JPH0756148A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display element having a high scattering characteristic, low driving voltage, excellent gradation characteristic and wide visual field angle characteristic with high productivity. CONSTITUTION:A nematic liquid crystal layer 20 having positive dielectric anisotropy is clamped between two sheets of substrates 11 and 12 provided with electrodes 13, 14. The twist angle 4 of the liquid crystal is + or -theta+180 deg. or + or -theta-180 deg. when psi is + or -theta in the state of not a voltage to the liquid crystal layer when the intersection angle of the liquid crystal molecule arrangement directions on two sheets of the substrates is theta(0 deg.<=theta<=90 deg.) and the cell twist angle determined to cause uniform twist arrangement on the surfaces of two sheets of the substrates is psi. The twist angle omega of the liquid crystal when psi is + or -(theta-180 deg.) is + or -theta. A conductor part 13a (14a) and non-conductor part 13b (14b) are formed in fine region unit of <=30mum on the electrode of each one picture element. The conductor part 13a (14a) of the one electrode and the non-conductor part 13b (14b) of the other electrode are arranged to face each other between both substrates. Both substrates have low-pretilt angle oriented films 15, 16 of <=2.5 deg. and the pretilt angle difference of both substrates is <=0.3 deg..

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 utilizing the light scattering of disclination.

[0002]

2. Description of the Related Art Generally, when a liquid crystal display device (hereinafter abbreviated as LCD) is classified from the viewpoint of light control, a device that causes a change in brightness and darkness due to a combination of a polarization effect of liquid crystal molecules and a polarizer and a phase transition of liquid crystal are used. However, it is classified into those generated by scattering and transmission of light, those added by adding a dye to control the visible light absorption amount of the dye, and those caused by a change in color shade.

L, which is a combination of the former polarization effect and a polarizer
CD is, for example, a twisted nematic (TN) type liquid crystal having a 90 ° twisted molecular arrangement. In principle, a thin liquid crystal layer and polarization control can be performed at a low voltage, so that a high response speed, low power consumption, and high contrast are achieved. The ratio is used for a clock, a calculator, a simple matrix drive, an active matrix drive provided with a switching element for each pixel, and in combination with a color filter, it is applied to a full color display liquid crystal TV or the like.

However, an LCD combining these polarization effects and a polarizer has a remarkably low transmissivity of the element since it uses a polarizing plate in principle, and the display color and the contrast ratio depend on the viewing angle / direction depending on the orientation of the molecular arrangement. Cold-cathode ray tube (CRT) that has a viewing angle dependency such as a large change in
The display performance of is completely exceeded.

On the other hand, the latter one utilizing the phase transition of liquid crystal and the LCD in which the visible light absorption amount of the dye is controlled, for example, from a cholesteric phase having a molecular structure of helical structure to a nematic phase of homeotropic molecular alignment. A PC-type liquid crystal which causes a phase transition by applying an electric field and a white Taylor type GH liquid crystal obtained by adding a dye to the PC-type liquid crystal, which does not use a polarizer and theoretically does not use a polarization effect.
It is bright and has a wide viewing angle, and is used in automobile equipment and projection displays.

However, in order to obtain sufficient light scattering, it is necessary to make the liquid crystal phase thick enough or to increase the helical strength that causes the scattering, which requires a high driving voltage and an extremely slow response speed. Therefore, it has been difficult to apply it to a display element having a large display amount (number of pixels). In addition, it has been considered difficult to provide gradation because the transmittance changes abruptly as the applied voltage increases.
Further, the applied voltage-transmittance characteristic has a hysteresis, and there is a practical problem that it is difficult to perform multiplex driving.

To further explain, when the polarization effect and the polarizer are used, the transmittance is lowered in principle, and the viewing angle dependency is caused. That is, since at least one polarizing plate is used, the amount of transmitted light is at least 50% or less, and a pretilt angle is provided for manufacturing and stabilization of orientation, which affects the viewing angle characteristics. Especially in principle, the transmittance is low,
Using this method is an unavoidable problem.

When the phase transition of the liquid crystal is used, these problems such as low transmittance and viewing angle dependence do not occur, but in order to sufficiently scatter light, the liquid crystal layer thickness should be sufficiently thick as described above. , It is necessary to increase the helical strength. This is because the scattering of light is due to various liquid crystal molecule arrangements. In other words, in order to scatter light sufficiently,
For example, in the case of a cholesteric phase having a helical molecular arrangement, it becomes necessary to have a helical axis in every direction with respect to the incident light direction. As described above, in order to have the helical axes in many directions, the liquid crystal phase thickness must be increased. In addition, a means (generally called the DS effect) for obtaining a scattering property by applying a high voltage at a low frequency using Nn liquid crystal in which a conductive substance such as an organic electrolyte is dissolved has been proposed. In order to obtain the property, it is necessary to have the above problems. Of course, the same applies when the phase transition is caused by the thermo-optic effect.

Further, in the methods utilizing these various phase transitions, the molecular alignment of the liquid crystal is remarkably different between the light scattering state and the light transmitting state. Therefore, the mutual change between the above two states can be achieved by electric field control. In that case, hysteresis will occur in the electro-optical characteristics. The cause of this hysteresis has not been clarified due to various theories, but it occurs when the molecular arrangement is significantly different, and it also occurs in the light-scattering state (the molecular arrangement of liquid crystals is a collection of fine domains) when no electric field is applied. It is known that this is more likely to occur when the body is in a state).

Further, as shown in FIG. 14 (a), the substrate 1,
A large number of capsules are formed in a polymer 3 held between two, and a liquid crystal 4 is encapsulated in the capsule 3, and a liquid crystal 6 is sandwiched between fibrous polymers 5 as shown in FIG. 14 (b). A polymer-dispersed LCD that uses a dispersed fibrous polymer structure to enhance the scattering property has been proposed, but the required properties such as high scattering property, sufficiently low driving voltage and response speed have not yet been obtained. This is because, due to the manufacturing method and the principle of the shape of the polymer, there is a restriction on the mixing ratio of the polymer and the liquid crystal layer, and again, when trying to satisfy the required driving characteristics, sufficient scattering cannot be obtained. Is.

Also in these systems, since the molecular alignment of the liquid crystal is significantly different between the light scattering state and the light transmitting state,
As described above, hysteresis occurs in electro-optical characteristics. On the other hand, the liquid crystal molecular alignment in the scattering state is controlled to some extent (for example, a polymer is mixed with a hydrophobic substance to control the liquid crystal molecular alignment on the inner surface of the capsule).
However, it is possible to reduce the hysteresis, but this also weakens the light scattering and is not practical.

Capsule-like polymer dispersion type NCAP type L
The CD is a scattering mode liquid crystal display element, and since it does not have a polarizing plate, it is bright and has a wide viewing angle, and is applied to automobile equipment, projection type displays and the like. However, the voltage applied from the outside is divided between the organic polymer and the liquid crystal, and only a part of the applied voltage is applied to the liquid crystal, which causes a problem that the operating voltage is practically increased. Further, in order to obtain sufficient light scattering, it is necessary to make the liquid crystal thickness sufficiently thick, and there is a problem that the response speed is extremely slow, so that it is difficult to apply it to a display element with a large display amount (number of pixels). Was there. Further, the applied voltage-transmittance characteristic has a hysteresis, and there is a practical problem that it is difficult to perform multiplex driving. The polymer-dispersed LCD in which liquid crystal is held in a network organic polymer of fibrous polymer, which operates on the same operation principle, has the same problem.

Further, as a method of scattering light, an alignment treatment is performed for each fine region so that liquid crystal molecules are arranged in various directions on the surfaces of two electrode-attached substrates, and these are treated as inner surfaces to form a gap facing each other. It may be possible to sandwich the liquid crystal, but this is not a means for solving the above-mentioned problem of hysteresis, and a means for realizing such a structure has not been found, which is a realistic method. Absent. The reason why such a configuration cannot be realized is that it is difficult to make the orientation processing direction (for example, the rubbing direction) different for each fine region.

[0014]

As described above, the conventional liquid crystal display device has a low transmittance and a viewing angle dependency.
There was a problem that a high drive voltage was required and the response speed was slow.

Therefore, as means for scattering light,
Does not require any medium other than liquid crystal to obtain the light scattering state,
Moreover, the above-mentioned problems do not occur as long as the molecular arrangement of the liquid crystal is not significantly different from that in the light-transmitting state and a good light-scattering state is obtained, and there is no restriction in the manufacturing method.

The present invention provides a novel structure satisfying this condition.

[0017]

Means for Solving the Problem As a means for solving the problem, the present invention is a liquid crystal composed of a nematic liquid crystal having a positive dielectric anisotropy between two substrates each having electrodes forming a plurality of pixels facing each other. It has a means for inducing a tilt alignment that sandwiches the layers and causes the major axes of the liquid crystal molecules to be aligned in one direction on the surface of the substrate, and the crossing angle of the alignment directions of the liquid crystal molecules on the two substrates is θ (0 (° ≦ θ ≦ 90 °), and in the liquid crystal display element in which the cell twist angle is ψ that is determined so that the liquid crystal is uniformly twisted by the pretilt angle due to the tilt alignment on the surfaces of the two substrates, a voltage is applied to the liquid crystal layer. With no voltage applied, when ψ is ± θ (for convenience, when the twist direction is counterclockwise +, clockwise when −), the twist angle ω of the liquid crystal is ± θ + 180 ° or ± θ-18.
When the angle is 0 ° and ψ is ± (θ−180 °), the liquid crystal twist angle ω is ± θ (the same order as above), and the narrowest width of the electrodes of both substrates is 30 μm or less for each pixel. It is composed of two kinds of a conductor portion and a non-conductor portion in which a fine region is a unit, and a conductor portion of one electrode and a non-conductor portion of the other electrode are arranged to face each other between both substrates, Moreover, the liquid crystal display device is characterized in that the pretilt angle between both substrates is 2.5 ° or less, and the difference between the pretilt angles between both substrates is 0.3 ° or less.

Further, the present invention provides a liquid crystal display device characterized in that the alignment films on both substrates are composed of a main chain type organic compound having no side chains.

[0019]

According to the present invention, when the liquid crystal is not arranged in a uniform twist arrangement, the light scattering effect of the disclination line generated by utilizing the change in the orientation of the liquid crystal molecules depending on the presence or absence of an applied voltage having a lateral electric field component is enhanced. The conductive part and the non-conductive part are formed in a minute area of the electrode, and the conductive part of one electrode and the non-conductive part of the other electrode are sandwiched between the substrates and face each other across the liquid crystal layer. Face to face.

Moreover, in order to accurately change the orientation of the liquid crystal molecules, it is necessary to control the pretilt angle, and selection of the alignment film is an important factor.

As a premise for explaining the operation of the present invention, a pretilt angle, a uniform twist arrangement, and a non-uniform twist arrangement will be described.

The nematic liquid crystal molecules are in the shape of elongated rods. When the liquid crystal molecules come into contact with the rubbed alignment film on the substrate, the long axis of the rod-shaped molecule is aligned in a certain direction depending on the property of the alignment film surface. For example, when the alignment film is a polyimide alignment film, the long axes of liquid crystal molecules are aligned along the rubbing direction. Further, in the case of the polystyrene alignment film, the long axes of the liquid crystal molecules are arranged in the film plane direction in a direction perpendicular to the rubbing direction.

As another method of alignment treatment, there is a method of depositing an alignment film on a substrate. When silicon oxide is obliquely vapor-deposited on the surface of the substrate at an incident angle of 85 °, the long axes of the liquid crystal molecules are oriented in the direction of the vapor deposition source.

However, in these alignment treatments, the liquid crystal molecules M are not actually aligned parallel to the alignment film surface S, but are tilted with respect to the alignment film surface, that is, the substrate surface S as shown in FIG. It rises and is oriented at a certain angle α 0. This angle α 0 is about 1 for polyimide alignment film.
It is ~ 15 °. The angle α0 formed by the long axis LA of the liquid crystal molecules in contact with the substrate surface on the substrate surface is called a pretilt angle.

At this time, as shown in FIG. 2A, when the end portion of the liquid crystal molecule long axis LA raised from the substrate is the leading portion L and the end portion approaching the substrate side is the trailing portion T, the alignment is performed. In order to explain the liquid crystal molecules M that have been generated, FIG.
As in (b), for example, an arrow R from the T direction to the L direction is displayed on the plane of the alignment film.

In the example of FIG. 3, as shown in (a), the molecular arrangement of the front substrate, that is, the upper substrate 1 is F (solid arrow).
Thus, the rear substrate, that is, the lower substrate 2 is subjected to the orientation treatment so that the molecular arrangement becomes R (arrow of a broken line), and each arrangement is in the opposite direction, that is, 180 ° on the substrate plane.
Facing different directions.

In this structure, when a nematic liquid crystal having a positive dielectric anisotropy (for example, a chiral agent is not mixed) such that the liquid crystal molecule does not have twist, the liquid crystal molecule M is formed as shown in FIG.
As shown in (b), the liquid crystal layer 3 is arranged at a constant and uniform angle from the upper substrate 1 to the lower substrate 2 over the entire thickness thereof. Generally, such a molecular arrangement is called a uniform arrangement, which is a basic configuration of a conventional liquid crystal display device.

In the liquid crystal display device having this structure, when a voltage equal to or higher than the threshold voltage, that is, a driving voltage is applied to the liquid crystal layer, the liquid crystal molecules M are aligned as shown in FIG. Are uniformly arranged in a direction substantially perpendicular to the substrate.

FIG. 6 is a view assuming a case where the lower substrate 2 is twisted by an angle θ (≦ 90 °) with respect to the upper substrate 1 from the state of FIG. 3A. In order to maintain the uniform molecular alignment at this time, the liquid crystal must be twisted counterclockwise by the angle ψ (rotation direction of the arrow in the figure) between both substrates. The liquid crystal material may be selected so that it can be twisted by ψ. The molecular sequence thus obtained can be called a twisted uniform sequence,
In this case, this angle ψ is called the twist angle of the uniform arrangement. By the way, the conventional ST-LCD has 9
It has a twisted uniform arrangement of 0 ° to 270 °.

FIG. 5 shows the relationship between the transmittance of the LCD and the applied voltage in the ST-LCD in which φ is 180 °. From this figure, the ST-LCD rapidly changes its state at a certain voltage, that is, at the threshold voltage Vth or higher. From this, it is considered that the ST-type LCD has a molecular arrangement close to a state in which no voltage is applied under an applied voltage lower than the threshold voltage, and the twist angle of the liquid crystal is 90 ° as in this ST-LCD. When defining the molecular arrangement of the LCD above 270 ° or less, it is defined under the applied voltage state below this threshold voltage (when no voltage is applied). Further, in such a transmittance-applied voltage characteristic (curve of FIG. 5), the steepness of the characteristic is generally represented by the difference between the applied voltage values of 90% and 10%. It is represented by the value γ divided by the value of.

In the liquid crystal display device having this structure, when a voltage higher than the threshold voltage is applied to the liquid crystal layer (when a voltage is applied), as in the case of the twist-free uniform alignment described above,
The liquid crystal molecules M are arranged in a direction substantially perpendicular to the substrates as if the liquid crystal molecules M are twisted in the arrangement of FIG.

As can be seen from FIG. 6, the twist angle ψ of the uniform arrangement is an angle from the trailing portion TF of the liquid crystal molecules of the orientation F of the upper substrate to the leading portion LR of the liquid crystal molecules of the orientation R of the lower substrate. Is represented.

Ψ is + θ in the counterclockwise direction as shown in FIG.
You can define clockwise as -θ and two ways. On the other hand, an arrangement of liquid crystal molecules as shown in FIG. 8B is also possible. Similar to the arrangement of FIG. 3 (b) described above, such an arrangement can be achieved by maintaining a nematic liquid crystal composition that does not cause twist in the structure of FIG. 8 (a).

In such a molecular arrangement, the molecular arrangements F and R on the upper and lower substrates are in the same direction, and as shown in FIG. 8B, the tilt angle of the liquid crystal molecules is the pretilt angle α 0 of the upper substrate 11 as shown in FIG. 8B.
After that, the angle gradually decreases and becomes parallel to the substrate 11 at the midpoint d / 2 of the liquid crystal layer thickness d, and then the pretilt angle α of the lower substrate 12
It is designed to incline in the opposite angle until it reaches 0. That is, the leading portions LF and LR are arranged close to each other, and the trailing portions TF and TR are arranged apart from each other. Such a non-uniform array is called a spray array.

Next, it will be considered to obtain a structure in which the splay array is twisted as in the uniform array described above. As shown in FIG. 9, considering that the splay array is formed in the state where the orientation R of the upper substrate 11 intersects the orientation R of the lower substrate 12 by θ similarly to the uniform array of FIG. 6, as shown in FIG. That is, the liquid crystal molecules must be twisted at an angle between the trailing portion TF having the orientation F of the upper substrate 11 and the trailing portion TR having the orientation R of the lower substrate. If this twist angle in the splay array is ω, and ω is counterclockwise in FIG. 9, ω is positive,
The splay array twist angle ωL is (θ + 180 °), and when ω is taken clockwise, ω is negative, so the splay array twist angle ωR is its complementary angle (θ−180 °).

Considering the configuration as shown in FIG. 10, when ω is taken clockwise, ω is negative, so the splay array twist angle ωR is (−θ−180 °), and ω is counterclockwise.
Since ω is positive, the splay array twist angle ωL is its complementary angle (−θ + 180 °).

As described above, in the configurations of FIGS. 9 and 10, the splay array twist angle ω is (± θ + 180 °) and (± θ−1).
It can take any of the four twist states of 80 °). As described above, also in the spray arrangement, the twist arrangement can be realized corresponding to + θ and −θ of the twist angle ψ in the uniform arrangement.

Considering the twist angle ψ in the case where the uniform twist arrangement is used, each ω described in FIGS. 9 and 10 is ψ = + θ, −θ, and the angle θ is 0 ≦ θ ≦ 9.
In the range of 0 °, in order to realize the twisted splay arrangement when ψ is ± θ, the twist angle ω is (± θ +
180 °) and (± θ−180 °), it means that it does not hold. In this case, the range of possible values of ω is
ω = | θ ± 180 ° | = 90 ° to 270 °, and this twist angle agrees with the practical solution of the conventional ST-LCD.
In other words, it is a twisted splay array and the conventional ST-
Considering to obtain a twist angle equal to the twist angle of the LCD, the twist angle ψ of the uniform array is ± θ and the twist angle ω of the liquid crystal is (± θ + 180 °) or (±
θ−180 °), which is the first feature of the liquid crystal display element of the present invention. The molecular arrangement of the liquid crystal display device of the present invention is conceptually shown in FIG.

The twisting direction and the twisting degree of the liquid crystal molecules can be controlled by the kind and mixing amount of the chiral liquid crystal agent mixed in the liquid crystal. As a concrete material, octyl-2-oxy-4- (4'-n-) is added to the counterclockwise chiral agent.
Hexyloxy) -benzol such as S-811 (manufactured by Merck Japan), 4-cyano-4 'as a clockwise chiral agent.
-(2-methylbutyl) -biphenyl such as CB-1
5 (manufactured by Merck Limited).

FIG. 11 shows the influence on the molecular alignment when the electrode shapes are different when the alignment directions and pretilt angles α 0 of the liquid crystal molecules on the surfaces of the upper and lower substrates 11 and 12 are the same and the liquid crystal molecules are not twisted. So (a)
7A to 7C show states when no voltage is applied, and FIGS. 8D to 8F show states when voltage is applied. Where (a),
(D) shows a state where the upper and lower substrates have the same electrode shape and an electric field is applied only in the thickness direction of the liquid crystal layer.

The position of the liquid crystal molecule is parallel to the substrate.
0 is provided at the middle point of the liquid crystal layer thickness d, and even if a voltage is applied to the electrodes 13 and 14 from the power source v0 as shown in FIG. FIG. 11B shows the lower substrate 12.
Electrode 14 is formed in the left half of the figure, the right half is an electrodeless area, the other electrode 13 of the upper substrate 11 is formed in the right half of the figure, and the left half is an electrodeless area. Electrode 1
Reference numerals 3 and 14 face the electrodeless region.

When the voltage v0 is applied, an electric field having a lateral electric field component is applied to the liquid crystal layer due to the mutual displacement of the electrodes, and an electric force line e having an upward rising arrow ER component shown in the figure is generated. As shown in FIG. 6 (e), the molecules M have a steeply rising molecular arrangement.

On the other hand, FIG. 11C shows the electrode 1 of the lower substrate 12.
4 is formed in the right half of the drawing, the left half is an electrodeless region, the other electrode 13 of the upper substrate 11 is formed in the left half of the drawing, and the right half is an electrodeless region. , 14 face the electrodeless region. As shown in (f) of FIG.
When 0 is applied, an electric field having a lateral electric field component is applied to the liquid crystal layer due to the mutual displacement of the electrodes, and an electric force line e having an upwardly rising arrow EL component shown in the drawing is generated.
The direction of is a steeply rising array. That is, the alignment of liquid crystal molecules when a voltage is applied depends on the formation of a lateral electric field.

Therefore, as shown in FIG. 1 (b) showing the present embodiment, the upper electrode 13 has an electrode pattern in which a plurality of stripe-shaped conductor portions 13a are arranged at equal intervals through non-conductor portions 13b, and The lower electrode 14 has a pattern in which a plurality of stripe-shaped conductor portions 14a are arranged at equal intervals through the non-conductor portion 14b, and when these electrodes are opposed to each other, the conductor portion 13a or 14a of one electrode is formed. Overlap so as to form a gap between the substrates so as to face the non-conductor portion 14b or 13b of the other electrode. In this case, rubbing treatment is performed so that the liquid crystal alignment directions of the upper and lower substrates are the same. As a result, when no voltage is applied, the liquid crystal maintains the splay alignment state in an orderly manner, but when a voltage is applied, the conductor parts are displaced between the upper and lower electrodes, so that an oblique electric field having a transverse electric field component is generated between the electrodes. , The electric force lines e whose inclination directions are alternately changed are formed as shown in the drawing. Since the liquid crystal molecules M rise and align along the lines of electric force, the liquid crystal alignment becomes discontinuous at the boundary between the obliquely upward electric field rising to the left and the oblique electric field rising left to generate a disclination line DL.

If a large number of conductive parts and non-conductive parts of electrodes are formed within one pixel, the rising direction of liquid crystal molecules is divided into minute parts, so that many disclination lines are generated within one pixel. It is possible to cause light scattering in this part. Since the width of the light scattering area is 5 to 30 μm around the boundary, if the size of the fine area is made to match within this value range, or if it is divided to a value smaller than this value, one pixel entire surface The light can be scattered at, and the liquid crystal molecules are continuously arrayed in the state where no voltage is applied, so that a light equivalent state can be obtained. Therefore, according to the present invention, it is possible to perform electric field control to obtain a light transmission state when no voltage is applied and a light scattering state when a voltage is applied.

Here, in the present invention, since the tilt direction of the liquid crystal molecules is controlled by the direction of the applied electric field, it is desirable that the pretilt angles of the upper and lower substrates are equal, and the difference is 0.5 ° in practical use. It is desirable that the angle is 0.3 ° or less. The magnitude of the pretilt angle depends on the material of the alignment film and the alignment treatment method. When the alignment treatment is a rubbing treatment, the pretilt angle changes according to the change in the rubbing intensity. The pretilt angle is 2.5 ° in order to keep the difference in the pretilt angle between the upper and lower substrates as small as possible, regardless of the variation in the rubbing process in manufacturing.
Good results can be obtained by using the following alignment film materials having a low pretilt angle.

As the low pretilt angle alignment film material, a main chain type organic alignment film having no side chains is suitable. For example,

[Chemical 1] Can be mentioned.

FIG. 12 shows changes in the pretilt angle (degree) with respect to the rubbing strength (mm) of a main chain type alignment film having no side chain (trade name, manufactured by AL-1051 Japan Synthetic Rubber) and a side chain type alignment film. Curve A is the main chain type and curve B is the side chain type. It can be seen from the curve A that the main chain type alignment film material is stable with respect to a change in rubbing strength at a pretilt angle of 1.5 °. On the other hand, the side chain type material changes greatly as shown by the curve B.

From a microscopic view of the behavior of the liquid crystal molecules, the change in the molecular arrangement in each region is equal to the change in the molecular arrangement, and the response speed takes a value in accordance with this. Therefore, the response speed is the same as in the conventional uniform twist arrangement. TN-LCD and STN-
It has been found that it is even faster than LCDs and homogeneously arranged LCDs, and therefore the liquid crystal display device of the present invention can also obtain extremely fast response speed (Japanese Patent Application No. 3 of the prior application).
-344592, Japanese Patent Application No. 3-34493).

Further, according to the present invention, it is possible to obtain an element having the following operational effects with high productivity.

Since the light transmission state and the light scattering state are obtained by a slight change in the alignment of liquid crystal molecules, no hysteresis occurs in the electro-optical characteristics.

Further, since the combination of the molecular alignment states at the boundaries of the above-mentioned regions is different depending on the twist angle (including 0 °) of the liquid crystal, various combinations are possible,
It is possible to realize various things such as one having steep electro-optical characteristics and one having gentle characteristics. However, if the twist angle is larger than 270 °, the molecular arrangement in the voltage applied state may be memorized when the voltage applied state is switched to the non-applied state. This is not preferable because it results in a hysteresis in the electro-optical characteristics. Therefore, the twist angle of the liquid crystal is preferably 0 ° to 270 °.

Further, a liquid crystal display element was manufactured with a twist angle of 0 °, and each rubbing direction (which is the same direction in the upper and lower substrates in the cell plane) between two orthogonal polarizing plates and absorption of one polarizing plate. When combined so that the axes are parallel, a transmissive display can be obtained even when a scattered light source is used. In this case, an optical mode utilizing the birefringence effect is obtained, and the above-mentioned transmittance is lowered, but since the light transmission state is realized by the light scattering state of the liquid crystal layer, there is an effect that the viewing angle dependency is small. In particular, since the phenomenon of display inversion does not occur when gradation display is performed, it is possible to obtain display characteristics superior to those of the conventional TN-LCD as a direct-view display.

Further, since the light scattering state of the liquid crystal layer can be realized by a slight change in the alignment of the liquid crystal molecules, the applied voltage becomes a very small value. Therefore, an advantage that low voltage driving is possible can be obtained.

[0055]

EXAMPLES Examples of the liquid crystal display device of the present invention will be described below.

(Embodiment) FIG. 1 shows this embodiment.
FIG. 1A is a perspective view showing patterns of upper and lower electrodes, FIG.
FIG. 3 is a schematic cross-sectional view of a liquid crystal cell in which electrodes are opposed to each other.

A transparent common electrode 13 of ITO is formed on the entire surface of one surface of an upper substrate 11 made of glass, and an upper alignment film (AL-1051, made by Japan Synthetic Rubber) 15 which is a main chain type polyimide is formed on the surface. They are stacked. A 300 μm × 300 μm pixel electrode 1 made of ITO and arranged in a mosaic pattern on one surface of a lower electrode 12 made of the other glass.
4 is provided, and a lower alignment film (AL-1051, made by Japan Synthetic Rubber) 16 of the same main chain polyimide as the upper alignment film is laminated on the surface. The pretilt angle of the upper and lower alignment films 15 and 16 is 1
°.

The upper electrode 13 has a plurality of slits each having a width of 20 μm, that is, a non-conductive portion 13b, for each pixel p and has a width of 20.
The conductive portions 13a of μm are arranged in a stripe pattern at a pitch of 40 μm.
The conductive portion 13a of the book is formed.

The opposing lower electrodes 14 also have a pattern in which conductive portions 14a having a width of 20 μm and non-conductive portions 14b having a width of 20 μm are arranged at equal intervals, and six conductive portions 14a are formed within a width of 300 μm. . The conductive portions of these electrodes are offset from each other by 20 μm with the upper and lower substrates facing each other, and the conductive portion 13a or 14a of one electrode faces the non-conductive portion 14b or 13b of the other electrode. The lower electrode 14 is T
It has an FT switching element 17 and is connected to a gate line 18 and a signal line 19.

A cell is formed with the orientation directions F and R of the upper and lower substrates perpendicular to the conductive parts of the electrodes and in the same direction as shown in the figure, with the gap between the upper and lower substrates being 10 μm. Nematic liquid crystal (ZLI-
3926 (manufactured by Merck Japan) to fill the liquid crystal layer 20. This liquid crystal has a large Δn of 0.2030, so that the liquid crystal layer is selected to be as thick as 10 μm and the light scattering property is enhanced.

A voltage was applied from the power supply 21 to the liquid crystal display element of this example thus obtained through the TFT 17 and the degree of occurrence of disclination lines was observed with a microscope. 20
Disclination lines corresponding to the slit electrodes having a width of μm were uniformly generated.

That is, when a voltage is applied, an electric field having a lateral electric field component is generated between the electrodes, and the direction of the lateral electric field component changes in a minute range of one pixel. Therefore, the liquid crystal molecules M of the liquid crystal layer 20 respond to the electric field. Change the array. Therefore, a large number of disclination lines DL are generated at the boundaries of the liquid crystal alignment to create a light scattering state.

In order to obtain the transmittance-applied voltage curve of the device, He-Ne laser light was made incident on the liquid crystal display device,
The transmittance was measured. The spot diameter of the light was 2 mm, and the transmitted laser light was detected by a photodiode located at a distance of 20 cm from the liquid crystal display element. 0V in Figure 13
Gradually increase the applied voltage from 5V to 5V
The transmittance-applied voltage curve when decreasing to V is shown. The transmittance was about 80% when no voltage was applied (0 V was applied). Further, when the applied voltage was 2.8 V, the minimum transmittance was 0.4%, and a good scattering state was obtained. Further, when the response speed was measured at an applied voltage of 2.8 V and 0 V, an extremely fast value of 7 msec for rising and 25 msec for falling was obtained.

(Comparative Example) A liquid crystal display element was produced under the same conditions as in Example except that a side chain type polyimide (AL-3046, manufactured by Japan Synthetic Rubber) having a pretilt angle of 3 ° was used as the alignment film. When this element was driven by applying a voltage, a disclination line was generated, but when observing the location where it was observed with a microscope, the disclination line corresponding to the slit of 20 μm pitch provided in the electrode of one pixel was found. Occurrence was about 80% of the entire surface of the device. When the pretilt angles at a large number of points on both substrate surfaces were examined, it was found that the element surfaces varied from 2.5 ° to 4 °.

As described above with reference to the embodiments, other materials (for example, trade name HL-1100, manufactured by Hitachi Chemical Co., Ltd., trade name RN-) can be used as long as they are alignment films that induce a low pretilt angle of 2.5 ° or less in the present invention. 256, manufactured by Nissan Kagaku Co., Ltd. can be used, and it becomes easy to set the difference in pretilt angle between both substrates within the range of 0.3 ° or less. Also, simple matrix type,
It is needless to say that the present invention can be applied to various display elements such as an active matrix type and a display element that uses other elements such as MIM in addition to TFTs as its switching elements.

[0066]

According to the present invention, the liquid crystal molecule alignment behavior according to the applied oblique voltage can be obtained, and the liquid crystal display device having a high contrast ratio and excellent gradation can be obtained with high productivity.

[Brief description of drawings]

1A and 1B are diagrams illustrating an embodiment of a liquid crystal display element of the present invention, in which FIG. 1A is a perspective view of an electrode, and FIG.

2A and 2B are views for explaining a pretilt angle, where FIG. 2A is a schematic sectional view and FIG. 2B is a schematic plan view.

3A and 3B are diagrams illustrating a uniform arrangement, in which FIG. 3A is a schematic plan view and FIG. 3B is a schematic cross-sectional view.

FIG. 4 is a schematic cross-sectional view illustrating the behavior of liquid crystal molecules in a uniform twist alignment when a voltage is applied.

FIG. 5 is a curve diagram illustrating the relationship between applied voltage and transmittance.

FIG. 6 is a schematic plan view illustrating a uniform twist arrangement.

FIG. 7 is a schematic plan view illustrating a uniform twist arrangement.

8A and 8B are diagrams illustrating a spray arrangement, in which FIG. 8A is a schematic plan view and FIG. 8B is a schematic cross-sectional view.

FIG. 9 is a schematic plan view illustrating a splay twist arrangement.

FIG. 10 is a schematic plan view illustrating a splay twist arrangement.

11A to 11F are schematic cross-sectional views illustrating the behavior of liquid crystal molecules in a splay alignment depending on the presence or absence of an applied voltage.

FIG. 12 is a curve diagram showing changes in pretilt angle with respect to rubbing strength of a main chain type alignment film having no side chains and an alignment film having side chains.

FIG. 13 is a transmittance-applied voltage curve diagram of the device of the example of the invention.

14A and 14B are schematic cross-sectional views of a capsule-like structure and FIG. 14B is a schematic cross-sectional view of a fibrous polymer structure for explaining a conventional device.

[Explanation of symbols]

 11 ... Upper substrate 12 ... Lower substrate 13 ... Upper electrode 13a ... Conductor part 13b ... Non-conductor part 14 ... Lower electrode 14a ... Conductor part 14b ... Non-conductor part 15, 16 ... Alignment film 20 ... Liquid crystal layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Hato 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Incorporated company Toshiba Yokohama Office

Claims (2)

[Claims] 1. A liquid crystal layer made of a nematic liquid crystal having a positive dielectric anisotropy is sandwiched between two substrates each having electrodes forming a plurality of pixels facing each other, and a long axis of a liquid crystal molecule is formed on the surface of the substrate. Has an alignment film that induces a tilt alignment for arranging the liquid crystal molecules in one direction, and the intersection angle of the liquid crystal molecule alignment directions on the two substrates is θ (0 ° ≦ θ ≦ 90 °). In a liquid crystal display element with a cell twist angle of ψ, which is determined by the pretilt angle on the substrate surface so that the liquid crystal is in uniform twist alignment, ψ is ± θ (for convenience, the twist direction is When the counterclockwise direction is +, and when the clockwise direction is −, the twist angle ω of the liquid crystal is ± θ + 180 ° or ± θ−180 °.
When ψ is ± (θ-180 °), the liquid crystal twist angle ω is ±
θ (the same order as above), the electrodes of both substrates are made up of a conductive portion and a non-conductive portion in units of a fine region having a narrowest width of 30 μm or less for each pixel. At least a part of the conductor portion of one electrode and the non-conductor portion of the other electrode are arranged to face each other, and the pretilt angle in both the substrates is 2.5 ° or less. The liquid crystal display element is characterized in that the angle is 0.3 ° or less. 2. The liquid crystal display device according to claim 1, wherein the alignment films on both substrates are made of a main chain type organic compound having no side chains.