JP3463132B2 - Liquid crystal display device - Google Patents

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 capable of obtaining a wide viewing angle without defining a director of liquid crystal molecules with an alignment film.

[0002]

2. Description of the Related Art Generally, TN is used as a liquid crystal display device.
(Twisted nematic) type is used. In this TN type liquid crystal display element, a transparent electrode and an alignment film are provided on the inner surfaces of a pair of transparent substrates that face each other across a liquid crystal layer, and the molecules of the liquid crystal in the liquid crystal layer are disposed between the pair of substrates. The twist angle of the liquid crystal molecules is generally 90 ° to 90 °.
It is set in the range of 270 °.

By the way, the conventional TN type liquid crystal display device is
The alignment films provided on the inner surfaces of the pair of substrates are each subjected to an alignment treatment by rubbing or the like, and the molecules of the liquid crystal are controlled by the alignment films in the alignment direction in the vicinity of each substrate, It has a twist orientation.

However, in this liquid crystal display element, since the director of the liquid crystal molecule is defined by the alignment treatment direction of the alignment film, the voltage-transmittance characteristic has a viewing angle dependency, and therefore the viewing angle is narrow. There is.

Therefore, research has been conventionally conducted to improve the viewing angle of a TN type liquid crystal display device, and as one of the means, a wide viewing angle is provided without defining the director of liquid crystal molecules with an alignment film. A liquid crystal display device to be obtained is considered.

In this liquid crystal display element, an alignment film that is not subjected to alignment treatment is provided on the inner surfaces of a pair of substrates that face each other across the liquid crystal layer, and the molecules of the liquid crystal have a twist angle according to the twistability of the liquid crystal material. The twist orientation is set, and the twist angle is set to a predetermined angle by selecting the twistability of the liquid crystal material according to the gap between the pair of substrates.

That is, the above-mentioned liquid crystal material is a nematic liquid crystal to which a chiral substance used as an optically active substance for twisting liquid crystal molecules at a predetermined pitch is added. The twist pitch (natural pitch) can be arbitrarily selected by adjusting the addition amount of the optically active substance. Therefore, a liquid crystal material that twists at a predetermined angle in the gap according to the gap between the pair of substrates is selected. If used,
The desired twist angle is obtained.

In this liquid crystal display element, since the director of the liquid crystal molecules is not defined by the alignment film, even if the twist angles of the liquid crystal molecule molecules between the substrates are the same throughout the liquid crystal layer, they are microscopically different. Since the directors of (1) have various orientations, there is almost no dependence of the voltage-transmittance characteristic on the viewing angle, and therefore a wide viewing angle can be obtained.

In this liquid crystal display element, conventionally, a pair of substrates provided with electrodes and an alignment film which is not subjected to alignment treatment are bonded to each other through a frame-shaped sealing material to assemble a liquid crystal cell, and the inside of the liquid crystal cell is assembled. In addition, the liquid crystal material is injected by a vacuum injection method while being heated to a temperature at which it becomes an isotropic phase, and then slowly cooled to return the liquid crystal material in the cell to the nematic phase.

[0010]

However, in the above liquid crystal display device, in order to obtain a random twist alignment state, the liquid crystal material is injected into the liquid crystal cell while being heated to a temperature at which it is in an isotropic phase, and then slowly. Since it is manufactured by the method of returning the liquid crystal material in the cell to the nematic phase by cooling, it takes time to manufacture the liquid crystal display element, and therefore the manufacturing efficiency is poor, and the composition of the liquid crystal material may change due to heating. Therefore, there is a problem that the reliability of the manufactured liquid crystal display element is low.

The present invention can be efficiently manufactured in a short time as a liquid crystal display device in which a director of liquid crystal molecules is not defined by an alignment film and a wide viewing angle is obtained, and a composition change of a liquid crystal material is also obtained. The purpose of the present invention is to provide a product that can improve reliability without it.

[0012]

The present invention provides liquid crystal molecules.
A chiral substance for twisting at a specified pitch is added.
A liquid crystal display in which alignment films that are not subjected to alignment treatment are provided on the inner surfaces of a pair of substrates that face each other across the applied liquid crystal layer, and the liquid crystal molecules are twist-aligned at a twist angle according to the twistability of the liquid crystal material. In the device, the polar force component of the surface energy of the alignment film is less than 15 dyn / cm, 4
dyn / cm or more to see the liquid crystal molecules microscopically
In addition, the director at each point is oriented in various directions .

Further, in the invention, in the liquid crystal display device, the orientation film has a polar component of 4 dyn / cm or less.
Top, having a surface energy of less than 8 dyn / cm
Is characterized by.

Thus, the surface energy of the alignment film is
Polarity component of less than 15 dyn / cm, 4 dyn / cm
And more preferably 4 dyn / cm or more and 8
By setting less than dyn / cm, even if the liquid crystal material is injected in a nematic phase, the liquid crystal molecules adjacent to the alignment film surface are oriented in random directions, and the molecules in the layer thickness direction are twisted in the liquid crystal material. Since the twist alignment is performed at a twist angle corresponding to, it is possible to obtain a good alignment state in which the directors of liquid crystal molecules at various points in a microscopic view are in various directions.

Therefore, according to the present invention, the liquid crystal material is injected at room temperature to obtain a liquid crystal display element having a wide viewing angle in which the directors of liquid crystal molecules at various points in a microscopic view are in various directions. Therefore, the liquid crystal display device can be manufactured efficiently in a short time, and since it is not necessary to heat the liquid crystal material to a temperature at which it becomes an isotropic phase as in the conventional case, the composition of the liquid crystal material by heating can be improved. The reliability can be improved without any change.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to a liquid crystal display device in which the twist angle of liquid crystal molecules is approximately 90 ° will be described below. In this embodiment, a transparent electrode and an alignment film that is not aligned are provided on the inner surfaces of a pair of transparent substrates that face each other across the liquid crystal layer, and the molecules of the liquid crystal are twisted by the liquid crystal material to form a pair of substrates. In the liquid crystal display element in which the twist alignment is carried out at a twist angle of about 90 ° between them, the surface energy of the alignment film is 51 dy.
It is less than n / cm, or the polar force component of the surface energy of the alignment film is less than 15 dyn / cm.

Although the liquid crystal display element is not shown in the drawing, the liquid crystal cell is assembled by joining a pair of substrates provided with an alignment film which is not subjected to alignment treatment through a frame-shaped sealing material. Manufactured by a method of injecting the above liquid crystal material into the liquid crystal cell by a vacuum injection method from a liquid crystal injection port formed by removing a part of the sealing material, and then sealing the liquid crystal injection port. Polarizing plates are arranged on the outer surfaces of both substrates, respectively.

The above-mentioned liquid crystal material is a nematic liquid crystal to which a chiral substance used as an optically active substance for twisting liquid crystal molecules at a predetermined pitch is added, and its twisting property, that is, the inherent twisting of the liquid crystal material. The pitch (hereinafter referred to as natural pitch) P is determined by the amount of the optically active substance added.

In this embodiment, the natural pitch P is set so that the liquid crystal molecules are arranged between the pair of substrates at a predetermined twist angle. For example, a liquid crystal material having a natural pitch P of 20 μm is used,
Gap between the pair of substrates (hereinafter referred to as cell gap)
By setting d to 5 μm, the twist angle of the liquid crystal molecules is set to about 90 °.

That is, the twist angle of the liquid crystal molecules between the pair of substrates is determined by the ratio (d / P) of the cell gap d and the natural pitch P of the liquid crystal material. The cell gap d is d = 5 μm and the natural pitch of the liquid crystal material is When the pitch P is P = 20 μm, since d / P = 5/20 = 0.25, the twist angle of the liquid crystal molecules is 360 ° × 0.25 = 90 °.

In the above liquid crystal display device, since the director of the liquid crystal molecules is not defined by the alignment film, even if the twist angles of the liquid crystal molecule molecules between the substrates are the same throughout the liquid crystal layer, they are microscopically different. Since the directors of (1) have various orientations, there is almost no dependence of the voltage-transmittance characteristic on the viewing angle, and therefore a wide viewing angle can be obtained.

Then, as in the liquid crystal display device of this embodiment, the surface energy of the alignment film provided on the inner surfaces of the pair of substrates is set to less than 51 dyn / cm, or the polar component of the surface energy of the alignment film is set. Since it is less than 15 dyn / cm, the interaction between the alignment film and the liquid crystal molecules is weakened, and the liquid crystal molecules aligned along the flow of the liquid crystal generated when the liquid crystal is injected may be adsorbed to the alignment film. Disappear.

Therefore, even if the liquid crystal material is injected in the nematic phase, the molecules in the layer thickness direction are twist-aligned at a twist angle according to the twistability of the liquid crystal material. Therefore, it is possible to obtain a good alignment state in which the directors of liquid crystal molecules at various points in a microscopic view are in various directions.

Therefore, according to this liquid crystal display element, the liquid crystal material is injected at room temperature, and the directors of the liquid crystal molecules at various points in a microscopic view have a wide viewing angle. Therefore, it is possible to efficiently manufacture the liquid crystal material in a short time, and since it is not necessary to heat the liquid crystal material to a temperature at which the liquid crystal material is in the isotropic phase as in the conventional case, the composition change of the liquid crystal material due to the heating The reliability can be improved without it.

[0025]

EXAMPLE A specific example of the present invention will be described. In this example, an alignment treatment is performed in which the alignment films provided on the inner surfaces of a pair of substrates are each made of a polyimide film having a surface energy of less than 51 dyn / cm. The alignment film is not applied, and the liquid crystal material has a natural pitch P of 20 μm, a dielectric anisotropy Δn of 0.090, an NI point of 86.9 ° C., a dielectric anisotropy Δε of 4.5, and a threshold voltage Vth of With a physical property of 2.37 V, the cell gap d was set to 5 μm, and the twist angle of liquid crystal molecules was set to about 90 °.

According to this embodiment, since the surface energy of the alignment films provided on the inner surfaces of the pair of substrates is less than 51 dyn / cm, the liquid crystal material is injected in the nematic phase state during the manufacture of the liquid crystal display device. In addition, the liquid crystal molecules adjacent to the alignment film surface are oriented in random directions, and the molecules in the layer thickness direction are twisted at a twist angle according to the twistability of the liquid crystal material. A good alignment state in which the directors of liquid crystal molecules in various directions are obtained can be obtained.

In the following [Table 1], five kinds of liquid crystal display elements were prototyped by using the alignment films A to E having different surface energies, and the liquid crystal materials described above were applied to these liquid crystal display elements at room temperature (nematic phase). State), and the results of examining the alignment state of liquid crystal molecules after the injection and the presence or absence of domains are shown.

[0028]

[Table 1]

As shown in [Table 1], a liquid crystal display device using an alignment film of A, B, and C having a surface energy of 51 dyn / cm or more has an alignment state of liquid crystal molecules after a liquid crystal substance is injected. , The uneven state in which the trace of the flow of the liquid crystal substance at the time of injection was left was observed. That is, the directors of the liquid crystal molecules adjacent to the surface of the alignment film are partially aligned in the flow direction, and domains are generated.

On the other hand, the surface energy is 45 dy.
In the liquid crystal display device using the D and E alignment films as small as n / cm or 41 dyn / cm, the alignment state of the liquid crystal molecules after the liquid crystal substance is injected does not leave any trace of the flow of the liquid crystal substance at the time of injection. It is in a good state, and because the directors of liquid crystal molecules at various points on a microscopic scale are in various directions,
There is no domain.

[Table 1] shows the alignment state of liquid crystal molecules and the presence or absence of domains in each of the five types of liquid crystal display elements using the alignment films A to E. The surface energy of the alignment film provided on the inner surface is 51d.
When it is less than yn / cm, the alignment state of liquid crystal molecules after the liquid crystal substance is injected is in a good state, and no domain is generated.

That is, the surface energy of the alignment film is 51
When the liquid crystal material is less than dyn / cm and 41 dyn / cm or more , even if the liquid crystal material is injected in a nematic phase, the molecules have twist angles according to the twistability of the liquid crystal material, and
The directors of the liquid crystal molecules at each microscopic point are oriented in various orientations in good orientation.

Therefore, according to this embodiment, a liquid crystal display device having a wide viewing angle in which liquid crystal material is injected at room temperature and directors of liquid crystal molecules at various points viewed microscopically are in various directions. Since it is possible to obtain the liquid crystal display element, it is possible to efficiently manufacture the liquid crystal display element in a short time. Further, since it is not necessary to heat the liquid crystal material to a temperature at which the liquid crystal material is in an isotropic phase as in the conventional case, the liquid crystal material is The reliability can be improved without changing the composition.

In this embodiment, the more desirable surface energy of the alignment film is 41 dyn / cm or more, 4 or more.
It is less than 5 dyn / cm (see [Table 1]), and if the surface energy of the alignment film is in this range, a better alignment state of liquid crystal molecules can be obtained.

Next, another specific embodiment of the present invention will be described. In this embodiment, the alignment films provided on the inner surfaces of the pair of substrates have a polar force component of surface energy of 15 respectively.
In addition to an alignment film that is not subjected to an alignment treatment and is composed of a polyimide film of less than dyn / cm, the liquid crystal material has the above-mentioned physical properties (natural pitch P of 20 μm, dielectric anisotropy Δn of 0.090, and NI point. 86.9 ° C., a dielectric anisotropy Δε of 4.5, and a threshold voltage Vth of 2.37 V) were used, the cell gap d was set to 5 μm, and the twist angle of the liquid crystal molecules was set to about 90 °.

According to this embodiment, the polar component of the surface energy of the alignment films provided on the inner surfaces of the pair of substrates is 15 dy.
Since it is less than n / cm, even if a liquid crystal material is injected in the state of a nematic phase when manufacturing a liquid crystal display element,
Liquid crystal molecules adjacent to the alignment film surface are oriented in random directions, and molecules in the layer thickness direction are twisted at a twist angle according to the twistability of the liquid crystal material. A good alignment state in which the directors of liquid crystal molecules are in various directions can be obtained.

In the following [Table 2], five kinds of liquid crystal display elements were experimentally produced by using alignment films F to J having different polar force components of surface energy, and the above liquid crystal materials were applied to these liquid crystal display elements at room temperature. The results of examining the alignment state of liquid crystal molecules after injection and the presence or absence of domains are shown.

[0038]

[Table 2]

As shown in [Table 2], the liquid crystal display element using the F, G, and H alignment films whose surface energy has a polar force component of 15 dyn / cm or more is used. It was observed that the alignment state of 1 was uneven with traces of the flow of the liquid crystal substance at the time of injection. That is, the directors of the liquid crystal molecules adjacent to the alignment film surface are partially aligned in the direction of the flow, and domains are generated.

On the other hand, the liquid crystal display element using the I and J alignment films having a surface energy NO polar component of as small as 8 dyn / cm or 4 dyn / cm is the alignment state of the liquid crystal molecules after the liquid crystal substance is injected. However, it is in a good state in which no trace of the flow of the liquid crystal substance at the time of injection remains, and since the directors of liquid crystal molecules at various points in a microscopic view are in various directions, no domain is generated.

[Table 2] shows the alignment state of liquid crystal molecules and the presence or absence of domains in each of the five types of liquid crystal display elements using the alignment films F to J. When the polar force components of the surface energy of the alignment film provided on the inner surface are each less than 15 dyn / cm, the alignment state of the liquid crystal molecules after injection of the liquid crystal substance is in a good state and no domain is generated.

That is, when the polar force component of the surface energy of the alignment film is less than 15 dyn / cm and 4 dyn / cm or more , even if the liquid crystal material is injected in a nematic phase, the molecules thereof have a twisting property of the liquid crystal material. The directors of the liquid crystal molecules are aligned in various orientations at various twist angles according to the above and at microscopically different points.

Therefore, according to this embodiment, the liquid crystal material is injected at room temperature, and the liquid crystal display element having a wide viewing angle in which the directors of the liquid crystal molecules at each microscopic point are in various directions. Since it is possible to obtain the liquid crystal display element, it is possible to efficiently manufacture the liquid crystal display element in a short time. Further, since it is not necessary to heat the liquid crystal material to a temperature at which the liquid crystal material is in an isotropic phase as in the conventional case, the liquid crystal material is The reliability can be improved without changing the composition.

In this example, the polar force component of the surface energy of the alignment film is more preferably 4 dyn / c.
It is in the range of m or more and less than 8 dyn / cm (see [Table 2]), and if the polar force component of the surface energy of the alignment film is in this range, a better alignment state of liquid crystal molecules can be obtained.

Further, in each of the above-mentioned examples, only the surface energy of the alignment film or its polar force component was focused, but in the most preferred embodiment of the present invention, the surface energy of the alignment film is less than 51 dyn / cm (desirably). Is 41 dyn
/ Cm or more and less than 45 dyn / cm), and the polar force component is less than 15 dyn / cm (desirably 4 dy).
n / cm or more and less than 8 dyn / cm). By doing so, a better alignment state of liquid crystal molecules can be obtained.

Further, the present invention is not limited to the liquid crystal display device in which the twist angle of the liquid crystal molecules is about 90 °, but can be widely applied to the liquid crystal display device in which the twist angle of the liquid crystal molecules is arbitrarily set.

[0047]

According to the present invention, an alignment film that is not subjected to alignment treatment is provided on the inner surfaces of a pair of substrates that face each other across a liquid crystal layer, and the molecules of the liquid crystal have a twist angle according to the twistability of the liquid crystal material. in the liquid crystal display device are twisted, polar force component of the surface energy of the previous SL alignment film 15
Less than dyn / cm , 4 dyn / cm or more, more preferable
More preferably, 4 dyn / cm or more and less than 8 dyn / cm
Therefore , even if the liquid crystal material is injected in the nematic phase, the liquid crystal molecules adjacent to the alignment film surface are oriented randomly, and the molecules in the layer thickness direction have a twist angle according to the twistability of the liquid crystal material. Since the twist alignment is performed, it is possible to obtain a good alignment state in which the directors of liquid crystal molecules at various points in a microscopic view are in various directions.

Therefore, according to the present invention, it is possible to efficiently manufacture the liquid crystal display element in a short time and to obtain a wide viewing angle without defining the director of the liquid crystal molecule by the alignment film, and at the same time, the liquid crystal can be manufactured. It is possible to provide a material that can improve reliability without changing the composition of the material.

Claims (2)

(57) [Claims] 1. Alignment films that are not subjected to alignment treatment are provided on the inner surfaces of a pair of substrates facing each other with a liquid crystal layer added with a chiral substance for twisting liquid crystal molecules at a predetermined pitch interposed therebetween. In a liquid crystal display element in which is twisted according to the twistability of the liquid crystal material, the polar force component of the surface energy of the alignment film is 15 dyn.
/ Cm or less and 4 dyn / cm or more, and the molecules of the liquid crystal
Orienting the director at various points from a micro perspective
A liquid crystal display device characterized by being made . 2. An alignment provided on each of the inner surfaces between a pair of substrates.
The membrane has a polar component of 4 dyn / cm or more, 8 dyn / c
Claims characterized by having a surface energy of less than m
Item 2. The liquid crystal display device according to item 1.