A method for preparing polyamic acid solution and the obtained polyamic acid solution

Abstract

The invention discloses a method for preparing a polyamic acid solution and the obtained high-purity polyamic acid solution. The preparation method comprises mixing a dianhydride monomer, a solvent and an optional additive under high-speed shearing to form a slurry, dissolving a diamine monomer in the solvent to form a solution, and then adding the slurry to the diamine solution for polymerization reaction to obtain a polyamic acid solution. The method of the invention avoids directly adding a solid dianhydride monomer to a reaction system, greatly improves the mass transfer efficiency, and better solves the above-mentioned problems of microgel and agglomerates, and can be used to prepare a high-purity polyamic acid solution.

Description

Technical Field

[0001] The present invention relates to the field of polyimide, and in particular to a method for preparing a polyamic acid solution and a high-purity polyamic acid solution obtained therefrom. The method can effectively solve the problem of impurities such as microgels and lumps existing in the polyamic acid solution. Background Art

[0002] Polyimide (PI) refers to a class of aromatic heterocyclic polymers containing imide rings on the main chain. It is one of the polymer materials with the highest heat resistance level to date. In addition to outstanding thermal stability (starting decomposition temperature>500℃), polyimide also has excellent low temperature resistance (no brittle fracture under liquid helium at -269℃), radiation resistance, and good mechanical properties, chemical corrosion resistance and dielectric properties. It is usually in the form of film, fiber, foam, engineering plastic or composite material, and is widely used in aerospace, microelectronics, solar cells, high temperature filtration, machinery, separation membranes and OLED.

[0003] The structure of a large number of imide rings and aromatic rings on the main chain of polyimide determines its insoluble and infusible characteristics, which makes it difficult to process and shape, thus seriously affecting its application value. To solve this problem, the precursor of polyimide, polyamic acid solution, is usually synthesized first, and after the polyamic acid solution is processed and shaped, the polyimide material is obtained by thermal imidization and other methods. Therefore, high-quality polyamic acid solution is a prerequisite for the preparation of high-quality polyimide materials.

[0004] Polyamic acid is usually prepared by low-temperature polycondensation of dianhydride monomers and diamine monomers in a non-protonic polar solvent. The traditional method is to dissolve the diamine monomer in a non-protonic polar solvent, and then add the powdered dianhydride monomer to the above solution to prepare a polyamic acid solution. This method is widely used but has the following shortcomings:

[0005] 1. Due to the high viscosity of the system in the later stage of polymerization, it is very difficult for the powdered dianhydride monomer to transfer mass in the solution, and the reaction is difficult to proceed fully. This will cause more gel particles and lumps in the solution, resulting in more impurities in the solution, which seriously affects the subsequent processing and molding and the performance of the corresponding polyimide material;

[0006] 2. The solubility of dianhydride monomer in aprotic polar solvents is very low, and it is difficult to evenly disperse the dianhydride monomer in the solvent using conventional methods;

[0007] 3. When the two monomers of diamine and dianhydride are close to equivalent, a slight change in their molar ratio will cause a huge change in the viscosity of the solution. That is to say, when adding dianhydride monomer to the solution, a small metering error will lead to a large change in viscosity. This poses a great challenge to the control of the viscosity of polyamic acid solution, especially in industrial production. Summary of the invention

[0008] Based on the above background technology content, the technical problem to be solved by the present invention is the above-mentioned deficiencies in the method for preparing a polyamic acid solution in the prior art, and a method for preparing a polyamic acid solution is provided, which can conveniently and effectively solve the problem of excessive impurities such as microgels and lumps in the solution, and can prepare a high-purity polyamic acid solution.

[0009] In order to solve the above technical problems, one of the objects of the present invention is to provide a method for preparing a polyamic acid solution, comprising mixing a dianhydride monomer, a solvent and optional additives under high-speed shearing to form a slurry, dissolving a diamine monomer in the solvent to form a diamine solution, and then adding the slurry to the diamine solution to carry out a polymerization reaction to obtain a polyamic acid solution.

[0010] In the above technical solution, the diamine monomer is one or a mixture of two or more diamines represented by formula (I):

[0011] H2N-Ar1NH2, (I);

[0012] In the formula, Ar1 is a divalent aromatic residue containing at least one carbon six-membered ring,

[0013] Preferably, Ar1 has the structure shown below:

[0014]

[0015] In the formula, R2 is any one of H-, CH3-, Cl-, Br-, F-, CH3O-, etc.

[0016] In the above technical solution, the dianhydride monomer is one or a mixture of two or more dianhydrides represented by formula (II):

[0017]

[0018] In the formula, Ar2 is a tetravalent aromatic residue containing at least one carbon six-membered ring,

[0019] Preferably, Ar2 has the structure shown below:

[0020]

[0021] In the formula, R1 is any one of H-, CH3-, Cl-, Br-, F-, CH3O-, etc.

[0022] In the above technical solution, the solvent is a non-protonic polar solvent, preferably one or a mixture of two or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0023] In the above technical solution, the additive is butyrolactone and / or isophorone.

[0024] In the above technical solution, the additive preferably accounts for 1-5% of the total mass of the solvent, specifically 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0025] In the above technical solution, there is no special restriction on the concentration of the dianhydride monomer in the slurry, and it only needs to meet the solid content restriction in the end.

[0026] In the above technical scheme, the shear speed of the high-speed shearing is 1000-30000rpm, preferably 5000-20000rpm, specifically 1000rpm, 5000rpm, 6000rpm, 7000rpm, 8000rpm, 9000rpm, 10000rpm, 11000rpm, 12000rpm, 13000rpm, 14000rpm, 15000rpm, 16000rpm, 17000rpm, 18000rpm, 19000rpm, 20000rpm, 25000rpm, 30000rpm and the like.

[0027] In the above technical solution, the molar ratio of dianhydride to diamine units in the finally obtained polyamic acid is 0.95 to 1.05, preferably 0.98 to 1.02.

[0028] In the above technical solution, the polymerization reaction temperature is -10 to 60°C, and the preferred reaction temperature is 0 to 40°C.

[0029] In the above technical solution, the solid content of the polyamic acid solution is 5 to 30 wt %, preferably 10 to 20 wt %.

[0030] In the above technical solution, the preparation method preferably comprises the following steps:

[0031] (1) dissolving a diamine monomer in a non-protonic polar solvent to obtain a diamine solution;

[0032] (2) forming a slurry with a dianhydride monomer and a non-protonic polar solvent optionally containing an additive under the action of high-speed shearing;

[0033] (3) adding the slurry prepared in step (2) to the diamine solution prepared in step (1) to carry out a polymerization reaction to obtain the polyamic acid solution.

[0034] The conventional method for preparing polyamic acid solution is to add powdered dianhydride monomer to diamine solution for reaction. Due to the rapid rise of solution viscosity in the above-mentioned reaction later stage, mass transfer efficiency is greatly reduced, and solid powdered dianhydride monomer will be reunited when added to solution, and react with diamine to form high polymer on the surface, thereby hindering the internal dianhydride monomer to react, so that microgel and agglomerate will be formed, which greatly limits the performance and application of the product. The present invention forms a slurry mixture (hereinafter referred to as slurry) by first dianhydride monomer and solvent under high-speed shear, and then the above-mentioned slurry is added to diamine solution for reaction, and the method greatly improves mass transfer efficiency due to avoiding directly adding solid dianhydride monomer directly to reaction system, and preferably solves the problem of above-mentioned microgel and agglomerate.

[0035] The second object of the present invention is to provide a polyamic acid solution obtained by the preparation method.

[0036] The number of particles larger than 1 μm in the polyamic acid solution is preferably less than 100 / ml, more preferably less than 50 / ml; the number of particles larger than 2 μm in the polyimide film prepared from the polyamic acid solution detected by an optical automatic detection system within a range of 20×20 mm is selected to be less than 500, more preferably less than 200.

[0037] The preparation method of the present invention has obvious advantages over the traditional preparation method of polyamic acid solution. Since the solubility of dianhydride monomer in the corresponding solvent is very low, the traditional preparation method of polyamic acid solution is to dissolve the diamine monomer in the solvent, and then add the dianhydride monomer to the above solution in the form of solid powder. The disadvantage of this method is that when the viscosity of the system is large, it is very difficult for the powdered dianhydride monomer to transfer mass in the solution, and the reaction is difficult to fully proceed, which will cause the presence of more impurities such as microgel particles and lumps in the polyamic acid solution. In addition, when the dianhydride monomer is mixed with the solvent to form a slurry, the shear rate is not enough or the dispersant such as butyrolactone or isophorone is not added, the dispersion effect of the dianhydride and the solvent is not good, and it is difficult to achieve the desired effect. When the diamine monomer and the dianhydride monomer are close to equivalent, a slight change in their molar ratio will cause a huge change in the viscosity of the solution, that is, when the dianhydride monomer is added to the solution, a slight metering error will cause a large viscosity change, which is very challenging to the control of the viscosity of the polyamic acid solution, especially in industrial production.

[0038] The method provided by the present invention solves these problems well. On the one hand, the mass transfer difficulty of the slurry formed by the dianhydride monomer and the aprotic polar solvent under the joint action of high-speed shear and additives is greatly reduced, and it is not easy to form lumps. On the other hand, for the dianhydride with the same effective mole number, the mass of the slurry is significantly greater than the mass of the dianhydride solid powder, and the solution viscosity change caused by the same degree of measurement error is much smaller than that of the latter. The method provided by the present invention can effectively reduce impurities such as microgels and lumps in the polyamic acid solution, which is of great significance for subsequent processing and preparation of various polyimide (PI) materials.

[0039] Compared with the prior art, the present invention has the following purposes and effects:

[0040] 1. The present invention adopts a method of first mixing the dianhydride monomer and a non-protonic polar solvent optionally with additives such as butyrolactone or isophorone under high-speed shearing to form a slurry, and then adding the above slurry to a diamine solution to prepare a polyamic acid solution. This method solves the problem of difficult mass transfer of dianhydride monomers in high-viscosity solutions and effectively reduces the number of impurities such as microgels and lumps.

[0041] 2. The present invention adopts the method of adding dianhydride slurry to diamine solution for polymerization. Compared with dianhydride solid powder, dianhydride slurry is equivalent to the effective ingredient being diluted. Therefore, compared with directly adding dianhydride powder to the solution, the viscosity change caused by the same degree of metering error is greatly reduced, and the operating window is wider.

[0042] Since the purity of the polyamic acid solution has a great influence on its processing performance and the performance of the corresponding polyimide material, the present invention has an important promoting significance for improving the purity of the polyamic acid solution and further improving the performance and quality of the corresponding polyimide material.

[0043] By adopting the technical scheme of the present invention, the obtained polyamic acid solution has good purity, and the prepared polyamic acid solution has fewer impurity particles tested by a particle counter. The above polyamic acid solution is prepared into a polyimide film and detected by an AOI (optical automatic detection, Automated Optical Insection) system, and the effect of reducing impurities is significant, as shown in the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the AOI inspection image of the imide film prepared in Example 1.

[0045] Figure 2 This is the AOI inspection image of the imide film prepared in Example 2.

[0046] Figure 3 This is the AOI inspection image of the imide film prepared in Example 3.

[0047] Figure 4 This is the AOI inspection image of the imide film prepared in Example 4.

[0048] Figure 5 This is the AOI inspection image of the imide film prepared in Example 5.

[0049] Figure 6 This is the AOI inspection image of the imide film prepared in Example 6.

[0050] Figure 7 This is the AOI inspection image of the imide film prepared in Example 7.

[0051] Figure 8 This is the AOI inspection image of the imide film prepared in Example 8.

[0052] Fig. 9 This is the AOI inspection image of the imide film prepared in Example 9.

[0053] Fig.10 This is the AOI inspection image of the imide film prepared in Example 10.

[0054] Fig.11 This is the AOI inspection image of the imide film prepared in Example 11.

[0055] Fig.12 This is the AOI inspection image of the imide film prepared in Comparative Example 1.

[0056] Fig.13 This is the AOI inspection image of the imide film prepared in Comparative Example 2.

[0057] Fig.14 This is the AOI inspection image of the imide film prepared in Comparative Example 3. DETAILED DESCRIPTION

[0058] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0059] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present invention are all disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0060] The present invention adopts a particle counter (AccuSizer A7000 SIS) to detect the number of particles in the polyamic acid solution; and adopts an AOI (Automated Optical Insection, model HS-1000) system to detect the number of particles in the polyimide film.

[0061] [Example 1]

[0062] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 567.35g of N,N-dimethylacetamide (DMAc), stir at 25°C, and set aside after it is completely dissolved; add 108.41g (0.497mol) of isophthalic anhydride (PMDA) to 614.29g of DMAc and add 11.8g of butyrolactone to form a slurry under high-speed shearing at 10000rpm; add this slurry to the above-mentioned ODA DMAc solution and stir it thoroughly at 25°C to obtain a polyamic acid solution (molar ratio 0.994, solid content 15%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 42 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was detected using an AOI (Automated Optical Insection) system, as follows Figure 1 As shown in the figure (the red dots in the figure represent impurity particles, the same below), the number of particles larger than 2μm in the range of 20×20mm is 151, which can meet the use requirements (<500) in high-end fields such as electronics.

[0063] [Example 2]

[0064] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 567.35g of N,N-dimethylacetamide (DMAc), stir at 25°C, and set aside after it is completely dissolved; add 107.97g (0.495mol) of isophthalic anhydride (PMDA) to 611.83g of DMAc and add 12.0g of isophorone to form a slurry under high-speed shearing at 8000rpm; add this slurry to the above-mentioned ODA DMAc solution and stir it thoroughly at 25°C to obtain a polyamic acid solution (molar ratio 0.99, solid content 15%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 49 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was detected using an AOI (Automated Optical Insection) system, as follows Figure 2 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 170, which can meet the requirements of use in high-end fields such as electronics (<500).

[0065] [Example 3]

[0066] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 901.08g of NMP, stir at 0°C, and set aside after it is completely dissolved; add 109.06g (0.5mol) of isophthalic anhydride (PMDA) to 981.54g of NMP and add 19.1g of butyrolactone to form a slurry under 15000rpm high-speed shearing; add this slurry to the above-mentioned ODA NMP solution and stir thoroughly at 0°C to obtain a polyamic acid solution (molar ratio 1, solid content 10%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 45 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was tested with an AOI (Automated Optical Insection) system, as follows Figure 3 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 161, which can meet the requirements of use in high-end fields such as electronics (<500).

[0067] [Example 4]

[0068] Dissolve 108.14g (1 mol) of p-phenylenediamine (PDA) in 432.56g of DMF, stir at 40°C, and set aside after it is completely dissolved; add 279.51g (0.95mol) of biphenyltetracarboxylic dianhydride (BPDA) to 1118.04g of DMF and add 77.0g of butyrolactone to form a slurry under high-speed shearing at 25000rpm; add this slurry to the above-mentioned DMF solution of PDA and stir it thoroughly at 40°C to obtain a polyamic acid solution (molar ratio 0.95, solid content 20%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 59 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was tested using an AOI (Automated Optical Insection) system, as follows Figure 4 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 253, which can meet the requirements for use in high-end fields such as electronics (<500).

[0069] [Example 5]

[0070] Dissolve 200.24g (1 mol) of diphenyl ether diamine (ODA) in 1802.16g of DMSO, stir at 50°C, and set aside after it is completely dissolved; add 338.34g (1.05mol) of 3,3',4,4'-dibenzophenone tetraacid dianhydride (BTDA) to 3045.06g of DMSO and add 50.2g of isophorone to form a slurry under high-speed shearing at 1000rpm; add this slurry to the above-mentioned ODA DMSO solution and stir thoroughly at 50°C to obtain a polyamic acid solution (molar ratio 1.05, solid content 10%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 67 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was detected using an AOI (Automated Optical Insection) system, as follows Figure 5 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 339, which can meet the requirements of use in high-end fields such as electronics (<500).

[0071] [Example 6]

[0072] 100.12g (0.5mol) of diphenyl ether diamine (ODA) and 54.07g (0.5mol) of p-phenylenediamine (PDA) were dissolved in 1387.71g of NMP, stirred at 60°C, and used after being completely dissolved; 111.24g (0.51mol) of phthalic anhydride (PMDA) and 150.05g (0.51mol) of biphenyltetracarboxylic anhydride (BPDA) were added to 2351.63g of DMAc and 93.5g of butyrolactone were added to form a slurry under 30000rpm high-speed shearing; the slurry was added to the above-mentioned NMP solution of ODA and PDA and stirred at 60°C to obtain a polyamic acid solution (molar ratio 1.02, solid content 10%). The prepared solution was tested by a particle counter, and the number of particles >1μm was 64 / ml. The polyimide film was prepared using the polyamic acid solution and inspected using an AOI (Automated Optical Inspection) system as follows: Figure 6 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 296, which can meet the requirements of use in high-end fields such as electronics (<500).

[0073] [Example 7]

[0074] 100.12g (0.5mol) of diphenyl ether diamine (ODA) and 54.07g (0.5mol) of p-phenylenediamine (PDA) were dissolved in 1387.71g of DMAc, stirred at 10°C, and used after being completely dissolved; 106.88g (0.49mol) of phthalic anhydride (PMDA) and 144.17g (0.49mol) of biphenyltetracarboxylic anhydride (BPDA) were added to 2259.43g of DMAc and 110.0g of butyrolactone were added to form a slurry under high-speed shearing at 15000rpm; the slurry was added to the above-mentioned DMAc solution of ODA and PDA and stirred thoroughly at 10°C to obtain a polyamic acid solution (molar ratio 0.98, solid content 10%). The prepared solution was tested by a particle counter, and the number of particles >1μm was 11 per milliliter. The polyimide film was prepared using the polyamic acid solution and inspected using an AOI (Automated Optical Inspection) system as follows: Figure 7 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 89, which can meet the requirements of use in high-end fields such as electronics (<500).

[0075] [Example 8]

[0076] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 1902.28g of DMAc, stir at -10°C, and set aside after it is completely dissolved; add 106.88g (0.49mol) of isophthalic anhydride (PMDA) to 2030.72g of DMAc and add 80.1g of isophorone to form a slurry under high-speed shearing at 5000rpm; add this slurry to the above-mentioned ODA DMAc solution and stir thoroughly at -10°C to obtain a polyamic acid solution (molar ratio 0.98, solid content 5%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 32 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was tested using an AOI (Automated Optical Insection) system, as follows Figure 8 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 111, which can meet the requirements of use in high-end fields such as electronics (<500).

[0077] [Example 9]

[0078] Dissolve 54.07g (0.5mol) of p-phenylenediamine (PDA) in 1027.33g of DMAc, stir at 40°C, and set aside after it is completely dissolved; add 139.75g (0.475mol) of biphenyltetracarboxylic dianhydride (BPDA) to 2655.34g of DMAc and add 100.0g of isophorone to form a slurry under high-speed shearing at 15000rpm; add this slurry to the above-mentioned PDA DMAc solution and stir thoroughly at 40°C to obtain a polyamic acid solution (molar ratio 0.95, solid content 5%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 39 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was tested using an AOI (Automated Optical Insection) system, as follows Fig. 9 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 149, which can meet the requirements of use in high-end fields such as electronics (<500).

[0079] [Example 10]

[0080] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) and 54.07g (0.5mol) of p-phenylenediamine (PDA) in 873.74g of DMAc, stir at 20°C, and set aside after complete dissolution; add 307.12g (0.99mol) of 4,4'-diphenyl ether dianhydride (ODPA) to 1740.38g of DMAc and add 55.0g of butyrolactone to form a slurry under high-speed shearing at 15000rpm; add this slurry to the above-mentioned ODA and PDA DMAc solution and stir thoroughly at 20°C to obtain a polyamic acid solution (molar ratio 0.99, solid content 15%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 28 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was detected using an AOI (optical automatic detection, Automated Optical Insection) system, as follows Fig.10 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 89, which can meet the requirements of use in high-end fields such as electronics (<500).

[0081] [Example 11]

[0082] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 901.08g of NMP, stir at 0°C, and set aside after it is completely dissolved; add 109.06g (0.5mol) of isophthalic anhydride (PMDA) to 981.54g of NMP to form a slurry under 15000rpm high-speed shearing; add this slurry to the above-mentioned ODA NMP solution and stir thoroughly at 0°C to obtain a polyamic acid solution (molar ratio 1, solid content 10%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 546 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was tested with an AOI (Automated Optical Insection) system, as follows Fig.11 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 1725.

[0083] [Comparative Example 1]

[0084] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 1181.64g of N,N-dimethylacetamide (DMAc), stir at 25°C, and set aside after it is completely dissolved; add 108.41g (0.497mol) of phthalic anhydride (PMDA) to the above ODA DMAc solution and stir thoroughly at 25°C to obtain a polyamic acid solution (molar ratio 0.994, solid content 15%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 2899 / ml. The above polyamic acid solution was used to prepare a polyimide film, and was tested with an AOI (Automated Optical Insection) system, as follows Fig.12 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 10392, which cannot meet the requirements for use in high-end fields such as electronics (<500).

[0085] [Comparative Example 2]

[0086] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 1179.18g of N,N-dimethylacetamide (DMAc), stir at 25°C, and set aside after it is completely dissolved; add 107.97g (0.495mol) of phthalic anhydride (PMDA) to the above ODA DMAc solution and stir thoroughly at 25°C to obtain a polyamic acid solution (molar ratio 0.99, solid content 15%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 3301 / ml. The above polyamic acid solution was used to prepare a polyimide film, and was tested with an AOI (Automated Optical Insection) system, as follows Fig.13 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 15178, which cannot meet the requirements for use in high-end fields such as electronics (<500).

[0087] [Comparative Example 3]

[0088] Dissolve 100.12g (0.5mol) of diphenyl ether diamine (ODA) in 901.08g of NMP, stir at 0°C, and set aside after it is completely dissolved; add 109.06g (0.5mol) of isophthalic anhydride (PMDA) to 981.54g of NMP and add 19.1g of butyrolactone to form a slurry under 600rpm high-speed shearing; add this slurry to the above-mentioned ODA NMP solution and stir thoroughly at 0°C to obtain a polyamic acid solution (molar ratio 1, solid content 10%). The prepared solution was tested with a particle counter, and the number of particles >1μm was 368 / ml. The above-mentioned polyamic acid solution was used to prepare a polyimide film, and was tested with an AOI (Automated Optical Insection) system, as follows Fig.14 As shown, the number of particles larger than 2 μm in the range of 20×20 mm is 1307, which cannot meet the requirements for use in high-end fields such as electronics (<500).

Claims

1. A method for preparing a polyamic acid solution, comprising mixing a dianhydride monomer, a solvent and an additive under high-speed shearing to form a slurry, dissolving a diamine monomer in a solvent to form a diamine solution, and then adding the slurry into the diamine solution for polymerization to obtain a polyamic acid solution; the additive is butyrolactone and / or isophorone, and the additive accounts for 1 to 5% of the total mass of the solvent; and the shear speed of the high-speed shearing is 1000 to 30000 rpm.

2. The method for preparing a polyamic acid solution according to claim 1, wherein: The diamine monomer is one or a mixture of two or more diamines represented by formula (I), H2N-Ar1-NH2 (I), Wherein, Ar1 is a divalent aromatic residue containing at least one carbon six-membered ring.

3. The method for preparing a polyamic acid solution according to claim 2, wherein: Ar1 has the following structure, R2 is H-, CH3-, Cl-, Br-, F-, CH3O-.

4. The method for preparing a polyamic acid solution according to claim 1, wherein: The dianhydride monomer is one or a mixture of two or more dianhydrides represented by formula (II). Wherein, Ar2 is a tetravalent aromatic residue containing at least one carbon six-membered ring.

5. The method for preparing a polyamic acid solution according to claim 4, wherein: Ar2 has the following structure, R1 is H-, CH3-, Cl-, Br-, F-, CH3O-.

6. The method for preparing a polyamic acid solution according to claim 1, wherein: The solvent is an aprotic polar solvent.

7. The method for preparing a polyamic acid solution according to claim 6, wherein: The solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

8. The method for preparing a polyamic acid solution according to claim 1, wherein: The shearing speed of the high-speed shearing is 5000-20000 rpm.

9. The method for preparing a polyamic acid solution according to claim 1, wherein: The polymerization reaction temperature is -10 to 60°C.

10. The method for preparing a polyamic acid solution according to claim 1, characterized in that: The molar ratio of the dianhydride unit to the diamine unit in the polyamic acid is 0.95 to 1.

05.

11. The method for preparing a polyamic acid solution according to claim 10, characterized in that: The molar ratio of the dianhydride unit to the diamine unit in the polyamic acid is 0.98 to 1.

02.

12. The method for preparing a polyamic acid solution according to claim 1, characterized in that: The solid content of the polyamic acid solution is 5 to 30 wt %.

13. The polyamic acid solution obtained by the preparation method according to any one of claims 1 to 12, wherein the number of particles larger than 1 μm in the polyamic acid solution is less than 100 / ml; and the number of particles larger than 2 μm in the polyimide film prepared from the polyamic acid solution within a range of 20×20 mm is less than 500.

14. The polyamic acid solution according to claim 13, characterized in that: The number of particles larger than 1 μm in the polyamic acid solution is less than 50 / ml; the number of particles larger than 2 μm in the polyimide film prepared from the polyamic acid solution is less than 200 within a range of 20×20 mm.

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