Preparation method of anti-corrosion coating and application of anti-corrosion coating in steel-plastic composite steel pipe

Abstract

The invention relates to the technical field of coating preparation, in particular to a preparation method of an anti-corrosion coating and application of the anti-corrosion coating in a steel-plastic composite steel pipe. The preparation method of the anti-corrosion coating comprises the following steps: preparing the modified urea-formaldehyde resin and the mixed emulsion; and preparing the anti-corrosion coating. Formaldehyde and urea are combined to form urea-formaldehyde resin, melamine and xylitol are used for modifying the urea-formaldehyde resin, melamine contains a triazine ring structure and can form a more stable cross-linked network with formaldehyde and urea, and active amino of melamine can be combined with formaldehyde, so that the formaldehyde-formaldehyde composite material is prepared. The hydroxyl structure of xylitol can also react with formaldehyde to form chemical bonds, groups of xylitol and formaldehyde can form macromolecules after being combined with formaldehyde, the macromolecules are cured on molecular chains of the urea-formaldehyde resin, free formaldehyde in the urea-formaldehyde resin is reduced, volatilization of formaldehyde is reduced, and the environmental protection performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coating preparation, and in particular to a method for preparing an anti-corrosion coating and application thereof in a steel-plastic composite steel pipe. Background Art

[0002] Steel-plastic pipe, also known as steel-plastic composite pipe or plastic-coated steel pipe, is a composite pipe with a steel pipe as the base. A plastic layer is welded to the inner surface of the steel pipe through processes such as spraying, roller coating, dipping, and suction coating. The dissolved plastic layer inside this pipe provides good sanitary conditions and can be used to transport liquid components such as water and oil. In addition, a layer of anti-corrosion coating is applied to the surface of the steel-plastic pipe to prevent corrosion and damage during use, reducing maintenance costs. The anti-corrosion coating applied to the surface of the steel-plastic pipe can be divided into polyethylene coating and epoxy resin coating.

[0003] Epoxy resin coating itself has certain chemical corrosion resistance, and the coating after curing is more durable, construction method is also very convenient, can be directly coated on the steel base pipe surface of steel-plastic pipe by spraying or brushing, after adding urea-formaldehyde resin to epoxy resin, can further improve the acid and alkali resistance of coating, and can also make coating have good self-repairing performance and anti-corrosion effect, however, urea-formaldehyde resin is a kind of resin obtained by the reaction of urea and formaldehyde, may release free formaldehyde during curing, there is certain environmental risk, and urea-formaldehyde resin is formed by urea and formaldehyde under acidic or alkaline conditions. Its molecular structure is mainly composed of linear or slightly cross-linked polymers, this linear structure makes the interaction between molecular chains weaker, causes the paint film formed after urea-formaldehyde resin is cured to be brittle, easily cracks when mechanical shock or temperature change, hardness also declines thereupon, in addition, its shrinkage rate is larger during curing, may cause the gluing ability between paint film and substrate to decline. Therefore, the present invention provides a kind of preparation method of corrosion-resistant coating and its application in steel-plastic composite steel pipe, to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing an anti-corrosion coating and its application in steel-plastic composite steel pipes.

[0005] A method for preparing an anti-corrosion coating comprises the following steps:

[0006] S1: Preparation of modified urea-formaldehyde resin and mixed emulsion

[0007] Weighing urea and formaldehyde solutions, mixing them, then adding melamine and xylitol, adjusting the pH, heating in a water bath for reaction, and then standing at room temperature to obtain a modified urea-formaldehyde resin; ultrasonically dispersing diglyceride and cerium oxide, then adding sodium lignin sulfonate, and simultaneously adding deionized water, centrifuging, and then adding ammonium chloride solution and resorcinol to obtain a pre-emulsion, which is then centrifuged again to obtain a mixed emulsion;

[0008] S2: Preparation of anti-corrosion coating

[0009] After mixing the mixed emulsion and the modified urea-formaldehyde resin, the pH value is adjusted, and the mixture is heated in a water bath and stirred. The product is then cooled, filtered, and washed with deionized water until neutral. After drying, microcapsules are obtained. The epoxy resin E44 is mixed with the curing agent, ultrasonicated, and then 1-3% of the system mass of the microcapsules is added, stirred, and ultrasonicated again to obtain an anti-corrosion coating.

[0010] Furthermore, step S1 of preparing the modified urea-formaldehyde resin and the mixed emulsion comprises the following steps:

[0011] S1.1: Weigh 1-2 parts by mass of urea and 2-3 parts by mass of formaldehyde solution, add 0.5-0.8 parts by mass of melamine and 2-3 parts by mass of xylitol, adjust the pH to 8-9, heat in a water bath to 70-80°C, react for 1-2 hours, and then let stand at room temperature of 22-24°C for 5-6 hours to obtain a modified urea-formaldehyde resin;

[0012] S1.2: Ultrasonic disperse 5-8 parts by mass of diglyceride and 0.05-0.08 parts by mass of cerium oxide for 2-3 minutes, then add 0.1-0.15 parts by mass of sodium lignin sulfonate and 120-130 parts by mass of deionized water, centrifuge at 5000-5500 r / min for 3-4 minutes, then add 0.5-0.6 parts by mass of ammonium chloride solution and 0.5-0.8 parts by mass of resorcinol to obtain a pre-emulsion, and then centrifuge again at 5000-5500 r / min for 5-8 minutes to obtain a mixed emulsion.

[0013] Furthermore, step S2 of preparing the anti-corrosion coating comprises the following steps:

[0014] S2.1: After mixing 10-20 parts by mass of the mixed emulsion and 3-5 parts by mass of the modified urea-formaldehyde resin, the pH value is adjusted to 3-4 with hydrochloric acid solution, and the mixture is heated to 60-65°C in a water bath and stirred at 500-550 rpm for 3-4 hours. The product is then cooled at 10-15°C, filtered, and washed with deionized water until neutral, and dried to obtain microcapsules;

[0015] S2.2: Epoxy resin E44 and curing agent were mixed in a mass ratio of (3-4):1, ultrasonicated for 10-15 minutes, and then microcapsules were added at 1-3% of the system weight. The mixture was stirred for 2-5 minutes and ultrasonicated for 15-20 minutes to obtain an anti-corrosion coating.

[0016] Furthermore, the preparation method of diglyceride is specifically as follows:

[0017] Glycerol and soybean oil are mixed in a mass ratio of (3-3.5):1, and then lipase is added for catalytic reaction. The amount of lipase added is 1000U / g. The water bath is heated to 45-50°C, and the enzyme catalytic reaction is carried out for 8-8.5 hours under shaking on a shaker at 100-150r / min. After the reaction is completed, it is allowed to stand at room temperature of 22-24°C and centrifuged for 5-10 minutes. The upper oil layer is collected and distilled and purified to obtain diglyceride.

[0018] Furthermore, the mass fraction of the formaldehyde solution is 40 wt%.

[0019] Furthermore, the concentration of the ammonium chloride solution is 0.4 mol / L.

[0020] Furthermore, the lipase is Novozym435 lipase.

[0021] Furthermore, the concentration of the hydrochloric acid solution is 1.5 mol / L.

[0022] Furthermore, the curing agent is specifically polyetheramine D230.

[0023] An application of an anti-corrosion coating in a steel-plastic composite steel pipe, wherein the anti-corrosion coating prepared by the above-mentioned anti-corrosion coating preparation method is sprayed on the surface of the alloy steel pipe through a spray gun, with a coating thickness of 10-12 μm. The coating is cured at room temperature for 5-5.5 hours and then transferred to a 100-110°C oven for curing for 5-6 hours.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] 1. The present invention combines formaldehyde and urea to form a urea-formaldehyde resin, and uses melamine and xylitol to modify the urea-formaldehyde resin. Melamine contains a triazine ring structure and can form a more stable cross-linked network with formaldehyde and urea. The active amino group of melamine can combine with formaldehyde, and the hydroxyl structure of xylitol can also react with formaldehyde to form a chemical bond. Therefore, the urea-formaldehyde resin formed by formaldehyde and urea will carry groups of melamine and xylitol at the same time. Melamine and xylitol undergo an etherification reaction under the addition of an alkaline catalyst to generate hydroxyalkyl derivatives, thereby improving the hardness and bonding strength of the resin. When the urea-formaldehyde resin prepared by the combination of the three is added to a coating, it can bring about a better hardness improvement to the coating. In addition, the improvement in bonding strength can make the coating less likely to be corroded and decomposed, thereby improving the corrosion resistance of the coating. At the same time, the groups of the two can form macromolecules after combining with formaldehyde and solidify on the molecular chain of the urea-formaldehyde resin, reducing free formaldehyde in the urea-formaldehyde resin, thereby reducing formaldehyde volatilization and improving environmental performance.

[0026] 2. In the present invention, diglycerol and cerium oxide are subjected to a composite reaction through sodium lignin sulfonate and added to a modified urea-formaldehyde resin. Diglycerol can also serve as a surface modifier to improve the surface properties of cerium oxide nanoparticles, thereby making the particle size of microcapsules prepared with cerium oxide as the core smaller and more evenly distributed. At the same time, cerium oxide can undergo a cross-linking reaction with the hydroxyl groups in the urea-formaldehyde resin. The diglycerol molecule contains multiple hydroxyl groups, which can serve as cross-linking points and react with the active groups in cerium oxide and urea-formaldehyde resin. Therefore, the addition of diglycerol can further improve the cross-linking structure in cerium oxide and urea-formaldehyde resin, thereby improving the stability of the cross-linking structure and preventing the disintegration of the cross-linking structure, thereby improving the chemical corrosion resistance of the resin and the coating.

[0027] 3. The present invention combines microcapsules prepared from cerium oxide and modified urea-formaldehyde resin with epoxy resin. The modified urea-formaldehyde resin has a good adhesive effect and can bond cerium oxide particles to epoxy resin, thereby enhancing the bonding force between the cerium oxide particles and the epoxy resin. In addition, cerium oxide is used to form a self-repairing passivation film in a corrosive environment. The passivation film releases internal substances for self-repair, effectively preventing further expansion of corrosion, thereby achieving a better anti-corrosion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable one skilled in the relevant art to make and use the present disclosure.

[0029] Figure 1 This is an electron microscope image of the microcapsules of the anti-corrosion coating used in the embodiment of the present invention. DETAILED DESCRIPTION

[0030] The following describes in detail an anti-corrosion coating and its preparation method provided by the present invention, with reference to the accompanying drawings and specific embodiments. It is also noted that, to provide a more detailed description, the following embodiments are best and preferred embodiments, and those skilled in the art may employ alternative methods for implementing known techniques. Furthermore, the accompanying drawings are intended only to provide a more detailed description of the embodiments and are not intended to limit the present invention.

[0031] Example 1:

[0032] A method for preparing an anti-corrosion coating and its application in a steel-plastic composite steel pipe comprises the following steps:

[0033] S1: Preparation of modified urea-formaldehyde resin and mixed emulsion

[0034] S1.1: Weigh 1 part by mass of urea and 2 parts by mass of formaldehyde solution, then add 0.5 parts by mass of melamine and 2 parts by mass of xylitol. Adjust the pH to 8 and the mass fraction of the formaldehyde solution to 40 wt%. Heat in a water bath to 70°C for 1 hour, then let it stand at room temperature of 22°C for 5 hours to obtain a modified urea-formaldehyde resin.

[0035] S1.2: Ultrasonic dispersion of 5 parts by mass of diglyceride and 0.05 parts by mass of cerium oxide for 2 min was performed, followed by the addition of 0.1 parts by mass of sodium lignin sulfonate and 120 parts by mass of deionized water. The mixture was centrifuged at 5000 r / min for 3 min, followed by the addition of 0.5 parts by mass of 0.4 mol / L ammonium chloride solution and 0.5 parts by mass of resorcinol to obtain a pre-emulsion, which was then centrifuged again at 5000 r / min for 5 min to obtain a mixed emulsion.

[0036] Wherein, the preparation method of diglyceride is specifically as follows:

[0037] Glycerol and soybean oil were mixed in a mass ratio of 3:1, and Novozym435 lipase was added to catalyze the reaction. The amount of lipase added was 1000 U / g. The water bath was heated to 45°C, and the enzyme-catalyzed reaction was carried out for 8 hours under shaking at 100 r / min. After the reaction was completed, it was allowed to stand at room temperature of 22°C and centrifuged for 5 minutes. The upper oil layer was collected and distilled and purified to obtain diglyceride.

[0038] S2: Preparation of anti-corrosion coating

[0039] S2.1: After mixing 10 parts by mass of the mixed emulsion and 3 parts by mass of the modified urea-formaldehyde resin, the pH value was adjusted to 3 with a 1.5 mol / L hydrochloric acid solution, and the mixture was heated to 60°C in a water bath and stirred at a speed of 500 r / min for 3 h. The product was then cooled at 10°C, filtered, and washed with deionized water until neutral. After drying, microcapsules were obtained, such as Figure 1As shown, it can be seen that complete spherical particles are formed in the electron microscope image;

[0040] S2.2: Epoxy resin E44 and curing agent were mixed in a mass ratio of 3:1, ultrasonicated for 10 min, and then 1% of the system mass of microcapsules was added, stirred for 2 min, and ultrasonicated for 15 min to obtain an anti-corrosion coating.

[0041] The anti-corrosion coating was sprayed on the surface of the alloy steel pipe by a spray gun, with a coating thickness of 10 μm. After curing at room temperature for 5 hours, it was transferred to a 100° C. oven for curing for 5 hours to obtain a steel-plastic composite steel pipe.

[0042] Example 2:

[0043] A method for preparing an anti-corrosion coating and its application in a steel-plastic composite steel pipe comprises the following steps:

[0044] S1: Preparation of modified urea-formaldehyde resin and mixed emulsion

[0045] S1.1: Weigh 2 parts by mass of urea and 3 parts by mass of formaldehyde solution, mix them, add 0.8 parts by mass of melamine and 3 parts by mass of xylitol, adjust the pH to 8, and adjust the mass fraction of the formaldehyde solution to 40 wt %. Heat in a water bath to 70°C, react for 1 hour, and then let stand at room temperature of 22°C for 5 hours to obtain a modified urea-formaldehyde resin.

[0046] S1.2: Ultrasonic dispersion of 8 parts by mass of diglyceride and 0.08 parts by mass of cerium oxide for 2 min was performed, followed by the addition of 0.15 parts by mass of sodium lignin sulfonate and 130 parts by mass of deionized water. The mixture was centrifuged at 5000 r / min for 3 min, followed by the addition of 0.6 parts by mass of 0.4 mol / L ammonium chloride solution and 0.8 parts by mass of resorcinol to obtain a pre-emulsion. The mixture was then centrifuged again at 5000 r / min for 5 min to obtain a mixed emulsion.

[0047] Wherein, the preparation method of diglyceride is specifically as follows:

[0048] Glycerol and soybean oil were mixed in a mass ratio of 3.5:1, and Novozym435 lipase was added for catalytic reaction. The amount of lipase added was 1000U / g. The water bath was heated to 45°C, and the enzyme-catalyzed reaction was carried out for 8 hours under shaking at 100r / min. After the reaction was completed, it was allowed to stand at room temperature of 22°C and centrifuged for 5 minutes. The upper oil layer was collected and purified by distillation to obtain diglyceride.

[0049] S2: Preparation of anti-corrosion coating

[0050] S2.1: After mixing 20 parts by mass of the mixed emulsion and 5 parts by mass of the modified urea-formaldehyde resin, the pH value was adjusted to 3 with 1.5 mol / L hydrochloric acid solution, and the mixture was heated to 60°C in a water bath and stirred at 500 rpm for 3 hours. The product was then cooled at 10°C, filtered, and washed with deionized water until neutral, and dried to obtain microcapsules;

[0051] S2.2: Epoxy resin E44 and curing agent were mixed in a mass ratio of 4:1, ultrasonicated for 10 min, and then 3% of the system weight of microcapsules were added. The mixture was stirred for 2 min and ultrasonicated for 15 min to obtain an anti-corrosion coating.

[0052] The anti-corrosion coating was sprayed on the surface of the alloy steel pipe by a spray gun, with a coating thickness of 10 μm. After curing at room temperature for 5 hours, it was transferred to a 100° C. oven for curing for 5 hours to obtain a steel-plastic composite steel pipe.

[0053] Example 3:

[0054] A method for preparing an anti-corrosion coating and its application in a steel-plastic composite steel pipe comprises the following steps:

[0055] S1: Preparation of modified urea-formaldehyde resin and mixed emulsion

[0056] S1.1: Weigh 1 part by mass of urea and 2 parts by mass of formaldehyde solution, then add 0.5 parts by mass of melamine and 2 parts by mass of xylitol. Adjust the pH to 9 and the mass fraction of the formaldehyde solution to 40 wt%. Heat in a water bath to 80°C for 2 hours, then let stand at room temperature (24°C) for 6 hours to obtain a modified urea-formaldehyde resin.

[0057] S1.2: Ultrasonic dispersion of 5 parts by mass of diglyceride and 0.05 parts by mass of cerium oxide for 3 minutes was performed, followed by the addition of 0.1 parts by mass of sodium lignin sulfonate and 120 parts by mass of deionized water. The mixture was centrifuged at 5500 r / min for 4 minutes. 0.5 parts by mass of 0.4 mol / L ammonium chloride solution and 0.5 parts by mass of resorcinol were then added to obtain a pre-emulsion. The mixture was then centrifuged again at 5500 r / min for 8 minutes to obtain a mixed emulsion.

[0058] Wherein, the preparation method of diglyceride is specifically as follows:

[0059] Glycerol and soybean oil were mixed in a mass ratio of 3:1, and Novozym435 lipase was added for catalytic reaction. The amount of lipase added was 1000 U / g. The water bath was heated to 50°C, and the enzyme-catalyzed reaction was carried out for 8.5 hours under shaking at 150 rpm. After the reaction was completed, the mixture was allowed to stand at room temperature of 24°C and centrifuged for 10 minutes. The upper oil layer was collected and purified by distillation to obtain diglyceride.

[0060] S2: Preparation of anti-corrosion coating

[0061] S2.1: After mixing 10 parts by mass of the mixed emulsion and 3 parts by mass of the modified urea-formaldehyde resin, the pH value was adjusted to 4 with a 1.5 mol / L hydrochloric acid solution. The mixture was heated to 65°C in a water bath and stirred at 550 rpm for 3 h. The product was then cooled at 15°C, filtered, and washed with deionized water until neutral. After drying, microcapsules were obtained.

[0062] S2.2: Epoxy resin E44 and curing agent were mixed in a mass ratio of 3:1, ultrasonicated for 15 min, and then 1% of the system mass of microcapsules was added, stirred for 5 min and ultrasonicated for 20 min to obtain an anti-corrosion coating.

[0063] The anti-corrosion coating is sprayed on the surface of the alloy steel pipe by a spray gun, with a coating thickness of 10-12 μm. After curing at room temperature for 5 hours, it is transferred to a 100° C. oven for curing for 5 hours to obtain a steel-plastic composite steel pipe.

[0064] Example 4:

[0065] A method for preparing an anti-corrosion coating and its application in a steel-plastic composite steel pipe comprises the following steps:

[0066] S1: Preparation of modified urea-formaldehyde resin and mixed emulsion

[0067] S1.1: Weigh 1 part by mass of urea and 2 parts by mass of formaldehyde solution, then add 0.5 parts by mass of melamine and 2 parts by mass of xylitol. Adjust the pH to 8 and the mass fraction of the formaldehyde solution to 40 wt%. Heat in a water bath to 70°C for 1 hour, then let it stand at room temperature of 22°C for 5 hours to obtain a modified urea-formaldehyde resin.

[0068] S1.2: Ultrasonic dispersion of 5 parts by mass of diglyceride and 0.05 parts by mass of cerium oxide for 2 min was performed, followed by the addition of 0.1 parts by mass of sodium lignin sulfonate and 120 parts by mass of deionized water. The mixture was centrifuged at 5000 r / min for 3 min, followed by the addition of 0.5 parts by mass of 0.4 mol / L ammonium chloride solution and 0.5 parts by mass of resorcinol to obtain a pre-emulsion, which was then centrifuged again at 5000 r / min for 5 min to obtain a mixed emulsion.

[0069] Wherein, the preparation method of diglyceride is specifically as follows:

[0070] Glycerol and soybean oil were mixed in a mass ratio of 3:1, and Novozym435 lipase was added to catalyze the reaction. The amount of lipase added was 1000 U / g. The water bath was heated to 45°C, and the enzyme-catalyzed reaction was carried out for 8 hours under shaking at 100 r / min. After the reaction was completed, it was allowed to stand at room temperature of 22°C and centrifuged for 5 minutes. The upper oil layer was collected and distilled and purified to obtain diglyceride.

[0071] S2: Preparation of anti-corrosion coating

[0072] S2.1: 10 parts by mass of the mixed emulsion and 3 parts by mass of the modified urea-formaldehyde resin were mixed, the pH value was adjusted to 3 with 1.5 mol / L hydrochloric acid solution, and the mixture was heated to 60°C in a water bath and stirred at 500 rpm for 3 h. The product was then cooled at 10°C, filtered, and washed with deionized water until neutral, and dried to obtain microcapsules;

[0073] S2.2: Epoxy resin E44 and curing agent were mixed in a mass ratio of 3:1, ultrasonicated for 10 min, and then 1% of the system mass of microcapsules was added, stirred for 2 min, and ultrasonicated for 15 min to obtain an anti-corrosion coating.

[0074] The anti-corrosion coating was sprayed on the surface of the alloy steel pipe by a spray gun, with a coating thickness of 12 μm. After curing at room temperature for 5.5 hours, it was transferred to a 110° C. oven for curing for 6 hours to obtain a steel-plastic composite steel pipe.

[0075] Comparative Example 1:

[0076] Comparative Example 1 is to spray the steel-plastic pipe with a commercially available anti-corrosion coating. The specific steps of coating are: spray the commercially available anti-corrosion coating on the surface of the alloy steel pipe through a spray gun, the coating thickness is 10 μm, and then cure it at room temperature for 5 hours and then transfer it to a 100°C oven for curing for 5 hours. The obtained steel-plastic composite steel pipe is recorded as Comparative Example 1.

[0077] Comparative Example 2:

[0078] Compared with Example 1, the difference of Comparative Example 2 is that melamine is not added in step S1.1. Specifically, "S1.1: weigh 1 part by mass of urea and 2 parts by mass of formaldehyde solution, mix them, then add 2 parts by mass of xylitol, and adjust the pH value to 8, the mass fraction of the formaldehyde solution is 40wt%, heat to 70°C in a water bath, react for 1h, and then let stand at room temperature of 22°C for 5h to obtain a modified urea-formaldehyde resin". The other steps remain unchanged, and the prepared steel-plastic composite steel pipe is recorded as Comparative Example 2.

[0079] Comparative Example 3:

[0080] Compared with Example 1, the difference of Comparative Example 3 is that xylitol is not added in step S1.1. Specifically, "S1.1: weigh 1 part by mass of urea and 2 parts by mass of formaldehyde solution, mix them, then add 0.5 parts by mass of melamine, and adjust the pH value to 8, the mass fraction of the formaldehyde solution is 40wt%, heat to 70°C in a water bath, react for 1h, and then let stand at room temperature of 22°C for 5h to obtain a modified urea-formaldehyde resin". The other steps remain unchanged, and the prepared steel-plastic composite steel pipe is recorded as Comparative Example 3.

[0081] Comparative Example 4:

[0082] Compared with Example 1, the difference of Comparative Example 4 is that cerium oxide is not added in step S1.2. Specifically, "5 parts by mass of diglyceride and 0.1 parts by mass of sodium lignin sulfonate are mixed, and 120 parts by mass of deionized water are added at the same time, and the mixture is centrifuged at a speed of 5000 r / min for 3 minutes, and then 0.5 parts by mass of 0.4 mol / L ammonium chloride solution and 0.5 parts by mass of hydroquinone are added to obtain a pre-emulsion, and then the mixture is centrifuged again at a speed of 5000 r / min for 5 minutes to obtain a mixed emulsion." The other steps remain unchanged, and the prepared steel-plastic composite steel pipe is recorded as Comparative Example 4.

[0083] Comparative Example 5:

[0084] Compared with Example 1, the difference of Comparative Example 5 is that no modified urea-formaldehyde resin is added in step S2.1, specifically "S2.1: After mixing 10 parts by mass of the mixed emulsion and 3 parts by mass of the modified urea-formaldehyde resin, the pH value is adjusted to 3 with 1.5 mol / L hydrochloric acid solution, and heated to 60°C in a water bath, stirred at a speed of 500 r / min for 3 hours, and then the product is cooled at 10°C, filtered, and washed with deionized water until neutral, and dried to obtain microcapsules", and the remaining steps remain unchanged. The prepared steel-plastic composite steel pipe is recorded as Comparative Example 5.

[0085] Examples 1-4 and Comparative Examples 1-3 were placed in sealed containers, respectively. After 24 hours of illumination, the formaldehyde concentrations in the sealed containers were measured, as shown in Table 1.

[0086] The hardness of Examples 1-4 and Comparative Examples 1-3 was tested using GB / T6739-2022 “Paint and varnish pencil method for determination of paint film hardness”, as shown in Table 2.

[0087] The corrosion resistance of Examples 1-4, Comparative Example 1, Comparative Example 4 and Comparative Example 5 was tested using GB / T1771-2007 “Determination of Neutral Salt Spray Resistance of Paints and Varnishes”, as shown in Table 3.

[0088] Table 1

[0089] <![CDATA[Formaldehyde concentration mg / m 3 > Example 1 0.73 Example 2 0.81 Example 3 0.74 Example 4 0.78 Comparative Example 1 1.23 Comparative Example 2 1.12 Comparative Example 3 1.18

[0090] Table 2

[0091] Pencil hardness Example 1 5H Example 2 5H Example 3 5H Example 4 5H Comparative Example 1 4H Comparative Example 2 3H Comparative Example 3 3H

[0092] Table 3

[0093]

[0094] As can be seen from Table 1, the maximum formaldehyde concentration released by Examples 1-4 after 24 hours of illumination does not exceed 0.81 mg / m 3, while Comparative Example 1 is a commercially available coating, which releases formaldehyde concentration of 1.23 mg / m after 24 hours of light exposure. 3 , which is higher than that of the embodiment. It can be seen that the present invention has a lower formaldehyde emission and is more environmentally friendly than commercially available products. The formaldehyde concentrations of Comparative Examples 2 and 3 after 24 hours of illumination are 1.12 mg / m 3 and 1.18 mg / m 3 , indicating that the formaldehyde release amount of single use of melamine or xylitol is higher than that of using both together, indicating that the composite use of melamine and xylitol in the present invention reduces the formaldehyde release amount.

[0095] As can be seen from Table 2, the pencil hardness of Examples 1-4 is all 5H, while the commercially available product of Comparative Example 1 has a hardness of 4H. Comparative Examples 2 and 3, in which only melamine or xylitol is added, cannot form a tighter cross-linked structure with the urea-formaldehyde resin, and therefore the hardness is lower than that of the examples, only 3H.

[0096] As can be seen from Table 3, after the 1000-hr neutral salt spray test, the surfaces of Examples 1-4 remained free of cracks and rust. However, after the 1000-hr neutral salt spray test, the commercially available product of Comparative Example 1 could only ensure that the surface was free of cracks, but still had rust. The rust indicated that the coating surface had been chemically corroded, indicating that the corrosion resistance of the present invention was better than that of the commercially available product. Comparative Examples 4 and 5 showed cracks and rust after the 1000-hr neutral salt spray test, indicating that the addition of cerium oxide can provide certain corrosion resistance, and the modified urea-formaldehyde resin as a binder improves the adhesion of the coating, prevents the coating from decomposing after chemical corrosion occurs, and thus improves the corrosion resistance of the coating.

[0097] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing an anti-corrosion coating, characterized in that: The steps include: S1: Preparation of modified urea-formaldehyde resin and mixed emulsion Weighing urea and formaldehyde solutions, mixing them, then adding melamine and xylitol, adjusting the pH, heating in a water bath for reaction, and then standing at room temperature to obtain a modified urea-formaldehyde resin; ultrasonically dispersing diglyceride and cerium oxide, then adding sodium lignin sulfonate, and simultaneously adding deionized water, centrifuging, and then adding ammonium chloride solution and resorcinol to obtain a pre-emulsion, which is then centrifuged again to obtain a mixed emulsion; S2: Preparation of anti-corrosion coating After mixing the mixed emulsion and the modified urea-formaldehyde resin, the pH value is adjusted, and the mixture is heated in a water bath and stirred. The product is then cooled, filtered, and washed with deionized water until neutral. After drying, microcapsules are obtained. The epoxy resin E44 is mixed with the curing agent, ultrasonicated, and then 1-3% of the system mass of the microcapsules is added, stirred, and ultrasonicated again to obtain an anti-corrosion coating.

2. The method for preparing an anti-corrosion coating according to claim 1, characterized in that: Step S1 prepares modified urea-formaldehyde resin and mixed emulsion, comprising the following steps: S1.1: Weigh 1-2 parts by mass of urea and 2-3 parts by mass of formaldehyde solution, add 0.5-0.8 parts by mass of melamine and 2-3 parts by mass of xylitol, adjust the pH to 8-9, heat in a water bath to 70-80°C, react for 1-2 hours, and then let stand at room temperature of 22-24°C for 5-6 hours to obtain a modified urea-formaldehyde resin; S1.2: Ultrasonic disperse 5-8 parts by mass of diglyceride and 0.05-0.08 parts by mass of cerium oxide for 2-3 minutes, then add 0.1-0.15 parts by mass of sodium lignin sulfonate and 120-130 parts by mass of deionized water, centrifuge at 5000-5500 r / min for 3-4 minutes, then add 0.5-0.6 parts by mass of ammonium chloride solution and 0.5-0.8 parts by mass of resorcinol to obtain a pre-emulsion, and then centrifuge again at 5000-5500 r / min for 5-8 minutes to obtain a mixed emulsion.

3. The method for preparing an anti-corrosion coating according to claim 2, characterized in that: Step S2 is to prepare the anti-corrosion coating, comprising the following steps: S2.1: After mixing 10-20 parts by mass of the mixed emulsion and 3-5 parts by mass of the modified urea-formaldehyde resin, the pH value is adjusted to 3-4 with hydrochloric acid solution, and the mixture is heated to 60-65°C in a water bath and stirred at 500-550 rpm for 3-4 hours. The product is then cooled at 10-15°C, filtered, and washed with deionized water until neutral, and dried to obtain microcapsules; S2.2: Epoxy resin E44 and curing agent were mixed in a mass ratio of (3-4):1, ultrasonicated for 10-15 minutes, and then microcapsules were added at 1-3% of the system weight. The mixture was stirred for 2-5 minutes and ultrasonicated for 15-20 minutes to obtain an anti-corrosion coating.

4. The method for preparing an anti-corrosion coating according to claim 3, characterized in that: The preparation method of diglyceride is specifically as follows: Glycerol and soybean oil are mixed in a mass ratio of (3-3.5):1, and then lipase is added for catalytic reaction. The amount of lipase added is 1000U / g. The water bath is heated to 45-50°C, and the enzyme catalytic reaction is carried out for 8-8.5 hours under shaking on a shaker at 100-150r / min. After the reaction is completed, it is allowed to stand at room temperature of 22-24°C and centrifuged for 5-10 minutes. The upper oil layer is collected and distilled and purified to obtain diglyceride.

5. The method for preparing an anti-corrosion coating according to claim 4, characterized in that: The mass fraction of the formaldehyde solution is 40 wt%.

6. The method for preparing an anti-corrosion coating according to claim 3, characterized in that: The concentration of ammonium chloride solution is 0.4 mol / L.

7. The method for preparing an anti-corrosion coating according to claim 5, characterized in that: The lipase was Novozym 435 lipase.

8. The method for preparing an anti-corrosion coating according to claim 5, characterized in that: The concentration of hydrochloric acid solution is 1.5 mol / L.

9. The method for preparing an anti-corrosion coating according to claim 5, characterized in that: The curing agent is specifically polyetheramine D230.

10. An application of an anti-corrosion coating in a steel-plastic composite steel pipe, characterized in that: The anti-corrosion coating prepared by the above-mentioned preparation method of the anti-corrosion coating is sprayed on the surface of the alloy steel pipe by a spray gun, with a coating thickness of 10-12 μm. After curing at room temperature for 5-5.5 hours, it is transferred to a 100-110° C. oven for curing for 5-6 hours.

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