CN114085378A

CN114085378A - Polyamide acid solution and preparation method thereof, polyimide film and preparation method and application thereof

Info

Publication number: CN114085378A
Application number: CN202111356070.7A
Authority: CN
Inventors: 马晓宇; 赵贺; 杨天宇; 张求学; 吕庆龙
Original assignee: Jilin Optical and Electronic Materials Co Ltd
Current assignee: Jilin Optical and Electronic Materials Co Ltd
Priority date: 2021-11-16
Filing date: 2021-11-16
Publication date: 2022-02-25
Anticipated expiration: 2041-11-16
Also published as: CN114085378B

Abstract

The invention relates to the technical field of high polymer materials, and particularly discloses a polyamic acid solution which comprises a compound I, a compound II and ionic liquid, wherein the chemical structural formulas of the compound I and the compound II are limited, and the specific composition of the ionic liquid is limited; also disclosed is a polyimide film prepared from the polyamic acid solution; the preparation method comprises the steps of coating a polyamic acid solution on a substrate, drying, controlling temperature rise, and curing, so that the polyimide film has low coefficient of linear expansion (CTE), low birefringence and excellent heat resistance; also disclosed is the use of the polyimide film in a display, a touch panel or a solar cell substrate.

Description

Polyamide acid solution and preparation method thereof, polyimide film and preparation method and application thereof

Technical Field

The invention relates to the technical field of high polymer materials, in particular to a polyamic acid solution and a preparation method thereof, a polyimide film and a preparation method and application thereof.

Background

The aromatic polyimide has excellent physical and chemical properties such as mechanical property, heat resistance and dielectric property, so that the aromatic polyimide has wide application in the fields of aerospace, semiconductor industry, electronic industry and the like. With the development of the display industry, people are actively promoting the development of polyimide film materials to replace ITO glass, the polyimide film materials endow the display with flexibility and light weight, and continuous production can be carried out by adopting a winding process so as to reduce the production cost. However, aromatic polyimides have a yellowish brown color due to intramolecular conjugation and formation of a charge transfer complex, and thus have poor optical formation of polyimide films.

At present, researchers have proposed many methods for improving optical properties of polyimide by polymerizing in an ionic liquid to obtain a colorless transparent polyimide film. A method for producing a transparent polyimide film having excellent thermal properties by introducing fluorine atoms into the molecule to thereby suppress the formation of intramolecular conjugation and a charge transfer complex, as in the patent publication No. CN 105492496B; the invention of patent publication No. 107531902A discloses a polyimide resin which is colorless and transparent while having improved heat resistance and mechanical properties, and which is obtained by copolymerizing a dianhydride monomer and a 1, 3-bis (4-aminophenoxy) phenylenediamine monomer. The invention patent with publication number CN105367795 is a method for polymerizing dianhydride and diamine in ionic liquid, which can cure polyimide at low temperature to avoid high-temperature yellowing during film forming, thereby obtaining colorless and transparent polyimide film. According to the invention patent with the publication number of CN112175184A, the ionic liquid is introduced into the aliphatic polyimide, so that the conjugated electron cloud density is reduced, the conjugation is cut off, the transparency of the film is improved, and the flexible polyimide film with high transparency and low chroma is prepared. However, the birefringence of the polyimide film disclosed above is generally poor, and when light passes through the film having a large birefringence, problems such as incorrect color display, color blurring or reduction of the viewing angle may occur, and such technical problems often limit the application of the polyimide material.

Therefore, it is a technical problem to be solved by those skilled in the art to provide a polyimide film having excellent heat resistance and mechanical properties, and a method for preparing the same and applications thereof.

Disclosure of Invention

In view of the above, the present invention provides a polyamic acid solution and a preparation method thereof, and discloses a polyimide film obtained by thermally curing the polyamic acid solution, such that the polyimide film has a low coefficient of linear expansion (CTE), a low birefringence, and excellent heat resistance.

In order to achieve the purpose, the invention adopts the following technical scheme:

a polyamic acid solution, which comprises a compound I, a compound II and an ionic liquid; the chemical structural formula of the compound I is shown as the formula I:

the chemical structural formula of the compound II is shown as the formula II:

in the formula I and the formula II, X is an aliphatic cyclic or aromatic cyclic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4; y is aliphatic cyclic or aromatic cyclic 2-valent diamine residue with the carbon number more than or equal to 4; n is an integer of 50-300; m is an integer of 50-300;

the chemical structural formula of Z is formula III:

in the formula III, R is C2-18 olefin, C1-10 alkylsilyl, C1-8 alkoxy, C3-8 cycloalkoxy, alkali metal ion, ammonium ion, imidazolium ion or pyridinium ion;

the ionic liquid is one or a mixture of 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride and 1-butyl-3-methylimidazole chloride.

Preferably, in the polyimide solution, the total content of a first compound in which X is a residue of an aromatic cyclic 4-valent tetracarboxylic dianhydride having not less than 4 carbon atoms and Y is a residue of an aromatic cyclic 2-valent diamine having not less than 4 carbon atoms and a second compound in which X is a residue of an aromatic cyclic 4-valent tetracarboxylic dianhydride having not less than 4 carbon atoms and Y is a residue of an aromatic cyclic 2-valent diamine having not less than 4 carbon atoms is more than 50 mol% based on the total of the first compound and the second compound.

Preferably, in the polyimide solution, the total content of a first compound in which X is a residue of an aromatic cyclic 4-valent tetracarboxylic dianhydride having not less than 4 carbon atoms and Y is a residue of an aromatic cyclic 2-valent diamine having not less than 4 carbon atoms and a second compound in which X is a residue of an aromatic cyclic 4-valent tetracarboxylic dianhydride having not less than 4 carbon atoms and Y is a residue of an aromatic cyclic 2-valent diamine having not less than 4 carbon atoms is more than 80 mol% based on the total content of the first compound and the second compound.

Preferably, in the polyimide solution, the total content of a first compound in which X is a residue of an aromatic cyclic 4-valent tetracarboxylic dianhydride having not less than 4 carbon atoms and Y is a residue of an aromatic cyclic 2-valent diamine having not less than 4 carbon atoms and a second compound in which X is a residue of an aromatic cyclic 4-valent tetracarboxylic dianhydride having not less than 4 carbon atoms and Y is a residue of an aromatic cyclic 2-valent diamine having not less than 4 carbon atoms is more than 90 mol% based on the total content of the first compound and the second compound.

Preferably, the chemical structural formula of X is formula IV:

in the formula IV, A is any one of direct bonding, ether bond, methylene, ester bond, ketone bond, amido bond, dimethylsilylene, alkylene with 1-6 carbon atoms and aromatic group with less than 12 carbon atoms, and R₁Is any one of hydrogen atom, aromatic group with less than 12 carbon atoms, alkyl with 1-3 carbon atoms, halogen and hydroxyl, R₂Is an aromatic hydrocarbon with hydrogen atom and carbon number less than 12Any one of a group, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group, and p is an integer of 0 to 3.

Preferably, A is a direct bond and R is₁Is a hydrogen atom, said R₂Is a hydrogen atom, and p is 1; the polyimide film obtained can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

Preferably, the X is a residue of a 4-valent tetracarboxylic dianhydride, and the 4-valent tetracarboxylic dianhydride may be pyromellitic acid, 2,3,5, 6-pyridinetetracarboxylic acid, 3,3',4,4' -biphenyltetracarboxylic acid, 2,3,3',4' -biphenyltetracarboxylic acid, 2',3,3' -biphenyltetracarboxylic acid; 3,3',4,4' -benzophenone tetracarboxylic acid, 2',3,3' -benzophenone tetracarboxylic acid, 3,4' -oxydiphthalic anhydride, 1, 4-bis (trifluoromethyl) -2,3,5, 6-benzenetetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) sulfone, bis (3, 4-dicarboxyphenyl) ether, 1,4,5, 8-naphthalenetetracarboxylic dianhydride, 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 3,4,9, 10-perylenetetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) sulfide dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) propane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) propane dianhydride, P-phenylene-bistrimelliate dianhydride, p-ethylene-bistrimelliate dianhydride, ethylene glycol bistrimellitic anhydride, 4,4'- (4,4' -isopropyldiphenoxy) bis (phthalic anhydride), 3',4,4' -triphendiether tetracarboxylic dianhydride, and the like, 4- (2, 5-dioxotetrahydrofuran-3-yl) -1,2,3, 4-tetrahydronaphthalene-1, 2-dicarboxylic anhydride, 1,6,7, 12-tetra-t-butylphenoxyperylene-3, 4,9, 10-tetracarboxylic dianhydride, and the like, and two or more of these monomers may be used in combination.

Preferably, the chemical structural formula of Y is formula V:

in the formula V, B is direct bond, ether bond, methylene, ester bond, ketone bond, amido bond, dimethylsilylene, alkylene with 1-6 carbon atoms, and aromatic group with 12 or less carbon atomsAny one of the radicals, R₃Any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; r₄Any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; q is an integer of 0 to 3.

Preferably, B is a direct bond and R is₃Is a hydrogen atom, said R₄Is a hydrogen atom, and p is 1; the polyimide film obtained can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

Preferably, Y is a 2-valent diamine residue, and the 2-valent diamine may be m-phenylenediamine, p-phenylenediamine, 3, 5-diaminobenzoic acid, 1, 5-naphthalenediamine, 2, 6-naphthalenediamine, 9, 10-anthracenediamine, 2, 7-diaminofluorene, 4 '-diaminobenzanilide, 3,4' -diaminodiphenyl ether, 2, 4-diaminofluorobenzene, 2, 5-diaminofluorobenzene, 2, 4-diaminotoluene, 2-methyl-1, 4-phenylenediamine, 2, 5-diaminobenzotrifluoride, 3, 5-diaminobenzotrifluoride, 2, 3-diaminopyridine, 2, 4-diaminopyridine, 2, 5-diaminopyridine, 3, 4-diaminophenol, 2, 5-diaminophenol, m-xylenol, 3, 6-diaminocarbazole, 2, 6-diaminopyrazine, 1, 5-naphthalenediamine, 1, 8-naphthalenediamine, 2, 3-naphthalenediamine, 1, 4-naphthalenediamine, 2, 7-naphthalenediamine, benzidine, 3 '-dimethylbenzidine, 4' -diaminodiphenylsulfone, 3 '-diaminodiphenylsulfone, 2' -diaminodiphenylsulfone, 4 '-diaminodiphenylmethane, 3' -diaminodiphenylmethane, 3,4 '-diaminodiphenylmethane, 4' -diaminodiphenylether, 3 '-diaminodiphenylether, 3,4' -diaminodiphenylether, 2, 6-diaminoanthraquinone, 4 '-diaminobenzophenone, 3' -diaminobenzophenone, 1, 5-naphthalenediamine, 1, 8-naphthalenediamine, 2, 3-diaminodiphenylether, 3,4 '-diaminodiphenylether, 3' -diaminobenzophenone, 4 '-diaminodiphenylether, 2, 6-diaminoanthraquinone, 4' -diaminobenzophenone, 3 '-diaminobenzophenone, 2, 4' -diaminobenzophenone, and the like, 4,4' -aminobenzyl bibenzyl, 4' -diaminodiphenyl disulfide, 2' -diaminodiphenyl disulfide, 4' -diaminobenzanilide, 3' -diaminobenzanilide, 2' -diaminobenzanilide, 3',5,5' -tetramethyl-4, 4' -diaminodiphenylmethane, 1, 4-bis (4-aminophenoxy) benzene, and the like, and these diamine monomers may be used alone or in combination of two or more.

Preferably, Z represents a terminal capping agent of polyamic acid, and is represented by formula iii, preferably any one of dimethyl dicarbonate, diisopropyl dicarbonate, di-tert-butyl dicarbonate, diethyl peroxydicarbonate, fluorenylmethoxycarbonyl chloride, acetyl chloride, benzoyl chloride, maleic anhydride, 3-phenylethynylphthalic anhydride, itaconic anhydride, benzyl chloroformate, and 1,2,3, 6-tetrahydrophthalic anhydride.

Preferably, the ionic liquid is imidazole ionic liquid.

Further preferably, the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium acetate, 1-n-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium sulfate, 1-ethyl-3-methylimidazolium dicyanamide, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium trifluoroacetate, 1-propyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hydroxyethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrachloride, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, or mixtures thereof, 1-ethyl-3-methylimidazole, 1-butyl-3-methylimidazole trifluoromethanesulfonate, 1, 3-bis (2-methoxy-2-oxyethyl) imidazole chloride and 1, 3-bis (2-methoxy-2-oxyethyl) imidazole tetrafluoroborate.

Still more preferably, the ionic liquid is 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride or 1-n-butyl-3-methylimidazole chloride.

Preferably, the concentration of the ionic liquid is < 5000 ppm.

Preferably, the concentration of the ionic liquid is < 3000 ppm.

Further preferably, the concentration of the ionic liquid is 500-1000 ppm.

Preferably, the weight average molecular weight of the polyamic acid solution is 30000-100000 g/mol, and the width of molecular weight distribution is 1.1-3.0.

Preferably, the viscosity of the polyamic acid solution is 500cp to 10000cp at 25 ℃.

Further preferably, the viscosity of the polyamic acid solution is 1000cp to 8000cp at 25 ℃. When the viscosity is more than 1000cp, polyamic acid with higher molecular weight can be obtained, thereby ensuring the mechanical strength of polyimide, and when the viscosity is more than 8000cp, the fluidity is poor when coating and film forming are carried out, and a uniform and smooth film is difficult to obtain.

Preferably, the solid content of the polyamic acid solution is 5 wt% to 70 wt%.

More preferably, the polyamic acid solution has a solid content of 5 wt% to 50 wt%.

Further preferably, the solid content of the polyamic acid solution is 10 wt% to 30 wt%.

If the solid content of the polyamic acid solution is 10 wt% or less, a variation in film thickness is not easily controlled when a polyimide film is formed by imidization, and if the solid content is 30 wt% or more, a thickness of a polyimide film obtained in the process of preparing a polyimide film is difficult to control.

The invention also provides a preparation method of the polyamic acid solution, which comprises the following steps:

(1) adding diamine and dianhydride into an aprotic polar solvent under inert gas to carry out polymerization reaction to obtain a first-stage mixed solution;

(2) adding diamine, dianhydride, a capping agent and ionic liquid into an aprotic polar solvent under inert gas for polymerization reaction, separating out the obtained reaction liquid in a poor solvent, filtering and drying to obtain first-grade mixed powder;

(3) and adding the first-stage mixed powder into the first-stage mixed solution, and mixing and dissolving to obtain the polyamic acid solution.

The beneficial effects of the preferred technical scheme are as follows: in the subsequent imidization process of polyamic acid, because hydrogen bonds formed between imidazole ionic liquid containing nitrogen heterocycles and polyimide molecular chains replace Van der Waals force between the polyimide molecular chains, a polyimide network crosslinked by the ionic liquid is more likely to be formed inside, so that the distribution of the molecular chains is disturbed, the probability of orderly arrangement of the molecular chains is reduced, the isotropic molecular chain structure is more likely to be formed inside, and the birefringence is reduced. Meanwhile, the cross-linked structure can increase the light passing path, and further can reduce the birefringence of the polyimide film under the condition of not damaging the thermal property and the mechanical property of the polyimide.

Preferably, the molar ratio of the diamine to the dianhydride in step (1) is (0.9-1.1): 1; the temperature of the polymerization reaction is 20-120 ℃, and the time is 1-12 h;

the molar ratio of the diamine to the dianhydride in the step (2) is (0.9-1.1): 1; the mass ratio of the ionic liquid to the dianhydride is (0.05-0.5): 1; the mass ratio of the end-capping reagent to the diamine is 0.01-5%; the temperature of the polymerization reaction is 20-120 ℃, and the time is 1-12 h; the mass ratio of the poor solvent to the reaction solution is 1: (5-50).

Preferably, the aprotic polar solvent includes N-methylpyrrolidone, N-ethylpyrrolidone, N-dimethylacetamide, N-dimethylformamide, N-diethylacetamide, N-diethylformamide, 3-methoxy-N, N-dimethylpropionamide, 3-N-butoxy-N, N-dimethylpropionamide, N-dimethylisobutylamide, 1, 3-dimethyl-2-imidazolidinone, N-dimethylpropylurea, dimethyl sulfoxide, N-methyl-2-oxazolidinone, delta-valerolactone, gamma-butyrolactone, cyclohexanone, diethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, N-dimethylacetamide, N-dimethylformamide, N-methoxy-N, N-dimethylpropionamide, 3-N-butoxy-N, N-dimethylpropionamide, N-dimethyl-N, N-dimethylpropionamide, N-dimethylisobutyramide, 1, 3-dimethyl-2-imidazolidinone, N-dimethylpropylurea, N-methyl-2-oxazolidinone, delta-valerolactone, gamma-butyrolactone, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, and N-methyl-butyl ether, Ethylene glycol monobutyl ether, propylene glycol diacetate, propylene glycol methyl ether, propylene glycol propyl ether, propylene glycol butyl ether, propylene glycol phenyl ether, dipropylene glycol methyl ether, dipropylene glycol propyl ether, 1, 4-butanediol diacetate, 1, 3-butanediol diacetate, 1, 6-hexanediol diacetate, 3-methoxybutanol, 1, 3-butanediol, 3-methoxy-3-methyl-1-butanol, methanol, ethanol, n-propanol, isopropanol, ethyl lactate, butyl benzoate, diacetone alcohol.

Preferably, the poor solvent in step (2) comprises one or more of water, methanol and ethanol.

Preferably, the inert gas in step (1) and step (2) comprises nitrogen or argon.

Preferably, the molar ratio of the diamine to the dianhydride in step (1) and step (2) is (0.95-1.05): 1.

preferably, the mass ratio of the ionic liquid to the dianhydride in the step (2) is (0.1-0.3): 1.

preferably, the mass ratio of the poor solvent to the reaction solution in the step (2) is 1: (10-25).

Preferably, the mass ratio of the poor solvent to the reaction solution in the step (2) is 1: (5-15).

The beneficial effects of the preferred technical scheme are as follows: when the ionic liquid added in the polymerization process is too little or the ratio of the poor solvent is too high when the polyamic acid powder is separated out, the content of the ionic liquid remaining at the end is too low; when the ionic liquid added in the polymerization process is too much or the ratio of the poor solvent is too low when the polyamic acid powder is precipitated, the content of the ionic liquid remaining at the end is too high, and the heat resistance of the formed polyimide is not satisfactory.

Preferably, the polymerization temperature in step (1) and step (2) is 30 ℃ to 100 ℃.

Further preferably, the polymerization temperature in step (1) and step (2) is 40 ℃ to 80 ℃.

Preferably, the polymerization reaction time in the step (1) and the step (2) is 2h-8 h.

Further preferably, the polymerization reaction time in step (1) and step (2) is 3h to 6 h.

The invention also provides a polyimide film prepared from the polyamic acid solution.

Preferably, the polyimide film has a light transmittance of > 70% at a wavelength of 500 nm. More preferably, the polyimide film has a light transmittance of > 75% at a wavelength of 500 nm.

Further, the polyimide film preferably has a birefringence of < 0.1. More preferably, the polyimide film has a birefringence of < 0.05. Still more preferably, the polyimide film has a birefringence of < 0.01. The birefringence is a difference between a refractive index in a direction perpendicular to the film surface and a refractive index in a direction horizontal to the film surface.

Preferably, the polyimide film has a linear expansion coefficient of < 30 ppm/DEG C at 50-200 ℃. Further preferably, the polyimide film has a linear expansion coefficient of < 10 ppm/DEG C at 50 ℃ to 200 ℃.

Preferably, the polyimide film has a birefringence of 0.05 or less and a linear expansion coefficient of < 10 ppm/DEG C at 50-200 ℃.

The invention also provides a preparation method of the polyimide film, which comprises the following steps: coating the polyamic acid solution on a substrate, drying, and then controlling temperature rise to perform curing treatment to obtain the polyimide film; the drying temperature is 80-180 ℃, and the drying time is 10-100 min; the maximum temperature of the curing is 350-480 ℃, the holding time of 150-250 ℃ in the temperature rising process is more than 10min, and the curing time is 2-5 h.

Preferably, the drying temperature is 110 ℃ to 180 ℃.

Preferably, the drying temperature is 80-150 ℃.

Preferably, the curing treatment is carried out by heating from room temperature to 80-100 ℃ at a heating rate of 1-5 ℃/min, and maintaining at 80-100 ℃ for 60-120 min; then the temperature is raised to 120-170 ℃ at the temperature raising rate of 1-5 ℃/min, and the temperature is maintained at 120-170 ℃ for 30-120 min; then the temperature is raised to 280 ℃ at the temperature raising rate of 1-5 ℃/min, and the temperature is maintained at 280 ℃ of 220 ℃ to 120 min; finally, the temperature is raised to 350-480 ℃ at the heating rate of 1-5 ℃/min, and the temperature is maintained at 350-480 ℃ for 10-120 min.

In addition, the invention provides an application of the polyimide film in a display, a touch panel or a solar cell substrate.

According to the technical scheme, compared with the prior art, the invention discloses a polyamic acid solution and a preparation method thereof, a polyimide film and a preparation method and application thereof, and the polyamic acid solution has the following beneficial effects:

according to the invention, 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole chloride and other ionic solutions are added in the reaction process of dianhydride and diamine to play a role in catalysis, so that the reaction is more complete, and meanwhile, the ionic liquid remained in the reaction is discovered unexpectedly, so that the birefringence performance of the film can be improved under the condition of not affecting the mechanical performance and the thermal performance;

the polyamic acid solution obtained by the synthesis method can be imidized to obtain a polyimide film with excellent heat resistance, low birefringence and low coefficient of linear expansion (CTE);

further, the polyimide film obtained from the polyamic acid solution disclosed in the present invention can be used as a substrate to obtain a flexible and highly reliable image display device, solar cell panel, or the like.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The compounds used in the examples are hereinafter described in short.

PDA: p-phenylenediamine

BPDA: 3,3',4,4' -Biphenyltetracarboxylic dianhydride

And (3) DAE: 4,4' -diaminodiphenyl ether

BTDA: 3,3',4,4' -benzophenone tetracarboxylic acid

NMP: n-methyl-2-pyrrolidone

PDA-Boc: n- (tert-butoxy) -1, 4-benzenediamine

Boc: di-tert-butyl dicarbonate

Example 1

The embodiment 1 of the invention discloses a polyamic acid solution, which comprises a compound I, a compound II and an ionic liquid; the chemical structural formula of the compound I is shown as the formula I:

the chemical structural formula of the compound II is shown as the formula II:

the chemical structural formula of Z is formula III:

the ionic liquid is one or more of 1-butyl-3-methylimidazole trifluoroacetate, chlorinated 1-hydroxyethyl-3-methylimidazole and chlorinated 1-butyl-3-methylimidazole.

In order to optimize the technical scheme, in the polyimide solution, the total content of a first compound in which X is an aromatic cyclic 4-valent tetracarboxylic dianhydride residue with the carbon number not less than 4 and Y is an aromatic cyclic 2-valent diamine residue with the carbon number not less than 4 and a second compound in which X is an aromatic cyclic 4-valent tetracarboxylic dianhydride residue with the carbon number not less than 4 and Y is an aromatic cyclic 2-valent diamine residue with the carbon number not less than 4 is more than 50mol percent relative to the first compound and the second compound.

In order to optimize the technical scheme, in the polyimide solution, the total content of a first compound in which X is an aromatic cyclic 4-valent tetracarboxylic dianhydride residue with the carbon number not less than 4 and Y is an aromatic cyclic 2-valent diamine residue with the carbon number not less than 4 and a second compound in which X is an aromatic cyclic 4-valent tetracarboxylic dianhydride residue with the carbon number not less than 4 and Y is an aromatic cyclic 2-valent diamine residue with the carbon number not less than 4 is more than 80mol percent relative to the first compound and the second compound.

In order to optimize the technical scheme, in the polyimide solution, the total content of a first compound in which X is an aromatic cyclic 4-valent tetracarboxylic dianhydride residue with the carbon number not less than 4 and Y is an aromatic cyclic 2-valent diamine residue with the carbon number not less than 4 and a second compound in which X is an aromatic cyclic 4-valent tetracarboxylic dianhydride residue with the carbon number not less than 4 and Y is an aromatic cyclic 2-valent diamine residue with the carbon number not less than 4 is more than 90mol percent relative to the first compound and the second compound.

In order to optimize the technical scheme, X is an aromatic ring 4-valent tetracarboxylic dianhydride residue with the carbon atom number more than or equal to 4; y is an aromatic cyclic 2-valent diamine residue having 4 or more carbon atoms.

In order to optimize the technical scheme, the chemical structural formula of X is shown as formula IV:

in the formula IV, A is any one of direct bonding, ether bond, methylene, ester bond, ketone bond, amido bond, dimethylsilylene, alkylene with 1-6 carbon atoms and aromatic group with less than 12 carbon atoms, R₁Is any one of hydrogen atom, aromatic group with less than 12 carbon atoms, alkyl with 1-3 carbon atoms, halogen and hydroxyl, R₂Is any one of a hydrogen atom, an aromatic group having less than 12 carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group, and p is an integer of 0 to 3.

In order to optimize the technical scheme, A is direct bonding, R₁Is a hydrogen atom, R₂Is a hydrogen atom and p is 1. The polyimide film obtained can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

In order to optimize the technical scheme, X is a 4-valent tetracarboxylic dianhydride residue, and the 4-valent tetracarboxylic dianhydride can be pyromellitic acid, 2,3,5, 6-pyridinetetracarboxylic acid, 3,3',4,4' -biphenyltetracarboxylic acid, 2,3,3',4' -biphenyltetracarboxylic acid, 2',3,3' -biphenyltetracarboxylic acid; 3,3',4,4' -benzophenonetetracarboxylic acid, 2',3,3' -benzophenonetetracarboxylic acid, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane, 2-bis (2, 3-dicarboxyphenyl) hexafluoropropane, 2-bis (3, 4-dicarboxyphenyl) propane, 2-bis (2, 3-dicarboxyphenyl) propane, 1-bis (3, 4-dicarboxyphenyl) ethane, 1-bis (2, 3-dicarboxyphenyl) ethane, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] hexafluoropropane, 2-bis [4- (2, 3-dicarboxyphenoxy) phenyl ] hexafluoropropane, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl propane, 2-bis [4- (2, 3-dicarboxyphenoxy) phenyl ] propane, 1,2,5, 6-naphthalene tetracarboxylic acid, 1,4,5, 8-naphthalene tetracarboxylic acid, 2,3,6, 7-naphthalene tetracarboxylic acid, 3,4,9, 10-perylene tetracarboxylic acid.

In order to optimize the technical scheme, the chemical structural formula of Y is shown as formula V:

in the formula V, B is any one of direct bonding, ether bond, methylene, ester bond, ketone bond, amido bond, dimethylsilylene, alkylene with 1-6 carbon atoms and aromatic group with less than 12 carbon atoms, R₃Any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; r₄Any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; q is an integer of 0 to 3.

In order to optimize the technical scheme, B is direct bonding, R₃Is a hydrogen atom, R₄Is a hydrogen atom, p is 1; the polyimide film obtained can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

For optimization of the technical scheme, Y is a 2-valent diamine residue, and the 2-valent diamine may be m-phenylenediamine, p-phenylenediamine, 3, 5-diaminobenzoic acid, 1, 5-naphthalenediamine, 2, 6-naphthalenediamine, 9, 10-anthracenediamine, 2, 7-diaminofluorene, 4 '-diaminobenzanilide, 3,4' -diaminodiphenyl ether, 4 '-diaminodiphenyl ether, 3-carboxy-4, 4' -diaminodiphenyl ether, 3-sulfonic acid-4, 4 '-diaminodiphenyl ether, 3,4' -diaminodiphenylmethane, 4 '-diaminodiphenylmethane, 3,4' -diaminodiphenylsulfone, 4 '-diaminodiphenylsulfone, 3,4' -diaminodiphenylsulfide, o, 4,4 '-diaminodiphenyl sulfide, 4-aminophenyl 4-aminobenzoate, 9-bis (4-aminophenyl) fluorene, 1, 3-bis (4-anilino) tetramethyldisiloxane, such as 4,4' -diaminobiphenyl, 2 '-dimethyl-4, 4' -diaminobiphenyl, 2 '-diethyl-4, 4' -diaminobiphenyl, 3 '-dimethyl-4, 4' -diaminobiphenyl, 3 '-diethyl-4, 4' -diaminobiphenyl, bis (4-aminophenoxyphenyl) sulfone, bis (3-aminophenoxyphenyl) sulfone, bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl ] ether, bis (4-aminophenoxy) phenyl) ether, bis (4-aminophenyl) fluorene, and the like, 2, 2-bis [4- (4-aminophenoxy) phenyl ] propane and 2, 2-bis [4- (4-aminophenoxy) phenyl ] hexafluoropropane.

In order to optimize the technical scheme, Z is any one of dimethyl dicarbonate, diisopropyl dicarbonate, di-tert-butyl dicarbonate, diethyl peroxydicarbonate, fluorenylmethoxycarbonyl acyl chloride, acetyl chloride, benzoyl chloride, maleic anhydride, 3-phenylethynyl phthalic anhydride, itaconic anhydride, benzyl chloroformate and 1,2,3, 6-tetrahydrophthalic anhydride.

In order to optimize the technical scheme, the ionic liquid is imidazole ionic liquid.

Further in order to optimize the technical scheme, the ionic liquid is 1-ethyl-3-methylimidazole tetrafluoroborate, 1-ethyl-3-methylimidazole acetate, 1-n-butyl-3-methylimidazole bromide, 1-ethyl-3-methylimidazole ethyl sulfate, 1-ethyl-3-methylimidazole dicyanamide salt, 1-ethyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole trifluoroacetate, 1-propyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole tetrafluoroborate, 1-hydroxyethyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole tetrachloroiron, 1-butyl-3-methylimidazole hexafluorophosphate, 1-ethyl-3-methylimidazole sulfate, sodium hydrogen chloride, sodium hydrogen chloride, sodium chloride, 1-ethyl-3-methylimidazole, 1-butyl-3-methylimidazole trifluoromethanesulfonate, 1, 3-bis (2-methoxy-2-oxyethyl) imidazole chloride and 1, 3-bis (2-methoxy-2-oxyethyl) imidazole tetrafluoroborate.

Further in order to optimize the technical scheme, the ionic liquid is 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride or 1-n-butyl-3-methylimidazole chloride.

In order to optimize the technical scheme, the concentration of the ionic liquid is less than 5000 ppm.

In order to optimize the technical solution, the concentration of the ionic liquid is less than 3000 ppm.

Further, in order to optimize the technical scheme, the concentration of the ionic liquid is 500-1000 ppm.

In order to optimize the technical scheme, the weight average molecular weight of the polyamic acid solution is 30000-100000 g/mol, and the molecular weight distribution width is 1.1-3.0.

In order to optimize the technical scheme, the viscosity of the polyamide acid solution is 500cp-10000cp at 25 ℃.

Further to optimize the technical scheme, the viscosity of the polyamic acid solution at 25 ℃ is 1000cp-8000 cp.

In order to optimize the technical scheme, the solid content of the polyamic acid solution is 5-70 wt%.

In order to optimize the technical scheme, the solid content of the polyamic acid solution is 5 wt% -50 wt%.

Further, in order to optimize the technical scheme, the solid content of the polyamic acid solution is 10 wt% -30 wt%.

Example 2

The embodiment 2 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and a first-grade mixed solution is obtained for standby after reaction for 3 hours;

(2) under the protection of nitrogen, 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after reaction for 3 hours, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

(3) the polyamic acid powder obtained by drying was dissolved in the first-order mixed solution to obtain a polyamic acid solution having a solid content of 18 wt%.

Example 3

Embodiment 3 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) under the protection of nitrogen, 350g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and a first-grade mixed solution is obtained for standby after reaction for 3 hours;

(2) under the protection of nitrogen, 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after reaction for 3 hours, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate; filtering out the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12h to obtain polyamic acid powder;

(3) the polyamic acid powder obtained by drying was dissolved in the first-order mixed solution to obtain a polyamic acid solution having a solid content of 10 wt%.

Example 4

Embodiment 4 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) under the protection of nitrogen, 83.3g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and a first-grade mixed solution is obtained for standby after reaction for 3 hours;

(2) under the protection of nitrogen, adding 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA into a four-neck flask with a stirring paddle and a thermometer, stirring at the rotation speed of 300rpm at 55 ℃ until the PDA is dissolved, adding 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc, reacting for 3 hours to obtain a reaction product, slowly adding the reaction product into 3000g of purified water under the stirring condition at the rotation speed of 500rpm to separate out a yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at the temperature of 80 ℃ for 12 hours to obtain polyamide acid powder;

Example 5

Embodiment 5 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) under the protection of nitrogen, 83.3g of NMP and 4.6g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 15.22g of BTDA and 10g of NMP are added, and after reaction for 3 hours, a first-grade mixed solution is obtained for later use;

(2) under the protection of nitrogen, 81.1g of NMP, 1.84g of 1-butyl-3-methylimidazole trifluoroacetate and 4.6g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 15.22g of BTDA, 10g of NMP and 0.41g of PDA-Boc are added, and after reaction for 3 hours, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

Example 6

Embodiment 6 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) under the protection of nitrogen, 83.3g of NMP and 8.03g of DAE are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until PDA is dissolved, 11.8g of BPDA and 10g of NMP are added, and a first-grade mixed solution is obtained for standby after reaction for 3 hours;

(2) under the protection of nitrogen, 81.1g of NMP, 3.212g of 1-butyl-3-methylimidazole trifluoroacetate and 8.03g of DAE are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until PDA is dissolved, 11.8g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after reaction for 3 hours, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

Example 7

Embodiment 7 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(2) under the protection of nitrogen, 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.43g of Boc are added, and after reaction for 3 hours, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

Example 8

Embodiment 8 of the present invention discloses a method for preparing a polyamic acid solution, which specifically comprises the following steps:

under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and a first-grade mixed solution is obtained for standby after reaction for 3 hours;

under the protection of nitrogen, 81.1g of NMP, 1.064g of 1-butyl-3-methylimidazole trifluoroacetate, 1.064g of 1-hydroxyethyl-3-methylimidazole chloride and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after reaction for 3 hours, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder; the polyamic acid powder obtained by drying was dissolved in the first-order mixed solution to obtain a polyamic acid solution having a solid content of 18 wt%.

Example 9

Embodiment 9 of the present invention discloses a method for preparing a polyamic acid solution, which specifically comprises the following steps:

(2) under the protection of nitrogen, 81.1g of NMP, 0.71g of 1-butyl-3-methylimidazole trifluoroacetate, 0.71g of 1-hydroxyethyl-3-methylimidazole chloride, 0.71g of 1-butyl-3-methylimidazole chloride and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer at the rotating speed of 300rpm and stirred until the PDA is dissolved at 55 ℃, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and reaction is carried out for 3 hours to obtain a reaction product; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

Example 10

The embodiment 10 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(2) under the protection of nitrogen, 81.1g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and reaction is carried out for 3 hours to obtain a reaction product; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

(3) the polyamic acid powder obtained by drying was dissolved in the primary mixed solution, and 0.1111g of 1-butyl-3-methylimidazolium trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 11

Embodiment 11 of the present invention discloses a method for preparing a polyamic acid solution, which specifically comprises the following steps:

(3) the polyamic acid powder obtained by drying was dissolved in the primary mixed solution, and 0.1333g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 12

Embodiment 12 of the present invention discloses a method for preparing a polyamic acid solution, which specifically comprises the following steps:

(3) the polyamic acid powder obtained by drying was dissolved in the first-order mixed solution, and 0.1667g of 1-butyl-3-methylimidazolium trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 13

Embodiment 13 of the present invention discloses a method for preparing a polyamic acid solution, which specifically comprises the following steps:

(3) the polyamic acid powder obtained by drying was dissolved in the first-order mixed solution, and 0.222g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 14

The embodiment 14 of the invention discloses a preparation method of a polyimide film, which specifically comprises the following steps:

the polyamic acid solutions prepared in example 2 were each placed on a silicon plate, coated to form a film using a spin coater, and then the silicon wafer coated with the film was transferred to a heating plate at 120 ℃ to be dried for 15 min. Putting the mixture into a high-temperature clean oven to perform imidization and film formation after drying. The curing process is as follows: heating from room temperature to 100 deg.C at a heating rate of 5 deg.C/min, and maintaining at 100 deg.C for 60 min; then the temperature is raised to 170 ℃ at the temperature raising rate of 5 ℃/min, and the temperature is maintained at 170 ℃ for 30 min; then raising the temperature to 280 ℃ at a temperature raising rate of 5 ℃/min, and maintaining the temperature at 280 ℃ for 100 min; finally, the temperature is raised to 450 ℃ at the temperature raising rate of 5 ℃/min, and the temperature is maintained at 450 ℃ for 20 min. And naturally cooling to room temperature, soaking the silicon crystal plate with the film in water, peeling and drying to obtain the polyimide film.

Example 15

Embodiment 15 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 3".

Example 16

Embodiment 16 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 4".

Example 17

Embodiment 15 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 5".

Example 18

Embodiment 18 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 6".

Example 19

Embodiment 19 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 7".

Example 20

Embodiment 20 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 8".

Example 21

Embodiment 21 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 9".

Example 22

Embodiment 15 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 10".

Example 23

Embodiment 15 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 11".

Example 24

Embodiment 24 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 12".

Example 25

Embodiment 15 of the present invention discloses a method for producing a polyimide film, which is different from embodiment 14 only in that "the polyamic acid solution produced in embodiment 2" is replaced with "the polyamic acid solution produced in embodiment 13".

Comparative example 1

The invention discloses a preparation method of a polyimide film, which comprises the following steps:

(1) under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after reaction for 3 hours, a mixed solution is obtained for later use;

(2) in a four-necked flask equipped with a stirring paddle and a thermometer, 81.1g of NMP and 5.32g of PDA were charged under nitrogen atmosphere at 300rpm under 55 ℃ with stirring until the PDA was dissolved, and 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc were added to react for 3 hours, thereby obtaining a reaction product. Slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

(3) dissolving the dried polyamic acid powder in the mixed solution, adding 0.0556g of 1-butyl-3-methylimidazole trifluoroacetate to obtain a polyamic acid solution with the solid content of 18 wt%;

(4) in the same manner as in example 13, only "the polyamic acid solution prepared in example 2" was replaced with "the polyamic acid solution prepared in step (3)".

Comparative example 2

(2) under the protection of nitrogen, 81.1g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and reaction is carried out for 3 hours to obtain a reaction product;

slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

(3) the polyamic acid powder obtained by drying was dissolved in the mixed solution, and 0.555g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Comparative example 3

(1) introducing nitrogen into a three-neck flask provided with a mechanical stirring device, adding 10.64g of PDA, then adding 399.9g of ionic liquid 1, 3-bis (2-methoxy-2-oxyethyl) imidazole tetrafluoroborate, starting the mechanical stirring, and heating to dissolve the ionic liquid 1, 3-bis (2-methoxy-2-oxyethyl) imidazole tetrafluoroborate, wherein the temperature of a mixed solution in the three-neck flask is not higher than 50 ℃; adding 28.95g of BPDA into the three-neck flask after the diamine is completely dissolved, stirring for 10min, and extruding a nitrogen bag to remove air in the three-neck flask as much as possible; slowly heating the mixed solution in the three-neck flask to 180 ℃, stirring at the constant temperature of 180 ℃ for 9 hours, and then naturally cooling to room temperature to obtain a faint yellow polyimide prepolymer;

(2) pouring 65mL of methanol into a three-neck flask filled with a faint yellow polyimide prepolymer solution, stirring for 10min, standing, separating out faint yellow precipitates, washing at least three times with 65mL of methanol each time, performing suction filtration (the filtration mode can be suction filtration), and drying in a vacuum oven at 80 ℃ for 12h to obtain brown polyimide prepolymer powder; dissolving 1.50g of dried polyimide prepolymer powder into 6.83g of polar solution N, N-dimethylacetamide solution to prepare clear polyimide prepolymer glue solution with the solid content of 10%;

(3) uniformly coating the obtained polyimide prepolymer glue solution on a clean flat plate which can be a glass plate at 50 ℃, and putting the flat plate into a vacuum oven for curing, wherein the curing process comprises the following steps: curing at 50 ℃ for 1h, curing at 80 ℃ for 1h, then curing at 100 ℃ for 1h, then curing at 130 ℃ for 1h, then curing at 160 ℃ for 1h, then curing at 180 ℃ for 3h, finally closing an oven, cooling to room temperature, and stripping to obtain film-shaped polyimide; after the film-like polyimide was naturally cooled to room temperature, the film-like polyimide was peeled off from the glass plate with warm water to obtain a colorless transparent polyimide film having a thickness of 20 μm.

Comparative example 4

(1) 172.2g of NMP and subsequently 10.64g of PDA were placed in a 500ml three-necked flask equipped with nitrogen protection and mechanical stirring and dissolved at 10 ℃ with stirring; then 0.0945mol of 4,4' - (trifluoromethyl phenyl isopropyl) diphenyl anhydride is added to react with diamine, and the mixture is stirred for 8 hours at the temperature of 10 ℃ to obtain a copolyamide acid solution; adding 14.17g of 1-butyl-3-methylimidazole trifluoroacetate into the transparent copolyamide acid solution, and mechanically stirring for 3 hours to uniformly disperse the solution in the transparent copolyamide acid solution to finally form a colorless and transparent homogeneous mixed solution;

(2) defoaming the colorless and transparent homogeneous mixed liquid for one hour, casting the mixture onto a clean and dust-free glass plate, coating the mixture to a preset thickness by using a scraper, and putting the glass plate with the film (raw material) into an oven to complete thermal imidization according to the following processes of 150 ℃, 40 minutes, 240 ℃, 40 minutes, 310 ℃, 40 minutes, 350 ℃ and 40 minutes; and after a period of time, cooling the temperature of the oven to room temperature, and taking out the glass substrate to obtain the transparent polyimide composite film.

Comparative example 5

(3) dissolving the dried polyamic acid powder in the mixed solution to obtain a polyamic acid solution with the solid content of 18 wt%;

Comparative example 6

(1) under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and the mixture reacts for 3 hours to obtain a polyamic acid solution for later use;

(2) under the protection of nitrogen, adding 81.1g of NMP, 2.128g of sodium n-hexane sulfonate and 5.32g of PDA into a four-neck flask with a stirring paddle and a thermometer, stirring at the rotating speed of 300rpm at 55 ℃ until the PDA is dissolved, adding 14.475g of BPDA and 10g of NMP, and reacting for 3 hours to obtain a reaction product; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

(3) the polyamic acid powder obtained by drying was dissolved in a polyamic acid solution to obtain a polyamic acid solution having a solid content of 18% by weight.

Comparative example 7

(2) under the protection of nitrogen, 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotating speed is 300rpm, the mixture is stirred at the temperature of 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and reaction is carried out for 3 hours to obtain a reaction product; slowly adding the reaction product into 3000g of purified water under the stirring condition of the rotating speed of 500rpm to separate out yellow precipitate, filtering the yellow precipitate, and drying in a vacuum oven at 80 ℃ for 12 hours to obtain polyamic acid powder;

(3) dissolving the polyamic acid powder obtained by drying in the mixed solution to obtain a polyamic acid solution with the solid content of 18 wt%;

Effect verification

1. Viscosity test of Polyamic acid solution

The following table 1-3 shows the viscosity of the polyamic acid solution used in examples 14-25, the polyamic acid solution prepared in steps (3) of comparative examples 1-2 and comparative examples 5-7, the polyimide prepolymer glue solution prepared in step (2) of comparative example 3, and the colorless and transparent homogeneous mixed solution obtained in step (1) of comparative example 4, measured by a Brookfiled rotational viscometer at a temperature of 25 ℃.

2. Polyamic acid solution molecular weight and polydispersity index of molecular weight test

The following tables 1 to 3 show the results of taking the polyamic acid solutions used in examples 14 to 25, the polyamic acid solutions prepared in comparative examples 1 to 2 and comparative examples 5 to 7 in the step (3), the polyimide prepolymer dope prepared in the step (2) in the comparative example 3, and the colorless and transparent homogeneous mixed solution obtained in the step (1) in the comparative example 4, and testing the weight average molecular weight and the polydispersity index of the molecular weight of the polyamic acid by using gel permeation chromatography (Waters-2695, Waters), polystyrene as a standard, Waters Styrage as a column, N-methyl-2-pyrrolidone as a mobile phase, and 40 ℃.

3. Polyimide film 500nm light transmittance

The polyamic acid films prepared in examples 14 to 25 and comparative examples 1 to 7 were measured for light transmittance at a wavelength of 550nm using an ultraviolet-visible spectrophotometer (model TU-1810PC), and the results obtained are shown in tables 1 to 3 below.

4. Linear Coefficient of Thermal Expansion (CTE) of polyimide film:

the polyamic acid films prepared in examples 14 to 25 and comparative examples 1 to 7 were taken, and polyimide films having a thickness of about 10 μm were cut into a rectangular shape of 13mm by 4mm, respectively, and used as test sample sheets. The test piece was placed in the middle of a jig having a length of 10mm, tested using a TMA4000 thermomechanical expansion analyzer from Perkin Elmer, with a load of about 0.15N applied, and measured by heating the test piece from 30 ℃ to 400 ℃ at a first stage at a heating rate of 10 ℃/min to 150 ℃ for 30min, at a second stage at a heating rate of 5 ℃/min to 30 ℃ and at a third stage at a heating rate of 5 ℃/min. The linear thermal expansion coefficient of the material at 50 ℃ to 300 ℃ is measured, and the final results are shown in tables 1 to 3 below.

5. Glass transition temperature (Tg) of polyimide film:

taking the polyamic acid films prepared in examples 14 to 25 and comparative examples 1 to 7, polyimide films having a thickness of about 10 μm were prepared as test sample pieces, respectively, and cut into 15mm by 5mm rectangular samples with a knife washed with acetone, and the test pieces were heated from room temperature to 500 ℃ in a nitrogen stream at a temperature rising rate of 5 ℃/min using a dynamic thermo-mechanical analyzer (DMA, model Q800) manufactured by usa. The temperature corresponding to the peak value of the damping coefficient (Tan delta) in the energy curve is measured, namely the glass transition temperature of the film, and the final results are shown in the following tables 1-3.

6. Thermal decomposition temperature Td (Td 1% and Td 5%)

Taking the polyamic acid films prepared in the examples 14 to 25 and the comparative examples 1 to 7, preparing a polyimide film with a thickness of about 10 μm as a test sample piece, taking about 10mg of the sample, using a thermogravimetric analyzer with German relaxation-resistant model TG209F1 to enable the sample piece to be heated to 150 ℃ at a heating rate of 10 ℃/min in the first stage, keeping the temperature for 30min, cooling to 50 ℃ in the second stage, and heating from 50 ℃ to 800 ℃ at a heating rate of 10 ℃/min in the third stage. From the resulting weight-temperature curves, the 1% and 5% weight loss temperatures were determined, with the final results shown in tables 1-3 below.

7. Polyimide film tensile Strength (Strength), tensile Modulus (Modulus), Elongation at break (Elongation):

polyimide films having a thickness of 10 μm were prepared as test samples from the polyamic acid films prepared in examples 14 to 25 and comparative examples 1 to 7, respectively, and cut into dumbbell shapes having a size of 50mm 4mm using a press die, the film samples were stretched using a universal tester (model: AG-I, Shimadzu, Kyoto, Japan) at a clamp pitch of 3mm and a stretching rate of 2mm/min, and the tensile strength, tensile modulus and elongation at break were determined from the curves by converting the tensile data into stress-strain curves, and the final results are shown in tables 1 to 3 below.

8. Determination of Birefringence

The refractive index of TE (n (TE)) and the refractive index of TM (n (TM)) at a wavelength of 632.8nm were measured for each of the polyamic acid films prepared in examples 14 to 26 and comparative examples 1 to 7 using a prism coupler (PC 2010, manufactured by METRICON). n (te) and n (tm) are refractive indices in the parallel direction and the perpendicular direction with respect to the polyimide film surface, respectively. The average refractive index n (AV) is calculated from ((2 xn (TE)2+ n (TM)2)/3) ^0.5, and the birefringence is calculated as the difference between n (TE) and n (TM) (n (TE) -n (TM)), and the final results are shown in tables 1 to 3 below.

9. Determination of ionic liquid content

The polyamic acid solutions used in examples 14 to 25, the polyamic acid solutions prepared in comparative examples 1 to 2 and comparative examples 5 to 7 in step (3), the polyimide prepolymer glue solution prepared in step (2) in comparative example 3, and the colorless and transparent homogeneous mixture obtained in step (1) in comparative example 4 were measured by a liquid chromatography mass spectrometer (liquid chromatography: LC-20A manufactured by Shimadzu corporation, Mass spectrometer: API4000 manufactured by AB Sciexpte. Ltd., Ltd.), and the ionic liquid content in the polyamic acid solution was measured by preparing a standard curve from tetrahydrofuran and the product obtained in comparative example 5, and the results are shown in tables 1 to 3 below.

TABLE 1

TABLE 2

TABLE 3

	Comparative example 3	Comparative example 4	Comparative example 5	Comparative example 6	Comparative example 7
						Viscosity (CP)	5364	4061	4632	5023	8130
Mw	62423	65721	66872	69482	88690
						Mw/Mn	2.94	1.96	1.83	1.89	2.6
Light transmittance (400nm)	70	84	81	80	69
						Content of ionic liquid	215	9462	0	731	687
Double refractive index	0.06	0.1	0.05	0.04	0.02
						CTE(ppm/℃)	26	4	22.5	8.8	21.1
Tg(℃)	370.3	353.4	314.5	432.9	306.0
						Td1％	467.4	456.8	415.3	501.6	385.4
Td5％	508.3	501.3	463.9	431.2	455.8
						Breaking stress (Mpa)	361	329	239	254	303
Young's modulus (Gpa)	3.1	2.6	3.5	3.2	1.4
						Elongation at Break (%)	23.5	26.5	25.3	26.7	11％

As can be seen from the test data in tables 1-3, the polyimide film prepared by the invention has smaller linear expansion coefficient and smaller birefringence performance at high temperature. Examples 22 to 25 show that the content of the ionic liquid is inversely proportional to the birefringence properties within a certain range by adding the ionic liquid in an amount within the range claimed in the patent. Comparative examples 1-2 when the content of the ionic liquid was changed out of the range claimed in the present invention, there was a clear tendency that the birefringence of the polyimide film was increased. Comparative examples 3 to 4 polyimide films were synthesized by a known method, and the residual amount of ionic liquid was not in the range of patent claims, thus showing inferior birefringence properties. Examples 5 and 6 adopt formulations without imidazole ionic liquid and without ionic liquid, respectively, and the birefringence performance of the final polyimide film is also poor. Example 7 without adding a blocking agent, the polyimide film obtained had poor thermal and birefringence properties.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The polyamic acid solution is characterized by comprising a compound I, a compound II and an ionic liquid; the chemical structural formula of the compound I is shown as the formula I:

the chemical structural formula of the compound II is shown as the formula II:

the chemical structural formula of Z is formula III:

the ionic liquid is one or a mixture of more of 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride and 1-butyl-3-methylimidazole chloride, and the mass concentration of the ionic liquid relative to the polyamic acid solution is 500-1000 ppm-.

2. The polyamic acid solution of claim 1 wherein X has the formula iv:

in the formula IV, A is any one of direct bonding, ether bond, methylene, ester bond, ketone bond, amido bond, dimethylsilylene, alkylene with 1-6 carbon atoms and aromatic group with less than 12 carbon atoms, and R₁Is any one of hydrogen atom, aromatic group with less than 12 carbon atoms, alkyl with 1-3 carbon atoms, halogen and hydroxyl, R₂Is any one of a hydrogen atom, an aromatic group having less than 12 carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group, and p is an integer of 0 to 3.

3. The polyamic acid solution of claim 1, wherein Y has the formula v:

4. The polyamic acid solution according to claim 1, having a viscosity of 500 to 10000cp at 25 ℃ and a solid content of 5 to 70 wt%; the weight average molecular weight of the polyamic acid solution is 30000-100000 g/mol, and the molecular weight distribution width is 1.1-3.0.

5. The method for preparing a polyamic acid solution according to any one of claims 1 to 4, comprising the steps of:

6. The method for producing a polyamic acid solution according to claim 5, wherein the molar ratio of said diamine and said dianhydride in step (1) is (0.9-1.1): 1; the temperature of the polymerization reaction is 20-120 ℃, and the time is 1-12 h;

the molar ratio of the diamine to the dianhydride in the step (2) is (0.9-1.1): 1; the mass ratio of the ionic liquid to the dianhydride is (0.05-0.5): 1; the mass ratio of the end capping agent to the diamine is 0.01-5%; the temperature of the polymerization reaction is 20-120 ℃, and the time is 1-12 h; the mass ratio of the poor solvent to the reaction solution is 1: (5-50).

7. The method for producing a polyamic acid solution according to claim 5, wherein the mass ratio of said poor solvent to said reaction solution in step (2) is 1: (5-15).

8. A polyimide film produced from the polyamic acid solution according to any one of claims 1 to 4.

9. The preparation method of the polyimide film according to claim 8, comprising the following steps: coating the polyamic acid solution on a substrate, drying, and then controlling temperature rise to perform curing treatment to obtain the polyimide film; the drying temperature is 80-180 ℃, and the drying time is 10-100 min; the maximum temperature of the curing is 350-480 ℃, the holding time of 150-250 ℃ in the temperature rising process is more than 10min, and the curing time is 2-5 h.

10. Use of the polyimide film according to claim 8 in a display, a touch panel or a solar cell substrate.