JP2000267085A - Reflective liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain bright, high contrast and excellent color characteristics with little dependence of the change of properties on external light conditions. SOLUTION: The reflective liquid crystal display device is provided with a liquid crystal cell 1 comprising a liquid crystal enclosed between a pair of substrates 12a, 12b, at least a polarizing film 10 and a reflection means. The liquid crystal molecules existing almost in the central part of a liquid crystal layer 16 formed inside the pair of the substrates concerning a direction normal to the substrates are defined as mid-plane liquid crystal molecules 17 and a plane incorporating them is defined as an observation plane. The projected direction of the direction of the principal incident light on the observation plane and the tilt direction of the mid-plane liquid crystal molecules under an applied electric field are made to mutually be opposite with respect to the normal of the substrate on the observation plane. Besides projected direction of the line of sight of an observer on the observation plane and the tilt direction of the mid-plane liquid crystal molecules under the applied electric field are made to mutually be on the same side concerning to the normal of the substrate on the observation plane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements are thin and light, and thus are widely used in various applications including displays for portable information terminals. The liquid crystal display element is a light-receiving element that performs display by changing the light transmission intensity without emitting light by itself, and can be driven with an effective voltage of several volts, so it has a reflector under the liquid crystal display element If it is used as a reflection type in which a display is viewed by reflected light of external light, a display element with extremely low power consumption can be obtained.

A conventional reflection type color liquid crystal display device comprises a liquid crystal cell provided with a color filter and a pair of polarizing films disposed so as to sandwich the liquid crystal cell. The color filter is provided on one substrate of the liquid crystal cell, and the color filter is formed on the substrate, and the transparent electrode is further formed thereon. By applying a voltage to this liquid crystal cell,
Color display is performed by changing the alignment state of liquid crystal molecules to change the light transmittance of each color filter.

The transmittance of one polarizing film is at most about 45%. At this time, the transmittance of polarized light parallel to the absorption axis of the polarizing film is almost 0%, and the transmittance of perpendicular polarized light is about 90%. It is. Therefore, in a reflection type liquid crystal display device using two polarizing films, light is emitted four times through the polarizing film, and therefore, when the absorption of the color filter is not considered, (Equation 1) is obtained. 33
It reaches a plateau at%.

[0005]

(0.9) 4 × 50% = 32.8% Therefore, in order to brighten the display, only one polarizing film is provided on the upper side of the liquid crystal cell, and the liquid crystal cell is combined with one polarizing film. There have been proposed some configurations in which the film is sandwiched between reflectors (for example, Japanese Patent Application Laid-Open No. 07-146469,
No. 7-84252). In this case, two polarizing films
Since the light passes through the filter only once, it becomes (Equation 2) when the absorption of the color filter is not considered. At the maximum, an improvement of the reflectance of about 23.5% can be expected with respect to the configuration using two polarizing films.

[0006]

(0.9) 2 × 50% = 40.5%

However, the reflective liquid crystal display device having such a configuration has only one polarizing film, even if it is a reflective liquid crystal display device in which a pair of polarizing films are provided above and below a liquid crystal cell. The reflective liquid crystal display element used does not display with a constant light source like a backlight system like a transmissive liquid crystal display element, but uses external light that changes variously depending on environmental conditions. indicate. For this reason, direct light and indirect light, and parallel light and scattered light are mixed in the external light. Therefore, it is very rare that the incident light is incident from only one direction. The liquid crystal display element utilizes light incident from a direction having a certain spread.

For this reason, the conventional reflection type liquid crystal display element has a problem that the characteristics of brightness, contrast, and color greatly change depending on the conditions of external light. One of the causes is that a change in display characteristics when the incident angle of light is different due to a narrow viewing angle of the reflective liquid crystal display element is cited. That is, in the case of a transmissive liquid crystal display element, the incident path of light can be made constant, but in the case of a reflective liquid crystal display element, it is necessary to use light having various incident angles as described above.

[0008] The present invention is directed to solving the above-mentioned problems of the prior art, and by making the characteristic change small with respect to the angle change in the light incident direction, it is possible to reduce the amount of external light. It is an object of the present invention to provide a reflection type liquid crystal display element having a small dependence of a characteristic change on conditions.

[0009]

In order to achieve this object, in a reflection type liquid crystal display device according to the present invention, a liquid crystal layer is sealed between a pair of substrates each having an electrode for applying an electric field inside. A liquid crystal cell, comprising a polarizing film disposed on at least one of the pair of substrates outside the liquid crystal cell, and a reflection means, and is substantially at the center with respect to the substrate normal direction of the liquid crystal layer formed inside the pair of substrates. When the liquid crystal molecules are mid-plane liquid crystal molecules and the plane containing the mid-plane liquid crystal molecules is the observation plane, the direction of projection of the main incident direction of light to the observation plane and the tilt of the mid-plane liquid crystal molecules when an electric field is applied are shown. The directions are opposite to each other with respect to the substrate normal on the observation plane.

[0010] The projection angle of the main incident direction of the light onto the observation plane is 0 to 45 °.

A liquid crystal cell in which a liquid crystal layer is sealed between a pair of substrates each having an electrode for applying an electric field inside; a polarizing film disposed on at least one of the pair of substrates outside the liquid crystal cell; A reflection means, and a liquid crystal molecule substantially at the center with respect to the substrate normal direction of the liquid crystal layer formed inside the pair of substrates is a midplane liquid crystal molecule, and a plane containing the midplane liquid crystal molecule is an observation plane. When the direction of projection of the observer's line of sight to the observation plane and the tilt direction of the liquid crystal molecules on the midplane when applying an electric field are
It is characterized by being on the same side with respect to the substrate normal on the observation plane.

[0012] Further, the angle of projection of the line of sight of the observer on the observation plane is 0 to 45 °.

According to the above configuration, it is possible to obtain a bright, high-contrast and good color characteristic with a small dependence of the characteristic change on the condition of the external light.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view showing a reflection type liquid crystal display device according to Embodiment 1 of the present invention. In FIG. 1, 1 is a liquid crystal cell, 10 is a polarizing film, 11a, 11
b is a polymer film, 12a is a transparent substrate, 12b is a substrate, 13 is a color filter, 14 is a transparent electrode, 15a,
Reference numeral 15b denotes an alignment layer, 16 denotes a liquid crystal layer, 17 denotes a liquid crystal molecule of a midplane, and 18 denotes a metal reflective electrode.

FIG. 2 is a conceptual diagram showing the relationship between the main light incident direction of the reflective liquid crystal display device and the liquid crystal molecule direction of the midplane in the first embodiment. In FIG. 2, 5 is a substrate normal, 6 is an observation plane, 7 is a mid-plane liquid crystal molecule, 7a is a mid-plane liquid crystal molecule direction,
Reference numeral 20 denotes an incident direction of main light, 21 denotes a projection direction of the main light incident direction onto the observation plane, and 22 denotes an angle of projection of the main light incident direction onto the observation plane.

Here, non-alkali glass substrates (for example, 1737: manufactured by Corning Incorporated) are used as the transparent substrates 12a and 12b, and the color filter 13 is a pigment-dispersed type of red, green and blue on the upper transparent substrate 12a. A pixel having a stripe arrangement was formed by photolithography, and a pixel electrode was formed thereon using indium, tin, and oxide as a transparent electrode. Also, on the lower substrate 12b,
After depositing 300 nm of titanium, 200
A diffused (scattering) reflection type metal reflective electrode 18 was formed by forming a layer having a thickness of 3 nm and forming an uneven surface with an average inclination angle of 3 ° to 12 °.

A 5% by weight solution of polyimide γ-butyrolactone is printed on the transparent electrode 14 and the metal reflection electrode 18 and cured at 250 ° C., and then a rayon cloth is used to realize a twist angle of 63 °. The alignment process was performed by a rotating rubbing method to form alignment layers 15a and 15b.

Then, a glass fiber having a diameter of 4.0 μm is added to the peripheral portion on the upper transparent substrate 12a by 1.0% by weight.
The mixed thermosetting seal resin (for example, Struct Bond: manufactured by Mitsui Toatsu Chemicals, Inc.) is printed, and the lower substrate 12 is printed.
b. Resin beads having a diameter of 3.0 μm
Pieces / mm ² , the upper transparent substrate 12a and the lower substrate 12b are adhered to each other, and the sealing resin is cured at 150 ° C., and then a fluorine ester type nematic liquid crystal having a birefringence Δn _LC = 0.08. Has a chiral pitch of 80 μm
Vacuum injection of liquid crystal mixed with chiral liquid crystal so that
After sealing with an ultraviolet curable resin, the resin was cured by ultraviolet light.

On the transparent substrate 12a on the upper side of the liquid crystal cell 1 thus formed, polymer films 11a and 11b composed of two polycarbonate films are adhered as an optical compensation layer for normally whitening. As the film 10, a neutral gray polarizing film (SQ-1852AP, manufactured by Sumitomo Chemical Co., Ltd.) that had been subjected to anti-glare (AG) and anti-reflection (AR) treatments was attached.

The liquid crystal molecule direction 7a of the midplane is determined by the direction of the rotational rubbing on the transparent substrates 12a and 12b. The optical characteristics of the reflective liquid crystal display device were evaluated by changing the angle 22 of projection of the main light on the observation plane 6 containing the liquid crystal molecules of the midplane in the incident direction 20. Here, the condition of light to the reflection type liquid crystal display element was such that direct light from a fluorescent lamp of 1000 lux was added under indirect illumination of 500 lux. The incident direction of the light of the fluorescent lamp was defined as the main light incident direction.

FIG. 3 is a characteristic diagram showing the relationship between the angle of projection of the main light incident direction on the reflection type liquid crystal display element on the observation plane and the reflectance in the first embodiment. Where condition A
Indicates a case where the projection direction 21 of the main light incident direction to the observation plane and the liquid crystal molecule direction 7a of the midplane are on opposite sides with respect to the substrate normal line 5, and the condition B is on the same side.

From these results, first, condition A is better than condition B
It can be seen that a brighter display can be obtained with a higher reflectance than that of the first embodiment.
Next, even under the condition A, it was found that a high reflectance was obtained when the angle of projection 22 of the main light incident direction onto the observation plane was 0 to 45 °.

Further, by visual confirmation, it was confirmed that, under the above-mentioned conditions for obtaining a bright display having a high reflectance, good contrast and achromatic white and black display can be obtained.

(Embodiment 2) In Embodiment 2 of the present invention, since the reflection type liquid crystal display device is the same as that of Embodiment 1, the sectional view of the reflection type liquid crystal display device is as follows. FIG. 1 described above is used.

FIG. 4 is a conceptual diagram showing the relationship between the direction of the observer's line of sight and the direction of the liquid crystal molecules on the midplane of the reflective liquid crystal display device according to the second embodiment. In FIG.
5 is the substrate normal, 6 is the observation plane, 7 is the mid-plane liquid crystal molecules, 7a is the mid-plane liquid crystal molecule direction, 25 is the direction of the observer's line of sight, 26 is the direction of the observer's line of sight to the observation plane. The projection direction 27 is the angle of projection of the observer's line of sight onto the observation plane.

The liquid crystal molecule direction 7a of the midplane is determined by the direction of the rotational rubbing on the transparent substrates 12a and 12b. The optical characteristics of the reflective liquid crystal display device were evaluated by changing the angle 27 of projection of the observer's line of sight 25 onto the observation plane 6 containing the liquid crystal molecules of the midplane. Actually, the detector of the measuring device was installed so as to overlap in the direction of the line of sight of the observer. Here, the condition of light to the reflection type liquid crystal display element was such that direct light from a fluorescent lamp of 1000 lux was added under indirect illumination of 500 lux. The incident direction of the light of the fluorescent lamp was defined as the main light incident direction.

FIG. 5 is a characteristic diagram showing the relationship between the angle of projection of the line of sight of the observer onto the observation plane and the reflectivity in the reflective liquid crystal display device according to the second embodiment. Here, the condition A is that the projection direction 26 of the direction of the observer's line of sight to the observation plane and the liquid crystal molecule direction 7a of the midplane are the substrate normal 5
, And the condition B indicates the case where they are on the same side.

According to the result, first, the condition B is better than the condition A
It can be seen that a brighter display can be obtained with a higher reflectance than that of the first embodiment.
Next, even under the condition A, it was found that a high reflectance was obtained when the angle of projection 27 of the main light incident direction onto the observation plane was 0 to 45 °.

Further, by visual confirmation, it was confirmed that under the condition that a bright display having a high reflectance was obtained, good contrast and achromatic white and black display could be obtained.

The above results indicate that the observer usually has no observer's own direction, so that the light cannot enter the observer's own direction. Therefore, the direction of the observer's line of sight and the principal incident direction of the light are the normal to the substrate. Are opposite to each other, so that the result of the first embodiment is also compatible.

From these results, in order to make the direction of the line of sight of the observer actually a specific direction, in an actual reflection type liquid crystal display element, the above-described condition is set with respect to the position of the observer assumed when using. It can be seen that the orientation of the liquid crystal should be determined so as to satisfy the condition.

The effect of the present invention is not limited to the liquid crystal cell described in the embodiment of the present invention, but may be applied to a reflection type liquid crystal display device using two polarizing films. Alternatively, STN, homeotropic, homogeneous, or the like may be used, that is, a reflective liquid crystal display device using one polarizing film, and the same effect can be obtained by satisfying the constituent requirements of the present invention.

[0033]

As described above, according to the present invention,
There is an effect that a reflection type liquid crystal display device having small brightness, high contrast, and good color characteristics with little dependence of the characteristic change on external light conditions can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a reflective liquid crystal display element according to Embodiments 1 and 2 of the present invention.

FIG. 2 is a conceptual diagram illustrating a relationship between a main light incident direction and a liquid crystal molecule direction of a midplane of the reflective liquid crystal display element according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a reflection angle and a projection angle of a main light incident direction on a reflection type liquid crystal display element according to a first embodiment of the present invention.

FIG. 4 is a conceptual diagram showing the relationship between the direction of the observer's line of sight and the direction of liquid crystal molecules on the midplane of the reflective liquid crystal display element according to the second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing the relationship between the angle of projection of the direction of the observer's line of sight to the observation plane and the reflectivity on the reflective liquid crystal display element according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal cell 5 Substrate normal 6 Observation plane 7, 17 Mid plane liquid crystal molecule 7a Mid plane liquid crystal molecule direction 10 Polarizing film 11a, 11b Polymer film 12a Transparent substrate 12b Substrate 13 Color filter 14 Transparent electrode 15a, 15b Alignment layer Reference Signs List 16 liquid crystal layer 18 metal reflective electrode 20 main light incident direction 21 main light incident direction onto observation plane projection direction 22 main light incident direction onto observation plane projection angle 25 observer's line of sight 26 observer 27 Projection direction of gaze direction to observation plane 27 Angle of projection of observer's gaze direction to observation plane

 ──────────────────────────────────────────────────の Continued on the front page (72) Yoshihiro Sakurai 1006 Kadoma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Yoshio Iwai 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co. F term (reference) 2H091 FA08X FA08Z FA14Y FD01 GA06 KA05 LA15 LA17

Claims (4)

[Claims] A liquid crystal cell having a liquid crystal layer sealed between a pair of substrates each having an electrode for applying an electric field inside thereof;
A polarizing film disposed on at least one of the pair of substrates outside the liquid crystal cell; and a reflection unit, and a liquid crystal substantially at the center with respect to a substrate normal direction of a liquid crystal layer formed inside the pair of substrates. When the molecules are liquid crystal molecules of the midplane, and the plane containing the liquid crystal molecules of the midplane is the observation plane, the projection direction of the main incident direction of light onto the observation plane and the liquid crystal molecules of the midplane when an electric field is applied are determined. A reflection type liquid crystal display element, wherein tilt directions are opposite to each other with respect to the substrate normal on the observation plane. 2. The reflection type liquid crystal display device according to claim 1, wherein an angle of projection of the main incident direction of the light onto an observation plane is 0 to 45 °. 3. A liquid crystal cell having a liquid crystal layer sealed between a pair of substrates each having an electrode for applying an electric field inside thereof,
A polarizing film disposed on at least one of the pair of substrates outside the liquid crystal cell; and a reflection unit, and a liquid crystal substantially at the center with respect to a substrate normal direction of a liquid crystal layer formed inside the pair of substrates. When the molecules are liquid crystal molecules of the midplane, and the plane containing the liquid crystal molecules of the midplane is the observation plane, the direction of projection of the observer's line of sight to the observation plane and the tilt of the liquid crystal molecules of the midplane when an electric field is applied. A reflective liquid crystal display device, wherein directions are on the same side with respect to the substrate normal on the observation plane. 4. The reflection type liquid crystal display device according to claim 3, wherein an angle at which the line of sight of the observer is projected onto an observation plane is 0 to 45 °.