CN114100996A - Secondary coating method for steel plate with coating defects - Google Patents
Secondary coating method for steel plate with coating defects Download PDFInfo
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- CN114100996A CN114100996A CN202111390701.7A CN202111390701A CN114100996A CN 114100996 A CN114100996 A CN 114100996A CN 202111390701 A CN202111390701 A CN 202111390701A CN 114100996 A CN114100996 A CN 114100996A
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- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
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- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
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- C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
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Abstract
The invention provides a secondary coating method for a steel plate with coating defects, which can effectively improve the adhesive force and corrosion resistance of a secondary coating paint film. Which comprises the following steps: (1) pre-treating the edge of the original coating; (2) preparing a strengthening treatment solution: the strengthening treatment liquid comprises the following raw materials: dimercapto compound, sulfosalicylic acid, 2-bipyridine, carboxymethyl chitosan, ethanol, gamma-mercaptopropyl triethoxysilane and deionized water; (3) strengthening the edge of the original coating: spraying the strengthening treatment liquid obtained in the step (2) on the edge of the original coating and the surface of the steel plate at the joint after the treatment in the step (1); (4) electrochemical activation: taking a steel plate to be subjected to secondary coating and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, and taking an inert electrode as the other pole to perform electrochemical activation; (5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
Description
Technical Field
The invention relates to a coating method, in particular to a secondary coating method for a steel plate with coating defects, and belongs to the technical field of steel structure engineering.
Background
Compared with other structural forms, the steel structure engineering has the advantages of good earthquake resistance, short construction period, high industrialization degree, less pollution, light dead weight and the like, and is widely applied to the fields of high-rise and large-span structures and the like. Looking around the world, the steel structure development of the countries such as the United states, the United kingdom, Singapore and the like is particularly prosperous. In recent years, under the big background of novel infrastructure of national layout, steel structure engineering in China also appears like bamboo shoots in spring after raining, and a plurality of representative steel structure engineering symbolize that the theory and design of the steel structure in China are gradually improved. Moreover, with the progress of the times and the development of the society, the steel structure is widely adopted in the modern bridge construction, which greatly promotes the continuous progress of the bridge design level in China.
In the construction process of steel structure engineering, a paint film with good protective performance is formed by coating a plurality of layers of paint with anti-corrosion performance on the surface of a steel plate, which is the most common anti-corrosion means in the field of steel structure manufacturing at present. The epoxy zinc-rich paint is often used as a primer of a steel structure anticorrosive coating due to the excellent electrochemical protection effect on steel. However, after the coating is formed into a film, occasional defects such as sand inclusion, sagging, pinholes, shrinkage cavities, bubbling, peeling, cracking and the like of the paint film inevitably occur due to factors such as operating conditions, technical schemes and the like. Particularly, the problems of poor paint film adhesion and the like can be caused due to improper pretreatment process, poor matching of the epoxy zinc-rich primer and a steel plate and the like, and serious large-area foaming and peeling phenomena are generated. Under the condition, the part with the coating defect is often required to be treated as soon as possible, the defect of the coating is repaired in time by adopting a secondary coating mode after the defect coating is removed, and the overall quality of the steel structure is ensured.
At present, after coating defects are found in the manufacturing process, the original paint film is generally and simply removed, and then the epoxy zinc-rich primer, the intermediate paint and the finish paint are sprayed in the same way as the original coating process. However, the steel plate after removing the original paint film generally has lower surface energy, the original paint film is often poorer in binding force compared with the secondary coating of the epoxy zinc-rich primer, and the new paint film and the old paint film cannot be effectively bound with each other, so that a good anticorrosion effect cannot be obtained by adopting the same way as the original coating process. Therefore, the development of a method capable of effectively improving the adhesion and corrosion resistance of the coating after secondary coating is of great significance to the field of steel structure manufacturing.
Disclosure of Invention
The invention aims to provide a secondary coating method for a steel plate with coating defects, which can effectively improve the adhesion and corrosion resistance of a secondary coating paint film.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a secondary coating method for a steel plate with coating defects comprises the following steps:
(1) pre-treating the edge of the original coating;
(2) preparing a strengthening treatment solution: the strengthening treatment liquid comprises the following raw materials: dimercapto compound, sulfosalicylic acid, 2-bipyridine, carboxymethyl chitosan, ethanol, gamma-mercaptopropyl triethoxysilane and deionized water;
(3) strengthening the edge of the original coating: spraying the strengthening treatment liquid obtained in the step (2) on the edge of the original coating and the surface of the steel plate at the joint after the treatment in the step (1);
(4) electrochemical activation: taking a steel plate to be subjected to secondary coating and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, and taking an inert electrode as the other pole to perform electrochemical activation;
(5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
According to the preferable scheme of the secondary coating method for the steel plate with the coating defects, the preparation of the strengthening treatment liquid comprises the following specific steps: weighing 2.0-20.0 g of dimercapto compound, 5.0-20.0 g of sulfosalicylic acid, 0.1-3.0 g of 2, 2-bipyridine and 0.5-2.0 g of carboxymethyl chitosan, sequentially adding the materials into 900 mL of ethanol, uniformly stirring, adding 70 mL of gamma-mercaptopropyltriethoxysilane, uniformly stirring, adding 30 mL of deionized water in a dropwise manner within 1.0 h, and continuously stirring for 0.5 h to finish the preparation of the strengthening treatment solution.
According to the preferable scheme of the secondary coating method for the steel plate with the coating defects, the dimercapto compound is one or a combination of two of dimercapto polyethylene glycol, dimercapto ethylene glycol acetate, m-dibenzyl mercaptan, 1, 2-benzenedithiol, 1, 3-benzenedithiol and 1, 4-benzenedithiol.
According to the preferable scheme of the secondary coating method for the steel plate with the coating defects, the edge strengthening treatment of the original coating comprises the following specific steps: spraying the strengthening treatment liquid newly prepared in the step (2) on the edge of the original coating and the surface of the steel plate at the joint after the treatment in the step (1) by using a spray gun, spraying reduced iron powder with the particle size of 3000-800 meshes on the part coated with the strengthening treatment liquid by using air flow after 5-120 s so as to enable the reduced iron powder to be intensively adhered to the edge of the original coating, and washing the residual reduced iron powder by using deionized water after 10-600 s.
According to the preferable scheme of the secondary coating method of the steel plate with coating defects, the electrochemical activation comprises the following specific treatment steps: taking a steel plate to be coated for the second time and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, taking an inert electrode with the area of 1 square decimeter as the other pole to carry out electrochemical activation, separating the two electrodes by sponge soaked with electrochemical activation liquid with the temperature of 15-35 ℃, controlling the activation time of all parts to be activated to be 0.5-10 minutes by sine wave alternating current with the current amplitude of 5.0-10.0A and the frequency of 60 Hz, cleaning by absolute ethyl alcohol after the completion and drying by cold air, and completing the electrochemical activation; the electrochemical activation solution is prepared by the following steps: respectively weighing 5.0-30.0 g of citric acid, 3.0-30.0 g of sulfosalicylic acid and 2.0-6.0 g of carboxymethyl chitosan, sequentially dissolving in 1L of deionized water and uniformly stirring, heating to 50-95 ℃, adding 1.0-2.0 g of phenanthroline and uniformly stirring, sequentially adding 0.5-2.0 g of hydroxylamine hydrochloride and 1.0-8.0 g of ammonium ferrous sulfate and uniformly stirring, and adjusting the pH to 3.0-5.0.
According to the preferable scheme of the secondary coating method for the steel plate with the coating defects, when the passing electric quantity of the electrochemical activating solution in the sponge exceeds 0.3 A.h, the electrochemical activating solution in the sponge needs to be extruded out and soaked in new electrochemical activating solution again.
According to the preferable scheme of the secondary coating method for the steel plate with the coating defects, the inert electrode in the step (4) is one of a stainless steel electrode, a graphite electrode and a titanium electrode.
The invention has the advantages that:
the method for coating the steel plate with the coating defects comprises the step (1), the epoxy zinc-rich primer of the original paint film is exposed, so that the epoxy zinc-rich primer at the edge of the original paint film can be integrated with the steel plate at the joint through the subsequent step (3) and the subsequent step (4), the compatibility of the secondary coating paint film with the steel plate and the original paint film is improved, the problem that the adhesion force of the paint film is obviously degraded after the secondary coating is carried out when the steel plate coating defects are found in the field of steel structure manufacturing at present can be solved, and the corrosion resistance can be greatly improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
FIG. 1 is a schematic diagram of a secondary coating process for a steel plate with coating defects;
FIG. 2 is a Tafel plot of the paint film obtained after the test has been run for a second time after 240 h of neutral salt spray test in 3.5% NaCl solution.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A secondary coating method for a steel plate with coating defects comprises the following steps:
(1) pre-treating the edge of the original coating: polishing off the finish paint and the intermediate paint on the edge of the original paint film by adopting a shot blasting mode, exposing the fresh epoxy zinc-rich primer of the original paint film, and cleaning the residual particles, dirt, dust and the like on the surface by adopting a dust suction device;
(2) preparing a strengthening treatment solution: weighing 2.0-20.0 g of dimercapto compound, 5.0-20.0 g of sulfosalicylic acid, 0.1-3.0 g of 2, 2-bipyridine and 0.5-2.0 g of carboxymethyl chitosan, sequentially adding the materials into 900 mL of ethanol, uniformly stirring, adding 70 mL of gamma-mercaptopropyltriethoxysilane, uniformly stirring, adding 30 mL of deionized water in 1.0 h in a dropwise manner, and continuously stirring for 0.5 h to finish the preparation of the strengthening treatment solution; wherein the dimercapto compound is one or the combination of two of dimercapto polyethylene glycol, dimercapto acetic glycol ester, m-dibenzyl mercaptan, 1, 2-benzene dithiol, 1, 3-benzene dithiol and 1, 4-benzene dithiol;
(3) strengthening the edge of the original coating: spraying the strengthening treatment liquid newly prepared in the step (2) on the edge of the original coating and the surface of the steel plate at the joint after the treatment in the step (1) by using a spray gun, spraying reduced iron powder with the particle size of 3000-800 meshes on the part coated with the strengthening treatment liquid by using air flow after 5-120 s so as to be densely adhered to the edge of the original coating, and washing the residual reduced iron powder by using deionized water after 10-600 s;
(4) electrochemical activation: taking a steel plate to be coated for the second time and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, taking an inert electrode with the area of 1 square decimeter as the other pole to carry out electrochemical activation, separating the two electrodes by sponge soaked with electrochemical activation liquid with the temperature of 15-35 ℃, controlling the activation time of all parts to be activated to be 0.5-10 minutes by sine wave alternating current with the current amplitude of 5.0-10.0A and the frequency of 60 Hz, cleaning by absolute ethyl alcohol after the completion and drying by cold air, and completing the electrochemical activation; the electrochemical activation solution is prepared by the following steps: respectively weighing 5.0-30.0 g of citric acid, 3.0-30.0 g of sulfosalicylic acid and 2.0-6.0 g of carboxymethyl chitosan, sequentially dissolving in 1L of deionized water and uniformly stirring, heating to 50-95 ℃, adding 1.0-2.0 g of phenanthroline and uniformly stirring, sequentially adding 0.5-2.0 g of hydroxylamine hydrochloride and 1.0-8.0 g of ammonium ferrous sulfate and uniformly stirring, and adjusting the pH to 3.0-5.0;
(5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
In this embodiment, the inert electrode in the step (4) is one of a stainless steel electrode, a graphite electrode, and a titanium electrode.
In this embodiment, when the amount of electricity passed through the electrochemical activation solution in the sponge soaked with the electrochemical activation solution in the step (4) exceeds 0.3A · h, the electrochemical activation solution in the sponge needs to be squeezed out, and a new electrochemical activation solution needs to be soaked in the sponge again.
In the secondary coating method for a steel plate with a coating defect according to the embodiment, sulfosalicylic acid in the strengthening treatment solution prepared in the step (2) may complex zinc ions, ferrous ions and iron ions, and 2, 2-bipyridine may complex ferrous ions. The carboxymethyl chitosan in the strengthening treatment fluid is a metal ion complexing agent and can play a role in thickening, so that the strengthening treatment fluid can well cover the part to be treated. The dimercapto compound in the strengthening treatment fluid may rely on two mercapto groups to couple the two metals. In the preparation process of the strengthening treatment liquid in the step (2), the gamma-mercaptopropyltriethoxysilane can be dissociated into gamma-mercaptopropylsilanol after the slow addition of deionized water, so that mercapto and trihydroxy coupling metal/metal or epoxy resin/metal is utilized.
Through the step (1), exposing the epoxy zinc-rich primer of the original paint film, and after the step (3) spraying the newly prepared strengthening treatment liquid on the edge of the original paint film treated in the step (1) and the surface of the steel plate at the joint, the sulfosalicylic acid, the 2, 2-bipyridine and the carboxymethyl chitosan in the strengthening treatment liquid enable the zinc oxide film in the epoxy zinc-rich primer of the original paint film and the oxide film on the surface of the steel plate at the joint to be actively dissolved, so that fresh metal is exposed. Zinc and iron and the dimercapto compound in the strengthening treatment liquid form a high-strength chemical bond by utilizing the mercapto group, so that the dimercapto compound is adsorbed on the surface sprayed with the strengthening treatment liquid; the gamma-mercaptopropyl silanol can be tightly combined with zinc, epoxy resin in the epoxy zinc-rich primer and the surface of a steel plate at a joint through a mercapto group, and can also be tightly combined with zinc in the epoxy zinc-rich primer and the surface of the steel plate at the joint through a trihydroxy group. When the reduced iron powder is sprayed on the part coated with the strengthening treatment liquid through air flow, the reduced iron powder is bonded with the adsorbed dimercapto compound and the mercapto and hydroxyl on the gamma-mercaptopropylsilanol, so that the reduced iron powder is firmly fixed on the surface of the original coating zinc-rich primer and the steel plate at the joint. In the step (4), when anode current passes through the surfaces of the steel plate and the adhered reduced iron powder, the iron and steel oxide film can be removed by using citric acid, sulfosalicylic acid and phenanthroline in the electrochemical activation solution as strong complexing agents of ferrous ions and ferric ions, the iron is subjected to anodic oxidation at an accelerated speed and fresh iron is exposed under the action of the strong complexing agents of the ferrous ions, an epoxy resin-iron chemical bond is formed between the iron and the primer, so that the adhesive force of the paint film is improved, the grain boundary is etched first, the roughness of the surface of the iron and steel is increased, and the mechanical adhesive force of a subsequent paint film can be increased; when the surfaces of the exposed steel plate and the adhered reduced iron powder pass through cathode current, ferrous ions in the electrochemical activation liquid can be reduced to form metallic iron, and the over-corrosion of steel in the oxidation process is compensated. Generally, iron can be continuously etched and deposited under the action of alternating current, so that the surface of the steel can maintain an active state; the current efficiency of anodic etching is higher than that of cathodic deposition, so that the surface roughness can be increased, and the adhesive force of the subsequent epoxy zinc-rich primer is improved through high-strength chemical bonding and mechanical riveting.
The beneficial effects of the invention were verified by the following tests:
test one: after removing the original defect paint film at the defect part, the secondary coating method for the steel plate with the coating defect in the test is carried out according to the following steps:
(1) pre-treating the edge of the original coating: polishing off the finish paint and the intermediate paint on the edge of the original paint film by adopting a shot blasting mode, exposing the fresh epoxy zinc-rich primer of the original paint film, and cleaning the residual particles, dirt, dust and the like on the surface by adopting a dust suction device;
(2) preparing a strengthening treatment solution: weighing 2.0 g of dimercaptopolyethylene glycol, 20.0 g of sulfosalicylic acid, 0.1 g of 2, 2-bipyridine and 0.5 g of carboxymethyl chitosan, sequentially adding the weighed materials into 900 mL of ethanol, uniformly stirring, adding 70 mL of gamma-mercaptopropyltriethoxysilane, uniformly stirring, adding 30 mL of deionized water in a dropwise manner within 1.0 h, and continuously stirring for 0.5 h to finish the preparation of the strengthening treatment solution;
(3) strengthening the edge of the original coating: spraying the strengthening treatment liquid newly prepared in the step (2) on the edge of the original coating processed in the step (1) and the surface of the steel plate at the joint by using a spray gun, spraying reduced iron powder with the particle size of 3000 meshes on the part coated with the strengthening treatment liquid by using air flow after 120 s so as to enable the reduced iron powder to be densely adhered to the edge of the original coating, and washing the residual reduced iron powder clean by using deionized water after 10 s;
(4) electrochemical activation: taking a steel plate to be coated for the second time and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, taking a stainless steel electrode with the area of 1 square decimeter as the other pole to carry out electrochemical activation, separating the two electrodes by a sponge soaked with an electrochemical activation solution at 15 ℃, and extruding the electrochemical activation solution in the sponge and re-soaking the sponge in a new electrochemical activation solution when the electric quantity of the electrochemical activation solution in the sponge exceeds 0.3 A.h by sine wave alternating current with the current amplitude of 5.0A and the frequency of 60 Hz; controlling the activation time of all parts needing to be activated to be 10 minutes, cleaning the parts with absolute ethyl alcohol after the activation is finished, and drying the parts with cold air to finish the electrochemical activation; the electrochemical activation solution is prepared by the following steps: respectively weighing 30.0 g of citric acid, 3.0 g of sulfosalicylic acid and 6.0 g of carboxymethyl chitosan, sequentially dissolving the citric acid, the sulfosalicylic acid and the carboxymethyl chitosan in 1L of deionized water, uniformly stirring, heating to 50 ℃, adding 1.0 g of phenanthroline, uniformly stirring, sequentially adding 0.5 g of hydroxylamine hydrochloride and 1.0 g of ammonium ferrous sulfate, uniformly stirring, and adjusting the pH to 5.0;
(5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
And (2) test II: after removing the original defect paint film at the defect part, the secondary coating method for the steel plate with the coating defect in the test is carried out according to the following steps:
(1) pre-treating the edge of the original coating: polishing off the finish paint and the intermediate paint on the edge of the original paint film by adopting a shot blasting mode, exposing the fresh epoxy zinc-rich primer of the original paint film, and cleaning the residual particles, dirt, dust and the like on the surface by adopting a dust suction device;
(2) preparing a strengthening treatment solution: weighing 5.0 g of ethylene glycol dimercaptoacetate, 5.0 g of 1, 2-benzenedithiol, 10.0 g of sulfosalicylic acid, 1.5 g of 2, 2-bipyridine and 1.5 g of carboxymethyl chitosan, sequentially adding the materials into 900 mL of ethanol, uniformly stirring, adding 70 mL of gamma-mercaptopropyltriethoxysilane, uniformly stirring, adding 30 mL of deionized water in a dropwise manner within 1.0 h, and continuously stirring for 0.5 h to finish the preparation of the strengthening treatment solution;
(3) strengthening the edge of the original coating: spraying the strengthening treatment liquid newly prepared in the step (2) on the edge of the original coating processed in the step (1) and the surface of the steel plate at the joint by using a spray gun, spraying reduced iron powder with the particle size of 1600 meshes on the part coated with the strengthening treatment liquid by using air flow after 60 s so as to enable the reduced iron powder to be densely adhered to the edge of the original coating, and washing the residual reduced iron powder clean by using deionized water after 120 s;
(4) electrochemical activation: taking a steel plate to be coated for the second time and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, taking a stainless steel electrode with the area of 1 square decimeter as the other pole to carry out electrochemical activation, separating the two electrodes by a sponge soaked with electrochemical activation liquid at 25 ℃, and extruding the electrochemical activation liquid in the sponge and re-soaking the sponge in new electrochemical activation liquid when the electric quantity of the electrochemical activation liquid in the sponge exceeds 0.3 A.h by sine wave alternating current with the current amplitude of 7.0A and the frequency of 60 Hz; controlling the activation time of all parts needing to be activated to be 5 minutes, cleaning the parts with absolute ethyl alcohol after the activation is finished, and drying the parts with cold air to finish the electrochemical activation; the electrochemical activation solution is prepared by the following steps: respectively weighing 16.0 g of citric acid, 21.0 g of sulfosalicylic acid and 3.0 g of carboxymethyl chitosan, sequentially dissolving the citric acid, the sulfosalicylic acid and the carboxymethyl chitosan in 1L of deionized water, uniformly stirring, heating to 80 ℃, adding 1.3 g of phenanthroline, uniformly stirring, sequentially adding 1.0 g of hydroxylamine hydrochloride and 6.0 g of ammonium ferrous sulfate, uniformly stirring, and adjusting the pH to 3.5;
(5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
And (3) test III: after removing the original defect paint film at the defect part, the secondary coating method for the steel plate with the coating defect in the test is carried out according to the following steps:
(1) pre-treating the edge of the original coating: polishing off the finish paint and the intermediate paint on the edge of the original paint film by adopting a shot blasting mode, exposing the fresh epoxy zinc-rich primer of the original paint film, and cleaning the residual particles, dirt, dust and the like on the surface by adopting a dust suction device;
(2) preparing a strengthening treatment solution: weighing 10.0 g of ethylene glycol dimercaptoacetate, 10.0 g of m-dibenzyl mercaptan, 5.0 g of sulfosalicylic acid, 3.0 g of 2, 2-bipyridine and 2.0 g of carboxymethyl chitosan, sequentially adding the materials into 900 mL of ethanol, uniformly stirring, adding 70 mL of gamma-mercaptopropyltriethoxysilane, uniformly stirring, adding 30 mL of deionized water dropwise within 1.0 h, and continuously stirring for 0.5 h to finish the preparation of the strengthening treatment solution;
(3) strengthening the edge of the original coating: spraying the strengthening treatment liquid newly prepared in the step (2) on the edge of the original coating processed in the step (1) and the surface of the steel plate at the joint by using a spray gun, spraying reduced iron powder with the particle size of 800 meshes on the part coated with the strengthening treatment liquid by using air flow after 5 s so as to be densely adhered to the edge of the original coating, and washing the residual reduced iron powder by using deionized water after 600 s;
(4) electrochemical activation: taking a steel plate to be coated for the second time and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, taking a stainless steel electrode with the area of 1 square decimeter as the other pole to carry out electrochemical activation, separating the two electrodes by a sponge soaked with electrochemical activation liquid at 35 ℃, and extruding the electrochemical activation liquid in the sponge and re-soaking the sponge in new electrochemical activation liquid when the electric quantity of the electrochemical activation liquid in the sponge exceeds 0.3 A.h through sine wave alternating current with the current amplitude of 10.0A and the frequency of 60 Hz; controlling the activation time of all parts needing to be activated to be 0.5 minute, cleaning the parts with absolute ethyl alcohol after the activation is finished, and drying the parts with cold air to finish the electrochemical activation; the electrochemical activation solution is prepared by the following steps: respectively weighing 5.0 g of citric acid, 30.0 g of sulfosalicylic acid and 2.0 g of carboxymethyl chitosan, sequentially dissolving the citric acid, the sulfosalicylic acid and the carboxymethyl chitosan in 1L of deionized water, uniformly stirring, heating to 95 ℃, adding 2.0 g of phenanthroline, uniformly stirring, sequentially adding 2.0 g of hydroxylamine hydrochloride and 8.0 g of ammonium ferrous sulfate, uniformly stirring, and adjusting the pH to 3.0;
(5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
And (4) testing: after removing the original defect paint film at the defect part, the secondary coating method for the steel plate with the coating defect in the test is carried out according to the following steps:
(1) pre-treating the edge of the original coating: polishing off the finish paint and the intermediate paint on the edge of the original paint film by adopting a shot blasting mode, exposing the fresh epoxy zinc-rich primer of the original paint film, and cleaning the residual particles, dirt, dust and the like on the surface by adopting a dust suction device;
(2) preparing a strengthening treatment solution: weighing 3.0 g of ethylene glycol dimercaptoacetate, 3.0 g of m-dibenzyl mercaptan, 8.0 g of sulfosalicylic acid, 2.0 g of 2, 2-bipyridine and 0.8 g of carboxymethyl chitosan, sequentially adding the materials into 900 mL of ethanol, uniformly stirring, adding 70 mL of gamma-mercaptopropyltriethoxysilane, uniformly stirring, adding 30 mL of deionized water dropwise within 1.0 h, and continuously stirring for 0.5 h to finish the preparation of the strengthening treatment solution;
(3) strengthening the edge of the original coating: spraying the strengthening treatment liquid newly prepared in the step (2) on the edge of the original coating processed in the step (1) and the surface of the steel plate at the joint by using a spray gun, spraying reduced iron powder with the particle size of 3000 meshes on the part coated with the strengthening treatment liquid by using air flow after 90 s so as to enable the reduced iron powder to be densely adhered to the edge of the original coating, and washing the residual reduced iron powder clean by using deionized water after 300 s;
(4) electrochemical activation: taking a steel plate to be coated for the second time and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, taking a stainless steel electrode with the area of 1 square decimeter as the other pole to carry out electrochemical activation, separating the two electrodes by a sponge soaked with an electrochemical activation solution at 30 ℃, and extruding the electrochemical activation solution in the sponge and re-soaking the sponge in a new electrochemical activation solution when the electric quantity of the electrochemical activation solution in the sponge exceeds 0.3 A.h by sine wave alternating current with the current amplitude of 7.5A and the frequency of 60 Hz; controlling the activation time of all parts needing to be activated to be 6 minutes, cleaning the parts with absolute ethyl alcohol after the activation is finished, and drying the parts with cold air to finish the electrochemical activation; the electrochemical activation solution is prepared by the following steps: respectively weighing 12.0 g of citric acid, 16.0 g of sulfosalicylic acid and 3.5 g of carboxymethyl chitosan, sequentially dissolving the citric acid, the sulfosalicylic acid and the carboxymethyl chitosan in 1L of deionized water, uniformly stirring, heating to 75 ℃, adding 1.6 g of phenanthroline, uniformly stirring, sequentially adding 1.6 g of hydroxylamine hydrochloride and 5.0 g of ammonium ferrous sulfate, uniformly stirring, and adjusting the pH to 4.5;
(5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
Fig. 1 is a schematic view of a secondary coating process of a steel sheet having a coating defect according to the first to fourth tests. The secondary coating obtained in the first to fourth tests was subjected to a cross-cut method to determine the coating adhesion force, the cutter gap was 3 mm, the cross-cut area was pasted with 3M tape, the coating was observed to peel off after being rapidly pulled open, the regenerated coating not treated according to the test (control test) was also subjected to a cross-cut method to determine the coating adhesion force, and the results of the coating adhesion force are shown in table 1.
Table 1 coating adhesion test results
| Test No.) | Test No. two | Experiment three | Experiment four | Control | |
| Paint film surface Status of state | The cutting edge being completely flat Slippery, no one lattice falling off | The cutting edge being completely flat Slippery, no one lattice falling off | The cutting edge being completely flat Slippery, no one lattice falling off | The cutting edge being completely flat Slippery, no one lattice falling off | The coating at the scribing edge is seriously peeled off, and there were 13 cases where the coating was peeled off. |
| ISO class | Level 0 | Level 0 | Level 0 | Level 0 | Stage 2 |
The two-coat coating obtained in accordance with test one, after a 240 h neutral salt spray test in 3.5% NaCl solution, has a Tafel plot as shown in FIG. 2, with a corrosion current of only 5.22X 10-11 A·cm-2The coating still has very good corrosion resistance, and can continuously protect the steel plate. The coating adhesion force of the coating after the salt spray test is measured by a cross-hatch method, and the result is ISO grade 1, which indicates that the coating is corroded by salt spray even if the coating is subjected to salt sprayStill has better adhesive force.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A secondary coating method for a steel plate with coating defects is characterized by comprising the following steps:
(1) pre-treating the edge of the original coating;
(2) preparing a strengthening treatment solution: the strengthening treatment liquid comprises the following raw materials: dimercapto compound, sulfosalicylic acid, 2-bipyridine, carboxymethyl chitosan, ethanol, gamma-mercaptopropyl triethoxysilane and deionized water;
(3) strengthening the edge of the original coating: spraying the strengthening treatment liquid obtained in the step (2) on the edge of the original coating and the surface of the steel plate at the joint after the treatment in the step (1);
(4) electrochemical activation: taking a steel plate to be subjected to secondary coating and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, and taking an inert electrode as the other pole to perform electrochemical activation;
(5) secondary coating: and spraying the activated part with the epoxy zinc-rich primer, the intermediate coat and the finish coat in turn to finish secondary coating.
2. The secondary coating method for a steel sheet having a coating defect according to claim 1, characterized in that: the preparation method of the strengthening treatment solution comprises the following specific steps: weighing 2.0-20.0 g of dimercapto compound, 5.0-20.0 g of sulfosalicylic acid, 0.1-3.0 g of 2, 2-bipyridine and 0.5-2.0 g of carboxymethyl chitosan, sequentially adding the materials into 900 mL of ethanol, uniformly stirring, adding 70 mL of gamma-mercaptopropyltriethoxysilane, uniformly stirring, adding 30 mL of deionized water in a dropwise manner within 1.0 h, and continuously stirring for 0.5 h to finish the preparation of the strengthening treatment solution.
3. The secondary coating method for a steel sheet having a coating defect according to claim 2, characterized in that: the dimercapto compound is one or two of dimercapto polyethylene glycol, dimercapto ethylene glycol acetate, m-dibenzyl mercaptan, 1, 2-benzenedithiol, 1, 3-benzenedithiol and 1, 4-benzenedithiol.
4. The secondary coating method for a steel sheet having a coating defect according to claim 1, characterized in that: the method comprises the following specific steps of: spraying the strengthening treatment liquid newly prepared in the step (2) on the edge of the original coating and the surface of the steel plate at the joint after the treatment in the step (1) by using a spray gun, spraying reduced iron powder with the particle size of 3000-800 meshes on the part coated with the strengthening treatment liquid by using air flow after 5-120 s so as to enable the reduced iron powder to be intensively adhered to the edge of the original coating, and washing the residual reduced iron powder by using deionized water after 10-600 s.
5. The secondary coating method for a steel sheet having a coating defect according to claim 1, characterized in that: the electrochemical activation comprises the following specific treatment steps: taking a steel plate to be coated for the second time and the edge of the original coating processed in the step (3) as one pole of an electrolytic cell, taking an inert electrode with the area of 1 square decimeter as the other pole to carry out electrochemical activation, separating the two electrodes by sponge soaked with electrochemical activation liquid with the temperature of 15-35 ℃, controlling the activation time of all parts to be activated to be 0.5-10 minutes by sine wave alternating current with the current amplitude of 5.0-10.0A and the frequency of 60 Hz, cleaning by absolute ethyl alcohol after the completion and drying by cold air, and completing the electrochemical activation; the electrochemical activation solution is prepared by the following steps: respectively weighing 5.0-30.0 g of citric acid, 3.0-30.0 g of sulfosalicylic acid and 2.0-6.0 g of carboxymethyl chitosan, sequentially dissolving in 1L of deionized water and uniformly stirring, heating to 50-95 ℃, adding 1.0-2.0 g of phenanthroline and uniformly stirring, sequentially adding 0.5-2.0 g of hydroxylamine hydrochloride and 1.0-8.0 g of ammonium ferrous sulfate and uniformly stirring, and adjusting the pH to 3.0-5.0.
6. The secondary coating method for a steel sheet having a coating defect according to claim 5, characterized in that: when the passing electric quantity of the electrochemical activation solution in the sponge exceeds 0.3 A.h, the electrochemical activation solution in the sponge needs to be extruded out and soaked in new electrochemical activation solution again.
7. The secondary coating method for a steel sheet having a coating defect according to any one of claims 1 to 6, characterized in that: and (4) the inert electrode is one of a stainless steel electrode, a graphite electrode and a titanium electrode.
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