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CN112500570B - Flexible display device, polyamic acid varnish for display, and polyimide film - Google Patents

Flexible display device, polyamic acid varnish for display, and polyimide film Download PDF

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CN112500570B
CN112500570B CN202110151361.6A CN202110151361A CN112500570B CN 112500570 B CN112500570 B CN 112500570B CN 202110151361 A CN202110151361 A CN 202110151361A CN 112500570 B CN112500570 B CN 112500570B
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polyamic acid
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acid varnish
surface tension
dianhydride
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肖桂林
颜枫
鲁丽平
朱双全
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Wuhan Rouxian Technology Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
    • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
    • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • C08G73/1085—Polyimides with diamino moieties or tetracarboxylic segments containing heterocyclic moieties
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
    • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
    • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • C08G73/1003—Preparatory processes
    • C08G73/1007—Preparatory processes from tetracarboxylic acids or derivatives and diamines
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    • C09D179/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
    • C09D179/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
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    • G09F9/301—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements flexible foldable or roll-able electronic displays, e.g. thin LCD, OLED
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    • C08J2379/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
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Abstract

The invention discloses a flexible display device, polyamide acid varnish for a display and a polyimide film, belonging to the technical field of photoelectric display. The flexible display device comprises a flexible substrate and a display unit, wherein the flexible substrate comprises a polyimide film formed by a polyamic acid varnish, and the polyamic acid varnish comprises a polar organic solvent and polyamic acid with a repeating unit represented by the following formula (1);
Figure 507420DEST_PATH_IMAGE001
formula (1) in the formula (1), X includes the following formula (2), Y includes the following formula (3); r1And R2Each independently selected from a hydrogen atom or an alkyl group having 1 to 6 carbon atoms;
Figure 624281DEST_PATH_IMAGE002
formula (2)
Figure 853793DEST_PATH_IMAGE003
The surface tension of the polyamic acid varnish shown in the formula (3) is 30-50mN/m, and the molecular weight distribution is 1.1-1.6. The polyamide acid varnish provided by the invention has good wetting effect with a glass substrate; the film is easy to process into a film, and the formed PI film has low thermal expansion coefficient and is suitable for a flexible display.

Description

Flexible display device, polyamic acid varnish for display, and polyimide film
Technical Field
The invention relates to the technical field of photoelectric display, in particular to a flexible display device, and polyamide acid varnish and a polyimide film for a display.
Background
The aromatic polyimide has excellent mechanical property, outstanding thermal property, excellent chemical resistance and good dielectric property, and is widely applied to the preparation of flexible OLED substrates. The film forming property of the polyimide film on the substrate is one of indexes of the comprehensive performance of the polyimide film, the lower the surface tension of the polyamic acid varnish is, the smaller the contact angle of the polyamic acid varnish on the glass substrate is, the better the wetting effect is, and the better the film forming property of the polyimide film is. At present, the surface tension of polyimide is mainly regulated and controlled by adding a low-surface-tension solvent, a surfactant and the like, and the problems of poor environmental protection and complex components exist. Although the surface tension can be reduced by adopting the low-surface tension solvent, most of the low-surface tension solvents such as normal hexane and the like have the problems of poor environmental protection and difficult control of later-stage film forming property due to strong volatility; the addition of the surfactant not only makes the preparation process complicated, but also affects other properties of the polyimide, and causes difficult regulation and control of the comprehensive properties of the product and increases the cost. The solid content is a measure of the concentration of the polyamic acid slurry, and the lower the solid content of the polyamic acid and the higher the solvent content are, the lower the surface tension of the polyamic acid varnish is, but the low-solid-content polyamic acid varnish causes poor film-forming property of polyimide, thereby affecting the thermal property and mechanical property of the polyimide film.
The molecular weight distribution index is an index for evaluating the dispersibility of the polymer. The width of the molecular weight distribution greatly influences the rheological property of the polyamic acid varnish, and further influences the film forming property of the polyamic acid varnish on glass. The narrower the molecular weight distribution, the smaller the dispersibility of the polyamic acid solution, and the more favorable the polyimide film having excellent properties can be obtained. Further studies have shown that the narrower the molecular weight distribution, the more pronounced the pseudoplasticity of the polyamic acid solution. Therefore, obtaining a polyamic acid varnish having a narrow molecular weight distribution is advantageous for obtaining a polyimide film having excellent overall properties. However, the molecular weight distribution is too narrow, the viscosity of the high molecular weight polyamic acid is increased, which is not favorable for obtaining the polyamic acid varnish with low surface tension, and the prior art does not determine the width of the polyamic acid molecular weight distribution, the correlation of the surface tension and the correlation, so that the problem of obtaining the polyamic acid varnish with low surface tension, narrow molecular weight distribution, excellent thermodynamic performance and simple system is solved.
Disclosure of Invention
The present invention has been made to solve the above problems, and an object of the present invention is to provide a flexible display device, a polyamic acid varnish for a display, and a polyimide film.
The invention firstly provides a flexible display device, which comprises a flexible substrate and a display unit, wherein the flexible substrate comprises a polyimide film formed by polyamic acid varnish, and the polyamic acid varnish comprises a polar organic solvent and polyamic acid with a repeating unit represented by the following formula (1);
Figure 794689DEST_PATH_IMAGE001
formula (1)
In the formula (1), X comprises the following formula (2), and the formula (2) accounts for more than 80mol% of the total amount of X; and/or Y comprises the following formula (3), wherein the formula (3) accounts for more than 80mol% of the total amount of Y; r1And R2Each independently selected from a hydrogen atom or an alkyl group having 1 to 6 carbon atoms;
Figure 774147DEST_PATH_IMAGE002
formula (2)
Figure 553884DEST_PATH_IMAGE003
Formula (3)
The surface tension of the polyamic acid varnish at 25 ℃ is 30-50 mN/m; and/or the molecular weight distribution of the polyamic acid is 1.1-1.6;
the surface tension of the polyamic acid varnish is tested by a plate method, and the balance time is 8 min; the surface tension of the polyamic acid varnish at 50 ℃ is 0.91 to 0.96 of the surface tension at 25 ℃, and the surface tension of the polyamic acid varnish at 80 ℃ is 0.8 to 0.86 of the surface tension at 25 ℃.
The invention provides a polyamic acid varnish used for preparing a display device, which comprises a polar organic solvent and polyamic acid with a repeating unit represented by the following formula (1);
Figure 762142DEST_PATH_IMAGE001
formula (1)
In the formula (1), X comprises the following formula (2), and the formula (2) accounts for more than 80mol% of the total amount of X; and/or Y comprises the following formula (3), wherein the formula (3) accounts for more than 80mol% of the total amount of Y; r1And R2Each independently selected from a hydrogen atom or an alkyl group having 1 to 6 carbon atoms;
Figure 576515DEST_PATH_IMAGE002
formula (2)
Figure 398977DEST_PATH_IMAGE003
Formula (3)
The surface tension of the polyamic acid varnish at 25 ℃ is 30-50 mN/m; and/or the molecular weight distribution of the polyamic acid is 1.1-1.6; the surface tension of the polyamic acid varnish at 50 ℃ is 0.91-0.96 of the surface tension at 25 ℃, and the surface tension of the polyamic acid varnish at 80 ℃ is 0.8-0.86 of the surface tension at 25 ℃. Specifically, the surface tension of the polyamic acid varnish of the present invention was measured by the plate method, and the equilibration time was 8 min.
Preferably, the surface tension of the polyamic acid varnish at 25 ℃ is 33-46 mN/m; and/or the molecular weight distribution of the polyamic acid is 1.15-1.45.
Further, the solid content of the polyamic acid varnish is 5-20wt.%, preferably 10-20 wt.%.
Further, the X also comprises a structure formed by dianhydrides in the following group: aromatic dianhydride and/or alicyclic dianhydride; and/or, the Y also comprises a structure formed by aromatic diamine.
Preferably, the aromatic dianhydride includes one or more of pyromellitic dianhydride (PMDA), 2,3, 3', 4' -biphenyltetracarboxylic dianhydride (a-BPDA), 4,4' -oxydiphthalic anhydride (ODPA), 3,3',4,4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), 3,3',4,4' -diphenyl ether tetracarboxylic dianhydride (DEDA), and 2, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane dianhydride (BSAA). The alicyclic dianhydride includes, but is not limited to, cyclobutanetetracarboxylic dianhydride (CBDA).
Preferably, the aromatic diamine comprises one or more of diamine containing a benzimidazole structure, diamine containing a benzoxazole structure and diamine containing silicon.
Still further preferably, the diamine containing a benzimidazole structure comprises 2- (3-aminophenyl) -5-aminobenzimidazole and/or 2- (4-aminophenyl) -5-aminobenzimidazole;
the diamine containing the benzoxazole structure comprises 2- (4-aminophenyl) -5-aminobenzoxazole and/or 5, 7-benzoxazole diamine;
the silicon-containing diamine comprises 1, 3-bis (3-aminopropyl) tetramethyldisiloxane (SIDA);
the aromatic diamine also includes 1, 3-phenylenediamine (m-PDA), 1, 2-phenylenediamine (o-PDA), 4 '-diaminodiphenyl sulfone (4, 4' -DDS), 3 '-diaminodiphenyl sulfone (3, 3' -DDS), 4 '-diaminodiphenyl sulfide (ASD), 4' -diaminodiphenyl ether (4, 4 '-ODA), 3' -diaminodiphenyl ether (3, 3 '-ODA), 2, 4-diaminodiphenyl ether, 3, 4' -diaminodiphenyl ether, 4 '-bis (3-aminophenoxy) biphenyl (3-BAPB), and 4,4' -bis (4-aminophenoxy) biphenyl (4-BAPB), 9-bis (3- (3-aminobenzamide) -4-hydroxyphenyl) Fluorene (FDH), One or more of 2, 2-bis [3- (3-aminobenzamide) -4-hydroxyphenyl ] hexafluoropropane (HFHA) and 9, 9-bis (4- (4-aminophenoxy) phenyl) fluorene (BPF-AN).
Preferably, the formula (2) accounts for more than 90mol% of the total amount of X; and/or the formula (3) accounts for more than 90mol% of the total amount of Y.
Further, the polar organic solvent is one or more of N-methyl-2-pyrrolidone (NMP), N-Dimethylformamide (DMF), and N, N-dimethylacetamide (DMAc).
The surface tension of the polar organic solvent in the invention is measured at 25 ℃, and the equilibrium time is 8 min.
Further, the end-capping agent for forming the polyamic acid includes one or more of monoanhydride, monocarboxylic acid, monoacid chloride compound, mono-active ester compound, dicarbonate compound, vinyl ether compound, monoamine, or monoalcohol. Preferably, the end-capping agent for forming the polyamic acid includes one or more of Phthalic Anhydride (PA), 4-phenylethynylphthalic anhydride (PEPA), Nadic Anhydride (NA), Maleic Anhydride (MAH), and 3-hydroxyphthalic anhydride (HP). Further, the adding amount of the end capping agent is 1-6% of the total molar amount of the diamine monomer or the dianhydride monomer.
The viscosity of the polyamic acid varnish provided by the first aspect of the invention is 1000-7000 cP.
The polyamic acid varnish provided by the first aspect of the present invention has a light transmittance of less than 20% at a wavelength of 400nm and an optical path length of 1cm, and has a light transmittance of less than 40% at a wavelength of 500nm and an optical path length of 1 cm.
The polyamic acid varnish provided by the first aspect of the invention is stored for one year at a low temperature of-20 ℃, and the change of the viscosity is not more than 10%.
In a second aspect, the present invention provides a polyimide film formed from the polyamic acid varnish provided in the first aspect of the present invention.
Specifically, the polyamic acid varnish provided by the first aspect of the present invention is prepared by coating, drying and curing. More specifically, the coating is carried out on a coating machine, the curing temperature is 250-400 ℃, and the maximum curing temperature is 400-500 ℃.
The polyimide film provided by the second aspect of the present invention has a thermal expansion coefficient of less than 10 ppm/DEG C within a range of 50 to 450 ℃, is excellent in film thickness uniformity, and is free from a haze phenomenon and cracks.
A third aspect of the present invention provides a display device comprising the polyimide film provided by the second aspect of the present invention. Specifically, the display device, such as a flexible display device, provided by the invention comprises a flexible substrate and a display unit. The flexible substrate comprises the polyimide film provided by the second aspect of the invention.
Compared with the prior art, the invention has the following beneficial effects:
the polyamic acid varnish provided by the invention has the advantages that the surface tension is low, the molecular weight distribution is narrow, the wetting effect with a glass substrate is good, the film thickness uniformity of the obtained polyimide film on glass is within 5%, and the phenomenon of white turbidity and cracks do not occur; the provided polyamic acid varnish is easy to process into a film, and a polyimide film prepared by coating, hot vacuum drying (HCVD) and baking (Oven) has good film forming property and lower thermal expansion coefficient, and is suitable to be used as a substrate material for a flexible display.
Drawings
Fig. 1 is a schematic view of a flexible display device according to the present invention.
Description of reference numerals: 1-a rigid substrate; 2-a polyimide film; 3-an inorganic layer; 4-electronic circuit layer.
Detailed Description
The present invention provides a flexible display device and a polyamic acid varnish and a polyimide film for display, and the present invention will be described with reference to specific embodiments. It should be noted that the following examples are illustrative of the present invention, and are not intended to limit the present invention. Other combinations and various modifications within the spirit or scope of the present invention may be made without departing from the spirit or scope of the present invention.
< Polyamic acid varnish >
The invention provides a polyamic acid varnish, which comprises a polar organic solvent and a polyamic acid with a repeating unit represented by the following formula (1);
Figure 728327DEST_PATH_IMAGE001
formula (1)
In the formula (1), X comprises the following formula (2), and the formula (2) accounts for more than 80mol% of the total amount of X; and/or Y comprises the following formula (3), wherein the formula (3) accounts for more than 80mol% of the total amount of Y; r1And R2Each independently selected from a hydrogen atom or an alkyl group having 1 to 6 carbon atoms;
Figure 927227DEST_PATH_IMAGE002
formula (2)
Figure 596106DEST_PATH_IMAGE003
Formula (3)
The surface tension of the polyamic acid varnish is 30-50 mN/m; and/or the molecular weight distribution of the polyamic acid is 1.1-1.6. Wherein the surface tension of the polyamic acid varnish is tested by a plate method, and the balance time is 8 min.
Wherein X in the formula (1) is a structure formed by dianhydride. Further, the formula (2) is a structure formed by 3,3',4,4' -biphenyltetracarboxylic dianhydride (BPDA), and the formula (2) is a main component of X.
Y in the formula (1) is a structure formed by diamine. Further, the formula (3) is a structure formed by p-Phenylenediamine (PDA), and the formula (3) is a main component of Y.
In some preferred embodiments of the present invention, the formula (2) accounts for 90mol% or more of the total amount of X; and/or the formula (3) accounts for more than 90mol% of the total amount of Y.
Further, X in the formula (1) of the invention also comprises minor components; and/or, the Y further comprises a minor component.
Furthermore, in the formula (1), X also comprises a structure formed by aromatic dianhydride and/or alicyclic dianhydride as a secondary component; and/or, Y in the formula (1) of the invention also comprises a structure formed by aromatic diamine as a minor component.
The aromatic dianhydride may be pyromellitic dianhydride, 3,3',4,4' -biphenyltetracarboxylic dianhydride, 2,3, 3', 4' -biphenyltetracarboxylic dianhydride, 2 ', 3,3' -biphenyltetracarboxylic dianhydride, 3,3',4,4' -terphenyltetracarboxylic dianhydride, 3,3', 44' -oxydiphthalic dianhydride, 2,3, 3', 4' -oxydiphthalic dianhydride, 2,3,2 ', 3' -oxydiphthalic dianhydride, diphenylsulfone-3, 3',4,4' -tetracarboxylic dianhydride, benzophenone-3, 3',4,4' -tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) acetic dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 1,4- (3, 4-dicarboxyphenoxy) benzene dianhydride, 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 9-bis (3, 4-dicarboxyphenyl) fluorene dianhydride, 2,3,5, 6-pyridinetetracarboxylic dianhydride, 3,4,9, 10-tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane anhydride, 2-bis (4- (3, 4-dicarboxyphenoxy) phenyl) hexafluoropropane dianhydride, 1, 6-difluoropyromellitic dianhydride, 1-trifluoromethylpyromellitic dianhydride, Examples of the acid dianhydride compound include, but are not limited to, 1, 6-bistrifluoromethylpyromellitic dianhydride, 2 '-bis (trifluoromethyl) -4, 4' -bis (3, 4-dicarboxyphenoxy) biphenyl dianhydride, 2 '-bis [ (dicarboxyphenoxy) phenyl ] propane dianhydride, 2' -bis [ (dicarboxyphenoxy) phenyl ] hexafluoropropane dianhydride, and acid dianhydride compounds in which the hydrogen atom of the aromatic ring is substituted with an alkyl group, an alkoxy group, a halogen atom, or the like.
In some preferred embodiments of the present invention, the aromatic dianhydride forming X is preferably one or more of pyromellitic dianhydride (PMDA), 2,3, 3', 4' -biphenyltetracarboxylic dianhydride (a-BPDA), 4,4' -oxydiphthalic anhydride (ODPA), 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4' -diphenylethertetracarboxylic dianhydride (DEDA), 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane dianhydride (BSAA).
Alicyclic dianhydrides include, but are not limited to, 1,2,3, 4-cyclobutanetetracarboxylic dianhydride, 1,2,3, 4-cyclopentanetetracarboxylic dianhydride, 1,2,4, 5-cyclohexanetetracarboxylic dianhydride, 1,2,3, 4-cyclopentanetetracarboxylic dianhydride, 1,2,3, 4-tetramethyl-1, 2,3, 4-cyclobutanetetracarboxylic dianhydride, 1, 2-dimethyl-1, 2,3, 4-cyclobutanetetracarboxylic dianhydride, 1, 3-dimethyl-1, 2,3, 4-cyclobutanetetracarboxylic dianhydride, 1,2,3, 4-cycloheptanetetracarboxylic dianhydride, 3, 4-dicarboxy-1-cyclohexylsuccinic dianhydride, 2,3, 5-tricarboxycyclopentylacetic dianhydride, 3, 4-dicarboxy-1, 2,3, 4-tetrahydro-1-naphthalene succinic dianhydride, bicyclo [3,3, 0] octane-2, 4,6, 8-tetracarboxylic dianhydride, bicyclo [4,3,0] nonane-2, 4,7, 9-tetracarboxylic dianhydride, bicyclo [4,4,0] decane-2, 4,8, 10-tetracarboxylic dianhydride, bicyclo [2,2,2] octane-2, 3,5, 6-tetracarboxylic dianhydride, bicyclo [2,2,1] heptane-5-carboxymethyl-2, 3, 6-tricarboxylic acid dianhydride, 7-oxabicyclo [2,2,1] heptane-2, 4,6, 8-tetracarboxylic dianhydride, octahydronaphthalene-1, 2,6, 7-tetracarboxylic dianhydride, decatetrahydroanthracene-1, 2,8, 9-tetracarboxylic dianhydride, 3',4,4' -dicyclohexyltetracarboxylic dianhydride, 3',4,4' -oxydicyclohexatetracarboxylic dianhydride, or the like.
In some preferred embodiments of the present invention, the aromatic diamine forming Y comprises one or more of a diamine containing a benzimidazole structure, a diamine containing a benzoxazole structure, and a diamine containing silicon. From the viewpoint of reducing the surface tension of the polyamic acid varnish, it is preferable to add a diamine containing a benzimidazole structure, a diamine containing a benzoxazole structure, or a diamine containing silicon. Wherein, the adding amount of the diamine containing the benzimidazole structure and/or the diamine containing the benzoxazole structure is preferably more than 0 and less than or equal to 20 percent of the total molar amount of the diamine monomers; the amount of silicon-containing diamine added is preferably 0 to 10% of the total molar amount of diamine monomers.
In some more preferred embodiments of the present invention, the benzimidazole structure-containing diamine forming Y comprises 2- (3-aminophenyl) -5-aminobenzimidazole and/or 2- (4-aminophenyl) -5-aminobenzimidazole; and/or the diamine containing a benzoxazole structure that forms Y comprises 2- (4-aminophenyl) -5-aminobenzoxazole and/or 5, 7-benzoxazole diamine. The silicon-containing diamine comprises 1, 3-bis (3-aminopropyl) tetramethyldisiloxane.
In some more preferred embodiments of the invention, the aromatic diamines forming Y further comprise 1, 3-phenylenediamine (m-PDA), 1, 2-phenylenediamine (o-PDA), 4 '-diaminodiphenyl sulfone (4, 4' -DDS), 3 '-diaminodiphenyl sulfone (3, 3' -DDS), 4 '-diaminodiphenyl sulfide (ASD), 4' -diaminodiphenyl ether (4, 4 '-ODA), 3' -diaminodiphenyl ether (3, 3 '-ODA), 2, 4-diaminodiphenyl ether, 3, 4' -diaminodiphenyl ether, 4 '-bis (3-aminophenoxy) biphenyl (3-BAPB) and 4,4' -bis (4-aminophenoxy) biphenyl (4-BAPB), 9, 9-bis (3- (3-aminobenzamide) -4-hydroxyphenyl) Fluorene (FDH), 2-bis [3- (3-aminobenzamide) -4-hydroxyphenyl ] hexafluoropropane (HFHA) and 9, 9-bis (4- (4-aminophenoxy) phenyl) fluorene (BPF-AN).
The polar organic solvent in the polyamic acid varnish is one or more of N-methyl-2-pyrrolidone (NMP), N-Dimethylformamide (DMF) and N, N-dimethylacetamide (DMAc). The dosage of the polar organic solvent in the polyamic acid varnish is determined according to the required solid content.
Further, an end-capping agent is needed for forming the polyamic acid of the present invention, and the end-capping agent is used to adjust the molecular weight, and thus the surface tension of the polyamic acid varnish. The end capping agent accounts for 1-6% of the total molar weight of the diamine monomer or the dianhydride monomer, the end capping agent is lower than 1% of the total molar weight of the diamine monomer or the dianhydride monomer, the polyamic acid varnish has large molecular weight and high surface tension, and the polyimide film has poor uniformity; the end capping agent is higher than 6 percent of the total molar weight of the diamine monomer or the dianhydride monomer, the polyamic acid varnish has small molecular weight and low surface tension, and the polyimide film is easy to have white turbidity and cracks.
For polyamic acid with excess diamine, a capping agent is selected to react with the diamine, including monoanhydrides, monocarboxylic acids, monoacyl chloride compounds, mono-active ester compounds, dicarbonate compounds, vinyl ether compounds, and the like.
For the dianhydride excess polyamic acid, an end-capping agent is selected to react with the dianhydride, including a monoamine compound, a monohydric alcohol.
As the end-capping agent to be reacted with the diamine, acid anhydrides, i.e., monoanhydrides, monocarboxylic acids, monoacid chloride compounds and monoactive ester compounds, may be selected from phthalic anhydride, maleic anhydride, nadic anhydride, cyclohexane anhydride, 3-hydroxyphthalic anhydride and the like, 2-carboxyphenol, 3-carboxyphenol, 4-carboxyphenol, 2-carboxythiophenol, 3-carboxythiophenol, 4-carboxythiophenol, 1-hydroxy-8-carboxynaphthalene, 1-hydroxy-7-carboxynaphthalene, 1-hydroxy-6-carboxynaphthalene, 1-hydroxy-5-carboxynaphthalene, 1-hydroxy-4-carboxynaphthalene, 1-hydroxy-3-carboxynaphthalene, 1-hydroxy-2-carboxynaphthalene, 1-mercapto-8-carboxynaphthalene, 1-mercapto-7-carboxynaphthalene, 1-mercapto-6-carboxynaphthalene, 1-mercapto-5-carboxynaphthalene, 1-mercapto-4-carboxynaphthalene, 1-mercapto-3-carboxynaphthalene, 1-mercapto-2-carboxynaphthalene, 2-carboxybenzenesulfonic acid, 3-carboxybenzenesulfonic acid, 4-carboxybenzenesulfonic acid, 2-acetylenecarboxylic acid, 3-acetylenecarboxylic acid, 4-acetylenecarboxylic acid, 2, 4-diacetylenebenzoic acid, 2, 5-diacetylenebenzoic acid, 2, 6-diacetylenebenzoic acid, 3, 4-diacetylenebenzoic acid, 3, 5-diacetylenebenzoic acid, 2-ethynyl-1-naphthoic acid, 2-carboxynaphthalene, 1-mercapto-6-carboxynaphthalene, 1-mercapto-5-carboxynaphthalene, 1-thionaphthalene, Monocarboxylic acids such as 3-ethynyl-1-naphthoic acid, 4-ethynyl-1-naphthoic acid, 5-ethynyl-1-naphthoic acid, 6-ethynyl-1-naphthoic acid, 7-ethynyl-1-naphthoic acid, 8-ethynyl-1-naphthoic acid, 2-ethynyl-2-naphthoic acid, 3-ethynyl-2-naphthoic acid, 4-ethynyl-2-naphthoic acid, 5-ethynyl-2-naphthoic acid, 6-ethynyl-2-naphthoic acid, 7-ethynyl-2-naphthoic acid, and 8-ethynyl-2-naphthoic acid, and monoacyl chloride compounds obtained by acylating a carboxyl group of these monocarboxylic acids, and an active ester compound obtained by reacting a monoacid chloride compound, which is obtained by chlorinating only 1 carboxyl group of dicarboxylic acids such as terephthalic acid, phthalic acid, maleic acid, cyclohexanedicarboxylic acid, 3-hydroxyphthalic acid, 5-norbornene-2, 3-dicarboxylic acid, 1, 2-dicarboxylnaphthalene, 1, 3-dicarboxylnaphthalene, 1, 4-dicarboxylnaphthalene, 1, 5-dicarboxylnaphthalene, 1, 6-dicarboxylnaphthalene, 1, 7-dicarboxylnaphthalene, 1, 8-dicarboxylnaphthalene, 2, 3-dicarboxylnaphthalene, 2, 6-dicarboxylnaphthalene, 2, 7-dicarboxylnaphthalene and the like, with N-hydroxybenzotriazole and N-hydroxy-5-norbornene-2, 3-dicarboxylimide.
The dicarbonate compound may be selected from di-t-butyl dicarbonate, diphenyl dicarbonate, dibenzyl dicarbonate, dimethyl dicarbonate, and diethyl dicarbonate, but is not limited thereto.
Examples of the vinyl ether compound include t-butyl chloroformate, n-butyl chloroformate, isobutyl chloroformate, benzyl chloroformate, allyl chloroformate, ethyl chloroformate, isopropyl chloroformate, fluorenyl methyl chloroformate, 2,2, 2-trichloroethyl chloroformate and other chloroformates, butyl isocyanate, 1-naphthyl isocyanate, octadecyl isocyanate, phenyl isocyanate and other isocyanate compounds, butyl vinyl ether, cyclohexyl vinyl ether, ethyl vinyl ether, 2-ethylhexyl vinyl ether, isobutyl vinyl ether, isopropyl vinyl ether, n-propyl vinyl ether, t-butyl vinyl ether, benzyl vinyl ether and the like.
Monoamine capping agents include 5-amino-8-hydroxyquinoline, 4-amino-8-hydroxyquinoline, 1-hydroxy-8-aminonaphthalene, 1-hydroxy-7-aminonaphthalene, 1-hydroxy-6-aminonaphthalene, 1-hydroxy-5-aminonaphthalene, 1-hydroxy-4-aminonaphthalene, 1-hydroxy-3-aminonaphthalene, 1-hydroxy-2-aminonaphthalene, 1-amino-7-hydroxynaphthalene, 2-hydroxy-7-aminonaphthalene, 2-hydroxy-6-aminonaphthalene, 2-hydroxy-5-aminonaphthalene, 2-hydroxy-4-aminonaphthalene, 2-hydroxy-3-aminonaphthalene, 2-hydroxy-8-aminonaphthalene, 1-hydroxy-3-aminonaphthalene, 1-hydroxy-6-aminonaphthalene, 1-hydroxy-3-aminonaphthalene, 1-hydroxy-5-, 1-amino-2-hydroxynaphthalene, 1-carboxy-8-aminonaphthalene, 1-carboxy-7-aminonaphthalene, 1-carboxy-6-aminonaphthalene, 1-carboxy-5-aminonaphthalene, 1-carboxy-4-aminonaphthalene, 1-carboxy-3-aminonaphthalene, 1-carboxy-2-aminonaphthalene, 1-amino-7-carboxynaphthalene, 2-carboxy-7-aminonaphthalene, 2-carboxy-6-aminonaphthalene, 2-carboxy-5-aminonaphthalene, 2-carboxy-4-aminonaphthalene, 2-carboxy-3-aminonaphthalene, 1-amino-2-carboxynaphthalene, 2-aminobenzoic acid, 3-aminobenzoic acid, 4-aminobenzoic acid, 2-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid, 4-aminobenzenesulfonic acid, 3-amino-4, 6-dihydroxypyrimidine, 2-aminophenol, 3-aminophenol, 4-aminophenol, 1-mercapto-8-aminonaphthalene, 1-mercapto-7-aminonaphthalene, 1-mercapto-6-aminonaphthalene, 1-mercapto-5-aminonaphthalene, 1-mercapto-4-aminonaphthalene, 1-mercapto-3-aminonaphthalene, 1-mercapto-2-aminonaphthalene, 2-mercapto-7-aminonaphthalene, 2-mercapto-6-aminonaphthalene, 2-mercapto-5-aminonaphthalene, 2-mercapto-4-aminonaphthalene, 2-mercapto-3-aminonaphthalene, 1-amino-2-mercaptonaphthalene, 3-amino-4, 6-dimercaptopyrimidine, 2-aminothiophenol, 3-aminothiophenol, 4-aminothiophenol, 2-ethynylaniline, 3-ethynylaniline, 4-ethynylaniline, 2, 4-diethynylaniline, 2, 5-diethynylaniline, 2, 6-diethynylaniline, 3, 4-diethynylaniline, 3, 5-diethynylaniline, 1-ethynyl-2-aminonaphthalene, 1-ethynyl-3-aminonaphthalene, 1-ethynyl-4-aminonaphthalene, 1-ethynyl-5-aminonaphthalene, 1-ethynyl-6-aminonaphthalene, 1-ethynyl-7-aminonaphthalene, 1-ethynyl-8-aminonaphthalene, 2-ethynyl-1-aminonaphthalene, 2-ethynyl-3-aminonaphthalene, 2-ethynyl-4-aminonaphthalene, 2-ethynyl-5-aminonaphthalene, 2-ethynyl-6-aminonaphthalene, 2-ethynyl-7-aminonaphthalene, 2-ethynyl-8-aminonaphthalene, 3, 5-diacetyl-1-aminonaphthalene, 3, 5-diacetyl-2-aminonaphthalene, 3, 6-diacetyl-1-aminonaphthalene, 3, 6-diacetyl-2-aminonaphthalene, 3, 7-diacetylene-1-aminonaphthalene, 3, 7-diacetylene-2-aminonaphthalene, 4, 8-diacetylene-1-aminonaphthalene, 4, 8-diacetylene-2-aminonaphthalene, and the like, but is not limited thereto.
In some preferred embodiments of the present invention, the end-capping agent forming the polyamic acid includes one or more of Phthalic Anhydride (PA), 4-phenylethynylphthalic anhydride (PEPA), Nadic Anhydride (NA), Maleic Anhydride (MAH), and 3-hydroxyphthalic anhydride (HP). In some more preferred embodiments of the invention, maleic anhydride is used as the capping agent.
The invention is favorable for obtaining the polyamic acid varnish with proper surface tension by introducing one or more of imidazole, oxazole and silicon-containing groups into the diamine monomer. In some preferred embodiments of the present invention, the polyamic acid varnish has a surface tension of 33 to 46mN/m, more preferably 36 to 40mN/m, at 25 ℃. The surface tension is too high, the leveling property of the polyamic acid varnish is poor, and the film thickness uniformity of the polyimide film is poor. The surface tension is too low, and the polyimide film is easily clouded and cracked.
Further, the polyamic acid varnish of the present invention has a surface tension at 50 ℃ of from 0.91 to 0.96, and from 30 to 43mN/m, preferably from 30 to 40mN/m, of the surface tension at 25 ℃; the polyamic acid varnish has a surface tension at 80 ℃ of 27 to 40mN/m, preferably 28 to 36mN/m, of 0.8 to 0.86 of the surface tension at 25 ℃. With increasing temperature, the surface tension of the polyamic acid varnish decreases at a rate too small to easily cause white turbidity and cracking of the polyimide film.
In a specific embodiment of the present invention, the surface tension test equilibration times of the polyamic acid varnish at 25 ℃, 50 ℃ and 80 ℃ are all 8 min.
In the present embodiment, the method for measuring the surface tension of the solvent is the same as the method for measuring the surface tension of the polyamic acid varnish, and the equilibration time is 8 min.
In some preferred embodiments of the present invention, the polyamic acid of the present invention has a molecular weight distribution of 1.15 to 1.45, more preferably 1.15 to 1.35.
Further, the solid content of the polyamic acid varnish is 5-20wt.%, preferably 10-20 wt.%. The solid content of the polyamic acid varnish is adjusted by adding the solvent, the solid content is lower than 5wt.%, the surface tension of the polyamic acid varnish is too low, and the film-forming property of the polyimide film is poor; the solid content is higher than 20wt.%, the surface tension of the polyamic acid varnish is increased, the leveling property of the polyimide film is poor, and the uniformity of the film thickness is poor.
Further, the viscosity of the polyamic acid varnish provided by the first aspect of the invention is 1000-7000 cP, preferably 2000-5500 cP, which facilitates obtaining a polyimide film with good film-forming property.
The polyamic acid varnish provided by the first aspect of the present invention has a low surface tension and a narrow molecular weight distribution, has a smaller contact angle on glass, has good wettability, has a more uniform surface, and is easy to obtain a polyimide film having a small film thickness uniformity.
The polyamic acid varnish provided by the first aspect of the present invention has a light transmittance of less than 20% at a wavelength of 400nm and an optical path length of 1cm, and has a light transmittance of less than 40% at a wavelength of 500nm and an optical path length of 1 cm.
The polyamic acid varnish provided by the first aspect of the invention is stored for one year at a low temperature of-20 ℃, and the change of the viscosity is not more than 10%. The polyamic acid varnish provided by the first aspect of the invention has low viscosity change rate and strong storage stability.
The preparation method of the polyamic acid varnish provided by the first aspect of the invention comprises the following steps: the corresponding diamine and dianhydride monomers are polymerized in polar organic solvent according to the corresponding proportion and sequence. The conditions for the polymerization reaction are not particularly limited, and usually carried out at-10 ℃ to 90 ℃ for 2 to 48 hours in an inert atmosphere such as nitrogen or argon.
Further preferable scheme is that main ingredient diamine and polar organic solvent are mixed firstly, all dianhydride is added after the main ingredient diamine is completely dissolved, and reaction is carried out for 4-12 hours at 30-90 ℃, preferably 30-70 ℃; then cooling to 0-40 ℃, adding secondary ingredient diamine and polar organic solvent into the reaction solution in turn, and reacting for 3-20h at 0-40 ℃. Finally adding a polar organic solvent and an end-capping reagent, and reacting for 3-20h at 0-40 ℃.
In a specific embodiment of the present invention, the preparation method of the polyamic acid varnish comprises: mixing p-phenylenediamine and a polar organic solvent, adding all dianhydride after the p-phenylenediamine is completely dissolved, and reacting for 4-12 hours at 30-90 ℃, preferably 30-70 ℃; then cooling to 0-40 ℃, adding secondary ingredient diamine and polar organic solvent into the reaction solution in turn, and reacting for 3-20h at 0-40 ℃. And finally adding a polar organic solvent and an end-capping reagent, and reacting for 3-20h at 0-40 ℃ to obtain the polyamic acid varnish. The reaction temperature in the first step is too high, and the ratio of the surface tension of the polyamic acid varnish at a higher temperature (more than 25 ℃) to the surface tension of the polyamic acid varnish at 25 ℃ is larger, so that the polyimide film is easily subjected to white turbidity and cracking.
< polyimide film >
In a second aspect, the present invention provides a polyimide film formed from the polyamic acid varnish provided in the first aspect.
Further, the polyimide film is prepared from the polyamic acid varnish provided by the first aspect of the invention through film coating, drying and curing.
Further, first, the polyamic acid varnish provided in the first aspect of the present invention is applied to a support. The support is selected from a wafer substrate such as silicon or gallium arsenic, a glass substrate such as sapphire glass, soda lime glass, or alkali-free glass, a metal substrate such as stainless steel or copper, a metal foil, a ceramic substrate, and a substrate containing silicon atoms, but is not limited thereto. The glass substrate is preferably used as a support.
As the coating method, a blade coating method, a spin coating method, a slit coating method, a dip coating method, a spray coating method, a printing method, or the like can be selected, and these methods can be combined. A knife coating method is preferred as the coating method.
The support may be pretreated before coating. For example, the following methods can be mentioned: the surface of the support is treated by a method such as spin coating, slit die coating, bar coating, dip coating, spray coating, or vapor treatment using a solution obtained by dissolving a pretreatment agent in an amount of 0.5 to 30 mass% in a solvent such as isopropyl alcohol, ethanol, methanol, water, tetrahydrofuran, N-methyl 2-pyrrolidone, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, ethyl lactate, or diethyl adipate. The reaction between the support and the pretreatment agent may be carried out by performing a reduced pressure drying treatment as required and then performing a heat treatment at 50 to 300 ℃.
Next, after the coating, the coating film of the varnish is usually dried. As the drying method, drying under reduced pressure, drying by heating, or a combination thereof can be used. The reduced-pressure drying is performed, for example, by placing the support having the coating film formed thereon in a vacuum chamber and reducing the pressure in the vacuum chamber. The heat drying is performed using a hot plate, an oven, infrared rays, or the like. In the case of using a hot plate, the coating film is directly held on the plate or held on a jig such as a fixing pin provided on the plate, and is heated and dried. The height of the fixing pin can be variously selected depending on the size of the support, the kind of solvent used in the solution, the drying method, and the like, and is preferably about 0.1 to 10 mm. The heating temperature varies depending on the kind and purpose of the solvent used in the solution, and it is preferable to dry the solution at 80 ℃ for 1 hour.
Finally, the dried wet film is cured at the temperature of 400 ℃ for 250-. And peeling the obtained polyimide film glass plate, performing mechanical property, thermal property and optical property characterization, preparing samples according to the requirements of different test instruments and test methods, and then testing according to national standards or enterprise standards.
The second aspect of the present invention provides that the polyimide film has a thermal expansion coefficient of less than 10 ppm/deg.C, further less than 5 ppm/deg.C, further less than 3 ppm/deg.C, and even less than 2 ppm/deg.C within a temperature range of 50-450 deg.C. The thickness uniformity of the polyimide film provided by the second aspect of the invention is less than or equal to 5 percent, and the polyimide film is derived from the polyamic acid varnish which has low surface tension and is easy to form a film.
< display device >
A third aspect of the invention provides a display device including, but not limited to, OLED, TFT-LCD, etc. flexible displays. A display device provided by a third aspect of the present invention uses the polyimide film provided by the second aspect of the present invention as a substrate.
In a flexible display, the flexible substrate of the flexible display device includes a polyimide film, wherein the polyimide film is a polyimide film formed from the polyamic acid varnish provided in the first aspect of the present invention or a polyimide film provided in the second aspect of the present invention. As shown in fig. 1, the step of manufacturing a flexible display device using a polyimide film includes: a step of applying a polyamic acid varnish to a rigid substrate 1 and curing the polyamic acid varnish to obtain a polyimide film 2, thereby obtaining a flexible substrate; a step of providing an inorganic layer 3 as a barrier layer on a polyimide film 2 of a flexible substrate; a step of forming a display cell as an electronic circuit layer 4 on the inorganic layer 3; a polymer having an electronic circuit layer 4 formed on the surface thereofAnd a step of peeling the imide film from the rigid substrate 1. The display device claimed in the present invention is not limited thereto, and a display device using the polyamic acid varnish and the polyimide film provided in the present invention as a substrate is within the scope of the present invention. The inorganic layer 3 may be, for example, a layer containing a material selected from silicon nitride (SiN)x) Silicon oxide (SiO)x) Silicon oxynitride (SiO)xNy) Alumina (Al)2O3) Titanium oxide (TiO)2) Zirconium oxide (ZrO)2) And inorganic films of inorganic substances in the group consisting of metal oxides, metal nitrides and metal oxynitrides. Generally, as a method for forming these inorganic films, known physical vapor deposition methods such as vacuum vapor deposition, sputtering, and ion plating, chemical vapor deposition methods (chemical vapor deposition methods) such as plasma CVD, catalytic chemical vapor deposition (Cat-CVD), and the like can be used. The electronic circuit layer 4 differs depending on the kind of device. If the display device is a TFT liquid crystal display device, the electronic circuit layer is an amorphous silicon TFT, and the TFT comprises a grid metal layer, an amorphous silicon film and other semiconductor layers, a silicon nitride grid dielectric layer and an ITO pixel electrode. Further, the material of the rigid substrate 1 according to the present invention is not limited, and an inorganic substrate, such as a glass substrate of soda lime glass, borosilicate glass, or alkali-free glass, or a metal substrate of iron, stainless steel, or the like, is generally used.
The display device provided by the invention can also use a multilayer PI (polyimide) laminate as a substrate, wherein the polyimide film and the inorganic film in the laminate are alternately laminated. The preparation method of the display device taking the PI laminated body as the substrate is the same as the preparation method of the display device taking the polyimide film as the substrate.
The above and other advantages of the present invention will be better understood by the following examples, which are not intended to limit the scope of the present invention. The relevant abbreviations in the examples are as follows:
BPDA: 3,3',4,4' -biphenyltetracarboxylic dianhydride
And (3) PMDA: pyromellitic dianhydride
ODPA: 4, 4-oxydiphthalic dianhydride
DEDA: 3,3',4,4' -Diphenyl Ether Tetraformic dianhydride
BSAA: 2, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane dianhydride
CBDA: cyclobutanetetracarboxylic dianhydride
PDA: p-phenylenediamine
DAPBI: 2- (4-aminophenyl) -5-aminobenzimidazole
DAPBO: 2- (4-aminophenyl) -5-aminobenzoxazole
And (3) SIDA: 1, 3-bis (3-aminopropyl) tetramethyldisiloxane
4,4' -ODA: 4,4' -diaminodiphenyl ether
FDH: 9, 9-bis (3- (3-aminobenzamide) -4-hydroxyphenyl) fluorene
HFHA: 2, 2-bis [3- (3-aminobenzamide) -4-hydroxyphenyl ] hexafluoropropane
BPF-AN: 9, 9-bis (4- (4-aminophenoxy) phenyl) fluorene
NA: norbornene dicarboxylic anhydride
PA: phthalic anhydride
PEPA: 4-phenylethynyl phthalic anhydride
MAH: maleic anhydride
HP: 3-hydroxyphthalic anhydride
NMP: n-methyl-2-pyrrolidone
DMF: n, N-dimethylformamide
DMAc: n, N-dimethyl acetamide
Example 1
A1L three-necked flask equipped with a mechanical stirrer, a bulb-shaped condenser and a nitrogen introduction head was charged with 136.12 g of NMP and 0.09mol of PDA, and after PDA was completely dissolved, 0.085mol of BPDA, 0.01mol of PMDA and 0.004mol of CBDA were further charged into the flask, and then the mixture was reacted at 30 ℃ for 8 hours. Subsequently, the reaction temperature was lowered to 20 ℃ and 0.01mol of DAPBI and 0.001mol of DAPBO were added to the reaction solution in this order, followed by 20g of NMP, followed by polymerization at 20 ℃ for 10 hours. 0.001mol of PEPA and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 20 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 2
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas head was charged with 158.1 g of NMP and 0.08mol of PDA, and after PDA was completely dissolved, 0.085mol of BPDA, 0.01mol of DEDA and 0.005mol of PMDA were further charged into the flask, and the mixture was reacted at 70 ℃ for 2 hours. Subsequently, the reaction temperature was lowered to 15 ℃ and 0.02mol of DAPBI and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 15 ℃ for 6 hours after completion of the addition. 0.002mol of HP and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 15 ℃ for 6 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 3
A1L three-necked flask equipped with a mechanical stirrer, a bulb condenser and a nitrogen gas head was charged with 204.7 g of NMP and 0.09mol of PDA, after PDA was completely dissolved, 0.08mol of BPDA, 0.016mol of PMDA and 0.004mol of BSAA were further charged into the flask, and the mixture was reacted at 90 ℃ for 2 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.01mol of DAPBO and 20g of NMP were added to the reaction solution in this order, followed by polymerization at 10 ℃ for 6 hours. To the reaction solution were added 0.004mol of HP and 10g of NMP in this order, and the reaction was continued at 10 ℃ for 6 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 4
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen guide was charged with 263.2 g of NMP and 0.08mol of PDA, and after PDA was completely dissolved, 0.08mol of BPDA, 0.017mol of ODPA and 0.003mol of PMDA were further charged into the flask, and then the mixture was reacted at 45 ℃ for 6 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.02mol of DAPBI and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 10 hours after completion of the addition. 0.005mol of PEPA and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 10 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 5
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas guide was charged with 302.6 g of NMP and 0.09mol of PDA, and after PDA was completely dissolved, 0.085mol of BPDA, 0.011mol of PMDA and 0.004mol of BTDA were charged into the flask, and the mixture was reacted at 60 ℃ for 10 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.01mol of DAPBO and 20g of NMP were added to the reaction solution in this order, followed by polymerization at 10 ℃ for 10 hours. 0.004mol of MAH and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 10 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 6
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas guide was charged with 254.7 g of NMP and 0.095mol of PDA, and after the PDA was completely dissolved, 0.09mol of BPDA, 0.008mol of BTDA and 0.002mol of DEDA were charged into the flask, and the mixture was reacted at 50 ℃ for 2 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.01mol of DAPBO, 0.001mol of SIDA and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 3 hours after completion of the addition. To the reaction solution were added 0.005mol of NA, 0.001mol of PEPA and 10g of NMP in this order, and the reaction was continued at 10 ℃ for 3 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 7
A1L three-necked flask equipped with a mechanical stirrer, a bulb condenser and a nitrogen gas head was charged with 261.4 g of NMP and 0.09mol of PDA, and after PDA was completely dissolved, 0.08mol of BPDA, 0.016mol of PMDA and 0.004mol of BSAA were charged into the flask, and then the mixture was reacted at 60 ℃ for 4 hours. Subsequently, the reaction temperature was lowered to 15 ℃ and 0.01mol of DAPBO, 0.0015mol of SIDA and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 15 ℃ for 9 hours after completion of the addition. 0.005mol of PEPA and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 15 ℃ for 9 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 8
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas head was charged with 304.7 g of NMP and 0.1mol of PDA, and after PDA was completely dissolved, 0.08mol of BPDA, 0.017mol of BTDA and 0.003mol of CBDA were further charged into the flask, and then the mixture was reacted at 65 ℃ for 4 hours. Subsequently, the reaction temperature was lowered to 15 ℃ and 0.009mol of SIDA and 20g of NMP were added to the reaction solution in this order, and after completion of the addition, polymerization was carried out at 15 ℃ for 6 hours. 0.006mol of MAH and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 15 ℃ for 6 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 9
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas head was charged with 167.7 g of DMF and 0.09mol of PDA, and after PDA was completely dissolved, 0.08mol of BPDA and 0.02mol of CBDA were further charged into the flask, and the mixture was reacted at 42 ℃ for 8 hours. Subsequently, the reaction temperature was lowered to 20 ℃ and 0.002mol of FDH, 0.002mol of SIDA, 0.01mol of DAPBI and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 20 ℃ for 10 hours after the completion of the addition. 0.002mol of HP and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 20 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 10
A1L three-necked flask equipped with a mechanical stirrer, a bulb condenser and a nitrogen introduction head was charged with 134.7 g of DMAc and 0.09mol of PDA, and after the PDA was completely dissolved, 0.09mol of BPDA, 0.005mol of PMDA and 0.005mol of DEDA were further charged into the flask, and then the mixture was reacted at 40 ℃ for 10 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.004mol of HFHA, 0.01mol of DAPBO and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 10 hours after completion of the addition. 0.001mol of PEPA and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 10 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Example 11
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen head was charged with 94.7 g of NMP, 58 g of DMF and 0.085mol of PDA, and after the PDA was completely dissolved, 0.08mol of BPDA, 0.01mol of BSAA and 0.01mol of ODPA were added to the flask, and then the mixture was reacted at 55 ℃ for 3 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.01mol of BPF-AN, 0.01mol of DAPBO and 20g of NMP were added to the reaction solution in this order, followed by polymerization at 10 ℃ for 10 hours after completion of the addition. 0.003mol of MAH and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 10 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Comparative example 1
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas inlet was charged with 122.1 g of NMP and 0.05mol of PDA, and after PDA was completely dissolved, 0.06mol of ODPA and 0.04mol of PMDA were charged into the flask, and the mixture was reacted at 20 ℃ for 2 hours. Subsequently, the reaction temperature was lowered to 2 ℃ and 0.05mol of HFHA, 0.001mol of SIDA, 0.005mol of DAPBI and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 2 ℃ for 4 hours after completion of the addition. 10g of NMP was added to the reaction solution, and the reaction was continued at 2 ℃ for 4 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Comparative example 2
A1L three-necked flask equipped with a mechanical stirrer, a bulb condenser and a nitrogen gas head was charged with 146.3 g of NMP and 0.08mol of PDA, and after the PDA was completely dissolved, 0.08mol of ODPA and 0.02mol of BPDA were charged into the flask, and the mixture was reacted at 95 ℃ for 6 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.001mol of SIDA, 0.026mol of DAPBI and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 4 hours after completion of the addition. 10g of NMP was added to the reaction mixture, and the reaction was continued at 10 ℃ for 4 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Comparative example 3
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas head was charged with 298.4 g of NMP and 0.07mol of PDA, after PDA was completely dissolved, 0.057mol of BPDA, 0.031 mol of PMDA and 0.01mol of ODPA were further charged into the flask, and the mixture was reacted at 105 ℃ for 5 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.003mol of SIDA, 0.03mol of DAPBI and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 15 hours after completion of the addition. 0.003mol of PEPA and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 10 ℃ for 15 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Comparative example 4
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen introduction head was charged with 298.9 g of NMP and 0.1mol of PDA, and after PDA was completely dissolved, 0.06mol of BPDA and 0.04mol of PMDA were further charged into the flask, and the mixture was reacted at 85 ℃ for 6 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.002mol of FDH, 0.005mol of DAPBI and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 10 hours after completion of the addition. 0.001mol of PA and 10g of NMP were added to the reaction mixture in this order, and the reaction was continued at 10 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Comparative example 5
A1L three-necked flask equipped with a mechanical stirrer, a spherical condenser and a nitrogen gas guide was charged with 399.4 g of NMP and 0.08mol of PDA, and after the PDA was completely dissolved, 0.079mol of BPDA and 0.021mol of ODPA were further charged into the flask, and the mixture was reacted at 90 ℃ for 6 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.001mol of DAPBO, 0.004mol of 4-BAPB, 0.018mol of SIDA and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 15 hours after the completion of the addition. To the reaction mixture were added 0.009mol of NA and 10g of NMP in this order, and the reaction was continued at 10 ℃ for 15 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
Comparative example 6
A1L three-necked flask equipped with a mechanical stirrer, a bulb-shaped condenser and a nitrogen introduction head was charged with 421.7 g of NMP and 0.08mol of PDA, and after PDA was completely dissolved, 0.03mol of BPDA and 0.08mol of PMDA were further charged into the flask, and the mixture was reacted at 105 ℃ for 6 hours. Subsequently, the reaction temperature was lowered to 10 ℃ and 0.003mol of DAPBO, 0.01mol of FDH, 0.01mol of SIDA and 20g of NMP were added to the reaction solution in this order, and polymerization was carried out at 10 ℃ for 10 hours after completion of the addition. 0.007mol of PA and 10g of NMP were added to the reaction solution in this order, and the reaction was continued at 10 ℃ for 10 hours to obtain a polyamic acid varnish.
And (2) forming a uniform slit film on a glass substrate by the obtained polyamic acid varnish through a coating machine, drying the obtained wet film in HVCD at 80 ℃ for 15 minutes, transferring the obtained gel state film to infrared high-temperature OVEN, and curing the gel film at 450 ℃ through gradually raising the temperature to obtain the polyimide film.
The monomer raw materials and process parameters of examples 1 to 11 and comparative examples 1 to 6 are shown in Table 1.
TABLE 1 ingredient and parameter tables for examples and comparative examples
Figure 402519DEST_PATH_IMAGE005
Figure 156849DEST_PATH_IMAGE007
The surface tension and molecular weight distribution of the polyamic acid varnish obtained in examples and comparative examples were measured by the following test methods, and the polyamic acid varnish obtained was coated, dried and cured to prepare a polyimide film, and the thermal expansion coefficient and film thickness uniformity of the polyimide film were measured and the film forming property thereof was observed to obtain data shown in table 2.
Measurement method
The solid content of the invention is the content of polyamic acid in the polyamic acid varnish, and the determination method comprises the following steps: the polyamic acid varnish was uniformly coated in a glass container, and the sample mass m was measured1. And (3) heating the coated sample in an oven, keeping the temperature at 100 ℃ for 30min, heating to 350 ℃ at the speed of 5 ℃/min, and keeping the temperature at 350 ℃ for 30 min. Weighing the sample after the sample is cooled2. The solid content of the sample was calculated according to the following formula (4):
solid content = (m)2/ m1) X 100% formula (4)
The viscosity measuring method comprises the following steps: using a DHR (TA instruments) rotational viscometer at a temperature of 25 ℃ and a shear rate of 1s-1Then, the viscosity of the polyamic acid was measured.
Transmittance test method of polyamic acid varnish: the liquid was loaded into a 1cm thick standard cell using a spectrophotometer (perkin elmer LAMBDA 365 uv/visible spectrophotometer) and the transmission of the varnish in the visible range was tested.
Surface tension test method of polyamic acid varnish: the plate method is used for testing, and the specific operation is as follows: the surface tension of the polyamic acid is tested by using a KRUSS K100 full-automatic surface tension meter at 25 ℃, 50 ℃ and 80 ℃, and the specific operation is as follows: the platinum plate with known perimeter is washed by deionized water and burned to red by an alcohol lamp, and the surface active substances on the platinum plate are removed. And fixing the cooled platinum plate on a balance hook, pouring 50mL of a sample to be measured into a measuring beaker, moving the measuring beaker to a position with the liquid level about 2mm away from the platinum plate, and balancing for 1-10min to obtain the surface tension data of the polyamic acid. In a specific test of the surface tension of the polyamic acid varnish obtained in the examples of the present invention and the comparative examples, the equilibration time was selected to be 8 min. The testing method of the surface tension of the organic solvent is the same as that of the polyamic acid varnish, and the balance time is 8 min.
Method for testing molecular weight distribution of polyamic acid varnish: the Gel Permeation Chromatography (GPC) method is adopted for testing.
Coefficient of linear expansion CTE measurement of polyimide film: the polyimide film sample was cut into a short strip having a width of 4mm, and the strip was used as an experimental piece using a TMA tester (TA-Q400) in a nitrogen atmosphere at a temperature rise rate of 10 ℃/min. The sample was warmed once in TMA before testing to remove relaxation effects.
The film thickness uniformity refers to the statistical deviation of the film thickness of a plurality of points and different positions measured on the whole glass. The polyimide film thus obtained was observed for the presence of white turbidity and cracks, wherein the absence of white turbidity was denoted as "X", the presence of slight white turbidity was denoted as "O", and the presence of severe white turbidity was denoted as "OO".
Table 2 examples and comparative examples PAA and PI testing
Figure DEST_PATH_IMAGE009
The polyimide varnish and the polyimide film provided by the invention can be applied to the technical fields of photoelectric display such as substrates of solar cells, printed circuits, touch panels and the like, liquid crystal alignment films of liquid crystal elements and the like.

Claims (8)

1. A flexible display device comprising a flexible substrate, a display unit, the flexible substrate comprising a polyimide film formed from a polyamic acid varnish comprising a polar organic solvent and a polyamic acid having the following formula (1) as a repeating unit;
Figure 159351DEST_PATH_IMAGE001
formula (1)
In the formula (1), X comprises the following formula (2), and the formula (2) accounts for more than 80mol% of the total amount of X; and Y comprises the following formula (3), wherein the formula (3) accounts for more than 80mol% of the total amount of Y; r1And R2Each independently selected from a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; the X also includes the structure formed by the following dianhydrides: pyromellitic anhydride, 2,3, 3', 4' -biphenyltetracarboxylic dianhydride, 4,4' -oxydiphthalic anhydride, 3,3',4,4' -benzophenonetetracarboxylic dianhydride, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl group]One or more of propane dianhydride and cyclobutane tetracarboxylic dianhydride;
the Y also includes the structure formed by the following diamines: more than one of diamine containing benzimidazole structure, diamine containing benzoxazole structure and diamine containing silicon;
the end-capping reagent for forming the polyamic acid comprises more than one of monoanhydride, monocarboxylic acid, monoacid chloride compound, mono-active ester compound, dicarbonate compound, vinyl ether compound, monoamine or monohydric alcohol, and the adding amount of the end-capping reagent is 1-6% of the total molar amount of diamine monomer or dianhydride monomer;
Figure 896363DEST_PATH_IMAGE002
formula (2)
Figure 419748DEST_PATH_IMAGE003
Formula (3)
The surface tension of the polyamic acid varnish at 25 ℃ is 33-46 mN/m; and, the polyamic acid has a molecular weight distribution of 1.15 to 1.45;
the surface tension of the polyamic acid varnish is tested by a plate method, and the balance time is 8 min; the surface tension of the polyamic acid varnish at 50 ℃ is 0.91 to 0.96 of the surface tension at 25 ℃, and the surface tension of the polyamic acid varnish at 80 ℃ is 0.8 to 0.86 of the surface tension at 25 ℃.
2. A polyamic acid varnish for a display, comprising a polar organic solvent and a polyamic acid having a repeating unit represented by the following formula (1);
Figure 849593DEST_PATH_IMAGE004
formula (1)
In the formula (1), X comprises the following formula (2), and the formula (2) accounts for more than 80mol% of the total amount of X; and Y comprises the following formula (3), wherein the formula (3) accounts for more than 80mol% of the total amount of Y; r1And R2Each independently selected from a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; the X also includes the structure formed by the following dianhydrides: pyromellitic anhydride, 2,3, 3', 4' -biphenyltetracarboxylic dianhydride, 4,4' -oxydiphthalic anhydride, 3,3',4,4' -benzophenonetetracarboxylic dianhydride, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl group]One or more of propane dianhydride and cyclobutane tetracarboxylic dianhydride;
the Y also includes the structure formed by the following diamines: more than one of diamine containing benzimidazole structure, diamine containing benzoxazole structure and diamine containing silicon;
the end-capping reagent for forming the polyamic acid comprises more than one of monoanhydride, monocarboxylic acid, monoacid chloride compound, mono-active ester compound, dicarbonate compound, vinyl ether compound, monoamine or monohydric alcohol, and the adding amount of the end-capping reagent is 1-6% of the total molar amount of diamine monomer or dianhydride monomer;
Figure 28901DEST_PATH_IMAGE002
formula (2)
Figure 304025DEST_PATH_IMAGE003
Formula (3)
The surface tension of the polyamic acid varnish at 25 ℃ is 33-46 mN/m; and, the polyamic acid has a molecular weight distribution of 1.15 to 1.45;
the surface tension of the polyamic acid varnish is tested by a plate method, and the balance time is 8 min; the surface tension of the polyamic acid varnish at 50 ℃ is 0.91 to 0.96 of the surface tension at 25 ℃, and the surface tension of the polyamic acid varnish at 80 ℃ is 0.8 to 0.86 of the surface tension at 25 ℃.
3. The polyamic acid varnish according to claim 2, wherein the diamine containing a benzimidazole structure comprises 2- (3-aminophenyl) -5-aminobenzimidazole and/or 2- (4-aminophenyl) -5-aminobenzimidazole;
the diamine containing a benzoxazole structure comprises 2- (4-aminophenyl) -5-aminobenzoxazole;
the silicon-containing diamine comprises 1, 3-bis (3-aminopropyl) tetramethyldisiloxane;
the Y also includes the structure formed by the following diamines: 1, 3-phenylenediamine, 1, 2-phenylenediamine, 4 '-diaminodiphenyl sulfone, 3' -diaminodiphenyl sulfone, 4 '-diaminodiphenyl sulfide, 4' -diaminodiphenyl ether, 3,3 '-diaminodiphenyl ether, 3, 4' -diaminodiphenyl ether, 4 '-bis (3-aminophenoxy) biphenyl, 4' -bis (4-aminophenoxy) biphenyl, 9-bis (3- (3-aminobenzamide) -4-hydroxyphenyl) fluorene, 2-bis [3- (3-aminobenzamide) -4-hydroxyphenyl ] hexafluoropropane, 9-bis (4- (4-aminophenoxy) phenyl) fluorene.
4. The polyamic acid varnish according to claim 2, wherein the formula (2) accounts for 90mol% or more of the total amount of X; and/or the formula (3) accounts for more than 90mol% of the total amount of Y.
5. The polyamic acid varnish according to claim 2, wherein the polar organic solvent is one or more of N-methyl-2-pyrrolidone, N-dimethylformamide, and N, N-dimethylacetamide.
6. The polyamic acid varnish according to claim 2, wherein the end-capping agent forming the polyamic acid comprises one or more of phthalic anhydride, 4-phenylethynylphthalic anhydride, nadic anhydride, maleic anhydride, and 3-hydroxyphthalic anhydride; the addition amount of the end capping agent is 1-6% of the total molar amount of the diamine monomer or the dianhydride monomer.
7. A polyimide film obtained from the polyamic acid varnish according to any one of claims 2 to 6, wherein the polyimide film is formed from the polyamic acid varnish.
8. A display device, characterized in that the display device comprises the polyimide film according to claim 7.
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