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

Abstract

The invention provides a liquid crystal alignment agent, a liquid crystal alignment film and a liquid crystal display element, and relates to the technical field of liquid crystal display materials. The liquid crystal aligning agent comprises (a) a polymer, wherein the polymer is selected from one or more of polyamic acid and imidization polymer; (b) a crosslinking agent having one or more groups selected from the group consisting of an epoxy group, a urea group, a hydroxyl group, and a polymerizable unsaturated bond; (c) the low-temperature curing accelerator has a general formula represented by a structural formula (1), in the structural formula (1), R1 and R3 are respectively and independently an amino group, a hydroxyl group, a sulfydryl group, a carboxyl group and a sulfo group, and R2 is a single bond, an unsubstituted or substituted C1-C6 alkyl group, an unsubstituted or substituted C2-C6 alkenyl group, an unsubstituted or substituted C2-C6 alkynyl group, a C3-C8 cycloalkyl group, a C3-C8 cycloalkenyl group, a C1-C6 alkoxy group and a C1-C6 alkylamino group. According to the liquid crystal alignment agent provided by the invention, the release speed of residual charges can be effectively increased, and the hardness of a liquid crystal alignment film is improved.

Description

Technical Field

[0001] This application relates to the field of liquid crystal display materials technology, and in particular to a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element. Background Technology

[0002] In recent years, liquid crystal displays (LCDs) have been widely used in high-precision fields such as aerospace, automotive, and medical applications due to their advantages of low power consumption, ease of miniaturization, and planarization. For LCDs used in these applications, the ability to operate for extended periods in harsh environments is crucial. The liquid crystal alignment layer is one of the key components in the LCD manufacturing process. Its main function is to ensure that liquid crystal molecules are aligned in a specific direction, thereby achieving precise control of the pixels. During the use of an LCD, the hardness of the liquid crystal alignment layer affects the mechanical stability of the panel. If the hardness of the liquid crystal alignment layer formed by the liquid crystal alignment agent is insufficient, it can easily lead to surface scratches and wear, thus affecting the display effect and causing problems such as abnormal display at scratched areas or decreased local contrast.

[0003] Furthermore, with the development of liquid crystal display technology, many problems have arisen during display. For example, when an LCD monitor displays a single image for an extended period and then switches to a new image, the original image may remain in the next image; this phenomenon is known as image retention. Therefore, the liquid crystal alignment film must not only meet certain abrasion resistance requirements but also ensure that the film has a certain charge release capability to quickly dissipate image retention caused by charge accumulation.

[0004] Typically, a high cyclization rate in the liquid crystal alignment film results in greater rigidity and hardness, giving it a certain degree of abrasion resistance and enabling long-term use of liquid crystal display elements in harsh environments. However, the absence of free charge after curing leads to poor electrical properties. Therefore, the traditional design approach for liquid crystal alignment films involves retaining a certain proportion of carboxyl groups after curing to ensure abrasion resistance while dissipating charge. This design requires controlling the cyclization rate of the PI film between 70% and 90% to maintain a balance between abrasion resistance and charge dissipation. With increasingly demanding requirements for end products, traditional liquid crystal alignment films are no longer sufficient. Therefore, we need to ensure sufficient hardness while also possessing excellent charge dissipation capabilities. Summary of the Invention

[0005] This application provides a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element. Since the liquid crystal alignment agent contains a low-temperature curing accelerator with a specific structure, it is beneficial to the transfer of charge in the liquid crystal alignment film, thereby enabling the residual charge accumulated due to DC voltage to be released more quickly, and at the same time improving the hardness of the liquid crystal alignment film.

[0006] In a first aspect, this application provides a liquid crystal alignment agent, comprising:

[0007] (a) A polymer selected from one or more polyamic acids and imidized polymers;

[0008] (b) A crosslinking agent having one or more groups selected from epoxy, urea, hydroxyl, and polymerizable unsaturated bonds;

[0009] (c) A low-temperature curing accelerator, wherein the low-temperature curing accelerator has the general formula represented by structural formula (1),

[0010]

[0011] In the structural formula (1), R1 and R3 are each independently an amino group, a hydroxyl group, a mercapto group, a carboxyl group, and a sulfonic acid group, and R2 is a single bond, an unsubstituted or substituted C1-C6 alkyl group, an unsubstituted or substituted C2-C6 alkenyl group, an unsubstituted or substituted C2-C6 alkynyl group, a C3-C8 cycloalkyl group, a C3-C8 cycloalkenyl group, a C1-C6 alkoxy group, or a C1-C6 alkylamine group. The amount of the low-temperature curing accelerator added is 1-20 parts by mass based on 100 parts by mass of the polymer.

[0012] In one possible implementation, in the structural formula (1), R1 is an amino group or a hydroxyl group, and R3 is a carboxyl group or a sulfonic acid group.

[0013] In one possible implementation, in the structural formula (1), R2 is an unsubstituted C1-C3 alkyl, an unsubstituted C2-C3 alkenyl, an unsubstituted C2-C3 alkynyl, or a C3-C6 cycloalkyl.

[0014] In one possible implementation, the low-temperature curing accelerator is selected from one or more of the following compounds:

[0015]

[0016]

[0017] In one possible implementation, in the structural formula (1), R2 is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclobutyl, dimethylcyclobutyl, or methylcyclopentyl.

[0018] In one possible implementation, the low-temperature curing accelerator is selected from one or more of the following compounds:

[0019]

[0020] In one possible implementation, the amount of the low-temperature curing accelerator added is 1 to 5 parts by weight, based on 100 parts by weight of the polymer added.

[0021] In one possible implementation, the amount of crosslinking agent added is 0.1 to 50 parts by weight, based on 100 parts by weight of the polymer added, and the crosslinking agent is selected from one or more of the following compounds:

[0022]

[0023] Secondly, this application provides a liquid crystal alignment film formed from the liquid crystal alignment agent described in any embodiment of the first aspect.

[0024] Thirdly, this application provides a liquid crystal display element, including the liquid crystal alignment film described in the second aspect.

[0025] In the above technical solution, by adding a low-temperature curing accelerator with a specific structure to the liquid crystal alignment agent, the cyclization rate of polyamic acid can be effectively improved. The imide ring structure in the polyimide molecular chain increases the rigidity of the molecular chain and enhances the intermolecular forces, thereby improving the hardness of the liquid crystal alignment film. Simultaneously, the low-temperature curing accelerator itself can promote charge transfer in the liquid crystal alignment film, allowing residual charges accumulated due to DC voltage to be released more quickly, compensating for the poor electrical performance caused by complete cyclization. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] It should be understood that the term "and / or" as used in this application specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0028] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0029] It should be noted that the following embodiments are examples of this application and are used only to illustrate this application, and are not intended to limit this application. Other combinations and various modifications within the scope of this application are possible without departing from the spirit or scope of this application.

[0030] The liquid crystal alignment agent provided in this application, due to the presence of a low-temperature curing accelerator with a specific structure, can effectively improve the cyclization rate of the liquid crystal alignment film, achieving 100% cyclization. The imide ring structure in the polyimide molecular chain increases the rigidity of the molecular chain and enhances the intermolecular forces, thereby improving the hardness of the liquid crystal alignment film and meeting the requirements for long-term use of liquid crystal display elements in harsh environments. Simultaneously, the low-temperature curing accelerator provided in this application can promote charge transfer in the liquid crystal alignment film, allowing residual charges accumulated due to DC voltage to be released more quickly. This compensates for the poor electrical performance caused by complete cyclization, enabling the liquid crystal alignment film to meet abrasion resistance requirements while possessing a certain charge release capability to quickly dissipate image retention caused by charge accumulation.

[0031] The liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display element provided in this application will be described in detail below.

[0032] The liquid crystal alignment agent provided in this application includes (a) a polymer; (b) a crosslinking agent; and (c) a low-temperature curing accelerator. Each component is described below in turn.

[0033] <(a) Polymer>

[0034] (a) The polymer is a polymer selected from at least one of a polyamic acid obtained by reacting a diamine component with a dianhydride component and a polyimide obtained by imidizing the polyamic acid. (a) The polymer is preferably a polyamic acid.

[0035] As a dianhydride component for obtaining polymer (a), examples include tetracarboxylic acid, tetracarboxylic dianhydride, tetracarboxylic acid dihalide, tetracarboxylic acid dialkyl ester, or tetracarboxylic acid dialkyl ester dihalide, which are collectively referred to as dianhydride components in this invention. The preferred dianhydride component is tetracarboxylic dianhydride as shown in the following structural formula (2).

[0036]

[0037] In structural formula (2), A is a tetravalent organic group. If specific examples are listed, the structures of the following formulas (A-1) to (A-21) can be listed.

[0038]

[0039] In order to further improve the reliability of the obtained liquid crystal alignment film, the dianhydride component is preferably composed only of a structure such as (A-1) to (A-10) or (A-18) to (A-21), and more preferably of a structure shown in (A-1) to (A-5).

[0040] As a diamine component for obtaining polymer (a), it may optionally contain the diamine shown in the following structural formula (3).

[0041]

[0042] In structural formula (3), R3 and R4 each independently represent a hydrogen atom and an alkyl group having 1 to 5 carbon atoms. From the viewpoint of monomer reactivity, R3 and R4 are preferably hydrogen atoms or methyl groups. Furthermore, if the structure of B is shown, the following formulas (B-1) to (B-32) can be listed.

[0043]

[0044] In order to further improve the reliability of the obtained liquid crystal alignment film, the diamine component is preferably composed of only (B-1) to (B-4), (B-11) to (B-16), or (B-25) to (B-34), and more preferably the structure shown in (B-25) to (B-34).

[0045] The polyamic acid used in this application is obtained by reacting a diamine component with a dianhydride component according to a known method. The polyimide precursor used in this application preferably has the structural unit shown in structural formula (4).

[0046]

[0047] In structural formula (4), A comes from structural formula (2), and B comes from structural formula (3). Polyamic acid can be manufactured by reacting dianhydride and diamine in the presence of an organic solvent at -20 to 150°C, preferably at 10 to 100°C, for 2 to 24 hours.

[0048] From the perspective of the solubility of the monomer and (a) polymer, the organic solvent used in the above reaction is preferably N,N-dimethylformamide, N-methyl-2-pyrrolidone, γ-butyrolactone, dimethyl sulfoxide, etc., and one or more of them can be used. From the viewpoint of minimizing polymer precipitation and easily obtaining high molecular weight polymers, the concentration of (a) polymer in the reaction system is preferably 5 to 15% by mass. From the viewpoint of obtaining suitable (a) polymer molecular weight and resin viscosity, the ratio of diamine to dianhydride in the reaction system is 50 to 99.9 mol%, preferably 80 to 99.9 mol%.

[0049] <(b) Crosslinking agent>

[0050] Adding (b) a crosslinking agent is beneficial for improving the hardness and density of the liquid crystal alignment film. The crosslinking agent has one or more groups selected from epoxy, urea, hydroxyl, and polymerizable unsaturated bonds.

[0051] Examples of (b) crosslinking agents with epoxy groups include 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexylcarbamate, di(3,4-epoxycyclohexylmethyl)adipic acid ester, N,N,N',N'-tetragoxypropyl-4,4'-diaminodiphenylmethane, bisphenol A type epoxy resin, bisphenol F type epoxy resin; propylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, glycerol triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, etc.

[0052] Examples of (b) crosslinking agents with urea groups include N,N'-bis(hydroxymethyl)urea, N,N'-bis(methoxymethyl)urea, 2,4-trimethylenebis(2-hydroxyethyl)urea, bis(2-hydroxyethyl)-2,4-trimethyleneurea, bismethoxymethylurea, bishydroxymethylated vinylurea, and monomethoxymethylated vinylurea.

[0053] Examples of (b) crosslinking agents containing hydroxyl groups include ethylene glycol, propylene glycol, neopentyl glycol, hydrogenated bisphenol A, hydrogenated bisphenol F, 4-tert-butylcatechol, 4-acetylcatechol, 3-methoxycatechol, 4-phenylcatechol, N,N,N',N'-tetra(2-hydroxyethyl)hexamethylenediamide, N,N,N',N'-tetra(2-hydroxypropyl)hexamethylenediamide, N-hydroxymethyl (meth)acrylamide, N,N'-bis(2-hydroxypropyl)-3,3',4,4'-dibenzoyldiimide, and 2,2'-oxobis[N-(2-hydroxypropyl)acetamide].

[0054] Examples of (b) crosslinking agents with polymerizable unsaturated bonds include N,N'-bis(2-hydroxypropyl)-2-butenediamide, styrene, divinylbenzene, 4-vinyltoluene, N-vinylcaprolactam, methylenebisacrylamide, N,N-dimethylacrylamide, and N-hydroxymethylacrylamide.

[0055] If the alignment ability of the liquid crystal alignment agent is insufficient, it will lead to poor image retention. In order to further improve the crosslinking density and alignment ability of the obtained liquid crystal alignment film, preferably, (b) the crosslinking agent is selected from one or more of the following compounds:

[0056]

[0057] More preferably, (b) the crosslinking agent is selected from one or more of the following compounds:

[0058]

[0059] Based on 100 parts by weight of polymer (a), the amount of crosslinking agent added is 0.1 to 50 parts by weight. Among them, in order to improve the efficiency of crosslinking reaction and improve the optical performance of product, the amount of crosslinking agent added is preferably 0.1 to 20 parts by weight, more preferably 1 to 15 parts by weight.

[0060] <(c) Low-temperature curing accelerator>

[0061] (c) The low-temperature curing accelerator has the general formula represented by structural formula (1).

[0062]

[0063] In structural formula (1), R1 and R3 are each independently an amino group, hydroxyl group, mercapto group, carboxyl group and sulfonic acid group, and R2 is a single bond, an unsubstituted or substituted C1-C6 alkyl group, an unsubstituted or substituted C2-C6 alkenyl group, an unsubstituted or substituted C2-C6 alkynyl group, a C3-C8 cycloalkyl group, a C3-C8 cycloalkenyl group, a C1-C6 alkoxy group, or a C1-C6 alkylamine group.

[0064] Examples of unsubstituted or substituted C1-C6 alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, tert-pentyl, n-hexyl, isohexyl, and the above groups that are monosubstituted or polysubstituted by fluorine atoms, chlorine atoms, etc.

[0065] Examples of unsubstituted or substituted C2-C6 alkenyl groups include vinyl, propenyl, butenyl, isobutenyl, and hexenyl groups, as well as those mono- or poly-substituted by fluorine or chlorine atoms. Examples of unsubstituted or substituted C2-C6 ynyl groups include ethynyl, propynyl, butynyl, isobutynyl, and hexynyl groups, as well as those mono- or poly-substituted by fluorine or chlorine atoms.

[0066] Examples of C3-C8 cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclobutyl, dimethylcyclobutyl, ethylcyclobutyl, methylcyclopentyl, cycloheptyl, methylcyclohexyl, cyclooctyl, and methylcycloheptyl. Examples of C3-C8 cycloalkenyl groups include cyclopropenyl, cyclobutenyl, cyclopentenyl, methylcyclobutenyl, cyclohexenyl, methylcyclopentenyl, cycloheptenyl, methylcyclohexenyl, cyclooctenyl, and ethylcyclopentenyl.

[0067] Examples of C1-C6 alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, isopentoxy, sec-pentoxy, neopentoxy, tert-pentoxy, hexoxy, and isohexoxy. Examples of C1-C6 alkylamino groups include methylamino, dimethylamino, ethylamino, diethylamino, methylethylamino, n-propylamino, isopropylamino, di-n-propylamino, diisopropylamino, methylpropylamino, n-butylamino, isobutylamino, methylbutylamino, n-pentamino, isopentamino, n-hexylamino, and isohexylamino.

[0068] In order to further improve the charge dissipation capability of the obtained liquid crystal alignment film, preferably, in the structural formula (1), R1 is an amino group or a hydroxyl group, and R3 is a carboxyl group or a sulfonic acid group.

[0069] Since benzoic acid or benzenesulfonic acid groups are highly acidic and can easily reduce the storage stability of liquid crystal alignment agents, inserting other substituents into R3 and the benzene ring can improve stability. For the purpose of improving the storage stability of the obtained liquid crystal alignment agent, preferably, in structural formula (1), R2 is an unsubstituted C1-C3 alkyl, C2-C3 alkenyl, C2-C3 alkynyl, or C3-C6 cycloalkyl group.

[0070] In this application, the low-temperature curing accelerator is selected from one or more of the following compounds:

[0071]

[0072] In a further preferred embodiment, in structural formula (1), R2 is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclobutyl, dimethylcyclobutyl, or methylcyclopentyl.

[0073] Low-temperature curing accelerators are selected from one or more of the following compounds:

[0074]

[0075] In this application, based on 100 parts by weight of polymer (a), the amount of low-temperature curing accelerator added is 1 to 20 parts by weight. To improve the cyclization rate and charge dissipation rate, the amount of low-temperature curing accelerator added is preferably 1 to 10 parts by weight, more preferably 1 to 5 parts by weight. If the amount added is too high, it will reduce the crosslinking density and alignment ability of the liquid crystal alignment agent, resulting in insufficient film hardness and poor image retention. If the amount added is too low, it will cause the cyclization rate of the liquid crystal alignment agent to be lower than expected, resulting in insufficient film hardness and abnormal phenomena such as debris appearing in reliability tests, affecting product quality.

[0076] Solvent

[0077] Organic solvents are preferred as solvents. Specific examples include: N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl sulfone, γ-butyrolactone, 1,3-dimethylimidazolium ketone, 3-methoxy-N,N-dimethylpropaneamide, etc. One solvent or a mixture of two or more can be used as a solvent.

[0078] In addition to the aforementioned organic solvents, liquid crystal alignment agents may also contain solvents used to improve the uniformity of the coating when the liquid crystal alignment agent is applied to the substrate. These solvents typically have lower surface tension compared to the aforementioned organic solvents. Specific examples include ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, ethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol, 1-phenoxy-2-propanol, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol-1-monomethyl ether-2-acetate, propylene glycol-1-monoethyl ether-2-acetate, butyl cellosolve acetate, dipropylene glycol, 2-(2-ethoxypropoxy)propanol, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, and isoamyl lactate. Two or more of these solvents can be used in combination.

[0079] Other components included in the liquid crystal alignment agent, besides those mentioned above, include, for example, antioxidants, metal chelate compounds, curing accelerators, surfactants, fillers, dispersants, and photosensitizers. The proportions of these other components can be appropriately selected based on the specific compound, without compromising the effectiveness of this disclosure.

[0080] Regarding the solid content in the liquid crystal alignment agent (the proportion of the total mass of the components other than the solvent in the liquid crystal alignment agent to the total mass of the liquid crystal alignment agent), from the perspective of film formation quality, it is 0.1 to 20% by mass, such as 1% by mass, 2% by mass, 5% by mass, 10% by mass, 15% by mass or 20% by mass, preferably 1% to 10% by mass.

[0081] Liquid crystal alignment film

[0082] The liquid crystal alignment film is a coating obtained by coating a substrate with the liquid crystal alignment liquid provided in this application and heating it. It is then aligned by brushing or light irradiation, or, in applications such as vertical alignment, it can be prepared without alignment treatment. Preferably, the coating obtained after heating is subjected to light irradiation.

[0083] The substrate is not particularly limited as long as it has high transparency; glass substrates, acrylic substrates, polycarbonate substrates, and other plastic substrates can be used. Furthermore, from the viewpoint of simplifying the process, a substrate with ITO electrodes for liquid crystal driving is preferred. In reflective liquid crystal display elements, if only a single-sided substrate is used, opaque materials such as silicon wafers can be used, and the electrodes can be made of light-reflective materials such as aluminum.

[0084] There are no particular limitations on the coating method; in industry, screen printing, offset printing, flexographic printing, and inkjet printing are commonly used. Other coating methods include dip coating, roller coating, slot coater, and spin coater, which can be used depending on the purpose.

[0085] The purpose of heating is to remove the solvent, specifically at 50–300°C, preferably 80–250°C, to evaporate the solvent and form a coating film. To fully remove the solvent, a programmed temperature rise can be used, such as drying at 50–120°C, preferably 60–90°C, for 1–10 minutes, followed by firing at 150–300°C, preferably 180–250°C, for 5–120 minutes.

[0086] There is no particular limitation on the coating thickness, but the preferred thickness of the coating after firing is 5-300 nm, and more preferably 10-200 nm.

[0087] Liquid crystal display element

[0088] A third aspect of this invention provides a liquid crystal display element comprising a liquid crystal alignment film provided in the second aspect of this invention. It can be obtained by the following method: using the method described above, a substrate with the liquid crystal alignment film of the second aspect of this invention is obtained from the liquid crystal alignment agent provided in the first aspect of this invention; after alignment treatment, a liquid crystal cell is fabricated using a known method, thereby obtaining the liquid crystal display element. Various types of liquid crystal display elements according to this invention, such as twisted nematic (TN), vertical alignment (VA), and horizontal alignment (IPS), can be listed. The liquid crystal display element of this invention is preferably a narrow bezel liquid crystal display element.

[0089] There are no particular limitations on the manufacturing method of the liquid crystal cell. Examples of methods include: for a pair of substrates with a liquid crystal alignment film, with the liquid crystal alignment film surface facing inward, a spacer preferably 1 to 30 μm, more preferably 2 to 10 μm, is sandwiched between them, and then the surrounding area is fixed with an encapsulant, and liquid crystal is injected for encapsulation.

[0090] There are no particular restrictions on the method of liquid crystal encapsulation. Examples include the vacuum method, which involves injecting liquid crystal after depressurizing the liquid crystal cell, and the drop-addition method, which involves adding liquid crystal and then encapsulating it.

[0091] Example

[0092] Hereinafter, examples etc. are given to illustrate the present application, but the present application is not limited by these examples. First, the evaluation methods and test methods in each example and comparative example are described.

[0093] <Pencil hardness>

[0094] Place the liquid crystal alignment film to be tested on the instrument workbench and fix it. Insert the sharpened pencil into the main body hole of the pencil hardness tester, with the pencil edge touching the workbench. Then tighten the screw to lock it and add the required test weight. Set the forward movement speed at about 1 - 5 mm per second. Start from the hardest pencil and draw five 3 - mm - long marks for each level of pencil until a pencil that does not damage the film layer is found. The hardness of this pencil represents the pencil hardness of the measured coating film.

[0095] <DC release>

[0096] The DC release test equipment for liquid crystal display elements is a CA410 color analyzer. The method is as follows: First step, clean the upper and lower surfaces of the test sample with a dust - free cloth, then use a soldering iron and indium wire to weld the three electrodes of the test glass to three wires, connect the wires of the left and right pixels together, and let it stand to eliminate static electricity. Second step, place the sample on the carrier of the equipment, turn on the backlight switch, adjust the angles of the upper and lower polarizers, and adjust the brightness in the black state to the lowest. Third step, then light up the sample with a power supply, apply a bias voltage at half - gray level (23% brightness of the bright state), find the bias voltage vcom when the flicker is the best, then light it up for 5 min at the first - stage half - gray - level voltage, light it up for 60 min with a 1 - V DC voltage added at the second - stage half - gray - level voltage, and light it up for 30 min at the third - stage half - gray - level voltage. Test the brightness changes in each stage, and finally compare the percentage of the remaining brightness at 75 min.

[0097] <Molecular weight determination>

[0098] Use a normal - temperature gel permeation chromatography (GPC) device (Agilent 1260) (manufactured by Agilent Technologies, Inc.) and a column (PLgei 5μm MIXED - C 300*7.5mm) (manufactured by Agilent Technologies, Inc.) to perform the determination in the following manner.

[0099] Column temperature: 50°C

[0100] Eluent: N,N′ - dimethylformamide (as an additive, phosphoric acid / anhydrous crystal (orthophosphoric acid) is 25 mmol / L)

[0101] Flow rate: 1.0 ml / min

[0102] Standard samples for calibration curve preparation: standard polystyrene (molecular weight; approximately 10,000, 20,000, 40,000, 100,000, 200,000 and 400,000) (manufactured by Agilent Technologies).

[0103] <Viscosity Measurement>

[0104] The viscosity of the polymer solution was measured using a DHR1 rheometer (manufactured by TA Instruments, USA) at a sample volume of 0.35 mL, a cone plate (1°, 40 mm), and a temperature of 25°C.

[0105] The embodiments of this application are described in detail below. First, the abbreviations and numbers corresponding to some compounds involved in the embodiments and comparative examples are explained.

[0106] <Dianhydride composition>

[0107] A1:

[0108] A2:

[0109] <Diamine component>

[0110] B1:

[0111] B2:

[0112] B3:

[0113] B4:

[0114] B5:

[0115] B6:

[0116] Solvent

[0117] NMP: N-methyl-2-pyrrolidone

[0118] BCS: Butyl Solvent

[0119] <Polymer>

[0120] Synthesis Example 1 (Synthesis of Polymer a-1)

[0121] Measure 4.762 g (20 mmol) of B1, 5.983 g (20 mmol) of B2, 2.181 g (20 mmol) of B3, 6.423 g (20 mmol) of B4, and 4.002 g (20 mmol) of B5 into a 1000 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube. Add 210.16 g of NMP and stir while introducing nitrogen gas to dissolve the substances. Add 9.800 g (50 mmol) of A1 and 15.501 g (50 mmol) of A2 under water cooling and stirring, then add 227.71 g of NMP. Stir at 25 °C for 6 hours under a nitrogen atmosphere to obtain a polymer a-1 solution (resin solids content 10%, molecular weight 86150, viscosity 183 mPa·s).

[0122] Synthesis Example 2 (Synthesis of Polymer a-2)

[0123] Measure 5.983 g (20 mmol) of B2, 2.181 g (20 mmol) of B3, 6.423 g (20 mmol) of B4, 4.002 g (20 mmol) of B5, and 3.041 g (20 mmol) of B6 into a 1000 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube. Add 194.67 g of NMP and stir while introducing nitrogen gas to dissolve the substances. Add 9.800 g (50 mmol) of A1 and 15.501 g (50 mmol) of A2 under water cooling and stirring, then add 227.71 g of NMP. Stir at 25 °C for 6 hours under a nitrogen atmosphere to obtain a polymer a-2 solution (resin solids content 10%, molecular weight 93245, viscosity 196 mPa·s).

[0124] Crosslinking agent

[0125] All crosslinking agents used in this application are commercially available compounds, and their types and numbers are listed in Table 1 below.

[0126] Table 1. Types and numbers of crosslinking agents

[0127]

[0128] Low-temperature curing accelerator

[0129] All low-temperature curing accelerators used in this application are commercially available compounds, and their types and numbers are listed in Table 2 below.

[0130] Table 2. Types and Numbers of Low-Temperature Curing Accelerators

[0131]

[0132] Example 1

[0133] Take 10.00g of polymer a-1 solution obtained in Synthesis Example 1 and add it to a 50mL Erlenmeyer flask with a stir bar. Add 0.10g of crosslinking agent b-1, 0.10g of low-temperature curing accelerator c-1, 3.8g of NMP and 6g of BCS, and stir at room temperature for 2 hours to obtain liquid crystal alignment agent 1.

[0134] A liquid crystal cell with an IPS-mode liquid crystal display element structure is fabricated. First, a substrate with electrodes is prepared. The substrate is a glass substrate with dimensions of 30mm × 35mm and a thickness of 0.7mm. On the substrate, as the first layer, an ITO electrode constituting the opposing electrode is formed across the entire surface. On the opposing electrode of the first layer, as the second layer, a SiN (silicon nitride) film formed using a CVD method is formed. The SiN film of the second layer has a thickness of 500nm and functions as an interlayer insulating film. On the SiN film of the second layer, as the third layer, a comb-shaped pixel electrode formed by patterning the ITO film is disposed, thereby forming the first pixel and the second pixel. The dimensions of each pixel are approximately 10mm vertically and 5mm horizontally. At this point, the opposing electrode of the first layer and the pixel electrode of the third layer are electrically insulated by the SiN film of the second layer.

[0135] The pixel electrodes of the third layer have a comb-like shape formed by arranging multiple "<" shaped electrode elements with a centrally curved portion. Each electrode element has a width of 10 μm in the width direction, and the spacing between electrode elements is 10 μm. Since the pixel electrodes forming each pixel are composed of multiple "<" shaped electrode elements with a centrally curved portion, the shape of each pixel is not rectangular, but rather has a shape similar to a bold "<" shaped, with the same centrally curved portion as the electrode elements. Furthermore, each pixel is divided vertically by this central curved portion, having a first region above the curved portion and a second region below it.

[0136] When comparing the first and second regions of each pixel, the formation directions of the electrode elements constituting their pixel electrodes are different. That is, taking the direction of the line segment projected onto the substrate by the polarization plane of the polarized ultraviolet light (described later) as a reference, the electrode elements of the pixel electrode are formed at an angle of +10° (clockwise) in the first region of the pixel, and at an angle of -10° (clockwise) in the second region of the pixel. In other words, the first and second regions of each pixel are configured such that the directions of the rotational movement (planar transition) of the liquid crystal induced by applying a voltage between the pixel electrode and the opposing electrode within the substrate surface are opposite to each other.

[0137] Next, liquid crystal alignment agent 1 was applied to the prepared electrode substrate using a coater method. The coated film was then baked at approximately 120°C for 120 seconds to evaporate the solvent, followed by baking at 230°C for 30 minutes to imidize the polyamic acid. Next, the PI film was exposed using an exposure apparatus manufactured by Ushio: APL-L01212S1-AXH01, employing 254nm polarized light perpendicular to the substrate with an integrated light intensity of 400mJ / cm². The exposed film was then baked at 230°C for 30 minutes to evaporate the small molecules that had broken down after exposure, forming liquid crystal alignment film 1.

[0138] In addition, as the opposing substrate, a glass substrate with ITO electrodes formed on the back side and columnar spacers with a height of 4 μm was subjected to alignment treatment in the same manner as described above, resulting in a substrate with a polyimide liquid crystal alignment film 1. A uniformly thick sealant was applied to the substrate by gas extrusion to bond the substrate and seal the liquid crystal; liquid crystal RXA10300 (negative liquid crystal manufactured by Seiji Yonghua Co., Ltd.) was dropped using a high-precision titration device, and the two substrates were bonded together under a pressure of 1 Pa; the sealant in the bonded substrate was irradiated with 365 nm wavelength UV light, with a cumulative light intensity of 10000 mJ / cm2, to cause the photoinitiator to react; the UV-cured substrate was baked at 100°C for 2 hours to fully cure the sealant; IPS mode liquid crystal cell 1 was obtained, and it was placed at 25°C overnight before being used for application evaluation.

[0139] Examples 2-6 & Comparative Examples 1-2

[0140] Examples 2-6 and Comparative Examples 1-2 all provide liquid crystal alignment agents, liquid crystal alignment films and liquid crystal cells. Their preparation methods are roughly the same as those in Example 1, except that the selection and ratio of polymers, crosslinking agents and low-temperature curing accelerators are different. The specific formulations are shown in Table 3.

[0141] Table 3. Composition of liquid crystal alignment agents in Examples 1-6 and Comparative Examples 1-2

[0142]

[0143]

[0144] The liquid crystal alignment films and liquid crystal cells prepared in Examples 1-6 and Comparative Examples 1-2 were evaluated for properties such as pencil hardness and DC release. The results are shown in Table 4.

[0145] Table 4 shows the evaluation results of the liquid crystal alignment films and liquid crystal cells provided in Examples 1-6 and Comparative Examples 1-2.

[0146]

[0147] As shown in Examples 1-6, when R1 is an amino group or a hydroxyl group, and R3 is a carboxyl group or a sulfonic acid group, the pencil hardness and DC release performance of the liquid crystal alignment agent are significantly better compared to when R1 and R3 are independently selected from amino groups, hydroxyl groups, mercapto groups, carboxyl groups, and sulfonic acid groups. Meanwhile, when R2 is a C3-C6 monocycloalkyl group, the DC release performance is even better compared to when R2 is composed of other groups.

[0148] As shown in Comparative Example 1, when using low-temperature curing accelerators with other structures, the residual brightness of the liquid crystal alignment film after DC release is greater than 40%, indicating poor electrical performance. As shown in Comparative Example 2, when no low-temperature curing accelerator is added, the hardness of the liquid crystal alignment film is significantly insufficient, and the residual brightness after DC release is greater than 40%, indicating poor electrical performance.

[0149] Examples 6-12 & Comparative Examples 3-4

[0150] Examples 6-12 and Comparative Examples 3-4 all provide liquid crystal alignment agents, liquid crystal alignment films and liquid crystal cells. Their preparation methods are roughly the same as those in Example 1, except that the selection and ratio of polymers, crosslinking agents and low-temperature curing accelerators are different. The specific formulations are shown in Table 5.

[0151] Table 5. Composition of liquid crystal alignment agents in Examples 6-12 and Comparative Examples 3-4

[0152] polymer Crosslinking agent Low-temperature curing accelerator Example 6 10g a-1 0.10g b-1 0.10g c-6 Example 7 10g a-1 0.10g b-1 0.30g c-6 Example 8 10g a-1 0.10g b-1 0.50g c-6 Example 9 10g a-1 0.10g b-1 1.00g c-6 Example 10 10g a-1 0.10g b-1 2.00g c-6 Example 11 10g a-2 0.10g b-1 0.30g c-6 Example 12 10g a-2 0.10g b-1 0.50g c-6 Comparative Example 3 10g a-1 0.10g b-1 3.00g c-6 Comparative Example 4 10g a-1 0.10g b-1 0.05g c-6

[0153] The liquid crystal alignment films and liquid crystal cells prepared in Examples 6-12 and Comparative Examples 3-4 were evaluated for properties such as pencil hardness and DC release. The results are shown in Table 6.

[0154] Table 6 shows the evaluation results of the liquid crystal alignment films and liquid crystal cells provided in Examples 6-12 and Comparative Examples 3-4.

[0155]

[0156] As shown in Examples 6-12 and Comparative Examples 3-4, when the amount of polymer added is 1-20 parts by mass and the amount of low-temperature curing accelerator added is 100 parts by mass, the pencil hardness of the liquid crystal alignment film is ≥2H and the residual brightness of DC release is less than 28%. When the amount of low-temperature curing accelerator added is 1-5 parts by mass, the pencil hardness of the liquid crystal alignment film is ≥3H. When the amount of low-temperature curing accelerator added is too large, the hardness of the liquid crystal alignment film will decrease significantly. When the amount of low-temperature curing accelerator added is too small, both the hardness and charge release capability of the liquid crystal alignment film will decrease, and the charge release capability will decrease significantly.

[0157] As can be seen from Examples 7-8 and Examples 11-12, when the type of polymer changes, the effect on the hardness and DC release of the liquid crystal alignment film is relatively small.

[0158] Examples 6, 13-18 & Comparative Examples 5-7

[0159] Examples 6, 13-18 and Comparative Examples 5-7 all provide liquid crystal alignment agents, liquid crystal alignment films and liquid crystal cells. Their preparation methods are roughly the same as those in Example 1, except that the selection and ratio of polymers, crosslinking agents and low-temperature curing accelerators are different. The specific formulations are shown in Table 7.

[0160] Table 7. Composition of liquid crystal alignment agents in Examples 6, 13-18 and Comparative Examples 5-7

[0161] polymer Crosslinking agent Low-temperature curing accelerator Example 6 10g a-1 0.10g b-1 0.10g c-6 Example 13 10g a-1 0.10g b-2 0.10g c-6 Example 14 10g a-1 0.10g b-3 0.10g c-6 Example 15 10g a-1 1.00g b-1 0.10g c-6 Example 16 10g a-1 1.50g b-1 0.10g c-6 Example 17 10g a-1 5.00g b-1 0.10g c-6 Example 18 10g a-1 0.01g b-1 0.10g c-6 Comparative Example 5 10g a-1 / 0.10g c-6 Comparative Example 6 10g a-1 0.10g b-4 0.10g c-6 Comparative Example 7 10g a-1 8.00g b-1 0.10g c-6

[0162] The liquid crystal alignment films and liquid crystal cells prepared in Examples 6, 13-18 and Comparative Examples 5-7 were evaluated for properties such as pencil hardness and DC release. The results are shown in Table 8.

[0163] Table 8 Evaluation results of the liquid crystal alignment films and liquid crystal cells provided in Examples 6, 13-18 and Comparative Examples 5-7

[0164]

[0165]

[0166] Examples 6 and 13-14 show that when the crosslinking agent has one or more groups selected from epoxy, urea, hydroxyl, and polymerizable unsaturated bonds, the pencil hardness of the liquid crystal alignment film is ≥2H, and the residual brightness released by DC is less than 28%. When the crosslinking agent is a compound with a b-1 or b-2 structure, the hardness of the liquid crystal alignment film is better. Comparative Examples 5 and 6 show that when crosslinking agents with other structures are used or no crosslinking agent is added, the hardness of the liquid crystal alignment film is poor, only 1H.

[0167] As shown in Examples 6 and 15-18, when the amount of polymer added is 100 parts by mass and the amount of crosslinking agent added is 0.1-50 parts by mass, the pencil hardness of the liquid crystal alignment film is ≥2H. When the amount of crosslinking agent added is 1-15 parts by mass, the pencil hardness of the liquid crystal alignment film is ≥3H, and the charge dissipation performance is excellent. As shown in Comparative Example 7, when the amount of crosslinking agent added is too high, the hardness and charge dissipation performance of the liquid crystal alignment film are both poor.

[0168] Although the embodiments of this application have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for this application. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, this application is not limited to the specific details and embodiments shown and described herein.

Claims

1. A liquid crystal alignment agent, characterized in that, include: (a) A polymer selected from one or more polyamic acids and imidized polymers; (b) A crosslinking agent having one or more groups selected from epoxy, urea, hydroxyl, and polymerizable unsaturated bonds; (c) A low-temperature curing accelerator, said low-temperature curing accelerator having the general formula represented by structural formula (1), In the structural formula (1), R1 and R3 are each independently an amino group, a hydroxyl group, a mercapto group, a carboxyl group, and a sulfonic acid group, and R2 is a single bond, an unsubstituted or substituted C1-C6 alkyl group, an unsubstituted or substituted C2-C6 alkenyl group, an unsubstituted or substituted C2-C6 alkynyl group, a C3-C8 cycloalkyl group, a C3-C8 cycloalkenyl group, a C1-C6 alkoxy group, or a C1-C6 alkylamine group. The amount of the low-temperature curing accelerator added is 1-20 parts by mass based on 100 parts by mass of the polymer.

2. The liquid crystal alignment agent according to claim 1, characterized in that, In the structural formula (1), R1 is an amino group or a hydroxyl group, and R3 is a carboxyl group or a sulfonic acid group.

3. The liquid crystal alignment agent according to claim 1, characterized in that, In the structural formula (1), R2 is an unsubstituted C1-C3 alkyl, an unsubstituted C2-C3 alkenyl, an unsubstituted C2-C3 alkynyl, or a C3-C6 cycloalkyl.

4. The liquid crystal alignment agent according to any one of claims 1 to 3, characterized in that, The low-temperature curing accelerator is selected from one or more of the following compounds:

5. The liquid crystal alignment agent according to claim 4, characterized in that, In the structural formula (1), R2 is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclobutyl, dimethylcyclobutyl, or methylcyclopentyl.

6. The liquid crystal alignment agent according to claim 5, characterized in that, The low-temperature curing accelerator is selected from one or more of the following compounds:

7. The liquid crystal alignment agent according to any one of claims 1 to 3, characterized in that, Based on 100 parts by weight of the polymer, the amount of the low-temperature curing accelerator added is 1 to 5 parts by weight.

8. The liquid crystal alignment agent according to any one of claims 1 to 3, characterized in that, Based on 100 parts by weight of the polymer, the amount of the crosslinking agent added is 0.1 to 50 parts by weight, and the crosslinking agent is selected from one or more of the following compounds:

9. A liquid crystal alignment film, characterized in that, Formed from the liquid crystal alignment agent according to any one of claims 1 to 8.

10. A liquid crystal display element, characterized in that, Includes the liquid crystal alignment film as described in claim 9.

Images