JP3102973B2 - Liquid crystal display device and method of manufacturing the same - 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.
More specifically, the present invention relates to a structure of a display element that performs bistable switching of a dye-mixed nematic liquid crystal.

[0002]

2. Description of the Related Art In recent years, various liquid crystal display devices have been devised with the development of personal computers, word processors and the like. Among them, the display method that is currently widely used is TN (Twisted nemati).
c) and STN (Super twisted nematic). Each of these display systems is a system that utilizes the optical rotation of the liquid crystal.

On the other hand, a dichroic dye is mixed with the liquid crystal,
A system utilizing the absorption of light by a dye is a dye-mixed liquid crystal display device. Conventionally, a Heilmeier type and a white tailor type display element have been devised for a dye-mixed type liquid crystal display device. The Heilmeier type is a method in which a liquid crystal mixed with a dichroic dye is combined with a single polarizing plate, and the white tailor type uses a chiral material to make the molecules of the dichroic dye mixed type liquid crystal spiral between substrates. They are arranged and do not require a polarizing plate.

However, since these operating principles are of the field effect type utilizing the dielectric anisotropy of liquid crystal molecules, the response speed is only on the order of several hundreds to several tens msec, and a higher response speed is required. It is insufficient for applications such as CAD terminals.
In addition, the electro-optic effect is caused by a dichroic dye molecule in an alignment state parallel to the substrate and a state in which the dichroic dye molecule is raised on the substrate surface.
Since switching is performed using the difference in the light absorption characteristics between the two states, viewing angle dependence cannot be avoided in principle. Also, it is not suitable for large-capacity display due to lack of memory.

On the other hand, as a liquid crystal device having a high response speed, there are two types of liquid crystal devices: NAClark and Lagabal.
Gerwall) has proposed a surface-stabilized ferroelectric liquid crystal device, and it is conceivable to apply this to a dye-mixed liquid crystal display. SSFLC (Surface stabil
A symmetric ferro-electric liquid crystal display is a device that uses the electrical interaction between the polarity of the spontaneous polarization of a smectic liquid crystal and the polarity of an electric field to switch on a cone where liquid crystal molecules can move. It has the advantage that switching at an extremely high speed is possible as compared with liquid crystal, and there is no dependence on the viewing angle. On the other hand, since the smectic liquid crystal has a layer structure, it is difficult to control the alignment,
Further, there remains a problem that the orientation once broken by an impact or the like is difficult to recover.

For the above method, Georges. Duran has proposed two types of bistable liquid crystal display devices using a nematic liquid crystal, and it is conceivable to use these as a dye-mixed display. One of the bistable liquid crystal display devices using a nematic liquid crystal uses chiral ions as a driving torque (International Publication No. WO
No. 91/11747), both right-handed and left-handed chiral ions are mixed in a liquid crystal, and a bias is created in the ion distribution by a voltage, which is used as a driving torque. In this system, liquid crystal molecules can be switched in parallel to the substrate surface by applying a pulsed electric field as in the SSFLCD. However, since this method uses ions as impurities for driving, there remains an essentially large problem in reliability.

The other is a method in which flexo-polarization caused by orientation distortion is used as a driving torque (International Publication No. WO 92/00546).
No.), this method does not cause problems such as impurities, and high reliability is expected. In this method, similarly to the SSFLCD, it is possible to switch the liquid crystal molecules in parallel to the substrate surface by applying a pulsed electric field, and the response speed is 10 times.
In about 0 μsec, there is no viewing angle dependency because the liquid crystal molecules switch in parallel to the substrate surface. Further, since the nematic liquid crystal is used, there is no problem such as alignment control and weakness against impact unlike the SSFLCD, and the operating temperature range can be sufficiently widened.

[0008] Georges. The configuration of a nematic bistable display device based on flexo polarization, which has been reported by Durand, is as shown in FIG. In FIG. 1, (1) and (2) are glass substrates, (3) is a liquid crystal layer, and (4)
Is a transparent electrode, (5) is a SiO alignment film, and (6) is a spacer. The deposition angle of the SiO alignment film is 74 ° from the substrate radiation, the film thickness is 30 °, and the diameter of the spacer is about 1 to 3 μm. Under these conditions, the alignment direction of the liquid crystal molecules in the direction C perpendicular to the SiO deposition direction shown in FIG. 2 and parallel to the substrate surface becomes stable. However, since the anchoring energy between the interface and the liquid crystal is small, when twist power is added by adding a chiral agent, the substrate surface is tilted by θ °, and the direction projected on the substrate surface is α ° and −α from the SiO deposition direction. The orientation of the tilted directions A and B appears.

FIG. 3 shows the direction of SiO deposition and the direction in which the alignment of liquid crystal molecules can be stabilized. The orientation direction of the upper and lower substrates is antiparallel to the direction of SiO deposition on the upper and lower substrates.
It is configured by twisting 45 ° from As the liquid crystal material, a single liquid crystal to which a chiral material is added so as to be twisted by 22.5 ° between the upper and lower substrates is used. The twist direction is opposite to the twist in the SiO deposition direction between the upper and lower substrates shown in FIG. When a liquid crystal material is injected under such conditions, the alignment that can be stably present is limited by the effect of the chiral material, and the liquid crystal molecules are stable in two combinations of 1-3 ′ and 3-2 ′.

FIG. 4 is a cross-sectional view of the cell.
1-3 'and b correspond to the 3-2' orientation. If the molecular shape of the liquid crystal used here is wedge-shaped, flexo-polarization occurs due to the orientation distortion of the spray. The arrow in the figure indicates the direction of flexopolarization. Here, in a and b, the vertical component of flexo polarization is in the opposite direction. Therefore, bistable switching between the two states a and b can be performed by inverting the vertical component of flexo polarization by applying a pulse electric field. It is considered that this device is applied to a dye-mixed liquid crystal display device.

[0011]

However, if the above structure is applied to a dye-mixed display by mixing dichroic dyes, the efficiency of light utilization deteriorates because the rotation angle of the long axis of the molecule is about 45 °. There's a problem. The present invention has been made to solve the above problems.

[0012]

According to the present invention, upper and lower substrates having electrodes on the surface of a substrate and having an orientation over the entire surface thereof are arranged substantially in parallel and opposed to each other. In a liquid crystal display device comprising a liquid crystal interposed, a polarizing plate provided outside at least one of the substrates, and a driving device for switching a long axis of liquid crystal molecules, the liquid crystal is a dye mixture exhibiting a bistable nematic phase. The alignment film is made of a polymer film that has been uniaxially aligned, and the substrate has an alignment direction of an alignment film of an upper substrate and an alignment film of an alignment film of a lower substrate. The direction of processing is almost 9
The drive device is configured to be twisted by 0 °, and by applying a voltage, the molecular long axis of the upper substrate and the liquid crystal has a constant tilt angle, the molecular long axis of the lower substrate and the liquid crystal are parallel, and State 1 in which the major axes of the liquid crystal molecules near the upper and lower substrates projected on the substrate surface are almost the same as the orientation processing direction of the lower substrate, and the cross-sectional direction of the lower substrate and the major axis of the liquid crystal molecules have a fixed tilt angle. The longitudinal direction of the liquid crystal molecules is parallel to the cross-sectional direction of the upper substrate, and the long axes of the liquid crystal molecules near the upper and lower substrates projected on the substrate surface are almost the same as the orientation processing direction of the upper substrate. 2 is selectively switched. Further, according to the present invention, by performing an alignment treatment on the alignment film while controlling the rubbing strength, the alignment direction and the tilt angle of the liquid crystal molecules are controlled to a bistable nematic mode alignment. A manufacturing method is provided.

The orientation film in the present invention is a polymer film whose material has at least one 6-membered ring group,
The film itself has an in-plane orientation, and is a film which is further subjected to a uniaxial orientation treatment. For example, when the in-plane orientation is applied by a spin coating method or the like, an orientation in the centrifugal direction can be obtained. In addition, the non-oriented film is stretched in a predetermined direction, and then stretched in the lateral direction, and the film is obtained by orienting in-plane orientation. Either case is included in the alignment film. However, it is preferably formed by centrifugation. In the present invention, it is essential that the alignment film once formed as described above is subjected to uniaxial alignment treatment. As the method of the uniaxial treatment, a rubbing treatment is preferable.

The degree of the alignment film of the present invention can be measured by the alignment direction of the nematic liquid crystal on the alignment film. Two orientations of the nematic liquid crystal in the vicinity of the orientation film appear: a direction substantially parallel to the direction of the uniaxial treatment, and a direction of 10 ° to 80 ° with respect to the direction of the treatment.

The present invention will be described below with reference to the drawings. FIG.
1 is a panel configuration diagram of the present invention. (7) in FIG. 5,
(8) is a substrate, (9) is a liquid crystal layer, (10) is a transparent electrode,
(11) is a liquid crystal aligning polymer alignment film, (12) is a spacer, and (14) is a polarizing plate. As the substrate of the present invention, a light-transmitting insulating substrate is used, and a glass substrate is usually used. This insulating substrate has InO _3, SnO _2, IT
A transparent electrode having a predetermined pattern made of a conductive thin film such as O (Indium Tin Oxide) is formed.

An insulating film is arbitrarily formed thereon. As the insulating film, for example, an inorganic thin film such as SiO _2, SiNx, or Al ₂ O ₃ , or an organic thin film such as polyimide, a photoresist resin, or a polymer liquid crystal can be used. When the insulating film is an inorganic thin film, vapor deposition, sputtering, CVD
(Chemical Vapor Deposition) method or solution coating method. When the insulating film is an organic thin film, a solution in which an organic substance is dissolved or a precursor solution thereof is applied by a spinner coating method, a dipping coating method, a screen printing method, a roll coating method, etc. A method of forming by curing under conditions (heating, light irradiation, etc.), or a method of forming by vapor deposition, sputtering, CVD, etc.
It can also be formed by a B (Langumuir-Blodgett) method or the like.

The thickness of the insulating film is preferably 0.01 to 1 μm. Further, the thickness is preferably 0.02 to 0.5 μm, and most preferably 0.05 to 0.2 μm. If the thickness is less than 0.01 μm, the surface of the glass or the surface of the transparent electrode is undesirably affected. The thickness is 1 μm
If it is thicker, it causes a step with the glass surface portion, which is not preferable. A polymer alignment film having liquid crystal alignment is formed on the arbitrarily formed insulating film or transparent electrode.

As a material of the polymer alignment film having liquid crystal alignment, a vinyl compound having a 6-membered ring functional group, for example, a phenyl group in a side chain is preferable. For example, polystyrene, poly (2
-Bromostyrene), poly (3-bromostyrene), poly (4-bromostyrene), poly (2-chlorostyrene), poly (3-chlorostyrene), poly (4-chlorostyrene), and the like. , Poly (2-vinylpyridine), poly (4-vinylpyridine), polyvinylcarbazole, poly (2-nitrostyrene), poly (2-phenylstyrene), poly (2-methylstyrene), poly (2-methoxystyrene) ) Or poly (2-
Hydroxystyrene) and the like.

As a method for applying the alignment film, a method in which a polymer-dissolved solution is applied to a surface to be applied with a centrifugal force applied thereto, and the solvent is removed to orient in the direction of the centrifugal force can be applied.

The method of orienting in the direction of centrifugal force involves flowing a viscous solution in which a polymer is dissolved by centrifugal force and orienting the polymer chains along the direction of centrifugal force. Higher force and lower viscosity facilitate orientation.
Examples of the solvent used include aromatic hydrocarbons such as benzene, toluene, and xylene; halides such as carbon tetrachloride; and ketones such as ethyl methyl ketone. It is dissolved in these solvents at 10 to 50% by weight, and centrifuged at a temperature of 10 to 70 ° C. for orientation. Specific centrifugation conditions are determined by the type of the polymer and the degree of polymerization thereof, and thus it is difficult to express the condition in general. However, the rotation speed is, for example, 100 to 2,000 rpm.

An alignment process, for example, a rubbing process, is performed on the liquid crystal polymer alignment film. The rubbing treatment conditions are controlled by changing the type of cloth, the length of the fur, and the number of rotations of the roller during the rubbing treatment. In the polymer alignment film having liquid crystal alignment, the main chain direction of the polymer is aligned with the rubbing direction, and the side chain direction is arranged to be perpendicular to the rubbing direction. At this time, the liquid crystal molecules are uniformly aligned substantially parallel to the main chain direction of the polymer or the substrate surface when the rubbing is sufficiently strong on the alignment film, and parallel to the side chains of the polymer when the rubbing is weak. Alternatively, if the rubbing strength is appropriately selected, the substrate is uniformly oriented in an intermediate direction between the two states when the substrate is uniformly oriented with a certain tilt angle with respect to the substrate.

As described above, the orientation of the liquid crystal polymer alignment film can be adjusted by appropriately selecting the rubbing strength so that the orientation of the liquid crystal is parallel to the direction of the alignment treatment and 10% with respect to the direction of the alignment treatment. It is possible to obtain two orientation directions, ie, an orientation having an angle of ゜ 80 ° and an orientation film having various tilt angles. Thus, SiO
The same film quality as that of the obliquely deposited film can be realized uniformly and simply over a large area.

In the present invention, it is preferable that the orientation directions of the orientation film on one substrate and the orientation film on the other substrate are different from each other, particularly, 0 to 90 °. . Further, this angle is preferably 45 °. FIG. 8 shows the rubbing direction and the direction in which the liquid crystal molecule alignment can be stabilized in this case. The liquid crystal used is mixed with a chiral agent, and the twist direction is opposite to the rubbing direction between the upper and lower substrates. Further, the amount of the chiral agent varies depending on the type of the liquid crystal and the chiral agent.
And the chiral pitch (p) of the liquid crystal are preferably amounts that satisfy the following relationship: 0.05 <d / p <0.15.
Most preferably, p is about 0.125. Under the above conditions, only two combinations of the liquid crystal molecules 1-2 ′ and 2-1 ′ are completely stable. At this time, the state of 1-2 ′ is oriented in a splay shape extending obliquely downward, and the state of 2-1 ′ is oriented in a splay shape extending obliquely upward. Are expressed in opposite directions. Therefore, bistable switching between the two states can be performed by inverting the vertical component of flexo polarization by applying a pulse electric field. As a result, an ideal orientation can be obtained uniformly over a large area, and stable bistable switching can be realized.

The nematic liquid crystal of the present invention includes Schiff base, azo, azoxy, benzoate, biphenyl, terphenyl, cyclohexylcarboxylate, phenylcyclohexane, pyrimidine and dioxane liquid crystals. A multi-component liquid crystal which is a mixture thereof is exemplified. Specific examples of commercially available mixed liquid crystals include Merck's Z series (Z-1625, Z-1565,
Z-1780, Z-1800, Z1840, Z-182
5), E-series made by BDH (E-7, E-37, E
-31LV, E-80, E-44), R series manufactured by Roche (R-200, R-623, R-701, R-6)
19, R-627C), L series (L-
GR46, L-9106, L-EN24, L-P23N
N23) and D series (D-6) manufactured by Dainippon Ink.
01T, D-X01A, D-800). Further, these liquid crystals may be appropriately mixed and used.

Next, a chiral agent (optically active compound) is added to the liquid crystal. Thereby, the helical pitch of the liquid crystal phase is adjusted. Specific chiral agents are cholesteryl bromide, cholesteryl-n-hexyl ether, cholesteryl benzoate, cholesteryl n-hexylheptanoate, cholesteryl nunanoate,
[4- (2-methylbutyl) phenyl] benzene acid 4 '
-Cyanophenyl ester, t-4- (2-methylbutyl) cyclohexylcarboxylic acid cyanobiphenyl ester, 4-n-hexyloxybenzene acid 4 '-(2
-Butoxycarbonyl) phenyl ester, 4- (4 ′
-Methylbutyl) -4 "-cyano-p-terphenyl,
N- (4-ethoxybenzylidene) -4- (2-methylbutyl) aniline, 4- (2-methylbutyl) benzene acid 4'-n-hexyloxyphenyl ester, 4-n
-Heptoxy-4 '-(2-methylbutyloxycarbonyl) biphenyl, 4- (2-methylbutyl) -4'-
Carbonylphenyl, 4- [4- (2-methylbutyl)
[Phenyl] benzene acid 4'-butylphenyl ester and the like.

The liquid crystal is further added with a guest-host type dichroic dye. Here, as examples of dichroic dye compounds, those showing magenta are G214 and G24.
For example, 1 indicates green, such as a mixture of G282 and G232, cyan indicates G282 and G279, red indicates G205 and G156, yellow indicates G232, G143, and blue indicates G27
4, G277 (all manufactured by Japan Photographic Dye Laboratories) and the like.

Compounds other than the above compounds may be appropriately mixed in the nematic liquid crystal. This compound does not necessarily have to exhibit a liquid crystal phase, but (a) a compound for adjusting the temperature range of the liquid crystal phase of the composition to be produced; (b) a large spontaneous polarization in the ferroelectric liquid crystal phase or an induction. Optically active compounds.

After injection, UV of epoxy, acrylic, etc.
The injection port is sealed with a curable resin to form a liquid crystal cell. Further, a polarizing plate having a polarization axis substantially orthogonal to the liquid crystal cell is disposed on at least one of the upper and lower substrates of the liquid crystal cell, and the polarization axis of the polarizing plate is substantially coincident with the alignment processing direction of the substrate on which the liquid crystal cell is disposed. it can.

[0029]

【Example】

Example 1 Hereinafter, the present invention will be described in more detail. The bistable nematic liquid crystal cell portion was prepared by the following procedure. FIG.
Shows a cross section of the liquid crystal display unit.

1. 1 on each of glass substrates 7 and 8
A transparent electrode (10) having a thickness of 000 Å was formed. The thickness of the transparent electrode can be set in the range of 300 to 5000 angstroms, preferably 1000 to 3000 angstroms (1000 angstroms in this embodiment). 2.7 Polystyrene (1
A solution obtained by dissolving about 1% by weight of 1) was applied at a liquid temperature of about 25 ° C. at a rotation speed of 1,000 rpm by a spin coating method. At this time, the film thickness can be set in the range of 400 to 600 Å (5 in this embodiment).
00 angstroms).

3. Next, a rubbing process is performed on the substrate.
At this time, the pushing amount of the rubbing cloth was 0.2 mm, the rubbing cloth rotation speed was 100 rpm, and the substrate transfer speed was 6000 mm /
Minutes. 4. The rubbing directions of the upper and lower substrates were set such that the directions projected onto the substrates were shifted by 90 ° from the same direction.

Silica beads having a diameter of 1.5 μm were dispersed between the upper and lower substrates after the steps 5.1 to 4 and bonded together with a sealing member made of epoxy resin. The diameter of the silica beads can be set in the range of 1 to 3 μm, preferably 1.2 to 1.8 μm. A panel prepared through steps 6.1 to 5 is provided with a nematic liquid crystal (a host liquid crystal 5CB and a chiral agent S-811 in a volume of 0.1%).
72 wt% black pigment LMA-056 mixed with 20 wt%) was injected by a vacuum injection method. After the injection, the injection port was sealed with an acrylic UV curable resin.

A polarizing plate (14) was set on one side (7) of the panel prepared through steps 7.1 to 6. At this time, the polarization direction of the polarizing plate was adjusted so as to match the rubbing direction of the alignment film on the side where the polarizing plate was installed. 8. FIG. 7 shows the relationship between the electric field strength and the pulse width at the time of switching when a pulse electric field is applied to the panel prepared by the above procedure.

Embodiment 2 As shown in FIG. 6, in the liquid crystal panel prepared in Embodiment 1, a reflection plate (1) is provided between a substrate (8) and a transparent electrode (10).
A reflective liquid crystal display device was prepared in the same manner as in Example 1 except that 3) was installed. The contrast of the reflected light at this time was 5.

[0035]

According to the present invention, the light use efficiency is high.
It has become possible to provide a dye-mixed bistable liquid crystal display device having a high contrast and a wide viewing angle.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a prior art liquid crystal display device.

FIG. 2 is a schematic diagram showing a stable direction of liquid crystal molecules on a SiO alignment film.

FIG. 3 is a schematic diagram showing the relationship between the SiO deposition direction and the liquid crystal molecular alignment in the prior art.

FIG. 4 is a schematic view showing the orientation of liquid crystal in a cross section of a liquid crystal cell and the direction of flexopolarization generated at that time.

FIG. 5 is a schematic diagram of a liquid crystal display device of the present invention.

FIG. 6 is a schematic view of a reflection type liquid crystal display device of the present invention.

FIG. 7 is a diagram showing a relationship between an applied pulse width and an applied voltage during switching in the liquid crystal display device of the present invention.

FIG. 8 is a schematic view showing a rubbing direction and a stable direction of liquid crystal molecules in the liquid crystal display device of the present invention.

[Explanation of symbols]

 (1), (2) Glass substrate (3) Nematic liquid crystal layer (4) Transparent electrode (5) SiO vapor deposition film (6) Spacer (7), (8) Glass substrate (9) Nematic liquid crystal layer (10) Transparent electrode (11) Liquid crystal aligning polymer alignment film layer (12) Spacer (13) Reflector (14) Polarizer A Liquid crystal molecule at SiO interface B Liquid crystal molecule at SiO interface C Liquid crystal molecule at SiO interface 1,1 ′ Orientation of liquid crystal molecules on the substrate surface 2,2 'Orientation of liquid crystal molecules on the substrate surface 3,3' Orientation of liquid crystal molecules on the substrate surface

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shuichi Kanzaki 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-4-211225 (JP, A) JP-A-3-3 164713 (JP, A) JP-A-3-126918 (JP, A) JP-A-2-93431 (JP, A) JP-A-2-77016 (JP, A) JP-A-2-24627 (JP, A) JP-A-1-137237 (JP, A) JP-A-61-236526 (JP, A) WO 92/546 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1 / 1337 G02F 1/137

Claims (4)

(57) [Claims] An upper and lower substrate having electrodes on the surface of a substrate and having an orientation over the entire surface thereof is disposed substantially in parallel and opposed to each other, and a liquid crystal is interposed between these substrates. A liquid crystal display device provided with a polarizing plate on the outside of the device, and a driving device for switching the long axis of liquid crystal molecules, wherein the liquid crystal is composed of a dye-mixed liquid crystal composition exhibiting a bistable nematic phase, and The film is composed of a polymer film that is uniaxially oriented, and the substrate is oriented such that the orientation direction of the orientation film of the upper substrate and the orientation direction of the orientation film of the lower substrate are twisted by about 90 °. The driving device is configured such that, by applying a voltage, the molecular long axes of the upper substrate and the liquid crystal have a fixed tilt angle, and the molecular long axes of the lower substrate and the liquid crystal are parallel and projected onto the substrate surface. Near the upper and lower substrates State 1 in which the major axis of the crystal molecule is substantially the same as the orientation processing direction of the lower substrate, the sectional direction of the lower substrate and the major axis of the liquid crystal molecule have a certain tilt angle, and the sectional direction of the upper substrate and the liquid crystal molecule have the same tilt angle. The state 2 in which the major axes are parallel and the major axes of the liquid crystal molecules near the upper and lower substrates projected on the substrate surface are substantially in the same direction as the alignment processing direction of the upper substrate is selectively switched. Liquid crystal display device. 2. An alignment direction of a liquid crystal on an alignment film, the direction being parallel to the direction of the alignment treatment and the direction of the alignment treatment being 10 times.
2. The liquid crystal display device according to claim 1, wherein there are two alignment directions having an angle of not less than ゜ and not more than 80 °, and the pretilt angles in both alignment directions are different from each other. 3. The polymer is polystyrene, poly (2-bromostyrene), poly (3-bromostyrene), poly (4-bromostyrene), poly (2-chlorostyrene), poly (3-chlorostyrene). , Poly (4-chlorostyrene), poly (2-vinylpyridine), poly (4-
Vinylpyridine), polyvinylcarbazole, poly (2
-Nitrostyrene), poly (2-phenylstyrene),
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is poly (2-methylstyrene), poly (2-methoxystyrene) or poly (2-hydroxystyrene). 4. The liquid crystal display according to claim 1, wherein the alignment direction of the liquid crystal molecules and the tilt angle are controlled to a bistable nematic mode alignment by performing an alignment treatment on the alignment film while controlling the rubbing strength. Device manufacturing method.