A self-drying impact-resistant protective coating and preparation method thereof

Abstract

The present invention relates to the technical field of coating preparation, and discloses a self-drying impact-resistant protective coating and a preparation method thereof. The self-drying impact-resistant protective coating comprises the following components: acrylic resin, epoxy resin, modified polyurethane emulsion, stearic acid glyceryl ester, styrene-butadiene-styrene block copolymer, modified tackifying resin, deionized water, ethylene glycol tert-butyl ether, ethanol, silicone defoamer, silicone leveling agent, impact-resistant agent methyl methacrylate-butadiene-styrene copolymer, polyurethane elastomer particles, organic bentonite, black slurry, isooctanoic acid. The self-drying impact-resistant protective coating of the present invention not only has excellent mechanical properties, impact resistance, corrosion resistance, wear resistance, and UV resistance, but also has self-healing properties and antibacterial properties.

Description

Technical Field

[0001] The invention relates to the technical field of coating preparation, in particular to a self-drying impact-resistant protective coating and a preparation method thereof. Background Art

[0002] Cars are subject to various external impacts during driving, such as stone splashing, collision, etc., so the impact resistance of car coatings is one of its important performance indicators. Good impact resistance can not only protect the car surface from damage, but also extend the service life of the coating and reduce the cost of car maintenance.

[0003] Chinese patent application CN201510780959.6 provides an impact-resistant and environmentally friendly water-based coating, the raw materials of which include, by weight: 90-110 parts of modified epoxy resin emulsion, 14-18 parts of water, 3-5 parts of triethylene glycol monoethyl ether, 10-15 parts of attapulgite, 5-8 parts of talc, 5-10 parts of titanium dioxide, 5-10 parts of negative ion powder, 0.2-0.4 parts of wetting agent H-140, 4-5 parts of triethylhexyl phosphate, 0.2-0.3 parts of polyvinyl pyrrolidone, 0.1-0.2 parts of polyethylene oxide, 0.3-0.4 parts of emulsifier OP-10, 0.1-0.2 parts of polyoxyethylene polyoxypropylene pentaerythritol ether, 0.03-0.07 parts of emulsified silicone oil, and preservative N-369 0.04-0.06 parts, dimethyl fumarate 0.02-0.04 parts, leveling agent 0.4-0.5 parts. The coating of this application has high impact resistance, good crack resistance and good environmental performance, but its anti-corrosion and anti-ultraviolet performance needs to be improved. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a self-drying impact-resistant protective coating, comprising the following steps:

[0005] Step (1) using urea as a raw material to prepare graphite phase carbon nitride, and then pre-treating it to obtain pre-treated graphite phase carbon nitride;

[0006] Step (2) obtaining epoxy-modified graphite phase carbon nitride by reacting γ-glycidyloxypropyltrimethoxysilane with pretreated graphite phase carbon nitride;

[0007] Step (3) obtaining modified chitosan by reacting carboxylated chitosan with epoxy-modified graphite phase carbon nitride;

[0008] Step (4) adding the modified chitosan to the ethanol dispersion of the calcium phosphate oligomer and stirring to obtain an organic-inorganic hybrid modifier;

[0009] Step (5) using polycarbonate diol, dimethylolbutyric acid, toluene diisocyanate, organic-inorganic hybrid modifier, 4,4-diaminodiphenyl sulfide as reactants and 1,4-butanediol as a chain extender to obtain a modified polyurethane emulsion;

[0010] Step (6) weighing acrylic resin, epoxy resin, modified polyurethane emulsion, stearic acid glyceryl ester, styrene-butadiene-styrene block copolymer, modified tackifying resin, deionized water, ethylene glycol tert-butyl ether, ethanol, silicone defoamer, silicone leveling agent according to proportion, stirring and mixing evenly, then adding impact resistant agent methyl methacrylate-butadiene-styrene copolymer and polyurethane elastomer particles and mixing evenly, finally adding organic bentonite, black slurry and isooctanoic acid to obtain a self-drying impact resistant protective coating;

[0011] The preparation method of the modified tackifying resin comprises the following steps:

[0012] Step A1, modifying rosin by hydrogenating sorbic acid to obtain modified rosin resin;

[0013] Step A2: grafting the modified rosin resin with 4-aminocatechol to obtain a modified tackifying resin.

[0014] Preferably, in step (1), the preparation method of the pretreated graphite phase carbon nitride is as follows: calcining urea at 520-580°C for 100-150 min, cooling to room temperature to obtain graphite phase carbon nitride; adding the graphite phase carbon nitride to a 63wt% formaldehyde aqueous solution, stirring at 80-90°C and a speed of 700-900r / min for 100-150min, filtering, washing, and drying to obtain the pretreated graphite phase carbon nitride; wherein the amount ratio of graphite phase carbon nitride to formaldehyde aqueous solution is (10-15)g:(200-400)mL;

[0015] In the above process, urea is used as a raw material and then calcined to obtain graphite-phase carbon nitride, which presents two-dimensional flaky nanostructures, and can not only produce a complex maze phenomenon and effectively block the invasion of corrosive agents, but also play a role in shielding ultraviolet rays; further, abundant hydroxyl groups are introduced on the surface of graphite-phase carbon nitride through the reaction of amino groups of graphite-phase carbon nitride with formaldehyde.

[0016] Preferably, in step (2), the preparation method of the epoxy-modified graphite phase carbon nitride is as follows: at 22-26°C, ethanol and γ-glycidyloxypropyltrimethoxysilane are mixed, and then pretreated graphite phase carbon nitride is added, ultrasonic dispersion is performed for 1-2h, heating to 70-90°C and stirring for reaction for 4-6h, cooling to room temperature, filtering, washing, and drying to obtain epoxy-modified graphite phase carbon nitride; wherein the mass ratio of ethanol, γ-glycidyloxypropyltrimethoxysilane, and pretreated graphite phase carbon nitride is (20-40):1:(0.1-0.3);

[0017] In the above process, the silanol bonds formed by the hydrolysis of γ-glycidyloxypropyltrimethoxysilane react with the hydroxyl groups on the surface of the pretreated graphite carbon nitride to introduce epoxy groups on the surface of the graphite carbon nitride.

[0018] Preferably, in step (3), the preparation method of the modified chitosan is as follows: epoxy-modified graphite phase carbon nitride is mixed with water, and ultrasonically dispersed for 40-80 minutes to obtain a mixed solution, wherein the mass ratio of epoxy-modified graphite phase carbon nitride to water is (2-6):(30-50); carboxylated chitosan is dissolved in water at a mass ratio of (1.5-4):(50-100), and is dripped into the above-obtained mixed solution at a rate of 0.8-1.2 mL / min at 22-26°C, and the reaction is stirred for 20-30 hours, filtered, washed, and dried to obtain modified chitosan; wherein the mass ratio of epoxy-modified graphite phase carbon nitride to carboxylated chitosan is (2-6):(1.5-4);

[0019] In the above process, the amino groups in the carboxylated chitosan react with the epoxy groups in the epoxy-modified graphite phase carbon nitride, and the graphite phase carbon nitride is connected to the network structure of the carboxylated chitosan by forming a chemical bond.

[0020] Preferably, in step (4), the preparation method of the organic-inorganic hybrid modifier is as follows: adding modified chitosan to an ethanol dispersion of calcium phosphate oligomers, stirring at a speed of 500-700 r / min for 3-4 hours, and distilling off the solvent to obtain an organic-inorganic hybrid modifier; wherein the amount ratio of modified chitosan to the ethanol dispersion of calcium phosphate oligomers is (2-4) g: (30-50) mL;

[0021] The ethanol dispersion of calcium phosphate oligomers is prepared by the following method: dissolving calcium chloride in ethanol at 22-26° C., adding triethylamine, stirring for 10-30 minutes, adding 0.09 g / mL ethanol solution of phosphoric acid, continuing to stir for 12-15 hours, centrifuging after the reaction, washing, and re-dispersing in ethanol to obtain an ethanol dispersion of calcium phosphate oligomers with a concentration of 13-15 mg / mL; wherein the dosage ratio of calcium chloride, ethanol, triethylamine, and ethanol solution of phosphoric acid is (4.4-6.6) g: (600-1000) mL: (60-90) g: (30-50) mL;

[0022] In the above process, calcium phosphate oligomers with a particle size of less than 1 nanometer are obtained using calcium chloride and phosphoric acid as the main raw materials, and then the calcium phosphate oligomers are mixed with modified chitosan. The abundant carboxyl and hydroxyl groups in the modified chitosan are connected with the calcium phosphate oligomers through ionic crosslinking and dynamic hydrogen bonds to form a tight, mutually penetrating organic-inorganic hybrid network.

[0023] Preferably, in step (5), the preparation method of the modified polyurethane emulsion is as follows: polycarbonate diol, dihydroxymethyl butyric acid and methyl ethyl ketone are mixed, stirred until the solid is completely dissolved, toluene diisocyanate and dibutyltin dilaurate are added, heated to 65-75°C for reaction for 150-200 minutes, organic-inorganic hybrid modifier and 4,4-diaminodiphenyl sulfide are added, the temperature is raised to 75-85°C for reaction for 2.5-3.5 hours, 1,4-butanediol is added, the reaction degree of isocyanate groups is detected during the reaction, when all isocyanate groups have reacted, the temperature is lowered to 30-35°C, triethylamine is added dropwise as a neutralizing agent, the reaction is continued for 20-40 minutes, deionized water is added under stirring conditions of 500-600 r / min, Maintain for 20-40 minutes, then remove the solvent by rotary evaporation at a temperature of 36-40°C and a vacuum degree of (-0.09)-(-0.095) MPa to obtain a modified polyurethane emulsion with a solid content of 33-38wt%; wherein the mass ratio of polycarbonate diol, dimethylolbutyric acid, toluene diisocyanate, organic-inorganic hybrid modifier, 4,4-diaminodiphenyl sulfide, 1,4-butanediol, triethylamine, deionized water, methyl ethyl ketone, and dibutyltin dilaurate is (6-9):(0.5-1):(1.2-1.8):(1.5-3.5):(0.4-1):(0.08-0.15):(0.5-0.8):(3-5):(32-48):(0.08-0.12);

[0024] In the above process, polycarbonate diol, dimethylolbutyric acid and toluene diisocyanate are reacted for prepolymerization, and the isocyanate group in the obtained prepolymer reacts with the amino group, hydroxyl group and amino group of 4,4-diaminodiphenyl sulfide in the organic-inorganic hybrid modifier, and the organic-inorganic hybrid modifier and 4,4-diaminodiphenyl sulfide are introduced into the polyurethane structure, and the organic-inorganic hybrid network in the organic-inorganic hybrid modifier is cross-linked with the polyurethane chain, and the carbamate in the polyurethane structure can form more hydrogen bonds, and cooperate with the ionic cross-linking effect formed by the calcium phosphate oligomer to enhance the cross-linking density of the polyurethane structure; further, the dynamic disulfide bonds introduced by the grafting of 4,4-diaminodiphenyl sulfide cooperate with the dynamic hydrogen bonds to show excellent self-healing properties.

[0025] Preferably, in step (6), the contents of the components in the self-drying impact-resistant protective coating are, by weight, 50-80 parts of acrylic resin, 60-90 parts of epoxy resin, 30-50 parts of modified polyurethane emulsion, 5-6 parts of glyceryl stearate, 4-8 parts of styrene-butadiene-styrene block copolymer, 18-35 parts of modified tackifying resin, 80-120 parts of deionized water, 5-15 parts of ethylene glycol tert-butyl ether, 30-50 parts of ethanol, 0.5-2 parts of silicone defoaming agent, 0.4-1.2 parts of silicone leveling agent, 10-18 parts of impact-resistant agent methyl methacrylate-butadiene-styrene copolymer, 5-9 parts of polyurethane elastomer particles, 1-3 parts of organic bentonite, 5-10 parts of black slurry, and 2.5-4.5 parts of isooctanoic acid; wherein the black slurry comprises at least one of carbon black slurry and iron black slurry.

[0026] In the above process, the addition of styrene-butadiene-styrene block copolymer, impact-resistant agent methyl methacrylate-butadiene-styrene copolymer, and polyurethane elastomer particles helps to improve the wear resistance and impact resistance of the coating.

[0027] Preferably, in the step (6), in the modified tackifying resin preparation step A1, the modified rosin resin is prepared by the following method: sorbic acid, xylene and rosin are mixed in a mass ratio of (20-35):50:(30-50), heated to 270-280°C for polymerization reaction for 50-80 minutes, after the reaction is completed, 4-5wt% of Pd / Al catalyst in the total amount of the reaction mixture is added, hydrogenation treatment is carried out for 80-100 minutes at a temperature of 220-240°C and a pressure of 7.5-8MPa, after the reaction is completed, a crude product is obtained, the crude product is dissolved and purified with hot acetic acid at 60-80°C, filtered, the obtained filter residue is washed with hot acetic acid at 60-80°C and hot water at 60-80°C, and dried;

[0028] In the above process, both rosin and sorbic acid contain unsaturated bonds and carboxyl groups. Through the addition of unsaturated bonds, the hydrogenated sorbic acid structure is introduced into the rosin, thereby enhancing the polarity of the rosin and introducing new carboxyl groups.

[0029] Preferably, in the step (6), in the modified tackifying resin preparation step A2, the modified tackifying resin is prepared by the following method: in a nitrogen atmosphere, at room temperature, taking the modified rosin resin and adding it to ethanol, stirring for 20-40 minutes, then adding 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide, continuing to stir for 150-200 minutes, then adding 4-aminocatechol, and adjusting the reaction mixture system with 1 mol / L hydrochloric acid aqueous solution. The pH value is 5.4-5.6, and the reaction is carried out for 20-28 hours. After the reaction is completed, the mixture is filtered, and the residue is washed with methanol for 5-10 times and dried. The usage ratio of the modified rosin resin, ethanol, 1,3-dicyclohexylcarbodiimide, N-hydroxysuccinimide and 4-aminocatechol is (4.1-8.2) g: (300-500) mL: (3.7-7.4) g: (2.1-4.2) g: (4.2-8.4) g.

[0030] In the above process, the carboxyl groups in the modified rosin resin are first activated by 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide, and the activated carboxyl groups react with the amino groups in 4-aminocatechol to introduce the polar groups of catechol.

[0031] The self-drying anti-impact protective coating is prepared by the method for preparing the self-drying anti-impact protective coating.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention pre-treats and epoxy-modifies graphite phase carbon nitride, and then chemically bonds it with carboxylated chitosan to obtain modified chitosan. The modified chitosan is combined with calcium phosphate oligomers to form an organic-inorganic hybrid modifier with a tight, mutually penetrating organic-inorganic hybrid network that is ion-crosslinked and dynamically hydrogen-bonded. The introduction of graphite phase carbon nitride and calcium phosphate oligomers exhibits excellent corrosion resistance by extending the corrosion path, and the addition of graphite phase carbon nitride and calcium phosphate oligomers can significantly increase the wear resistance of the system. In addition, the addition of graphite phase carbon nitride can enhance the anti-ultraviolet effect of the organic-inorganic hybrid modifier, and the carboxylated chitosan can also enhance the antibacterial performance of the organic-inorganic hybrid modifier. Therefore, the present invention The organic-inorganic hybrid modifier is introduced into the polyurethane structure in the form of chemical bonds, thereby improving the compatibility of graphite phase carbon nitride and calcium phosphate oligomers with polyurethane, and the organic-inorganic hybrid network in the organic-inorganic hybrid modifier is cross-linked with the polyurethane chain, and the carbamate in the polyurethane can participate in the formation of more hydrogen bonds, strengthen the ionic cross-linking effect, and improve the cross-linking density of the polyurethane structure, thereby obtaining a modified polyurethane with excellent mechanical properties, corrosion resistance, wear resistance, impact resistance, UV resistance, and antibacterial properties. Furthermore, 4,4-diaminodiphenyl sulfide introduces dynamic disulfide bonds in the polyurethane structure to cooperate with dynamic hydrogen bonds, thereby exhibiting self-healing properties; therefore, adding the modified polyurethane emulsion to the coating can improve the comprehensive properties of the coating.

[0034] 2. The modified tackifying resin in the present invention is obtained by grafting rosin with hydrogenated sorbic acid and modifying it with 4-aminocatechol. The modification of hydrogenated sorbic acid and 4-aminocatechol not only increases the polarity of rosin, thereby improving the adhesion of the modified tackifying resin and its compatibility with other components, but also introduces a catechol group with an ultraviolet absorption effect into the modified tackifying resin, thereby improving the anti-ultraviolet performance of the coating system; further, the phenolic hydroxyl group in the catechol can form hydrogen bonds with components such as polyurethane in the system, thereby further improving the dispersibility and compatibility of the modified tackifying resin in the coating; therefore, the present invention adds the modified tackifying resin to the self-drying impact-resistant protective coating, which can better enhance the adhesion, internal cohesion and anti-ultraviolet effect of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a process flow chart of a method for preparing a self-drying impact-resistant protective coating of the present invention;

[0036] Figure 2 It is a comparison chart of the impact resistance test of the self-drying impact-resistant protective coatings of Examples 2-5 of the present invention and Comparative Examples 4-11;

[0037] Figure 3 It is a comparison chart of the salt spray resistance time test of the self-drying impact-resistant protective coatings of Examples 2-5 of the present invention and Comparative Examples 4-11;

[0038] Figure 4 It is a comparison chart of the tensile strength retention rate test of the self-drying impact-resistant protective coatings of Examples 2-5 of the present invention and Comparative Examples 4-11. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment discloses a method for preparing a modified tackifying resin, comprising the following steps:

[0042] Step A1, sorbic acid, xylene and rosin are mixed in a mass ratio of 28:50:40, heated to 276°C for polymerization reaction for 65 minutes, and after the reaction, 4.5wt% of the total amount of the reaction mixture is added with a Pd / Al catalyst, hydrogen is introduced to maintain the pressure at 7.8MPa, and hydrogenation is performed at a temperature of 230°C for 90 minutes. After the reaction, a crude product is obtained, and the crude product is dissolved and purified with 70°C hot acetic acid, filtered, and the obtained filter residue is washed with 70°C hot acetic acid and 70°C hot water, and dried to obtain a modified rosin resin;

[0043] Step A2, in a nitrogen atmosphere, at room temperature, take 6.2g of modified rosin resin and add it to 400mL of ethanol, stir for 30min, then add 5.6g of 1,3-dicyclohexylcarbodiimide and 3.2g of N-hydroxysuccinimide, continue stirring for 180min, then add 6.3g of 4-aminocatechol, adjust the pH of the reaction mixture to 5.5 with 1mol / L hydrochloric acid aqueous solution, react for 24h, filter after the reaction, wash the obtained residue 8 times with methanol, and dry to obtain a modified tackifying resin.

[0044] Example 2

[0045] This embodiment discloses a method for preparing a self-drying impact-resistant protective coating, comprising the following steps:

[0046] Step (1) calcining urea at 520° C. for 150 min, cooling to room temperature, and obtaining graphite phase carbon nitride; adding the graphite phase carbon nitride to a 63 wt % formaldehyde aqueous solution, stirring at 80° C. and a speed of 700 r / min for 150 min, filtering, washing, and drying to obtain pretreated graphite phase carbon nitride; wherein the amount ratio of graphite phase carbon nitride to formaldehyde aqueous solution is 10 g:200 mL;

[0047] Step (2) at 22°C, ethanol and γ-glycidyloxypropyltrimethoxysilane are mixed, and then pretreated graphite phase carbon nitride is added, ultrasonic dispersion is performed for 1 hour, the mixture is heated to 70°C and stirred for reaction for 6 hours, the mixture is cooled to room temperature, filtered, the filter residue is washed with deionized water for 5 times, and vacuum dried at 60°C for 24 hours to obtain epoxy-modified graphite phase carbon nitride; wherein the mass ratio of ethanol, γ-glycidyloxypropyltrimethoxysilane and pretreated graphite phase carbon nitride is 20:1:0.1;

[0048] Step (3) 2 g of epoxy-modified graphite phase carbon nitride is mixed with 30 g of water, and ultrasonically dispersed for 40 min to obtain a mixed solution; 1.5 g of carboxylated chitosan is dissolved in 50 g of water, and dripped into the mixed solution at a rate of 0.8 mL / min at 22° C., stirred for reaction for 20 h, filtered, and the obtained filter residue is washed with deionized water 5 times, and vacuum dried at 50° C. for 15 h to obtain modified chitosan;

[0049] Step (4) at 22°C, 4.4g of calcium chloride is dissolved in 600mL of ethanol, 6g of triethylamine is added, and after stirring for 10min, 30mL of 0.09g / mL phosphoric acid ethanol solution is added, and stirring is continued for 12h. After the reaction is completed, centrifugation is performed, and the centrifuged product is washed with ethanol for 3 times, and then dispersed in ethanol to obtain an ethanol dispersion of calcium phosphate oligomers with a concentration of 13mg / mL; 2g of modified chitosan is added to 30mL of the ethanol dispersion of calcium phosphate oligomers, and the mixture is stirred at a speed of 500r / min for 4h, and the solvent is distilled off to obtain an organic-inorganic hybrid modifier;

[0050] Step (5) 6 g of polycarbonate diol, 0.5 g of dihydroxymethyl butyric acid, and 32 g of methyl ethyl ketone were mixed and stirred until the solid was completely dissolved, and then 1.2 g of toluene diisocyanate and 0.08 g of dibutyltin dilaurate were added, and the mixture was heated to 65 ° C for reaction for 150 min, and then 1.5 g of organic-inorganic hybrid modifier and 0.4 g of 4,4-diaminodiphenyl sulfide were added, and the mixture was heated to 75 ° C for reaction for 2.5 h, and then 0.08 g of 1,4-Butanediol was used as a chain extender. The reaction degree of the isocyanate group was detected during the reaction. When all the isocyanate groups had reacted, the temperature was lowered to 30°C, 0.5g of triethylamine was added dropwise as a neutralizing agent, and the reaction was continued for 20min. 3g of deionized water was added under stirring conditions of 500r / min and maintained for 20min. The solvent was then removed by rotary evaporation at a temperature of 36°C and a vacuum degree of -0.09MPa to obtain a modified polyurethane emulsion with a solid content of 33wt%;

[0051] Step (6) In parts by weight, 50 parts of acrylic resin, 60 parts of epoxy resin, 30 parts of modified polyurethane emulsion, 5 parts of glyceryl stearate, 4 parts of styrene-butadiene-styrene block copolymer, 18 parts of modified tackifying resin, 80 parts of deionized water, 5 parts of ethylene glycol tert-butyl ether, 30 parts of ethanol, 0.5 parts of organosilicon defoaming agent, and 0.4 parts of organosilicon leveling agent are stirred and mixed evenly, and then 10 parts of impact-resistant agent methyl methacrylate-butadiene-styrene copolymer and 5 parts of polyurethane elastomer particles are added and mixed evenly, and finally 1 part of organic bentonite, 5 parts of carbon black slurry, and 2.5 parts of isooctanoic acid are added to obtain a self-drying impact-resistant protective coating.

[0052] Example 3

[0053] This embodiment discloses a method for preparing a self-drying impact-resistant protective coating, comprising the following steps:

[0054] Step (1) calcining urea at 580° C. for 100 min, cooling to room temperature, and obtaining graphite phase carbon nitride; adding the graphite phase carbon nitride to a 63 wt % formaldehyde aqueous solution, stirring at 90° C. at a speed of 900 r / min for 100 min, filtering, washing, and drying to obtain pretreated graphite phase carbon nitride; wherein the amount ratio of graphite phase carbon nitride to formaldehyde aqueous solution is 15 g:400 mL;

[0055] Step (2) at 26°C, ethanol and γ-glycidyloxypropyltrimethoxysilane are mixed, and then pretreated graphite phase carbon nitride is added, ultrasonic dispersion is performed for 2 hours, the mixture is heated to 90°C and stirred for reaction for 6 hours, the mixture is cooled to room temperature, filtered, the filter residue is washed 8 times with deionized water, and vacuum dried at 80°C for 12 hours to obtain epoxy-modified graphite phase carbon nitride; wherein the mass ratio of ethanol, γ-glycidyloxypropyltrimethoxysilane and pretreated graphite phase carbon nitride is 40:1:0.3;

[0056] Step (3) 6 g of epoxy-modified graphite phase carbon nitride was mixed with 50 g of water, and ultrasonically dispersed for 80 min to obtain a mixed solution; 4 g of carboxylated chitosan was dissolved in 100 g of water, and dripped into the mixed solution at a rate of 1.2 mL / min at 26° C., stirred for reaction for 30 h, filtered, and the obtained filter residue was washed 8 times with deionized water, and vacuum dried at 70° C. for 10 h to obtain modified chitosan;

[0057] Step (4) at 26°C, dissolving 6.6g of calcium chloride in 1000mL of ethanol, adding 90g of triethylamine, stirring for 30min, adding 50mL of 0.09g / mL phosphoric acid ethanol solution, continuing to stir for 15h, centrifuging after the reaction is completed, washing the centrifuged product with ethanol for 8 times, and then dispersing it in ethanol to obtain an ethanol dispersion of calcium phosphate oligomers with a concentration of 15mg / mL; adding 4g of modified chitosan to 50mL of the ethanol dispersion of calcium phosphate oligomers, stirring at a speed of 700r / min for 3h, and distilling off the solvent to obtain an organic-inorganic hybrid modifier;

[0058] Step (5) 9 g of polycarbonate diol, 1 g of dihydroxymethylbutyric acid, and 48 g of methyl ethyl ketone were mixed and stirred until the solid was completely dissolved, and then 1.8 g of toluene diisocyanate and 0.12 g of dibutyltin dilaurate were added, and the mixture was heated to 75° C. and reacted for 150 min. Then 3.5 g of organic-inorganic hybrid modifier and 1 g of 4,4-diaminodiphenyl sulfide were added, and the mixture was heated to 85° C. and reacted for 2.5 h. Then 0.15 g of 1,4-butanediol was added as a chain extender. During the reaction, the reaction degree of the isocyanate group was detected. After all the isocyanate groups had reacted, the mixture was cooled to 35° C., 0.8 g of triethylamine was added dropwise as a neutralizing agent, and the reaction was continued for 40 min. 5 g of deionized water was added under stirring at 600 r / min, and the mixture was kept for 40 min. Then, the solvent was removed by rotary evaporation at a temperature of 40° C. and a vacuum degree of -0.095 MPa to obtain a modified polyurethane emulsion with a solid content of 38 wt %;

[0059] Step (6) In parts by weight, 80 parts of acrylic resin, 90 parts of epoxy resin, 50 parts of modified polyurethane emulsion, 6 parts of glyceryl stearate, 8 parts of styrene-butadiene-styrene block copolymer, 35 parts of modified tackifying resin, 120 parts of deionized water, 15 parts of ethylene glycol tert-butyl ether, 50 parts of ethanol, 2 parts of organosilicon defoaming agent, and 1.2 parts of organosilicon leveling agent are stirred and mixed evenly, and then 18 parts of impact-resistant agent methyl methacrylate-butadiene-styrene copolymer and 9 parts of polyurethane elastomer particles are added and mixed evenly, and finally 3 parts of organic bentonite, 10 parts of carbon black slurry, and 4.5 parts of isooctanoic acid are added to obtain a self-drying impact-resistant protective coating.

[0060] Example 4

[0061] This embodiment discloses a method for preparing a self-drying impact-resistant protective coating, comprising the following steps:

[0062] Step (1) calcining urea at 550° C. for 120 min, cooling to room temperature, and obtaining graphite phase carbon nitride; adding the graphite phase carbon nitride to a 63 wt % formaldehyde aqueous solution, stirring at 85° C. at a speed of 800 r / min for 120 min, filtering, washing, and drying to obtain pretreated graphite phase carbon nitride; wherein the amount ratio of graphite phase carbon nitride to formaldehyde aqueous solution is 12 g:300 mL;

[0063] Step (2) at 25°C, ethanol and γ-glycidyloxypropyltrimethoxysilane are mixed, and then pretreated graphite phase carbon nitride is added, ultrasonic dispersion is performed for 1.5 hours, the mixture is heated to 80°C and stirred for reaction for 5 hours, the mixture is cooled to room temperature, filtered, the filter residue is washed with deionized water for 7 times, and vacuum dried at 70°C for 18 hours to obtain epoxy-modified graphite phase carbon nitride; wherein the mass ratio of ethanol, γ-glycidyloxypropyltrimethoxysilane and pretreated graphite phase carbon nitride is 30:1:0.2;

[0064] Step (3) 4 g of epoxy-modified graphite phase carbon nitride is mixed with 40 g of water, and ultrasonically dispersed for 60 min to obtain a mixed solution; 2.8 g of carboxylated chitosan is dissolved in 80 g of water, and dripped into the mixed solution at a rate of 1 mL / min at 25° C., stirred for reaction for 25 h, filtered, and the obtained filter residue is washed with deionized water 7 times, and vacuum dried at 60° C. for 12 h to obtain modified chitosan;

[0065] Step (4) at 25°C, 5.5g of calcium chloride is dissolved in 800mL of ethanol, and then 75g of triethylamine is added. After stirring for 20min, 40mL of 0.09g / mL phosphoric acid ethanol solution is added, and stirring is continued for 14h. After the reaction is completed, centrifugation is performed, and the centrifugal product is washed with ethanol for 6 times, and then dispersed in ethanol to obtain an ethanol dispersion of calcium phosphate oligomers with a concentration of 14mg / mL; 3g of modified chitosan is added to 40mL of the ethanol dispersion of calcium phosphate oligomers, and the mixture is stirred at a speed of 600r / min for 3.5h, and the solvent is removed by distillation to obtain an organic-inorganic hybrid modifier;

[0066] Step (5) 7.5 g of polycarbonate diol, 0.8 g of dihydroxymethyl butyric acid, and 40 g of methyl ethyl ketone were mixed and stirred until the solid was completely dissolved, and then 1.5 g of toluene diisocyanate and 0.1 g of dibutyltin dilaurate were added, and the mixture was heated to 70 ° C for reaction for 180 min, and then 2.5 g of organic-inorganic hybrid modifier and 0.7 g of 4,4-diaminodiphenyl sulfide were added, and the mixture was heated to 80 ° C for reaction for 3 h, and then 0.12 g of 1,4-Butanediol was used as a chain extender. The reaction degree of the isocyanate group was detected during the reaction. When all the isocyanate groups had reacted, the temperature was lowered to 33°C, 0.6 g of triethylamine was added dropwise as a neutralizing agent, and the reaction was continued for 30 min. 4 g of deionized water was added under stirring conditions of 550 r / min and maintained for 30 min. The solvent was then removed by rotary evaporation at a temperature of 38°C and a vacuum degree of -0.092 MPa to obtain a modified polyurethane emulsion with a solid content of 35 wt%;

[0067] Step (6) In parts by weight, 65 parts of acrylic resin, 75 parts of epoxy resin, 40 parts of modified polyurethane emulsion, 5.5 parts of glyceryl stearate, 6 parts of styrene-butadiene-styrene block copolymer, 27 parts of modified tackifying resin, 100 parts of deionized water, 10 parts of ethylene glycol tert-butyl ether, 40 parts of ethanol, 1.3 parts of organosilicon defoaming agent, and 0.8 parts of organosilicon leveling agent are stirred and mixed evenly, and then 14 parts of impact-resistant agent methyl methacrylate-butadiene-styrene copolymer and 7 parts of polyurethane elastomer particles are added and mixed evenly, and finally 2 parts of organic bentonite, 7.5 parts of carbon black slurry, and 3.5 parts of isooctanoic acid are added to obtain a self-drying impact-resistant protective coating.

[0068] Example 5

[0069] This embodiment discloses a method for preparing a self-drying impact-resistant protective coating, comprising the following steps:

[0070] Step (1) calcining urea at 550° C. for 120 min, cooling to room temperature, and obtaining graphite phase carbon nitride; adding the graphite phase carbon nitride to a 63 wt % formaldehyde aqueous solution, stirring at 85° C. at a speed of 800 r / min for 120 min, filtering, washing, and drying to obtain pretreated graphite phase carbon nitride; wherein the amount ratio of graphite phase carbon nitride to formaldehyde aqueous solution is 12 g:300 mL;

[0071] Step (2) at 25°C, ethanol and γ-glycidyloxypropyltrimethoxysilane are mixed, and then pretreated graphite phase carbon nitride is added, ultrasonic dispersion is performed for 1.5 hours, the mixture is heated to 80°C and stirred for reaction for 5 hours, the mixture is cooled to room temperature, filtered, the filter residue is washed with deionized water for 7 times, and vacuum dried at 70°C for 18 hours to obtain epoxy-modified graphite phase carbon nitride; wherein the mass ratio of ethanol, γ-glycidyloxypropyltrimethoxysilane and pretreated graphite phase carbon nitride is 30:1:0.2;

[0072] Step (3) 4 g of epoxy-modified graphite phase carbon nitride is mixed with 40 g of water, and ultrasonically dispersed for 60 min to obtain a mixed solution; 2.8 g of carboxylated chitosan is dissolved in 80 g of water, and dripped into the mixed solution at a rate of 1 mL / min at 25° C., stirred for reaction for 25 h, filtered, and the obtained filter residue is washed with deionized water 7 times, and vacuum dried at 60° C. for 12 h to obtain modified chitosan;

[0073] Step (4) at 25°C, 5.5g of calcium chloride is dissolved in 800mL of ethanol, and then 75g of triethylamine is added. After stirring for 20min, 40mL of 0.09g / mL phosphoric acid ethanol solution is added, and stirring is continued for 14h. After the reaction is completed, centrifugation is performed, and the centrifugal product is washed with ethanol for 6 times, and then dispersed in ethanol to obtain an ethanol dispersion of calcium phosphate oligomers with a concentration of 14mg / mL; 3g of modified chitosan is added to 40mL of the ethanol dispersion of calcium phosphate oligomers, and the mixture is stirred at a speed of 600r / min for 3.5h, and the solvent is removed by distillation to obtain an organic-inorganic hybrid modifier;

[0074] Step (5) 7.5 g of polycarbonate diol, 0.8 g of dihydroxymethyl butyric acid, and 40 g of methyl ethyl ketone were mixed and stirred until the solid was completely dissolved, and then 1.5 g of toluene diisocyanate and 0.1 g of dibutyltin dilaurate were added, and the mixture was heated to 70 ° C for reaction for 180 min, and then 2.5 g of organic-inorganic hybrid modifier and 0.7 g of 4,4-diaminodiphenyl sulfide were added, and the mixture was heated to 80 ° C for reaction for 3 h, and then 0.12 g of 1,4-Butanediol was used as a chain extender. The reaction degree of the isocyanate group was detected during the reaction. When all the isocyanate groups had reacted, the temperature was lowered to 33°C, 0.6 g of triethylamine was added dropwise as a neutralizing agent, and the reaction was continued for 30 min. 4 g of deionized water was added under stirring conditions of 550 r / min and maintained for 30 min. The solvent was then removed by rotary evaporation at a temperature of 38°C and a vacuum degree of -0.092 MPa to obtain a modified polyurethane emulsion with a solid content of 35 wt%;

[0075] Step (6) In parts by weight, 65 parts of acrylic resin, 75 parts of epoxy resin, 40 parts of modified polyurethane emulsion, 5.5 parts of glyceryl stearate, 6 parts of styrene-butadiene-styrene block copolymer, 27 parts of modified tackifying resin, 100 parts of deionized water, 10 parts of ethylene glycol tert-butyl ether, 40 parts of ethanol, 1.3 parts of organosilicon defoaming agent, and 0.8 parts of organosilicon leveling agent are stirred and mixed evenly, and then 14 parts of impact-resistant agent methyl methacrylate-butadiene-styrene copolymer and 7 parts of polyurethane elastomer particles are added and mixed evenly, and finally 2 parts of organic bentonite, 7.5 parts of iron black slurry, and 3.5 parts of isooctanoic acid are added to obtain a self-drying impact-resistant protective coating.

[0076] The modified tackifying resin in the above Examples 2-5 adopts the modified tackifying resin prepared in Example 1.

[0077] Comparative Example 1

[0078] Comparative Example 1 Compared with Example 1, in the process of preparing the modified tackifying resin in Comparative Example 1, rosin was used instead of the modified rosin resin, and other conditions remained unchanged.

[0079] Comparative Example 2

[0080] Comparative Example 2 Compared with Example 1, Comparative Example 2 uses modified rosin resin as the modified tackifying resin, and other conditions remain unchanged.

[0081] Comparative Example 3

[0082] Comparative Example 3 Compared with Example 1, in Comparative Example 3, modified rosin resin and 4-aminocatechol are directly mixed as modified tackifying resin, and other conditions remain unchanged.

[0083] Comparative Example 4

[0084] Comparative Example 4 Compared with Example 4, the self-drying impact-resistant protective coating of Comparative Example 4 adopts the modified tackifying resin prepared in Comparative Example 1, and other conditions remain unchanged.

[0085] Comparative Example 5

[0086] Comparative Example 5 Compared with Example 4, the self-drying impact-resistant protective coating of Comparative Example 5 uses the modified tackifying resin prepared in Comparative Example 2, and other conditions remain unchanged.

[0087] Comparative Example 6

[0088] Comparative Example 6 Compared with Example 4, the self-drying impact-resistant protective coating of Comparative Example 6 uses the modified tackifying resin prepared in Comparative Example 3, and other conditions remain unchanged.

[0089] Comparative Example 7

[0090] Comparative Example 7 Compared with Example 4, in the process of preparing modified chitosan in Comparative Example 7, pretreated graphite phase carbon nitride is used instead of epoxy-modified graphite phase carbon nitride, and other conditions remain unchanged.

[0091] Comparative Example 8

[0092] Comparative Example 8 Compared with Example 4, in the process of preparing the organic-inorganic hybrid modifier in Comparative Example 8, carboxylated chitosan was used instead of modified chitosan, and other conditions remained unchanged.

[0093] Comparative Example 9

[0094] Comparative Example 9 Compared with Example 4, in the process of preparing the modified polyurethane emulsion in Comparative Example 9, modified chitosan is used instead of the organic-inorganic hybrid modifier, and other conditions remain unchanged.

[0095] Comparative Example 10

[0096] Comparative Example 10 Compared with Example 4, in the process of preparing the modified polyurethane emulsion in Comparative Example 10, no 4,4-diaminodiphenyl sulfide was added, and other conditions remained unchanged.

[0097] Comparative Example 11

[0098] Comparative Example 11 Compared with Example 4, in the process of preparing the organic-inorganic hybrid modifier in Comparative Example 11, pretreated graphite phase carbon nitride is used instead of modified chitosan, and other conditions remain unchanged.

[0099] In the above examples and comparative examples, carboxylated chitosan was obtained from Wuhan Huaxiang Kejie Biotechnology Co., Ltd., with a carboxylation degree of 60%; polycarbonate diol (Mn: 2000 g / mol, purity 99.5%) was purchased from Baichuan Chemical Co., Ltd. (Jining, China); rosin, with an acid value of 15 mgKOH / g, was obtained from Guangxi Wuzhou Richeng Forest Products Chemical Co., Ltd.; acrylic resin was a liquid water-based acrylic resin obtained from Shandong Haoyao New Materials Co., Ltd., with a product number of HY56654 and a viscosity of 3000 (S); epoxy resin Ester, brand E-44, from Shandong Luxing Chemical Co., Ltd.; styrene-butadiene-styrene block copolymer, brand: HT-S600, from Dongguan Zhangmutou Hengtai Plastic Raw Materials Business Department, particle size: 300 mesh; silicone defoamer BYK028, silicone leveling agent BYK346, from Guangzhou Haoliangda International Trade Co., Ltd.; polyurethane elastomer particles from Dongguan Hualixing Plastic Raw Materials Co., Ltd., brand: TPU powder, particle size: 300 mesh; organic bentonite, model BENTONE 27, from Shanghai Zhenlishi Network Technology Co., Ltd.; carbon black paste is BASF 0066 water-based carbon black paste, from Anhui Jingzhicai New Materials Co., Ltd.; iron black paste, model BK9011-SB, from Shanghai Jiahong Materials Technology Co., Ltd.; methyl methacrylate-butadiene-styrene copolymer comes from Shenzhen Shansu New Materials Co., Ltd., brand: Japan TH-21, model: MBS TP-803 Guangzhou S050, density: 1.09-1.11.

[0100] Experimental example

[0101] The substrate material is a tinplate sheet (120 mm × 50 mm, thickness 0.28 mm) that meets the requirements of GB / T2520-2000. The surface of the tinplate sheet is first treated by the GB / T9271-2008 grinding method, first polished with 200-mesh sandpaper, and then with 800-mesh sandpaper to obtain a rough surface, cleaned with ethanol and ultrasound, and dried in an oven. The coatings prepared in the above Examples 2-5 and Comparative Examples 4-11 are evenly scraped on the polished surface of the tinplate sheet and left at room temperature for 24 hours to obtain the corresponding coating.

[0102] 1. Impact resistance test: refer to GB / T1732-93 "Determination of impact resistance of paint film". Use paint film impactor (OCJ, Tianjin Material Testing Machine Factory, China) for testing. According to the standard, the heavy hammer impact resistance height of 0-65cm is evaluated.

[0103] 2. Hardness test: Test according to GB / T6739-2006 "Determination of film hardness by pencil method for paints and varnishes". Use a film pencil hardness scratch hardness tester (QHQ, Tianjin Material Testing Machine Factory) to test and grade the pencil hardness, with a rating range of 9B-9H.

[0104] 3. Salt spray test: Test the salt spray resistance of the sample in accordance with GB / T1771-2007 to determine the corrosion resistance of the sample.

[0105] 4. Coating adhesion test: The coating adhesion test is carried out in accordance with GB∕T 1720-2020 "Paint film circle test". The paint film is rated on a scale of 1-7, with 1 being the best and 7 being the worst.

[0106] 5. Anti-ultraviolet performance test: The tinplate coated with each group of coatings was placed in a light-oxidation aging test chamber. A high-pressure mercury lamp was used as the light source for the artificial accelerated ultraviolet aging experiment. The ultraviolet irradiation intensity on the sample surface was 2200µw / cm 2 , aging temperature is 45℃, aging time is 18d, by comparing the tensile strength of the samples before and after aging, calculate the tensile strength retention rate to judge the anti-ultraviolet performance. Among them, the tensile strength is tested according to the national standard GB / T1040-2006; the test results are shown in Table 1:

[0107] Table 1

[0108] Impact resistance / cm Hardness / Grade Salt spray resistance time / h Adhesion grade Tensile strength retention rate / % Example 2 63 4H 3600 1 94.8 Example 3 65 5H 3700 1 95.7 Example 4 64 5H 3650 1 95.3 Example 5 64 5H 3650 1 95.2 Comparative Example 4 53 3H 3460 4 94.0 Comparative Example 5 54 3H 3480 4 93.3 Comparative Example 6 56 3H 3500 3 94.4 Comparative Example 7 61 4H 3550 1 94.7 Comparative Example 8 62 2H 3400 1 93.2 Comparative Example 9 51 2H 3460 1 95.0 Comparative Example 10 60 4H 3520 1 95.1 Comparative Example 11 58 3H 3500 1 94.5

[0109] It can be seen from the test results of Table 1 that the self-drying impact-resistant protective coating prepared in Examples 2-4 of the present invention has excellent impact resistance, wear resistance, corrosion resistance, adhesion and UV resistance. From the comparison of Comparative Examples 4-6 with Example 4, it can be seen that the grafting of hydrogenated sorbic acid and 4-aminocatechol in the modified tackifying resin affects the adhesion and compatibility of the modified tackifying resin by changing the polarity of rosin and introducing catechol groups, thereby affecting the impact resistance, wear resistance, corrosion resistance, adhesion and UV resistance of the coating. Further, the introduction of hydrogenated sorbic acid and 4-aminocatechol in the form of chemical bonds can exert better effects; from the comparison of Comparative Examples 7-8 with Example 4, it can be seen that the graphite phase carbon nitride has a large influence on the corrosion resistance, wear resistance and UV resistance of the coating due to its high hardness two-dimensional flaky structure and UV shielding effect, and the graphite phase carbon nitride is epoxy-modified, which affects its own inorganic The dispersion of the material and the connection strength with the organic network have a negative impact on the comprehensive performance of the coating; from the comparison of comparative example 9 and example 4, it can be seen that the addition of calcium phosphate oligomers has an important influence on the formation of the organic-inorganic hybrid network, and forms ionic crosslinks with the organic system, thereby affecting the impact resistance, wear resistance and corrosion resistance of the coating; from the comparison of comparative example 10 and example 4, it can be seen that 4,4-diaminodiphenyl sulfide introduces dynamic disulfide bonds and dynamic hydrogen bonds in the polyurethane structure to improve the self-healing properties of the coating, thereby affecting other properties; from the comparison of comparative example 11 and example 4, it can be seen that the introduction of the modifier carboxylated chitosan affects the performance of the coating by enhancing the crosslinking strength and density of the organic-inorganic hybrid network.

[0110] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a self-drying impact-resistant protective coating, characterized in that: The following steps are involved: Step (1) using urea as a raw material to prepare graphite phase carbon nitride, and then pre-treating it to obtain pre-treated graphite phase carbon nitride; Step (2) obtaining epoxy-modified graphite phase carbon nitride by reacting γ-glycidyloxypropyltrimethoxysilane with pretreated graphite phase carbon nitride; Step (3) obtaining modified chitosan by reacting carboxylated chitosan with epoxy-modified graphite phase carbon nitride; Step (4) adding the modified chitosan to the ethanol dispersion of the calcium phosphate oligomer and stirring to obtain an organic-inorganic hybrid modifier; Step (5) using polycarbonate diol, dimethylolbutyric acid, toluene diisocyanate, organic-inorganic hybrid modifier, 4,4-diaminodiphenyl sulfide as reactants and 1,4-butanediol as a chain extender to obtain a modified polyurethane emulsion; Step (6) weighing acrylic resin, epoxy resin, modified polyurethane emulsion, stearic acid glyceryl ester, styrene-butadiene-styrene block copolymer, modified tackifying resin, deionized water, ethylene glycol tert-butyl ether, ethanol, silicone defoamer, silicone leveling agent according to proportion, stirring and mixing evenly, then adding impact resistant agent methyl methacrylate-butadiene-styrene copolymer and polyurethane elastomer particles and mixing evenly, finally adding organic bentonite, black slurry and isooctanoic acid to obtain a self-drying impact resistant protective coating; The content of each component is as follows: 50-80 parts of acrylic resin, 60-90 parts of epoxy resin, 30-50 parts of modified polyurethane emulsion, 5-6 parts of glyceryl stearate, 4-8 parts of styrene-butadiene-styrene block copolymer, 18-35 parts of modified tackifying resin, 80-120 parts of deionized water, 5-15 parts of ethylene glycol tert-butyl ether, 30-50 parts of ethanol, 0.5-2 parts of organosilicon defoamer, 0.4-1.2 parts of organosilicon leveling agent, 10-18 parts of impact-resistant agent methyl methacrylate-butadiene-styrene copolymer, 5-9 parts of polyurethane elastomer particles, 1-3 parts of organic bentonite, 5-10 parts of black paste, and 2.5-4.5 parts of isooctanoic acid; The black slurry includes at least one of a carbon black slurry and an iron black slurry; The preparation method of the modified tackifying resin comprises the following steps: Step A1, modifying rosin by hydrogenating sorbic acid to obtain modified rosin resin; Step A2: grafting the modified rosin resin with 4-aminocatechol to obtain a modified tackifying resin.

2. The method for preparing the self-drying impact-resistant protective coating according to claim 1, characterized in that: In the step (1), the preparation method of the pretreated graphite phase carbon nitride is as follows: calcining urea at 520-580°C for 100-150min, cooling to room temperature to obtain graphite phase carbon nitride; adding the graphite phase carbon nitride to a 63wt% formaldehyde aqueous solution, stirring at 80-90°C and a speed of 700-900r / min for 100-150min, filtering, washing, and drying to obtain the pretreated graphite phase carbon nitride; wherein the amount ratio of graphite phase carbon nitride to formaldehyde aqueous solution is (10-15)g:(200-400)mL.

3. The method for preparing the self-drying impact-resistant protective coating according to claim 1, characterized in that: In the step (2), the preparation method of the epoxy-modified graphite phase carbon nitride is as follows: at 22-26°C, ethanol and γ-glycidyloxypropyltrimethoxysilane are mixed, and then pretreated graphite phase carbon nitride is added, ultrasonic dispersion is performed for 1-2 hours, heating to 70-90°C and stirring for reaction for 4-6 hours, cooling to room temperature, filtering, washing, and drying to obtain epoxy-modified graphite phase carbon nitride; wherein the mass ratio of ethanol, γ-glycidyloxypropyltrimethoxysilane, and pretreated graphite phase carbon nitride is (20-40):1:(0.1-0.3).

4. The method for preparing the self-drying impact-resistant protective coating according to claim 1, characterized in that: In the step (3), the preparation method of the modified chitosan is as follows: epoxy-modified graphite phase carbon nitride is mixed with water, and ultrasonically dispersed for 40-80 minutes to obtain a mixed solution, wherein the mass ratio of epoxy-modified graphite phase carbon nitride to water is (2-6):(30-50); carboxylated chitosan is dissolved in water at a mass ratio of (1.5-4):(50-100), and is dripped into the above-obtained mixed solution at a rate of 0.8-1.2 mL / min at 22-26°C, and the reaction is stirred for 20-30 hours, filtered, washed, and dried to obtain modified chitosan; wherein the mass ratio of epoxy-modified graphite phase carbon nitride to carboxylated chitosan is (2-6):(1.5-4).

5. The method for preparing the self-drying impact-resistant protective coating according to claim 1, characterized in that: In the step (4), the preparation method of the organic-inorganic hybrid modifier is as follows: adding modified chitosan to an ethanol dispersion of calcium phosphate oligomers, stirring at a speed of 500-700 r / min for 3-4 hours, and distilling off the solvent to obtain an organic-inorganic hybrid modifier; wherein the amount ratio of modified chitosan to the ethanol dispersion of calcium phosphate oligomers is (2-4) g: (30-50) mL; The ethanol dispersion of the calcium phosphate oligomer is prepared by the following method: dissolving calcium chloride in ethanol at 22-26°C, adding triethylamine, stirring for 10-30 minutes, adding 0.09g / mL ethanol solution of phosphoric acid, continuing to stir for 12-15 hours, centrifuging after the reaction, washing, and re-dispersing in ethanol to obtain an ethanol dispersion of the calcium phosphate oligomer with a concentration of 13-15mg / mL; wherein the dosage ratio of calcium chloride, ethanol, triethylamine, and ethanol solution of phosphoric acid is (4.4-6.6)g:(600-1000)mL:(60-90)g:(30-50)mL.

6. The method for preparing the self-drying impact-resistant protective coating according to claim 1, characterized in that: In the step (5), the preparation method of the modified polyurethane emulsion is as follows: polycarbonate diol, dihydroxymethyl butyric acid, and methyl ethyl ketone are mixed, stirred until the solid is completely dissolved, toluene diisocyanate and dibutyltin dilaurate are added, heated to 65-75°C for reaction for 150-200 minutes, an organic-inorganic hybrid modifier and 4,4-diaminodiphenyl sulfide are added, the temperature is raised to 75-85°C for reaction for 2.5-3.5 hours, 1,4-butanediol is added, the reaction degree of the isocyanate group is detected during the reaction, and when all the isocyanate groups have reacted, the temperature is lowered to 30-35°C, triethylamine is added dropwise as a neutralizing agent, the reaction is continued for 20-40 minutes, deionized water is added under stirring conditions of 500-600 r / min, and the reaction is maintained. The invention relates to a polyurethane emulsion comprising the steps of: preparing the polyurethane emulsion by stirring for 20-40 minutes, and then removing the solvent by rotary evaporation at a temperature of 36-40°C and a vacuum degree of (-0.09)-(-0.095) MPa to obtain a modified polyurethane emulsion with a solid content of 33-38 wt %; wherein the mass ratios of polycarbonate diol, dihydroxymethylbutyric acid, toluene diisocyanate, organic-inorganic hybrid modifier, 4,4-diaminodiphenyl sulfide, 1,4-butanediol, triethylamine, deionized water, methyl ethyl ketone and dibutyltin dilaurate are (6-9):(0.5-1):(1.2-1.8):(1.5-3.5):(0.4-1):(0.08-0.15):(0.5-0.8):(3-5):(32-48):(0.08-0.12).

7. The method for preparing the self-drying impact-resistant protective coating according to claim 1, characterized in that: In the step (6), in the modified tackifying resin preparation step A1, the modified rosin resin is prepared by the following method: sorbic acid, xylene and rosin are mixed in a mass ratio of (20-35):50:(30-50), heated to 270-280°C for polymerization reaction for 50-80 minutes, after the reaction is completed, a Pd / Al catalyst of 4-5wt% of the total amount of the reaction mixture is added, and hydrogenation treatment is carried out for 80-100 minutes at a temperature of 220-240°C and a pressure of 7.5-8MPa. After the reaction is completed, a crude product is obtained, and the crude product is dissolved and purified with hot acetic acid at 60-80°C, filtered, and the obtained filter residue is washed with hot acetic acid at 60-80°C and hot water at 60-80°C, and then dried.

8. The method for preparing the self-drying impact-resistant protective coating according to claim 1, characterized in that: In the step (6), in the modified tackifying resin preparation step A2, the modified tackifying resin is prepared by the following method: in a nitrogen atmosphere, at room temperature, taking the modified rosin resin and adding it to ethanol, stirring for 20-40 minutes, then adding 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide, continuing to stir for 150-200 minutes, then adding 4-aminocatechol, adjusting the pH of the reaction mixture to 5.4-5.6 with a 1 mol / L hydrochloric acid aqueous solution, reacting for 20-28 hours, filtering after the reaction is completed, washing the obtained filter residue with methanol for 5-10 times, and drying; The dosage ratio of modified rosin resin, ethanol, 1,3-dicyclohexylcarbodiimide, N-hydroxysuccinimide and 4-aminocatechol is (4.1-8.2) g: (300-500) mL: (3.7-7.4) g: (2.1-4.2) g: (4.2-8.4) g.

9. A self-drying impact-resistant protective coating prepared by the method according to any one of claims 1 to 8.

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