JPH07294932A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory display of high contrast and wide visual field by preventing the change of liquid crystal orientation in the twisting direction in the liquid crystal display device which has plural areas different by orientation directions. CONSTITUTION:In the liquid crystal display device which has plural areas different by orientation directions, a twist angle 1 is within the range of 80 to 100 deg., and a chiral pitch 2 is within the range of 20 to 200mum. Besides these conditions, one or more areas of one or both of substrates 17 and 18 have pretilt angles within the range of 0 to 1.5 deg., By this constitution, a high contrast is secured without bringing about reverse twist orientation.

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 device, and more particularly to a liquid crystal display device capable of obtaining a display having a wide field of view and good contrast.

[0002]

2. Description of the Related Art As a conventional liquid crystal display device capable of obtaining a display having a wide field of view and good contrast, Japanese Patent Application Laid-Open No. 63-63242 is known.
There is one disclosed in Japanese Patent Laid-Open No. 106624. The conventional technique will be described taking this as an example. 12 is a plan view of this liquid crystal display element, and FIG. 13 is a sectional view of the liquid crystal display element (a sectional view taken along the line aa 'in FIG. 12). On one glass substrate 22, a display transparent electrode 20 for each pixel, an alignment film 10, and a thin film transistor 13 for driving the transparent electrode 20 are formed. On the other glass substrate 21, a display transparent electrode 19 and an alignment film 9 are formed.
The alignment films 9 and 10 are both made of polyimide. The pixels B formed between the transparent electrodes 19 and 20 facing each other are, for example, squares of 200 μm in length and width, and are arranged in a matrix. A strip-shaped spacer 2 made of polyimide is formed at the center of the display transparent electrode forming the pixel B.
3 is provided. As a result, each pixel B is divided into regions I and II by the strip spacer 23. The divided regions I and II are typically formed as shown in FIG. That is, the other glass substrate 22 facing the one glass substrate 21 is rubbed in the direction of the arrow shown in FIG.

In order to explain the effect of improving the visual dependency in this conventional example, FIG. 14 shows that the observation direction is 45 ° in the azimuth direction.
FIG. 15 is a plan perspective view showing the rubbing direction and the twisting direction of the liquid crystal alignment between the upper and lower substrates when changed. In the figure,
7 is a divided region I, 8 is a divided region II, 25 is a rubbing direction on the first substrate, 26 is a rubbing direction on the second substrate, and 27 is a twist of liquid crystal alignment between the upper and lower substrates. Indicates a corner. Further, FIG. 16 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along line bb 'in FIG. In the figure, 5 is a liquid crystal substance, 6 is a rising direction of liquid crystal alignment by an electric field, 17 is a first substrate, and 18 is a second substrate.

In this conventional example, the liquid crystal alignment in each of the divided regions has the same spiral twist (also called twist) as shown in FIG.
As shown in FIG. 6, the directions of angles (also called pretilt angles) with respect to the substrate surface are different. When the voltage is applied, the rising direction of liquid crystal molecules (also referred to as the tilt direction) is different as indicated by arrow 6 in FIG. 16 due to the difference in the angle with respect to the substrate surface. Therefore, when light is incident from an oblique direction inclined from the vertical direction with respect to the substrate. In addition, the respective regions compensate each other's optical characteristics. As a result, the visual dependence upon voltage application is canceled by the regions of different orientations in each pixel between the upper and lower substrates, and optical characteristics with little visual dependence are obtained. In particular, the phenomenon of gradation inversion is no longer observed even when the viewing angle is changed during gradation display.

As a conventional example having a smaller number of steps than the conventional example based on the same principle as this conventional example, SID '92 digest (SID'9) in the United States of America.
2 Digest) page 798, and Japan Display '92 digest (Japan).
n Display '92 Digest) shown on page 591, as well as the SID '92 Digest of the United States of America (SID '92 Digest).
Some are shown on page 269. In these examples, as in the case of the above-described conventional example, the liquid crystal orientation in each of the divided regions has the same spiral twist direction but different angles with respect to the substrate surface. However, what is different from the above-mentioned conventional example is the configuration of the direction and the angle of the alignment regulating force applied to the liquid crystal on the substrate surface. In order to clarify the difference between these examples and the above-mentioned conventional example, a plan perspective view showing the rubbing direction and the twisting direction of the liquid crystal alignment between the upper and lower substrates and the substrate surface are also shown for these three types of conventional examples. 3A and 3B are cross-sectional views showing the rising direction of the alignment regulating force in 1 and the rising direction of the liquid crystal alignment between the upper and lower substrates by the electric field.

FIG. 17 shows the SID '92 digest of the United States of America (SID '92 Digest).
It is a plane perspective view showing the rubbing direction and the twisting direction of the liquid crystal alignment between the upper and lower substrates in the conventional example shown on page 798. FIG. 18 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along the line cc ′ in FIG. In this example, the upper substrate has one rubbing direction and the lower substrate has one rubbing direction, and the materials are changed in the regions I and II of the upper and lower substrates. As a result, as shown in FIG. 18, in the region I, the angle of the liquid crystal in the lower substrate 18 with respect to the substrate surface is higher than that in the upper substrate 17,
In II, the angle of the liquid crystal in the lower substrate 18 with respect to the substrate surface is lower than the angle in the upper substrate 17. As a result, when a voltage is applied, the liquid crystal alignment rises in the direction of the alignment control force on the lower substrate in the region I as shown by the arrow 6 in the figure, and in the direction of the alignment control force on the upper substrate in the region II. Stands up.

FIG. 19 shows Japan Display Japan '.
92 Digest (Japan Display '92
FIG. 9 is a plan perspective view showing a rubbing direction and a twisting direction of liquid crystal alignment between upper and lower substrates in a conventional example shown on page 591 of Digest. FIG. 20 shows FIG. 19 as d-d ′.
FIG. 6 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along the line. In this example, the upper substrate has one rubbing direction and the lower substrate has two rubbing directions. Further, as shown in FIG. 20, the angle of the liquid crystal of the lower substrate with respect to the substrate surface is higher than the angle of the upper substrate in both the regions I and II, and the directions I and II of the lower substrate are different in the direction of the alignment control force. As a result, when a voltage is applied, liquid crystal alignment rises in the direction of the alignment regulating force on the lower substrate in both regions I and II as indicated by arrow 6 in the figure.

FIG. 21 shows the SID '92 Digest 2 of the United States.
It is a plane perspective view of the rubbing direction and the twist direction of the liquid crystal alignment between the upper and lower substrates in the conventional example shown on page 69. 22 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along line ee 'in FIG. In this example, the upper substrate has one rubbing direction, the lower substrate has one rubbing direction, and the upper and lower substrates have the same angle of liquid crystal with respect to the substrate surface. However, the direction of the alignment control force in each region is different between the upper and lower substrates, the liquid crystal alignment in the center is kept horizontal when no voltage is applied, and when voltage is applied, the liquid crystal direction rises due to the oblique electric field shown in the figure. The direction is determined.

In these three types of conventional examples, the number of steps is reduced as compared with the above-described conventional example by devising the structure as shown in FIGS. However, in any method, when the voltage is applied, the rising direction of the liquid crystal molecule is as shown in FIGS.
Since each region is different as shown in FIG. 22, when light is incident from an oblique direction inclined from the vertical direction with respect to the substrate,
The respective areas mutually compensate each other's optical characteristics. As a result, the visual dependence upon voltage application is canceled by the regions of different orientations in each pixel between the upper and lower substrates, and optical characteristics with little visual dependence are obtained.

[0010]

In order to realize the wide field of view characteristics of such a liquid crystal display device, it is essential that each pixel has a stable region in which the alignment direction of the liquid crystal is different. In the above-described four types of conventional examples having the configuration described in the section of the conventional example, the orientation direction is divided into a plurality of regions. However, when the applied voltage is high or when pressure is applied from the outside of the substrate due to a user's contact or the like, a good visual improvement effect may not be obtained. Such a phenomenon frequently occurred particularly in the above-mentioned three types of conventional examples having a small number of steps.
As a result of investigating this phenomenon, it was found that the region is divided into a plurality of regions within one pixel, but the cause is that the alignment direction of the liquid crystal in one or all regions is changed.

This change was as follows. In a conventional liquid crystal display device with a small number of steps, instead of reducing the number of steps, the rising direction of the liquid crystal orientation due to the electric field is determined by the orientation direction or angle on one of the upper and lower substrates or the direction of the newly provided electric field. To be configured. Therefore, as shown in FIG. 18, FIG. 20, and FIG. 22, there are regions where the orientation directions of the liquid crystal are different on the upper and lower substrates. Specifically, the area I of the conventional example of FIG.
And region II, the region II of the conventional example in FIG. 20, and the regions I and II of the conventional example in FIG. Such a configuration of the liquid crystal alignment direction is energetically unstable as compared with a configuration in which the liquid crystal alignment directions on the upper and lower substrates are the same. Such a configuration in which the liquid crystal alignment directions on the upper and lower substrates are different from each other is referred to as “π-pretilt” below, and a configuration in which the liquid crystal alignment directions are the same on the upper and lower substrates is referred to as “normal pretilt”. In other words, the π-type pretilt is more energetically unstable than the normal pretilt.

Here, for example, in the region I of FIGS. 17 and 18, there may be a structure in which the rubbing direction is the same but the twisting direction of the liquid crystal between the upper and lower substrates is different. FIG. 23 shows the rubbing direction and the twisting direction of the liquid crystal alignment between the upper and lower substrates in the structure in which the twisting directions are different. 23 is shown in FIG.
The rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, which are cut along -f ', are shown. In such a region where the twisting direction is different, the liquid crystal is twisted in a spiral type in a direction countering the spontaneous twisting force of the liquid crystal material, so that the twisting direction is more energetically than the configuration of the region I in FIG. It is unstable. The case where the direction of the spontaneous twisting force of the liquid crystal material and the direction in which the liquid crystal is actually twisted between the upper and lower substrates (also called the twist direction) does not match is called “reverse twist” in the following, and it is called the “reverse twist”. The case where the normal twisting force direction and the actual twisting direction of the liquid crystal between the upper and lower substrates are the same is called "normal twist". That is, with respect to the twisting direction, FIG. 23 shows the reverse twist, which is more unstable in terms of energy than the normal twist in the region I of FIG. However, in the configuration of FIG. 23, as shown in FIG. 24, the alignment directions of liquid crystal on the upper and lower substrate surfaces are the same.
Because of the pretilt structure, the rising direction of the liquid crystal from the substrate is more energy stable than the π-type pretilt structure in the region I of FIG. That is, the π-type pretilt and the normal twist are shown in FIGS.
Other liquid crystal alignment configurations such as those shown in FIGS. 23 and 24, which are the normal pretilt and the reverse twist for the region I of FIG. It is considered that the configuration of these two orientations can be easily changed to another configuration if the magnitude relation of energy is reversed.

FIG. 25 shows an example of calculation of changes in the liquid crystal alignment energy of the normal twist structure with the π-type pretilt and the energy of the reverse twist structure with the normal pretilt according to the applied voltage. In the figure, the solid line represents the energy of the liquid crystal alignment of the normal twist structure with the π-type pretilt, and the dashed line represents the energy of the liquid crystal alignment of the normal twist structure with the reverse twist. In both configurations, the liquid crystal orientation rises in the direction of the electric field as the applied voltage increases, so that the energy increases as compared to the steady state when no voltage is applied. Of particular note here is that the normal twist configuration with π-type pretilt is more stable in terms of energy when no voltage is applied, as shown in the figure, but when the voltage becomes high, the normal pretilt reverse The twist structure is more stable in terms of energy and the structure of liquid crystal alignment may change. The cause of the reversal phenomenon in the energy of each component is not clearly known. However, when the effect of improving the viewing angle characteristics is not observed in the conventional liquid crystal display device, the liquid crystal alignment having such a structure in which the twist directions are different is generated. It was confirmed by observation using this scope image.

For example, when one region of the liquid crystal display device which divides one pixel into two is changed to such an orientation, it is obvious that the effect of compensating for the viewing angle characteristics disappears. Also, 2
Even when both regions of the liquid crystal display device to be divided change to such an orientation, they do not change at the same time in all pixels, but change individually, so that they are observed as burn-in on the display. Furthermore, even when the applied voltage is such that the normal twist structure with π-type pretilt is more unstable in terms of energy, the normal pretilt structure does not necessarily immediately change to the reverse twist structure. It is considered that when a pressure is applied by the user's contact or the like, the liquid crystal orientation changes due to the prompting of such a change, and the effect of improving the viewing angle dependency does not appear.

It is not clear why the energy reversal phenomenon of each component occurs when the applied voltage becomes high or pressure is applied by the contact of the user from the outside of the substrate. However, it is possible to stabilize the energy of the desired configuration, ie to prevent changes in the orientation direction in the twist direction, by studying various conditions that affect the energy. Further, it is possible to examine how much contrast performance the liquid crystal display device can exhibit under such conditions.

That is, an object of the present invention is to prevent a change in the alignment direction in the twist direction of the liquid crystal in a liquid crystal display device which realizes a wide viewing angle by having a plurality of regions in which the alignment directions of the liquid crystal are different. Another object of the present invention is to provide a liquid crystal display device capable of displaying a wide field of view with high contrast and good quality.

[0017]

According to a first aspect of the present invention, there is provided a liquid crystal display device comprising a liquid crystal substance sandwiched between a pair of support substrates and having a plurality of regions having different liquid crystal alignment directions between the support substrates. The twist angle of the liquid crystal alignment between the upper and lower substrates is in the range of 20 ° to 100 °, and 20 μm to 20 μm.
The liquid crystal display device is characterized by having a spontaneous twisting force of the liquid crystal material in the range of 0 μm.

FIG. 1 shows a first substrate 17 and a second substrate 18.
Between two regions I (7) having different liquid crystal alignment directions
FIG. 3 is a perspective view of a liquid crystal display device of the first invention having the above and II (8), in which 1 is a twist angle of liquid crystal alignment between upper and lower substrates in a range of 80 ° to 100 °, and 2 is 20 μm to 200 μ.
It shows a spontaneous twisting force in the range of m.

A second aspect of the invention is a liquid crystal display device comprising a pair of supporting substrates and a liquid crystal material sandwiched between the supporting substrates, and a plurality of regions having different liquid crystal alignment directions between the supporting substrates, in the range of 80 ° to 100 °. The twist angle of the liquid crystal alignment between the upper and lower substrates, and the spontaneous twisting force of the liquid crystal material in the range of 20 μm to 200 μm, and in the range of 0 ° to 1.5 ° And a rising angle from the substrate surface of the alignment control force on the substrate surface of at least one region of at least one of the substrates.

FIG. 2 shows a first substrate 17 and a second substrate 18.
Between two regions I (7) having different liquid crystal alignment directions
2 is a perspective view of a liquid crystal display device according to a second invention having II and (8), where 1 is the twist angle of the liquid crystal alignment between the upper and lower substrates in the range of 80 ° to 100 °, and 2 is 20 μm to 200 μm.
Spontaneous twisting force in the range of m is 3 from 0 ° to 1.5 °
The rising angle of the alignment regulating force on the substrate surface in the range of 4 from the substrate surface is 4, and the rising angle of 4 is higher than the angle 3.

[0021]

In order to explain the operation of the present invention, first, the twist angle (also called the twist angle) of liquid crystal alignment between the upper and lower substrates and the spontaneous twisting force of the liquid crystal material (also called the chiral pitch) are described. explain.

FIG. 9 shows a schematic diagram of liquid crystal alignment for explaining the twist angle of the liquid crystal alignment between the upper and lower substrates. There are various methods for giving the alignment regulating force to the liquid crystal alignment on the substrate, but here, it is assumed that the liquid crystal alignment is provided on the upper and lower substrates 17 and 18 by the rubbing method, and the rubbing direction is shown in the figure. It was Set the rubbing direction on the first substrate to 2
5, the rubbing direction on the second substrate is indicated by 26. When the rubbing direction is at a twisted position between the upper and lower substrates, the liquid crystal existing between the upper and lower substrates is twisted in a spiral shape so as to satisfy the condition of the alignment regulating force on the substrates. Of the angles formed by the upper and lower rubbing directions at this time, the angle θ of the portion including the tip portion of the liquid crystal alignment shown in a cylindrical shape in the drawing is called a twist angle. In the figure, this twist angle is indicated by 27.

Further, FIG. 10 shows a schematic diagram of liquid crystal alignment for explaining the spontaneous twisting force of the liquid crystal material. Chiral molecules are added to the nematic liquid crystal currently used, and it has a spontaneous twisting force without giving a twisting angle between the upper and lower substrates and naturally twists in a certain direction. Be done. By this spontaneous twisting force, the distance measured in the direction of the central axis (helix axis) of the rotation from the liquid crystal alignment direction on the lower substrate (glass substrate 21) to one spiral turn as shown in FIG. It is called the twisting power (chiral pitch). That is, the shorter the chiral pitch, the stronger the spontaneous twisting force. In the figure, 28 indicates the chiral pitch.

In a liquid crystal display device having a plurality of regions having different alignment directions, the following two points can be considered as conditions under which the change to the reverse twist alignment as described in the section of the problem to be solved is unlikely to occur. The first point is that the twist angle of the liquid crystal alignment between the upper and lower substrates is narrow, and the second point is that the spontaneous twisting force is strong, that is, the chiral pitch is short. The reason why these two points are unlikely to cause a change in orientation is as follows. The narrow twist angle (θ in FIG. 9) between the upper and lower substrates means that the twist angle (180) when the reverse twist orientation is achieved.
That is, ° -θ) is wide. The configuration with a narrow twist angle is considered to be more energy-stable than the configuration with a wide twist angle, so it is less likely to change to the reverse twist orientation when the twist angle between the upper and lower substrates is narrow.
Further, the fact that the voluntary twisting force is strong, that is, the chiral pitch is short, means that the liquid crystal has a strong tendency to spontaneously twist in a certain direction. That is, when the spontaneous twisting force is strong, it is difficult to change to the reverse twist orientation in which the upper and lower substrates are twisted in the direction opposite to the spontaneous twisting force. Such a tendency is consistent with the wide width of the voltage range in which the reverse twist orientation does not occur when an actual liquid crystal display device is manufactured and evaluated by changing the applied voltage. Such examples are described in the Examples, and reference is now made to the drawings.

FIG. 5 is a contour line showing the upper limit of the voltage range in which the reverse twist orientation did not occur at all when the orientational twisting force between the upper and lower substrates was changed. As can be seen from the figure, when the chiral pitch is short and the twist angle of the alignment between the upper and lower substrates is narrow, the voltage range in which the reverse twist alignment does not occur is wide. However, in the actual use of the display device, even if the orientation of each region is stable up to a high voltage range, it cannot be put to practical use unless a sufficient contrast ratio can be secured within that voltage range. FIG. 26 shows the results of measuring the dependency of the contrast ratio on the applied voltage by changing the conditions of the twist angle of the liquid crystal alignment and the chiral pitch between the upper and lower substrates as shown in Table 1.

[0026]

[Table 1]

As can be seen from the comparison between the solid line and the broken line in FIG. 26, the higher the twist angle between the upper and lower substrates, the higher the contrast ratio at a low applied voltage. Further, as can be seen from the comparison between the solid line and the dotted line in the figure, the longer the chiral pitch, the higher the contrast ratio at a low applied voltage. That is, from the standpoint of contrast ratio, it is advantageous that the twist angle between the upper and lower substrates is wide and the chiral pitch is long, contrary to the condition that the reverse twist orientation does not occur. As described above, a difference can be seen between the conditions in which the reverse twist orientation is unlikely to occur and the conditions in which a sufficient contrast ratio can be secured. Considering this point, as a result of studying from the viewpoint of the contrast ratio which can be secured under the condition that the reverse twist orientation does not occur, a contour map as shown in FIG. 6 is obtained unlike the voltage range of FIG. In the present invention, as shown in the embodiment, conditions are determined in which reverse twist orientation is not generated and a sufficient contrast ratio can be secured.

Further, the requirements of the present invention were determined in consideration of the following conditions. Red (620nm) and green (550n) when no voltage is applied when the twist of the liquid crystal between the upper and lower substrates is changed.
FIG. 27 shows the measurement results of the transmitted light intensities of the light of each wavelength of m) and blue (460 nm). In the figure, the dotted line shows the transmitted light intensity of red light, the solid line shows the green light, and the alternate long and short dash line shows the transmitted light intensity of blue light. Since the liquid crystal display device used for this measurement is designed with reference to green light, the transmitted light intensity does not change significantly with respect to green light even if the twist angle changes. However, with red light and blue light, the transmitted light intensity changes significantly when the twist angle changes.

When the twist angle between the upper and lower substrates is narrower than 80 ° or wider than 100 °, the difference between the transmitted light intensities of the red light and the blue light exceeds 10% of the respective light intensities, and the dependence on the wavelength is present. It becomes intense and it becomes impossible to reproduce the correct color. This tendency is exacerbated in the case of designing other than green light.

Therefore, in the present invention, the range of the twist angle between the upper and lower substrates is determined by the condition that the reverse twist orientation does not occur and the condition of the color reproducibility. Also, regarding the chiral pitch, the value of 20 μm is
The thickness is almost four times the thickness of the liquid crystal portion of the N-type liquid crystal display device, and under this condition, when the thickness of the liquid crystal portion is 5 μm, the TN-type liquid crystal orientation is naturally twisted by 90 °. A chiral pitch shorter than this value does not make much sense in actual use, and as shown in FIG. 26, when the chiral pitch becomes shorter, the voltage value required to obtain a sufficient contrast ratio becomes too high. , It becomes unsuitable for driving during actual use. In addition, as shown in the example, 20
0 μm (that is, approximately 40 times the thickness of the normal liquid crystal part)
If it exceeds, the reverse twist orientation is likely to occur and the contrast ratio cannot be secured, so the value of 20 μm to 200 μm is determined.

In the present invention, optimum conditions are selected for various conditions as shown in the section of this operation and the embodiment, and the conditions as in the present invention are determined. As described above, according to the first aspect of the present invention, by controlling the twist angle and the chiral pitch of the liquid crystal alignment between the upper and lower substrates within a certain range, the alignment of a liquid crystal display device having a plurality of regions with different alignment directions can be stabilized. To ensure good display.

Further, the operation of the second invention will be described.
In the second invention, in addition to the conditions of the first invention, the rising angle (that is, the pretilt angle) of the alignment regulating force on the substrate surface in at least one region of at least one substrate from 0 ° to 1. A condition is given such that it is 5 °. This condition stabilizes the state of the normal twist configuration by the π-type pretilt by lowering the pretilt angle of one or both of the upper and lower substrates in the normal twist region by the π-type pretilt in the conventional example having a small number of steps.
In the conventional example of FIGS. 18 and 20, the π-type pretilt configuration is substantially the same as the normal pretilt configuration with respect to the pretilt angle by lowering the pretilt angle on the substrate side having a lower pretilt angle than the other of the upper and lower substrates. Uses energy so that normal pretilt makes it difficult to change to the reverse twist configuration. Also, FIG.
In the conventional example No. 2, the upper and lower substrates have substantially the same pretilt angle, but by lowering both of these pretilt angles, the structure of the π-type pretilt is stabilized.

In contrast to FIG. 25, when the pretilt angle on one of the substrates is lowered, the energy of the liquid crystal alignment of the normal twist structure by the π type pretilt and the energy of the reverse twist structure by the normal pretilt are changed by the applied voltage. An example of calculation of is shown in FIG. With such a change in the pretilt angle condition, the voltage range in which the orientation is stable is widened, and at the same time, the contrast ratio that can be secured is also increased. 0
The range from ° to 1.5 ° is 1.5 as shown in the embodiment.
If it exceeds 2 ° and becomes 2 ° or more, it is difficult to secure a sufficient contrast ratio under most conditions of the first invention, and 0
Is determined to be sufficiently stable under almost all the conditions of the first invention. As described above, according to the second aspect of the present invention, by controlling the pretilt angle within a certain range, the stability of alignment of the liquid crystal display device having a plurality of regions having different alignment directions is ensured and a good display is obtained.

[0034]

Embodiments of the present invention will be described with reference to FIGS. As a first embodiment of the first invention, the present invention is applied to a conventional liquid crystal display device shown in FIGS. 19 and 20 of a conventional liquid crystal display device having a plurality of regions in which liquid crystal alignment directions are different. Here is an example:

FIG. 3 is a perspective view showing a first embodiment of the first invention. FIG. 4 is a schematic diagram showing the thin film transistor array used in this example. In this embodiment, a thin film transistor 14 made of amorphous silicon is used as an active element, and the size of one unit pixel is 15 in the vertical direction.
The width was 0 μm and the width was 100 μm. The scanning electrode lines 15 and the signal electrode lines 16 are chromium (C) formed by a sputtering method.
r) was used and the line width was set to 10 μm. Silicon nitride (SiNx) was used for the gate insulating film. The pixel electrode 13 was formed by sputtering using ITO (indium tin oxide) which is a transparent electrode. Thus, the thin film transistor 1
The glass substrate on which 4 was formed in an array was used as the first substrate 17. In addition, a transparent electrode using ITO was formed on the second substrate 18 on the opposite side, color filters were further formed in an array by a dyeing method, and a protective layer using silica was provided on the upper surface thereof. An alignment film made of polyimide was applied on the first substrate 17. On the surface of the alignment film 9, 5 shown in Table 2 below.
A rubbing process was performed in the azimuth direction [degree] of each kind.

[0036]

[Table 2]

With the combination of the alignment film and the rubbing conditions at this time, the angle of the liquid crystal alignment on the substrate surface is approximately 1.
It was 5 °. The second substrate 18 was coated with an alignment film made of polyimide having a different structure from the first substrate 17 and subjected to the first alignment treatment in the same manner as the first substrate, but the rubbing directions are shown in Table 2. The azimuth angle direction [degree] shown was used.

The second substrate 18 that has been once rubbed
A positive resist was applied on the surface, and an area of 75 μm corresponding to half the vertical width of one pixel was masked and exposed to light to develop the resist in the exposed area. As shown in the azimuth angle direction [degrees] shown in Table 2, a rubbing treatment was performed in a direction different from the first rubbing direction by 180 °, and then the resist was peeled off. As a result, the angle of the liquid crystal alignment on the substrate surface was about 3.5 °. The two substrates were bonded together with an adhesive via a spacer made of silica particles, and five kinds of nematic liquid crystal materials having positive dielectric anisotropy and having a chiral pitch shown in Table 3 were injected. The chiral pitch of the liquid crystal material was changed by changing the amount of chiral molecules added.

[0039]

[Table 3]

Polarizing plates mainly made of polycarbonate were attached to both sides of the liquid crystal cell. In this example, when a voltage was applied, the alignment was divided into two parts within one pixel with the pixel central part as a boundary. FIG. 5 is a contour diagram showing the upper limit of the voltage in the liquid crystal display device of this embodiment in which the reverse twist alignment, which changes in the twist direction of the liquid crystal alignment, does not occur even when pressure or the like is applied from the outside. As shown in the figure, when the chiral pitch was short and the twist angle of the alignment between the upper and lower substrates was narrow, the voltage range in which the reverse twist alignment did not occur was wide, and the divided alignment was stable.

FIG. 6 is a contour map showing the contrast ratio secured in this liquid crystal display device under the condition that reverse twist alignment does not occur. As shown in FIG. 6, in the present embodiment, in order to secure the contrast ratio of 100 and to prevent the display disorder due to the reverse twist alignment at all, the chiral pitch is set to be shorter than 100 μm and the alignment between the upper and lower substrates is made smaller. It has been found that the twist angle needs to be greater than approximately 88 °. Further, as shown in the section of action, a chiral pitch shorter than 20 μm and a twist angle narrower than 80 ° or wider than 100 ° are not practical. Therefore, the practical chiral pitch in this example was 20 to 100 μm, and the twist angle was in the range of 88 ° to 100 °.

Next, as a second embodiment of the first invention,
An example in which the present invention is applied to the conventional liquid crystal display device shown in FIGS. 17 and 18 of a conventional liquid crystal display device having a plurality of regions in which the orientation directions of liquid crystal are different. In this example, the steps up to the application of the alignment film were performed in the same manner as in the first example, and the bonding between the substrates and the liquid crystal material used were also the same. A rubbing method was performed using two different alignment films on the same substrate, using different alignment treatments. Specifically, first, an alignment film made of polyimide having a rising angle from the substrate surface of about 1.5 ° was applied to both the first substrate 17 and the second substrate 18. On this alignment film, another polyimide alignment film having a rising angle from the substrate surface of about 3.5 ° was applied by a printing method using a print mask having a width of 75 μm which is half the vertical width of the pixel. Then the first
The substrate 17 was rubbed in the azimuth direction [degrees] shown in Table 2, and the second substrate 18 was rubbed in the azimuth direction [degrees] shown in the second rubbing direction in Table 2. Also in this example, when a voltage was applied, the orientation was divided into two parts within one pixel with the pixel central part as a boundary. Further, the contour map showing the contrast ratio secured under the condition that the reverse twist orientation does not occur in this liquid crystal display device is the same as that in FIG.

Further, as a third embodiment of the first invention,
An example in which the present invention is applied to a conventional liquid crystal display device shown in FIGS. 21 and 22 of a conventional liquid crystal display device having a plurality of regions in which liquid crystal orientation directions are different is shown. In this embodiment, only the shape of the transparent electrode on the second substrate 18 forming the color filter and the method of the orientation treatment are different from those in the first embodiment. Specifically, it carried out as follows. Second
The transparent electrode on the substrate 18 is wider than the pixel electrode 13 on the first substrate 17 by 5 μm on all sides. As a result, an electric field in the direction shown in FIG. 22 is generated between the upper and lower electrodes. Further, both substrates are coated with an alignment film made of polyimide, and the first substrate 17 has an azimuth direction [degree] shown in Table 2.
Then, the second substrate 18 was rubbed in the azimuth direction [degrees] shown in the second rubbing direction in Table 2. At this time, the rising angle from the substrate surface was 1.5 °. Also in this example, when a voltage was applied, the orientation was divided into two parts within one pixel with the pixel central part as a boundary. Further, the contour map showing the contrast ratio secured under the condition that the reverse twist orientation does not occur in this liquid crystal display device is the same as that in FIG.

Next, as a first embodiment of the second invention of the present invention, a conventional liquid crystal display device having a plurality of regions in which liquid crystal alignment directions are different from each other is shown in FIG. 19 and FIG. An example in which the present invention is applied to a liquid crystal display device will be shown. In this embodiment, the first substrate 17 is different from the first embodiment of the first invention.
Only the type of alignment film above was changed. Specifically, depending on the type of the alignment film and the rubbing condition, the rising angle of the liquid crystal alignment from the substrate surface of the first substrate 17 is 2.0 °, 1.0 °,
It was set to 0.5 ° and 0.0 °.

FIG. 7 shows the chiral pitch [μm] of the liquid crystal material and the twisting of the alignment between the upper and lower substrates when the rising angle of the first substrate 17 on the substrate surface is 1.0 ° in this embodiment. The figure which shows the upper limit of the contrast ratio which can be ensured by the contour line under the condition that the reverse twist orientation does not occur at all when the angle [degree] is changed is shown. Compared with FIG. 6 showing the upper limit value of the contrast ratio that can be ensured when the rising angle on the substrate surface of the first embodiment of the first invention is 1.5 °, compared with FIG. 6, the range of the contrast ratio 100 is much larger. Has become wide. Especially, the twist angle between the upper and lower substrates is 90 °
At that time, a contrast ratio of 100 could be secured up to a chiral pitch of about 180 μm.

Further, FIG. 8 shows the chiral pitch [μm] of the liquid crystal material and the alignment between the upper and lower substrates when the rising angle of the first substrate 17 on the substrate surface is 0.5 ° in this embodiment. The figure which shows the upper limit of the contrast ratio which can be ensured by the contour line on the condition that reverse twist orientation does not occur at all when the twist angle [degree] is changed is shown. In this figure, the range of the contrast ratio is much wider than in FIG. 7. In addition, the rising angle on the substrate surface is 0.
When it was set to 0 °, the contrast ratio of 100 was always ensured when the twist angle was in the range of 80 ° to 100 ° and the chiral pitch was in the range of 20 μm to 200 μm. On the other hand, when the rising angle from the substrate surface was 2.0 °, there was almost no condition that the contrast ratio of 100 could be secured within this range. Similar results were obtained when the pretilt angle was changed by changing the firing conditions of the alignment film or the rubbing strength of the rubbing treatment.

Next, as a second embodiment of the second invention,
An example in which the present invention is applied to the conventional liquid crystal display device shown in FIGS. 17 and 18 of a conventional liquid crystal display device having a plurality of regions in which the orientation directions of liquid crystal are different. In this example, the steps up to the application of the alignment film were performed in the same manner as in the first example, and the bonding between the substrates and the liquid crystal material used were also the same. A different method was used only for the orientation treatment, and two kinds of combinations of the oblique vapor deposition method and the rubbing method were used. First, the first
Of silicon oxide (SiO) on the substrate 17 of 60 ° from the direction normal to the substrate surface, that is, at an angle of 30 ° from the substrate surface, the azimuth azimuth is 90 ° from the rubbing direction of the first substrate shown in Table 2. Deposition was performed at an angle forming a direction. Similarly, the second substrate 18 is made of silicon oxide (SiO) at an angle of 60 ° from the normal direction of the substrate surface, that is, at an angle of 30 ° from the substrate surface, and is the same as the second substrate shown in Table 2 in the azimuth direction. Deposition was performed at an angle of 90 ° with the second rubbing direction. By this method, the liquid crystal alignment is aligned in the second rubbing direction shown in Table 2 at an angle of 0.0 °. An alignment film made of polyimide having a rising angle of about 3.5 ° from the substrate surface is printed on the alignment film made of the oblique deposition film by using a printing mask having a width of 75 μm which is half the vertical width of the pixel. Applied. After that, the first substrate 17 was rubbed in the azimuth direction [degrees] shown in Table 2, and the second substrate 18 was rubbed in the azimuth direction [degrees] shown in the second second rubbing direction. Also in this embodiment, the twist angle is 80 as in the first embodiment when the rising angle on the substrate surface is 0.0 °.
The contrast ratio of 100 was always ensured in the range of 20 to 200 μm in the range of 20 to 200 μm in the range of 90 to 100 °.

In all of these examples, the characteristics of a wide field of view are not impaired even when pressure is applied from the outside of the substrate by the user, etc., and the phenomenon such as image sticking is not observed, and A characteristic with a contrast ratio of 100 or more was obtained. Further, the color reproducibility of the display was good because the dependence on the wavelength of the light used was small.

[0049]

By applying the present invention, it is possible to prevent the alignment in the twisting direction from becoming unstable in a liquid crystal display device having a plurality of regions having different alignment directions. As a result, the characteristics of a wide field of view are not impaired even when the applied voltage becomes high and pressure is applied by the user from the outside of the substrate, and the phenomenon such as burn-in is not observed. In addition, by using in the range as shown in the embodiment, it is possible to always secure a practically sufficient contrast ratio. As a result, it is possible to easily obtain a liquid crystal display device having a wide field of view, high contrast, good color reproducibility, and no problem such as burn-in.

[Brief description of drawings]

FIG. 1 is a perspective view of a liquid crystal display device of a first invention.

FIG. 2 is a perspective view of a liquid crystal display device of a second invention.

FIG. 3 is a perspective view showing a first embodiment of the first invention.

FIG. 4 is a plan view showing a thin film transistor array in a first embodiment of the first invention.

FIG. 5 shows the reverse twist alignment when the chiral pitch [μm] of the liquid crystal material and the twist angle [degree] of the alignment between the upper and lower substrates are changed in the first embodiment of the first invention. It is the figure which showed the upper limit [V] of the voltage range which did not occur by the contour line.

FIG. 6 shows the reverse twist alignment when the chiral pitch [μm] of the liquid crystal material and the twist angle [degree] of the alignment between the upper and lower substrates are changed in the first embodiment of the first invention. It is the figure which showed the upper limit of the contrast ratio which can be ensured on the condition that it does not occur with the contour line.

FIG. 7 shows the chiral pitch [μm] of the liquid crystal material and the twist of the alignment between the upper and lower substrates when the rising angle on the surface of one substrate is 1.0 ° in the first embodiment of the second invention. FIG. 8 is a diagram showing contour lines showing the upper limit value of the contrast ratio that can be ensured under the condition that reverse twist alignment does not occur at all when the tilt angle [degree] is changed.

FIG. 8 is a view showing the chiral pitch [μm] of the liquid crystal material and the twisting of the alignment between the upper and lower substrates when the rising angle on the surface of one substrate is 0.5 ° in the first embodiment of the second invention. FIG. 8 is a diagram showing contour lines showing the upper limit value of the contrast ratio that can be ensured under the condition that reverse twist alignment does not occur at all when the tilt angle [degree] is changed.

FIG. 9 is a schematic diagram of liquid crystal alignment for explaining a twist angle (also referred to as a twist angle) of liquid crystal alignment between upper and lower substrates in order to explain the operation of the present invention.

FIG. 10 is a schematic diagram of liquid crystal alignment for explaining a spontaneous twisting force (also called a chiral pitch) of a liquid crystal material in order to explain the operation of the present invention.

FIG. 11 is a view showing a condition of FIG. 25 and a normal twist structure with a π-type pretilt and a reverse twist structure with a normal pretilt when only the lower pretilt angle is changed to explain the operation of the present invention. It is a figure which shows the example of calculation of the change with the applied voltage of the energy of.

FIG. 12 is a plan view of a conventional liquid crystal display device in which a region is divided for the purpose of wide field of view.

FIG. 13 is a cross-sectional view taken along line aa ′ in FIG.

FIG. 14 is a schematic diagram of a rubbing direction of a liquid crystal display device in which a conventional area is divided.

15 is a plan perspective view showing a rubbing direction and a twisting direction of liquid crystal alignment between the upper and lower substrates when FIG. 14 is observed from a direction in which an azimuth angle is different by 45 °.

16 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along the line bb 'in FIG.

FIG. 17 is a transparent plan view showing a rubbing direction and a twisting direction of liquid crystal alignment between upper and lower substrates of a liquid crystal display device in which a conventional region is divided.

FIG. 18 is a cross-sectional view taken along line cc ′ in FIG. 17, showing the rising direction of the alignment control force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field.

FIG. 19 is a plan perspective view showing a rubbing direction and a twisting direction of liquid crystal alignment between upper and lower substrates of a liquid crystal display device in which a conventional region is divided.

20 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along line dd 'in FIG.

FIG. 21 is a transparent plan view showing a rubbing direction and a twisting direction of liquid crystal alignment between upper and lower substrates of a liquid crystal display device in which a conventional region is divided.

22 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along line ee 'in FIG.

23 is a plan perspective view showing a rubbing direction and a twisting direction of liquid crystal alignment between upper and lower substrates when liquid crystal orientations in which twisting directions of liquid crystals are different between the upper and lower substrates in a region I of FIG. .

FIG. 24 is a cross-sectional view showing the rising direction of the alignment regulating force on the substrate surface and the rising direction of the liquid crystal alignment between the upper and lower substrates due to the electric field, taken along line ff ′ in FIG. 23.

FIG. 25 is a diagram showing a calculation example of a change in energy with an applied voltage in a normal twist configuration with a π-type pretilt and a reverse twist configuration with a normal pretilt.

FIG. 26 is a diagram showing the results of measuring the voltage dependence of the contrast ratio by changing the conditions of the twist angle of the liquid crystal alignment between the upper and lower substrates and the conditions of the spontaneous twisting force of the liquid crystal.

FIG. 27 shows the results of measuring the transmittance of light of each wavelength of red (620 nm), green (550 nm), and blue (460 nm) when no voltage is applied when the twist of the liquid crystal between the upper and lower substrates is changed. It is a figure.

[Explanation of symbols]

1 Twisting angle of liquid crystal alignment between upper and lower substrates in the range of 80 ° to 100 ° 2 Spontaneous twisting force of liquid crystal material in the range of 20 μm to 200 μm On the substrate surface in the range of 30 ° to 1.5 ° Rising angle of the alignment regulating force from the substrate surface 4 The rising angle of the liquid crystal alignment on the substrate surface higher than 3 5 Liquid crystal substance (liquid crystal layer) 6 The rising direction of the liquid crystal alignment by the electric field 7 Divided region 1 8 Divided Region 2 9,10 Alignment film 11 Pixel 13 Pixel electrode 14 Thin film transistor 15 Scan electrode line 16 Signal electrode line 17 First substrate 18 Second substrate 19,20 Transparent electrode 21,22 Glass substrate 23 Strip spacer 25 First substrate Rubbing direction at 26 26 rubbing direction at second substrate 27 twist angle of liquid crystal alignment between upper and lower substrates 28 chiral pitch aa ', bb', c- c ', d-d', ee ',
f-f 'Sectional cutting line

Claims (2)

[Claims] 1. A liquid crystal display device comprising a pair of supporting substrates and a liquid crystal material sandwiched between the supporting substrates and having a plurality of regions having different liquid crystal alignment directions. A liquid crystal display device characterized by having a twist angle of liquid crystal alignment between the two and having a spontaneous twisting force of the liquid crystal material in the range of 20 μm to 200 μm. 2. A liquid crystal display device, comprising a pair of supporting substrates and a liquid crystal material sandwiched between the supporting substrates, and a plurality of regions having different alignment directions of liquid crystals between the supporting substrates. The upper and lower substrates are in the range of 80 ° to 100 °. The twist angle of the liquid crystal orientation between the two, the spontaneous twisting force of the liquid crystal material in the range of 20 μm to 200 μm, and the range of 0 ° to 1.5 °. A liquid crystal display device, wherein at least one region of at least one of the substrates has a rising angle from the substrate surface of an alignment control force on the substrate surface.