TW202128838A - Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element using same - Google Patents

Abstract

Provided is a liquid crystal alignment agent, using which a liquid crystal alignment film is obtained which exhibits excellent liquid crystal alignment stability and is unlikely to cause flickering during driving. A liquid crystal alignment agent containing one or more types of polymer (A) selected from the group consisting of a polyimide precursor (a1) having a repeating unit represented by formula (1) and an imidized polymer (a2) of the polyimide precursor (a1), the liquid crystal alignment agent being characterized in that the polyimide precursor (a1) includes a structure in which Y1 in formula (1) is a divalent group represented by formula (Y1-1), and a structure in which Y1 in formula (1) is a divalent group represented by (Y1-2). (In formula (1), X1 is a tetravalent organic group, Y1 is a divalent organic group, and R1, R2, A1 and A2 each independently represent a hydrogen atom or a C1-4 alkyl group. In the molecular chain of the polyimide precursor (a1), X1, R1, R2, A1 and A2 may be one type of atom/group or may be two or more types mixed with one another. Y1 may be two or more types mixed with one another.) (In formula (Y1-1) and formula (Y1-2), Z1, Z2, Z3 and Z4 each independently represent a halogen atom or a C1-4 alkyl group, and n is an integer of 0-4. n may be the same or may differ. When n is an integer of 2 or higher, Z1, Z2, Z3 and Z4 may be the same or may differ from one another.).

Description

Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element using the same

The present invention relates to a liquid crystal alignment agent, a liquid crystal alignment film obtained by the liquid crystal alignment agent, and a liquid crystal display element having a liquid crystal alignment film using the liquid crystal alignment agent.

Liquid crystal display elements are widely used as display units of personal computers, mobile phones, smart phones, televisions, and the like. The liquid crystal display element is equipped with, for example, a liquid crystal layer sandwiched between a device substrate and a color filter substrate, a pixel electrode and a common electrode that apply an electric field to the liquid crystal layer, an alignment film that controls the alignment of liquid crystal molecules in the liquid crystal layer, and a switch Thin film transistors (TFT), etc. for electrical signals supplied to pixel electrodes. As driving methods of liquid crystal molecules, vertical electric field methods such as TN method and VA method, or transverse electric field methods such as IPS method and FFS method are known. The transverse electric field method in which electrodes are formed on only one side of the substrate and an electric field is applied in a direction parallel to the substrate is known to be the system A liquid crystal display element with wide viewing angle characteristics and high-quality display.

Although the viewing angle characteristic of the liquid crystal cell of the lateral electric field method is excellent, since the electrode portion formed in the substrate is small, if the voltage holding ratio is low, a sufficient voltage will not be applied to the liquid crystal, and the display contrast will decrease. In addition, if the stability of the liquid crystal alignment is small, the liquid crystal system cannot return to the initial state when the liquid crystal is driven for a long period of time, which may cause a decrease in contrast or a residual image. Therefore, the stability of the liquid crystal alignment is important. Furthermore, static electricity is easy to accumulate in the liquid crystal cell. Even if the positive and negative asymmetric voltage generated by driving is applied, the electric charge is still accumulated in the liquid crystal cell. The display is affected, and the display quality of the liquid crystal element is significantly reduced. In addition, even if the backlight is irradiated on the liquid crystal cell shortly after driving, problems such as accumulation of electric charge occur, and after-images occur even in short-time driving, or the size of flicker changes during driving.

As a liquid crystal alignment agent that has excellent voltage retention and reduces charge accumulation when used in such a liquid crystal display element of the transverse electric field method, Patent Document 1 discloses that it contains a specific diamine and an aliphatic tetracarboxylic acid derivative. Liquid crystal alignment agent for polymers obtained by polycondensation. However, with the higher performance of liquid crystal display elements, the characteristics required for the liquid crystal alignment film are becoming more and more stringent, and it is difficult for these conventional technologies to fully satisfy all the required characteristics. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Manual of International Publication No. WO2004/021076

[The problem to be solved by the invention]

The subject of the present invention is to provide a liquid crystal alignment agent for a liquid crystal alignment film that can obtain excellent liquid crystal alignment stability and is not prone to flicker during driving, a liquid crystal alignment film obtained by the liquid crystal alignment agent, and use thereof The liquid crystal display element. [Means to solve the problem]

The inventors of the present invention conducted active reviews to solve the above-mentioned problems and found that by introducing a plurality of specific structures into the polymer contained in the liquid crystal alignment agent, the above-mentioned problems were improved, and the present invention was completed.

(式(1)中，X₁ 為4價之有機基，Y₁ 為2價之有機基，R₁ 、R₂ 、A₁ 、A₂ 係各自獨立為氫原子，或碳數1～4之烷基。聚醯亞胺前驅物(a1)之分子鏈中，X₁ 、R₁ 、R₂ 、A₁ 、及A₂ 係各自可為1種，亦可有2種以上混合存在。Y₁ 亦可有2種以上混合存在)。

(式(Y1-1)、式(Y1-2)中，Z₁ 、Z₂ 、Z₃ 、及Z₄ 係各自獨立為鹵素原子，或碳數1～4之烷基，n為0～4之整數。n可為相同亦可不同。n為2以上之整數之情況中，Z₁ 、Z₂ 、Z₃ 、及Z₄ 各自係可相同亦可不同)。 [發明之效果]The present invention is based on this knowledge and has the following content as its main points. A liquid crystal alignment agent comprising a polyimide precursor (a1) having a repeating unit represented by the following formula (1) and an imidized polymer (a1) of the polyimide precursor (a1) a2) A liquid crystal alignment agent of at least one polymer (A) selected from the group, wherein the polyimide precursor (a1) includes the following formula (1), and Y ₁ is the following divalent group of the structure 2 of the formula (Y1-1) represented by the, structure 2 and the price of the group represented by the following formula (1), Y ₁ is represented by the following formula (Y1-2).

(In formula (1), X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group, R ₁ , R ₂ , A ₁ , and A ₂ are each independently a hydrogen atom, or a carbon number of 1 to 4 Alkyl. In the molecular chain of the polyimide precursor (a1), X ₁ , R ₁ , R ₂ , A ₁ , and A ₂ may each be one type, or two or more types may be mixed. Y ₁ There may also be a mixture of two or more).

(In formula (Y1-1) and formula (Y1-2), Z ₁ , Z ₂ , Z ₃ , and Z ₄ are each independently a halogen atom or an alkyl group with 1 to 4 carbon atoms, and n is 0 to 4 N may be the same or different. When n is an integer of 2 or more, each of Z ₁ , Z ₂ , Z ₃ , and Z ₄ may be the same or different). [Effects of Invention]

According to the liquid crystal alignment agent of the present invention, it is possible to obtain a liquid crystal alignment film that has excellent liquid crystal alignment stability and is not prone to flicker during driving.

The liquid crystal alignment agent of the present invention contains the polymer (A) described below. ＜Polymer (A)＞ The polymer (A) used in the present invention is composed of the polyimide precursor (a1) containing the repeating unit represented by the aforementioned formula (1) and the imidization of the polyimide precursor (a1) At least one polymer selected from the group of polymer (a2).

In the aforementioned formula (1), Y ₁ is a divalent organic group. The aforementioned polyimide precursor (a1) includes a structure in which Y ₁ is the divalent group represented by the aforementioned formula (Y1-1) in the aforementioned formula (1), and in the aforementioned formula (1), Y ₁ is The structure of the divalent base represented by the aforementioned formula (Y1-2).

In formula (Y1-1) and formula (Y1-2), Z ₁ , Z ₂ , Z ₃ , and Z _{4 are} preferably each independently a fluorine atom or a methyl group, and n is preferably an integer of 0 to 1.

(式(D2-1)～(D2-5)中，＊係表示鍵結鍵)。The divalent group represented by the formula (Y1-1) is preferably at least one selected from the group of the structures represented by the following formulas (D2-1) to (D2-5).

(In formulas (D2-1) to (D2-5), * represents a bonding bond).

(式(D4-1)～(D4-5)中，＊係表示鍵結鍵)。The divalent group represented by the formula (Y1-2) is preferably at least one selected from the group of the structures represented by the following formulas (D4-1) to (D4-5).

(In formulas (D4-1) to (D4-5), * represents a bonding bond).

In the aforementioned polyimide precursor (a1), Y ₁ is the ratio of the divalent group represented by the formula (Y1-1) and Y ₁ is the ratio of the divalent group represented by the formula (Y1-2). It is not particularly limited, however, with respect to the total structure of formula (1) possessed by the polyimide precursor (a1), _{the ratio of Y 1} to formula (Y1-1) is preferably 10-50 mol%, More preferably, it is 20-40 mol%, and _{the ratio of Y 1} being formula (Y1-2) is preferably 10-50 mol%, more preferably 20-40 mol%. In addition, _{the total of the ratio of Y 1} being the formula (Y1-1) and the ratio of Y ₁ being the formula (Y1-2) is preferably 20 to 80 mol%, more preferably 40 to 60 mol%.

The molecular chain of the aforementioned polyimide precursor (a1) may further include the aforementioned formula (1), where Y ₁ is a structure of a divalent organic group other than formula (Y1-1) and formula (Y1-2) . In addition, in the molecular chain of the polyimide precursor (a1), _{the structure of Y 1} of groups other than formula (Y1-1) and formula (Y1-2) may be one type, or two or more types may be mixed. .

_{The following are specific examples of preferred Y 1} other than formula (Y1-1) and formula (Y1-2), but the present invention is not limited by these.

又，Y₁ 亦可為下述之任一基之結構。

In addition, Y ₁ may have any of the following structures.

上述Boc係表示下述所表示之基。

The above-mentioned Boc represents the basis shown below.

Y ₁ is the total ratio of the aforementioned formulas (Y1-3) to (Y1-10) and formulas (5-1) to (5-9), relative to the formula (a1) possessed by the polyimide precursor (a1) 1) The entire structure is preferably 10 to 80 mol%, more preferably 20 to 60 mol%, and still more preferably 40 to 60 mol%.

In the aforementioned polyimide precursor (a1), X ₁ is a tetravalent organic group. _{The following shows the preferred structure of X 1 in} the polyimide precursor (a1), but the present invention is not limited by these.

In the aforementioned polyimide precursor (a1), R ₁ , R ₂ , A ₁ , and A ₂ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Preferably, R ₁ , R ₂ , A ₁ , and A ₂ are each independently a hydrogen atom or a methyl group.

The polyimide precursor (a1) used in the present invention can be obtained by polycondensation of a tetracarboxylic acid derivative component and a diamine component, wherein the tetracarboxylic acid derivative component contains the formula (1) the sources of the tetracarboxylic acid derivative) of the X _1, the diamine component comprising a diamine-based sources of Y becomes formula (1) of the _1. Examples of polyimide precursors include polyamide acid, polyamide acid ester, and the like. Examples of tetracarboxylic acid derivatives include tetracarboxylic dianhydride, tetracarboxylic acid disilyl ester, tetracarboxylic acid dichloride, tetracarboxylic acid dialkyl ester, tetracarboxylic acid dienyl ester, tetracarboxylic acid Carboxylic acid dialkyl ester dichloride, etc. In addition, the aforementioned polyimide precursor (a1) may also be a polymer obtained by modifying or capping the end of the main chain. The polyimide precursor (a1) after the main chain end is modified or capped can be used for the tetracarboxylic acid derivative during the polycondensation reaction of the tetracarboxylic acid derivative component and the diamine component or after the polycondensation reaction The component and/or the diamine component are obtained by reacting a monofunctional compound. Examples of the monofunctional compound include monoamines, monoisocyanates, compounds having one acid anhydride group, and compounds having one chloro group. The reaction conditions for synthesizing the polyimide precursor (a1) using the tetracarboxylic acid derivative component and the diamine component are not particularly limited, and conventional methods can be used.

The imidized polymer (a2) used in the polymer (A) of the present invention has A ₁ -OR ₁ and/or A ₂ -OR _{2 separated} from the aforementioned polyimide precursor (a1) A polymer with a closed ring (also known as imidization) structure. In this case, the ring closure rate (also referred to as the imidization rate) can be arbitrarily selected according to needs. In addition, the “imination rate” in this specification refers to the total amount of the amide group derived from the tetracarboxylic dianhydride or its derivative and the carboxyl group (or its derivative), the percentage of which the amide group occupies Proportion. In the imidization polymer, the imidization rate does not necessarily have to be 100%, and it can be arbitrarily prepared according to the application or purpose. The imidization rate of the imidized polymer used in the present invention is preferably 20-100%, more preferably 50-99%. The imidized polymer (a2) may be a polyimide precursor (a1) that is imidized by a known method, or it may be of formula (1) after imidization The structure of raw materials (for example, the diamine compound containing the imine group described in Japanese Patent Application Publication No. 9-185064).

In the present invention, if a good coating film can be formed, the molecular weight of the polymer (A) is not particularly limited. However, for example, the weight average molecular weight is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and still more preferably 10,000 ~100,000. In addition, 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.

＜Liquid crystal alignment agent＞ In addition to the polymer (A), the liquid crystal alignment agent of the present invention may also contain polymers other than the polymer (A). The types of polymers other than polymer (A) are not particularly limited. However, for example, polyamide, polyamide, polyimide, polysiloxane, polyester, and cellulose can be mentioned. Derivatives, polyacetals, polystyrene derivatives, poly(styrene-maleimide) derivatives, poly(meth)acrylates, etc. Among polymers other than the polymer (A), the polymer (B) shown below is preferable as a component contained in the liquid crystal alignment agent of the present invention.

Polymer (B): It is a polyimide precursor (b1) having a repeating unit represented by the following formula (2), and an imidized polymer of the polyimide precursor (b1) (b2) At least one polymer selected from the group, wherein the polyimide precursor (b1) includes the following formula (2), and Y ₂ has (i) bonded to aromatic The polymer of the structure of the nitrogen atom of the group group or (ii) the divalent organic group of the nitrogen-containing aromatic heterocyclic ring.

(式(2)中，X₂ 為4價之有機基，Y₂ 為2價之有機基，A₃ 、A₄ 係各自獨立為氫原子或碳數1～4之烷基。聚醯亞胺前驅物(b1)之分子鏈中，X₂ 、Y₂ 、A₃ 、及A₄ 係各自可為1種，亦可有2種以上混合存在)。

(In formula (2), X ₂ is a tetravalent organic group, Y ₂ is a divalent organic group, and A ₃ and A ₄ are each independently a hydrogen atom or an alkyl group with 1 to 4 carbon atoms. Polyimide In the molecular chain of the precursor (b1), each of X ₂ , Y ₂ , A ₃ , and A ₄ series may be one type, or two or more types may be mixed).

The polymer (B) is preferably at least one polymer selected from the aforementioned polyimide precursor (b1).

The following is a specific example of a structure having (i) a nitrogen atom bonded to an aromatic group or (ii) a structure of _{Y 2 which is a nitrogen-containing aromatic heterocyclic ring.}

The polymer (B) may also contain a structure in which Y ₂ is a divalent organic group other than the above. Examples of divalent organic groups other than the above include _{the specific structure of Y 1} exemplified in the polymer (A), or 2,5-diaminobenzoic acid and 3,5-diaminobenzoic acid The structure in which two amino groups are removed from a diamine with a carboxyl group, 1,3-bis(4-aminophenethyl)urea, 1,3-bis(4-aminobenzyl)urea, 1,3-bis( 3-aminobenzyl)urea, 1-(4-aminobenzyl)-3-(4-aminophenethyl)urea, etc., have a structure in which two amino groups are removed from a diamine with a urea bond, but they are not affected by this And so on.

As a _{preferable example of the structure of X 2 , the specific structure of X 1} exemplified by the polymer (A), the tetravalent group shown below, and the like can be cited.

The molecular weight of the polymer (B) is not particularly limited as long as it can form a good coating film. However, for example, the weight average molecular weight is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and still more preferably 10,000 to 100,000. In addition, 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.

When the liquid crystal alignment agent of the present invention contains the polymer (A) and the polymer (B), the content of the polymer (B) is preferably 20 to the total of the polymer (A) and the polymer (B). 80% by mass.

The liquid crystal alignment agent of the present invention may also contain components other than polymers. Examples of components other than polymers include dielectrics or conductive materials for the purpose of changing the electrical properties of the liquid crystal alignment film, such as the permittivity or conductivity, to improve the adhesion between the liquid crystal alignment film and the substrate. The purpose of the silane coupling agent, the crosslinking compound for the purpose of increasing the hardness or density of the film when used as a liquid crystal alignment film, and further to make the imidization of polyamide acid when the coating film is sintered efficiently proceed as The purpose of the imidization accelerator, etc.

The liquid crystal alignment agent of the present invention is a manufacturer used to make a liquid crystal alignment film. From the viewpoint of making it into a uniform thin film, it is preferably a coating solution in which the above-mentioned components are dissolved in an organic solvent. The concentration of the coating liquid can be appropriately changed according to the coating device to be used and the thickness of the liquid crystal alignment film to be obtained. From the viewpoint of forming a uniform and defect-free coating film, it is preferably 1% by mass or more, and from the viewpoint of storage stability of the solution, it is preferably 10% by mass or less. The concentration of the particularly preferred polymer is 2-8% by mass. The content of the polymer (A) in the liquid crystal alignment agent can be appropriately changed according to the coating method of the liquid crystal alignment agent or the film thickness of the intended liquid crystal alignment film, but it is preferably 2-10% by mass, particularly preferably 3-7 quality%.

The organic solvent used in the coating liquid is not particularly limited as long as it dissolves the polymer component uniformly. If specific examples are given, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, Dimethyl sulfene, γ-butyrolactone, 1,3-dimethyl-2-imidazolinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, etc. Among them, it is preferable to use N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone. Two or more of these solvents can also be used in combination.

Furthermore, in the composition for the purpose of forming a coating film, in addition to the above-mentioned solvent, a mixed solvent added with a solvent that improves the coating properties or improves the smoothness of the coating film surface is generally used in the liquid crystal alignment of the present invention. Among the agents, such mixed solvents are also suitable. The following are specific examples of mixed organic solvents, but are not limited by these examples.

For example, ethanol, isopropanol, 1-butanol, 2-butanol, isobutanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl- 1-butanol, isoamyl alcohol, tert-pentanol, 3-methyl-2-butanol, neopentanol, 1-hexanol, 2-methyl-1-pentanol, 2-methyl-2- Pentanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, cyclohexane Alcohol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2 -Butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-Ethyl-1,3-hexanediol, dipropyl ether, dibutyl ether, dihexyl ether, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethyl Glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, 4-hydroxy-4-methyl-2-pentanone, diethylene glycol methyl ethyl ether, diethyl Dibutyl glycol ether, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, 3-ethoxybutyl acetate, 1-methylpentyl acetic acid Ester, 2-ethylbutyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, ethylene carbonate, ethylene carbonate, 2 -(Methoxymethoxy)ethanol, ethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, 2-(hexyloxy)ethanol, furfuryl alcohol, diethylene glycol , Propylene glycol, propylene glycol monobutyl ether, 1-(butoxyethoxy) propanol, propylene glycol monomethyl ether acetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol Dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monoethyl Ester, ethylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy) ethyl ethyl Ester, diethylene glycol acetate, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, N-Butyl acetate, propylene glycol monoethyl ether acetate, methyl pyruvate, ethyl pyruvate, methyl 3-methoxypropionate, methyl ethyl 3-ethoxypropionate, 3-methoxy Ethyl propionate, 3-ethoxypropionic acid, 3-methoxypropionic acid, propyl 3-methoxypropionate, butyl 3-methoxypropionate, methyl lactate, ethyl lactate, lactic acid n-propyl ester, n-butyl lactate, isoamyl lactate, solvents represented by the following formulas [D-1] to [D-3], etc.

(式[D-1]及式[D-2]中之R係表示碳數1～3之烷基，式[D-3]中之R係表示碳數1～4之烷基)。

(R in formula [D-1] and formula [D-2] represents an alkyl group with 1 to 3 carbons, and R in formula [D-3] represents an alkyl group with 1 to 4 carbons).

Among the above, preferred are 1-hexanol, cyclohexanol, 1,2-ethanediol, 1,2-propanediol, propylene glycol monobutyl ether, diethylene glycol diethyl ether, 4-hydroxy- 4-methyl-2-pentanone, ethylene glycol monobutyl ether or dipropylene glycol dimethyl ether. The type and content of such a solvent can be appropriately selected according to the coating device, coating conditions, coating environment, etc. of the liquid crystal alignment agent. Moreover, these solvents can also use 2 or more types together.

＜Liquid crystal alignment film＞ The liquid crystal alignment film of the present invention can be obtained from the above-mentioned liquid crystal alignment agent of the present invention. If one of the methods for obtaining a liquid crystal alignment film from a liquid crystal alignment agent is given, it can be mentioned that the film obtained by coating the liquid crystal alignment agent in the form of a coating liquid on the substrate, drying and sintering, is processed by rubbing treatment or photo alignment treatment The method of applying the alignment processing.

The substrate on which the liquid crystal alignment agent is applied is not particularly limited, and plastic substrates such as glass substrates, silicon nitride substrates, acrylic substrates, or polycarbonate substrates can also be used. At this time, if a substrate formed with ITO electrodes for driving liquid crystals, etc. is used, it is preferable from the viewpoint of simplifying the manufacturing process. In addition, if the reflective liquid crystal display element is a substrate with only one side, opaque objects such as silicon wafers can also be used. In this case, materials that reflect light such as aluminum can also be used for the electrodes. The coating method of the liquid crystal alignment agent is not particularly limited. However, industrially, it is generally screen printing, offset printing, flexographic printing, inkjet method, etc. Other coating methods include dipping, roll coating, slit coating, spin coating, spraying, etc. These methods can also be used depending on the purpose.

After the liquid crystal alignment agent is coated on the substrate, the solvent is evaporated and sintered by heating means such as a heating plate, a thermal cycle oven, and an IR (infrared) oven. Any temperature and time can be selected for the drying and sintering steps after coating the liquid crystal alignment agent. Generally, in order to sufficiently remove the contained solvent, it is possible to sinter at 50 to 120°C for 1 to 10 minutes, and then sinter at 150 to 300°C for 5 to 120 minutes. The thickness of the sintered liquid crystal alignment film is not particularly limited. However, if it is too thin, the reliability of the liquid crystal display element may be reduced. Therefore, the range of 5 to 300 nm is preferable, and the range of 10 to 200 nm is more preferable. The liquid crystal alignment film of the present invention is suitable as a liquid crystal alignment film of a liquid crystal display element of a transverse electric field method such as an IPS method or an FFS method, and is particularly useful as a liquid crystal alignment film of a liquid crystal display element of the FFS method.

＜Liquid crystal display element＞ The liquid crystal display element of the present invention is a liquid crystal cell produced by a known method after obtaining a substrate with a liquid crystal alignment film obtained from the above liquid crystal alignment agent, and using the liquid crystal cell as an element. The following is an example of a manufacturing method of a liquid crystal cell, but the present invention is not limited by it.

First, a substrate with a set of electrodes for driving liquid crystals is prepared. This electrode system can be, for example, an ITO electrode, and is patterned in a manner that can display a desired image. In addition, switching elements such as TFT (Thin Film Transistor) may be provided in each pixel portion constituting the image display. A liquid crystal alignment film is formed on the substrate in the same manner as described above.

Next, place a UV curable sealant at a specific position on one of the two substrates on which the liquid crystal alignment film is formed, and further place liquid crystals on specific positions on the liquid crystal alignment film surface to make the liquid crystal The alignment film is bonded to another substrate with the alignment film facing each other. After the liquid crystal is spread out on the front surface of the liquid crystal alignment film by pressure bonding, the entire substrate is irradiated with ultraviolet rays to harden the sealant, thereby obtaining a liquid crystal cell. Or, as a step after forming a liquid crystal alignment film on a substrate, when arranging a sealant in a specific place on one of the substrates, first install an opening that can be filled with liquid crystal from the outside, and then attach the substrate after the liquid crystal is not installed. , The liquid crystal material is injected into the liquid crystal cell through the opening provided in the sealant, and then the opening is sealed with an adhesive to obtain the liquid crystal cell. The liquid crystal material can be injected by vacuum injection method or by capillary phenomenon in the atmosphere. In any of the above methods, in order to ensure the space for filling the liquid crystal material in the liquid crystal cell, it is preferable to arrange columnar protrusions on one of the substrates, or to spread spacers on one of the substrates, or to mix in the sealant Spacers, or combinations of these, etc.

Examples of the above-mentioned liquid crystal materials include nematic liquid crystals and smectic liquid crystals. Among them, nematic liquid crystals are preferred, and either a positive liquid crystal material or a negative liquid crystal material can be used. Next, proceed to the setting of the polarizing plate. Specifically, it is preferable to stick a pair of polarizing plates on the surfaces of the two substrates on the opposite side to the liquid crystal layer. [Example]

The following is a detailed description of the present invention with examples, etc., but the present invention is not limited by these examples. In addition, the abbreviations and characteristic evaluation methods of compounds and solvents are as described below.

NMP: N-methyl-2-pyrrolidone BCS: Butyl cellosolve DA-1～DA-10: Compounds of the following structural formulas CA-1～CA-3: Compounds of the following structural formulas AD-1 and AD-2: Compounds of the following structural formulas

[Determination of Viscosity] In the following synthesis example, the viscosity of the polymer solution is based on the E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.), with a sample volume of 1.1 mL and a cone rotor TE-1 (1°34', R24) , Measure at a temperature of 25°C.

＜Synthesis of polymers＞ (Synthesis example 1) Add DA-1 (1.980g, 8.1mmol), DA-2 (1.471g, 5.4mmol), DA-3 (0.876g, 8.1mmol), to a 200mL four-necked flask with a stirring device and a nitrogen introduction tube After DA-4 (2.152 g, 5.4 mmol), NMP (65.49 g) was added, and it was stirred and dissolved while sending nitrogen gas. While stirring this solution, CA-1 (5.750g, 25.7mmol) and NMP (24.17g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-A1)的NMP solution. The viscosity of this polyamide acid solution is 378mPa·s.

(Synthesis example 2) Add DA-1 (2.052g, 8.4mmol), DA-2 (1.525g, 5.6mmol), DA-3 (0.908g, 8.4mmol), to a 200mL four-necked flask with a stirring device and a nitrogen inlet tube. After DA-5 (1.912 g, 5.6 mmol), NMP (65.23 g) was added, and it was stirred and dissolved while sending nitrogen gas. While stirring this solution, CA-1 (6.026 g, 26.9 mmol) and NMP (25.90 g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-A2)的NMP solution. The viscosity of this polyamic acid solution is 408mPa·s.

(Synthesis example 3) Add DA-7 (19.925g, 100.0mmol) and DA-9 (7.460g, 25.0mmol) to a 1000mL four-necked flask with a stirring device and a nitrogen inlet tube, then add NMP (365.63g) while delivering nitrogen While stirring and dissolving. While stirring this solution, CA-3 (34.939g, 118.8mmol) and NMP (91.41g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-B1)的NMP solution. The viscosity of this polyamic acid solution is 398mPa·s.

(Synthesis example 4) Add DA-7 (19.925 g, 100.0 mmol) and DA-9 (7.460 g, 25.0 mmol) to a 1000 mL four-neck flask with a stirring device and a nitrogen inlet tube, and then add NMP (359.54 g) while delivering nitrogen While stirring and dissolving. While stirring this solution, CA-2 (22.552g, 115.0mmol) and NMP (89.89g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-B2)的NMP solution. The viscosity of this polyamic acid solution is 135mPa·s.

(Synthesis example 5) Add DA-7 (9.963g, 50.0mmol), DA-8 (10.664g, 50.0mmol), DA-9 (7.460g, 25.0mmol) to a 1000mL four-necked flask with a stirring device and a nitrogen introduction tube , NMP (366.36g) was added, and it was stirred and dissolved while sending nitrogen gas. While stirring this solution, CA-2 (22.797g, 116.2mmol) and NMP (91.59g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-B3)的NMP solution. The viscosity of this polyamic acid solution is 91mPa·s.

(Comparative Synthesis Example 1) Add DA-1 (9.161g, 37.5mmol), DA-6 (12.014g, 37.5mmol), DA-3 (2.704g, 25.0mmol), to a 1000mL four-necked flask with a stirring device and a nitrogen inlet tube. After DA-4 (9.963 g, 25.0 mmol), NMP (310.37 g) was added, and it was stirred and dissolved while sending nitrogen gas. While stirring this solution, CA-1 (26.620g, 118.7 mmol) and NMP (133.02g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-C1)的solution. The viscosity of this polyamic acid solution is 405mPa·s.

(Comparative Synthesis Example 2) Add DA-1 (5.863g, 24.0mmol), DA-6 (7.689g, 24.0mmol), DA-3 (1.730g, 16.0mmol), to a 1000mL four-necked flask with a stirring device and a nitrogen inlet tube. After DA-5 (5.463 g, 16.0 mmol), NMP (194.41 g) was added, and it was stirred and dissolved while sending nitrogen gas. While stirring this solution, CA-1 (17.127g, 76.4mmol) and NMP (83.32g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-C2)的solution. The viscosity of this polyamic acid solution is 426mPa·s.

(Comparative Synthesis Example 3) Add DA-1 (9.161g, 37.5mmol), DA-10 (6.458g, 25.0mmol), DA-3 (4.055g, 37.5mmol), to a 1000mL four-necked flask with a stirring device and a nitrogen inlet tube. After DA-4 (9.963 g, 25.0 mmol), NMP (288.79 g) was added, and it was stirred and dissolved while sending nitrogen gas. While stirring this solution, CA-1 (26.620, 118.8mmol) and NMP (123.77g) were added, and then stirred at 50°C for 12 hours to obtain polyamide acid (PAA-C3) Solution. The viscosity of this polyamide acid solution is 399mPa·s.

(Examples and Comparative Examples) The polymer solutions obtained in Synthesis Examples 1 to 5 and Comparative Synthesis Examples 1 to 3, AD-1, AD-2, NMP, and BCS were mixed, and stirred at room temperature for 2 hours to obtain the following table The liquid crystal alignment agent of the composition shown in 1 (the number in parentheses indicates mass%).

Using the liquid crystal alignment agent obtained by performing the above-mentioned method, an FFS driving liquid crystal cell was produced by the steps shown below, and characteristics were evaluated.

[Construction of FFS driven liquid crystal cell] The liquid crystal cell system used in the fringe field switching (Fringe Field Switching: FFS) mode is composed of the following first glass substrate and the following second glass substrate as a set, wherein the first glass substrate is formed on the surface including a surface shape Common electrode-Insulating layer-FOP (Finger on Plate) electrode layer of a comb-shaped pixel electrode. The second glass substrate has a columnar spacer with a height of 3.5 μm on the surface and an ITO is formed on the back for antistatic. Film. The above-mentioned pixel electrode has a 3μm wide electrode element bent at an internal angle of 160° in a comb-tooth shape arranged in parallel at intervals of 6μm. One pixel has a first area and a second area. In the domain, the first domain and the second domain are bounded by the line connecting the curved portions of the plurality of electrode elements. In addition, the liquid crystal alignment film formed on the first glass substrate is aligned so that the direction of halving the inner corner of the pixel bending part is orthogonal to the alignment direction of the liquid crystal, and the liquid crystal formed on the second glass substrate The alignment film is processed in such a way that the alignment direction of the liquid crystal on the first substrate is consistent with the alignment direction of the liquid crystal on the second substrate when the liquid crystal cell is fabricated.

[Production of liquid crystal cell] After filtering the liquid crystal alignment agent with a filter with a pore size of 1.0 μm, spin coating is performed on the substrate with the above-mentioned electrode and the counter substrate, respectively. Then, after drying for 2 minutes on a hot plate at 80°C, and sintering at 230°C for 30 minutes, as a coating film with a film thickness of 100 nm, a polyimide film was obtained on each substrate. The coating film surface is irradiated with ultraviolet rays with a wavelength of 254nm after a linearly polarized light with an extinction ratio of 26:1 through a polarizing plate at 200mJ/cm ^2. Furthermore, the substrate was sintered at 230°C for 30 minutes to obtain a substrate with a liquid crystal alignment film. Next, one of the above-mentioned set of substrates with a liquid crystal alignment film is printed with a sealant, and the other substrate is bonded so that the faces of the liquid crystal alignment film face each other, and the sealant is hardened to produce an empty cell. In this empty cell, liquid crystal (MLC-3019, manufactured by Merck & Co., Ltd.) is vacuum-injected at room temperature by a pressure-reduced injection method, and the injection port is sealed to obtain an FFS-driven liquid crystal cell. After that, the obtained liquid crystal cell was heated at 120° C. for 1 hour and left overnight before being used in various evaluations.

＜Evaluation of the stability of liquid crystal alignment＞ For the FFS-driven liquid crystal cell fabricated above, an AC voltage of ±5V was applied at a frequency of 60 Hz for 120 hours under a constant temperature environment of 60°C. After that, the pixel electrode and the counter electrode of the liquid crystal cell are short-circuited, and they are left at room temperature for one day. Regarding the liquid crystal cell that has undergone the above-mentioned processing, in a state where no voltage is applied, the offset between the alignment direction of the liquid crystal in the first area and the alignment direction of the liquid crystal in the second area of the pixel is calculated as an angle. Specifically, a liquid crystal cell is installed between two polarizing plates arranged so that the polarization axis becomes orthogonal, and the backlight is turned on to adjust the liquid crystal cell to minimize the intensity of the transmitted light in the first area of the pixel. The arrangement angle of the cell, and then the rotation angle required to rotate the liquid crystal cell in such a way that the transmitted light intensity in the second area of the pixel becomes the smallest. The smaller the value of the rotation angle, the better the stability of the liquid crystal alignment. If the value of the rotation angle is 0.1° or less, it is evaluated as "good", and if it exceeds 0.1°, it is evaluated as "bad".

＜Evaluation of flickering during driving＞ The liquid crystal cell produced above is placed between two polarizing plates arranged so that the polarization axis becomes orthogonal, and the LED backlight is turned on under no voltage applied, so that the brightness of the transmitted light is minimized Adjust the arrangement angle of the liquid crystal cell. Next, the V-T curve (voltage-transmittance curve) was measured while applying an alternating voltage with a frequency of 30 Hz to the liquid crystal cell, and an alternating voltage with a relative transmittance of 23% was calculated as the drive voltage.

In the measurement of flicker, the LED backlight that was lit first is temporarily extinguished, and after being shaded for 72 hours, the LED backlight is turned on again, and when the backlight starts to light up, an AC with a frequency of 30 Hz with a relative transmittance of 23% is applied. Voltage and drive the liquid crystal cell for 60 minutes to track the flicker amplitude. The flicker amplitude is to pass the transmitted light of the LED backlight of the two polarizing plates and the liquid crystal cell between them, through the photodiode and the IV conversion amplifier connected to the data collection/data recording switching device 34970A (manufactured by Agilent technologies) Read it. Use this data as the basis and use the value calculated by the following formula as the degree of flicker. Flicker degree (%)={flicker amplitude／(2×z)}×100

In the above formula, z is the brightness after driving with an AC voltage of 30 Hz with a relative transmittance of 23%, and the value read by the data collection/data recording switching device 34970A. The flicker evaluation refers to the case where the degree of flicker is maintained below 3.0% from the time when the LED backlight is turned on and the AC voltage is applied to 60 minutes has elapsed, and it is defined as an evaluation of "○". If the degree of flicker exceeds 3.0% within 60 minutes, it is defined as an evaluation of "×". The evaluation of the degree of flicker performed according to the above-mentioned method is performed under the temperature condition that the temperature of the liquid crystal cell is 23°C.

＜Evaluation result＞ Table 2 shows the evaluation results of the stability of the liquid crystal alignment and the occurrence of flicker during driving of the liquid crystal display element using the respective liquid crystal alignment agents of the above-mentioned Examples and Comparative Examples.

According to Examples 1 to 5, a liquid crystal alignment film with excellent liquid crystal alignment stability and less flicker can be obtained. On the other hand, in the liquid crystal alignment films obtained by Comparative Examples 1 to 3, although the stability of the liquid crystal alignment was "good", the degree of flicker was "×". [Industrial availability]

The liquid crystal alignment agent of the present invention is used for liquid crystal display elements of TN mode, VA mode, etc., or transverse electric field mode, such as IPS mode, FFS mode, etc., and is particularly widely used for horizontal electric field mode such as IPS mode and FFS mode. The liquid crystal display element.

In addition, the entire contents of the specification, scope of patent application, and abstract of Japanese Patent Application No. 2019-206332 filed on November 14, 2019 are incorporated herein as the disclosure content of the specification of the present invention.

Claims (14)

A liquid crystal alignment agent comprising a polyimide precursor (a1) having a repeating unit represented by the following formula (1) and an imidized polymer (a1) of the polyimide precursor (a1) a2) A liquid crystal alignment agent of at least one polymer (A) selected from the group, wherein the polyimide precursor (a1) includes the following formula (1), and Y ₁ is the following The structure of the divalent group represented by the formula (Y1-1), and in the following formula (1), Y ₁ is the structure of the divalent group represented by the following formula (Y1-2):

(In formula (1), X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group, R ₁ , R ₂ , A ₁ , and A ₂ are each independently a hydrogen atom, or a carbon number of 1 to 4 Alkyl; In the molecular chain of the polyimide precursor (a1), X ₁ , R ₁ , R ₂ , A ₁ , and A ₂ may each be one type, or two or more types may be mixed; Y ₁ (There can also be a mixture of more than 2 types)

(In formula (Y1-1) and formula (Y1-2), Z ₁ , Z ₂ , Z ₃ , and Z ₄ are each independently a halogen atom or an alkyl group with 1 to 4 carbon atoms, and n is 0 to 4 N may be the same or different; when n is an integer of 2 or more, Z ₁ , Z ₂ , Z ₃ , and Z ₄ may be the same or different). The liquid crystal alignment agent described in claim 1, wherein the divalent group represented by the aforementioned formula (Y1-1) is formed by the structure represented by the following formulas (D2-1) to (D2-5) At least 1 selected by the group:

(In formulas (D2-1) to (D2-5), * represents a bonding bond). The liquid crystal alignment agent described in claim 1 or 2, wherein the divalent group represented by the aforementioned formula (Y1-2) is a structure represented by the following formulas (D4-1) to (D4-5) At least one selected from the group:

(In formulas (D4-1) to (D4-5), * represents a bonding bond). The liquid crystal alignment agent according to any one of claims 1 to 3, wherein _{the ratio of Y 1} to the divalent group represented by formula (Y1-1) is relative to the polyimide precursor (a1) The total structure of formula (1) is 10-50 mol%, and _{the ratio of Y 1} to the divalent group represented by formula (Y1-2) is relative to the polyimide precursor (a1) The total structure of formula (1) is 10-50 mol%. The liquid crystal alignment agent according to any one of claims 1 to 4, wherein the polyimide precursor (a1) further comprises the above formula (1), and Y ₁ is the following formula (Y1-3 ) ~ Formula (Y1-10) and formula (5-1) ~ Formula (5-9) in any one of the divalent base represented by the structure:

(In the above formula, Boc represents the base shown below)

. The liquid crystal alignment agent according to any one of claims 1 to 5, wherein X ₁ of the aforementioned formula (1) is formed by the structure represented by the following formulas (X1-1) to (X1-14) At least 1 selected by the group:

. The liquid crystal alignment agent as described in any one of claims 1 to 6, which further contains a polyamide acid, polyamide ester, polyimide, polysiloxane, polyester, and cellulose derivative At least one polymer selected from the group consisting of polyacetal, polystyrene derivative, poly(styrene-maleimide) derivative, and poly(meth)acrylate. The liquid crystal alignment agent described in claim 7, wherein the aforementioned polymer is the following polymer (B): Polymer (B): which is composed of a polyamide having a repeating unit represented by the following formula (2) The imine precursor (b1), and at least one polymer selected from the group consisting of the imidized polymer (b2) of the polyimide precursor (b1), wherein the aforementioned polyimide The precursor (b1) includes the following formula (2), Y ₂ is a structure having (i) a nitrogen atom bonded to an aromatic group or (ii) a divalent organic group of a nitrogen-containing aromatic heterocyclic ring polymer;

(In formula (2), X ₂ is a tetravalent organic group, Y ₂ is a divalent organic group, A ₃ and A ₄ are each independently a hydrogen atom or an alkyl group with 1 to 4 carbon atoms; polyimide In the molecular chain of the precursor (b1), each of X ₂ , Y ₂ , A ₃ , and A ₄ series may be one type, or two or more types may be mixed). The liquid crystal alignment agent as described in claim 8, wherein, in formula (2), a divalent organic group having (i) a nitrogen atom bonded to an aromatic group or (ii) a nitrogen-containing aromatic heterocyclic ring At least one selected from the following:

. The liquid crystal alignment agent according to any one of claims 1 to 9, wherein the polymer (A) is a polymer obtained by modifying or capping the end of the main chain. The liquid crystal alignment agent according to any one of claims 1 to 10, which further contains a group consisting of a dielectric, a conductive material, a silane coupling agent, a crosslinking compound, and an imidization accelerator At least one additive selected. A liquid crystal alignment film obtained from the liquid crystal alignment agent described in any one of claims 1-11. A liquid crystal display element having the liquid crystal alignment film as described in claim 12. The liquid crystal display element described in claim 13 is a liquid crystal display element of an IPS method or an FFS method.