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, and the polyimide and epoxy resin composite modified fluorocarbon resin coating comprises the following components in percentage by weight: 0.4-0.8% of monomer diamine, 0.4-0.8% of monomer dianhydride, 60-70% of N, N-dimethylacetamide, 10-20% of epoxy resin, 0.2-0.5% of epoxy curing agent, 1-2% of fluorocarbon resin curing agent and 15-25% of fluorocarbon resin. The preparation method comprises the following specific steps: reacting monomer diamine and dianhydride in N, N-dimethylacetamide, sequentially compounding with epoxy resin and an epoxy curing agent to obtain a composite modifier, and adding the composite modifier and a fluorocarbon resin curing agent into a fluorocarbon resin solution to obtain the polyimide and epoxy resin composite modified fluorocarbon resin coating. Compared with an existing fluorocarbon resin coating, the performance of the fluorocarbon resin coating is greatly improved in the aspects of mechanical performance, heat resistance, adhesive force and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorocarbon resin synthesis, and specifically 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 bond in its molecular structure gives it excellent chemical stability and heat resistance. Compared with traditional coatings, it has extremely high durability, weather resistance, corrosion resistance, high temperature resistance, etc. It can maintain 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 high, and its processing technology is complicated, which limits its wide application in certain fields. In addition, compared with some metals or other high-performance polymers, the thermal performance of fluorocarbon resin still needs to be improved.

[0003] Epoxy resin has excellent physical and mechanical properties, and its coating has excellent adhesion to polar substrates such as metal (steel, aluminum, etc.), ceramics, glass, concrete and wood. It has excellent chemical resistance and electrical insulation properties, and is available in a variety of varieties at a low price. Polyimide has very high heat resistance, excellent mechanical properties, and is highly tolerant to a variety of chemicals (such as acids, alkalis and organic solvents). Therefore, using polyamic acid-modified epoxy resin to modify FEVE-type fluororesin is expected to improve the thermal and mechanical properties of FEVE, while solving the cost defects and improving the comprehensive performance of FEVE-type fluororesin. 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, a fluorocarbon resin coating with excellent performance is obtained, and the cost is reduced.

[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: Step (1): Under room temperature, weigh 10 to 15 parts by weight of a monomer diamine and a monomer dianhydride, respectively, and place the monomer diamine and the monomer dianhydride 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 seal and place them in a desiccator for storage; treat 20 parts of N,N-dimethylacetamide with a 4Å molecular sieve, and seal and store them for use; 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, 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 and 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; Step (3): adding the polyamic acid obtained in step (2), 0.2-0.5 parts of epoxy curing agent and 10-20 parts of epoxy resin into a beaker, and mechanically stirring for 2-4 hours in a water bath at 60-90° C. to obtain a uniform light yellow mixed solution, and then placing the mixed solution into a vacuum oven, setting the temperature to 90° C., the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid and 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 and 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.

[0006] The technical solution further defined in the present invention is: 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.

[0007] Furthermore, N,N-dimethylacetamide is an organic solvent, which can be replaced by one of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide. The solid mass content of polyamic acid is 10-15%, and the solid content of fluorocarbon resin is 15%-25%.

[0008] 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 anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic acid, and 3,3',4,4'-benzophenonetetracarboxylic anhydride.

[0009] Furthermore, the molar ratio of the monomeric diamine to the monomeric dianhydride is 1:1.02.

[0010] Furthermore, the epoxy curing agent is one of N-methylimidazole, 4,4'-diaminodiphenyl sulfone and 2,4,6-tris(dimethylaminomethyl)phenol.

[0011] Furthermore, the fluorocarbon resin curing agent is one of hexamethylene diisocyanate, toluene diisocyanate and isophorone diisocyanate.

[0012] Furthermore, the epoxy resin is at least one of E-39, E-44 and E-51, and the mass fraction of the epoxy resin is 10 to 20%.

[0013] Furthermore, the mass fraction of the fluorocarbon resin is 15 to 25%.

[0014] The beneficial effects of the present invention are: Fluorocarbon resin is mainly composed of fluorine-containing polymers. The stable carbon-fluorine bond in its molecular structure gives it excellent chemical stability and heat resistance. Compared with traditional coatings, it has extremely high durability, weather resistance, corrosion resistance, high temperature resistance, etc. It can maintain color and gloss for a long time under extreme climatic conditions, and is not prone to fading, powdering and aging. Epoxy resin has excellent physical and mechanical properties. Its coating has excellent adhesion to polar substrates such as metal (steel, aluminum, etc.), ceramics, glass, concrete and wood. It has excellent chemical resistance and electrical insulation properties. It has a variety of varieties and is cheap and easy to obtain. Polyimide has very high heat resistance, excellent mechanical properties, and is also highly tolerant to a variety of chemicals (such as acids, alkalis and organic solvents). Therefore, using polyamic acid-modified epoxy resin to modify FEVE-type fluororesin is expected to improve the thermal and mechanical properties of FEVE, while solving the cost defects and improving the comprehensive performance of FEVE-type fluororesin.

[0015] The surface tension between the interfaces of the various components of the fluorocarbon resin coating prepared by the present invention is low, so that they can be better mutually soluble to form a stable solution system; the fluorocarbon resin coating provided by the present invention does not produce free low surface energy substances during use, and the coating formed by applying the fluorocarbon resin on the surface of the painted workpiece can, on the one hand, isolate the painted workpiece from the spray painting environment, making the painted workpiece easy to clean and reducing the cleaning cost; on the other hand, it does not affect the spray painting effect and avoids the appearance of shrinkage holes on the surface of the paint film. The fluorocarbon resin coating of the present invention has excellent aging resistance and comprehensive performance of the paint film, excellent performance in various aspects, and uses a small amount of fluorine-containing monomers, and has a low cost. DETAILED DESCRIPTION

[0016] 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.

[0017] This embodiment provides a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps: Step (1): Under room temperature, weigh 10 to 15 parts by weight of a monomer diamine and a monomer dianhydride, respectively, and place the monomer diamine and the monomer dianhydride 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 seal and place them in a desiccator for storage; treat 20 parts of N,N-dimethylacetamide with a 4Å molecular sieve, and seal and store them for use; 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, 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 and 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; Step (3): adding the polyamic acid obtained in step (2), 0.2-0.5 parts of epoxy curing agent and 10-20 parts of epoxy resin into a beaker, and mechanically stirring for 2-4 hours in a water bath at 60-90° C. to obtain a uniform light yellow mixed solution, and then placing the mixed solution into a vacuum oven, setting the temperature to 90° C., the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid and 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 and 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.

[0018] 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 epoxy curing agent to epoxy resin is 1:20, and the mass ratio of fluorocarbon resin curing agent to fluorocarbon resin is 1:15.

[0019] 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%.

[0020] As a preferred experimental scheme, the monomer diamine is 4,4'-diaminodiphenyl sulfone and 2,2-bis(4-aminophenyl)hexafluoropropane, and the monomer dianhydride is 4,4'-(hexafluoroisopropylene) diphthalic anhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0021] The molar ratio of the monomeric diamine to the monomeric dianhydride is 1:1.02.

[0022] As a preferred experimental scheme, the epoxy resin curing agent is methyldiaminodiphenylmethane.

[0023] As a preferred experimental scheme, the fluorocarbon resin curing agent is hexamethylene diisocyanate.

[0024] As a preferred experimental scheme, the epoxy resin is E-44, and the mass fraction of the epoxy resin is 10 to 20%.

[0025] As a preferred experimental scheme, the mass fraction of fluorocarbon resin is 15-25%.

[0026] 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

[0027] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps: (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 a nitrogen atmosphere, and 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. (2) Cooling to 5°C, adding 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, stirring at a speed of 500 r / min, and reacting for 1 h; (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; (4) adding 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic anhydride, and 10 g of N,N-dimethylformamide, stirring at a speed of 800 r / min, and reacting for 5 h to obtain a polyamic acid solution; (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 in sequence, with a stirring speed of 500 r / min and stirring for 3 h to obtain a uniform light yellow mixed solution; (6) placing the mixed solution in a vacuum oven, setting the temperature to 80° C., the vacuum degree to −0.1 MPa, and pre-curing for 3 h to obtain a polyamic acid and epoxy resin composite modifier; (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; (8) 5.3 g of polyamic acid and 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

[0028] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps: (1) At room temperature, 2.091 g 4,4'-diaminodiphenyl sulfone 248.30, 2.815 g 2,2-bis(4-aminophenyl)hexafluoropropane 334.26, and then 33.75 g N,N-dimethylformamide were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice water bath and stirred for 1 h. (2) Cooling to 5°C, adding 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, stirring at a speed of 500 r / min, and reacting for 1 h; (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; (4) adding 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic anhydride, and 10 g of N,N-dimethylformamide, stirring at a speed of 800 r / min, and reacting for 5 h to obtain a polyamic acid solution; (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 in sequence, with a stirring speed of 500 r / min and stirring for 3 h to obtain a uniform light yellow mixed solution; (6) placing the mixed solution in a vacuum oven, setting the temperature to 80° C., the vacuum degree to −0.1 MPa, and pre-curing for 3 h to obtain a polyamic acid and epoxy resin composite modifier; (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; (8) 3.5 g of polyamic acid and 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

[0029] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps: (1) At room temperature, 2.091 g 4,4'-diaminodiphenyl sulfone 248.30, 2.815 g 2,2-bis(4-aminophenyl)hexafluoropropane 334.26, and then 33.75 g N,N-dimethylformamide were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice water bath and stirred for 1 h. (2) Cooling to 5°C, adding 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, stirring at a speed of 500 r / min, and reacting for 1 h; (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; (4) adding 1.272 g of 4,4′-(hexafluoroisopropylene) diphthalic anhydride, 0.823 g of 3,3′,4,4′-biphenyltetracarboxylic anhydride, and 10 g of N,N-dimethylformamide, stirring at a speed of 800 r / min, and reacting for 5 h to obtain a polyamic acid solution; (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 in sequence, with a stirring speed of 500 r / min and stirring for 3 h to obtain a uniform light yellow mixed solution; (6) placing the mixed solution in a vacuum oven, setting the temperature to 80° C., the vacuum degree to −0.1 MPa, and pre-curing for 3 h to obtain a polyamic acid and epoxy resin composite modifier; (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; (8) 2.7 g of polyamic acid and 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

[0030] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps: (1) At room temperature, 1.316 g 4,4'-diaminodiphenyl sulfone 248.30, 3.542 g 2,2-bis(4-aminophenyl)hexafluoropropane 334.26, and then 33.75 g N,N-dimethylformamide were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h. (2) Cooling to 5°C, adding 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, stirring at a speed of 500 r / min, and reacting for 1 h; (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 a speed of 500 r / min, and react for 1 h; (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 a speed of 500 r / min, and react for 1 h; (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 in sequence, with a stirring speed of 500 r / min and stirring for 3 h to obtain a uniform light yellow mixed solution; (6) placing the mixed solution in a vacuum oven, setting the temperature to 80° C., the vacuum degree to −0.1 MPa, and pre-curing for 3 h to obtain a polyamic acid and epoxy resin composite modifier; (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; (8) 5.3 g of polyamic acid and 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

[0031] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps: (1) At room temperature, 1.316 g 4,4'-diaminodiphenyl sulfone 248.30, 3.542 g 2,2-bis(4-aminophenyl)hexafluoropropane 334.26, and then 33.75 g N,N-dimethylformamide were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h. (2) Cooling to 5°C, adding 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, stirring at a speed of 500 r / min, and reacting for 1 h; (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 a speed of 500 r / min, and react for 1 h; (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 a speed of 500 r / min, and react for 1 h; (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 in sequence, with a stirring speed of 500 r / min and stirring for 3 h to obtain a uniform light yellow mixed solution; (6) placing the mixed solution in a vacuum oven, setting the temperature to 80° C., the vacuum degree to −0.1 MPa, and pre-curing for 3 h to obtain a polyamic acid and epoxy resin composite modifier; (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; (8) 3.5 g of polyamic acid and 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

[0032] This embodiment discloses a method for preparing a polyimide and epoxy resin composite modified fluorocarbon resin coating, comprising the following steps: (1) At room temperature, 1.316 g 4,4'-diaminodiphenyl sulfone 248.30, 3.542 g 2,2-bis(4-aminophenyl)hexafluoropropane 334.26, and then 33.75 g N,N-dimethylformamide were added to a 100 mL three-necked flask equipped with a mechanical stirrer under nitrogen atmosphere. The stirring speed was 300 r / min. After 20 min, the mixture was cooled in an ice-water bath and stirred for 1 h. (2) Cooling to 5°C, adding 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, stirring at a speed of 500 r / min, and reacting for 1 h; (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 a speed of 500 r / min, and react for 1 h; (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 a speed of 500 r / min, and react for 1 h; (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 in sequence, with a stirring speed of 500 r / min and stirring for 3 h to obtain a uniform light yellow mixed solution; (6) placing the mixed solution in a vacuum oven, setting the temperature to 80° C., the vacuum degree to −0.1 MPa, and pre-curing for 3 h to obtain a polyamic acid and epoxy resin composite modifier; (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; (8) 2.7 g of polyamic acid and 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.

[0033] The properties of the fluorocarbon resins obtained in the above embodiments are shown in the following table. The peel strength, cross-hatch test, circle-scratch test, impact resistance and salt spray test are obtained by taking a certain amount of fluorocarbon resin solution and forming a film on an aluminum plate, and the 5% weight loss temperature is obtained by taking a certain amount of fluorocarbon resin solution and forming a film on a glass plate and demolding to obtain a film sample. The test method is as follows: Peel strength test: sample width 25 mm, peel speed set to 50 mm / min.

[0034] Adhesion test: According to GB / T 9286-1998 "Testing adhesion strength of paint film by cross-cut test method", the cross-cut test method is adopted, and a 10×10 grid is cut out with a specified knife, and the grid spacing is 1mm. 3M tape is pressed on the grid and torn off, and the coating is graded according to the degree of coating shedding.

[0035] Hardness test: According to GB / T 6739-2006 "Pencil method for measuring paint film hardness", the maximum pencil hardness that will not scratch the coating with a scratch of 3mm is the hardness of the coating.

[0036] Impact resistance test: According to GB / T 1732-93 "Determination of impact resistance of paint film", place the coated side upwards, adjust the height of the heavy hammer, let it fall freely, and observe whether there are cracks or wrinkles around the pit where the heavy hammer falls.

[0037] Thermogravimetric analysis: nitrogen flow rate 40 mL / min, test temperature range 25 ~ 800 ° C, heating rate 20 ° C / min.

[0038] Salt spray test: According to GB1771-91 "Determination of neutral salt spray resistance of paints and varnishes", the sample is not scratched, the test room temperature is 50°C, the saturated barrel temperature is 65°C, the constant temperature timing is 2min, and the spray time is 6min. 24h is a test cycle.

[0039] Table 1: Performance test table of Examples 1-6 name Peel strength (N / cm) Cross-cut test 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 It can be seen from the above table that the fluorocarbon resin modified by polyimide and epoxy resin has good corrosion resistance, high thermal decomposition temperature, excellent adhesion and impact resistance, and has excellent comprehensive performance.

[0040] 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, weigh 10 to 15 parts by weight of a monomer diamine and a monomer dianhydride, respectively, and place the monomer diamine and the monomer dianhydride 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 seal and place them in a desiccator for storage; treat 20 parts of N,N-dimethylacetamide with a 4Å molecular sieve, and seal and store them for use; 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, 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 and 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; Step (3): adding the polyamic acid obtained in step (2), 0.2-0.5 parts of epoxy curing agent, and 10-20 parts of epoxy resin into a beaker, and mechanically stirring for 2-4 hours in a water bath at 60-90° C. to obtain a uniform light yellow mixed solution, and then placing the mixed solution into a vacuum oven, setting the temperature to 90° C., the vacuum degree to -0.1 MPa, and pre-curing for 3 hours to obtain a polyamic acid and 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 and 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 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 1:2-1:3, the mass ratio of the fluorocarbon resin to the epoxy resin is 1:1-2:1, the mass ratio of the epoxy curing agent to the epoxy resin is 1:20-1:25, and the mass ratio of the fluorocarbon resin curing agent to the fluorocarbon resin is 1:10-1:

15.

3. The 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 one of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide. The solid mass content of the polyamic acid is 10-15%, and the solid content of the fluorocarbon resin is 15%-25%.

4. The 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 anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic acid, and 3,3',4,4'-benzophenonetetracarboxylic anhydride.

5. The 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 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 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 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, and the mass fraction of the epoxy resin is 10 to 20%.

9. The polyimide and epoxy resin composite modified fluorocarbon resin coating according to claim 2, characterized in that: The mass proportion of the fluorocarbon resin is 15-25%.