JPH0713122A - Liquid crystal display panel - Google Patents

Abstract

PURPOSE:To realize a liquid crystal display panel for an OHP having the high utilization efficiency of incident light and having a bright projection screen. CONSTITUTION:Droplet state liquid crystal and transparent high-molecular matrix are mixed to synthesize a high-molecular/liquid crystal composite 24. Space between a glass board 21a coated with a transparent pixel electrode 22 and a glass board 21b coated with a transparent common electrode 23 is filled with the high-molecular/liquid crystal composite 24. A liquid crystal display panel 20 thus obtained is placed on the upper surface of the Fresnel lens of a transmission type OHP. When a picture signal is inputted in the panel 20, the transmitting/shielding of the light of each pixel is controlled by impressed voltage. The projection screen becomes brighter and the utilization efficiency of the light becomes higher than in the panel using a polarizing plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel used for an overhead projector or the like.

[0002]

2. Description of the Related Art Overhead projectors (OH
In P), characters, figures, photographs, etc. created by handwriting or printing on a transparent film sheet (hereinafter referred to as OHP film) are placed on the OHP and light is projected.
In this case, it takes a lot of time to prepare the OHP film, and when the OHP is used at a conference, a lecture, etc., the replacement work becomes complicated when the number of OHP films increases.

In order to improve such inconvenience, OHP
Electronic OHP devices that do not require films have been put to practical use. The electronic OHP device uses a transmissive liquid crystal display panel instead of the OHP film to project characters, images and the like. A transmissive liquid crystal display panel used in an electronic OHP device is introduced, for example, in Shoichi Matsumoto and Yoshikazu Kakuda, "Basics and Applications of Liquid Crystals [1991 Edition] page 329".

FIG. 4 is an explanatory view showing the structure of the electronic OHP device. In this figure, the liquid crystal display panel 1 is a transmissive OHP.
It is mounted on the personal computer 2 and is connected to a control device such as the personal computer 3. The light emitted from the lamp built in the transmissive OHP 2 is condensed by the Fresnel lens 4, passes through the liquid crystal display panel 1, and then enters the imaging lens 5. This light is reflected by the projection mirror 6 and enters the screen 7. In this way, the image of the liquid crystal display panel 1 is enlarged and projected on the screen 7. The display data output from the personal computer 3 is instantly displayed on the screen 7.

Next, a conventional OHP liquid crystal display panel 1 will be described with reference to FIG. FIG. 5 is a schematic sectional view showing the structure of a conventional liquid crystal display panel. In this figure, a transparent pixel electrode 11a and a liquid crystal molecule alignment film 12b are formed on one glass substrate 10a. The other glass substrate 10
For b, the transparent common electrode 11b and the liquid crystal molecular alignment film 12b are formed in this order. And two glass substrates 10a,
The liquid crystal 13 is filled in between 10b together with the spacer. Next, the first polarizing plate 14a is attached to the upper surface of the glass substrate 10a, and the second polarizing plate 14b is attached to the lower surface of the glass substrate 10b.

In such a transmissive liquid crystal display panel 1, a nematic liquid crystal having a positive dielectric anisotropy is used as the liquid crystal 13. The nematic liquid crystal has a twisted arrangement (T) in which its molecular long axis is continuously twisted by 90 ° between the upper and lower substrates.
N).

The light emitted from the transmissive OHP2 lamp is linearly polarized by the second polarizing plate 14b. The polarization direction is 9 along the twist of the liquid crystal molecules while passing through the liquid crystal 13.
Rotate 0 ° (rotate 90 °). However, the transparent pixel electrode 11
When a voltage higher than a certain value is applied between the a and the transparent common electrode 11b, the long axes of the nematic liquid crystal molecules are rearranged in the electric field direction. Therefore, the light passing through the liquid crystal 13 is not polarized at 90 °.

In the state where the two polarizing plates 14a and 14b facing each other form a parallel polarizer, the incident light is blocked when no voltage is applied, and the incident light is transmitted when a voltage is applied. When the polarizing plates 14a and 14b form a crossed polarizer, the incident light is transmitted when no voltage is applied,
The incident light is blocked when no voltage is applied.

[0009]

In a liquid crystal display panel using such a TN type liquid crystal, it is necessary to linearly polarize incident light using a polarizing plate, and the polarizing plates 14a and 14b are indispensable. However, due to the presence of the polarizing plates 14a and 14b, the light reaching the screen 7 is reduced to about half, and the light utilization efficiency decreases. In addition, the projection screen on the screen 7 is dark, and it is difficult to use the electronic OHP device in a bright room. Further, since the polarizing plates 14a and 14b absorb much of the incident light, there is a problem that the polarizing plate 14 itself may deteriorate or the temperature of the liquid crystal display panel 1 may rise and the display quality may deteriorate.

The present invention has been made in view of the above conventional problems, and it is an object of the present invention to realize a liquid crystal display panel for OHP, which does not require a polarizing plate and can improve the utilization efficiency of incident light. To aim.

[0011]

The present invention is a liquid crystal display panel which is used as a film for an overhead projector and which converts an input image signal into an image and displays it on a screen. It is characterized by comprising a polymer / liquid crystal composite in which a molecular matrix is mixed, and a pair of transparent substrates sandwiching the polymer / liquid crystal composite on which transparent pixel electrodes and transparent common electrodes are coated respectively. It is a thing.

[0012]

According to the present invention having such characteristics, when the irradiation light is incident on the liquid crystal display panel, the molecular orientation direction of the liquid crystal becomes random in a state where no voltage is applied to the transparent pixel electrode and the transparent common electrode, Incident light is scattered at the interface with the polymer matrix. When a voltage is applied to both electrodes, the alignment direction of the liquid crystal molecules becomes the same as the electric field direction, and the incident light is transmitted without being scattered at this boundary. For this reason, the light transmittance of the liquid crystal in the bright state becomes high, and the projection screen becomes bright.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display panel according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of an essential part showing the configuration of a liquid crystal display panel 20 of this embodiment. In FIG. 1, the transparent pixel electrode 22 is provided on the lower surface of one glass substrate 21a. The transparent pixel electrode 22 is a substantially rectangular pixel electrode arranged in a matrix on the lower surface of the glass substrate 21a. The transparent common electrode 23 is provided on the upper surface of the other glass substrate 21b. The transparent common electrode 23 is a common electrode coated over the entire surface of the glass substrate 22b.

Next, the polymer / liquid crystal composite 24 is filled together with the spacer between the glass substrates 21a and 21b. The polymer / liquid crystal composite 24 is one in which droplet-shaped liquid crystals are dispersed and held in a polymer matrix as described later.

FIG. 2 is a plan view showing the structure of the liquid crystal display panel 20 of this embodiment. As shown in this figure, the glass substrate 1
0a has a plurality of scanning bus lines 25 formed in the X direction and a plurality of signal bus lines 26 formed in the Y direction.
A switching element 27 is provided at each intersection of the scanning bus lines 25 and the signal bus line 26, and the transparent pixel electrode 22 shown by the hatched portion is connected to the switching element 27.

The liquid crystal display panel 20 having the above structure
4, when an image or character signal is output from the personal computer 3 shown in FIG. 4, the scanning voltage is supplied to the scanning bus line 25 via the drive circuit built in the liquid crystal display panel 20, and the signal voltage is changed to the signal bus line. 26. By doing so, a voltage is applied to the selected transparent pixel electrode 22 and transparent common electrode 23, and incident light from the lamp passes or is blocked for each cell.

Next, the operation principle of the liquid crystal display panel 20 including the polymer / liquid crystal composite 24 will be described with reference to FIG. FIG. 3 is a schematic diagram showing the electro-optical characteristics of the polymer / liquid crystal composite 24. As shown in the figure, the polymer / liquid crystal composite 24 is composed of droplet-shaped liquid crystal 24a (hereinafter referred to as liquid crystal 24a) and a transparent polymer matrix 24b. The polymer liquid crystal composite 24 has a glass substrate 21a coated with a transparent pixel electrode 22 and a transparent common electrode 23.
It is sandwiched between the glass substrates 21b coated with. The glass substrates 21a and 21b may be transparent substrates such as PET films. The liquid crystal 24a is a nematic liquid crystal having a positive dielectric anisotropy, and the linear mark shown in FIG. 3 indicates the alignment direction of the nematic liquid crystal molecules.

As shown in FIG. 3A, when no voltage is applied to the polymer / liquid crystal composite 24, the molecular orientation of the liquid crystal 24a is random in the polymer matrix 24b. When the incident light A is emitted from one side of the liquid crystal display panel 20 in such a state, the incident light is scattered at the boundary surface due to the mismatch of the refractive indexes of the liquid crystal 24a and the polymer matrix 24b. Therefore, the incident light A is not transmitted, and the scattered light C is emitted from the polymer / liquid crystal composite 24 as shown by the dashed arrow.
Are scattered in random directions. As a result, the liquid crystal display panel 20 becomes clouded, and the pixels in this portion do not reach the screen 7 in FIG.

Next, as shown in FIG. 3B, when a voltage E is applied to the specific transparent pixel electrode 22 and the transparent common electrode 23,
Due to the positive dielectric anisotropy of the nematic liquid crystal, the liquid crystal 24
The molecules of a are oriented in the direction of the electric field. If the ordinary refractive index of the nematic liquid crystal is set to be substantially equal to the refractive index of the polymer matrix 24b in advance, the incident light A will be incident on the polymer / liquid crystal composite 2
Pass by 4 without being scattered. At this time, the selected cell of the liquid crystal display panel 20 becomes transparent, and the transmitted light B is projected as bright on the screen 7 through the imaging lens 5 and the transparent mirror 6 of FIG.

Generally, in the polymer / liquid crystal composite 24,
When the weight ratio of the liquid crystal 24a to the polymer matrix 24b becomes about 50%, the droplet-shaped liquid crystal 24a is formed.
Adhere to each other and form a continuous layer of liquid crystal. Thus, the basic function of the electro-optical characteristics of the light scattering mode is achieved by maintaining the liquid crystal 24a dispersed in the polymer matrix 24b in a droplet shape. A liquid crystal light control film using such a polymer / liquid crystal composite has been partially put into practical use. (For example, Ajinomoto Co., Inc., trade name ACT, etc.)

Various methods have been developed as a method for producing a polymer / composite having the above electro-optical characteristics. For example, (1) a method in which a liquid crystal is mixed with a water-soluble polymer such as PVA and a carrier medium to form an emulsion, and the dried carrier medium is removed and dried to microcapsulate the liquid crystal (JP-A-58-501631). ), (2) A method of using an epoxy resin as a polymer matrix (JP-A-61-502128),
(3) A method of using a UV-curable resin as a polymer matrix (JP-A-4-180019), (4) A method of coating a concentrated solution of a polymer and liquid crystal on a substrate and evaporating a solvent to form a film (electron IEICE Technical Report, Vol.89, No.42
2, pp.15-22 (1990)), etc.

When manufacturing the liquid crystal display panel 20 of this embodiment, it is not necessary to volatilize a solvent or the like on the substrate, and a polymer matrix is formed by an ultraviolet curable resin suitable for precise layer separation type control. The method of forming is preferred.

Next, a process of manufacturing the liquid crystal display panel 20 using such a method will be described. As shown in FIG. 2, a scanning glass line 25, a signal bus line 26, and a first glass substrate 21a on which transparent pixel electrodes 22 are formed;
A second glass substrate 21b having a transparent common electrode 23 is prepared as shown in FIG. These glass substrates 21a, 2
In order to synthesize the polymer / liquid crystal composite 24 during 1b, a uniform solution of liquid crystal and an optional component such as an ultraviolet curable monomer or oligomer and a polymerization initiator is prepared. Next, this solution is filled between the glass substrates 21a and 21b to form a cell. At this time, the cell gap is constantly controlled by the spacer. When it is irradiated with ultraviolet rays, the ultraviolet-curable monomer or oligomer is polymerized to form a resin matrix. At this time, the liquid crystal 24a is simultaneously deposited in the form of droplets to form the polymer / liquid crystal composite 24. The ratio of the liquid crystal 24a in the polymer / liquid crystal composite 24 is preferably 40 to 80% by weight.

In the liquid crystal display panel 20 in which the polymer / liquid crystal composite 24 is used as a liquid crystal layer as described above, it is not necessary to once convert incident light into linearly polarized light in order to control transmission or scattering of incident light. Therefore, the polarizing plate which has been conventionally required in the TN type liquid crystal cell is not required, and the light utilization efficiency is improved. When such a liquid crystal display panel 20 is used for an OHP, a bright projection screen can be realized.

[0025]

As described in detail above, according to the present invention, incident light can be scattered and transmitted based on a signal by using a polymer / liquid crystal composite in a liquid crystal layer. Therefore, the liquid crystal display panel does not need a polarizing plate, and the light utilization efficiency is improved. By using this liquid crystal display panel, a projection type overhead projector having a bright projection screen is realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a main part of a liquid crystal display panel according to an embodiment of the present invention.

FIG. 2 is a plan view showing a configuration of a liquid crystal display panel of this embodiment.

FIG. 3 is a schematic diagram showing electro-optical characteristics of a polymer / liquid crystal composite used in the liquid crystal display panel of this example.

FIG. 4 is an explanatory diagram showing a configuration of an electronic OHP device.

FIG. 5 is a cross-sectional view of essential parts showing the configuration of a conventional liquid crystal display panel used in an electronic OHP device.

[Explanation of symbols]

 2 Transmission type OHP 3 Personal computer 4 Fresnel lens 5 Imaging lens 6 Projection mirror 7 Screen 20 Liquid crystal display panel 21a, 21b Glass substrate 22 Transparent pixel electrode 23 Transparent common electrode 24 Polymer / liquid crystal composite 24a Liquid crystal 24b Polymer matrix 25 Scanning bus line 26 Signal bus line 27 Switching element A Incident light B Transmitted light C Scattered light

Claims (2)

[Claims] 1. A liquid crystal display panel, which is used as a film for an overhead projector and converts an input image signal into an image and displays the image on a screen. The liquid crystal display panel comprises a mixture of droplet-shaped liquid crystal and a transparent polymer matrix. A liquid crystal display panel, comprising: a molecule / liquid crystal composite, and a pair of transparent substrates on which a transparent pixel electrode and a transparent common electrode are respectively coated and which sandwich the polymer / liquid crystal composite. 2. The polymer / liquid crystal composite, wherein the mixing ratio of the droplet-shaped liquid crystal is 40 by weight.
The liquid crystal display panel according to claim 1, wherein the liquid crystal display panel is in the range of -80%.