WO2014148440A1 - Liquid crystal aligning agent for in-plane switching - Google Patents

Abstract

Provided are: a liquid crystal aligning agent which is capable of eliminating a feeling of strangeness about the color of a display screen in an in-plane switching liquid crystal display element, said feeling of strangeness being based on a black component; a liquid crystal alignment film; and a liquid crystal display element. A liquid crystal aligning agent for in-plane switching, which is characterized by containing a polyimide that is obtained by ring-closing a polyimide precursor that has a structural unit represented by formula (1) as a structural unit that is derived from a tetracarboxylic acid dianhydride. In formula (1), X¹ represents a tetravalent organic group represented by formula (X¹); and R¹ represents a hydrogen atom or an alkyl group having 1-10 carbon atoms.

Description

Liquid crystal alignment treatment agent for lateral electric field drive

The present invention relates to a liquid crystal alignment treatment agent used for a horizontal electric field drive type liquid crystal element, a liquid crystal alignment film using the same, and a horizontal electric field drive type liquid crystal element.

Liquid crystal display elements are display elements that utilize electro-optical changes in liquid crystals, and their characteristics such as small size and light weight and low power consumption have attracted attention. In recent years, they have made remarkable progress as display devices for various displays. ing.
As a liquid crystal display device, there are a type of display in which liquid crystal molecules aligned in parallel with a pair of opposed transparent substrates are driven by applying an electric field in a direction perpendicular to the substrate, and a type parallel to the substrate. There is a type that performs display by applying an electric field in the direction. The former is called a TN mode liquid crystal display device, and the latter is called a transverse electric field drive (IPS) liquid crystal display device.

Since the liquid crystal display device of the horizontal electric field driving method basically sees only the minor axis direction of the liquid crystal molecules even if the viewpoint is moved, there is no dependency on the viewing angle of the “standing” of the liquid crystal molecules, A wider viewing angle than a TN mode liquid crystal display device can be achieved (see Patent Document 1). Therefore, in recent years, IPS mode liquid crystal display devices tend to be used more frequently than TN mode liquid crystal display devices.

As the liquid crystal alignment film in such a horizontal electric field drive type liquid crystal display device, a polyimide-based liquid crystal alignment film is most commonly used in terms of chemical stability, thermal stability, and the like.
The polyimide-based liquid crystal alignment film is obtained by applying a polyamic acid (also referred to as polyamic acid) solution, which is a polyimide precursor, onto a substrate, baking it at a temperature of 150 ° C. or higher, imidizing it, and then performing a rubbing treatment. In general, a liquid crystal alignment film is obtained.

Japanese Unexamined Patent Publication No. 2-37324

From the viewpoint of producing liquid crystal display elements, properties such as adhesion of the alignment film to the substrate, printability, and rubbing resistance are important. In particular, the rubbing treatment is a liquid crystal alignment treatment method adopted industrially, but the liquid crystal alignment film peels off from the substrate due to friction during rubbing, or the liquid crystal alignment film is scratched, resulting in display characteristics. There was a problem affecting it.

The liquid crystal alignment film obtained from the conventional polyimide-based liquid crystal alignment treatment agent has the advantages and disadvantages that both the solvent-soluble polyimide and polyamic acid contained in the liquid crystal alignment treatment agent are opposite to each other as the liquid crystal alignment film, It is not always easy to satisfy all the characteristics required for a liquid crystal alignment film. For this reason, there has been a strong demand for a liquid crystal alignment treatment agent that is particularly excellent in printability, adhesion, and rubbing resistance to a substrate and has high reliability.

In addition, according to the knowledge of the present inventor, when the liquid crystal alignment film is formed from a polyimide-based liquid crystal alignment treatment agent in the above-described lateral electric field drive type liquid crystal display element, -It was found that there was a problem with the black level in the display, which caused a sense of discomfort in the color of the screen. This is because the orientation of the director in which the liquid crystal molecules are arranged is determined by performing a rubbing process on the liquid crystal alignment film in the liquid crystal display element of the horizontal electric field drive system. For this reason, the initial alignment may vary through the rubbing process. The deterioration of the black level is considered to be a phenomenon caused by the disturbance of the initial orientation and is a problem to be solved.

Here, as one of the means for eliminating the disturbance of the initial alignment, there is a method of forming a liquid crystal alignment film by applying a solution containing a solvent-soluble polyimide to a substrate and baking it. However, solvent-soluble polyimides generally have poor solubility compared to polyimide precursors, and diamines that can be used are limited. In particular, when a diamine having high crystallinity is used, the solubility tends to deteriorate, and there is a problem that the amount of introduction is limited when such a diamine is used.

Thus, the object of the present invention does not have the problem that the screen color tone based on the black element is uncomfortable, and in addition, it has excellent printability and adhesion to the substrate, and does not peel off from the substrate during rubbing. Also, a polyimide-based liquid crystal alignment treatment agent for a liquid crystal display element of a lateral electric field drive method, a liquid crystal alignment film using the liquid crystal alignment film, and a liquid crystal of a horizontal electric field drive method, which can obtain a liquid crystal alignment film that is hardly damaged by rubbing. It is to provide an element.

The present inventor has conducted earnest research to achieve the above object, and as a polyimide-based liquid crystal alignment treatment agent, a solvent-soluble polyimide is used, and one of the raw materials of the solvent-soluble polyimide is a tetracarboxylic dianhydride component. The idea was to use bicyclo [3.3.0] octane-2,4,6,8-tetracarboxylic dianhydride as And, by using a liquid crystal alignment treatment agent containing such solvent-soluble polyimide, in particular, the problem that the screen color tone based on the black element causes a sense of incongruity in the lateral electric field drive type liquid crystal display element affects other characteristics. It was found that it can be solved without any problems.

The present invention is based on this finding and has the following gist.
1. Liquid crystal alignment for transverse electric field characterized by containing polyimide obtained by dehydrating and ring-closing a polyimide precursor having a structural unit represented by the following formula (1) as a structural unit derived from tetracarboxylic dianhydride Processing agent.

In the formula (1), X ¹ is a tetravalent organic group represented by the following formula (X ¹ ), and R ¹ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

2. 2. The liquid crystal alignment treatment agent for lateral electric field according to 1 above, wherein the polyimide precursor has a structural unit represented by the following formula (2) as a structural unit derived from diamine.

In the formula (2), n is 1 to 12.

3. 3. The lateral electric field driving according to 1 or 2 above, wherein the tetravalent organic group represented by the formula (X ¹ ) is a single component selected from isomers of the formulas [IV] to [VI], or a mixture thereof. Liquid crystal alignment treatment agent.

4). 4. The liquid crystal alignment treatment agent for driving a horizontal electric field according to 3 above, wherein the content of isomer [IV] is 90% or more.
5. 5. The transverse electric field according to any one of 1 to 4 above, wherein the content of the structural unit represented by the formula (1) is 30 to 100 mol% with respect to 1 mol of all the structural units derived from the tetracarboxylic acid derivative. Liquid crystal alignment treatment agent.
6). 6. The horizontal electric field liquid crystal alignment according to any one of 1 to 5 above, wherein the content of the structural unit represented by the formula (2) is 20 to 100 mol% with respect to 1 mol of all structural units derived from diamine. Processing agent.
7). A liquid crystal alignment film for driving a horizontal electric field obtained by applying the liquid crystal alignment treatment agent according to any one of 1 to 6 above to a substrate and baking it.
8). 8. A liquid crystal display element for driving a horizontal electric field, comprising the liquid crystal alignment film according to 7 above.

According to the liquid crystal alignment treatment agent of the present invention, in the lateral electric field drive type liquid crystal display element, it is possible to solve the problem of an uncomfortable feeling in the color tone of the screen based on the black element, and it is excellent in printability and adhesion to the substrate, In addition, a liquid crystal alignment film that does not peel off from the substrate during rubbing and is difficult to damage the alignment film due to rubbing can be obtained.

The reason why the liquid crystal alignment treatment agent of the present invention can solve the problem that the screen tone based on the black element in the horizontal electric field drive type liquid crystal display element can cause a sense of incongruity is not necessarily clear, It is estimated as follows.
A circuit having severe unevenness is formed on the actual substrate in the liquid crystal display element, and therefore, it is necessary to uniformly align the liquid crystal even in the flat portion and the step portion. While strong liquid crystal alignment is required at the flat part, the stretchability of the polymer chain is important at the step part. Since portions having different rubbing conditions are generated due to the influence of the step, it is effective to improve the stretching characteristics by imparting flexibility to the film to the step portion. In this invention, it is thought that it is the result of having improved the alignment order in a flat part and a level | step difference part by using the specific tetracarboxylic dianhydride which has the specific diamine compound which has favorable orientation, and a softness | flexibility. .

<Liquid crystal alignment agent>
The liquid-crystal aligning agent of this invention contains the polyimide obtained by ring-closing the polyimide precursor which has a structural unit represented by following formula (1) as a structural unit derived from tetracarboxylic dianhydride. And

In the formula (1), X ¹ is a tetravalent organic group represented by the following formula (X ¹ ), and R ¹ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

The structure represented by the formula (X ¹ ) is derived from bicyclo [3.3.0] -octane-2,4,6,8-tetracarboxylic acid. In bicyclo [3.3.0] -octane-2,4,6,8-tetracarboxylic acid, (X ¹ ) has structural isomers of the following formulas [IV], [V], and [VI]. However, in the present invention, a polyimide precursor may be produced using one of the isomers, or a polyimide precursor may be produced using a mixture of isomers. From the viewpoint of polymerization reactivity in the production of the polyimide precursor, the content of isomer [IV] is preferably 90% or more, and more preferably 95% or more.

In the polyimide precursor of the present invention, the structural unit of the formula (1) is preferably 30 to 100 mol%, more preferably 50 to 80 mol based on 1 mol of all structural units derived from the tetracarboxylic acid derivative. %.

The polyimide precursor used in the present invention may contain a structural unit represented by the following formula (3) as a structural unit derived from a tetracarboxylic acid derivative.

In the formula (3), R ² is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and X is a tetravalent organic group. However, the case where X is X ¹ in the above formula (1) is excluded.
Specific examples of X include the following (X-1) to (X-42).

In the above formula (X-1), R ³ to R ⁶ each independently represents a hydrogen atom, a methyl group or a phenyl group. Among these, from the viewpoint of availability of the compound, the structure of X has the formula (X-1) (wherein R ³ to R ⁶ are all hydrogen atoms, or R ³ and R ⁵ are methyl groups, and R ⁴ and R ⁶ are hydrogen atoms) In the case of atoms), (X-2), (X-5), (X-6), (X-7), (X-17), (X-25), (X-26), (X- 27), (X-28), (X-32), and (X-39). Further, from the viewpoint of obtaining a liquid crystal alignment film in which the residual charge accumulated by direct current voltage can be quickly relaxed, it is preferable to use tetracarboxylic dianhydride having an aromatic ring structure. 26), (X-27), (X-28), (X-32), (X-35), and (X-37) are more preferable.

In the formula (3), specific examples of the alkyl group in R ² include methyl group, ethyl group, propyl group, i-propyl group, n-butyl group, i-butyl group, s-butyl group, and t-butyl. Group, n-pentyl group and the like.

The proportion of the structural unit represented by the formula (3) in the polyimide precursor used in the present invention is preferably 0 to 70 mol%, more preferably 20 to 50 mol, relative to 1 mol of the structural unit of the polyimide precursor. Mol%.

Moreover, the polyimide precursor used for this invention may contain the structural unit represented by following formula (4) as a structural unit derived from diamine.

In the formula (4), A ¹ and A ² are each independently a hydrogen atom, an alkyl group having 1 to 15 carbon atoms which may have a substituent, or an alkyl group having 1 to 15 carbon atoms which may have a substituent. Or an alkynyl group having 1 to 15 carbon atoms which may have a substituent. In the formula (4), these groups include not only chain-like groups but also those having a ring structure.
Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a t-butyl group, a hexyl group, an octyl group, a decyl group, a cyclopentyl group, a cyclohexyl group, and a bicyclohexyl group. Examples of the alkenyl group include those obtained by replacing one or more CH—CH structures present in the above alkyl group with C═C structures, and more specifically, vinyl groups, allyl groups, 1-propenyl groups. And isopropenyl group, 2-butenyl group, 1,3-butadienyl group, 2-pentenyl group, 2-hexenyl group, cyclopropenyl group, cyclopentenyl group, cyclohexenyl group and the like. Alkynyl groups include those in which one or more CH ₂ —CH ₂ structures present in the alkyl group are replaced with C≡C structures, and more specifically, ethynyl groups, 1-propynyl groups, 2 -Propynyl group and the like.

The above alkyl group, alkenyl group, and alkynyl group may have a substituent, and may further form a ring structure by the substituent. Note that forming a ring structure with a substituent means that the substituents or a substituent and a part of the mother skeleton are bonded to form a ring structure.
Examples of this substituent include halogen groups, hydroxyl groups, thiol groups, nitro groups, aryl groups, organooxy groups, organothio groups, organosilyl groups, acyl groups, ester groups, thioester groups, phosphate ester groups, amide groups, alkyls. A group, an alkenyl group and an alkynyl group.

Examples of the halogen group as a substituent include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
A phenyl group is mentioned as an aryl group which is a substituent. This aryl group may be further substituted with the other substituent described above.

The organooxy group which is a substituent can have a structure represented by OR. The organothio group as a substituent can have a structure represented by —S—R. The organosilyl group as a substituent can have a structure represented by —Si— (R) ₃ . The acyl group as a substituent can have a structure represented by —C (O) —R. As the ester group which is a substituent, a structure represented by —C (O) O—R or —OC (O) —R can be shown. The thioester group which is a substituent can have a structure represented by —C (S) O—R or —OC (S) —R. The phosphate group which is a substituent can have a structure represented by —OP (O) — (OR) ₂ . Examples of the substituent amide group include —C (O) NH ₂ , —C (O) NHR, —NHC (O) R, —C (O) N (R) ₂ , —NRC (O) R. The structure represented by can be shown.

These Rs may be the same or different, and examples thereof include the alkyl group, alkenyl group, alkynyl group, and aryl group described above. These Rs may be further substituted with the substituent described above.

Specific examples of the organooxy group include methoxy group, ethoxy group, propyloxy group, butoxy group, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group and the like.
Specific examples of the organothio group include a methylthio group, an ethylthio group, a propylthio group, a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group, and an octylthio group.

Specific examples of the organosilyl group include a trimethylsilyl group, a triethylsilyl group, a tripropylsilyl group, a tributylsilyl group, a tripentylsilyl group, a trihexylsilyl group, a pentyldimethylsilyl group, and a hexyldimethylsilyl group.
Specific examples of the acyl group include formyl group, acetyl group, propionyl group, butyryl group, isobutyryl group, valeryl group, isovaleryl group, benzoyl group and the like.

Examples of the aryl group as a substituent include the same aryl groups as described above. This aryl group may be further substituted with the other substituent described above.
Examples of the alkyl group as a substituent include the same alkyl groups as described above. This alkyl group may be further substituted with the other substituent described above.
Examples of the alkenyl group as a substituent include the same alkenyl groups as described above. This alkenyl group may be further substituted with the other substituent described above.
Examples of the alkynyl group that is a substituent include the same alkynyl groups as described above. This alkynyl group may be further substituted with the other substituent described above.

In general, when a bulky structure is introduced, there is a possibility that the reactivity of the amino group and the liquid crystal orientation may be lowered. Therefore, as A ¹ and A ² , a hydrogen atom or a carbon atom that may have a substituent is 1 An alkyl group of 1 to 5 is more preferable, and a hydrogen atom, a methyl group, or an ethyl group is particularly preferable.
Y is a divalent organic group, and its structure is not particularly limited, and two or more kinds may be mixed. For example, the following Y-1 to Y-118 are given as specific examples.

Among them, in order to obtain good liquid crystal alignment, it is preferable to introduce a highly linear diamine into the polyamic acid ester. Y is Y-7, Y-21, Y-22, Y-23, Y-25, Y-26, Y-27, Y-43, Y-44, Y-45, Y-46, Y-48, Y-63, Y-71, Y-73, Y-74, Y- More preferred are diamines of 75, Y-98, Y-99, and Y-100. In order to increase the pretilt angle, it is preferable to introduce a diamine having a long chain alkyl group, aromatic ring, aliphatic ring, steroid skeleton, or a combination thereof in the side chain into the polyamic acid ester. -76, Y-77, Y-78, Y-79, Y-80, Y-81, Y-82, Y-83, Y-84, Y-85, Y-86, Y-87, Y-88 , Y-89, Y-90, Y-91, Y-92, Y-93, Y-9), Y-95, Y-96, Y-97 are more preferred. By adding 1 to 50 mol% of these diamines, any pretilt angle can be expressed. Also, Y-118 diamine is preferred for improving rubbing resistance.

In formula (Y-109), m and n are each an integer from 1 to 11, m + n is an integer from 2 to 12, and in formula (Y-114), h is an integer from 1 to 3, In (Y-111) and (Y-117), j is an integer of 0 to 3.

In addition, the polyimide precursor used in the present invention includes a structural unit represented by the following formula (2) as a structural unit represented by the above formula (4) as a structural unit derived from diamine. From the point of view, it is preferable.

N in the formula (2) is 1 to 12, preferably 1 to 5.

The content of the structural unit represented by the formula (2) with respect to 1 mol of the structural unit represented by the formula (4) is preferably 10 to 100 mol%, more preferably 20 to 100 mol%, Particularly preferred is 40 to 100 mol%.

<Polyamic acid ester>
When the polyimide precursor used in the present invention is a polyamic acid ester, the polyamic acid ester can be synthesized by the following methods (1) to (3).
(1) When synthesizing from polyamic acid The polyamic acid ester can be synthesized by esterifying a polyamic acid obtained from tetracarboxylic dianhydride and diamine.
Specifically, the polyamic acid and the esterifying agent are reacted in the presence of an organic solvent at −20 ° C. to 150 ° C., preferably 0 ° C. to 50 ° C., for 30 minutes to 24 hours, preferably 1 to 4 hours. Can be synthesized.

The esterifying agent is preferably one that can be easily removed by purification, and N, N-dimethylformamide dimethyl acetal, N, N-dimethylformamide diethyl acetal, N, N-dimethylformamide dipropyl acetal, N, N-dimethylformamide Dineopentyl butyl acetal, N, N-dimethylformamide di-t-butyl acetal, 1-methyl-3-p-tolyltriazene, 1-ethyl-3-p-tolyltriazene, 1-propyl-3-p -Tolyltriazene, 4- (4,6-dimethoxy-1,3,5-triazin-2-yl) -4-methylmorpholinium chloride and the like. The addition amount of the esterifying agent is preferably 2 to 6 molar equivalents per 1 mol of the polyamic acid repeating unit.

The solvent used in the above reaction is preferably N, N-dimethylformamide, N-methyl-2-pyrrolidone, or γ-butyrolactone in view of polymer solubility. These may be used alone or in combination of two or more. Good. The concentration at the time of synthesis is preferably 1 to 30% by mass, and more preferably 5 to 20% by mass from the viewpoint that polymer precipitation is unlikely to occur and a high molecular weight product is easily obtained.

(2) When synthesized by reaction of tetracarboxylic acid diester dichloride and diamine Polyamic acid ester can be synthesized from tetracarboxylic acid diester dichloride and diamine.
Specifically, tetracarboxylic acid diester dichloride and diamine in the presence of a base and an organic solvent at −20 ° C. to 150 ° C., preferably 0 ° C. to 50 ° C., for 30 minutes to 24 hours, preferably 1 to 4 hours. It can be synthesized by reacting.

As the base, pyridine, triethylamine, 4-dimethylaminopyridine and the like can be used, but pyridine is preferable because the reaction proceeds gently. The addition amount of the base is preferably 2 to 4 times the molar amount of the tetracarboxylic acid diester dichloride from the viewpoint of easy removal and high molecular weight.
The solvent used in the above reaction is preferably N-methyl-2-pyrrolidone or γ-butyrolactone in view of the solubility of the monomer and polymer, and these may be used alone or in combination. The polymer concentration at the time of synthesis is preferably 1 to 30% by mass, and more preferably 5 to 20% by mass from the viewpoint that polymer precipitation is difficult to occur and a high molecular weight product is easily obtained. In order to prevent hydrolysis of the tetracarboxylic acid diester dichloride, the solvent used for the synthesis of the polyamic acid ester is preferably dehydrated as much as possible, and it is preferable to prevent mixing of outside air in a nitrogen atmosphere.

(3) When a polyamic acid is synthesized from a tetracarboxylic acid diester and a diamine The polyamic acid ester can be synthesized by polycondensation of a tetracarboxylic acid diester and a diamine.
Specifically, tetracarboxylic acid diester and diamine in the presence of a condensing agent, a base, and an organic solvent at 0 ° C. to 150 ° C., preferably 0 ° C. to 100 ° C., for 30 minutes to 24 hours, preferably 3 to 15 hours. It can be synthesized by reacting.

Examples of the condensing agent include triphenyl phosphite, dicyclohexylcarbodiimide, 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride, N, N′-carbonyldiimidazole, dimethoxy-1,3,5-triazide. Nylmethylmorpholinium, O- (benzotriazol-1-yl) -N, N, N ′, N′-tetramethyluronium tetrafluoroborate, O- (benzotriazol-1-yl) -N, N , N ′, N′-tetramethyluronium hexafluorophosphate, (2,3-dihydro-2-thioxo-3-benzoxazolyl) phosphonate diphenyl, and the like. The addition amount of the condensing agent is preferably 2 to 3 times the molar amount of the tetracarboxylic acid diester.
As the base, tertiary amines such as pyridine and triethylamine can be used. The addition amount of the base is preferably 2 to 4 times mol with respect to the diamine component from the viewpoint of easy removal and high molecular weight.

In the above reaction, the reaction proceeds efficiently by adding Lewis acid as an additive. As the Lewis acid, lithium halides such as lithium chloride and lithium bromide are preferable. The addition amount of the Lewis acid is preferably 0 to 1.0 times mol with respect to the diamine component.
Among the methods for synthesizing the three polyamic acid esters, since a high molecular weight polyamic acid ester is obtained, the synthesis method (1) or (2) is particularly preferable.
The polyamic acid ester solution obtained as described above can be polymerized by pouring into a poor solvent while stirring well. Precipitation is performed several times, and after washing with a poor solvent, a purified polyamic acid ester powder can be obtained at room temperature or by heating and drying. Although a poor solvent is not specifically limited, Water, methanol, ethanol, hexane, butyl cellosolve, acetone, toluene etc. are mentioned.

<Polyamic acid>
The polyamic acid which is a polyimide precursor used in the present invention can be synthesized by the following method.
Specifically, tetracarboxylic dianhydride and diamine are reacted in the presence of an organic solvent at −20 ° C. to 150 ° C., preferably 0 ° C. to 50 ° C. for 30 minutes to 24 hours, preferably 1 to 12 hours. Can be synthesized.
The organic solvent used in the above reaction is preferably N, N-dimethylformamide, N-methyl-2-pyrrolidone, or γ-butyrolactone in view of the solubility of the monomer and polymer. These are used alone or in combination. May be. The concentration of the polymer is preferably 1 to 30% by mass, and more preferably 5 to 20% by mass from the viewpoint that polymer precipitation is difficult to occur and a high molecular weight body is easily obtained.

The polyamic acid obtained as described above can be recovered by precipitating the polymer by pouring into the poor solvent while thoroughly stirring the reaction solution. Moreover, the powder of polyamic acid refine | purified by performing precipitation several times, washing | cleaning with a poor solvent, and normal temperature or heat-drying can be obtained. Although a poor solvent is not specifically limited, Water, methanol, ethanol, hexane, butyl cellosolve, acetone, toluene etc. are mentioned.

<Polyimide>
The polyimide used for this invention can be manufactured by imidating the said polyamic acid ester or polyamic acid which is a polyimide precursor. When a polyimide is produced from a polyamic acid ester, chemical imidization in which a basic catalyst is added to a polyamic acid solution obtained by dissolving the polyamic acid ester solution or the polyamic acid ester resin powder in an organic solvent is simple. Chemical imidization is preferable because the imidization reaction proceeds at a relatively low temperature and the molecular weight of the polymer does not easily decrease during the imidization process.

Chemical imidation can be performed by stirring the polyamic acid ester to be imidized in an organic solvent in the presence of a basic catalyst. As an organic solvent, the solvent used at the time of the polymerization reaction mentioned above can be used. Examples of the basic catalyst include pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine and the like. Of these, triethylamine is preferred because it has sufficient basicity to allow the reaction to proceed.

The temperature during the imidation reaction is −20 ° C. to 140 ° C., preferably 0 ° C. to 100 ° C., and the reaction time can be 1 to 100 hours. The amount of the basic catalyst is 0.5 to 30 moles, preferably 2 to 20 moles, of the amic acid ester group. The imidation ratio of the resulting polymer can be controlled by adjusting the amount of catalyst, temperature, and reaction time. Since the added catalyst or the like remains in the solution after the imidation reaction, the obtained imidized polymer is recovered by the means described below, redissolved in an organic solvent, and the liquid crystal alignment according to the present invention. A treating agent is preferred.

When manufacturing a polyimide from a polyamic acid, chemical imidation which adds a catalyst to the solution of the said polyamic acid obtained by reaction with a diamine component and tetracarboxylic dianhydride is simple. Chemical imidization is preferable because the imidization reaction proceeds at a relatively low temperature and the molecular weight of the polymer does not easily decrease during the imidization process.
Chemical imidation can be performed by stirring a polymer to be imidized in an organic solvent in the presence of a basic catalyst and an acid anhydride. As an organic solvent, the solvent used at the time of the polymerization reaction mentioned above can be used. Examples of the basic catalyst include pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine and the like. Of these, pyridine is preferable because it has an appropriate basicity for proceeding with the reaction. Examples of the acid anhydride include acetic anhydride, trimellitic anhydride, pyromellitic anhydride and the like. Among them, use of acetic anhydride is preferable because purification after completion of the reaction is facilitated.

The temperature during the imidation reaction is −20 ° C. to 140 ° C., preferably 0 ° C. to 100 ° C., and the reaction time can be 1 to 100 hours. The amount of the basic catalyst is 0.5 to 30 mol times, preferably 2 to 20 mol times the amic acid group, and the amount of the acid anhydride is 1 to 50 mol times, preferably 3 to 30 mol times the amic acid group. Is double. The imidation ratio of the resulting polymer can be controlled by adjusting the amount of catalyst, temperature, and reaction time.

In the solution after the imidation reaction of polyamic acid ester or polyamic acid, the added catalyst and the like remain, so the obtained imidized polymer is recovered by the means described below, and redissolved in an organic solvent. Thus, the liquid crystal aligning agent of the present invention is preferable.
The polyimide solution obtained as described above can be polymerized by pouring into a poor solvent while stirring well. Precipitation is performed several times, and after washing with a poor solvent, a purified polyamic acid ester powder can be obtained at room temperature or by heating and drying.
The poor solvent is not particularly limited, and examples thereof include methanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, and benzene.

<Liquid crystal alignment agent>
The liquid crystal aligning agent used in the present invention has a form of a solution in which a soluble polyimide having a specific structure is dissolved in an organic solvent. The molecular weight of the polyimide having a specific structure is preferably 2,000 to 500,000 in terms of weight average molecular weight, more preferably 5,000 to 300,000, and still more preferably 10,000 to 100,000. The number average molecular weight is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and still more preferably 5,000 to 50,000.
The concentration of the polymer of the liquid crystal aligning agent used in the present invention can be appropriately changed depending on the setting of the thickness of the coating film to be formed, but it is 1 from the viewpoint of forming a uniform and defect-free coating film. The content is preferably not less than wt%, and is preferably not more than 10 wt% from the viewpoint of storage stability of the solution.

As the organic solvent contained in the liquid crystal aligning agent used in the present invention, a solvent in which a polymer having a specific structure is uniformly dissolved is used. Preferred examples are N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-methylcaprolactam, Examples include 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl sulfone, γ-butyrolactone, 1,3-dimethyl-imidazolidinone, 3-methoxy-N, N-dimethylpropanamide and the like.
Of these, N, N-dimethylformamide, N-methyl-2-pyrrolidone and γ-butyrolactone are preferred, and N-methyl-2-pyrrolidone is particularly preferred.
The above organic solvents may be used alone or in combination. Moreover, even if it is a solvent which cannot melt | dissolve a polymer uniformly independently, if it is a range in which a polymer does not precipitate, said organic solvent will be mixed and used.

The liquid-crystal aligning agent used for this invention contains the solvent for improving the coating-film uniformity at the time of apply | coating a liquid-crystal aligning agent to a board | substrate other than the organic solvent for dissolving the polymer of a specific structure. May be. As such a solvent, a solvent having a surface tension lower than that of the organic solvent is generally used. Specific examples thereof include ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, ethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2 -Propanol, 1-phenoxy-2-propanol, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol-1-monomethyl ether-2-acetate, propylene glycol-1-monoethyl ether-2-acetate, butyl cellosolve acetate, di Propylene glycol, 2- (2-ethoxypropoxy) propanol, lactate methyl ester, lactate ethyl ester, lactate n-propyl ester, lactate n-butyl ester, lactic acid Isoamyl ester, and the like. Two types of these solvents may be used in combination.

In addition to the above, other materials may be added to the liquid crystal aligning agent of the present invention as long as the effects of the present invention are not impaired. Other materials include (A) a polymer other than the polymer described in the present invention, (B) a dielectric or conductive material for the purpose of changing electrical properties such as dielectric constant and conductivity of the liquid crystal alignment film, (C ) A silane coupling agent for the purpose of improving the adhesion between the liquid crystal alignment film and the substrate, (D) a crosslinkable compound for the purpose of increasing the hardness and density of the liquid crystal alignment film, and (E) coating Examples include an imidization accelerator for the purpose of efficiently progressing imidization by heating the polyimide precursor when the film is baked.

<Liquid crystal alignment film>
The liquid crystal alignment film of the present invention is a film obtained by applying the liquid crystal alignment treatment agent to a substrate, drying and baking. The substrate to which the liquid crystal alignment treatment agent of the present invention is applied is not particularly limited as long as it is a highly transparent substrate, and a glass substrate, a silicon nitride substrate, an acrylic substrate, a polycarbonate substrate such as a polycarbonate substrate, or the like can be used. It is preferable to use a substrate on which an ITO electrode or the like for driving is formed from the viewpoint of simplification of the process. In the reflective liquid crystal display element, an opaque material such as a silicon wafer can be used as long as only one substrate is used. In this case, a material that reflects light, such as aluminum, can also be used.

Examples of the method for applying the liquid crystal aligning agent of the present invention include spin coating, printing, and inkjet. Arbitrary temperature and time can be selected for the drying and baking process after apply | coating the liquid-crystal aligning agent of this invention. Usually, in order to sufficiently remove the organic solvent contained, drying is performed at 50 ° C. to 120 ° C. for 1 minute to 10 minutes, and then baking is performed at 150 ° C. to 300 ° C. for 5 minutes to 120 minutes. The thickness of the coating film after firing is not particularly limited, but if it is too thin, the reliability of the liquid crystal display element may be lowered, so it is 5 to 300 nm, preferably 10 to 200 nm.
Examples of a method for aligning the obtained liquid crystal alignment film include a rubbing method and a photo-alignment processing method.

As a specific example of the photo-alignment treatment method, there is a method of imparting liquid crystal alignment ability by irradiating the coating film surface with radiation deflected in a certain direction, and further subjecting to a temperature of 150 to 250 ° C. in some cases. Can be mentioned. As the radiation, ultraviolet rays and visible rays having a wavelength of 100 to 800 nm can be used. Of these, ultraviolet rays having a wavelength of 100 to 400 nm are preferable, and those having a wavelength of 200 to 400 nm are particularly preferable. Further, in order to improve the liquid crystal orientation, radiation may be irradiated while heating the coated substrate at 50 to 250 ° C. Dose of the radiation is preferably 1 ~ 10,000mJ / cm ^2, particularly preferably 100 ~ 5,000mJ / cm ^2. The liquid crystal alignment film produced as described above can stably align liquid crystal molecules in a certain direction.

[Liquid crystal display element]
The liquid crystal display element of the present invention is obtained by obtaining a substrate with a liquid crystal alignment film from the liquid crystal alignment treatment agent of the present invention by the above-described method, performing alignment treatment by rubbing treatment, etc. This is a display element.

A method for manufacturing a liquid crystal cell of a liquid crystal display element of a lateral electric field drive type is not particularly limited. For example, a pair of substrates on which a liquid crystal alignment film is formed is preferably 1 with the liquid crystal alignment film surface inside. A method is generally used in which a spacer having a spacer of ˜30 μm, more preferably 2 to 10 μm is placed and then the periphery is fixed with a sealant, and liquid crystal is injected to seal. The method for enclosing the liquid crystal is not particularly limited, and examples thereof include a vacuum method of injecting liquid crystal after reducing the pressure inside the produced liquid crystal cell, and a dropping method of sealing after dropping the liquid crystal.

The present invention will be described in more detail with reference to the following examples, but the present invention should not be construed as being limited thereto. Abbreviations used in the following examples and comparative examples are as follows.
<Tetracarboxylic acid component>
CA-1: 1,2,3,4-cyclobutanetetracarboxylic dianhydride CA-2: bicyclo [3.3.0] octane-2,4,6,8-tetracarboxylic dianhydride (isomer) [IV] content is 97%)
CA-3: pyromellitic dianhydride CA-4: 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride

<Diamine component>
DA-1: 1,5-bis (4-aminophenoxy) pentane DA-2: 3,5-diaminobenzoic acid DA-3: N- (3-pyridylmethyl) -3,5-diaminobenzoic acid amide DA- 4: 3-aminobenzylamine DA-5: p-phenylenediamine DA-6: 1,3-diamino-4-n-dodecyloxybenzene DA-7: 4,4'-diaminodiphenylmethane DA-8: 4,4 '-Diaminodiphenylamine <solvent>
BCS: Butyl cellosolve NMP: N-methyl-2-pyrrolidone

<Measurement of molecular weight of polyimide precursor and polyimide>
The molecular weights of the polyimide precursor and the polyimide in the synthesis example are determined using a normal temperature gel permeation chromatography (GPC) apparatus (GPC-101) (manufactured by Showa Denko KK) and columns (KD-803, KD-805) (manufactured by Shodex). The measurement was performed as follows.
Column temperature: 50 ° C
Eluent: N, N′-dimethylformamide (as additive, lithium bromide-hydrate (LiBr · H ₂ O) 30 mmol / L (liter), phosphoric acid / anhydrous crystal (o-phosphoric acid) 30 mmol) / L, 10 ml / L of tetrahydrofuran (THF))
Flow rate: 1.0 ml / min Standard sample for preparing a calibration curve: TSK standard polyethylene oxide (molecular weight: about 900,000, 150,000, 100,000, and 30,000) (manufactured by Tosoh Corporation) and polyethylene glycol (molecular weight; (About 12,000, 4,000, and 1,000) (manufactured by Polymer Laboratory).

(Measurement of imidization ratio of polyimide)
The imidation ratio of polyimide in the synthesis example was measured as follows. 20 mg of polyimide powder was put into an NMR (nuclear magnetic resonance) sample tube (NMR sampling tube standard, φ5 (manufactured by Kusano Kagaku)), and deuterated dimethyl sulfoxide (DMSO-d6, 0.05 mass% TMS (tetramethylsilane)). (Mixed product) (0.53 ml) was added and completely dissolved by applying ultrasonic waves. This solution was measured for proton NMR at 500 MHz with an NMR measuring instrument (JNW-ECA500) (manufactured by JEOL Datum). The imidation rate is determined based on protons derived from structures that do not change before and after imidation as reference protons, and the peak integrated value of these protons and proton peaks derived from NH groups of amic acid that appear in the vicinity of 9.5 ppm to 10.0 ppm. It calculated | required by the following formula | equation using the integrated value.
Imidization rate (%) = (1−α · x / y) × 100
In the above formula, x is a proton peak integrated value derived from NH group of amic acid, y is a peak integrated value of reference proton, α is one NH group proton of amic acid in the case of polyamic acid (imidation rate is 0%) Is the number ratio of the reference proton to.

[Synthesis Example 1]
DA-1 (14.32 g, 50.0 mmol), DA-2 (4.56 g, 30.0 mmol), DA-3 (4.85 g, 20.0 mmol) and CA-2 (12.51 g, 50.0 mmol) ) In NMP (207.4 g) and reacted at 50 ° C. for 6 hours. Thereafter, CA-1 (9.51 g, 48.5 mmol) and NMP (51.9 g) were added and reacted at 40 ° C. overnight to obtain a polyamic acid solution (1) having a resin solid content concentration of 15 mass%.
After adding NMP to the obtained polyamic acid solution (1) (100.0 g) and diluting to 5% by mass, acetic anhydride (22.41 g) and pyridine (8.69 g) were added as imidization catalysts, For 2 hours. This reaction solution was poured into methanol (1500 ml), and the resulting precipitate was filtered off. This deposit was wash | cleaned with methanol, and it dried under reduced pressure at 100 degreeC, and obtained the polyimide powder (1). The imidation ratio of this polyimide was 50%, the number average molecular weight was 24,800, and the weight average molecular weight was 88,000.

[Synthesis Example 2]
DA-1 (18.61 g, 65.0 mmol), DA-2 (5.93 g, 39.0 mmol), DA-3 (6.30 g, 26.0 mmol) and CA-2 (24.40 g, 97.5 mmol) ) In NMP (195.3 g) and reacted at 50 ° C. for 6 hours. Thereafter, CA-1 (5.79 g, 29.5 mmol) and NMP (48.8 g) were added and reacted at 40 ° C. overnight to obtain a polyamic acid solution (2) having a resin solid content concentration of 20 mass%.
After adding NMP to the obtained polyamic acid solution (2) (100.0 g) and diluting to 5% by mass, acetic anhydride (10.87 g) and pyridine (8.43 g) were added as an imidization catalyst, and 90 ° C. For 2.5 hours. This reaction solution was poured into methanol (1500 ml), and the resulting precipitate was filtered off. This deposit was wash | cleaned with methanol, and it dried under reduced pressure at 100 degreeC, and obtained the polyimide powder (2). The imidation ratio of this polyimide was 50%, the number average molecular weight was 24,800, and the weight average molecular weight was 76,230.

[Synthesis Example 3]
After adding NMP to the polyamic acid solution (2) (60 g) obtained in Synthesis Example 2 and diluting to 5% by mass, acetic anhydride (13.05 g) and pyridine (4.05 g) were added as imidization catalysts, The reaction was carried out at 100 ° C. for 3 hours. This reaction solution was poured into methanol (900 ml), and the resulting precipitate was separated by filtration. This deposit was wash | cleaned with methanol, and it dried under reduced pressure at 100 degreeC, and obtained the polyimide powder (3). The imidation ratio of this polyimide was 70%, the number average molecular weight was 22,100, and the weight average molecular weight was 70,000.

[Synthesis Example 4]
DA-1 (30.78 g, 107 mmol), DA-2 (13.08 g, 86.0 mmol), DA-3 (5.21 g, 21.5 mmol) and CA-2 (40.35 g, 161 mmol) were mixed with NMP ( 278.4 g) and reacted at 50 ° C. for 6 hours. Thereafter, CA-1 (9.99 g, 50.9 mmol) and NMP (119.3 g) were added and reacted at 40 ° C. overnight to obtain a polyamic acid solution (3) having a resin solid content concentration of 20 mass%.
After adding NMP to the obtained polyamic acid solution (3) (50.0 g) and diluting to 3.5% by mass, acetic anhydride (11.04 g) and pyridine (3.42 g) were added as imidization catalysts, The reaction was carried out at 100 ° C. for 3 hours. This reaction solution was put into methanol (750 ml), and the resulting precipitate was separated by filtration. This deposit was wash | cleaned with methanol, and it dried under reduced pressure at 100 degreeC, and obtained the polyimide powder (4). The imidation ratio of this polyimide was 67%, the number average molecular weight was 28,500, and the weight average molecular weight was 99,600.

[Synthesis Example 5]
DA-1 (36.94 g, 129 mmol), DA-2 (13.08 g, 86.0 mmol) and CA-2 (40.35 g, 167 mmol) were mixed in NMP (280.2 g) and mixed at 50 ° C. for 6 Reacted for hours. Thereafter, CA-1 (9.70 g, 49.5 mmol) and NMP (120.1 g) were added and reacted at 40 ° C. overnight to obtain a polyamic acid solution (4) having a resin solid content concentration of 20 mass%.
After adding NMP to the obtained polyamic acid solution (4) (50.0 g) and diluting to 4% by mass, acetic anhydride (10.96 g) and pyridine (3.40 g) were added as an imidization catalyst, and 100 ° C. For 3 hours. This reaction solution was put into methanol (750 ml), and the resulting precipitate was separated by filtration. This deposit was wash | cleaned with methanol, and it dried under reduced pressure at 100 degreeC, and obtained the polyimide powder (5). The imidation ratio of this polyimide was 69%, the number average molecular weight was 36,700, and the weight average molecular weight was 134,800.

[Synthesis Example 6]
DA-1 (16.04 g, 55.9 mmol), DA-2 (6.39 g, 42.0 mmol), DA-4 (5.13 g, 42.0 mmol) and CA-3 (7.02 g, 32.2 mmol) ) In NMP (194.7 g) and reacted at 23 ° C. for 1 hour. Thereafter, CA-2 (26.27 g, 105 mmol) and NMP (48.68 g) were added and reacted at 40 ° C. overnight to obtain a polyamic acid solution (5) having a resin solid content concentration of 20 mass%.
After adding NMP to the obtained polyamic acid solution (5) (40.0 g) and diluting to 5% by mass, acetic anhydride (4.66 g) and pyridine (3.61 g) were added as an imidization catalyst, and 90 ° C. For 2.5 hours. This reaction solution was poured into methanol (600 ml), and the resulting precipitate was separated by filtration. This deposit was wash | cleaned with methanol, and it dried under reduced pressure at 100 degreeC, and obtained the polyimide powder (6). The imidation ratio of this polyimide was 69%, the number average molecular weight was 13,900, and the weight average molecular weight was 40,600.

[Examples 1 to 6]
NMP (106.67 g) is added to each of the polyimide powders (1) to (6) (10.0 g each) obtained by the synthesis methods of Synthesis Examples 1 to 6, and stirred at 80 ° C. for 24 hours to dissolve. It was. To this solution, BCS (50.0 g) was added and stirred at 23 ° C. for 2 hours to obtain liquid crystal aligning agents (1) to (6). None of the liquid crystal aligning agents (1) to (6) was found to be a uniform solution with no abnormality such as turbidity or generation of precipitates.

[Comparative Example 1]
With reference to Japanese Patent Application Laid-Open No. 8-220541, solvent-soluble polyimides of CA-4 (100) / DA-5 (90) and DA-6 (10) and CA-1 (100) / DA-7 ( 100) polyamic acid was mixed at a ratio of 95: 5 to obtain a comparative liquid crystal aligning agent (A). This comparative liquid crystal aligning agent (A) was confirmed to be a uniform solution with no abnormalities such as turbidity and generation of precipitates.

[Comparative Example 2]
With reference to the pamphlet of WO 2004/053583, the polyamic acid of CA-1 (80), CA-4 (20) / DA-8 (80), DA-7 (20), and CA-3 (100) / DA -1 (100) polyamic acid was mixed at a ratio of 80:20 to obtain a comparative liquid crystal aligning agent (B). This comparative liquid crystal aligning agent (B) was confirmed to be a uniform solution with no abnormalities such as turbidity and generation of precipitates.

<Production of liquid crystal cell>
The obtained liquid crystal alignment treatment agent is filtered through a 1.0 μm filter, spin-coated on a glass substrate with a transparent electrode, dried on a hot plate at 70 ° C. for 2 minutes, and then baked at 230 ° C. for 15 minutes. A coating film having a thickness of 100 nm was obtained. After rubbing this polyimide film with a rayon cloth (roll diameter 120 mm, rotation speed 1000 rpm, moving speed 20 mm / sec, pushing amount 0.4 mm), ultrasonic irradiation was performed in pure water for 1 minute, and 80 ° C. for 10 minutes. Dried.
After preparing two substrates with such a liquid crystal alignment film, the two substrates are combined so that the rubbing directions are antiparallel, and a liquid crystal injection port is formed using a sealant mixed with 5% by weight of a 4 μm spacer. The periphery was sealed and the empty cell having a cell gap of 4 μm was produced. Liquid crystal (“MLC-2041”, manufactured by Merck & Co., Inc.) was vacuum injected into this cell at room temperature, and the injection port was sealed to obtain an anti-parallel liquid crystal cell.

<Black level evaluation>
A liquid crystal cell (Examples 1 to 6, Comparative Examples 1 and 2) prepared in the same manner as described above (preparation of a liquid crystal cell) was placed between two polarizing plates arranged so that the polarization axes were orthogonal to each other, and no voltage was applied. In this state, the backlight was turned on, and the arrangement angle of the liquid crystal cell was adjusted so that the luminance of transmitted light was minimized. The liquid crystal cells were observed using a digital CCD camera “C8800-21C” manufactured by Hamamatsu Photonics, and the captured images were digitized using the analysis software “ExDcam Image capture Software”. .
When the luminance value of these liquid crystal cells is 500 to 550, “◎” is indicated, and when the luminance value is 550 to 600, “◯” is indicated.

The liquid crystal aligning agent of the present invention is industrially useful because it can solve the problem that the color tone of the screen based on the black element in the horizontal electric field drive type liquid crystal display element is uncomfortable.
The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2013-57263 filed on March 19, 2013 are incorporated herein as the disclosure of the specification of the present invention. It is.

Claims (8)

1. A liquid crystal alignment treatment for a transverse electric field comprising a polyimide obtained by ring-closing a polyimide precursor having a structural unit represented by the following formula (1) as a structural unit derived from tetracarboxylic dianhydride Agent.
   

   

   (In Formula (1), X ¹ is a tetravalent organic group represented by the following Formula (X ¹ ), and R ¹ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.)
   

   
2. The liquid crystal aligning agent for horizontal electric fields of Claim 1 in which the said polyimide precursor has a structural unit represented by following formula (2) as a structural unit derived from diamine.
   

   

   (In the formula (2), n is 1 to 12.)
3. The transverse electric field according to claim 1 or 2, wherein the tetravalent organic group represented by the formula (X ¹ ) is a single component selected from isomers of the formulas [IV] to [VI], or a mixture thereof. Liquid crystal aligning agent for driving.
   

   
4. The liquid crystal aligning agent for driving a transverse electric field according to claim 3, wherein the content of isomer [IV] is 90% or more.
5. The content of the structural unit represented by the formula (1) is 30 to 100 mol% with respect to 1 mol of all structural units derived from the tetracarboxylic acid derivative. Liquid crystal alignment agent for horizontal electric field.
6. The transverse electric field according to any one of claims 1 to 5, wherein the content of the structural unit represented by the formula (2) is 20 to 100 mol% with respect to 1 mol of all structural units derived from diamine. Liquid crystal alignment treatment agent.
7. A liquid crystal alignment film for driving a horizontal electric field obtained by applying the liquid crystal alignment treatment agent according to any one of claims 1 to 6 to a substrate and baking the substrate.
8. A liquid crystal display element for driving a horizontal electric field, comprising the liquid crystal alignment film according to claim 7.