JPH04136821A - Optical writing type liquid crystal display element - Google Patents

Abstract

PURPOSE:To make projection display with a specific high resolution and high capacity by laminating a liquid crystal panel in order of a photoconductive layer, dielectric mirror and nematic/cholesteric phase transfer type liquid crystal. CONSTITUTION:The state of the NCh phase transfer type liquid crystal having positive dielectric anisotropy changes when the voltage impressed thereto decreases. The state shifts from a nematic phase H in a metastable state (nematic H') then shifts to a cholesteric phase F. The mode of the nematic/ cholesteric phase transfer type liquid crystal has hysteresis as shown in fig. in a voltage (V)-transmittance (T)(%) relation. The liquid crystal panel A of the optical writing liquid crystal display element is constituted by laminating the photoconductive layer 2, the dielectric mirror 4 and the nematic/cholesteric phase transfer type liquid crystal 6 in this order. Such three components are interposed between two sheets of substrates 10a and 10b provided with transparent conductive films 8 on one side. Oriented films 12a, 12b are further provided on the respective substrates 10a, 10b.

Description

[Detailed Description of the Invention] [4 Already Required] Regarding an optically written liquid crystal display element consisting of a liquid crystal panel, for the purpose of obtaining a high brightness and high density projected image by optical addressing, the liquid crystal panel is coated with a photoconductive layer and a dielectric mirror. , and a nematic-cholesteric phase transition type liquid crystal are stacked in this order.

[Industrial application field]

The present invention relates to an optically written liquid crystal display element, and more particularly to an optically written liquid crystal display element that enables high brightness and high density display, and an image forming method using such a liquid crystal display element.

[Prior Art and Problems to be Solved by the Invention] A method of irradiating a liquid crystal display panel on which a high-density image is formed with light from a projection light source to enlarge and display the image is to obtain a large screen of several tens of inches diagonally. This method is well known. In particular, recently, projection displays using active matrix liquid crystal panels such as TPT (Thin Film Transistor) have been sold for consumer use, and are becoming a familiar display element among the general public.

Commercially available active matrix liquid crystal panels use an electric field for writing, so the liquid crystal panel section is extremely necessary and compact. However, since a thin film transistor must be formed for each picture element, it is thought that the limit for increasing display density is about 5 lines/1 mm. Particularly in large panels of about 10 inches, increasing the density is extremely difficult due to the increase in line impedance.

Increasing the density of a display image is an essential requirement for an enlarged projection display, and in particular, in order to apply it to a high-definition television (HDTV), it is necessary to simultaneously increase the display capacity and increase the density. However, such technology is considered difficult to implement with conventional amorphous silicon TPT liquid crystal panels.

In this way, in a liquid crystal panel such as a TPT, a transistor, an electrode pattern, etc. are required for each picture element, and therefore resolution is limited. Particularly in large-area panels, impedance between electrodes increases, and even if high patterning resolution is achieved, it is extremely difficult to function as an actual liquid crystal panel.

Therefore, in order to realize high-density display, it is necessary to adopt a writing method that does not require patterning of electrodes.

As one such method, a method is known in which a liquid crystal layer and a photoconductive layer are connected in series and writing is performed using light. In this method, the writing density is determined by the optical address and the resolution of the optical image guiding layer, and it is known that a sufficient resolution of about 40 to 3 Q1ine/mm is possible. Conventionally, a projection type liquid crystal display using electric field control birefringence using optical addressing has been known, but although this increases the display density, since the liquid crystal display requires two polarizing films, it is difficult to project. The image becomes dark. Further, there was a problem in that the temperature of the liquid crystal 7N677 rose due to absorption of projected light by the polarizing film.

[Means for solving the problem, action and effects of the invention]

The present invention has been made to solve such problems, and the optically written liquid crystal display element of the present invention is an optically written liquid crystal display element consisting of a liquid crystal panel, the liquid crystal panel having a light guide layer and a dielectric mirror. , and a nematic-cholesteric phase transition liquid crystal are stacked in this order.

Furthermore, the image display method of the present invention is characterized in that the optically written liquid crystal display element, which has been optically written on, is irradiated with light from the liquid crystal layer side to enlarge and project the image onto a screen.

In other words, the present inventors have conducted intensive research to enable bright projection display that does not require a polarizing film while taking advantage of high-density display using optical addressing.As a result, the inventors have developed a nematic-cholesteric phase liquid crystal display mode. The present invention was completed based on the knowledge that by employing a transition mode (N-Ch PTM), the above problems could be solved and a bright and easy-to-see high-density image display could be obtained.

This will be further explained below.

FIG. 1 is a diagram showing the display principle of N-Ch PTM.

That is, an NCh phase transition type liquid crystal having positive dielectric anisotropy changes its state as the applied voltage increases. That is, it transitions from a cloudy state (cholesteric phase F) to a transparent state (nematic phase H) (at a voltage of 2 Vd or more).

When the voltage is reduced, the liquid crystal transitions from the nematic phase H to a metastable state (nematic phase H') and then to the cholesteric phase F.

As described above, the mode of the nematic-cholesteric phase transition type liquid crystal has hysteresis in the relationship between voltage (V) and transmittance (T) (%) as shown in FIG.

By utilizing such a hysteresis phenomenon, a cloudy state and a transparent state can be arbitrarily selected.

Therefore, as will be described later, projection type liquid crystal display using optical addressing becomes possible.

A second example of the structure of the optically written liquid crystal display element of the present invention using such a nematic-cholesteric phase transition type liquid crystal is shown below.
As shown in the figure.

That is, the liquid crystal panel A of the optically written liquid crystal display element of the present invention is constructed by laminating a photoconductive layer 2, a dielectric mirror 4, and a nematic-cholesteric phase change type liquid crystal 6 in this order. Two substrates 10a are provided with a transparent conductive film 8 on one side of these three components.

10b. Note that each board 10. , 10□ further includes an alignment film 12. ．． 12. is provided.

The light guiding layer 2 constituting such a liquid crystal display element of the present invention
is typically made of amorphous silicon, but other materials such as CdS can also be used.

Further, the dielectric mirror 4 can be formed by laminating thin films of 5iO7 and TlO2, for example, but it can also be formed only from a thin film of 5102. Furthermore, examples of the nematic-cholesteric phase transition liquid crystal include phenylcyclohexane-based or tolan-based liquid crystal.

The principle of optical writing using such a liquid crystal display element will be explained below with reference to FIG.

(a) in FIGS. 3(a) to 3(d) schematically shows a liquid crystal panel, and this liquid crystal panel 10 consists of a light guide layer 12 and a liquid crystal layer 14. In addition, (b) in FIGS. 2(a) to d) shows the transmittance T(
%) and applied voltage (V).

First, vO is applied as a bias voltage to the liquid crystal display element. At this time, vO is set so that a voltage of Vd (as shown in FIG. 3(a)) is applied to the liquid crystal layer 14.

In this state, the crystal panel 10 is in a light scattering state, so
The projected image becomes dark (black). (FIG. 3(a)) Next, when writing light is irradiated from the photoconductive layer 12 side (FIG. 3(b))
(See (a)), the resistance of the irradiated portion on the light guide layer 12 side decreases, and the voltage applied to the liquid crystal layer increases to 2Vd. Due to this increase in applied voltage, the liquid crystal becomes transparent (the first
(H state in the figure) (FIG. 3(b)). Even after the light is removed, Vd continues to be applied to the liquid crystal layer, so the transparent state (H' state in Figure 1) is maintained (Figure 3 (C)). )). On the other hand, since Vd continues to be applied to the portions that are not irradiated with light, they remain in a light scattering state (FIG. 3(d)).

Writing is possible in the above manner. When erasing the entire screen at once, either set vO to a higher voltage so that a voltage of 2V[j is applied to the liquid crystal layer, or irradiate the entire photoconductive layer with light while keeping Vo applied. do it.

The present invention will be further explained below with reference to Examples.

〔Example〕

One substrate was prepared by forming a transparent conductive film (ITO) of 600A on a non-alkali glass substrate with a size of 5 am x 6 cm XL, 0 + n + n by high frequency excited ion blating method. On the other substrate, a phototransfer layer was formed by laminating about 1 #l of amorphous silicon on ITO, and then 810□ and TlO2 were alternately stacked at about 1800 A.
A dielectric mirror was formed by stacking layers. This board and the IT
Polyvinyl alcohol was applied to both substrates to which only O was applied by using a spin coater at about 60 OA, and then heated at 140° C. for 1 hour to form an alignment film. Using these substrates, a cell was fabricated using silicon balls with a grain size of 8.0 as spacers, and a nematic-cholesteric phase transition liquid crystal with a pitch of 1.1 in the helical group containing phenylcyclohexane and tolan as main components was fabricated. It was sealed and used as a liquid crystal panel to create an optical writing liquid crystal display element.

When this liquid crystal panel was applied with 40V as vO shown in Fig. 3 and irradiated with a 3mWm power output He-Ne laser beam (pot diameter l mmφ) from the leading conductor layer side, the liquid crystal layer changed from scattering to transparent. It was confirmed. Furthermore, the liquid crystal layer remained transparent even after the laser light was removed. On the other hand, when the voltage VO was increased from 40 V to 90 V after removing the laser beam, the entire liquid crystal layer could be made transparent.

The time required for the optical state change of these liquid crystal layers is shown in Table 1 below.
The following margin applied voltage Vo (V) Table 1 Response time scattering - Transparent (ms) 1) Transparent → Scattering 30 10, 2 35 6, 8 40 5, 2 Note 1 in Table 1 above indicates the change in transmittance 10 Note 2 is the time required for the change in transmittance to change from 90% to 10%.

Regarding the data for "scattering → transparent" in the table above, the response time of the liquid crystal is approximately 10 m when the applied voltage Vo is 30 V.
5 and the video rate when displaying normal video; 33
．． Since it is faster than 3 ms (30 seconds), this is the time that allows video display. Also, regarding the data of "transparent → scattering", when Vo = 30V, it is 3.0 ms, and the rising time is 3.0 ms.
Both the falling edge and the response time (ms) that enable video display are 2).

An example of enlarged projection display using the liquid crystal display element produced in this manner will be explained based on FIG. 4.

Liquid crystal display element 2 using CRT or laser light as a light source in advance
Optical writing is performed from the light guide layer side of No. 4. Light from the light source 20 is irradiated onto the optically written liquid crystal display element 24 from the liquid crystal layer side, and the reflected light is focused by the condensing lens system 26, and the slit 2
8 and then passes through a projection lens system 30 and is enlarged and projected onto a screen 32.

Projection display was performed as described above, and the contrast ratio was measured. As a result, a contrast ratio of 95:1 and a maximum screen brightness of 480 fL were obtained under the conditions of a screen gain of 5 and a light source of metal halide of 250 W.

These values are approximately 15 times higher than those of conventional liquid crystal projectors that require polarizing films. As described above, it can be seen that when the display element of the present invention is used, extremely bright projection display is possible.

In addition, as a result of condensing the He-Ne laser beam used as writing light and irradiating it onto the liquid crystal panel with a spot diameter of 50,1/In or less, the resolution on the liquid crystal panel was 2.
Q] I confirmed that ine/mm is possible. Furthermore,
Higher resolution can be obtained by further narrowing down the laser beam diameter.

Next, display performance was confirmed using a green cathode ray tube (CRT) instead of a laser beam as the writing light. The configuration of the system is shown in FIG.
Optical writing is performed using RT. In this case as well, a projected image almost equivalent to laser writing was obtained. Especially C
In the case of R and T writing, video rate writing is possible, so projection television display is possible.

Note that, unlike the above method, optical writing is performed by scanning a laser beam from the light guide layer side (back side) of the liquid crystal display element 24, or while performing optical writing using a CRT as a light source.
At the same time, it is also possible to project the light from the light source 20 from the liquid crystal layer side (front surface) of the display element to display the projected image on the screen 32 in the same manner as described above.

〔Effect of the invention〕

As explained above, the optically written liquid crystal display element comprising the liquid crystal panel of the present invention is configured such that the liquid crystal panel is laminated in this order: a leading transfer layer, a dielectric mirror, and a nematic-cholesteric phase transition type liquid crystal. Therefore, 2
A high-resolution, large-capacity projection display of 0.011ne/mm or more can be realized with a brightness more than 10 times that of conventional liquid crystal projection displays, and
This has the effect of enabling easy-to-read, high-density display.

Further, by using a CRT as a writing light source, video rate projection display is possible, and a bright television display can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the display principle of the nematic-cholesteric phase transition mode, FIG. 2 is a block diagram of the optically written liquid crystal display element of the present invention, and FIG. 3 is a diagram showing the optically written state and V- FIG. 4 is a diagram showing the relationship with the T relationship diagram. FIG. 4 is a configuration diagram of a projection optical system using the optical writing liquid crystal display element of the present invention. 2... Light guide image layer, 4... Dielectric mirror 6... Nematic cholesteric crystal, A... Liquid crystal panel. Tsuku phase change liquid

Claims (1)

[Scope of Claims] 1. An optically written liquid crystal display element consisting of a liquid crystal panel, where the liquid crystal panel has a structure in which a photoconductive layer, a dielectric mirror, and a nematic-cholesteric phase transition liquid crystal are laminated in this order. An optical writing liquid crystal display element characterized by: 2. An image display method, comprising irradiating the optically written liquid crystal display element according to claim 1 with light from the liquid crystal layer side to enlarge and project an image onto a screen. 3. The image display method according to claim 2, wherein the light source for optical writing is a CRT (cathode ray tube) or a laser beam.