A kind of polyimide wire enamel and preparation method thereof

Abstract

The present application provides a polyimide wire enamel and a preparation method thereof. The preparation method of the polyimide wire enamel comprises: mixing a volatile acid with a diamine, a dianhydride and a solvent and reacting them to obtain the polyimide wire enamel. The preparation method adds an acid to the reaction system to inhibit the reaction of the acid anhydride with water, so that the acid anhydride can react with the amine preferentially, thereby reducing the requirement of the reaction system for water content, greatly reducing the production cost, and the addition of the acid does not affect the reaction process of the diamine and the dianhydride, ensuring that the product has good film-forming properties.

Description

Technical Field

[0001] The present application relates to the technical field of wire enamels, and in particular to a polyimide wire enamel and a preparation method thereof. Background Art

[0002] Wire enamel is an indispensable electrical insulation coating used in electrical equipment. Polyimide (PI) wire enamel is currently the most heat-resistant organic polymer wire enamel. The large number of stable five-membered heterocycles on its molecular chain give it excellent properties such as high mechanical properties, high and low temperature resistance, flame retardancy, and radiation resistance. Polyimide wire enamel is obtained by the reaction of diamine and dianhydride. Since dianhydride reacts with water, the preparation of polyimide wire enamel needs to be carried out under nitrogen protection and anhydrous solvents must be used. This process not only consumes nitrogen and makes the production cost high, but also because the water content in the solvent is difficult to control, it is not conducive to the full reaction, and the performance of the obtained product is poor. Summary of the invention

[0003] In view of this, the present application provides a new method for preparing polyimide wire enamel, which adds an acid to the reaction system to inhibit the reaction of anhydride and water, so that the anhydride can react with amine preferentially, thereby reducing the requirement of the reaction system for water content, greatly reducing production costs, and the addition of volatile acid does not affect the reaction process of diamine and dianhydride and the composition of the final product, ensuring that the product has good film-forming properties.

[0004] A first aspect of the present application provides a method for preparing a polyimide wire enamel, comprising: mixing a volatile acid with a diamine, a dianhydride and a solvent and reacting the mixture to obtain the polyimide wire enamel.

[0005] Optionally, the acidity coefficient pKa of the volatile acid is less than or equal to 1.

[0006] Optionally, the saturated vapor pressure of the volatile acid at 25° C. is greater than or equal to 8 mm Hg.

[0007] Optionally, the volatile acid includes one or more of hydrochloric acid, trifluoromethanesulfonic acid, trifluoroacetic acid, trichloroacetic acid or trichloroacetic acid.

[0008] Optionally, the molar ratio of the diamine, the dianhydride, the volatile acid and the solvent is: (0.95-1):(0.95-1):(0.0001%-0.5%):(25-200).

[0009] Optionally, the molar ratio of the diamine, the dianhydride, the volatile acid and the solvent is: (0.95-1):(0.95-1):(0.001%-0.1%):(25-200).

[0010] Optionally, the reaction temperature is 60°C to 120°C, and the reaction time is 0.5h to 10h.

[0011] Optionally, the mixing stirring rate is 100 rpm to 300 rpm.

[0012] Optionally, the preparation method comprises: mixing the volatile acid, the diamine and the solvent to obtain a mixed liquid, and then adding the dianhydride to the mixed liquid to obtain the polyimide wire enamel after reaction.

[0013] Optionally, the dianhydride is slowly added into the mixed solution, and the adding time of the dianhydride is 1 h to 12 h.

[0014] Optionally, the solvent includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0015] Optionally, the diamine includes o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 1,3-diamino-2-methylpropane, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenyl sulfone, N,N-bis(4-aminophenyl)-1,4-phenylenediamine, and 9,9-bis(4-aminophenyl)fluorene.

[0016] Optionally, the dianhydride includes one or more of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-tetracarboxybenzophenone dianhydride, 3,3',4,4'-tetracarboxybiphenyl sulfone dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylmethane dianhydride, and 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride.

[0017] In a second aspect, the present application provides a polyimide compound, which is prepared by the method for preparing the polyimide wire enamel as described in the first aspect.

[0018] Optionally, the viscosity of the polyimide wire enamel is 10000 cPa to 30000 cPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A reaction process diagram of a polyimide wire enamel provided in one embodiment of the present application;

[0020] Figure 2 A flow chart for preparing a polyimide wire enamel provided in one embodiment of the present application. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] See also Figure 1 , Figure 1 The reaction process diagram of the polyimide wire enamel provided in one embodiment of the present application, the polyimide wire enamel is obtained by the reaction of diamine and dianhydride. In the actual reaction process, since dianhydride is electrophilic and can react with water in air or solvent, the preparation of polyimide wire enamel requires nitrogen protection and adopts a reaction system of anhydrous solvent. The above reaction conditions have high production costs, such as the loss of nitrogen and anhydrous solvent; on the other hand, the reaction solvents of the existing polyimide wire enamel have strong water absorption, such as N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide, which absorb more than 300ppm of water when exposed to air for 5 minutes under 50% humidity. This property makes it difficult to control the moisture in the reaction system, resulting in an increase in side reactions, deviations in the ratio of reactants, unstable composition of the final product, and poor product performance. In order to reduce the production cost of polyimide wire enamel and ensure that the obtained polyimide wire enamel has good performance. The invention provides a novel preparation method of polyimide wire enamel, comprising: mixing volatile acid with diamine, dianhydride and solvent and reacting the mixture to obtain the polyimide wire enamel.

[0023] The present application can inhibit the ionization of water by adding a volatile acid into the reaction system, so that water cannot ionize to produce hydroxide that can nucleophilically attack the acid anhydride, thereby reducing the requirement of the reaction system for water content, so the reaction does not need to be carried out under nitrogen protection, and there is no need to use anhydrous solvents, which greatly reduces the production cost; and when water and amines are present in the reaction system at the same time, due to electrical reasons, the acid anhydride can react with the amine first, thereby maintaining the reaction ratio of diamine to dianhydride, ensuring that the product polyimide has a higher molecular weight and a reasonable molecular weight distribution, thereby obtaining a polyimide wire enamel with moderate viscosity, good film-forming performance and good dielectric properties; in addition, after the reaction is completed, the acid in the product can volatilize, thereby eliminating the influence of the acidic substance on the film properties, ensuring that the polyimide wire enamel has good performance.

[0024] See also Figure 2 , Figure 2 A preparation flow chart of a polyimide wire enamel provided in one embodiment of the present application includes:

[0025] Step 100: mixing a volatile acid, a diamine and a solvent to obtain a mixed solution;

[0026] Step 200: adding dianhydride to the mixed solution to obtain polyimide wire enamel after reaction.

[0027] In step 100 of the present application, the volatile acid used is a strong acid with volatility. In some embodiments of the present application, the acidity coefficient pKa of the volatile acid is less than or equal to 1, and the volatile acid can ionize more hydrogen ions, thereby effectively inhibiting the ionization of water in the solvent. In some embodiments of the present application, the saturated vapor pressure of the volatile acid at 25°C is greater than or equal to 8mmHg. The saturated vapor pressure of the volatile acid can be specifically but not limited to 8mmHg, 10mmHg, 12mmHg or 15mmHg. The greater the saturated vapor pressure of the volatile acid, the better the volatility. After the reaction is completed, the volatile acid can be volatilized and removed by itself, thereby eliminating the effect of the acid on the film-forming properties of the product. In some embodiments, the volatile acid includes one or more of hydrochloric acid, trifluoromethanesulfonic acid, trifluoroacetic acid, nitrogen sulfur square acid or trichloroacetic acid, wherein, when the volatile acid includes hydrochloric acid, the hydrochloric acid can be dispersed in an organic solvent to form a solution, and the organic solvent can be 1,4 dioxane, that is, a 1,4 dioxane solution of hydrochloric acid is formed. In some embodiments of the present application, the volatile acid includes trifluoromethanesulfonic acid, which has a stronger acidity and can more effectively inhibit the ionization of water. In some embodiments of the present application, the diamine includes o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 1,3-diamino-2-methylpropane, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenyl sulfone, N,N-bis(4-aminophenyl)-1,4-phenylenediamine, and 9,9-bis(4-aminophenyl)fluorene. In some embodiments, the diamine includes one or more of 4,4'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl sulfone, 1,3-diamino-2-methylpropane, N,N-bis(4-aminophenyl)-1,4-phenylenediamine, and 9,9-bis(4-aminophenyl)fluorene. In some embodiments, the solvent includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide. In the present application, since a volatile acid is added to the reaction system, there is no strict requirement for the water content in the solvent, and the reaction can be carried out under an atmospheric environment. In some embodiments, the solvent can be a chemically pure solvent. Although the water content of the chemically pure solvent is higher than 800ppm, the preparation method of the present application does not require special dehydration of the solvent, which is conducive to simplifying the production process and reducing production costs.

[0028] In step 200 of the present application, the mixed solution is first cooled to -15°C to 20°C, and then the dianhydride is slowly added to the mixed solution. The stirring speed of the reaction system during the addition of the dianhydride is 100rpm to 300rpm. In some embodiments of the present application, the addition time of the dianhydride is 1h to 12h, and the addition time of the dianhydride can be, but is not limited to, 1h, 3h, 5h, 8h, 10h or 12h. Slowly adding the dianhydride to the mixed solution of the volatile acid, diamine and solvent is conducive to the full mixing of the components and inhibits the agglomeration of the reactants. In some embodiments of the present application, the dianhydride includes 2,3,3',4'-diphenyl ether tetracarboxylic acid dianhydride, 3,3',4,4'-tetracarboxy benzophenone dianhydride, 3,3',4,4'-tetracarboxy biphenyl sulfone dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylmethane dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride. In some embodiments, the dianhydride includes one or more of pyromellitic anhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride.

[0029] In some embodiments of the present application, the molar ratio of diamine, dianhydride, volatile acid and solvent in the reaction solution is (0.95-1): (0.95-1): (0.0001%-0.5%): (25-200). In some embodiments, the molar ratio of diamine, dianhydride, volatile acid and solvent is (0.95-1): (0.95-1): (0.001%-0.1%): (25-200). When the molar ratio of diamine, dianhydride, volatile acid and solvent is controlled within the above range, the resulting product can have excellent film-forming properties. In some embodiments, the volatile acid is trifluoromethanesulfonic acid, and the molar ratio of diamine, dianhydride, volatile acid and solvent is (0.95-1): (0.95-1): (0.005%-0.05%): (25-200).

[0030] In some embodiments of the present application, after adding dianhydride to the mixed solution, the reaction system is heated to 60°C to 120°C, and the polyimide wire enamel is obtained after being kept warm for 0.5h to 10h. Among them, the reaction temperature can be, but not limited to, 60°C, 80°C, 100°C or 120°C, and the reaction temperature can be, but not limited to, 0.5h, 1h, 3h, 5h, 8h or 10h. In some embodiments of the present application, the stirring rate during the reaction is 100rpm to 300rpm, and the stirring rate during the reaction can be, but not limited to, 100rpm, 150rpm, 200rpm, 250rpm or 300rpm. Controlling the stirring speed is conducive to the volatile acid effectively blocking the reaction of dianhydride and water, ensuring that dianhydride and diamine achieve sufficient reaction.

[0031] The preparation method of the polyimide wire enamel provided in the present application has simple steps, and the whole reaction process does not require nitrogen protection, and there is no need to specially remove water from the solvent, which is beneficial to reducing costs; and the amount of volatile acid added is extremely small, which has little impact on the cost, and no impurity removal is required after the reaction. The addition of acid does not affect the reaction of diamine and dianhydride, and the obtained product has good performance and has broad application prospects.

[0032] The present application also provides a polyimide wire enamel, which is obtained by the preparation method of the present application, and has good film-forming properties, dielectric properties and moderate viscosity, which is conducive to its application in wire enamel. In some embodiments of the present application, the viscosity of the polyimide wire enamel is 10000cPa to 30000cPa. Within the above viscosity range, the polyimide wire enamel is easy to be coated on the surface of the metal wire, and the coating layer is not easy to generate bubbles. In some embodiments of the present application, the dielectric constant of the polyimide wire enamel is 3.1 to 3.6.

[0033] The technical solution of the present application is further described below with reference to a number of embodiments.

[0034] Example 1

[0035] A method for preparing a polyimide wire enamel comprises:

[0036] 24.88 g of 9,9-bis(4-aminophenyl)fluorene, 140 g of dimethyl sulfoxide and 0.023 g of trifluoroacetic acid were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0037] 25.11 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was slowly added into the kettle over 6 hours with a stirring rate of 200 rpm.

[0038] The reactor was heated to 60° C. with a stirring rate of 200 rpm. After being kept warm for 2 hours, the temperature was lowered to room temperature to obtain a polyimide wire enamel.

[0039] Example 2

[0040] A method for preparing a polyimide wire enamel comprises:

[0041] 29.00 g of N,N-bis(4-aminophenyl)-1,4-phenylenediamine, 154 g of N,N-dimethylformamide and 0.0013 g of trifluoromethanesulfonic acid were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0042] 25.11 g of pyromellitic anhydride was slowly added into the kettle over 4 hours with a stirring rate of 150 rpm.

[0043] The reactor was heated to 80° C. with a stirring rate of 150 rpm. After being kept warm for 2 hours, the reactor was cooled to room temperature to obtain a polyimide wire enamel.

[0044] Example 3

[0045] A method for preparing a polyimide wire enamel comprises:

[0046] 28.78 g of 1,3-diamino-2-methylpropane, 140 g of N,N-dimethylformamide and 0.092 g of trichloroacetic acid were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0047] 31.29 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was slowly added into the kettle over 4 hours with a stirring rate of 130 rpm.

[0048] The reactor was heated to 70° C. with a stirring rate of 130 rpm, and after being kept warm for 2 hours, the temperature was lowered to room temperature to obtain a polyimide wire enamel.

[0049] Example 4

[0050] A method for preparing a polyimide wire enamel comprises:

[0051] 28.78 g of 1,3-diamino-2-methylpropane, 140 g of N,N-dimethylformamide and 0.28 g of trichloroacetic acid were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0052] 31.29 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was slowly added into the kettle over 4 hours with a stirring rate of 130 rpm.

[0053] The reactor was heated to 70° C. with a stirring rate of 130 rpm, and after being kept warm for 2 hours, the temperature was lowered to room temperature to obtain a polyimide wire enamel.

[0054] Example 5

[0055] A method for preparing a polyimide wire enamel comprises:

[0056] 24.88 g of 9,9-bis(4-aminophenyl)fluorene, 140 g of dimethyl sulfoxide and 0.023 g of trifluoroacetic acid were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0057] 25.11 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was slowly added into the kettle over 6 hours with a stirring rate of 60 rpm.

[0058] The reactor was heated to 60° C. with a stirring rate of 60 rpm, and after being kept warm for 2 hours, it was cooled to room temperature to obtain a polyimide wire enamel.

[0059] Example 6

[0060] A method for preparing a polyimide wire enamel comprises:

[0061] 29.00 g of N,N-bis(4-aminophenyl)-1,4-phenylenediamine, 154 g of N,N-dimethylformamide and 0.0013 g of nitrogen-sulfuric acid were put into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0062] 25.11 g of pyromellitic anhydride was slowly added into the kettle over 4 hours with a stirring rate of 150 rpm.

[0063] The reactor was heated to 80° C. with a stirring rate of 150 rpm. After being kept warm for 2 hours, the reactor was cooled to room temperature to obtain a polyimide wire enamel.

[0064] Example 7

[0065] A method for preparing a polyimide wire enamel comprises:

[0066] 24.88 g of 9,9-bis(4-aminophenyl)fluorene, 140 g of dimethyl sulfoxide, and 0.023 g of a 1,4-dioxane solution (4M) of hydrochloric acid were sequentially added into a reaction kettle, stirring was started, and the temperature was lowered to 0°C.

[0067] 25.11 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was slowly added into the kettle over 6 hours with a stirring rate of 200 rpm.

[0068] The reaction kettle was heated to 60° C. with a stirring rate of 200 rpm. After being kept warm for 2 hours, the temperature was lowered to room temperature to obtain a polyimide wire enamel.

[0069] Example 8

[0070] A method for preparing a polyimide wire enamel comprises:

[0071] 29.00 g of N,N-bis(4-aminophenyl)-1,4-phenylenediamine, 354 g of N,N-dimethylformamide and 0.0013 g of trifluoromethanesulfonic acid were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0072] 25.11 g of pyromellitic anhydride was slowly added into the kettle over 4 hours with a stirring rate of 150 rpm.

[0073] The reactor was heated to 80° C. with a stirring rate of 150 rpm. After being kept warm for 2 hours, the reactor was cooled to room temperature to obtain a polyimide wire enamel.

[0074] Example 9

[0075] A method for preparing a polyimide wire enamel comprises:

[0076] 24.88 g of 9,9-bis(4-aminophenyl)fluorene, 140 g of dimethyl sulfoxide and 0.023 g of propionic acid were put into a reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0077] 25.11 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was slowly added into the kettle over 6 hours with a stirring rate of 200 rpm.

[0078] The reactor was heated to 60° C. with a stirring rate of 200 rpm. After being kept warm for 2 hours, the temperature was lowered to room temperature to obtain a polyimide wire enamel.

[0079] Example 10

[0080] A method for preparing a polyimide wire enamel comprises:

[0081] 24.88 g of 9,9-bis(4-aminophenyl)fluorene, 140 g of dimethyl sulfoxide and 0.023 g of acetic acid were put into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0082] 25.11 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was slowly added into the kettle over 6 hours with a stirring rate of 200 rpm.

[0083] The reactor was heated to 60° C. with a stirring rate of 200 rpm. After being kept warm for 2 hours, the temperature was lowered to room temperature to obtain a polyimide wire enamel.

[0084] Comparative Example 1

[0085] A method for preparing a polyimide wire enamel comprises:

[0086] 28.78 g of 1,3-diamino-2-methylpropane and 140 g of N,N-dimethylformamide were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0087] 31.29 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride was slowly added into the kettle over 4 hours.

[0088] The reactor was heated to 70° C., kept warm for 2 hours, and then cooled to room temperature to obtain a polyimide wire enamel.

[0089] Comparative Example 2

[0090] 29.00 g of N,N-bis(4-aminophenyl)-1,4-phenylenediamine, 154 g of N,N-dimethylformamide and 0.0013 g of sulfuric acid were added into the reaction kettle in sequence, stirring was started, and the temperature was lowered to 0°C.

[0091] 25.11 g of pyromellitic anhydride was slowly added into the kettle over 4 hours with a stirring rate of 150 rpm.

[0092] The reactor was heated to 80° C. with a stirring rate of 150 rpm. After being kept warm for 2 hours, the reactor was cooled to room temperature to obtain a polyimide wire enamel.

[0093] Effect Example

[0094] In order to verify the performance of the electrode plates and batteries prepared in this application, this application also provides an effect embodiment.

[0095] 1) The dielectric constants of the products obtained in Examples 1 to 10 were tested using the ASTM D150-18 method. Since the products of Comparative Examples 1 and 2 could not form films, the dielectric constants could not be measured. The test results are shown in Table 1.

[0096] 2) The film-forming properties of the polyimide wire enamel obtained in Examples 1-10 and Comparative Examples 1-2 were characterized. The specific evaluation criteria for the film-forming properties were as follows: a wet film of the corresponding solution was prepared by coating and casting on a clean glass plate; the wet film was transferred to an oven and heated for imidization according to the following heating program: 80°C / 2h, 120°C / 1h, 160°C / 1h, 180°C / 1h, 240°C / 1h, 280°C / 1h, 350°C / 1h, and the heating rate was 2°C / min. After the glass plate was cooled to room temperature, the glass plate covered with the polyimide film was immersed in deionized water to peel off the polyimide film to obtain the corresponding self-supporting PI film. The film-forming properties were evaluated specifically as follows: the film formed a whole piece of film material on the glass, the film surface was not broken and could remain intact after peeling, which was considered to be very good film formation. The film is a whole piece of film on the glass, the film surface is not broken and can be intact after peeling, which is considered to be a normal film. The film is broken into pieces on the glass and is considered to be unfilmable. The test results are shown in Table 1.

[0097] 3) The viscosity of the polyimide wire enamel obtained in Examples 1-10 and Comparative Examples 1-2 was characterized. The viscosity was tested by placing the obtained polyimide wire enamel in a wide-mouth glass bottle, fixing it on an iron stand, and then testing the rotational viscosity using a Brookfield rotational viscometer. Data was collected every 10 seconds, and the average of the five relatively stable data was taken as the experimental result.

[0098] Table 1 Performance of polyimide wire enamel obtained in Examples 1-10 and Comparative Examples 1-2

[0099]

[0100]

[0101] As can be seen from Table 1, the polyimide wire enamel prepared by the preparation method of the polyimide wire enamel of the present invention has moderate viscosity and good dielectric properties and film-forming properties. In Example 4, due to the large amount of volatile acid added in the reaction system, nucleophilic attack is suppressed, the polymerization degree of the obtained polyimide decreases, and the film-forming property of the product is reduced; in Example 5, the stirring speed during the reaction is too slow, the polymerization degree of the obtained polyimide is too high, and the viscosity of the product is large, which is not conducive to the application of the polyimide wire enamel; in Example 8, due to the large amount of solvent and low concentration of reactants, the polymerization degree of the obtained polyimide is low, resulting in general film-forming property of the product; in Example 9, the volatility of propionic acid is weak, and there is a certain amount of acid residue in the product, which makes the film-forming property of the product poor; in Example 10, the acidity of acetic acid is weak, and the acid has a weak inhibitory effect on the ionization of water in the reaction system, which makes the reaction ratio of diamine and dianhydride have a certain deviation, and the film-forming property of the product is poor and the viscosity is large.

[0102] In Comparative Example 1, a certain amount of water exists in the reaction system, which interferes with the reaction of diamine and dianhydride, resulting in the inability of the obtained product to form a film; in Comparative Example 2, the added acid is a non-volatile acid, and the residual acid in the reaction system makes the product unable to form a film.

[0103] The above is a preferred embodiment of the present application, but it should not be understood as limiting the scope of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application, and these improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A method for preparing a polyimide wire enamel, characterized in that: include: A volatile acid is mixed with a diamine, a dianhydride and a solvent and reacted to obtain a polyimide wire enamel, wherein the acidity coefficient pKa of the volatile acid is less than or equal to 1, and the molar ratio of the diamine, the dianhydride, the volatile acid and the solvent is (0.95-1):(0.95-1):(0.0001%-0.5%):(25-200).

2. The preparation method according to claim 1, wherein The saturated vapor pressure of the volatile acid at 25° C. is greater than or equal to 8 mmHg.

3. The preparation method according to claim 1, wherein The volatile acid includes one or more of hydrochloric acid, trifluoromethanesulfonic acid, trifluoroacetic acid or trichloroacetic acid.

4. The preparation method according to claim 1, wherein The reaction temperature is 60° C. to 120° C., and the reaction time is 0.5 h to 10 h.

5. The preparation method according to claim 1, wherein The stirring rate of the mixing is 100 rpm to 300 rpm.

6. The preparation method according to claim 1, wherein The preparation method comprises: mixing the volatile acid, the diamine and the solvent to obtain a mixed liquid, then adding the dianhydride to the mixed liquid, wherein the adding time of the dianhydride is 1 hour to 12 hours, and obtaining the polyimide wire enamel after reaction.

7. The preparation method according to claim 1, wherein The solvent includes one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; the diamine includes o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 1,3-diamino-2-methylpropane, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminobenzophenone, 3,3'-diamino One or more of diphenyl sulfone, N,N-bis(4-aminophenyl)-1,4-phenylenediamine, and 9,9-bis(4-aminophenyl)fluorene; the dianhydride includes one or more of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-tetracarboxybenzophenone dianhydride, 3,3',4,4'-tetracarboxydiphenylsulfone dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylmethane dianhydride, and 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride.

8. A polyimide wire enamel, characterized in that: The polyimide wire enamel is prepared by the preparation method of the polyimide wire enamel according to any one of claims 1 to 7.

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