A kind of surface anti-corrosion water-based back paint for alloy substrate and preparation method thereof

Abstract

The invention discloses a surface corrosion-resistant water-based back paint for alloy substrates and a preparation method thereof, belonging to the technical field of water-based back paint processing, and used to solve the technical problems that weak interface exists in the paint film of the water-based back paint in the prior art, a large number of bubbles are easily formed on the surface of the water-based paint film when the water-based back paint is coated and formed, and the impact resistance, surface corrosion resistance and durability of the paint film need to be further improved; the surface corrosion-resistant water-based back paint for alloy substrates is composed of modified polyester, modified drier, composite iron red, water and additives, and has a viscosity of 5500-6500 MPa·s; the modified polyester is prepared into modified castor oil rich in carboxyl groups by dehydration condensation of ricinoleic acid glyceride and phthalic anhydride; the invention not only effectively improves the impact resistance, salt spray resistance and wear resistance of the water-based back paint film, but also reduces the bubbling performance of the water-based back paint, and improves the flatness of the paint film surface.

Description

Technical Field

[0001] The invention relates to the technical field of water-based back paint processing, and in particular to a surface corrosion-resistant water-based back paint for an alloy substrate and a preparation method thereof. Background Art

[0002] In industrial production and daily life, alloy materials are widely used in various fields because they have excellent properties such as high strength, corrosion resistance and wear resistance. However, alloy materials may encounter some corrosion and surface degradation problems during long-term use, which not only affects their appearance, but also may reduce their service life and performance. Water-based back paint is a kind of paint with water as the medium. Compared with traditional organic solvent-based paint, it has the advantages of environmental protection, health and safety, easy cleaning and convenient construction. With the enhancement of environmental awareness and the continuous development of coating technology, water-based back paint has gradually become a popular surface protection technology;

[0003] The anti-corrosion water-based back paint in the prior art is usually composed of red iron oxide, a drying agent, a resin, an additive and water. The drying agent is mainly composed of manganese oxide. Red iron oxide is used as a pigment and a protective substrate, which can provide good color and anti-corrosion protection. However, red iron oxide and the drying agent are both inorganic metal materials, and their compatibility with other components of water-based back paints such as resins is poor. There is a weak interface in the paint film after the water-based back paint is dried, resulting in the impact resistance of the paint film of the water-based back paint to be further improved. The dispersion stability of the components constituting the water-based back paint in the water system is poor. When the water-based back paint is used, there is a large friction between the inorganic metal particles, the rheology of the paint is poor, and the construction and coating are inconvenient. When the water-based paint film is coated and formed, a large number of bubbles are easily formed on the surface of the water-based paint film, resulting in the surface corrosion resistance and durability of the paint film to be further improved.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0005] The object of the present invention is to provide a surface anti-corrosion water-based back paint for alloy substrates and a preparation method thereof, so as to solve the technical problems in the prior art that the compatibility between inorganic components and organic components in the water-based back paint is poor, the interface in the paint film is weak, there is a large friction between the inorganic components in the water-based paint film, the rheology of the coating is poor, the construction and coating are inconvenient, and a large number of bubbles are easily formed on the surface of the water-based paint film when the water-based paint film is coated and formed, resulting in the paint film The technical problems of the impact resistance, surface corrosion resistance and durability need to be further improved.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A surface anti-corrosion water-based back paint for alloy substrates, comprising modified polyester, modified drying agent, composite iron red, water and additives, and having a viscosity of 5500-6500 MPa·s;

[0008] The modified polyester is prepared by dehydration condensation of ricinoleic acid glyceride and phthalic anhydride to obtain modified castor oil rich in carboxyl groups, the modified castor oil undergoes esterification reaction with 2-hydroxymethyl-1,3-propanediol and then undergoes dehydration condensation with 1,2,4-trimethylbenzene anhydride, and then is post-treated to obtain;

[0009] The modified drying agent is prepared by reacting carboxymethyl triethoxysilane, tetraethoxysilane and 1,8-bis(triethoxysilyl)octane in an ethanol-water environment system to generate modified siloxane, and then the modified siloxane, 4-methyl-3-pentenoic acid and nano manganese dioxide are subjected to an esterification reaction under the action of a catalyst to obtain the modified drying agent;

[0010] The composite iron red is reacted with KH-550 and isophorone diisocyanate and then with oleic acid to generate a polymer, and then the polymer reacts with red iron oxide in an alkaline environment and is grafted and modified on the surface of the red iron oxide to obtain the composite iron red.

[0011] Furthermore, the dosage ratio of the modified polyester, modified drying agent, composite iron red, water and additives is 30g:3g:12g:40-60mL:3g, and the additives are composed of a dispersant, a wetting agent, a defoaming agent and a thickener in a dosage ratio of 2g:1g:1g:1g, wherein the dispersant is composed of one or more of polyethylene glycol, polyacrylate, and carboxymethyl cellulose, the wetting agent is composed of one or more of octylbenzene sulfonate, polyethylene glycol octyl ether, and alkyl ether silicone oil, the defoaming agent is one of polyethylene oxide alcohol, polyether siloxane, and polypropylene glycol, and the thickener is one of polyvinyl alcohol and hydroxypropyl methylcellulose.

[0012] A method for preparing a surface anti-corrosion water-based back paint for an alloy substrate comprises the following steps:

[0013] S1. Add phthalic anhydride and toluene in a ratio of 1 g:4 mL into a three-necked flask protected by nitrogen and stir. At room temperature, add 50 vt% ricinoleic acid glyceride toluene solution dropwise into the three-necked flask, react for 2-4 hours, and post-treat to obtain modified castor oil.

[0014] The synthetic reaction principle of modified castor oil is:

[0015]

[0016] S2, adding modified castor oil, toluene, 2-hydroxymethyl-1,3-propanediol and a catalyst into a three-necked flask and stirring, raising the temperature of the three-necked flask to 105-110° C., keeping the temperature for reaction for 4-6 hours, and post-treating to obtain castor oil polyester;

[0017] The synthetic reaction principle of castor oil polyester is:

[0018]

[0019] S3, adding castor oil polyester, toluene and 1,2,4-trimethylbenzene anhydride into a three-necked flask, raising the temperature of the three-necked flask to 50-60° C., keeping the temperature for reaction for 2-3 hours, adding ammonia water into the three-necked flask, adjusting the pH value of the system to 8-9, and post-treating to obtain modified polyester;

[0020] The synthetic reaction principle of modified polyester is:

[0021]

[0022] S4, modified polyester, modified drying agent, composite iron red, water and additives are added to a ball mill. After ball milling and mixing, they are discharged from the ball mill into a beaker. Purified water is added to the beaker under stirring to adjust the viscosity of the paint to 5500-6500 MPa·s to obtain a water-based back paint.

[0023] Furthermore, in step S1, the dosage ratio of phthalic anhydride to ricinoleic acid glyceride is 3M:1M; in step S2, the dosage ratio of modified castor oil and 2-hydroxymethyl-1,3-propanediol is 1M:1.1M, the dosage of toluene is 4 times the weight of the modified castor oil, and the dosage of the catalyst is 0.02 times the weight of the modified castor oil, wherein the catalyst is 98wt% sulfuric acid; in step S3, the dosage ratio of castor oil polyester and 1,2,4-trimethylbenzene anhydride is 3g:1g, and the dosage of toluene is 3 times the weight of castor oil polyester.

[0024] Further, the post-processing operation of step S1 includes: after the reaction is completed, the temperature of the three-necked flask is increased to 70-80° C., and toluene is distilled off under reduced pressure to obtain modified castor oil; the post-processing operation of step S2 includes: after the reaction is completed, the temperature of the three-necked flask is reduced to room temperature, purified water is added to the three-necked flask, stirred for 10-15 minutes, allowed to stand for separation, the organic phase is transferred to a rotary evaporator, the water bath temperature is set to 70-80° C., and distilled under reduced pressure until no liquid flows out to obtain castor oil polyester; the post-processing operation of step S3 includes: after the reaction is completed, 10wt% sodium chloride solution is added to the three-necked flask, stirred for 10-15 minutes, allowed to stand for separation, the organic phase is transferred to a rotary evaporator, the water bath temperature is set to 70-80° C., and distilled under reduced pressure until no liquid flows out to obtain modified polyester.

[0025] Furthermore, the modified drier is processed by the following steps:

[0026] A1. Carboxymethyl triethoxysilane, tetraethoxysilane, 1,8-bis(triethoxysilyl)octane and 80vt% ethanol solution are added to a three-necked flask and stirred. The temperature of the three-necked flask is raised to 40-50° C., 0.1M hydrochloric acid is added to the three-necked flask to adjust the pH of the system to 3-5, and the reaction is kept warm for 2-4 hours, and the modified siloxane is obtained by post-treatment;

[0027] A2. Add 4-methyl-3-pentenoic acid, nano manganese dioxide, modified siloxane, N-methylpyrrolidone, toluene and catalyst into a three-necked flask and stir. Raise the temperature of the three-necked flask to 180-190° C. and keep the temperature for 6-8 hours. Post-treat to obtain a modified drying agent.

[0028] Furthermore, in step A1, the dosage ratio of carboxymethyltriethoxysilane, tetraethoxysilane, 1,8-bis(triethoxysilyl)octane and 80vt% ethanol solution is 2g:3g:6g:20mL; in step A2, the dosage ratio of 4-methyl-3-pentenoic acid, nano-manganese dioxide, modified siloxane, N-methylpyrrolidone, toluene and catalyst is 2g:3g:2g:10mL:4mL:0.1g, and the catalyst is selenite.

[0029] Further, the post-processing operation of step A1 includes: after the reaction is completed, the three-necked flask is kept at 40-50°C, ethanol is evaporated under reduced pressure to precipitate solids, purified water is added to the three-necked flask, the solids are washed to neutrality, the solids are transferred to a drying oven at a temperature of 60-80°C, and dried to constant weight to obtain modified siloxane; the post-processing operation of step A2 includes: after the reaction is completed, the three-necked flask is kept at 180-190°C, the solvent is evaporated under reduced pressure, the temperature of the three-necked flask is lowered to room temperature, acetone is added to the three-necked flask, ultrasonic dispersion is performed for 20-30 minutes, suction filtration is performed, the filter cake is washed three times with acetone, and then transferred to a drying oven at a temperature of 50-60°C, and dried to constant weight to obtain a modified siccative.

[0030] Furthermore, the preparation method of the composite iron red is as follows: KH-550, isophorone diisocyanate and acetone are added to a three-necked flask protected by nitrogen and stirred, and the mixture is kept warm for reaction at room temperature for 30-50 minutes, oleic acid is added to the three-necked flask, the temperature of the three-necked flask is increased to 55-65° C., and the mixture is kept warm for reaction for 80-90 minutes, and then red iron oxide solution is added to the three-necked flask, and the mixture is stirred for 30-50 minutes, and the composite iron red is obtained by post-treatment.

[0031] The synthetic reaction principle of composite iron red is:

[0032]

[0033]

[0034] ●Red iron oxide

[0035] Furthermore, the preparation method of the red iron oxide solution is: add red iron oxide, acetone and 0.15M ammonia water into a three-necked flask at a dosage ratio of 1g:3mL:3mL, and ultrasonically disperse for 30-50min to obtain the red iron oxide solution.

[0036] Furthermore, the molar ratio of KH-550 to isophorone diisocyanate is 1:1, the amount of acetone is 5 times the weight of isophorone diisocyanate, the amount of oleic acid is 1.6 times the weight of isophorone diisocyanate, and the amount of red iron oxide is 2 times the amount of KH-550. The post-treatment operation includes: after the reaction is completed, filtering, washing the filter cake with acetone and then drying, transferring the filter cake to a drying oven at a temperature of 50-60°C, and drying to constant weight to obtain composite red iron oxide.

[0037] The present invention has the following beneficial effects:

[0038] 1. In the preparation process of the water-based back paint of the present invention, ricinoleic acid glyceride and phthalic anhydride are used as raw materials, and phthalic anhydride is grafted onto ricinoleic acid glyceride through dehydration polycondensation to prepare modified castor oil rich in carboxyl groups. The carboxyl groups on the modified castor oil and the hydroxyl groups on 2-hydroxymethyl-1,3-propanediol are esterified to generate castor oil polyester with a network cross-linked structure, and the cross-linking between ricinoleic acid glyceride molecules is enhanced, so that the molecular structure of the coating is more compact and stable, thereby improving the water resistance and salt spray resistance of the back paint. In the reaction process, the amount ratio of modified castor oil to 2-hydroxymethyl-1,3-propanediol is controlled, so that a large number of hydroxyl groups are surplus on the castor oil polyester, and the hydroxyl groups on the castor oil polyester After dehydration condensation with 1,2,4-tricaritic anhydride, the carboxyl group reacts with ammonia water through acid-base neutralization reaction to generate carboxylic acid ammonium salt, which makes the modified polyester more easily dispersed in the aqueous solution, thereby improving the stability of the dispersed state of the various components of the water-based back paint; the modified polyester, modified drying agent and composite iron red that constitute the water-based back paint all contain olefin double bonds, which can improve the weather resistance, flexibility and adhesion between the paint film and the substrate, so that the paint film has better impact resistance and resistance to ultraviolet oxidation. In addition, during the drying and curing process of the paint film, the olefin double bonds undergo polymerization or cross-linking reactions to form crosslinks in the paint film, forming a solid paint film structure, enhancing the chemical resistance of the paint film, and making it more resistant to chemical corrosion, durable and wear-resistant.

[0039] 2. In the preparation process of the water-based back paint of the present invention, carboxymethyl triethoxysilane, tetraethoxysilane and 1,8-bis(triethoxysilyl)octane are reacted in an ethanol water environment system to generate a modified siloxane with a carboxyl-terminated network cross-linking, and then the modified siloxane, 4-methyl-3-pentenoic acid and nano manganese dioxide are subjected to an esterification reaction under the action of a catalyst to generate a modified drier of an esterified polycondensate of manganese dioxide, 4-methyl-3-pentenoic acid and modified siloxane; manganese is an important component of the drier, reacts with oxygen in the coating, oxidizes double bonds or groups containing hydrogen atoms in the coating, generates free radicals or other active species, promotes oxidation curing of the coating, and accelerates the curing of the coating. drying; the modified siloxane and 4-methyl-3-pentenoic acid in the modified drier are stably cross-linked with manganese through ester bonds, which can enhance the wetting properties of the modified drier, enable it to better interact with other components in the coating, and promote the dispersion and dissolution of the drier in the coating; the addition of modified siloxane and 4-methyl-3-pentenoic acid can also improve the fluidity of the coating, reduce the viscosity of the coating, and the special structure of siloxane can reduce the surface tension of the coating, which is beneficial to the uniform coating of the coating and the formation of the coating film during the coating process, and a protective siloxane and 4-methyl-3-pentenoic acid film is formed on the surface of the paint film, which improves the water resistance and weather resistance of the paint film, making the paint film more durable.

[0040] 3. In the preparation process of the water-based back paint of the present invention, KH-550 and isophorone diisocyanate are reacted, and the amino group on KH-550 reacts with the isocyanate group on isophorone diisocyanate, and then reacts with oleic acid to generate a polymer of KH-550 and oleic acid with isophorone diisocyanate as a crosslinking agent, and then reacts with red iron oxide in an alkaline environment, the siloxane bond on KH-550 is broken, and then reacts with the surface active functional group of red iron oxide to prepare a composite red iron oxide; the oleic acid layer coated on the outside of the red iron oxide helps to improve its dispersibility in the coating, so that it is more evenly distributed in the coating, and improves the color uniformity and colorability of the coating. The invention discloses a kind of water-based back paint, which can improve the color effect and prevent the instability of the coating, so that the modified red iron oxide in the water-based back paint can maintain a stable suspension state and prevent the precipitation of red iron oxide particles in the coating; the oleic acid coating layer coated on the outside of the modified red iron oxide forms a protective barrier on the surface of the red iron oxide, reduces the friction between the red iron oxide particles, improves the rheological properties of the coating, and is beneficial to the construction and coating performance of the coating; the oleic acid coating increases the mutual adhesion between the red iron oxide particles, thereby improving the scratch resistance of the coating; and the coating layer on the surface of the red iron oxide can also reduce the contact between the red iron oxide particles and the external environment, thereby improving the weather resistance of the coating and enhancing the durability of the coating. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. 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 creative work are within the scope of protection of the present invention.

[0042] Example 1

[0043] The method for preparing a surface anti-corrosion water-based back paint for an alloy substrate of the present embodiment comprises the following steps:

[0044] Step 1: Preparation of modified polyester

[0045] Weigh: 44.4 g of phthalic anhydride and 177.6 mL of toluene are added into a three-necked flask protected by nitrogen and stirred. At room temperature, 136 g of a 50 vt% ricinoleic acid glyceride toluene solution is added dropwise into the three-necked flask. The reaction is carried out for 2 h. The temperature of the three-necked flask is raised to 70° C., and the toluene is evaporated under reduced pressure to obtain modified castor oil.

[0046] Weigh: 107.1 g of modified castor oil, 428.4 g of toluene, 11.7 g of 2-hydroxymethyl-1,3-propanediol, and 2.14 g of 98 wt% sulfuric acid, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 105° C., keep warm and react for 4 hours, separate the by-product water through a water separator during the reaction, lower the temperature of the three-necked flask to room temperature, add 215 mL of purified water into the three-necked flask, stir for 10 minutes, stand and separate the liquids, transfer the organic phase to a rotary evaporator, set the water bath temperature to 70° C., and distill under reduced pressure until no liquid flows out to obtain castor oil polyester;

[0047] Weigh: 30 g of castor oil polyester, 90 g of toluene and 10 g of 1,2,4-trimethylbenzene anhydride and add them into a three-necked flask, raise the temperature of the three-necked flask to 50°C, keep warm for 2 hours, add ammonia water to the three-necked flask, adjust the system pH to 8, add 100 mL of 10 wt% sodium chloride solution to the three-necked flask, stir for 10 minutes, let stand to separate the liquids, transfer the organic phase to a rotary evaporator, set the water bath temperature to 70°C, and distill under reduced pressure until no liquid flows out to obtain a modified polyester.

[0048] Step 2: Preparation of modified drier

[0049] Weigh: 10 g of carboxymethyl triethoxysilane, 15 g of tetraethoxysilane, 30 g of 1,8-bis(triethoxysilyl)octane and 100 mL of 80 vt% ethanol solution, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 40° C., add 0.1 M hydrochloric acid into the three-necked flask, adjust the system pH to 3, keep warm for 2 h, keep the three-necked flask at 40° C., evaporate ethanol under reduced pressure, precipitate solid, add 100 mL of purified water into the three-necked flask, wash the solid until it is neutral, transfer the solid into a drying oven at 60° C., dry to constant weight, and obtain modified siloxane;

[0050] Weigh: 10 g of 4-methyl-3-pentenoic acid, 15 g of nano manganese dioxide, 10 g of modified siloxane, 50 mL of N-methylpyrrolidone, 20 mL of toluene and 0.5 g of sodium selenite, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 180°C, keep warm for 6 hours, keep the three-necked flask at 180°C, evaporate the solvent under reduced pressure, lower the temperature of the three-necked flask to room temperature, add 60 mL of acetone into the three-necked flask, ultrasonically disperse for 20 minutes, filter, wash the filter cake three times with acetone, transfer it to a drying oven at 50°C, dry it to constant weight, and obtain a modified drying agent.

[0051] Step 3: Preparation of composite iron red

[0052] Add red iron oxide, acetone and 0.15M ammonia water into a three-necked flask at a ratio of 1 g:3 mL:3 mL, and disperse by ultrasonic for 30 min to obtain a red iron oxide solution;

[0053] Weigh: 22.1 g of KH-550, 22.2 g of isophorone diisocyanate and 111 g of acetone, add them into a three-necked flask protected by nitrogen, stir, and keep warm for reaction at room temperature for 30 min. Add 35.5 g of oleic acid into the three-necked flask, raise the temperature of the three-necked flask to 55°C, and keep warm for reaction for 80 min. Then add 44.2 g of red iron oxide solution into the three-necked flask, stir for 30 min, filter, wash the filter cake with acetone and then dry it, transfer the filter cake to a drying oven at a temperature of 50°C, and dry it to constant weight to obtain composite iron red.

[0054] Step 4: Prepare water-based back paint

[0055] Weigh: 60g of modified polyester, 6g of modified drying agent, 24g of composite iron oxide red, 80-120mL of water, 2.4g of polyethylene glycol, 1.2g of sodium octylbenzenesulfonate, 1.2g of polyethylene oxide alcohol and 1.2g of polyvinyl alcohol and add them into a ball mill, select ceramic grinding balls with a diameter of 3-5mm, set the ball mill speed to 450r / min, ball mill for 2h, and after ball milling and mixing, release it from the ball mill into a beaker, add purified water to the beaker under stirring, adjust the viscosity of the paint to 5500-6500MPa·s, and obtain a water-based back paint.

[0056] Example 2

[0057] The method for preparing a surface anti-corrosion water-based back paint for an alloy substrate of the present embodiment comprises the following steps:

[0058] Step 1: Preparation of modified polyester

[0059] Weigh: 44.4 g of phthalic anhydride and 177.6 mL of toluene are added into a three-necked flask protected by nitrogen and stirred. At room temperature, 136 g of a 50 vt% ricinoleic acid glyceride toluene solution is added dropwise into the three-necked flask. The reaction is carried out for 3 h. The temperature of the three-necked flask is raised to 75° C., and the toluene is evaporated under reduced pressure to obtain modified castor oil.

[0060] Weigh: 107.1 g of modified castor oil, 428.4 g of toluene, 11.7 g of 2-hydroxymethyl-1,3-propanediol, and 2.14 g of 98 wt% sulfuric acid, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 108° C., keep the temperature for 45 h, separate the by-product water through a water separator during the reaction, lower the temperature of the three-necked flask to room temperature, add 215 mL of purified water into the three-necked flask, stir for 13 min, stand for liquid separation, transfer the organic phase to a rotary evaporator, set the water bath temperature to 75° C., and distill under reduced pressure until no liquid flows out to obtain castor oil polyester;

[0061] Weigh: 30g of castor oil polyester, 90g of toluene and 10g of 1,2,4-trimethylbenzene anhydride and add them into a three-necked flask, raise the temperature of the three-necked flask to 55°C, keep warm for reaction for 2-3h, add ammonia water into the three-necked flask, adjust the system pH to 8.5, add 100mL of 10wt% sodium chloride solution into the three-necked flask, stir for 13min, stand for separation, transfer the organic phase into a rotary evaporator, set the water bath temperature to 75°C, and distill under reduced pressure until no liquid flows out to obtain a modified polyester;

[0062] Step 2: Preparation of modified drier

[0063] Weigh: 10 g of carboxymethyl triethoxysilane, 15 g of tetraethoxysilane, 30 g of 1,8-bis(triethoxysilyl)octane and 100 mL of 80 vt% ethanol solution, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 45° C., add 0.1 M hydrochloric acid into the three-necked flask, adjust the system pH to 4, keep warm for 3 h, keep the three-necked flask at 45° C., evaporate ethanol under reduced pressure, precipitate solid, add 100 mL of purified water into the three-necked flask, wash the solid until it is neutral, transfer the solid into a drying oven at 70° C., dry to constant weight, and obtain modified siloxane;

[0064] Weigh: 10 g of 4-methyl-3-pentenoic acid, 15 g of nano manganese dioxide, 10 g of modified siloxane, 50 mL of N-methylpyrrolidone, 20 mL of toluene and 0.5 g of potassium selenite, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 185°C, keep warm for 7 hours, keep the three-necked flask at 185°C, remove the solvent under reduced pressure, lower the temperature of the three-necked flask to room temperature, add 60 mL of acetone into the three-necked flask, ultrasonically disperse for 25 minutes, filter, wash the filter cake three times with acetone, transfer it to a drying oven at 55°C, dry it to constant weight, and obtain a modified drying agent.

[0065] Step 3: Preparation of composite iron red

[0066] Add red iron oxide, acetone and 0.15M ammonia water into a three-necked flask at a ratio of 1 g:3 mL:3 mL, and perform ultrasonic dispersion for 50 min to obtain a red iron oxide solution;

[0067] Weigh: 22.1 g of KH-550, 22.2 g of isophorone diisocyanate and 111 g of acetone, add them into a nitrogen-protected three-necked flask and stir, keep warm and react for 40 min at room temperature, add 35.5 g of oleic acid into the three-necked flask, raise the temperature of the three-necked flask to 60°C, keep warm and react for 85 min, then add 44.2 g of red iron oxide solution into the three-necked flask, stir for 40 min, filter, wash the filter cake with acetone and then dry it, transfer the filter cake to a drying oven at a temperature of 55°C, and dry it to constant weight to obtain composite iron red.

[0068] Step 4: Prepare water-based back paint

[0069] Weigh: 60g of modified polyester, 6g of modified drying agent, 24g of composite iron red, 80-120mL of water, 2.4g of polyacrylate, 1.2g of polyethylene glycol octyl ether, 1.2g of polyether siloxane and 1.2g of hydroxypropyl methylcellulose, and add them into a ball mill. Select ceramic grinding balls with a diameter of 3-5mm, set the ball mill speed to 500r / min, and ball mill for 2.5h. After ball milling and mixing, release it from the ball mill into a beaker, add purified water to the beaker under stirring, adjust the viscosity of the paint to 5500-6500MPa·s, and obtain a water-based back paint.

[0070] Example 3

[0071] The method for preparing a surface anti-corrosion water-based back paint for an alloy substrate of the present embodiment comprises the following steps:

[0072] Step 1: Preparation of modified polyester

[0073] Weigh: 44.4 g of phthalic anhydride and 177.6 mL of toluene are added to a three-necked flask protected by nitrogen and stirred. At room temperature, 136 g of a 50 vt% ricinoleic acid glyceride toluene solution is added dropwise to the three-necked flask. The reaction is carried out for 4 h. The temperature of the three-necked flask is raised to 70-80° C., and the toluene is evaporated under reduced pressure to obtain modified castor oil.

[0074] Weigh: 107.1 g of modified castor oil, 428.4 g of toluene, 11.7 g of 2-hydroxymethyl-1,3-propanediol, and 2.14 g of 98 wt% sulfuric acid, add them into a three-necked flask and stir, raise the temperature of the three-necked flask to 110° C., keep warm and react for 6 hours, separate the by-product water through a water separator during the reaction, lower the temperature of the three-necked flask to room temperature, add 215 mL of purified water into the three-necked flask, stir for 15 minutes, stand for liquid separation, transfer the organic phase to a rotary evaporator, set the water bath temperature to 80° C., and distill under reduced pressure until no liquid flows out to obtain castor oil polyester;

[0075] Weigh: 30 g of castor oil polyester, 90 g of toluene and 10 g of 1,2,4-trimethylbenzene anhydride and add them into a three-necked flask, raise the temperature of the three-necked flask to 60°C, keep warm and react for 3 hours, add ammonia water to the three-necked flask, adjust the system pH to 9, add 100 mL of 10 wt% sodium chloride solution to the three-necked flask, stir for 15 minutes, stand and separate the liquids, transfer the organic phase to a rotary evaporator, set the water bath temperature to 80°C, and distill under reduced pressure until no liquid flows out to obtain a modified polyester;

[0076] Step 2: Preparation of modified drier

[0077] Weigh: 10 g of carboxymethyl triethoxysilane, 15 g of tetraethoxysilane, 30 g of 1,8-bis(triethoxysilyl)octane and 100 mL of 80 vt% ethanol solution, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 50° C., add 0.1 M hydrochloric acid into the three-necked flask, adjust the system pH to 5, keep warm for 4 h, keep the three-necked flask at 50° C., evaporate ethanol under reduced pressure, precipitate solid, add 100 mL of purified water into the three-necked flask, wash the solid to neutrality, transfer the solid to a drying oven at 80° C., dry to constant weight, and obtain modified siloxane;

[0078] Weigh: 10 g of 4-methyl-3-pentenoic acid, 15 g of nano manganese dioxide, 10 g of modified siloxane, 50 mL of N-methylpyrrolidone, 20 mL of toluene and 0.5 g of ammonium selenite, add into a three-necked flask and stir, raise the temperature of the three-necked flask to 190°C, keep warm for 8 hours, keep the three-necked flask at 190°C, remove the solvent under reduced pressure, lower the temperature of the three-necked flask to room temperature, add 60 mL of acetone into the three-necked flask, ultrasonically disperse for 30 minutes, filter, wash the filter cake three times with acetone, transfer it to a drying oven at 60°C, dry it to constant weight, and obtain a modified drying agent.

[0079] Step 3: Preparation of composite iron red

[0080] Add red iron oxide, acetone and 0.15M ammonia water into a three-necked flask at a ratio of 1 g:3 mL:3 mL, and perform ultrasonic dispersion for 50 min to obtain a red iron oxide solution;

[0081] Weigh: 22.1 g of KH-550, 22.2 g of isophorone diisocyanate and 111 g of acetone, add them into a nitrogen-protected three-necked flask and stir, keep warm and react for 50 min at room temperature, add 35.5 g of oleic acid into the three-necked flask, raise the temperature of the three-necked flask to 65°C, keep warm and react for 90 min, then add 44.2 g of red iron oxide solution into the three-necked flask, stir for 50 min, filter, wash the filter cake with acetone and then dry it, transfer the filter cake to a drying oven at 60°C, dry to constant weight, and obtain composite iron red.

[0082] Step 4: Prepare water-based back paint

[0083] Weigh: 60g of modified polyester, 6g of modified drying agent, 24g of composite iron red, 120mL of water, 2.4g of carboxymethyl cellulose, 1.2g of alkyl ether silicone oil, 1.2g of polypropylene glycol and 1.2g of polyvinyl alcohol and add them into a ball mill, select ceramic grinding balls with a diameter of 3-5mm, set the ball mill speed to 550r / min, ball mill for 3h, and after ball milling and mixing, release it from the ball mill into a beaker, add purified water to the beaker under stirring, adjust the viscosity of the paint to 5500-6500MPa·s, and obtain a water-based back paint.

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 3 is that the modified polyester in step 4 is replaced by an equal amount of castor oil polyester in step 1.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 3 is that step 2 is eliminated and the modified drying agent in step 4 is replaced by an equal amount of metallic manganese dioxide.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 3 is that step 3 is eliminated and the composite iron red in step 4 is replaced by an equal amount of iron oxide red.

[0090] Performance Testing:

[0091] The surface of the alloy substrate was evenly polished with 400-mesh sandpaper. The water-based back paint prepared in Examples 1-3 and Comparative Examples 1-3 was allowed to stand for 10 minutes, and then evenly coated on the polished surface of the alloy substrate and placed in a drying oven at 60°C for drying to form a paint film on the surface of the alloy substrate. The impact resistance, chemical corrosion resistance and blistering grade of the paint film were tested. The impact resistance was measured by referring to the standard GB / T20624.2-2006 "Rapid deformation (impact resistance) test for paints and varnishes Part 2: Drop hammer test (small area punch)" to measure the impact strength of the sample; the chemical corrosion resistance was measured by referring to the standard GB / T 1771-2007 "Determination of neutral salt spray resistance of paints and varnishes" to measure the neutral salt spray resistance grade of the sample; the blistering grade was measured by referring to the standard GB / T The samples were tested in accordance with 30789.2-2014 "Evaluation of aging of paints and varnishes - Number and size of defects and identification of uniform changes in appearance: Part 2: Evaluation of blistering degree". The wear resistance was tested in accordance with GB / T 1768-2006 "Abrasion resistance test for paints and varnishes" to determine the mass loss of the samples. The specific test results are shown in the table below;

[0092]

[0093] Data Analysis:

[0094] The data of Examples 1-3 and Comparative Examples 1-3 were analyzed and compared. The impact strength of the water-based back paint prepared in Examples 1-3 of the present invention reached 3.0 kg·m, the salt spray resistance level reached level 0, and the mass loss rate was reduced to 2.5 mg, and the blister level reached blister level 2 (S2), indicating that the water-based back paint prepared in the present invention has good impact strength, salt spray resistance and wear resistance, and the number of bubbles on the surface of the paint film is small and the density is low, and the surface of the paint film is relatively smooth;

[0095] Comparing the data of comparative example 1 with those of examples 1-3, the various test data of comparative example 1 were significantly decreased. During the experiment, a group of comparative examples was added, and the water-based back paint of comparative example 1 was used, and it was fully stirred before coating. The various properties of the paint film prepared by the comparative example were not much different from the data of examples 1-3, and its salt spray resistance was better than that of examples 1-3. This shows that further modification of castor oil polyester to prepare modified polyester can effectively improve the dispersion stability of each component raw material in the water-based back paint;

[0096] Comparing the data of Comparative Example 2 with those of Examples 1-3, all test data of Comparative Example 2 except for the impact strength are significantly decreased, and the time for the paint film of Comparative Example 2 to completely dry is extended compared with that of Examples 1-3. During the experiment, a group of control examples was added, and the water-based back paint of Comparative Example 2 was used, and it was fully stirred before coating. The impact strength of the control example was decreased compared with that of Comparative Example 2, and the other test data were decreased compared with Comparative Example 2, indicating that the modified manganese oxide prepared by modifying manganese oxide can be compounded with modified polyester, composite iron red, etc., to improve the impact resistance, salt spray resistance, and wear resistance of the paint film, and reduce the blistering performance of the paint film;

[0097] Comparing the data of Comparative Example 3 with those of Examples 1-3, all test data of Comparative Example 3 except the impact strength have decreased significantly, and the data of all other items except the impact strength are lower than those of Comparative Example 2. During the experiment, a group of control examples was added, and the water-based back paint of Comparative Example 3 was used. It was fully stirred before coating. The impact strength and blistering grade of the control example were lower than those of Comparative Example 3, and the milk salt grade and wear resistance were higher than those of Comparative Example 3. This shows that the composite iron red prepared by modifying red iron oxide can be compounded with modified polyester, modified drying agent, etc. to improve the impact resistance, salt spray resistance and wear resistance of the paint film, and reduce the blistering performance of the paint film.

[0098] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A surface anti-corrosion water-based back paint for alloy substrates, characterized in that: It is composed of modified polyester, modified drier, composite iron red, water and additives, and has a viscosity of 5500-6500 MPa·s, wherein the amount ratio of the modified polyester, modified drier, composite iron red, water and additives is 30g:3g:12g:40-60mL:3g; The modified drier is processed by the following steps: A1. Add carboxymethyl triethoxysilane, tetraethoxysilane, 1,8-bis(triethoxysilyl)octane and 80 vol% ethanol solution into a three-necked flask and stir. The temperature of the three-necked flask is raised to 40-50° C., 0.1 M hydrochloric acid is added into the three-necked flask, the pH value of the system is adjusted to 3-5, and the reaction is kept warm for 2-4 hours. The modified siloxane is obtained by post-treatment, wherein the amount ratio of carboxymethyl triethoxysilane, tetraethoxysilane, 1,8-bis(triethoxysilyl)octane and 80 vol% ethanol solution is 2 g:3 g:6 g:20 mL; A2, 4-methyl-3-pentenoic acid, nano manganese dioxide, modified siloxane, N-methyl pyrrolidone, toluene and a catalyst were added to a three-necked flask and stirred, the temperature of the three-necked flask was raised to 180-190 ° C, and the reaction was kept warm for 6-8 hours, and a modified drier was obtained by post-treatment, wherein the amount ratio of 4-methyl-3-pentenoic acid, nano manganese dioxide, modified siloxane, N-methyl pyrrolidone, toluene and the catalyst was 2g:3g:2g:10mL:4mL:0.1g, and the catalyst was selenite; The modified polyester is obtained by the following steps: B1, adding phthalic anhydride and toluene in a ratio of 1 g:4 mL into a three-necked flask protected by nitrogen and stirring, adding dropwise 50 vol% ricinoleic acid glyceride toluene solution into the three-necked flask at room temperature, reacting for 2-4 hours, and post-treating to obtain modified castor oil, wherein the ratio of phthalic anhydride to ricinoleic acid glyceride is 3M:1M; B2, adding modified castor oil, toluene, 2-hydroxymethyl-1,3-propylene glycol and a catalyst into a three-necked flask and stirring, raising the temperature of the three-necked flask to 105-110° C., keeping the temperature for 4-6 hours, and post-treating to obtain castor oil polyester, wherein the amount ratio of modified castor oil and 2-hydroxymethyl-1,3-propylene glycol is 1M:1.1M, the amount of the catalyst is 0.02 times the weight of the modified castor oil, and the catalyst is 98wt% sulfuric acid; B3, castor oil polyester, toluene and 1,2,4-benzene trimellitic anhydride are added to a three-necked flask, the temperature of the three-necked flask is increased to 50-60°C, and the temperature is kept for reaction for 2-3 hours, ammonia water is added to the three-necked flask, the pH value of the system is adjusted to 8-9, and the modified polyester is obtained by post-treatment, wherein the amount ratio of castor oil polyester to 1,2,4-benzene trimellitic anhydride is 3g:1g; The preparation method of the composite iron red comprises: adding KH-550, isophorone diisocyanate and acetone into a three-necked flask protected by nitrogen, stirring, keeping warm for reaction at room temperature for 30-50 minutes, adding oleic acid into the three-necked flask, raising the temperature of the three-necked flask to 55-65° C., keeping warm for reaction for 80-90 minutes, then adding a red iron oxide solution into the three-necked flask, stirring for 30-50 minutes, and post-treating to obtain the composite iron red, wherein the molar ratio of the KH-550 and the isophorone diisocyanate is 1:1, the amount of the acetone is 5 times the weight of the isophorone diisocyanate, the amount of the oleic acid is 1.6 times the amount of the isophorone diisocyanate, and the amount of the red iron oxide is 2 times the amount of the KH-550; The preparation method of the red iron oxide solution is as follows: add red iron oxide, acetone and 0.15M ammonia water into a three-necked flask at a dosage ratio of 1g:3mL:3mL, and perform ultrasonic dispersion for 30-50min to obtain the red iron oxide solution.

2. The anti-corrosion water-based back paint for alloy substrate according to claim 1, characterized in that: The additives are composed of a dispersant, a wetting agent, a defoamer and a thickener in a dosage ratio of 2g:1g:1g:1g, wherein the dispersant is composed of one or more of polyethylene glycol, polyacrylate, and carboxymethyl cellulose, the wetting agent is composed of one or more of octylbenzene sulfonate and polyethylene glycol octyl ether, the defoamer is one of polyethylene oxide, polyether siloxane, and polypropylene glycol, and the thickener is one of polyvinyl alcohol and hydroxypropyl methylcellulose.

3. The anti-corrosion water-based back paint for alloy substrate according to claim 1, characterized in that: In step B2, the amount of toluene used is 4 times the weight of the modified castor oil; in step B3, the amount of toluene used is 3 times the weight of the castor oil polyester.

4. The anti-corrosion water-based back paint for alloy substrate according to claim 1, characterized in that: The post-processing operation in the preparation method of composite iron oxide red includes: after the reaction is completed, suction filtration, washing the filter cake with acetone and then drying it, transferring the filter cake to a drying oven at a temperature of 50-60° C., and drying to constant weight to obtain composite iron oxide red.

5. A method for preparing a surface anti-corrosion water-based back paint for an alloy substrate as claimed in any one of claims 1 to 4, characterized in that: The preparation method of the surface anti-corrosion water-based back paint for the alloy substrate comprises the following steps: adding modified polyester, modified drying agent, composite iron red, water and additives into a ball mill, mixing by ball milling, discharging the mixture from the ball mill into a beaker, adding purified water into the beaker under stirring, adjusting the viscosity of the paint to 5500-6500 MPa·s, and obtaining the water-based back paint.

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