JPH04265962A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a bright projected image with a high contrast ratio by lowering the brightness of the black display of the liquid crystal light valve of a projection type liquid crystal display device. CONSTITUTION:An optical anisotropic film 133 is provided on the incident side or the exiting side of a high polymer distributed type liquid crystal display element 131 which constitutes the projection type display device. The parallelism of incident light is enhanced by the film 133 and light distribution at the time of scattering light on the exiting side for the black display is controlled, so that scattered light is absorbed and exiting light is reduced. As a result, the contrast ratio is made high.

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. The device is characterized in that an optically anisotropic film is provided in which layers that transmit light and layers that absorb light are alternately laminated.

[0006]

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

FIG. 1 is a cross-sectional view of a liquid crystal display element (100) of a projection display device according to the present invention, in which (a) shows the light scattering state when no electric field is applied, and (b) shows the state of light scattering when no electric field is applied. This shows the light transmission state when .

A liquid crystal display element (100) is arranged such that a polymer dispersed liquid crystal (101) is sandwiched between two substrates. The polymer dispersed liquid crystal (101) is made of liquid crystal and a sponge-like polymer, and when there is no electric field, the liquid crystal molecules align along the interface, so that, for example, incident light (102) is directed to the liquid crystal display element (100). When incident, the molecular arrangement of the polymer dispersed liquid crystal (101) is in a scattering state, so the scattering is divided into back scattering (103) that returns to the incident side and forward scattering (104) that passes through and scatters. The direction is divided. Further, when an electric field is applied, the liquid crystal molecules are aligned in the direction of the electric field, so that the transmitted light (105) is transmitted forward without attenuating with respect to the intensity of the incident light (102).

As shown by the arrow (106) representing the intensity vector, the divergent intensity of these transmitted lights is such that the ratio of the intensity in the electric field application state to the divergent intensity in the scattered state becomes the contrast of the liquid crystal display device. Therefore, it is desirable that the scattered light be sufficiently smaller than the transmitted light. However, the intensity vector I0 of the scattered state is generally expressed by the following equation, although it depends on the cell thickness of the liquid crystal display element and the properties of the incident light.

I0=KIcosθ
K: Reflection coefficient Figure 2 is a diagram showing a liquid crystal display element of a projection type display device of the present invention. Figure 2 (a) shows a liquid crystal display element in which an optically anisotropic film is attached to the incident side of the liquid crystal display element using an optical adhesive or the like. 2(b) is a cross-sectional view of an example of a liquid crystal display element, and FIG. 2(b) is a perspective view for explaining the structure of the optically anisotropic film in an easy-to-understand manner. FIG. 2(c) is a cross-sectional view of an embodiment of the liquid crystal display element. FIG. 2 is a cross-sectional view showing an example of a liquid crystal display element in which films are pasted together.

[0011] On the incident light side of the liquid crystal display element (100),
A liquid crystal display element (100) is made of an optically anisotropic film (120) in which light-transmitting layers and light-absorbing layers made of materials such as cellulose, acetate, and butyrate are alternately laminated. )
to form a liquid crystal light valve. (Hereafter referred to as liquid crystal light valve.) This optically anisotropic film (1
Regarding the thickness 20), it is intended to improve parallelism regarding the light distribution characteristics of incident light, and as the thickness increases, parallelism increases. Furthermore, the pitch of the superimposition of light absorption and light transmission in the optically anisotropic film can be freely selected from several μm to several mm, and the parallelism of light can be controlled.

In the embodiment shown in FIG. 2(c) in which optically anisotropic films are laminated on each of the incident side and the output side, the optically anisotropic film on the incident side limits the incident light to parallel light. The light anisotropic film on the emission side absorbs the scattered light of the liquid crystal display element (100), thereby increasing the ratio of transmitted light to scattered light, that is, the contrast. The thickness of the optically anisotropic film on the exit side is determined by the aperture angle (swallowing angle) of the projection lens.
The thickness can be selected according to the size.

FIG. 3 is a block diagram showing the structure of the projection lens and liquid crystal light valve of the projection type display device of the present invention.

[0014] The projection lens of a projection type display device using liquid crystal generally uses a telecentric lens whose chief ray is parallel to the optical axis as shown in FIG. 3(a).

In the case of this lens, the smaller the F value of the aperture ratio, the larger the aperture angle and the brighter the lens becomes. However, when a polymer dispersed liquid crystal is used for the liquid crystal display element, non-selection of images in the scattering state The contrast of the scattered light in this state decreases because the larger the aperture angle (swallowing angle) of the projection lens is, the more light is swallowed.

As shown in FIG. 3(a), the projection lens (13
The aperture angle (135) of 0) is the same as that of the liquid crystal light valve (131
) with a chief ray (132) perpendicular to
The image is formed on the pixel electrode (134) of the liquid crystal. The optical anisotropic film (133) is an optical anisotropic film that has a plurality of light transmission layers for one pixel electrode (134), and has a numerical aperture (N.A. ;Numeri
cal Aperture) is determined.

FIG. 3(b) shows an embodiment of the tilting optical system in which the projection lens (130) is shifted in parallel, and the optically anisotropic film (133) is continuously aligned with the principal ray of the projection lens. The structure is such that the angle between the light-transmitting layer and the light-absorbing layer changes. Therefore, it is possible to increase the contrast even in the tilting optical system. In this example, the optically anisotropic film was provided only on the output side, but the contrast can be further enhanced by providing an optically anisotropic film on the incident side. Furthermore, the material of the optically anisotropic film is not limited to organic resin films such as cellulose, acetate, butyrate, etc., but may also be composed of a plurality of layers of mirror-finished metal mirrors, for example.

In this embodiment, a polymer-dispersed liquid crystal was used for the liquid crystal display element. In this polymer-dispersed liquid crystal, liquid crystal exists in a discontinuous state inside a sponge-like polymer, and its basic operation is as follows. For example, Nikkei Electronics June 11, 1990
As shown on page 102 of the issue, the refractive index of the granular liquid crystal is matched to that of the sponge-like polymer. 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.

Furthermore, the polymer dispersed liquid crystal is called PNLC (Pol
ymer-Network Liquid Crys
tal). This has a structure in which a polymer network is assembled in the liquid crystal layer, where the liquid crystal exists in a continuous state and takes advantage of the irregular orientation of the liquid crystal molecules. When no voltage is applied, the orientation of liquid crystal molecules is irregular, so light is scattered.
When a voltage is applied, the orientation is uniform and light is transmitted.

FIG. 4 is a block diagram of a projection type display device according to the present invention. Basically, three liquid crystal light valves (200) are used in which an optically anisotropic film is provided on the input side or the output side of the light valve. The light from the projection light source (201) is separated into three primary colors by a color separation system (202), and each color is modulated by three liquid crystal light valves (200).
The color composition system (203) synthesizes the images in full color again.
The image is enlarged and projected by a projection lens (204) and displayed on a screen (205). Color separation system (202
) and the color synthesis system (203) each consist of two dichroic mirrors and a reflecting mirror, and the wavelength characteristics can be arbitrarily determined.

[0021] The liquid crystal light valve (200) is a TF
It should be added that this method is effective for matrix address driving methods such as those using T, MIM type active elements, and time division driving, and is also effective for address driving methods using light or heat.

[0022]

As described above, according to the present invention, in a projection display device, by providing an optically anisotropic film on the incident side or the output side of a liquid crystal display element using polymer dispersed liquid crystal, By increasing the parallelism of the incident light and accurately absorbing the light scattering of the polymer-dispersed liquid crystal without being limited by the numerical aperture of the projection lens, we have achieved the most important contrast characteristic of a liquid crystal light valve. can be increased. Furthermore, a polarizing plate is not required, and a very bright image can be displayed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of a liquid crystal display element constituting a projection display device of the present invention, in which (a) is a cross-sectional view when no electric field is applied, and (b) is a cross-sectional view when an electric field is applied. FIG.

FIG. 2 is a diagram showing an embodiment of a liquid crystal display element laminated with an optically anisotropic film constituting the projection display device of the present invention.
) is a cross-sectional view, (b) is a perspective view, and (c) is a cross-sectional view.

FIG. 3 is a configuration diagram showing the configuration of a liquid crystal light valve and a projection lens that constitute the projection display device of the present invention; (a) is a configuration diagram when the principal rays are parallel; (b) is a configuration diagram when the principal rays are parallel; It is a block diagram in the case of a tilting optical system.

FIG. 4 is a configuration diagram of a projection type display device of the present invention in full color using three liquid crystal display elements.

[Explanation of symbols]

100...Liquid crystal display element 101...Polymer dispersed liquid crystal 102...Incoming light 103...Backscatter 104...All scattering 105...Transmitted light 106...Intensity vector 120...optical anisotropic film 130...projection lens 131...LCD light bulb 132...chief ray 134...pixel electrode 135...Aperture angle 201...Projection light source 202...Color separation system 203...Color synthesis system 205...Screen

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, comprising a light transmitting layer and a light absorbing layer on an incident side or an output side of the liquid crystal display element. 1. A projection type liquid crystal display device comprising an optically anisotropic film formed by alternately laminating layers.