolet cut filter 16 Dichlock mirror 18 Dichlock mirror 20 Condenser lens 22G dye-based polarizing plate 24G LCD panel 26G iodine polarizing plate 28 Dichlock mirror 30 Dichlock mirror 32 Projection lens

Claims (2)

[Claims] 1. A light source, a dye-based polarizing plate placed near the light source and transmitting only light rays polarized in a certain direction, a liquid crystal panel into which the light rays transmitted by the polarizing plate are incident, and the liquid crystal panel. A liquid crystal projector consists of an iodine-based polarizing plate placed behind the LCD panel that converts the partial rotation of the polarization direction of the liquid crystal panel into grayscale image information, and a projection lens. 2. The liquid crystal projector according to claim 1, wherein the light beam from the light source is separated into three primary colors.