JPH05303081A - Liquid crystal electrooptical device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal electrooptical device which exhibits the specified performance regardless of ambient temp. changes. CONSTITUTION:Detecting means 5, 6 for light necessary for the liquid crystal electrooptical device are separated from substrates 1 constituting a liquid crystal cell 4. The relation between these detecting means 5, 6 for light and the liquid crystal molecules within the liquid crystal cell 4 is not fixed but is arbitrarily changed according to the ambient temp. condition of the liquid crystal electrooptical device, by which the light past the liquid crystal cell 4 is detected in the finest state under the ambient temp. condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal electro-optical device which uses a ferroelectric liquid crystal, and more particularly to a liquid crystal electro-optical device which copes with a temperature change of a use environment.

[0002]

2. Description of the Related Art Recent advances in image processing technology have been remarkable, and accordingly, image forming apparatuses such as printers are required to have high density and high vividness. At the same time, for image display, high density and high vividness are beginning to be demanded. To meet this requirement, laser beam printers and LED printers have begun to be put to practical use in printers, and high-definition CRTs and high-duty matrix display devices have been put into practical use in image display.

However, each of the above-mentioned devices is expensive, the structure of the device is complicated, and it is very difficult to downsize it. Therefore, these devices, which are small in size, have a simple structure, are lightweight, and use an inexpensive liquid crystal material, are expected to be used. For example, in the case of a printer, liquid crystal is used for the shutter portion that blocks the light emitted to the photoconductor. Twisted nematic liquid crystal is used as the liquid crystal material, and generally the liquid crystal material is driven by utilizing the anisotropy of the dielectric constant of the liquid crystal material.

In this driving, an electric field externally applied to the liquid crystal material acts on the anisotropy of the dielectric constant of the molecules to align the liquid crystal molecules in the direction of the electric field or to move the liquid crystal molecules in the direction orthogonal to the direction of the electric field. Acts on liquid crystal molecules to align them. The response speed of a liquid crystal shutter using such a liquid crystal is at most about 2 to 3 msec, and when it is made to function as a high speed printer, the printing speed is slow and not suitable for practical use. Therefore, high-speed response of the liquid crystal shutter is required,
A response speed of at least several microseconds, preferably nanosecond order has been required.

On the other hand, as for display devices, there are direct-view type and projection type, and the use of liquid crystal materials is very positively made. Since a liquid crystal display device normally performs matrix display, it is required to increase the duty by increasing the number of electrodes in the row and column directions in order to achieve high density and high definition. Therefore, a high-speed response of the liquid crystal is required.
Only a response speed of about a second could be realized, and a faster response was required.

By the way, recently, a ferroelectric liquid crystal material having spontaneous polarization has been discovered and has been attracting attention. The liquid crystal material that exhibits this ferroelectricity has a spontaneous polarization portion that responds to an electric field applied from the outside, and does not respond by using dielectric anisotropy like conventional liquid crystal materials. Therefore, it was possible to realize a high-speed response with a maximum response speed of several nanoseconds. Therefore, liquid crystal electro-optical devices using such liquid crystal materials have been developed.

The liquid crystal material exhibiting the ferroelectricity usually exhibits the ferroelectricity only in the smectic C phase or the smectic H phase. This liquid crystal material takes various phase states depending on the holding temperature, and exhibits ferroelectricity at a relatively high temperature state. In addition, its temperature range is also limited, and at the beginning of the development of a liquid crystal electro-optical device using a ferroelectric liquid crystal material, the main focus is to widen this temperature range and lower the temperature at which ferroelectricity is expressed. Has been done.

Further, since the ferroelectric liquid crystal has various phase structures depending on the holding temperature,
The phase structure, that is, the orientation of liquid crystal molecules changes. Therefore, the liquid crystal molecules are in various states within the operating temperature range required for a normal liquid crystal electro-optical device, for example, between 0 ° C. and 50 ° C., and the degree of the electro-optical effect of the liquid crystal changes accordingly. Will be done.

[0009]

As described above, since the state of liquid crystal molecules changes depending on the ambient temperature condition, the state of the electro-optical effect also changes accordingly. That is, in a printer or a liquid crystal display device, this means that the ON / OFF ratio (contrast) of light, which is an important factor for performance evaluation, changes with temperature, which is a serious problem. An example of changes in the electro-optical effect due to temperature is shown in FIG. 2 and will be described.

FIG. 2 shows the value of the display contrast ratio when the ambient temperature is changed in a normal liquid crystal cell using a phenylpyrimidine ferroelectric liquid crystal.
In measuring the contrast ratio, the polarizing plate provided in the liquid crystal electro-optical device is a crossed Nicol, and the angle of the major axis of the liquid crystal molecule (extinction position) with respect to the polarizing plate when the light transmission is the minimum is the ambient temperature. It was determined at 25 ° C., fixed and measured.

The temperature range showing the ferroelectricity of the liquid crystal material used at this time is about -12 ° C. to 75 ° C. As is clear from FIG. 2, the contrast changes too much near room temperature in this temperature range. However, it can be seen that the degree of decrease in contrast corresponding to the temperature change becomes severe near the room temperature.

As described above, since the contrast changes, when actually used as a liquid crystal electro-optical device, the display state or the degree of light shielding of the optical shutter changes depending on the temperature condition of the use environment, which is practical. Was having problems. In order to solve this problem, conventional development methods have been developed to improve the liquid crystal material so that the change in electro-optical effect due to temperature change is minimized. And needed money.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a liquid crystal electro-optical device in which the change in the electro-optical effect due to the temperature change as described above is suppressed as much as possible. This problem is solved by the method of.

According to the structure of the present invention, the light detecting means required for the liquid crystal electro-optical device is separated from the substrate constituting the liquid crystal cell, and the relationship between the light detecting means and the liquid crystal molecules in the liquid crystal cell is fixed. Instead, the relationship is arbitrarily changed according to the ambient temperature condition of the liquid crystal electro-optical device, and the light passing through the liquid crystal cell is detected in the best condition under the ambient temperature condition. Is.

The inventors of the present invention have earnestly studied the situation in which the contrast of the light passing through the liquid crystal cell changes according to the ambient temperature change as shown in FIG. The inventors have obtained the finding that the directions (directions of the liquid crystal molecules in the liquid crystal cell in the liquid crystal cell) deviate from the initial conditions due to changes in the ambient temperature, and the present invention has been completed.

That is, in the conventional liquid crystal electro-optical device, the light detecting means (for example, the polarizing plate) is always attached to the glass substrate of the liquid crystal cell, and the attaching direction is an electric field under a specific temperature condition. It is usually determined based on optical property data. On the other hand, it has been found that the liquid crystal molecule changes its direction as the ambient temperature changes, and simultaneously changes the opening angle (cone angle) between the two possible states of the liquid crystal molecule. This situation is shown in FIG. FIG. 3 shows two angular positions that liquid crystal molecules can take when the temperature around the liquid crystal electro-optical device is changed, which means the extinction position obtained by changing the direction of the electric field applied to the liquid crystal. .. That is, the data shown by the white circles in FIG. 3 indicate the angular position of the extinction position obtained when an electric field is applied in one direction of the liquid crystal cell, and the data shown by the triangles are the opposite of those of the liquid crystal cell. It shows the angular position of the extinction position obtained when an electric field is applied in the direction of. Note that the angle at this time was 0 ° in the direction along a certain side of the substrate, and the angle was determined by rotating the angle between the polarizing plate and the substrate when determining the extinction position.

As described above, it has been well known that the angle (cone angle) between the two states of the ferroelectric liquid crystal molecule changes, but in addition, the direction of the liquid crystal molecule itself also changes with temperature. Therefore, if the polarizing plate is attached to the substrate according to the direction of the polarizing plate that was determined under specific temperature conditions as in the past, the cone angle will change due to the change in temperature and the direction of the liquid crystal molecules will also change. It was revealed that the contrast was lowered because the complete extinction position could not be obtained due to the deviation.

Whereas the conventional technique has tried to solve this problem by reducing the temperature change of the cone angle, which is a problem of the liquid crystal material itself, in the present invention, the deviation between the photo-detecting means and the liquid crystal molecules in the long axis direction. By minimizing the above, it is possible to realize a liquid crystal electro-optical device in which the change in contrast is small even when the temperature around the liquid crystal electro-optical device changes.

FIG. 1 shows a schematic sectional view of the liquid crystal electro-optical device of the present invention. In FIG. 1, reference numeral 1 denotes a substrate of a liquid crystal cell, and a space between the substrates is filled with a ferroelectric liquid crystal material 2. An electric field can be applied to the liquid crystal material 2 by an electrode 3 near the liquid crystal material 2, and the ferroelectric liquid crystal material 2 transits between two different states according to the direction of the electric field to exhibit a liquid crystal electro-optical effect.

Light detecting means 5 and 6 are provided at such positions as to sandwich the liquid crystal cell 4. The light detecting means is, for example, a polarizing plate, and the light detecting means is not fixed to the liquid crystal cell 4, but is supported by, for example, the fulcrum 7 in FIG.
The angle between the direction of the liquid crystal molecules in the liquid crystal cell and the light detecting means can be changed. The position of this fulcrum is not particularly limited to this place, and it can be provided near the center of the liquid crystal cell or at other places.

Further, the relationship between the angle of the light detecting means and the liquid crystal cell can be continuously changed by using means such as a spring, a bimetal material, a manipulator, a micromotor, etc. according to the ambient temperature condition. , Which allows control to obtain the best contrast at the temperature used.

[0022]

EXAMPLE A liquid crystal electro-optical device having a structure shown in FIG. 1 is basically used in this example. As the light detecting means, polarizing plates 5 and 6 on a commonly used film are used, and these polarizing plates are attached on another transparent plate 8 which is independent of the liquid crystal cell. In this example, the polarization directions of the polarizing plates 5 and 6 were set to crossed Nicols.

FIG. 5 is a top view showing the relationship between the plate 8 to which this polarizing plate is attached and the liquid crystal cell 4. Figure 5
(A) shows that the outer shapes of the plate 8 and the liquid crystal cell 4 are substantially parallel to each other. In this embodiment, in such a state, the contrast becomes highest near room temperature (25 ° C.). The polarizing plates 5 and 6 are attached to the plate 8. That is, in the state of FIG. 5 (A), the polarizing plates 5 and 6 are placed on the plate 8 so that the extinction position can be obtained in accordance with either one of the two possible states of liquid crystal molecules at 25 ° C. It is a crucifixion.

In this embodiment, the angle correction unit 10 is provided at a position away from the fulcrum 7 so that the best contrast of the liquid crystal electro-optical device can be automatically obtained by using the temperature sensor and the microcomputer, and the ambient temperature change. Corresponding to, the angle between the polarizing plate and the liquid crystal cell is corrected. That is, in advance, the relational conditions between the liquid crystal cell 4 and the plate 8 at which a good contrast can be obtained at a certain temperature within the usable temperature range of the liquid crystal material are investigated. Next, the operating temperature range is divided into appropriate blocks, and an external force is applied to the liquid crystal cell 4 or the plate 8 so that the temperature obtained by the temperature sensor forms an angle condition corresponding to the block containing the temperature. , Move slightly and get good contrast.

In the angle correction unit 10, the value of the temperature sensor is input to the microcomputer, and the microcomputer issues an instruction to the micromotor according to this temperature to convert the rotational movement of the motor into a linear movement, thereby the liquid crystal cell. 4 or plate 8 will be moved by applying force to the end surface.

This state is shown in FIG. In this way, the angle correction unit 10 is installed at a place different from the fulcrum 7, and by applying a linear force to the liquid crystal cell 4 or the plate 8 at this portion, the liquid crystal cell 4 or the plate 8 is centered on the fulcrum 7. As a result, it is possible to arbitrarily change the angle relationship between the polarizing plate that is rotated and, as a result, is attached to the plate 8 and the liquid crystal molecules in the liquid crystal cell 4.

In this embodiment, the angle is corrected by a complicated structure using the microcomputer, the motor, the sensor, etc. as described above, but there is no particular restriction on this structure, and other structures or manual operation are possible. Is. For example, the same effect can be achieved by using the characteristics of a bimetal and providing the temperature characteristics and bending direction of the bimetal so that the position from the fulcrum and the installation direction are matched so that they match the characteristics of the liquid crystal electro-optical device. can do.

The result of using the liquid crystal electro-optical device having such a structure is shown in FIG. The liquid crystal material used is the same as the liquid crystal material used when the data in FIG. 2 was taken, and is a phenylpyrimidine-based liquid crystal material. Thus, it is possible to exhibit a substantially constant contrast in the temperature range actually used. is made of. Particularly, the contrast is remarkably improved on the high temperature side.

[0029]

By adopting the constitution of the present invention, it is possible to minimize the change in the contrast of the liquid crystal electro-optical device which is affected by the temperature characteristics of the liquid crystal material.
It was possible to achieve a certain contrast in the operating temperature range. As a result, it becomes possible to use liquid crystal materials that could not be used in the conventional device because the temperature changes drastically, and it is possible to have a margin in material selection.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a liquid crystal electro-optical device of the present invention.

FIG. 2 shows how the contrast of a conventional liquid crystal electro-optical device changes with temperature.

FIG. 3 shows how the temperature changes in the direction taken by liquid crystal molecules in a conventional liquid crystal electro-optical device.

FIG. 4 shows how the contrast of the liquid crystal electro-optical device of the present invention changes with temperature.

FIG. 5 is a schematic view showing an example of a liquid crystal electro-optical device of the present invention.

[Explanation of symbols]

 1 ... Substrate 2 ... Liquid crystal material 4 ... Liquid crystal cell 5 and 6 / Polarizing plate

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Harumi Mori Inventor Harumi Mori 398 Hase, Atsugi, Kanagawa Prefecture

Claims (2)

[Claims] 1. A light detection means is provided separately from a liquid crystal cell having at least a pair of substrates, a liquid crystal material, and a means for applying an electric field to the liquid crystal material, and a substrate forming the liquid crystal cell.
A liquid crystal electro-optical device, wherein the relationship between the liquid crystal cell and the light detecting means is changeable. 2. The liquid crystal electro-optical device according to claim 1, wherein the relationship between the liquid crystal cell and the light detection means is varied according to the ambient temperature condition, and good contrast is realized in the operating temperature state. A liquid crystal electro-optical device characterized by: