JPH04251222A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain bright projected images having a high contrast ratio by lowering the brightness of a black display without changing the brightness of the white display of the projection type liquid crystal display device. CONSTITUTION:Light absorbers 7 are provided in the liquid crystal display element 100 of a high-polymer dispersion type constituting the projection type display device. The display is a white display and incident light is emitted as it is when an electric field is impressed thereto. The display is a black display at the time of non-electric fields. The light repeats scattering in the liquid crystal 9 and the much scattered light is absorbed by the light absorbers 7, by which the exit light is decreased. The contrast ratio is thereby increased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type liquid crystal display device using a liquid crystal display element that performs display by transmitting and scattering light.

0002

[Prior Art] Conventionally, polymer dispersed liquid crystal (PDLC) has been used as a liquid crystal display device that uses light transmission and scattering.
er-Dispersed Liquid Crys
Light control glass using tal) has been put into practical use. As shown in Figure 1, this is a special film that holds low-molecular liquid crystals within a spongy three-dimensional polymer network structure. Polymer-dispersed liquid crystals change from a light-scattering state to a light-transmitting state as voltage is applied, and this property is used as a display device. Projection type liquid crystal display devices generally display black in a light scattering state and white in a light transmitting state, and because they do not require a polarizing plate, they are expected to be a means of increasing brightness.

0003

However, when the above-mentioned prior art is used in a projection type display device, the contrast ratio becomes low because the scattered light of black display is swallowed by the projection lens. Further, in order to increase the contrast ratio, the F value of the projection lens can be increased and the swallowing angle can be decreased, but the image becomes dark.

SUMMARY OF THE INVENTION The present invention aims to solve these problems, and its object is to provide a projection type liquid crystal display device that has a high contrast ratio and is capable of bright display.

[0005]

[Means for Solving the Problems] A projection type liquid crystal display device of the present invention is a projection type liquid crystal display device using a liquid crystal display element that performs display by transmitting or scattering light, in which the liquid crystal display element has an area other than an effective display area. It is characterized by being made of a thick light absorber.

[0006]

[Embodiment] (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a liquid crystal display element 100 of a projection type display device according to the present invention. The liquid crystal display element 100 includes an active matrix type TFT as a switching element.
(Thin Film Transistor) is used. On the TFT substrate 1, the TFT
2, a wiring 3 consisting of a signal line and a scanning line, and a pixel electrode 4 are formed, and a counter electrode 6 and a light absorber 7 are formed on a counter substrate 5. Polymer dispersed liquid crystal 8 is attached to these two substrates.
are placed between them. The polymer dispersed liquid crystal 8 consists of a liquid crystal 9 and a sponge-like polymer 10, and in this example, nematic liquid crystal and PMMA (polymethyl methacrylate) were used.

FIG. 2 is a perspective view of the liquid crystal element 100, in which the light absorber 7 is arranged to cover the signal line 11, the scanning line 12, and the TFT 2, and allows light to pass through only the pixel electrode 4 portion of the effective display area. This is because normally when the TFT 2 is irradiated with light, leakage occurs and the performance deteriorates, so light is made to enter from the opposing substrate 5 side to prevent light from entering the TFT 2. Further, since an electric field is applied to the wiring 3 and unnecessary display is performed, the wiring 3 is similarly shielded from light.

Light incident on the liquid crystal element 100 from the side of the counter substrate 5 is transmitted between the pixel electrode 4 and the counter electrode 6 in the voltage applied portion, and is scattered in the portion to which no voltage is applied. The light is also absorbed in the light absorber 7. Here, the light absorber 7
used PrMnO3. The light absorber 7 is a liquid crystal element 10
It is sufficient to absorb the scattered light inside the 0. Conversely, absorbing incident light causes problems such as heat generation, so it is better to laminate it on a reflective metal such as chromium. Further, any material may be used as long as it absorbs light. For example, the filter may be made black by using the same manufacturing method as the color filter of a full-color liquid crystal display device. .

In this polymer dispersed liquid crystal 8, the liquid crystal 9 exists in a discontinuous state inside a sponge-like polymer 10, and its basic operation is shown, for example, in Nikkei Electronics June 11, 1990 issue, page 102. The refractive index of the granular liquid crystal 9 is matched to that of the sponge-like polymer 10 as shown in FIG. Then, when no voltage is applied, the liquid crystal molecules are aligned along the interface and the refractive index in the direction of light incidence is different, so the light is repeatedly reflected and scattered. Furthermore, when a voltage is applied, the liquid crystal molecules are aligned in the direction of light incidence and the refractive index becomes equal, allowing light to pass through.

Further, the polymer dispersed liquid crystal 8 is a PNLC (Po
lymer-Network Liquid Cry
stal). This has a structure in which a polymer network is assembled in the liquid crystal layer, in which the liquid crystal 9 exists in a continuous state and takes advantage of the irregular orientation of liquid crystal molecules. When no voltage is applied, the alignment of liquid crystal molecules is irregular and light is scattered, while when a voltage is applied, the alignment is uniform and light is transmitted.

FIG. 3 is an enlarged view of the liquid crystal element 100 showing the concept of light scattering state. a pixel electrode 4 of a TFT substrate 1;
When no electric field is applied between the opposing electrodes 6 of the opposing substrate 5, the incident light is scattered by the granular liquid crystals 9, the scattered light is again scattered by other granular liquid crystals 9, and so on. Reach the exit side repeatedly. At this time, much of the repeatedly scattered light enters the light absorber 7 and is absorbed there. Therefore, the luminous intensity distribution on the output side of the liquid crystal element 100 becomes as shown by the broken line, which is smaller than the luminous intensity distribution shown by the dashed-dotted line when the light absorber 7 is not provided. Then, in the scattering state, the amount of absorbed light becomes smaller with respect to the swallowing angle θ determined by the F value of the projection lens 14 in FIG. 4, so the black level on the screen 15 decreases. Furthermore, in the transmission state, the white level remains unchanged, so the contrast ratio increases.

[0013] This phenomenon is advantageous for high-definition applications and higher definition, because the smaller the pixel pitch, the higher the ability of the light absorber 7 to absorb scattered light. Furthermore, since one pixel is blocked by the light absorber 7, it is highly effective in reducing crosstalk that affects other pixels.

FIG. 4 is a block diagram showing the concept of the present invention. It is composed of a projection light source 13, a liquid crystal display element 100, and a projection lens 14. Light emitted from the projection light source 13 is modulated by the liquid crystal display element 100, and is enlarged and projected onto the screen 15 by the projection lens 14. The ray diagram shows the projection lens 14.
This is to explain the swallowing angle of the liquid crystal display element 10.
Of the light emitted from a certain point of 0, only the light included in the swallowing angle determined by the F value of the projection lens 14 appears on the screen 15. In order to lower the black level and increase the contrast ratio, the scattered light shown in FIG. 3 is not displayed on the screen 15 by reducing this swallowing angle. However, the amount of light for white display also decreases, making it impossible to provide a bright display. Furthermore, although it would be better to improve the parallelism of the projection light source 13, since there is no point light source, the light cannot be efficiently collected, resulting in darkness.

FIG. 5 is a block diagram of a projection type display device according to the present invention. Although it is basically the same as FIG. 4, three liquid crystal display elements 100 are used. The light from the projection light source 13 is separated into three primary colors in the color separation system 16, and each color is modulated by three liquid crystal display elements 100, and then the light is sent to the color synthesis system 1 again.
7, the images are combined in full color, enlarged and projected by the projection lens 14, and displayed as an image on the screen 15. The color separation system 16 and the color synthesis system 17 each include two dichroic mirrors and a reflection mirror, and the wavelength characteristics can be arbitrarily determined.

It should be noted that the liquid crystal display element 100 is effective not only for driving by the TFT 2 but also for matrix address driving methods such as the MIM method and time division driving, and is also effective for address driving methods using light or heat. .

(Embodiment 2) FIG. 6 is a sectional view of a liquid crystal display element 100 of a projection type display device showing another embodiment of the present invention. The configuration is the same as in Example 1, with a liquid crystal 9 and a sponge-like polymer 10 placed between a TFT substrate 1 that includes a TFT 2, wiring 3, and a pixel electrode 4, and a counter substrate 5 that includes a counter electrode 6.
A polymer dispersed liquid crystal 8 consisting of the following is held. Here, the light absorber 7 also functions as a spacer for maintaining a uniform gap between the TFT substrate 1 and the counter substrate 5. If the thickness varies within the plane of the liquid crystal display device 100, uneven contrast ratio and uneven brightness will appear, and when a full-color projection display device as shown in FIG. 5 is configured, color unevenness will occur and the image quality will deteriorate significantly. . Therefore, this light absorber 7 has a great effect on improving image quality.

[0018] In order to perform the function of a spacer, the material is preferably a hard insulator. Generally, glass or plastic bulbs are used, and can be dyed black with pigments or dyes to absorb light.

[0019]

As described above, according to the present invention, in a projection display device, the area other than the effective display portion of the liquid crystal display element using polymer dispersed liquid crystal is constructed with a light absorber. It has the effect of absorbing scattered light and displaying images with a high contrast ratio while ensuring performance. Furthermore, since a polarizing plate is not required and there is no need to narrow down the swallowing angle of the projection lens, extremely bright images can be displayed.

Furthermore, in the case of high-definition images such as high-definition images, the pixel pitch becomes smaller and the proportion of the light absorber becomes larger compared to the effective display area, so scattered light can be absorbed more efficiently. The above-mentioned effect becomes even more remarkable.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of a liquid crystal display element constituting a projection display device of the present invention.

FIG. 2 is a perspective view showing one embodiment of a liquid crystal display element constituting the projection display device of the present invention.

FIG. 3 is a conceptual diagram showing the behavior of light passing through a liquid crystal display element constituting the projection display device of the present invention.

FIG. 4 is a configuration diagram showing the concept of a projection display device of the present invention.

FIG. 5 is a configuration diagram of a projection type display device of the present invention in full color using three liquid crystal display elements.

FIG. 6 is a sectional view showing another embodiment of a liquid crystal display element constituting the projection display device of the present invention.

[Explanation of symbols]

1...TFT substrate 2...TFT 3...Wiring 4... Pixel electrode 5... Opposite board 6...Counter electrode 7...Light absorber 8...Polymer dispersed liquid crystal 9...LCD 10... Sponge-like polymer 11...Signal line 12...Scanning line 13...Projection light source 14...Projection lens 15...Screen 16...Color separation system 17...Color synthesis system

Claims (1)

[Claims] 1. A projection type liquid crystal display device using a liquid crystal display element that performs display by transmitting or scattering light, characterized in that the liquid crystal display element is constructed of a thick light absorber except for the effective display portion. A projection type liquid crystal display device.