A polyimide and epoxy resin composite modified fluorocarbon resin coating and preparation method thereof

Abstract

The invention discloses a polyimide and epoxy resin composite modified fluorocarbon resin coating and a preparation method thereof. The composition of the polyimide and epoxy resin composite modified fluorocarbon resin coating, measured by weight percentage, comprises: 0.4-0.8% of a diamine monomer, 0.4-0.8% of a dianhydride monomer, 60-70% of N,N-dimethylacetamide, 10-20% of an epoxy resin, 0.2-0.5% of an epoxy curing agent, 1-2% of a fluorocarbon resin curing agent, and 15-25% of a fluorocarbon resin. The preparation method comprises the following specific steps: reacting the diamine monomer and the dianhydride in N,N-dimethylacetamide, then compounding the composite modifier with the epoxy resin and the epoxy curing agent in sequence to obtain a composite modifier, and adding the composite modifier and the fluorocarbon resin curing agent together to a fluorocarbon resin solution to obtain the polyimide and epoxy resin composite modified fluorocarbon resin coating. The polyimide and epoxy resin composite modified fluorocarbon resin coating has greatly improved performance in mechanical properties, heat resistance, adhesion, and other aspects compared to existing fluorocarbon resin coatings.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorocarbon resin synthesis, and particularly relates to a polyimide and epoxy resin composite modified fluorocarbon resin coating and a preparation method thereof. Background Art

[0002] Fluorocarbon resin is mainly composed of fluorine-containing polymers. The stable carbon-fluorine bonds in its molecular structure give it excellent chemical stability and heat resistance. Compared with traditional coatings, it has extremely high durability, weather resistance, corrosion resistance, high temperature resistance, etc., and can maintain its color and gloss for a long time under extreme climatic conditions, and is not prone to fading, powdering and aging. Although fluorocarbon resin has many advantages, there are still some problems. For example, the impact resistance and hardness of fluorocarbon resin need to be further modified and improved. At the same time, the production cost of fluorocarbon resin is relatively high, and its processing technology is complicated, which limits its widespread application in certain fields. In addition, compared with certain metals or other high-performance polymers, the thermal performance of fluorocarbon resin still needs to be improved.

[0003] Epoxy resins possess excellent physical and mechanical properties. Their coatings exhibit excellent adhesion to polar substrates such as metals (steel, aluminum, etc.), ceramics, glass, concrete, and wood. They also exhibit excellent chemical resistance and electrical insulation properties. They are readily available in a wide variety of varieties and are inexpensive. Polyimides possess very high heat resistance, excellent mechanical properties, and are highly tolerant to a wide range of chemicals (such as acids, bases, and organic solvents). Therefore, modifying FEVE-type fluororesins with polyamic acid-modified epoxy resins is expected to improve their thermal and mechanical properties, while addressing cost limitations and enhancing the overall performance of FEVE-type fluororesins. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the current fluorocarbon resin has the disadvantages of high cost, poor thermal and mechanical properties, etc. Through composite modification, the adhesion, impact resistance and heat resistance of the film are improved, and a fluorocarbon resin coating with excellent performance is obtained, thereby reducing costs.

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0006] Step (1): Under room temperature, 10 to 15 parts by weight of a monomer diamine and a monomer dianhydride are weighed respectively, and the monomer diamine and the monomer dianhydride are placed in a forced air drying oven at 80°C and 150°C for 6 hours respectively to obtain prefabricated monomer diamine and monomer dianhydride, and the prefabricated monomer diamine and monomer dianhydride are sealed and placed in a desiccator for storage; 20 parts of N,N-dimethylacetamide are treated with 4Å molecular sieves and sealed for storage;

[0007] Step (2): 0.4-0.8 parts of monomer diamine and 2.5-5 parts of N,N-dimethylacetamide prepared in step (1) are added to a three-necked flask, mechanically stirred for 0.5h, after the solid is completely dissolved, cooled to 0-10°C in an ice-water bath, 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide are added, and the interval time is 0.5-1h, and 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide are added again, and the above operation is repeated for a total of three times of adding 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide, during which the ice-water bath temperature is kept at 0-10°C, and then the reaction is continued for 6-12h under stirring, and the resulting homogeneous viscous liquid is polyamic acid;

[0008] Step (3): Add the polyamic acid obtained in step (2), 0.2 to 0.5 parts of epoxy curing agent, and 10 to 20 parts of epoxy resin into a beaker, and mechanically stir in a water bath at 60 to 90° C. for 2 to 4 hours to obtain a uniform light yellow mixed solution. Then, place the mixed solution in a vacuum oven, set the temperature to 90° C., the vacuum degree to -0.1 MPa, and pre-cure for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0009] Step (4): 15 to 25 parts of fluorocarbon resin and 55.5 to 61 parts of N,N-dimethylacetamide are added to a three-necked flask and stirred at 50°C for 2 to 3 hours. Subsequently, the polyamic acid / epoxy resin composite modifier obtained in step (3) and 1 to 2 parts of fluorocarbon resin curing agent are also added to the three-necked flask. The temperature is controlled at 60 to 80°C and stirred for 3 to 6 hours to obtain a modified fluorocarbon resin coating.

[0010] The technical solution further defined in the present invention is:

[0011] Provided is a polyimide and epoxy resin composite modified fluorocarbon resin coating, wherein the mass ratio of polyamic acid to epoxy resin is 1:2-1:3, the mass ratio of fluorocarbon resin to epoxy resin is 1:1-2:1, the mass ratio of epoxy curing agent to epoxy resin is 1:20-1:25, and the mass ratio of fluorocarbon resin curing agent to fluorocarbon resin is 1:10-1:15.

[0012] Furthermore, N,N-dimethylacetamide is an organic solvent, which can be replaced by N-methylpyrrolidone or N,N-dimethylformamide. The solid mass content of polyamic acid is 10-15%, and the solid content of fluorocarbon resin is 15%-25%.

[0013] Furthermore, the monomer diamine is one or more of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-(hexafluoroisopropyl)bis(p-phenyloxy)diphenylamine, and 2,2-bis(4-aminophenyl)hexafluoropropane, and the monomer dianhydride is one or more of 4,4'-(hexafluoroisopropylene)diphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

[0014] Furthermore, the molar ratio of the monomeric diamine to the monomeric dianhydride is 1:1.02.

[0015] Furthermore, the epoxy curing agent is one of N-methylimidazole, 4,4'-diaminodiphenyl sulfone and 2,4,6-tris(dimethylaminomethyl)phenol.

[0016] Furthermore, the fluorocarbon resin curing agent is one of hexamethylene diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

[0017] Furthermore, the epoxy resin is at least one of E-39, E-44, and E-51.

[0018] The beneficial effects of the present invention are:

[0019] Fluorocarbon resins are primarily composed of fluorine-containing polymers. The strong carbon-fluorine bonds in their molecular structure impart exceptional chemical stability and heat resistance. Compared to traditional coatings, they offer significantly higher durability, weatherability, corrosion resistance, and high-temperature resistance. They can maintain their color and gloss for extended periods under extreme climate conditions, and are less susceptible to fading, chalking, and aging. Epoxy resins possess excellent physical and mechanical properties. Their coatings exhibit excellent adhesion to polar substrates such as metals (steel, aluminum, etc.), ceramics, glass, concrete, and wood. They also exhibit excellent chemical resistance and electrical insulation properties. They are readily available in a wide variety of varieties and are inexpensive. Polyimides possess very high heat resistance, excellent mechanical properties, and are highly tolerant to a wide range of chemicals, such as acids, bases, and organic solvents. Therefore, modifying FEVE-type fluororesins with polyamic acid-modified epoxy resins is expected to improve their thermal and mechanical properties, while addressing cost limitations and enhancing the overall performance of FEVE-type fluororesins.

[0020] The surface tension between the interfaces of the various components of the fluorocarbon resin coating prepared by the present invention is low, enabling better mutual dissolution and forming a stable solution system. The fluorocarbon resin coating provided by the present invention does not generate free low-surface-energy substances during use. The coating formed by applying the fluorocarbon resin to the surface of the painted workpiece can, on the one hand, isolate the painted workpiece from the painting environment, making the painted workpiece easy to clean and reducing cleaning costs; on the other hand, it does not affect the painting effect and avoids the appearance of shrinkage holes on the paint film surface. The fluorocarbon resin coating of the present invention has excellent aging resistance and comprehensive paint film performance, excellent various performances, and uses a small amount of fluorine-containing monomer, resulting in low cost. DETAILED DESCRIPTION

[0021] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention. Example 1

[0022] This embodiment provides a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0023] Step (1): Under room temperature, 10 to 15 parts by weight of a monomer diamine and a monomer dianhydride are weighed respectively, and the monomer diamine and the monomer dianhydride are placed in a forced air drying oven at 80°C and 150°C for 6 hours respectively to obtain prefabricated monomer diamine and monomer dianhydride, and the prefabricated monomer diamine and monomer dianhydride are sealed and placed in a desiccator for storage; 20 parts of N,N-dimethylacetamide are treated with 4Å molecular sieves and sealed for storage;

[0024] Step (2): Add 0.4-0.8 parts of monomer diamine and 2.5-5 parts of N,N-dimethylacetamide prepared in step (1) into a three-necked flask, stir mechanically for 0.5h, and after the solid is completely dissolved, cool to 0-10°C in an ice-water bath, add 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide, and add 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide again after an interval of 0.5-1h. Repeat the above operation to add 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide three times in total, and keep the ice-water bath temperature at 0-10°C. Then, continue the reaction for 6-12h under stirring, and the resulting homogeneous viscous liquid is polyamic acid;

[0025] Step (3): Add the polyamic acid obtained in step (2), 0.2 to 0.5 parts of epoxy curing agent, and 10 to 20 parts of epoxy resin into a beaker, and mechanically stir for 2 to 4 hours in a water bath at 60 to 90°C to obtain a uniform light yellow mixed solution. Then, place the mixed solution in a vacuum oven, set the temperature to 90°C, the vacuum degree to -0.1 MPa, and pre-cure for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0026] Step (4): 15 to 25 parts of fluorocarbon resin and 55.5 to 61 parts of N,N-dimethylacetamide are added to a three-necked flask and stirred at 50°C for 2 to 3 hours. Subsequently, the polyamic acid / epoxy resin composite modifier obtained in step (3) and 1 to 2 parts of fluorocarbon resin curing agent are also added to the three-necked flask. The temperature is controlled at 60 to 80°C and stirred for 3 to 6 hours to obtain a modified fluorocarbon resin coating.

[0027] As a preferred experimental scheme, the mass ratio of polyamic acid to epoxy resin is 2:5, the mass ratio of fluorocarbon resin to epoxy resin is 1:1, the mass ratio of the epoxy curing agent to epoxy resin is 1:20, and the mass ratio of fluorocarbon resin curing agent to fluorocarbon resin is 1:15.

[0028] The organic solvent is N,N-dimethylformamide, the solid mass content of the polyamic acid is 15%, and the solid content of the fluorocarbon resin solution is 25%.

[0029] As a preferred experimental scheme, the monomer diamine is 4,4'-diaminodiphenyl sulfone or 2,2-bis(4-aminophenyl)hexafluoropropane, and the monomer dianhydride is 4,4'-(hexafluoroisopropylene)diphthalic anhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0030] The molar ratio of the monomeric diamine to the monomeric dianhydride is 1:1.02.

[0031] As a preferred experimental solution, the epoxy resin curing agent is methyldiaminodiphenylmethane.

[0032] As a preferred experimental solution, the fluorocarbon resin curing agent is hexamethylene diisocyanate.

[0033] As a preferred experimental solution, the epoxy resin is E-44.

[0034] E-39, E-44, and E-51 are the specifications of epoxy resin, that is, the corresponding epoxy values ​​are 0.39, 0.44, and 0.51 respectively. Example 2

[0035] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0036] (1) At room temperature, 2.091 g of 4,4'-diaminodiphenyl sulfone and 2.815 g of 2,2-bis(4-aminophenyl)hexafluoropropane were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. Then, 33.75 g of N,N-dimethylformamide was added. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h.

[0037] (2) Cool to 5°C, add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0038] (3) Add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 600 r / min, and react for 1 h;

[0039] (4) Add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 800 r / min, and react for 5 h to obtain a polyamic acid solution;

[0040] (5) At room temperature, 6.72 g of polyamic acid solution, 16.80 g of E-44 epoxy resin, and 0.96 g of methyldiaminodiphenylmethane were added to a 50 mL three-necked flask equipped with a mechanical stirrer under a nitrogen atmosphere. The mixture was stirred at a speed of 500 r / min for 3 h to obtain a uniform light yellow mixed solution.

[0041] (6) placing the mixed solution in a vacuum oven, setting the temperature to 80°C and the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0042] (7) In a 50 mL three-necked flask equipped with a mechanical stirrer and under a nitrogen atmosphere, 10 g of N,N-dimethylformamide and 3.5 g of FEVE type fluorocarbon resin were added in sequence. The stirrer speed was adjusted to 500 r / min, the temperature was kept stable at 50°C, and the mixture was stirred for 1.5 h to obtain a FEVE type fluorocarbon resin solution.

[0043] (8) 5.3 g of polyamic acid / epoxy resin composite modifier and 0.6 g of hexamethylene diisocyanate were added, the rotation speed was adjusted to 600 r / min, the temperature was kept stable at 60 ° C, and the mixture was stirred for 5 h to obtain a modified FEVE type fluorocarbon resin solution. Example 3

[0044] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0045] (1) At room temperature, 2.091 g 4,4'-diaminodiphenyl sulfone (248.30 g) and 2.815 g 2,2-bis(4-aminophenyl)hexafluoropropane (334.26 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. Then, 33.75 g N,N-dimethylformamide was added. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h.

[0046] (2) Cool to 5°C, add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0047] (3) Add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 600 r / min, and react for 1 h;

[0048] (4) Add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 800 r / min, and react for 5 h to obtain a polyamic acid solution;

[0049] (5) At room temperature, 6.72 g of polyamic acid solution, 14.8 g of E-44 epoxy resin, and 0.96 g of methyldiaminodiphenylmethane were added to a 50 mL three-necked flask equipped with a mechanical stirrer under a nitrogen atmosphere. The mixture was stirred at a speed of 500 r / min for 3 h to obtain a uniform light yellow mixed solution.

[0050] (6) placing the mixed solution in a vacuum oven, setting the temperature to 80°C and the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0051] (7) In a 50 mL three-necked flask equipped with a mechanical stirrer and under a nitrogen atmosphere, 10 g of N,N-dimethylformamide and 3.5 g of FEVE type fluorocarbon resin were added in sequence. The stirrer speed was adjusted to 500 r / min, the temperature was kept stable at 50°C, and the mixture was stirred for 1.5 h to obtain a FEVE type fluorocarbon resin solution.

[0052] (8) 3.5 g of polyamic acid / epoxy resin composite modifier and 0.5 g of hexamethylene diisocyanate were added, the rotation speed was adjusted to 600 r / min, the temperature was kept stable at 60 ° C, and the mixture was stirred for 5 h to obtain a modified FEVE type fluorocarbon resin coating. Example 4

[0053] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0054] (1) At room temperature, 2.091 g 4,4'-diaminodiphenyl sulfone (248.30 g) and 2.815 g 2,2-bis(4-aminophenyl)hexafluoropropane (334.26 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. Then, 33.75 g N,N-dimethylformamide was added. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h.

[0055] (2) Cool to 5°C, add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0056] (3) Add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 600 r / min, and react for 1 h;

[0057] (4) Add 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 800 r / min, and react for 5 h to obtain a polyamic acid solution;

[0058] (5) At room temperature, 6.72 g of polyamic acid solution, 16.80 g of E-44 epoxy resin, and 0.96 g of methyldiaminodiphenylmethane were added to a 50 mL three-necked flask equipped with a mechanical stirrer under a nitrogen atmosphere. The mixture was stirred at a speed of 500 r / min for 3 h to obtain a uniform light yellow mixed solution.

[0059] (6) placing the mixed solution in a vacuum oven, setting the temperature to 80°C and the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0060] (7) In a 50 mL three-necked flask equipped with a mechanical stirrer and under a nitrogen atmosphere, 10 g of N,N-dimethylformamide and 3.5 g of FEVE type fluorocarbon resin were added in sequence. The stirrer speed was adjusted to 500 r / min, the temperature was kept stable at 50°C, and the mixture was stirred for 1.5 h to obtain a FEVE type fluorocarbon resin solution.

[0061] (8) 2.7 g of polyamic acid / epoxy resin composite modifier and 0.4 g of hexamethylene diisocyanate were added, the rotation speed was adjusted to 600 r / min, the temperature was kept stable at 60 ° C, and the mixture was stirred for 5 h to obtain a modified FEVE type fluorocarbon resin coating. Example 5

[0062] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0063] (1) At room temperature, 1.316 g 4,4'-diaminodiphenyl sulfone (248.30 g) and 3.542 g 2,2-bis(4-aminophenyl)hexafluoropropane (334.26 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. Then, 33.75 g N,N-dimethylformamide was added. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h.

[0064] (2) Cool to 5°C, add 1.601 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0065] (3) Add 1.601 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0066] (4) Add 1.600 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0067] (5) At room temperature, 6.72 g of polyamic acid solution, 16.80 g of E-44 epoxy resin, and 0.96 g of methyldiaminodiphenylmethane were added to a 50 mL three-necked flask equipped with a mechanical stirrer under a nitrogen atmosphere. The mixture was stirred at a speed of 500 r / min for 3 h to obtain a uniform light yellow mixed solution.

[0068] (6) placing the mixed solution in a vacuum oven, setting the temperature to 80°C and the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0069] (7) In a 50 mL three-necked flask equipped with a mechanical stirrer and under a nitrogen atmosphere, 20 g of N,N-dimethylformamide and 3.5 g of FEVE type fluorocarbon resin were added in sequence. The stirrer speed was adjusted to 500 r / min, the temperature was kept stable at 50°C, and the mixture was stirred for 1.5 h to obtain a FEVE type fluorocarbon resin solution.

[0070] (8) 5.3 g of polyamic acid / epoxy resin composite modifier and 0.6 g of hexamethylene diisocyanate were added, the rotation speed was adjusted to 600 r / min, the temperature was kept stable at 60 ° C, and the mixture was stirred for 5 h to obtain a modified FEVE type fluorocarbon resin coating. Example 6

[0071] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0072] (1) At room temperature, 1.316 g 4,4'-diaminodiphenyl sulfone (248.30 g) and 3.542 g 2,2-bis(4-aminophenyl)hexafluoropropane (334.26 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. Then, 33.75 g N,N-dimethylformamide was added. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h.

[0073] (2) Cool to 5°C, add 1.601 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0074] (3) Add 1.601 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0075] (4) Add 1.600 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0076] (5) At room temperature, 6.72 g of polyamic acid solution, 16.80 g of E-44 epoxy resin, and 0.96 g of methyldiaminodiphenylmethane were added to a 50 mL three-necked flask equipped with a mechanical stirrer under a nitrogen atmosphere. The mixture was stirred at a speed of 500 r / min for 3 h to obtain a uniform light yellow mixed solution.

[0077] (6) placing the mixed solution in a vacuum oven, setting the temperature to 80°C and the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0078] (7) In a 50 mL three-necked flask equipped with a mechanical stirrer and under a nitrogen atmosphere, 20 g of N,N-dimethylformamide and 3.5 g of FEVE type fluorocarbon resin were added in sequence. The stirrer speed was adjusted to 500 r / min, the temperature was kept stable at 50°C, and the mixture was stirred for 1.5 h to obtain a FEVE type fluorocarbon resin solution.

[0079] (8) 3.5 g of polyamic acid / epoxy resin composite modifier and 0.6 g of hexamethylene diisocyanate were added, the rotation speed was adjusted to 600 r / min, the temperature was kept stable at 60 ° C, and the mixture was stirred for 5 h to obtain a modified FEVE type fluorocarbon resin coating. Example 7

[0080] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps:

[0081] (1) At room temperature, 1.316 g 4,4'-diaminodiphenyl sulfone (248.30 g) and 3.542 g 2,2-bis(4-aminophenyl)hexafluoropropane (334.26 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. Then, 33.75 g N,N-dimethylformamide was added. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h.

[0082] (2) Cool to 5°C, add 1.601 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0083] (3) Add 1.601 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0084] (4) Add 1.600 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.530 g of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, and 10 g of N,N-dimethylformamide, stir at 500 r / min, and react for 1 h;

[0085] (5) At room temperature, 6.72 g of polyamic acid solution, 16.80 g of E-44 epoxy resin, and 0.96 g of methyldiaminodiphenylmethane were added to a 50 mL three-necked flask equipped with a mechanical stirrer under a nitrogen atmosphere. The mixture was stirred at a speed of 500 r / min for 3 h to obtain a uniform light yellow mixed solution.

[0086] (6) placing the mixed solution in a vacuum oven, setting the temperature to 80°C and the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid / epoxy resin composite modifier;

[0087] (7) In a 50 mL three-necked flask equipped with a mechanical stirrer and under a nitrogen atmosphere, 20 g of N,N-dimethylformamide and 3.5 g of FEVE type fluorocarbon resin were added in sequence. The stirrer speed was adjusted to 500 r / min, the temperature was kept stable at 50°C, and the mixture was stirred for 1.5 h to obtain a FEVE type fluorocarbon resin solution.

[0088] (8) 2.7 g of polyamic acid / epoxy resin composite modifier and 0.6 g of hexamethylene diisocyanate were added, the rotation speed was adjusted to 600 r / min, the temperature was kept stable at 60 ° C, and the mixture was stirred for 5 h to obtain a modified FEVE type fluorocarbon resin coating.

[0089] The properties of the fluorocarbon resins prepared in the above examples are shown in Table 1. The peel strength, cross-hatch test, circle-scratch test, impact resistance, and salt spray test were obtained by testing a film formed on an aluminum plate using a certain amount of fluorocarbon resin solution. The 5% weight loss temperature was obtained by testing a film sample formed on a glass plate using a certain amount of fluorocarbon resin solution and then demolded.

[0090] The test method is as follows:

[0091] Peel strength test: sample width 25 mm, peel speed set to 50 mm / min.

[0092] Adhesion test: According to GB / T 9286-1998 "Testing Adhesion Strength of Paint Film by Cross-cut Test Method", a cross-cut test method is used. A 10×10 grid is scratched with a specified knife with a grid spacing of 1mm. 3M tape is pressed on the grid and then removed. The coating is graded according to the degree of coating shedding.

[0093] Hardness test: According to GB / T 6739-2006 "Pencil method for measuring paint film hardness", the maximum pencil hardness that does not scratch the coating with a scratch of 3mm is the hardness of the coating.

[0094] Impact resistance test: According to GB / T 1732-93 "Determination of impact resistance of paint films", place the coated side upwards, adjust the height of the weight, and let it fall freely. Observe whether there are cracks or wrinkles around the pit where the weight falls.

[0095] Thermogravimetric analysis: nitrogen flow rate 40 mL / min, test temperature range 25-800 °C, heating rate 20 °C / min.

[0096] Salt spray test: in accordance with GB1771-91 "Determination of resistance of paints and varnishes to neutral salt spray", the sample is not scratched, the test room temperature is 50°C, the saturated barrel temperature is 65°C, the constant temperature timing is 2 minutes, the spray time is 6 minutes; 24 hours is one test cycle.

[0097] Table 1: Performance test table of Examples 1-6

[0098] name Peel strength (N / cm) Cross-cutting experiment hardness Impact resistance (cm) 5% weight loss temperature / ℃ Salt spray test / 72h Example 1 2.2 0 1H 50 281 No cracking or falling off Example 2 2.8 0 1H 50 247 No cracking or falling off Example 3 3.3 0 1H 35 235 No cracking or falling off Example 4 3.5 0 1H 50 271 No cracking or falling off Example 5 3.4 0 1H 50 270 No cracking or falling off Example 6 3.7 0 1H 50 269 No cracking or falling off

[0099] As can be seen from the above table, the fluorocarbon resin modified by polyimide and epoxy resin not only has good corrosion resistance, but also has a high thermal decomposition temperature, excellent adhesion and impact resistance, and has excellent comprehensive performance.

[0100] The above embodiments are only for illustrating the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, characterized in that: The steps include: Step (1): Under room temperature, 10 to 15 parts by weight of a monomer diamine and a monomer dianhydride are weighed respectively, and the monomer diamine and the monomer dianhydride are placed in a forced air drying oven at 80°C and 150°C for 6 hours respectively to obtain prefabricated monomer diamine and monomer dianhydride, and the prefabricated monomer diamine and monomer dianhydride are sealed and placed in a desiccator for storage; 20 parts of N,N-dimethylacetamide are treated with 4Å molecular sieves and sealed for storage; Step (2): 0.4-0.8 parts of monomer diamine and 2.5-5 parts of N,N-dimethylacetamide prepared in step (1) are added to a three-necked flask, mechanically stirred for 0.5h, after the solid is completely dissolved, cooled to 0-10°C in an ice-water bath, 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide are added, and the interval time is 0.5-1h, and 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide are added again, and the above operation is repeated for a total of three times of adding 0.1-0.2 parts of monomer dianhydride and 0.5-1 parts of N,N-dimethylacetamide, during which the ice-water bath temperature is kept at 0-10°C, and then the reaction is continued for 6-12h under stirring, and the resulting homogeneous viscous liquid is polyamic acid; Step (3): Add the polyamic acid obtained in step (2), 0.2 to 0.5 parts of epoxy curing agent, and 10 to 20 parts of epoxy resin into a beaker, and mechanically stir in a water bath at 60 to 90° C. for 2 to 4 hours to obtain a uniform light yellow mixed solution. Then, place the mixed solution in a vacuum oven, set the temperature to 90° C., the vacuum degree to -0.1 MPa, and pre-cure for 3 hours to obtain a polyamic acid / epoxy resin composite modifier; Step (4): 15 to 25 parts of fluorocarbon resin and 55.5 to 61 parts of N,N-dimethylacetamide are added to a three-necked flask and stirred at 50°C for 2 to 3 hours. Subsequently, the polyamic acid / epoxy resin composite modifier obtained in step (3) and 1 to 2 parts of fluorocarbon resin curing agent are also added to the three-necked flask. The temperature is controlled at 60 to 80°C and stirred for 3 to 6 hours to obtain a modified fluorocarbon resin coating.

2. The method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 1, characterized in that: The mass ratio of the polyamic acid to the epoxy resin is 1:2 to 1:3, the mass ratio of the fluorocarbon resin to the epoxy resin is 1:1 to 2:1, the mass ratio of the epoxy curing agent to the epoxy resin is 1:20 to 1:25, and the mass ratio of the fluorocarbon resin curing agent to the fluorocarbon resin is 1:10 to 1:

15.

3. The method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 2, characterized in that: The N,N-dimethylacetamide is an organic solvent and can be replaced by N-methylpyrrolidone or N,N-dimethylformamide. The solid mass content of the polyamic acid is 10-15%, and the solid content of the fluorocarbon resin is 15%-25%.

4. The method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 2 or 3, characterized in that: The monomer diamine is one or more of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-(hexafluoroisopropyl)bis(p-phenyloxy)diphenylamine, and 2,2-bis(4-aminophenyl)hexafluoropropane; the monomer dianhydride is one or more of 4,4'-(hexafluoroisopropylene)diphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

5. The method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 4, characterized in that: The molar ratio of the monomeric diamine to the monomeric dianhydride is 1:1.

02.

6. The method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 2, characterized in that: The epoxy curing agent is one of N-methylimidazole, 4,4'-diaminodiphenyl sulfone and 2,4,6-tris(dimethylaminomethyl)phenol.

7. The method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 2 or 3, characterized in that: The fluorocarbon resin curing agent is one of hexamethylene diisocyanate, toluene diisocyanate and isophorone diisocyanate.

8. The method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 2, characterized in that: The epoxy resin is at least one of E-39, E-44, and E-51.