Diamine compound, polyamic acid, liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display panel

Abstract

The application provides a diamine compound, a polyamide acid, a liquid crystal alignment agent, a liquid crystal alignment film and a liquid crystal display panel, which can improve the anchoring effect on liquid crystal molecules and realize stable alignment control of the liquid crystal molecules. The diamine compound provided by the application has a structure as shown in formula 1.

Description

Technical Field

[0001] This application relates to the field of display technology, specifically to a diamine compound, polyamic acid, liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display panel. Background Technology

[0002] Thin-film transistor liquid crystal displays (TFT-LCDs) are widely used as display components in electronic products such as laptops, smartphones, and televisions. The alignment layer is a crucial component, responsible for controlling the orientation of the liquid crystal molecules within the display.

[0003] Liquid crystal alignment film materials typically use polyimide (PI), which is generally obtained by imidizing polyamide acid (PAA) included in the liquid crystal alignment agent. To achieve stable alignment of liquid crystal molecules with the liquid crystal alignment film, the liquid crystal alignment film material needs to have a strong anchoring ability for the liquid crystal molecules to maintain a stable relationship between them.

[0004] However, existing liquid crystal alignment film materials have a relatively weak anchoring ability for liquid crystal molecules. This makes the liquid crystal molecules prone to alignment abnormalities when a subsequent electric field is applied. When the liquid crystal display switches to a new display screen, a residual image of the previous display can be observed with the naked eye, causing image retention. Therefore, the anchoring ability of existing liquid crystal alignment film materials for liquid crystal molecules still needs improvement. Summary of the Invention

[0005] In view of this, this application provides a diamine compound, polyamic acid, liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display panel, which can enhance the anchoring effect on liquid crystal molecules, thereby achieving stable alignment of liquid crystal molecules and improving the display image retention problem caused by abnormal liquid crystal molecule alignment.

[0006] This application provides a diamine compound having the structure shown in Formula 1:

[0007]

[0008] Where A is selected from any one of the structures shown in A1 to A3:

[0009]

[0010] * indicates AND The site of connection;

[0011] Selected from phenylene or cyclohexylene, m is 1 to 3;

[0012] C is selected from a straight-chain alkyl group with 1 to 15 carbon atoms or a straight-chain alkyl group with -CH2- at both ends replaced by -O-.

[0013] In one embodiment of this application, Select from any of the structures shown in B1 to B7:

[0014]

[0015] Here, # represents the site connected to C.

[0016] In one embodiment of this application, the diamine compound has a structure as shown in Formula 2-1 or 2-2:

[0017]

[0018] In one embodiment of this application, the diamine compound is selected from compounds with the following structure:

[0019]

[0020] This application provides a polyamic acid having repeating units with the structure shown in Formula 3:

[0021]

[0022] Each of R1 is independently selected from hydrogen atoms or alkyl groups with 1 to 10 carbon atoms;

[0023] R2 is independently selected from hydrogen atom, alkyl group of 1 to 10 carbon atoms, alkenyl group of 1 to 10 carbon atoms or alkynyl group of 1 to 10 carbon atoms;

[0024] Y is selected from divalent organic groups, including Y1, which has the structure shown in Formula 4:

[0025]

[0026] Where A is selected from any one of the structures shown in A1 to A3:

[0027]

[0028] * indicates AND The site of connection;

[0029] Selected from phenylene or cyclohexylene, m is 1 to 3;

[0030] C is selected from a straight-chain alkyl group with 1 to 15 carbon atoms or a straight-chain alkyl group with the methylene groups at both ends replaced by -O-.

[0031] X is selected from tetravalent organic groups, including structures as shown in Formula 5 and / or Formula 6:

[0032]

[0033] Ar1 is selected from aromatic rings with 6 to 10 ring atoms or aliphatic rings with 4 to 10 ring atoms;

[0034] D is selected from single bond,

[0035] In one embodiment of this application, Select from any of the structures shown in B1 to B7:

[0036]

[0037] Here, # represents the site connected to C.

[0038] In one embodiment of this application, Y1 has a structure as shown in Formula 7-1 and / or Formula 7-2:

[0039]

[0040] In one embodiment of this application, Y1 is selected from the structure shown below:

[0041]

[0042] In one embodiment of this application, Y further includes Y2, which is selected from one or more of the following structures:

[0043]

[0044] In this context, ## represents a site that connects to an adjacent structure.

[0045] In one embodiment of this application, the molar ratio of Y1 to Y2 is 1:1 to 1:9.

[0046] In one embodiment of this application, X includes one or more of the following structures:

[0047]

[0048] This application provides a liquid crystal alignment agent, including the polyamic acid described in the above embodiments.

[0049] This application provides a liquid crystal alignment film, which is prepared from the liquid crystal alignment agent described in the above embodiments.

[0050] This application also provides a liquid crystal display panel, including the liquid crystal alignment film described in the above embodiments.

[0051] The diamine compound provided in this application has a structure as shown in Formula 1, wherein the introduced B part is a structure with biphenyl or polycyclic aliphatic rings, which can increase the matching degree with the biphenyl or polycyclic aliphatic ring structures in liquid crystal molecules and enhance the π-π interaction between them; the introduced C part is an alkyl chain or an alkyl chain structure containing diether bonds, which can form van der Waals forces with the alkyl chain at one end of the liquid crystal molecule. Therefore, the diamine compound provided in this application, and the polyamic acid synthesized from the diamine compound and the dianhydride compound, can form a stronger interaction with liquid crystal molecules. When used as a liquid crystal alignment film material, it can enhance the anchoring effect on liquid crystal molecules, achieve stable alignment control of liquid crystal molecules, and thus improve the display retention problem caused by abnormal liquid crystal molecule alignment. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the structure of the liquid crystal display panel provided in the embodiments of this application.

[0053] Figure 2 This is a schematic diagram of the black and white checkerboard test screen of the liquid crystal display panel provided in the embodiments of this application when evaluating the image retention characteristics. Detailed Implementation

[0054] This application provides a diamine compound, polyamic acid, a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display panel. Various embodiments of the invention are described in the form of a range only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the invention. Therefore, the description of the range includes all possible sub-ranges as well as single numerical values ​​within that range. For example, it should be considered that a range description from 1 to 6 specifically discloses sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6. Furthermore, numerical ranges herein include any referenced numbers (fractions or integers) within the referred range.

[0055] In this invention, "alkyl" includes "straight-chain alkyl" and "branched-chain alkyl," which refer to monovalent groups obtained by removing one hydrogen atom from a straight-chain alkane molecule and a branched-chain alkane molecule, respectively. Specific examples of straight-chain alkyl include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and n-nonyl; specific examples of branched-chain alkyl include, but are not limited to, isopropyl, isobutyl, sec-butyl, tert-butyl, 2-ethylbutyl, 3,3-dimethylbutyl, isopentyl, neopentyl, tert-pentyl, 1-methylpentyl, 3-methylpentyl, 2-ethylpentyl, 4-methyl-2-pentyl, 1-methylhexyl, 2-ethylhexyl, 2-butylhexyl, 1-methylheptyl, 2,2-dimethylheptyl, 2-ethylheptyl, tert-octyl, 2-ethyloctyl, and 3,7-dimethyloctyl.

[0056] In this invention, alkenyl can be exemplified by replacing one or more CH2-CH2 structures present in the aforementioned alkyl group with C=C structures. More specifically, specific examples of alkenyl include, but are not limited to, vinyl, allyl, 1-propenyl, isopropenyl, 2-butenyl, 1,3-butadienyl, 2-pentenyl, 2-hexenyl, cyclopropenyl, cyclopentenyl, and cyclohexenyl.

[0057] In this invention, the alkynyl group can be exemplified by replacing one or more CH2-CH2 structures present in the aforementioned alkyl group with C≡C structures. More specifically, specific examples of the alkynyl group include, but are not limited to, ethynyl, 1-propynyl, and 2-propynyl.

[0058] In this invention, "ring atom number" refers to the total number of atoms constituting the ring itself in a compound obtained by atomic bonding to form a ring. For example, benzene has 6 ring atom numbers, naphthalene has 10 ring atom numbers, and thiophene has 5 ring atom numbers.

[0059] In this invention, "aromatic ring" may include monoaromatic ring, polyaromatic ring or fused aromatic ring. Specific examples of monoaromatic ring include, but are not limited to, phenyl. Specific examples of polyaromatic ring include, but are not limited to, biphenyl. Specific examples of fused aromatic ring include, but are not limited to, naphthyl and anthracene.

[0060] In this invention, "aliphatic ring" may include cycloalkanes, cyclomonoenes, or non-aromatic cyclopolyenes. Specific examples of cycloalkanes include, but are not limited to, cyclopropane, cyclobutane, cyclopentane, and cyclohexane. Cyclomonoenes may be exemplified by replacing one CH2-CH2 structure present in the aforementioned cycloalkanes with a C=C structure. Non-aromatic cyclopolyenes may be exemplified by replacing two or more CH2-CH2 structures present in the aforementioned cycloalkanes with C=C structures to obtain non-aromatic cyclopolyenes.

[0061] In this invention, This indicates that the chemical bond can be connected to any connectable carbon atom on the benzene ring.

[0062] This application provides a diamine compound having the structure shown in Formula 1:

[0063]

[0064] Where A is selected from any one of the structures shown in A1 to A3:

[0065]

[0066] * indicates AND The linking site. The A portion of the diamine compound provided in this application is a linker with an amide bond, a carbamate bond, or a urea bond. Under the synergistic effect of the polar part of the amide bond, carbamate bond, or urea bond and the interchain hydrogen bond built by this part, the diamine compound provided in this application can exhibit enhanced electronic conductivity. When the polyamic acid synthesized by it and the dianhydride compound is used as a liquid crystal alignment film material, it has excellent charge accumulation and release capabilities.

[0067] Selected from phenylene or cyclohexylene, m is 1 to 3.

[0068] In one embodiment of this application, Select from any of the structures shown in B1 to B7:

[0069]

[0070] Wherein, # represents the site connected to C. The diamine compound provided in this application introduces a B-moment with a biphenyl or polycyclic structure, which can increase the matching degree with the biphenyl or polycyclic structure in the liquid crystal molecule and enhance the π-π interaction between them. At the same time, the introduced B-moment is selected with a fully para-substituted structure in order to obtain good orientation consistency of the liquid crystal molecule.

[0071] C is selected from a straight-chain alkyl group with 1 to 15 carbon atoms or a straight-chain alkyl group with -CH2- at both ends replaced by -O-.

[0072] In one embodiment of this application, C is selected from the structure shown as C1 or C2:

[0073]

[0074] Wherein, n is 1 to 9. The diamine compound provided in the embodiments of this application introduces an alkyl chain or an alkyl chain structure containing a double ether bond as its C part, which can form van der Waals forces with the alkyl chain at one end of the liquid crystal molecule to enhance the intermolecular interaction between the diamine compound molecule and the liquid crystal molecule.

[0075] Therefore, by introducing the B and C parts into the molecular structure, the diamine compound provided in this application can form a stronger interaction with liquid crystal molecules.

[0076] In one embodiment of this application, the amino group on one side of the diamine compound forms a para- or meta-substitution with the C moiety on the benzene ring, resulting in better alignment consistency of the liquid crystal molecules. Specifically, the diamine compound has a structure as shown in Formula 2-1 or 2-2:

[0077]

[0078] One embodiment of this application provides a polyamic acid synthesized from a diamine compound and a dianhydride compound, having repeating units with the structure shown in Formula 3:

[0079]

[0080] Each of R1 is independently selected from hydrogen atoms or alkyl groups with 1 to 10 carbon atoms;

[0081] R2 is independently selected from hydrogen atom, alkyl group of 1 to 10 carbon atoms, alkenyl group of 1 to 10 carbon atoms or alkynyl group of 1 to 10 carbon atoms;

[0082] Y is a divalent organic group derived from diamine compounds, including Y1, which has the structure shown in Formula 4:

[0083]

[0084] Where A is selected from any one of the structures shown in A1 to A3:

[0085]

[0086] * indicates AND The site of connection;

[0087] Selected from phenylene or cyclohexylene, m is 1 to 3;

[0088] C is selected from a straight-chain alkyl group with 1 to 15 carbon atoms or a straight-chain alkyl group with methylene groups at both ends replaced by -O-.

[0089] As previously mentioned, by introducing the B and C parts in the molecular structure, the compound molecules can form a stronger interaction with the liquid crystal molecules. Therefore, the polyamic acid provided in this application embodiment can be used as a liquid crystal alignment film material and has a stronger anchoring effect on liquid crystal molecules, achieving a more stable alignment of liquid crystal molecules.

[0090] X is a tetravalent organic group derived from a tetracarboxylic acid derivative, including structures as shown in Formula 5 and / or Formula 6:

[0091]

[0092] Ar1 is selected from aromatic rings with 6 to 10 ring atoms or aliphatic rings with 4 to 10 ring atoms;

[0093] D is selected from single bond, In one embodiment of this application, Select from any of the structures shown in B1 to B7:

[0094]

[0095] Here, # represents the site connected to C.

[0096] In one embodiment of this application, Y1 is selected from the structures shown in Formula 7-1 and / or Formula 7-2:

[0097]

[0098] In one embodiment of this application, Y further includes Y2, which is selected from one or more of the following structures:

[0099]

[0100] Wherein, ## represents a site connected to an adjacent structure. In one embodiment, for consideration of liquid crystal orientation, Y2 is selected from at least two of the above structures.

[0101] In one embodiment of this application, the molar ratio of Y1 to Y2 in the polyamic acid ranges from 1:1 to 1:9. Within this range, the molar ratio of Y1 to Y2 in the polyamic acid enhances the anchoring effect of the polyamic acid on the liquid crystal molecules while simultaneously satisfying its requirements for liquid crystal orientation.

[0102] In one embodiment of this application, X includes one or more of the following structures:

[0103]

[0104] In one embodiment of this application, X is selected from 2 to 5 of the above structures, taking into account the liquid crystal orientation and photoalignment response sensitivity.

[0105] One embodiment of this application provides a liquid crystal alignment agent, comprising the polyamic acid described in the above embodiments.

[0106] In one embodiment of this application, the liquid crystal alignment agent further includes a solvent, wherein the mass fraction of the solute in the liquid crystal alignment agent is 1% to 10%. The solvents used include, but are not limited to, one or more of the following: 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.

[0107] One embodiment of this application provides a liquid crystal alignment film, which is prepared from the liquid crystal alignment agent described in the above embodiments. The liquid crystal alignment film includes polyimide, which can be obtained by imidization of polyamic acid as described in the above embodiments, that is, by dehydrating the amino and carboxyl groups in the repeating unit shown in Formula 3 to form an imide ring.

[0108] One embodiment of this application also provides a liquid crystal display panel, including the liquid crystal alignment film described in the above embodiments. For example... Figure 1 As shown, the liquid crystal display panel 100 includes a first substrate 11, a second substrate 15, liquid crystal molecules 13 located between the first substrate 11 and the second substrate 15, a liquid crystal alignment film 12 disposed on the first substrate 11, and a liquid crystal alignment film 14 disposed on the second substrate 15. The first substrate 11 may be an array substrate, which may include multiple scan lines, multiple data lines, multiple thin-film transistors, and multiple pixel electrodes disposed on the substrate. The second substrate 15 may be a color filter substrate, which may include a color filter, a black matrix, and an electrode layer disposed on the substrate. The driving method of the liquid crystal molecules 13 in the liquid crystal display panel 100 may be in-plane switching (IPS), fringe field switching (FFS), twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), etc.

[0109] Since the liquid crystal alignment agent contains the polyamic acid provided in the foregoing embodiments of this application, the anchoring effect of the liquid crystal alignment film formed using the liquid crystal alignment agent on the liquid crystal molecules in the liquid crystal display panel is enhanced, thereby achieving stable alignment of liquid crystal molecules and improving the image retention problem of the liquid crystal display panel caused by abnormal alignment of liquid crystal molecules.

[0110] The following specific embodiments illustrate the diamine compound, polyamic acid, liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display panel of this application.

[0111] Example 1: Synthesis of diamine compound 1

[0112]

[0113] Step 1: Synthesis of A2

[0114]

[0115] A1: 61.74 g (0.33 mol) of 4'-amino-4-biphenyl was dissolved in 244 g of tetrahydrofuran (THF). 1.66 g (0.165 mol) of triethylamine was added dropwise to the solution, followed by 0.33 mol of BOC-anhydride (72.75 g) at 0–5 °C. The mixture was stirred continuously for 6 hours. Excess solvent was removed by vacuum distillation. Ethyl acetate was added to the remaining solution, and the mixture was washed twice with water. The residue was chromatographically analyzed using a silica gel column (dichloromethane / hexane, 6:4). The product was added to ethanol, recrystallized, filtered, and dried to obtain product A2.

[0116] The NMR characterization results are as follows: 1 H NMR (500MHz, DMSO-d6) δ9.47(s,1H),8.67(s,1H),7.65(d,J=8.4Hz,2H),7.59(d,J=8.4Hz,2H),7.48(d,J=8.8Hz,2H),6.89–

[0117] 6.83 (m, 2H), 1.43 (s, 10H).

[0118] Step 2: Synthesis of A3

[0119]

[0120] 28.5 g (0.1 mol) of tert-butyl (4'-hydroxy-[1,1'-biphenyl]-4-yl)carbamate, 27.4 g (0.1 mol) of 1-(4-bromobutoxy)-4-nitrobenzene, and 13.82 g (0.1 mol) of potassium carbonate were dissolved in a mixed solvent of 130 ml toluene and 360 ml N,N-dimethylacetamide (DMAc). After removing water and toluene at 130 °C, the temperature was raised to 160 °C and reacted for 2 hours. Then, the temperature was cooled to 80 °C, and the solvent was removed by vacuum distillation. The residue was washed with water and extracted with dichloromethane. The extract was dried with magnesium sulfate to remove the solvent. The product was then chromatographically analyzed by silica gel column chromatography (dichloromethane / hexane, 6:4), recrystallized in ethanol solution, filtered, and dried to obtain product A3.

[0121] The NMR characterization results are as follows: 1 H NMR(500MHz,DMSO-d6)δ8.67(s,1H),8.19–8.13(m,2H),7.65(d,J=8.3Hz,2H),7.62–7.56(m,4H),7.12 (d,J=8.5Hz,2H),7.02–6.96(m,2H),4.05(td,J=5.2,4.8,2.7Hz,4H),1.95–1.86(m,4H),1.43(s,10H).

[0122] Step 3: A4 Synthesis

[0123]

[0124] 23.9 g (0.05 mol) of intermediate product A3 was added to 100 g of THF and stirred until dissolved. Then, 30 ml of dioxane hydrochloride solution was added to the solution and the mixture was stirred for 4 hours. The temperature was set to 20 °C and excess solvent was removed by rotary evaporation. 150 g of THF was added to the residue, and the pH was adjusted to 7 by adding saturated sodium bicarbonate. The mixture was stirred for another hour, then extracted and separated to obtain the crude product. The crude product was then recrystallized in ethanol solution, filtered, and dried to obtain product A4.

[0125] The NMR characterization results are as follows: 1 H NMR (500MHz, DMSO-d6) δ8.16(d,J=8.4Hz,2H),7.59(d,J=8.3Hz,2H),7.46(d,J=8.1Hz,2H),7.12(d,J=8.3Hz, 2H), 6.99 (d, J = 8.4Hz, 2H), 6.70 (d, J = 8.1Hz, 2H), 5.36 (s, 2H), 4.05 (qt, J = 3.5, 2.2Hz, 4H), 1.95–1.86 (m, 4H).

[0126] Step 4: A5 synthesis

[0127]

[0128] Dissolve 11.3 g (0.03 mol) of A4 in 36 ml of DMAc, then add 2.37 g (0.03 mol) of pyridine dropwise and stir until homogeneous. Add 5.56 g (0.03 mol) of 4-nitrobenzoyl chloride at room temperature, stir for 4 hours, then rinse in water, filter out the solid, wash with dilute hydrochloric acid and water, and dry under vacuum to obtain the crude product. Further recrystallize and purify in glacial acetic acid, filter, and dry to obtain product A5.

[0129] The NMR characterization results are as follows: 1 H NMR (500MHz, DMSO-d6) δ9.68(s,1H),8.34(d,J=8.4Hz,2H),8.19(d,J=8.6Hz,2H),7.73(d,J=8.3Hz,2H),7.65(d,J=8.3Hz,2H),7.59(d ,J=8.3Hz,2H),7.02–6.96(m,2H),6.71(d,J=8.5Hz,2H),6.53(d,J=8.5Hz,2H),4.71(s,2H),4.05(h,J=3.7Hz,4H),1.95–1.86(m,4H).

[0130] Step 5: Synthesis of diamine compound 1

[0131]

[0132] 9.95 g (0.02 mol) of A5 was added to 120 mL of anhydrous ethanol, and then 10% of palladium on carbon (Pd / C) catalyst was added. The mixture was hydrogenated at 3.5 standard atmospheres to obtain crude diamine. The crude diamine was recrystallized in water, filtered, and dried to obtain product diamine compound 1.

[0133] The NMR characterization results are as follows: 1 H NMR(500MHz,DMSO-d6)δ9.75(s,1H),7.87(d,J=8.1Hz,2H),7.73(d,J=8.3Hz,2H),7.65(d,J=8.3Hz,2H),7.59(d,J=8.3Hz,2H),7.02– 6.96(m,2H),6.69(dd,J=18.5,8.3Hz,4H),6.53(d,J=8.5Hz,2H),5.43(s,2H),4.71(s,2H),4.05(h,J=3.7Hz,4H),1.95–1.86(m,4H).

[0134] Example 2: Preparation of polyamic acid solution PAA-1

[0135]

[0136] In a 100 mL three-necked flask equipped with a stirrer and a nitrogen inlet tube, 0.854 g (7.89 mmol) of p-phenylenediamine (DA-1), 1.251 g (6.31 mmol) of 4,4'-diaminodiphenylmethane (DA-3), and 0.738 g (1.57 mmol) of diamine compound 1 were measured. 33.7 g of N,N-dimethylformamide (DMF) was added, and the mixture was stirred while introducing nitrogen gas until dissolved. While stirring, 1.635 g (7.5 mmol) of pyromellitic dianhydride (CA-1) and 1.471 g (7.5 mmol) of cyclobutanetetracarboxylic dianhydride (CA-2) were added. The mixture was stirred at 25 °C for 24 hours to obtain a polyamic acid solution PAA-1 with a solute mass fraction of 15%.

[0137] Example 3: Preparation of polyamic acid solution PAA-2

[0138] In a 100 mL three-necked flask equipped with a stirrer and a nitrogen inlet tube, 0.854 g (7.89 mmol) of DA 1, 0.625 g (3.15 mmol) of DA-3, and 2.214 g (4.73 mmol) of diamine compound 1 were measured. 3.7 g of DMF was added, and the mixture was stirred while introducing nitrogen gas until dissolved. Then, 1.635 g (7.5 mmol) of CA-1 and 1.471 g (7.5 mmol) of CA-2 were added while stirring. The mixture was stirred at 25 °C for 24 hours to obtain a polyamic acid solution PAA-2 with a solute mass fraction of 15%.

[0139] Comparative Example 1: Preparation of polyamic acid solution PAA-3

[0140] In a 100 mL three-necked flask equipped with a stirrer and a nitrogen inlet tube, 0.854 g (7.89 mmol) of DA 1 and 1.563 g (7.89 mmol) of DA-3 were measured, and 31.3 g of DMF was added. Nitrogen gas was introduced while stirring until dissolved. Then, 1.635 g (7.5 mmol) of CA-1 and 1.471 g (7.5 mmol) of CA-2 were added while stirring. The mixture was stirred at 25 °C for 24 hours to obtain a polyamic acid solution PAA-3 with a solute mass fraction of 15%.

[0141] Example 4: Preparation of liquid crystal alignment agent P1

[0142] The polyamic acid solution PAA-1 was diluted to a solute mass fraction of 3% using the solvents N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and ethylene glycol monobutyl ether (BC). The N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and ethylene glycol monobutyl ether (BC) accounted for 50%, 30%, and 20% of the total mass of the diluent, respectively.

[0143] Example 5: Preparation of liquid crystal alignment agent P2

[0144] It can be prepared by the same method as in Example 4, except that the liquid crystal alignment agent P2 is prepared by diluting the polyamic acid solution PAA-2 with a solvent.

[0145] Comparative Example 2: Preparation of Liquid Crystal Alignment Agent P3

[0146] It can be prepared by the same method as in Example 4, except that the liquid crystal alignment agent P3 is prepared by diluting the polyamic acid solution PAA-3 with a solvent.

[0147] Example 6: Fabrication of Liquid Crystal Display Panel A1

[0148] Liquid crystal alignment agent P1 was spin-coated onto two ITO electrode glass substrates. After baking at 90°C for 5 minutes, the substrates were then baked at 230°C for 30 minutes to form a polyimide film (liquid crystal alignment film) with a thickness of approximately 100 nm. The substrates were then irradiated with 500 mJ / cm². 2 254nm polarized ultraviolet light is used to mark the polarization direction. A sealant is applied to the surface of one substrate to form a sealing pattern. Liquid crystal is then dropped onto the substrate with the sealing pattern. The other substrate is then bonded together with a liquid crystal alignment film facing each other, with the polarization directions of the two substrates at 90° to each other. Finally, the sealant is cured to obtain the liquid crystal display panel A1.

[0149] Example 7: Fabrication of Liquid Crystal Display Panel A2

[0150] It can be prepared by the same method as in Example 6, except that liquid crystal alignment agent P2 is used for spin coating.

[0151] Comparative Example 3: Fabrication of Liquid Crystal Display Panel A3

[0152] It can be prepared by the same method as in Example 6, except that liquid crystal alignment agent P3 is used for spin coating.

[0153] Example 8: Fabrication of Liquid Crystal Display Panel B1

[0154] Liquid crystal alignment agent P1 was spin-coated onto an HFS mode test substrate with ITO comb electrodes and a clean glass substrate, respectively. After baking at 90°C for 5 minutes, the substrates were then baked at 230°C for 30 minutes to form a polyimide film (liquid crystal alignment film) with a thickness of approximately 100 nm. The substrates were then irradiated with 500 mJ / cm². 2 254nm polarized ultraviolet light was used to mark the polarization direction. A sealant was applied to the surface of a clean glass substrate to form a sealing pattern. Liquid crystal was then dropped onto the clean glass substrate with the sealing pattern. Next, another test substrate with ITO comb electrodes in HFS mode was bonded together with the liquid crystal alignment films facing each other, with the polarization directions of the two substrates parallel to each other. Finally, the sealant was cured to obtain the liquid crystal display panel B1.

[0155] Example 9: Fabrication of Liquid Crystal Display Panel B2

[0156] It can be prepared by the same method as in Example 8, except that liquid crystal alignment agent P2 is used for spin coating.

[0157] Comparative Example 4: Fabrication of Liquid Crystal Display Panel B3

[0158] It can be prepared by the same method as in Example 8, except that liquid crystal alignment agent P3 is used for spin coating.

[0159] Evaluation of the anchoring ability of liquid crystal molecules

[0160] The orientation angles of liquid crystal molecules in liquid crystal display panels A1, A2, and A3 were measured using an OPTIPRO-micro instrument from SHIINTECH, and the anchoring energy Ea was calculated using a formula. For a detailed calculation method of the anchoring energy Ea, please refer to "Optoelectronic Functional Polyimide Materials and Devices," 2020, pp. 91-94. The specific results are shown in Table 1.

[0161] Table 1: Anchoring Energy Test Results of Liquid Crystal Display Panels A1, A2, and A3

[0162]

[0163] As shown in Table 1, the anchoring energies of liquid crystal display panels A1 and A2 provided in this application embodiment are greater than those of liquid crystal display panel A3 provided in the comparative example. This means that the liquid crystal alignment film materials in liquid crystal display panels A1 and A2 have a stronger anchoring ability for liquid crystal molecules. For the liquid crystal display panel A3 provided in the comparative example, the polyamic acid PAA-3 in the liquid crystal alignment agent P3 was not prepared with the diamine compound 1 provided in this application embodiment. Therefore, the polyamic acids PAA-1 and PAA-2 prepared with the addition of the diamine compound 1 provided in this application embodiment exhibit a stronger anchoring ability for liquid crystal molecules when used as liquid crystal alignment film materials. Furthermore, the anchoring energy of liquid crystal display panel A2 is greater than that of liquid crystal display panel A1, indicating that in polyamic acid, as the number of structures corresponding to diamine compound 1 increases, its anchoring ability for liquid crystal molecules continuously strengthens.

[0164] Evaluation of image retention performance

[0165] Mark point MARK1 in the illuminated areas of LCD panels B1, B2, and B3. Measure the liquid crystal angle between the upper and lower domains of the comb electrodes of the pixels in this area, and record it as ∠. T0 Apply 8V AC voltage to make the LCD panel display as shown. Figure 2 The black and white checkerboard test screen shown is followed by a voltage shutdown after 24 hours. The common electrodes of LCD panels B1, B2, and B3, and the pixel electrodes controlling the illuminated areas are shorted for 10 minutes. The liquid crystal angle between the upper and lower domains of the comb-shaped electrodes of the pixels within the marked area (MARK1) is then tested again and denoted as ∠. T24 The angle difference between the two is δangle (δangle = ∠). T24 -∠ T0 To evaluate image retention level, a smaller δangle indicates stronger alignment stability of the liquid crystal alignment film material in the liquid crystal display panel for liquid crystal molecules, resulting in better image retention performance.

[0166] Table 2: Evaluation Results of Image Retention Performance of Liquid Crystal Display Panels B1, B2, and B3

[0167] LCD display panel B1 0.09 LCD display panel B2 0.07 LCD display panel B3 0.14

[0168] As shown in Table 2, the angle difference between liquid crystal display panels B1 and B2 before and after operation is smaller than that of liquid crystal display panel B3 provided in the comparative example. This indicates that the liquid crystal alignment film materials in liquid crystal display panels B1 and B2 exhibit stronger alignment stability for liquid crystal molecules, resulting in better image retention performance. For the liquid crystal display panel B3 provided in the comparative example, the polyamic acid PAA-3 in the liquid crystal alignment agent P3 was not prepared with the diamine compound 1 provided in the embodiments of this application. Therefore, the polyamic acids PAA-1 and PAA-2 prepared with the diamine compound 1 provided in the embodiments of this application exhibit stronger alignment stability for liquid crystal molecules when used as liquid crystal alignment film materials, thus resulting in better image retention performance. Furthermore, the angle difference between liquid crystal display panel B2 before and after operation is smaller than that of liquid crystal display panel B1, indicating that in polyamic acid, as the number of structures corresponding to diamine compound 1 increases, its alignment stability for liquid crystal molecules continuously strengthens, and correspondingly, the image retention performance continuously improves.

[0169] The foregoing has provided a detailed description of a diamine compound, polyamic acid, liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display panel provided in the embodiments of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this application, and should not be construed as a limitation on the scope of protection of this application.

Claims

1. A diamine compound, characterized in that, The diamine compound has the structure shown in Formula 1: Where A is selected from the structure shown in A1: ， Indicates and The site of connection; Selected from phenylene or cyclohexylene, m is 1 to 3; C is selected from the structure shown in C2: n is 1 to 9.

2. The diamine compound according to claim 1, characterized in that, Select from any of the structures shown in B1 to B7: ， Here, # represents the site connected to C.

3. The diamine compound according to claim 1, characterized in that, The diamine compound has a structure as shown in Formula 2-1 or 2-2: 。 4. The diamine compound according to claim 1, characterized in that, The diamine compound is selected from compounds with the following structure: 。 5. A polyamic acid, characterized in that, The polyamic acid has repeating units with the structure shown in Formula 3: ； Each of R1 is independently selected from hydrogen atoms or alkyl groups with 1 to 10 carbon atoms; R2 is independently selected from hydrogen atom, alkyl group of 1 to 10 carbon atoms, alkenyl group of 1 to 10 carbon atoms or alkynyl group of 1 to 10 carbon atoms; Y is selected from divalent organic groups, including Y1, which has the structure shown in Formula 4: ； Where A is selected from the structure shown in A1: ， Indicates and The site of connection; Selected from phenylene or cyclohexylene, m is 1 to 3; C is selected from the structure shown in C2: n is 1 to 9; X is selected from tetravalent organic groups, including structures as shown in Formula 5 and / or Formula 6: ; Ar1 is selected from aromatic rings with 6 to 10 ring atoms or aliphatic rings with 4 to 10 ring atoms; D is selected from single bond, or .

6. The polyamic acid as described in claim 5, characterized in that, Select from any of the structures shown in B1 to B7: ， Here, # represents the site connected to C.

7. The polyamic acid as described in claim 5, characterized in that, Y1 has the structure shown in Equation 7-1 and / or Equation 7-2: 。 8. The polyamic acid as described in claim 5, characterized in that, Y1 is selected from the structure shown below: 。 9. The polyamic acid as described in claim 5, characterized in that, Y also includes Y2, which is selected from one or more of the following structures: ， In this context, ## represents a site that connects to an adjacent structure.

10. The polyamic acid as described in claim 9, characterized in that, The molar ratio of Y1 to Y2 is 1:1 to 1:

9.

11. The polyamic acid as described in claim 5, characterized in that, X includes one or more of the following structures: 。 12. A liquid crystal alignment agent, characterized in that, Includes polyamic acid as described in any one of claims 5 to 11.

13. A liquid crystal alignment film, characterized in that, The liquid crystal alignment film is prepared from the liquid crystal alignment agent as described in claim 12.

14. A liquid crystal display panel, characterized in that, The liquid crystal display panel includes the liquid crystal alignment film as described in claim 13.

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