Display panel, liquid crystal orientation agent and preparation method of display panel

Abstract

The invention relates to a display panel, a liquid crystal alignment agent and a preparation method of the display panel. The display panel comprises a first substrate, a second substrate opposite to the first substrate, and a liquid crystal layer clamped between the first substrate and the second substrate, the liquid crystal alignment film is positioned on one side, close to the liquid crystal layer, of the first substrate and / or the second substrate; the liquid crystal alignment film is made of polyimide; the specific side chain group is introduced into the repeating unit of polyimide, so that the alignment uniformity of liquid crystal molecules at different positions can be improved, and the problem of uneven display such as bright spots caused by uneven alignment can be solved.

Description

Technical Field

[0001] The present application relates to the field of display technology, in particular to the field of liquid crystal material technology, and specifically to a display panel, a liquid crystal alignment agent, and a method for preparing the display panel. Background Art

[0002] Liquid Crystal Display (TFT-LCD) has been widely used as a display component for electronic products such as laptops, smart phones, and televisions. Liquid crystal alignment film (Alignment Layer) is one of the important parts, and its function is to control the deflection of liquid crystal molecules in liquid crystal displays.

[0003] The material of the liquid crystal alignment film is the liquid crystal alignment agent, and the matching between the liquid crystal and the liquid crystal alignment agent is the key to the technology. However, the liquid crystal alignment film made of the existing liquid crystal alignment agent will have problems such as residual images or bright spots after the liquid crystal is aligned. Summary of the invention

[0004] The embodiments of the present application provide a display panel, a liquid crystal alignment agent, and a method for preparing the display panel, which can improve the alignment uniformity of liquid crystal molecules at different positions, and further improve the problem of uneven display such as bright spots caused by uneven alignment.

[0005] In order to achieve the above object, according to a first aspect of the present application, a display panel is provided, comprising:

[0006] a first substrate;

[0007] a second substrate, arranged opposite to the first substrate;

[0008] a liquid crystal layer, sandwiched between the first substrate and the second substrate; and

[0009] A liquid crystal alignment film is located on a side of the first substrate and / or the second substrate close to the liquid crystal layer; the material of the liquid crystal alignment film includes a polymer represented by Formula I:

[0010]

[0011] Wherein, R1 represents a tetravalent organic group, and R2 and R3 represent divalent organic groups;

[0012] * indicates the attachment site;

[0013] n represents a positive integer;

[0014] The R2 and / or the R3 are selected from the group represented by formula II:

[0015]

[0016] R4, R5 and R6 are selected from any one of a single bond, an alkyl group, an alkoxy group, a fluoroalkyl group and a fluoroalkoxy group; at least two of R4, R5 and R6 are not selected from a single bond at the same time, and the sum of the number of carbon atoms in R4, the number of carbon atoms in R5 and the number of carbon atoms in R6 is selected from any integer from 2 to 11.

[0017] In some embodiments, R5 is selected from any one of alkoxy, fluoroalkyl and fluoroalkoxy; R6 is selected from any one of alkyl and fluoroalkyl.

[0018] In some embodiments, the group represented by Formula II is selected from at least one of the groups represented by Formula II-1 and Formula II-2:

[0019]

[0020] In some embodiments, the group represented by Formula II is selected from any one or more of the following groups:

[0021]

[0022]

[0023] In some embodiments, R1 is a tetravalent organic group derived from aliphatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride, or aromatic tetracarboxylic dianhydride;

[0024] The R2 is selected from the group represented by Formula II, the R3 is different from the R2, and the R3 is a divalent organic group derived from an aliphatic diamine, an alicyclic diamine or an aromatic diamine.

[0025] In some embodiments, the material of the liquid crystal alignment film includes a polymer represented by Formula I-1 or Formula I-2:

[0026]

[0027] According to a second aspect of the present application, a liquid crystal alignment agent is provided, wherein the material of the liquid crystal alignment agent includes at least one of a polyimide represented by Formula I and a polyamic acid represented by Formula III:

[0028]

[0029] Wherein, R1 represents a tetravalent organic group, and R2 and R3 represent divalent organic groups;

[0030] * indicates the attachment site;

[0031] n represents a positive integer;

[0032] The R2 and / or the R3 are selected from the group represented by formula II:

[0033]

[0034] R4, R5 and R6 are selected from any one of a single bond, an alkyl group, an alkoxy group, a fluoroalkyl group and a fluoroalkoxy group; at least two of R4, R5 and R6 are not selected from a single bond at the same time, and the sum of the number of carbon atoms in R4, the number of carbon atoms in R5 and the number of carbon atoms in R6 is selected from any integer from 2 to 11.

[0035] In some embodiments, the group represented by Formula II is selected from the group represented by Formula II-1 or Formula II-2:

[0036]

[0037] In some embodiments, the group represented by Formula II is selected from any one or more of the following groups:

[0038]

[0039] In some embodiments, R1 is a tetravalent organic group derived from aliphatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride, or aromatic tetracarboxylic dianhydride;

[0040] The R2 is selected from the group represented by Formula II, the R3 is different from the R2, and the R3 is a divalent organic group derived from an aliphatic diamine, an alicyclic diamine or an aromatic diamine.

[0041] In some embodiments, the material of the liquid crystal alignment agent includes at least one of a polyimide represented by Formula I-1, a polyimide represented by Formula I-2, a polyamic acid represented by Formula III-1, and a polyamic acid represented by Formula III-2:

[0042]

[0043] In some embodiments, the liquid crystal alignment agent further includes an organic solvent; the organic solvent includes at least one of N-methylpyrrolidone, N-ethylpyrrolidone, butyl carbonate, diethylene glycol ethyl ether, and diacetone alcohol.

[0044] According to a third aspect of the present application, a method for preparing a display panel is also provided, comprising the following steps:

[0045] providing a first substrate and a second substrate;

[0046] Providing the liquid crystal alignment agent as described above;

[0047] forming a liquid crystal alignment film on the first substrate and / or the second substrate using the liquid crystal alignment agent; and

[0048] The first substrate and the second substrate are arranged in a cell, and a liquid crystal layer is formed between the first substrate and the second substrate; and the liquid crystal alignment film is arranged close to the liquid crystal layer.

[0049] In some embodiments, the liquid crystal alignment agent includes a polyimide represented by Formula I, and the method for preparing the liquid crystal alignment agent includes:

[0050] Adding at least one tetracarboxylic dianhydride and at least one diamine in a preset ratio into a first organic solvent system, and reacting at a preset temperature to obtain a polyamic acid solution;

[0051] Dehydrating and ring-closing the polyamic acid in the polyamic acid solution to obtain a polyimide solution; and

[0052] Extracting polyimide from the polyimide solution, and adding the polyimide into a second organic solvent system to obtain the liquid crystal alignment agent;

[0053] Wherein, the at least one diamine comprises a side chain diamine represented by formula IV:

[0054]

[0055] In some embodiments, the side chain diamine represented by Formula IV is selected from at least one of the diamines represented by Formula IV-1 and Formula IV-2:

[0056]

[0057] In some embodiments, the side chain diamine represented by Formula IV is selected from at least one of the following structural formulas:

[0058]

[0059]

[0060] In some embodiments, in the solution composed of the at least one tetracarboxylic dianhydride and the at least one diamine, the mole percentage of the side chain diamine represented by Formula IV is greater than or equal to 10% and less than or equal to 20%.

[0061] In some embodiments, in the solution of the at least one tetracarboxylic dianhydride and the at least one diamine, the mole percentage of the at least one tetracarboxylic dianhydride is equal to 50%.

[0062] In some embodiments, the at least one tetracarboxylic dianhydride comprises 1,2,3,4-cyclobutanetetracarboxylic dianhydride and the at least one diamine further comprises 4,4'-diaminodiphenylmethane.

[0063] In some embodiments, the first solvent system includes N-methylpyrrolidone; the second organic solvent system includes N-methylpyrrolidone, N-ethylpyrrolidone, butyl carbonate, diethylene glycol ethyl ether and diacetone alcohol.

[0064] In the display panel, liquid crystal alignment agent and display panel preparation method of the embodiments of the present application, since the steric hindrance of the group represented by Formula II is low and the length is appropriate, by introducing the group represented by Formula II into the polyimide represented by Formula I as the side chain of the polyimide, when the polyimide is used as the material of the liquid crystal alignment film, the side chain group represented by Formula II has good support for the liquid crystal molecules in the liquid crystal layer and less disturbance, so that the liquid crystal molecules are evenly distributed on the surface of the liquid crystal alignment film, thereby improving the alignment uniformity of the liquid crystal molecules at different positions, and further improving the display unevenness problems such as bright spots caused by uneven alignment.

[0065] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0067] In order to more completely understand the present application and its beneficial effects, the following description will be given in conjunction with the accompanying drawings, wherein the same figure numbers represent the same parts in the following description.

[0068] Figure 1 is a schematic diagram of a cross-sectional structure of a display panel provided in an embodiment of the present application;

[0069] Figure 2 It is a schematic flow chart of a method for preparing a display panel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0070] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0071] like Figure 1 As shown, the embodiment of the present application provides a display panel 1, which includes a first substrate 2, a second substrate 3, a liquid crystal layer 4 and a liquid crystal alignment film 5; the second substrate 3 is arranged opposite to the first substrate 2, the liquid crystal layer 4 is sandwiched between the first substrate 2 and the second substrate 3, and the liquid crystal alignment film 5 is located on the side of the first substrate 2 and / or the second substrate 3 close to the liquid crystal layer 4. The material of the liquid crystal alignment film 5 includes a polymer represented by Formula I:

[0072]

[0073] Wherein, R1 represents a tetravalent organic group, and R2 and R3 represent divalent organic groups;

[0074] * indicates the attachment site;

[0075] n represents a positive integer;

[0076] R2 and / or R3 are selected from the group represented by formula II:

[0077]

[0078] R4, R5 and R6 are selected from any one of a single bond, an alkyl group, an alkoxy group, a fluoroalkyl group and a fluoroalkoxy group; at least two of R4, R5 and R6 are not selected from a single bond at the same time, and the sum of the number of carbon atoms in R4, the number of carbon atoms in R5 and the number of carbon atoms in R6 is selected from any integer from 2 to 11.

[0079] It can be understood that the polymer represented by Formula I is polyimide. The embodiment of the present application provides a new liquid crystal alignment film 5 material by improving the chemical structure of polyimide, which can improve the distribution uniformity of liquid crystal molecules on the surface of the liquid crystal alignment film 5, thereby improving the problem of uneven display such as bright spots.

[0080] It should be noted that in the embodiments of the present application, It means that the chemical bond can be connected to any connectable carbon atom on the benzene ring.

[0081] In the embodiment of the present application, since the steric hindrance of the group represented by Formula II is low and the length is appropriate, by introducing the group represented by Formula II into the polyimide represented by Formula I as the side chain of the polyimide, when the polyimide is used as the material of the liquid crystal orientation film 5, the side chain group represented by Formula II has good support for the liquid crystal molecules in the liquid crystal layer 4 and less disturbance, so that the liquid crystal molecules are evenly distributed on the surface of the liquid crystal orientation film 5, thereby improving the alignment uniformity of the liquid crystal molecules at different positions, and further improving the display unevenness problems such as bright spots caused by uneven alignment.

[0082] In some embodiments, the liquid crystal alignment film 5 is located on the side of the first substrate 2 and the second substrate 3 close to the liquid crystal layer 4. In other words, the liquid crystal alignment film 5 on the first substrate 2 and the second substrate 3 is made of the same material. This design makes the alignment uniformity of the liquid crystal alignment film 5 on the first substrate 2 and the second substrate 3 consistent, which is conducive to further improving the problem of uneven display such as bright spots.

[0083] In some embodiments, R5 is selected from any one of alkoxy, fluoroalkyl and fluoroalkoxy; R6 is selected from any one of alkyl and fluoroalkyl. In the group represented by Formula II, R5 and cyclohexane constitute the main unit, and the polarity of the group can be changed by introducing fluorine or oxygen into R5, which is beneficial to increase the affinity of liquid crystal; at the same time, R6 constitutes the supporting unit, and when R6 is selected from alkyl, it can provide better support for liquid crystal molecules, and the introduction of fluorine into R6 can further modify the group, so that the liquid crystal molecules are evenly distributed on the surface of the liquid crystal alignment film 5, which is beneficial to improve the liquid crystal alignment effect.

[0084] In some embodiments, R4 is selected from a single bond, but is not limited thereto.

[0085] In some embodiments, the group represented by Formula II is selected from at least one of the groups represented by Formula II-1 and Formula II-2:

[0086]

[0087] In a specific embodiment, the group represented by formula II is selected from any one or more of the following groups:

[0088]

[0089] In a preferred embodiment, the group represented by formula II is selected from at least one of the groups represented by formula II-1. In the group represented by formula II-1, the side chain has better uprightness and more reasonable spatial angle, which is more conducive to improving the alignment effect.

[0090] It should be noted that the polyimide represented by Formula I can be obtained by ring-closing dehydration (imidization) of the polyamic acid represented by Formula III.

[0091]

[0092] It can be understood that the polyamic acid represented by Formula III is obtained by copolymerization of at least one tetracarboxylic dianhydride compound and at least one diamine compound.

[0093] In some embodiments, R1 is a tetravalent organic group derived from aliphatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride, or aromatic tetracarboxylic dianhydride. In other words, R1 is a residue of a tetracarboxylic dianhydride compound. It can be understood that R1 is a structure after decarboxylation of the tetracarboxylic dianhydride compound.

[0094] In some embodiments, specific examples of aliphatic tetracarboxylic dianhydrides include, but are not limited to, butane tetracarboxylic dianhydride. Specific examples of alicyclic tetracarboxylic dianhydrides include, but are not limited to, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentyl acetic dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-8-methyl ... [1,2-c] furan-1,3-dione, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, ethylenediaminetetraacetic dianhydride, cyclopentanetetracarboxylic dianhydride, ethylene glycol bis(anhydrotrimellitate), 1,3-propylene glycol bis(anhydrotrimellitate), p-phenylene bis(trimellitic acid monoester anhydride). Specific examples of the aromatic tetracarboxylic dianhydride include, but are not limited to, pyromellitic dianhydride, 3,3',4,4'biphenyltetracarboxylic dianhydride, 2,2',3,3'biphenyltetracarboxylic dianhydride, 2,3,3',4'biphenyltetracarboxylic dianhydride, 3,3',4,4'benzophenonetetracarboxylic dianhydride, 2,3,3',4'benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride.

[0095] In one specific embodiment, R1 is a cyclobutyl group, and each carbon atom has one attachment site, but is not limited thereto. That is, R1 is a residue of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (abbreviated as CBDA). The chemical structure of 1,2,3,4-cyclobutanetetracarboxylic dianhydride is as follows:

[0096]

[0097] In some embodiments, R2 is selected from the group represented by Formula II, and R3 is different from R2.

[0098] In some embodiments, R3 is a divalent organic group derived from an aliphatic diamine, an alicyclic diamine, or an aromatic diamine. In other words, R3 is a residue of a diamine compound. It can be understood that R3 is a structure after the diamine compound is deaminated.

[0099] In some embodiments, specific examples of aliphatic diamines include, but are not limited to, m-phenylenediamine, 1,3-propylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, and 1,3-bis(aminomethyl)cyclohexane. Specific examples of alicyclic diamines include, but are not limited to, 1,4-diaminocyclohexane and 4,4'-methylenebis(cyclohexylamine). Specific examples of aromatic diamines include, but are not limited to, dodecyloxydiaminobenzene, tetradecyloxydiaminobenzene, pentadecyloxydiaminobenzene, hexadecyloxydiaminobenzene, octadecyloxydiaminobenzene, cholesteryloxydiaminobenzene, cholesteryl diaminobenzoate, cholesteryl diaminobenzoate, lanosteryl diaminobenzoate, 3,6-bis(4-aminobenzoyloxy)cholestane, 3,6-bis(4-aminophenoxy)cholestane, 1,1-bis(4-((aminophenyl)methyl)phenyl)-4-butylcyclohexane, 1, 1-bis(4-((aminophenyl)methyl)phenyl)-4-heptylcyclohexane, 1,1-bis(4-((aminophenoxy)methyl)phenyl)-4-heptylcyclohexane, 1,1-bis(4-((aminophenyl)methyl)phenyl)-4-(4-heptylcyclohexyl)cyclohexane, N-(2,4-diaminophenyl)-4-(4-heptylcyclohexyl)benzamide, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 4-aminophenyl-4'-aminobenzoate, 4,4'-diaminoazobenzene, 1,5-bis( 4-aminophenoxy)pentane, 1,7-bis(4-aminophenoxy)heptane, bis[2-(4-aminophenyl)ethyl]adipic acid, N,N-bis(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,7-diaminofluorene, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 9,9-bis(4-aminophenyl)fluorene, 2,2-bis[4-(4-aminophenoxy) [phenyl] hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-(p-phenylenediisopropylidene)dianiline, 4,4'-(m-phenylenediisopropylidene)dianiline, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 3,6-diaminocarbazole, 2,3-diaminopyridine, 2,6-diaminopyridine, 3,4-diaminopyridine, 2,4-diaminopyrimidine, 2,4-diamino6-hydroxypyrimidine, 2,4-diamino1,3,5-triazine, 2,6-diaminopurine, 3,5-diamino1,3,5-triazole.

[0100] In one embodiment, R3 is a residue of 4,4'-diaminodiphenylmethane (MDA for short). The chemical structure of 4,4'-diaminodiphenylmethane is as follows:

[0101]

[0102] In some embodiments, the material of the liquid crystal alignment film 5 includes a polymer represented by Formula I-1 or Formula I-2:

[0103]

[0104] It can be understood that the polymers represented by formula I-1 and formula I-2 are prepared using CBDA, MDA and a side chain diamine represented by the following structural formula as raw materials:

[0105]

[0106] In some embodiments, the first substrate 2 is an array substrate, and the second substrate 3 is a color filter substrate or an opposing substrate, but is not limited thereto.

[0107] In some embodiments, a support column is further provided on the side of the second substrate 3 facing the first substrate 2 , and the support column extends into the liquid crystal layer 4 , and the liquid crystal alignment film 5 can be arranged avoiding the support portion.

[0108] It can be understood that the embodiment of the present application does not limit the structures of the first substrate 2 and the second substrate 3 .

[0109] In some embodiments, the display panel 1 is a vertical alignment (VA), twisted nematic (TN) or in-plane switching (IPS) type liquid crystal display panel, but is not limited thereto.

[0110] In the embodiment of the present application, since the steric hindrance of the group represented by Formula II is low and the length is appropriate, by introducing the group represented by Formula II into the polyimide represented by Formula I as the side chain of the polyimide, when the polyimide is used as the material of the liquid crystal orientation film 5, the side chain group represented by Formula II has good support for the liquid crystal molecules in the liquid crystal layer 4 and less disturbance, so that the liquid crystal molecules are evenly distributed on the surface of the liquid crystal orientation film 5, thereby improving the alignment uniformity of the liquid crystal molecules at different positions, and further improving the display unevenness problems such as bright spots caused by uneven alignment.

[0111] The embodiment of the present application further provides a liquid crystal alignment agent, wherein the material of the liquid crystal alignment agent includes at least one of a polyimide represented by Formula I and a polyamic acid represented by Formula III:

[0112]

[0113] Wherein, R1 represents a tetravalent organic group, and R2 and R3 represent divalent organic groups;

[0114] * indicates the attachment site;

[0115] n represents a positive integer;

[0116] R2 and / or R3 are selected from the group represented by formula II:

[0117]

[0118] R4, R5 and R6 are selected from any one of a single bond, an alkyl group, an alkoxy group, a fluoroalkyl group and a fluoroalkoxy group; at least two of R4, R5 and R6 are not selected from a single bond at the same time, and the sum of the number of carbon atoms in R4, the number of carbon atoms in R5 and the number of carbon atoms in R6 is selected from any integer from 2 to 11.

[0119] It can be understood that the polyamic acid represented by formula III is a precursor of the polyimide represented by formula I, that is, the polyimide represented by formula I can be obtained by ring-closing dehydration of the polyamic acid represented by formula III.

[0120] In some embodiments, R5 is selected from any one of alkoxy, fluoroalkyl and fluoroalkoxy; R6 is selected from any one of alkyl and fluoroalkyl. In the group represented by Formula II, R5 and cyclohexane constitute the main unit, and the polarity of the group can be changed by introducing fluorine or oxygen into R5, which is beneficial to increase the affinity of liquid crystal; at the same time, R6 constitutes the supporting unit, and when R6 is selected from alkyl, it can provide better support for liquid crystal molecules, and the introduction of fluorine into R6 can further modify the group, so that the liquid crystal molecules are evenly distributed on the surface of the liquid crystal alignment film 5, which is beneficial to improve the liquid crystal alignment effect.

[0121] In some embodiments, R4 is selected from a single bond, but is not limited thereto.

[0122] In some embodiments, the material of the liquid crystal alignment agent may also include an intermediate compound in the imidization process of polyamic acid represented by Formula III, such as compounds represented by Formula V and Formula VI:

[0123]

[0124] In some embodiments, the group represented by Formula II is selected from at least one of the groups represented by Formula II-1 and Formula II-2:

[0125]

[0126] In a specific embodiment, the group represented by formula II is selected from any one or more of the following groups:

[0127]

[0128]

[0129] In a preferred embodiment, the group represented by formula II is selected from at least one of the groups represented by formula II-1. In the group represented by formula II-1, the side chain has better uprightness and more reasonable spatial angle, which is more conducive to improving the alignment effect.

[0130] In some embodiments, R1 is a tetravalent organic group derived from aliphatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride or aromatic tetracarboxylic dianhydride. Examples of aliphatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride and aromatic tetracarboxylic dianhydride can refer to the description of the above embodiments, which will not be repeated here.

[0131] In some embodiments, R2 is selected from the group represented by Formula II, and R3 is different from R2.

[0132] In some embodiments, R3 is a divalent organic group derived from an aliphatic diamine, an alicyclic diamine, or an aromatic diamine. Examples of aliphatic diamines, alicyclic diamines, and aromatic diamines can be found in the description of the above embodiments, and will not be repeated here.

[0133] In one embodiment, R1 is a residue of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA for short), and R3 is a residue of 4,4'-methylenediaminodiphenylmethane (MDA for short).

[0134] For example, the material of the liquid crystal alignment agent includes at least one of the polyimide represented by Formula I-1, the polyimide represented by Formula I-2, the polyamic acid represented by Formula III-1, and the polyamic acid represented by Formula III-2:

[0135]

[0136]

[0137] In some embodiments, the liquid crystal alignment agent further includes an organic solvent; the organic solvent includes at least one of N-methylpyrrolidone (NMP for short), N-ethylpyrrolidone (NEP for short), butyl carbonate (BC for short), diethylene glycol ethyl ether (DEDG for short) and diacetone alcohol (DAA for short), but is not limited thereto.

[0138] In the embodiment of the present application, the solid content of polyimide in the liquid crystal alignment agent and the physical parameters such as the viscosity of the liquid crystal alignment agent can be adjusted by using an organic solvent, which is beneficial to improving the film-forming effect.

[0139] In other embodiments, the organic solvent can also be selected from one or more of N-methyl-2-pyrrolidone, γ-butyrolactone, γ-butyrolactam, N,N-dimethylformamide, N,N-dimethylacetamide, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monomethyl ether, butyl lactate, butyl acetate, methyl methoxypropionate, ethyl ethoxypropionate, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, ethylene glycol-isopropyl ether, ethylene glycol-n-butyl ether (butyl cellosolve), ethylene glycol dimethyl ether, ethylene glycol ethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diisobutyl ketone, isoamyl propionate, isoamyl isobutyrate, diisoamyl ether, ethylene carbonate, and propylene carbonate.

[0140] In some embodiments, the liquid crystal alignment agent may further include additives for further adjusting the physical parameters of the liquid crystal alignment agent so that the film-forming effect meets the requirements.

[0141] In some embodiments, the liquid crystal alignment agent provided in the embodiments of the present application is used to manufacture the liquid crystal alignment film 5 of the display panel 1 described in the aforementioned embodiments. For a specific manufacturing method, refer to the description of the next embodiment.

[0142] In the embodiments of the present application, since the steric hindrance of the group represented by Formula II is low and the length is appropriate, the support for the liquid crystal molecules is good and the disturbance is small. By introducing the group represented by Formula II into the polyimide represented by Formula I and the polyamic acid represented by Formula III, when a liquid crystal alignment film is prepared using a liquid crystal alignment agent containing the polyimide represented by Formula I and / or the polyamic acid represented by Formula III, the obtained liquid crystal alignment film has good support for the liquid crystal molecules in the liquid crystal layer and the disturbance is small, so that the liquid crystal molecules are evenly distributed on the surface of the liquid crystal alignment film, thereby improving the alignment uniformity of the liquid crystal molecules at different positions, and further improving the display unevenness problems such as bright spots caused by uneven alignment.

[0143] Combination Figure 1 and Figure 2 As shown, the embodiment of the present application further provides a method for preparing a display panel 1 , and the preparation method includes steps S201 to S204 .

[0144] S201: providing a first substrate and a second substrate.

[0145] In some embodiments, Figure 1 As shown, the first substrate 2 is an array substrate, and the second substrate 3 is a color filter substrate or an opposing substrate, but is not limited thereto. It can be understood that the structures of the first substrate 2 and the second substrate 3 are not limited in the embodiment of the present application.

[0146] S201: providing a liquid crystal alignment agent; the liquid crystal alignment agent comprises at least one of a polyimide represented by Formula I and a polyamic acid represented by Formula III.

[0147] In some embodiments, the liquid crystal alignment agent includes a polyimide represented by Formula I, and correspondingly, the method for preparing the liquid crystal alignment agent includes:

[0148] Adding at least one tetracarboxylic dianhydride and at least one diamine in a preset ratio into a first organic solvent system, and reacting at a preset temperature to obtain a polyamic acid solution;

[0149] Dehydrating and ring-closing the polyamic acid in the polyamic acid solution to obtain a polyimide solution; and

[0150] extracting polyimide from the polyimide solution, and adding the polyimide to a second organic solvent system to obtain a liquid crystal alignment agent;

[0151] Wherein, at least one diamine comprises a side chain diamine represented by formula IV:

[0152]

[0153] In some embodiments, the side chain diamine represented by Formula IV is selected from at least one of the diamines represented by Formula IV-1 and Formula IV-2:

[0154]

[0155] In some embodiments, the side chain diamine represented by Formula IV is selected from at least one of the following structural formulas:

[0156]

[0157] In some embodiments, in a solution composed of at least one tetracarboxylic dianhydride and at least one diamine, the mole percentage of the side chain diamine represented by Formula IV is greater than or equal to 10% and less than or equal to 20%.

[0158] For example, in a solution of at least one tetracarboxylic dianhydride and at least one diamine, the molar percentage of the side chain diamine represented by formula IV is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0159] In some embodiments, in the solution of the at least one tetracarboxylic dianhydride and the at least one diamine, the mole percentage of the at least one tetracarboxylic dianhydride is equal to 50%.

[0160] In some embodiments, the at least one tetracarboxylic dianhydride comprises 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and the at least one diamine further comprises 4,4'-diaminodiphenylmethane (MDA).

[0161] In a specific embodiment, the raw materials mixed into the first solvent system include a side chain diamine represented by formula IV, CBDA and MDA. The molar percentage of the side chain diamine represented by formula IV in the raw materials is x, the molar percentage of CBDA is 50%, and the molar percentage of MDA is y, x is greater than or equal to 10% and less than or equal to 20%, and y=50%-x.

[0162] In some embodiments, the first solvent system includes N-methylpyrrolidone (NMP for short), and the solid content of NMP in the first solvent system is 30%.

[0163] In one embodiment, the preset temperature is 25° C. It is understandable that the preset temperature can be adjusted according to actual conditions.

[0164] In some embodiments, the process of dehydrating the polyamic acid in the polyamic acid solution to obtain the polyimide solution comprises the following steps:

[0165] Adding NMP to the obtained polyamic acid solution to dilute it to a mass fraction of the polyamic acid of about 6%; and

[0166] Add appropriate amounts of acetic anhydride and pyridine to the diluted polyamic acid solution, and react at 100° C. to obtain a polyimide solution.

[0167] In some embodiments, after acetic anhydride and pyridine are added to the diluted polyamic acid solution, the molar ratio of polyamic acid, acetic anhydride and pyridine is 1:1:0.8, but is not limited thereto.

[0168] It is understandable that the embodiment of the present application uses a catalyst to dehydrate and close the polyamic acid to obtain polyimide. Of course, in other embodiments, dehydration and closing the polyamic acid to obtain polyimide can also be achieved by heating.

[0169] In some embodiments, pyridine may be replaced by other catalysts, and acetic anhydride may be replaced by other anhydride compounds.

[0170] In some embodiments, the method of extracting polyimide from the polyimide solution includes precipitating the polyimide by formaldehyde, but is not limited thereto.

[0171] In some embodiments, the second organic solvent system includes N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), butyl carbonate (BC), diethylene glycol ethyl ether (DEDG) and diacetone alcohol (DAA). In the second organic solvent system, the volume ratio of NMP, NEP, BC, DEDG and DAA is 30:15:35:10:10, but is not limited thereto.

[0172] S203: forming a liquid crystal alignment film on the first substrate and / or the second substrate using a liquid crystal alignment agent.

[0173] In some embodiments, the liquid crystal alignment agent can be coated on the first substrate 2 and / or the second substrate 3 by spin coating, and the coated liquid crystal alignment agent is heated and baked to obtain a liquid crystal alignment film 5 .

[0174] S204: aligning the first substrate and the second substrate, and forming a liquid crystal layer between the first substrate and the second substrate; and arranging a liquid crystal alignment film close to the liquid crystal layer.

[0175] In some embodiments, when the first substrate 2 and the second substrate 3 are arranged in a box, the edge positions between the first substrate 2 and the second substrate 3 are fixedly connected by frame glue.

[0176] In some embodiments, the liquid crystal layer 4 may be formed by a One Drop Fill (ODF) process, but is not limited thereto.

[0177] The embodiments of the present application also provide 1 group of comparative examples and 9 groups of embodiments. By performing continuous lighting comparison on the ten test panels obtained from these embodiments and comparative examples, the effect of the liquid crystal alignment agent provided in the embodiments of the present application on solving the bright spot problem is verified.

[0178] Comparative Example

[0179] (1) Preparation of liquid crystal alignment agent

[0180] The side chain diamine used in the comparative example is 1,3-diamino-4-{4-〔trans-4-(trans-4-n-pentylcyclohexyl)cyclohexyl〕phenoxy}benzene (abbreviated as PBCH5DAB), and its structural formula is as follows:

[0181]

[0182] A three-necked flask is flushed with argon for 15 minutes, with an argon flow rate of 0.1-1 L / min; an NMP solution with a solid content of 30% is added to the three-necked flask, and CBDA, MDA and PBCH5DAB with a molar ratio of 50:20:30 are mixed, and the mixture is reacted at 25°C for 4 hours to obtain a polyamic acid solution; NMP is added to the polyamic acid solution to dilute it to a solid content of about 6%, and then appropriate amounts of acetic anhydride and pyridine catalysts are added to the diluted polyamic acid solution, with a molar ratio of polyamic acid, acetic anhydride and pyridine of 1:1:0.8. After reacting at 100°C for 3 hours, the reaction solution is added to methanol to obtain white polyimide powder; the polyimide powder is added to a mixed solvent of NMP, NEP, BC, DEDG and DAA with a volume ratio of 30:15:35:10:10 to obtain a liquid crystal alignment agent.

[0183] (2) Preparation of liquid crystal alignment film

[0184] The obtained liquid crystal alignment agent was spin-coated on an array substrate with a driving electrode and a color filter substrate with a supporting column, respectively; the array substrate and the color filter substrate coated with the liquid crystal alignment agent were baked on a hot plate at 80°C for 120s, and baked in a hot air circulation oven at 185°C for 1200s to obtain a liquid crystal alignment film of 100nm±5nm.

[0185] (3) Preparation of test panels

[0186] Use a glue coater to apply frame glue doped with 3.6um silicon balls on the periphery of the array substrate, and use a pipette gun to drop 5×5 matrix liquid crystal on the surface of the array substrate; assemble the array substrate and the color filter substrate under a 120℃ hot press for 2 minutes; finally, apply voltage to the two substrates and irradiate ultraviolet (UV) light to complete the orientation, and obtain test panel No. 1.

[0187] Example 1 to Example 9

[0188] Examples 1 to 9 adopt the same preparation process as the comparative example to obtain test panels No. 2 to No. 10 respectively. Unlike the comparative example, the side chain diamine used in Examples 1 to 9 is the structure represented by Formula IV-1-1 provided in the examples of the present application, that is, PBCH5DAB in the comparative example is replaced by the side chain diamine represented by Formula IV-1-1. Therefore, in Examples 1 to 9, when making the polyamic acid solution, the anhydride compound and diamine compound mixed into the NMP solution with a solid content of 30% are the side chain diamine, CBDA and MDA represented by Formula IV-1-1. Moreover, in the mixture of the anhydride compound and the diamine compound, the molar percentage of the side chain diamine represented by Formula IV-1-1 is x, the molar percentage of CBDA is equal to 50%, and the molar percentage of MDA is y, x is greater than or equal to 10% and less than or equal to 20%, and y=50%-x.

[0189] The structural formula of the side chain diamine represented by formula IV-1-1 is as follows:

[0190]

[0191] In Examples 1 to 9, the molar percentages of the diamines represented by Formula IV-1-1 are different from each other. Specifically, in Examples 1 to 9, the molar percentages x of the side chain diamines represented by Formula IV-1-1 are 0.5%, 1%, 3%, 5%, 10%, 15%, 20%, 25% and 30%, respectively. Correspondingly, in Examples 1 to 9, the molar percentages y of MDA are 49.5%, 49%, 47%, 45%, 40%, 35%, 30%, 25% and 20%, respectively.

[0192] Finally, in the embodiment of the present application, a DC voltage of 5V was applied to the test panels No. 1-10 obtained in the comparative example and Examples 1 to 9 for 72 hours of continuous lighting, and then the brightness level of each test panel was determined on the orthogonal polarizers. The results are shown in Table 1.

[0193] Table 1

[0194]

[0195] In Table 1, "×" means poor, that is, more bright spots with larger brightness can be observed under the orthogonal polarizers, indicating that the uniformity of the liquid crystal alignment is poor; "△" means medium, that is, more bright spots with smaller brightness can be observed under the orthogonal polarizers, indicating that the uniformity of the liquid crystal alignment is medium; "○" means good, that is, no bright spots can be observed under the orthogonal polarizers, indicating that the uniformity of the liquid crystal alignment is good.

[0196] As can be seen from Table 1, the liquid crystal alignment film is prepared by using the liquid crystal alignment agent provided in the embodiment of the present application, and in the process of preparing the liquid crystal alignment agent, the molar percentage of the side chain diamine represented by formula IV-1-1 is controlled within the range of 5% to 30%, which can play a certain role in improving the uneven display of bright spots. In addition, in the process of preparing the liquid crystal alignment agent, the molar percentage of the side chain diamine represented by formula IV-1-1 is controlled within the range of 10% to 20%, which can significantly improve the uneven display of bright spots.

[0197] The present application also provides a method for synthesizing the side chain diamine represented by formula IV-1-1. The preparation route of the side chain diamine represented by formula IV-1-1 is as follows:

[0198]

[0199] Synthesis process of intermediate A2:

[0200] Compound A1 (200 mmol) was weighed into a round-bottom flask and replaced by nitrogen (N2) three times. Then, SOCl2 (150 mmol) was added to the round-bottom flask and heated to 80°C under N2 atmosphere and refluxed to obtain compound A2 with a yield of 95%.

[0201] Synthesis process of intermediate A4:

[0202] Place intermediate A2 (190 mmol) in a round-bottom flask, add anisole (120 ml), and place the round-bottom flask in an ice bath to keep the temperature below 18°C; then add compound A3 (200 mmol) to the round-bottom flask and react for 3.5 hours under stirring; then pour the reaction solution into ice water (200 mL), extract the aqueous layer twice with CH2Cl2, wash the organic layer (water, 2% NaOH solution, water) and dry; remove the solvent anisole in vacuum to obtain intermediate A4 with a yield of 73%.

[0203] Synthesis process of compound IV-1-1:

[0204] The intermediate A4 (138 mmol) was added to a round-bottom flask, and DMF was added to dissolve the intermediate A4; SF4 (20 ml / min) was then introduced into the round-bottom flask, the reaction solution was back-extracted with ethyl acetate, and then the extracted reaction solution was washed with a saturated NaCl solution, and the washed reaction solution was dried with Na2SO4; the reaction solution was spin-dried and separated with a silica gel column to obtain compound IV-1-1 with a yield of 83%.

[0205] In the embodiments of the present application, since the steric hindrance of the group represented by Formula II is low and the length is appropriate, by introducing the group represented by Formula II into the polyimide represented by Formula I as the side chain of the polyimide, when the polyimide is used as the material of the liquid crystal orientation film, the side chain group represented by Formula II has good support for the liquid crystal molecules in the liquid crystal layer and less disturbance, so that the liquid crystal molecules are evenly distributed on the surface of the liquid crystal orientation film, thereby improving the alignment uniformity of the liquid crystal molecules at different positions, and further improving the display unevenness problems such as bright spots caused by uneven alignment.

[0206] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0207] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0208] The embodiments, implementation methods and related technical features of the present application can be combined and replaced with each other without conflict.

[0209] The above are only preferred embodiments of the present application and do not constitute any form of limitation to the present application. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application are still within the scope of the technical solution of the present application.

Claims

1. A display panel, characterized in that: include: a first substrate; a second substrate, arranged opposite to the first substrate; a liquid crystal layer, sandwiched between the first substrate and the second substrate; as well as A liquid crystal alignment film is located on a side of the first substrate and / or the second substrate close to the liquid crystal layer; the material of the liquid crystal alignment film includes a polymer represented by Formula I: Wherein, R1 represents a tetravalent organic group, and R2 and R3 represent divalent organic groups; * indicates the attachment site; n represents a positive integer; The R2 and / or the R3 are selected from the group represented by formula II: R4, R5 and R6 are selected from any one of a single bond, an alkyl group, an alkoxy group, a fluoroalkyl group and a fluoroalkoxy group; at least two of R4, R5 and R6 are not selected from a single bond at the same time, and the sum of the number of carbon atoms in R4, the number of carbon atoms in R5 and the number of carbon atoms in R6 is selected from any integer from 2 to 11.

2. The display panel according to claim 1, characterized in that: R5 is selected from any one of alkoxy, fluoroalkyl and fluoroalkoxy; R6 is selected from any one of alkyl and fluoroalkyl.

3. The display panel according to claim 1 or 2, characterized in that: The group represented by formula II is selected from at least one of the groups represented by formula II-1 and formula II-2:

4. The display panel according to claim 3, characterized in that: The group represented by formula II is selected from any one or more of the following groups:

5. The display panel according to claim 1, characterized in that: The R1 is a tetravalent organic group derived from aliphatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride, or aromatic tetracarboxylic dianhydride; The R2 is selected from the group represented by Formula II, the R3 is different from the R2, and the R3 is a divalent organic group derived from an aliphatic diamine, an alicyclic diamine or an aromatic diamine.

6. The display panel according to claim 5, characterized in that: The material of the liquid crystal alignment film includes a polymer represented by Formula I-1 or Formula I-2:

7. A liquid crystal alignment agent, characterized in that: The material of the liquid crystal alignment agent includes at least one of a polyimide represented by Formula I and a polyamic acid represented by Formula III: Wherein, R1 represents a tetravalent organic group, and R2 and R3 represent divalent organic groups; * indicates the attachment site; n represents a positive integer; The R2 and / or the R3 are selected from the group represented by formula II: R4, R5 and R6 are selected from any one of a single bond, an alkyl group, an alkoxy group, a fluoroalkyl group and a fluoroalkoxy group; at least two of R4, R5 and R6 are not selected from a single bond at the same time, and the sum of the number of carbon atoms in R4, the number of carbon atoms in R5 and the number of carbon atoms in R6 is selected from any integer from 2 to 11.

8. The liquid crystal alignment agent according to claim 7, characterized in that: The group represented by formula II is selected from the group represented by formula II-1 or formula II-2:

9. The liquid crystal alignment agent according to claim 8, characterized in that: The group represented by formula II is selected from any one or more of the following groups:

10. The liquid crystal alignment agent according to any one of claims 7 to 9, characterized in that: The R1 is a tetravalent organic group derived from aliphatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride, or aromatic tetracarboxylic dianhydride; The R2 is selected from the group represented by Formula II, the R3 is different from the R2, and the R3 is a divalent organic group derived from an aliphatic diamine, an alicyclic diamine or an aromatic diamine.

11. The liquid crystal alignment agent according to claim 10, characterized in that: The material of the liquid crystal alignment agent includes at least one of the polyimide represented by Formula I-1, the polyimide represented by Formula I-2, the polyamic acid represented by Formula III-1, and the polyamic acid represented by Formula III-2:

12. The liquid crystal alignment agent according to claim 8, characterized in that: The liquid crystal alignment agent further includes an organic solvent; the organic solvent includes at least one of N-methylpyrrolidone, N-ethylpyrrolidone, butyl carbonate, diethylene glycol ethyl ether and diacetone alcohol.

13. A method for preparing a display panel, characterized in that: The following steps are involved: providing a first substrate and a second substrate; Providing a liquid crystal alignment agent according to any one of claims 7 to 12; forming a liquid crystal alignment film on the first substrate and / or the second substrate using the liquid crystal alignment agent; as well as The first substrate and the second substrate are arranged in a cell, and a liquid crystal layer is formed between the first substrate and the second substrate; and the liquid crystal alignment film is arranged close to the liquid crystal layer.

14. The method for manufacturing a display panel according to claim 13, characterized in that: The liquid crystal alignment agent includes a polyimide represented by Formula I, and the method for preparing the liquid crystal alignment agent includes: Adding at least one tetracarboxylic dianhydride and at least one diamine in a preset ratio into a first organic solvent system, and reacting at a preset temperature to obtain a polyamic acid solution; Dehydrating and ring-closing the polyamic acid in the polyamic acid solution to obtain a polyimide solution; and Extracting polyimide from the polyimide solution, and adding the polyimide into a second organic solvent system to obtain the liquid crystal alignment agent; Wherein, the at least one diamine comprises a side chain diamine represented by formula IV:

15. The method for preparing a display panel according to claim 14, characterized in that: The side chain diamine represented by formula IV is selected from at least one of the diamines represented by formula IV-1 and formula IV-2:

16. The method for preparing a display panel according to claim 15, characterized in that: The side chain diamine represented by formula IV is selected from at least one of the following structural formulas:

17. The method for preparing a display panel according to claim 14, characterized in that: In the solution composed of the at least one tetracarboxylic dianhydride and the at least one diamine, the mole percentage of the side chain diamine represented by Formula IV is greater than or equal to 10% and less than or equal to 20%.

18. The method for preparing a display panel according to claim 17, characterized in that: In the solution composed of the at least one tetracarboxylic dianhydride and the at least one diamine, the molar percentage of the at least one tetracarboxylic dianhydride is equal to 50%.

19. The method for preparing a display panel according to claim 14, characterized in that: The at least one tetracarboxylic dianhydride includes 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and the at least one diamine also includes 4,4'-diaminodiphenylmethane.

20. The method for preparing a display panel according to claim 14, characterized in that: The first solvent system includes N-methylpyrrolidone; the second organic solvent system includes N-methylpyrrolidone, N-ethylpyrrolidone, butyl carbonate, diethylene glycol ethyl ether and diacetone alcohol.

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