Metal material surface protective coating and preparation method thereof

Abstract

The invention relates to the technical field of coating compositions, in particular to a metal material surface protective coating and a preparation method thereof. The coating is prepared from the following raw materials in percentage by weight: 100 to 110 parts of film forming matter, 5 to 10 parts of butyl glycidyl ether, 3 to 5 parts of non-reactive toughening agent, 10 to 15 parts of zinc phosphate, 0.5 to 2 parts of silicon dioxide, 0.5 to 1.5 parts of dispersing agent, 0.3 to 0.8 part of defoaming agent, 0.2 to 0.5 part of flatting agent, 0.5 to 1.5 parts of silane coupling agent, 6 to 12 parts of butyl acetate and 0.1 to 0.8 part of propylene glycol methyl ether acetate. A compact coating system with excellent adhesive force, high hardness, good toughness and corrosion resistance is constructed, and comprehensive and long-acting protection on a metal base material is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coating compositions, in particular to a metal material surface protective coating and a preparation method thereof. BACKGROUND

[0002] Most metals are in a thermodynamically unstable state, and when exposed to the atmosphere, seawater or industrial environment, they will spontaneously react with the surrounding oxygen, moisture and corrosive media or undergo electrochemical corrosion, leading to gradual degradation of the material, i.e. common rusting and corrosion. This process not only affects the appearance of the product, but also seriously damages its structural integrity, mechanical properties and service life. By forming a functional protective layer on the surface of the metal substrate, the contact of environmental media such as water, oxygen and corrosive ions with the metal surface can be effectively isolated, and the comprehensive performance of the metal material such as wear resistance, high temperature resistance and insulation can be improved, thereby prolonging the service period of the product and reducing the use cost. In practical applications, the coating in the aerospace field needs to have excellent high-temperature oxidation resistance and corrosion resistance to ensure the reliable operation of the engine hot end components, the coating in the marine engineering field needs to have long-term salt spray corrosion resistance and anti-biofouling ability to prolong the service life of marine steel structures, the coating in the automobile manufacturing field needs to improve the wear resistance and corrosion resistance of the chassis and engine components to reduce maintenance costs, and the coating in the electronic and electrical field needs to consider both insulation and reliability to ensure the stable operation of electronic components.

[0003] In the prior art, the high-temperature resistance of traditional acrylic resin coatings is generally insufficient, and in slightly high temperature environments such as industrial production and outdoor service, they are prone to softening, deformation or even peeling, making it difficult to maintain a stable protective state. At the same time, the hardness of such coatings is insufficient and is easily scratched or damaged. Traditional epoxy coatings, on the other hand, rely on amine curing agents for curing and molding, and during the curing process, internal stress is easily generated due to volume shrinkage of the system, which further accumulates with the extension of service time or fluctuations in environmental temperature and humidity, thereby damaging the interfacial bonding state between the coating and the metal substrate, eventually leading to phenomena such as peeling, cracking and even peeling of the coating, which severely weakens the protective effectiveness of the coating and shortens the actual service period of the metal material. SUMMARY

[0004] To solve the problems mentioned in the background art, the present application provides a metal material surface protective coating and a preparation method thereof.

[0005] To achieve the above-mentioned purposes, the present application adopts the following technical solutions: A metal material surface protective coating, comprising the following raw materials in percentage by weight: 100-110 parts of a film forming substance, 5-10 parts of butyl glycidyl ether, 3-5 parts of a non-reactive toughening agent, 10-15 parts of zinc phosphate, 0.5-2 parts of silicon dioxide, 0.5-1.5 parts of a dispersing agent, 0.3-0.8 parts of an antifoaming agent, 0.2-0.5 parts of a leveling agent, 0.5-1.5 parts of a silane coupling agent, 6-12 parts of butyl acetate, and 0.1-0.8 parts of propylene glycol methyl ether acetate.

[0006] Further, the film forming substance is prepared by the following steps: N-vinyl carbazole and butyl acrylate are added into a reactor pre-loaded with N, N-dimethylformamide, stirred for 10-30 min, the oil bath is heated, an initiator is added, and the reaction is continuously stirred for 12-24 h. After the reaction is completed, the product is precipitated and purified after cooling to room temperature to obtain the film forming substance.

[0007] Further, the non-reactive toughening agent comprises one or more of dibutyl phthalate, dioctyl phthalate, diisooctyl adipate, and dibutyl sebacate.

[0008] Further, the dispersing agent comprises one or more of dispersing agent BYK-161, dispersing agent BYK-163, dispersing agent EFKA-4010, and dispersing agent EFKA-4050.

[0009] Further, the antifoaming agent comprises at least one of silicone-based antifoaming agents or non-silicon polymer-based antifoaming agents.

[0010] Further, the leveling agent comprises one or more of leveling agent 333, leveling agent 306, leveling agent 358, or leveling agent 361.

[0011] Further, the silane coupling agent comprises one or more of silane coupling agent KH-570, silane coupling agent KH-560, silane coupling agent KH-550, or silane coupling agent A151.

[0012] Further, the mass ratio of N-vinyl carbazole to butyl acrylate is (6.5-8):(2.8-4.2), the amount of N, N-dimethylformamide added is 200-300% of the total mass of monomers, and the amount of initiator added is 0.5-1.5%, and the initiator is azobisisobutyronitrile.

[0013] Further, the stirring speed is 100-200 rpm, and the target temperature of the oil bath heating is 65-70℃.

[0014] According to another aspect of the present application, a preparation method of the above-mentioned metal material surface protective coating is provided, comprising the following steps: S1, each raw material is taken by weight fraction, standby, zinc phosphate, silicon dioxide is dried at 100-120 DEG C for 1-2h; S2, two-thirds of the formula amount of butyl acetate, propylene glycol methyl ether acetate, dispersant, defoaming agent and the dried zinc phosphate, silicon dioxide in step S1 are added to a dispersing machine, pre-dispersed at 800-1200 rpm for 15-30 min, to obtain a uniform slurry; S3, the speed is reduced to 300-500 rpm, the film forming material, butyl glycidyl ether, non-reactive toughening agent, leveling agent, silane coupling agent and the remaining one-third of butyl acetate are sequentially added to the slurry obtained in step S2, and the stirring is continued for 30-60 min to obtain a paint; S4, the paint obtained in step S3 is transferred to a sand mill or a three-roll mill for grinding to a fineness of ≤25 μm, and after grinding, it is filtered with a 200-400 mesh filter to obtain a metal material surface protective coating.

[0015] The beneficial effects of the present application are: 1, the film forming material in the technical scheme of the present application is prepared by free radical copolymerization of N-vinyl carbazole and butyl acrylate, wherein the bulky rigid carbazole ring contained in the N-vinyl carbazole unit significantly improves the rigidity of the polymer chain through steric hindrance effect and π-π stacking effect, and enhances the packing density between the molecular chains, thereby imparting the coating with higher glass transition temperature, thermal stability and bulk hardness. At the same time, the introduction of butyl acrylate flexible segment and the addition of non-reactive toughening agent effectively increase the movement ability of the high molecular segment, so that the coating can disperse energy through chain segment orientation and movement when bearing stress, avoiding the brittleness of pure rigid structure, realizing the balance of high hardness and good toughness, and significantly reducing the internal stress of the system.

[0016] 2, the present application constructs a multiple protection mechanism combining physical barrier, chemical passivation and interface enhancement, and the dense polymer matrix composed of rigid segments provides excellent basic shielding. When the corrosion medium penetrates to the metal interface, controllable hydrolysis can occur, and the released phosphate ions can react with the metal substrate to form a stable insoluble passivation film, effectively inhibiting the anodic dissolution process of the metal. The silane coupling agent forms a firm covalent bond between the organic coating and the inorganic metal substrate, greatly enhancing the adhesion of the coating, especially the wet adhesion, effectively preventing the peeling of the coating caused by interface failure.

[0017] 3, the synergistic effect of the defoaming agent and the leveling agent in the technical scheme of the present application effectively eliminates the defects such as bubbles, pinholes and surface unevenness that may occur during the preparation and film formation of the coating, and finally forms a continuous, dense, smooth and defect-free complete protective layer. DETAILED DESCRIPTION

[0018] The technical solutions of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of the present application.

[0019] Unless otherwise specified, the raw materials used in the present application are all obtained from market-purchased conventional products.

[0020] Preparation Example 1 The film-forming material is prepared by the following steps: 6.5 g of N-vinylcarbazole and 4.0 g of butyl acrylate are added to a reactor pre-charged with 21.0 g of N, N-dimethylformamide, stirred at a speed of 100 rpm for 10 min, the oil bath is heated to 65℃, 0.0525 g of azobisisobutyronitrile is added, and the stirring is continued at a speed of 100 rpm for 12 h. After the reaction is completed, the product is precipitated and filtered after cooling to room temperature, and dried at 50℃ to constant weight to obtain the film-forming material.

[0021] Preparation Example 2 The film-forming material is prepared by the following steps: 7.0 g of N-vinylcarbazole and 3.5 g of butyl acrylate are added to a reactor pre-charged with 26.25 g of N, N-dimethylformamide, stirred at a speed of 150 rpm for 20 min, the oil bath is heated to 68℃, 0.105 g of azobisisobutyronitrile is added, and the stirring is continued at a speed of 150 rpm for 18 h. After the reaction is completed, the product is precipitated and filtered after cooling to room temperature, and dried at 50℃ to constant weight to obtain the film-forming material.

[0022] Preparation Example 3 The film-forming material is prepared by the following steps: 8.0 g of N-vinylcarbazole and 2.8 g of butyl acrylate are added to a reactor pre-charged with 32.4 g of N, N-dimethylformamide, stirred at a speed of 200 rpm for 30 min, the oil bath is heated to 70℃, 0.162 g of azobisisobutyronitrile is added, and the stirring is continued at a speed of 200 rpm for 24 h. After the reaction is completed, the product is precipitated and filtered after cooling to room temperature, and dried at 50℃ to constant weight to obtain the film-forming material.

[0023] Example 1 A preparation method of a metal material surface protective coating, comprising the following steps: S1, the raw materials are weighed according to the weight fraction, and used, 10 parts of zinc phosphate and 0.5 parts of silicon dioxide are dried at 100℃ for 1 h; S2, 4 parts of butyl acetate, 0.1 part of propylene glycol methyl ether acetate, 0.5 part of dispersant BYK-161, 0.3 part of silicone antifoaming agent BYK-028 and the dried zinc phosphate, silicon dioxide in step S1 were added into a dispersing machine, and pre-dispersed at 800 rpm for 15 min to obtain a uniform slurry; S3, the speed was reduced to 300 rpm, and 100 parts of the film-forming material prepared in Preparation Example 1, 5 parts of butyl glycidyl ether, 3 parts of dibutyl phthalate, 0.2 parts of leveling agent 333, 0.5 parts of silane coupling agent KH-570 and 2 parts of butyl acetate were sequentially added into the slurry obtained in step S2, and the stirring was continued for 30 min to obtain a paint; S4, the paint obtained in step S3 was transferred to a sand mill for grinding to a fineness of 25 μm, and after the grinding was completed, it was filtered with a 200 mesh filter to obtain a metal material surface protective coating.

[0024] Example 2 A method for preparing a metal material surface protective coating, comprising the following steps: S1, the raw materials were weighed according to the proportions, and were ready for use, and 11 parts of zinc phosphate, 0.7 parts of silicon dioxide were dried at 104℃ for 1 h; S2, 4 parts of butyl acetate, 0.2 parts of propylene glycol methyl ether acetate, 0.6 parts of dispersant BYK-163, 0.4 parts of silicone antifoaming agent BYK-028 and the dried zinc phosphate, silicon dioxide in step S1 were added into a dispersing machine, and pre-dispersed at 900 rpm for 20 min to obtain a uniform slurry; S3, the speed was reduced to 350 rpm, and 101 parts of the film-forming material prepared in Preparation Example 2, 6 parts of butyl glycidyl ether, 3.1 parts of dioctyl phthalate, 0.3 parts of leveling agent 306, 0.6 parts of silane coupling agent KH-560 and 2 parts of butyl acetate were sequentially added into the slurry obtained in step S2, and the stirring was continued for 35 min to obtain a paint; S4, the paint obtained in step S3 was transferred to a sand mill or a three-roll mill for grinding to a fineness of 20 μm, and after the grinding was completed, it was filtered with a 250 mesh filter to obtain a metal material surface protective coating.

[0025] Example 3 A method for preparing a metal material surface protective coating, comprising the following steps: S1, the raw materials were weighed according to the proportions, and were ready for use, and 11.5 parts of zinc phosphate, 0.8 parts of silicon dioxide were dried at 105℃ for 1.5 h; S2, 6 parts of butyl acetate, 0.3 parts of propylene glycol methyl ether acetate, 0.9 parts of dispersant EFKA-4010, 0.5 parts of silicone antifoaming agent BYK-028 and the dried zinc phosphate, silicon dioxide in step S1 were added into a dispersing machine, and pre-dispersed at 1000 rpm for 20 min to obtain a uniform slurry; S3, the speed was reduced to 400 rpm, 105 parts of the film-forming material prepared in Preparation Example 3, 8 parts of butyl glycidyl ether, 4.6 parts of diisooctyl adipate, 0.4 parts of leveling agent 358, 0.9 parts of silane coupling agent KH-550 and 3 parts of butyl acetate were added into the slurry obtained in step S2 in sequence, and the stirring was continued for 40 min to obtain a paint; S4, the paint obtained in step S3 was transferred into a sand mill for grinding to a fineness of 25 μm, and after the grinding was completed, it was filtered with a 300 mesh filter to obtain a metal material surface protective coating.

[0026] Example 4 A method for preparing a metal material surface protective coating, comprising the following steps: S1, the raw materials were weighed according to the proportions, and were ready for use, and 13 parts of zinc phosphate and 1 part of silicon dioxide were dried at 112℃ for 1.5 h; S2, 6 parts of butyl acetate, 0.4 parts of propylene glycol methyl ether acetate, 1.1 parts of dispersant EFKA-4050, 0.6 parts of silicone antifoaming agent BYK-028 and the dried zinc phosphate, silicon dioxide in step S1 were added into a dispersing machine, and pre-dispersed at 1000 rpm for 20 min to obtain a uniform slurry; S3, the speed was reduced to 400 rpm, 106 parts of the film-forming material prepared in Preparation Example 1, 8 parts of butyl glycidyl ether, 4.8 parts of dibutyl sebacate, 0.4 parts of leveling agent 361, 1.2 parts of silane coupling agent KH-550 and 3 parts of butyl acetate were added into the slurry obtained in step S2 in sequence, and the stirring was continued for 50 min to obtain a paint; S4, the paint obtained in step S3 was transferred into a sand mill or a three-roll mill for grinding to a fineness of 20 μm, and after the grinding was completed, it was filtered with a 300 mesh filter to obtain a metal material surface protective coating.

[0027] Example 5 A method for preparing a metal material surface protective coating, comprising the following steps: S1, the raw materials were weighed according to the proportions, and were ready for use, and 14 parts of zinc phosphate and 1.5 parts of silicon dioxide were dried at 116℃ for 2 h; S2, 8 parts of butyl acetate, 0.7 parts of propylene glycol methyl ether acetate, 1.4 parts of dispersant BYK-161, 0.7 parts of silicone antifoaming agent BYK-028 and the dried zinc phosphate, silica in step S1 were added into a dispersing machine, and pre-dispersed at 1100 rpm for 25 min to obtain a uniform slurry; S3, the speed was reduced to 450 rpm, and 109 parts of the film-forming material prepared in Preparation Example 2, 9 parts of butyl glycidyl ether, 4.9 parts of dibutyl phthalate, 0.4 parts of leveling agent 333, 1.3 parts of silane coupling agent A151 and 4 parts of butyl acetate were sequentially added into the slurry obtained in step S2, and the stirring was continued for 55 min to obtain a paint; S4, the paint obtained in step S3 was transferred into a sand mill or a three-roll mill for grinding to a fineness of 10 μm, and after the grinding was completed, the paint was filtered through a 350-mesh screen to obtain a metal material surface protective coating.

[0028] Example 6 A method for preparing a metal material surface protective coating, comprising the following steps: S1, the raw materials were weighed according to the proportions, and were prepared for use, and 15 parts of zinc phosphate and 2 parts of silica were dried at 120℃ for 2 h; S2, 8 parts of butyl acetate, 0.8 parts of propylene glycol methyl ether acetate, 1.5 parts of dispersant BYK-163, 0.8 parts of silicone antifoaming agent BYK-028 and the dried zinc phosphate, silica in step S1 were added into a dispersing machine, and pre-dispersed at 1200 rpm for 30 min to obtain a uniform slurry; S3, the speed was reduced to 500 rpm, and 110 parts of the film-forming material prepared in Preparation Example 3, 10 parts of butyl glycidyl ether, 5 parts of dioctyl phthalate, 0.5 parts of leveling agent 306, 1.5 parts of silane coupling agent KH-570 and 4 parts of butyl acetate were sequentially added into the slurry obtained in step S2, and the stirring was continued for 60 min to obtain a paint; S4, the paint obtained in step S3 was transferred into a sand mill or a three-roll mill for grinding to a fineness of 10 μm, and after the grinding was completed, the paint was filtered through a 400-mesh screen to obtain a metal material surface protective coating.

[0029] Comparative Example 1 The difference between this comparative example and Preparation Example 1 is that N-vinyl carbazole is not added, and the other steps are the same as those in Preparation Example 1.

[0030] Comparative Example 2 The difference between this comparative example and Preparation Example 2 is that butyl acrylate is not added, and the other steps are the same as those in Preparation Example 2.

[0031] Comparative Example 3 The present comparative example differs from Example 1 in that the product prepared in Comparative Example 1 is used instead of the film-forming material prepared in Preparation Example 1, and the remaining steps are the same as in Example 1.

[0032] Comparative Example 4 The present comparative example differs from Example 2 in that the product prepared in Comparative Example 2 is used instead of the film-forming material prepared in Preparation Example 2, and the remaining steps are the same as in Example 2.

[0033] Comparative Example 5 The present comparative example differs from Example 3 in that the product prepared in Comparative Example 1 is used instead of the film-forming material prepared in Preparation Example 3, and the remaining steps are the same as in Example 4.

[0034] Comparative Example 6 The present comparative example differs from Example 4 in that the product prepared in Comparative Example 2 is used instead of the film-forming material prepared in Preparation Example 1, and the remaining steps are the same as in Example 4.

[0035] Comparative Example 7 The present comparative example differs from Example 5 in that no butyl glycidyl ether is added, and the remaining steps are the same as in Example 5.

[0036] Comparative Example 8 The present comparative example differs from Example 6 in that no dioctyl phthalate is added, and the remaining steps are the same as in Example 6.

[0037] A tinplate sheet with dimensions of 150 mm x 70 mm x 0.3 mm is prepared, and before use, the tinplate sheet is subjected to oil removal, polishing, cleaning and drying treatment to ensure that the surface is clean, rust-free and oil-free. A wire bar coater is used to uniformly coat the coating compositions prepared in Examples 1-6 and Comparative Examples 3-8 on the treated tinplate sheet, with the wet film thickness controlled at 100 μm. After all the coating samples are air-dried at room temperature, they are placed in a constant temperature air-drying oven and cured at 80°C for 1 h. After completion, they are cured at standard conditions (temperature 23±2°C, relative humidity 50±5%) for 24 h before testing as follows. At least 3 parallel samples are prepared for each group of samples.

[0038] I. Adhesion test: According to GB / T 9286-2021 “Paints and varnishes Cross-hatch test”, a 1 mm x 1 mm square is drawn on the coating using a sharp blade, and a special adhesive tape is attached. The tape is peeled off at a constant speed. The coating is rated from 0 (best) to 5 (worst) according to the area of coating that falls off.

[0039] II. Impact resistance test: According to GB / T 1732-2020 “Paint film impact resistance test method”, an impact tester is used to drop a 1 kg weight from a specified height of 50 cm to impact the front and back (concave surface) of the coating, and the presence or absence of cracks and peeling of the coating is observed.

[0040] Three, flexibility test: refer to GB / T 6742-2007 "Paint and Varnish - Bending Test (Cylinder Axis)", use the axis rod tester, bend the coated plate on the axis rod with different diameters by 180°, check whether the coating cracks, and express the minimum axis rod diameter (mm) that does not cause the coating damage.

[0041] Four, pencil hardness test: refer to GB / T 6739-2022 "Paint and Varnish - Determination of Film Hardness by Pencil Method", use a set of pencils from soft to hard (6B to 9H), push and scratch the coating surface at an angle of 45°, and take the highest hardness grade that does not scratch the coating as the pencil hardness of the coating.

[0042] Five, neutral salt spray resistance test: refer to GB / T 1771-2007 "Paint and Varnish - Determination of Resistance to Neutral Salt Spray", use a salt spray test chamber, configure a 5% NaCl solution, keep the temperature in the chamber at 35℃, draw an "X" mark on the surface of the sample plate (to the substrate), continuously spray, and take out the sample plate after 240h, 480h, and 720h respectively, and evaluate the corrosion spreading width (mm) of the single-sided scratch and the blistering on the plate surface.

[0043] Six, chemical resistance test: refer to GB / T 9274-1988 "Paint and Varnish - Determination of Resistance to Liquid Medium", immerse half of the area of the sample plate in a 5% H2SO4 solution to test the acid resistance, and immerse half of the area of the sample plate in a 3% NaOH solution to test the alkali resistance. After soaking at room temperature for 24h, take out and observe whether the coating has phenomena such as loss of luster, discoloration, blistering, and peeling.

[0044] The test results are shown in Tables 1 and 2: Table 1. Test results of part of the coating performance

[0045] Table 2. Test results of part of the coating performance

[0046] From Tables 1 and 2, it can be seen that the adhesion of Examples 1-6 is mostly at 0-1 level, showing good performance. N-vinylcarbazole and butyl acrylate in the film-forming material form a stable polymer network structure through polymerization, interact with fillers such as zinc phosphate and silicon dioxide, and various additives, and enhance the bonding force between the coating and the substrate. Comparative Examples 3 and 5 do not add N-vinylcarbazole, and Comparative Examples 4 and 6 do not add butyl acrylate, and the adhesion is obviously poor (3-4 level). N-vinylcarbazole and butyl acrylate play a key role in forming a good film structure and adhesion to the substrate during polymerization, and the absence of one of the components will lead to a decrease in the performance of the film-forming material, and then affect the bonding between the coating and the substrate.

[0047] The impact resistance of examples 1-6 is good, the impact height can reach 45-50 cm. The polymer formed by the film forming material has certain toughness and elasticity, which can absorb and disperse impact energy. At the same time, the reasonable collocation of fillers and additives also enhances the overall strength of the coating. Comparative examples 3, 5 do not add N-vinyl carbazole, comparative example 4 does not add butyl acrylate, the impact resistance is significantly reduced (15-25 cm). It shows that the polymer structure formed by N-vinyl carbazole and butyl acrylate can effectively buffer the impact force.

[0048] The flexibility of examples 3-6 is good, the minimum shaft rod diameter can reach 1-2 mm. The flexibility of comparative examples 3, 5, 7 is poor (3-10 mm). Not adding N-vinyl carbazole or butyl glycidyl ether will affect the flexibility of the polymer and the interaction between molecules, leading to the coating being more prone to cracking when bending.

[0049] The pencil hardness of examples 3-6 is high (2H-3H), which shows that the surface of the coating is relatively hard. The pencil hardness of comparative examples 3, 5 is low (B-HB), not adding N-vinyl carbazole will affect the formation and crosslinking of the polymer, leading to the hardness of the coating decreasing. Although the pencil hardness of comparative examples 4, 6 is similar to that of some examples, it can be known from the overall other performances that the lack of butyl acrylate will have an adverse effect on the overall performance of the coating.

[0050] The unilateral spread width of the scratch of examples 1-6 is small (1.5-3.8 mm) after 720 h salt spray test, which shows that the coating has good salt spray corrosion resistance. The salt spray resistance of comparative examples 3, 5 is poor (4.8-7.0 mm) without adding N-vinyl carbazole, and the salt spray resistance of comparative examples 4, 6 is poor without adding butyl acrylate. The lack of these components will affect the compactness and protective performance of the film forming material, making the salt spray more easily penetrate to the surface of the substrate, leading to corrosion spread.

[0051] Examples 3-6 have no change after being immersed in 5% H2SO4 solution for 24 h, and examples 1, 2 only have slight discoloration, which shows that the coating has good acid resistance. The acid resistance of comparative examples 3, 5 is significantly worse without adding N-vinyl carbazole, and serious discoloration and blistering phenomenon occurs. N-vinyl carbazole plays an important role in improving the chemical corrosion resistance of the coating, and the lack of it will lead to the coating being more easily damaged in the acidic environment.

[0052] Most of examples 1-6 only have slight discoloration or no change after being immersed in 3% NaOH solution for 24 h, which shows that the coating has good alkali resistance. The alkali resistance of comparative example 7 is poor without adding butyl glycidyl ether, and obvious discoloration and blistering phenomenon occurs. Butyl glycidyl ether may have a certain effect on improving the alkali resistance of the coating, and the lack of it will affect the stability of the coating in the alkaline environment.

[0053] In summary, the metal protective coating in the embodiments achieves synergistic complementarity between the rigid structure of N-vinylcarbazole and the flexible segments of butyl acrylate in the film-forming material. Furthermore, thanks to the optimized combination of functional fillers such as zinc phosphate and silica, as well as butyl glycidyl ether, various plasticizers, and additives, a dense coating system with excellent adhesion, high hardness, good toughness, and corrosion resistance is constructed, thus achieving comprehensive and long-lasting protection for the metal substrate.

[0054] In the description of this specification, the reference to terms such as "embodiment," "various embodiments," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or preparation example is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A protective coating for the surface of a metallic material, characterized in that, The raw materials, by weight, include: 100-110 parts film-forming substance, 5-10 parts butyl glycidyl ether, 3-5 parts non-reactive toughening agent, 10-15 parts zinc phosphate, 0.5-2 parts silica, 0.5-1.5 parts dispersant, 0.3-0.8 parts defoamer, 0.2-0.5 parts leveling agent, 0.5-1.5 parts silane coupling agent, 6-12 parts butyl acetate, and 0.1-0.8 parts propylene glycol methyl ether acetate; The film-forming substance is prepared by free radical copolymerization of N-vinylcarbazole and butyl acrylate.

2. The protective coating for a metal material surface according to claim 1, characterized in that, The film-forming substance is prepared by the following steps: N-vinylcarbazole and butyl acrylate were added to a reactor pre-filled with N,N-dimethylformamide and stirred for 10-30 min. The mixture was heated in an oil bath, and an initiator was added. The mixture was stirred continuously for 12-24 h. After the reaction was completed, the mixture was cooled to room temperature, and the product was precipitated and purified to obtain the film-forming substance.

3. The protective coating for a metal material surface according to claim 1, characterized in that, Non-reactive toughening agents include one or more of dibutyl phthalate, dioctyl phthalate, diisooctyl adipate, and dibutyl sebacate.

4. The protective coating for a metal material surface according to claim 1, characterized in that, The dispersant includes one or more of dispersant BYK-161, dispersant BYK-163, dispersant EFKA-4010 and dispersant EFKA-4050.

5. A protective coating for a metal material surface according to claim 1, characterized in that, Defoamers include at least one of silicone defoamers or non-silicone polymer defoamers.

6. The protective coating for a metal material surface according to claim 1, characterized in that, The leveling agent includes one or more of leveling agent 333, leveling agent 306, leveling agent 358 or leveling agent 361.

7. The protective coating for a metal material surface according to claim 1, characterized in that, Silane coupling agents include one or more of silane coupling agents KH-570, KH-560, KH-550, or A151.

8. A protective coating for a metal material surface according to claim 2, characterized in that, The mass ratio of N-vinylcarbazole to butyl acrylate is (6.5-8):(2.8-4.2). The amount of N,N-dimethylformamide added is 200-300% of the total mass of N-vinylcarbazole and butyl acrylate. The amount of initiator added is 0.5-1.5% of the total mass of N-vinylcarbazole and butyl acrylate. The initiator is azobisisobutyronitrile.

9. A protective coating for a metal material surface according to claim 2, characterized in that, The stirring speed is 100-200 rpm, and the target temperature for oil bath heating is 65-70℃.

10. A method for preparing a protective coating on the surface of a metallic material as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Weigh each raw material according to the weight proportions and set aside. Dry the zinc phosphate and silicon dioxide at 100-120℃ for 1-2 hours. S2. Add two-thirds of the formula amount of butyl acetate, propylene glycol methyl ether acetate, dispersant, defoamer, and the dried zinc phosphate and silica from step S1 into a disperser, and pre-disperse at 800-1200 rpm for 15-30 min to obtain a uniform slurry. S3. Reduce the rotation speed to 300-500 rpm, and add the film-forming substance, butyl glycidyl ether, non-reactive toughening agent, leveling agent, silane coupling agent and the remaining one-third butyl acetate to the slurry obtained in step S2 in sequence. Stir continuously for 30-60 minutes to obtain the paint. S4. Transfer the paint obtained in step S3 to a sand mill or a three-roll mill for grinding until the fineness reaches ≤25μm. After grinding, filter it with a 200-400 mesh filter to obtain a protective coating on the surface of the metal material.

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