JP4404090B2 - Liquid crystal aligning agent for photo-alignment and liquid crystal display device using the same - Google Patents

Description

  The present invention relates to a liquid crystal aligning agent for photo-alignment for forming a liquid crystal alignment film by a photo-alignment method, and a liquid crystal display element using the same.

  Liquid crystal display elements are currently widely used as display devices that are thin and light. It is known that the display characteristics of a liquid crystal display element are greatly affected by the orientation of the liquid crystal, the size of the pretilt angle of the liquid crystal, the stability of the pretilt angle, the electrical characteristics, and the like. In order to improve the display characteristics of such a liquid crystal display element, not only the liquid crystal material to be used but also a liquid crystal alignment film that directly contacts the liquid crystal and determines its alignment state is important.

  Currently, the liquid crystal alignment film mainly uses a resin solution of polyamic acid or polyimide as a liquid crystal alignment agent, and after applying them to the substrate, firing is performed, and the surface of the coating film is rubbed with rayon cloth or nylon cloth. It is formed by performing a so-called rubbing process. The method for obtaining a liquid crystal alignment film from polyimide or its precursor polyamic acid can create a coating film excellent in heat resistance and solvent resistance by a simple process such as coating and baking a resin solution, and a rubbing treatment. Since the liquid crystal can be easily aligned, it has become widespread industrially and has come to the present.

  However, in the case of rubbing, which is an alignment method that is currently widely used, display defects caused by scraping of the liquid crystal alignment film and adhesion of dust are problematic. In addition, there is a problem that a TFT (thin film transistor) element is destroyed by static electricity generated during rubbing, and as a result, a display defect occurs. Furthermore, in recent years, there has been a problem that uniform rubbing treatment is not performed due to an increase in size of the substrate.

  As a method for avoiding such a problem of rubbing treatment, a method (photo-alignment method) has been proposed in which a film formed on a substrate is irradiated with ultraviolet rays or the like to form a liquid crystal alignment film without rubbing treatment.

  Various proposals have also been made regarding film materials for this photo-alignment method. For example, as a material using polyimide, a material using a polyimide having an alicyclic structure in a structure portion derived from tetracarboxylic acid is used as a liquid crystal molecule. It has been reported that it can be uniformly and stably oriented (see, for example, Patent Document 1).

  On the other hand, as characteristics required for the liquid crystal alignment film, not only good alignment of liquid crystals but also electric characteristics when used as a liquid crystal element are important. Conventionally, as means for improving the electrical characteristics of a polyimide-based liquid crystal alignment film, a method using an additive of a compound, a method using an acid dianhydride or a diamine as a raw material for polyimide, and the like have been proposed. For example, as an example based on the selection of a diamine, it is known that a polyimide using a diamine having a paraphenylene structure has a high voltage holding ratio at a high temperature (see, for example, Patent Document 2).

  However, in the case of the photo-alignment method in which a chemical change is caused by irradiation with ultraviolet rays or the like, the electrical characteristics are often unexpected from the liquid crystal alignment film by the conventional rubbing treatment, and the electrical characteristics of the liquid crystal alignment film by the photo-alignment method In general, the electrical characteristics are often inferior to those of the liquid crystal alignment film by rubbing treatment. In particular, when the polymer is decomposed by ultraviolet rays or the like, there is a problem that the amount of impurity ions in the liquid crystal cell is increased and the voltage holding ratio is lowered as compared with the conventional rubbing method. This decrease in the voltage holding ratio causes problems such as a decrease in the reliability of the liquid crystal display panel, display unevenness, and sealant peripheral unevenness. Therefore, regarding the improvement of the electrical characteristics of the liquid crystal alignment film by the photo-alignment method, it is necessary to develop a material from a viewpoint different from the liquid crystal alignment film by the conventional rubbing treatment.

  As a means of improving the electrical characteristics of the film material for photo-alignment, a liquid crystal alignment film having good electrical characteristics can be obtained by using a polymer containing a polystyrene derivative structural unit or a maleimide structural unit having a conjugated enone structure in the side chain. Proposed. (For example, refer to Patent Document 3). A photo-alignment film having a good voltage holding ratio by using a photo-alignment film material made of a monomer having a polymerizable maleimide group has also been proposed (for example, see Patent Document 4).

  However, it cannot be said that the liquid crystal alignment film by the photo-alignment method has many options for the alignment film material as compared with the liquid crystal alignment film by the rubbing treatment. In particular, regarding a liquid crystal alignment film that has been used as a liquid crystal alignment film by rubbing, there has been no proposal of a structure suitable for a liquid crystal alignment film by a photo alignment method from the viewpoint of electrical characteristics.

JP-A-9-297313 JP-A-5-341291 JP 2000-281724 A JP 2002-317013 A

  The present invention has been made in view of the above circumstances, and not only good alignment properties of liquid crystals but also good electrical characteristics with respect to those using a proven polyimide-based material as a liquid crystal alignment film by rubbing treatment. In particular, it is an object to provide a liquid crystal aligning agent for obtaining a liquid crystal alignment film having characteristics such as a high voltage holding characteristic, a small amount of ions, and a small amount of accumulated charges by a photo-alignment method. It is another object of the present invention to provide a liquid crystal display element that eliminates problems associated with the rubbing treatment of the liquid crystal alignment film, has high reliability, and is less likely to cause display unevenness and stains around the sealing material.

The inventor of the present invention has found the present invention as a result of intensive studies to solve the above problems. That is, the present invention is the following liquid crystal aligning agent and liquid crystal display element for photo-alignment.
1. Obtained by reactive polymerization of a diamine component containing a diamine represented by the following formula (1) and a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride represented by the following formula (2). A liquid crystal aligning agent for photo-alignment, comprising at least one of a polyamic acid obtained or a polyimide obtained from the polyamic acid.

(Wherein, two are primary amino groups of R ¹ to R ^10, the remainder is a monovalent organic group other than a hydrogen atom or a primary amino group, but it may also be different and are each the same)

(Wherein R ^{11 to} R ¹⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms)
2 . A liquid crystal display element having a liquid crystal alignment film formed through a step of applying the liquid crystal aligning agent for photo-alignment described in 1 above to a substrate and a step of irradiating the substrate with polarized ultraviolet rays.

  The liquid crystal aligning agent for photo-alignment of the present invention can obtain a liquid crystal alignment film having excellent voltage holding characteristics, reducing the amount of ions, and having little accumulated charge by the photo-alignment method. Moreover, the liquid crystal display element which has the liquid crystal aligning film by the photo-alignment method obtained from the liquid crystal aligning agent of this invention eliminates the malfunction accompanying the rubbing process of a liquid crystal aligning film, and has the outstanding electrical property. For this reason, it is possible to provide a liquid crystal display device that is highly reliable and is less likely to cause display unevenness and spots around the sealing material, and includes a TN element, STN element, TFT liquid crystal element, and a horizontal electric field type liquid crystal display element. The liquid crystal display device can be suitably used for various types of display devices using nematic liquid crystal such as vertical alignment type liquid crystal display devices. Further, by selecting a liquid crystal to be used, it can be used for a ferroelectric and antiferroelectric liquid crystal display element.

The present invention is described in detail below.
The liquid crystal aligning agent of the present invention contains at least one of a polyamic acid obtained by reactive polymerization of a tetracarboxylic dianhydride component and a diamine component, or a polyimide obtained from the polyamic acid, In order to achieve orientation by polarized ultraviolet irradiation, high voltage holding characteristics, and low charge storage characteristics, at least a part of the tetracarboxylic dianhydride component is a tetracarboxylic dianhydride having an alicyclic structure, It is characterized in that at least a part of the diamine component is a diamine represented by the general formula (1).

  Specific examples of the tetracarboxylic dianhydride having an alicyclic structure used in the liquid crystal aligning agent of the present invention include 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 1,2-dimethyl-1. , 2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1, 2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 1,2 , 4,5-cyclohexanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 3,4-dicarboxy-1-cyclohexylsuccinic dianhydride, 3,4-di Rubokishi 1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride, and the like, but not limited thereto. These tetracarboxylic dianhydrides can be used alone or in combination.

  In addition, among tetracarboxylic dianhydrides having an alicyclic structure, the following formula (2) is shown in order to exhibit high voltage holding characteristics and to obtain excellent liquid crystal alignment properties by irradiation with polarized ultraviolet rays.

(Wherein R ^{11 to} R ¹⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms)
It is preferable to use a tetracarboxylic dianhydride represented by R ^{11 to} R ¹⁴ in the above formula are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. Specifically, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1 , 2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride is preferred, more preferably 1,2,3,4-cyclobutanetetracarboxylic dianhydride.

  The tetracarboxylic dianhydride component used in the liquid crystal aligning agent of the present invention may be used even in combination with the tetracarboxylic dianhydride having the above alicyclic structure and other tetracarboxylic dianhydrides. it can. Other tetracarboxylic dianhydrides include tetracarboxylic dianhydrides having an alicyclic structure such as bicyclo [3,3,0] octane-2,4,6,8-tetracarboxylic dianhydride, Aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic Acid dianhydride, 2,3,3 ′, 4′-benzophenonetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) sulfone Anhydride Fragrances such as 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride Group tetracarboxylic dianhydride, but is not limited thereto. Moreover, these tetracarboxylic dianhydrides can be used alone or in combination with a tetracarboxylic dianhydride having an alicyclic structure.

  Among these other tetracarboxylic dianhydrides, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic Although acid dianhydride and 1,4,5,8-naphthalenetetracarboxylic dianhydride tend to lower the voltage holding characteristics, they have excellent liquid crystal orientation and an effect of further reducing the accumulated charge. For this reason, when importance is attached to reducing the accumulated charge, it is preferable to use these tetracarboxylic dianhydrides in combination with a tetracarboxylic dianhydride having an alicyclic structure.

  In the tetracarboxylic dianhydride component used in the liquid crystal aligning agent of the present invention, the preferred ratio of the tetracarboxylic dianhydride having an alicyclic structure is 20 to 100 mol%, more preferably 50 to 100 mol. %. By increasing the ratio of tetracarboxylic dianhydride having an alicyclic structure, better photo-alignment properties can be obtained and high voltage holding characteristics can be obtained.

  General formula (1) used for the liquid crystal aligning agent of this invention

(In the formula, two of R ^{1 to} R ¹⁰ are primary amino groups and the rest are hydrogen atoms or monovalent organic groups other than primary amino groups, which may be the same or different)
Specific examples of the diamine represented by the formula (3) include diamines each having a primary amino group attached to different benzene rings as represented by the formula (3),

A diamine having two primary amino groups attached to the same benzene ring as represented by formula (4),

が挙げられる。また、これらのジアミンのベンゼン環上の水素原子は一級アミノ基以外の一価の有機基で置換されていてもよい。この一価の有機基としては、炭素数１〜２０のアルキル基やアルケニル基、シクロアルキル基、フェニル基、ビフェニル基、ターフェニル基、フッ素原子、又はこれらの組み合わせからなる基などが挙げられる。これら一般式（１）で表されるジアミンのうち、テトラカルボン酸二無水物との反応性および配向膜としたときの液晶配向性の観点から４，４’−ジアミノジフェニルアミン、２，４−ジアミノジフェニルアミンが好ましく、最も好ましいのは４，４’−ジアミノジフェニルアミンである。

Is mentioned. Moreover, the hydrogen atom on the benzene ring of these diamines may be substituted with a monovalent organic group other than the primary amino group. Examples of the monovalent organic group include groups having 1 to 20 carbon atoms, alkenyl groups, cycloalkyl groups, phenyl groups, biphenyl groups, terphenyl groups, fluorine atoms, or combinations thereof. Among these diamines represented by the general formula (1), 4,4′-diaminodiphenylamine and 2,4-diamino are considered from the viewpoints of reactivity with tetracarboxylic dianhydride and liquid crystal alignment when used as an alignment film. Diphenylamine is preferred, and most preferred is 4,4'-diaminodiphenylamine.

  Although the diamine component used for the liquid crystal aligning agent of this invention contains the diamine shown by General formula (1), it can also be used in combination with another diamine.

  Although the diamine which can be used in combination with the diamine shown by General formula (1) is not specifically limited, The following specific examples are mentioned. Examples of alicyclic diamines include 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, 4,4′-diaminodicyclohexylmethane, 4,4′-diamino-3,3′-dimethyldicyclohexylamine, and isophorone diamine Examples of carbocyclic aromatic diamines include o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, diaminotoluenes (for example, 2,4-diaminotoluene), 1,4-diamino -2-methoxybenzene, 2,5-diaminoxylenes, 1,3-diamino-4-chlorobenzene, 1,4-diamino-2,5-dichlorobenzene, 1,3-diamino-4-isopropylbenzene, 4, 4'-diaminodiphenyl-2,2'-propane, 4,4'-diaminodiph Nylmethane, 2,2′-diaminostilbene, 4,4′-diaminostilbene, 4,4′-diaminodiphenyl ether, 4,4′-diphenylthioether, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminodiphenyl Sulfone, 4,4′-diaminobenzoic acid phenyl ester, 2,2′-diaminobenzophenone, 4,4′-diaminobenzyl, bis (4-aminophenyl) phosphine oxide, bis (3-aminophenyl) methylsulfine oxide, Bis (4-aminophenyl) phenylphosphine oxide, bis (4-aminophenyl) cyclohexylphosphine oxide, N, N′-bis (4-aminophenyl) -N-phenylamine, N, N-bis (4-aminephenyl) ) -N-methylamine, 4,4'-diaminodiph Nilurea, 1,8-diaminonaphthalene, 1,5-diaminonaphthalene, 1,5-diaminoanthraquinone, diaminofluorene, bis (4-aminophenyl) diethylsilane, bis (4-aminophenyl) dimethylsilane, bis (4 -Aminophenyl) tetramethyldisiloxane, 3,4'-diaminodiphenyl ether, benzidine, 2,2'-dimethylbenzidine, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, bis [4- ( 4-aminophenoxy) phenyl] sulfone, 4,4′-bis (4-aminophenoxy) biphenyl, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 1,4-bis (4 -Aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene Etc.

  Furthermore, as heterocyclic diamines, 2,6-diaminopyridine, 2,4-diaminopyridine, 2,4-diamino-s-triazine, 2,7-diaminodibenzofuran, 2,7-diaminocarbazole, 3,7 Examples of aliphatic diamines include diaminophenothiazine, 2,5-diamino-1,3,4-thiadiazole, 2,4-diamino-6-phenyl-s-triazine, and the like. Diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane 1,3-diamino-2,2-dimethylpropane, 1,4-diamino-2,2-dimethylbutane, 1,6-dia No-2,5-dimethylhexane, 1,7-diamino-2,5-dimethylheptane, 1,7-diamino-4,4-dimethylheptane, 1,7-diamino-3-methylheptane, 1,9- Examples include diamino-5-methylnonane, 2,11-diaminododecane, 1,12-diaminooctadecane, 1,2-bis (3-aminopropoxy) ethane and the like.

  Of the diamines that can be used in combination with the diamine represented by the general formula (1), o-phenylenediamine, m-phenylenediamine, p-phenylenediamine and diaminotoluenes (for example, 2,4) from the viewpoint of photoalignment. -Diaminotoluene), 1,4-diamino-2-methoxybenzene, phenylenediamine derivatives such as 2,5-diaminoxylenes are preferred, and p-phenylenediamine is most preferred. When p-phenylenediamine is used in order to obtain good photoalignment, the preferred ratio is 10 mol% or more, more preferably 30 mol% or more.

  In addition, for the purpose of increasing the pretilt angle of the liquid crystal, a diamine having a structure in which an organic group known to increase the tilt angle such as a long chain alkyl group, a perfluoroalkyl group, or a steroid skeleton group is combined with the diamine is used in combination. May be. Specific examples thereof include 1,3-diamino-4-dodecyloxybenzene having a structure in which a long-chain alkyl group is bonded to the benzene ring of m-phenylenediamine via an ether bond.

  In the diamine component used in the liquid crystal aligning agent of the present invention, in order to obtain a high voltage holding ratio, the preferred ratio of the diamine represented by the general formula (1) is 10 to 100 mol%, more preferably 30 to 100. Mol%.

  The tetracarboxylic dianhydride component and diamine component used in the liquid crystal aligning agent of the present invention can be reacted to form a polyamic acid by mixing in an organic solvent, and polyimide can be obtained by dehydrating and ring-closing this polyamic acid. It can be.

  As a method of mixing the tetracarboxylic dianhydride component and the diamine component in an organic solvent, a solution in which the diamine component is dispersed or dissolved in the organic solvent is stirred, and the tetracarboxylic dianhydride component is used as it is or in an organic solvent. A method of adding by dispersing or dissolving in a solvent, a method of adding a diamine component to a solution in which a tetracarboxylic dianhydride component is dispersed or dissolved in an organic solvent, and a tetracarboxylic dianhydride component and a diamine component. The method of adding alternately etc. are mentioned, In this invention, any of these methods may be sufficient. Further, when the tetracarboxylic dianhydride component or the diamine component is composed of a plurality of types of compounds, the plurality of types of components may be reacted in a mixed state in advance or may be reacted individually and sequentially.

  The temperature at the time of making a tetracarboxylic dianhydride component and a diamine component react in an organic solvent is 0-150 degreeC normally, Preferably it is 5-100 degreeC, More preferably, it is 10-80 degreeC. When the temperature is higher, the polymerization reaction is completed earlier, but when it is too high, a high molecular weight polymer may not be obtained. The reaction can be carried out at any concentration, but if the concentration is too low, it is difficult to obtain a high molecular weight polymer, and if the concentration is too high, the viscosity of the reaction solution becomes too high and uniform stirring is difficult. Therefore, it is preferably 1 to 50% by weight, more preferably 5 to 30% by weight. The initial reaction may be carried out at a high concentration, and then an organic solvent may be added.

  The organic solvent used in the above reaction is not particularly limited as long as the produced polyamic acid can be dissolved, but specific examples thereof include N, N-dimethylformamide, N, N-dimethylacetamide, Examples thereof include N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethyl sulfoxide, tetramethyl urea, pyridine, dimethyl sulfone, hexamethyl sulfoxide, and γ-butyrolactone. These may be used alone or in combination. Furthermore, even if the solvent does not dissolve the polyamic acid, it may be used by mixing with the above solvent as long as the produced polyamic acid does not precipitate. In addition, since water in the organic solvent inhibits the polymerization reaction and further causes hydrolysis of the generated polyamic acid, it is preferable to use a dehydrated and dried organic solvent as much as possible.

  The ratio of the tetracarboxylic dianhydride component and the diamine component used for the polymerization reaction of polyamic acid is preferably 1: 0.8 to 1: 1.2 in terms of molar ratio. Similar to the normal polycondensation reaction, the closer the molar ratio is to 1: 1, the higher the molecular weight of the polyamic acid obtained. If the molecular weight of the polyamic acid is too small, the strength of the coating film obtained therefrom may be insufficient. Conversely, if the molecular weight of the polyamic acid is too large, the viscosity of the liquid crystal aligning agent produced therefrom will increase. Thus, workability during coating film formation and uniformity of the coating film may be deteriorated. Therefore, the polyamic acid used in the liquid crystal aligning agent of the present invention preferably has a weight average molecular weight (polyethylene glycol, polyethylene oxide equivalent) measured by GPC of 2000-250,000, more preferably 4000-200000.

  The polyamic acid obtained as described above may be used as it is in the liquid crystal aligning agent of the present invention, or may be used after being dehydrated and ring-closed polyimide. However, depending on the structure of the polyamic acid, it may be difficult to use it for the liquid crystal aligning agent by insolubilization by imidization reaction. In this case, all the amic acid groups in the polyamic acid may not be imidized, but may be imidized within a range where appropriate solubility can be maintained.

  The imidization reaction for dehydrating and ring-closing the polyamic acid is generally thermal imidation in which the polyamic acid solution is heated as it is, or chemical imidization in which a catalyst is added to the polyamic acid solution. Of these, chemical imidation in which the imidization reaction proceeds at a relatively low temperature is preferable because the molecular weight of the resulting polyimide is less likely to decrease.

  Chemical imidation can be performed by stirring polyamic acid in an organic solvent in the presence of a basic catalyst and an acid anhydride. The reaction temperature at this time is -20-250 degreeC, Preferably it is 0-180 degreeC, and reaction time can be performed in 1 to 100 hours. The amount of the basic catalyst is 0.5 to 30 mol times, preferably 2 to 20 mol times of the amic acid group, and the amount of the acid anhydride is 1 to 50 mol times, preferably 3 to 30 mol of the amic acid group. Is double. If the amount of the basic catalyst or acid anhydride is small, the reaction does not proceed sufficiently. If the amount is too large, it becomes difficult to completely remove the reaction after completion of the reaction. Examples of the basic catalyst used at this time include pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine and the like. Among them, pyridine is preferable because it has an appropriate basicity for proceeding with the reaction. Examples of the acid anhydride include acetic anhydride, trimellitic anhydride, pyromellitic anhydride, and the like. Of these, use of acetic anhydride is preferred because purification after completion of the reaction is facilitated. As an organic solvent, the solvent used at the time of the polyamic acid synthesis mentioned above can be used. The imidation rate by chemical imidation can be controlled by adjusting the amount of catalyst, reaction temperature, and reaction time.

  In the polyimide solution thus obtained, the added catalyst remains in the solution. Therefore, in order to use it for the liquid crystal aligning agent of the present invention, the polyimide solution is put into a poor solvent which is stirred and precipitated. It is preferable to collect. Although it does not specifically limit as a poor solvent used for precipitation collection | recovery of a polyimide, Methanol, acetone, hexane, a butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, benzene etc. can be illustrated. The polyimide precipitated by adding it to a poor solvent can be recovered by filtration, washing and drying at room temperature or under reduced pressure at normal temperature or by heating. If the operation of dissolving this powder in a good solvent and reprecipitating is repeated 2 to 10 times, the polyimide can be purified. When the impurities cannot be removed by a single precipitation recovery operation, it is preferable to perform this purification step. In this case, it is preferable to use three or more kinds of poor solvents such as alcohols, ketones, and hydrocarbons as the poor solvent because the purification efficiency is further increased.

  Polyamic acid can also be collected and purified by the same operation. When it is not desired to include the solvent used for the polymerization of the polyamic acid in the liquid crystal aligning agent of the present invention, or when unreacted monomer components and impurities are present in the reaction solution, this precipitation recovery and purification can be performed. Good.

  The liquid crystal aligning agent of the present invention contains at least one of a polyamic acid having a specific structure obtained as described above or a polyimide obtained by dehydrating and ring-closing the polyamic acid. A configuration of a resin solution dissolved in a solvent is taken. In order to obtain a resin solution, a reaction solution of polyamic acid or polyimide may be used as it is, or a precipitate recovered from the reaction solution may be redissolved in an organic solvent.

  The organic solvent is not particularly limited as long as it can dissolve the resin component contained therein, but specific examples thereof include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl- 2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, dimethylsulfoxide, tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide, γ-butyrolactone, and the like. May be used alone or in combination.

  Moreover, even if it is a solvent which does not dissolve a resin component alone, it can be mixed with the liquid crystal aligning agent of the present invention as long as the resin component does not precipitate. In particular, ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, ethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol, 1-phenoxy -2-propanol, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol-1-monomethyl ether-2-acetate, propylene glycol-1-monoethyl ether-2-acetate, dipropylene glycol, 2- (2-ethoxy Propoxy) solvents with low surface tension such as propanol, lactate methyl ester, lactate ethyl ester, lactate n-propyl ester, lactate n-butyl ester, lactyl isoamyl ester By mix whenever, when applied to a substrate are known to coating uniformity is improved, also suitably used in the liquid crystal aligning agent of the present invention.

  Although the solid content concentration of the liquid crystal aligning agent of this invention can be suitably changed with the setting of the thickness of the liquid crystal aligning film to form, it is preferable to set it as 1 to 10 weight%. If it is less than 1% by weight, it is difficult to form a uniform and defect-free coating film, and if it exceeds 10% by weight, the storage stability of the solution may deteriorate.

  In addition, in order to improve the adhesion of the coating film to the substrate, an additive such as a silane coupling agent may be added to the liquid crystal aligning agent of the present invention, and two or more kinds of polyamic acid and polyimide are mixed. Or other resin components may be added.

  The liquid crystal aligning agent of the present invention obtained as described above can be filtered, then applied to a substrate, dried and baked to form a coating film. It is used as a liquid crystal alignment film by irradiating the substrate surface in a certain direction and performing photo-alignment treatment.

  In this case, the substrate to be used is not particularly limited as long as it is a highly transparent substrate, and a glass substrate, a plastic substrate such as an acrylic substrate or a polycarbonate substrate, or the like can be used. It is preferable to use a substrate on which an ITO electrode or the like for driving liquid crystal is formed from the viewpoint of simplifying the process. Further, in the reflection type liquid crystal display element, an opaque material such as a silicon wafer can be used as long as the substrate is only on one side, and in this case, a material that reflects light such as aluminum can be used.

  Examples of the method for applying the liquid crystal aligning agent include a spin coating method, a printing method, and an ink jet method. Of these, the transfer printing method is widely used industrially from the viewpoint of productivity, and is also suitably used in the liquid crystal aligning agent of the present invention.

  The drying process after applying the liquid crystal aligning agent is not necessarily required, but if the time from application to baking is not constant for each substrate, or if baking is not performed immediately after application, a drying process is included. Is preferred. The drying is not particularly limited as long as the solvent is evaporated to such an extent that the shape of the coating film is not deformed by the conveyance of the substrate or the like. If a specific example is given, the method of drying on a hotplate of 50-150 degreeC, Preferably 80-120 degreeC for 0.5 to 30 minutes, Preferably it is 1 to 5 minutes is taken.

  Although baking of a liquid crystal aligning agent can be performed at 100-350 degreeC arbitrary temperatures, Preferably it is 150 to 300 degreeC, More preferably, it is 200 to 250 degreeC. When the liquid crystal aligning agent contains a polyamic acid, the conversion rate from the polyamic acid to the polyimide changes depending on the baking temperature, but the liquid crystal aligning agent of the present invention does not necessarily need to be imidized 100%. However, baking is preferably performed at a temperature higher by 10 ° C. or more than the heat treatment temperature required for the liquid crystal cell manufacturing process, such as sealing agent curing.

  If the thickness of the coating film after baking is too thick, it will be disadvantageous in terms of power consumption of the liquid crystal display element, and if it is too thin, the reliability of the liquid crystal display element may be lowered, so it is 5 to 300 nm, preferably 10 to 100 nm. It is.

  The polyimide film obtained as described above is irradiated with ultraviolet rays polarized through a polarizing plate from a certain direction with respect to the substrate. As the wavelength of ultraviolet rays to be used, ultraviolet rays in the range of 100 nm to 400 nm can be generally used, but it is particularly preferable to select an optimum wavelength through a filter or the like depending on the type of polyimide to be used. The irradiation time of ultraviolet rays is generally in the range of several seconds to several hours. However, considering the industrial productivity and the possibility of causing a decrease in voltage holding ratio due to an increase in irradiation amount, good orientation can be obtained. It is preferable to select the required amount according to the type of polyimide used.

  The liquid crystal display element of the present invention is a liquid crystal display element obtained by obtaining a substrate with a liquid crystal alignment film from the liquid crystal aligning agent of the present invention by the method described above, and then preparing a liquid crystal cell by a known method. As an example of liquid crystal cell production, an alignment direction by light irradiation is 0 to 270 ° between a pair of substrates on which a liquid crystal alignment film is formed and a spacer of 1 to 30 μm, preferably 2 to 10 μm is sandwiched between them. A method is generally used in which the angle is set to be fixed, the periphery is fixed with a sealant, and liquid crystal is injected and sealed. The method for enclosing the liquid crystal is not particularly limited, and examples thereof include a vacuum method of injecting liquid crystal after reducing the pressure inside the produced liquid crystal cell, and a dropping method of sealing after dropping the liquid crystal.

  Thus, since the liquid crystal display element produced using the liquid crystal aligning agent for photo-alignment of the present invention has excellent electrical characteristics, the reliability is high, and display unevenness and occurrence of spots around the sealing material are generated. It can be set as a liquid crystal display device which is hard to occur. Among them, the TN element, STN element, TFT liquid crystal element, and further, it is suitably used for various types of display elements using nematic liquid crystal such as a horizontal electric field type liquid crystal display element and a vertical alignment type liquid crystal display element. Further, by selecting a liquid crystal to be used, it can be used for a ferroelectric and antiferroelectric liquid crystal display element.

  The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

Explanation of abbreviations used in this example (tetracarboxylic dianhydride)
CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride
1,3DM-CBDA: 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride (diamine)
4,4′DADPA: 4,4′-diaminodiphenylamine p-PDA: p-phenylenediamine DDE: 4,4′-diaminodiphenyl ether (organic solvent)
NMP: N-methyl-2-pyrrolidone BCS: Butyl cellosolve

(Synthesis Example 1) CBDA / 4,4'DADPA
CBDA 19.61 g (0.1 mol) as a tetracarboxylic dianhydride component and 19.13 g (0.096 mol) 4,4'DADPA as a diamine component are mixed in 348.6 g of NMP and reacted at room temperature for 5 hours to give a polyamic acid solution A. Got. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured with GPC-101 (manufactured by Shodex). As a result, it was 50000 (in terms of polyethylene glycol and polyethylene oxide). Furthermore, NMP and BCS were added to this solution so that it might become 4 weight% of polyamic acid, 76 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Synthesis Example 2) CBDA / 4,4'DADPA, CBDA / p-PDA
19.61 g (0.1 mol) of CBDA as a tetracarboxylic dianhydride component and 10.38 g (0.096 mol) of p-PDA as a diamine component are mixed in 269.9 g of NMP and reacted at room temperature for 5 hours to obtain a polyamic acid solution B. It was. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured in the same manner as in Synthesis Example 1. As a result, it was 47000. The polyamic acid solution A and the polyamic acid solution B obtained in Synthesis Example 1 were mixed at a solid content ratio of 1: 1 to obtain a uniform solution. Furthermore, NMP and BCS were added to this solution so that it might become 4 weight% of polyamic acid, 76 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Comparative Synthesis Example 1) CBDA / p-PDA
NMP and BCS were added to the polyamic acid solution B obtained in Synthesis Example 2 so as to be 4% by weight of polyamic acid, 76% by weight of NMP, and 20% by weight of BCS to obtain a liquid crystal aligning agent for comparison.

(Comparative Synthesis Example 2) CBDA / DDE
CBDA 19.41 g (0.099 mol) as a tetracarboxylic dianhydride component and DDE 20.02 g (0.1 mol) as a diamine component were mixed in 223.48 g of NMP and reacted at room temperature for 5 hours to obtain a polyamic acid solution C. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured in the same manner as in Synthesis Example 1. As a result, it was 65,000. Furthermore, NMP and BCS were added to this solution so that it might become 4 weight% of polyamic acid, 76 weight% of NMP, and 20 weight% of BCS, and it was set as the liquid crystal aligning agent for a comparison.

Example 1
The liquid crystal aligning agent of the present invention obtained in Synthesis Example 1 was spin-coated on a glass substrate with a transparent electrode, dried on an 80 ° C. hot plate for 5 minutes, and then baked for 30 minutes in a 220 ° C. hot air circulation oven. And a coating film having a thickness of 100 nm was formed. This coating surface was irradiated with 5 J / cm ^{2 of} 313 nm ultraviolet light through a polarizing plate to obtain a substrate with a liquid crystal alignment film.

  In order to evaluate the electrical characteristics of the liquid crystal cell, two substrates with the above-mentioned liquid crystal alignment film were prepared, and 4 μm spacers were dispersed on the surface of the one liquid crystal alignment film. A sealant was printed from above, and another substrate was bonded so that the liquid crystal alignment film faced and the photoalignment direction was orthogonal, and then the sealant was cured to produce an empty cell. Liquid crystal MLC-2003 (manufactured by Merck Japan) was injected into this empty cell by a reduced pressure injection method, the injection port was sealed, and a twisted nematic liquid crystal cell was obtained. When this liquid crystal cell was heat-treated at 120 ° C. for 30 minutes and then slowly cooled to room temperature, the cell was observed. The orientation was good.

Evaluation of voltage holding characteristics A voltage of 4 V was applied to the liquid crystal cell at a temperature of 23 ° C. for 60 μs, and the voltage after 16.67 ms was measured to calculate how much the voltage was held as a voltage holding ratio. The same measurement was performed at a temperature of 90 ° C. As a result, the voltage holding ratio at 23 ° C. was 99.2%, and the voltage holding ratio at 90 ° C. was 86.4%.

Evaluation of Ion Density Using the “Liquid Crystal Cell / Ion Density Measurement System (Version 2.0)” (manufactured by Toyo Technica Co., Ltd.) at a temperature of 23 ° C., a triangular wave amplitude of 10 V and a frequency of 0.01 Hz is used. The ion density was measured under the conditions. As a result, the ion density was 110 pC / cm ² .

Evaluation of charge accumulation characteristics Applying a 30Hz / ± 3V square wave with a DC voltage of 3V superimposed on the above liquid crystal cell at a temperature of 23 ° C for 60 minutes, the residual voltage remaining in the liquid crystal cell immediately after switching off the DC voltage of 3V Was measured by an optical flicker elimination method. As a result, the accumulated charge was 0V.

(Example 2)
Using the liquid crystal aligning agent of the present invention obtained in Synthesis Example 2, the same evaluation as in Example 1 was performed. However, the light irradiation was performed by irradiating 1 J / cm ^{2 of} 254 nm ultraviolet light through a polarizing plate. The results are shown in Table 1 described later.

(Comparative Example 1)
Using the liquid crystal aligning agent obtained in Comparative Synthesis Example 2, the same evaluation as in Example 1 was performed. However, the light irradiation was performed by irradiating 1 J / cm ^{2 of} 254 nm ultraviolet light through a polarizing plate. The results are shown in Table 1 described later.

(Comparative Example 2)
Using the liquid crystal aligning agent obtained in Comparative Synthesis Example 2, the same evaluation as in Example 1 was performed. However, the light irradiation was performed by irradiating 1 J / cm ^{2 of} 254 nm ultraviolet light through a polarizing plate. The results are shown in Table 1 described later.

(Synthesis Example 3) CBDA / pPDA (0.7), 4,4'DADPA (0.3)
CBDA 18.63 g (0.095 mol) as tetracarboxylic dianhydride component, 7.57 g (0.07 mol) p-PDA and 5.98 g (0.03 mol) 4,4'DADPA as diamine component were mixed in 289.6 g NMP and room temperature For 5 hours to obtain a polyamic acid solution D. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured by GPC-101 (manufactured by Shodex). As a result, it was 28800 (in terms of polyethylene glycol and polyethylene oxide). Furthermore, NMP and BCS were added to this solution so that it might become 6 weight% of polyamic acid, 74 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Synthesis Example 4) CBDA / pPDA (0.5), 4,4'DADPA (0.5)
CBDA 18.63g (0.095mol) as tetracarboxylic dianhydride component, p-PDA 5.41g (0.05mol) and 4,4'DADPA 9.96g (0.05mol) as diamine component were mixed in 306.0g NMP, and room temperature For 5 hours to obtain a polyamic acid solution E. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured by GPC-101 (manufactured by Shodex). As a result, it was 28600 (in terms of polyethylene glycol and polyethylene oxide). Furthermore, NMP and BCS were added to this solution so that it might become 6 weight% of polyamic acid, 74 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Synthesis Example 5) 1,3DM-CBDA, CBDA / 4,4'DADPA
1,3DM-CBDA 11.21g (0.05mol) and CBDA 8.82g (0.045mol) as tetracarboxylic dianhydride components and 19.93g (0.1mol) 4,4'DADPA as diamine components were mixed in 359.6g NMP. The polyamic acid solution F was obtained by reacting at room temperature for 5 hours. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured by GPC-101 (manufactured by Shodex). As a result, it was 30300 (in terms of polyethylene glycol and polyethylene oxide). Furthermore, NMP and BCS were added to this solution so that it might become 6 weight% of polyamic acid, 74 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Synthesis Example 6) 1,3DM-CBDA, CBDA / p-PDA 1,3DM-CBDA, CBDA / DADPA
1,3DM-CBDA 11.21 g (0.05 mol) and CBDA 9.02 g (0.046 mol) as tetracarboxylic dianhydride components and p-PDA 10.81 g (0.1 mol) as diamine components were mixed in 279.4 g of NMP, and For 5 hours to obtain a polyamic acid solution G. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured by GPC-101 (manufactured by Shodex). As a result, it was 31300 (in terms of polyethylene glycol and polyethylene oxide). The polyamic acid solution F and the polyamic acid solution G obtained in Synthesis Example 5 were mixed at a solid content ratio of 1: 1 to obtain a uniform solution. Furthermore, NMP and BCS were added to this solution so that it might become 6 weight% of polyamic acid, 74 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Synthesis Example 7) CBDA / 4,4'DADPA, CBDA / DDE
The polyamic acid solution A obtained in Synthesis Example 1 and the polyamic acid solution C obtained in Comparative Synthesis Example 2 were mixed at a solid content ratio of 1: 1 to obtain a uniform solution. Furthermore, NMP and BCS were added to this solution so that it might become 4 weight% of polyamic acid, 76 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Synthesis Example 8) CBDA / 4,4'DADPA, DDE
CBDA 18.63g (0.095mol) as tetracarboxylic dianhydride component, DDE 10.01g (0.05mol) and 4,4'DADPA 9.96g (0.05mol) as diamine component were mixed in 347.4g of NMP and mixed at room temperature for 5 The polyamic acid solution H was obtained by reacting for a period of time. The polymerization reaction proceeded easily and uniformly, and the weight average molecular weight of the obtained polyamic acid was measured with GPC-101 (manufactured by Shodex), and as a result, it was 28000 (in terms of polyethylene glycol and polyethylene oxide). Furthermore, NMP and BCS were added to this solution so that it might become 6 weight% of polyamic acid, 74 weight% of NMP, and 20 weight% of BCS, and the liquid crystal aligning agent of this invention was obtained.

(Comparative Synthesis Example 3) 1,3DM-CBDA, CBDA / p-PDA
NMP and BCS were added to the solution G obtained in Synthesis Example 6 so that the polyamic acid was 6% by weight, NMP was 74% by weight, and BCS was 20% by weight to obtain a liquid crystal aligning agent for comparison.

(Example 3)
The same evaluation as in Example 1 was performed using the liquid crystal aligning agent of the present invention obtained in Synthesis Example 3. However, the light irradiation was performed by irradiating 1 J / cm ^{2 of} 254 nm ultraviolet light through a polarizing plate. The results are shown in Table 2 described later.

Example 4
Evaluation similar to Example 1 was performed using the liquid crystal aligning agent of the present invention obtained in Synthesis Example 4. However, the light irradiation was performed by irradiating 5 J / cm ^{2 of} 313 nm ultraviolet rays through a polarizing plate. The results are shown in Table 2 described later.

(Example 5)
The same evaluation as in Example 1 was performed using the liquid crystal aligning agent of the present invention obtained in Synthesis Example 5. However, light irradiation was performed by irradiating 313 nm ultraviolet rays at 2.5 J / cm ² through a polarizing plate. The results are shown in Table 2 described later.

(Example 6)
The same evaluation as in Example 1 was performed using the liquid crystal aligning agent of the present invention obtained in Synthesis Example 6. However, the light irradiation was performed by irradiating 0.5 J / cm ^{2 of} 254 nm ultraviolet light through a polarizing plate. The results are shown in Table 2 described later.

(Example 7)
The same evaluation as in Example 1 was performed using the liquid crystal aligning agent of the present invention obtained in Synthesis Example 7. However, the light irradiation was performed by irradiating 5 J / cm ^{2 of} 313 nm ultraviolet rays through a polarizing plate. The results are shown in Table 2 described later.

(Example 8)
The same evaluation as in Example 1 was performed using the liquid crystal aligning agent of the present invention obtained in Synthesis Example 7. However, the light irradiation was performed by irradiating 1 J / cm ^{2 of} 254 nm ultraviolet light through a polarizing plate. The results are shown in Table 2 described later.

(Comparative Example 3)
Using the liquid crystal aligning agent obtained in Comparative Synthesis Example 3, the same evaluation as in Example 1 was performed. However, the light irradiation was performed by irradiating 0.5 J / cm ^{2 of} 254 nm ultraviolet light through a polarizing plate. The results are shown in Table 2 described later.

  The contents of the entire specification of Japanese Patent Application No. 2004-050979 (filed with the Japan Patent Office on February 26, 2004), which is the basis for claiming priority of the present application, are cited herein, and the description of the present invention It is incorporated as a disclosure.

Claims (2)

Obtained by reactive polymerization of a diamine component containing a diamine represented by the following formula (1) and a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride represented by the following formula (2). A liquid crystal aligning agent for photo-alignment, comprising at least one of a polyamic acid obtained or a polyimide obtained from the polyamic acid.

(In the formula, two of R ^{1 to} R ¹⁰ are primary amino groups and the rest are hydrogen atoms or monovalent organic groups other than primary amino groups, which may be the same or different)

(Wherein R ^{11 to} R ¹⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms) The liquid crystal display element which has a liquid crystal aligning film formed through the process of apply | coating the liquid crystal aligning agent for photo-alignment of Claim 1 to a board | substrate, and the process of irradiating this board | substrate with polarized ultraviolet rays.