JP2001027759A - Liquid crystal display - Google Patents

Abstract

(57) [Problem] To provide a liquid crystal display device which can perform TFT driving even when a vertical alignment type liquid crystal material is used. A first substrate on which a first electrode is formed and a second substrate on which a second electrode is formed.
An alignment control means 28 and 50 formed on the first substrate and / or the second substrate; an alignment film 30 and 52 formed on the first substrate and / or the second substrate; Substrate and second
In the liquid crystal display device having the liquid crystal 60 having a negative dielectric anisotropy sealed between the substrate and the substrate, the alignment film includes an acid anhydride containing an alicyclic group and a component for vertically aligning the liquid crystal molecules. A polyamic acid containing a first diamine in a side chain and a second diamine having a higher dielectric constant than the first diamine.

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 using a vertically aligned liquid crystal material.

[0002]

2. Description of the Related Art Conventionally, as a liquid crystal display (LCD) using an active matrix, a liquid crystal molecule having a positive dielectric anisotropy is horizontally arranged on a substrate surface and between an opposing substrate. A TN (Twisted Nematic) mode liquid crystal display device, which is oriented so as to be twisted by 90 ° at, is widely used. However, the TN mode liquid crystal display device has a problem of poor visual characteristics, and various studies have been made to improve the visual characteristics.

In recent years, as a method replacing the TN mode, a liquid crystal material having a negative dielectric anisotropy is vertically aligned, and a projection or a slit provided on the substrate surface is used to tilt a liquid crystal molecule when a voltage is applied. MVA (Multi-
Domain Vertical Alignment) type liquid crystal display devices have been proposed.

A proposed MVA type liquid crystal display device will be described with reference to FIGS. 21 and 22. FIG. 21 is a conceptual diagram showing a proposed MVA liquid crystal display device. FIG. 22 is a conceptual diagram showing the orientation direction of liquid crystal molecules in the proposed MVA liquid crystal display device.

In an MVA type liquid crystal display device, a vertically aligned liquid crystal material is sealed between two glass substrates. On one glass substrate side, a pixel electrode 126 connected to a TFT (not shown) is formed, and on the other glass substrate side, a counter electrode 148 is formed. Then, projections 128 and 150 are formed on the pixel electrode 126 and the counter electrode 148, respectively.

When the TFT is in the OFF state, FIG.
As shown in (a), the liquid crystal molecules 162 are oriented in a direction perpendicular to the glass substrate.

[0007] When the TFT is turned on, an electric field is applied to the liquid crystal, and the tilt direction of the liquid crystal molecules is regulated by the state of formation of the projections. As a result, the liquid crystal molecules are aligned in a plurality of directions within one pixel, as shown in FIG. For example, as shown in FIG.
8, 150 are formed, the liquid crystal molecules are A,
It is oriented in the directions of B, C, and D, respectively. As described above, in the MVA liquid crystal display device, when the TFT is turned on, the liquid crystal molecules are aligned in a plurality of directions, so that good visual characteristics can be obtained.

[0008]

SUMMARY OF THE INVENTION However, MVA
The liquid crystal display device of the type uses a vertical alignment type liquid crystal material which is completely different from the liquid crystal material used in the conventional TN mode liquid crystal display device, and the TFT drive is performed using such a liquid crystal material. A high quality vertical alignment film that can be made has not been realized yet. For this reason, it has been difficult to provide a highly reliable MVA liquid crystal display device.

An object of the present invention is to provide a liquid crystal display device capable of driving a TFT even when a vertical alignment type liquid crystal material is used.

[0010]

The object of the present invention is to provide a first substrate on which a first electrode is formed, a second substrate on which a second electrode opposed to the first electrode is formed, and An alignment control unit formed on the first substrate and / or the second substrate; an alignment film formed on the first substrate and / or the second substrate; A liquid crystal display device having a liquid crystal having a negative dielectric anisotropy sealed between the substrate and the second substrate, wherein the alignment film includes an acid anhydride containing an alicyclic group and a component for vertically aligning the liquid crystal molecules. And a second diamine having a dielectric constant higher than that of the first diamine. Thus, a high-quality alignment film can be formed, so that an MVA liquid crystal display device with high reliability and high luminance can be provided.

In the above liquid crystal display device, it is preferable that the acid anhydride is composed of only an alicyclic group.

Further, in the above liquid crystal display device, it is preferable that the alignment film contains an organic compound which undergoes a thermal crosslinking reaction with a carboxylic acid group.

Further, in the above liquid crystal display device, it is preferable that the alignment film contains the first diamine in an amount of about 10% to 30%.

In the above liquid crystal display device, it is preferable that the alignment control means is a combination of a projection and / or a slit.

Further, in the above liquid crystal display device, the alignment control means is a first alignment control means which is a projection formed on the first substrate, and a projection formed on the second substrate. The first orientation control means and the second orientation control means have a height of about 1 to 1.5 μm, and the first orientation control means and the orientation control means have a height of about 1 to 1.5 μm. The width of the means is preferably about 5 to 10 μm, and the gap between the first orientation control means and the second orientation control means is preferably about 10 to 30 μm.

Further, in the above liquid crystal display device, the alignment control means is a first alignment control means which is a slit formed in the first electrode, and a slit formed in the second electrode. The first orientation control means and the second orientation control means have a width of about 10 to 20 μm, and the first orientation control means and the second orientation control means have a width of about 10 to 20 μm. The gap with the means is about 10-30μ
m is desirable.

Further, in the above liquid crystal display device, the alignment control means includes a first alignment control means which is a projection formed on the first electrode, and a slit formed on the second electrode. A second orientation control means, wherein the height of the first orientation control means is about 1 to 1.5 μm, the width of the first orientation control means is about 5 to 10 μm, The width of the second orientation control means is about 10 to 20 μm.
m, and the gap between the first alignment control means and the second alignment control means is preferably about 10 to 30 μm.

In the above liquid crystal display device, the alignment control means may include a first alignment control means formed on the first substrate and a second alignment control means formed on the second substrate. Wherein the gap between the first alignment control means and the second alignment control means is about 20 to 30 μm, and the alignment film contains about 30% of the first diamine. desirable.

In the above liquid crystal display device, the alignment control means may include a first alignment control means formed on the first substrate and a second alignment control means formed on the second substrate. Wherein the gap between the first alignment control means and the second alignment control means is about 10 to 20 μm, and the alignment film contains about 10% of the first diamine. desirable.

Further, in the above liquid crystal display device, the alignment control means has a projection formed on the first substrate and / or the second substrate, and the height of the projection is about 0. It is preferable that the thickness of the first diamine is about 30% in the alignment film.

In the above liquid crystal display device, the alignment control means has a protrusion formed on the first substrate and / or the second substrate, and the height of the protrusion is about 1. It is preferable that the thickness is 5 μm or more, and the alignment film contains about 30% of the first diamine.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an MVA type liquid crystal display device will be described with reference to FIGS. FIG.
It is a top view which shows the liquid crystal display device of an MVA system. FIG.
FIG. 2 is a sectional view taken along line AA ′ of FIG. In addition, the present invention
The present invention can be widely applied not only to the MVA type liquid crystal display device as shown in FIG. 1 but also to a liquid crystal display device using a vertical alignment type liquid crystal material.

As shown in FIG. 1 and FIG.
On CS, a CS electrode (auxiliary capacitance electrode) 12 for forming an auxiliary capacitance and a gate bus line 14 including a gate electrode of the TFT are formed. On the glass substrate 10 on which the CS electrode 12 and the gate bus line 14 are formed,
A gate insulating film 16 is formed. Gate insulating film 16
An active layer 18 forming a channel region of the TFT is formed thereon. On the gate insulating film 16 on which the active layer 18 is formed, a source electrode 20 connected to one side of the active layer 18 and a drain bus line 22 including a drain electrode connected to the other side of the active layer 18 are formed. Are formed.

Source electrode 20 and drain bus line 2
An insulating film 24 is formed on the gate insulating film 16 on which 2 is formed. On the insulating film 24, a pixel electrode 26 connected to the source electrode 20 is formed. Insulating film 24
On the pixel electrode 26, a projection 28 made of a light-transmitting material and provided in a zigzag shape is formed. On the insulating film 24 on which the pixel electrodes 26 and the protrusions 28 are formed, an alignment film 30 for vertically aligning liquid crystal molecules is formed. The alignment direction of the liquid crystal molecules may be controlled by forming a slit in the pixel electrode 26 instead of the projection 28.

On the other hand, on the glass substrate 40, a black matrix layer 42 is formed. On the glass substrate 40 on which the black matrix layer 42 is formed, a coloring (CF) resin layer 46 forming a color filter is formed. The counter electrode 48 is formed on the colored resin layer 46. On the opposing electrode 48, a projection 50 made of a light-transmitting material and formed to be bent in a zigzag manner at a half pitch from the projection 28 formed on the glass substrate 10 is formed. An alignment film 30 for aligning liquid crystal molecules in a vertical direction is formed on the counter electrode 48 on which the protrusion 50 is formed. Note that, instead of the protrusion 50, a slit may be formed in the counter electrode 48 to control the alignment direction of the liquid crystal molecules.

The glass substrate (TFT) thus configured
The substrate 10 and the glass substrate (CF substrate) 40 are arranged to face each other so that the alignment films 30 and 52 face each other, and a negative liquid crystal material 60 having a negative dielectric anisotropy is disposed between these substrates. Is sealed. In addition, the glass substrate 1
A spacer (not shown) for separating the substrates 10 and 40 at a predetermined distance is sandwiched between 0 and 40, thereby setting the thickness of the cell. Thus, an MVA liquid crystal display device is configured.

Next, a liquid crystal display according to an embodiment of the present invention will be described.

The liquid crystal display according to the present embodiment has one of the main features in that the TFT can be driven by using a high-quality vertical alignment film.

Conventionally, a high-quality vertical alignment film has not been proposed, and it is difficult to drive a TFT using a vertical alignment type liquid crystal material.
It has been difficult to provide a VA liquid crystal display device. The inventors of the present application have conducted intensive studies to provide a highly reliable MVA liquid crystal display device, and as a result, have found that a high-quality alignment film can be formed by using the following alignment film material.

The present inventors have conceived that it is important to use a polyamic acid having an alicyclic group as an acid anhydride as an alignment film material in order to form a high quality vertical alignment film.

That is, aromatics are widely used as acid anhydrides. However, aromatics have a bias of electrons, are liable to undergo oxidation-reduction reactions, and are susceptible to the influence of purification purity during synthesis. Therefore, when only an aromatic is used as the acid anhydride, a high-quality alignment film cannot be formed, and it is difficult to improve the electrical characteristics.

Therefore, in this embodiment, in order to improve the electrical characteristics of the liquid crystal display device, an alicyclic group is introduced into the alignment film material as an acid anhydride. In addition, as an acid anhydride, only an alicyclic group may be used, or an alicyclic group and an aromatic group may be used.

Further, the inventors of the present application have found that it is important to use, as the diamine contained in the alignment film material, a diamine having an alkyl chain in a side chain and a high dielectric constant diamine having no alkyl chain. I arrived.

The alkyl chain is a component that greatly contributes to the alignment of liquid crystal molecules. However, a diamine having an alkyl chain in the main chain cannot contribute to a decrease in surface tension and cannot vertically align liquid crystals. Therefore, in order to vertically align liquid crystal molecules, it is considered necessary to use a diamine having an alkyl chain in a side chain, that is, a side-chain type diamine.

However, the side chain type diamine is a diamine having an extremely low dielectric constant. For this reason, when a side chain type diamine is introduced into the alignment film material, the difference between the dielectric constant of the liquid crystal material and the dielectric constant of the alignment film increases, and the residual DC value of the liquid crystal display device increases accordingly. Would. When the residual DC value of the liquid crystal display device increases, burn-in tends to occur in the liquid crystal display device.

Therefore, in this embodiment, a high-dielectric-constant diamine having no alkyl chain is used in addition to the side-chain type diamine. Thus, the difference between the dielectric constant of the liquid crystal material and the dielectric constant of the alignment film can be reduced, so that the electrical characteristics of the liquid crystal display device can be improved.

In the MVA type liquid crystal display device, the alignment regulating force for the liquid crystal molecules differs depending on the arrangement conditions of the projections and slits. That is, the direction of tilt of the liquid crystal molecules and the propagation force of the tilt of the liquid crystal molecules when a voltage is applied to the liquid crystal differ depending on the arrangement conditions of the protrusions and slits. In order to improve the brightness of the liquid crystal display device, it is desirable to appropriately set the vertical alignment of the alignment film in accordance with the alignment regulating force of the projection or the slit. Therefore, introducing a high-dielectric-constant diamine having no alkyl chain into the alignment film material is important in setting the vertical alignment of the alignment film to an appropriate value.

When the above materials are used, it is difficult to prepare the alignment film material in a polyimide state. That is, in order to apply the alignment film on the substrate, it is necessary to dissolve the alignment film material in a solvent. However, when the alignment film material is prepared in a polyimide state, the components of the alignment film material, the combination ratio, etc. Is restricted. In addition, polyimide has the disadvantage that image sticking tends to occur and the wettability is not good. Further, it is difficult to uniformly apply polyimide in an MVA type liquid crystal display device having projections and slits.

Therefore, in this embodiment, a polyamic acid material is used as the alignment film material. Thereby, the restrictions such as the components of the alignment film material and the combination ratio can be relaxed, the screen burn-in can be suppressed, and the wettability can be improved. In addition, by using a polyamic acid material as an alignment film material, repelling can be improved and the alignment film can be uniformly applied.

However, since the material system of the polyamic acid contains a carboxylic acid group, the electrical characteristics are likely to deteriorate.

Therefore, in this embodiment, a thermosetting organic compound which reacts with carboxylic acid is added to the alignment film material. If a thermosetting organic compound that reacts with a carboxylic acid is added to the alignment film material, the thermosetting organic compound reacts with the carboxylic acid, so that deterioration of electrical characteristics can be suppressed.
The strength of the alignment film can also be improved.

The molecular weight of the polymer contained in the alignment film material is not always the same, and a polymer having a small molecular weight is also included in the alignment film material. A polymer having a small molecular weight easily dissolves into a liquid crystal material, and causes a deterioration in electrical characteristics of a liquid crystal display device.

Therefore, in this embodiment, an alignment film material made of a polymer having a large molecular weight is used. If an alignment film material made of a polymer having a large molecular weight is used, a polymer having a small molecular weight that is dissolved in a liquid crystal material can be relatively reduced.

In the MVA type liquid crystal display device, by appropriately setting the shapes of the projections and slits and the electric field distribution, the liquid crystal molecules are oriented in a desired direction, thereby performing switching. For this reason, the alignment control force applied to the liquid crystal molecules when a voltage is applied varies depending on parameters such as the height of the protrusion, the width of the protrusion and the slit, and the gap between the protrusion and the slit.

For example, when the alignment control force of the projections and slits is weak and the vertical alignment control force of the alignment film is also weak, the orientation direction of the liquid crystal molecules is easily disturbed when a voltage is applied, so that the brightness tends to decrease. Therefore, when the alignment regulating force of the projection or the slit is weak, it is desirable to increase the vertical alignment regulating force of the alignment film.

On the other hand, when the alignment regulating force of the projections and the slits is strong and the vertical alignment regulating force of the alignment film is also strong, the liquid crystal molecules are unlikely to be tilted even when a voltage is applied, and therefore, the brightness tends to be reduced. Therefore, when the alignment regulating force of the projection or the slit is strong, it is necessary to reduce the vertical alignment regulating force of the alignment film.

Therefore, in this embodiment, the vertical alignment regulating force of the alignment film is optimized according to parameters such as the height of the protrusion, the width of the protrusion and the slit, and the gap between the protrusion and the slit, and the liquid crystal having good display characteristics is obtained. A display device is provided.

As described above, according to the present embodiment, a high-quality vertical alignment film is used, and the vertical alignment regulating force is adjusted according to parameters such as the height of the projection, the width of the projection and the slit, and the gap between the projection and the slit. Is optimized, it is possible to provide an MVA type liquid crystal display device with high reliability and high luminance.

[Modified Embodiment] The present invention is not limited to the above-described embodiment, and various modifications are possible.

For example, in the above embodiment, a liquid crystal display device having projections formed on each substrate has been described as an example. However, a projection may be formed on one substrate and a slit may be formed on an electrode of the other substrate. Good. This makes it possible to manufacture the liquid crystal display device by a simple manufacturing process.

In the above embodiment, an MVA liquid crystal display device has been described as an example. However, the present invention is applicable not only to an MVA liquid crystal display device but also to any liquid crystal display device using a vertically aligned liquid crystal material. Can be.

[0052]

[Example 1] A two-divided MVA cell having a projection formed on each substrate was manufactured.

As a material of the projection, a resist LC-200 manufactured by Shipley Co., Ltd. was used, and as a liquid crystal material, a liquid crystal material MJ-95785 manufactured by Merck was used. MVA
The thickness of the evaluation cell was 3.5 μm.

As an alignment film material, a polyamic acid material containing an acid anhydride composed of aromatic and alicyclic groups and a monomer of a side chain type diamine was used.

The electrical characteristics of the MVA cell were measured by changing the introduction ratio of the alicyclic group in the acid anhydride.

As the aromatic used as the acid anhydride,

[0057]

Embedded image

The aromatic compound represented by the following formula was used.

The alicyclic group used as the acid anhydride includes

[0060]

Embedded image

The alicyclic group represented by the following formula was used.

As the side chain type diamine,

[0063]

Embedded image

(Wherein R ¹ is an alkyl group).

As specific examples of the side chain type diamine,
For example,

[0066]

Embedded image

A side-chain type diamine represented by

[0068]

Embedded image

A side chain type diamine represented by

[0070]

Embedded image

A side chain type diamine represented by

[0072]

Embedded image

There is a side chain type diamine represented by the following formula:

FIG. 3 shows the measurement results of the electrical characteristics of the MVA cell.
And FIG. FIG. 3 is a graph showing the relationship between the introduction ratio of alicyclic groups in the acid anhydride and the voltage holding ratio. The horizontal axis indicates the introduction ratio of alicyclic groups in the acid anhydride,
The vertical axis indicates the voltage holding ratio of the MVA cell. In addition,
The measurement condition of the voltage holding ratio was an ambient temperature of 70 ° C. FIG.
Is a graph showing the relationship between the introduction ratio of alicyclic groups in the acid anhydride and the ion density in the liquid crystal. The horizontal axis indicates the introduction ratio of alicyclic groups in the acid anhydride, and the vertical axis indicates the ion density in the liquid crystal. The measurement conditions of the ion density were set to an ambient temperature of 50 ° C.

As shown in FIG. 3, the voltage holding ratio was improved as the introduction ratio of the alicyclic group in the acid anhydride was increased. In particular, the introduction ratio of the alicyclic group in the acid anhydride is from 0 to 5
In the range of 0%, the improvement in the voltage holding ratio with respect to the increase in the alicyclic group introduction ratio was remarkable.

As shown in FIG. 4, the ion density is
It decreased as the introduction ratio of alicyclic groups in the acid anhydride increased. In particular, when the introduction ratio of the alicyclic group in the acid anhydride was in the range of 0 to 50%, the decrease of the ion density with the increase of the alicyclic group was remarkable. The same tendency was observed when an alicyclic group having a molecular structure different from that described above was introduced.

[Comparative Example 1] An MVA using an alignment film made of a polyimide material RN-783 manufactured by Nissan Chemical Industries, Ltd.
A cell was prepared.

The electrical characteristics of this MVA cell were measured. Table 1 is a table showing the measurement results of the electrical characteristics of the MVA cell. The conditions for measuring the voltage holding ratio and ion density are as follows:
Same as Example 1. The measurement condition of the residual DC value was an ambient temperature of 60 ° C. The residual DC value was measured using a flicker elimination method, and the voltage was measured 10 minutes after the application of the DC voltage of 3 V.

[0079]

[Table 1]

As shown in Table 1, the voltage holding ratio was 95.7.
%, The ion density in the liquid crystal was as high as 300 pC / cm ² , and the residual DC value was as high as 2.85 V.

[Comparative Examples 2 to 4] MVA cells having different materials from Comparative Example 1 were produced.

As an alignment film material, a polyamic acid material containing an aromatic acid anhydride and a side chain type diamine monomer was used. In Comparative Examples 2 to 4, the substituents of the side chain type diamine shown in Example 1 were appropriately substituted.

The electrical characteristics of such an MVA cell were measured. Table 1 shows the measurement results of the electrical characteristics of the MVA cell.

In each of Comparative Examples 2 to 4, the voltage holding ratio was low and the ion density in the liquid crystal was high.

Comparative Example 5 An MVA cell was manufactured using an alignment film different from that of Comparative Example 1.

As an alignment film material, a polyamic acid material containing an acid anhydride composed of aromatic and alicyclic groups and a monomer of a side chain type diamine was used.

The electrical characteristics of the MVA cell were measured by changing the introduction ratio of the alicyclic group in the acid anhydride.

As the aromatic used as the acid anhydride,

[0089]

Embedded image

An aromatic compound represented by the following formula was used. This aromatic is different from the aromatic used in Example 1 in having two benzene rings.

FIG. 3 shows the measurement results of the electrical characteristics of the MVA cell.
And FIG. The measurement condition of the voltage holding ratio was set to the ambient temperature of 70 ° C. as in Example 1, and the measurement condition of the ion density was set to the ambient temperature of 50 ° C. as in Example 1.

As shown in FIGS. 3 and 4, in each case, the electrical characteristics were inferior to those of Example 1. In particular, when the introduction ratio of alicyclic groups in the acid anhydride was small, the results were lower than those of Example 1. The electrical characteristics were significantly poor. The same tendency was observed when an alicyclic group having a molecular structure different from that of the alicyclic group shown in Example 1 was introduced.

Example 2 An MVA cell was manufactured in the same manner as in Example 1.

As the alignment film material, a material obtained by adding a thermosetting organic compound to a polyamic acid material containing an acid anhydride composed of an aromatic or alicyclic group and a monomer of a side chain type diamine was used.

The introduction ratio of the alicyclic group in the acid anhydride is 50.
%.

As the thermosetting organic compound,

[0097]

Embedded image

(Wherein R ² , R ³ and R ⁴ are the same or different organic groups, and at least one of these is an organic group containing a hetero atom, an aryl group, an alkylene group or an alkynyl group) Represents an acid, or R ² , R ³ and R ⁴
Represents a monocyclic or polycyclic N-containing heterocyclic ring together with the N atom to which they are bonded).

The hardness of the alignment film of the MVA cell was measured by changing the amount of the thermosetting organic compound added to the alignment film material. Table 2 shows the relationship between the amount of the thermosetting organic compound added to the alignment film material and the hardness of the alignment film. Table 2 shows the hardness of the alignment film as the pencil hardness. In Table 2, B indicates that the hardness of the alignment film is substantially the same as the hardness of the pencil of B, and HB indicates that the hardness of the alignment film is substantially the same as the hardness of the pencil of HB. 2H indicates that the hardness of the alignment film is almost the same as that of the pencil of 2H.

[0100]

[Table 2]

As shown in Table 2, as the amount of the thermosetting organic compound added increased, the hardness of the alignment film also increased.

Next, the amount of the thermosetting organic compound added to the alignment film material was changed, and the electrical characteristics of the MVA cell were measured. The measurement results of the electrical characteristics of the MVA cell are shown in FIGS. FIG. 5 is a graph showing the relationship between the amount of the thermosetting organic compound added and the voltage holding ratio. FIG. 6 is a graph showing the relationship between the amount of the thermosetting organic compound added and the ion density. FIG. 7 is a graph showing the relationship between the amount of the thermosetting organic compound added and the residual DC value.

As can be seen from FIG. 5, the voltage holding ratio did not change even when the addition amount of the thermosetting organic compound was changed.

Further, as can be seen from FIG. 6, the ion density decreased as the amount of the thermosetting organic compound added increased. However, the addition amount of the thermosetting organic compound is about 20 to 25.
%, The ion density was hard to decrease even when the addition amount of the thermosetting organic compound was increased.

Further, as can be seen from FIG. 7, the residual DC value decreased as the amount of the thermosetting organic compound added increased. However, the addition amount of the thermosetting organic compound is about 20 to 25.
%, The residual DC value was hard to decrease even when the amount of the thermosetting organic compound added was increased.

Example 3 As a material for an alignment film, a thermosetting organic compound was added to a polyamic acid material containing an acid anhydride composed of an aromatic or alicyclic group and a monomer of a side-chain type diamine. High dielectric constant diamines without chains were introduced.

The ratio of aromatic to alicyclic in the acid anhydride was 1: 1 and the amount of the thermosetting organic compound added to the alignment film material was 25%.

Before the introduction of the high dielectric constant diamine having no alkyl chain, the relative dielectric constant of the alignment film was about 3, but after the introduction of the high dielectric constant diamine, the relative dielectric constant of the alignment film became It improved to about 4.6.

Further, as the liquid crystal material, Merck's M
J-96213 was used.

The electric characteristics of the MVA cell were measured by changing the amount of the high dielectric constant diamine added to the alignment film material.

FIG. 8 shows the relationship between the added amount of the high dielectric constant diamine and the residual DC value. The horizontal axis in FIG. 8 indicates the amount of the high-dielectric-constant diamine added to the entire diamine contained in the alignment film material. In addition, M used when measuring the residual DC value was used.
The VA cell is the same as Example 1 except for the alignment film material and the liquid crystal material.

FIG. 9 shows the relationship between the added amount of the high dielectric constant diamine and the voltage holding ratio. FIG. 10 shows the relationship between the amount of high-diamine added and the ion density. The horizontal axis in FIGS. 9 and 10 indicates the amount of the high dielectric constant diamine added to the entire diamine contained in the alignment film material. The MVA cell used for measuring the voltage holding ratio and the ion density was manufactured in the same manner as the MVA cell except that no protrusions were formed, rubbing was not performed, the alignment film material was different, and the liquid crystal material was different. Same as Example 1.

As shown in FIG. 8, the residual DC value sharply decreased with an increase in the amount of the high dielectric constant diamine.
In particular, when the added amount of the high dielectric constant diamine was 35% or more, the residual DC value was extremely low.

On the other hand, as shown in FIG.
It decreased with an increase in the amount of the high dielectric constant diamine added. Further, as shown in FIG. 10, the ion density increases with an increase in the amount of the high dielectric constant diamine added. In particular, when the amount of the high-dielectric-constant diamine added was 75% or more, the ion density rapidly increased.

Therefore, in consideration of these characteristics, it is considered that the amount of the high-dielectric-constant diamine is preferably about 35% to 75%. As described above, the amount of addition shown in FIGS. 8 to 10 indicates the ratio of the high-dielectric-constant diamine to the entire diamine contained in the alignment film material. Therefore, when converted as an addition amount to the whole alignment film material, an appropriate value of the addition amount of the high dielectric constant diamine is about 10 to 30% with respect to the whole alignment film material.

[Examples 4 and 5] The solvent was added to the alignment film material to change the viscosity, and the change in the electrical characteristics of the MVA cell was measured.

In Example 4, when JALS-684 manufactured by JSR Corporation was used as the alignment film material, Example 5
JALS-688 manufactured by JSR Corporation as an alignment film material
This is the case where is used.

JALS-684 is a polyamic acid having an aromatic group and an alicyclic group as an acid anhydride, and the ratio of the aromatic group to the alicyclic group is 1: 1. JALS-688 is
It is a polyamic acid having one kind of alicyclic group as an acid anhydride.

An ordinary non-rubbing cell was used as the MVA cell, and MJ-9 manufactured by Merck was used as a liquid crystal material.
61213 was used.

FIG. 11 shows how the voltage holding ratio changes when the viscosity of the alignment film material is changed. FIG. 11 is a graph showing a change in the voltage holding ratio with respect to a change in the viscosity of the alignment film material.

As shown in FIG. 11, no particular change was observed in the voltage holding ratio in the range where the viscosity of the alignment film material was 400 cp or more, but in the range where the viscosity of the alignment film material was 400 cp or less, the voltage holding ratio was low. The rate dropped sharply.

In Example 5, even when the viscosity was low, the decrease in the voltage holding ratio was small compared to Example 4.

From this, it is considered that the decrease in the voltage holding ratio is smaller when only an alicyclic is used as the acid anhydride as in Example 5.

Example 6 An MVA cell having projections formed as shown in FIG. 12 was manufactured. FIG. 12 is a cross-sectional view of the MVA cell.

As an alignment film material, JALS-684 manufactured by JSR Corporation was used. JALS-684 is an alignment film material containing about 10% of a side chain type diamine that functions as a vertical alignment component.

Further, the thickness of the MVA cell was 3.5 μm, the width of the projection was 10 μm, and the width of the gap between adjacent projections was 20 μm.

By changing the heights h1 and h2 of the projections as appropriate,
The transmittance of the VA cell was measured. FIG. 13 is a graph showing a change in the transmittance with respect to a change in the height of the protrusion. In addition,
The applied voltage when measuring the transmittance was 5 V.

As can be seen from FIG. 13, the transmittance was maximized when the height of the protrusion was set to about 1.0 μm or more.

Next, FIGS. 14 and 15 show the alignment state when the height of the projection is changed. FIG. 14 and FIG.
It is the photograph which observed the MVA cell from the upper surface. In FIGS. 14 and 15, the black color observed in a stripe pattern is as follows.
This is the part where the projection is formed. 14A shows a case where the height of the protrusion is 1.1 μm, FIG. 14B shows a case where the height of the protrusion is 0.67 μm, and FIG. 14C shows a case where the height of the protrusion is 0.52 μm. FIG. 15 (a) shows that the height of the projection is 0.
In the case of 25 μm, FIG.
μm.

As can be seen from FIGS. 14 and 15, when the height of the protrusions is lower than about 1.0 μm, the alignment direction of the liquid crystal molecules is disturbed. However, when the height of the protrusions is about 0.5 μm or more, The alignment direction of the liquid crystal molecules was perpendicular to the extending direction of the projection.

However, when the height of the projection is reduced to about 0.5 μm or less, the alignment direction of the liquid crystal molecules starts to extend in the extending direction of the projection, and when the height of the projection is reduced to 0.25 μm,
The orientation direction of the liquid crystal was 45 ° with respect to the extending direction of the protrusion. It is considered that the reason why the height of the protrusion is 0.12 μm, which is higher than that of the protrusion when the height is 0.25 μm, is that the orientation direction of the liquid crystal molecules is in the extending direction of the protrusion.

Considering the above, the height of the projection is
It is considered desirable to set the thickness to at least 0.5 μm or more.

Next, an MVA cell was manufactured using JALS-2029-R2 manufactured by JSR Corporation as an alignment film material, and the alignment state was observed. JALS-2029-R2
Is an alignment film material containing about 30% of a side chain type diamine.

In this case, even if the height of the projection was reduced to 0.5 μm, no disturbance was caused in the alignment direction of the liquid crystal molecules.
However, when the height of the projection was reduced to 0.25 μm, the alignment state was almost the same as in the above-described case using JALS-684 as the liquid crystal material.

Example 7 An MVA cell having a projection on each substrate was manufactured using JALS-684 manufactured by JSR Corporation as an alignment film material. The cell thickness is 3.5
μm, the width of the projection was 10 μm, and the height of the projection was 1.5 μm.

The gap between adjacent protrusions was appropriately set, and the alignment state was observed 10 ms after the application of a DC voltage of 5 V. FIGS. 16 and 17 show the orientation state when the gap between adjacent protrusions is changed. 16 and 17 are photographs of the MVA cell observed from above. In FIGS. 16 and 17, black portions in a stripe shape are portions where protrusions are formed. FIG.
6A shows a case where the gap between adjacent projections is 6 μm, and FIG. 16B shows a case where the gap between adjacent projections is 15 μm.
17A shows the case where the gap between the adjacent projections is 30 μm, and FIG. 17B shows the case where the gap between the adjacent projections is 45 μm.

As shown in FIG. 16A, when the gap between adjacent projections is small, domains are formed so as to connect the projections. Such a domain
This is likely to occur when the gap between adjacent protrusions is reduced to 10 μm or less. Further, such domains were not eliminated even when the application of voltage to the liquid crystal was stopped.

On the other hand, when the gap between the adjacent protrusions is widened, the alignment regulating force by the protrusions becomes small, so that it becomes difficult for the liquid crystal molecules to be aligned in a predetermined direction.

As shown in FIG. 17A, if the gap between adjacent projections is widened to about 30 μm, it takes time to align the liquid crystal molecules.

Further, as shown in FIG. 17B, when the gap between adjacent projections is increased to about 45 μm,
The orientation state of the liquid crystal is close to random orientation, and a schlieren structure is observed.

From these observation results, it is considered appropriate that the gap between the adjacent protrusions is about 10 μm to 30 μm.

[Examples 8 to 13] The transmittance of the MVA cell was measured by appropriately changing the gap between the adjacent projections and the introduction ratio of the side-chain type diamine into the alignment film material. The height of each protrusion is 1.5 μm, and the width of each protrusion is
Each was 10 μm.

FIGS. 18 and 19 show the measurement results of the transmittance of the MVA cell. FIG. 18 is a graph showing transmittance characteristics when the gap between adjacent protrusions is set to 15 μm. Example 8 is the one in which 5% of the side-chain diamine is introduced, Example 9 is the one in which 10% of the side-chain diamine is introduced, and Example 10 is the one in which 40% of the side-chain diamine is introduced. .

FIG. 19 is a graph showing transmittance characteristics when the gap between adjacent protrusions is set to 30 μm. Example 11 is the one in which 5% of the side-chain diamine is introduced, Example 12 is the one in which 10% of the side-chain diamine is introduced, and Example 13 is the one in which 40% of the side-chain diamine is introduced. .

As shown in Examples 8 to 10, when the gap between adjacent projections is as narrow as 15 μm, that is, when the alignment regulating force of the projections is strong, the side chain type diamine contained in the alignment film material is used. Was 10%, the transmittance was highest.

On the other hand, as shown in Examples 11 to 13,
When the gap between adjacent projections is as large as 30 μm, that is, when the alignment regulating force of the projections is weak, the transmittance becomes the highest when the proportion of the side chain type diamine contained in the alignment film material is 40%. Got higher.

FIG. 20 shows the change in transmitted light intensity when the amount of side chain type diamine introduced was changed. FIG. 20 is a graph showing transmitted light intensity with respect to the introduction amount of the side chain type diamine. FIG. 20 shows that the introduction amount of the side chain type diamine was 10
%, And the transmitted light intensity is relatively expressed assuming that the transmitted light intensity when the applied voltage is 6 V is 1.

As can be seen from FIG. 20, Examples 8 to 1
In the case of 0, that is, when the alignment regulating force of the projection was large, the transmitted light intensity was highest when the introduction amount of the side chain type diamine was 10%. On the other hand, in Examples 11 to 13, that is, in the case where the alignment regulating force of the protrusion was small, the transmitted light intensity increased as the amount of the side chain type diamine introduced increased.

Example 14 Instead of forming protrusions, an MVA cell having a slit formed in an electrode was manufactured.

By changing the width of the slit formed in the electrode,
The measurement of the transmittance of the MVA cell and the observation of the alignment state of the liquid crystal were performed.

As a result, when a slit is formed,
It was found that similar characteristics were obtained when the width of the slit was set to about twice the width of the protrusion having a height of about 1.2 μm.

Example 15 The height of the projections was 1.6 μm, and JALS-684 and JALS-2 were used as alignment film materials.
An MVA cell was manufactured using 008-R2 or JALS-2029-R2, and the alignment state was observed.

JALS-684 has a side chain type diamine,
That is, about 10.4% of the vertical alignment component is contained. JALS-2008-R2 contains about 21% of a side chain type diamine. Also, JALS-2029-R
2 contains about 30% of a side chain type diamine.

JALS-684 or JALS-200
When 8-R2 was used, light leakage was observed at the edge of the protrusion even in a dark state where no voltage was applied.

On the other hand, when JALS-2029-R2 was used, no light leakage was observed.

From these results, when the height of the protrusion is as high as 1.6 μm, it is considered necessary to use an alignment film material containing a large amount of side chain type diamine.

[0157]

As described above, according to the present invention, a high-quality vertical alignment film is used, and the vertical alignment is restricted according to parameters such as the height of the projection, the width of the projection and the slit, and the gap between the projection and the slit. Since the power is optimized, an MVA liquid crystal display device with high reliability and high luminance can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an MVA liquid crystal display device.

FIG. 2 is a sectional view taken along line AA ′ of FIG.

FIG. 3 is a graph showing a relationship between an introduction ratio of an alicyclic group in an acid anhydride and a voltage holding ratio.

FIG. 4 is a graph showing a relationship between an introduction ratio of an alicyclic group in an acid anhydride and an ion density in a liquid crystal.

FIG. 5 is a graph showing the relationship between the addition amount of a thermosetting organic compound and the voltage holding ratio.

FIG. 6 is a graph showing the relationship between the addition amount of a thermosetting organic compound and the ion density.

FIG. 7 is a graph showing the relationship between the amount of a thermosetting organic compound added and the residual DC value.

FIG. 8 is a graph showing the relationship between the added amount of a high dielectric constant diamine and the residual DC value.

FIG. 9 is a graph showing the relationship between the added amount of a high dielectric constant diamine and the voltage holding ratio.

FIG. 10 is a graph showing the relationship between the amount of high-diamine added and the ion density.

FIG. 11 is a graph showing a change in voltage holding ratio with respect to a change in viscosity of an alignment film material.

FIG. 12 is a cross-sectional view of an MVA cell.

FIG. 13 is a graph showing a change in transmittance with respect to a change in height of a protrusion.

FIG. 14 is a photograph (part 1) of the MVA cell observed from above.

FIG. 15 is a photograph (part 2) of the MVA cell observed from above.

FIG. 16 is a photograph (part 3) of the MVA cell observed from above.

FIG. 17 is a photograph (No. 4) of the MVA cell observed from above.

FIG. 18 is a graph (1) showing transmittance characteristics.

FIG. 19 is a graph (part 2) showing transmittance characteristics.

FIG. 20 is a graph showing transmitted light intensity characteristics.

FIG. 21 is a conceptual diagram showing a proposed MVA liquid crystal display device.

FIG. 22 is a conceptual diagram showing an orientation direction of liquid crystal molecules of a proposed MVA liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Glass substrate 12 ... CS electrode 14 ... Gate bus line 16 ... Gate insulating film 18 ... Active layer 20 ... Source electrode 22 ... Drain bus line 24 ... Insulating film 26 ... Pixel electrode 28 ... Protrusion 30 ... Alignment film 40 ... Glass substrate 42 black matrix layer 46 CF resin layer 48 counter electrode 50 protrusion 52 alignment film 60 liquid crystal material 126 pixel electrode 128 protrusion 148 counter electrode 150 protrusion 162 liquid crystal molecules

Continued on the front page F term (reference) 2H090 HA16 HB09Y HB10Y HD11 MA01 MB14 4J002 CM041 EF126 FD147 GH00 GP00 GQ00

Claims (5)

[Claims] A first substrate on which a first electrode is formed;
A second electrode formed with a second electrode facing the first electrode;
A substrate, an alignment control means formed on the first substrate and / or the second substrate, an alignment film formed on the first substrate and / or the second substrate, A liquid crystal display device having a liquid crystal having a negative dielectric anisotropy sealed between the substrate and the second substrate, wherein the alignment film comprises: an acid anhydride containing an alicyclic group; A liquid crystal display device comprising: a polyamic acid containing a first diamine having, in a side chain, a component capable of vertically aligning, and a second diamine having a higher dielectric constant than the first diamine. 2. The liquid crystal display device according to claim 1, wherein the acid anhydride comprises only an alicyclic group. 3. The liquid crystal display device according to claim 1, wherein the alignment film contains an organic compound that undergoes a thermal crosslinking reaction with a carboxylic acid group. 4. The liquid crystal display device according to claim 1, wherein the alignment film contains the first diamine in an amount of about 10% to 30%.
A liquid crystal display device comprising: 5. The liquid crystal display device according to claim 1, wherein said alignment control means is a combination of protrusions and / or slits.