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

Abstract

The invention relates to the technical field of LCD material display application, in particular to a liquid crystal orientation agent, a liquid crystal orientation film and a liquid crystal display element. The liquid crystal aligning agent comprises a polyimide precursor and / or polyimide obtained by imidizing the polyimide precursor, and the polyimide precursor is obtained by carrying out polymerization reaction on a diamine monomer and a dianhydride monomer and reacting with an end-capping reagent, wherein the diamine monomer comprises at least one of o-phenylenediamine and m-phenylenediamine and p-phenylenediamine; the ratio of the molar weight of the p-phenylenediamine to the total molar weight of the o-phenylenediamine and the m-phenylenediamine is (990-999): (1-10). According to the invention, p-phenylenediamine is taken as a main diamine monomer, at least one of o-phenylenediamine and m-phenylenediamine is combined, and the end-capping reagent is adopted for end capping, so that the molecular weight can be obviously regulated, and the flowability of the whole orientation agent is improved by utilizing the rigidity of a para-position structure and the adjustment of a meta-position or large-volume structure on free volume and chain piling.

Description

Technical Field

[0001] This invention relates to the field of LCD material display technology, specifically to a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element. Background Technology

[0002] Liquid crystal display (LCD) elements are now widely used to achieve thin and light display devices. LCD devices typically consist of liquid crystal, a liquid crystal alignment film, electrodes, and a substrate. The liquid crystal alignment film, used to control the alignment of liquid crystal molecules, is widely used, and polyimide-based liquid crystal alignment films are commonly employed. The alignment process for liquid crystal alignment films typically involves applying pressure and rubbing the surface of the film with a cloth made of raw materials such as rayon. While this friction alignment process can be performed with simple equipment and yields effective and excellent results, the friction debris generated during the process pollutes the environment and causes display defects. Therefore, photo-alignment methods are widely used.

[0003] Liquid crystal alignment film materials typically use polyimide (PI), which is generally obtained by imidizing polyamide acid (PAA), a component included in liquid crystal alignment agents. In the polyamide acid system, it is mainly obtained by polymerization of acid anhydrides and diamines. How to control the molecular weight of the entire polyimide system to obtain polyimide alignment agents with higher fluidity is a technical problem in this field. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element. By using p-phenylenediamine, o-phenylenediamine and / or m-phenylenediamine are introduced, enabling the liquid crystal alignment agent to combine the processability, thermal stability, and alignment capability of various diamines.

[0005] The present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a liquid crystal alignment agent comprising a polyimide precursor and / or a polyimide obtained by imidizing the polyimide precursor, wherein the polyimide precursor is obtained by polymerizing a diamine monomer and a dianhydride monomer and reacting with an end-capping agent, wherein: the diamine monomer comprises at least one of o-phenylenediamine and m-phenylenediamine and p-phenylenediamine; the ratio of the molar amount of p-phenylenediamine to the total molar amount of o-phenylenediamine and m-phenylenediamine is (990~999):(1~10).

[0007] Furthermore, the capping agent includes any one of 4-chloroaniline, 4-fluoroaniline, and aniline.

[0008] Furthermore, the ratio of the molar amount of p-phenylenediamine, the total molar amount of o-phenylenediamine and m-phenylenediamine, and the molar amount of the capping agent is (990~999):(1~10):1.

[0009] Furthermore, the polyimide precursor is represented by structural formula 1:

[0010]

[0011] Structural Formula 1

[0012] Where X1 is X2 is X3 is W is , , Any one of them; Y is a divalent organic group, Ar is a tetravalent organic group; d:a=(1~9):1, a:(b+c) = (990~999):(1~10), b and c are not both 0.

[0013] Furthermore, Ar is selected from at least one of the following structures:

[0014] .

[0015] Furthermore, Y is selected from at least one of the following structures:

[0016]

[0017] Secondly, the present invention also provides a liquid crystal alignment film, which is obtained by coating and baking the above-mentioned liquid crystal alignment agent.

[0018] Thirdly, the present invention also provides a liquid crystal display element, including the liquid crystal alignment film described above.

[0019] The liquid crystal alignment agent of the present invention uses p-phenylenediamine combined with at least one of o-phenylenediamine and m-phenylenediamine as a diamine monomer, and is end-capped with an end-capping agent. This allows for significant molecular weight control, and by utilizing the rigidity of the para structure and the adjustment of free volume and chain stacking by the meta or large volume structure, the overall flowability of the alignment agent is improved, enabling the liquid crystal alignment agent to take into account the processability, thermal stability and alignment ability of various diamines. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] This invention provides a liquid crystal alignment agent, comprising a polyimide precursor and / or a polyimide obtained by imidizing the polyimide precursor, wherein the polyimide precursor is obtained by polymerizing a diamine monomer and a dianhydride monomer and reacting with an end-capping agent, wherein: the diamine monomer comprises at least one of o-phenylenediamine and m-phenylenediamine and p-phenylenediamine; the molar ratio of the p-phenylenediamine to the total molar ratio of the o-phenylenediamine and m-phenylenediamine is (990~999):(1~10).

[0022] The liquid crystal alignment agent of the present invention uses p-phenylenediamine combined with at least one of o-phenylenediamine and m-phenylenediamine as a diamine monomer, and is end-capped with an end-capping agent. This allows for significant molecular weight control, and improves the overall flowability of the alignment agent by utilizing the rigidity of the para structure and the adjustment of free volume and chain stacking by the meta or large volume structure.

[0023] This invention utilizes p-phenylenediamine as the main component, supplemented by o-phenylenediamine and m-phenylenediamine. The two amino groups of p-phenylenediamine are located at the para-position of the benzene ring, forming a rigid structure that can form a high-strength, symmetrical polymer backbone with acid anhydrides. In liquid crystal alignment agents, the polymer backbone formed by p-phenylenediamine exhibits high regularity and linearity, which is beneficial for achieving uniform alignment in photoalignment processes, inducing ordered liquid crystal arrangement, and providing stable liquid crystal alignment capability. The rigid structure imparts a high glass transition temperature (Tg) and thermal decomposition temperature. The dense molecular chain packing and low polarity contribute to a low dielectric constant. However, p-phenylenediamine suffers from poor solubility, limiting processability and resulting in a brittle film.

[0024] This invention addresses the defects of p-phenylenediamine in alignment agents by introducing small amounts of o-phenylenediamine and / or m-phenylenediamine. In o-phenylenediamine and m-phenylenediamine, the two amino groups are located in an asymmetric structure. The flexible and irregularly bent polymer chain segments formed with acid anhydrides enhance the solubility of the alignment agent in organic solvents, facilitating coating. Simultaneously, due to steric hindrance, o-phenylenediamine and m-phenylenediamine can appropriately reduce reactivity, thus regulating molecular weight. However, o-phenylenediamine and m-phenylenediamine also have their own drawbacks. Due to the flexibility and irregularity of the chain segments, the alignment order of the formed liquid crystal alignment film is relatively low, which may lead to a small or unstable liquid crystal pretilt angle. The flexible chains also cause a decrease in glass transition temperature and thermal stability.

[0025] Therefore, by limiting the molar ratio of p-phenylenediamine to o-phenylenediamine and / or m-phenylenediamine, the present invention enables the liquid crystal alignment agent to take into account the processability, thermal stability and alignment ability of the three diamines, thereby achieving the optimal performance of the liquid crystal alignment agent.

[0026] Specifically, in some embodiments of the present invention, the capping agent includes any one of 4-chloroaniline, 4-fluoroaniline, and aniline. The introduction of amino and halogen groups into the capping agent, on the one hand, due to its high electronegativity, can increase the dipole-dipole interactions between polymer chains and liquid crystal molecules, theoretically improving the stability of the alignment film and its anchoring ability to liquid crystal molecules; on the other hand, its moderate reactivity allows for effective and controllable termination of polymerization, resulting in a polymer with a more uniform molecular weight distribution.

[0027] Specifically, in some embodiments of the present invention, the molar ratio of the p-phenylenediamine, the total molar amount of the o-phenylenediamine and m-phenylenediamine, and the molar amount of the capping agent is (990~999):(1~10):1. Excessive use of the capping agent will result in an excessively low molecular weight, potentially leading to insufficient film strength.

[0028] Specifically, in some embodiments of the present invention, the diamine monomer further includes at least one of the compounds in Table 1:

[0029] Table 1

[0030] Compound 1-1 Compounds 1-2 Compounds 1-3 Compounds 1-4 Compounds 1-5 Compounds 1-6 Compounds 1-7 Compounds 1-8 Compounds 1-9 Compounds 1-10 Compounds 1-11 Compounds 1-12 Compounds 1-13 Compounds 1-14 Compounds 1-15 Compounds 1-16 Compounds 1-17 Compounds 1-18 Compounds 1-19 Compounds 1-20

[0031] Specifically, in some embodiments of the present invention, the dianhydride monomer includes at least one of the compounds in Table 2:

[0032] Table 2

[0033] Compound 2-1 Compound 2-2 Compounds 2-3 Compounds 2-4 Compounds 2-5 Compounds 2-6 Compounds 2-7 Compounds 2-8 Compounds 2-9 Compound 2-10 Compound 2-11 Compound 2-12

[0034] Specifically, in some embodiments of the present invention, the polyimide precursor is represented by structural formula 1:

[0035]

[0036] Structural Formula 1

[0037] Where X1 is X2 is X3 is W is , , Any one of them; Y is a divalent organic group, Ar is a tetravalent organic group; d:a=(1~9):1, a:(b+c) = (990~999):(1~10), b and c are not both 0.

[0038] Specifically, in some embodiments of the present invention, Ar is selected from at least one of the following structures:

[0039] .

[0040] Specifically, in some embodiments of the present invention, Y is selected from at least one of the following structures:

[0041]

[0042] Specifically, as one embodiment of the present invention, the preparation method of the polyimide precursor is as follows: under room temperature and nitrogen protection conditions, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, ... , Dissolve in an organic solvent, then add The mixture is stirred continuously for 3-12 hours to obtain the polyimide precursor.

[0043] Specifically, as one embodiment of the present invention, the above-mentioned organic solvents are not particularly limited as long as they can dissolve the generated polyimide precursor. Examples include: N,N-dimethylformamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethyl sulfone, pyridine, isopropanol, diethylene glycol dimethyl ether, ethylene glycol butyl ether, n-hexane, methyl acetate, etc. These organic solvents can be used alone or in combination.

[0044] The present invention also provides a liquid crystal alignment film, which is obtained by coating and baking the above-mentioned liquid crystal alignment agent.

[0045] The present invention also provides a liquid crystal display element, including the above-described liquid crystal alignment film.

[0046] The liquid crystal alignment agent of the present invention will be further described below with reference to specific embodiments.

[0047] Example 1

[0048] The preparation method of the polyimide precursor in this embodiment is as follows:

[0049] Take 5.3107 g (21.7 mmol) under nitrogen protection at room temperature. (Compounds 1-17) 1.5593 g (14.42 mmol) p-phenylenediamine, 3.918 mg (0.0362 mmol) o-phenylenediamine, 3.918 mg (0.0362 mmol) m-phenylenediamine, and 1 mg (0.01 mmol) aniline were dissolved in 85 g NMP (N-methyl-2-pyrrolidone). After stirring until the solid was completely dissolved, 8.1221 g (36.2 mol) dimethylcyclobutanetetracarboxylic anhydride was added. (Compound 2-2), after continuous stirring for 6 hours, a polyimide precursor with a solid content of 15% can be obtained.

[0050] Examples 2-23 and Comparative Examples 1-3

[0051] Examples 2-23 and Comparative Examples 1-3 are basically the same as Example 1, except that the content and / or type of each component are different. See Tables 3-6 for details.

[0052] Test method:

[0053] 1. Leveling performance test

[0054] The synthesized polyimide precursor was adjusted to a solid content of 5.0±0.1% and a viscosity of 25±1cp by adding solvent. The solvent system contained NMP (N-methyl-2-pyrrolidone) and BC (ethylene glycol monobutyl ether) in a ratio of 70:30. Then, the leveling performance was evaluated.

[0055] As mentioned above, the viscosity, solid content, and solvent system of the polyimide precursors in each embodiment and comparative example are quite similar. By applying oscillation or shear at different rates using a rotational rheometer, the viscoelastic nature of the material is revealed, which is the key to evaluating the influence of polymer structure.

[0056] The equipment used is Anton Paar MCR302e. The specific testing method is as follows: The sample to be tested is subjected to static or centrifugation treatment to ensure that the sample is free of air bubbles. The equipment is turned on and the system is preheated for 15-30 minutes. The rotor is selected as a conical plate, the temperature is set to 25℃, the oscillation frequency is 1Hz, the strain range is from 0.1% to 100%, logarithmic scan is selected, and 3-5 points are selected for each order of magnitude. After the test starts, the equipment will record the stress response of the sample, thereby calculating the loss modulus (G", representing viscosity).

[0057] It measures a material's ability to "dissipate" energy (converting it into heat) through internal friction during flow. The higher the G, the more "liquid-like" the material is, and the greater the flow resistance.

[0058] According to the test results, a loss modulus G" ≤ 0.08 Pa indicates good fluidity, while a value greater than this indicates poor fluidity.

[0059] 2. Coating performance test

[0060] The liquid crystal alignment agents prepared in each example and comparative example were coated onto glass plates, dried under vacuum at 80-100°C to remove the solvent, then purged with nitrogen and heated to 230°C for 30 minutes to obtain liquid crystal alignment films. The coating performance of the liquid crystal alignment films prepared in each example and comparative example was tested.

[0061] The Young's modulus test method refers to the national standard GB / T 25898-2010 "Instrumented Nanoindentation Test Method for Indentation Hardness and Elastic Modulus of Thin Films". The indentation depth should not exceed 1 / 10 of the film thickness.

[0062] A membrane strength E value > 5.5 GPa indicates excellent membrane strength; a membrane strength E value of 4.5 GPa ≤ E ≤ 5.5 GPa indicates good membrane strength; and a value below 4.5 GPa indicates poor membrane strength.

[0063] Table 3 shows the relevant parameters and test results for Examples 1-6, Examples 22-23, and Comparative Examples 1-4. The difference between Examples 2-6, Examples 22-23, and Comparative Examples 1-4 and Example 1 lies in the relevant parameters in the table, mainly involving the molar values ​​of p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, other diamines, dianhydrides, and capping agents.

[0064] Table 3

[0065] Group molar value of p-phenylenediamine (mmol) molar value of o-phenylenediamine (mmol) molar value of m-phenylenediamine (mmol) The ratio of the molar amount of p-phenylenediamine to the total molar amount of o-phenylenediamine and m-phenylenediamine. Other types of diamines and their molar values ​​(mmol). Types and molar values ​​(mmol) of dianhydrides Types and molar values ​​(mmol) of capping agents The ratio of the molar amount of p-phenylenediamine, the total molar amount of o-phenylenediamine and m-phenylenediamine, to the molar amount of the capping agent. Loss modulus G (Pa) Thin film strength E (GPa) Example 1 14.42 0.0362 0.0362 995:5 21.7 36.2 0.01 995:5:1 0.04 7.2 Example 2 9.92 0.04 0.04 992:8 2 12 0.01 992:8:1 0.03 6.8 Example 3 4.95 0.025 0.025 990:10 1 6 0.005 990:10:1 0.04 7.0 Example 4 19.98 0.01 0.01 999:1 2 22 0.02 999:1:1 0.02 6.2 Example 5 9.92 0.08 0 992:8 2 12 0.01 992:8:1 0.01 7.3 Example 6 9.92 0 0.08 992:8 2 12 0.01 992:8:1 0.03 6.9 Example 7 9.92 0 0.08 992:8 2 12 0.04 992:8:4 0.04 5.0 Example 8 9.92 0 0.08 992:8 2 12 0.10 992:8:10 0.03 4.5 Comparative Example 1 9.92 0 0 / 2 12 0.01 / 0.14 6.8 Comparative Example 2 0 0.04 0 / 2 12 0.01 / 0.02 3.7 Comparative Example 3 0 0 0.04 / 2 12 0.01 / 0.03 3.9 Comparative Example 4 9.88 0.06 0.06 988:12 2 12 0.01 988:12:1 0.03 4.2

[0066] As can be seen from the test results of Examples 1-6 and Comparative Examples 1-4 in Table 3, this invention, by combining p-phenylenediamine with o-phenylenediamine and / or m-phenylenediamine, can fully utilize the interaction between different diamines. By leveraging the rigidity of the para-position structure and the adjustment of free volume and chain stacking by the meta-position or large-volume structure, an orientation agent with good flowability can be obtained. Furthermore, by employing a p-phenylenediamine-dominant composition with o-phenylenediamine and m-phenylenediamine as auxiliary components, when the molar ratio of p-phenylenediamine to the total molar ratio of o-phenylenediamine and m-phenylenediamine is (990~999):(1~10), the advantages of various diamines can be fully utilized, and their respective defects can be neutralized, resulting in optimal flowability of the liquid crystal orientation agent. If the content of p-phenylenediamine is too low, it will result in insufficient rigidity, small molecular weight, and low strength of the liquid crystal alignment agent. If only p-phenylenediamine is used, the polymer backbone formed by p-phenylenediamine and acid anhydride has strong rigidity and symmetrical structure, resulting in poor flowability. If only o-phenylenediamine or m-phenylenediamine is used, the flexible segments will improve the flowability of the liquid crystal alignment agent, but the molecular weight is small, the film strength is low, and the overall performance of the alignment agent is poor.

[0067] As can be seen from the test results of Examples 1-6 and Examples 7-8, when the molar ratio of p-phenylenediamine to the total molar ratio of o-phenylenediamine and m-phenylenediamine is (990~999):(1~10), the liquid crystal alignment agent exhibits good leveling properties. When the molar ratio of p-phenylenediamine, the total molar ratio of o-phenylenediamine and m-phenylenediamine, and the molar ratio of the end-capping agent is further satisfied to (990~999):(1~10):1), a liquid crystal alignment film with superior film strength can be obtained. Furthermore, by controlling the amount of end-capping agent, a polymer with a more uniform molecular weight distribution can be obtained. Excessive use of end-capping agent will result in an excessively low molecular weight, leading to reduced film strength.

[0068] Table 4 shows the relevant parameters and test results for Examples 2 and 9-15. The difference between Examples 9-15 and Example 2 lies in the relevant parameters in the table, which mainly involve the types of other diamines.

[0069] Table 4

[0070] Group Other types of diamines Loss modulus G (Pa) Thin film strength E (GPa) Example 2 Compounds 1-17 0.03 6.8 Example 9 Compound 1-1 0.03 6.5 Example 10 Compounds 1-2 0.04 6.3 Example 11 Compounds 1-5 0.02 7.0 Example 12 Compounds 1-6 0.03 6.9 Example 13 Compounds 1-12 0.01 7.1 Example 14 Compounds 1-13 0.02 7.2 Example 15 Compounds 1-15 0.03 6.7

[0071] As shown in Table 4, when the diamine monomer contains at least one of o-phenylenediamine and m-phenylenediamine and p-phenylenediamine, and satisfies the ratio of the molar amount of p-phenylenediamine to the total molar amount of o-phenylenediamine and m-phenylenediamine is (990~999):(1~10), introducing different other diamines as diamine monomers can yield polyimide precursors with good flowability, indicating that different other diamine monomers have universality for the liquid crystal alignment agent of the present invention.

[0072] Table 5 shows the relevant parameters and test results for Examples 2 and 16-19. The difference between Examples 16-19 and Example 2 lies in the relevant parameters in the table, which mainly involve the types of dianhydride monomers.

[0073] Table 5

[0074] Group Types of dianhydrides Loss modulus G (Pa) Thin film strength E (GPa) Example 2 Compound 2-2 0.03 6.8 Example 16 Compound 2-1 0.03 6.5 Example 17 Compounds 2-5 0.02 7.0 Example 18 Compounds 2-8 0.04 6.8 Example 19 Compound 2-11 0.03 6.4

[0075] As shown in Table 5, when the diamine monomer contains at least one of o-phenylenediamine and m-phenylenediamine and p-phenylenediamine, and satisfies the ratio of the molar amount of p-phenylenediamine to the total molar amount of o-phenylenediamine and m-phenylenediamine is (990~999):(1~10), different dianhydride monomers can be introduced to obtain polyimide precursors with good flowability, indicating that different dianhydride monomers have universality for the liquid crystal alignment agent of the present invention.

[0076] Table 6 shows the relevant parameters and test results for Examples 2 and 20-23. The difference between Examples 20-23 and Example 2 lies in the relevant parameters in the table, mainly involving the type of capping agent.

[0077] Table 6

[0078] Group Types of capping agents Loss modulus G (Pa) Thin film strength E (GPa) Example 2 aniline 0.03 6.8 Example 20 4-Chloroaniline 0.04 6.7 Example 21 4-Fluoroaniline 0.01 6.9 Example 22 3-Aminophenylacetylene 0.07 6.4 Example 23 3-Aminostyrene 0.08 6.6

[0079] As shown in Table 6, when the diamine monomer contains at least one of o-phenylenediamine and m-phenylenediamine and p-phenylenediamine, and the molar ratio of p-phenylenediamine to the total molar ratio of o-phenylenediamine and m-phenylenediamine is (990~999):(1~10), polyimide precursors with good flowability can be obtained by using different end-capping agents. Preferably, any one of 4-chloroaniline, 4-fluoroaniline, and aniline is used as the end-capping agent. The introduction of amino and halogen groups in the end-capping agent can improve the stability of the alignment film and its anchoring ability to liquid crystal molecules. Moreover, moderate reactivity helps to obtain polymers with more uniform molecular weight distribution, resulting in better flowability of the alignment agent and improved performance of the alignment agent.

[0080] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A liquid crystal alignment agent, characterized in that, The invention comprises a polyimide precursor and / or a polyimide obtained by imidizing the polyimide precursor, wherein the polyimide precursor is obtained by polymerizing a diamine monomer and a dianhydride monomer and reacting with an end-capping agent, wherein: the diamine monomer comprises at least one of o-phenylenediamine, m-phenylenediamine and p-phenylenediamine; and the ratio of the molar amount of p-phenylenediamine to the total molar amount of o-phenylenediamine and m-phenylenediamine is (990~999):(1~10).

2. The liquid crystal alignment agent according to claim 1, characterized in that, The capping agent includes any one of 4-chloroaniline, 4-fluoroaniline, and aniline.

3. The liquid crystal alignment agent according to claim 1, characterized in that, The ratio of the molar amount of p-phenylenediamine, the total molar amount of o-phenylenediamine and m-phenylenediamine, and the molar amount of the capping agent is (990~999):(1~10):

1.

4. The liquid crystal alignment agent according to any one of claims 1-3, characterized in that, The polyimide precursor is represented by structural formula 1: Structural Formula 1 Where X1 is X2 is X3 is W is , , Any one of them; Y is a divalent organic group, Ar is a tetravalent organic group; d:a=(1~9):1, a:(b+c) = (990~999):(1~10), b and c are not both 0.

5. The liquid crystal alignment agent according to claim 4, characterized in that, Ar is selected from at least one of the following structures: 。 6. The liquid crystal alignment agent according to claim 4, characterized in that, Y is selected from at least one of the following structures:

7. A liquid crystal alignment film, characterized in that, It is obtained by coating and baking the liquid crystal alignment agent according to any one of claims 1-6.

8. A liquid crystal display element, characterized in that, Includes the liquid crystal alignment film as described in claim 7.

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