A surface coating for a highly corrosion-resistant galvanized steel sheet and a preparation method thereof

Abstract

The present invention discloses a surface coating for a highly corrosion-resistant galvanized steel sheet and a preparation method thereof, belonging to the technical field of corrosion-resistant coatings. The method comprises the following steps: S1, cleaning and decontaminating the galvanized steel sheet; S2, preparing an inorganic reaction agent; S3, spraying the inorganic reaction agent; S4, preparing an organic polymer layer; S5, surface cleaning; S6, drying with hot air. The galvanized steel sheet obtained by the present invention has excellent corrosion resistance. The organic polymer film for outer environment shielding is long-chain polyurethane, which has the characteristic of high strength and can effectively shield the media in the environment, especially can block O2, H2O and Cl ‑ from corroding and damaging the galvanized layer; the inorganic functional film in the inner layer has functions of graft polymerization catalysis, photocatalysis and self-repair.

Description

Technical Field

[0001] The present invention relates to a surface coating for a highly corrosion-resistant galvanized steel sheet and a preparation method thereof, belonging to the technical field of corrosion-resistant coatings. Background Art

[0002] At present, the vast majority of galvanized steel sheets in China are passivated with high-concentration or medium-concentration chromate solutions, although the construction processes may vary. However, since Cr 6+ is a highly toxic substance and has strong carcinogenicity, with the prominent global environmental problems in recent years, many countries and organizations have introduced relevant regulations to restrict the use of heavy metals, and the use and emission of Cr 6+ are also increasingly restricted by environmental protection regulations around the world. Therefore, it is urgent to use an environmentally friendly chromium-free passivation solution to replace the chromate passivation solution.

[0003] In the past, the matrix metal was usually protected by surface galvanizing, which could significantly reduce the corrosion of ferrous metals in the steel industry. However, the chemical substances of zinc are relatively active, and it is prone to corrosion under closed or humid air conditions. To improve the corrosion resistance of the galvanized layer and the adhesion between the coating and the substrate.

[0004] In summary, those skilled in the art urgently need to develop a galvanized sheet coating and a preparation method thereof that are both highly corrosion-resistant and environmentally friendly to solve the above problems. Summary of the Invention

[0005] The present invention aims to provide a preparation method for a surface coating of a highly corrosion-resistant galvanized steel sheet. The obtained galvanized steel sheet has excellent corrosion resistance, and the film layer has high strength, effectively shielding the medium and impact damage in the environment.

[0006] Meanwhile, the present invention provides a surface coating for a highly corrosion-resistant galvanized steel sheet.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A preparation method for a surface coating of a highly corrosion-resistant galvanized steel sheet, comprising the following steps:

[0009] S1, cleaning and decontaminating the galvanized steel sheet;

[0010] S2, preparing an inorganic reaction agent: roasting the silicocerite powder at 1500-1700 °C for 3-6 h, then crushing and ball-milling the roasted silicocerite powder, and mixing it evenly with styrene according to a mass ratio of 1:(5-7);

[0011] S3, spraying the inorganic reaction agent: evenly spraying the inorganic reaction agent mixed in S2 onto both surfaces of the galvanized steel sheet, and drying it to form an inorganic functional layer on the surface of the galvanized steel sheet;

[0012] S4, Preparation of the organic polymer layer: Diphenylmethane diisocyanate, diol, methanesulfonic acid, and toluene diisocyanate are mixed at a molar ratio of 1:1.2:0.5:0.7, and then placed into a pressurized reaction kettle. The reaction temperature is 170 - 180°C, the pressure is 1.7 - 1.9 MPa, and after reacting for 3 - 4.5 h, an organic reactant is obtained. Subsequently, the galvanized steel sheet coated with the inorganic functional layer is placed into the pressurized reaction kettle, the pH value is adjusted to 5.8 - 6.7, and the reaction is carried out for 1.2 - 1.8 h at a reaction temperature of 170 - 180°C and a pressure of 1.7 - 1.9 MPa;

[0013] S5, Surface cleaning: Take out the galvanized steel sheet with the organic polymer layer prepared and dry it, and then rinse the surface with clean water;

[0014] S6, Hot air drying: The surface film of the galvanized steel sheet cleaned in S5 is dried with hot air to obtain the final product.

[0015] In the present invention, the gadolinite powder is natural gadolinite powder; it contains

[0016] In S3, the spraying temperature is 50 - 68°C, the spraying speed is 500 - 600 mm / s, and the spraying thickness is 42 - 65 μm.

[0017] The thickness of the organic polymer layer prepared by the present invention is 300 - 650 μm.

[0018] In the present invention, malic acid and methylamine are used to adjust the pH value of the organic reactant to 5.8 - 6.7. If the pH value is too high, it is adjusted with malic acid; if the pH value is too low, it is adjusted with methylamine.

[0019] Among them, the diol specifically refers to propylene glycol;

[0020] In S1, the method of cleaning and decontamination is: Remove the surface stains of the galvanized steel sheet, and then clean and dry it for standby.

[0021] In S2, the particle size of the ball - milled gadolinite powder is 1.7 - 6.5 μm.

[0022] In S3, the drying temperature is 180 - 230°C, and the time is 5 - 8 h.

[0023] In S5, the drying temperature is 80 - 95°C, and the time is 1 - 2.5 h.

[0024] In S6, the temperature of hot air drying is 55 - 75°C, and the time is 0.5 - 1.3 h.

[0025] The surface coating of the highly corrosion - resistant galvanized steel sheet obtained by the preparation method of the present invention includes an outer organic polymer layer and an inner inorganic functional layer.

[0026] The surface coating was immersed in a 15 wt% aqueous NaCl solution at a temperature of 25 ± 2 °C for 8 days, and the corrosion area was 1.12 - 1.37%; the contact angle of the surface coating was 163 - 168°; the strength of the organic polymer layer of the surface coating was 53 - 58 MPa.

[0027] Application of the surface coating of the highly corrosion-resistant galvanized steel sheet of the present invention in the highly corrosion-resistant galvanized steel sheet.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The surface coating of the highly corrosion-resistant galvanized steel sheet of the present invention has a double-layer structure of an outer polymer film and an inner functional film, enabling the galvanized steel sheet to have excellent corrosion resistance.

[0030] The corrosion resistance principle is as follows:

[0031] 1. The main component of the inner inorganic functional film is treated silicocerite powder, rich in CeO 2 , when forming the organic polymer layer in the high-pressure reaction, CeO 2 reacts under acidic conditions to form tetravalent ions (the reaction formula is CeO 2 + 4H + = Ce 4+ + 2H 2 O), triggering the grafting / copolymerization reaction of polyurethane functional groups, increasing the polyurethane chain length, making its film layer have high strength, and effectively shielding the medium and impact damage in the environment.

[0032] 2. The CeO 2 and TiO 2 rich in the inner inorganic functional film have photocatalytic effects, and they can generate a large number of photoelectron holes under the action of sunlight, and then catalyze the reaction of CO 2 and H 2 O in the corrosion environment to generate reducing CO and H 2 . On the one hand, it reduces the acidity in the corrosion environment and inhibits corrosion; on the other hand, the reducing atmosphere can reduce the Zn 2+ generated by corrosion into Zn elemental, protecting the zinc layer on the outer layer of the galvanized steel sheet.

[0033] 3. After the inner inorganic functional film is damaged due to corrosion, the oxide particles inside it can be deposited at the damaged place, repairing the corrosion notch and hindering the transmission of electrons and zinc ions in the electrochemical corrosion of the zinc layer, thus comprehensively inhibiting the further development of the corrosion reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the microstructural diagram of the surface coating of the highly corrosion-resistant galvanized steel sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0036] The main components of the perovskite powder, Ce 2 O 3 and La 2 O 3 contents can reach 22.15 - 23.03% and 12.73 - 13.65% respectively, TiO 2 content is 16.05 - 19.27%, FeO and Fe 2 O 3 contents are 4.59 - 6.32% and 6.17 - 7.99% respectively, CaO content is 3.39 - 5.11%, Al 2 O 3 content is 0.08 - 0.17%, and the rest are other inevitable components. (Purchased from Anhui Xinjingtong New Materials Technology Co., Ltd.)

[0037] Example 1

[0038] A method for preparing a surface coating of a highly corrosion-resistant galvanized steel sheet, specifically the following steps:

[0039] S1, cleaning and decontamination: Remove the surface stains of the galvanized steel sheet, and then clean and dry it for later use;

[0040] S2, preparation of inorganic reactant: Calcinate the perovskite powder at 1500 °C for 3 h, then crush and ball-mill the calcined perovskite powder to about 1.7 μm, and then mix it evenly with styrene at a mass ratio of 1:5;

[0041] S3, spraying of inorganic reactant: Spray the inorganic reactant mixed in S2 evenly on the surface of the galvanized steel sheet and dry it. The drying temperature is 180 °C and the time is 5 h; the spraying temperature is 68 °C, the spraying speed is 600 mm / s, and the spraying thickness is about 42 μm; form an inorganic functional layer on the surface of the galvanized steel sheet;

[0042] S4, preparation of organic polymer layer: Mix diphenylmethane diisocyanate, propylene glycol, methanesulfonic acid, and toluene diisocyanate in a molar ratio of 1:1.2:0.5:0.7, then put them into a pressure reaction kettle. The reaction temperature is 170 °C, the pressure is 1.7 MPa, and after reacting for 3 h, an organic reactant is obtained. Then put the galvanized steel sheet coated with the inorganic functional layer into the pressure reaction kettle, adjust the pH value to 5.8, and react for 1.2 h. The reaction temperature is 170 °C and the pressure is 1.7 MPa; obtain an organic polymer layer with a thickness of about 300 μm;

[0043] S5, Surface cleaning: Take out the galvanized steel sheet with the organic polymer layer prepared and dry it. The drying temperature is 80°C and the drying time is 1 h; then rinse the surface with clean water;

[0044] S6, Hot air drying: After hot air drying the surface film of the galvanized steel sheet cleaned in S5, the final product is obtained. The hot air drying temperature is 55°C and the time is 1.3 h.

[0045] As Figure 1 shown, the surface coating of this embodiment has a double-layer structure, namely an outer organic polymer film and an inner inorganic functional film.

[0046] Example 2

[0047] A preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet, specifically the following steps:

[0048] S1, Cleaning and decontamination: Remove the surface stains of the galvanized steel sheet, then clean and dry it for standby;

[0049] S2, Preparation of inorganic reactant: Roast the silicocerite powder at 1700°C for 6 h, then crush and ball-mill the roasted silicocerite powder to about 6.5 μm, and then mix it evenly with styrene at a mass ratio of 1:7;

[0050] S3, Spraying of inorganic reactant: Evenly spray the inorganic reactant mixed in S2 onto the surface of the galvanized steel sheet and dry it. The drying temperature is 230°C and the time is 8 h; the spraying temperature is 50°C, the spraying speed is 500 mm / s, and the spraying thickness is about 65 μm; form an inorganic functional layer on the surface of the galvanized steel sheet;

[0051] S4, Preparation of organic polymer layer: Mix diphenylmethane diisocyanate, propylene glycol, methanesulfonic acid, and toluene diisocyanate in a molar ratio of 1:1.2:0.5:0.7, then put them into a pressure reaction kettle. The reaction temperature is 180°C, the pressure is 1.9 MPa, and after reacting for 4.5 h, an organic reactant is obtained. Then put the galvanized steel sheet coated with the inorganic functional layer into the pressure reaction kettle, adjust the pH value to 6.7, and react for 1.8 h. The reaction temperature is 180°C and the pressure is 1.9 MPa; obtain an organic polymer layer with a thickness of about 650 μm;

[0052] S5, Surface cleaning: Take out the galvanized steel sheet with the organic polymer layer prepared and dry it. The drying temperature is 95°C and the drying time is 2.5 h; then rinse the surface with clean water;

[0053] S6, Hot air drying: After hot air drying the surface film of the galvanized steel sheet cleaned in S5, the final product is obtained. The hot air drying temperature is 75°C and the time is 0.5 h.

[0054] Example 3

[0055] A preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet, specifically including the following steps:

[0056] S1, Cleaning and decontamination: Remove the surface stains of the galvanized steel sheet, and then clean and dry it for later use;

[0057] S2, Preparation of inorganic reactant: Roast the silicium titanium cerite ore powder at 1600 °C for 4.5 h, then crush and ball-mill the roasted silicium titanium cerite ore powder to about 3 μm, and then mix it evenly with styrene at a mass ratio of 1:6;

[0058] S3, Spraying of inorganic reactant: Evenly spray the inorganic reactant mixed in S2 onto the surface of the galvanized steel sheet, and then dry it. The drying temperature is 200 °C and the time is 6 h; the spraying temperature is 60 °C, the spraying speed is 550 mm / s, and the spraying thickness is about 50 μm; form an inorganic functional layer on the surface of the galvanized steel sheet;

[0059] S4, Preparation of organic polymer layer: Mix diisocyanate, propylene glycol, methanesulfonic acid, and toluene diisocyanate in a molar ratio of 1:1.2:0.5:0.7, then put them into a pressurized reaction kettle. The reaction temperature is 175 °C, the pressure is 1.8 MPa, and after reacting for 3.5 h, an organic reactant is obtained. Then put the galvanized steel sheet coated with the inorganic functional layer into the pressurized reaction kettle, adjust the pH value to 6.0, and react for 1.5 h. The reaction temperature is 175 °C and the pressure is 1.8 MPa; obtain an organic polymer layer with a thickness of about 450 μm;

[0060] S5, Surface cleaning: Take out and dry the galvanized steel sheet with the organic polymer layer prepared. The drying temperature is 85 °C and the drying time is 1.5 h; then rinse the surface with clean water;

[0061] S6, Drying with hot air: Dry the surface film of the galvanized steel sheet cleaned in S5 with hot air to obtain the final product. The temperature for drying with hot air is 65 °C and the time is 1.0 h.

[0062] Comparative example 1

[0063] Commercially available hot-dip galvanized steel sheet, grade: Q195.

[0064] Comparative example 2

[0065] The difference between this comparative example and Example 1 is only that: replace the silicium titanium cerite ore powder with a cerium-free silicium titanium ore powder. By preparation, the content of SiO 2 in the silicium titanium ore powder is 18.16%, the content of TiO 2 is 17.62%, the content of La 2 O 3 is 45.82%, and the content of FeO and Fe 2 O3 The content is 8.27% and 2.85%, the CaO content is 3.39%, and the Al 2 O 3 content is 2.52% and the balance is MgO.

[0066] Comparative Example 3

[0067] The difference between this comparative example and Example 1 is only that: the gadolinite powder is replaced with silicon powder. By formulation, in the silicon powder, the SiO 2 content is 18.16%, the La 2 O 3 content is 63.44%, the FeO and Fe 2 O 3 content is 8.27% and 2.85%, the CaO content is 3.39%, and the Al 2 O 3 content is 2.52% and the balance is MgO.

[0068] Comparative Example 4

[0069] The difference between this comparative example and Example 1 is only that: no gadolinite powder is added.

[0070] Comparative Example 5

[0071] S1, cleaning and decontamination: Remove the surface stains of the galvanized steel sheet, and then wash and dry it for use;

[0072] S2, roast the gadolinite powder at 1500 °C for 3 h, and then crush and ball-mill the roasted gadolinite powder to about 1.7 μm;

[0073] S2, preparation of the organic polymer layer: Mix diphenylmethane diisocyanate, propylene glycol, methanesulfonic acid, and toluene diisocyanate in a molar ratio of 1:1.2:0.5:0.7 to obtain a mixture. Add gadolinite powder, and the gadolinite powder is 3% of the mass of the mixture. Put it into a pressure reaction kettle, the reaction temperature is 170 °C, the pressure is 1.7 MPa, and after reacting for 3 h, an organic reaction agent is obtained. Then put the galvanized steel sheet into the pressure reaction kettle, adjust the pH value to 5.8, and react for 1.2 h, the reaction temperature is 170 °C, the pressure is 1.7 MPa; obtain an organic polymer layer with a thickness of about 340 μm;

[0074] S3, surface cleaning: Take out the galvanized steel sheet with the organic polymer layer prepared and dry it, the drying temperature is 80 °C, and the drying time is 1 h; then rinse the surface with clean water;

[0075] S4, hot air drying: Hot air dry the surface film of the galvanized steel sheet cleaned in S3 to obtain the final product. The temperature of hot air drying is 55 °C and the time is 1.3 h.

[0076] Compared with the single layer and the double layer, the corrosion resistance and mechanical properties decrease. The main reasons are as follows: 1. The polymer layer will completely wrap the ore powder, making it difficult to reflect the functions of the inorganic functional membranes in the inner layers in beneficial effects 2 and 3. 2. After the ore powder particles are mixed in the polymer layer, an interface between the polymer and the particles will be formed, which will become a weak point when stressed, reducing the mechanical properties of the polymer layer.

[0077] The test results of the properties of the coatings obtained in Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0078] For the corrosion resistance test, specimens (8×6 cm 2 ) were immersed in an aqueous solution of NaCl with a mass percentage of 15% at a temperature of 25 ± 2 °C, and the corrosion resistance was determined by the corrosion area of the specimens after 8 days of corrosion.

[0079] The method for gel permeation chromatography test is as follows: The gel chromatograph is Waters 1515 gel chromatograph of Waters Company, USA. The gel permeation chromatography column is Sepax MonoGPC-100, model specification: 10×300 mm, 5 μm. Analytical conditions: mobile phase / solvent: tetrahydrofuran; flow rate 1 mL / min; column temperature 35 °C, pressure not exceeding 3.5 Mpa. After scraping 1 g of the organic polymer layer and putting it into 10 mL of tetrahydrofuran for dissolution, the dissolution temperature is (25 ± 2) °C and the dissolution time is 30 ± 10 min. After complete dissolution, the test solution is obtained by filtration.

[0080] The test method for the strength of the organic layer is as follows: After corroding the metal with a corrosive agent and only retaining the outer organic layer, the strength test is carried out using a universal electronic testing machine (conventional strength test method).

[0081] The test method for the contact angle is: Conic cone method.

[0082] Table 1 Test results of properties

[0083]

[0084]

[0085] As can be seen from Table 1, both the number-average relative molecular mass and the weight-average relative molecular mass represent the molecular weight size and can characterize the long chain, indicating that the polyurethane functional groups of the present invention undergo graft copolymerization reaction to form long-chain polymers. The organic polymer membrane with outer environment shielding is long-chain polyurethane, which has the characteristic of high strength and can effectively shield the media in the environment, especially can block O 2 , H 2Corrosion damage of O and Cl⁻ to the galvanized layer. The inner inorganic functional film has functions of graft polymerization catalysis, photocatalysis and self-repair. The molecular weight distribution index (PDI) of the present invention is relatively narrow, indicating that the polyurethane long chains are relatively uniform.

[0086] It should be understood that, in order to streamline the present disclosure and assist in understanding one or more of the various inventive aspects, in the above description of the exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, the disclosed method should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected by the claims, the inventive aspects lie in less than all the features of the previously disclosed embodiments. Thus, the claims following the detailed description are hereby expressly incorporated into the detailed description, where each claim itself serves as a separate embodiment of the present invention.

[0087] Although the present invention has been described in terms of a limited number of embodiments, those skilled in the art in this technical field will appreciate, based on the above description, that other embodiments can be contemplated within the scope of the present invention thus described. In addition, it should be noted that the language used in this specification has been principally selected for readability and teaching purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Thus, many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. For the scope of the present invention, the disclosure of the present invention is illustrative and not restrictive, and the scope of the present invention is defined by the appended claims.

[0088] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet, characterized in that, it includes the following steps: S1, cleaning and decontaminating the galvanized steel sheet; S2, preparation of the inorganic reactant: roasting the silicium-titanium-cerium ore powder at 1500 - 1700 °C for 3 - 6 h, then crushing and ball-milling the roasted silicium-titanium-cerium ore powder, and mixing it evenly with styrene in a mass ratio of 1:(5 - 7); S3, spraying the inorganic reactant: evenly spraying the inorganic reactant mixed in S2 onto the surface of the galvanized steel sheet, and drying it to form an inorganic functional layer on the surface of the galvanized steel sheet; S4, preparation of the organic polymer layer: mixing diphenylmethane diisocyanate, diol, methanesulfonic acid, and toluene diisocyanate in a molar ratio of 1:1.2:0.5:0.7, then putting it into a pressurized reaction kettle, with a reaction temperature of 170 - 180 °C, a pressure of 1.7 - 1.9 MPa, reacting for 3 - 4.5 h to obtain an organic reactant, and then putting the galvanized steel sheet coated with the inorganic functional layer into the pressurized reaction kettle, adjusting the pH value to 5.8 - 6.7, reacting for 1.2 - 1.8 h, with a reaction temperature of 170 - 180 °C and a pressure of 1.7 - 1.9 MPa to obtain the organic polymer layer; S5, surface cleaning: taking out the galvanized steel sheet with the prepared organic polymer layer and drying it, then rinsing the surface with clean water; S6, hot air drying: hot air drying the surface film of the galvanized steel sheet cleaned in S5 to obtain the final product.

2. The preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet according to claim 1, characterized in that, in S3, the spraying temperature is 50 - 68 °C, the spraying speed is 500 - 600 mm / s, and the spraying thickness is 42 - 65 µm.

3. The preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet according to claim 1, characterized in that, The cerite powder is a natural cerite powder containing Ce 2 O 3 .

4. The preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet according to claim 1, characterized in that, in S2, the particle size of the ball-milled silicium-titanium-cerium ore powder is 1.7 - 6.5 µm.

5. The preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet according to claim 1, characterized in that, in S3, the drying temperature is 180 - 230 °C, and the time is 5 - 8 h.

6. The preparation method for the surface coating of a highly corrosion-resistant galvanized steel sheet according to claim 1, characterized in that, the diol is propylene glycol.

7. The preparation method according to claim 1, characterized in that, in S6, the hot air drying temperature is 55 - 75 °C, and the time is 0.5 - 1.3 h.

8. The surface coating of a highly corrosion-resistant galvanized steel sheet obtained by the preparation method according to any one of claims 1 - 7, characterized in that, the surface coating includes an outer organic polymer layer and an inner inorganic functional layer.

9. The surface coating of a highly corrosion-resistant galvanized steel sheet according to claim 8, characterized in that, the surface coating is immersed in a 15 wt% NaCl aqueous solution at a temperature of 25 ± 2 °C for 8 days, and the corrosion area ratio is 1.12 - 1.37%; the contact angle of the surface coating is 163 - 168°; the strength of the organic polymer layer of the surface coating is 53 - 58 MPa.

10. Use of the surface coating of the highly corrosion-resistant galvanized steel sheet according to claim 8 in the highly corrosion-resistant galvanized steel sheet.

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