Outer weld joint repair coating and preparation method thereof

Abstract

The invention relates to the technical field of coatings for metal packaging, in particular to an outer weld joint repair coating and a preparation method thereof. The external weld joint repair coating prepared by the invention is prepared from acrylic resin, modified acrylic resin, a cross-linking agent, wax powder, polyester modified polydimethylsiloxane, a polysiloxane solution, polyolefin, phosphate polyester and an alcohol ether solvent according to a specific weight part ratio. The preparation method comprises the steps of preparing a solution, dispersing wax powder, grinding wax slurry, mixing and stirring, detecting and packaging and the like. The coating disclosed by the invention does not contain bisphenol A, has the characteristics of high gloss, high hardness, strong adhesive force, scratch resistance, good water resistance, high temperature resistance, sterilization, excellent corrosion resistance and the like, and is suitable for repair coating of welding seams outside tin printing can welding.

Description

Technical Field

[0001] This invention belongs to the technical field of coatings for metal packaging, specifically relating to an external weld repair coating and its preparation method. Background Technology

[0002] In the metal packaging industry, weld seam repair coating of tinplate cans is a crucial step in ensuring can quality. Weld seam repair coatings fill defects at the weld seams, prevent corrosion, and maintain the can's appearance. Currently, external weld seam repair coatings, needing to meet requirements such as resistance to boiling water at 121°C and copper sulfate, are primarily epoxy-based. However, conventional epoxy products are prone to yellowing and contain bisphenol A (BPA), which does not comply with the EU's regulation issued in December 2024 to eliminate BPA in metal packaging coatings by 2027. Furthermore, single acrylic systems have insufficient metal adhesion and weak solvent resistance, failing to meet stringent requirements such as high-temperature sterilization. Regarding resin modification, existing technologies often use epoxy monomers containing benzene rings to modify acrylic resins. While this increases cross-linking, it introduces aromatic structures, weakening the coating's high-temperature sterilization performance. Moreover, the modified resin has poor compatibility with the base resin, easily leading to phase separation, further reducing coating gloss and adhesion. Therefore, it is of great significance to develop a BPA-free coating that also has properties such as high gloss, high hardness, strong adhesion and corrosion resistance for external weld repair. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention uses acrylic resin and epoxy-modified acrylic resin as the main film-forming materials. The aliphatic structure avoids the risks of yellowing and toxicity. An interpenetrating network is formed through the bridging reaction of a crosslinking agent. The branched rigid structure of the modified resin and the continuous skeleton of the main network are combined to form a double-layer interpenetrating network, achieving a balance between high performance and environmental friendliness.

[0004] In a first aspect, this application provides an external weld repair coating, comprising the following components in the indicated weight ratios: 40-50 parts acrylic resin, 15-20 parts modified acrylic resin, 15-25 parts crosslinking agent, 12-16 parts wax powder, 1-3 parts polyester-modified polydimethylsiloxane, 2-4 parts polysiloxane solution, 3-5 parts polyolefin, 3-6 parts phosphate polyester, and 14-20 parts alcohol ether solvent; The modified acrylic resin is obtained by modifying the acrylic resin with cyclohexanediol diglycidyl ether.

[0005] Preferably, the acrylic resin has a hydroxyl value of 80-120 mgKOH / g, the polyester-modified polydimethylsiloxane includes any one of polydimethylsiloxane-polyhexane adipate copolymer and polydimethylsiloxane-polyethylene terephthalate copolymer; the polysiloxane solution includes any one of hydroxyl polysiloxane solution and methyl polysiloxane solution; the polyolefin includes any one of polypropylene with a number average molecular weight of 500-1000 and polyethylene with a number average molecular weight of 500-1000; the phosphate polyester includes any one of polyethylene glycol monophosphate polyester and polypropylene glycol diphosphate polyester.

[0006] Preferably, the crosslinking agent is an isocyanate crosslinking agent, which includes either hexamethylene diisocyanate trimer or dicyclohexylmethane diisocyanate.

[0007] In this process, the isocyanate groups (-NCO) of the acrylic resin and isocyanate crosslinking agent undergo a nucleophilic addition reaction to form urethane bonds (-NHCOO-), providing the basic crosslinking backbone. The modified acrylic resin, due to the ring-opening reaction between the epoxy groups and the hydroxyl groups in the acrylic resin, introduces rigid cyclohexane segments and more branched hydroxyl groups. The remaining -NCO groups react with the branched hydroxyl groups of the modified acrylic resin to form a secondary network characterized by high branching and high rigidity. This crosslinking structure has high bond energy, giving the coating excellent high-temperature resistance, capable of withstanding sterilization at 121℃; the network density is uniform, avoiding localized stress concentration and improving the coating's impact resistance and adhesion; strong hydrophobicity reduces water molecule penetration and enhances water resistance.

[0008] Preferably, the wax powder includes any one of polyethylene wax powder, polytetrachloroethylene wax powder, and polypropylene wax powder, and the average particle size of the wax powder is 5-8 μm.

[0009] In this case, the wax powder is evenly dispersed in the coating after dispersion and grinding. Due to the difference in surface tension, it migrates to the surface of the coating and forms a dense microcrystalline film, which can effectively reduce the surface energy of the coating, reduce the coefficient of friction, and improve scratch resistance; fill the micro-defects on the surface of the coating, reflect light more evenly, and improve gloss; the hydrophobicity of the wax film further enhances the water resistance of the coating.

[0010] Preferably, the alcohol ether solvent is a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether, wherein the mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is (6-8):(2-4).

[0011] In this case, propylene glycol methyl ether acetate has moderate polarity and strong solubility for acrylic resins and modified acrylic resins, ensuring complete resin dissolution; ethylene glycol ethyl ether has slightly higher polarity and good compatibility with isocyanate crosslinking agents, preventing premature reaction of the crosslinking agents during dissolution; the boiling points and evaporation rates of both are matched, allowing for slow and uniform evaporation during film formation, avoiding pinholes, bubbles, or cracks in the coating caused by excessive solvent evaporation, and ensuring coating density.

[0012] Secondly, this application provides a method for preparing an external weld repair coating, the method comprising the following steps: S1: Add alcohol ether solvent to dispersion vessel, add acrylic resin and modified acrylic resin while stirring until the resin is completely dissolved; add crosslinking agent and stir evenly to obtain pre-prepared acrylic resin mixture; S2: Add wax powder to a disperser and disperse to obtain a pre-prepared wax powder dispersion; S3: Transfer the pre-prepared wax powder dispersion to a sand mill, grind at 900-1000 rpm for 40-50 min, sieve, and obtain the mixed wax slurry; S4: Mix the mixed wax slurry with the pre-made acrylic resin mixture, and add polyester-modified polydimethylsiloxane, polysiloxane solution, polyolefin and phosphate polyester in sequence during the stirring process. Mix evenly to obtain the external weld repair coating.

[0013] Preferably, the method for preparing the modified acrylic resin includes the following steps: Add acrylic resin and cyclohexanediol diglycidyl ether to the reactor, stir at 300-400 rpm, heat to 50-60℃, and maintain for 30-60 min; Add diglycidyl ether and hydroquinone sequentially to the reaction vessel and stir for 10-30 minutes until the mixture is homogeneous; Add triethylamine dropwise over 5-8 minutes, heat to 80-100°C, turn on nitrogen protection, and stir at 300-400 rpm for 2-3 hours. Samples were taken every 30 minutes, and the reaction endpoint was determined when the residual epoxy value was 0.02-0.05 eq / 100g, thus obtaining the modified acrylic resin.

[0014] Preferably, the acrylic resin, cyclohexanediol diglycidyl ether, diglycidyl ether, hydroquinone, and triethylamine are formulated in the following weight ratios: 100 parts acrylic resin, 30-50 parts cyclohexanediol diglycidyl ether, 15-25 parts diglycidyl ether, 0.1-0.2 parts hydroquinone, and 0.5-1 parts triethylamine.

[0015] Preferably, in S2, the disperser speed is 1200-1300 rpm, the dispersion time is 30-40 min, and the temperature is 25-45℃.

[0016] Preferably, in step S4, the mixer speed is kept stable at 800-1000 rpm, and the mixing time is 30-60 min.

[0017] Beneficial technical effects: This invention uses acrylic resin and cyclohexanediol diglycidyl ether-modified acrylic resin as the main body. The acrylic resin undergoes a nucleophilic addition reaction with the isocyanate groups (-NCO) of the isocyanate crosslinking agent to generate urethane bonds (-NHCOO-), providing the basic crosslinking backbone. The cyclohexanediol diglycidyl ether-modified acrylic resin introduces rigid cyclohexane segments and more branched hydroxyl groups through ring-opening reactions between the epoxy groups and the hydroxyl groups in the acrylic resin. The remaining -NCO groups react with the branched hydroxyl groups of the modified acrylic resin to form a secondary network characterized by high branching and high rigidity. Combining the branched rigid structure of the modified resin with the crosslinking backbone of the acrylic resin main network, a dense bilayer interpenetrating network is ultimately formed at the molecular scale. This provides the structural basis for the high hardness and corrosion resistance of the coating, ultimately overcoming the limitations of traditional epoxy resins' tendency to yellow and the insufficient performance of pure acrylic resins, achieving a comprehensive performance balance.

[0018] Meanwhile, polyester-modified polydimethylsiloxane and polysiloxane solution optimize surface leveling and hydrophobicity, while polyolefin balances hardness and flexibility; the mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether ensures film-forming stability. Through synergistic effects, the components form an external weld repair coating with both high crosslinking density and complementary functions without the intervention of phenolic structures. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation process of an external weld repair coating provided by the present invention.

[0020] Figure 2 This is a photograph of the external weld repair coating prepared in Example 1. Specific implementation methods To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0021] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0022] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. The invention will be further described below with reference to embodiments, but is not limited thereto.

[0023] Example 1 This embodiment provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 45 parts acrylic resin, 20 parts modified acrylic resin, 15 parts hexamethylene diisocyanate trimer, 14 parts polyethylene wax powder, 1 part polydimethylsiloxane-polyhexamethylene adipate copolymer, 2 parts 30 wt.% hydroxyl polysiloxane solution, 3 parts polypropylene, 4 parts polyethylene glycol monophosphate polyester, and 15 parts a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether. The acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 80 mgKOH / g; The mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is 6:2; The number average molecular weight of polypropylene is 500; The preparation of the modified acrylic resin includes the following steps: Add 100 parts of acrylic resin and 30 parts of cyclohexanediol diglycidyl ether to the reaction vessel, stir at 300 rpm, heat to 50°C, and maintain for 30 min; Then add 15 parts of diglycidyl ether and 0.1 parts of hydroquinone to the reaction vessel in sequence, and stir for 30 minutes until the mixture is uniform; Add 0.5 parts of triethylamine dropwise to the reactor over a period of 5 minutes, heat to 80°C, turn on nitrogen protection, and stir at 400 rpm for 2 hours. Samples were taken every 30 minutes, and the residual epoxy value was measured to be 0.03 eq / 100g, thus obtaining the modified acrylic resin.

[0024] The preparation method of the external weld repair coating is as follows: Figure 1 As shown, it includes the following steps: S1: Add a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether to the dispersion vessel and start stirring; add acrylic resin and modified acrylic resin until the resin is completely dissolved; add hexamethylene diisocyanate trimer and stir evenly to obtain a pre-prepared acrylic resin mixture for later use; S2: Take polyethylene wax powder with an average particle size of 5μm and add it to a disperser. Disperse it at 25℃ and 1200rpm for 30min to obtain a pre-prepared wax powder dispersion for later use. S3: Transfer the pre-prepared wax powder dispersion to a sand mill and grind it at 900 rpm for 30 minutes. Separate the coarse impurities through a 200-mesh sieve to obtain a mixed wax slurry for later use. S4: Mix the mixed wax slurry and the pre-prepared acrylic resin mixture evenly, then add polydimethylsiloxane-polyhexyl adipate copolymer, hydroxyl polysiloxane solution, polypropylene, and polyethylene glycol monophosphate polyester in sequence, mix evenly, and stir at 1000 rpm for 30 minutes to obtain the external weld repair coating. Figure 2 As shown.

[0025] Example 2 This embodiment provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 50 parts acrylic resin, 18 parts modified acrylic resin, 17 parts dicyclohexylmethane diisocyanate, 14 parts polytetrachloroethylene wax powder, 2 parts polydimethylsiloxane-polyethylene terephthalate copolymer, 3 parts 30 wt.% methyl polysiloxane solution, 3 parts polyethylene, 4 parts polypropylene glycol diphosphate polyester, and 16 parts a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether.

[0026] The acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 100 mgKOH / g; The mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is 7:2; The number average molecular weight of polyethylene is 800; The preparation of the modified acrylic resin includes the following steps: Add 100 parts of acrylic resin and 40 parts of cyclohexanediol diglycidyl ether to the reactor, stir at 400 rpm, heat to 60°C, and maintain for 30 min. Then add 20 parts of diglycidyl ether and 0.2 parts of hydroquinone to the reaction vessel in sequence, and stir for 30 minutes until the mixture is uniform; Add 1 part of triethylamine dropwise to the reactor over 5 minutes, heat to 90°C, turn on nitrogen protection, and stir at 400 rpm for 2 hours. Samples were taken every 30 minutes, and the residual epoxy value was measured to be 0.04 eq / 100g, thus obtaining the modified acrylic resin.

[0027] The preparation method of the external weld repair coating is as follows: Figure 1 As shown, it includes the following steps: S1: Add a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether to the dispersion vessel and start stirring; slowly add acrylic resin and modified acrylic resin until the resin is completely dissolved; add dicyclohexylmethane diisocyanate and stir evenly to obtain a pre-prepared acrylic resin mixture for later use. S2: Add polytetrachloroethylene wax powder with an average particle size of 6μm into a disperser and disperse at 25℃ and 1200rpm for 30min to obtain a pre-prepared wax powder dispersion for later use. S3: Transfer the pre-prepared wax powder dispersion to a sand mill and grind it at 900 rpm for 30 minutes. Separate the coarse impurities through a 200-mesh sieve to obtain a mixed wax slurry for later use. S4: Mix the mixed wax slurry and the pre-prepared acrylic resin mixture evenly, and then add polydimethylsiloxane-polyethylene terephthalate copolymer, methyl polysiloxane solution, polyethylene and polypropylene glycol diphosphate polyester in sequence. Mix evenly and stir at 1000 rpm for 30 minutes to obtain the external weld repair coating.

[0028] Example 3 This embodiment provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 40 parts acrylic resin, 15 parts modified acrylic resin, 20 parts dicyclohexylmethane diisocyanate, 16 parts polytetrachloroethylene wax powder, 3 parts polydimethylsiloxane-polyhexyl adipate copolymer, 4 parts 30 wt.% hydroxyl polysiloxane solution, 5 parts polyethylene, 6 parts polypropylene glycol diphosphate polyester, and 20 parts a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether.

[0029] The acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 90 mgKOH / g; The mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is 8:4; The number average molecular weight of polyethylene is 800; The preparation of the modified acrylic resin includes the following steps: Add 100 parts of acrylic resin and 50 parts of cyclohexanediol diglycidyl ether to the reaction vessel, stir at 300 rpm, heat to 50°C, and maintain for 30 min; Then add 25 parts of diglycidyl ether and 0.15 parts of hydroquinone to the reaction vessel in sequence, and stir for 30 minutes until the mixture is uniform. Add 0.8 parts of triethylamine dropwise to the reactor over a period of 5 minutes, heat to 80°C, turn on nitrogen protection, and stir at 400 rpm for 2 hours. Samples were taken every 30 minutes, and the residual epoxy value was measured to be 0.03 eq / 100g, thus obtaining the modified acrylic resin.

[0030] The preparation method of the external weld repair coating is as follows: Figure 1 As shown, it includes the following steps: S1: Add a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether to the dispersion vessel and start stirring; slowly add acrylic resin and modified acrylic resin until the resin is completely dissolved; add dicyclohexylmethane diisocyanate and stir evenly to obtain a pre-prepared acrylic resin mixture for later use. S2: Add polytetrachloroethylene wax powder with an average particle size of 7μm into a disperser and disperse at 25℃ and 1200rpm for 30min to obtain a pre-prepared wax powder dispersion for later use. S3: Transfer the pre-prepared wax powder dispersion to a sand mill and grind it at 900 rpm for 30 minutes. Separate the coarse impurities through a 200-mesh sieve to obtain a mixed wax slurry for later use. S4: Mix the mixed wax slurry and the pre-prepared acrylic resin mixture evenly, and then add polydimethylsiloxane-polyhexane adipate copolymer, hydroxyl polysiloxane solution, polyethylene and polypropylene glycol diphosphate polyester in sequence. Mix evenly and stir at 1000 rpm for 30 min to obtain the external weld repair coating.

[0031] Example 4 This embodiment provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 48 parts acrylic resin, 17 parts modified acrylic resin, 23 parts hexamethylene diisocyanate trimer, 12 parts polypropylene wax powder, 1 part polydimethylsiloxane-polyethylene terephthalate copolymer, 3 parts 30 wt.% hydroxyl polysiloxane solution, 4 parts polypropylene, 5 parts polypropylene glycol diphosphate polyester, and 19 parts a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether.

[0032] The acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 100 mg KOH / g.

[0033] The mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is 8:2; The number average molecular weight of polypropylene is 600; The preparation of the modified acrylic resin includes the following steps: Add 100 parts of acrylic resin and 35 parts of cyclohexanediethanol diglycidyl ether to the reaction vessel, stir at 300 rpm, heat to 60°C, and maintain for 60 min; Then add 22 parts of diglycidyl ether and 0.18 parts of hydroquinone to the reaction vessel in sequence, and stir for 30 minutes until the mixture is uniform; Add 0.7 parts of triethylamine dropwise to the reactor over a period of 5 minutes, heat to 80°C, turn on nitrogen protection, and stir at 400 rpm for 2 hours. Samples were taken every 30 minutes, and the residual epoxy value was measured to be 0.04 eq / 100g, thus obtaining the modified acrylic resin.

[0034] The preparation method of the external weld repair coating is as follows: Figure 1 As shown, it includes the following steps: S1: Add a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether to the dispersion vessel and start stirring; slowly add acrylic resin and modified acrylic resin until the resin is completely dissolved; add hexamethylene diisocyanate trimer and stir evenly to obtain a pre-prepared acrylic resin mixture for later use; S2: Add polypropylene wax powder with an average particle size of 7μm into a disperser and disperse at 25℃ and 1300rpm for 30min to obtain a pre-prepared wax powder dispersion for later use. S3: Transfer the pre-prepared wax powder dispersion to a sand mill and grind it at 900 rpm for 30 minutes. Separate the coarse impurities through a 200-mesh sieve to obtain a mixed wax slurry for later use. S4: Mix the mixed wax slurry and the pre-prepared acrylic resin mixture evenly, and then add polydimethylsiloxane-polyethylene terephthalate copolymer, hydroxyl polysiloxane solution, polypropylene and polypropylene glycol diphosphate polyester in sequence. Mix evenly and stir at 1000 rpm for 30 min to obtain the external weld repair coating.

[0035] Example 5 This embodiment provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 45 parts acrylic resin, 25 parts modified acrylic resin, 18 parts hexamethylene diisocyanate trimer, 14 parts polyethylene wax powder, 1 part polydimethylsiloxane-polyhexamethylene adipate copolymer, 3 parts 30 wt.% methyl polysiloxane solution, 3 parts polypropylene, 4 parts polypropylene glycol diphosphate polyester, and 15 parts a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether.

[0036] The acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 110 mgKOH / g; The mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is 7:2; The number average molecular weight of polyethylene is 1000; The preparation of the modified acrylic resin includes the following steps: Add 100 parts of acrylic resin and 45 parts of cyclohexanediethanol diglycidyl ether to the reaction vessel, stir at 400 rpm, heat to 50°C, and maintain for 30 min; Then add 18 parts of diglycidyl ether and 0.13 parts of hydroquinone to the reaction vessel in sequence, and stir for 30 minutes until the mixture is uniform; Add 0.9 parts of triethylamine dropwise to the reactor over a period of 5 minutes, heat to 80°C, turn on nitrogen protection, and stir at 400 rpm for 2 hours. Samples were taken every 30 minutes, and the residual epoxy value was measured to be 0.03 eq / 100g, thus obtaining the modified acrylic resin.

[0037] The preparation method of the external weld repair coating is as follows: Figure 1 As shown, it includes the following steps: S1: Add a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether to the dispersion vessel and start stirring; slowly add acrylic resin and modified acrylic resin until the resin is completely dissolved; add hexamethylene diisocyanate trimer and stir evenly to obtain a pre-prepared acrylic resin mixture for later use; S2: Take polyethylene wax powder with an average particle size of 5μm and add it to a disperser. Disperse at 25℃ and 1300rpm for 30min to obtain a pre-prepared wax powder dispersion for later use. S3: Transfer the pre-prepared wax powder dispersion to a sand mill and grind it at 900 rpm for 30 minutes. Separate the coarse impurities through a 200-mesh sieve to obtain a mixed wax slurry for later use. S4: Mix the mixed wax slurry and the pre-prepared acrylic resin mixture evenly, and then add polydimethylsiloxane-polyhexane adipate copolymer, methyl polysiloxane solution, polypropylene and polypropylene glycol diphosphate polyester in sequence. Mix evenly and stir at 1000 rpm for 30 min to obtain the external weld repair coating.

[0038] Example 6 This embodiment provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 43 parts acrylic resin, 25 parts modified acrylic resin, 16 parts dicyclohexylmethane diisocyanate, 14 parts polyethylene wax powder, 1 part polydimethylsiloxane-polyethylene terephthalate copolymer, 2 parts 30 wt.% methyl polysiloxane solution, 3 parts polypropylene, 4 parts polypropylene glycol diphosphate polyester, and 14 parts a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether.

[0039] The acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 90 mgKOH / g; The mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is 8:3; The number average molecular weight of polypropylene is 900; The preparation of the modified acrylic resin includes the following steps: Add 100 parts of acrylic resin and 38 parts of cyclohexanediethanol diglycidyl ether to the reaction vessel, stir at 400 rpm, heat to 50°C, and maintain for 30 min; Then add 17 parts of diglycidyl ether and 0.16 parts of hydroquinone to the reaction vessel in sequence, and stir for 30 minutes until the mixture is uniform; Add 0.9 parts of triethylamine dropwise to the reactor over a period of 5 minutes, heat to 80°C, turn on nitrogen protection, and stir at 400 rpm for 2 hours. Samples were taken every 30 minutes, and the residual epoxy value was measured to be 0.04 eq / 100g, thus obtaining the modified acrylic resin.

[0040] The preparation method of the external weld repair coating is as follows: Figure 1 As shown, it includes the following steps: S1: Add a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether to the dispersion vessel and start stirring; slowly add acrylic resin and modified acrylic resin until the resin is completely dissolved; add dicyclohexylmethane diisocyanate and stir evenly to obtain a pre-prepared acrylic resin mixture for later use. S2: Add polyethylene wax powder with an average particle size of 6μm into a disperser and disperse at 25℃ and 1300rpm for 30min to obtain a pre-prepared wax powder dispersion for later use. S3: Transfer the pre-prepared wax powder dispersion to a sand mill and grind it at 900 rpm for 30 minutes. Separate the coarse impurities through a 200-mesh sieve to obtain a mixed wax slurry for later use. S4: Mix the mixed wax slurry and the pre-prepared acrylic resin mixture evenly, and then add polydimethylsiloxane-polyethylene terephthalate copolymer, methyl polysiloxane solution, polypropylene and polypropylene glycol diphosphate polyester in sequence. Mix evenly and stir at 1000 rpm for 30 min to obtain the external weld repair coating.

[0041] Comparative Example 1 This comparative example provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 55 parts acrylic resin, 10 parts dicyclohexylmethane diisocyanate, 14 parts polyethylene wax powder, 12 parts polydimethylsiloxane-polyethylene terephthalate copolymer polyester-modified polydimethylsiloxane, 4 parts polyethylene glycol monophosphate polyester, and 15 parts alcohol ether mixed solvent.

[0042] The acrylic resin is a hydroxyl acrylic resin with a hydroxyl value of 80 mg KOH / g.

[0043] The mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the alcohol-ether mixed solvent is 7:2. The number average molecular weight of polyethylene is 500; The preparation of the external weld repair coating includes the following steps: S1: Add alcohol-ether mixed solvent to the dispersion vessel and start stirring; slowly add acrylic resin until the resin is completely dissolved; add crosslinking agent dicyclohexylmethane diisocyanate and stir evenly; S2: Add polyethylene wax powder, mix evenly, then add polydimethylsiloxane-polyethylene terephthalate copolymer polyester modified polydimethylsiloxane and polyethylene glycol monophosphate polyester phosphate polyester wetting and dispersing agent in sequence, mix evenly, and obtain a mixed coating; Comparative Example 2 This comparative example provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 35 parts hydroxy acrylic resin, 15 parts zinc powder, 8 parts mica powder, 14 parts propylene glycol methyl ether acetate, 2 parts anti-settling agent, 0.5 parts accelerator, and 12 parts hexamethylene diisocyanate trimer.

[0044] The preparation of the external weld repair coating includes the following steps: S1: Add barium sulfate, mica powder and propylene glycol methyl ether acetate solvent to a sand mill and grind at 1200 rpm for 30 min; S2: Add hydroxyl acrylic resin to the dispersion vessel, add pigment and filler slurry while stirring at 800 rpm, mix for 30 min, then add the remaining additives, stir for 20 min, add hexamethylene diisocyanate trimer, and obtain the external weld repair coating.

[0045] Comparative Example 3 This comparative example provides an external weld repair coating, which is made of the following components in the indicated weight ratios: 40 parts thermoplastic acrylic resin, 10 parts rutile titanium dioxide, 8 parts talc, 8-12 parts barium sulfate, 20 parts ethyl acetate-toluene mixed solvent, 0.5 parts ultraviolet absorber, 0.3 parts leveling agent, and 0.3 parts defoamer.

[0046] The preparation of the external weld repair coating includes the following steps: S1: Add ethyl acetate-toluene mixed solvent to the dispersion vessel, start stirring at 1000 rpm, add titanium dioxide, talc and barium sulfate in sequence, and disperse for 40 min; S2: Add thermoplastic acrylic resin, heat to 50℃, and stir for 30 minutes until completely dissolved; S3: Cool to room temperature, then add UV absorber, leveling agent and defoamer, stir at low speed for 15 minutes, and filter to obtain the external weld repair coating.

[0047] The coatings for external weld repair prepared in Examples 1-6 and Comparative Examples 1-3 of this application were tested and compared in terms of gloss, adhesion, scratch resistance, solvent resistance, hardness, etc. The results are shown in Table 1.

[0048] Test method: Gloss level: Measured using a 60° gloss meter, the gloss level is determined by the light reflectance. "Excellent" corresponds to high reflectance and uniform reflection.

[0049] Adhesion: Use a cross-cutting tool to cut 1mm×1mm squares on the surface of the tin-plated coating (cut through the coating to the substrate). After peeling off with tape, grade according to the degree of square peeling (Grade 1 is no peeling, Grade 3 is peeling area >15%).

[0050] Scratch resistance: A scratch tester is used to apply different weights (such as 300g, 400g, 600g) of load to the scratch needle and scratch the coating surface. The tester observes whether obvious scratches appear and takes the maximum load that does not produce scratches as the scratch resistance value.

[0051] Solvent resistance: Use degreased cotton soaked in methyl ethyl ketone (MEK) to apply a constant pressure of 1 kg and wipe the coating surface back and forth once as one cycle until the coating shows damage such as exposure of the substrate or discoloration. Record the number of wipings before damage.

[0052] Hardness: Select pencils of different hardness (such as HB, 1H, 2H), scratch the coating surface at a 45° angle and a 500g load, and observe whether scratches are left. The hardness of the coating is the hardness of the hardest pencil that does not produce scratches.

[0053] High-temperature water boiling test: Immerse the tin-plated sheet coated with the sample in boiling water at 121℃ for 45 minutes, then remove it and allow it to cool naturally to room temperature. Observe whether the coating peels off, water spots, rust, or other phenomena occur.

[0054] Corrosion resistance: Immerse the tin-plated sheet with the sample (exposed weld seam) in a 20% copper sulfate solution for a certain period of time (estimated to be 5 minutes based on the table), then remove it and observe whether rust appears on the weld seam and coating surface.

[0055] Table 1 Performance test results of the external weld repair coatings prepared in the examples and comparative examples

[0056] As shown in Table 1, the test results of Comparative Examples 1-3 are significantly different from those of Examples 1-6 of the present invention.

[0057] This is because Examples 1-6 use acrylic resin and epoxy-modified acrylic resin as the main components. The two react synergistically with isocyanate crosslinking agents to form a three-dimensional network structure, laying the foundation for the coating's high hardness, solvent resistance, and weather resistance. Epoxy-modified acrylic resin, as an interface reinforcing agent, forms a chemical anchor with the metal surface through strong polar epoxy groups, achieving Grade 1 adhesion. Its acrylic segments ensure compatibility with the main resin. At the same time, precisely dispersed and ground wax powder forms a physical barrier to improve scratch resistance, polysiloxane additives optimize gloss and leveling, and phosphate polyester ensures uniform dispersion of components. Ultimately, this solves the pain points of traditional epoxy coatings, such as the presence of bisphenol A, weak adhesion, poor appearance, and uneven performance, achieving a balance between environmental protection and comprehensive performance.

[0058] It should be understood that the above are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, other modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A coating for repairing external weld seams, characterized in that, The product comprises the following components in parts by weight: 40-50 parts acrylic resin, 15-20 parts modified acrylic resin, 15-25 parts crosslinking agent, 12-16 parts wax powder, 1-3 parts polyester-modified polydimethylsiloxane, 2-4 parts polysiloxane solution, 3-5 parts polyolefin, 3-6 parts phosphate polyester, and 14-20 parts alcohol ether solvent. The modified acrylic resin is obtained by modifying the acrylic resin with cyclohexanediol diglycidyl ether.

2. The external weld repair coating according to claim 1, characterized in that, The acrylic resin has a hydroxyl value of 80-120 mgKOH / g; the polyester-modified polydimethylsiloxane includes any one of polydimethylsiloxane-polyhexane adipate copolymer and polydimethylsiloxane-polyethylene terephthalate copolymer; the polysiloxane solution includes any one of hydroxyl polysiloxane solution and methyl polysiloxane solution; the polyolefin includes any one of polypropylene with a number average molecular weight of 500-1000 and polyethylene with a number average molecular weight of 500-1000; the phosphate polyester includes any one of polyethylene glycol monophosphate polyester and polypropylene glycol diphosphate polyester.

3. The external weld repair coating according to claim 1, characterized in that, The crosslinking agent is an isocyanate crosslinking agent, which includes either hexamethylene diisocyanate trimer or dicyclohexylmethane diisocyanate.

4. The external weld repair coating according to claim 1, characterized in that, The wax powder includes any one of polyethylene wax powder, polytetrachloroethylene wax powder, and polypropylene wax powder, and the average particle size of the wax powder is 5-8 μm.

5. The external weld repair coating according to claim 1, characterized in that, The alcohol ether solvent is a mixed solvent of propylene glycol methyl ether acetate and ethylene glycol ethyl ether, wherein the mass ratio of propylene glycol methyl ether acetate to ethylene glycol ethyl ether in the mixed solvent is (6-8):(2-4).

6. A method for preparing an external weld repair coating according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Add alcohol ether solvent to dispersion vessel, add acrylic resin and modified acrylic resin while stirring until the resin is completely dissolved; add crosslinking agent and stir evenly to obtain pre-prepared acrylic resin mixture; S2: Add wax powder to a disperser and disperse to obtain a pre-prepared wax powder dispersion; S3: Transfer the pre-prepared wax powder dispersion to a sand mill, grind at 900-1000 rpm for 40-50 min, sieve, and obtain the mixed wax slurry; S4: Mix the mixed wax slurry with the pre-made acrylic resin mixture, and add polyester-modified polydimethylsiloxane, polysiloxane solution, polyolefin and phosphate polyester in sequence during the stirring process. Mix evenly to obtain the external weld repair coating.

7. The method for preparing an external weld repair coating according to claim 6, characterized in that, The preparation method of the modified acrylic resin described in S1 includes the following steps: Add acrylic resin and cyclohexanediol diglycidyl ether to the reactor, stir at 300-400 rpm, heat to 50-60℃, and maintain for 30-60 min; Add diglycidyl ether and hydroquinone sequentially to the reaction vessel and stir for 10-30 minutes until the mixture is homogeneous; Add triethylamine dropwise over 5-8 minutes, heat to 80-100°C, turn on nitrogen protection, and stir at 300-400 rpm for 2-3 hours. Samples were taken every 30 minutes, and the reaction endpoint was determined when the residual epoxy value was 0.02-0.05 eq / 100g, thus obtaining the modified acrylic resin.

8. The method for preparing an external weld repair coating according to claim 7, characterized in that, The acrylic resin, cyclohexanediol diglycidyl ether, diglycidyl ether, hydroquinone, and triethylamine are formulated in the following weight ratios: 100 parts acrylic resin, 30-50 parts cyclohexanediol diglycidyl ether, 15-25 parts diglycidyl ether, 0.1-0.2 parts hydroquinone, and 0.5-1 parts triethylamine.

9. The method for preparing an external weld repair coating according to claim 6, characterized in that, The disperser in S2 operates at a speed of 1200-1300 rpm, a dispersion time of 30-40 min, and a temperature of 25-45℃.

10. The method for preparing an external weld repair coating according to claim 6, characterized in that, In S4, the mixer speed is kept stable at 800-1000 rpm, and the mixing time is 30-60 min.

Images