Organic resin coating for galvannealed steel sheets for motor housings and process for the preparation thereof

Abstract

The application provides an organic resin coating for motor shell electroplated zinc steel plate and a preparation process thereof, and relates to the technical field of coatings.The raw materials of the organic resin coating include N-butyl pyrrolidone, butyl hydroxytoluene, cellulose nanocrystal, isophorone diisocyanate, porous ceramic microspheres loaded with silicon dioxide nanoparticles and nitrogen-doped graphene; the preparation process comprises the following steps: preparing modified polyurethane resin prepolymer by taking N-butyl pyrrolidone and polypropylene glycol as raw materials; adding modified cellulose nanocrystal suspension, nitrogen-doped graphene and the like into the modified polyurethane resin prepolymer to obtain a composite emulsion; and obtaining the organic resin coating after cross-linking and curing.The organic resin coating has a dense coating structure, hard particles are introduced, the hardness and wear resistance of the coating surface and the mechanical strength are increased, and the coating has good adhesion, mechanical strength, wear resistance and corrosion resistance after film formation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coatings and ship coating technology, in particular to an organic resin coating for motor shell electro-galvanized steel plate and a preparation process thereof. BACKGROUND

[0002] The organic resin coating for electro-galvanized steel plate is mainly epoxy, acrylic and polyurethane coatings. The epoxy group in the molecular structure of the epoxy coating can chemically bond with the metal atoms on the surface of the electro-galvanized steel plate to form a stable bonding layer. Ordinary epoxy coatings can enhance the oxidation resistance of the motor shell. The coating film made of acrylic coating has bright colors and long-lasting gloss, and has excellent gloss and color retention performance. When used in outdoor environments, the acrylic coating layer can withstand ultraviolet radiation and weathering for a long time, and the coating film is not easy to fade and powder, allowing the motor shell to always maintain its appearance. Polyurethane coatings perform excellently in terms of wear resistance and flexibility, and their unique molecular chain structure endows the coating film with good anti-friction and deformation recovery capabilities. In some harsh mechanical performance requirements, the motor shell is frequently subjected to friction or slight impact, and the polyurethane coating can effectively play a role, and the coating film can withstand a certain degree of bending and friction without breaking, effectively protecting the surface of the electro-galvanized steel plate.

[0003] The existing coatings also have obvious shortcomings in terms of adhesion to electro-galvanized steel plate. Due to the special surface characteristics of electro-galvanized steel plate, some coatings are difficult to form a firm chemical bond or physical adsorption with it. Over a long period of use, affected by factors such as temperature changes and humidity fluctuations, the thermal expansion and contraction of the coating and the steel plate are not synchronized, causing them to gradually separate. Once the coating layer separates locally, corrosive media will penetrate and accumulate between the coating and the steel plate, accelerating the corrosion of the steel plate and significantly shortening the protective life of the coating and the overall service life of the motor shell.

[0004] In summary, the existing technology of electro-galvanized steel plate surface coating has the problems of poor adhesion, poor mechanical strength, poor corrosion resistance and poor wear resistance. SUMMARY

[0005] The present application provides an organic resin coating for motor shell electro-galvanized steel plate and a preparation process thereof, which solves the technical problems of poor adhesion, poor mechanical strength, poor corrosion resistance and poor wear resistance of the electro-galvanized steel plate surface coating in the prior art.

[0006] To achieve the above-mentioned application purposes, the technical solutions provided by the present application are as follows:

[0007] An organic resin coating for motor housing electro-galvanized steel plate, raw materials of which include N-butyl pyrrolidone, butyl hydroxy toluene, cellulose nanocrystal, isophorone diisocyanate, dibutyl tin dilaurate, polypropylene glycol, dimethylol propionic acid, diethylene glycol, trimethylol propane, triethylamine, porous ceramic microspheres loaded with silicon dioxide nanoparticles, nitrogen-doped graphene, polyaziridine crosslinking agent and acetone.

[0008] A preparation process of the organic resin coating, comprising the following steps:

[0009] S1, placing cellulose nanocrystal into acetone, adding isophorone diisocyanate and dibutyl tin dilaurate after dispersion, stirring, adding N, N-dimethyl ethanolamine to obtain modified cellulose nanocrystal;

[0010] S2, mixing N-butyl pyrrolidone, polypropylene glycol and isophorone diisocyanate to react for 1, then adding dimethylol propionic acid to react for 2, adding diethylene glycol, trimethylol propane and dibutyl tin dilaurate to react for 3, adding triethylamine to neutralize to obtain modified polyurethane resin prepolymer;

[0011] Reaction 1 is an addition reaction, the terminal hydroxyl group (-OH) of polypropylene glycol reacts with the isocyanate group (-NCO) of IPDI to generate urethane bond (-NH-CO-O-) to form the main chain of the prepolymer. IPDI is in excess, leaving unreacted -NCO groups to provide active sites for subsequent crosslinking, and the reaction equation is as follows,

[0012] HO-(CH2CH2O) n H+2IPDI→O=C=N-IPDI-O-(CH2CH2O) n -NCO+H2O (I)

[0013] In reaction 2, dimethylol propionic acid (DMPA) introduces carboxyl groups to perform chain extension reaction and introduce hydrophilic groups. One hydroxyl group (-OH) of DMPA reacts with -NCO of the prepolymer to access the molecular chain to form a chain extension structure.

[0014] In reaction 3, the double hydroxyl group of diethylene glycol reacts with -NCO of the prepolymer to extend the molecular chain (chain extension) to form a linear structure. The three hydroxyl groups of trimethylol propane (TMP) react with -NCO of multiple prepolymers to form a three-dimensional network crosslinking structure to improve the hardness and mechanical strength of the prepolymer. The catalyst dibutyl tin dilaurate accelerates the reaction of -NCO and -OH.

[0015] S3, adding the modified cellulose nanocrystal into deionized water, adding ethylenediamine after ultrasonic dispersion, and stirring to obtain a modified cellulose nanocrystal suspension;

[0016] S4, the modified cellulose nanocrystal suspension, porous ceramic microspheres loaded with silica nanoparticles and nitrogen-doped graphene are added to the modified polyurethane resin prepolymer, emulsified at a speed of 1500 r / min for 30 min, and the reaction is completed. After rotary evaporation to remove acetone, a composite emulsion is obtained;

[0017] S5, butylated hydroxytoluene and polyaziridine crosslinking agent are added to the composite emulsion for crosslinking reaction to obtain an organic resin coating base;

[0018] S6, the organic resin base is coated on the zinc-plated steel sheet, and after drying, an organic resin coating is obtained.

[0019] Preferably, the mass ratio of the cellulose nanocrystal, isophorone diisocyanate, dibutyl tin dilaurate and N, N-dimethyl ethanolamine in S1 is 1:40-45:0.01-0.015:20-23.

[0020] Preferably, the mass ratio of N-butyl pyrrolidone, polypropylene glycol, isophorone diisocyanate, dimethylol propionic acid, diethylene glycol, trimethylolpropane, dibutyl tin 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.

[0021] Preferably, the reaction temperature of the reaction 1 in S2 is 80-85℃, and the reaction time is 1.5-2h, and the reaction temperature of the reaction 2 is 80-85℃.

[0022] Preferably, the reaction temperature of the reaction 3 in S2 is 70-75℃, and the reaction time is 1.5-2h.

[0023] Preferably, the reaction temperature of the neutralization reaction in S2 is 38-40℃, and the reaction time is 30-40min.

[0024] Preferably, the mass ratio of the modified cellulose nanocrystal, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene and modified polyurethane resin prepolymer in S4 is 0.3-0.4:3-4:0.1-0.15:23.

[0025] Preferably, the modified cellulose nanocrystal in S4 is long rod-shaped, and the average diameter of the modified cellulose nanocrystal is less than 100nm.

[0026] Preferably, the average diameter of the porous ceramic microspheres in S4 is 30-40 microns, and the average pore size of the pores on the porous ceramic microspheres is 300-400nm.

[0027] The adhesion of the organic resin coating is improved by the effect of the amphiphilic modification and the effect of the nitrogen-doped graphene.

[0028] The effect of the amphiphilic modification: In the S1 step, the cellulose nanocrystals are modified to have both hydrophilic and lipophilic groups. This helps the modified cellulose nanocrystals to disperse better in the system when mixed with the modified polyurethane resin prepolymer in the subsequent step, and the lipophilic groups can interact with the organic components in the polyurethane resin, while the hydrophilic groups can form hydrogen bonds or other chemical bonds with the polar groups on the surface of the electrogalvanized steel sheet, thereby improving the adhesion between the coating and the electrogalvanized steel sheet.

[0029] The effect of the nitrogen-doped graphene: The nitrogen-doped graphene has a large specific surface area and unique surface properties. When added to the modified polyurethane resin prepolymer in the S4 step, it can increase the contact area between the coating and the steel sheet surface, and the nitrogen atoms on its surface can form chemical bonds or strong physical adsorption with the metal atoms on the steel sheet surface, further enhancing the adhesion of the coating.

[0030] The mechanical strength of the organic resin coating is improved by the reinforcing effect of the 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.

[0031] The reinforcing effect of the modified cellulose nanocrystals: The cellulose nanocrystals themselves have high strength and rigidity, and after modification, they act as reinforcing fillers in the composite emulsion. When added to the modified polyurethane resin prepolymer in the S4 step, they can disperse uniformly in the resin matrix, withstand external forces, and hinder the relative sliding of the resin molecular chains, thereby improving the mechanical strength of the coating and making it better able to resist external forces such as impact and vibration, reducing the generation of cracks.

[0032] The cross-linked structure of the polyurethane resin: In the S2 step, the modified polyurethane resin prepolymer is prepared through a multi-step reaction, introducing various functional monomers and cross-linking agents. In the subsequent S5 step, the polyaziridine cross-linking agent is added for cross-linking reaction, forming a three-dimensional network cross-linked structure. This cross-linked structure makes the combination between resin molecular chains more compact, limiting the movement of the molecular chains, improving the hardness and strength of the coating, and also enhancing its resistance to deformation.

[0033] The synergistic effect of the porous ceramic microspheres and the nitrogen-doped graphene: The porous ceramic microspheres loaded with silica nanoparticles have a certain rigidity and strength, and play a supporting role in the coating, improving the overall mechanical properties of the coating. The nitrogen-doped graphene has excellent mechanical properties such as high strength and high toughness, and synergizes with the porous ceramic microspheres and the polyurethane resin matrix to further improve the mechanical strength of the coating, enabling it to maintain a certain flexibility while having high hardness.

[0034] The present application improves the corrosion resistance of organic resin coatings through the dense coating structure and the improvement of chemical stability.

[0035] The dense coating structure: The organic resin coating obtained by the above preparation process forms a relatively dense coating structure due to the uniform dispersion of modified cellulose nanocrystals, porous ceramic microspheres, nitrogen-doped graphene and other components in the polyurethane resin matrix. This dense structure can effectively block the contact of external corrosive media such as sulfur dioxide, hydrogen chloride and other corrosive gases and acid-base liquids with the surface of the electroplated zinc steel plate, slowing down the penetration speed of the corrosive medium, thereby improving the corrosion resistance of the coating.

[0036] The improvement of chemical stability: The modified polyurethane resin prepolymer improves its chemical stability after crosslinking reaction, and can resist the erosion of chemical corrosive media. At the same time, cellulose nanocrystals, silica nanoparticles and nitrogen-doped graphene and other components also have good chemical stability, which further enhances the corrosion resistance of the coating, so that the coating can maintain good performance in harsh chemical environments and prolong the service life of the electroplated zinc steel plate.

[0037] The present application improves the wear resistance of organic resin coatings through the enhancement of hard particles and the role of crosslinking structure.

[0038] The enhancement of hard particles: In the coating, porous ceramic microspheres loaded with silica nanoparticles and modified cellulose nanocrystals and other hard particles are introduced. These hard particles are uniformly distributed in the polyurethane resin matrix, which can increase the hardness and wear resistance of the coating surface. When the coating is subjected to friction, the hard particles can bear part of the friction force, reducing the wear of the resin matrix, thereby improving the wear resistance of the coating.

[0039] The role of crosslinking structure: As mentioned earlier, the polyurethane resin forms a three-dimensional network crosslinking structure through crosslinking reaction, which makes the coating have good elasticity and toughness, and can quickly recover its shape when subjected to friction, reducing wear. At the same time, the crosslinking structure also improves the bonding force between the resin matrix and the hard particles, so that the hard particles can better play the role of wear resistance, further improving the wear resistance of the coating.

[0040] In addition, the long rod-shaped modified cellulose nanocrystals in the coating system of the present application can be inserted into the pores of the porous ceramic microspheres loaded with silica nanoparticles, which can enhance the mechanical strength, wear resistance, corrosion resistance and heat dissipation performance of the coating after film formation. N-butyl pyrrolidone improves the dispersibility and film uniformity; butylated hydroxytoluene has antioxidant properties, prevents resin oxidative degradation and prolongs service life.

[0041] The nitrogen (N) element is introduced into the nitrogen-doped graphene, the interaction between the nitrogen-doped graphene and the soft and hard segments of the modified waterborne polyurethane is enhanced, the microphase separation degree of the polyurethane is changed, and the mechanical properties and wear resistance of the coating after film formation are obviously improved; in addition, the nitrogen-doped graphene participates in the generation of the solid lubricating film together with the coating layer debris in the wear process, the friction resistance can be reduced, and the wear resistance of the coating is further improved.

[0042] Compared with the prior art, the scheme of the present application has at least the following beneficial effects:

[0043] The uniform dispersion of the modified cellulose nanocrystals, porous ceramic microspheres, nitrogen-doped graphene and other components in the polyurethane resin matrix forms a relatively dense coating structure. The dense structure can effectively block the contact of external corrosive media, such as sulfur dioxide, hydrogen chloride and other corrosive gases, and acid and alkali liquids, with the surface of the electroplated zinc steel plate, slows down the penetration speed of the corrosive medium, thereby improving the corrosion resistance of the coating, so the coating of the present application can also be applied to the field of ship corrosion prevention.

[0044] The porous ceramic microspheres loaded with silicon dioxide nanoparticles and the modified cellulose nanocrystals and other hard particles are introduced into the coating. The hardness, wear resistance and mechanical strength of the coating surface can be increased.

[0045] The long rod-shaped modified cellulose nanocrystals in the coating system can be inserted into the pores of the porous ceramic microspheres loaded with silicon dioxide nanoparticles, which can enhance the mechanical strength, wear resistance, corrosion resistance and heat dissipation performance of the coating after film formation. DETAILED DESCRIPTION

[0046] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0047] The specific raw materials used in the following embodiments are as follows.

[0048] The cargo number of butyl pyrrolidone is 3470-98-2. Isophorone diisocyanate, dimethylol propionic acid, triethylamine, polyaziridine crosslinking agent (abbreviated as SaC-100, CAS number: 26338-45-4) and polypropylene glycol (Mn = 1000, CAS number: 25322-69-4) are purchased from Shanghai Titan Technology Co., Ltd. Dibutyltin dilaurate, diethylene glycol, and trimethylolpropane are purchased from the Chemical Reagent Company of China National Pharmaceutical Group.

[0049] Cellulose nanocrystals can be prepared by conventional methods, the preparation method of cellulose nanocrystals used in the following examples and comparative examples is as follows: 3 g of microcrystalline cellulose (purchased from Shanghai Titan Technology Co., Ltd., and the average diameter of microcrystalline cellulose can be purchased according to the needs) is mixed with 64% sulfuric acid at a solid-liquid ratio of 1:15 (g:mL) in a three-necked flask equipped with a condenser reflux device, heated to 55°C in an oil bath, and magnetically stirred for 40 min, and then cooled to room temperature. The product is uniformly placed in a centrifuge tube, and each time it is washed with 30 mL of deionized water for 5 times, until the upper layer appears suspended. The suspension is collected and dialyzed in deionized water until it is neutral, and then vacuum freeze-dried at -50°C for 48 h to obtain solid cellulose nanocrystals (the amount of each substance can be scaled up according to the needs).

[0050] The preparation process of the porous ceramic microspheres loaded with silica nanoparticles can refer to the following preparation method.

[0051] In 800 mL of deionized water, 32 g of silica sol (particle size of 15-20 nm, solid content of 15 wt%) is added, then 0.5 wt.% of dispersant FCS-31 is added, and then ammonia water is added to adjust the solution pH to 10. After magnetic stirring at a speed of 1000 rpm for 10 min, 2 mL of perfluorosilicone (analytical pure, content ≥97%) is added. After magnetic stirring at 50°C for 12 h, 24 g of porous ceramic particles (purchased from Nanjing Chaorun New Material Technology Co., Ltd., and the average diameter and pore size of the porous ceramic particles can be purchased according to the needs) is added. After magnetic stirring at a speed of 1000 rpm for 10 min, 2 mL of perfluorosilicone is added again, and then the final aqueous unit cell suspension is obtained by magnetic stirring at 50°C for 24 h. The final aqueous unit cell suspension is dried by spray drying at 160°C to obtain the final porous ceramic microspheres loaded with silica nanoparticles.

[0052] 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, and a direct current arc discharge device is used.

[0053] First, place a graphite rod on the support frame of the sealed chamber, then vacuumize the chamber, and introduce a mixture of 1:1 hydrogen and nitrogen gas into the chamber until the gas pressure in the chamber reaches 19 KPa, then arc discharge for 15 min with the graphite rod as the anode, then introduce pure nitrogen gas into the sealed chamber to remove the mixture of hydrogen and nitrogen gas, and finally open the chamber. The black powder obtained is nitrogen-doped graphene.

[0054] Example 1

[0055] The embodiment provides an organic resin coating for motor shell electroplated zinc steel plate, raw materials of which include N-butyl pyrrolidone, butyl hydroxytoluene, cellulose nanocrystal, isophorone diisocyanate, dibutyltin dilaurate, polypropylene glycol, dimethylol propionic acid, diethylene glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silicon dioxide nanoparticles, nitrogen-doped graphene, polyaziridine crosslinking agent and acetone.

[0056] A preparation process of the organic resin coating is provided.

[0057] S1, 1g of cellulose nanocrystal is put into 200mL of acetone and ultrasonic dispersion is carried out for 1h, 40g of isophorone diisocyanate and 0.01g of dibutyltin dilaurate are added after dispersion, stirring is carried out for 12h, 20g of N,N-dimethyl ethanolamine is added, and modified cellulose nanocrystal is obtained;

[0058] S2, 0.15g of N-butyl pyrrolidone, 10g of polypropylene glycol and 11.2 isophorone diisocyanate are mixed and reacted for 1h, the reaction temperature is 80 DEG C, and the reaction time is 2h; 0.95g of dimethylol propionic acid is further added, reaction 2 is carried out at 80 DEG C for 1h; 2g of diethylene glycol, 0.5g of trimethylolpropane and 0.01g of dibutyltin dilaurate are added, reaction 3 is carried out at 70 DEG C for 2h; 0.75g of triethylamine is added for neutralization reaction, the reaction temperature is 38 DEG C, and the reaction time is 40min, and modified polyurethane resin prepolymer is obtained;

[0059] S3, the modified cellulose nanocrystal is added into deionized water, ultrasonic homogenization is carried out, ethylenediamine is added, and stirring is uniformly carried out, and the modified cellulose nanocrystal suspension is obtained, wherein the ratio of the modified cellulose nanocrystal, deionized water and ethylenediamine is 2g:5g:80mL;

[0060] S4, the modified cellulose nanocrystal suspension, the porous ceramic microspheres loaded with silicon dioxide nanoparticles and the nitrogen-doped graphene are added into the modified polyurethane resin prepolymer, emulsification is carried out at a rotation speed of 1500r / min for 30min, the reaction is completed, acetone is removed by rotary evaporation, and the composite emulsion is obtained; the mass ratio of the modified cellulose nanocrystal, the porous ceramic microspheres loaded with silicon dioxide nanoparticles, the nitrogen-doped graphene and the modified polyurethane resin prepolymer is 0.3:3:0.1:23. The modified cellulose nanocrystal is long rod-shaped, the average diameter of the modified cellulose nanocrystal is less than 100nm, the average diameter of the porous ceramic microspheres is 30 microns, and the average pore size of the pores on the porous ceramic microspheres is 300nm.

[0061] S5, 0.1 g of butylated hydroxyl toluene and 0.4 mL of polyaziridine crosslinking agent are added to the composite emulsion for crosslinking reaction to obtain an organic resin coating base;

[0062] S6, the organic resin base is coated on the electro-galvanized steel sheet, and after standing at room temperature for 24 h and drying at 60 DEG C for 12 h, an organic resin coating is obtained.

[0063] Example 2

[0064] The embodiment provides an organic resin coating for electro-galvanized steel sheet of motor shell, raw materials of which include N-butyl pyrrolidone, butylated hydroxyl toluene, cellulose nanocrystal, isophorone diisocyanate, dibutyl tin dilaurate, polypropylene glycol, dimethylol propionic acid, diethylene glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silicon dioxide nanoparticles, nitrogen-doped graphene, polyaziridine crosslinking agent and acetone.

[0065] A preparation process of the organic resin coating is provided, which comprises the following steps:

[0066] S1, 1 g of cellulose nanocrystal is put into 200 mL of acetone and ultrasonically dispersed for 1 h, 45 g of isophorone diisocyanate and 0.015 g of dibutyl tin dilaurate are added after dispersion, stirring is conducted for 24 h, 23 g of N, N-dimethyl ethanolamine is added to obtain modified cellulose nanocrystal;

[0067] S2, 0.2 g of N-butyl pyrrolidone, 11 g of polypropylene glycol and 12 isophorone diisocyanate are mixed to react for 1 h, the reaction temperature is 85 DEG C, and the reaction time is 1.5 h; 1 g of dimethylol propionic acid is further added to conduct reaction 2 at 85 DEG C for 1 h, 2.5 g of diethylene glycol, 0.6 g of trimethylolpropane and 0.015 g of dibutyl tin dilaurate are added to conduct reaction 3, the reaction temperature is 75 DEG C, and the reaction time is 1.5 h; 0.65 g of triethylamine is added to conduct neutralization reaction, the reaction temperature is 40 DEG C, and the reaction time is 30 min, to obtain modified polyurethane resin prepolymer;

[0068] S3, the modified cellulose nanocrystal is added into deionized water, ethylenediamine is added after ultrasonic dispersion, and the modified cellulose nanocrystal suspension is obtained after uniform stirring, wherein the ratio of the modified cellulose nanocrystal, deionized water and ethylenediamine is 2 g:5 g:80 mL;

[0069] S4, the modified cellulose nanocrystal suspension, silica nanoparticle loaded porous ceramic microspheres and nitrogen-doped graphene are added to the modified polyurethane resin prepolymer, emulsified at a speed of 1500 r / min for 30 min, the reaction is completed, and the acetone is removed by rotary evaporation to obtain a composite emulsion; the mass ratio of the modified cellulose nanocrystal, silica nanoparticle loaded porous ceramic microspheres, nitrogen-doped graphene and modified polyurethane resin prepolymer is 0.4:4:0.15:23. The modified cellulose nanocrystal is a long rod, and the average diameter of the modified cellulose nanocrystal is less than 100 nm. The average diameter of the porous ceramic microspheres is 40 microns, and the average pore size of the pores on the porous ceramic microspheres is 400 nm.

[0070] S5, 0.5 g of butylated hydroxytoluene and 0.4 mL of polyaziridine crosslinking agent are added to the composite emulsion for crosslinking reaction to obtain an organic resin coating base;

[0071] S6, the organic resin base is coated on the electro-galvanized zinc steel plate, and after standing at room temperature for 24 h and drying at 60℃ for 12 h, an organic resin coating is obtained.

[0072] Example 3

[0073] The embodiment provides an organic resin coating for a motor shell electro-galvanized zinc steel plate, raw materials of which include N-butyl pyrrolidone, butylated hydroxytoluene, cellulose nanocrystal, isophorone diisocyanate, dibutyl tin dilaurate, polypropylene glycol, dimethylol propionic acid, diethylene glycol, trimethylolpropane, triethylamine, silica nanoparticle loaded porous ceramic microspheres, nitrogen-doped graphene, polyaziridine crosslinking agent and acetone.

[0074] A preparation process of the organic resin coating is provided, which comprises the following steps:

[0075] S1, 1 g of cellulose nanocrystal is placed in 200 mL of acetone and ultrasonically dispersed for 1 h, then 42 g of isophorone diisocyanate and 0.012 g of dibutyl tin dilaurate are added, stirred for 20 h, and then 22 g of N,N-dimethyl ethanolamine is added to obtain modified cellulose nanocrystal;

[0076] S2, 0.16 g of N-butyl pyrrolidone, 10.5 g of polypropylene glycol and 11.5 isophorone diisocyanate were mixed and reacted for 1 h at a reaction temperature of 83 °C and a reaction time of 1.8 h; 0.98 g of dimethylol propionic acid was added and reacted for 1 h at 83 °C to carry out reaction 2; 2.4 g of diethylene glycol, 0.55 g of trimethylolpropane and 0.013 g of dibutyl tin dilaurate were added to carry out reaction 3 at a reaction temperature of 73 °C and a reaction time of 1.7 h; 0.7 g of triethylamine was added to carry out neutralization reaction at a reaction temperature of 39 °C and a reaction time of 35 min to obtain a modified polyurethane resin prepolymer;

[0077] S3, the modified cellulose nanocrystal was added to deionized water, ultrasonic dispersion was carried out, then ethylenediamine was added, and after stirring uniformly, a modified cellulose nanocrystal suspension was obtained, wherein the ratio of the modified cellulose nanocrystal, deionized water and ethylenediamine was 2 g:5 g:80 mL;

[0078] S4, the modified cellulose nanocrystal suspension, the porous ceramic microspheres loaded with silica nanoparticles and nitrogen-doped graphene were added to the modified polyurethane resin prepolymer, emulsified at a speed of 1500 r / min for 30 min, and the reaction was completed; acetone was removed by rotary evaporation to obtain a composite emulsion; the mass ratio of the modified cellulose nanocrystal, the porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene and the modified polyurethane resin prepolymer was 0.3.5:3.5:0.12:23. The modified cellulose nanocrystal was long rod-shaped, and the average diameter of the modified cellulose nanocrystal was less than 100 nm. The average diameter of the porous ceramic microspheres was 35 microns, and the average pore size of the pores on the porous ceramic microspheres was 350 nm.

[0079] S5, 0.2 g of butylhydroxytoluene and 0.4 mL of polyaziridine crosslinking agent were added to the composite emulsion to carry out crosslinking reaction to obtain an organic resin coating base;

[0080] S6, the organic resin base was coated on the zinc-plated steel plate, and after standing at room temperature for 24 h and drying at 60 °C for 12 h, an organic resin coating was obtained.

[0081] Comparative Example 1

[0082] This comparative example is the same as Example 1, except that the average diameter of the modified cellulose nanocrystal in this comparative example is 500 nm.

[0083] Comparative Example 2

[0084] This comparative example is the same as Example 1, except that the porous ceramic microspheres loaded with silica nanoparticles in this comparative example are replaced by an equal amount of nitrogen-doped graphene.

[0085] Comparative Example 3

[0086] The comparative example is the same as example 1, except that in the comparative example, the porous ceramic microspheres loaded with silica nanoparticles are replaced by an equivalent amount of nitrogen-doped graphene.

[0087] Comparative Example 4

[0088] The comparative example is the same as example 1, except that in the comparative example, S1 and S3 are omitted, and the porous ceramic microspheres loaded with silica nanoparticles and the modified cellulose nanocrystals in the original S4 are replaced by an equivalent amount of nitrogen-doped graphene.

[0089] Comparative Example 5

[0090] The comparative example is the same as example 1, except that in the 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 in S4 is 0.5:5:0.2:23.

[0091] Comparative Example 6

[0092] The comparative example is the same as example 1, except that in the 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 in S4 is 0.2:2:0.1:23.

[0093] The organic resin coating thin layer in examples 1-3 and comparative examples 1-6 was tested as follows.

[0094] (1) Tensile mechanical property test, the sample was cut into dumbbell-shaped sample by a tablet press, and the film thickness was measured by a thickness gauge. The film was measured by an electronic universal testing machine. The tensile rate was 50 mm / min, and each sample was measured 5 times. The test results of each group are shown in Table 1.

[0095] Table 1 Mechanical strength test

[0096] Group Sample 1 / MPa Sample 3 / MPa Sample 3 / MPa Sample 4 / MPa Sample 5 / MPa Average / 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

[0097] (2) Hardness test, the pencil hardness of the composite film was determined 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, and the higher the hardness, the better the wear resistance.

[0098] Table 2 Pencil hardness

[0099] 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

[0100] (3) Adhesion test

[0101] The adhesion force can reflect the firmness of the coating after curing and bonding with the metal substrate. In the experiment, a manual adhesion force detector (KS-M type, Zibo Senyuan Electrical Co., Ltd.) was used to test the adhesion force of the coating. In the experiment, the organic resin coating base was coated on the surface of a clean Q235 steel plate, the bonding agent was applied on the matched spindle, and the spindle was bonded vertically with the coating. After the bonding agent was fully cured, a pulling instrument was used to press the hydraulic rod at a constant speed until the coating and the steel plate were separated, and the value was read. The test results are shown in Table 3.

[0102] Table 3 Adhesion force test results

[0103] 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

[0104] (4) Corrosion resistance was judged by salt water immersion experiment

[0105] The sample was subjected to corrosion immersion experiment according to the national standard GB / T 9274-1988 with 1 mol / L NaCl solution as the medium. After immersion for 168 h, the change of the coating surface was observed, as shown in Table 4.

[0106] Table 4 Corrosion resistance test

[0107] 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 result No change No change No change No change Whitening phenomenon was obvious, but did not peel Partial whitening Whitening phenomenon was obvious, but did not peel Partial whitening Partial whitening

[0108] It can be seen that the coating of the present application has good salt corrosion resistance and can be sprayed on the surface of a ship for corrosion protection.

[0109] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A process for the preparation of an organic resinous coating for galvanised steel sheets for motor housings, characterised in that, It comprises the following steps: S1, cellulose nanocrystals are put into acetone, after dispersion, isophorone diisocyanate and dibutyltin dilaurate are added, stirring, N, N-dimethyl ethanolamine is added, to obtain modified cellulose nanocrystals, the mass ratio of cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate and N, N-dimethyl ethanolamine is 1:40-45:0.01-0.015:20-23; S2, N-butyl pyrrolidone, polypropylene glycol and isophorone diisocyanate are mixed to react 1, then dimethylol propionic acid is added to react 2, glycol, trimethylolpropane and dibutyltin dilaurate are added to react 3, triethylamine is added to neutralize the reaction, to obtain modified polyurethane resin prepolymer, the mass ratio of N-butyl pyrrolidone, polypropylene glycol, isophorone diisocyanate, dimethylol propionic acid, glycol, trimethylolpropane, dibutyltin dilaurate and triethylamine 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; S3, the modified cellulose nanocrystals are added to deionized water, ultrasonic dispersion, then ethylenediamine is added, to obtain modified cellulose nanocrystals suspension; S4, the modified cellulose nanocrystals suspension, porous ceramic microspheres loaded with silica nanoparticles and nitrogen-doped graphene are added to the modified polyurethane resin prepolymer, after emulsification, to obtain a composite emulsion, the mass ratio of modified cellulose nanocrystals, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene and modified polyurethane resin prepolymer is 0.3-0.4:3-4:0.1-0.15:23; S5, butylated hydroxyltoluene and polyaziridine crosslinking agent are added to the composite emulsion to carry out crosslinking reaction, to obtain organic resin coating base; S6, the organic resin coating base is coated on the zinc electroplated steel plate, after drying, to obtain organic resin coating.

2. The manufacturing process of claim 1, wherein, The reaction temperature of reaction 1 in S2 is 80-85℃, 1.5-2h, the reaction temperature of reaction 2 is 80-85℃.

3. The manufacturing process of claim 1, wherein, The reaction temperature of reaction 3 in S2 is 70-75℃, the reaction time is 1.5-2h.

4. The manufacturing process of claim 1, wherein, The reaction temperature of neutralization reaction in S2 is 38-40℃, the time is 30-40min.

5. The manufacturing process of claim 1, wherein, The modified cellulose nanocrystals in S4 are long rod-like, the average diameter of the modified cellulose nanocrystals is less than 100nm.

6. The manufacturing process of claim 1, wherein, The average diameter of the porous ceramic microspheres in S4 is 30-40 microns, the average pore size of the pores on the porous ceramic microspheres is 300-400nm.

7. An organic resin coating for a galvannealed steel sheet for a motor case, prepared by the production process according to claim 1, characterized in that, The raw materials thereof include N-butyl pyrrolidone, butylated hydroxyltoluene, cellulose nanocrystals, isophorone diisocyanate, dibutyltin dilaurate, polypropylene glycol, dimethylol propionic acid, glycol, trimethylolpropane, triethylamine, porous ceramic microspheres loaded with silica nanoparticles, nitrogen-doped graphene, polyaziridine crosslinking agent and acetone.