KR101399532B1 - Liquid crystal aligning film, liquid crystal aligning agent, and liquid crystal display device - Google Patents

Abstract

The present invention relates to a liquid crystal aligning agent capable of controlling orientation of a main chain by a photo alignment treatment and arbitrarily giving a pretilt angle of liquid crystal, a liquid crystal alignment film formed using the liquid crystal aligning agent, and a liquid crystal display element Lt; / RTI >

The present invention relates to a liquid crystal aligning agent for forming a liquid crystal alignment film for a liquid crystal display element, which comprises irradiating a substrate on which a polyamic acid has been coated with light whose polarization has been controlled and then imidizing the film to form a main chain of the polyimide in the liquid crystal alignment film A method of producing a liquid crystal aligning agent which produces a liquid crystal aligning agent which is oriented in a specific direction and which exhibits a pretilt angle of liquid crystal and which uses the liquid crystal aligning agent to produce a liquid crystal alignment film and a method of manufacturing a liquid crystal display element having the liquid crystal alignment film .

Liquid crystal, alignment, pre-tilt, polyamic acid, diamine

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal alignment film, a liquid crystal alignment film, a liquid crystal alignment film, a liquid crystal alignment film, a liquid crystal alignment film, a liquid crystal alignment film,

[TECHNICAL FIELD]

The present invention is characterized in that the main chain of the polyimide in the polyimide film is oriented in a specific direction by irradiating the light with the polarization control not subjected to the rubbing treatment to perform orientation treatment of the polyamic acid film, A liquid crystal aligning agent capable of forming the liquid crystal alignment layer, and a liquid crystal display element having the liquid crystal alignment layer.

BACKGROUND ART [0002]

BACKGROUND ART Liquid crystal display devices are used in various types of liquid crystal display devices such as monitors of notebook computers and desktop computers, viewfinders of video cameras, projection displays, and the like, and recently, they are also used in televisions. It is also used as an opto-electronics related element such as an optical printer head, an optical Fourier transform element, and a light valve. In the conventional liquid crystal display element, a display element using a nematic liquid crystal is mainstream, and a liquid crystal layer in which TN (1), in which the alignment direction of the liquid crystal on one substrate side and the alignment direction of the liquid crystal on the other substrate side is twisted by 90 degrees twisted nematic liquid crystal display device, a super twisted nematic (STN) type liquid crystal display device in which the alignment direction is usually twisted at an angle of 180 degrees or more, and a so-called thin-film-transistor type liquid crystal display device using thin film transistors .

However, in these liquid crystal display devices, a viewing angle capable of properly recognizing an image is narrow, and when viewed in an oblique direction, luminance and contrast may be lowered, and luminance inversion may occur in a halftone color tone. In recent years, the viewing angle problem can be solved by a TN type liquid crystal display device using an optical compensation film, a multi-domain vertical alignment (MVA) type liquid crystal display device using a combination of vertical and projection structures, -plane switching type liquid crystal display devices (see, for example, Patent Documents 1 to 3).

The development of the technology of the liquid crystal display element is achieved not only by improving the driving method and device structure thereof but also by improving the constituent member used for the display element. Of the constituent members used in the display device, in particular, the liquid crystal alignment film is one of the important factors influencing the display quality of the liquid crystal display device, and the liquid crystal alignment film is becoming more important as the display device is improved in quality.

In such a liquid crystal alignment film, the molecular alignment of the liquid crystal must be uniformly controlled for the uniform display characteristics of the liquid crystal display element, so that the liquid crystal molecules on the substrate are uniformly aligned in one direction, and a uniform tilt angle ) Should be expressed. As described above, a liquid crystal alignment film for uniformly aligning the directions of liquid crystal molecules on a substrate is an important and indispensable technique in the process of manufacturing a liquid crystal display element.

The liquid crystal alignment film is produced by a liquid crystal aligning agent. At present, the liquid crystal aligning agent mainly used is a solution in which a polyamic acid or a soluble polyimide is dissolved in an organic solvent. This solution is applied to a substrate, and then a film is formed by means such as heating to form a polyimide-based liquid crystal alignment film. Various liquid crystal orientation systems other than polyamic acid have been studied, but they have hardly been put to practical use in terms of heat resistance, chemical resistance (liquid-phase stability), coating property, liquid crystal alignment property, electrical characteristics, optical characteristics and display characteristics.

Industrially, a rubbing method capable of simply carrying out a large-area high-speed processing is widely used as an orientation treatment method. The rubbing process is a process in which the surface of the liquid crystal alignment film is rubbed in one direction by using a fabric including fibers such as nylon, rayon, and polyester, thereby obtaining liquid crystal molecules of the same orientation. However, problems such as generation of dust by the rubbing method and occurrence of static electricity have been pointed out.

Up to now, as the alignment mechanism of the liquid crystal in the liquid crystal alignment film subjected to alignment treatment by the rubbing treatment, the following two proposals have been proposed.

(1) Surface shape effect due to microgrooves generated by rubbing treatment

(2) Intermolecular interaction between the uniaxially oriented liquid crystal alignment film by the rubbing treatment and the liquid crystal single molecular layer contacting with the liquid crystal alignment film

In recent years, it has been confirmed that the contribution of (1) to the surface shape effect is relatively small, and the contribution due to the intermolecular interaction of (2) is dominant.

On the other hand, as to the photo-alignment method of irradiating light for alignment, many alignment mechanisms such as a photo-decomposition method, a photo-isomerization method, a photo-dimerization method, and an optical metrology method have been proposed (for example, Reference). In particular, since the photo-alignment method is a non-contact alignment method unlike the rubbing method, it is considered that only the intermolecular interaction of (2) acts as the alignment mechanism of the liquid crystal. In addition, since the photo-alignment treatment method is non-contact, in principle dust generation and generation of static electricity are less than rubbing treatment.

Accordingly, by using a liquid crystal alignment film having excellent uniaxial alignment, which has been subjected to alignment treatment by the photo alignment method, the molecular alignment state of the liquid crystal monocrystalline layer in contact with the liquid crystal alignment film can be controlled to improve the performance as a liquid crystal display device. On the other hand, in the photo alignment method, there is room for examination for control of a wide range of pretilt angles.

[Patent Document 1] Japanese Patent Publication No. 63-21907

[Patent Document 2] JP-A-6-160878

[Patent Document 3] JP-A-9-15650

[Patent Document 4] JP-A-2005-275364

Disclosure of the Invention Problems to be Solved by the Invention An object of the present invention is to provide a photo-alignment material which irradiates light to perform alignment treatment, and is a liquid crystal aligning agent which has less defects due to dust or static electricity and is easy to control the pretilt angle of the liquid crystal, And a liquid crystal display element having the liquid crystal alignment film.

The present inventors have repeatedly studied to solve the above problems.

As a result, it is possible to obtain a liquid crystal alignment film capable of imparting alignment of the main chain and pre-tilt angle of the liquid crystal by irradiating the liquid crystal alignment film obtained from the liquid crystal aligning agent produced under specific conditions with light controlled by the polarization, A liquid crystal display device using a liquid crystal alignment film can industrially and stably control a pretilt angle easily, and the present invention has been completed.

The present invention is configured as follows.

[1] A liquid crystal alignment film obtained by imidizing a polyamic acid which is oriented in a predetermined direction by irradiation of light in a polyamic acid film containing an azo group in its main chain, as a reaction product of a tetracarboxylic dianhydride and a diamine, Wherein at least one of the carboxylic acid dianhydride and the diamine has a branched structure and the orientation index of the main chain of the polyimide in the liquid crystal alignment film obtained by the following formula (1) is in the range of 0.03 to 1.00, Wherein the pretilt angle of the liquid crystal when the display element is formed is in the range of 2 to 90 degrees.

? = (| A∥-A⊥ |) / (A∥ + A⊥) × d / d '

In the formula (1), A∥ denotes a polarizing direction of the polarized infrared light, which is perpendicular to the surface of the liquid crystal alignment film and in which the polarizing direction of the infrared light is parallel to the average alignment direction of the main chain of the polyimide Represents the integrated absorbance due to the CNC stretching vibration of the imide ring at a wave number of about 1360 cm ^-1 at the time of incidence and A⊥ represents the polarized infrared light perpendicularly to the surface of the liquid crystal alignment film and to the average orientation of the main chain of the polyimide to the direction shown by the integral absorption wave number imide ring CNC stretching vibration 1360cm ^-1 in the vicinity at which the polarization direction of the infrared light is incident on the liquid crystal alignment film so that it is perpendicular, d denotes the thickness of the liquid crystal alignment layer, d Indicates the actual film thickness of the photo-aligned region of the liquid crystal alignment film.

[2] The polyamic acid is a reaction product of a tetracarboxylic acid dianhydride having no side chain structure, a diamine having no side chain structure containing an azo group between two amino groups, and a diamine having a side chain structure, The liquid crystal alignment layer according to item [1], wherein the diamine is contained in an amount of 7 to 90 mol% based on the total amount of the diamine.

[3] The liquid crystal alignment layer according to item [2], wherein the diamine having no side chain structure including an azo group between the two amino groups is 4,4'-diamino azobenzene.

[4] The liquid crystal alignment layer according to item [2], wherein the tetracarboxylic dianhydride is pyromellitic dianhydride.

[5] Liquid crystal alignment layer according to item [2], characterized in that the diamine having the branched structure is a compound represented by the following formula (I'-11)

In the above formula, R ²⁴ represents alkyl having 1 to 10 carbon atoms or alkoxy having 1 to 10 carbon atoms.

[6] A liquid crystal aligning agent comprising a reaction product of a tetracarboxylic dianhydride and a diamine, a polyamic acid containing an azo group in a main chain, and a solvent, wherein the diamine has a diamine having a branched structure.

[7] The polyamic acid is a reaction product of a tetracarboxylic acid dianhydride having no side chain structure, a diamine having no side chain structure containing an azo group between two amino groups, and a diamine having a side chain structure, The liquid crystal aligning agent according to item [6], wherein the diamine is contained in the range of 7 to 90 mol% based on the total amount of the diamine.

[8] A liquid crystal display device comprising: a pair of substrates arranged to face each other; an electrode formed on one or both sides of opposing surfaces of the pair of substrates; and a liquid crystal alignment film And a liquid crystal layer formed between the pair of substrates, wherein one or both of the liquid crystal alignment layers formed on the opposing surfaces of the pair of substrates are the liquid crystal alignment layers defined in any one of items [1] to [5] Wherein the liquid crystal alignment layer is a liquid crystal alignment layer according to any one of the items.

[9] A process for producing a polyamic acid, comprising the steps of: irradiating a film of a polyamic acid containing an azo group in its main chain to a polyamic acid in the film as a reaction product of a tetracarboxylic dianhydride and a diamine; Wherein a compound having a side chain structure is used in at least one of the tetracarboxylic dianhydride and the diamine and the polyamic acid is oriented in an orientation of the polyamic acid in the film, In this process,

(A) irradiating the film with a light that changes the azo group-containing geometric isomer from an anti isomer to a syn isomer, and when the polyamic acid in the film is viewed in a direction perpendicular to the surface of the film, Orientation, and

Irradiating the surface of the film of the polyamic acid with light from an oblique direction and orienting the polyamic acid in an oblique direction with respect to the surface of the film,

(B) irradiating the film with the light that changes the geometrical isomer of the azo group from an isomer to a new isomer from an oblique direction to the surface of the film, and when the polyamic acid in the film is viewed in a direction perpendicular to the surface of the film, Oriented in a predetermined direction, and simultaneously oriented in an oblique direction with respect to the surface of the film.

BEST MODE FOR CARRYING OUT THE INVENTION [

In the present invention, a pretilt angle of arbitrary liquid crystal can be generated by irradiating a film of a liquid crystal aligning agent with a specific light such as light whose polarization component is controlled, and performing orientation treatment. By using such a liquid crystal alignment film, Thereby realizing a liquid crystal display element.

The liquid crystal alignment film in the present invention is obtained by imidizing a polyamic acid which is oriented in a predetermined direction by irradiating light to the polyamic acid film.

The polyamic acid includes polyamic acid, which is a reaction product of tetracarboxylic dianhydride and diamine, and derivatives thereof. The polyamic acid is a component dissolved in a solvent in a later-described liquid crystal aligning agent, and is a component capable of forming a liquid crystal alignment film containing polyimide as a main component when it is a liquid crystal alignment film to be described later. Examples of the polyamic acid derivatives contained in the polyamic acid in the present invention include soluble polyimides, polyamic acid esters, and polyamic acid amides. More specifically, 1) a polyimide in which all amino groups of a polyamic acid and a carboxy group undergo dehydration ring closure reaction, 2) a partial polyimide partially dehydrated ring closure reaction, 3) a part of tetracarboxylic dianhydride is substituted with an organic dicarboxylic acid, A polyamic acid-polyamide copolymer obtained, and 4) a polyamideimide obtained by subjecting a part or the whole of the polyamic acid-polyamide copolymer to dehydration ring closure reaction. In the polyamic acid, the molar ratio of the tetracarboxylic dianhydride and the diamine is preferably the same to obtain a sufficiently large molecular weight of the polyamic acid. However, when the molecular weight is decreased for a specific reason, this ratio can be changed in the range of 90: 100 to 100: 90, preferably 95: 100 to 100: 95.

The polyamic acid contains an azo group in its main chain. The polyamic acid containing an azo group in its main chain is a polyamic acid in which, when the molecular structure excluding the branched molecular structure is a main chain of an acid or a diamine, of the molecular structure connecting two acid anhydride groups or two amino groups, A tetracarboxylic acid dianhydride containing an azo group or a diamine, or both of them as raw materials. The azo group may be contained in both the tetracarboxylic acid dianhydride and the diamine, but may be contained in only one side. The polyamic acid preferably has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of 10,000 or more to prevent deterioration of the orientation film with time, and is preferably 200,000 or less for ease of handling Do.

At least either of the tetracarboxylic acid dianhydride and the diamine has a branched structure. The tetracarboxylic acid dianhydride having a branched structure has a molecular structure branched from the main chain of the acid. The diamine having a branched structure has a molecular structure branched from the main chain of the amine. At least one of the tetracarboxylic acid dianhydride and the diamine has a side chain structure. By reacting these tetracarboxylic dianhydrides with the diamine, a polyamic acid (branched polyamic acid) having a branched structure with respect to the polymer main chain can be provided. A liquid crystal alignment film formed of a liquid crystal aligning agent containing a polyamic acid having a branched structure can increase the pretilt angle in a liquid crystal display element.

Examples of the branched structure include groups having 3 or more carbon atoms. More specifically,

(Cyclohexyl) phenylene which may have a substituent, or an alkyl, alkenyl or alkynyl group having 3 or more carbon atoms, a cycloalkyl group which may have a substituent,

2) phenyloxy which may have a substituent, cyclohexyloxy which may have a substituent, bis (cyclohexyl) oxy which may have a substituent, phenylcyclohexyloxy which may have a substituent, a substituent Cyclohexylphenyloxy which may be present or alkyloxy, alkenyloxy or alkynyloxy having 3 or more carbon atoms,

3) phenylcarbonyl, or alkylcarbonyl, alkenylcarbonyl or alkynylcarbonyl having 3 or more carbon atoms,

4) phenylcarbonyloxy, or alkylcarbonyloxy having 3 or more carbon atoms, alkenylcarbonyloxy or alkynylcarbonyloxy,

5) phenyloxycarbonyl which may have a substituent, cyclohexyloxycarbonyl which may have a substituent, bis (cyclohexyl) oxycarbonyl which may have a substituent, bis which may have a substituent (cyclo Hexyl) phenyloxycarbonyl, cyclohexyl (phenyl) oxycarbonyl which may have a substituent, or alkyloxycarbonyl, alkenyloxycarbonyl or alkynyloxycarbonyl having 3 or more carbon atoms,

6) phenylaminocarbonyl, or alkylaminocarbonyl having 3 or more carbon atoms, alkenylaminocarbonyl or alkynylaminocarbonyl,

7) cyclic alkylene having 3 or more carbon atoms,

8) cyclohexylalkylene optionally having substituent (s), phenylalkylene optionally having substituent (s), bis (cyclohexyl) alkylene optionally having substituent (s), cyclohexylphenylalkylene optionally having substituent (Cyclohexyl) phenylalkylene which may have a substituent, phenylalkyloxy which may have a substituent, alkylphenyloxycarbonyl, or alkylbiphenyloxycarbonyl,

9) phenyl or cyclohexyl substituted by alkyl, fluoro substituted alkyl, or alkoxy,

10) an alkyl, fluorine-substituted alkyl group, or a substituted or unsubstituted alkyl group having two or more benzene rings or cyclohexane rings bonded through a single bond or -O-, -COO-, -OCO-, -CONH-, , Or a ring-substituted group substituted by alkoxy, but are not limited thereto.

Here, examples of the "substituent" include alkyl, alkoxy, alkoxyalkyl, and the like.

Further, bis (cyclohexyl) or bis (phenyl) may be interrupted by alkylene.

In the present specification, the term "alkyl", "alkenyl", or "alkynyl" may be either linear or branched.

The tetracarboxylic acid dianhydride may be any aromatic group (including a complex aromatic ring system) in which a dicarboxylic acid anhydride is directly bonded to an aromatic ring, or an aliphatic (including a heterocyclic ring) group in which a dicarboxylic anhydride is not directly bonded to an aromatic ring . The polyamic acid is preferably a structure free from oxygen or sulfur, such as ester or ether bond, which is liable to deteriorate the electric characteristics of the liquid crystal display element. Therefore, the tetracarboxylic acid dianhydride is also preferably a structure free from oxygen or sulfur. However, even if it has such a structure, there is no problem if the amount is within a range that does not adversely affect the electric characteristics.

Specific examples of the tetracarboxylic acid dianhydrides usable in the present invention are as follows.

Among Expressions 1-1 to 1-38, Expression 1-1, Expression 1-2, Expression 1-7, Expression 1-13, Expression 1-17, Expression 1-18, Expression 1-19, Expression 1-20, The tetracarboxylic dianhydrides represented by formulas 1-27, 1-28, and 1-29 are preferred. More preferred are tetracarboxylic dianhydrides represented by Formula 1-1, Formula 1-7, Formula 1-13, Formula 1-17, Formula 1-19, Formula 1-20, and Formula 1-29.

The tetracarboxylic dianhydride is not limited to these, and it goes without saying that other compounds having various molecular structures exist within the scope of the object of the present invention. These tetracarboxylic acid dianhydrides may be used singly or in combination of two or more.

Examples of the diamine include a diamine having an azo group, a diamine having a branched structure, and a diamine having no branched structure as a structure for carrying out a photoisomerization reaction. In the present invention, these diamines can be used in combination.

As the diamine having an azo group, one or two or more kinds of various diamines including an azo group can be used in the main chain of the amine. Particularly preferred are diamines represented by the following formula (3).

As the diamine having a branched structure, one or more diamines having various branched side chains branched from the main chain of the amine may be used. As the diamine having a branched structure, a diamine represented by the general formula (I) is preferably used in order to uniformly express all properties such as orientation stability and pretilt angle.

In the general formula (I), the two amino groups are bonded to the phenyl ring carbon, but preferably the bond positional relationship of the two amino groups is meta or para. The two amino groups are preferably bonded to the 3 rd and 5 rd positions, or the 2 rd and 5 rd positions, respectively, when the bonding position of "R ² -R ¹ -" is taken as the first position.

In the general formula (I), R ¹ represents a single bond, -O-, -COO-, -OCO-, -CO-, -CONH- or - (CH ₂ ) _m - R ² is an alkyl having 1 to 20 carbon atoms when the positional relationship between the group having a steroid skeleton, the group represented by the following general formula (II) or the two amino groups bonded to the benzene ring is para, or is the positional relationship between the meta it indicates 1 to 10 carbon atoms of alkyl or phenyl, in the alkyl, independently, any -CH ₂ - is _{-CF 2 -, -CHF-, -O-,} -CH = CH- Or -C≡C- (provided that oxygen is not continuous), -CH ₃ may be substituted with -CH ₂ F, -CHF ₂ or -CF ₃ , and the ring-forming carbon of the phenyl hydrogen which is bonded is, or may independently be substituted with _{-F, -CH 3, -OCH 3,} -OCH 2 F, -OCHF 2 or -OCF _3.

In formula (II), A ¹ and A ² each independently represent a single bond, -O-, -COO-, -OCO-, -CONH-, -CH = CH- or alkylene having 1 to 20 carbon atoms R ³ and R ⁴ are each independently -F or -CH ₃ , and the ring S is 1,4-phenylene, 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl , pyrimidine-2,5-diyl, pyridine-2,5-diyl, naphthalene-1,5-diyl, naphthalene-2,7-diyl or anthracene-9,10-diyl, and, R ⁵ is -H, - F, alkyl having a carbon number of 1 to 20, 1 to 20 carbon atoms, fluorine substituted alkyl, having 1 to 20 carbon atoms alkoxy, -CN, and -OCH ₂ F, -OCHF ₂ or -OCF _3, a and b are independently 0, respectively represents an integer of ~4, or a is a ¹ or a ² is different from the groups neighboring when b is 2~4, c, d and e each independently represents an integer of 0~3, e is 2 or 3 A plurality of rings S may be the same or different and f and g are each independently an integer of 0 to 2 High, and also c + d + e≥1.

Examples of the diamine represented by the general formula (I) include diamines represented by the general formulas (I-1) to (I-11).

In the formula, R ¹⁹ is preferably an alkyl having 3 to 12 carbon atoms or an alkoxy having 3 to 12 carbon atoms, more preferably an alkyl having 5 to 12 carbon atoms or an alkoxy having 5 to 12 carbon atoms. R ²⁰ is preferably an alkyl having 1 to 10 carbon atoms or an alkoxy having 1 to 10 carbon atoms, more preferably an alkyl having 3 to 10 carbon atoms or an alkoxy having 3 to 10 carbon atoms.

Among these, diamines represented by the formulas (I-2), (I-4), (I-5) and (I-6) are more preferred.

The diamine of the present invention may contain the diamine represented by the above general formula (I) alone or two or more diamines.

In addition, as long as the object of the present invention is not impaired, a diamine having a side chain structure other than the diamine represented by the general formula (I) can be used. Examples of such diamines having a branched structure include diamines represented by the formulas (I'-1) to (I'-20).

In the formulas (I'-1) to (I'-3), R ²¹ is preferably an alkyl having 4 to 16 carbon atoms, more preferably an alkyl having 6 to 16 carbon atoms. In the formula (I'-4), R ²² is preferably an alkyl having 6 to 20 carbon atoms, more preferably an alkyl having 8 to 20 carbon atoms.

In the formula, R ²³ is preferably an alkyl having 3 to 12 carbon atoms or an alkoxy having 3 to 12 carbon atoms, more preferably an alkyl having 5 to 12 carbon atoms or an alkoxy having 5 to 12 carbon atoms. R ²⁴ is preferably an alkyl having 1 to 10 carbon atoms or an alkoxy having 1 to 10 carbon atoms, more preferably an alkyl having 3 to 10 carbon atoms or an alkoxy having 3 to 10 carbon atoms.

As the diamine having no branched structure, one or two or more of various diamines not containing an azo group in the main chain of an amine having no branching structure branched from the main chain of the amine can be used. As the diamine having no branched structure, the following diamines are preferably used.

Examples of the diamine having no branched structure include diamines represented by the formulas (III-1) and (III-2).

Examples of the diamine having no branched structure include diamines represented by the formulas (IV-1) to (IV-3).

Examples of the diamine having no branched structure include diamines represented by the formulas (V-1) to (V-7).

Examples of the diamine having no branched structure include diamines represented by the formulas (VI-1) to (VI-30).

Examples of the diamine having no branched structure include diamines represented by the formulas (VII-1) to (VII-6).

Examples of the diamine having no branched structure include diamines represented by the formulas (VIII-1) to (VIII-11).

Of these, diamines having no branched structure are more preferably used as the diamines having the branched structures of the formulas (V-1) to (V-7), VI-1 to VI- Diamines represented by the following formulas (VI-1 to VI-27), (VII-1), (VII-2), Include diamines represented by formulas (V-6), (V-7) and (VI-1) to (VI-12).

Examples of other diamines that can be used in combination with the diamines usable in the present invention include siloxane-based diamines having a siloxane bond. The siloxane-based diamine is not particularly limited, but those represented by the general formula (4) can be preferably used in the present invention.

In the general formula (4), R ₆ and R ₇ are independently alkyl having 1 to 3 carbon atoms or phenyl, and R ₈ is methylene, phenylene or alkyl-substituted phenylene. x is an integer of 1 to 6, and y is an integer of 1 to 10.

The diamines usable in the present invention are not limited thereto, and it is needless to say that compounds having various molecular structures are also present within the scope of attaining the object of the present invention. These diamines may be used alone or in combination of two or more.

On the other hand, with respect to the diamines usable in the present invention, as with the above-mentioned tetracarboxylic acid dianhydrides, aromatic compounds (including complex aromatic rings) directly bonded with amino groups to aromatic rings, aliphatic Including subpoenas) may belong to any group. Among them, an aliphatic diamine having an aromatic structure and a ring structure and having a ring structure is preferable because it maintains good orientation of the liquid crystal. Further, those having a structure that does not contain oxygen or sulfur such as an ester or an ether bond, which is liable to deteriorate the electric characteristics of the liquid crystal display element, are preferable. However, even if it has such a structure, there is no problem if the amount is within a range that does not adversely affect the electric characteristics.

In addition to these tetracarboxylic acid dianhydrides and diamines, monoamine and / or monocarboxylic acid anhydride which forms a reaction terminal of a polyamic acid can be used in combination. In order to improve the adhesion to the substrate, an aminosilicon compound may be introduced.

Aminosilicon compounds include, but are not limited to, para-aminophenyltrimethoxysilane, para-aminophenyltriethoxysilane, metaaminophenyltrimethoxysilane, metaaminophenyltriethoxysilane, aminopropyltrimethoxysilane, aminopropyltriethoxysilane And the like.

The ratio of the diamine having a side chain structure to the diamine having no side chain structure can be arbitrarily selected depending on the electric characteristics and the pretilt angle. The ratio of the diamine having a side chain structure to the total diamine is preferably in the range of 7 to 90 mol%, more preferably 10 to 70 mol%. When the proportion of the diamine having the branched structure is 7 mol% or more, a good liquid crystal pretilt angle is obtained. When the proportion is 90 mol% or less, good orientation of the polyimide main chain can be obtained.

In the liquid crystal alignment film of the present invention, the alignment index? Of the main chain of the polyimide in the liquid crystal alignment film obtained by the following formula (1) is in the range of 0.03 to 1.00.

The orientation (?) Of the polyimide backbone can be evaluated by infrared absorption spectroscopy using polarized infrared light. In this method, infrared ray absorption amount when two linearly polarized infrared rays orthogonal to the sample are incident is detected with different infrared dichroism depending on the molecular orientation direction, and molecular orientation is evaluated.

That is, a polarizer is disposed between a light source of an infrared spectrophotometer (preferably FT-IR) and a sample holder holding a sample having a polyimide liquid crystal alignment film, and a polarizer is disposed in a direction parallel to the surface of the liquid crystal orientation film The sample is fixed to the sample holder so that the average alignment direction of the main chain is parallel to the polarization direction of the polarizer and at the same time the infrared light is incident perpendicularly to the surface of the sample, and the infrared absorbance is measured. Then, the polarizer was rotated 90 degrees while the sample was fixed to the sample holder, and the polarizing direction of the infrared light passed through the polarizer was perpendicular to the average alignment direction of the main chain of the polyimide in the direction parallel to the surface of the liquid crystal alignment film The infrared absorbance is measured. In the infrared absorbance thus obtained,? Is calculated from the peak value or the integral value of the absorption band due to the molecular vibration polarized so as to be parallel to the molecular axis of the polyimide main chain.

On the other hand, in this method, a sample produced on a substrate through which infrared light passes, such as silicon or calcium fluoride (fluorite: CaF ₂ ) can be used.

In the present invention, the average orientation direction of the main chain of the polyimide means a direction in which the polyimide main chain is oriented on average when the liquid crystal alignment film is viewed from the direction perpendicular to the surface of the liquid crystal alignment film. That is, when the polarizer is appropriately rotated and the infrared absorption spectrum is measured in the above-described measurement arrangement, the peak value or the integral value of the absorption band due to the molecular vibration polarized in parallel to the molecular axis of the polyimide main chain becomes maximum The direction of polarization by the polarizer is the average orientation direction of the main chain of the polyimide.

Characteristic group frequencies of the polyimide in the present invention, the polyimide is a strong infrared absorption peak near 1360cm ^-1 (imide ring CNC stretching vibration), 1510cm ^-1 vicinity (CC stretching vibration of phenyl), and the vicinity of 1720cm ^-1 (C = O stretching vibration of the imide). Any infrared absorption peak can be used. However, a change in the infrared absorption peak due to the polyimide composition along the main chain of the polyimide due to the molecular vibration is relatively small at around 1360 cm ^-1 (CNC stretching vibration of the imide ring) It is particularly preferable to use them. In addition, since the infrared dichroic ratio may differ depending on the film thickness of the liquid crystal alignment film, it is preferable to evaluate the orientation of the polyimide main chain by using the infrared two-color difference from which the influence of the film thickness is removed.

From the above, in the present invention, anisotropy in the direction parallel to the surface of the liquid crystal alignment film in the orientation of the liquid crystal alignment film is evaluated by the infrared two-color difference in the vicinity of 1360 cm ^-1 (CNC stretching vibration of imide ring). On the other hand, the absorbance in the vicinity of 1360 cm ^-1 in the present invention indicates the integrated value (1330 to 1430 cm ^-1 ) of the band attributed to the CNC stretching vibration of the imide ring. Further, in order to correct the influence of the film thickness, the film thickness of the liquid crystal alignment film and the absorption coefficient? At the wavelength of the light used for the photo alignment treatment are measured.

In the present invention, the orientation of the polyimide main chain was evaluated by the orientation index? Of the liquid crystal alignment film after alignment treatment represented by the following formula (1).

? = (| A∥-A⊥ |) / (A∥ + A⊥) × d / d '

In Equation (1), A∥ indicates the fact that the polarized infrared light is incident on the liquid crystal alignment film so that the polarizing direction of the infrared light is parallel to the surface of the liquid crystal alignment film and to the average alignment direction of the main chain of the polyimide represents the integral absorption by the imide ring of a wave number of 1360cm ^-1 CNC stretching vibration near the time, A⊥ are the polarized infrared light, perpendicular to the surface of the liquid crystal alignment film, and the average direction of orientation of the polyimide main chain Represents the integral absorbance due to the CNC stretching vibration of the imide ring near the wave number of 1360 cm < ^-1 > when incident on the liquid crystal alignment film so that the polarization direction of the infrared light is perpendicular. and d represents the film thickness of the liquid crystal alignment film. and d 'represents a substantial thickness of the photo-aligned region of the liquid crystal alignment film.

The substantial thickness d 'of the region where the liquid crystal alignment film is optically aligned is obtained from the following equation (2).

d '= (1 /?) x? (2)

In the formula (2),? Is the absorption coefficient of the polyamic acid film not subjected to the photo-alignment treatment at the wavelength of the light used for the photo-alignment treatment. ? is the correction coefficient of the thickness of the liquid crystal alignment film due to imidization, and d / d _PAA is the film thickness of the polyamic acid film before imidization, which is d _PAA . If d is less than d ', then d' = d. On the other hand, the film thickness of the polyamic acid film before imidization can be measured by an ellipsometer, a contact step system, or the like.

The absorption coefficient? Is determined by measuring the transmittance spectrum of the ultraviolet-visible region of the polyamic acid film having the film thickness d _PAA measured by a step system or an ellipsometer, by means of a spectrophotometer at ultraviolet-visible before the photo alignment treatment. Assuming that the transmittance of the substrate coated with the polyamic acid film is T _sample and the transmittance of the substrate only is T _sub at the wavelength of light used for the photo alignment treatment, the absorption coefficient? Is obtained by the following equation (3).

? = (1 / d _PAA ) ln (T _sub / T _sample ) (3)

The liquid crystal alignment film in the present invention has an orientation index? In a range of 0.03 or more and 1.00 or less, preferably 0.10 or more and 0.95 or less, and more preferably 0.20 or more and 0.90 or less. When the orientation index? Is 0.03 or more, the orientation of the main chain of the polyimide is sufficient, and a stable liquid crystal display element can be obtained.

The liquid crystal alignment film in the present invention has a pretilt angle in a range of 2 to 90 degrees when the liquid crystal display element is formed. The pretilt angle is preferably 3 to 90 degrees.

The pretilt angle can be measured using, for example, a liquid crystal property evaluation apparatus OMS-CA3 of Juno Kogyo Co., Ltd., Journal of Applied Physics, Vol. 48, No. 5, p. And the crystal rotation method described in JP-A-1783-1792 (1977). Or the pretilt angle is determined according to the method described in Mol. Cryst. Liq. Cryst. 241 (1994) 147.

The thickness of the liquid crystal alignment film in the present invention is usually 5 to 500 nm from the viewpoints of uniformity of film thickness and mechanical, optical and electrical characteristics. The film thickness of the liquid crystal alignment film is preferably 5 to 200 nm, more preferably 5 to 150 nm.

The film thickness of the liquid crystal alignment film can be measured by an ellipsometer or a contact type step system. The film thickness of the liquid crystal alignment film can be adjusted by the concentration of the liquid crystal aligning agent, the viscosity, and the coating conditions of the liquid crystal aligning agent.

For the formation of the liquid crystal alignment film in the present invention, a liquid crystal aligning agent can be used. This liquid crystal aligning agent is a varnish in which a polyamic acid containing an azo group in the above main chain and having a side chain structure in its main chain is dissolved in a solvent. This liquid crystal aligning agent is coated on the substrate, and the solvent is dried and then subjected to alignment treatment to form the liquid crystal alignment film in the present invention. The polyamic acid may be a copolymer such as a random copolymer, a block copolymer or the like, or may include a plurality of the above-mentioned polyamic acid.

The liquid crystal aligning agent usable in the present invention is a liquid crystal aligning agent characterized by containing a polyamic acid obtained by reacting a diamine with a tetracarboxylic acid dianhydride. The liquid crystal aligning agent comprises at least one kind of a diamine having a branched structure and a tetracarboxylic dianhydride , A diamine containing an azo group in its main chain, and a tetracarboxylic dianhydride. More preferably, as the diamine, a diamine containing a diamine having a side chain structure and a polyamine acid using a diamine having no side chain structure including an azo group in the main chain are contained. As the liquid crystal aligning agent in the present invention, the above-mentioned tetracarboxylic dianhydride and diamine can be used in the liquid crystal alignment film.

The liquid crystal aligning agent of the present invention preferably contains 7 to 90 mol% of the diamine having a side chain structure with respect to the total amount of the diamine. As described above, the pretilt angle of a good liquid crystal in the liquid crystal display element, In order to obtain a good orientation of the main chain of the polyimide.

The concentration of the polyamic acid in the liquid crystal aligning agent in the present invention is not particularly limited, but is preferably 0.1 to 40% by mass. When the liquid crystal aligning agent is applied to the substrate, it may be necessary to dilute the polyamic acid contained in advance with a solvent in order to adjust the film thickness. If the concentration of the polyamic acid is 40 mass% or less, the viscosity of the liquid crystal aligning agent is preferable, and if it is necessary to dilute the liquid crystal aligning agent for adjusting the film thickness, the solvent can be easily mixed with the liquid crystal aligning agent Therefore, it is preferable.

In the case of a coating method such as a spinner method or a printing method, in order to maintain a good film thickness, the amount is usually set to 10% by mass or less. In the other application methods such as the dipping method and the ink-jet method, the concentration may be lower. On the other hand, when the concentration of the polyamic acid is 0.1% by mass or more, the film thickness of the obtained liquid crystal alignment film can be easily made preferable. Therefore, the concentration of the polyamic acid is 0.1% by mass or more, preferably 0.5 to 10% by mass in a coating method such as a general spinner method or a printing method. However, depending on the application method of the above-mentioned liquid crystal aligning agent, it may be used in a more dilute concentration.

In the liquid crystal aligning agent of the present invention, the solvent which can be used together with the polyamic acid is not particularly limited as long as it is a solvent capable of dissolving the polyamic acid. Such a solvent may widely include a solvent commonly used in the production and use of polyamic acid, and may be appropriately selected depending on the purpose of use. These solvents are exemplified as follows.

Examples of the aprotic polar organic solvent which is a two-solvent for the polyamic acid include N-methyl-2-pyrrolidone, dimethylimidazolidinone, N-methylcaprolactam, N-methylpropionamide, N, N-dimethylacetamide , Lactones such as dimethylsulfoxide, N, N-dimethylformamide, N, N-diethylformamide, N, N-diethylacetamide and? -Butyrolactone.

Examples of the solvent other than the above solvent other than those for the purpose of improving the coating property include ethylene glycol such as alkyl lactate, 3-methyl-3-methoxybutanol, tetralin, isophorone, ethylene glycol monobutyl ether Propylene glycol monoalkyl ethers such as ethylene glycol monoalkyl and phenylacetate, triethylene glycol monoalkyl ether and propylene glycol monobutyl ether, diethylene glycol monoalkyl ethers such as diethylene glycol monoalkyl ether and diethylene glycol monoethyl ether, Dipropylene glycol monoalkyl ethers such as diethyl malonate such as ethyl and dipropylene glycol monomethyl ether, and ester compounds such as glycol monoethers.

Of these, the solvent is preferably selected from the group consisting of N-methyl-2-pyrrolidone, dimethylimidazolidinone,? -Butyrolactone, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monobutyl ether, Glycol monomethyl ether or the like is particularly preferably used.

The liquid crystal aligning agent in the present invention may contain various additives if necessary. For example, in order to improve the coatability, a surfactant for the purpose of the object is added, an antistatic agent is added to improve the antistatic property, and a silane coupling agent or a titanium-type coupling agent is added in an appropriate amount in order to improve the adhesion with the substrate It is possible.

A liquid crystal display device according to the present invention is a liquid crystal display device comprising: a pair of substrates arranged opposite to each other; an electrode formed on one or both sides of the opposing surfaces of the pair of substrates; And a liquid crystal layer formed between the pair of substrates. The liquid crystal display element in the present invention can be constructed in the same manner as a conventional liquid crystal display element except for the liquid crystal alignment film. The above-described liquid crystal alignment film of the present invention can be used for one or both of the liquid crystal alignment films formed on the opposing surfaces of the pair of substrates.

A suitable substrate may be used for the substrate depending on the use thereof. The substrate is preferably a transparent substrate such as glass for display, and in order to confirm the orientation index? Of the liquid crystal alignment film, a substrate which transmits infrared light such as silicon or calcium fluoride is preferable.

The electrode is not particularly limited as long as it is an electrode formed on one surface of the substrate. Examples of such electrodes include a vapor-deposited film of ITO or metal. The electrode may be formed on the entire surface of one side of the substrate, or may be formed in a predetermined pattern, for example. The predetermined shape of the electrode is, for example, a comb-like or zigzag structure. The electrodes may be formed on one substrate of a pair of substrates or on both substrates. For example, in the case of an IPS type liquid crystal display device, electrodes are arranged in one direction of the pair of substrates, and in the case of other liquid crystal display devices, An electrode is disposed on both of the pair of substrates. The liquid crystal alignment film is formed on the substrate or the electrode.

The liquid crystal layer is formed in a form in which the liquid crystal composition is sandwiched by the pair of substrates facing each other on which the liquid crystal alignment film is formed. In the formation of the liquid crystal layer, a spacer such as fine particles, a resin sheet, or the like, which is interposed between the pair of substrates and forms an appropriate gap, can be used as needed.

The liquid crystal composition usable in the liquid crystal display of the present invention is not particularly limited, and various liquid crystal compositions having a positive dielectric anisotropy can be used. Examples of preferred liquid crystal compositions are disclosed in Japanese Patent No. 3086228, Japanese Patent No. 2635435, Japanese Patent Laid-Open Nos. 5-501735, 8-157826, 8-231960, and 9-241644 (Specification of EP885272A1), JP-A No. 9-302346 (specification of EP-806466A1), JP-A No. 8-199168 (specification of EP-722998A1), JP-A No. 9-235552, JP-A No. 9-255956, (Japanese Patent Application Laid-Open No. 885271A1), Japanese Patent Application Laid-Open No. 10-204016 (specification of EP844229A1), Japanese Patent Application Laid-Open No. 10-204436, Japanese Patent Application Laid-Open Nos. 10-231482, 2000-087040, 2001-48822 .

Various liquid crystal compositions having negative dielectric anisotropy can be used. Examples of preferable liquid crystal compositions are disclosed in Japanese Patent Application Laid-Open Nos. 57-114532, 57-2425, 64-24865, 64-10386, 68-104869, -168076, JP-A-10-168453, JP-A-10-236989, JP-A-10-236990, JP-A-10-236992, JP-A-10-236993, JP-A-10-236994 10-237000, 10-237004, 10-237024, 10-237035, 10-237075, and 10-237076, the disclosures of which are incorporated herein by reference. 10-237448 (Specification of EP967261A1), No. 10-287874, No. 10-287875, No. 10-291945, No. 11-029581, No. 11-080049 Japanese Patent Application Laid-Open No. 2000-256307, Japanese Patent Application Laid-Open No. 2001-019965, Japanese Patent Application Laid-Open Nos. 2001-072626, 2001-192657, etc.

There is no problem in using one or more optically active compounds added to the liquid crystal composition having a positive or negative dielectric anisotropy.

In the liquid crystal display element of the present invention, the pair of substrates face each other in such a manner that the average orientation direction of the main chain of the polyimide in the liquid crystal alignment film on each substrate is in a specific direction, depending on the type of the liquid crystal display element. For example, when the liquid crystal display element is a TN type liquid crystal display element, an electrode or a liquid crystal alignment film is formed on the pair of substrates so that the average alignment direction of the main chain of the polyimide in the liquid crystal alignment film of each substrate intersects 90 degrees Facing the inner side. When the liquid crystal display element is an STN type liquid crystal display element, the average orientation direction of the main chain of the polyimide in the liquid crystal alignment film of each substrate is set so that the average orientation direction crosses the normal reverse direction, that is, The pair of substrates face each other with the surface on which the electrodes or the liquid crystal alignment film are formed facing inward.

The liquid crystal display element according to the present invention may have other members depending on the type of the liquid crystal display element. For example, in a TFT-type liquid crystal device of color display using a thin film transistor, a thin film transistor, an insulating film, a protective film, a pixel electrode, and the like are formed on the first transparent substrate. On the second transparent substrate, A black matrix, a color filter, a planarization film, a pixel electrode, and the like.

Further, in the IPS liquid crystal display device, the liquid crystal is sandwiched between the first transparent substrate on which the thin film transistor is formed, the opposing second transparent substrate, and these substrates. The first transparent substrate has pixel electrodes and common electrodes formed so that combs alternately extend. Like the conventional liquid crystal display device, the second transparent substrate has a black matrix, a color filter, a planarization film, and the like that shield light other than the pixel region. The comb-like electrode is formed, for example, by depositing a metal such as Cr on a transparent substrate such as glass by sputtering or the like, and then etching the resist pattern of a predetermined shape using a mask.

In the MVA type liquid crystal display device, there is a case where a minute protrusion is formed on the transparent substrate, or a multi-domain process is performed by the light irradiation process through the masking process.

The liquid crystal alignment film according to the present invention is characterized by comprising a step of orienting a polyamic acid in a film by irradiating light of a polyamic acid film containing an azo group in its main chain as a reaction product of a tetracarboxylic dianhydride and a diamine, And a step of imidizing the polyamic acid. At least one of the tetracarboxylic acid dianhydride and the diamine may be a compound having a branched structure.

The film of the polyamic acid can be formed, for example, by applying the above-described liquid crystal aligning agent of the present invention onto a substrate or an electrode. As a method of applying the liquid crystal aligning agent, a spinner method, a printing method, a dipping method, a dropping method, an ink jet method, and the like are generally known. These methods are equally applicable to the present invention.

The azo group contained in the skeletal structure of the polyamic acid can usually take two geometric isomers, i.e., neo and anti. Usually, the anti-isomer is stable, but when light of a suitable energy is irradiated to the polyamic acid, light is absorbed and the azo group is converted into a new isomer. Since the new isomer is less stable than the anti-isomer, the azo group returns to the anti-isomer, but the anti-isomer returned from the new isomer is directed in a random direction. At this time, when the light polarized in a specific direction is irradiated, the antis is directed to a specific direction is selectively changed into a new isomer, and the new isomer is accompanied by a random orientation change to return to the antis isomer. Since the anti-synoptic isomerization is repeated until no light absorption occurs, after sufficient light irradiation, the anti-isomer is oriented perpendicular to the polarization direction of the light. In the present invention, such a photo-isomerization reaction is used for controlling the orientation of the polyamic acid.

In the step of orienting the polyamic acid in the film, the main chain of the polyamic acid is oriented by irradiation of light. Such a photo-alignment treatment condition may be in any form as long as the object of the present invention is achieved. As the light source used for the photo-alignment treatment, a low pressure mercury lamp, a high pressure mercury lamp, a deuterium lamp, a metal halide lamp, an argon resonance lamp, a xenon lamp, a Deep UV lamp, an excimer laser and the like can be used.

In the case of the present invention using the photo-isomerization reaction of an azo group, the wavelength of light used for the photo-alignment treatment is 300 to 600 nm, more preferably 340 to 500 nm. This is because photolysis of the coating film is difficult to occur in the light having a wavelength of 300 nm or more and easy to proceed with the light isomerization in the light having a wavelength of 600 nm or less. In addition, it is preferable to remove light having a low wavelength using a long-wavelength transmission filter or a band-pass filter or the like. On the other hand, it is preferable to simultaneously use ultraviolet / visible continuous light sources and a band-pass filter to simultaneously irradiate ultraviolet light and visible light.

The amount of light irradiated by the light used for orienting the polyamic acid in the direction parallel to the surface of the liquid crystal alignment film differs depending on the kind of the liquid crystal aligning agent used, the wavelength of the light source, and the irradiation conditions. However, And a high orientation index? Is obtained. As a reference, Deep light irradiation dose when using a UV lamp and a band-pass filter of 340~500nm perform the alignment treatment is not less than 2J / cm ^2, and preferably at least 30J / cm ^2, and more preferably 100J / cm < ^{2 &} gt ;. Although there is no particular upper limit to the light irradiation amount, it is preferably 2,000 J / cm ² or less in order to avoid deterioration of the liquid crystal alignment film, and it is preferably 300 J / cm ² or less in view of cost efficiency such as facilities and processing.

The main chain of the polyamic acid in the film can be oriented in a predetermined direction by irradiating the film with light whose polarization is controlled. The main chain of the polyamic acid is oriented in a direction perpendicular to the polarization direction of the irradiated light. Examples of the light whose polarization is controlled include linearly polarized light, circularly polarized light, and elliptically polarized light. Here, non-polarized light is randomly polarized light, and polarized light is included in the controlled light. The polarization control can be performed by a polarizing filter or a polarization prism. Alternatively, light can be transmitted through a tilted glass plate.

When the polyamic acid is oriented in a predetermined direction when viewed in a direction perpendicular to the surface of the film, the light with the polarization-controlled light can be used as the light for changing the geometrical isomer of the azo group from an isomer to a new isomer. In order to align the surface of the polyamic acid film in the oblique direction, the surface of the polyamic acid film is irradiated with light from an oblique direction.

The light irradiated from the oblique direction with respect to the surface of the film of the polyamic acid can be changed in order to obtain the intended orientation of the polyimide main chain and the pretilt angle of the liquid crystal.

The irradiation angle when irradiating light from the oblique direction with respect to the surface of the film is not particularly limited. However, in order to obtain an arbitrary pretilt angle, it is preferably 20 to 70 degrees with respect to the surface of the liquid crystal alignment film or the substrate surface, To 60 degrees is more preferable in order to obtain a good polyimide main chain orientation and a liquid crystal pre-tilt angle.

In the present invention, the light that changes the geometrical isomer of the azo group from the isomer to the new isomer is irradiated from the oblique angle with respect to the surface (substrate surface) of the film, so that the polyamic acid in the film parallel to the surface of the film It is possible to control both the orientation (average alignment direction) and the orientation of the polyamic acid (inclination angle with respect to the substrate surface) on the incident surface of the light. In the present invention, a preferred method of controlling the orientation of the polyamic acid in the film is to irradiate linearly polarized light from the perpendicular direction to the surface (substrate surface) of the film, and then to irradiate a vertical plane in the polarization direction of the linearly polarized light And irradiates unpolarized light at the irradiation angle as a plane. By doing so, it is possible to increase the degree of alignment of the main chains of the polyimide (orientation index?), And to obtain alignment of the liquid crystal having the pretilt angle by the same method.

In the production of the liquid crystal alignment film, it is preferable to further perform a step of drying the film of the liquid crystal aligning agent obtained on the transparent substrate. The drying step is preferably performed before the above-described photo-alignment treatment. As the drying step, a method of heating in an oven or an infrared lamp, a method of heating on a hot plate, and the like are generally known. These methods are equally applicable to the present invention. The drying process is preferably performed at a relatively low temperature within a range in which evaporation of the solvent is possible.

Imidization of the polyamic acid oriented in the film is usually carried out by heating. Also in the present invention, the heat treatment can be applied to the imidization of the polyamic acid after orientation. As the method of the heat treatment step, the same method as the above-mentioned drying step is applicable. The heat treatment is preferably performed at a temperature of about 150 to 300 캜.

The liquid crystal display element in the present invention can be produced by a method including the steps of preparing a liquid crystal alignment film on a substrate as described above and then assembling the substrate with the spacer interposed therebetween, sealing the liquid crystal composition and sealing the polarizing film ≪ / RTI >

The liquid crystal display element in the present invention may be subjected to a cleaning treatment with a cleaning liquid. Examples of the cleaning method include jet spray, steam cleaning, and ultrasonic cleaning. These methods may be used alone or in combination. As the cleaning liquid, it is possible to use pure water, alcohols such as methyl alcohol, ethanol or isopropyl alcohol, aromatic hydrocarbons such as benzene, toluene or xylene, halogenated hydrocarbons such as methylene chloride, or ketones such as acetone or methyl ethyl ketone , But are not limited thereto. Needless to say, these cleaning liquids can be sufficiently purified and have less impurities.

The ratio of the tetracarboxylic acid dianhydride and / or diamine having a photo-isomerization structure to the total monomer, which can be used in the present invention, should be from 10 to 90 mol%, preferably from 15 to 80 mol% Should be 20 to 70 mol%. If the ratio of the tetracarboxylic acid dianhydride and / or diamine having a photo-isomerization structure is 10 mol% or more, the orientation of the polymer main chain is improved by photoisomerization and the ratio of the tetracarboxylic dianhydride and / or diamine having a photo- If it is 90 mol% or less, the pretilt angle becomes good.

[Example]

Hereinafter, the present invention will be described by way of examples and comparative examples, but the present invention is not limited to these examples. On the other hand, the names of tetracarboxylic acid dianhydrides, diamines and solvents used in Examples and Comparative Examples are denoted by the abbreviation. The following abbreviations are used in some cases.

Tetracarboxylic acid dianhydride

  Pyromellitic dianhydride: PMDA

Diamine

  4,4'-diamino azobenzene: DAZ

Diamine having branched structure

  A compound of the following structural formula 1: T1

  A compound of formula 2: T2

solvent

  N-methyl-2-pyrrolidone: NMP

Example  One

1) Production of liquid crystal aligning agent A1

2.1104 g and 0.4802 g of DAZ and T1, respectively, and 30.00 g of dehydrated NMP were introduced into a 200 mL four-necked flask equipped with a thermometer, a stirrer, a feed inlet and a nitrogen gas inlet, and stirred and dissolved in a dry nitrogen stream. While the temperature of the reaction system was maintained at 5 占 폚, 2.4096 g of PMDA was added and reacted for 30 hours. Then, 65.00 g of dehydrated NMP was added to prepare a liquid crystal aligning agent of polyamic acid having a polymer component concentration of 5% by mass. When the temperature rises due to the reaction heat during the reaction of the raw materials, the reaction temperature is limited to about 70 캜 or lower and the reaction is carried out.

2) Measurement of absorbance of infrared light, film thickness of liquid crystal alignment film, and calculation of orientation index?

The obtained liquid crystal aligning agent A1 of PMDA / DAZ / T1 (molar ratio of raw material = 50/45/5) was diluted with NMP to 1.34% by mass, and then coated on a CaF ₂ substrate (thickness 2 mm) with a spinner. The application condition was 3,000 rpm, 60 seconds. After the coating, a 500 W deep UV lamp (UXM-501MD) manufactured by Ushio Electric Co., Ltd. was irradiated with light as a light source. The wavelength region of the irradiated light was made 340 to 500 nm by transmitting a band-pass filter (manufactured by Joil Spectroscopy) having a transmission wavelength range of 340 to 500 nm.

First, the linearly polarized light was irradiated from the perpendicular direction to the substrate surface through the Gran Taylor polarizing prism. The dose was 156 J / cm ² . Subsequently, light of unpolarized light was irradiated at an incident angle (defined by the normal of the substrate) at 45 degrees with the vertical plane as the incident surface in the polarization direction of the light in the first linearly polarized light irradiation. The dose was 221 J / cm ² . Then, the irradiated sample was heat-treated at 250 캜 for 60 minutes in a nitrogen atmosphere to form a liquid crystal alignment film.

The film thickness d _PAA of the polyamic acid film before imidization and the film thickness d of the liquid crystal alignment film were measured using an automatic polarization analyzer (manufactured by Shimadzu Corporation, APE-100 (He-Ne laser) at an incident angle of 62.5, and d _PAA = 19 nm and d = 11 nm, respectively. From the ratio of the film thickness before and after the imidation, the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidation was 0.58.

The infrared absorption spectrum of the resulting liquid crystal alignment film was measured using an FT-IR apparatus (spectrometer: Mattson Galaxy 3020, detector: mercury cadmium telluride) under the conditions of a measurement temperature of 32 캜 and an integration of 400 times.

The infrared light transmitted through the polarizer was irradiated from the direction perpendicular to the substrate surface of the liquid crystal alignment film. The infrared light spectrum when measured so that the average alignment direction of the sample and the polarization direction were parallel to each other and the infrared light spectrum when measured to be perpendicular were measured. (| A∥-A⊥ |) of the liquid crystal alignment film and the integrated value of the absorption band around 1360 cm ^-1 attributed to the CNC stretching vibration of the infrared light spectrum measured in parallel and perpendicular to each other And the sum of the absorbances (A? + A?) Was calculated.

To obtain the absorption coefficient? Of the polyamic acid film before imidation, 2.00 mass% of a polyamic acid solution was applied to a CaF ₂ substrate ( ₂ mm thick) with a spinner. The application condition was 3,000 rpm, 60 seconds. The film thickness of the polyamic acid film without light irradiation was measured and found to be 36 nm. The ultraviolet / visible absorption spectrum of the polyamic acid film before imidization was measured. As a result, the absorbance (= log (T _sub / T _sample )) at a wavelength of 364 nm was 0.36. From the formula (3), the absorption coefficient? Of the polyamic acid film before imidization is determined to be 0.023. The ultraviolet / visible absorption spectrum can be measured by, for example, an ultraviolet / visible spectrophotometer (Shimadzu MPS-2000).

From α = 0.023 and γ = 0.58, the actual film thickness d 'of the region subjected to photo-alignment treatment of the liquid crystal alignment film was 25 nm. D / d '= 1 because d <d' in the case of the film thickness of 11 nm. Therefore, by calculating the values of (A∥-A⊥ |) and (A⊥ + A∥) obtained, Of the main chain of polyimide was 0.28.

3) Measurement of pretilt angle of liquid crystal

A pair of CaF ₂ substrates on which liquid crystal alignment films were produced under the same conditions were sandwiched by spacers with a polyester film having a thickness of 25 탆 and opposed to each other so that the liquid crystal alignment film-formed side was on the inner side to prepare an antiparallel cell. The anti-parallel cell referred to herein means a cell formed such that the irradiation direction of unpolarized light when the photo-alignment treatment is applied to the film of the polyamic acid coated on the substrate is parallel and opposite to the irradiation direction.

A cyanophenyl liquid crystal (5CB) represented by the following structural formula (5) was injected into the cell at 80 ° C and gradually cooled to room temperature to prepare a cell for pretilt angle measurement (liquid crystal display device). The pretilt angle of the liquid crystal of the prepared pretilt angle measurement cell was measured, and as a result, the pretilt angle was 3.3 degrees. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light. The pretilt angle was measured using a He-Ne laser (oscillation wavelength 632.8 nm) by a crystal rotation method. The temperature at the time of measuring the pretilt angle was 25 占 폚. The NI point (nematic isotropic phase transition temperature) of 5CB was 35 占 폚, and the refractive index at wavelength 632.8 nm was n _e = 1.706 (ideal light) and n _o = 1.530 (normal light).

Example  2

A liquid crystal aligning agent A2 of PMDA / DAZ / T2 (molar ratio of raw material = 50 / 37.5 / 12.5) was prepared in place of the liquid crystal aligning agent A1 in Example 1. A liquid crystal aligning agent A2 is obtained, carried out in Example 1, Method a CaF ₂ substrate on a spinner coating, irradiation, sintering, pursuant to, thereby forming a liquid crystal alignment film having a thickness of 9nm. The film thickness d _PAA of the polyamic acid film before imidization was 18 nm and the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidization was 0.50. The absorption coefficient? Of the polyamic acid film before imidization was 0.015, and the substantial thickness d 'of the liquid crystal alignment film was 33 nm.

Subsequently, the orientation index? Of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1 to find that it was 0.17. An antiparallel cell was prepared by the method according to Example 1, and the pretilt angle was measured to be 71.3 degrees. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light.

Example  3

A liquid crystal aligning agent A3 of PMDA / DAZ / T2 (molar ratio of raw material = 50/25/25) was prepared in place of the liquid crystal aligning agent A1 in Example 1. A liquid crystal aligning agent A3 obtained, carried out in Example 1, Method a CaF ₂ substrate coated on a spinner, irradiation, sintering, pursuant to, and film forming the liquid crystal alignment film having a thickness of 11nm. The film thickness d _PAA of the polyamic acid film before imidization was 19 nm, and the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidization was 0.58. The absorption coefficient? Of the polyamic acid film before imidization was 0.009, and the substantial film thickness d 'of the liquid crystal alignment film was 64 nm.

Subsequently, the alignment index? Of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, and as a result, it was found to be 0.06. An antiparallel cell was produced by the method according to Example 1, and the pretilt angle was measured to be 89.6 degrees. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light.

Example  4

A liquid crystal aligning agent A4 of PMDA / DAZ / T1 (molar ratio of raw material = 50 / 43.75 / 6.25) was prepared in place of the liquid crystal aligning agent A1 in Example 1. The obtained liquid crystal aligning agent A4 was coated on a CaF ₂ substrate with a spinner in the same manner as in Example 1, and light irradiation and firing were performed to form a liquid crystal alignment film having a thickness of 12 nm. The film thickness d _PAA of the polyamic acid film before imidization was 20 nm and the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidization was 0.60. The absorption coefficient? Of the polyamic acid film before imidization was 0.022, and the actual film thickness d 'of the liquid crystal alignment film was 27 nm.

Subsequently, the orientation index? Of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, and found to be 0.27. An antiparallel cell was prepared by the method according to Example 1, and the pretilt angle was measured to be 4.8 degrees. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light.

Example  5

A liquid crystal aligning agent A5 of PMDA / DAZ / T1 (molar ratio of raw material = 50 / 42.5 / 7.5) was prepared in place of the liquid crystal aligning agent A1 in Example 1. A liquid crystal aligning agent obtained A5, carried out in Example 1, Method a CaF ₂ substrate on a spinner coating, irradiation, sintering, pursuant to, thereby forming a liquid crystal alignment film having a thickness of 10nm. The film thickness d _PAA of the polyamic acid film before imidization was 17 nm and the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidation was 0.59. The absorption coefficient? Of the polyamic acid film before imidization was 0.020, and the substantial film thickness d 'of the liquid crystal alignment film was 30 nm.

Subsequently, the alignment index? Of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, and found to be 0.25. An antiparallel cell was manufactured by the method according to Example 1, and the pretilt angle was measured to be 5.8 degrees. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light.

Example  6

A liquid crystal aligning agent A6 of PMDA / DAZ / T1 (molar ratio of raw material = 50 / 37.5 / 12.5) was prepared in place of the liquid crystal aligning agent A1 in Example 1. A liquid crystal aligning agent obtained A6, carried out in Example 1, Method a CaF ₂ substrate on a spinner coating, irradiation, sintering, pursuant to, thereby forming a liquid crystal alignment film having a thickness of 10nm. The film thickness d _PAA of the polyamic acid film before imidization was 15 nm and the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidization was 0.66. The absorption coefficient? Of the polyamic acid film before imidization was 0.020, and the substantial film thickness d 'of the liquid crystal alignment film was 33 nm.

Subsequently, the alignment index? Of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, and found to be 0.20. An antiparallel cell was produced by the method according to Example 1, and the pretilt angle was measured to be 75.4 degrees. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light.

Comparative Example  One

A liquid crystal aligning agent B1 of PMDA / DAZ (molar ratio of raw material = 50/50) was prepared in place of the liquid crystal aligning agent A1 in Example 1. A first B1 obtained liquid crystal alignment, carried out in Example 1, Method a CaF ₂ substrate on a spinner coating, irradiation, sintering, pursuant to, thereby forming a liquid crystal alignment film having a thickness of 10nm. Incidentally, the baking time was 120 minutes. The film thickness d _PAA of the polyamic acid film before imidization was 16 nm, and the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidization was 0.63. The absorption coefficient? Of the polyamic acid film before imidization was 0.028, and the substantial film thickness d 'of the liquid crystal alignment film was 23 nm.

Subsequently, the orientation index? Of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, and found to be 0.27. An antiparallel cell was prepared by the method according to Example 1, and the pretilt angle was measured to be 1.4 degrees. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light.

Comparative Example  2

A liquid crystal aligning agent B2 of PMDA / DAZ / T1 (molar ratio of raw material = 50 / 47.5 / 2.5) was prepared in place of the liquid crystal aligning agent A1 in Example 1. B2 the liquid crystal aligning agent thus obtained, carried out in Example 1, Method a CaF ₂ substrate on a spinner coating, irradiation, sintering, pursuant to, thereby forming a liquid crystal alignment film having a thickness of 12nm. The film thickness d _PAA of the polyamic acid film before imidization was 18 nm and the correction coefficient gamma of the thickness of the liquid crystal alignment film due to imidization was 0.67. The absorption coefficient? Of the polyamic acid film before imidization was 0.026, and the substantial film thickness d 'of the liquid crystal alignment film was 26 nm.

Subsequently, the orientation index? Of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, and found to be 0.33. An antiparallel cell was produced by the method according to Example 1, and the pretilt angle was measured to be 1.0 degree. The oblique direction of the liquid crystal was the direction of irradiation of unpolarized light.

Comparative Example  3

Except that the linearly polarized light was irradiated from the direction perpendicular to the substrate surface after the heat treatment at 250 캜 for 60 minutes in a nitrogen atmosphere, that is, the polyamine acid film was imidated by heat and ultraviolet light of linearly polarized light was irradiated, A pair of liquid crystal alignment films were formed by the method according to Example 1.

Then, the pretilt angle was tried to be measured by the method according to Experimental Example 1, but the pretilt angle and the orientation index? Could not be measured because of the orientation defects.

Table 1 shows the mole% of the liquid crystal aligning agent raw materials in the respective Examples and Comparative Examples.

[Table 1]

Table 2 shows the film thicknesses of the liquid crystal alignment films in each of the Examples and Comparative Examples, the orientation index? Of the polyimide main chain and the measurement results of the pretilt angles.

[Table 2]

From the results of Examples 1, 2, 3, 4, 5 and 6 and Comparative Examples 1, 2 and 3, it was confirmed that the content ratio of diamines in the side chain structure to the entire diamine was changed, It can be seen that a liquid crystal display element having a wide range of liquid crystal pretilt angles can be obtained by using an orientation film.

In particular, a substrate coated with a liquid crystal aligning agent having at least 10% of a branched diamine in a total molar ratio with respect to the total diamine is applied, and alignment treatment is performed by irradiating the polarized light to obtain a liquid crystal aligning agent B1 It can be seen that a pretilt angle larger than the pretilt angle generated by the same liquid crystal alignment film can be produced.

According to the present invention, there is provided a liquid crystal display device capable of providing a liquid crystal display device which is less susceptible to the generation of dust and static electricity and which can easily control the pretilt angle, and at the same time is capable of providing a liquid crystal alignment film capable of forming the liquid crystal alignment film, An alignment agent can be provided.

Claims (9)

As a reaction product of a tetracarboxylic dianhydride and a diamine, in a film of a polyamic acid containing an azo group in its main chain, in a liquid crystal alignment film obtained by imidizing a polyamic acid which is oriented in a predetermined direction by irradiation of light, At least one of the tetracarboxylic dianhydride and the diamine has a branched structure, The orientation index? Of the main chain of the polyimide in the liquid crystal alignment film obtained by the following formula (1) is in the range of 0.03 to 1.00, Wherein the pretilt angle of the liquid crystal when forming the liquid crystal display element including the liquid crystal alignment film is in the range of 2 to 90 degrees: ? = (| A∥-A⊥ |) / (A∥ + A⊥) × d / d ' In the formula (1), A∥ denotes a polarizing direction of the polarized infrared light, which is perpendicular to the surface of the liquid crystal alignment film and in which the polarizing direction of the infrared light is parallel to the average alignment direction of the main chain of the polyimide Represents the integrated absorbance due to the CNC stretching vibration of the imide ring at a wave number of about 1360 cm ^-1 at the time of incidence and A⊥ represents the polarized infrared light perpendicularly to the surface of the liquid crystal alignment film and to the average orientation of the main chain of the polyimide to the direction that indicate the integral absorption by the imide ring of a wave number of 1360cm ^-1 CNC stretching vibration near the time that the polarization direction of the infrared light is incident on the liquid crystal alignment film so that it is perpendicular, d denotes the thickness of the liquid crystal alignment film, d 'represents the actual film thickness of the photo-aligned region of the liquid crystal alignment film. The method according to claim 1, The polyamic acid is a reaction product of a tetracarboxylic acid dianhydride having no side-chain structure, a diamine having no side chain structure containing an azo group between two amino groups, and a diamine having a side chain structure, Wherein the diamine having the branched structure is contained in an amount of 7 to 90 mol% based on the total amount of the diamine. 3. The method of claim 2, Wherein the diamine having no side chain structure including an azo group between the two amino groups is 4,4'-diamino azobenzene. 3. The method of claim 2, Wherein the tetracarboxylic dianhydride is pyromellitic dianhydride. 3. The method of claim 2, Wherein the diamine having a branched structure is a compound represented by the following formula (I'-11):

In the above formula, R ²⁴ represents alkyl having 1 to 10 carbon atoms or alkoxy having 1 to 10 carbon atoms. A reaction product of a tetracarboxylic dianhydride and a diamine, wherein the polyamine acid comprises an azo group in the main chain; And solvent Wherein the diamine comprises a diamine having a branched structure, As a liquid crystal aligning agent for producing a liquid crystal alignment film obtained by imidizing a polyamic acid which is oriented in a predetermined direction by irradiation of light, Wherein the liquid crystal alignment film has an orientation index? Of the main chain of the polyimide in the liquid crystal alignment film obtained by the following formula (1) is in the range of 0.03 to 1.00, Wherein the pretilt angle of the liquid crystal when the liquid crystal display element including the liquid crystal alignment film is formed is in the range of 2 to 90 degrees, ? = (| A∥-A⊥ |) / (A∥ + A⊥) × d / d ' In the formula (1), A∥ denotes a polarizing direction of the polarized infrared light, which is perpendicular to the surface of the liquid crystal alignment film and in which the polarizing direction of the infrared light is parallel to the average alignment direction of the main chain of the polyimide Represents the integrated absorbance due to the CNC stretching vibration of the imide ring at a wave number of about 1360 cm ^-1 at the time of incidence and A⊥ represents the polarized infrared light perpendicularly to the surface of the liquid crystal alignment film and to the average orientation of the main chain of the polyimide to the direction shown by the integral absorption wave number imide ring CNC stretching vibration 1360cm ^-1 in the vicinity at which the polarization direction of the infrared light is incident on the liquid crystal alignment film so that it is perpendicular, d denotes the thickness of the liquid crystal alignment layer, d Indicates the actual film thickness of the photo-aligned region of the liquid crystal alignment film. The method according to claim 6, The polyamic acid is a reaction product of a tetracarboxylic acid dianhydride having no side-chain structure, a diamine having no side chain structure containing an azo group between two amino groups, and a diamine having a side chain structure, Wherein the diamine having the branched structure is contained in an amount of 7 to 90 mol% based on the total amount of the diamine. A liquid crystal alignment film formed on an opposing face of each of the pair of substrates, a pair of substrates opposed to each other, an electrode formed on one or both sides of the opposed faces of the pair of substrates, A liquid crystal display element having a liquid crystal layer formed between a pair of substrates, The liquid crystal display element according to any one of claims 1 to 5, wherein one or both of the liquid crystal alignment layers formed on the opposing surfaces of the pair of substrates are the liquid crystal alignment layers according to any one of claims 1 to 5. As a reaction product of tetracarboxylic dianhydride and diamine, a step of orienting the polyamic acid in the film by irradiating light to a film of polyamic acid containing an azo group in the main chain and a step of imidizing the polyamic acid oriented in the film A method for producing a liquid crystal alignment film by imidizing the polyamic acid, Wherein at least one of the tetracarboxylic acid dianhydride and the diamine has a side chain structure, In the step of orienting the polyamic acid in the film, (A) when the film is irradiated with light that changes the geometrical isomer of the azo group from an anti isomer to a syn isomer, and when the polyamic acid in the film is viewed in a direction perpendicular to the surface of the film, Direction, and Irradiating the surface of the film of the polyamic acid with light from an oblique direction and orienting the polyamic acid in an oblique direction with respect to the surface of the film, (B) irradiating the film with light that changes the geometrical isomer of the azo group from an isomer to a new isomer from the oblique direction to the surface of the film, and when the polyamic acid in the film is viewed in a direction perpendicular to the surface of the film , Orienting the film in a predetermined direction, and simultaneously orienting the film in an oblique direction with respect to the surface of the film.