JP2002229039A - Photo-alignment material, and method for manufacturing photo-alignment layer using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photo-alignment material with no contaminating property for a liquid crystal, having superior display performance and heat resistance, a photo-alignment layer using the same and a liquid crystal display element using the same. SOLUTION: The photo-alignment material, containing an aromatic ester compound made of a bisphenol compound and an aromatic dicarboxylic acid compound, the photo-alignment layer using the same, the method for manufacturing the same and the liquid crystal display element using the same are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photo-alignment material, and more particularly, to a photo-alignment material capable of aligning liquid crystal molecules by irradiating light without performing a rubbing treatment.

[0002]

2. Description of the Related Art In a liquid crystal display device, the state of the molecular arrangement of liquid crystal is changed by the action of an electric field or the like, and the resulting change in optical characteristics is used for a display element or the like. In many cases, the liquid crystal is used in a state sandwiched between a gap between two substrates. Here, in order to align the liquid crystal molecules in a specific direction, an alignment process is performed inside the substrate. Usually, in the alignment treatment, a rubbing method is used in which a polymer film such as polyimide is provided on a substrate such as glass, and the polymer film is rubbed in one direction with a cloth or the like. As a result, the liquid crystal molecules in contact with the substrate are arranged so that their major axes (directors) are parallel to the rubbing direction. For example, twisted nematic (TN)
In the cell, two substrates coated with a hard film are opposed to each other between two orthogonal polarizers, and the rubbing directions are arranged so as to be orthogonal to each other to enable display by a change in light transmittance. ing.

The rubbing method has an advantage that the manufacturing apparatus is simple, but static electricity and dust are generated in the manufacturing process, so that a cleaning step is required after the alignment treatment.
In particular, in a TFT (thin-layer transistor) type liquid crystal cell, which is widely used in recent years, a TFT element provided on a substrate in advance is destroyed by static electricity, and this causes a reduction in the yield in manufacturing.

On the other hand, in the liquid crystal display device, since the inclination of the liquid crystal molecules constituting the liquid crystal device has directionality, the viewing angle dependency such that the display color or contrast changes depending on the direction in which the display device is viewed becomes a problem. I have. As one method of improving this, one pixel is divided and the pretilt angle of liquid crystal molecules (JP-A-62-159119) and the alignment direction (JP-A-63-106624) are changed for each region. An orientation division method has been devised. Such an orientation for each divided region requires a complicated process in the conventional rubbing method, and is not suitable for practical use.

In order to solve such a problem, a liquid crystal alignment control technique that does not use a rubbing method has recently attracted attention. As such a rubbingless orientation technique, an oblique deposition method,
An LB (Langmuir-Blodgett) film method, a photolithography method, a photo-alignment film method, and the like are being studied. In particular, a photo-alignment method for irradiating a coating film provided on a substrate with polarized light to generate liquid crystal alignment is simple and has been actively studied. The mechanism of this photo-alignment includes photo-isomerization by azo groups in organic molecules, photo-dimerization by cinnamoyl groups, coumarin groups, chalcone groups, etc., photo-crosslinking by benzophenone groups, photo-decomposition by polyimides, aromatic polyesters and aromatics. Intramolecular transition by aromatic polyamides and the like have been reported.

As a photo-alignment material utilizing photoisomerization, photodimerization or photocrosslinking, a polymer material is often used so that a uniform film can be obtained when applied to a substrate such as glass. A photosensitive group such as a group or a cinnamoyl group is often introduced into a side chain or a main chain of the polymer material. In some cases, a molecule having photo-alignment property is used as a guest molecule and dispersed in a host compound formed of a high molecular compound.
However, in such a conventional technique, for example, in the case of the photoisomerization type, the molecules are cis-tra
Since ns isomerization is used, isomerization occurs again when light is irradiated after the alignment treatment, and there is a problem in stability of the alignment state. In addition, in the case of the photodecomposition type, since the liquid crystal may be contaminated by decomposition products generated during the alignment treatment, it is necessary to wash the substrate after the treatment, and the features such as no need to wash the photoalignment film are lost. Will be

In the case of the photocrosslinking type, a benzophenone group is known (JP-A-9-80440). In this technique, a hydrogen atom donor is required for the progress of the photocrosslinking reaction. When the compound itself in the photo-alignment material becomes a hydrogen atom donor, the compound decomposes and causes contamination of the liquid crystal as in the photo-decomposition type, and it cannot be said that the photo-crosslinking reaction occurs uniformly. Even if a hydrogen atom donor substance is intentionally included in order to prevent the decomposition of the compound in the photo-alignment material and to improve the uniformity of the crosslinking reaction, it also causes liquid crystal contamination.

On the other hand, as photo-alignment materials utilizing intramolecular transition, aromatic polyesters and aromatic polyamides are disclosed in JP-A-9-230354 and Nagase et al. (The Proceedings of 6 ^TH IDW '99, 21, 1999). Etc. have been reported. Here, when using a specific aromatic polyamide,
A material that aligns liquid crystal molecules at a high tilt alignment angle is described. However, the production of the aromatic polyamides described requires the use of highly toxic aromatic amines as raw materials. On the other hand, it is described that the orientation of the liquid crystal is weak in the case of an aromatic polyester using bisphenol A.

[0009]

The problem to be solved by the present invention is to provide a photo-alignment material having excellent display performance and heat resistance without contamination of liquid crystal, a photo-alignment film using the same, and a photo-alignment film using the same. A liquid crystal display element is provided.

[0010]

The present inventors have conducted intensive studies and as a result have completed the present invention. That is, the present invention provides a photo-alignment material containing an aromatic ester compound (A) comprising a biphenol compound and an aromatic dicarboxylic acid compound.

Further, the present invention provides (B) a photo-alignment film using the photo-alignment material of the above A, a method for producing the same, and a liquid crystal display device using the same.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photo-alignment material containing an aromatic ester compound having a photo-intramolecular transition structure, a photo-alignment film using the same, a method for producing the same, and a liquid crystal using the photo-alignment film. It relates to a display element. The aromatic ester compound having an intramolecular photomolecular transfer structure of the present invention can be obtained by subjecting an aromatic dicarboxylic acid compound and a biphenol compound to a polycondensation reaction.

As the aromatic dicarboxylic acid compound, known and commonly used ones can be used, for example, terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6- Naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, 4,4'-
Examples thereof include bifunctional aromatic carboxylic acids such as diphenyl ether dicarboxylic acid and 4,4'-diphenylmethane dicarboxylic acid. Among them, terephthalic acid, isophthalic acid and orthophthalic acid are preferred. Further, the aromatic ring of the aromatic dicarboxylic acid compound is an alkyl group, a halogen group,
It may be substituted with an alkyl ether group, a silyl group, a silanol group, or the like.

These aromatic dicarboxylic acid compounds may be used alone or in combination of two or more. Particularly, a combination of terephthalic acid and isophthalic acid is preferable. Isophthalic acid or a combination of isophthalic acid and terephthalic acid is 1
It has a high solubility even in a solvent having a low boiling point of 00 ° C. or lower, and particularly, a molar ratio of isophthalic acid: terephthalic acid is 60:40.
To 100: 0 is particularly preferred because of its high solubility.
0 to 90:10 is more preferred.

These aromatic dicarboxylic acid compounds can be reacted as they are, or can be used as an esterified product or an acid chloride of the dicarboxylic acid compound. For example, in an interfacial polymerization method or a solution polymerization method, an acid chloride of a dicarboxylic acid compound is used, and in a melt polymerization method,
A dicarboxylic acid compound or a carboxylic acid ester thereof is used.

As the biphenol compound, for example,
4,4′-biphenol, 3,3 ′, 5,5′-tetramethyl-4,4′-biphenol, 3,3 ′, 5,5 ′
-Tetrabutyl-4,4'-biphenol and the like. Among them, it is preferable to use 3,3 ′, 5,5′-tetramethyl-4,4′-biphenol from the viewpoint of solubility in a solvent and heat resistance. These biphenol compounds may be used alone or in combination of two or more.

The terminal of the aromatic ester compound is phenol, p-cresol, p-ethylphenol, p-te
rt-butylphenol, p-cumylphenol, p-
A monovalent hydroxy compound such as octylphenol or a monovalent carboxylic acid compound such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, benzoic acid, p-methylbenzoic acid and p-tert-butylbenzoic acid; It may be sealed.

The glass transition point (hereinafter, abbreviated as Tg) of the aromatic ester compound of the present invention is not particularly limited as long as it is 60 ° C. or higher, but is preferably 180 ° C. or higher. At a temperature lower than this, the heat resistance is insufficient, and a heating step required for producing the liquid crystal cell, for example, when a thermosetting resin is used for bonding the alignment film substrates, there is a heating step for the liquid crystal cell,
As a result, the alignment film may be plasticized and the alignment performance may be lost. These heating steps are approximately 170
Since it is often carried out at about ° C, an alignment film material having a Tg of 180 ° C or more is preferably used as an alignment film material that can withstand such treatment.

The ester compound of the present invention is specifically represented by the general formula (1)

Embedded image

Wherein R is independently a hydrogen atom or 1
Indicate alkyl groups containing up to 8 carbon atoms. It is preferable to use those represented by the formula (1), and among them, those in which all R are methyl groups are more preferable because of good photoalignment performance and Tg balance.

The aromatic ester compound having a photo-intramolecular transfer structure of the present invention can be produced by a commonly used ester polycondensation reaction. For example, a transesterification polycondensation method in which an esterified product of a dicarboxylic acid compound is reacted with a dihydroxy compound, a deacetic acid polycondensation method in which an acetate compound of a dicarboxylic acid compound is reacted with a dihydroxy compound, and a direct polycondensation in which a dicarboxylic acid compound is reacted with a dihydroxy compound. Synthetic method, solution condensation method in which dicarboxylic acid chloride reacts with an alkali metal salt of dihydroxy compound in the presence of a base component such as pyridine in a solvent, interfacial polycondensation in which dicarboxylic acid chloride in an organic solvent also reacts with a dihydroxy compound in alkaline water Legal and the like.

In these methods, when the aromatic ester compound represented by the general formula (1) is produced, terephthalic acid, isophthalic acid, orthophthalic acid, or a combination thereof is used as the aromatic dicarboxylic acid compound. Used, and as a biphenol compound, 3,3 ′, 5,5′-
Using tetramethyl-4,4'-biphenol, it can be produced by a deacetic acid polycondensation method or an interfacial polycondensation method.

The weight average molecular weight of the aromatic ester compound thus obtained is preferably from 600 to 1,000,000, and from the viewpoint of physical properties and handling balance, it is preferably 10,000.
~ 500,000, more preferably 100,000 ~ 2.
00,000 is most preferred.

In the aromatic ester compound of the present invention, an aliphatic dicarboxylic acid compound, an aliphatic dihydroxy compound, or an aromatic bisphenol such as bisphenol A may be used in combination as a part of the raw materials. In addition, the aromatic ester compound of the present invention is usually used alone, but may be used as a mixture with a polymer material such as polyvinyl alcohol or polyimide.

The photo-alignment material of the present invention is dissolved in an appropriate solvent to form a photo-alignment solution to form a photo-alignment film. As the solvent, known and commonly used ones can be used.
Chloroform and the like are generally used. Above all, the aromatic ester compound having a repeating structure represented by the general formula (1) shows good solubility even in a low boiling point solvent, and therefore, it is particularly preferable to use these as a solvent. In particular, when a low-boiling solvent such as tetrahydrofuran, dichloromethane, or chloroform is used, a film-forming process, for example, a spin coating method or a printing method is applied to a substrate such as glass to form an alignment film on the substrate. It is preferable because the solvent can be quickly removed without particularly heating, and high-speed film formation can be performed, and productivity can be improved.

After film formation, an optical alignment operation is performed. This optical alignment operation is performed by irradiating polarized light. The wavelength of the polarized light is selected so that the intramolecular transition efficiently reacts with light.
Visible light, ultraviolet light and the like can be mentioned, and among them, ultraviolet light is preferable. As the polarized light, linearly polarized light or elliptically polarized light is often used. In particular, linearly polarized light obtained by obtaining light from an ultraviolet light source such as a xenon lamp, a high-pressure mercury lamp, and a metal halide lamp through a polarizing filter or a polarizing prism such as Glan-Thompson or Glan-Taylor is preferable. At this time, in order to obtain the pretilt of the liquid crystal molecules, a method of irradiating the substrate with polarized light in an oblique direction or a method of irradiating polarized light with unpolarized light in an oblique direction may be used.

An example of a method for manufacturing a liquid crystal display device using the photo-alignment film of the present invention will be described below. The photo-alignment material solution of the present invention was applied to the surfaces of two glass substrates provided with transparent electrodes such as ITO on which the electrodes were provided, dried, and then subjected to a photo-alignment operation. Obtain a photo-alignment film substrate. An epoxy adhesive containing, for example, styrene beads as a spacer is applied around these photo-alignment film substrates, leaving a liquid crystal injection port, so that the alignment surfaces face each other and the direction of polarized light is orthogonal. Liquid crystal is injected into the gap between the bonded photo-alignment film substrates, and the adhesive is heated and cured. The alignment direction and transmission of the photo-alignment film on each substrate are outside the liquid crystal cell thus manufactured. A liquid crystal display element is obtained by attaching a polarizing plate so that the polarization direction of the liquid crystal matches the polarization direction.

In the present invention, a photo-alignment material containing an aromatic ester compound having an intramolecular photo-molecular transition structure is coated on a substrate, dried, and then irradiated with polarized light to obtain a photo-alignment having high heat stability. Obtain a membrane. In addition, the aromatic ester compound of the present invention has high solvent solubility and is soluble in a solvent having a low boiling point, so that there is no need to heat for drying after coating,
Also, it has the feature that high productivity can be obtained because it is dried in a short time.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Synthesis Examples, Comparative Synthesis Examples, Examples and Comparative Examples, but the present invention is not limited to these ranges.

[Synthesis Example 1] In a reactor equipped with a stirring blade and a distilling apparatus, 3,3 ', 5,5'-tetramethyl-4,4'-
Biphenol 24.23 g (0.10 mol), acetic anhydride 22.46 g (0.22 mol), terephthalic acid 3.3
2 g (0.02 mol), 13.29 g of isophthalic acid
(0.08 mol) at 140 ° C. with stirring.
A reflux operation for a time was performed. Thereafter, the internal pressure of the reactor was reduced to 26 Pa while the internal temperature was raised to 250 ° C. over 1 hour. The temperature was maintained at 250 ° C. for 6 hours, and the temperature was raised to 280 ° C. over 1 hour. During that time, the acetic acid distilled out was drawn out of the system through the distillator. 280 ° C to 2
After holding for a time, the product was once removed from the reactor.
After powdering the obtained product, it was charged into an eggplant-shaped flask, and kept at 280 ° C. for 3 hours under a reduced pressure of 13 Pa while rotating the flask to obtain a powder of an aromatic ester compound.

The powder of the obtained aromatic ester compound was once dissolved in dichloromethane and poured into acetone to obtain a precipitate. The obtained precipitate is further washed with acetone, and dried in a vacuum dryer at 80 ° C. and 100 Pa for 2 hours to obtain 35 g.
Was obtained. The weight average molecular weight of this aromatic ester compound was measured by GPC and found to be 12
It was 0000. Dissolve this in dichloromethane and add 1
0% solution, apply it on a glass plate, and dry to a thickness of 80
A μm film was obtained. The Tg of this film was measured using a viscoelastic spectrometer (EXS
When measured using TAR6000 DMS) under the conditions of a sample width of 5 mm, a temperature rising rate of 1 ° C./min, and a frequency of 1 Hz, the glass transition point viewed from the tan δ peak temperature was 283.
° C.

Synthesis Example 2 A reactor equipped with a stirring blade and a nitrogen inlet was charged with 500 ml of deoxygenated water, and 8.8 g (0.22 mol) of sodium hydroxide was dissolved while introducing nitrogen. In this solution, 24.23 g (0.10 mol) of 3,3 ′, 5,5′-tetramethyl-4,4′-biphenol was dissolved to obtain an aqueous solution. Separately, 4.06 g (0.02 mol) of terephthalic acid chloride, 16.24 g (0.08 mol) of isophthalic acid chloride, and 0.68 g of methyltrioctylammonium chloride were dissolved in 450 ml of dichloromethane to obtain an organic solution. While stirring the aqueous solution under a nitrogen stream, the organic solution was added, and stirring was continued at 25 ° C. for 30 minutes. Then, after removing the aqueous phase, the organic solution phase containing the product was washed with ion-exchanged water.

The organic solution was poured into acetone to obtain a precipitate. The obtained precipitate was further washed with acetone and dried in a vacuum dryer at 80 ° C. and 100 Pa for 2 hours to obtain 32 g of an aromatic ester compound. The weight average molecular weight of this aromatic ester compound was determined to be 220,0 by GPC.
00. This was dissolved in dichloromethane to form a 10% solution, applied on a glass plate, and dried to obtain a film having a thickness of 80 μm. The Tg of this film was measured using a viscoelastic spectrometer at a sample width of 5 mm and a heating rate of 1 ° C. /
As a result, the glass transition point was 286 ° C. as viewed from the tan δ peak temperature.

[Comparative Synthesis Example 1]
5,5'-tetramethyl-4,4'-biphenol 2
The same operation was performed except that 4.23 g (0.10 mol) was replaced with 22,483 g (0.10 mol) of 4,4'-isopropylidene-diphenol, to obtain 32 g of an aromatic ester compound. The weight average molecular weight of this aromatic ester compound was 120,000, and the glass transition point was 162 ° C.

[Comparative Synthesis Example 2]
5,5'-tetramethyl-4,4'-biphenol 2
The same operation was performed except that 4.23 g (0.10 mol) of 4,4′-isopropylidene-diphenol was replaced by 22.83 g (0.10 mol), thereby obtaining 30 g of an aromatic ester compound. The weight average molecular weight of this aromatic ester compound was 240,000, and the glass transition point was 167 ° C.

A photo-alignment film was prepared using the photo-alignment materials obtained in the above synthesis examples and comparative synthesis examples, and physical properties were evaluated. The method for forming the photo-alignment film and the method for evaluating physical properties were performed according to the following methods.

[Method of Forming Photo-Alignment Film] a. Preparation of Photo-Alignment Material Solution The aromatic ester compound obtained in the above Synthesis Example was dissolved in dichloromethane to give a solution having a solid concentration of 2%, which was filtered through a 0.1 μm filter to obtain a photo-alignment material solution.

B. Preparation of photo alignment film a. The photo-alignment material solution obtained by the method of the above is uniformly coated on a glass substrate with an ITO electrode by a spin coater,
Drying was performed at room temperature for 30 minutes. Next, an integrated light amount of 30 J / cm ² was applied to the surface of the obtained coating film using an ultra-high pressure mercury lamp.
Irradiated with linearly polarized ultraviolet light having a wavelength of about 365 nm to form a photo-alignment film.

C. Preparation of liquid crystal cell b. An epoxy-based adhesive containing styrene beads with a diameter of 8 μm is applied around the photo-alignment film substrate obtained in step 2 except for the liquid crystal injection port, so that the orientation planes face each other and the polarization directions are orthogonal to each other. Overlap and crimp, apply adhesive 1
Curing was performed at 50 ° C. for 90 minutes. Next, a nematic liquid crystal (5CB) was vacuum-injected and filled with an isotropic phase from the liquid crystal injection port, and then the liquid crystal injection port was sealed with an epoxy-based adhesive.

[Evaluation Method of Photo Alignment Film] a. Evaluation of liquid crystal alignment property The above c. The liquid crystal cell obtained by the method described above is sandwiched between two polarizing plates whose polarization directions are orthogonal to each other, and a voltage of 5 V is applied between the electrodes to turn on / off and switch between light and dark, thereby changing the orientation of the liquid crystal. evaluated.

B. Measurement of voltage holding ratio c. A DC voltage of 5 V was applied to the liquid crystal cell obtained by the above method for 64 microseconds, and subsequently, the voltage was retained for 16.6 milliseconds, and the voltage holding ratio with respect to the initial applied voltage was measured.

Example 1 Using the aromatic ester compound obtained in Synthesis Example 1, a photo-alignment film was formed according to the above-described method for forming a photo-alignment film. A liquid crystal cell was prepared using the obtained photo-alignment film, and physical properties were evaluated according to the above evaluation methods. As a result, the voltage holding ratio was 99%, and the liquid crystal alignment was good.

Example 2 A photo-alignment film was prepared in the same manner as in Example 1 using the aromatic ester compound obtained in Synthesis Example 2. A liquid crystal cell was prepared using the obtained photo-alignment film, and physical properties were evaluated according to the above evaluation methods. As a result, the voltage holding ratio was 99%, and the liquid crystal alignment was good.

Comparative Example 1 Using the aromatic ester compound obtained in Comparative Synthesis Example 1, a photo-alignment film was formed in the same manner as in Example 1. A liquid crystal cell was prepared using the obtained photo-alignment film, and physical properties were evaluated according to the above evaluation methods. As a result, the voltage holding ratio was 63%, and no liquid crystal alignment was observed.

Comparative Example 1 Using the aromatic ester compound obtained in Comparative Synthesis Example 2, a photo-alignment film was formed in the same manner as in Example 1. A liquid crystal cell was prepared using the obtained photo-alignment film, and physical properties were evaluated according to the above evaluation methods. As a result, the voltage holding ratio was 75%, and no liquid crystal alignment was observed.

[0046]

The photo-alignment material containing the aromatic ester compound of the present invention has a high solvent solubility and is soluble in a solvent having a low boiling point. It is excellent in productivity. In addition, the obtained photo-alignment film has no liquid crystal contamination and high Tg, and thus has high stability against heat. A liquid crystal display device using the same has a high voltage holding ratio and good alignment stability. .

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masanobu Fukuda 1-27-1-B212 Osakidai, Sakura-shi, Chiba F-term (reference) 2H090 HB07Y HC08 HC13 HD14 HD15 4J029 AA03 AB01 AC01 AC02 AD01 AD09 AE03 BB10A CB05A CB06A KB02

Claims (9)

[Claims] 1. A photo-alignment material containing an aromatic ester compound comprising a biphenol compound and an aromatic dicarboxylic acid compound. 2. The method according to claim 1, wherein the aromatic dicarboxylic acid compound is isophthalic acid and / or terephthalic acid, and the molar ratio of isophthalic acid: terephthalic acid is from 60:40 to 100: 0. Photo alignment material. 3. An aromatic ester compound represented by the general formula (1): ## STR1 ## (Wherein, R independently represents a hydrogen atom or an alkyl group containing 1 to 8 carbon atoms). 4. The photo-alignment material according to claim 3, wherein all Rs in the general formula (1) are methyl groups. 5. The photo-alignment material according to claim 1, wherein the aromatic ester compound has a weight average molecular weight of 600 to 1,000,000. 6. A photo-alignment film using the photo-alignment material according to claim 1. 7. A liquid crystal display device using the photo-alignment film according to claim 6. 8. A method for producing a photo-alignment film, comprising applying the photo-alignment material according to any one of claims 1 to 5 on a substrate, drying the coating, and then applying polarized light. 9. The method for producing a photo-alignment film according to claim 8, wherein the polarized light to be applied is ultraviolet light.