TW202546200A - Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element - Google Patents

Abstract

The liquid crystal alignment agent of this invention comprises an organic solvent and a polymer. The polymer comprises at least one of the units shown in Formula I-1 and Formula I-2, and the polymer structure includes a tetravalent organic group shown in Formula II and a divalent organic group shown in Formula III. The substituents in Formulas I-1, I-2, II, and III are defined as described in the specification and the scope of the patent application. This invention also provides a liquid crystal alignment film formed from the liquid crystal alignment agent, and a liquid crystal display element comprising the liquid crystal alignment film and thus having good reliability.

Description

Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element

This invention relates to the field of liquid crystal display technology, and particularly to a liquid crystal alignment agent, a liquid crystal alignment film formed by the liquid crystal alignment agent, and a liquid crystal display element comprising the liquid crystal alignment film.

In liquid crystal displays (LCDs), the alignment film is used to align liquid crystal molecules at a uniform pre-tilt angle (PTA). The properties of the alignment film have a crucial impact on the performance of the LCD, making it a subject of intense research in both industry and academia.

For example, Chinese patent CN103172531A proposed by the applicant discloses a liquid crystal alignment agent that focuses on enabling liquid crystal display elements to have both low ion density and relatively high voltage retention rate, in order to improve the image retention problem of liquid crystal display elements.

Therefore, the primary objective of this invention is to provide a novel liquid crystal alignment agent that addresses the technical problem of reliability in liquid crystal display elements.

Therefore, the present invention comprises an organic solvent and a polymer, the polymer comprising at least one of the units shown in Formula I-1 and Formula I-2, Formula I-1 Formula I-2 .

In this polymer, ^R1 and ^R2 each independently represent tetravalent organic groups, and ^R3 and ^R4 each independently represent divalent organic groups. The tetravalent organic groups include those shown in Formula II, and the divalent organic groups include those shown in Formula III. Formula II Formula III .

In Formula II, ^R5 to ^R8 each independently represent hydrogen, _CF3 , C1 to C5 alkyl or C1 to C5 alkoxy.

In Formula III, ^R9 and ^R10 each independently represent hydrogen, _CF3 , C1 to C20 alkyl, C1 to C20 alkoxy or a monovalent organic group having an aromatic ring.

Therefore, the second objective of this invention is to provide a liquid crystal alignment film.

Therefore, the liquid crystal alignment film of the present invention is formed by the liquid crystal alignment agent as described above.

Therefore, the third objective of this invention is to provide a liquid crystal display element.

Therefore, the liquid crystal display element of the present invention includes the liquid crystal alignment film as described above.

The advantage of this invention is that the polymer in the liquid crystal alignment agent of this invention has a structure including a tetravalent organic group as shown in Formula II and a divalent organic group as shown in Formula III, thereby making the liquid crystal display element containing the liquid crystal alignment film formed by the liquid crystal alignment agent have good reliability.

In this article, the asterisk (*) in the chemical structure formula represents the bond position.

[Liquid Crystal Orientant]

The liquid crystal alignment agent of this invention comprises an organic solvent and a polymer, the polymer comprising at least one of the units shown in Formula I-1 and Formula I-2. Specifically, the polymer is at least one of the group consisting of polyamide, polyamide ester, at least partially amide-iminated polyamide, and at least partially amide-iminated polyamide ester, Formula I-1 Formula I-2 .

In this polymer, ^R1 and ^R2 each independently represent tetravalent organic groups, and ^R3 and ^R4 each independently represent divalent organic groups. The tetravalent organic groups include those shown in Formula II, and the divalent organic groups include those shown in Formula III. Formula II Formula III .

In Formula II, ^R5 to ^R8 each independently represent hydrogen, _CF3 , C1 to C5 alkyl, or C1 to C5 alkoxy. In some embodiments, ^R5 to ^R8 each independently represent hydrogen or C1 to C5 alkyl. In some embodiments, ^R5 to ^R8 each independently represent hydrogen or _CH3 . In some embodiments, Formula II is selected from one or more tetravalent organic groups shown in Formulas II-1 to II-3. Formula II-1 Formula II-2 Formula II-3 .

In some embodiments, the total amount of ^R1 and ^R2 is 100 mol%, and the tetravalent organic group represented by Formula II accounts for 10 mol% to 100 mol%.

In some embodiments, the tetravalent organic group in the polymer further includes at least one of the tetravalent organic groups represented by formulas B1 to B2, wherein formula B1 Formula B2 .

In some embodiments, with the total amount of ^R1 and ^R2 being 100 mol%, at least one of the tetravalent organic groups shown in Formulas B1 to B2 accounts for 1 mol% to 60 mol.

In Formula III, ^R9 and ^R10 each independently represent hydrogen, _CF3 , C1 to C20 alkyl, C1 to C20 alkoxy, or a monovalent organic group having an aromatic ring. In some embodiments, ^R9 and ^R10 each independently represent hydrogen, _CH3 , or _CF3 . In some embodiments, Formula III is selected from one or more of the divalent organic groups shown in Formulas III-1 to III-3. Formula III-1 Formula III-2 Formula III-3 .

In some embodiments, the total amount of ^R3 and ^R4 is 100 mol%, and the divalent organic group represented by Formula III accounts for 5 mol% to 70 mol%. In some embodiments, the total amount of ^R3 and ^R4 is 100 mol%, and the divalent organic group represented by Formula III accounts for 5 mol% to 50 mol%.

In some embodiments, the divalent organic group in the polymer further includes at least one of the divalent organic groups represented by formulas A1 to A5, wherein formula A1 Formula A2 Formula A3 Formula A4 Formula A5 .

In some embodiments, with the total amount of ^R3 and ^R4 being 100 mol%, at least one of the divalent organic groups shown in Formulas A1 to A5 accounts for 1 mol% to 80 mol%. In some embodiments, with the total amount of ^R3 and ^R4 being 100 mol%, at least one of the divalent organic groups shown in Formulas A1 to A5 accounts for 20 mol% to 60 mol.

The cyclization rate of the polymer can be adjusted arbitrarily according to the application and purpose. Even if the cyclization rate of the polymer is low, the liquid crystal alignment agent containing the polymer will be heated during or after the formation of the liquid crystal alignment film, so that the cyclization rate of the liquid crystal alignment film reaches a value that meets the required application and purpose.

In some embodiments, the polymer has a weight-average molecular weight ranging from 1,000 to 1,000,000. In some embodiments, the polymer has a weight-average molecular weight ranging from 10,000 to 100,000. In some exemplary embodiments, the polymer has a weight-average molecular weight ranging from 36,000 to 98,000.

The synthesis of this polymer includes the following steps: mixing a diamine monomer, a tetracarboxylic dianhydride monomer, and a solvent component to prepare a reactant with a solid content of 10 to 20% by weight, and subjecting the reactant to a dehydration and ring-closing reaction. The tetracarboxylic dianhydride monomers corresponding to the tetravalent organic groups shown in Formulas II-1 to II-3 and B1 to B2, and the diamine monomers corresponding to the divalent organic groups shown in Formulas III-1 to III-3 and A1 to A5, are listed in the table below. Tetravalent organic groups Tetracarboxylic dianhydride monomer Formula II-1 Formula II-2 Formula II-3 Formula B1 Formula B2 Divalent organic groups diamine monomer Formula III-1 Formula III-2 Formula III-3 Formula A1 Formula A2 Formula A3 Formula A4 Formula A5

In some embodiments, the amino group content of the diamine monomer is 0.5 to 2 equivalents, with the anhydride group content of the tetracarboxylic dianhydride monomer being 1 equivalent. In some exemplary embodiments, the amino group content of the diamine monomer is 0.7 to 1.5 equivalents, with the anhydride group content of the tetracarboxylic dianhydride monomer being 1 equivalent.

In some embodiments, the solvent component includes an organic solvent with good solubility for the polymer, such as, but not limited to, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylcaprolactam, dimethyl sulfoxide, tetramethylurea, hexamethylphosphamide, γ-butyrolactone, or pyridine, etc., and the above organic solvents may be used alone or in combination. In some embodiments, the solvent component includes organic solvents with poor solubility in the polymer, such as, but not limited to, methanol, ethanol, isopropanol, n-butanol, cyclohexanol, ethylene glycol, ethylene glycol methyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethyl ether, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, tetrahydrofuran, dichloromethane, chloroform, 1,2-dichloroethane, benzene, toluene, xylene, n-hexane, n-heptane, or n-octane, etc., and the above organic solvents can be used alone or in combination. In some embodiments, the solvent component includes the above-mentioned organic solvents with good solubility in the polymer and the above-mentioned organic solvents with poor solubility in the polymer. It should be noted that the terms "better solubility for the polymer" and "poorer solubility for the polymer" are relative concepts. Even organic solvents with poorer solubility for the polymer can still dissolve the polymer.

The dehydration and ring-closing reaction can be carried out by directly heating the reactant (hereinafter referred to as Method 1), or in the presence of a dehydrating agent and a catalyst (hereinafter referred to as Method 2).

Method 1 involves heating the reactants to 50 to 300°C to carry out the dehydration and ring-closing reaction. In some embodiments, the reactants are heated to 100 to 250°C to carry out the dehydration and ring-closing reaction.

Method 2 involves carrying out the dehydration and ring-closing reaction of the reactants at -20 to 150°C in the presence of a dehydrating agent and a catalyst. In some embodiments, the dehydration and ring-closing reaction is carried out at 0 to 120°C. The dehydrating agent is, for example, but not limited to, acid anhydrides such as acetic anhydride, propionic anhydride, or trifluoroacetic anhydride. The amount of the dehydrating agent is adjusted according to the desired ring-closing rate, and the amount ranges, for example, but not limited to, 0.01 to 20 moles per mole of the polymer unit. The catalyst is, for example, but not limited to, tertiary amines such as triethylamine, pyridine, or dimethylpyridine. The amount of catalyst is adjusted according to the amount of dehydrating agent. For every 1 mole of dehydrating agent, the amount of catalyst ranges, for example, but not limited to, 0.01 to 10 moles.

The organic solvent in the liquid crystal alignment agent is, for example but not limited to, diethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylcaprolactam, dimethyl sulfoxide, γ-butyrolactone, γ-butyrolactam, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, or ethylene glycol monobutyl ether, etc., and the above organic solvents can be used alone or in combination. In some embodiments, the organic solvent is a mixed solvent composed of N-methyl-2-pyrrolidone and diethylene glycol monobutyl ether.

The preparation of the liquid crystal alignment agent includes the following steps: dissolving the polymer in the organic solvent. In some embodiments, the solid content of the liquid crystal alignment agent ranges, for example, but not limited to, 1 to 10% by weight.

[Liquid crystal alignment film]

The liquid crystal alignment film of this invention is formed from the liquid crystal alignment agent as described above.

Liquid crystal display (LCD) components

The liquid crystal display element of the present invention includes the liquid crystal alignment film as described above.

The present invention will be further illustrated by the following embodiments, but it should be understood that the embodiments are for illustrative purposes only and should not be construed as limiting the embodiments of the present invention.

[Polymer X1]

According to the types and amounts of diamine monomers and tetracarboxylic dianhydride monomers shown in Table 1, N-methyl-2-pyrrolidone was added to prepare a reactant with a solid content of 15% by weight. The reactant was reacted at room temperature (25°C) for 4 to 6 hours to obtain polymer X1 composed of the units shown in Formula I-2.

[Polymers X2 to X5, Y1 to Y6]

The preparation of polymers X2 to X5 and Y1 to Y6 differs from that of polymer X1 in that the types and amounts of the modified diamine monomer and tetracarboxylic dianhydride monomer are as shown in Table 1.

The weight-average molecular weights of polymers X1 to X5 and Y1 to Y6 were measured using a gel osmosis chromatography (GPC, Waters Corporation, model 2695) and the results are shown in Table 1.

[Implementation Example 1]

Polymer X1 was dissolved in a mixed solvent composed of N-methyl-2-pyrrolidone and diethylene glycol monobutyl ether (the weight ratio of N-methyl-2-pyrrolidone to diethylene glycol monobutyl ether was 7:3) to prepare a polymer solution with a solid content of 5 to 6 wt%. The polymer solution was then stirred and mixed at 25°C for 1 hour to obtain the liquid crystal alignment agent of Example 1.

A rotary coating machine (model RMT-SC150S) is used to uniformly coat the liquid crystal alignment agent onto a glass substrate with an ITO film to form a coating layer. Then, the glass substrate with the coating layer on its surface is placed on a heating plate and baked at 100°C for 1 minute. Next, the glass substrate baked at 100°C is placed in an oven at 230°C and baked for 30 minutes to dry the coating layer and form a thin film with a thickness of 0.06 micrometers to 0.15 micrometers, thus producing a coated glass. Next, the coated glass is irradiated with polarized ultraviolet light with a polarization wavelength of 254 nm, and the irradiation dose of the polarized ultraviolet light is 200 to 400 mJ/ ^cm² . Then, the coated glass irradiated with polarized ultraviolet light is placed in an oven at 230°C and baked for 30 minutes to obtain a liquid crystal alignment substrate. Another liquid crystal alignment film substrate is then prepared using the same steps and conditions.

Next, a frame adhesive is applied to the glass substrate of one liquid crystal alignment film substrate, and a spacer is sprayed onto the glass substrate of the other liquid crystal alignment film substrate. The two liquid crystal alignment film substrates are then assembled with their application directions opposite to each other. Liquid crystal (manufacturer: daxin, model: LC21913) is injected into the gap between the two liquid crystal alignment film substrates and then sealed to obtain a liquid crystal display element. The liquid crystal display element is heated at 105°C for 60 minutes, removed, discharged, and used for subsequent evaluation.

[Implementation Examples 2 to 5, Comparative Examples 1 to 6]

The difference between the preparation of the liquid crystal alignment agents in Examples 2 to 5 and Comparative Examples 1 to 6 and that in Example 1 is that the type of polymer is changed, as shown in Table 2.

The preparation steps of the liquid crystal alignment film and liquid crystal display element in Examples 2 to 5 and Comparative Examples 1 to 6 are the same as those in Example 1.

[Performance Analysis of Liquid Crystal Display Components]

The testing procedures for the following performance analyses are described using the liquid crystal display element of Example 1 as an example. The performance analyses of the other examples and comparative examples are performed according to the same testing procedures.

Voltage retention rate at 60°C: The liquid crystal display element of Example 1 was placed in an oven at 60°C, and an initial voltage of 0.6 Hz and ±5V rectangular wave was applied to the liquid crystal display element. Then, a measured voltage of the liquid crystal display element was measured after 1667 milliseconds of open-circuit operation. The voltage retention rate of the liquid crystal display element was calculated using the following formula: VHR = (V2/V1) × 100%, where V1 is the initial voltage and V2 is the measured voltage.

85/85 Reliability Test: The liquid crystal display element of Example 1 was placed in a dual 85 environment (85°C and 85% relative humidity) for 48 hours, and an initial voltage of 5V, a rectangular wave with a frequency of 0.6Hz and a wave height of ±5V, was applied. Then, a measured voltage of the liquid crystal display element was measured after 1667 milliseconds following an open circuit. The voltage retention rate of the liquid crystal display element in the dual 85 environment was then calculated using the formula described above. If the change in voltage retention rate of the liquid crystal display element in the dual 85°C environment compared to the voltage retention rate in the 60°C environment is less than 5%, it is rated as "excellent"; if the change is between 5% and 10%, it is rated as "medium"; and if the change is greater than 10%, it is rated as "poor".

Pressure cooker reliability test: The liquid crystal display element of Example 1 was placed in a high-temperature and high-pressure environment of 121°C, 100% relative humidity, and 2 atm for 6 hours, and an initial voltage of 5V, a rectangular wave with a frequency of 0.6Hz and a wave height of ±5V was applied. Then, a measured voltage of the liquid crystal display element was measured after 1667 milliseconds of open circuit. The voltage retention rate of the liquid crystal display element under the high-temperature and high-pressure environment was then calculated using the above formula. If the change in voltage retention rate of the liquid crystal display element under high temperature and high pressure environment compared to the change in voltage retention rate under 60°C environment is less than 5%, it is rated as "excellent"; if the change is between 5% and 10%, it is rated as "medium"; and if the change is greater than 10%, it is rated as "poor".

Table 1 Tetracarboxylic dianhydride monomer diamine monomer Weight average molecular weight polymer X1 97 mol% D1 50 mol% D4 + 50 mol% D5 93,000 X2 98 mol% D1 50 mol% D4 + 50 mol% D6 67,000 X3 98 mol% D1 50 mol% D9 + 50 mol% D5 84,000 X4 100 mol% D2 50 mol% D3 + 50 mol% D5 59,000 X5 100 mol% D2 100 mol% D5 48,000 Y1 97 mol% D1 50 mol% D4 + 50 mol% D7 98,000 Y2 97 mol% D1 50 mol% D4 + 50 mol% D8 88,000 Y3 100 mol% D1 50 mol% D4 + 50 mol% D10 36,000 Y4 98 mol% D1 50 mol% D4 + 50 mol% D11 43,000 Y5 100 mol% D2 50 mol% D3 + 50 mol% D7 52,000 Y6 98 mol% D2 100 mol% D7 58,000 D1 indicates (The resulting tetravalent organic group is formula II-1) D2 indicates (The resulting tetravalent organic group is formula II-2) D3 indicates (The resulting divalent organic group is of formula A1) D4 indicates (The resulting divalent organic group is of formula A2) D5 indicates (The resulting divalent organic group is represented by formula III-1) D6 indicates (The resulting divalent organic group is represented by formula III-2) D7 indicates D8 indicates D9 indicates (The resulting divalent organic group is of formula A3) D10 indicates D11 indicates

Table 2 polymer Voltage retention rate (%) in an environment with a temperature of 60℃ 85/85 Reliability Test Pressure cooker reliability test Implementation Examples 1 X1 97.3 Excellent Excellent 2 X2 93.4 Excellent Excellent 3 X3 97.5 Excellent Excellent 4 X4 98.1 Excellent Excellent 5 X5 98.2 Excellent Excellent Comparative example 1 Y1 96.5 middle middle 2 Y2 93.6 inferior inferior 3 Y3 96.8 middle middle 4 Y4 93.9 inferior middle 5 Y5 96.8 middle middle 6 Y6 95.6 middle middle

Referring to Table 2, the liquid crystal display elements of Examples 1 to 5 all achieved "Excellent" evaluation results in the 85/85 reliability test and the pressure cooker reliability test, indicating that the liquid crystal display elements of Examples 1 to 5 have good reliability. Moreover, compared with the liquid crystal display elements of Comparative Examples 1 to 6, the liquid crystal display elements of Examples 1 to 5 have better reliability, indicating that liquid crystal displays including the liquid crystal display elements of Examples 1 to 5 will have a longer service life.

However, the above description is merely an example of the present invention and should not be used to limit the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the patent specification shall still fall within the scope of the present invention.

Claims (14)

A liquid crystal alignment agent comprises: an organic solvent; and a polymer, including at least one of the units shown in Formula I-1 and Formula I-2; Formula I-1 Formula I-2 In this polymer, ^R1 and ^R2 each independently represent tetravalent organic groups, and ^R3 and ^R4 each independently represent divalent organic groups. The tetravalent organic groups include those shown in Formula II, and the divalent organic groups include those shown in Formula III. Formula II Formula III In Formula II, ^R5 to ^R8 each independently represent hydrogen, _CF3 , C1 to C5 alkyl or C1 to C5 alkoxy; in Formula III, ^R9 and ^R10 each independently represent hydrogen, _CF3 , C1 to C20 alkyl, C1 to C20 alkoxy or a monovalent organic group having an aromatic ring. The liquid crystal alignment agent as described in claim 1, wherein in formula III, ^R9 and ^R10 each independently represent hydrogen, _CH3 or _CF3 . The liquid crystal alignment agent as described in claim 2, wherein Formula III is selected from one or more of the divalent organic groups shown in Formulas III-1 to III-3, Formula III-1 Formula III-2 Formula III-3 . The liquid crystal alignment agent as claimed in claim 1, wherein the total amount of ^R3 and ^R4 is 100 mol%, and the divalent organic group represented by Formula III accounts for 5 mol% to 70 mol%. The liquid crystal alignment agent as claimed in claim 1, wherein in formula II, ^R5 to ^R8 each independently represent hydrogen or C1 to C5 alkyl groups. The liquid crystal alignment agent as described in claim 5, wherein Formula II is selected from one or more tetravalent organic groups shown in Formulas II-1 to II-3, Formula II-1 Formula II-2 Formula II-3 . The liquid crystal alignment agent as described in claim 1, wherein the total amount of ^R1 and ^R2 is 100 mol%, and the tetravalent organic group represented by Formula II accounts for 10 mol% to 100 mol%. The liquid crystal alignment agent as described in claim 1, wherein the divalent organic group in the polymer further includes at least one of the divalent organic groups represented by formulas A1 to A5, wherein formula A1 Formula A2 Formula A3 Formula A4 Formula A5 . The liquid crystal alignment agent as described in claim 8, wherein the total amount of ^R3 and ^R4 is 100 mol%, and at least one of the divalent organic groups shown in formulas A1 to A5 accounts for 1 mol% to 80 mol. The liquid crystal alignment agent as described in claim 1, wherein the tetravalent organic group in the polymer further includes at least one of the tetravalent organic groups represented by formulas B1 to B2, wherein formula B1 Formula B2 . The liquid crystal alignment agent as described in claim 10, wherein the total amount of ^R1 and ^R2 is 100 mol%, and at least one of the tetravalent organic groups shown in formulas B1 to B2 accounts for 1 mol% to 60 mol. The liquid crystal alignment agent as described in claim 1, wherein the polymer has a weight-average molecular weight in the range of 1,000 to 1,000,000. A liquid crystal alignment film formed from a liquid crystal alignment agent as described in any one of claims 1 to 12. A liquid crystal display element comprising a liquid crystal alignment film as described in claim 13.