Modified polyimide and preparation method thereof

Abstract

The invention belongs to the technical field of material science, provides modified polyimide and a preparation method thereof, and solves the problems of uneven spraying of a polyimide orientation agent and edge film thickness uniformity. The preparation method comprises the following steps: carrying out copolymerization reaction on a diamine monomer, a dianhydride monomer and N-methyl pyrrolidone to obtain a polyimide acid solution; mixing the polyimide acid solution with a solvent to obtain a reaction system; and reacting the reaction system with a modifier to obtain the modified polyimide. The water-based compatibility of the polyimide is mainly improved, the affinity or compatibility of the modified polyimide to water is obviously improved, precipitation or hydrolysis of the polyimide is not easily caused, the problem of uneven film thickness caused by spraying during mass production can be effectively solved, and meanwhile, the length of a halo region can be effectively widened by matching with mixed solvents in different proportions, so that the film thickness is increased, and the film thickness is increased. And defects caused by non-uniform edge film thickness are reduced.

Description

Technical Field

[0001] The present invention relates to the field of material science and technology, and in particular to a modified polyimide and a preparation method thereof. Background Art

[0002] TFT-LCDs are a mainstream product in the display industry due to their superior performance, ease of mass production, high degree of automation, and broad potential for development. However, the production process and manufacturing process for TFT-LCDs are complex. During the cell manufacturing process, a thin polymer organic film, called an alignment layer, is used to anchor the liquid crystal. Polyimide (PI) is the most widely used material for this liquid crystal alignment film.

[0003] With the advancement of TFT device manufacturing processes, the size of glass substrates has increased, placing higher and higher demands on TFT manufacturing processes and the control of mura defects caused by film layers. PI film coating is a core process in the PI film formation process. In large-scale production, inkjet coating is used to complete PI film coating using PI spray (Inkjet) equipment. Coating anomalies are mainly divided into uneven coating and bubbles in the PI liquid. Inkjet coating uses a nozzle to discharge PI liquid, which is then evenly distributed across the entire substrate. If a nozzle becomes clogged during this process, no PI film is applied at the blocked area or the discharge volume is too small, resulting in a thin film thickness. Thin PI film thickness in a certain area can lead to uneven overall PI liquid coating, which appears as Suji Mura (fine diagonal unevenness) on inspection machines. In severe cases, this can affect product yield. Furthermore, the distance between the substrate edge and the PI liquid edge requires a certain level of precision. After the PI edge enters the pre-baking equipment, the outer edge of the PI edge is heated more than the inner edge, resulting in faster solvent evaporation and a higher PI liquid concentration. This results in a thicker halo zone forming around the perimeter. While this can be improved through process and substrate design, improving the halo zone through PI material design is more beneficial, broadening the PI material's application range, increasing the material's tolerance to production processes, and reducing the risk of uneven film thickness at the edge.

[0004] Polyimide-based alignment agents are typically formed by polycondensing aromatic diamines with tetracarboxylic anhydride to form a five-membered imide ring, resulting in a molecular chain. These characteristics contribute to polyimide's high rigidity and strong interchain interactions, making it relatively insoluble. Furthermore, polyimide materials are susceptible to hydrolysis, making the polyimide (PI) solution sensitive to water. Prolonged exposure to air can absorb moisture and cause spraying problems or clogging during mass production, when the sprayer is switching between PI solutions or when idle, impacting production capacity and yield. Furthermore, because the outer edge of the PI is heated more than the inner edge during pre-baking or curing, solvent evaporation occurs more rapidly, leading to higher PI solution concentrations. This creates a halo zone around the periphery, where the PI film is thicker. This uneven edge thickness is primarily due to factors such as solvent and surface tension. Therefore, addressing this edge thickness issue is crucial for producing high-quality TFT-LCD products. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a modified polyimide and a preparation method thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a modified polyimide, comprising the following steps:

[0008] (1) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0009] (2) mixing the polyimide acid solution and a solvent to obtain a reaction system;

[0010] (3) reacting the reaction system and the modifier to obtain the modified polyimide;

[0011] or;

[0012] (a) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0013] (b) mixing a polyimide acid solution, a dehydrating agent, a catalyst, and N-methylpyrrolidone to carry out an imidization reaction to obtain a polyimide solution;

[0014] (c) mixing the polyimide solution and a solvent to obtain a reaction system;

[0015] (d) reacting the reaction system and the modifier to obtain the modified polyimide;

[0016] or;

[0017] (A) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0018] (B) mixing the polyimide acid solution and a solvent to obtain a first reaction system;

[0019] (C) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0020] (D) mixing a polyimide acid solution, a dehydrating agent, a catalyst, and N-methylpyrrolidone to carry out an imidization reaction to obtain a polyimide solution;

[0021] (E) mixing the polyimide solution and a solvent to obtain a second reaction system;

[0022] (F) mixing the first reaction system and the second reaction system and aging them to obtain an aging system;

[0023] (G) reacting the aging system with the modifier to obtain the modified polyimide.

[0024] Preferably, the molar ratio of the diamine monomer to the dianhydride monomer in step (1), step (a), step (A) and step (C) is independently 100:80-105;

[0025] The solid content of the polyimide acid solution in step (1), step (a), step (A) and step (C) is independently 5 to 50%.

[0026] Preferably, the temperature of the copolymerization reaction in step (1), step (a), step (A) and step (C) is independently -20 to 120°C, and the time of the copolymerization reaction is independently 0.5 to 48 hours.

[0027] Preferably, the solvent in step (2), step (c), step (B) and step (E) is independently one or more of γ-butyrolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, 2-pyrrolidone, N-vinyl-2-pyrrolidone, ethylene glycol dimethyl ether, ethylene glycol monobutyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, 1,2-butoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diacetone alcohol and dipropylene glycol dimethyl ether;

[0028] The solid content of the reaction system in step (2) is 1 to 5 wt%; the solid content of the reaction system in step (c) is 1 to 5 wt%; the solid content of the first reaction system in step (B) is 1 to 5 wt%; and the solid content of the second reaction system in step (E) is 1 to 5 wt%.

[0029] Preferably, the structure of the modifier in step (3), step (d) and step (G) is:

[0030]

[0031] Wherein, Ra is a hydroxyalkyl group;

[0032] X1 is -(CH2) a -or-(CH2) a -A group in which any methylene group is independently substituted by -O-, -COO-, or -CO-, wherein a is an integer from 2 to 10;

[0033] Rb and Rc are independently a hydrogen atom or a carbon atom;

[0034] When it is a carbon atom, it is independently an alkyl group having 1 to 6 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, or a benzene ring;

[0035] When they are carbon atoms, Ra and Rb are independent of each other or linked to form a ring.

[0036] Preferably, the molar amount of the modifier in step (3) and step (d) is independently 0.01 to 5% of the molar sum of the diamine monomer and the dianhydride monomer;

[0037] In step (G), the mass ratio of the modifier to the aging system is 0.1-0.5:800-1200;

[0038] The reaction temperature in step (3), step (d) and step (G) is independently 0 to 80° C., and the reaction time is independently 0.5 to 4 h.

[0039] Preferably, the dehydrating agent in step (b) and step (D) is independently one or more of acetic anhydride, propionic anhydride and trifluoroacetic anhydride; the catalyst in step (b) and step (D) is independently one or more of pyridine, collidine, lutidine and triethylamine;

[0040] The molar amount of the dehydrating agent in step (b) and step (d) is independently 1 to 20 times the molar amount of the dianhydride;

[0041] The molar amount of the catalyst in step (b) and step (D) is independently 1 to 10 times the molar amount of the dianhydride;

[0042] The solid content of the polyimide solution in step (b) and step (d) is independently 10 to 20 wt %.

[0043] Preferably, the temperature of the imidization reaction in step (b) and step (D) is independently -20 to 200°C, and the time of the imidization reaction is independently 0.5 to 48 hours.

[0044] Preferably, in step (F), the mass ratio of the first reaction system to the second reaction system is 5-10:1-5;

[0045] The aging temperature in step (F) is 60-80° C. and the aging time is 0.5-4 h.

[0046] The present invention also provides the modified polyimide prepared by the preparation method of the modified polyimide.

[0047] The present invention provides a method for preparing a modified polyimide. The present invention mainly improves the water compatibility of the polyimide. The modified polyimide has significantly improved affinity or compatibility with water, is less likely to cause polyimide precipitation or hydrolysis, and can effectively solve the uneven film thickness caused by spraying during mass production. At the same time, by using mixed solvents in different proportions, the length of the halo zone can be effectively widened, reducing the undesirable problem of uneven film thickness at the edge. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a standard white light interference test pattern;

[0049] Figure 2 It is a standard white light interference 3D diagram;

[0050] Figure 3 is a cross-sectional contour line drawing;

[0051] Figure 4 This is a schematic diagram of the halo area. DETAILED DESCRIPTION

[0052] The present invention provides a method for preparing a modified polyimide, comprising the following steps:

[0053] (1) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0054] (2) mixing the polyimide acid solution and a solvent to obtain a reaction system;

[0055] (3) reacting the reaction system and the modifier to obtain the modified polyimide;

[0056] or;

[0057] (a) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0058] (b) mixing a polyimide acid solution, a dehydrating agent, a catalyst, and N-methylpyrrolidone to carry out an imidization reaction to obtain a polyimide solution;

[0059] (c) mixing the polyimide solution and a solvent to obtain a reaction system;

[0060] (d) reacting the reaction system and the modifier to obtain the modified polyimide;

[0061] or;

[0062] (A) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0063] (B) mixing the polyimide acid solution and a solvent to obtain a first reaction system;

[0064] (C) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution;

[0065] (D) mixing a polyimide acid solution, a dehydrating agent, a catalyst, and N-methylpyrrolidone to carry out an imidization reaction to obtain a polyimide solution;

[0066] (E) mixing the polyimide solution and a solvent to obtain a second reaction system;

[0067] (F) mixing the first reaction system and the second reaction system and aging them to obtain an aging system;

[0068] (G) reacting the aging system with the modifier to obtain the modified polyimide.

[0069] In the present invention, there are no special requirements for the diamine monomer and the dianhydride monomer. The diamine monomer is selected from alicyclic diamines, aromatic diamines, heterocyclic diamines or aliphatic diamines. The following are seven specific diamine monomers:

[0070]

[0071] In the present invention, there is no special requirement for the dianhydride monomer. Five specific dianhydride monomers are given below:

[0072]

[0073] In the present invention, the molar ratio of the diamine monomer to the dianhydride monomer in step (1), step (a), step (A) and step (C) is preferably independently 100:80 to 105, more preferably independently 100:85 to 100, and even more preferably independently 100:90 to 95.

[0074] In the present invention, the solid content of the polyimide acid solution in step (1), step (a), step (A) and step (C) is preferably independently 5 to 50%, more preferably independently 10 to 40%, and even more preferably independently 20 to 30%.

[0075] In the present invention, in step (1), step (a), step (A) and step (C), the diamine monomers are first mixed and then dissolved in N-methylpyrrolidone, and the dianhydride monomer is added under the protection of a protective gas to carry out a copolymerization reaction.

[0076] In the present invention, the protective gas is preferably nitrogen, argon or helium.

[0077] In the present invention, the temperature of the copolymerization reaction in step (1), step (a), step (A) and step (C) is independently preferably -20 to 120°C, further independently preferably 0 to 100°C, and more independently preferably 20 to 80°C; the time of the copolymerization reaction is independently preferably 0.5 to 48h, further independently preferably 4 to 40h, and more independently preferably 10 to 30h.

[0078] In the present invention, the solvents in step (2), step (c), step (B) and step (E) are independently one or more of γ-butyrolactone (GBL), N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-diethylformamide (DEF), 2-pyrrolidone, N-vinyl-2-pyrrolidone, ethylene glycol dimethyl ether, ethylene glycol monobutyl ether (BC), ethylene glycol diethyl ether, ethylene glycol dibutyl ether, 1,2-butoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diacetone alcohol (DAA) and dipropylene glycol dimethyl ether (DME).

[0079] In the present invention, there is no special requirement for the solvent, as long as it ensures that the synthesized polyimide acid does not precipitate.

[0080] In the present invention, the solid content of the reaction system in step (2) is preferably 1 to 5 wt%, more preferably 1.5 to 4.5 wt%, more preferably 2 to 3 wt%; the solid content of the reaction system in step (c) is preferably 1 to 5 wt%, more preferably 1.5 to 4.5 wt%, more preferably 2 to 3 wt%; the solid content of the first reaction system in step (B) is preferably 1 to 5 wt%, more preferably 1.5 to 4.5 wt%, more preferably 2 to 3 wt%; the solid content of the second reaction system in step (E) is preferably 1 to 5 wt%, more preferably 1.5 to 4.5 wt%, more preferably 2 to 3 wt%.

[0081] In the present invention, the structure of the modifier in step (3), step (d) and step (G) is:

[0082]

[0083] Wherein, Ra is a hydroxyalkyl group;

[0084] X1 is -(CH2) a -or-(CH2) a -A group in which any methylene group is independently substituted by -O-, -COO-, or -CO-, wherein a is an integer from 2 to 10;

[0085] Rb and Rc are independently a hydrogen atom or a carbon atom;

[0086] When it is a carbon atom, it is independently an alkyl group having 1 to 6 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, or a benzene ring;

[0087] When they are carbon atoms, Ra and Rb are independent of each other or linked to form a ring.

[0088] In the present invention, 10 kinds of modifiers with different structures are provided, as shown below:

[0089]

[0090] In the present invention, the molar amount of the modifier in step (3) and step (d) is preferably independently 0.01 to 5% of the molar sum of the diamine monomer and the dianhydride monomer, further independently preferably 1 to 4% of the molar sum of the diamine monomer and the dianhydride monomer, and even more independently preferably 2 to 3% of the molar sum of the diamine monomer and the dianhydride monomer.

[0091] In the present invention, the mass ratio of the modifier to the aging system in step (G) is preferably 0.1-0.5:800-1200, more preferably 0.2-0.4:900-1100, and even more preferably 0.25-0.35:950-1000.

[0092] In the present invention, the reactions in step (3), step (d) and step (G) are carried out in a protective gas, which is preferably nitrogen, argon or helium.

[0093] In the present invention, the reaction temperature in step (3), step (d) and step (G) is independently preferably 0 to 80° C., further independently preferably 10 to 70° C., and more independently preferably 20 to 50° C.; the reaction time is independently preferably 0.5 to 4 h, further independently preferably 1 to 3 h, and more independently preferably 1.5 to 2.5 h.

[0094] In the present invention, the dehydrating agent in step (b) and step (D) is independently one or more of acetic anhydride, propionic anhydride and trifluoroacetic anhydride; and the catalyst in step (b) and step (D) is independently one or more of pyridine, collidine, lutidine and triethylamine.

[0095] In the present invention, the molar amount of the dehydrating agent in step (b) and step (D) is preferably independently 1 to 20 times the molar amount of the dianhydride, more preferably independently 5 to 15 times, and even more preferably independently 8 to 12 times.

[0096] In the present invention, the molar amount of the catalyst in step (b) and step (D) is preferably independently 1 to 10 times the molar amount of the dianhydride, more independently preferably 2 to 8 times, and even more independently preferably 4 to 6 times.

[0097] In the present invention, the solid content of the polyimide solution in step (b) and step (D) is preferably independently 10 to 20 wt %, more independently 12 to 18 wt %, and even more independently 14 to 16 wt %.

[0098] In the present invention, the temperature of the imidization reaction in step (b) and step (D) is independently preferably -20 to 200° C., more independently preferably 20 to 120° C., and more independently preferably 60 to 100° C.; the time of the imidization reaction is independently preferably 0.5 to 48 h, more independently preferably 10 to 40 h, and more independently preferably 20 to 30 h.

[0099] In the present invention, the mass ratio of the first reaction system to the second reaction system in step (F) is preferably 5-10:1-5, more preferably 6-9:2-4, and even more preferably 7-8:2.5-3.

[0100] In the present invention, the aging temperature in step (F) is preferably 60-80°C, more preferably 65-75°C, more preferably 68-72°C; the aging time is preferably 0.5-4h, more preferably 1-3.5h, more preferably 2-3h.

[0101] The present invention also provides the modified polyimide prepared by the preparation method of the modified polyimide.

[0102] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0103] In the embodiments provided by the present invention, the diamine monomers used are as follows:

[0104]

[0105] The dianhydride monomers used are as follows:

[0106]

[0107] The modifiers used are as follows:

[0108]

[0109] Example 1

[0110] In a nitrogen-protected reactor, 7.81 g (15 mmol) of A-6, 1.52 g (10 mmol) of A-5, 3.97 g (20 mmol) of A-2, 2.16 g (20 mmol) of A-1, 7.01 g (35 mmol) of A-3, and 172.81 g of NMP were added sequentially and stirred at 25°C for 30 min to ensure complete dissolution. 15.69 g (30 mmol) of G-1 and 14.71 g (70 mmol) of G-2 were then added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%.

[0111] After the reaction was completed, 86.13 g of NMP, 103.35 g of NEP, 310.06 g of BC, 155.03 g of DEF, 103.35 g of DAA, and 103.35 g of DME were added, mixed, stirred, and diluted to 4.0% wt to obtain a reaction system.

[0112] Under nitrogen protection, the modifier ADD-3 was gradually added dropwise to the reaction system. The addition amount was 0.33 g, which was 1% of the total molar amount of diamine and dianhydride (0.2 mol). The stirring reaction time was 2 h and the reaction temperature was 60° C. to obtain modified polyimide.

[0113] Example 2

[0114] In a nitrogen-protected reactor, 6.34 g (15 mmol) of A-7, 1.99 g (10 mmol) of A-4, 3.97 g (20 mmol) of A-2, 2.70 g (25 mmol) of A-1, 7.01 g (30 mmol) of A-3, and 170.32 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. 5.88 g (20 mmol) of G-4 and 15.69 g (80 mmol) of G-1 were then added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%.

[0115] Then, 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were added, followed by 44.95 g of NMP, resulting in a solid content of 15 wt %. The mixture was reacted at 25° C. for 2 h for chemical imidization. After the imidization was completed, most of the pyridine and solvent were removed by rotary evaporation at 100° C., followed by the addition of 120 g of NMP solvent. This cycle was repeated three times to remove most of the pyridine and acetic acid, thereby obtaining a polyimide solution with a final solid content greater than 20%. After the reaction was completed, the solid content was determined to be 25.31% by hot plate method. 180.93 g of NMP, 102.19 g of NEP, 255.49 g of BC, 153.29 g of DEF, 102.19 g of DAA, and 102.19 g of DME were added, mixed, and diluted to 4.0% wt to obtain a reaction system.

[0116] Under nitrogen protection, the modifier ADD-3 was gradually added dropwise to the reaction system. The addition amount was 0.33 g, which was 1% of the total molar amount of diamine and dianhydride (0.2 mol). The stirring reaction time was 2 h and the reaction temperature was 60° C. to obtain modified polyimide.

[0117] Example 3

[0118] In a nitrogen-protected reactor, 7.812 g (15 mmol) of A-7, 1.99 g (10 mmol) of A-4, 3.97 g (20 mmol) of A-2, 2.70 g (25 mmol) of A-1, 7.01 g (30 mmol) of A-3, and 170.32 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. 5.88 g (20 mmol) of G-4 and 15.69 g (80 mmol) of G-1 were then added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%.

[0119] Then, 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were added, followed by 47.40 g of NMP, resulting in a solid content of 15 wt %. The mixture was reacted at 25° C. for 2 h for chemical imidization. A rotary evaporation at 100° C. was performed to remove most of the pyridine and solvent, followed by the addition of 120 g of NMP. This cycle was repeated three times to remove most of the pyridine and acetic acid, thereby obtaining a polyimide solution with a final solid content of greater than 20%. After the reaction was completed, the solid content was determined to be 23.56% by hot plate method. 174.26 g of NMP, 105.72 g of NEP, 264.32 g of BC, 158.59 g of DEF, 158.59 g of DAA, and 105.73 g of DME were added, mixed, and diluted to 4.0% wt to obtain a reaction system.

[0120] Under nitrogen protection, the modifier ADD-9 was gradually added dropwise to the reaction system. The addition amount was 0.35 g, which was 1% of the total molar amount of diamine and dianhydride (0.2 mol). The stirring reaction time was 2 h and the reaction temperature was 60° C. to obtain modified polyimide.

[0121] Example 4

[0122] In a nitrogen-protected reactor, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-3, and 147.49 g of NMP were added sequentially and stirred at 25°C for 30 min to ensure complete dissolution. Then, 19.61 g (100 mmol) of G-1 was added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solids content of 20 wt%.

[0123] 73.74 g NMP, 88.50 g NEP, 265.48 g BC, 132.74 g DEF, 89.50 g DAA, and 89.50 g DME were added, mixed, stirred, and diluted to 4.0% wt to obtain a first reaction system.

[0124] In a nitrogen-protected reactor, 20.83 g (40 mmol) of A-6, 4.56 g (30 mmol) of A-5, 5.94 g (30 mmol) of A-2, and 261.79 g of NMP were added in sequence, stirred at 25 ° C for 30 min, and confirmed to be completely dissolved. Then 21.01 g (100 mmol) of G-2 were added in sequence, and the reaction was stirred at 25 ° C for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. Then 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were added, and 61.24 g of NMP was added to obtain a solid content of 15 wt%. Chemical imidization was carried out at 60 ° C for 2 h. First, most of the pyridine and solvent were removed by rotary evaporation at 100 ° C, and then 120 g of NMP solvent was added. This cycle was repeated 3 times to remove most of the pyridine and acetic acid, thereby obtaining a polyimide solution with a final solid content greater than 20%. After the reaction was completed, the solid content was determined to be 20.39% by hot plate method. 109.72 g NMP, 125.65 g NEP, 376.98 g BC, 188.48 g DEF, 125.66 g DAA, and 125.66 g DME were added, mixed, and diluted to 4.0% wt to obtain a second reaction system.

[0125] Take 700 g of the first reaction system and 300 g of the second reaction system obtained in the above two steps, and then stir and mature them at 60 ° C for 1 h to obtain a uniformly mixed 1000 g matured system. Under nitrogen protection, the modifier ADD-3 is gradually added dropwise to the above system in an amount of 0.33 g. The stirring reaction time is 2 h and the reaction temperature is 60 ° C to obtain a modified polyimide.

[0126] Example 5

[0127] In a nitrogen-protected reactor, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-3, and 147.49 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. 19.61 g (100 mmol) of G-1 was then added sequentially. The mixture was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. 117.99 g of NMP, 88.50 g of NEP, 221.24 g of BC, 132.74 g of DEF, 89.50 g of DAA, and 89.50 g of DME were added and mixed and stirred to dilute to 4.0% wt, thus obtaining the first reaction system.

[0128] In a nitrogen-protected reactor, 10.42 g (20 mmol) of A-6, 8.45 g (20 mmol) of A-7, 4.56 g (30 mmol) of A-5, 5.95 g (30 mmol) of A-2, and 201.58 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. 21.01 g (100 mmol) of G-2 was then added sequentially and stirred at 25°C for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were then added, followed by an additional 57.97 g of NMP, resulting in a solid content of 15 wt%. The mixture was reacted at 60°C for 2 h for chemical imidization. First, a rotary evaporation at 100°C was performed to remove most of the pyridine and solvent, followed by the addition of 120 g of NMP solvent. This cycle was repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solids content greater than 20%. After the reaction was completed, the solids content was determined to be 25.86% by hot plate method. 218.36 g of NMP, 120.94 g of NEP, 302.37 g of BC, 181.42 g of DEF, 120.95 g of DAA, and 120.95 g of DME were added, mixed, and diluted to 4.0% by weight to obtain a second reaction system.

[0129] Take 700 g of the first reaction system and 300 g of the second reaction system obtained in the above two steps, and then stir and mature them at 60 ° C for 1 h to obtain a uniformly mixed 1000 g mature system. Under nitrogen protection, the modifier ADD-9 is gradually added dropwise to the polyamide solution in an amount of 0.35 g. The stirring reaction time is 2 h and the reaction temperature is 60 ° C to obtain a modified polyimide.

[0130] Comparative Example 1

[0131] In a nitrogen-protected reactor, 7.81 g (15 mmol) of A-6, 1.52 g (10 mmol) of A-5, 3.97 g (20 mmol) of A-2, 2.16 g (20 mmol) of A-1, 7.01 g (35 mmol) of A-3, and 172.81 g of NMP were added in sequence and stirred at room temperature for 30 min to confirm complete dissolution. 15.69 g (30 mmol) of G-1 and 14.71 g (70 mmol) of G-2 were then added in sequence. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 499.54 g of NMP, 206.71 g of GBL, and 155.03 g of BC were added and diluted with stirring to 4.0% wt to obtain a polyamic acid solution.

[0132] Comparative Example 2

[0133] In a nitrogen-protected reactor, 6.34 g (15 mmol) of A-7, 1.99 g (10 mmol) of A-4, 3.97 g (20 mmol) of A-2, 2.70 g (25 mmol) of A-1, 6.01 g (30 mmol) of A-3, and 170.32 g of NMP were added sequentially and stirred at room temperature for 30 min to confirm complete dissolution. 5.88 g (20 mmol) of G-4 and 15.69 g (80 mmol) of G-1 were then added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%.

[0134] Then, 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were added, followed by 44.95 g of NMP, resulting in a solid content of 15 wt %. The mixture was reacted at 25° C. for 2 h for chemical imidization. A rotary evaporation at 100° C. was performed to remove most of the pyridine and solvent, followed by the addition of 120 g of NMP. This cycle was repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solid content greater than 20%. After the reaction was completed, the solid content was determined to be 23.17% by hot plate method. 523.07 g of NMP, 204.39 g of GBL, and 153.29 g of BC were added, stirred, and diluted to 4.0% wt to obtain a polyimide solution.

[0135] Comparative Example 3

[0136] In a nitrogen-protected reactor, 7.812 g (15 mmol) of A-7, 1.99 g (10 mmol) of A-4, 3.97 g (20 mmol) of A-2, 2.70 g (25 mmol) of A-1, 7.01 g (30 mmol) of A-3, and 170.32 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. 5.88 g (20 mmol) of G-4 and 15.69 g (80 mmol) of G-1 were then added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%.

[0137] Then, 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were added, followed by 47.40 g of NMP, resulting in a solid content of 15 wt %. The mixture was reacted at 25° C. for 2 h for chemical imidization. A rotary evaporation at 100° C. was performed to remove most of the pyridine and solvent, followed by the addition of 120 g of NMP. This cycle was repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solid content greater than 20%. After the reaction was completed, the solid content was determined to be 21.85% by hot plate method. 529.68 g of NMP, 211.46 g of GBL, and 158.59 g of BC were added, stirred, and diluted to 4.0% wt to obtain a polyimide solution.

[0138] Comparative Example 4

[0139] In a nitrogen-protected reactor, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-3, and 147.49 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. Then, 19.61 g (100 mmol) of G-1 was added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 427.73 g of NMP, 176.99 g of GBL, and 132.74 g of BC were added and diluted to 4.0% wt with stirring to obtain polyamic acid solution A.

[0140] In a nitrogen-protected reactor, 10.42 g (20 mmol) of A-6, 8.45 g (20 mmol) of A-7, 4.56 g (30 mmol) of A-5, 5.95 g (30 mmol) of A-2, and 201.58 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. 21.01 g (100 mmol) of G-2 was then added sequentially and stirred at 25°C for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were then added, followed by an additional 57.97 g of NMP, resulting in a solid content of 15 wt%. The mixture was reacted at 60°C for 2 h for chemical imidization. First, remove most of the pyridine and solvent by rotary evaporation at 100°C, then add 120g of NMP solvent. Repeat this cycle three times to remove most of the pyridine and acetic acid, obtaining a polyimide solution with a final solids content greater than 20%. After the reaction, the solids content was determined to be 27.63% by hot plate method. Then, 654.15g of NMP, 241.89g of GBL, and 181.42g of BC were added and stirred to dilute to 4.0% wt., yielding polyimide solution B.

[0141] Take 700 g of liquid A and 300 g of liquid B obtained in the above two steps, and then stir and mature them at 60°C for 1 hour.

[0142] Comparative Example 5

[0143] In a nitrogen-protected reactor, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-3, and 147.49 g of NMP were added sequentially and stirred at 25°C for 30 min to confirm complete dissolution. Then, 19.61 g (100 mmol) of G-1 was added sequentially. The reaction was stirred at 25°C for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 427.73 g of NMP, 176.99 g of GBL, and 132.74 g of BC were added and diluted to 4.0% wt with stirring to obtain polyamic acid solution A.

[0144] In a nitrogen-protected reactor, 20.83 g (40 mmol) of A-6, 4.56 g (30 mmol) of A-5, 5.94 g (30 mmol) of A-2, and 209.43 g of NMP were added in sequence, stirred at 25 ° C for 30 min, and confirmed to be completely dissolved. 21.01 g (100 mmol) of G-2 were then added in sequence, and the reaction was stirred at 25 ° C for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. 10.2 g (100 mmol) of acetic anhydride and 15.82 g (200 mmol) of pyridine were then added, followed by 61.24 g of NMP, at which point the solid content was 15 wt%. Chemical imidization was performed at 60 ° C for 2 h. First, most of the pyridine and solvent were removed by rotary evaporation at 100 ° C, and then 120 g of NMP solvent was added. This cycle was repeated 3 times to remove most of the pyridine and acetic acid, thereby obtaining a polyimide solution with a final solid content greater than 20%. After the reaction was completed, the solid content was determined to be 23.88% by hot plate method. 649.89 g of NMP, 251.31 g of GBL, and 188.49 g of BC were added and stirred to dilute the mixture to 4.0% wt to obtain polyimide solution B.

[0145] Take 700 g of liquid A and 300 g of liquid B obtained in the above two steps, and then stir and mature them at 60°C for 1 hour.

[0146] The polyimides prepared in Examples 1-5 and Comparative Examples 1-5 were filtered through a microporous filter membrane. The synthesized alignment agent was sprayed onto a single panel. The sprayed film was pre-baked at 80°C for 2 minutes and then dried at 230°C for 30 minutes. The uniformity of the coating, including evaluation of the center and edges of the film, was evaluated. Furthermore, after coating and subsequent cell fabrication processes, the liquid crystal cell was tested for tilt angle and electrical properties.

[0147] Performance Testing

[0148] PI film surface uniformity evaluation: Test equipment: white light interferometer; Instrument model: Bruker GontourX-500; Interference objective lens: 2.5×, 0.55×; Standard white light interferometer test chart as shown below Figure 1 As shown, the standard white light interference 3D diagram is as follows Figure 2 As shown, the cross-section contour line is as Figure 3 shown.

[0149] To compare the film surface uniformity of different samples, the height difference between adjacent peaks and troughs was measured. The smaller the height difference, the smoother the film surface. Three profile lines were taken for each sample to calculate ΔZ. The results are shown in Table 1.

[0150] Table 1 PI film surface characterization data (unit: nm)

[0151] Sample name ΔZ1 ΔZ2 ΔZ3 average value Example 1 0.904 0.878 0.863 0.882 Example 2 0.848 0.733 0.728 0.770 Example 3 0.575 0.677 0.478 0.577 Example 4 0.761 0.842 0.651 0.751 Example 5 0.434 0.593 0.487 0.505 Comparative Example 1 2.608 2.689 2.868 2.722 Comparative Example 2 2.825 2.536 2.902 2.754 Comparative Example 3 2.763 2.885 2.595 2.748 Comparative Example 4 2.481 2.845 2.336 2.554 Comparative Example 5 2.677 2.861 2.728 2.755

[0152] PI film edge evaluation: Test equipment: white light interferometer; Instrument model: Bruker GontourX-500; Interference objective lens: 5×, 0.55×.

[0153] Definition of halo zone: The edge area where the film thickness is less than 90% of the normal area is the halo zone. Figure 4 shown.

[0154] The edge of the PI film is evaluated by the width of the halo zone. The shorter the width of the halo zone, the better the uniformity of the edge film thickness. The results are shown in Table 2.

[0155] Table 2 PI film surface characterization data (unit: μm)

[0156]

[0157]

[0158] Liquid crystal box electrical performance test conditions:

[0159] Test equipment: 6254C

[0160] VHR measurement conditions: voltage 5V, pulse width 60us / frame, period 1667ms, measurement temperature 23℃ / 90℃.

[0161] Ion density measurement conditions: voltage 5V, pulse width 60µs / frame, period 1667ms, and measurement temperature 23°C / 90°C. The test results are shown in Table 3.

[0162] Table 3 Electrical performance test results

[0163]

[0164] From the above examples, it can be seen that the modified polyimide provided by the present invention significantly improves the uniformity of the film surface by adding the modifier; significantly reduces the width of the halo zone, improves the uniformity of the edge film thickness; and has excellent electrical properties.

[0165] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a modified polyimide, characterized in that: It includes the following steps: (1) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution; (2) mixing the polyimide acid solution and a solvent to obtain a reaction system; (3) reacting the reaction system and the modifier to obtain the modified polyimide; or; (a) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution; (b) mixing a polyimide acid solution, a dehydrating agent, a catalyst, and N-methylpyrrolidone to carry out an imidization reaction to obtain a polyimide solution; (c) mixing the polyimide solution and a solvent to obtain a reaction system; (d) reacting the reaction system and the modifier to obtain the modified polyimide; or; (A) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution; (B) mixing the polyimide acid solution and a solvent to obtain a first reaction system; (C) copolymerizing a diamine monomer, a dianhydride monomer, and N-methylpyrrolidone to obtain a polyimide acid solution; (D) mixing a polyimide acid solution, a dehydrating agent, a catalyst, and N-methylpyrrolidone to carry out an imidization reaction to obtain a polyimide solution; (E) mixing the polyimide solution and a solvent to obtain a second reaction system; (F) mixing the first reaction system and the second reaction system and aging them to obtain an aging system; (G) reacting the aging system with the modifier to obtain the modified polyimide.

2. The method for preparing a modified polyimide according to claim 1, wherein: The molar ratio of the diamine monomer to the dianhydride monomer in step (1), step (a), step (A) and step (C) is independently 100:80 to 105; The solid content of the polyimide acid solution in step (1), step (a), step (A) and step (C) is independently 5 to 50%.

3. The method for preparing a modified polyimide according to claim 2, wherein: The temperature of the copolymerization reaction in step (1), step (a), step (A) and step (C) is independently -20 to 120°C, and the time of the copolymerization reaction is independently 0.5 to 48 hours.

4. The method for preparing a modified polyimide according to claim 3, wherein: In step (2), step (c), step (B) and step (E), the solvent is independently one or more of γ-butyrolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, 2-pyrrolidone, N-vinyl-2-pyrrolidone, ethylene glycol dimethyl ether, ethylene glycol monobutyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, 1,2-butoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diacetone alcohol and dipropylene glycol dimethyl ether; The solid content of the reaction system in step (2) is 1 to 5 wt%; the solid content of the reaction system in step (c) is 1 to 5 wt%; the solid content of the first reaction system in step (B) is 1 to 5 wt%; and the solid content of the second reaction system in step (E) is 1 to 5 wt%.

5. The method for preparing the modified polyimide according to claim 4, wherein: The structure of the modifier in step (3), step (d) and step (G) is: Wherein, Ra is a hydroxyalkyl group; X1 is -(CH2) a -or-(CH2) a -A group in which any methylene group is independently substituted by -O-, -COO-, or -CO-, wherein a is an integer from 2 to 10; Rb and Rc are independently a hydrogen atom or a carbon atom; When it is a carbon atom, it is independently an alkyl group having 1 to 6 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, or a benzene ring; When they are carbon atoms, Ra and Rb are independent of each other or linked to form a ring.

6. The method for preparing the modified polyimide according to claim 5, wherein: The molar amount of the modifier in step (3) and step (d) is independently 0.01 to 5% of the molar sum of the diamine monomer and the dianhydride monomer; In step (G), the mass ratio of the modifier to the aging system is 0.1-0.5:800-1200; The reaction temperature in step (3), step (d) and step (G) is independently 0 to 80° C., and the reaction time is independently 0.5 to 4 h.

7. The method for preparing the modified polyimide according to claim 6, wherein: In step (b) and step (D), the dehydrating agent is independently one or more of acetic anhydride, propionic anhydride and trifluoroacetic anhydride; in step (b) and step (D), the catalyst is independently one or more of pyridine, collidine, lutidine and triethylamine; The molar amount of the dehydrating agent in step (b) and step (d) is independently 1 to 20 times the molar amount of the dianhydride; The molar amount of the catalyst in step (b) and step (D) is independently 1 to 10 times the molar amount of the dianhydride; The solid content of the polyimide solution in step (b) and step (d) is independently 10 to 20 wt %.

8. The method for preparing the modified polyimide according to claim 7, wherein: The temperature of the imidization reaction in step (b) and step (d) is independently -20 to 200°C, and the time of the imidization reaction is independently 0.5 to 48 hours.

9. The method for preparing the modified polyimide according to claim 8, wherein: In step (F), the mass ratio of the first reaction system to the second reaction system is 5-10:1-5; The aging temperature in step (F) is 60-80° C. and the aging time is 0.5-4 h.

10. The modified polyimide prepared by the method for preparing the modified polyimide according to any one of claims 1 to 9.

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