JP2007248637A - Liquid crystal alignment layer, liquid crystal aligning agent and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal aligning agent that can control alignment of a main chain by a photo-alignment process and impart any pretilt angle to a liquid crystal, and to provide a liquid crystal alignment layer formed by using the aligning agent, and a liquid crystal display device having the liquid crystal alignment layer. <P>SOLUTION: The liquid crystal aligning agent for forming a liquid crystal alignment layer of a liquid crystal display device is prepared so that such a liquid crystal alignment layer is formed by applying a polyamic acid on a substrate, irradiating the substrate with light having controlled polarization, and imidizing the polyamic acid layer to align the main chain of polyimide to a specified direction in the alignment layer and to develop a pretilt angle of a liquid crystal. The liquid crystal aligning agent is used to form the liquid crystal alignment layer. A liquid crystal display device having the liquid crystal alignment layer is manufactured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, the main chain of polyimide in the polyimide film is oriented in a specific direction by irradiating the light with polarization controlled without performing rubbing treatment and then performing the orientation treatment of the polyamic acid film, followed by imidization. The present invention relates to a liquid crystal alignment film capable of developing a pretilt angle of liquid crystal, a liquid crystal alignment agent capable of forming the same, and a liquid crystal display element having the liquid crystal alignment film.

  Liquid crystal display elements are used in various liquid crystal display devices such as monitors for notebook computers and desktop computers, video camera viewfinders, and projection displays. Recently, they have also been used in televisions. . Furthermore, it is also used as an optoelectronic-related element such as an optical printer head, an optical Fourier transform element, or a light valve. As a conventional liquid crystal display element, a display element using a nematic liquid crystal is mainly used, and the alignment direction of the liquid crystal on one substrate side and the alignment direction of the liquid crystal on the other substrate side in the liquid crystal layer are twisted at an angle of 90 degrees. TN (Twisted Nematic) type liquid crystal display element, STN (Super Twisted Nematic) type liquid crystal display element in which the alignment direction is twisted at an angle of usually 180 degrees or more, so-called TFT (Thin-film-transistor) using a thin film transistor Type liquid crystal display elements have been put into practical use.

  However, these liquid crystal display elements have a narrow viewing angle at which an image can be properly viewed, and when viewed from an oblique direction, luminance and contrast may be reduced, and luminance inversion may occur in a halftone. In recent years, with respect to the problem of viewing angle, a TN liquid crystal display element using an optical compensation film, an MVA (Multi-domain Vertical Alignment) liquid crystal display element using a technique of vertical alignment and protrusion structure, or a horizontal electric field method The IPS (In-Plane Switching) type liquid crystal display element (see, for example, Patent Documents 1 to 3) has been improved and put into practical use.

  The development of the technology of the liquid crystal display element has been achieved not only by improving the drive system and the element structure, but also by improving the components used for the display element. Among the constituent members used in display elements, the liquid crystal alignment film is one of the important elements related to the display quality of the liquid crystal display element, and the role of the liquid crystal alignment film is increasing as the quality of the display element increases. It has become important year after year.

  In such a liquid crystal alignment film, it is necessary to uniformly control the molecular arrangement of the liquid crystal for the uniform display characteristics of the liquid crystal display element. For this purpose, the liquid crystal molecules on the substrate are uniformly aligned in one direction. Furthermore, it is required to develop a certain tilt angle (pretilt angle) from the substrate surface. Thus, a liquid crystal alignment film that uniformly aligns the directions of liquid crystal molecules on a substrate is an important and indispensable technique in the manufacturing process of a liquid crystal display element.

  The liquid crystal alignment film is prepared from a liquid crystal aligning agent. Currently, the liquid crystal aligning agent mainly used is a solution in which polyamic acid or soluble polyimide is dissolved in an organic solvent. After applying such a solution to a substrate, a polyimide-based liquid crystal alignment film is formed by film formation by means such as heating. Various liquid crystal aligning agents other than polyamic acid are also being studied, but they are almost practical in terms of heat resistance, chemical resistance (liquid crystal resistance), coating properties, liquid crystal alignment properties, electrical properties, optical properties, display properties, etc. It has not been converted.

Industrially, a rubbing method that is simple and capable of high-speed processing over a large area is widely used as an alignment processing method. The rubbing method is a process of rubbing the surface of the liquid crystal alignment film in one direction using a cloth in which fibers of nylon, rayon, polyester, or the like are planted, and this makes it possible to obtain uniform alignment of liquid crystal molecules. However, problems such as dust generation by static rubbing and generation of static electricity have been pointed out.

So far, the following two have been proposed as the alignment mechanism of the liquid crystal on the liquid crystal alignment film subjected to the alignment treatment by the rubbing treatment.
(1) Surface shape effect due to microgroups generated by rubbing treatment (2) Intermolecular interaction between liquid crystal alignment film uniaxially aligned by rubbing treatment and liquid crystal monolayer in contact with the liquid crystal alignment film (1) The contribution of the surface shape effect is relatively small, and it has been confirmed that the contribution of the intermolecular interaction (2) is dominant.

  On the other hand, with respect to a photo-alignment method in which alignment treatment is performed by irradiating light, many alignment mechanisms such as a photolysis method, a photoisomerization method, a photodimerization method, and a photocrosslinking method have been proposed (for example, see Patent Document 4) .) 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 (2) acts as the alignment mechanism of the liquid crystal. In addition, since the photo-alignment treatment method is non-contact, the generation of dust and static electricity is less in principle than the rubbing treatment.

Therefore, by using a liquid crystal alignment film with good uniaxial alignment that has been subjected to alignment treatment by the photo alignment method, the molecular alignment state of the liquid crystal monolayer in contact with the liquid crystal alignment film can be controlled to provide a liquid crystal display element. Can be expected to improve performance. On the other hand, in the photo-alignment method, there remains room for studying control of a wide range of pretilt angles.
Japanese Examined Patent Publication No. 63-21907 JP-A-6-160878 JP-A-9-15650 JP 2005-275364 A

  An object of the present invention relates to a photo-alignment material that performs alignment treatment by irradiating light, and uses a liquid crystal aligning agent that is less susceptible to dust and static electricity and that can easily control the pretilt angle of liquid crystal. And a liquid crystal display element having the liquid crystal alignment film.

The present inventors diligently studied to solve the above problems. As a result, the alignment of the main chain and the pretilt angle of the liquid crystal can be imparted to the liquid crystal alignment film obtained from the liquid crystal alignment agent prepared under specific conditions by irradiating light with controlled polarization. A liquid crystal alignment film was obtained, and a liquid crystal display device using the liquid crystal alignment film was found to be industrially stable and easy to control the pretilt angle, and the present invention was completed based on this finding.
The present invention has the following configuration.

[1] A liquid crystal alignment film obtained by imidizing a polyamic acid which is a reaction product of tetracarboxylic dianhydride and diamine and is aligned in a predetermined direction by light irradiation in a polyamic acid film containing an azo group in the main chain In this case, at least one of the tetracarboxylic dianhydride and the diamine has a side chain structure, and the orientation index Δ of the main chain of the polyimide in the liquid crystal alignment film obtained by the following formula 1 is 0.03 to 1.00. A liquid crystal alignment film having a pretilt angle of 2 to 90 degrees when a liquid crystal display element including a liquid crystal alignment film is formed.
Δ = (| A‖−A⊥ |) / (A‖ + A⊥) × d / d ′ (1)
(In the formula (1), A 、 represents polarized infrared light perpendicular to the surface of the liquid crystal alignment film and the polarization direction of the infrared light is parallel to the average alignment direction of the main chain of polyimide. Represents the integrated absorbance due to C—N—C stretching vibration of the imide ring near the wave number of 1360 cm ⁻¹ when incident on the liquid crystal alignment film so that A becomes the polarized infrared light of the liquid crystal alignment film. perpendicular to the surface, and the imide ring around the wave number 1360 cm ^-1 when is incident on the liquid crystal alignment film so that the polarization direction of the infrared light to the average orientation direction of the main chain of the polyimide is perpendicular The integrated absorbance due to C—N—C stretching vibration is represented, d represents the film thickness of the liquid crystal alignment film, and d ′ represents the effective film thickness of the liquid crystal alignment film subjected to the photo-alignment treatment.)

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

[3] The liquid crystal alignment film according to [2], wherein the diamine containing an azo group between the two aminos and having no side chain structure is 4,4'-diaminoazobenzene.

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

[5] The liquid crystal alignment film according to [2], wherein the diamine having a side chain structure is a compound represented by the following general formula (I′-11). However ^{Shikichu, R 24} represents an alkoxy having 1 to 10 carbon alkyl or a C 1 to 10 carbon atoms.

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

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

[8] A pair of substrates disposed opposite to each other, an electrode formed on one or both of the surfaces facing each other of the pair of substrates, and a surface facing each of the pair of substrates. In the liquid crystal display element having the liquid crystal alignment film and the liquid crystal layer formed between the pair of substrates, one or both of the liquid crystal alignment films formed on the opposing surfaces of the pair of substrates are [ A liquid crystal display element, which is the liquid crystal alignment film according to any one of 1] to [5].

[9] A step of irradiating a film of polyamic acid, which is a reaction product of tetracarboxylic dianhydride and diamine and containing an azo group in the main chain, to orient the polyamic acid in the film; A process for producing a liquid crystal alignment film obtained by imidizing the polyamic acid, wherein at least one of the tetracarboxylic dianhydride and the diamine includes a side chain. The step of orienting the polyamic acid in the film using a compound having a structure,
(A) When the film is irradiated with light that changes the geometric isomer of the azo group from an anti isomer to a syn isomer and the polyamic acid in the film is viewed from a direction perpendicular to the surface of the film, Or an operation of orienting in a direction and irradiating light from a direction oblique to the surface of the polyamic acid film to orient the polyamic acid in a direction oblique to the surface of the film, Or (B) irradiating the film with light that changes the geometric isomer of the azo group from an anti isomer to a syn isomer from an oblique direction with respect to the surface of the film, and the polyamic acid in the film is A method comprising aligning in a predetermined direction when viewed from a direction perpendicular to the surface and aligning in an oblique direction with respect to the surface of the film.

  According to the present invention, it is possible to provide a liquid crystal display element with less dust generation and static electricity problems and easy control of the pretilt angle, and to form a liquid crystal alignment film and the liquid crystal alignment film that make it possible. It is possible to provide a liquid crystal aligning agent that can be used.

  The present invention can induce a pretilt angle of an arbitrary liquid crystal by irradiating a liquid crystal aligning agent film with specific light such as light having a controlled polarization component to perform alignment treatment, and uses this liquid crystal aligning film. Thus, an industrially stable liquid crystal display element is realized.

  The liquid crystal alignment film in the present invention is obtained by imidizing a polyamic acid aligned 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 liquid crystal aligning agent described later, and is a component capable of forming a liquid crystal aligning film containing polyimide as a main component when a liquid crystal aligning film described later is used. Examples of the derivative of polyamic acid contained in the polyamic acid in the present invention include soluble polyimide, polyamic acid ester, and polyamic acid amide. More specifically, 1) a polyimide in which all amino groups and carboxyl groups of polyamic acid are subjected to a dehydration ring-closing reaction, 2) a partial polyimide in which a partial dehydration ring-closing reaction is performed, and 3) a part of tetracarboxylic dianhydride is organic A polyamic acid-polyamide copolymer obtained by reacting with a dicarboxylic acid, and 4) a polyamideimide obtained by subjecting a part or all of the polyamic acid-polyamide copolymer to a dehydration ring-closing reaction.

  The polyamic acid contains an azo group in the main chain. When the polyamic acid containing an azo group in the main chain is a molecular structure that connects two acid anhydride groups or two amino groups, except for a branched molecular structure, the main chain of the acid or diamine, This acid or diamine can be obtained by using a tetracarboxylic dianhydride or diamine containing an azo group in the main chain of the acid or diamine, or both as raw materials. The azo group may be contained in both tetracarboxylic dianhydride and diamine, but may be contained in only one of them.

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

Examples of the side chain structure include groups having 3 or more carbon atoms. More specifically,
1) phenyl which may have a substituent, cyclohexylphenylene which may have a substituent, bis (cyclohexyl) phenylene which may have a substituent, alkyl having 3 or more carbon atoms, alkenyl or Alkynyl,
2) phenyloxy which may have a substituent, cyclohexyloxy which may have a substituent, bis (cyclohexyl) oxy which may have a substituent, which may have a substituent Phenylcyclohexyloxy, optionally substituted cyclohexylphenyloxy, 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, alkenylcarbonyloxy or alkynylcarbonyloxy having 3 or more carbon atoms,
5) phenyloxycarbonyl which may have a substituent, cyclohexyloxycarbonyl which may have a substituent, bis (cyclohexyl) oxycarbonyl which may have a substituent, which has a substituent Bis (cyclohexyl) phenyloxycarbonyl which may be substituted, cyclohexylbis (phenyl) oxycarbonyl which may have a substituent, or alkyloxycarbonyl having 3 or more carbon atoms, alkenyloxycarbonyl or alkynyloxycarbonyl,
6) phenylaminocarbonyl, or alkylaminocarbonyl having 3 or more carbon atoms, alkenylaminocarbonyl or alkynylaminocarbonyl,
7) Cyclic alkylene having 3 or more carbon atoms,
8) Cycloalkylalkylene which may have a substituent, phenylalkylene which may have a substituent, bis (cyclohexyl) alkylene which may have a substituent, which may have a substituent Cyclohexyl phenylalkylene, optionally substituted bis (cyclohexyl) phenylalkylene, optionally substituted phenylalkyloxy, alkylphenyloxycarbonyl, or alkylbiphenylyloxycarbonyl,
9) phenyl or cyclohexyl substituted by alkyl, fluorine-substituted alkyl, or alkoxy, and
10) Alkyl or fluorine in which two or more benzene rings or cyclohexane rings are bonded by a single bond, or bonded through —O—, —COO—, —OCO—, —CONH—, or alkylene having 1 to 3 carbon atoms. Examples thereof include, but are not limited to, substituted alkyl or a ring assembly group substituted by alkoxy.

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

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

  In the present specification, the terms “alkyl”, “alkenyl”, and “alkynyl” may be linear or branched.

The tetracarboxylic dianhydride includes an aromatic system (including a heteroaromatic ring system) in which a dicarboxylic acid anhydride is directly bonded to an aromatic ring, and an aliphatic system (complexed in which a dicarboxylic acid anhydride is not directly bonded to an aromatic ring. (Including a ring system). The polyamic acid preferably has a structure that does not contain oxygen or sulfur such as an ester or an ether bond that tends to cause a decrease in the electrical characteristics of the liquid crystal display element. Therefore, the tetracarboxylic dianhydride preferably has a structure containing no oxygen or sulfur. However, even if it has such a structure, there is no problem as long as the amount is within a range that does not adversely affect the electrical characteristics.

Specific examples of the tetracarboxylic dianhydride that can be used in the present invention are as follows.

  Among formulas 1-1 to 1-38, formula 1-1, formula 1-2, formula 1-7, formula 1-13, formula 1-17, formula 1-18, formula 1-19, formula 1-19 20, tetracarboxylic dianhydrides represented by Formula 1-27, Formula 1-28, and Formula 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. .

  Needless to say, the tetracarboxylic dianhydride is not limited to these, and other compounds having various molecular structures exist within the scope of achieving the object of the present invention. Moreover, these tetracarboxylic dianhydrides can also be used individually or in combination of 2 or more types.

  The diamine may include a diamine having an azo group as a structure that undergoes a photoisomerization reaction, a diamine having a side chain structure, and a diamine having no side chain structure. In the present invention, these diamines can be used in combination.

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

  As the diamine having a side chain structure, one or more of various diamines having a side chain structure branched from the main chain of the amine can be used. The diamine having a side chain structure is preferably a diamine represented by the general formula (I) from the viewpoint of expressing various properties such as orientation stability and pretilt angle in a balanced manner.

In the general formula (I), the two amino groups are bonded to the phenyl ring carbon. Preferably, the bonding positional relationship between the two amino groups is meta or para. Further, each of the two amino groups is preferably bonded to the 3rd and 5th positions or the 2nd and 5th positions when the bonding position of “R ² —R ¹ —” is the 1st position.

In the general formula (I), R ¹ is a single bond, —O—, —COO—, —OCO—, —CO—, —CONH— or — (CH ₂ ) _m —, where m is 1 R ² is an integer of -6, R ² is a group having a steroid skeleton, a group represented by the following general formula (II), or carbon when the positional relationship between two amino groups bonded to the benzene ring is para When the positional relationship is meta, it is alkyl having 1 to 10 carbons or phenyl, and in the alkyl, any —CH ₂ — is independently —CF ₂ —, — CHF -, - O -, - CH = CH- or -C≡C- may be replaced by, may be -CH ₃ is replaced by _-CH 2 F, -CHF ₂ or -CF _3, The hydrogen bonded to the ring-forming carbon of the phenyl is independently -F, -CH ₃ , —OCH ₃ , —OCH ₂ F, —OCHF _2, or —OCF ₃ may be substituted.

In the general formula (II), A ¹ and A ² are each independently 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 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, R ⁵ is —H, —F, alkyl having 1 to 20 carbons, fluorine-substituted alkyl having 1 to 20 carbons, alkoxy having 1 to 20 carbons , —CN, —OCH ₂ F, —OCHF ₂ or —OCF ₃ , a and b each independently represent an integer of 0 to 4, and when a or b is 2 to 4, adjacent A ¹ or A ² is a different group, c, d and e independently represents an integer of 0 to 3, and when e is 2 or 3, the plurality of rings S may be the same group or different groups, and f and g are each independently It represents an integer of 0 to 2 and c + d + e ≧ 1.

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

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

  Of these, diamines represented by formula (I-2), formula (I-4), formula (I-5), and formula (I-6) are more preferable.

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

  Furthermore, 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 a diamine having a side chain structure include diamines represented by formulas (I′-1) to (I′-20).

In the formulas (I′-1) to (I′-3), R ²¹ is preferably alkyl having 4 to 16 carbons, and more preferably alkyl having 6 to 16 carbons. 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 alkyl having 3 to 12 carbons or alkoxy having 3 to 12 carbons, more preferably alkyl having 5 to 12 carbons or alkoxy having 5 to 12 carbons. R ²⁴ is preferably an alkoxy having 1 to 10 several alkyl or C 1 to 10 carbon atoms, more preferably an alkoxy alkyl or 3 to 10 carbon atoms having 3 to 10 carbon atoms.

  As the diamine having no side chain structure, one or more of various diamines that do not have a side chain structure branched from the main chain of the amine and do not contain an azo group in the main chain of the amine can be used. . Preferably, the diamine having no side chain structure includes the following diamines.

  For example, examples of the diamine having no side chain structure include diamines represented by formulas (III-1) and (III-2).

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

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

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

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

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

  Of these, diamines having no side chain structure are more preferably formulas (V-1) to (V-7), formulas (VI-1) to (VI-12), formula (VI-26), Examples include diamines represented by formula (VI-27), formula (VII-1), formula (VII-2), formula (VII-6), and formulas (VIII-1) to (VIII-5). Preferable examples include diamines represented by formula (V-6), formula (V-7), and formulas (VI-1) to (VI-12).

  Furthermore, the siloxane type diamine which has a siloxane bond can be mentioned as another diamine which can be used with this invention and can be used together with said diamine. Although this siloxane type diamine is not specifically limited, What is represented by General formula (4) can be preferably used in this invention.

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

  The diamine that can be used in the present invention is not limited to these, and it goes without saying that other compounds having various molecular structures exist within the range in which the object of the present invention is achieved. These diamines can be used alone or in combination of two or more.

  On the other hand, diamines that can be used in the present invention are also aromatic systems (including heteroaromatic ring systems) in which an amino group is directly bonded to an aromatic ring, as well as the tetracarboxylic dianhydrides described above. It may belong to any group of an aliphatic system (including a heterocyclic system) to which no group is bonded. Among them, aromatic diamines having a ring structure and aliphatic diamines having a ring structure are preferable because the orientation of liquid crystals is kept good. Furthermore, the thing of the structure which does not contain oxygen and sulfur, such as an ester and an ether bond which tends to cause the electrical characteristic of a liquid crystal display element to fall is preferable. However, even if it has such a structure, there is no problem as long as the amount is within a range that does not adversely affect the electrical characteristics.

  Furthermore, in addition to these tetracarboxylic dianhydrides and diamines, monoamines and / or monocarboxylic anhydrides that form reaction ends of polyamic acids can be used in combination. In order to improve the adhesion to the substrate, an aminosilicone compound can be introduced.

  Examples of aminosilicone compounds include paraaminophenyltrimethoxysilane, paraaminophenyltriethoxysilane, metaaminophenyltrimethoxysilane, metaaminophenyltriethoxysilane, aminopropyltrimethoxysilane, and aminopropyltriethoxysilane.

  The ratio of the diamine having a side chain structure to the diamine having no side chain structure can be arbitrarily selected according to the electrical 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 ratio of the diamine having the side chain structure is 7 mol% or more, a good liquid crystal pretilt angle is obtained, and when the ratio is 90 mol% or less, a good orientation of the polyimide main chain is obtained.

  In the liquid crystal alignment film of the present invention, the orientation index Δ 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 (Δ) of the polyimide main chain can be evaluated by infrared absorption spectroscopy using polarized infrared light. This method evaluates the molecular orientation by detecting infrared dichroism that the amount of infrared absorption when two linearly polarized infrared rays orthogonal to the sample are incident differs depending on the molecular orientation.

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 polyimide in a direction parallel to the surface of the liquid crystal alignment film The sample is fixed to the sample holder so that the average orientation direction of the main chain is parallel to the polarization direction of the polarizer and the infrared light is incident perpendicular to the sample surface, and the infrared absorbance is measured. taking measurement. Next, the polarizer is rotated 90 degrees with the sample fixed to the sample holder, and the average of the main chain of polyimide in the direction in which the polarization direction of the infrared light passing through the polarizer is parallel to the surface of the liquid crystal alignment film The infrared absorbance is measured so as to be perpendicular to the orientation direction. In the infrared absorbance thus obtained, Δ is calculated from the peak value or integral value of the absorption band caused by molecular vibration polarized parallel to the molecular axis of the polyimide main chain.

In this method, a sample made on a substrate that transmits infrared light, such as silicon or calcium fluoride (fluorite: CaF ₂ ), is used.

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

The characteristic base frequency of the polyimide in the present invention is 1360 cm ⁻¹ (C—N—C stretching vibration of imide ring), 1510 cm ⁻¹ (C—C stretching vibration of phenyl) as a strong infrared absorption peak of polyimide, and Appears in the vicinity of 1720 cm ⁻¹ (C═O stretching vibration of imide group). Any infrared absorption peak may be used, but the direction of polarization caused by molecular vibration is along the polyimide main chain, and the change of the infrared absorption peak due to the polyimide composition is relatively small (around 1360 cm ^−1. -N-C stretching vibration) can be used particularly preferably. Furthermore, since the infrared dichroic ratio may differ depending on the film thickness of the liquid crystal alignment film, it is preferable to evaluate the alignment of the polyimide main chain using the infrared dichroic difference from which the influence of the film thickness has been removed.

From the above, in the present invention, the anisotropic orientation of the liquid crystal alignment film in the direction parallel to the surface of the liquid crystal alignment film due to the infrared dichroism near 1360 cm ⁻¹ (C—N—C stretching vibration of the imide ring). Assess sex. Note that the absorbance around 1360 cm ^-1 in the present invention (from 1330 1430 cm ^-1) the integral value of the band attributed to a C-N-C stretching vibration of an imide ring as indicating. Further, in order to correct the influence of the film thickness, the film thickness of the liquid crystal alignment film and the absorption coefficient α at the wavelength of 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 Δ of the liquid crystal orientation film after the orientation treatment represented by the following formula (1).
Δ = (| A‖−A⊥ |) / (A‖ + A⊥) × d / d ′ (1)

In Formula (1), A‖ represents polarized infrared light perpendicular to the surface of the liquid crystal alignment film, and the polarization direction of the infrared light is parallel to the average orientation direction of the main chain of polyimide. Represents the integrated absorbance due to C—N—C stretching vibration of the imide ring near the wave number of 1360 cm ⁻¹ when being incident on the liquid crystal alignment film, and A⊥ represents polarized infrared light on the surface of the liquid crystal alignment film. C of the imide ring near a 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 to the average alignment direction of the main chain of the polyimide -Indicates the integrated absorbance due to N-C stretching vibration. d represents the film thickness of the liquid crystal alignment film. d ′ represents the effective film thickness of the region of the liquid crystal alignment film that has been subjected to photo-alignment treatment.

The effective film thickness d ′ of the region of the liquid crystal alignment film that is subjected to the photo-alignment treatment is obtained from the following formula (2).
d ′ = (1 / α) × γ (2)

In formula (2), α is the absorption coefficient of the polyamic acid film not subjected to photo-alignment treatment at the wavelength of light used for the photo-alignment treatment. γ is a correction coefficient for the thickness of the liquid crystal alignment film by imidization, and is given by d / d _PAA where the film thickness of the polyamic acid film before imidization is d _PAA . If d is smaller than d ′, d ′ = d. In addition, the film thickness of the polyamic acid film before imidation can be measured by ellipsometry or a contact step meter.

The absorption coefficient α is determined by measuring the transmission spectrum in the ultraviolet-visible light region of the polyamic acid film having a film thickness d _PAA measured by a step gauge or an ellipsometer by using an ultraviolet-visible spectrophotometer before the photo-alignment treatment. Is done. At the wavelength of the light used for optical alignment treatment, the transmittance T _sample substrate polyamic acid film is applied, the α absorption coefficient and the transmissivity of the substrate only the T _sub, is given by the following equation (3).
α = (1 / d _PAA ) × ln (T _sub / T _sample ) (3)

  The liquid crystal alignment film of the present invention has an orientation index Δ in the range of 0.03 to 1.00, Δ is preferably 0.10 to 0.95, and Δ is 0.20 to 0. More preferably, it is 90 or less. When the orientation index Δ 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.

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

  The pretilt angle can be determined by using, for example, Chuo Seiki liquid crystal characteristic evaluation apparatus OMS-CA3 type, Journal of Applied Physics, Vol. 48, no. 5, p. 1783-1792 (1977), and can be measured by the crystal rotation method. Alternatively, the pretilt angle can be measured by a crystal rotation method described in Mol. Cryst. Liq. Cryst. 241 (1994) 147.

  The film thickness of the liquid crystal alignment film in the present invention is usually from 5 to 500 nm from the viewpoints of film thickness uniformity 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 ellipsometry or a contact step meter. Moreover, the film thickness of a liquid crystal aligning film can be adjusted with the density | concentration of a liquid crystal aligning agent, a viscosity, and the application conditions of a liquid crystal aligning agent.

  A liquid crystal aligning agent is used for forming the liquid crystal alignment film in the present invention. This liquid crystal aligning agent is a varnish in which a polyamic acid containing an azo group in the main chain and having a side chain structure in the main chain is dissolved in a solvent. The liquid crystal aligning film in the present invention is formed by applying this liquid crystal aligning agent on the substrate, drying the solvent, and applying an alignment treatment. The polyamic acid may be a copolymer such as a random copolymer or a block copolymer, and a plurality of types of the polyamic acid may be contained.

The liquid crystal aligning agent used in the present invention is a liquid crystal aligning agent characterized by containing a polyamic acid obtained by reacting a diamine with tetracarboxylic dianhydride. It contains a polyamic acid using at least one kind of acid dianhydride and at least one kind of diamine having an azo group in the main chain and tetracarboxylic dianhydride. More preferably, the diamine contains a polyamic acid using a diamine containing a diamine having a side chain structure and a diamine having an azo group in the main chain and no side chain structure. For the liquid crystal aligning agent in the present invention, the tetracarboxylic dianhydride and diamine described above in the liquid crystal aligning film are used.

  As described above, the liquid crystal aligning agent in the present invention contains a diamine having a side chain structure in an amount of 7 to 90 mol% based on the total amount of the diamine. From the viewpoint of obtaining good orientation of the main chain of the polyimide.

  Although the density | concentration of the polyamic acid in the liquid crystal aligning agent in this invention is not specifically limited, It is preferable that it is 0.1-40 mass%. When the liquid crystal aligning agent is applied to the substrate, an operation of diluting the contained polyamic acid with a solvent in advance may be required to adjust the film thickness. When the concentration of the polyamic acid is 40% by mass or less, the viscosity of the liquid crystal aligning agent becomes preferable. When the liquid crystal aligning agent needs to be diluted to adjust the film thickness, a solvent is added to the liquid crystal aligning agent. This is preferable because it can be easily mixed.

  In the case of a coating method such as a spinner method or a printing method, the amount is usually 10% by mass or less in order to maintain a good film thickness. Other coating methods such as a dipping method or an ink jet method may further reduce the concentration. On the other hand, when the concentration of the polyamic acid is 0.1% by mass or more, the thickness of the obtained liquid crystal alignment film tends to be preferable. Accordingly, 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 normal spinner method or printing method. However, depending on the application method of the liquid crystal aligning agent, it may be used at a dilute concentration.

  The solvent used together with the polyamic acid in the liquid crystal aligning agent in the present invention can be applied without particular limitation as long as it is a solvent having the ability to dissolve the polyamic acid. Such solvents widely include solvents usually used in the production and use of polyamic acid, and can be appropriately selected according to the purpose of use. Examples of these solvents are as follows.

  Examples of aprotic polar organic solvents that are good solvents for polyamic acids include N-methyl-2-pyrrolidone, dimethylimidazolidinone, N-methylcaprolactam, N-methylpropionamide, N, N-dimethylacetamide, Examples include lactones such as dimethyl sulfoxide, N, N-dimethylformamide, N, N-diethylformamide, N, N-diethylacetamide, and γ-butyrolactone.

  Examples of other solvents other than the above-mentioned solvents for the purpose of improving coatability include ethylene glycol such as alkyl lactate, 3-methyl-3-methoxybutanol, tetralin, isophorone, ethylene glycol monobutyl ether, etc. Monoalkyl ether, diethylene glycol monoalkyl ether such as diethylene glycol monoethyl ether, ethylene glycol monoalkyl and phenyl acetate, propylene glycol monoalkyl ether such as triethylene glycol monoalkyl ether, propylene glycol monobutyl ether, dialkyl malonate such as diethyl malonate Dipropylene glycol monoalkyl ethers such as dipropylene glycol monomethyl ether, and ethers such as these glycol monoethers It can be exemplified ether compound.

  Among these, the solvent particularly includes N-methyl-2-pyrrolidone, dimethylimidazolidinone, γ-butyrolactone, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and the like. It can be preferably used.

The liquid crystal aligning agent in this invention can contain various additives as needed. For example, when it is desired to improve the coating property, a surfactant according to such purpose, an antistatic agent when it is necessary to improve the antistatic property, and a silane coupling agent or the like when it is desired to improve the adhesion to the substrate. An appropriate amount of a titanium coupling agent may be blended.

  A liquid crystal display element according to the present invention includes a pair of substrates disposed opposite to each other, electrodes formed on one or both of the surfaces opposed to each of the pair of substrates, and the pair of substrates opposed to each other. And a liquid crystal layer formed between the pair of substrates. The liquid crystal display element in the present invention can be configured in the same manner as the conventional liquid crystal display element except for the liquid crystal alignment film. The liquid crystal alignment film of the present invention described above is used for one or both of the liquid crystal alignment films formed on the opposing surfaces of the pair of substrates.

  As the substrate, an appropriate substrate is used according to the application. From the viewpoint of display, the substrate is preferably a transparent substrate such as glass, and from the viewpoint of confirming the orientation index Δ of the liquid crystal alignment film, a substrate that transmits infrared light such as silicon or calcium fluoride is used. 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 ITO and metal vapor deposition films. Further, the electrode may be formed on the entire surface of one surface of the substrate, or may be formed in a desired shape that is patterned, for example. Examples of the desired shape of the electrode include a comb shape or a zigzag structure. The electrode may be formed on one of the pair of substrates, or may be formed on both substrates. The form of electrode formation varies depending on the type of liquid crystal display element. For example, in the case of an IPS liquid crystal display element, an electrode is disposed on one of the pair of substrates, and in the case of other liquid crystal display elements, the electrodes of the pair of substrates are arranged. Electrodes are arranged on both sides. The liquid crystal alignment film is formed on the substrate or electrode.

  The liquid crystal layer is formed in such a manner that the liquid crystal composition is sandwiched between 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 or a resin sheet that is interposed between the pair of substrates to form an appropriate interval can be used as necessary.

  The liquid crystal composition used in the liquid crystal display element of the present invention is not particularly limited, and various liquid crystal compositions having positive dielectric anisotropy can be used. Examples of preferred liquid crystal compositions include Japanese Patent No. 3086228, Japanese Patent No. 2635435, Japanese Patent Laid-Open No. 5-501735, Japanese Patent Laid-Open No. 8-157826, Japanese Patent Laid-Open No. 8-231960, and Japanese Patent Laid-Open No. 9-241644. (EP885272A1 specification), JP-A-9-302346 (EP806466A1 specification), JP-A-8-199168 (EP722998A1 specification), JP-A-9-235552, JP-A-9-255958, JP-A-9-241463 (EP885271A1 specification), JP-A-10-204016 (EP844229A1 specification), JP-A-10-204436, JP-A-10-231482, JP-A-2000-087040, In JP 2001-48822 A, etc. It is shown.

Various liquid crystal compositions having a negative dielectric anisotropy can be used. Examples of preferred liquid crystal compositions include JP-A-57-141432, JP-A-2-4725, JP-A-4-224858, JP-A-8-40953, JP-A-8-104869, Japanese Laid-Open Patent Publication No. 10-168076, Japanese Laid-Open Patent Publication No. 10-168453, Japanese Laid-Open Patent Publication No. 10-236989, Japanese Laid-Open Patent Publication No. 10-236990, Japanese Laid-Open Patent Publication No. 10-236992, Japanese Laid-Open Patent Publication No. 10-236993, Japanese Laid-open Patent Publication No. -236994, JP-A-10-237000, JP-A-10-237004, JP-A-10-237024, JP-A-10-237035, JP-A-10-237075, JP-A-10-237076 JP, 10-237448, (EP967261A1 specification), JP 10-10
No. 287874, JP-A-10-287875, JP-A-10-291945, JP-A-11-029581, JP-A-11-080049, JP-A-2000-256307, JP-A-2001-019965 This is disclosed in Japanese Patent Laid-Open No. 2001-072626, Japanese Patent Laid-Open No. 2001-192657, and the like.

  One or more optically active compounds may be added to the liquid crystal composition having a positive or negative dielectric anisotropy.

  In the liquid crystal display element according to the present invention, the pair of substrates face each other so that the average alignment direction of the main chain of polyimide in the liquid crystal alignment film on each substrate is a specific direction according to the type of the liquid crystal display element. For example, when the liquid crystal display element is a TN liquid crystal display element, electrodes and a liquid crystal alignment film are formed on the pair of substrates so that the average alignment direction of the main chain of polyimide in the liquid crystal alignment film of each substrate intersects at 90 degrees. Facing each other facing inward. 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 usually the reverse direction, that is, 180 degrees, or intersects at an angle larger than that. As described above, the pair of substrates face each other with the surfaces on which the electrodes and the liquid crystal alignment film are formed facing inward.

  Moreover, the liquid crystal display element in this invention may have another other member according to the kind of liquid crystal display element. For example, in a color display TFT liquid crystal element using a thin film transistor, a thin film transistor, an insulating film, a protective film, a pixel electrode, and the like are formed on a first transparent substrate, and a pixel is formed on a second transparent substrate. A black matrix, a color filter, a planarization film, a pixel electrode, and the like that block light outside the region are included.

  In the IPS liquid crystal display element, a liquid crystal is sandwiched between a first transparent substrate on which a thin film transistor is formed, a second transparent substrate facing the thin film transistor, and the substrates. The first transparent substrate has pixel electrodes and common electrodes formed so that comb teeth alternately extend. Similar to the conventional liquid crystal display element, the second transparent substrate has a black matrix, a color filter, a flattening film, and the like that block light outside the pixel region. The comb-like electrode is formed, for example, by depositing a transparent substrate such as glass using a metal sputtering method such as Cr and then performing etching using a resist pattern having a predetermined shape as a mask.

  Further, in the MVA type liquid crystal display element, there are cases where a minute projection is formed on a transparent substrate, or multi-domain formation is performed by a light irradiation process through a masking process.

  The liquid crystal alignment film in the present invention is a reaction product of tetracarboxylic dianhydride and diamine, and irradiates light to a polyamic acid film containing an azo group in the main chain to align the polyamic acid in the film; And imidating the polyamic acid oriented in the film. A compound having a side chain structure is used for at least one of the tetracarboxylic dianhydride and the diamine.

  The polyamic acid film can be formed, for example, by applying the above-described liquid crystal aligning agent in the present invention on a substrate or an electrode. As a method for 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 similarly applicable in the present invention.

The azo group contained in the skeleton structure of polyamic acid can usually take two geometric isomers of syn and anti. Usually, the anti isomer is stable, but when the polyamic acid is irradiated with light of an appropriate energy, the light is absorbed and the azo group changes to the syn isomer. Since the syn isomer is less stable than the anti isomer, the azo group returns to the anti isomer, but the anti isomer returned from the syn isomer points in a random direction. At this time, when light polarized in a specific direction is irradiated, the anti isomer pointing in the specific direction is selectively changed to the syn isomer, and the syn isomer is converted into the anti isomer with a random orientation change. Return. Since the anti-syn photoisomerization reaction is repeated until no light absorption occurs, after sufficient light irradiation, the anti isomer is oriented so as to be perpendicular to the polarization direction of the light. In the present invention, such a photoisomerization reaction is used to control the orientation of the polyamic acid.

  In the step of aligning the polyamic acid in the film, the main chain of the polyamic acid is aligned by light irradiation. Such photo-alignment treatment conditions may be any as long as the object of the present invention is achieved. As a 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, or the like can be used.

  In the case of the present invention using the photoisomerization 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 light having a wavelength of 300 nm or more hardly causes photodecomposition of the coating film, and light having a wavelength of 600 nm or less facilitates the photoisomerization reaction. Moreover, it is preferable to remove low-wavelength light using a long-wavelength transmission filter or a band-pass filter. Note that it is preferable to use an ultraviolet / visible continuous light source and a bandpass filter in combination, and simultaneously irradiate ultraviolet light and visible light.

The amount of light used for the alignment treatment of the polyamic acid in the direction parallel to the surface of the liquid crystal alignment film depends on the type of the liquid crystal aligning agent used, the wavelength of the light source, and the irradiation conditions. The treatment becomes stronger and a high orientation index Δ is obtained. As a guide, the amount of light irradiation when performing alignment treatment using a Deep UV lamp and a bandpass filter of 340 to 500 nm is ² J / cm ² or more, preferably 30 J / cm ² or more, more preferably 100 J / cm ² or more. Light irradiation amount is particularly no upper limit, in order to avoid deterioration of the liquid crystal alignment film is preferably 2,000 J / cm ² or less, in consideration of the economics of cost and the like according to the equipment and process 300 J / It is preferable that it is cm ² or less.

  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 also included as light having random polarization as light with controlled polarization. The polarization can be controlled by a polarizing filter or a polarizing prism. Alternatively, light can be transmitted through an obliquely placed glass plate.

  In order to orient the polyamic acid in a predetermined direction when viewed from a direction perpendicular to the film surface, the polarized light is used as light for changing the geometric isomer by the azo group from the anti isomer to the syn isomer. Controlled light can be used. In order to align the surface of the polyamic acid film in an oblique direction, light is applied to the surface of the polyamic acid film from an oblique direction.

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

  The irradiation angle when irradiating light from an oblique direction with respect to the surface of the film is not particularly limited, but in order to obtain an arbitrary pretilt angle, the surface of the liquid crystal alignment film or the substrate surface is used. It is preferably 20 to 70 degrees, and more preferably 30 to 60 degrees, from the viewpoint of obtaining good polyimide main chain alignment and liquid crystal pretilt angle.

  In the present invention, light that changes the geometric isomer of the azo group from an anti isomer to a syn isomer is irradiated from an oblique angle with respect to the surface (substrate surface) of the film, thereby causing a direction parallel to the surface of the film. It is possible to control both the orientation of polyamic acid in the film (average orientation direction) and the orientation of polyamic acid on the light incident surface (inclination angle with respect to the substrate surface). In the present invention, a preferred method for controlling the orientation of the polyamic acid in the film is to irradiate linearly polarized light from a direction perpendicular to the film surface (substrate surface), and then to obtain a direction perpendicular to the polarization direction of the linearly polarized light. It is to irradiate non-polarized light with the irradiation angle as a plane of incidence. As a result, the degree of orientation of the main chain of the polyimide (orientation index Δ) can be increased, and a liquid crystal orientation having a uniform pretilt angle can be obtained.

  In the production of the liquid crystal alignment film, it is preferable to further perform a step of drying the liquid crystal aligning agent film 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 heat treatment in an oven or an infrared furnace, a method of heat treatment on a hot plate, and the like are generally known. These methods are equally applicable in the present invention. The drying step is preferably performed at a relatively low temperature within a range where the solvent can be evaporated.

  The imidization of the polyamic acid oriented in the film is usually performed by heating. Also in the present invention, the heat treatment can be applied to imidation of the polyamic acid after orientation. As a method for the heat treatment process, the same technique as that for the drying process described above can be applied. In general, the heat treatment step is preferably performed at a temperature of about 150 to 300 ° C.

  The liquid crystal display element in the present invention is a process for producing a liquid crystal alignment film on a substrate as described above, and then assembling the substrate with the substrate facing each other through a spacer, a process for encapsulating a liquid crystal composition, and a process for attaching a polarizing film It is manufactured through such processes.

  The liquid crystal display element in the present invention can 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 performed alone or in combination. The cleaning liquid is pure water, alcohols such as methyl alcohol, ethyl alcohol 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. Although it can be used, it is not limited to these. Of course, these cleaning liquids are sufficiently purified and have few impurities.

  The ratio of the tetracarboxylic dianhydride having a photoisomerization structure and / or diamine used in the present invention to the total monomers needs to be 10 to 90 mol%, preferably 15 to 80 mol%, more preferably. It needs to be 20-70 mol%. When the proportion of tetracarboxylic dianhydride having a photoisomerization structure and / or diamine is 10 mol% or more, the orientation of the polymer main chain is improved by photoisomerization, and the tetracarboxylic dianhydride having a photoisomerization structure is obtained. When the ratio of the product and / or diamine is 90 mol% or less, the pretilt angle becomes good.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention, this invention is not limited to these Examples. In addition, the name of the tetracarboxylic dianhydride, diamine, and solvent which are used by an Example and a comparative example is shown by an abbreviation. This abbreviation may be used in the following description.

Tetracarboxylic acid dianhydride pyromellitic dianhydride: PMDA
Diamine 4,4'-Diaminoazobenzene: DAZ
Diamine having side chain structure Compound of the following structural formula 1: T1
Compound of the following structural formula 2: T2
Solvent N-methyl-2-pyrrolidone: NMP

Example 1
1) Preparation of liquid crystal aligning agent A1 In a 200 mL four-necked flask equipped with a thermometer, stirrer, raw material charging inlet and nitrogen gas inlet, DAZ and T1 were 2.1104 g and 0.4802 g, respectively, and dehydrated NMP was 30. 00 g was introduced and dissolved by stirring under a dry nitrogen stream. While keeping the temperature of the reaction system at 5 ° C., 2.4096 g of PMDA was added and reacted for 30 hours, and 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 mass%. Prepared. When the temperature rose due to reaction heat during the reaction of the raw materials, the reaction was carried out while keeping the reaction temperature at about 70 ° C. or lower.

2) Measurement of the absorbance of infrared light, the thickness of the liquid crystal alignment film, and the calculation of the orientation index Δ The obtained PMDA / DAZ / T1 (raw material molar ratio = 50/45/5) liquid crystal aligning agent A1 was diluted with NMP. After being 1.34% by mass, it was coated on a CaF ₂ substrate (thickness 2 mm) with a spinner. The coating conditions were 3,000 rpm and 60 seconds. After the coating, light irradiation was performed using a 500 W Deep UV lamp (UXM-501MD) manufactured by USHIO INC. As a light source. The wavelength range of the irradiated light was set to 340 to 500 nm by transmitting through a bandpass filter (manufactured by Asahi Spectroscopic Co., Ltd.) having a transmission wavelength range of 340 to 500 nm.

First, light that was linearly polarized through a Grand Taylor polarizing prism was irradiated from a direction perpendicular to the substrate surface. The irradiation amount was 156 J / cm ² . Next, the surface perpendicular to the polarization direction of light in the first irradiation with linearly polarized light was used as the incident surface, and non-polarized light was irradiated at an incident angle (defined from the substrate normal) of 45 degrees. The irradiation amount was 221 J / cm ² . Thereafter, the sample irradiated with light was heat-treated at 250 ° C. for 60 minutes in a nitrogen atmosphere to form a liquid crystal alignment film.

The film thickness d of the polyamic acid film before imidization The film thickness d of the _PAA and the liquid crystal alignment film is the thickness of the polyimide film produced in the same process except that no light irradiation is performed. Using an apparatus (APE-100), measurement was performed at a measurement wavelength of 632.8 nm (He-Ne laser) and an incident angle of 62.5 degrees, and d _PAA = 19 nm and d = 11 nm, respectively. From the ratio of the film thickness before and after imidization, the correction coefficient γ for the thickness of the liquid crystal alignment film by imidization was 0.58.

  The infrared absorption spectrum of the obtained liquid crystal alignment film was measured using a FT-IR apparatus (spectrometer: Mattson Galaxy 3020, detector: mercury cadmium telluride) at a measurement temperature of 32 ° C. and a total of 400 times. .

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 was measured when the average orientation direction and the polarization direction of the sample were measured in parallel, and the infrared light spectrum when measured in the vertical direction. Using the integral value of the absorption band near 1360 cm ⁻¹ attributed to the C—N—C stretching vibration of the infrared light spectrum measured in parallel and perpendicular, the difference in absorbance of the liquid crystal alignment film (| A‖−A⊥) |) And the sum of the absorbance of the liquid crystal alignment film (A⊥ + A‖).

In order to obtain the absorption coefficient α of the polyamic acid film before imidization, a 2.00% by mass polyamic acid solution was applied onto a CaF ₂ substrate (thickness 2 mm) with a spinner. The coating conditions were 3,000 rpm and 60 seconds. The thickness of the polyamic acid film not subjected to light irradiation was measured and found to be 36 nm. When the ultraviolet / visible absorption spectrum of the polyamic acid film before imidization was measured in a vertical transmission configuration, the absorbance at a wavelength of 364 nm (= log (T _sub / T _sample )) was 0.36. From equation (3), the absorption coefficient α of the polyamic acid film before imidation 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 = 0.024 and γ = 0.58, the effective film thickness d ′ of the region subjected to the photo-alignment treatment of the liquid crystal alignment film was 25 nm. When the film thickness is 11 nm, since d <d ′, d / d ′ = 1 can be set, and calculation is performed from the obtained values (| A ｜ −A⊥ |) and (A⊥ + A‖). Then, the orientation index Δ of the polyimide main chain of the liquid crystal alignment film was 0.28.

3) Measurement of the pretilt angle of the liquid crystal A pair of CaF ₂ substrates on which the liquid crystal alignment film was produced under the same conditions are opposed to each other with the surface on which the liquid crystal alignment film is formed sandwiched as a 25 μm thick polyester film as a spacer. An anti-parallel cell was produced. The anti-parallel cell here means a cell assembled so that the irradiation directions of non-polarized light are parallel and opposite when the photo-alignment treatment is performed on the polyamic acid film applied to the substrate.

A cyanobiphenyl liquid crystal (5CB) represented by the following structural formula (5) was injected into the cell at 80 ° C. and slowly cooled to room temperature to prepare a pretilt angle measurement cell (liquid crystal display element). When the pretilt angle of the liquid crystal of the prepared pretilt angle measurement cell was measured, the pretilt angle was 3.3 degrees. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light. The pretilt angle was measured by a crystal rotation method using a He—Ne laser (oscillation wavelength 632.8 nm). The temperature at the time of measuring the pretilt angle was 25 ° C. NI point of 5CB (nematic isotropic phase transition temperature) is 35 ° C., the refractive index at a wavelength of 632.8nm is n _e = 1.706 (extraordinary light), n _o = 1.530 (ordinary) met It was.

Example 2
Instead of liquid crystal aligning agent A1 in Example 1, PMDA / DAZ / T2 (raw material molar ratio = 50 / 37.5 / 12.5) liquid crystal aligning agent A2 was prepared. The obtained liquid crystal aligning agent A2 was applied onto a CaF ₂ substrate with a spinner by the method according to Example 1, irradiated with light, and baked to form a 9 nm-thick liquid crystal aligning film. The film thickness d _PAA of the polyamic acid film before imidation is 18 nm.
The correction coefficient γ for the thickness of the liquid crystal alignment film by imidization was 0.50. The absorption coefficient α of the polyamic acid film before imidization was 0.015, and the effective film thickness d ′ of the liquid crystal alignment film was 33 nm.

  Subsequently, when the alignment index Δ of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, it was 0.17. Furthermore, an antiparallel cell was produced by the method according to Example 1 and the pretilt angle was measured to be 71.3 degrees. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light.

Example 3
Instead of the liquid crystal aligning agent A1 in Example 1, PMDA / DAZ / T2 (raw material molar ratio = 50/25/25) liquid crystal aligning agent A3 was prepared. The obtained liquid crystal aligning agent A3 was applied onto a CaF ₂ substrate with a spinner by the method according to Example 1, irradiated with light, and baked to form a liquid crystal alignment film having a thickness of 11 nm. The film thickness d _PAA of the polyamic acid film before imidization was 19 nm, and the correction coefficient γ for the thickness of the liquid crystal alignment film by imidization was 0.58. The absorption coefficient α of the polyamic acid film before imidization was 0.009, and the effective film thickness d ′ of the liquid crystal alignment film was 64 nm.

  Next, when the orientation index Δ of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, it was 0.06. Furthermore, an antiparallel cell was produced by the method according to Example 1 and the pretilt angle was measured to be 89.6 degrees. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light.

Example 4
Instead of liquid crystal aligning agent A1 in Example 1, liquid crystal aligning agent A4 of PMDA / DAZ / T1 (raw material molar ratio = 50 / 43.75 / 6.25) was prepared. The obtained liquid crystal aligning agent A4 was applied onto a CaF ₂ substrate with a spinner by the method according to Example 1, irradiated with light, and baked to form a liquid crystal aligning 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 γ of the thickness of the liquid crystal alignment film by imidization was 0.60. The absorption coefficient α of the polyamic acid film before imidization was 0.022, and the effective film thickness d ′ of the liquid crystal alignment film was 27 nm.

  Subsequently, when the alignment index Δ of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, it was 0.27. Furthermore, an antiparallel cell was produced by a method according to Example 1, and the pretilt angle was measured to be 4.8 degrees. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light.

Example 5
Instead of the liquid crystal aligning agent A1 in Example 1, PMDA / DAZ / T1 (raw material molar ratio = 50 / 42.5 / 7.5) liquid crystal aligning agent A5 was prepared. The obtained liquid crystal aligning agent A5 was applied onto a CaF ₂ substrate with a spinner by the method according to Example 1, irradiated with light, and baked to form a liquid crystal aligning film having a thickness of 10 nm. The film thickness d _PAA of the polyamic acid film before imidization was 17 nm, and the correction coefficient γ for the thickness of the liquid crystal alignment film by imidization was 0.59. The absorption coefficient α of the polyamic acid film before imidization was 0.020, and the effective film thickness d ′ of the liquid crystal alignment film was 30 nm.

  Subsequently, when the orientation index Δ of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, it was 0.25. Furthermore, an antiparallel cell was produced by a method according to Example 1 and the pretilt angle was measured to be 5.8 degrees. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light.

Example 6
Instead of the liquid crystal aligning agent A1 in Example 1, a liquid crystal aligning agent A6 of PMDA / DAZ / T1 (raw material molar ratio = 50 / 37.5 / 12.5) was prepared. The obtained liquid crystal aligning agent A6 was applied onto a CaF ₂ substrate with a spinner by the method according to Example 1, irradiated with light, and baked to form a liquid crystal alignment film having a thickness of 10 nm. The film thickness d _PAA of the polyamic acid film before imidization was 15 nm, and the correction coefficient γ of the thickness of the liquid crystal alignment film by imidization was 0.66. The absorption coefficient α of the polyamic acid film before imidization was 0.020, and the effective film thickness d ′ of the liquid crystal alignment film was 33 nm.

  Subsequently, when the alignment index Δ of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, it was 0.20. Furthermore, an antiparallel cell was produced by the method according to Example 1, and the pretilt angle was measured to be 75.4 degrees. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light.

Comparative Example 1
Instead of the liquid crystal aligning agent A1 in Example 1, PMDA / DAZ (raw material molar ratio = 50/50) liquid crystal aligning agent B1 was prepared. The obtained liquid crystal aligning agent B1 was applied onto a CaF ₂ substrate with a spinner by the method according to Example 1, irradiated with light, and baked to form a liquid crystal aligning film having a thickness of 10 nm. However, the firing time was 120 minutes. The film thickness d _PAA of the polyamic acid film before imidization was 16 nm, and the correction coefficient γ of the thickness of the liquid crystal alignment film by imidization was 0.63. The absorption coefficient α of the polyamic acid film before imidization was 0.028, and the effective film thickness d ′ of the liquid crystal alignment film was 23 nm.

  Subsequently, when the alignment index Δ of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, it was 0.27. Furthermore, an antiparallel cell was produced by the method according to Example 1 and the pretilt angle was measured to be 1.4 degrees. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light.

Comparative Example 2
Instead of liquid crystal aligning agent A1 in Example 1, PMDA / DAZ / T1 (raw material molar ratio = 50 / 47.5 / 2.5) liquid crystal aligning agent B2 was prepared. The obtained liquid crystal aligning agent B2 was applied onto a CaF ₂ substrate with a spinner by the method according to Example 1, irradiated with light, and baked to form a liquid crystal aligning film having a thickness of 12 nm. The film thickness d _PAA of the polyamic acid film before imidization was 18 nm, and the correction coefficient γ for the thickness of the liquid crystal alignment film by imidization was 0.67. The absorption coefficient α of the polyamic acid film before imidization was 0.026, and the effective film thickness d ′ of the liquid crystal alignment film was 26 nm.

  Subsequently, when the alignment index Δ of the polyimide main chain of the liquid crystal alignment film was evaluated by the method according to Example 1, it was 0.33. Furthermore, an antiparallel cell was produced by a method according to Example 1 and the pretilt angle was measured to be 1.0 degree. The direction in which the liquid crystal is tilted is the direction of irradiation with non-polarized light.

Comparative Example 3
Except for irradiating linearly polarized light from a direction perpendicular to the substrate surface after heat treatment at 250 ° C. for 60 minutes in a nitrogen atmosphere, that is, linearly polarized ultraviolet light after imidizing the polyamic acid film with heat A pair of liquid crystal alignment films was formed by the method according to Example 1 except that irradiation was performed.

Next, an attempt was made to measure the pretilt angle by a method according to Experimental Example 1, but the pretilt angle and the orientation index Δ were not measured due to poor alignment.

  Table 1 shows the raw material mol% of the liquid crystal aligning agent of each Example and each Comparative Example.

  Table 2 shows the measurement results of the film thickness of the liquid crystal alignment film, the orientation index Δ of the polyimide main chain, and the pretilt angle of each example and each comparative example.

  From the results of Examples 1, 2, 3, 4, 5, and 6 and Comparative Examples 1, 2, and 3, the content of the side chain structure diamine with respect to the total diamine was changed, and the alignment treatment was performed by irradiating light with controlled polarization It can be seen that a liquid crystal display element having a wide range of liquid crystal pretilt angles can be obtained by using the liquid crystal alignment film having the above-described properties.

  In particular, the side chain structure diamine is included by irradiating the substrate with a liquid crystal alignment agent into which at least 10% of the side chain structure diamine is introduced in a molar ratio with respect to the total diamine, by applying light with controlled polarization. It can be seen that a pretilt angle larger than the pretilt angle generated by the liquid crystal alignment film similarly produced using the liquid crystal aligning agent B1 can be generated.

Claims (9)

In a liquid crystal alignment film formed by imidizing a polyamic acid that is a reaction product of tetracarboxylic dianhydride and a diamine and that is a polyamic acid film containing an azo group in the main chain and aligned in a predetermined direction by light irradiation,
At least one of the tetracarboxylic dianhydride and the diamine has a side chain structure,
The orientation index Δ 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,
A liquid crystal alignment film having a pretilt angle of 2 to 90 degrees when a liquid crystal display element including the liquid crystal alignment film is formed.
Δ = (| A‖−A⊥ |) / (A‖ + A⊥) × d / d ′ (1)
(In the formula (1), A 、 represents polarized infrared light perpendicular to the surface of the liquid crystal alignment film and the polarization direction of the infrared light is parallel to the average alignment direction of the main chain of polyimide. to become so represents the integrated absorbance by C-N-C stretching vibration of an imide ring around wave number 1360 cm ^-1 when is incident on the liquid crystal alignment film, A⊥ is polarized infrared light, the liquid crystal alignment film 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 to the surface and to the average alignment direction of the main chain of the polyimide. The integrated absorbance due to C—N—C stretching vibration is represented, d represents the film thickness of the liquid crystal alignment film, and d ′ represents the effective film thickness of the liquid crystal alignment film subjected to the photo-alignment treatment.) The polyamic acid is a reaction product of a tetracarboxylic dianhydride having no side chain structure, a diamine having an azo group between two amino groups and having no side chain structure, and a diamine having a side chain structure. Is a thing,
2. The liquid crystal alignment film according to claim 1, wherein the diamine having the side chain structure is contained in a range of 7 to 90 mol% with respect to the total amount of the diamine.   The liquid crystal alignment film according to claim 2, wherein the diamine having an azo group between the two amino groups and having no side chain structure is 4,4′-diaminoazobenzene.   The liquid crystal alignment film according to claim 2, wherein the tetracarboxylic dianhydride is pyromellitic dianhydride. The liquid crystal alignment film according to claim 2, wherein the diamine having a side chain structure is a compound represented by the following general formula (I'-11).

(In the formula, R ²⁴ represents alkyl having 1 to 10 carbons or alkoxy having 1 to 10 carbons.)   A liquid crystal aligning agent characterized in that it is a reaction product of a tetracarboxylic dianhydride and a diamine, contains a polyamic acid containing an azo group in the main chain and a solvent, and the diamine contains a diamine having a side chain structure. . The polyamic acid is a reaction product of a tetracarboxylic dianhydride having no side chain structure, a diamine having an azo group between two amino groups and having no side chain structure, and a diamine having a side chain structure. Is a thing,
The liquid crystal aligning agent according to claim 6, wherein the diamine having a side chain structure is contained in a range of 7 to 90 mol% with respect to the total amount of the diamine.   A pair of substrates arranged opposite to each other, electrodes formed on one or both of the opposed surfaces of each of the pair of substrates, and liquid crystal alignment formed on the opposed surfaces of each of the pair of substrates In a liquid crystal display element having a film and a liquid crystal layer formed between the pair of substrates, one or both of the liquid crystal alignment films formed on the opposing surfaces of the pair of substrates are defined in claims 1 to 2. A liquid crystal display element, which is the liquid crystal alignment film according to claim 5. Irradiating light to a polyamic acid film, which is a reaction product of tetracarboxylic dianhydride and diamine and containing an azo group in the main chain, to align the polyamic acid in the film, and a polyamic aligned in the film Including a step of imidizing an acid, and a method of producing a liquid crystal alignment film formed by imidizing the polyamic acid,
A compound having a side chain structure is used for at least one of the tetracarboxylic dianhydride and the diamine,
The step of orienting the polyamic acid in the film is as follows:
(A) When the film is irradiated with light that changes the geometric isomer of the azo group from an anti isomer to a syn isomer and the polyamic acid in the film is viewed from a direction perpendicular to the surface of the film, Operation to orient in the direction;
Irradiating light from a direction oblique to the surface of the polyamic acid film and orienting the polyamic acid in a direction oblique to the surface of the film, or (B) the azo group The film is irradiated with light that changes the geometric isomer from anti isomer to syn isomer from an oblique direction with respect to the surface of the film, and the polyamic acid in the film is perpendicular to the surface of the film. A method of aligning in a predetermined direction when viewed from above and aligning in an oblique direction with respect to the surface of the film.