Composite coating and preparation method thereof

Abstract

The invention discloses a composite coating which mainly comprises two layers, the inner layer is a phytic acid-vanadate composite conversion film and is mainly used for providing a certain protection effect on a steel substrate and increasing the adhesive force with a subsequent polyaniline material layer; the outer layer is mainly made of a tannic acid doped polyaniline material, and the inner layer composite conversion film and the outer layer tannic acid doped polyaniline material both have self-repairing performance. The invention belongs to the technical field of material surface protection, and particularly relates to a composite coating and a preparation method thereof.

Description

Technical Field

[0001] The invention belongs to the technical field of material surface protection, and specifically refers to a composite coating and a preparation method thereof. Background Art

[0002] In recent years, the conversion coating technology with green phytic acid as the main material has emerged as a promising technology and has been widely used in the surface modification and anti-corrosion protection of magnesium alloys, aluminum alloys and low-carbon steel. The phytic acid coating can not only form a thin and effective barrier to prevent corrosive substances from diffusing to the metal / coating interface, but also improve the adhesion between the metal substrate and the organic coating. The traditional conversion film can only provide corrosion protection for the metal substrate for a period of time. The single phytic acid film has many cracks due to hydrogen evolution reaction and subsequent drying and dehydration, which is not conducive to corrosion protection. Composite treatment can significantly improve the anti-corrosion efficiency of the conversion film.

[0003] Once defects appear on the coating surface, the shielding effect of the coating will be quickly lost. At present, hybrid coatings with self-healing properties have been proven to be very promising applications for improving the corrosion resistance of steel substrates. Phytic acid will show a certain self-healing ability after being compounded with other film layers. At the same time, the polyaniline epoxy resin coating containing phytic acid is applied to galvanized steel, which has a significant passivation effect and a certain degree of self-healing effect. Summary of the invention

[0004] The invention relates to the preparation of a self-repairing conversion film, the preparation of a self-repairing polyaniline material, and the organic combination of the two, in particular to a method for preparing a polyaniline composite coating with self-repairing performance.

[0005] In order to achieve the above functions, the technical solution adopted by the present invention is as follows: a composite coating mainly has two layers, the inner layer is a phytic acid-vanadate composite conversion film, which mainly provides a certain protection for the steel substrate and increases the adhesion with the subsequent polyaniline material layer;

[0006] The outer layer is mainly composed of tannic acid-doped polyaniline material, and the structure of polyaniline and doped polyaniline is as follows:

[0007]

[0008] The composite coating preparation method comprises the following specific steps:

[0009] S1. Preparation of phytic acid conversion film: The steel sheet was polished with different meshes of water sandpaper (400, 600, 800, 1200, 2000 mesh) on a polishing machine, and the mirror-like steel sheet was ultrasonically degreased in ethanol and acetone for 10 minutes, dried and placed in a dryer for use; a phytic acid solution with a concentration of 5-20g / L was prepared, and the pH was adjusted to 4-7 with 10wt.% (mass fraction) of sodium hydroxide, and the phytic acid conversion solution was placed in a 30-60℃ water bath for preheating for 20 minutes, and then the steel sheet was immersed in the conversion solution for 20-80 minutes. After the conversion was completed, it was washed with distilled water and dried at 30-60℃ for 2h.

[0010] S2. The phytic acid film sample obtained in step S1 is post-treated with a sodium metavanadate solution, and dried for later use. The sodium metavanadate concentration is 2.0-5.0 g / L, and the treatment is carried out at 30°C for 20 min or 40 min, and they are marked as 1 (0.2, 20 min), 2 (0.5, 20 min), 3 (0.2, 40 min), 4 (0.5, 40 min), and electrochemical tests are performed to characterize their self-healing properties.

[0011] S3. Weigh a certain amount of dry tannic acid, add it to water placed in a reaction vessel, stir (magnetic) to dissolve it, and add aniline dropwise to the reactor, ultrasonicate for 10 minutes to dissolve it into a microemulsion, fix it to an iron stand, and cool it with ice for later use. Under magnetic stirring, add the ammonium persulfate solution dropwise to the reactor to obtain the tannic acid / aniline solution, react it at 0-5°C under stirring conditions for 8 hours, and then cool it to room temperature to obtain a dark green tannic acid-doped polyaniline solution;

[0012] S4. Add the tannic acid-doped polyaniline obtained in S4 to the epoxy resin, and heat and cure.

[0013] Furthermore, in step S4, the coating layer can be prepared by coating or spraying.

[0014] The present invention adopts the above structure to achieve the following beneficial effects: the present invention improves and enhances (repair performance) the reason why the spray-coated polyaniline coating has poor corrosion resistance (easy to fall off). In order to further enhance the bonding force between the spray-coated polyaniline coating and the steel substrate, a green and chromium-free pretreatment technology is used to pre-treat the substrate. Phytic acid is used to pre-treat the steel substrate and is compounded with sodium metavanadate to further improve the corrosion resistance and self-repair performance of the pre-treatment film. Compared with the inconvenience caused by the electrochemical preparation of polyaniline coatings, the coating is prepared by selecting a spraying process to achieve a simple and practical preparation of the coating. After the coating is damaged, its protective effect is greatly weakened. Therefore, self-repairing functional materials such as tannic acid-Fe complexes are added to the spray liquid, and the photothermal conversion effect of tannic acid and iron ions with good biocompatibility to form a complex is used as a functional material to prepare a self-repairing anti-corrosion coating on the steel surface, optimize the preparation process, and prepare a composite repair coating, which provides experimental support for the preparation of a simpler coating for subsequent polyaniline coatings. DETAILED DESCRIPTION

[0015] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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.

[0016] A composite coating mainly has two layers, the inner layer is a phytic acid-vanadate composite conversion film, which mainly provides a certain protection for the steel substrate and increases the adhesion with the subsequent polyaniline material layer;

[0017] The outer layer is mainly composed of tannic acid-doped polyaniline material, and the structure of polyaniline and doped polyaniline is as follows:

[0018]

[0019]

[0020] Embodiment 1:

[0021] The composite coating preparation method comprises the following specific steps:

[0022] S1. Preparation of phytic acid conversion film: The steel sheet was polished with different mesh sizes of water sandpaper (400, 600, 800, 1200, 2000 mesh) on a polishing machine, and the mirror-like steel sheet was ultrasonically degreased in ethanol and acetone for 10 minutes, dried and placed in a dryer for use; a phytic acid solution with a concentration of 5g / L was prepared, and the pH was adjusted to 4 with 10wt.% (mass fraction) of sodium hydroxide, and the phytic acid conversion solution was placed in a 30°C water bath for preheating for 20 minutes, and then the steel sheet was immersed in the conversion solution for 20 minutes. After the conversion was completed, it was washed with distilled water and dried at 30°C for 2h.

[0023] S2. The phytic acid film sample obtained in step S1 is post-treated with a sodium metavanadate solution, and can be dried for later use. The sodium metavanadate concentration is 2.0 g / L, and the treatment is carried out at 30°C for 20 min or 40 min, and they are marked as 1 (0.2, 20 min), 2 (0.5, 20 min), 3 (0.2, 40 min), 4 (0.5, 40 min), respectively, and electrochemical tests are performed to characterize their self-healing properties;

[0024] S3. Weigh a certain amount of dry tannic acid, add it to water placed in a reaction vessel, stir (magnetic) to dissolve it, and add aniline dropwise to the reactor, ultrasonicate for 10 minutes to dissolve it into a microemulsion, fix it to an iron stand, and cool it with ice for later use. Under magnetic stirring, add the ammonium persulfate solution dropwise to the reactor to obtain the tannic acid / aniline solution, react it at 1°C under stirring conditions for 8 hours, and then cool it to room temperature to obtain a dark green tannic acid-doped polyaniline solution;.

[0025] S4. Add the tannic acid-doped polyaniline obtained in S4 to the epoxy resin by spraying, and heat and cure.

[0026] Embodiment 2:

[0027] S1. Preparation of phytic acid conversion film: The steel sheet was polished with different mesh sizes of water sandpaper (400, 600, 800, 1200, 2000 mesh) on a polishing machine, and the mirror-like steel sheet was ultrasonically degreased in ethanol and acetone for 10 minutes, dried and placed in a dryer for use; a phytic acid solution with a concentration of 15g / L was prepared, and the pH was adjusted to 6 with 10wt.% (mass fraction) of sodium hydroxide, and the phytic acid conversion solution was placed in a 50°C water bath for preheating for 20 minutes, and then the steel sheet was immersed in the conversion solution for 60 minutes. After the conversion was completed, it was washed with distilled water and dried at 50°C for 2h.

[0028] S2. The phytic acid film sample obtained in step S1 is post-treated with a sodium metavanadate solution, and can be dried for later use. The sodium metavanadate concentration is 4.0 g / L, and the treatment is carried out at 30°C for 20 min or 40 min, and they are marked as 1 (0.2, 20 min), 2 (0.5, 20 min), 3 (0.2, 40 min), 4 (0.5, 40 min), respectively, and electrochemical tests are carried out to characterize their self-healing properties;

[0029] S3. Weigh a certain amount of dry tannic acid, add it to water placed in a reaction vessel, stir (magnetic) to dissolve it, and add aniline dropwise to the reactor, ultrasonicate for 10 minutes to dissolve it into a microemulsion, fix it to an iron stand, and cool it with ice for later use. Under magnetic stirring, add the ammonium persulfate solution dropwise to the reactor to obtain the tannic acid / aniline solution, react it at 2°C under stirring conditions for 8 hours, and then cool it to room temperature to obtain a dark green tannic acid-doped polyaniline solution;.

[0030] S4. Add the tannic acid-doped polyaniline obtained in S4 to the epoxy resin by spraying, and heat and cure.

[0031] Embodiment three:

[0032] S1. Preparation of phytic acid conversion film: The steel sheet was polished with different mesh sizes of water sandpaper (400, 600, 800, 1200, 2000 mesh) on a polishing machine, and the mirror-like steel sheet was ultrasonically degreased in ethanol and acetone for 10 minutes, dried and placed in a dryer for use; a phytic acid solution with a concentration of 20g / L was prepared, and the pH was adjusted to 7 with 10wt.% (mass fraction) of sodium hydroxide, and the phytic acid conversion solution was placed in a 60°C water bath for preheating for 20 minutes, and then the steel sheet was immersed in the conversion solution for 80 minutes. After the conversion was completed, it was washed with distilled water and dried at 60°C for 2h.

[0033] S2. The phytic acid film sample obtained in step S1 is post-treated with a sodium metavanadate solution, and can be dried for later use. The sodium metavanadate concentration is 5.0 g / L, and the treatment is carried out at 30°C for 20 min or 40 min, and they are marked as 1 (0.2, 20 min), 2 (0.5, 20 min), 3 (0.2, 40 min), 4 (0.5, 40 min), respectively, and electrochemical tests are performed to characterize their self-healing properties;

[0034] S3. Weigh a certain amount of dry tannic acid, add it to water placed in a reaction vessel, stir (magnetic) to dissolve it, and add aniline dropwise to the reactor, ultrasonicate for 10 minutes to dissolve it into a microemulsion, fix it to an iron stand, and cool it with ice for later use. Under magnetic stirring, add the ammonium persulfate solution dropwise to the reactor to obtain the tannic acid / aniline solution, react it at 5°C under stirring conditions for 8 hours, and then cool it to room temperature to obtain a dark green tannic acid-doped polyaniline solution;.

[0035] S4. Add the tannic acid-doped polyaniline obtained in S4 to the epoxy resin by spraying, and heat and cure.

[0036] The present invention and its implementation methods are described above, and such description is not restrictive. In short, if a person skilled in the art is inspired by it and, without departing from the purpose of the invention, designs structures and embodiments similar to the technical solution without creativity, they should all fall within the protection scope of the present invention.

Claims

1. A composite coating, mainly comprising two layers, characterized in that: The inner layer is a phytic acid-vanadate composite conversion film, which mainly provides a certain degree of protection for the steel substrate and increases the adhesion with the subsequent polyaniline material layer; The outer layer is mainly composed of tannic acid-doped polyaniline material, and the structure of polyaniline and doped polyaniline is shown in the figure:

2. A composite coating and a preparation method thereof according to claim 1, characterized in that: A method for preparing a composite coating is described, and the specific steps are as follows: S1. Preparation of phytic acid conversion film: polish the steel sheet with different mesh sizes of water sandpaper (400, 600, 800, 1200, 2000 mesh) on a polishing machine, ultrasonically degrease the mirror-like steel sheet in ethanol and acetone for 10 minutes, dry and place in a dryer for use; prepare a phytic acid solution with a concentration of 5-20g / L, use 10wt.% (mass fraction) of sodium hydroxide to adjust the pH to 4-7, place the phytic acid conversion solution in a 30-60℃ water bath to preheat for 20 minutes, and then soak the steel sheet in the conversion solution for 20-80 minutes. After the conversion is completed, wash with distilled water and dry at 30-60℃ for 2h; S2. The phytic acid film sample obtained in step S1 is post-treated with a sodium metavanadate solution, and dried for later use. The sodium metavanadate concentration is 2.0-5.0 g / L, and the treatment is carried out at 30°C for 20 min or 40 min, and they are marked as 1 (0.2, 20 min), 2 (0.5, 20 min), 3 (0.2, 40 min), 4 (0.5, 40 min), and electrochemical tests are performed to characterize their self-healing properties. S3. Weigh a certain amount of dry tannic acid, add it to water placed in a reaction vessel, stir (magnetic) to dissolve it, and add aniline dropwise to the reactor, ultrasonicate for 10 minutes to dissolve it into a microemulsion, fix it to an iron stand, and cool it with ice for later use. Under magnetic stirring, add the ammonium persulfate solution dropwise to the reactor to obtain the tannic acid / aniline solution, react it at 0-5°C under stirring conditions for 8 hours, and then cool it to room temperature to obtain a dark green tannic acid-doped polyaniline solution; S4. Add the tannic acid-doped polyaniline obtained in S4 to the epoxy resin, and heat and cure.

3. A composite coating and a preparation method thereof according to claim 1, characterized in that: In the step S4, the coating layer can be prepared by coating or spraying.

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