JPH10197874A - Production of liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain high pretilt angles in spite of low-temp. firing by incorporating orientation control film components, their solvents and materials to lower the surface energy of the orientation control films into an orientation control film soln. at the time of forming the orientation control films by forming the orientation control films by applying an orientation control film soln. on transparent substrates and firing the coatings. SOLUTION: This liquid crystal element is composed by applying the orientation control film soln. on the transparent substrates 1, 1' having a pair of electrode patterns and firing the coatings to form the orientation control films, then holding liquid crystals 8 between the transparent substrates. The orientation control film soln. contains the orientation control film components, their solvents and the materials to lower the surface energy of the orientation control films. The orientation control film components are formed of polyamic acid or polyamide. The solvents to dissolve the orientation control components are composed of N-methyl-2-pyrrolidone as a good solvent and normal-butyl-Cellosolve as a lean solvent. The materials for lowering the surface energy of the orientation control films are preferably composed of acrylic acid-base solvents.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal device, and more particularly to a method for forming an alignment control film capable of obtaining a high pretilt angle when an alignment control film solution is applied and fired at a low temperature. The present invention relates to a method for manufacturing a liquid crystal element.

[0002]

2. Description of the Related Art Clark and Lagerwall have proposed a display device of a type that controls transmitted light in combination with a polarizing element utilizing the refractive index anisotropy of ferroelectric liquid crystal molecules. .
(JP-A-56-107216, U.S. Pat.
No. 7924). This ferroelectric liquid crystal generally has a chiral smectic C phase (Sm) in a specific temperature range.
C ^* ) or H phase (SmH ^* ), and takes either the first or second optically stable state (orientation state) in response to an electric field applied in this state, and no electric field is applied. It has the property of maintaining that state, that is, has bistability, and has a quick response to a change in electric field, and is expected to be widely used as a high-speed and storage-type display element.

A ferroelectric liquid crystal element is an optical modulation element using a liquid crystal having bistability, in which a ferroelectric liquid crystal is sandwiched between a pair of substrates provided with transparent electrodes. An alignment control film is provided on the transparent electrode of the substrate as a layer in contact with the ferroelectric liquid crystal layer. The alignment control film is a layer for aligning the liquid crystal of the liquid crystal element. In order for an optical modulation element using such a bistable liquid crystal to exhibit predetermined driving characteristics, the liquid crystal disposed between a pair of parallel substrates needs to have the above two stable states regardless of the applied state of an electric field. It is necessary to be in a molecular alignment state in which conversion between the states occurs effectively.

By the way, as for the orientation direction of the ferroelectric liquid crystal, a molecular layer organized by a plurality of molecules forming a smectic liquid crystal can be uniaxially oriented along a normal line in a large area. It is desirable that the manufacturing process can be realized by a simple rubbing treatment. As an alignment method for a ferroelectric liquid crystal, particularly a chiral smectic liquid crystal, for example, a method described in US Pat. No. 4,561,726 is known. As an orientation method for uniaxial orientation, uniform orientation by high pretilt interface by oblique deposition of SiO (Matsushita Electric Co., Ltd., JAPAN PLAY '86 464-
467) have been reported. However, this alignment method is not suitable for uniformly aligning a large screen. Therefore,
A high pretilt by rubbing alignment treatment which is excellent in productivity is desired.

Conventionally, a polyimide film, a polyamide film, or the like has been generally used as an alignment control film of a liquid crystal element. For the formation of this polyimide film, an alignment control film solution in which polyamic acid (an alignment control film component) is dissolved is used.
After applying the solution to a glass substrate (transparent substrate),
A polyimide film is obtained by baking at 00 ° C. and dehydration and ring closure. A good solvent such as NMP (N-methyl-2-pyrrolidone) is used as the solvent. Here, the “good solvent” refers to a solvent having a high dissolving ability and relatively dissolving the orientation control film component more.

On the other hand, to form a polyamide film, an alignment control film solution obtained by dissolving a polyamide (orientation control film component) in a good solvent such as NMP is used. A polyamide film is obtained.

However, if the orientation control film solution is prepared by simply dissolving the components of the orientation control film such as polyamic acid or polyamide in a good solvent such as NMP, unevenness tends to occur after firing. NBC for leveling to prevent this
A solution to which a poor solvent such as (normal-butyl-cellsolve) is added is generally used. Here, the term "poor solvent" refers to a solvent that has a lower dissolving ability than a good solvent and does not significantly dissolve the alignment control film component. Further, since nBC is easily evaporated and has poor printability, a high boiling point solvent such as n-butyl carbitol (diethylene glycol monobutyl ether) may be added to improve this point.

[0008]

Incidentally, the firing conditions of the alignment control film obtained by applying and firing the alignment control solution must be 250 ° C. or less due to restrictions on the constituent materials of the liquid crystal panel. In the alignment control film obtained at a temperature lower than the firing temperature, imidization of the film does not proceed sufficiently and the liquid crystal is stably aligned, and high pre-tilt alignment cannot be uniformly achieved in the liquid crystal panel plane, and 10 ° to 13 ° Only a low pretilt angle could be obtained.

Accordingly, an object of the present invention is to provide a method of manufacturing a liquid crystal element which can obtain a high pretilt angle even when firing at a low firing temperature of 250 ° C. or less when forming an alignment control film. It is assumed that.

[0010]

That is, according to the present invention, an alignment control film solution is applied and baked on a transparent substrate having a pair of electrode patterns to form an alignment control film. Wherein the alignment control film solution contains an alignment control film component, a solvent that dissolves the alignment control film component, and a substance that lowers the surface energy of the alignment control film. This is a method for manufacturing a liquid crystal element.

In the present invention, the orientation control film component is a polyamic acid or a polyamide, and the solvent for dissolving the orientation control film component is N-methyl-2-pyrrolidone as a good solvent and normal-butyl-cellsolve as a poor solvent. Is preferred.

Preferably, the substance which lowers the surface energy of the alignment control film is an acrylic acid-based solution, and its content is not more than 10% by weight with respect to the alignment control film solution. Preferably, the liquid crystal is a ferroelectric liquid crystal.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION
A method for manufacturing a liquid crystal element by coating and firing an alignment control film solution on a transparent substrate having a pair of electrode patterns to form an alignment control film, and sandwiching a liquid crystal between the pair of transparent substrates. The control film solution is characterized by adding an alignment control film component, a solvent for dissolving the alignment control film component, and a solvent that further applies the alignment control film solution and reduces the surface energy of the alignment control film after firing. And

In general, the smaller the value of the surface energy of the film after the formation of the alignment control film, the more uniform the high pretilt alignment can be obtained in the liquid crystal panel. According to the experiments of the present inventors, by adding an acrylic acid-based solution as a solvent, the surface energy after forming an alignment control film can be reduced by 4 to 8 dyne / cm as compared with an alignment control film not added. High pretilt is obtained even after rubbing, and uniform high pretilt alignment over the entire liquid crystal panel,
For example, it has become possible to obtain a pretilt angle of about 18 ° to 25 °.

In the present invention, the content of the acrylic acid-based solution to be added to the orientation control film solution is preferably 10% or less, more preferably 3 to 8% by weight based on the orientation control film solution. If the content exceeds 10%, the coating film is repelled on a substrate, which is not preferable.

Examples of the acrylic acid-based solution include hexanediol acrylate and hydroxyethyl methacrylate.

In the present invention, examples of the orientation control film component include polyamic acid and polyimide.
The content of the orientation control film component is 1.0 to 3.0% or less, preferably 1.5 to 2.0% by weight based on the orientation control film solution.
% Is desirable.

Further, the solvent for dissolving the orientation control film component includes:
A mixed solvent of a good solvent and a poor solvent is used. Examples of the good solvent include N-methyl-2-pyrrolidone, and examples of the poor solvent include normal-butyl-cellosolve. The content of the good solvent is 10 to 80%, preferably 50 to 65% by weight based on the orientation control film solution. The content of the poor solvent is preferably 10 to 80%, more preferably 20 to 40% by weight based on the orientation control film solution.

The manufacturing method of the present invention comprises a TN liquid crystal mode,
It is optimally applied to a method of manufacturing a liquid crystal element such as a TN liquid crystal mode or a ferroelectric liquid crystal mode using a chiral smectic liquid crystal.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples.

Embodiment 1 FIG. 1 schematically shows a cross section of a ferroelectric liquid crystal device according to an embodiment of the present invention, wherein 10 is a cell structure, 1 and 1 '.
Denotes a substrate, 2 ′ denotes a transparent electrode group, 3, 3 ′ denotes an insulating film,
4, 4 'are alignment control films, 5 is a sealing material, 6 is a spacer, 7 is an adhesive bead, and 8 is a ferroelectric liquid crystal. This cell structure 10 was created as follows.

First, ITO stripe electrodes 2 and 2 'are formed on two glass substrates 1 and 1' having a thickness of 1.1 mm, and an insulating film made of a Ta ₂ O ₅ film is formed thereon by sputtering. After forming the films 3 and 3 'to a thickness of 1000 °, polyimide alignment control films 4 and 4' were formed. In this embodiment, the composition of the solution of the polyimide alignment control films 4 and 4 'is 2.0% by weight of polyamic acid, 61.0% of NMP (N-methyl-2-pyrrolidone), and nBC (normal-butyl- (Cell Solve) 27.0%, hexanediol acrylate 10.0%, and after coating on a substrate, 24
The resultant was baked on a hot plate at 0 ° C. for 10 minutes to form a polyimide orientation control film having a thickness of about 200 °. The surface energy of the formed polyimide orientation control film was measured by the following method.

[Method of Measuring Surface Energy] A method of measuring surface energy will be briefly described with reference to FIG.
The surface energy γ is generally an important amount for determining the properties of the interface and the degree of contamination. The surface energy γ, that is, the wettability of the surface can be determined by measuring the contact angle. A method widely used as a contact angle measuring method includes a droplet method, a tilting plate method, a capillary rising method, and the like. In the present invention, the droplet method was used. In this droplet method, a droplet is placed on the surface of the orientation control film 11 serving as a sample,
Using a low magnification microscope, the droplet 12 is made into an enlarged image as shown in FIG. And the straight line 1 in the field of view
3 is rotated about the contact point with the droplet 12, and the angle at the position of the tangent is read. In the present invention, the contact angles of three types of liquids (α-bromonaphthalene, methylene iodide, and water) were measured by a droplet method, and the surface energy γ was calculated. When the surface energy γ was determined by the above method, 27 dyne / cm
Met.

A rubbing treatment is performed on a substrate on which the polyimide alignment control film is formed by using a rubbing cloth having a raised pile. Thereafter, a sealing material 5 is formed on the first substrate 1 by a printing method, and the sealing material 5 is formed by a spray method. Spacer 6 on substrate 1
And adhesive beads 7 were sprayed. The first substrate 1 thus obtained was bonded so that the rubbing directions of the second substrate 1 'were substantially parallel.

In the liquid crystal injection, a panel is introduced into an injection tank which can be heated and pressurized, and the inside of the panel is evacuated by evacuating the injection tank. Blocked. Thereafter, the temperature in the injection tank was increased to lower the viscosity of the liquid crystal, and the inside of the tank was pressurized to fill the entire panel with the liquid crystal. After the injection of the liquid crystal was completed, the liquid crystal panel was cooled down to the SmC ^* phase, and then the injection port was covered with an epoxy resin adhesive. The injected ferroelectric liquid crystal is a pyrimidine-based mixed liquid crystal exhibiting the following phase transition.

[0026]

(Equation 1)

Observation of the orientation of the panel after injecting the liquid crystal showed no defective orientation due to the addition of hexanediol diacrylate. Next, a pretilt angle measurement cell was prepared. However, they were bonded so that the rubbing directions of the upper and lower substrates were antiparallel. The pretilt angle was measured by the following method.

[Method of Measuring Pretilt Angle α] The pretilt angle is measured by a crystal rotation method (Jpn.
J. Appl. Phys. Vol. 119) (198)
0) No. Short Notes 2031). The liquid crystal for measuring the pretilt angle was measured by injecting, as a standard liquid crystal, a mixture of a ferroelectric liquid crystal (CS-1014 manufactured by Chisso Corporation) and a compound represented by the following structural formula at a weight ratio of 20%.

[0029]

Embedded image In addition, this mixed liquid crystal composition has a SmA
Phase.

In the measurement procedure, a helium-neon laser beam having a polarization plane forming an angle of 45 ° with the rotation axis is rotated while rotating the liquid crystal panel on a plane perpendicular to the upper and lower substrates and including an alignment processing axis (rubbing axis). Irradiation was performed from a direction perpendicular to the axis, and the transmitted light intensity was measured by a photodiode through a polarizing plate having a transmission axis parallel to the incident polarization plane on the opposite side.
Then, a pretilt angle α was determined by a simulation of fitting a theoretical curve, equations (1) and (2) to the transmitted light intensity spectrum generated by the interference.

[0031]

(Equation 2)

[0032]

(Equation 3) The pretilt angle obtained by the above method was 19.2 °.

Example 2 A liquid crystal cell was prepared in the same manner as in Example 1, and a similar liquid crystal was injected. However, the composition of the solution of the polyimide alignment control films 4 and 4 'was 2.0% by weight of polyamic acid, NMP6
1.0%, nBC 29.0%, and hydroxyethyl methacrylate 8.0% were applied on a substrate, and baked on a hot plate at 220 ° C. for 10 minutes to form a polyimide alignment control film having a thickness of about 200 °.

When the surface energy of the substrate on which the polyimide orientation control film was formed was measured, it was 26.5 dyne / c.
m. When the liquid crystal was injected and the alignment was observed in the same manner as in Example 1, no defective alignment due to the addition of hydroxyethyl methacrylate was observed. Further, a pretilt angle measuring cell was prepared and the pretilt angle was measured to be 18.7 °.

Comparative Example 1 A liquid crystal cell was prepared in the same manner as in Example 1, and the same liquid crystal was injected. However, the composition of the solution of the polyimide alignment control films 4 and 4 'is 2.0% by weight of polyamic acid, NMP
61.0%, nBC37.0%, applied on the substrate,
Bake on a hot plate at 240 ° C for 10 minutes, about 200
A polyimide alignment control film having a thickness of Å was formed.

When the surface energy of the substrate on which the polyimide alignment control film was formed was measured, it was found to be 34 dyne / c.
m. Also, create a pretilt angle measurement cell,
When the pretilt angle was measured, it was 12.5 °.

Comparative Example 2 A liquid crystal cell was prepared in the same manner as in Example 1, and the same liquid crystal was injected. However, the composition of the solution of the polyimide alignment control films 4 and 4 'is 2.0% by weight of polyamic acid, NMP
61.0%, nBC 24.0%, hexanediol diacrylate 13.0%, coated on a substrate, 240 ° C
For 10 minutes. However, the coating film was repelled on the substrate, and did not function as an alignment control film.

[0038]

As described above, according to the present invention,
In a liquid crystal element formed by applying an alignment control film solution,
By adding an acrylic acid-based solution as a solvent for the alignment control film solution, it is possible to apply the alignment control film solution and reduce the surface energy of the alignment control film after firing. A high pretilt angle can also be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of a liquid crystal element according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a method of measuring a contact angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1 'Substrate 2, 2' Transparent electrode group 3, 3 'Insulating film 4, 4' Alignment control film 5 Sealing material 6 Spacer 7 Adhesive beads 8 Ferroelectric liquid crystal 10 Cell structure 11 Alignment control film 12 Droplet 13 straight line

Claims (5)

[Claims] 1. A method for manufacturing a liquid crystal device, comprising forming an alignment control film by applying and firing an alignment control film solution on a transparent substrate having a pair of electrode patterns, and then sandwiching a liquid crystal between the transparent substrates. 3. The method for producing a liquid crystal device according to claim 1, wherein the alignment control film solution contains an alignment control film component, a solvent for dissolving the alignment control film component, and a substance that reduces the surface energy of the alignment control film. 2. The method according to claim 1, wherein the orientation control film component is polyamic acid or polyamide, and the solvent for dissolving the orientation control film component is N-methyl-2-pyrrolidone as a good solvent and normal-butyl-cellsolve as a poor solvent. 2. The method for manufacturing a liquid crystal device according to item 1. 3. The substance for lowering the surface energy of the alignment control film is an acrylic acid-based solution.
The manufacturing method of the liquid crystal element of the description. 4. The method for manufacturing a liquid crystal device according to claim 1, wherein the content of the substance that lowers the surface energy of the alignment control film with respect to the alignment control film solution is 10% or less by weight. 5. The liquid crystal according to claim 1, wherein said liquid crystal is a ferroelectric liquid crystal.
The manufacturing method of the liquid crystal element of the description.