A fusible polytetrafluoroethylene coating material, a method for producing the same, and a coated workpiece

Abstract

The present application provides a fusible polytetrafluoroethylene coating, a coated film workpiece and a preparation method thereof, the fusible polytetrafluoroethylene coating comprises an amide group terminated fusible polytetrafluoroethylene compound, the amide group terminated fusible polytetrafluoroethylene compound comprises one or more of the compounds shown in structural formula 1, structural formula 2 and structural formula 3, wherein R F is an aliphatic substituent of C6-C19 or an aromatic substituent of C6-C19 for the prepared fusible polytetrafluoroethylene. The fusible polytetrafluoroethylene coating provided by the present application improves the stability, mechanical properties, weather resistance, solvent resistance and service life of the coating.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to fusible polytetrafluoroethylene coatings and their preparation methods, as well as coated workpieces. Background Technology

[0002] In fluoropolymer materials, tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ethers (PAVE) are produced through free radical copolymerization technology to produce products with excellent heat resistance, solvent resistance, and high purity, and are therefore widely used in chemical, electronic, medical and other fields.

[0003] In the aforementioned application areas, especially when used as a high-performance coating material, PFA can generate unstable groups such as -COF and -COOH under certain conditions due to the initiator used, chain transfer during polymerization, and β-fracture occurring in PAVE. During use, this can cause continuous molecular chain breakage, and the generation of HF and other substances can exacerbate the molecular chain breakage, resulting in a decrease in the mechanical properties and corrosion resistance of the coating film, and a reduction in the product's service life. Summary of the Invention

[0004] To address the problem of unstable end groups in fusible polytetrafluoroethylene (PTFE) causing a decline in coating performance in existing technologies, this invention provides a fusible PTFE coating, its preparation method, and the coated workpiece.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] This invention provides a fusible polytetrafluoroethylene (PTFE) coating, characterized in that it comprises an amide-terminated fusible PTFE compound, wherein the amide-terminated fusible PTFE compound comprises one or more compounds shown in structural formulas 1, 2, and 3.

[0007]

[0008] Among them, R F For the preparation of fusible polytetrafluoroethylene, R is selected from aliphatic substituents or aromatic substituents of C6-C19.

[0009] The fusible polytetrafluoroethylene (PTFE) coating provided by this invention comprises an amide-terminated PTFE compound including at least one compound shown in structural formula 1, structural formula 2, or structural formula 3. The compound shown in structural formula 1 is a grafted PTFE, while the compounds shown in structural formulas 2 and 3 are products of micro-crosslinking of PTFE with isocyanate. By combining the compound shown in structural formula 1, structural formula 2, or structural formula 3 in the fusible PTFE coating with a plastic coating, graft modification or the generation of a micronetwork structure is achieved, enhancing adhesion to the primer or substrate and maximizing the retention of the mechanical properties, solvent resistance, high and low temperature resistance, and service life advantages of PTFE.

[0010] Optionally, R is an aliphatic or aromatic substituent of C6-C19 linked to the isocyanate group in the isocyanate compound, wherein the aliphatic or aromatic substituent of C6-C19 is selected from one or more of dicyclohexylmethane, methylcyclohexyl, methylene-3,5,5-trimethylcyclohexyl, hexamethylene, trimethylhexamethylene, m-phenylenedimethyl, toluene, and diphenylmethane.

[0011] Optionally, the fusible polytetrafluoroethylene coating further includes a first dispersant, which is a mixture of an emulsifier and / or a perfluorinated anionic surfactant.

[0012] On the other hand, the present invention also provides a method for preparing the meltable polytetrafluoroethylene coating as described in any one of the above claims, comprising the following steps:

[0013] Obtain a fusible polytetrafluoroethylene resin R containing carboxyl groups. f COOH;

[0014] An end-capping compound containing at least one isocyanate functional group is added to the fusible polytetrafluoroethylene resin to obtain an anhydride compound. The anhydride compound is then heated to obtain an amide-terminated fusible polytetrafluoroethylene compound.

[0015] Optionally, obtain a fusible polytetrafluoroethylene resin R containing carboxyl groups. f The COOH step includes: adding a solvent, a second dispersant, a chain transfer agent, and the perfluoroalkyl vinyl ether to a reaction vessel to obtain a mixed solution;

[0016] The mixture is heated to the reaction temperature, and tetrafluoroethylene is introduced into the mixed solution to the reaction pressure. Then, an initiator is added to the mixed solution to carry out the reaction.

[0017] Tetrafluoroethylene and an initiator are added to the mixed solution, and the pressure of the reaction vessel is maintained within the reaction pressure range until the reaction is completed, to obtain a fusible polytetrafluoroethylene emulsion with -COF.

[0018] A hydrolysis reaction is carried out by adding water to a fusible polytetrafluoroethylene emulsion containing -COF groups to obtain a fusible polytetrafluoroethylene resin R containing carboxyl groups. f COOH.

[0019] Optionally, the solvent includes one or more of 1,3-bis(trifluoromethyl)benzene, trifluoromethylbenzene, hydrofluoroether, ethyl perfluorobutyl ether, methyl perfluorobutyl ether, ethyl nonafluorobutyl ether, and fluorinated hydrocarbons.

[0020] The fluorinated hydrocarbon includes one or more of perfluorocarbons, perfluoroamines, and perfluoromorpholines; the perfluorocarbon includes one or more of perfluorocyclobutane, perfluoromethylcyclobutane, and perfluorocyclohexane; the perfluoroamine includes perfluorotributylamine; and the perfluoromorpholine includes at least one of perfluoro-N-methylmorpholine and perfluoro-N-isopropylmorpholine.

[0021] The second dispersant includes one or more of perfluoropolyether carboxylic acid or its salt, perfluoropolyether ammonium formate, and perfluoropolyether formate;

[0022] The chain transfer agent includes one or more of methane, ethane, propane, cyclohexane, and hydrogen.

[0023] Optionally, the amount of water added in the hydrolysis reaction is 0.001%-5% of the molar amount of perfluoroalkyl vinyl ether added; the content of isocyanate functional groups in the added end-capping compound is 1.05-1.2 times the molar amount of water added in the hydrolysis reaction.

[0024] Optionally, the capping compound includes one or more of dicyclohexylmethane diisocyanate, methylcyclohexyl diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophenyl dimethyl isocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and polyphenyl polymethylene polyisocyanate.

[0025] On the other hand, the present invention also provides a coated workpiece, comprising a substrate, a primer layer and a fluoropolymer layer, wherein the primer layer is disposed on the surface of the substrate and the fluoropolymer layer is disposed on the side of the primer layer facing away from the substrate; the fluoropolymer layer is formed by coating with a fusible polytetrafluoroethylene coating as described in any one of the preceding claims, or the fluoropolymer layer is formed by coating with a fusible polytetrafluoroethylene coating prepared by the method for preparing fusible polytetrafluoroethylene coating as described in any one of the preceding claims.

[0026] Optionally, the primer layer is formed by coating with a plastic resin, which includes one or more of polyacrylic resin coatings, polyurethane coatings, polyamide coatings, polyimide coatings, and polyether coatings.

[0027] The method for preparing fusible polytetrafluoroethylene coatings provided by the present invention involves end-capping modification of fusible polytetrafluoroethylene resin containing carboxyl groups with isocyanate-containing end-capping compounds to obtain grafted or micro-crosslinked products. This results in fusible polytetrafluoroethylene coatings with advantages such as high and low temperature resistance, solvent resistance, good mechanical properties, long service life, anti-yellowing, anti-aging, anti-salt spray, and low ion content. Attached Figure Description

[0028] Figure 1 The infrared spectrum of the amide-terminated polytetrafluoroethylene compound in Example 1 is shown. Detailed Implementation

[0029] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] This invention provides a fusible polytetrafluoroethylene (PTFE) coating comprising an amide-terminated fusible PTFE compound, wherein the amide-terminated fusible PTFE compound comprises one or more compounds represented by structural formulas 1, 2, and 3.

[0031]

[0032] Among them, R F For the preparation of fusible polytetrafluoroethylene, R is selected from aliphatic substituents or aromatic substituents of C6-C19.

[0033] In this embodiment, the amide-terminated fusible polytetrafluoroethylene (PTFE) compound includes at least one of the compounds shown in structural formulas 1, 2, and 3. The compound shown in structural formula 1 is a grafted fusible PTFE, while the compounds shown in structural formulas 2 and 3 are products of micro-crosslinking of fusible PTFE with isocyanate. By combining the compound shown in structural formula 1, 2, or 3 in the fusible PTFE coating with the plastic coating, graft modification or the generation of a micronetwork structure is achieved, enhancing adhesion to the primer or substrate and maximizing the retention of the mechanical properties, solvent resistance, high and low temperature resistance, and service life advantages of fusible PTFE.

[0034] In some embodiments, R is an aliphatic or aromatic substituent of C6-C19 in the isocyanate compound that is attached to the isocyanate group, wherein the aliphatic or aromatic substituent of C6-C19 is selected from one or more of dicyclohexylmethane, methylcyclohexyl, methylene-3,5,5-trimethylcyclohexyl, hexamethylene, trimethylhexamethylene, m-phenylenedimethyl, toluene, and diphenylmethane.

[0035] In some embodiments, the fusible polytetrafluoroethylene coating further includes a first dispersant, which is a mixture of an emulsifier and / or a perfluorinated anionic surfactant. Specifically, the first dispersant is selected from OP series, Span series, and Tween series emulsifiers and / or mixtures of perfluorinated anionic surfactants.

[0036] On the other hand, one embodiment of the present invention also provides a method for preparing the meltable polytetrafluoroethylene coating as described in any of the above claims, comprising the following steps:

[0037] Obtain a fusible polytetrafluoroethylene resin R containing carboxyl groups. f COOH;

[0038] An end-capping compound containing at least one isocyanate functional group is added to the fusible polytetrafluoroethylene resin to obtain an anhydride compound. The anhydride compound is then heated to obtain an amide-terminated fusible polytetrafluoroethylene compound.

[0039] In this embodiment, a carboxyl-containing fusible polytetrafluoroethylene resin is end-capped and modified by an isocyanate-containing end-capping compound to obtain a grafted or micro-crosslinked product, which gives the fusible polytetrafluoroethylene coating the advantages of high and low temperature resistance, solvent resistance, good mechanical properties, long service life, anti-yellowing, anti-aging, anti-salt spray, and low ion content.

[0040] In one embodiment, when the fusible polytetrafluoroethylene coating is a water-based coating, an aqueous solution containing a first dispersant is added to a solution of the fusible polytetrafluoroethylene compound containing amide-terminated groups, and the solvent in the solution of the polytetrafluoroethylene compound containing amide-terminated groups is subjected to vacuum distillation to obtain a water-based fusible polytetrafluoroethylene coating.

[0041] In one embodiment, the heating temperature of the anhydride compound to obtain the amide-terminated polytetrafluoroethylene compound is 70-90°C.

[0042] In some embodiments, a fusible polytetrafluoroethylene resin R containing carboxyl groups is obtained. f The COOH step includes adding a solvent, a second dispersant, a chain transfer agent, and the perfluoroalkyl vinyl ether (PAVE) into a reaction vessel to obtain a mixed solution.

[0043] The mixture is heated to the reaction temperature, and tetrafluoroethylene is introduced into the mixed solution to the reaction pressure. Then, an initiator is added to the mixed solution to initiate the reaction. Specifically, the reaction temperature is 10–90°C, and the reaction pressure is 0.6–5.0 MPa.

[0044] Tetrafluoroethylene and an initiator are added to the mixed solution, and the pressure in the reaction vessel is maintained within the reaction pressure range until the reaction is completed, yielding a fusible polytetrafluoroethylene emulsion with -COF. Specifically, tetrafluoroethylene, an initiator, and a perfluoroalkyl vinyl ether can also be added to the mixed solution.

[0045] A hydrolysis reaction is carried out by adding water to a fusible polytetrafluoroethylene emulsion containing -COF groups to obtain a fusible polytetrafluoroethylene resin R containing carboxyl groups. f The hydrolysis reaction of COOH can be carried out at 25-30℃, and heating can also increase the reaction rate.

[0046] In some embodiments, the solvent includes one or more of 1,3-bis(trifluoromethyl)benzene, trifluoromethylbenzene, hydrofluoroether, ethyl perfluorobutyl ether, methyl perfluorobutyl ether, ethyl nonafluorobutyl ether, and fluorinated hydrocarbons.

[0047] The fluorinated hydrocarbon includes one or more of perfluorocarbons, perfluoroamines, and perfluoromorpholines. The perfluorocarbon includes one or more of perfluorocyclobutane, perfluoromethylcyclobutane, and perfluorocyclohexane. The perfluoroamine includes perfluorotributylamine. The perfluoromorpholine includes at least one of perfluoro-N-methylmorpholine and perfluoro-N-isopropylmorpholine.

[0048] The second dispersant comprises one or more of perfluoropolyether carboxylic acid or its salt, perfluoropolyether ammonium formate, and perfluoropolyether formate. Specifically, the amount of the second dispersant added is 0.01% to 2% of the solvent mass.

[0049] The chain transfer agent includes one or more of methane, ethane, propane, cyclohexane, and hydrogen.

[0050] In one embodiment, the perfluoroalkyl vinyl ether has the general structural formula CF2=CF(OC) n F 2n+1 ), where n is an integer from 1 to 6.

[0051] In one embodiment, the initiator comprises an organic peroxide initiator selected from benzoyl peroxide, di-tert-butyl peroxide, di-tert-pentyl peroxide, azobisisobutyronitrile, tert-butyl peroxide, dicumyl peroxide, and perfluoroacyl peroxide [R]. f One or more of C(=O)O]2. R fIt is one or more perfluoroalkyl groups with 1 to 6 carbon atoms, such as [F7C3C(=O)O]2.

[0052] In one embodiment, the amount of the initiator is 0.0001% to 0.5% of the solvent mass.

[0053] The total amount of initiator added in multiple additions is 0.00001% to 0.05% of the solvent mass.

[0054] In some embodiments, the number of replenishments is 1-5.

[0055] In some embodiments, after adding tetrafluoroethylene and an initiator, the reaction is carried out for 1-12 hours, preferably 1.5-3 hours, until the reaction ends.

[0056] In some embodiments, the amount of water added in the hydrolysis reaction is 0.001%-5% of the molar amount of perfluoroalkyl vinyl ether added. The amount of the end-capping compound added is 1.05-1.2 times the molar amount of water added in the hydrolysis reaction. Specifically, the water is pure water.

[0057] In some embodiments, the capping compound includes one or more of dicyclohexylmethane diisocyanate (HMDI), methylcyclohexylmethane diisocyanate (HTDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMDI), isophenyl dimethyl isocyanate (XDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and polyphenyl polymethylene polyisocyanate (PAPI).

[0058] Preferably, the capping compound is selected from bifunctional aliphatic isocyanates.

[0059] On the other hand, one embodiment of the present invention also provides a coated workpiece, including a substrate, a primer layer, and a fluoropolymer layer. The primer layer is disposed on the surface of the substrate, and the fluoropolymer layer is disposed on the side of the primer layer facing away from the substrate. The fluoropolymer layer is formed by coating with a fusible polytetrafluoroethylene coating as described in any one of the preceding claims, or by coating with a fusible polytetrafluoroethylene coating prepared by the method described in any one of the preceding claims.

[0060] In some embodiments, the primer layer is formed by coating with a plastic resin, which includes one or more of polyacrylic resin coatings, polyurethane coatings, polyamide coatings, polyimide coatings, and polyether coatings. It should be noted that the plastic resin can also be other coatings that provide polar groups for bonding with the fluoropolymer layer.

[0061] In this embodiment, an organic fluorine peroxide is used as an initiator to initiate a copolymerization reaction of TFE-PAVE in a fluorocarbon solvent, resulting in a fusible polytetrafluoroethylene solution with trace amounts of unstable -COF end groups. Because the perfluorinated organic peroxide initiator and gaseous chain transfer agent used do not produce unstable groups such as -CF2CF2OH, -CF2CF2COOH, -CONH2, -CH2OH, and CF2H, trace amounts of water are used to convert the -COF generated by β-chain transfer in PAVE into -COOH. Then, isocyanate is used for end-capping modification to obtain a grafted or micro-crosslinked product. When this product is combined with a highly adhesive plastic resin coating, a coated workpiece with advantages such as high and low temperature resistance, solvent resistance, good mechanical properties, long service life, anti-yellowing, anti-aging, salt spray resistance, and low ion exudation can be obtained. The specific reaction principle is as follows:

[0062]

[0063] The present invention will be further illustrated by the following examples.

[0064] Example 1

[0065] In a 100L polymerization reactor, add 60L of ethyl nonafluorobutyl ether, 65g of methane, 300g of CF3O(CF2O)3CF2COONH4, and 1065g of perfluoropropyl vinyl ether (PPVE). Evacuate the reactor and purge with nitrogen. Once the oxygen content in the polymerization reactor is less than 10ppm, raise the temperature to 30℃, add tetrafluoroethylene to a pressure of 1.8MPa, and add 20.45g of perfluoroacyl peroxide [C3F7C(=O)O] as an initiator to start the reaction. After raising the temperature to 50℃, maintain this temperature and continuously add tetrafluoroethylene monomer and PPVE monomer at a mass ratio of 100:2. When the amount of tetrafluoroethylene added is 5000g and the amount of PPVE added is 100g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 10000g and the amount of PPVE added is 200g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 15000g and the amount of PPVE added is 300g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time. Two hours after the start of the polymerization reaction, a total of 15000g of tetrafluoroethylene, 300g of PPVE, and 0.075g of [CF3CF2CF2C(=O)O]2 are added. Stop the reaction, vent the unreacted gas in the reactor, transfer the solution to the intermediate tank, add 1.8g of pure water to the intermediate tank, stir slowly for 5 hours, add 15.7g of HMDI (dicyclohexylmethane diisocyanate), heat to 70℃ and react for 3 hours, then add 1000g of Span 80 to the vacuum concentration reactor to increase the solid content of the solution to 50% and then discharge the material for later use.

[0066] Example 2

[0067] In a 100L polymerization reactor, add 60L of ethyl nonafluorobutyl ether, 65g of methane, 300g of CF3O(CF2O)3CF2COONH4, and 1365g of perfluoropropyl vinyl ether (PPVE). Evacuate the reactor and purge with nitrogen. When the oxygen content in the polymerization reactor is less than 10ppm, raise the temperature to 30℃, add tetrafluoroethylene to a pressure of 1.8MPa, add 20.45g of perfluoroacyl peroxide [C3F7C(=O)O] as an initiator, and start the reaction. After raising the temperature to 50℃, maintain this temperature and continuously add tetrafluoroethylene monomer. When the amount of tetrafluoroethylene added is 5000g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at a time; when the amount of tetrafluoroethylene added is 10000g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at a time; when the amount of tetrafluoroethylene added is 15000g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at a time. Two hours after the start of the polymerization reaction, a total of 15000g of tetrafluoroethylene and 0.075g of [CF3CF2CF2C(=O)O]2 are added. Stop the reaction, vent the unreacted gas in the reactor, transfer the solution to the intermediate tank, add 1.8g of pure water to the intermediate tank, stir slowly for 5 hours, add 15.7g of HMDI (dicyclohexylmethane diisocyanate), heat to 70℃ and react for 3 hours, then add 1000g of Span 80 to the vacuum concentration reactor to increase the solid content of the solution to 50% and then discharge the material for later use.

[0068] Example 3

[0069] In a 100L polymerization reactor, add 60L of ethyl nonafluorobutyl ether, 65g of methane, 300g of CF3O(CF2O)3CF2COONH4, and 1065g of perfluoropropyl vinyl ether (PPVE). Evacuate the reactor and purge with nitrogen. Once the oxygen content in the polymerization reactor is less than 10ppm, raise the temperature to 30℃, add tetrafluoroethylene to a pressure of 1.8MPa, and add 20.45g of perfluoroacyl peroxide [C3F7C(=O)O] as an initiator to start the reaction. After raising the temperature to 50℃, maintain this temperature and continuously add tetrafluoroethylene monomer and PPVE monomer at a mass ratio of 100:2. When the amount of tetrafluoroethylene added is 5000g and the amount of PPVE added is 100g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 10000g and the amount of PPVE added is 200g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 15000g and the amount of PPVE added is 300g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time. Two hours after the start of the polymerization reaction, a total of 15000g of tetrafluoroethylene, 300g of PPVE, and 0.075g of [CF3CF2CF2C(=O)O]2 are added. Stop the reaction, vent the unreacted gas in the reactor, transfer the solution to the intermediate tank, add 1.8g of pure water to the intermediate tank, stir slowly for 5 hours, add 15.7g of HMDI (dicyclohexylmethane diisocyanate), heat to 70℃ and react for 3 hours, add 18kg of aqueous solution containing 1000g of OP-10 and distill to remove ethyl nonafluorobutyl ether, then transfer to a vacuum concentration reactor, increase the solid content of the solution to 50% and then discharge for later use.

[0070] Example 4

[0071] In a 100L polymerization reactor, add 60L of perfluoro-N-methylmorpholine, 65g of methane, 300g of CF3O(CF2O)3CF2COONH4, and 1065g of perfluoropropyl vinyl ether (PPVE). Evacuate the reactor and purge with nitrogen. Once the oxygen content in the polymerization reactor is less than 10ppm, raise the temperature to 30℃, add tetrafluoroethylene to a pressure of 1.8MPa, and add 20.45g of perfluoroacyl peroxide [C3F7C(=O)O] as an initiator to start the reaction. After raising the temperature to 50℃, maintain this temperature and continuously add tetrafluoroethylene monomer and PPVE monomer at a mass ratio of 100:2. When the amount of tetrafluoroethylene added is 5000g and the amount of PPVE added is 100g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 10000g and the amount of PPVE added is 200g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 15000g and the amount of PPVE added is 300g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time. Two hours after the start of the polymerization reaction, a total of 15000g of tetrafluoroethylene, 300g of PPVE, and 0.075g of [CF3CF2CF2C(=O)O]2 are added. Stop the reaction, vent the unreacted gas in the reactor, transfer the solution to the intermediate tank, add 1.8g of pure water to the intermediate tank, stir slowly for 5h, add 15.7g of HMDI (dicyclohexylmethane diisocyanate), react at 50℃ for 3h, add 15kg of aqueous solution containing 1000g of OP-10 for distillation treatment, separate and remove perfluoro-N-methylmorpholine, transfer to a vacuum concentration reactor, increase the solid content of the solution to 50%, and then discharge for later use.

[0072] Example 5

[0073] This embodiment is basically the same as Example 1, except that the end-capping compound is diphenylmethane diisocyanate.

[0074] Comparative Example 1

[0075] In a 100L polymerization reactor, add 60L of pure water, 65g of methane, 300g of CF3O(CF2O)3CF2COONH4, and 1065g of perfluoropropyl vinyl ether (PPVE). Evacuate the reactor and purge with nitrogen. Once the oxygen content in the reactor is less than 10ppm, raise the temperature to 70℃, add tetrafluoroethylene to a pressure of 1.8MPa, add 22.8g of ammonium persulfate, and begin the reaction. Continuously add tetrafluoroethylene monomer and PPVE monomer at a mass ratio of 100:2. When the amount of tetrafluoroethylene added is 5000g and the amount of PPVE added is 100g, 2.13g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 10000g and the amount of PPVE added is 200g, 2.13g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 15000g and the amount of PPVE added is 300g, 2.13g of [CF3CF2CF2C(=O)O]2 is added at one time. After 10 hours from the start of the polymerization reaction, a total of 15000g of tetrafluoroethylene, 300g of PPVE, and 6.39g of [CF3CF2CF2C(=O)O]2 are added. Stop the reaction, cool down, vent the unreacted gas in the reactor, transfer it to the intermediate tank, add 1000g of OP-10 to the vacuum concentrator, increase the solid content of the solution to 50%, and then discharge the material for later use.

[0076] Comparative Example 2

[0077] In a 100L polymerization reactor, add 60L of ethyl nonafluorobutyl ether, 65g of methane, 300g of CF3O(CF2O)3CF2COONH4, and 1065g of perfluoropropyl vinyl ether (PPVE). Evacuate the reactor and purge with nitrogen. Once the oxygen content in the polymerization reactor is less than 10ppm, raise the temperature to 30℃, add tetrafluoroethylene to a pressure of 1.8MPa, and add 20.45g of perfluoroacyl peroxide [C3F7C(=O)O] as an initiator to start the reaction. After raising the temperature to 50℃, maintain this temperature and continuously add tetrafluoroethylene monomer and PPVE monomer at a mass ratio of 100:2. When the amount of tetrafluoroethylene added is 5000g and the amount of PPVE added is 100g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 10000g and the amount of PPVE added is 200g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 15000g and the amount of PPVE added is 300g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time. Two hours after the start of the polymerization reaction, a total of 15000g of tetrafluoroethylene, 300g of PPVE, and 0.075g of [CF3CF2CF2C(=O)O]2 are added. Stop the reaction, vent the unreacted gas in the reactor, add 1000g of OP-10 to the vacuum concentrator, increase the solid content of the solution to 50%, and then discharge the material for later use.

[0078] Comparative Example 3

[0079] In a 100L polymerization reactor, add 60L of ethyl nonafluorobutyl ether, 65g of methane, 300g of CF3O(CF2O)3CF2COONH4, and 1065g of perfluoropropyl vinyl ether (PPVE). Evacuate the reactor and purge with nitrogen. Once the oxygen content in the polymerization reactor is less than 10ppm, raise the temperature to 30℃, add tetrafluoroethylene to a pressure of 1.8MPa, and add 20.45g of perfluoroacyl peroxide [C3F7C(=O)O] as an initiator to start the reaction. After raising the temperature to 50℃, maintain this temperature and continuously add tetrafluoroethylene monomer and PPVE monomer at a mass ratio of 100:2. When the amount of tetrafluoroethylene added is 5000g and the amount of PPVE added is 100g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 10000g and the amount of PPVE added is 200g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time; when the amount of tetrafluoroethylene added is 15000g and the amount of PPVE added is 300g, 0.025g of [CF3CF2CF2C(=O)O]2 is added at one time. Two hours after the start of the polymerization reaction, a total of 15000g of tetrafluoroethylene, 300g of PPVE, and 0.075g of [CF3CF2CF2C(=O)O]2 are added. Stop the reaction, vent the unreacted gas in the reactor, add 18 kg of aqueous solution containing 1000 g of OP-10 and distill to separate and remove ethyl nonafluorobutyl ether. Then transfer the solution to a vacuum concentration reactor and increase the solid content of the solution to 50% before discharging for later use.

[0080] Performance testing

[0081] The fusible polytetrafluoroethylene coatings prepared in the examples and comparative examples were used in conjunction with acrylic resin coatings. An acrylic resin primer was first coated on the substrate, and after 24 hours, the fusible polytetrafluoroethylene coating was coated on the substrate before performance testing was performed.

[0082] Adhesion strength: The adhesive strength of the polymer after it has been prepared as a coating was determined according to ISO 4624 standard (adhesion pull-off test). The test was conducted at 25°C and 50% relative humidity.

[0083] The aqueous fluoropolymer solutions provided in the above embodiments and comparative examples were impregnated onto aluminum plates, which were then dried in a sintering furnace at 120°C for 10 minutes, followed by sintering at 380°C for 30 minutes to form a coating film. After cooling to room temperature, the coating was removed, and the performance of the aqueous fluoropolymer coating film was tested using the following methods:

[0084] Stability: Mechanical high-speed stirring demulsification was performed at a stirring speed of 15,000 rpm, and the demulsification time was observed.

[0085] Pencil hardness: GB / T 6739-1996;

[0086] Water resistance: Tested according to Method A of GB / T 1733-1993. In addition to sealing the edges, the back of the test panels must also be sealed before testing. Immerse three test panels in Class III water as specified in GB / T 6682. If two of the three test panels do not show any coating defects such as blistering, powdering, or obvious discoloration, they can be rated as "no abnormalities". If the above coating defects are present, they should be described according to GB / T 1766.

[0087] Weather resistance: GB 1767-79, test 60° gloss retention rate.

[0088] Aging resistance: GB / T 9755-2001; the test shall be conducted in accordance with GB / T 1865, and the evaluation of the results shall be conducted in accordance with GB / T 1766, of which the evaluation of the color change grade shall be conducted in accordance with 4.2.2 of GB / T 1766-1995.

[0089] Acid resistance: After soaking in 10% sulfuric acid at 25°C for 168 hours, its mechanical properties were compared with those before soaking.

[0090] Alkali resistance: After soaking in 10% NaOH solution at 25℃ for 168 hours, the mechanical properties were compared with those before the test.

[0091] Mechanical properties after acid and alkali resistance: The minimum elongation at break after acid or alkali immersion is evaluated as a percentage of the initial elongation at break.

[0092] Elongation at break of paint film: Tested according to GB / T 1040.1-2006.

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] Based on the test data from Examples 1-5, it can be seen that the fusible polytetrafluoroethylene coating of this example is suitable for both water-based coatings and coatings based on organic solvents. The test data from Examples 1 and 4 show that the end-capping compound and R... f Although the end-capping products of COOH differed at different cross-linking end-capping temperatures, they did not affect the performance of the final coating. Test data from Example 1 and Comparative Examples 1-3 show that when the unstable end groups of the fusible polytetrafluoroethylene resin were not treated, the resulting coating exhibited significantly lower water resistance, weather resistance, aging resistance, adhesion, elongation at break, and mechanical properties after acid and alkali treatment compared to the examples.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a fusible polytetrafluoroethylene coating, characterized in that, The fusible polytetrafluoroethylene coating comprises an amide-terminated fusible polytetrafluoroethylene compound, and the method includes the following steps: S1. Add the solvent, the second dispersant, the chain transfer agent, and the perfluoroalkyl vinyl ether to a reaction vessel to obtain a mixed solution; the chain transfer agent includes one or more of methane, ethane, propane, cyclohexane, and hydrogen. The mixture is heated to the reaction temperature, and tetrafluoroethylene is introduced into the mixed solution to the reaction pressure. Then, an initiator is added to the mixed solution to carry out the reaction. Tetrafluoroethylene and an initiator are added to the mixed solution, and the pressure of the reaction vessel is maintained within the reaction pressure range until the reaction is completed, yielding a fusible polytetrafluoroethylene emulsion with -COF; the initiator in step S1 is selected from perfluoroacyl peroxide [R f C(=O)O] 2， R f It is a perfluoroalkyl group with 1-6 carbon atoms; S2. Add water to a fusible polytetrafluoroethylene emulsion with -COF to carry out a hydrolysis reaction to obtain a fusible polytetrafluoroethylene resin containing carboxyl groups. S3. Add a capping compound to the carboxyl-containing fusible polytetrafluoroethylene resin, wherein the capping compound modifies the carboxyl-containing fusible polytetrafluoroethylene resin by capping, thereby obtaining a grafted or micro-crosslinked product, wherein the grafted or micro-crosslinked product is an amide-capped fusible polytetrafluoroethylene compound, and the capping compound contains at least one isocyanate functional group.

2. The method for preparing the fusible polytetrafluoroethylene coating according to claim 1, characterized in that, The fusible polytetrafluoroethylene coating further includes a first dispersant, which is a perfluorinated anionic surfactant.

3. The method for preparing the fusible polytetrafluoroethylene coating according to claim 1, characterized in that, The fusible polytetrafluoroethylene coating further includes a first dispersant, which is an emulsifier.

4. The method for preparing the fusible polytetrafluoroethylene coating according to claim 1, characterized in that, The solvent includes one or more of 1,3-bis(trifluoromethyl)benzene, trifluoromethylbenzene, ethyl perfluorobutyl ether, methyl perfluorobutyl ether, ethyl nonafluorobutyl ether, perfluorocarbon, perfluoroamine, and perfluoromorpholine; The perfluorocarbon includes one or more of perfluorocyclobutane, perfluoromethylcyclobutane, and perfluorocyclohexane; the perfluoroamine includes perfluorotributylamine; and the perfluoromorpholine includes at least one of perfluoro-N-methylmorpholine and perfluoro-N-isopropylmorpholine. The second dispersant includes one or more of perfluoropolyether carboxylic acids or their salts.

5. The method for preparing the fusible polytetrafluoroethylene coating according to claim 1, characterized in that, The amount of water added in the hydrolysis reaction is 0.001%-5% of the molar amount of perfluoroalkyl vinyl ether added; the content of isocyanate functional groups in the added end-capping compound is 1.05-1.2 times the molar amount of water added in the hydrolysis reaction.

6. The method for preparing the fusible polytetrafluoroethylene coating according to claim 1, characterized in that, The end-capping compound includes one or more of dicyclohexylmethane diisocyanate, methylcyclohexyl diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophenyl dimethyl isocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and polyphenyl polymethylene polyisocyanate.

7. A coated workpiece, characterized in that, It includes a substrate, a primer layer, and a fluoropolymer layer, wherein the primer layer is disposed on the surface of the substrate, and the fluoropolymer layer is disposed on the side of the primer layer facing away from the substrate; the fluoropolymer layer is formed by coating a fusible polytetrafluoroethylene coating prepared by the method for preparing fusible polytetrafluoroethylene coating according to any one of claims 1-6.

8. The coated workpiece according to claim 7, characterized in that, The primer layer is formed by coating one or more of the following: polyacrylic resin coating, polyurethane coating, polyamide coating, polyimide coating, and polyether coating.

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