High-adhesion modified polyamide curing agent as well as preparation method and application thereof

Abstract

The invention discloses a high-adhesion modified polyamide curing agent as well as a preparation method and application thereof, and belongs to the technical field of high polymer materials. The preparation method comprises the following steps: (1) reacting a bifunctional epoxy diluent with an amino-terminated silane coupling agent to prepare an epoxy-terminated chain extender; (2) reacting the phosphate monomer with a chlorination reagent to prepare a phosphate acyl chloride intermediate; (3) carrying out nucleophilic substitution on a polyamide curing agent and the phosphate acyl chloride intermediate under an alkaline condition to form P-N bond grafted phosphate; and (4) terminating by using an epoxy-terminated chain extender to obtain a final product. Through the synergistic effect that phosphate groups and metal oxide form P-O-Me covalent bonds, and siloxane groups are hydrolyzed to form Si-O bonds, the problem that a traditional polyamide curing agent is poor in adhesive force to a low-surface-energy metal base material is solved; and phosphate is covalently grafted to avoid migration and precipitation, so that the hydrolysis resistance and the storage stability are improved. The paint can be used for metal anticorrosive paint and adhesives, and has excellent paint film adhesion, salt fog resistance and boiling resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a structural modification preparation technology of polyamide curing agent, and especially relates to a high-adhesion modified polyamide curing agent and a preparation method and application thereof. BACKGROUND

[0002] Polyamide curing agents are widely used in the fields of epoxy coatings and adhesives due to their good compatibility with epoxy resins, excellent flexibility and strong impact resistance of the cured paint film. However, the traditional polyamide curing agent lacks groups that can form strong chemical bonds with low surface energy metal substrates (such as aluminum alloy, galvanized steel, and stainless steel) in its molecular structure, resulting in a large contact angle with these substrates. The combination is achieved through physical adsorption, which has the defects of insufficient adhesion and easy peeling, limiting its application in high-end metal corrosion prevention fields (such as lightweight aluminum alloy parts for automobiles and galvanized steel components).

[0003] With the improvement of the performance requirements of downstream industries for coating, the modification direction of polyamide curing agents has gradually focused on "adhesion enhancement" and "environmental stability improvement". In the prior art, there have been attempts to improve adhesion by introducing functional groups: Chinese invention patent CN110240711A discloses a waterborne epoxy emulsifier containing phosphate structure, which improves the wettability and adhesion of waterborne epoxy emulsion on metal surface by introducing phosphate into the emulsifier molecule. However, this technology only targets waterborne epoxy emulsifiers and does not involve modification of polyamide curing agents themselves. Moreover, the phosphate is dispersed by physical mixing and is prone to migration and precipitation during curing, resulting in a decrease in long-term water resistance. Chinese invention patent CN120365876A discloses a high-toughness high-adhesion epoxy resin adhesive, which improves the bonding strength to difficult-to-bond metals by simultaneously adding a phosphate-based toughening agent, a modified polyamide curing agent, and a silane coupling agent to the adhesive system. However, this technology relies on the physical compounding of multiple components and does not covalently graft phosphate groups to the main chain of the polyamide curing agent, which poses the risk of poor compatibility and layering during storage. Moreover, the synergistic mechanism of silane coupling agent and phosphate is not clear, which makes it difficult to ensure the stability of adhesion.

[0004] In summary, the existing technologies have the following deficiencies: 1. Most of them target emulsifiers or adhesive systems and do not achieve stable grafting of functional groups from the molecular structure of polyamide curing agents; 2. Phosphates are mostly introduced by physical mixing, which is prone to migration and precipitation, affecting the hydrolysis resistance and storage stability; 3. The synergistic effect of phosphates and siloxanes is not fully utilized, and the adhesion to low surface energy metal substrates is limited.

[0005] Therefore, it is an urgent problem in the field to develop a polyamide curing agent that covalently introduces dual functional groups and has high adhesion and stability. SUMMARY

[0006] In order to solve the problems of poor adhesion to low surface energy metal substrates, insufficient hydrolysis resistance and poor storage stability of the conventional polyamide curing agent in the prior art, the application provides a high-adhesion modified polyamide curing agent, a preparation method and application thereof, a phosphate group is covalently grafted on a polyamide main chain through molecular structure design, and a siloxane chain extender is introduced, so that the adhesion is synergistically enhanced by "phosphate-siloxane", and the stability of the product is ensured. The application is realized through the following technical scheme: A high-adhesion modified polyamide curing agent is prepared from the following raw materials by weight: 50-150 parts of a bifunctional epoxy diluent 30-60 parts of an amino-terminated silane coupling agent 10-20 parts of a phosphate monomer 5-20 parts of a chlorinating agent 80-100 parts of a polyamide curing agent 4-6 parts of a basic catalyst The modified polyamide curing agent is amber transparent liquid, the viscosity is 2500-3500 mPa s, and the amine value is 170-175 mgKOH / g based on solid.

[0007] Further, the preparation method of the high-adhesion modified polyamide curing agent is as follows: (1) Preparation of an epoxy-terminated silane chain extender: the amino-terminated silane coupling agent and solvent A are weighed and put into a reaction device, and under stirring, the temperature is raised to 55-70 DEG C, the bifunctional epoxy diluent is added, and the reaction is kept for 2-3 h to prepare the epoxy-terminated silane chain extender; (2) Preparation of a phosphate acid chloride intermediate: the phosphate monomer and solvent B are weighed and put into a dry reaction device, and the temperature is lowered to 0 DEG C by ice bath, the chlorinating agent is added under nitrogen protection, the temperature is raised to room temperature 23-27 DEG C after the heat is removed, and the reaction is kept for 4-5 h, and the excess chlorinating agent and solvent B are removed by distillation under reduced pressure to prepare the phosphate acid chloride intermediate; (3) Reaction of polyamide grafted phosphate: the polyamide curing agent is dissolved in solvent C, the temperature is raised to 50-60 DEG C, the phosphate acid chloride intermediate prepared in step (2) is added dropwise under vigorous stirring, the reaction temperature is controlled at 50-60 DEG C, and the reaction is kept for 1-2 h to prepare the polyamide intermediate grafted with phosphate; (4) End-capping reaction: the epoxy-terminated silane chain extender prepared in step (1) is added to the polyamide intermediate prepared in step (3), the temperature is raised to 70-80 DEG C, the reaction is kept for 3 h, the temperature is lowered, and the product is discharged to prepare the high-adhesion modified polyamide curing agent; The raw materials are formulated in the proportions of the high-adhesion modified polyamide curing agent described above, and solvents A, B, and C are not included in the proportions by weight.

[0008] Further, in step (1), the molar ratio of the epoxy group provided by the bifunctional epoxy diluent to the amino group provided by the terminal amino silane coupling agent is 2:1; Solvent A is isopropanol.

[0009] Furthermore, the bifunctional epoxy diluent is selected from one or more of polyethylene glycol diglycidyl ether, 1,4-cyclohexanediethanol diglycidyl ether, and 1,4-butanediol diglycidyl ether. The terminal aminosilane coupling agent is selected from one or more of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

[0010] Further, in step (2), the molar ratio of the chlorinating agent to the hydroxyl group in the phosphate ester monomer is 1.2:1; The chlorinating agent is one or more of oxalyl chloride and phosphorus oxychloride; Solvent B is anhydrous tetrahydrofuran.

[0011] Furthermore, the phosphate monomer is selected from one or more of diethyl phosphate, diphenyl phosphate, bis(2-methacryloyloxyethyl) phosphate, and pentaerythritol phosphate.

[0012] Furthermore, the phosphate monomer is selected from one or both of bis(2-methacryloyloxyethyl) phosphate and pentaerythritol phosphate.

[0013] Furthermore, the polyamide curing agent is selected from one or more of 200 low molecular weight polyamide, 300 low molecular weight polyamide, and 400 low molecular weight polyamide; The solvent propylene glycol methyl ether is used. The alkaline catalyst is triethylamine.

[0014] Furthermore, the polyamide curing agent is a 400 low molecular weight polyamide.

[0015] Furthermore, in step (1), the reaction apparatus needs to be pre-dried, and nitrogen gas is introduced for protection during the reaction process; In step (2), the vacuum degree of the reduced pressure distillation is -0.09 to -0.1 MPa, and the distillation temperature is 40 to 50 °C.

[0016] Furthermore, the high-adhesion modified polyamide curing agent prepared according to the above technical solution is used in water-based or solvent-based epoxy coating systems, specifically in metal anti-corrosion coatings and adhesives; The substrate of the metal anti-corrosion coating includes low surface energy metal substrates such as galvanized steel sheet, aluminum alloy, and stainless steel.

[0017] Compared with the prior art, the present invention has the following advantages: 1. Step (1) uses isopropanol to ensure a reduction in system viscosity, making the bifunctional epoxy diluent easier to disperse when added, and ensuring the uniformity of the chain extender structure. Step (2) uses anhydrous tetrahydrofuran to ensure efficient acyl chloride reaction. Step (3) uses propylene glycol methyl ether to ensure polyamide dissolution and grafting reaction, avoiding solvent cross-interference. 2. By adopting a bifunctional modification strategy of covalent grafting of phosphate esters and chain extension and end-capping of siloxanes, the phosphate ester groups form PO-Me covalent bonds with metal oxides, and the siloxane groups are hydrolyzed to form Si-O bonds. The synergistic effect of the two chemical bonds significantly improves the adhesion, solving the problem of poor adhesion of low surface energy metal substrates at the molecular level and breaking through the limitations of traditional physical compounding. 3. By employing a nucleophilic substitution reaction to form PN covalent bonds, phosphate ester groups are stably grafted onto the polyamide backbone, avoiding precipitation problems caused by physical mixing. This also improves the product's hydrolysis resistance and solves the defects of easy migration and poor storage stability of phosphate esters in existing technologies. The product also has high adhesion, high toughness, and high environmental stability. It shows no significant corrosion in a 1000-hour salt spray test, which is superior to traditional polyamide curing agents. Furthermore, it has good compatibility with pigments, fillers, and additives, and is applicable to a wide range of substrates. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention are further described below with reference to embodiments, but the present invention is not limited to these embodiments.

[0019] All raw materials used in the examples were commercially available conventional products: 400 low molecular weight polyamide curing agent was purchased from Jiangsu Sanmu Group; polyethylene glycol diglycidyl ether (XY225, XY245), 1,4-butanediol diglycidyl ether (XY622), and 1,4-cyclohexanediethanol diglycidyl ether (XY630) were purchased from Anhui Xinyuan Chemical; amino-terminated silane coupling agents SCA-A10E (3-aminopropyltriethoxysilane), SCA-A10M (3-aminopropyltrimethoxysilane), and SCA- A10F (3-aminopropylmethyldiethoxysilane) and SCA-A10T (3-aminopropylmethyldimethoxysilane) were purchased from Nanjing Nengde; phosphate monomers (diethyl phosphate, bis(2-methacryloyloxyethyl) phosphate (BMEP), pentaerythritol phosphate (PEPA), diphenyl phosphate) were purchased from Aladdin Reagent; chlorination reagent (oxaloyl chloride), solvent (isopropanol, anhydrous tetrahydrofuran, propylene glycol methyl ether), and basic catalyst (triethylamine) were all purchased from Sinopharm Chemical Reagent Co., Ltd.

[0020] The structural formula of bis(2-methacryloyloxyethyl) phosphate (BMEP) is as follows: The structural formula of pentaerythritol phosphate (PEPA) is as follows: Example 1 This embodiment provides a high-adhesion modified polyamide curing agent, and the preparation steps are as follows: (1) Preparation of terminal epoxy silane chain extender: Take a pre-dried 500mL four-necked flask, purge with nitrogen for protection, add 50 parts by weight of SCA-A10E (3-aminopropyltriethoxysilane) and 50 parts by weight of solvent A (isopropanol), stir and heat to 60℃. Slowly add 100 parts by weight of polyethylene glycol diglycidyl ether (XY225), and after the addition is complete, keep the temperature at 60℃ for 2.5h to obtain the terminal epoxy silane chain extender for later use.

[0021] (2) Preparation of phosphate ester acyl chloride intermediate: Take a dry 250 mL four-necked flask, add 12 parts by weight of diethyl phosphate (containing 1 hydroxyl group, molar number ≈ 0.087 mol) and 50 mL of solvent ethyl (anhydrous tetrahydrofuran), and cool to 0 °C in an ice bath. Under nitrogen protection, slowly add 9.5 parts by weight of oxalyl chloride (molar ratio to hydroxyl group 1.2:1, molar number ≈ 0.104 mol), controlling the temperature not to exceed 5 °C during the addition process. After the exothermic reaction is completed, raise the temperature to room temperature (25 °C) and maintain the reaction for 4.5 h. Subsequently, distill under reduced pressure at a vacuum degree of -0.095 MPa and a temperature of 45 °C to remove excess oxalyl chloride and solvent, obtaining a viscous oily diethyl phosphate acyl chloride intermediate for later use.

[0022] (3) Reaction of polyamide grafted with phosphate: Take a 500 mL four-necked flask, add 100 parts by weight of 400 low molecular weight polyamide curing agent and 150 mL of solvent propylene glycol methyl ether, stir and heat to 55 °C, and add 5 parts by weight of alkaline catalyst (triethylamine). Under vigorous stirring, slowly add the phosphate ester acyl chloride intermediate obtained in step (2), and after the addition is complete, control the temperature at 55 °C and keep the reaction at 1.5 h to obtain the polyamide intermediate grafted with phosphate.

[0023] (4) End-capping reaction: Add the terminal epoxy silane chain extender obtained in step (1) to the polyamide intermediate in step (3), heat to 75°C and keep it at that temperature for 3 hours. After the reaction is completed, cool down to 40°C and discharge the material to obtain a high-adhesion modified polyamide curing agent.

[0024] Example 2 This embodiment provides a high-adhesion modified polyamide curing agent, and the preparation steps are as follows: (1) Preparation of terminal epoxy silane chain extender: Take a dry 500mL four-necked flask, purge with nitrogen, add 40 parts by weight of SCA-A10E and 40 parts by weight of isopropanol, stir and heat to 55℃. Slowly add 80 parts by weight of 1,4-butanediol diglycidyl ether (XY622), and after the addition is complete, keep the temperature at 55℃ for 3h to obtain the terminal epoxy silane chain extender for later use.

[0025] (2) Preparation of phosphate acyl chloride intermediate: Take a dry 250 mL four-necked flask, add 15 parts by weight of BMEP (containing 2 hydroxyl groups, molar number ≈ 0.043 mol) and 50 mL of anhydrous tetrahydrofuran, and cool to 0 °C in an ice bath. Under nitrogen protection, add 11.5 parts by weight of oxalyl chloride (molar ratio to hydroxyl group 1.2:1, molar number ≈ 0.103 mol), and control the temperature ≤ 5 °C. After the exothermic reaction, keep the reaction at room temperature (24 °C) for 4 h, and then distill under reduced pressure at -0.09 MPa and 40 °C to obtain BMEP acyl chloride intermediate for later use.

[0026] (3) Reaction of polyamide grafted with phosphate: Take a 500 mL four-necked flask, add 95 parts by weight of 400 low molecular weight polyamide and 140 mL of propylene glycol methyl ether, heat to 50 °C, and add 4.5 parts by weight of triethylamine. Add the intermediate from step (2) dropwise under vigorous stirring. After the addition is complete, keep the temperature at 50 °C for 2 h to obtain the grafted polyamide intermediate.

[0027] (4) End-capping reaction: Add the terminal epoxy silane chain extender obtained in step (1) to the polyamide intermediate in step (3), heat to 70°C and keep it at that temperature for 3 hours, then cool down and discharge the material to obtain a high-adhesion modified polyamide curing agent.

[0028] Example 3 This embodiment provides a high-adhesion modified polyamide curing agent, and the preparation steps are as follows: (1) Preparation of terminal epoxy silane chain extender: Take a dry 500mL four-necked flask, purge with nitrogen, add 60 parts by weight of SCA-A10M and 60 parts by weight of isopropanol, stir and heat to 70℃. Slowly add 120 parts by weight of 1,4-cyclohexanediethanol diglycidyl ether (XY630), and after the addition is complete, keep the reaction at 70℃ for 2h to obtain the chain extender for later use.

[0029] (2) Preparation of phosphate acyl chloride intermediate: Take a dry 250 mL four-necked flask, add 18 parts by weight of PEPA (containing 4 hydroxyl groups, molar number ≈ 0.032 mol) and 50 mL of anhydrous tetrahydrofuran, and place in an ice bath at 0℃. Under nitrogen protection, add 18.5 parts by weight of oxalyl chloride (molar ratio to hydroxyl group 1.2:1, molar number ≈ 0.154 mol), and control the temperature ≤ 5℃. After the exothermic reaction, keep the reaction at room temperature (26℃) for 5 h, and then distill under reduced pressure at -0.1 MPa and 50℃ to obtain the PEPA acyl chloride intermediate for later use.

[0030] (3) Reaction of polyamide grafted with phosphate: Take a 500 mL four-necked flask, add 100 parts by weight of 400 low molecular weight polyamide and 160 mL of propylene glycol methyl ether, heat to 60 °C, and add 6 parts by weight of triethylamine. Add the intermediate from step (2) dropwise under vigorous stirring. After the addition is complete, keep the temperature at 60 °C for 1 h to obtain the grafted polyamide intermediate.

[0031] (4) End-capping reaction: Add the terminal epoxy silane chain extender obtained in step (1) to the polyamide intermediate in step (3), heat to 80°C and keep it at that temperature for 3 hours, then cool down and discharge to obtain a high-adhesion modified polyamide curing agent.

[0032] Example 4 This embodiment provides a high-adhesion modified polyamide curing agent (mixed raw materials), and the preparation steps are as follows: (1) Preparation of terminal epoxy silane chain extender: Take a dry 500mL four-necked flask, purge with nitrogen, add 25 parts by weight of SCA-A10E + 25 parts by weight of SCA-A10T (total 50 parts by weight) and 50 parts by weight of isopropanol, stir and heat to 65℃. Slowly add 50 parts by weight of XY245 + 50 parts by weight of XY622 (total 100 parts by weight of bifunctional epoxy diluent), and after the addition is complete, keep the reaction at 65℃ for 2.5h to obtain the chain extender for later use.

[0033] (2) Preparation of phosphate ester acyl chloride intermediate: Take a dry 250 mL four-necked flask, add 8 parts by weight of BMEP + 8 parts by weight of PEPA (total 16 parts by weight, total hydroxyl moles ≈ 0.052 mol) and 50 mL of anhydrous tetrahydrofuran, and place in an ice bath at 0℃. Under nitrogen protection, add 14 parts by weight of oxalyl chloride (molar ratio to hydroxyl 1.2:1, moles ≈ 0.062 mol), and control the temperature ≤ 5℃. After the exothermic reaction, keep the reaction at room temperature (25℃) for 4.5 h, and distill under reduced pressure (-0.095 MPa, 45℃) to obtain a mixed phosphate ester acyl chloride intermediate for later use.

[0034] (3) Reaction of polyamide grafted with phosphate: Take a 500 mL four-necked flask, add 98 parts by weight of 400 low molecular weight polyamide and 150 mL of propylene glycol methyl ether, heat to 55 °C, and add 5 parts by weight of triethylamine. Add the intermediate from step (2) dropwise under vigorous stirring. After the addition is complete, keep the temperature at 55 °C for 1.5 h to obtain the grafted polyamide intermediate.

[0035] (4) End-capping reaction: Add the terminal epoxy silane chain extender obtained in step (1) to the polyamide intermediate in step (3), heat to 75°C and keep it at that temperature for 3 hours, then cool down and discharge to obtain a high-adhesion modified polyamide curing agent.

[0036] Example 5 This embodiment provides a high-adhesion modified polyamide curing agent (low-dosage raw material), and the preparation steps are as follows: (1) Preparation of terminal epoxy silane chain extender: Take a dry 500mL four-necked flask, purge with nitrogen, add 30 parts by weight of SCA-A10F and 30 parts by weight of isopropanol, stir and heat to 60℃. Slowly add 50 parts by weight of XY225, and after the addition is complete, keep the reaction at 60℃ for 2.5h to obtain the chain extender for later use.

[0037] (2) Preparation of phosphate ester acyl chloride intermediate: Take a dry 250 mL four-necked flask, add 10 parts by weight of diphenyl phosphate (containing 1 hydroxyl group, molar number ≈ 0.042 mol) and 50 mL of anhydrous tetrahydrofuran, and place in an ice bath at 0℃. Under nitrogen protection, add 5.7 parts by weight of oxalyl chloride (molar ratio to hydroxyl group 1.2:1, molar number ≈ 0.050 mol), and control the temperature ≤ 5℃. After the exothermic reaction is completed, keep the reaction at room temperature (25℃) for 4 h, and then distill under reduced pressure (-0.09 MPa, 45℃) to obtain the diphenyl phosphate ester acyl chloride intermediate for later use.

[0038] (3) Reaction of polyamide grafted with phosphate: Take a 500 mL four-necked flask, add 80 parts by weight of 400 low molecular weight polyamide and 120 mL of propylene glycol methyl ether, heat to 55 °C, and add 4 parts by weight of triethylamine. Add the intermediate from step (2) dropwise under vigorous stirring. After the addition is complete, keep the temperature at 55 °C for 1.5 h to obtain the grafted polyamide intermediate.

[0039] (4) End-capping reaction: Add the terminal epoxy silane chain extender obtained in step (1) to the polyamide intermediate in step (3), heat to 75°C and keep it at that temperature for 3 hours, then cool down and discharge to obtain a high-adhesion modified polyamide curing agent.

[0040] The high-adhesion modified polyamide curing agents prepared in Examples 1-5 were labeled as Samples 1-5, and then mixed with epoxy resin E-51 at a mass ratio of 35:100. The mixtures were then applied to different substrates, including galvanized steel sheets, aluminum alloys, stainless steel, etc., to obtain coatings that could be tested for performance.

[0041] Comparative Example Traditional polyamide curing agent: Take 100 parts by weight of 400 low molecular weight polyamide curing agent (without phosphate ester grafting and silane chain extension modification), mix it directly with epoxy resin E-51 at a mass ratio of 35:100, and apply it to the same substrate as in Examples 1 to 5 for testing.

[0042] The test was conducted according to the following standard method: Adhesion: According to the requirements of the national standard GB / T9286-1998, the resistance of the coating to penetrate to the substrate and detach when cut with a right-angled grid pattern is rated to assess the adhesion of different coatings. Impact resistance: The impact resistance of different coatings was tested in accordance with the requirements of the national standard GB / T1732-1993. Salt spray resistance test: The salt spray resistance of different coatings was tested in accordance with the requirements of the national standard GB / T10125-1977. Water resistance test: The water resistance of different coatings was tested in accordance with the requirements of the national standard GB / T5237-2000.

[0043] Table 1. Performance Comparison of Examples 1-5 and Comparative Examples As shown in Table 1 above, the high-adhesion modified polyamide curing agents prepared in Examples 1-5 of this invention are significantly superior to traditional polyamide curing agents (comparative examples) in terms of adhesion, salt spray resistance, and boiling water resistance. Among them, Example 3 (using XY630+SCA-A10M+PEPA) and Example 4 (mixed raw materials) have the best overall performance. Although the performance of Example 5 (low-dosage raw materials) is slightly lower, it is still better than the comparative examples. This proves that the dual-function modification strategy of this invention can effectively solve the adhesion problem of traditional curing agents to low surface energy metal substrates.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A high-adhesion modified polyamide curing agent, characterized in that, The modified polyamide curing agent is prepared from the following raw materials in parts by weight: 50-150 parts of bifunctional epoxy diluent 30-60 parts of amino-terminated silane coupling agent 10-20 parts of phosphate ester monomer 5-20 parts of chlorination reagent 80-100 parts of polyamide curing agent 4-6 parts of alkaline catalyst; The modified polyamide curing agent is an amber-colored transparent liquid with a viscosity of 2500~3500 mPa. The amine value, calculated on a solid basis, is 170~175 mg KOH / g.

2. A method for preparing the high-adhesion modified polyamide curing agent as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of terminal epoxy silane chain extender: Weigh the terminal amino silane coupling agent and solvent A and put them into the reaction apparatus. Under stirring, heat to 55~70℃, add the bifunctional epoxy diluent, keep the reaction at the temperature for 2~3h, and obtain the terminal epoxy silane chain extender. (2) Preparation of phosphate ester acyl chloride intermediate: Weigh the phosphate ester monomer and solvent B and put them into a drying reaction apparatus. Cool the mixture to 0°C in an ice bath. Add the chlorination reagent under nitrogen protection. After the exothermic reaction is completed, raise the temperature to room temperature of 23~27°C and keep the reaction at this temperature for 4~5 hours. Remove excess chlorination reagent and solvent B by vacuum distillation to obtain phosphate ester acyl chloride intermediate. (3) Reaction of polyamide grafted phosphate: Weigh the polyamide curing agent and dissolve it in solvent C, heat it to 50~60℃, add alkaline catalyst, and dropwise add the phosphate ester acyl chloride intermediate obtained in step (2) under vigorous stirring. Control the reaction temperature to 50~60℃ and keep the reaction at the temperature for 1~2h to obtain the polyamide intermediate grafted with phosphate. (4) End-capping reaction: Add the terminal epoxy silane chain extender obtained in step (1) to the polyamide intermediate obtained in step (3), heat to 70~80℃, keep the reaction at the temperature for 3h, cool down and discharge the material to obtain a high adhesion modified polyamide curing agent. Wherein, the weight proportions of the raw materials are as described in claim 1, and solvents A, B, and C are not included in the weight proportions.

3. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of the epoxy group provided by the bifunctional epoxy diluent to the amino group provided by the terminal amino silane coupling agent is 2:

1. Solvent A is isopropanol.

4. The preparation method according to claim 3, characterized in that, The bifunctional epoxy diluent is selected from one or more of polyethylene glycol diglycidyl ether, 1,4-cyclohexanediethanol diglycidyl ether, and 1,4-butanediol diglycidyl ether. The terminal aminosilane coupling agent is selected from one or more of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

5. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of the chlorinating agent to the hydroxyl group in the phosphate ester monomer is 1.2:1; The chlorinating agent is one or more of oxalyl chloride and phosphorus oxychloride; Solvent B is anhydrous tetrahydrofuran.

6. The preparation method according to claim 5, characterized in that, The phosphate monomer is selected from one or more of diethyl phosphate, diphenyl phosphate, bis(2-methacryloyloxyethyl) phosphate, and pentaerythritol phosphate.

7. The preparation method according to claim 6, characterized in that, The phosphate monomer is selected from one or both of bis(2-methacryloyloxyethyl) phosphate and pentaerythritol phosphate.

8. The preparation method according to claim 2, characterized in that, The polyamide curing agent is selected from one or more of 200 low molecular weight polyamide, 300 low molecular weight polyamide, and 400 low molecular weight polyamide; The solvent propylene glycol methyl ether is used. The alkaline catalyst is triethylamine.

9. The preparation method according to claim 8, characterized in that, The polyamide curing agent is 400 low molecular weight polyamide.

10. The preparation method according to claim 2, characterized in that, In step (1), the reaction apparatus needs to be dried beforehand, and nitrogen gas is introduced for protection during the reaction process; In step (2), the vacuum degree of the reduced pressure distillation is -0.09 to -0.1 MPa, and the distillation temperature is 40 to 50 °C.

11. An application of the high-adhesion modified polyamide curing agent as described in claim 1, characterized in that, This curing agent is used in water-based or solvent-based epoxy coating systems, specifically in metal anti-corrosion coatings and adhesives. The substrate of the metal anti-corrosion coating includes low surface energy metal substrates such as galvanized steel sheet, aluminum alloy, and stainless steel.

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