Polyimide film and preparation method thereof

Abstract

The invention provides a polyimide film and a preparation method thereof, and belongs to the technical field of polyimide materials. The polyimide film is prepared from polyamic acid slurry through imidization, and the preparation raw materials of the polyamic acid slurry comprise aromatic dianhydride, aromatic diamine, an end-capping reagent and a solvent; the end-capping reagent comprises a dicarbonate ester compound. The polyamide acid slurry provided by the invention has the characteristics of high solid content, low viscosity and good stability, can be stored for a long time at room temperature and can be cured at low temperature, and a polyimide film prepared from the polyamide acid slurry has excellent mechanical properties and thermodynamic properties.

Description

[0001] This application is a divisional application. The application number of the parent application is 202410768166.1, the application date is June 13, 2024, and the name of the invention is "A polyamic acid slurry, its preparation method and application". Technical Field

[0002] The invention relates to the technical field of polyimide materials, and in particular to a polyimide film and a preparation method thereof. Background Art

[0003] Polyimide refers to a precursor polyamic acid slurry prepared by condensing aromatic diamines and aromatic dianhydrides in polar organic solvents, which is then further imidized to obtain polyimide. Commonly used polar organic solvents are N-methylpyrrolidone (NMP), N-dimethylacetamide (DMAc) or N,N-dimethylformamide (DMF), etc. In order to facilitate subsequent processing, the viscosity of the polyamic acid slurry must be controlled. According to the working conditions of the casting machine during film formation, it is generally 80000-200000cp (25°C), and the corresponding solid content can only be maintained below 25%. Due to the presence of a large amount of organic solvents, higher processing temperatures and longer times are required during the curing and imidization process, resulting in slow casting speeds and low production capacity, which is not conducive to economic efficiency; if the solid content is increased, the viscosity of the polyamic acid slurry will be too large, which is not conducive to casting and affects processing.

[0004] CN111808285A discloses a method for preparing a polyamic acid composition with low viscosity and controllable solid content, the method comprising the following steps: (a) adding a solvent and an active agent into a reactor, and adding diamine or dianhydride to dissolve; (b) adding diamine and / or dianhydride in batches to the solution obtained in step (a) to react and obtain a polyamic acid composition. The polyamic acid composition prepared by this technical scheme has a viscosity of less than 10wcp at 30°C and a solid content of 10% to 30%. CN117050304A discloses a low-viscosity, high-solid content polyamic acid slurry and its preparation method and application, the preparation method is carried out according to the following steps: S1: under an inert atmosphere, reacting dianhydride and monohydric alcohol in a non-protonic polar solvent for a certain time to obtain a mixed solution of dianhydride and monoanhydride monoester monocarboxylic acid compound; S2: under an inert atmosphere, cooling the mixed solution to below -10°C, adding diamine, then slowly heating up, reacting for a certain time, and obtaining a polyamic acid slurry. The low-viscosity polyamic acid slurry obtained by this technical solution has controllable viscosity and good film-forming stability. However, the above technical solutions all adopt the method of adding water or alcohol to the reaction system for hydrolysis or esterification of anhydride. It is necessary to react the dianhydride with water or alcohol first, and then add diamine. This method has extremely stringent requirements on the water content of the solvent, otherwise the batch stability is difficult to guarantee. CN104292459A discloses a preparation method of a high-solid content low-viscosity polyimide material, the preparation method comprising the following steps: under the protection of an inert gas, dissolving an aromatic diamine in an organic solvent, mechanically stirring, and after the aromatic diamine is completely dissolved, adding an aromatic dianhydride, a tackifier and a capping agent, and reacting at room temperature to obtain a polyamic acid solution, i.e., a polyimide prepolymer. The solid content of the polyamic acid solution provided by this technical solution can be controlled between 30% and 35%, but the prepared polyimide film has low performance. CN103788651A discloses a polyamic acid solution with low apparent viscosity and a preparation method thereof. The process steps and conditions of the preparation method are as follows: (1) a polyamic acid solution is obtained by polymerizing a diamine monomer and a dianhydride monomer, and then 5 to 40% by weight of trimethylchlorosilane is added, and the mixture is stirred at room temperature for 1 to 5 hours to obtain a polyamic acid solution with an apparent viscosity of 0.2 to 1.5 wcp; or (2) all the diamine monomers and 60 to 90 wt% of the dianhydride monomers are first polymerized to obtain a solution containing polyamic acid, and then trimethylchlorosilane and the remaining dianhydride monomers are added, and the mixture is stirred at room temperature for 1 to 5 hours, wherein the molar ratio of the diamine monomer to the dianhydride monomer is 1:1, and the amount of trimethylchlorosilane added is 5 to 25% of the total weight of the polyamic acid. This technical solution greatly reduces the apparent viscosity of the polyamic acid solution by adding trimethylchlorosilane, but the imidization process will not only reduce the thermodynamic and mechanical properties of the polyimide film, but also produce HCl during thermal decomposition during heating, which will corrode the instrument.

[0005] Although there are some technical solutions in the prior art that can achieve the goal of obtaining polyamic acid slurry with a high solid content, there are still problems such as low mechanical properties or thermodynamic properties after film formation, extremely stringent requirements on the water content of the reaction solvent, and difficulty in stable batch processing and production.

[0006] Therefore, it is necessary to develop a polyamic acid slurry with high solid content and excellent mechanical properties and thermal stability after curing into a film. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a polyamic acid slurry and a preparation method and application thereof. The polyamic acid slurry has high solid content, low viscosity, good stability, can be stored for a long time at room temperature, and can be cured at low temperature. The polyimide film prepared from the polyamic acid slurry has excellent mechanical properties and thermodynamic properties.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a polyamic acid slurry, wherein raw materials for preparing the polyamic acid slurry include aromatic dianhydride, aromatic diamine, a capping agent and a solvent; and the capping agent includes a dicarbonate compound.

[0010] The present invention adopts dicarbonate compounds as end-capping agents for the reaction of aromatic dianhydrides and aromatic diamines, and the polyamic acid slurry obtained by the condensation reaction has the characteristics of high solid content and low viscosity, which helps to increase the casting speed during production, improve the processing rate, increase production capacity, further reduce energy consumption and thus save energy. Compared with traditional polyamic acid slurries, the polyamic acid slurry requires less solvent to evaporate during curing, so energy consumption can be reduced. The polyimide film prepared from the polyamic acid slurry has excellent mechanical and thermodynamic properties, and will not reduce the excellent mechanical and thermodynamic properties of the polyimide itself. At the same time, the stability of the polyamic acid slurry is significantly improved, and the polyamic acid slurry has excellent long-term room temperature storage stability, and the casting stability of the polyimide film is good during processing. The polyamic acid slurry can be cured at low temperature (≤450°C), which is beneficial to environmental protection.

[0011] Preferably, the aromatic dianhydride comprises pyromellitic dianhydride (PMDA), hexafluorodianhydride (6FDA),

[0012] Any one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-phthalic anhydride ether (ODPA) or 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) or a combination of at least two thereof.

[0013] Preferably, the aromatic diamine includes any one of 4,4'-diaminodiphenyl ether (ODA), 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine (TFDB), 4,4'-diamino-2,2'-dimethylbiphenyl (MTD) or p-phenylenediamine (PDA) or a combination of at least two thereof.

[0014] Preferably, the dicarbonate compound has a structure as shown in Formula 1 below.

[0015]

[0016] In Formula 1, R1 is selected from any one of methyl, ethyl, propyl, isopropyl, butyl, tert-butyl or isobutyl, and R2 is selected from any one of methyl, ethyl, propyl, isopropyl, butyl, tert-butyl or isobutyl.

[0017] Preferably, the dicarbonate compound includes any one of di-tert-butyl dicarbonate (Boc-anhydride), diisopropyl dicarbonate or diethyl pyrocarbonate, or a combination of at least two thereof.

[0018] Preferably, the solvent comprises a first type of organic solvent and / or a second type of organic solvent.

[0019] Preferably, the first type of organic solvent includes any one of N,N-dimethylformamide, dimethyl sulfoxide (DMSO), N-dimethylacetamide, N-methylpyrrolidone or γ-butyrolactone, or a combination of at least two thereof.

[0020] Preferably, the second type of organic solvent includes aliphatic ester solvents.

[0021] Preferably, the molar ratio of the aromatic dianhydride to the aromatic diamine is 0.95-1.05:1, for example, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1.01:1, 1.02:1, 1.03:1 or 1.04:1.

[0022] Preferably, the molar ratio of the end-capping agent to the aromatic diamine is 0.2 to 2:10, for example, 0.3:10, 0.5:10, 0.7:10, 0.9:10, 1.1:10, 1.3:10, 1.5:10, 1.7:10 or 1.9:10, etc.

[0023] In the present invention, the molar ratio of the end-capping agent to the aromatic diamine is preferably 0.2 to 2:10. When the molar ratio of the end-capping agent to the aromatic diamine is too low, the viscosity of the polyamic acid slurry obtained by polymerization is too high, and it is difficult to achieve high solid content and low viscosity; when the molar ratio of the end-capping agent to the aromatic diamine is too high, the prepared polyamic acid slurry can achieve a higher solid content, but it is difficult to complete the film curing or the mechanical properties of the obtained polyimide film are sharply reduced.

[0024] Preferably, the solid content of the polyamic acid slurry is 18% to 35% (eg, 20%, 22%, 24%, 26%, 28%, 30%, 32% or 34%, etc.), and more preferably, 25% to 33%.

[0025] Preferably, the initial viscosity of the polyamic acid slurry at 25° C. is 50,000 to 200,000 cp, for example, 70,000 cp, 90,000 cp, 110,000 cp, 130,000 cp, 150,000 cp, 170,000 cp or 190,000 cp.

[0026] In the present invention, the solid content can be adjusted by adjusting the content of the end-capping agent to obtain the desired viscosity.

[0027] In a second aspect, the present invention provides a method for preparing the polyamic acid slurry as described in the first aspect, the preparation method comprising the following steps:

[0028] (1) mixing an aromatic diamine, a blocking agent and a solvent, and reacting them to obtain an intermediate product;

[0029] (2) The intermediate product obtained in step (1) and aromatic dianhydride are mixed and reacted to obtain the polyamic acid slurry.

[0030] Preferably, the reaction temperature in step (1) is 40-100°C (e.g., 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, etc.), more preferably 60-80°C.

[0031] Preferably, the reaction time of step (1) is 1 to 5 h (e.g., 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h or 4.5 h, etc.), more preferably 2 to 4 h.

[0032] Preferably, the mixing in step (2) comprises adding aromatic dianhydride to the intermediate product in batches.

[0033] Preferably, the number of times of adding the aromatic dianhydride in batches is 1 to 8 times, for example, 2 times, 3 times, 4 times, 5 times, 6 times or 7 times.

[0034] Preferably, the reaction temperature in step (2) is 0-40°C, for example, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C or 35°C.

[0035] Preferably, the reaction time in step (2) is 3 to 15 h, for example, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h or 14 h.

[0036] In a third aspect, the present invention provides a polyimide film, wherein the polyimide film is prepared by imidizing the polyamic acid slurry as described in the first aspect.

[0037] Preferably, the polyimide film is prepared by the following method: the polyamic acid slurry as described in the first aspect is cast onto a steel belt and baked to obtain a film, and imidized to obtain the polyimide film.

[0038] Preferably, the baking temperature is 100°C to 250°C.

[0039] In the present invention, the baking process is used to remove a large amount of solvent to form the polyamic acid slurry into a film.

[0040] Preferably, the speed of the cast steel belt is 4.5-8 m / min, for example, 5 m / min, 5.5 m / min, 6 m / min, 6.5 m / min, 7 m / min or 7.5 m / min.

[0041] Preferably, the imidization is carried out in an imidization furnace, and the imidization temperature is ≤450°C, for example, 170°C, 200°C, 230°C, 260°C, 290°C, 320°C, 350°C, 380°C, 410°C or 440°C.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention adopts dicarbonate as an end-capping agent for the reaction of aromatic dianhydride and aromatic diamine, and the polyamic acid slurry obtained by the condensation reaction has the characteristics of high solid content and low viscosity, which is helpful to improve the casting speed during production, improve the processing rate, improve the production capacity, further reduce energy consumption and thus save energy. Compared with the traditional polyamic acid slurry, the polyamic acid slurry needs less solvent to evaporate during curing, so energy consumption can be reduced. The polyimide film prepared by the polyamic acid slurry has excellent mechanical properties and thermodynamic properties, and will not reduce the excellent mechanical properties and thermodynamic properties of the polyimide itself. At the same time, the stability of the polyamic acid slurry is significantly improved, and the polyamic acid slurry has excellent long-term room temperature storage stability, and the casting stability is good during the processing of the polyimide film. The polyamic acid slurry can be cured at low temperature, which is beneficial to environmental protection. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0045] Example 1

[0046] The present embodiment provides a polyamic acid slurry, a preparation method thereof, and a polyimide film. The raw materials for preparing the polyamic acid slurry include aromatic dianhydride (PMDA), aromatic diamine (ODA), a capping agent (Boc-anhydride) and a solvent (DMAc). The molar ratio of the aromatic dianhydride to the aromatic diamine is 1:1; the molar ratio of the capping agent to the aromatic diamine is 0.2:10.

[0047] The preparation method of the polyamic acid slurry comprises the following steps:

[0048] (1) Add 272 kg of DMAc to a 500 L reactor, then add 61.25 kg of ODA, add 1.34 kg of Boc-anhydride while stirring, and then heat to 70 ° C for 2 h to obtain an intermediate product;

[0049] (2) After the temperature of the reaction system obtained in step (1) was lowered to 25° C., 66.75 kg of PMDA was added to the reactor in five batches, and the system temperature was maintained at 25° C. The reaction was carried out for 8 hours to obtain the polyamic acid slurry.

[0050] The polyimide film is prepared by the following method: the polyamic acid slurry is cast onto a steel belt, the flow rate of the die is adjusted by controlling the rotation speed of a metering pump to control the thickness of the polyamic acid slurry, the speed of the steel belt is 5.8 m / min, a large amount of solvent is removed by baking, the highest baking temperature is 225° C., and a film is obtained. Subsequently, the film is peeled off from the steel belt and then passes through a roller and enters an imidization furnace for imidization. During the imidization process, five temperature intervals are set in sequence along the direction of movement of the film, namely 170° C., 250° C., 350° C., 420° C., and 280° C., to obtain a polyimide film.

[0051] Example 2

[0052] The present embodiment provides a polyamic acid slurry, a preparation method thereof, and a polyimide film. The raw materials for preparing the polyamic acid slurry include aromatic dianhydride (PMDA), aromatic diamine (ODA), a capping agent (Boc-anhydride) and a solvent (DMAc). The molar ratio of the aromatic dianhydride to the aromatic diamine is 0.95:1; the molar ratio of the capping agent to the aromatic diamine is 0.6:10.

[0053] The preparation method of the polyamic acid slurry comprises the following steps:

[0054] (1) Add 260 kg of DMAc to a 500 L reactor, then add 68.7 kg of ODA, add 4.49 kg of Boc-anhydride under stirring, and then heat to 70 ° C for 2 h to obtain an intermediate product;

[0055] (2) After the temperature of the reaction system obtained in step (1) was lowered to 25° C., 71.3 kg of PMDA was added to the reactor in five batches, and the system temperature was maintained at 25° C. The reaction was carried out for 8 hours to obtain the polyamic acid slurry.

[0056] The polyimide film is prepared by the following method: a polyamic acid slurry is cast onto a steel belt, and the thickness of the polyamic acid slurry is controlled by adjusting the flow rate of the die head by controlling the rotation speed of a metering pump, the speed of the steel belt is 6.4 m / min, a large amount of solvent is removed by baking, and the highest baking temperature is 230° C. to obtain a film, and then the film is peeled off from the steel belt and then passes through a roller and enters an imidization furnace for imidization, and the imidization process sets five temperature intervals in the direction of film movement, namely 180° C., 260° C., 350° C., 420° C., and 280° C., to obtain a polyimide film.

[0057] Example 3

[0058] The present embodiment provides a polyamic acid slurry, a preparation method thereof, and a polyimide film. The raw materials for preparing the polyamic acid slurry include aromatic dianhydride (PMDA), aromatic diamine (ODA), a capping agent (Boc-anhydride) and a solvent (DMAc). The molar ratio of the aromatic dianhydride to the aromatic diamine is 1.05:1; the molar ratio of the capping agent to the aromatic diamine is 0.2:10.

[0059] The preparation method of the polyamic acid slurry comprises the following steps:

[0060] (1) Add 272 kg of DMAc to a 500 L reactor, then add 61.25 kg of ODA, add 1.34 kg of Boc-anhydride while stirring, and then heat to 85 ° C for 1.5 hours to obtain an intermediate product;

[0061] (2) After the temperature of the reaction system obtained in step (1) was lowered to 20° C., 70 kg of PMDA was added to the reactor in five batches, and the system temperature was maintained at 20° C. The reaction was carried out for 5 hours to obtain the polyamic acid slurry.

[0062] The polyimide film is prepared by the following method: a polyamic acid slurry is cast onto a steel belt, and the thickness of the polyamic acid slurry is controlled by adjusting the flow rate of the die head by controlling the rotation speed of a metering pump, the speed of the steel belt is 6.8 m / min, a large amount of solvent is removed by baking, and the highest baking temperature is 230° C. to obtain a film, and then the film is peeled off from the steel belt and then passes through a roller and enters an imidization furnace for imidization, and five temperature intervals are set in sequence along the direction of movement of the film at 170° C., 250° C., 350° C., 420° C., and 280° C. to obtain a polyimide film.

[0063] Example 4

[0064] This embodiment provides a polyamic acid slurry and a preparation method thereof and a polyimide film. The only difference between this embodiment and embodiment 1 is that Boc-anhydride is replaced with the same molar amount of diethyl pyrocarbonate (1.17 kg). The rest is the same as embodiment 1.

[0065] Example 5

[0066] This embodiment provides a polyamic acid slurry, a preparation method thereof, and a polyimide film. The only difference between this embodiment and embodiment 1 is that PMDA is replaced with BPDA (96.17 kg) of the same molar amount; in the preparation of the polyimide film, the speed of the steel belt is adjusted to 6.6 m / min, and the maximum baking temperature is adjusted to 235°C; the rest is the same as embodiment 1.

[0067] Example 6

[0068] This embodiment provides a polyamic acid slurry, a preparation method thereof, and a polyimide film. The only difference between this embodiment and embodiment 1 is that 66.75 kg of ODA is replaced by 11.57 kg of PDA and 43.41 kg of ODA; in the preparation of the polyimide film, the speed of the steel belt is adjusted to 6 m / min; the rest is the same as embodiment 1.

[0069] Example 7

[0070] This embodiment provides a polyamic acid slurry and a preparation method thereof and a polyimide film. The only difference between this embodiment and embodiment 1 is that the molar ratio of the end capping agent to the aromatic diamine is adjusted to 1.0:10, the mass of Boc-anhydride is adjusted to 7 kg, the speed of the steel belt is adjusted to 6.2 m / min, the maximum baking temperature is 235°C, and the rest is the same as embodiment 1.

[0071] Example 8

[0072] This embodiment provides a polyamic acid slurry and a preparation method thereof and a polyimide film. The only difference between this embodiment and embodiment 1 is that the molar ratio of the end capping agent to the aromatic diamine is adjusted to 1.9:10, the mass of Boc-anhydride is adjusted to 13 kg, the speed of the steel strip is adjusted to 6.6 m / min, the maximum baking temperature is 240°C, and the rest is the same as embodiment 1.

[0073] Example 9

[0074] This embodiment provides a polyamic acid slurry and a preparation method thereof and a polyimide film. The only difference between this embodiment and embodiment 1 is that the molar ratio of the end capping agent to the aromatic diamine is adjusted to 2.2:10, the mass of Boc-anhydride is adjusted to 15 kg, the speed of the steel belt is adjusted to 7.2 m / min, the maximum baking temperature is adjusted to 245°C, and the rest is the same as embodiment 1.

[0075] Comparative Example 1

[0076] This comparative example provides a polyamic acid slurry and a preparation method thereof and a polyimide film, which differs from Example 1 only in that the raw materials for preparing the polyamic acid slurry do not include a capping agent (Boc-anhydride); the preparation method of the polyamic acid slurry is adjusted as follows: 272 kg DMAc is added to a 500 L reactor, followed by 61.25 kg ODA, 66.75 kg PMDA is added to the reactor in 5 batches at 25°C, the system temperature is maintained at 25°C, and the reaction is performed for 3 hours to obtain the polyamic acid slurry. The rest is the same as Example 1.

[0077] Comparative Example 2

[0078] This comparative example provides a polyamic acid slurry and a preparation method thereof and a polyimide film, which differs from Example 1 only in that the raw materials for preparing the polyamic acid slurry do not include a capping agent (Boc-anhydride); the preparation method of the polyamic acid slurry is adjusted as follows: 266.5 kg DMAc is added to a 500L reactor, followed by 30.625 kg ODA, 33.375 kg PMDA is added to the reactor in 5 batches at 25°C, the system temperature is maintained at 25°C, and the reaction is performed for 8 hours to obtain the polyamic acid slurry. In the preparation of the polyimide film, the speed of the steel belt is adjusted to 3.5 m / min, and the maximum baking temperature is adjusted to 220°C. Others are the same as Example 1.

[0079] Comparative Example 3

[0080] This comparative example provides a polyamic acid slurry and a preparation method thereof, which is different from Example 1 only in that Boc-anhydride is replaced with maleic anhydride in the same molar amount. Other aspects are the same as Example 1.

[0081] The following performance tests were performed on the polyamic acid slurries and polyimide films provided in the examples and comparative examples.

[0082] (1) Solid content: Take an aluminum foil plate with a diameter of 60 mm and weigh it as m0; take 1±0.1 g of the polyamic acid slurry to be tested and place it in the aluminum plate, and weigh the total weight of the aluminum plate and the polyamic acid slurry as m1; put the aluminum plate containing the polyamic acid slurry in a forced air oven at 180±5°C, take it out after 1 hour, and weigh the mass as m2; Solid content = (m2-m0) / (m1-m0)×100%.

[0083] (2) Viscosity: The initial viscosity of the polyamic acid slurry was tested at 25°C using an American Boller cone and plate viscometer. The slurry was stored at 25°C and then the viscosity was tested after 3 days, 10 days, and 20 days.

[0084] (3) Mechanical properties of polyimide film: The tensile strength, elongation at break and modulus of polyimide film were tested according to GB / T13542.6-2006.

[0085] The test results are shown in Table 1 and Table 2.

[0086] Table 1

[0087]

[0088] In Table 1, “-” means that the result was not measured.

[0089] Table 2

[0090]

[0091] In Table 2, “-” means that the result was not measured.

[0092] It can be seen from the test results in Table 1 and Table 2 that the polyamic acid slurry provided by the present invention has the characteristics of high solid content and low viscosity. The addition of dicarbonate compounds can greatly improve the room temperature storage stability of the polyamic acid slurry; the polyimide film prepared from the polyamic acid slurry provided in Examples 1-9 has a tensile strength of 110 to 158 MPa, an elongation at break of 45 to 115%, and a modulus of 2.1 to 3.3 GPa.

[0093] The role of baking in the preparation process of the polyimide film of Examples 1 and 7-9 is to remove a large amount of solvent to form the polyamic acid slurry into a film. When the baking temperature is in the range of 100°C to 250°C, it will not affect the performance of the obtained polyimide film. As the baking temperature increases, the solvent removal speed increases. The baking temperature can be adjusted according to the difference in the speed of the steel belt to achieve solvent removal.

[0094] From the comparison of Examples 1, 7-9, it can be seen that when the molar ratio of the end-capping agent to the aromatic diamine is within the range of 0.2-2:10, increasing the amount of the end-capping agent can effectively reduce the viscosity of the polyamic acid slurry, and the speed can be increased during the film casting, without significant effect on the performance of the obtained polyimide film. If the molar ratio of the end-capping agent to the aromatic diamine is too large (Example 9), the viscosity of the polyamic acid slurry can be further improved, and the speed can be further increased, but the mechanical properties of the polyimide film obtained after the film casting are significantly reduced. It can be seen that when the molar ratio of the end-capping agent to the aromatic diamine is within the range of 0.2-2:10, the performance of the obtained polyamic acid slurry is better.

[0095] Compared with Example 1, if no end-capping agent is added (Comparative Example 1), the viscosity of the prepared polyamic acid slurry is too high, there is no fluidity, and it cannot be coated; if no end-capping agent is added, only by lowering the solid content can a polyamic acid slurry with relatively low viscosity be prepared (Comparative Example 2).

[0096] Compared with Example 1, if Boc-anhydride is replaced with the same molar amount of maleic anhydride (Comparative Example 3), a polyamic acid with the same solid content and similar viscosity can be obtained and also has good stability, but a complete polyimide film with certain mechanical properties cannot be prepared through the imidization process, and the obtained polyimide film is easily broken when stretched. The reason is that the polyamic acid obtained after maleic anhydride end-capping cannot remove the end-capping agent during heating imidization, and further polymerization cannot be achieved, so the low molecular weight polyimide is the main chain; while when Boc-anhydride is used as the end-capping, not only imidization is achieved during heating imidization, but Boc-anhydride will be removed after heating, so that the terminal amino group is further exposed and the chain extension can be further achieved after heating. Therefore, the polyimide slurry with Boc-anhydride as the end-capping agent has a larger molecular weight and better mechanical properties during the imidization process.

[0097] It can be seen that in the present invention, by adding dicarbonate compounds as end-capping agents, the solid content of the polyamic acid slurry can be effectively increased while maintaining a low level of viscosity; the addition of dicarbonate compounds causes the viscosity of the polyamic acid slurry to first decrease and then increase, while when no end-capping agent is added, the viscosity of the polyamic acid slurry gradually increases, and the stability is extremely poor. At the same time, the use of the polyamic acid slurry described in the present invention can effectively improve production efficiency, and the polyimide film obtained by imidization can also maintain excellent mechanical properties.

[0098] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate a polyamic acid slurry and its preparation method and application, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A polyimide film, characterized in that: The polyimide film is prepared by imidization of polyamic acid slurry; The raw materials for preparing the polyamic acid slurry include aromatic dianhydride, aromatic diamine, end-capping agent and solvent; the end-capping agent includes dicarbonate compounds; The aromatic dianhydride includes any one of pyromellitic dianhydride, hexafluoro dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-phthalic anhydride ether or 3,3',4,4'-biphenyltetracarboxylic dianhydride or a combination of at least two thereof; The aromatic diamine includes any one or a combination of at least two of 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine, 4,4'-diamino-2,2'-dimethylbiphenyl or p-phenylenediamine; The molar ratio of the end-capping agent to the aromatic diamine is 0.2 to 2:

10.

2. The polyimide film according to claim 1, characterized in that: The dicarbonate compound has a structure as shown in Formula 1 below: In Formula 1, R1 is selected from any one of methyl, ethyl, propyl, isopropyl, butyl, tert-butyl or isobutyl, and R2 is selected from any one of methyl, ethyl, propyl, isopropyl, butyl, tert-butyl or isobutyl.

3. The polyimide film according to claim 2, characterized in that: The dicarbonate compound includes any one of di-tert-butyl dicarbonate, diisopropyl dicarbonate or diethyl pyrocarbonate, or a combination of at least two thereof.

4. The polyimide film according to any one of claims 1 to 3, characterized in that: The solvent includes a first type of organic solvent and / or a second type of organic solvent; The first type of organic solvent includes any one or a combination of at least two of N,N-dimethylformamide, dimethyl sulfoxide, N-dimethylacetamide, N-methylpyrrolidone or γ-butyrolactone; The second type of organic solvents includes aliphatic ester solvents.

5. The polyimide film according to claim 4, characterized in that: The solid content of the polyamic acid slurry is 18% to 35%; The initial viscosity of the polyamic acid slurry at 25° C. is 50,000 to 200,000 cp.

6. The polyimide film according to claim 5, characterized in that: The preparation method of the polyamic acid slurry comprises the following steps: (1) mixing an aromatic diamine, a blocking agent and a solvent, and reacting them to obtain an intermediate product; (2) The intermediate product obtained in step (1) and aromatic dianhydride are mixed and reacted to obtain the polyamic acid slurry.

7. The polyimide film according to claim 6, characterized in that: The reaction temperature of step (1) is 40-100° C. and the reaction time is 1-5 h. The mixing in step (2) comprises adding aromatic dianhydride to the intermediate product in batches; The number of times of adding the aromatic dianhydride in batches is 1 to 8 times; The reaction temperature in step (2) is 0-40° C., and the reaction time is 3-15 h.

8. The method for preparing a polyimide film according to any one of claims 1 to 7, characterized in that: The following steps are involved: Casting the polyamic acid slurry onto a steel belt, baking it to obtain a film, and imidizing it to obtain the polyimide film; The baking temperature is 100°C to 250°C.

9. The preparation method according to claim 8, characterized in that: The speed of the cast steel belt is 4.5-8 m / min; the temperature of the imidization is ≤450°C.

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