CN114685786A - Polyimide film and preparation method and application thereof - Google Patents

Polyimide film and preparation method and application thereof Download PDF

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CN114685786A
CN114685786A CN202011567117.XA CN202011567117A CN114685786A CN 114685786 A CN114685786 A CN 114685786A CN 202011567117 A CN202011567117 A CN 202011567117A CN 114685786 A CN114685786 A CN 114685786A
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polyimide film
dianhydride
film
tetracarboxylic dianhydride
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CN114685786B (en
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范琳
王畅鸥
翟磊
何民辉
莫松
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Institute of Chemistry CAS
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    • C—CHEMISTRY; METALLURGY
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    • 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
    • C08G73/1067—Wholly aromatic polyimides, i.e. having both tetracarboxylic and diamino moieties aromatically bound
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    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
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    • C08G73/1007—Preparatory processes from tetracarboxylic acids or derivatives and diamines
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    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
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    • 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
    • C08G73/1039—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors comprising halogen-containing substituents
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Abstract

The invention relates to a polyimide film and a preparation method and application thereof, belongs to the technical field of polyimide, and solves the problems that the transparency of the polyimide film is poor and the turbidity and the yellowness of the polyimide film are increased at high temperature in the prior art. The polyimide film of the invention comprises the following raw materials: diamine, dianhydride, and end group protecting agent; the molar ratio of the end group protective agent to the diamine monomer is (0.02-0.24): 1; the molar ratio of the diamine monomer to the dianhydride monomer is 1 (0.90-0.99); the molecular main chain of the polyimide contains an end group protecting group. The preparation method of the polyimide film provided by the invention realizes effective protection of active end groups in molecular chains, enables the aggregation state structure of the film to be more stable, effectively improves the optical stability of the polyimide film in a high-temperature environment, and has important application in the fields of electronics, microelectronics, optical display, optical communication and the like.

Description

Polyimide film and preparation method and application thereof
Technical Field
The invention relates to the technical field of polyimide, in particular to a polyimide film and a preparation method and application thereof.
Background
The rapid development of the photoelectric technology puts an urgent application demand on high-performance optical film materials, and polymer optical materials with the advantages of good transparency, light weight, toughness and the like are increasingly emphasized. Among a plurality of polymer materials, the transparent polyimide material has become a preferred polymer substrate material in the field of flexible photoelectricity due to the outstanding heat resistance and the characteristics of excellent mechanical property, chemical stability and the like. Particularly, in the field of novel display, display enterprises at home and abroad develop novel flexible display devices based on transparent polyimide as a cover plate and a substrate. Companies such as samsung and hua shi also release folding cell phones using transparent polyimide films as cover materials, which shows a huge market application prospect. In addition, the transparent polyimide material has wide application in other fields such as flexible electronics, microelectronics, information communication and the like.
During the fabrication of display devices, the substrate material typically needs to undergo a series of high temperature processing processes. The preparation process of TFT, which is a key component of display drive, is very high in temperature, the high-temperature treatment temperature exceeds 350 ℃, and the short-time activation and dehydrogenation process is even as high as 450-500 ℃ as represented by OLED display technology. Therefore, as a transparent polymer substrate material showing the most promising application, a polyimide film must have both excellent optical properties and heat resistance. At present, research on transparent polyimide materials has been greatly progressed, light transmittance of a film in a visible light region can be achieved to 90% or more, yellowness (YI value) of the film is also greatly reduced, and glass transition temperature (T) is also greatly reducedg) And is also greatly improved. However, the stability of optical properties of transparent polyimide films in high-temperature environments is less of a concern. In practical application, the basic performance of the transparent polyimide film material isThe film can endure high use temperature, but the optical performance, namely the transparency of the film is easy to deteriorate at high temperature, the light transmittance is reduced, the turbidity is increased, the color of the film is deepened, namely the yellowness value is increased, and the quality and the performance stability of devices are seriously influenced. Therefore, how to realize that the transparent polyimide film material still keeps good transparency and low chroma at high temperature (not less than 300 ℃) and reduce the adverse effect of the high temperature on the optical performance of the film is an important technical problem to be solved urgently.
Disclosure of Invention
In view of the above technical current situation and problem analysis, the present invention aims to provide a polyimide film, a preparation method thereof and an application thereof, so as to solve the technical challenge that the optical performance of the existing polyimide film cannot be effectively maintained at a high temperature, and particularly, when the service temperature is above 300 ℃, the light transmittance of the transparent polyimide film is obviously reduced, and the haze and the yellowness value of the transparent polyimide film are increased.
The purpose of the invention is mainly realized by the following technical scheme:
in one aspect, the present invention provides a polyimide film, which is prepared from the following raw materials: diamine, dianhydride, and end group protecting agent; the molar ratio of the end group protective agent to the diamine monomer is (0.02-0.24): 1; the molar ratio of the diamine monomer to the dianhydride monomer is 1 (0.90-0.99); the main molecular chain of the polyimide contains an end group protecting group.
In a further improvement of the above polyimide film, the end-protecting agent comprises a mono-anhydride compound comprising one or more of phthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, 3-fluorophthalic anhydride, 4-fluorophthalic anhydride, 3,4,5, 6-tetrafluorophthalic anhydride and naphthalic anhydride.
Further improvement based on the above polyimide film, the diamine is 1, 4-p-phenylenediamine, 4 '-diaminodiphenyl ether, 4' -diaminodiphenyl sulfone, 3,4 '-diaminodiphenyl sulfone, 9-bis (4-aminophenyl) fluorene, 9-bis (3-fluoro-4-aminophenyl) fluorene, 9-bis (3-methyl-4-aminophenyl) fluorene, 1-bis (4-aminophenyl) cyclohexane, 1, 4-cyclohexanediamine, 4' -diaminobenzanilide, N '-bis (2-trifluoromethyl-4-aminophenyl) -terephthalamide, N' -bis (3-trifluoromethyl-4-aminophenyl) -terephthalamide, or mixtures thereof, N, N ' -3,3' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4' -diaminobenzamide, N ' -2,2' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4' -diaminobenzamide, N ' -2, 6-bis (trifluoromethyl) - (1, 1-biphenyl) -4,4' -diaminobenzamide, 2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl, 2' -bis (methyl) -4,4' -diaminobiphenyl, 2' -difluoro-4, 4' -diamino-biphenyl, 2' -bis (trifluoromethyl) -4, any one or more of 4 '-diaminophenyl ether, 1, 4-bis (2' -trifluoromethyl-4 '-aminophenoxy) benzene, 1, 4-bis (2' -trifluoromethyl-4 '-aminophenoxy) biphenyl, 2-bis (3-aminophenyl) hexafluoropropane and 2,2' -bis (4-aminophenoxyphenyl) hexafluoropropane.
Further improvement based on the above polyimide film, the dianhydride is 1,2,4, 5-pyromellitic dianhydride, 3,3',4,4' -biphenyltetracarboxylic dianhydride, 2,3,3',4' -biphenyltetracarboxylic dianhydride, 3,3',4,4' -benzophenonetetracarboxylic dianhydride, 3,3',4,4' -diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4' -diphenylethertetracarboxylic dianhydride, 2,5,7, 10-naphthalenetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, bicyclo [2.2.2] octa-2, 3,5, 6-tetracarboxylic dianhydride, hydrogenated naphthalenetetracarboxylic dianhydride, hydrogenated biphenyltetracarboxylic dianhydride, 9-bis (3, 4-dicarboxyphenyl) fluorene dianhydride, 3,3',4,4' -dibenzoic acid terephthalamide tetracarboxylic dianhydride, 4,4' - (2, 2-hexafluoroisopropylidene) diphthalic anhydride, norbornane-2-spiro- α -cyclopentanone- α ' -spiro-2 ' -norbornane-5, 5',6,6' -tetracarboxylic dianhydride, and p-phenylene-bistrimellic dianhydride.
Based on the further improvement of the polyimide film, after the polyimide film is endured for 1-2 hours at 300-400 ℃, the average transmittance change rate of the polyimide film in a visible light area is less than 5%, and the yellowness change rate is less than 10%.
On the other hand, the invention also provides a preparation method of the polyimide film, which is used for preparing the polyimide film and comprises the following steps:
step 1: performing polycondensation reaction on diamine and dianhydride in an organic solvent to obtain a polyamic acid solution;
and 2, step: partially imidizing a polyamic acid solution by an imidization method to obtain a precursor solution with a predetermined imidization degree;
and step 3: adding an end group protective agent into the precursor solution, forming a film, and obtaining the polyimide film by a thermal imidization method or a chemical imidization method.
Based on a further improvement of the above preparation method, the organic solvent in step 1 is one or more of N-methylpyrrolidone, N-ethylpyrrolidone, N '-dimethylformamide, N' -dimethylacetamide, N '-diethylformamide, N' -diethylacetamide, dimethylpropionamide, diethylpropionamide, dimethylsulfoxide, cyclopentanone, and butyrolactone.
The kind of the solvent may be selected from one or more according to the solubility of the monomer, and may be adjusted according to the long-term storage stability of the polyamic acid, the easy-removal ability of the solvent at high temperature, the solubility of the precursor after partial chemical imidization, and the like.
Based on a further improvement of the above preparation method, the imidization method in step 2 includes a thermal imidization method and a chemical imidization method.
Based on the further improvement of the preparation method, the heating temperature is 40-95 ℃ when the thermal imidization method is adopted in the step 2, and the reaction time is 0.5-24 hours.
The thermal imidization in step 2 is performed to obtain a certain degree of imidization. In the invention, the specific thermal imidization temperature (40-95 ℃) and the reaction time (0.5-24 hours) are selected in the step 2, so that the imidization degree can be controlled to be 10-60%.
Based on the further improvement of the preparation method, when the chemical imidization method is adopted in the step 2, the catalyst is one or more of trialkylamine, imidazole, methylimidazole, pyridine, picoline, quinoline and isoquinoline, and the dehydrating agent is one or more of acetic anhydride, trifluoroacetic anhydride, propionic anhydride and valerolactone; the molar ratio of the catalyst to the dehydrating agent is (0.2-1.5): 1.
based on the further improvement of the preparation method, the preset imidization degree of the precursor solution in the step 2 is 10-60%.
In order to obtain a preset imidization degree, when a chemical imidization method is adopted, polyimide systems with different structures can regulate and control the adding amount, the reaction temperature and the reaction time of a catalyst and a dehydrating agent to carry out targeted regulation; the imidization degree characterization method can be used for testing by an infrared spectroscopy method, a nuclear magnetic method and a thermal decomposition method.
The higher the imidization degree of the precursor solution is, the more polyamic acid is converted into polyimide, which is beneficial to the ordered and compact arrangement of molecular chains, and the aggregation structure of the film tends to be more stable and the optical performance stability of the film at high temperature is better by combining the subsequent high-temperature thermal imidization process. In contrast, in the film prepared by directly performing thermal imidization on polyamic acid, molecular chains are more randomly arranged, and the aggregation structure is unstably changed at high temperature, which is one of the reasons for the instability of the optical performance of the film.
If the pre-imidization degree is less than 10%, the regulation and control effect on the aggregation structure is not obvious, and if the pre-imidization degree is more than 60%, the solution becomes turbid or even gel due to poor solubility of the precursor, which is not beneficial to subsequent coating and film forming, and the quality and optical performance of the film are affected.
Based on further improvement of the preparation method, the molar ratio of the end group protective agent to the diamine monomer is (0.02-0.24): 1.
based on the further improvement of the preparation method, when the thermal imidization method is adopted in the step 3, the method comprises the steps of carrying out medium-low temperature imidization firstly and then carrying out high temperature imidization. Preferably, the heating temperature of the medium-low temperature imidization is 80-250 ℃, the heating time is 1-2 h, the heating temperature of the high-temperature imidization is 300-350 ℃, and the heating time is 0.5-2 h.
In the film drying stage after film coating and making, the film is dried at medium and low temperature, and then the film is dried at high temperature. In the middle-low temperature baking stage in the front section, a step heating and heat preservation process is adopted, such as 80 ℃/2h, 120 ℃/1h, 200 ℃/1h or 250 ℃/1h, and the stage mainly removes a solvent and an organic auxiliary agent to complete certain imidization. And in the later high-temperature baking stage, the film is heated at 300-350 ℃ for 0.5-2 hours at least, so that on one hand, the complete imidization of the film is realized, and on the other hand, the added organic auxiliary agent is thoroughly removed.
In addition, a chemical imidization method can also be adopted, namely, an imidization reagent consisting of a catalyst and a dehydrating agent is added firstly to obtain polyimide resin or solution, and then the film is dried at a medium-low temperature. The imide is completed by a chemical method, which is beneficial to reducing the subsequent film drying temperature and is very beneficial to the optical performance of the film.
The re-imidization in step 3 may be performed by the same imidization method and process conditions as those for partially imidizing the polyamic acid solution in step 2.
Based on the further improvement of the preparation method, when the chemical imidization method is adopted in the step 3, the molar ratio of the catalyst to the dehydrating agent is 1: (1-2.5), wherein the molar ratio of the dehydrating agent to the diamine monomer is (3-10): 1.
based on further improvement of the preparation method, step 3 is followed by high-temperature post-treatment, wherein the high-temperature post-treatment comprises the step of carrying out heat treatment on the polyimide film at 350-450 ℃ for 5-40 minutes.
The high-temperature post-treatment is embodied in two aspects, namely, thermal stress generated in the film preparation process is released at high temperature; secondly, the aggregation structure of the film is further stabilized.
The film can be flatly paved on a fixing device and subjected to certain unidirectional or bidirectional stretching during high-temperature post-treatment, which is beneficial to further orientation of a film molecular chain, increases the content of an ordered structure, improves the heat resistance, the size stability and the like of the film. In addition, the thermal imidization and the high-temperature post-treatment may be performed in a vacuum, air or oxygen-free environment, and are optimal in a vacuum and oxygen-free environment from the viewpoint of film transparency.
Based on the further improvement of the preparation method, in the step 1, the reaction condition of the synthesis of the polyamic acid is favorable for the reaction at low temperature (-10 ℃ to 20 ℃) when the diamine and the dianhydride monomer have good activity, and the low temperature is favorable for the forward progress of the polyamic acid reaction because the polyamic acid synthesis reaction is an exothermic reaction; if the diamine or dianhydride monomer has low activity, the reaction is favorably carried out by properly increasing the polycondensation reaction temperature (30 to 80 ℃), and the polymerization reaction of the monomer is unfavorably carried out by excessively lowering the reaction temperature, so that the polyamic acid with high molecular weight cannot be obtained.
Based on the further improvement of the preparation method, when the chemical imidization is adopted in the step 2, the catalyst is one or more of trialkylamine, imidazole, methylimidazole, pyridine, picoline, quinoline and isoquinoline; the dehydrating agent is one or more of acetic anhydride, trifluoroacetic anhydride, propionic anhydride and valerolactone; the molar ratio of the catalyst to the dehydrating agent is (0.2-1.5): 1.
heating or adding a catalyst can help to improve the imidization reaction rate of the polyamic acid, the dehydrating agent helps to remove water in the imidization reaction of the polyamic acid, and the generated product can be removed in time in subsequent high-temperature thermal imidization. The dosage of the catalyst and the dehydrating agent is adjusted according to the preset imidization degree of the polyamic acid, the addition amount of the catalyst and the dehydrating agent is correspondingly increased to obtain high imidization degree, and the addition amount of the catalyst and the dehydrating agent is not excessively large to avoid the influence of the residue of the auxiliary agent on the heat-resistant stability of the film.
Based on further improvement of the preparation method, the molar ratio of the end group protective agent to the diamine monomer is (0.02-0.24): 1.
The single-anhydride end group protective agent is favorable for eliminating amino (-NH) remained in the polyimide in the synthesis process2) And active terminal amino groups exposed at two ends of the molecular chain are inactivated, so that the yellowing of the film caused by the oxidation reaction of the active amino groups at high temperature is avoided.
When the addition amount of the single-anhydride end group protective agent is too low, the yellowing resistant effect of the film is not obvious due to insufficient reaction with active amino; when the amount is too high, the reaction into the polymer molecular chain is not completed due to the excess, and the heat resistance stability of the film is potentially adversely affected.
The terminal group protective agent is added when the polyamic acid has completed partial imidization reaction and reaches a certain imidization degree (10-60%). This helps to avoid the adverse effect of monofunctional endcapping agents on the molecular weight build of the polymer, providing a guarantee that high molecular weight polyamic acids and polyimides can be obtained. The end group protective agent is a monofunctional compound, and the early addition of the end group protective agent can break the equimolar equilibrium reaction of diamine and dianhydride, so that the viscosity of polyamic acid is too low, and a high-molecular-weight polymer cannot be obtained.
The invention also provides the polyimide film as a substrate material, which is widely applied to the fields of electronics, microelectronics, optical display or optical communication, in particular to the fields of flexible photoelectricity such as flexible display, flexible solar cells, flexible electronic devices and the like.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
(1) by introducing a terminal group protecting group into a main chain of a polyimide molecule, active terminal amino (-NH) in a molecular chain can be effectively led2) The film is inactivated, and the film yellowing phenomenon caused by the oxidation reaction of the active groups at high temperature is avoided.
(2) The invention adopts the preparation method that the polyamic acid is partially imidized to reach a certain imidization degree, and then the end group protective agent is added, thereby effectively avoiding the adverse effect of the monofunctional end capping agent on the increase of the molecular weight of the polymer and being beneficial to obtaining the high molecular weight polymer.
(3) The method combines the two-time imidization and high-temperature post-treatment, is not only beneficial to improving the final imidization degree of the film, but also beneficial to the regular arrangement of polymer molecular chains, and enables the aggregation state structure of the film to be more stable, thereby further improving the optical performance stability of the polyimide film in high-temperature application and avoiding the adverse effect of the aggregation state structure change on the transparency and the yellowness.
(4) The invention controls the specific temperature (40-95 ℃) and time (0.5-24 hours) for the first thermal imidization, so that the imidization degree can be controlled at 10-60%.
(5) The preparation method of the yellowing-resistant polyimide film provided by the invention is simple in process, realizes good optical performance stability of the film at high temperature on the basis of not changing the main structure of a molecular chain, and has the advantages that after the film is subjected to high temperature of 300-400 ℃ for 1-2 hours in an aerobic or anaerobic environment, the average transmittance change rate of the film in a visible light region is less than 5%, and the yellowing change rate is less than 10%.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
FIG. 1 shows the light transmittance at room temperature (curve 1) of the film of example 2 and the light transmittance after 1 hour of resistance at 350 ℃ in an air atmosphere (curve 2).
FIG. 2 shows the light transmittance of the film of comparative example 1 at room temperature (curve 3) and the light transmittance after 1 hour resistance at 350 ℃ in an air atmosphere (curve 4).
Detailed Description
The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples. The following examples select representative diamine, dianhydride monomer and end group protective agent, synthesize yellowing-resistant polyimide films with different main chain structures by the preparation method provided by the invention, replace the diamine and/or dianhydride monomer and/or end group protective agent in the examples with other diamine and/or dianhydride monomer and/or end group protective agent described in the disclosure, and the prepared homopolymerization or copolymerization type polyimide films all have similar effects as the same as the embodiments by the preparation method and conditions described in the disclosure.
In the present invention, the percentage content and the percentage concentration are both the mass percentage content and the mass percentage concentration unless otherwise specified. The starting materials are commercially available from published sources unless otherwise specified. In the embodiment, the thickness of the polyimide film can be regulated and controlled by adjusting the type of the coating roller and the solid content of the polyamic acid homogeneous solution.
Example 1
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl and 260 g of N-methylpyrrolidone are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the temperature of the system is reduced to minus 10 ℃, 26.39 g (0.059 mol) of 4,4' - (2, 2-hexafluoroisopropyl) diphthalic anhydride is added, after complete dissolution, the mixture is stirred for 24 hours at room temperature to obtain a homogeneous polyamic acid solution with solid content of about 15 wt% and viscosity of 26300 cP.
(2) 0.56 g (0.006 mol) of picoline and 1.02 g (0.01 mol) of acetic anhydride were added to the polyamic acid obtained in step 1, and partial chemical imidization was performed at room temperature for 4 hours to obtain a precursor solution having an imidization degree of 10%.
(3) 0.30 g (0.002 mol) of phthalic anhydride was added to the precursor solution obtained in step 2, and stirred at 25 ℃ for 6 hours to obtain a homogeneous partially imidized and end-capped precursor solution.
(4) To the solution obtained in step 3 were added 16.76 g (0.18 mol) of picoline and 18.38 g (0.18 mol) of acetic anhydride, and the mixture was stirred at 25 ℃ for 6 hours to obtain a solution of a terminal-capped polyimide. The solution was poured into ethanol to precipitate a resin solid and dried under vacuum at 120 ℃ for 12 hours.
(5) And (3) dissolving the polyimide resin obtained in the step (4) in N-methyl pyrrolidone with the solid content of 15 wt%, uniformly stirring, filtering, defoaming in vacuum, coating the polyimide resin on a dry glass plate with a smooth and flat surface, placing the glass plate in an oven, and heating in a nitrogen atmosphere. The specific process is as follows: 80 ℃/1 hour, 120 ℃/1 hour, 200 ℃/1 hour, 300 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the self-supporting film is placed in a high-temperature oven, the temperature is gradually increased to 400 ℃/5 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film PI-1, the film thickness is about 30 micrometers, and the main properties are shown in Table 1.
Example 2
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl and 245 g of N-methylpyrrolidone are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the temperature of the system is reduced to 5 ℃, 23.99 g (0.054 mol) of 4,4' - (2, 2-hexafluoroisopropyl) diphthalic anhydride is added, and after complete dissolution, the mixture is stirred for 24 hours at room temperature to obtain homogeneous polyamic acid solution with solid content of about 15 wt%, and the viscosity of the homogeneous polyamic acid solution is 23800 cP.
(2) 7.12 g (0.09 mol) of pyridine and 9.19 g (0.09 mol) of acetic anhydride were added to the polyamic acid obtained in step 1, and partial chemical imidization was performed at room temperature for 12 hours to obtain a precursor solution having an imidization degree of 60%.
(3) 0.31 g (0.002 mol) of hexahydrophthalic anhydride was added to the precursor solution obtained in step 2 and stirred at 25 ℃ for 12 hours to obtain a precursor solution which was homogeneously partially imidized and end-capped.
(4) To the solution obtained in step 3 were added 18.98 g (0.24 mol) of pyridine and 49.00 g (0.48 mol) of acetic anhydride, and the mixture was stirred at 25 ℃ for 8 hours to obtain a solution of end-capped polyimide. The solution was poured into ethanol to precipitate a resin solid, which was dried under vacuum at 120 ℃ for 12 hours.
(5) And (3) dissolving the polyimide resin obtained in the step (4) in N-methyl pyrrolidone with the solid content of 15 wt%, uniformly stirring, filtering, defoaming in vacuum, coating the polyimide resin on a dry glass plate with a smooth and flat surface, placing the glass plate in an oven, and heating in a nitrogen atmosphere. The specific process is as follows: 80 ℃/1.5 hours, 250 ℃/1 hour, 300 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the self-supporting film is placed in a high-temperature oven, the temperature is gradually increased to 350 ℃/40 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film PI-2, the film thickness is about 30 micrometers, and the main properties are shown in Table 1.
Example 3
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl and 250 g of N, N ' -dimethylacetamide are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the temperature of the system is reduced to 0 ℃, 25.32 g (0.057 mol) of 4,4' - (2, 2-hexafluoroisopropyl) diphthalic anhydride is added, after complete dissolution, the mixture is stirred for 24 hours at room temperature, and homogeneous polyamic acid solution with solid content of about 15 wt% is obtained, and the viscosity is 24800 cP.
(2) 3.87 g (0.03 mol) of quinoline and 6.13 g (0.06 mol) of acetic anhydride were added to the polyamic acid obtained in step 1, and partial chemical imidization was performed at room temperature for 8 hours to obtain a precursor solution having a degree of imidization of 40%.
(3) 0.90 g (0.0054 mol) of 3-fluorophthalic anhydride was added to the precursor solution obtained in step 2, and stirred at 25 ℃ for 6 hours to obtain a precursor solution which was partially imidized and end-capped in a homogeneous phase.
(4) To the solution obtained in step 3 were added 15.50 g (0.12 mol) of quinoline and 24.50 g (0.24 mol) of acetic anhydride, and stirred at 25 ℃ for 8 hours to obtain a solution of end-capped polyimide. The solution was poured into ethanol to precipitate a resin solid, which was dried under vacuum at 110 ℃ for 12 hours.
(5) And (3) dissolving the polyimide resin obtained in the step (4) in N, N' -dimethylacetamide with a solid content of 15 wt%, uniformly stirring, filtering, defoaming in vacuum, coating the mixture on a dry glass plate with a smooth and flat surface, placing the glass plate in an oven, and heating in a nitrogen atmosphere. The specific process is as follows: 80 ℃/2 hours, 200 ℃/1 hour, 300 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the self-supporting film is placed in a high-temperature oven, the temperature is gradually increased to 350 ℃/20 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film PI-3, the film thickness is about 30 micrometers, and the main properties are shown in Table 1.
Example 4
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl and 253 g of N, N ' -dimethylformamide are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the system is cooled to 10 ℃ and 25.32 g (0.057 mol) of 4,4' - (2, 2-hexafluoroisopropyl) diphthalic anhydride is added, after complete dissolution, the mixture is stirred for 24 hours at room temperature to obtain homogeneous polyamic acid solution with solid content of about 15 wt% and viscosity of 24300 cP.
(2) The polyamic acid obtained in step 1 was subjected to a thermal imidization reaction at 55 ℃ for 4 hours to obtain a precursor solution having an imidization degree of 40%.
(3) To the precursor solution obtained in step 2, 0.24 g (0.0015 mol) of 3-methylphthalic anhydride was added and stirred at 25 ℃ for 12 hours to obtain a precursor solution which was partially imidized and end-capped in homogeneous phase.
(4) To the solution obtained in step 3 were added 16.76 g (0.18 mol) of picoline and 36.75 g (0.36 mol) of acetic anhydride, and the mixture was stirred at 25 ℃ for 8 hours to obtain a terminal-capped polyimide solution. The solution was poured into ethanol to precipitate a resin solid and dried under vacuum at 80 ℃ for 24 hours.
(5) And (3) dissolving the polyimide resin obtained in the step (4) in N, N' -dimethylformamide with the solid content of 15 wt%, uniformly stirring, filtering, defoaming in vacuum, coating the polyimide resin on a dry glass plate with a smooth and flat surface, placing the glass plate in an oven, and heating in a nitrogen atmosphere. The specific process is as follows: 80 ℃/1 hour, 150 ℃/1 hour, 250 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the substrate is placed in a high-temperature oven, the temperature is gradually increased to 375 ℃/30 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film PI-4, the film thickness is about 30 microns, and the main properties are shown in Table 1.
Example 5
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl and 210 g of N-methylpyrrolidone are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the system is cooled to-10 ℃, 17.35 g (0.059 mol) of 3,3',4,4' -biphenyltetracarboxylic dianhydride is added, and after complete dissolution, the mixture is stirred for 24 hours at room temperature to obtain homogeneous polyamic acid solution with solid content of about 15 wt%, and the viscosity of the homogeneous polyamic acid solution is 39000 cP.
(2) 3.16 g (0.04 mol) of pyridine and 6.13 g (0.06 mol) of acetic anhydride were added to the polyamic acid obtained in step 1, and partial chemical imidization was performed at room temperature for 8 hours to obtain a precursor solution having a degree of imidization of 40%.
(3) And (3) adding 0.25 g (0.0015 mol) of 3-fluorophthalic anhydride into the precursor solution obtained in the step (2), and stirring at 25 ℃ for 6 hours to obtain a precursor solution which is partially imidized and terminated in a homogeneous phase.
(4) And (3) filtering and vacuum defoaming the precursor solution obtained in the step (3), coating the precursor solution on a dry glass plate with a smooth surface, placing the glass plate in an oven, and heating the glass plate in a nitrogen atmosphere. The specific process is as follows: 80 ℃/1 hour, 120 ℃/1 hour, 250 ℃/1 hour, 350 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the substrate is placed in a high-temperature oven, the temperature is gradually increased to 400 ℃/15 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film PI-5, the film thickness is about 30 micrometers, and the main properties are shown in table 1.
Example 6
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl and 230 g of N-methylpyrrolidone are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the system was cooled to 5 ℃ and 12.88 g (0.029 mol) of 4,4' - (2, 2-hexafluoroisopropyl) diphthalic anhydride and 8.53 g (0.029 mol) of 3,3',4,4' -biphenyltetracarboxylic dianhydride were added and, after complete dissolution, stirred at room temperature for 24 hours to give a homogeneous polyamic acid solution with a solids content of about 15 wt% and a viscosity of 36500 cP.
(2) 3.16 g (0.04 mol) of pyridine and 6.13 g (0.06 mol) of acetic anhydride were added to the polyamic acid obtained in step 1, and partial chemical imidization was performed for 12 hours to obtain a precursor solution having an imidization degree of 40%.
(3) 0.33 g (0.002 mol) of hexahydrophthalic anhydride was added to the precursor solution obtained in step 2 and stirred at 25 ℃ for 4 hours to obtain a homogeneous partially imidized and end-capped precursor solution.
(4) And (3) filtering and vacuum defoaming the precursor solution obtained in the step (3), coating the precursor solution on a dry glass plate with a smooth surface, placing the glass plate in an oven, and heating the glass plate in a nitrogen atmosphere. The specific process is as follows: 80 ℃/1 hour, 250 ℃/2 hour, 350 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the substrate is placed in a high-temperature oven, the temperature is gradually increased to 380 ℃/20 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film PI-6, the film thickness is about 30 micrometers, and the main properties are shown in Table 1.
Comparative example 1
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl and 310 g of N-methylpyrrolidone are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the temperature of the system is reduced to-5 ℃, 26.66 g (0.06 mol) of 4,4' - (2, 2-hexafluoroisopropyl) diphthalic anhydride is added, after complete dissolution, the mixture is stirred for 24 hours at room temperature, and homogeneous polyamic acid solution with solid content of about 15 wt% and viscosity of 27100cP is obtained.
(2) 11.87 g (0.15 mol) of pyridine and 30.63 g (0.30 mol) of acetic anhydride were added to the polyamic acid obtained in step 1, and chemical imidization was carried out for 12 hours to obtain a polyimide solution. The solution was poured into ethanol to precipitate a resin solid, which was dried under vacuum at 120 ℃ for 12 hours.
(3) And (3) dissolving the polyimide resin obtained in the step (2) in N-methyl pyrrolidone with the solid content of 15 wt%, uniformly stirring, filtering, defoaming in vacuum, coating the polyimide resin on a dry glass plate with a smooth and flat surface, placing the glass plate in an oven, and heating in a nitrogen atmosphere. The specific process is as follows: 80 ℃/1.5 hours, 250 ℃/1 hour, 300 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the self-supporting film is placed in a high-temperature oven, the temperature is gradually increased to 350 ℃/40 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film RPI-1, the film thickness is about 30 micrometers, and the main properties are shown in Table 1.
Comparative example 2
(1) Under the protection of inert gas, 19.21 g (0.06 mol) of 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl and 210 g of N-methylpyrrolidone are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the materials are completely dissolved; the system is cooled to 10 ℃ and 17.65 g (0.06 mol) of 3,3',4,4' -biphenyltetracarboxylic dianhydride is added, and after complete dissolution, the mixture is stirred for 24 hours at room temperature to obtain homogeneous polyamic acid solution with solid content of about 15 wt%, and the viscosity is 42200 cP.
(2) And (3) filtering and vacuum defoaming the polyamic acid solution obtained in the step (1), coating the polyamic acid solution on a dry glass plate with a smooth surface, placing the glass plate in an oven, and heating the glass plate in a nitrogen atmosphere. The specific process is as follows: 80 ℃/1 hour, 120 ℃/1 hour, 250 ℃/1 hour, 350 ℃/1 hour. And cooling to room temperature, soaking the substrate in deionized water, and automatically stripping and drying the film.
The obtained self-supporting film is laid on a substrate and fixed by a metal support frame, the self-supporting film is placed in a high-temperature oven, the temperature is gradually increased to 400 ℃/15 minutes to complete the high-temperature post-treatment of the film, the temperature is reduced to room temperature to obtain the final polyimide film RPI-2, the film thickness is about 30 micrometers, and the main properties are shown in Table 1.
TABLE 1 Main physical Properties and Properties of polyimide film
Figure BDA0002861956170000171
aTav: the average light transmittance of the film in the visible light area range is measured by a spectrophotometer; YI: film yellowness value, determined by colorimeter
bYellowing resistance performance investigation: and respectively placing the film in air or nitrogen atmosphere, and testing the change rate of the light transmittance and the yellowness of the film after the film is tolerant for 1-2 hours at 350 ℃.
Table 1 shows the main properties of the polyimide films prepared in examples 1 to 6. The data in the table show that the polyimide film prepared by the method provided by the invention has average transmittance change rate of less than 5% and yellowness change rate of less than 10% in a visible light region after the film is subjected to a test of enduring for 1-2 hours at 350 ℃ in air or nitrogen atmosphere, which indicates that the film has good optical property stability at high temperature. In contrast, the films obtained by the comparative examples 1 and 2 by adopting the traditional preparation method have obviously deteriorated light transmittance and yellowness value after being endured for 1-2 hours at 350 ℃, and particularly, the light transmittance is greatly reduced under the air atmosphere, which indicates that the optical performance stability of the films at high temperature is poor.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (10)

1. The polyimide film is characterized by comprising the following preparation raw materials: diamine, dianhydride, and end group protecting agent;
the molar ratio of the end group protective agent to the diamine monomer is (0.02-0.24): 1; the molar ratio of the diamine monomer to the dianhydride monomer is 1 (0.90-0.99);
the main molecular chain of the polyimide contains an end group protecting group.
2. The polyimide film of claim 1 wherein the end-protecting agent comprises a mono-anhydride based compound comprising one or more of phthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, 3-fluorophthalic anhydride, 4-fluorophthalic anhydride, 3,4,5, 6-tetrafluorophthalic anhydride, and naphthalic anhydride.
3. The polyimide film according to claim 1 or 2, wherein the diamine is 1, 4-p-phenylenediamine, 4 '-diaminodiphenyl ether, 4' -diaminodiphenyl sulfone, 3,4 '-diaminodiphenyl sulfone, 9-bis (4-aminophenyl) fluorene, 9-bis (3-fluoro-4-aminophenyl) fluorene, 9-bis (3-methyl-4-aminophenyl) fluorene, 1-bis (4-aminophenyl) cyclohexane, 1, 4-cyclohexanediamine, 4' -diaminobenzanilide, N '-bis (2-trifluoromethyl-4-aminophenyl) -terephthalamide, N' -bis (3-trifluoromethyl-4-aminophenyl) -terephthalamide, N, N ' -3,3' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4' -diaminobenzamide, N ' -2,2' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4' -diaminobenzamide, N ' -2, 6-bis (trifluoromethyl) - (1, 1-biphenyl) -4,4' -diaminobenzamide, 2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl, 2' -bis (methyl) -4,4' -diaminobiphenyl, 2' -difluoro-4, 4' -diamino-biphenyl, 2' -bis (trifluoromethyl) -4, any one or more of 4 '-diaminophenyl ether, 1, 4-bis (2' -trifluoromethyl-4 '-aminophenoxy) benzene, 1, 4-bis (2' -trifluoromethyl-4 '-aminophenoxy) biphenyl, 2-bis (3-aminophenyl) hexafluoropropane and 2,2' -bis (4-aminophenoxyphenyl) hexafluoropropane.
4. The polyimide film according to claim 1 or 2, wherein the dianhydride is 1,2,4, 5-pyromellitic dianhydride, 3,3',4,4' -biphenyl tetracarboxylic dianhydride, 2,3,3',4' -biphenyl tetracarboxylic dianhydride, 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 3,3',4,4' -diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4' -diphenyl ether tetracarboxylic dianhydride, 2,5,7, 10-naphthalene tetracarboxylic dianhydride, cyclobutane tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, bicyclo [2.2.2] octa-2, 3,5, 6-tetracarboxylic dianhydride, hydrogenated naphthalene tetracarboxylic dianhydride, hydrogenated biphenyl tetracarboxylic dianhydride, 9-bis (3, 4-dicarboxyphenyl) fluorene dianhydride, 3,3',4,4' -dibenzoic acid terephthalamide tetracarboxylic dianhydride, 4,4' - (2, 2-hexafluoroisopropylidene) diphthalic anhydride, norbornane-2-spiro- α -cyclopentanone- α ' -spiro-2 ' -norbornane-5, 5',6,6' -tetracarboxylic dianhydride, and p-phenylene-bistrimellic dianhydride.
5. The polyimide film according to claim 1, wherein the polyimide film has an average transmittance change rate of < 5% and a yellowing rate of < 10% in a visible light region after being endured at 300 to 400 ℃ for 1 to 2 hours.
6. A method for producing a polyimide film, which is used for producing the polyimide film according to any one of claims 1 to 5, comprising the steps of:
step 1: performing polycondensation reaction on diamine and dianhydride in an organic solvent to obtain a polyamic acid solution;
step 2: partially imidizing a polyamic acid solution by an imidization method to obtain a precursor solution with a predetermined imidization degree;
and step 3: adding an end group protective agent into the precursor solution to obtain an end-capped precursor solution, forming a film, and obtaining the polyimide film by a thermal imidization method or a chemical imidization method.
7. The method according to claim 6, wherein the organic solvent in step 1 is one or more selected from the group consisting of N-methylpyrrolidone, N-ethylpyrrolidone, N '-dimethylformamide, N' -dimethylacetamide, N '-diethylformamide, N' -diethylacetamide, dimethylpropionamide, diethylpropionamide, dimethylsulfoxide, cyclopentanone, and butyrolactone.
8. The method according to claim 6, wherein the imidization method in step 2 includes a thermal imidization method and a chemical imidization method.
9. The method according to claim 8, wherein the thermal imidization in step 2 is carried out at a heating temperature of 40 to 95 ℃ for 0.5 to 24 hours.
10. The polyimide film according to claims 1 to 5 is used as a substrate material in the fields of electronics, microelectronics, optical display or optical communication.
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