JP2001100253A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the accuracy of the pretilt angle. SOLUTION: A transparent electrode 4 and an alignment layer 25 are successively laminated on a glass substrate 2, while a transparent electrode 8 and an alignment layer 26 are successively laminated on a glass substrate 6. The glass substrate 2 and the glass substrate 6 are disposed facing each other through a guest-host liquid crystal. The guest-hot liquid crystal consists of a dichroic dye 10 and a nematic liquid crystal 11. The alignment layers 25, 26 gives a pretilt angle by irradiation of light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a guest-host liquid crystal display device.

[0002]

2. Description of the Related Art Twisted nematic (TN) mode and super twisted nematic (STN) mode are mainly used in liquid crystal display devices. In these types of liquid crystal display devices, at least one linear polarizer is provided. The above is provided.

However, the use of a linear polarizer has reduced the intensity of transmitted light or reflected light by more than half.

In order to solve this problem, a liquid crystal display device using no linear polarizer has been developed. For example, a display mode of a guest-host system has been proposed. Hereinafter, the guest host liquid crystal display device will be described.

A guest-host liquid crystal obtained by dissolving a dichroic dye in a nematic liquid crystal serving as a host is used as an electro-optical material, and the orientation of both the nematic liquid crystal molecules and the dichroic dye is controlled by the action of an electric field. By using the anisotropy of light absorption of the dichroic dye, the degree of light absorption of the liquid crystal material is changed, and ON / OFF switching is performed.

There are two types of guest-host liquid crystal display devices: a transmission type and a reflection type. When both display black and white, a black dichroic dye is used. Further, by combining micro color filters, a full-color image display can be obtained.

The guest-host liquid crystal is horizontally or vertically aligned in the cell, and the degree of light absorption of the dichroic dye is controlled by changing the state of the liquid crystal layer according to the applied state of the driving voltage. Display. In other words, if it is horizontally oriented in advance,
When the voltage is off (OFF), the display becomes black, and the voltage is turned on (O
In the state N), white display is performed. On the other hand, in the case where the liquid crystal molecules are vertically aligned in advance, the display becomes white due to reduced light absorption of the dichroic dye in the voltage-off (OFF) state, and the voltage is turned on (O
In the N) state, black display is performed.

Hereinafter, such an orientation state will be described with reference to FIGS.
This will be described below. 7 and 8 show a transmission type liquid crystal display device, and FIGS. 9 and 10 show a reflection type liquid crystal display device. Further, in the transmission type liquid crystal display device, FIG. 7 shows a case where the guest-host liquid crystal is horizontally aligned in a state where no voltage is applied in the cell (hereinafter abbreviated as a horizontal alignment cell), and FIG. (Hereinafter abbreviated as a vertical alignment cell). Similarly, FIG. 9 shows a horizontal alignment cell of the reflection type liquid crystal display device, and FIG. 10 shows its vertical alignment cell.

First, in the transmission type liquid crystal display device 1 shown in FIGS. 7 and 8, an electrically insulating protective film 3 made of SiO2 or the like is formed on a glass substrate 2, and a transparent electrode 4 is formed on the protective film 3. And the alignment film 5 are sequentially laminated, and the other glass substrate 6
An electrically insulating protective film 7 made of SiO2 or the like is also formed thereon, and a transparent electrode 8 and an alignment film 9 are sequentially laminated on the protective film 7. The transparent electrodes 4 and 8 are both arranged in a stripe pattern, and the glass substrate 2 and the glass substrate 6 are opposed to each other so that both are orthogonal to each other, and a guest-host liquid crystal is interposed therebetween. The guest host liquid crystal includes a dichroic dye 10 and a nematic liquid crystal 11. A polarizing plate 12 is provided on the outer surface of the glass substrate 6.

In the reflection type liquid crystal display device 13 shown in FIGS. 9 and 10, an electrically insulating protective film 15 made of SiO2 or the like, a transparent electrode 16, and an alignment film 17 are sequentially laminated on a glass substrate 14. Further, an electrically insulating protective film 19 made of SiO2 or the like, a transparent electrode 20, and an alignment film 21 are sequentially laminated on the other glass substrate 18. Both the transparent electrodes 16 and 20 are arranged in a stripe pattern, and both are orthogonal to each other, and a guest-host liquid crystal composed of a dichroic dye 10 and a nematic liquid crystal 11 is similarly interposed therebetween. And
On the outer surface of the glass substrate 18, a quarter-wave plate 22 and a light reflecting plate 2
3 are provided.

A liquid crystal panel constituting the transmission type liquid crystal display device 1 and the reflection type liquid crystal display device 13, that is, a liquid crystal panel having two glass substrates with a guest-host liquid crystal therebetween and having a common configuration (P in FIG. When the applied voltage and transmitted light intensity were measured in each of the horizontal alignment cell and the vertical alignment cell, the results shown in FIG. 11 were obtained.

In FIG. 1, the horizontal axis represents the applied voltage, the vertical axis represents the intensity of the transmitted light, and the intensity of the transmitted light corresponds to the liquid crystal panel P.
Of incident light to transmitted light.

As is clear from FIG. 11, in the case of the horizontal alignment cells shown in FIGS. 7 and 9, the intensity of transmitted light gradually increases as the applied voltage increases. Therefore, a high voltage is required to obtain a sufficient white display level. On the other hand, in the vertical alignment cells shown in FIGS. 8 and 10, the white level is high when no voltage is applied, and a sufficient black display level can be obtained with a relatively low voltage.

As described above, the vertical alignment cell can obtain a higher contrast by driving at a lower voltage than the horizontal alignment cell. Therefore, the vertical alignment cell is being developed (Japanese Patent Laid-Open Nos. 8-36174 and 10-174). -1111513
No.).

[0015]

In a vertical alignment cell, it is necessary to control the vertical alignment stably and with good reproducibility by using a guest-host liquid crystal material having negative dielectric anisotropy. As a method for controlling the orientation, a technique of giving a pretilt angle by a rubbing process has been proposed (see JP-A-10-31216).

However, even if a pretilt angle is provided by using this rubbing technique, stability and reproducibility are insufficient, and a satisfactory display characteristic has not yet been obtained.

The present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a highly reliable liquid crystal display device by giving a required pretilt angle to an alignment film.

[0018]

According to the liquid crystal display device of the present invention, one member formed by sequentially laminating one transparent electrode and an alignment layer on a transparent substrate, and the other transparent electrode on the transparent substrate are aligned with the other transparent electrode. In the device configuration in which pixels are arranged in a matrix with a guest-host liquid crystal having a negative dielectric anisotropy containing a dichroic dye between the other member formed by sequentially laminating the layers and The pretilt angle θ is set to 80 ° ≦ θ <90 ° by performing light irradiation treatment on the alignment layer of one member and / or the alignment layer of the other member.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to FIGS. 1 and 2 are cross-sectional views of main parts of a transmissive guest-host liquid crystal display device. FIG. 1 shows the state of guest-host liquid crystal molecules when no voltage is applied, and FIG. 2 shows the state of guest-host liquid crystal molecules when voltage is applied. The behavior is schematically shown. 3 and 4 are cross-sectional views of main parts of the reflective guest-host liquid crystal display device. FIG. 3 shows the state of the guest-host liquid crystal molecules when no voltage is applied, and FIG. 4 shows the state of the guest-host liquid crystal molecules when voltage is applied. The behavior is schematically shown. The same parts as those of the conventional liquid crystal display devices 1 and 13 are denoted by the same reference numerals. The transmissive guest-host liquid crystal display device will be described with reference to the liquid crystal display device 24 shown in FIGS. An electrically insulating protective film 3 made of SiO 2 or the like is formed on a glass substrate 2, and a transparent electrode 4 made of ITO or the like and an alignment film 25 made of a polyimide resin or the like are sequentially laminated on the protective film 3. An electrically insulating protective film 7 made of SiO2 or the like is also formed on the glass substrate 6 of FIG.
A transparent electrode 8 made of TO or the like and an alignment film 26 made of a polyimide resin or the like are sequentially laminated. Transparent electrodes 4, 8
Both are arranged in a stripe pattern, and the glass substrate 2 and the glass substrate 6 are arranged to face each other so that they are orthogonal to each other, and a guest-host liquid crystal is interposed. Further, a polarizing plate 12 is provided on the outer surface of the glass substrate 6.

The guest-host liquid crystal is a dichroic dye 10 having an absorption axis in the molecular major axis direction (for example, S4 manufactured by Mitsui Toatsu Chemicals, Inc.).
28) and the nematic liquid crystal 11 (for example, E. Merck
ZLI-4318, ZLI-2806, ZLI-2
586).

Next, the operation of the liquid crystal display device 24 having the above configuration will be described. In the state where no voltage is applied as shown in FIG. 1, the guest-host liquid crystal is aligned substantially vertically, and light is irradiated from outside of the glass substrate 6 by a backlight or the like.
The irradiation light can be represented by deflection components orthogonal to each other, and is divided into a vibration component X parallel to the drawing and a vibration component Y perpendicular to the drawing. The deflection plate 12 has a deflection axis parallel to the drawing.

According to the liquid crystal display device 24 having the above configuration, the vibration component Y of the irradiation light is cut off by the deflecting plate 12, but the vibration component X passes through the guest-host liquid crystal.

Next, when a voltage is applied as shown in FIG. 2, the guest-host liquid crystal shifts to horizontal alignment. Then, the vibration direction of the vibration component X transmitted through the deflection plate 12 matches the orientation direction of the guest-host liquid crystal, and is absorbed by the dichroic dye 10. Regarding the reflection type guest host liquid crystal display device, the liquid crystal display device 27 shown in FIGS. 3 and 4 will be described. An electrically insulating protective film 15 made of SiO 2 or the like, a transparent electrode 16 made of ITO or the like, and an alignment film 28 made of a polyimide resin or the like are sequentially laminated on a glass substrate 14. An electrically insulating protective film 19 made of, for example, a transparent electrode 20 made of ITO or the like, and an alignment film 29 made of polyimide resin or the like are sequentially laminated. Both the transparent electrodes 16 and 20 are arranged in a stripe pattern, and both are orthogonal to each other, and a guest-host liquid crystal composed of a dichroic dye 10 and a nematic liquid crystal 11 is similarly interposed therebetween. In addition, a quarter-wave plate 22 and a light reflecting plate 23 set in the direction of the optical axis optimal for the outer surface of the glass substrate 18 are provided.

Although the quarter-wave plate 22 and the light reflecting plate 23 are provided on the outer surface of the glass substrate 18, they may be provided on the inner surface of the glass substrate 18 in place of such an arrangement portion.

The guest-host liquid crystal contains a nematic liquid crystal 11 having a negative dielectric anisotropy as a main component and a P-type dichroic dye 10, and is oriented substantially vertically. That is, the angle (pretilt angle θ) between the horizontal direction of the substrate and the major axis of the liquid crystal molecules is approximately 90 °.

Next, the operation of the liquid crystal display device 27 having the above configuration will be described with reference to FIGS. According to the no-voltage application state shown in FIG. 3, the guest-host liquid crystal is oriented substantially vertically, and when light enters from outside the glass substrate 14,
Neither of the vibration components X and Y reaches the quarter-wave plate 22 without being light-absorbed, passes through the quarter-wave plate 22, and
The light is reflected at 3 and further passes through the quarter-wave plate 22, and the light is emitted without undergoing any light modulation even if the vibration directions are switched at that time.

As shown in FIG. 4, when the voltage is applied, the guest-host liquid crystal shifts to the horizontal alignment. When incident light enters from outside the glass substrate 14, the vibration component X is changed to the orientation direction of the guest-host liquid crystal. By matching the directions, P
The vibration component Y is absorbed by the type dichroic dye 10 and is transmitted without being absorbed by the guest-host liquid crystal because the vibration direction is perpendicular to the orientation direction. The vibration component Y is 1/4
The light passes through the wave plate 22, is reflected by the light reflecting plate 23, and passes through the quarter wave plate 22 again. At this time, the vibration direction is rotated by 90 °. As a result, the vibration direction matches the orientation direction of the guest-host liquid crystal, and is absorbed by the P-type dichroic dye 10. Regarding the alignment films 25, 26, 28, 29, in the transmission type liquid crystal display device 24, the alignment films 25, 2
In forming 6, a polyimide resin layer is applied and formed in advance, and the layer is solidified. Thereafter, both or one of the layers is subjected to light irradiation treatment, whereby the alignment films 25 and 26 having a pretilt angle as desired are provided. And And the nematic liquid crystal 11 and the dichroic dye 1
A pretilt angle is given to 0 as desired.

In the present invention, the alignment films 25, 2
Although light irradiation processing is performed on both of the light-emitting elements 6, light irradiation may be performed on only one of them. However, when the light irradiation treatment is performed on both layers 25 and 26, the pretilt angle can be given as desired.

Similarly, by subjecting both or one of the alignment films 28 and 29 provided on the reflection type liquid crystal display device 27 to a light irradiation treatment, the nematic liquid crystal 11 and the dichroic dye 1
A pretilt angle can be given to 0 as desired. When the light irradiation process is performed on both of the alignment films 25 and 26, the pretilt angle can be given more as desired than when only one of the alignment films 25 and 26 is irradiated with the light.

Next, the light irradiation process will be described in detail. Using a polyimide alignment film material (JALS204 made by Japan Synthetic Rubber Co., Ltd.) whose absorption wavelength characteristic has a peak near 250 nm, the material is coated on a transparent electrode and solidified. Then, a pretilt angle was given by irradiating the layer with polarized ultraviolet light having a wavelength of 250 nm at an angle of 45 °. According to such a pretilt angle, the polar angle direction is a direction perpendicular to the ultraviolet light deflection direction, and the azimuth direction is a direction parallel to the irradiation angle. The irradiation angle of 45 ° C. is an example,
Ultraviolet irradiation may be performed at an irradiation angle in the vicinity.

The magnitude of the pretilt angle is determined by the pretilt angle θ.
Is preferably set to 80 ° ≦ θ <90 °. It is good to make it vertical near 90 degrees within that range. Also,
When the angle is less than 80 °, the refractive index anisotropy is easily generated without applying a voltage.

In the present invention, when the light irradiation is performed as described above, the orientation layer is heated and the treatment is performed while maintaining the temperature at a constant temperature, so that the desired pretilt can be achieved with lower light irradiation energy. The corner is obtained.

The present inventor has proposed that the alignment layer be formed at 20 ° C., 40 ° C.
C. and 120.degree. C., and the light irradiation energy and the pretilt angle at each temperature were measured. The results shown in FIG. 6 were obtained.

As is apparent from this figure, the higher the temperature is, the more the desired pretilt angle can be obtained with lower light irradiation energy. According to experiments repeatedly conducted by the present inventors, the temperature was set to 70 ° C. to 120 ° C., preferably 80 ° C.
℃ ~ 100 ℃ is good, if within this range,
With a light irradiation energy of 0.1 to 0.5 J / cm 2, the pretilt angle θ with respect to the alignment layer is 80 ° ≦ θ <90 °
Thus, a desired pretilt angle can be provided with low light irradiation energy without causing damage such as vertical alignment.

Next, a common liquid crystal panel of the liquid crystal display devices 24 and 27, that is, 2
When the applied voltage and the transmitted light intensity were measured for a liquid crystal panel (indicated by P1 in the figure) having two glass substrates and having a common configuration, the results shown in FIG. 5 were obtained. .

In the figure, the horizontal axis is the applied voltage, the vertical axis is the intensity of the transmitted light, and the intensity of the transmitted light is
It is expressed by the ratio of transmitted light to incident light of 1. As a comparative example, the intensity of transmitted light in the conventional liquid crystal panel 1 subjected to the rubbing treatment is also shown.

As is clear from FIG. 5, the liquid crystal panel P1 of the present invention has better steepness of the voltage-light intensity characteristic than the conventional liquid crystal panel P, and has an excellent black display level when a voltage is applied. I have. For such a good result, the present inventor still cannot get out of the imaginable range, but by performing the light irradiation processing, the pretilt angle could be given with high precision, and It is considered that uniform processing cannot be performed over the entire surface of the substrate in the rubbing process, and that process control is difficult.

Thus, the liquid crystal display devices 24, 2 of the present invention
According to 7, the voltage is applied to the vertically aligned negative dielectric anisotropic nematic liquid crystal 11 and the guest-host liquid crystal containing the P-type dichroic dye 10, whereby the liquid crystal is switched to the horizontal alignment, and the light is turned on / off. However, by performing a light irradiation treatment on the alignment layer, a required pretilt angle could be given to the alignment film.

It should be noted that the present invention is not limited to the above embodiment, and various changes and improvements may be made without departing from the scope of the present invention. For example, the same function and effect can be obtained in a color liquid crystal display device provided with a color filter and in an active matrix type liquid crystal display device in which a thin film transistor for driving pixel switching is formed.

[0040]

As described above, according to the liquid crystal display device of the present invention, the pretilt angle θ is 80 ° ≦ θ <90 with stable and high reproducibility by irradiating the alignment layer with light.
°, which provided a high quality and highly reliable liquid crystal display device.

Further, according to the present invention, a desired pretilt angle can be provided with low light irradiation energy, the irradiation time can be shortened, and thus the manufacturing cost can be reduced and a low cost liquid crystal display device can be provided. Was.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a transmission type guest host liquid crystal display device of the present invention.

FIG. 2 is a sectional view of a main part of a transmission type guest host liquid crystal display device of the present invention.

FIG. 3 is a cross-sectional view of a main part of the reflective guest-host liquid crystal display device of the present invention.

FIG. 4 is a sectional view of a main part of a reflection type guest-host liquid crystal display device of the present invention.

FIG. 5 is a diagram showing a relationship between applied voltage and transmitted light intensity in a liquid crystal panel.

FIG. 6 is a diagram showing a relationship between light irradiation energy and a pretilt angle for an alignment layer.

FIG. 7 is a sectional view of a main part of a conventional transmission type guest host liquid crystal display device.

FIG. 8 is a sectional view of a main part of a conventional transmission type guest host liquid crystal display device.

FIG. 9 is a sectional view of a main part of a conventional reflection type guest-host liquid crystal display device.

FIG. 10 is a sectional view of a main part of a conventional reflection type guest host liquid crystal display device.

FIG. 11 is a diagram showing a relationship between an applied voltage and transmitted light intensity in a liquid crystal panel.

[Explanation of symbols]

 2,6,14,18. . . . Glass substrate 3, 7, 15, 19. . . . Protective film 4, 8, 16, 20. . . . Transparent electrode 10. . . . . . . . . . . Dichroic dye 11. . . . . . . . . . . Nematic liquid crystal 12. . . . . . . . . . . Deflection plate 22. . . . . . . . . . . 1/4 wavelength plate 23. . . . . . . . . . . Light reflector 24,27. . . . Liquid crystal display device 25, 26, 28, 29. . Alignment film θ. . . . . . . . . . . . Pretilt angle

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshiro Motomura 999-3, Hayato-cho, Aira-gun, Kagoshima Kyocera F-term (reference) 2H088 GA02 GA13 HA03 HA08 HA17 HA21 JA06 MA20 2H090 HB03X HB08Y KA06 LA04 LA08 LA20 MA01 MA11

Claims (1)

[Claims] 1. One member formed by sequentially laminating one transparent electrode and an alignment layer on a transparent substrate, and the other member formed by sequentially laminating another transparent electrode and an alignment layer on a transparent substrate. A liquid crystal display device comprising a dichroic dye and a guest-host liquid crystal having negative dielectric anisotropy interposed and arranged pixels in a matrix, wherein the alignment layer of the one member and A liquid crystal display device characterized in that the alignment layer of the other member is irradiated with light to set the pretilt angle θ to 80 ° ≦ θ <90 °.