Organic resin coating for electro-galvanized steel sheet of motor shell and preparation process of organic resin coating

Abstract

The invention provides an organic resin coating for an electro-galvanized steel plate of a motor shell and a preparation process of the organic resin coating, and relates to the technical field of coatings. The organic resin coating is prepared from the following raw materials: N-butyl pyrrolidone, butylated hydroxytoluene, cellulose nanocrystals, isophorone diisocyanate, porous ceramic microspheres loaded with silicon dioxide nanoparticles, nitrogen-doped graphene and the like; the preparation process comprises the following steps: preparing a modified polyurethane resin prepolymer by taking N-butyl pyrrolidone, polypropylene glycol and the like as raw materials; adding the modified cellulose nanocrystal suspension, nitrogen-doped graphene and the like into the modified polyurethane resin prepolymer to obtain a composite emulsion; and crosslinking and curing to obtain the organic resin coating. The organic resin coating forms a compact coating structure, hard particles are introduced, the hardness, wear resistance and mechanical strength of the surface of the coating are improved, and the coating has good adhesiveness, mechanical strength, wear resistance and corrosion resistance after film forming.

Description

Technical Field

[0001] The invention relates to the technical field of coatings and ship coatings, and in particular to an organic resin coating for electrogalvanized steel sheets of motor housings and a preparation process thereof. Background Art

[0002] Organic resin coatings for electrogalvanized steel sheets primarily include epoxy, acrylic, and polyurethane coatings. The epoxy groups in epoxy coatings' molecular structure chemically bond with the metal atoms on the surface of the electrogalvanized steel sheet, forming a strong bond. Conventional epoxy coatings can enhance the oxidation resistance of motor housings. Acrylic coatings produce vibrant, long-lasting films with excellent gloss and color retention. When used outdoors, acrylic coatings withstand UV radiation, wind and rain for extended periods, resist fading and chalking, and maintain the aesthetic appeal of the motor housing. Polyurethane coatings offer excellent wear resistance and flexibility, their unique molecular chain structure imparting excellent friction resistance and deformation recovery. Polyurethane coatings are effective in applications with demanding mechanical requirements and where motor housings are subject to frequent friction or minor impacts. Their films can withstand a certain degree of bending and friction without cracking, effectively protecting the surface of the electrogalvanized steel sheet.

[0003] Existing coatings also have significant shortcomings in their adhesion to electrogalvanized steel. Due to the unique surface properties of electrogalvanized steel, some coatings struggle to form strong chemical bonds or physical adsorption with it. Over long-term use, factors such as temperature and humidity fluctuations can cause the coating and steel to expand and contract asynchronously, leading to gradual separation. Once the coating partially detaches, corrosive media can penetrate and accumulate in the gaps between the coating and the steel, accelerating corrosion and significantly shortening the protective life of the coating and the overall service life of the motor housing.

[0004] In summary, the surface coatings of electrogalvanized steel sheets in the prior art have the problems of poor adhesion, poor mechanical strength, poor corrosion resistance and poor wear resistance. Summary of the Invention

[0005] The present invention provides an organic resin coating for electrogalvanized steel plates of motor housings and a preparation process thereof, which solves the technical problems in the prior art of poor adhesion, poor mechanical strength, poor corrosion resistance and poor wear resistance of surface coatings of electrogalvanized steel plates.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: The organic resin coating used for electroplated galvanized steel sheets of motor housings comprises raw materials including N-butylpyrrolidone, butylated hydroxytoluene, cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate, polypropylene glycol, dihydroxymethylpropionic acid, diethylene glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, polyaziridine crosslinker and acetone.

[0007] A process for preparing the organic resin coating of the present invention comprises the following steps: S1. Place cellulose nanocrystals in acetone, disperse them, add isophorone diisocyanate and dibutyltin dilaurate, stir, and add N,N-dimethylethanolamine to obtain modified cellulose nanocrystals; S2, mixing N-butyl pyrrolidone, polypropylene glycol and isophorone diisocyanate to carry out reaction 1, then adding dimethylol propionic acid to carry out reaction 2, adding diethylene glycol, trimethylolpropane and dibutyltin dilaurate to carry out reaction 3, and adding triethylamine to carry out neutralization reaction to obtain a modified polyurethane resin prepolymer; Reaction 1 is an addition reaction, where the terminal hydroxyl groups (-OH) of polypropylene glycol react with the isocyanate groups (-NCO) of IPDI to form urethane bonds (-NH-CO-O-), forming the prepolymer backbone. Excess IPDI leaves unreacted -NCO groups, providing active sites for subsequent crosslinking. See Formula 1 below for the reaction equation. HO-(CH2CH2O) n H+2IPDI→O=C=N-IPDI-O-(CH2CH2O) n -NCO+H2O (Ⅰ) In reaction 2, dimethylolpropionic acid (DMPA) introduces a carboxyl group, which acts as a chain extension and introduces a hydrophilic group. One of the hydroxyl groups (-OH) in DMPA reacts with the -NCO group in the prepolymer, joining the molecular chain and forming a chain extension structure.

[0008] In reaction 3, the dihydroxyl group of diethylene glycol reacts with the -NCO group of the prepolymer, extending the molecular chain (chain extension) and forming a linear structure. The trihydroxyl group of trimethylolpropane (TMP) reacts with multiple -NCO groups in the prepolymer to form a three-dimensional cross-linked network structure, improving the hardness and mechanical strength of the prepolymer. The catalyst dibutyltin dilaurate accelerates the reaction between -NCO and -OH.

[0009] S3, adding the modified cellulose nanocrystals to deionized water, adding ethylenediamine after ultrasonic dispersion, and stirring to obtain a modified cellulose nanocrystal suspension; S4, adding the modified cellulose nanocrystal suspension, porous ceramic microspheres loaded with silica nanoparticles, and nitrogen-doped graphene to the modified polyurethane resin prepolymer, emulsifying at a speed of 1500 r / min for 30 min, and removing acetone by rotary evaporation after the reaction is completed to obtain a composite emulsion; S5, adding butylated hydroxytoluene and polyethylenimine crosslinking agent to the composite emulsion to carry out a crosslinking reaction to obtain an organic resin coating base material; S6. Applying the organic resin base material to the electrogalvanized steel plate, and obtaining the organic resin coating after drying.

[0010] Preferably, the mass ratio of the cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate and N,N-dimethylethanolamine in S1 is 1:40-45:0.01-0.015:20-23.

[0011] Preferably, the mass ratio of N-butylpyrrolidone, polypropylene glycol, isophorone diisocyanate, dimethylolpropionic acid, diethylene glycol, trimethylolpropane, dibutyltin dilaurate and triethylamine in S2 is 0.15-0.2:10-11:11.2-12:0.95-1:2-2.5:0.5-0.6:0.01-0.015:0.65-0.75.

[0012] Preferably, the reaction temperature of reaction 1 in S2 is 80-85°C for 1.5-2h, and the reaction temperature of reaction 2 is 80-85°C.

[0013] Preferably, the reaction temperature of reaction 3 in S2 is 70-75° C. and the reaction time is 1.5-2 h.

[0014] Preferably, the neutralization reaction in S2 is carried out at a temperature of 38-40° C. and for 30-40 min.

[0015] Preferably, the mass ratio of the modified cellulose nanocrystals, the porous ceramic microspheres loaded with silica nanoparticles, the nitrogen-doped graphene and the modified polyurethane resin prepolymer in S4 is 0.3-0.4:3-4:0.1-0.15:23.

[0016] Preferably, the modified cellulose nanocrystals in S4 are in the shape of long rods, and the average diameter of the modified cellulose nanocrystals is less than 100 nm.

[0017] Preferably, the average diameter of the porous ceramic microspheres in S4 is 30-40 micrometers, and the average pore size of the pores on the porous ceramic microspheres is 300-400 nm.

[0018] In the present invention, the adhesion of the organic resin coating is improved through the effects of amphiphilic modification and nitrogen-doped graphene.

[0019] The role of amphiphilic modification: In step S1, the cellulose nanocrystals are modified to possess both hydrophilic and lipophilic groups. This helps the modified cellulose nanocrystals better disperse in the system when subsequently mixed with the modified polyurethane resin prepolymer. Furthermore, the lipophilic groups interact with the organic components in the polyurethane resin, while the hydrophilic groups facilitate hydrogen bonding or other chemical bonding with polar groups on the surface of the electrogalvanized steel sheet, thereby improving the adhesion between the coating and the electrogalvanized steel sheet.

[0020] The role of nitrogen-doped graphene: Nitrogen-doped graphene has a large specific surface area and unique surface properties. After being added to the modified polyurethane resin prepolymer in step S4, it can increase the contact area between the coating and the steel plate surface. At the same time, the nitrogen atoms on its surface can form chemical bonds or strong physical adsorption with the metal atoms on the steel plate surface, further enhancing the adhesion of the coating.

[0021] In the present invention, the mechanical strength of the organic resin coating is improved through the reinforcing effect of modified cellulose nanocrystals, the cross-linked structure of the polyurethane resin, and the synergistic effect of the porous ceramic microspheres and the nitrogen-doped graphene.

[0022] The reinforcing effect of modified cellulose nanocrystals: Cellulose nanocrystals inherently possess high strength and rigidity. After modification, they act as reinforcing fillers in composite emulsions. When added to the modified polyurethane resin prepolymer in step S4, they are evenly dispersed within the resin matrix, withstanding external forces and hindering the relative sliding of the resin molecular chains. This improves the mechanical strength of the coating, making it more resistant to external forces such as impact and vibration, and reduces the occurrence of cracks.

[0023] Cross-linked structure of polyurethane resin: In step S2, a modified polyurethane resin prepolymer is prepared through a multi-step reaction, introducing various functional monomers and cross-linking agents. Subsequently, in step S5, a polyethylenimine cross-linking agent is added to initiate a cross-linking reaction, forming a three-dimensional network of cross-linked structures. This cross-linked structure strengthens the bonds between the resin molecular chains, restricting their movement, improving the coating's hardness and strength, and enhancing its resistance to deformation.

[0024] The synergistic effect of porous ceramic microspheres and nitrogen-doped graphene: The porous ceramic microspheres loaded with silica nanoparticles possess a certain degree of rigidity and strength, acting as a supporting framework in the coating and improving the coating's overall mechanical properties. Nitrogen-doped graphene, with its excellent mechanical properties, such as high strength and toughness, synergizes with the porous ceramic microspheres and polyurethane resin matrix to further enhance the coating's mechanical strength, allowing it to possess a high degree of hardness while maintaining a certain degree of flexibility.

[0025] The present invention improves the corrosion resistance of the organic resin coating by improving the dense coating structure and chemical stability.

[0026] Dense coating structure: The organic resin coating obtained through the above preparation process has a relatively dense coating structure due to the uniform dispersion of modified cellulose nanocrystals, porous ceramic microspheres, nitrogen-doped graphene, and other components within the polyurethane resin matrix. This dense structure effectively blocks external corrosive media, such as sulfur dioxide, hydrogen chloride, and other corrosive gases, as well as acidic and alkaline liquids, from contact with the surface of the electrogalvanized steel sheet, slowing the penetration of corrosive media and thereby improving the coating's corrosion resistance.

[0027] Improved chemical stability: After cross-linking, the modified polyurethane resin prepolymer exhibits enhanced chemical stability, making it resistant to chemically corrosive media. Furthermore, components such as cellulose nanocrystals, silica nanoparticles, and nitrogen-doped graphene possess inherently good chemical stability. These, combined with the polyurethane resin matrix, further enhance the coating's corrosion resistance, enabling it to maintain excellent performance in harsh chemical environments and extending the life of the electrogalvanized steel sheet.

[0028] The invention improves the wear resistance of the organic resin coating by reinforcing the hard particles and acting on the cross-linked structure.

[0029] Hard particle reinforcement: Hard particles such as porous ceramic microspheres loaded with silica nanoparticles and modified cellulose nanocrystals are incorporated into the coating. These hard particles are evenly distributed within the polyurethane resin matrix, increasing the coating's surface hardness and wear resistance. When the coating is subjected to friction, the hard particles absorb some of the frictional forces, reducing wear on the resin matrix and thus improving the coating's wear resistance.

[0030] The role of the cross-linked structure: As mentioned above, polyurethane resin forms a three-dimensional network of cross-linked structures through cross-linking reactions. This structure gives the coating excellent elasticity and toughness, allowing it to quickly recover its shape when subjected to friction, reducing wear. Furthermore, the cross-linked structure strengthens the bond between the resin matrix and the hard particles, allowing the hard particles to better exert their wear-resistant properties, further enhancing the coating's wear resistance.

[0031] Furthermore, the long, rod-shaped modified cellulose nanocrystals in the coating system of this invention may be embedded in the pores of porous ceramic microspheres loaded with silica nanoparticles, enhancing the mechanical strength, wear resistance, corrosion resistance, and thermal conductivity and heat dissipation properties of the coating film after formation. N-butylpyrrolidone improves dispersibility and film uniformity; butylated hydroxytoluene, an antioxidant, prevents oxidative degradation of the resin and extends its service life.

[0032] Nitrogen (N) is introduced into nitrogen-doped graphene, which enhances the interaction between it and the soft and hard segments of the modified waterborne polyurethane, changing the degree of microphase separation of the polyurethane, thereby significantly improving the mechanical properties and wear resistance of the coating after film formation; in addition, during the wear process, nitrogen-doped graphene participates in the formation of a solid lubricating film together with the coating layer debris, which can reduce friction resistance and further improve the wear resistance of the coating.

[0033] Compared with the prior art, the solution of the present invention has at least the following beneficial effects: The uniform dispersion of modified cellulose nanocrystals, porous ceramic microspheres, and nitrogen-doped graphene within a polyurethane resin matrix creates a dense coating structure. This dense structure effectively blocks external corrosive media, such as sulfur dioxide, hydrogen chloride, and other corrosive gases, as well as acidic and alkaline liquids, from contacting the surface of electrogalvanized steel sheets, slowing their penetration and improving the coating's corrosion resistance. Therefore, the coating is also applicable to ship corrosion protection.

[0034] The coating incorporates hard particles such as porous ceramic microspheres loaded with silica nanoparticles and modified cellulose nanocrystals, which can increase the hardness, wear resistance, and mechanical strength of the coating surface.

[0035] The long rod-shaped modified cellulose nanocrystals in the coating system may be inserted into the pores of porous ceramic microspheres loaded with silica nanoparticles, which can enhance the mechanical strength, wear resistance, corrosion resistance, thermal conductivity and heat dissipation properties of the coating after film formation. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The details of the raw materials used in the following examples are as follows.

[0038] The product number for butylpyrrolidone is 3470-98-2. Isophorone diisocyanate, dimethylolpropionic acid, triethylamine, polyethylenimine crosslinker (SaC-100, CAS number: 26338-45-4), and polypropylene glycol (Mn = 1000, CAS number: 25322-69-4) were purchased from Shanghai Titan Technology Co., Ltd. Dibutyltin dilaurate, diethylene glycol, and trimethylolpropane were purchased from Sinopharm Chemical Reagent Company.

[0039] Cellulose nanocrystals can be prepared using conventional methods. The cellulose nanocrystals used in the following examples and comparative examples were prepared as follows: 3g of microcrystalline cellulose (purchased from Shanghai Titan Technology Co., Ltd.; microcrystalline cellulose with the desired average diameter can be purchased as needed) was mixed with 64% sulfuric acid at a solid-to-liquid ratio of 1:15 (g:mL) in a three-necked flask equipped with a reflux system. The mixture was heated to 55°C in an oil bath, magnetically stirred for 40 minutes, and then cooled to room temperature. The product was evenly distributed in a centrifuge tube and washed by centrifugation five times with 30mL of deionized water each time until a suspension appeared on the upper layer. This suspension was collected and dialyzed against deionized water until neutral. The suspension was then freeze-dried at -50°C under vacuum for 48 hours to obtain solid cellulose nanocrystals. (The amounts of each substance can be scaled up as needed.)

[0040] The preparation process of porous ceramic microspheres loaded with silica nanoparticles can refer to the following preparation method; 32g of silica sol (particle size 15-20 nm, solid content 15 wt%) was added to 800mL of deionized water, followed by 0.5wt% of dispersant FCS-31. Ammonia was then added to adjust the solution to pH 10. After magnetic stirring at 1000rpm for 10min, 2mL of perfluorosiloxane (analytical grade, content ≥97%) was added. After heating in a water bath at 50°C and magnetic stirring for 12h, 24g of porous ceramic particles (purchased from Nanjing Chaorun New Materials Technology Co., Ltd.; porous ceramic particles with desired average diameter and pore size can be purchased as needed) were added. After magnetic stirring at 1000rpm for 10min, 2mL of perfluorosiloxane was added. The solution was then heated in a water bath at 50°C and magnetic stirring for 24h to obtain the final aqueous unit cell suspension. The final aqueous unit cell suspension was spray dried at 160°C to obtain the final porous ceramic microspheres loaded with silica nanoparticles.

[0041] Nitrogen-doped graphene can be prepared by conventional methods. The preparation method of nitrogen-doped graphene used in the following examples and comparative examples can refer to the following preparation method using a DC arc discharge device.

[0042] First, place the graphite rod on the support frame of the sealed chamber, then evacuate the chamber to a vacuum state, and introduce a 1:1 mixture of hydrogen and nitrogen into it until the chamber pressure reaches 19 KPa. Then, use the graphite rod as the anode for arc discharge for 15 minutes, and then introduce pure nitrogen into the sealed chamber to exhaust the mixture of hydrogen and nitrogen. Finally, open the chamber, and the black powder obtained is nitrogen-doped graphene.

[0043] Example 1 This embodiment provides an organic resin coating for electroplating galvanized steel sheets of motor housings, the raw materials of which include N-butylpyrrolidone, butylated hydroxytoluene, cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate, polypropylene glycol, dihydroxymethylpropionic acid, diethylene glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, a polyaziridine crosslinker, and acetone.

[0044] A process for preparing the organic resin coating of the present invention comprises the following steps: S1. Place 1 g of cellulose nanocrystals in 200 mL of acetone and perform ultrasonic dispersion for 1 h. After dispersion, add 40 g of isophorone diisocyanate and 0.01 g of dibutyltin dilaurate. Stir for 12 h, and then add 20 g of N,N-dimethylethanolamine to obtain modified cellulose nanocrystals. S2, 0.15g N-butyl pyrrolidone, 10g polypropylene glycol and 11.2 isophorone diisocyanate were mixed to carry out reaction 1, the reaction temperature was 80 ° C, and the reaction time was 2h; then 0.95g dimethylol propionic acid was added, and the reaction was carried out at 80 ° C for 1h, and reaction 2 was carried out; 2g diethylene glycol, 0.5g trimethylolpropane and 0.01g dibutyltin dilaurate were added, and reaction 3 was carried out, the reaction temperature was 70 ° C, and the time was 2h; 0.75g triethylamine was added for neutralization reaction, the reaction temperature was 38 ° C, and the time was 40min to obtain a modified polyurethane resin prepolymer; S3, adding the modified cellulose nanocrystals to deionized water, adding ethylenediamine after ultrasonic homogenization, and stirring to obtain a modified cellulose nanocrystal suspension, wherein the ratio of the modified cellulose nanocrystals, deionized water, and ethylenediamine is 2g:5g:80mL; S4. Add the modified cellulose nanocrystal suspension, porous ceramic microspheres loaded with silica nanoparticles, and nitrogen-doped graphene to the modified polyurethane resin prepolymer, and emulsify at 1500 r / min for 30 min. After the reaction is completed, remove the acetone by rotary evaporation to obtain a composite emulsion. The mass ratio of the modified cellulose nanocrystals, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, and modified polyurethane resin prepolymer is 0.3:3:0.1:23. The modified cellulose nanocrystals are long rods with an average diameter of less than 100 nm. The porous ceramic microspheres have an average diameter of 30 microns, and the average pore size of the pores in the porous ceramic microspheres is 300 nm.

[0045] S5, adding 0.1 g of butylated hydroxytoluene and 0.4 mL of a polyethylenimine crosslinking agent to the composite emulsion for a crosslinking reaction to obtain an organic resin coating base; S6. Apply the organic resin base material to the electrogalvanized steel plate, let it stand at room temperature for 24 hours, and then dry it at 60° C. for 12 hours to obtain an organic resin coating.

[0046] Example 2 This embodiment provides an organic resin coating for electroplating galvanized steel sheets of motor housings, the raw materials of which include N-butylpyrrolidone, butylated hydroxytoluene, cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate, polypropylene glycol, dihydroxymethylpropionic acid, diethylene glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, a polyaziridine crosslinker, and acetone.

[0047] A process for preparing the organic resin coating of the present invention comprises the following steps: S1. Place 1 g of cellulose nanocrystals in 200 mL of acetone and perform ultrasonic dispersion for 1 h. After dispersion, add 45 g of isophorone diisocyanate and 0.015 g of dibutyltin dilaurate. Stir for 24 h, and then add 23 g of N,N-dimethylethanolamine to obtain modified cellulose nanocrystals. S2, 0.2g N-butyl pyrrolidone, 11g polypropylene glycol and 12-isophorone diisocyanate were mixed to carry out reaction 1, the reaction temperature was 85°C, and the reaction time was 1.5h; then 1g dimethylolpropionic acid was added, and the reaction was carried out at 85°C for 1h, and reaction 2 was carried out, 2.5g diethylene glycol, 0.6g trimethylolpropane and 0.015g dibutyltin dilaurate were added, and reaction 3 was carried out, the reaction temperature was 75°C, and the reaction time was 1.5h; 0.65g triethylamine was added for neutralization reaction, the reaction temperature was 40°C, and the reaction time was 30min to obtain a modified polyurethane resin prepolymer; S3, adding the modified cellulose nanocrystals to deionized water, adding ethylenediamine after ultrasonic dispersion, and stirring evenly to obtain a modified cellulose nanocrystal suspension, wherein the ratio of the modified cellulose nanocrystals, deionized water, and ethylenediamine is 2 g:5 g:80 mL; S4. Add the modified cellulose nanocrystal suspension, porous ceramic microspheres loaded with silica nanoparticles, and nitrogen-doped graphene to the modified polyurethane resin prepolymer and emulsify at 1500 r / min for 30 min. After the reaction is completed, remove the acetone by rotary evaporation to obtain a composite emulsion. The mass ratio of the modified cellulose nanocrystals, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, and modified polyurethane resin prepolymer is 0.4:4:0.15:23. The modified cellulose nanocrystals are long rods with an average diameter of less than 100 nm. The porous ceramic microspheres have an average diameter of 40 microns, and the average pore size of the pores in the porous ceramic microspheres is 400 nm.

[0048] S5, adding 0.5 g of butylated hydroxytoluene and 0.4 mL of a polyethylenimine crosslinking agent to the composite emulsion for a crosslinking reaction to obtain an organic resin coating base; S6. Apply the organic resin base material to the electrogalvanized steel plate, let it stand at room temperature for 24 hours, and then dry it at 60° C. for 12 hours to obtain an organic resin coating.

[0049] Example 3 This embodiment provides an organic resin coating for electroplating galvanized steel sheets of motor housings, the raw materials of which include N-butylpyrrolidone, butylated hydroxytoluene, cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate, polypropylene glycol, dihydroxymethylpropionic acid, diethylene glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, a polyaziridine crosslinker, and acetone.

[0050] A process for preparing the organic resin coating of the present invention comprises the following steps: S1. Place 1 g of cellulose nanocrystals in 200 mL of acetone and perform ultrasonic dispersion for 1 h. After dispersion, add 42 g of isophorone diisocyanate and 0.012 g of dibutyltin dilaurate. Stir for 20 h, and then add 22 g of N,N-dimethylethanolamine to obtain modified cellulose nanocrystals. S2, 0.16g N-butyl pyrrolidone, 10.5g polypropylene glycol and 11.5 isophorone diisocyanate were mixed to carry out reaction 1, the reaction temperature was 83 ° C, and the reaction time was 1.8h; then 0.98g dimethylol propionic acid was added, and the reaction was carried out at 83 ° C for 1h, and reaction 2 was carried out; 2.4g diethylene glycol, 0.55g trimethylolpropane and 0.013g dibutyltin dilaurate were added, and reaction 3 was carried out, the reaction temperature was 73 ° C, and the time was 1.7h, and 0.7g triethylamine was added for neutralization reaction, the reaction temperature was 39 ° C, and the time was 35min to obtain a modified polyurethane resin prepolymer; S3, adding the modified cellulose nanocrystals to deionized water, adding ethylenediamine after ultrasonic dispersion, and stirring evenly to obtain a modified cellulose nanocrystal suspension, wherein the ratio of the modified cellulose nanocrystals, deionized water, and ethylenediamine is 2 g:5 g:80 mL; S4. Add the modified cellulose nanocrystal suspension, porous ceramic microspheres loaded with silica nanoparticles, and nitrogen-doped graphene to the modified polyurethane resin prepolymer, and emulsify at 1500 r / min for 30 min. After the reaction is completed, remove the acetone by rotary evaporation to obtain a composite emulsion. The mass ratio of the modified cellulose nanocrystals, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, and modified polyurethane resin prepolymer is 0.3.5:3.5:0.12:23. The modified cellulose nanocrystals are long rods with an average diameter of less than 100 nm. The average diameter of the porous ceramic microspheres is 35 microns, and the average pore size of the pores in the porous ceramic microspheres is 350 nm.

[0051] S5, adding 0.2 g of butylated hydroxytoluene and 0.4 mL of a polyethylenimine crosslinking agent to the composite emulsion for a crosslinking reaction to obtain an organic resin coating base; S6. Apply the organic resin base material to the electrogalvanized steel plate, let it stand at room temperature for 24 hours, and then dry it at 60° C. for 12 hours to obtain an organic resin coating.

[0052] Comparative Example 1 This comparative example is the same as Example 1, except that the average diameter of the modified cellulose nanocrystals in this comparative example is 500 nm.

[0053] Comparative Example 2 This comparative example is the same as Example 1, except that in this comparative example, the porous ceramic microspheres loaded with silica nanoparticles are replaced by nitrogen-doped graphene in equal amounts.

[0054] Comparative Example 3 This comparative example is the same as Example 1, except that in this comparative example, an equal amount of nitrogen-doped graphene is replaced by porous ceramic microspheres loaded with silica nanoparticles.

[0055] Comparative Example 4 This comparative example is the same as Example 1, except that S1 and S3 are omitted in this comparative example, and the porous ceramic microspheres loaded with silica nanoparticles and modified cellulose nanocrystals in the original S4 are replaced by nitrogen-doped graphene in equal amounts.

[0056] Comparative Example 5 This comparative example is the same as Example 1, except that in this comparative example, the mass ratio of the modified cellulose nanocrystals, the porous ceramic microspheres loaded with silica nanoparticles, the nitrogen-doped graphene and the modified polyurethane resin prepolymer described in S4 is 0.5:5:0.2:23.

[0057] Comparative Example 6 This comparative example is the same as Example 1, except that the mass ratio of the modified cellulose nanocrystals, the porous ceramic microspheres loaded with silica nanoparticles, the nitrogen-doped graphene and the modified polyurethane resin prepolymer in S4 is 0.2:2:0.1:23.

[0058] The thin layers of organic resin coatings in Examples 1-3 and Comparative Examples 1-6 were subjected to the following tests.

[0059] (1) For the tensile mechanical property test, the samples were cut into dumbbell-shaped strips using a sheet press, and the film thickness was measured using a thickness gauge. The film was tested using an electronic universal testing machine. The tensile rate was 50 mm / min, and each sample was measured five times. The test results for each group are shown in Table 1.

[0060] Table 1 Mechanical strength test Group Sample 1 / MPa Sample 3 / MPa Sample 3 / MPa Sample 4 / MPa Sample 5 / MPa Average value / MPa Example 1 37.12 35.74 37.82 35.21 34.93 36.16 Example 2 37.58 36.17 35.65 35.94 37.13 36.49 Example 3 35.73 35.26 35.87 34.89 36.92 35.73 Comparative Example 1 33.91 33.72 33.27 33.93 33.25 33.62 Comparative Example 2 27.52 27.13 27.46 27.93 27.87 27.58 Comparative Example 3 31.22 30.63 30.57 30.25 30.34 30.60 Comparative Example 4 26.13 27.15 27.97 26.51 26.48 26.85 Comparative Example 5 32.16 31.67 31.45 31.31 31.39 31.60 Comparative Example 6 29.30 29.54 29.26 29.58 29.43 29.42 (2) Hardness test: The pencil hardness of the composite film was measured according to the national standard GB / T6739-2006. The test results are shown in Table 2. The hardness can predict the wear resistance of the coating after film formation. The higher the hardness, the better the wear resistance.

[0061] Table 2 Pencil hardness Group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Pencil hardness 4H 4H 4H 4H 3H 4H 3H 4H 3H (3) Adhesion test Adhesion reflects the strength of the coating's bond to the metal substrate after curing. This experiment used a manual adhesion tester (KS-M, Zibo Senyuan Electric Co., Ltd.) to test the coating's adhesion. An organic resin coating base was applied to a clean Q235 steel plate. The adhesive was then applied to a matching spindle and bonded perpendicularly to the coating. After the adhesive fully cured, a puller was used to press a hydraulic rod at a constant speed until the coating separated from the steel plate. The readings were then read. The test results are shown in Table 3.

[0062] Table 3 Adhesion test results Group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Adhesion / MPa 2.56 2.67 2.71 2.43 2.21 2.33 1.92 2.38 2.12 (4) Corrosion resistance is judged by salt water immersion test The samples were subjected to corrosion immersion tests in a 1 mol / L NaCl solution according to the national standard GB / T 9274-1988. After immersion for 168 hours, changes in the coating surface were observed, as shown in Table 4.

[0063] Table 4 Corrosion resistance test Group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Observation results No change No change No change No change Whitening is obvious, but there is no peeling Partial whitening Whitening is obvious, but there is no peeling Partial whitening Partial whitening It can be seen that the coating of the present invention has good salt corrosion resistance and can be sprayed onto the surface of ships for corrosion protection.

[0064] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An organic resin coating for electrogalvanized steel sheets for motor housings, characterized in that: Its raw materials include N-butylpyrrolidone, butylated hydroxytoluene, cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate, polypropylene glycol, dihydroxymethylpropionic acid, diethylene glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, polyaziridine crosslinker and acetone.

2. A process for preparing an organic resin coating as claimed in claim 1, characterized in that: The following steps are involved: S1. Place cellulose nanocrystals in acetone, disperse them, add isophorone diisocyanate and dibutyltin dilaurate, stir, and add N,N-dimethylethanolamine to obtain modified cellulose nanocrystals; S2, mixing N-butyl pyrrolidone, polypropylene glycol and isophorone diisocyanate to carry out reaction 1, then adding dimethylol propionic acid to carry out reaction 2, adding diethylene glycol, trimethylolpropane and dibutyltin dilaurate to carry out reaction 3, and adding triethylamine to carry out neutralization reaction to obtain a modified polyurethane resin prepolymer; S3, adding the modified cellulose nanocrystals to deionized water, ultrasonically dispersing the mixture, and then adding ethylenediamine to obtain a modified cellulose nanocrystal suspension; S4, adding the modified cellulose nanocrystal suspension, porous ceramic microspheres loaded with silicon dioxide nanoparticles, and nitrogen-doped graphene to the modified polyurethane resin prepolymer, and emulsifying to obtain a composite emulsion; S5, adding butylated hydroxytoluene and polyethylenimine crosslinking agent to the composite emulsion to carry out a crosslinking reaction to obtain an organic resin coating base material; S6. Applying the organic resin base material to the electrogalvanized steel plate, and obtaining the organic resin coating after drying.

3. The preparation process according to claim 2, characterized in that The mass ratio of the cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate and N,N-dimethylethanolamine in S1 is 1:40-45:0.01-0.015:20-23.

4. The preparation process according to claim 2, characterized in that The mass ratio of N-butylpyrrolidone, polypropylene glycol, isophorone diisocyanate, dimethylolpropionic acid, diethylene glycol, trimethylolpropane, dibutyltin dilaurate and triethylamine in S2 is 0.15-0.2:10-11:11.2-12:0.95-1:2-2.5:0.5-0.6:0.01-0.015:0.65-0.

75.

5. The preparation process according to claim 2, characterized in that: The reaction temperature of reaction 1 in S2 is 80-85°C for 1.5-2h, and the reaction temperature of reaction 2 is 80-85°C.

6. The preparation process according to claim 2, characterized in that: The reaction temperature of reaction 3 in S2 is 70-75° C. and the reaction time is 1.5-2 h.

7. The preparation process according to claim 2, characterized in that: The reaction temperature of the neutralization reaction in S2 is 38-40° C. and the reaction time is 30-40 min.

8. The preparation process according to claim 2, characterized in that: The mass ratio of the modified cellulose nanocrystals, the porous ceramic microspheres loaded with silica nanoparticles, the nitrogen-doped graphene and the modified polyurethane resin prepolymer described in S4 is 0.3-0.4:3-4:0.1-0.15:

23.

9. The preparation process according to claim 2, characterized in that: The modified cellulose nanocrystals in S4 are in the shape of long rods, and the average diameter of the modified cellulose nanocrystals is less than 100 nm.

10. The preparation process according to claim 2, characterized in that: The average diameter of the porous ceramic microspheres in S4 is 30-40 micrometers, and the average pore size of the pores on the porous ceramic microspheres is 300-400 nm.