JP2940147B2 - Projection type liquid crystal display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type liquid crystal display device that projects a display image of a liquid crystal light valve on a screen.

[Conventional technology]

As disclosed in Japanese Patent Application Laid-Open No. 61-99118, a conventional projection-type liquid crystal display device separates white light from a light source into three primary colors of red, green, and blue using a color separation dichroic mirror,
Each of the separated light beams illuminates three transmission-type liquid crystal light valves, and the light beams transmitted through the liquid crystal light valves are combined into one light beam by a color combining dichroic prism, and then the liquid crystal light valve is projected using a projection lens. Was enlarged and projected on the screen.

[Problems to be Solved by the Invention] However, in the conventional projection type liquid crystal display device, it is difficult to completely combine the respective light beams due to the characteristics of the color combining dichroic prism. FIG. 3 is a diagram illustrating spectral characteristics of a color combining dichroic prism. The color synthesizing dichroic prism is provided with a dichroic film of a red reflecting mirror (P) 20 and a blue reflecting mirror (P) 21. However, the wavelength region of a portion inclined by spectral characteristics, that is, the red reflecting mirror (P) ) A wavelength range of 580-620nm at 20,
The light in the wavelength region of 470 to 510 nm in the blue reflection mirror (P) 21 has both transmission and reflection development.

FIG. 4 is a plan view of a color combining optical system of a conventional projection type liquid crystal display device. Here, the projected light of each of the three primary colors (red projected light)
37R, green projected light 37G, blue projected light 37B), among which green projected light 37G
The problem will be described using an example. The green projection light 37G is incident on the green liquid crystal light valve 32G, is linearly polarized by the polarizer 35G, is modulated by the liquid crystal in accordance with the image signal, and is intensity-modulated by the analyzer 36G. Becomes The modulated green projection light 37G enters the dichroic prism 31, passes through the red reflection mirror 33, and the blue reflection mirror 34,
The light is projected on the screen by the projection lens 30. As described above, the red reflection mirror 33 and the blue reflection mirror 34 not only transmit light but also reflect light in the wavelength region where the spectral characteristics are inclined due to spectral characteristics. Therefore, the reflected light 38G, 39G
Enter the blue liquid crystal light valve 32B and the red liquid crystal light valve 32R, respectively. Reflected light 38G, 39G is analyzer 36B,
The light is reflected on the surface of the 36R, the inside of the liquid crystal light valves 32B, 32R, and the like, and a part of the light is projected as flare light on the screen. The reflected light 38G and 39G are analyzers.
36B, 36R, polarizer 35B, 35R, and liquid crystal light valve 32
This also causes heat generation due to light absorption inside the B and 32R and causes deterioration of the element. In addition, the liquid crystal light valve 32
In the case of an active matrix type in which B, 32G, and 32R are driven by thin film transistors, the characteristics are degraded due to a rise in temperature or an increase in leakage current of the transistor due to light irradiation, and a problem occurs in that a good projected image cannot be obtained.

Although the green projection light 37G has been described as an example, the same applies to the blue projection light 37B and the red projection light 37R, and the projection light not synthesized by the dichroic prism 31 has the other liquid crystal light valves 32R, 32G, and 32B opposed thereto. And causes deterioration or deterioration of the characteristics of the element, which causes deterioration of the image quality of the projected image.

SUMMARY OF THE INVENTION An object of the present invention is to provide a projection type liquid crystal display device capable of reducing light that is not combined by a tiechroic prism, preventing deterioration in characteristics and deterioration of elements such as a liquid crystal light valve, and obtaining a good projection image. It is in.

[Means for solving the problem]

The present invention provides a light source, a color separation dichroic prism that separates white light into three primary colors of red, green, and blue; three liquid crystal light valves that intensity-modulate transmitted light corresponding to the three primary colors; In a projection type liquid crystal display device comprising a color synthesizing dichroic prism to be synthesized and a projection lens for projecting an image formed on the liquid crystal light valve onto a screen, an optical path between the color separating dichroic prism and the liquid crystal light valve. A dichroic mirror whose wavelength selection range is narrower than the wavelength selection range of the spectral characteristics of the color separation dichroic prism and the color combining dichroic prism.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a projection type liquid crystal display device showing one embodiment of the present invention, and FIG. 2 is a graph showing spectral characteristics of a dichroic prism and a Leroyic mirror used in this embodiment.

This projection type liquid crystal display device comprises a light source 1 and a reflector 2
And a lamp house 3 for storing them, a cold mirror 4, a color separation dichroic prism 5, a dichroic mirror 6R, 6G, 6B, 7R, 7G, 7B, a liquid crystal light valve 8R, 8G, 8B, and a color synthesis. Dichroic prism 9
And a projection lens 10.

In the above configuration, the light source 1 uses a high-intensity white light source such as a xenon lamp, a metal halide lamp, or a halogen lamp, and the projection light 11 is converted into a parallel light beam by a reflector 2 of a cuboid mirror provided with a cold mirror. Have been.
The lamp house 3 prevents light from leaking to the outside and has a cooling means such as air cooling (not shown). The cold mirror 4 reflects only visible light by the dielectric multilayer film,
By transmitting infrared light that causes heat, the temperature of other optical components is prevented from rising.

The color separating dichroic prism 5 and the color synthesizing dichroic prism 9 are respectively formed by joining four right-angle prisms, and two orthogonal joining surfaces thereof are respectively provided with a red reflecting mirror (P) 20 shown in FIG. Mirror (P)
A dichroic film made of a dielectric multilayer film having spectral characteristics of 21 is provided to separate white light into three light fluxes of red, green and blue (color separation dichroic prism 5), or vice versa. , Blue light into one white light beam (color combining dichroic prism 9).

Dichroic mirrors 6R, 6G, 6B and 7R, 7G, 7B
Are red reflection mirrors (M) 22, green reflection mirrors (M) 23, and blue reflection mirrors (M) shown in FIG.
A dichroic film made of a dielectric multilayer film having 24 spectral characteristics is provided, and its wavelength selection width is set to be narrower than the wavelength selection width of the color separation dichroic prism 5 and the color synthesis dichroic prism 9. The liquid crystal light valves 8R, 8G, 8B are twisted nematic (TN) type liquid crystal display elements, which are not explicitly shown in the drawing.
The intensity of the projection light is modulated according to signal processing and an image signal from a liquid crystal drive circuit. Here, in particular, an active matrix type in which thin film transistors are arranged for each pixel to drive liquid crystal is used, and a high-quality image can be formed. The projection light 16 synthesized by the color synthesizing dichroic prism 9 is incident on the projection lens 10, and as a result, the display image formed on each of the liquid crystal light valves 8R, 8G, 8B is projected as a full color image on the screen. .

In the optical path between the color separation dichroic prism 5 and each liquid crystal light valve 8R, 8G, 8B, a dichroic mirror 6R,
The effect of arranging 6G, 6B and 7R, 7G, 7B is as follows.

When the white light of the projection light 11 from the light source 1 is separated by the color separation dichroic prism 5 into three light beams 12R, 12G and 12B of red, green and blue, as described above, the red reflection shown in FIG. The light in the wavelength region inclined by the spectral characteristics of the mirror (P) 20 and the blue reflection mirror (P) 21 is not completely separated and is included in a plurality of light fluxes. When the light in this wavelength region directly enters the color synthesizing dichroic prism 9, a part of the light enters the liquid crystal light valves 8R, 8G, and 8B from the direction opposite to the direction of the projection light without being synthesized. Causes deterioration. Here, the color separation dichroic prism 5
When the dichroic mirrors 6R, 6G, 6B and 7R, 7G, 7B are arranged in the optical path between the liquid crystal light valves 8R, 8G, 8B and
As shown in the spectral characteristics of FIG. 2, the wavelength selection width of each dichroic mirror 6R, 6G, 6B and 7R, 7G, 7B is larger than the wavelength selection width of the color separation dichroic prism 5 and the color synthesis dichroic prism 9. Because it is set narrow,
Light in the wavelength region inclined by the spectral characteristics of the red reflection mirror (P) 20 and the blue reflection mirror (P) 21 is a dichroic mirror
6R, 6G, 6B, and 7R, 7G, 7B are transmitted, and unnecessary light 13R, 13
G, 13B and 14R, 14G, 14B are excluded outside the optical system. Therefore, each liquid crystal light valve 8R, 8G, 8B, and each projection light incident on the color synthesizing dichroic prism 9
15R, 15G, and 15B are sufficiently narrow band, and in the process of being synthesized by the color synthesis dichroic prism 9,
The amount of light incident on the liquid crystal light valves 8R, 8G, 8B from the opposite direction without being synthesized by the color synthesizing dichroic prism 9 is sufficiently reduced. As a result, the characteristics of the element such as the liquid crystal light valve are not deteriorated or deteriorated, so that a good projected image can be obtained.

In the above description, dichroic mirrors 6R, 7R, 6G, 7G, 6B, 7B
May be either aluminum reflecting mirrors. The liquid crystal light valves 8R, 8G, and 8B may be of a driving method such as a simple matrix type, and the same effect can be obtained when not only a TN type liquid crystal but also a liquid crystal of another operation mode such as a ferroelectric liquid crystal is used. Can be

〔The invention's effect〕

As described above, according to the present invention, by reducing light that is not synthesized by the dichroic prism, the characteristics of elements such as a liquid crystal tight valve are prevented from deteriorating, and deterioration is prevented, and a projection type liquid crystal display capable of displaying a good projection image is provided. The device was obtained. In addition, by arranging the dichroic mirror in each projection optical path, the wavelength of each projection light is narrowed, and a projection image with high color saturation is obtained, and the projection image due to the incident angle dependence of the dichroic prism is obtained. Also, there is an effect that the color unevenness can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view of a projection type liquid crystal display device showing one embodiment of the present invention, FIG. 2 is a graph showing spectral characteristics of a dichroic prism and a dichroic mirror used in this embodiment, and FIG. 3 is a color combining dichroic. FIG. 4 is a plan view showing a color combining optical system of a conventional projection type liquid crystal display device. 1 light source 5 color separation dichroic prism 6
R, 6G, 6B, 7R, 7G, 7B …… Dichroic mirror, 8R, 8G, 8B
…… a liquid crystal light valve, 9… a color synthesis dichroic prism, 10 …… a projection lens.

Claims (1)

(57) [Claims] 1. A color separating dichroic prism for separating incident white light into three primary colors and a color combining dichroic prism for combining the incident three primary colors, said color separating dichroic prism and said color combining dichroic prism. A projection-type liquid crystal projection device that reflects light separated by each color between the liquid crystal light valves and transmits the light that is color-synthesized by a color-synthesizing dichroic prism onto a screen through a projection lens. The light of each color separation between the separation dichroic prism and the liquid crystal light valve is reflected by at least two dichroic mirrors and then incident on the liquid crystal light valve. Than the wavelength selection width with the color synthesis dichroic prism Projection-type liquid crystal display device comprising that no.