Zinc-rich epoxy coating and preparation method thereof

Abstract

The invention provides a zinc-rich epoxy coating and a preparation method thereof, the zinc-rich epoxy coating comprises epoxy resin, zinc powder, a solvent, a curing agent and an additive, the additive comprises a Go / magnesium cerium LDH composite material, magnesium salt and cerium salt are dissolved in water to form a uniform solution, graphene oxide slurry is dissolved in water to form a suspension, and the suspension is dried to obtain the zinc-rich epoxy coating. And adding the suspension into the uniform solution, mixing, adding alkali to adjust the pH value, and carrying out hydrothermal reaction to obtain the Go / magnesium cerium LDH composite material. Cerium ions with a corrosion inhibition effect are used as LDH main laminate cations, a corrosion inhibition passivation effect can be generated to generate an oxide, hydroxide is deposited at the interface defect position of a coating metal matrix, and corrosion of the metal matrix is delayed; meanwhile, the LDH grows on the graphene oxide in situ, so that the electrical property of the Go / magnesium cerium LDH composite material is regulated and controlled, the corrosion promoting effect of the graphene is inhibited, and the conductive path of the zinc powder is increased.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion materials technology, specifically to a zinc-rich epoxy coating and its preparation method. Background Technology

[0002] Zinc-rich epoxy primer is a traditional type of heavy-duty anti-corrosion coating. However, adding a high content of zinc powder to the resin matrix can easily lead to many problems, such as zinc corrosion products encapsulating zinc particles and blocking conductive paths, poor film density, and low zinc utilization.

[0003] Graphene possesses superior conductivity, high specific surface area, chemical stability, and thermal stability. Its sheet-like structure also exhibits hydrophobicity and impermeability, effectively blocking the passage of corrosive media (water, oxygen, etc.). These properties make it highly valuable in the field of metal corrosion protection. However, the strong van der Waals forces and π-π conjugation between the layers of multilayered graphene make it difficult to disperse and prone to aggregation in solvents, leading to decreased corrosion resistance. Furthermore, its high conductivity can also promote metal corrosion. Graphene oxide contains more oxygen-containing groups such as carboxyl, hydroxyl, and epoxy groups on its surface than graphene. Modification through non-covalent physical adsorption and covalent bond modification, followed by reduction through chemical reactions, can effectively solve the graphene aggregation problem and suppress the metal corrosion problem caused by graphene's high conductivity [Luo Jian, Wang Jihu, Wen Shaoguo, et al. Research progress of graphene in anti-corrosion coatings [J]. Coating Industry, 2017, 47(11):69-76.].

[0004] Therefore, different methods can be designed to modify graphene to improve its corrosion resistance in anti-corrosion coatings [Li Wenguan, Zhang Ruizhi, Luo Fangwei, et al. Research progress on the application of modified graphene-based fillers in anti-corrosion coatings. Coatings Industry, 2020, 50(4):81-87.]. For example, inorganic metal salt ions can be adsorbed and chemically transformed to grow in situ on the surface of graphene oxide, obtaining uniformly distributed and size-controllable nanoparticles, which can be used as fillers in anti-corrosion coatings to enhance the shielding effect of the coating and improve its anti-corrosion ability. [Gui Xiaolu, Cheng Xuan, et al. Graphene dispersion methods and research progress in waterborne epoxy zinc-rich coatings. Materials Reports, 2024, 38(3):22060047.]. However, the above strategies still cannot effectively and significantly improve the corrosion resistance of the coating. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to improve the corrosion resistance of zinc-rich epoxy coatings.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] The first aspect of this invention provides a zinc-rich epoxy coating, comprising epoxy resin, zinc powder, solvent, curing agent, and additives. The zinc powder accounts for 70% of the solid content of the zinc-rich epoxy coating. The additives include a Go / magnesium-cerium LDH composite material, which is obtained by the following method:

[0008] Magnesium salt and cerium salt are dissolved in water to form a homogeneous solution. Graphene oxide slurry is dissolved in water to form a suspension. The suspension is then added to the homogeneous solution and mixed. An alkali is added to adjust the pH. After hydrothermal reaction, Go / magnesium cerium LDH composite material is obtained.

[0009] Beneficial effects: In the Go / magnesium-cerium LDH composite material of the present invention, the magnesium-cerium LDH material can exchange the corrosion-promoting chloride ions in the zinc-rich epoxy coating to the interlayer and release the original interlayer anions, thereby reducing the corrosion damage of chloride ions to the metal substrate; the present invention uses cerium ions with corrosion-inhibiting effect as cations in the main layer of magnesium-cerium LDH, which can generate oxides and hydroxides that are deposited at the interface defects of the coating metal substrate, thus delaying the corrosion of the metal substrate; at the same time, magnesium-cerium LDH is grown in situ on graphene oxide, which regulates the electrical properties of the Go / magnesium-cerium LDH composite material, inhibits the corrosion-promoting effect of graphene, and increases the conductivity of zinc powder.

[0010] Preferably, the zinc powder is in the form of spherical particles with a particle size of 5–10 μm.

[0011] Preferably, the Go / magnesium-cerium LDH composite material accounts for 0.2% to 1.2% of the solid content of the zinc-rich epoxy coating.

[0012] Preferably, the molar ratio of magnesium salt to cerium salt is 3:1.

[0013] Preferably, the magnesium salt includes one or more of magnesium nitrate hexahydrate and magnesium chloride hexahydrate.

[0014] Preferably, the cerium salt includes one or more of cerium nitrate hexahydrate, cerium trichloride, and cerium sulfate.

[0015] Preferably, the mass ratio of graphene oxide to the total mass of magnesium and cerium salts is 1:1 to 2.

[0016] Preferably, the alkali is sodium hydroxide or potassium hydroxide.

[0017] Preferably, the pH is 9-10.

[0018] Preferably, the hydrothermal reaction temperature is 140–160°C and the hydrothermal reaction time is 20–28 h.

[0019] The second aspect of the present invention provides a method for preparing the above-mentioned zinc-rich epoxy coating, comprising the following steps: dissolving additives and epoxy resin in a solvent, adding zinc powder and stirring to mix, and then adding a curing agent and mixing evenly to finally obtain the zinc-rich epoxy coating.

[0020] Beneficial effects: The present invention adds Go / magnesium cerium LDH composite material to zinc-rich epoxy coating, which further improves the corrosion resistance of zinc-rich epoxy coating. Attached Figure Description

[0021] Figure 1 This is a transmission electron microscope image of the Go / magnesium cerium LDH composite material in Example 1 of the present invention;

[0022] Figure 2 The infrared spectrum of the Go / magnesium cerium LDH composite material in Example 1 of this invention;

[0023] Figure 3 The images show scanning electron microscope (SEM) images of the zinc-rich epoxy coatings in Example 2 and Comparative Example 1 after immersion for 60 days, where (a) is the coating of Example 2 and (b) is the coating of Comparative Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0026] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0027] Example 1

[0028] This embodiment provides a zinc-rich epoxy coating and its preparation method, specifically including the following steps:

[0029] S1 Preparation of Go / Magnesium-Cerium LDH Composite Material

[0030] 7.5g of 10mg / g graphene oxide slurry was dispersed in 75ml of deionized water and ultrasonically dispersed for 30min to obtain a graphene oxide suspension.

[0031] 0.3 mM magnesium nitrate hexahydrate and 0.1 mM cerium nitrate hexahydrate were dissolved in deionized water and stirred to form a homogeneous solution. Then, a graphene oxide suspension was added and stirred for 5 minutes. The mass ratio of graphene oxide to the total mass of magnesium nitrate hexahydrate and cerium nitrate hexahydrate was 1:1.6. NaOH was added to adjust the pH to 10 to obtain the solution.

[0032] The solution was transferred to a hydrothermal reactor and reacted at 150°C for 24 hours. After the reaction was complete, the mixture was washed with water to obtain the Go / magnesium cerium LDH composite material. Figure 1 As shown, LDH appears as a flat, two-dimensional nanostructure stacked on graphene oxide, with each small sheet exhibiting uniform unidirectional lattice lines. According to... Figure 2 As shown, low wavenumber 500cm -1 The corresponding metal -OH vibration in the layered hydroxide is at a high wavenumber of 3708 cm⁻¹. -1 A sharp free hydroxyl peak appears at this point, which is consistent with the OH group in LDH. - This indicates that LDH is uniformly grown in situ on graphene oxide.

[0033] S2 Preparation of Zinc-Rich Epoxy Coatings

[0034] Based on a solid content of 100wt% for the zinc-rich epoxy coating, the composition includes 14.9wt% epoxy resin E51, 70wt% zinc powder, 14.9wt% curing agent, and 0.2wt% Go / magnesium cerium LDH composite material; the zinc powder is spherical particles with a particle size of 5-10μm, and the curing agent is polyamide 650.

[0035] The specific process is as follows: 0.02g of Go / magnesium cerium LDH composite material and 1.49g of epoxy resin E51 are dissolved in 1g of xylene and ultrasonically stirred for 30min. Then, 7g of zinc powder is added and stirred on a magnetic stirrer for 20min. Finally, 1.49g of curing agent is added and stirred for 10min to obtain zinc-rich epoxy coating.

[0036] Example 2

[0037] This embodiment provides a zinc-rich epoxy coating and its preparation method. The difference between this embodiment and Example 1 is that in S2, the epoxy resin E51 is 14.4 wt%, the zinc powder is 70 wt%, the curing agent is 14.4 wt%, and the Go / magnesium cerium LDH composite material is 1.2 wt%. The zinc powder is spherical particles with a particle size of 5-10 μm, and the curing agent is polyamide 650.

[0038] The specific process is as follows: 0.12g of Go / magnesium cerium LDH composite material and 1.44g of epoxy resin E51 are dissolved in 1g of xylene and ultrasonically stirred for 30min. Then, 7g of zinc powder is added and stirred on a magnetic stirrer for 20min. Finally, 1.44g of curing agent is added and stirred for 10min to obtain zinc-rich epoxy coating.

[0039] Example 3

[0040] This embodiment provides a zinc-rich epoxy coating and its preparation method. The difference between this embodiment and Example 1 is that in S2, the epoxy resin E51 is 13.5 wt%, the zinc powder is 70 wt%, the curing agent is 13.5 wt%, and the Go / magnesium cerium LDH composite material is 3 wt%. The zinc powder is spherical particles with a particle size of 5-10 μm, and the curing agent is polyamide 650.

[0041] The specific process is as follows: 0.30g of Go / magnesium cerium LDH composite material and 1.35g of epoxy resin E51 are dissolved in 1g of xylene and ultrasonically stirred for 30min. Then, 7g of zinc powder is added and stirred on a magnetic stirrer for 20min. Finally, 1.35g of curing agent is added and stirred for 10min to obtain zinc-rich epoxy coating.

[0042] Example 4

[0043] This embodiment provides a zinc-rich epoxy coating and its preparation method. The difference between this embodiment and embodiment 2 is that in S1, magnesium nitrate hexahydrate is replaced with magnesium chloride hexahydrate, and the mass ratio of the graphene oxide to the total mass of magnesium chloride hexahydrate and cerium nitrate hexahydrate is 1:1.4. All other aspects are the same.

[0044] Example 5

[0045] This embodiment provides a zinc-rich epoxy coating and its preparation method. The difference between this embodiment and embodiment 2 is that in S1, cerium nitrate hexahydrate is replaced with cerium trichloride, and the mass ratio of graphene oxide to the total mass of magnesium nitrate hexahydrate and cerium trichloride is 1:1.2. All other aspects are the same.

[0046] Example 6

[0047] This embodiment provides a zinc-rich epoxy coating and its preparation method. The difference between this embodiment and embodiment 2 is that in S1, cerium nitrate hexahydrate is replaced with cerium sulfate, and the mass ratio of the graphene oxide to the total mass of magnesium nitrate hexahydrate and cerium sulfate is 1:1.8. All other aspects are the same.

[0048] Comparative Example 1

[0049] This comparative example provides a zinc-rich epoxy coating and its preparation method. The difference between this comparative example and Example 2 is that in S2, the Go / magnesium cerium LDH composite material was not added, while all other aspects are the same.

[0050] Comparative Example 2

[0051] This comparative example provides a zinc-rich epoxy coating and its preparation method. The difference between this comparative example and Example 2 is that in S2, the Go / magnesium cerium LDH composite material is replaced with graphene oxide suspension, while all other aspects are the same.

[0052] Comparative Example 3

[0053] This comparative example provides a zinc-rich epoxy coating and its preparation method. The difference between this comparative example and Example 2 is that: in S1, no graphene oxide suspension was added to obtain the LDH composite material; in S2, the Go / magnesium-cerium LDH composite material was replaced with magnesium-cerium LDH composite material, and all other aspects are the same.

[0054] Comparative Example 4

[0055] This comparative example provides a zinc-rich epoxy coating and its preparation method. The difference between this comparative example and Example 2 is that in S2, the epoxy resin E51 is 29.4 wt%, the zinc powder is 40 wt%, the curing agent is 29.4 wt%, and the Go / magnesium cerium LDH composite material is 1.2 wt%. The zinc powder is spherical particles with a particle size of 5-10 μm, and the curing agent is polyamide 650.

[0056] The specific process is as follows: 0.12g of Go / magnesium cerium LDH composite material and 2.94g of epoxy resin E51 are dissolved in 1g of xylene and ultrasonically stirred for 30min. Then, 6g of zinc powder is added and stirred on a magnetic stirrer for 20min. Finally, 2.94g of curing agent is added and stirred for 10min to obtain zinc-rich epoxy coating.

[0057] Comparative Example 5

[0058] This comparative example provides a zinc-rich epoxy coating and its preparation method. The difference between this comparative example and Example 2 is that in S2, the epoxy resin E51 is 19.4 wt%, the zinc powder is 60 wt%, the curing agent is 19.4 wt%, and the Go / magnesium cerium LDH composite material is 1.2 wt%. The zinc powder is spherical particles with a particle size of 5-10 μm, and the curing agent is polyamide 650.

[0059] The specific process is as follows: 0.12g of Go / magnesium cerium LDH composite material and 1.94g of epoxy resin E51 are dissolved in 1g of xylene and ultrasonically stirred for 30min. Then, 6g of zinc powder is added and stirred on a magnetic stirrer for 20min. Finally, 1.94g of curing agent is added and stirred for 10min to obtain zinc-rich epoxy coating.

[0060] Comparative Example 6

[0061] This comparative example provides a zinc-rich epoxy coating and its preparation method. The difference between this comparative example and Example 2 is that in S2, the epoxy resin E51 is 9.4 wt%, the zinc powder is 80 wt%, the curing agent is 9.4 wt%, and the Go / magnesium cerium LDH composite material is 1.2 wt%. The zinc powder is spherical particles with a particle size of 5-10 μm, and the curing agent is polyamide 650.

[0062] The specific process is as follows: 0.12g of Go / magnesium cerium LDH composite material and 0.94g of epoxy resin E51 are dissolved in 1g of xylene and ultrasonically stirred for 30min. Then, 8g of zinc powder is added and stirred on a magnetic stirrer for 20min. Finally, 0.94g of curing agent is added and stirred for 10min to obtain zinc-rich epoxy coating.

[0063] Comparative Example 7

[0064] This comparative example provides a zinc-rich epoxy coating and its preparation method. The difference from Example 2 is that in S1, cerium nitrate hexahydrate is replaced with aluminum nitrate monohydrate to obtain a Go / magnesium aluminum LDH composite material. All other aspects are the same.

[0065] Experimental Example

[0066] A 10×20mm tinplate substrate was pretreated by grinding it with a roughness of 600 grit to remove the oxide layer. The ground substrate was then ultrasonically removed from the surface by immersing it in anhydrous ethanol. After drying, the coatings from Examples 1-3 and Comparative Examples 1-7 were applied to the substrate surface, with a coating thickness controlled at 50μm±10μm. The coatings were then cured at 70℃ for 5 hours to obtain the final coating. The low-frequency impedance modulus of the electrochemical impedance spectroscopy was measured after immersing the coating in a 3.5wt% sodium chloride solution for 60 days; the results are shown in Table 1.

[0067] Low-frequency impedance modulus testing method: Electrochemical testing was performed using a three-electrode system of the Donghua electrochemical workstation, with the coated sample as the working electrode and a test area of ​​1 cm². 2Ag / AgCl (0.197V vs. SHE) was used as the reference electrode, and a platinum sheet was used as the counter electrode. After reaching a stable open-circuit potential, EIS tests were performed in a 3.5wt% NaCl solution under ambient conditions, with a frequency range of 10⁵ to 10⁻² Hz. Polarization curves were measured between -250 mV and +250 mV and OCP, with a potential scan rate of 0.6 mV / s.

[0068] Table 1. Examples and Comparative Examples as a function of soaking time |Z| 0.01Hz (Ω·cm 2 Numerical table

[0069]

[0070] According to Table 1, the test results of Examples 1-3 show that the coating of Example 2 has the best overall corrosion resistance. The solid content of the Go / magnesium cerium LDH composite material in the coating of Example 3 is 3%, which may agglomerate in the coating. It has the best anti-corrosion effect at 1 day, but it affects the performance of the coating in the later stage. Therefore, the overall corrosion resistance of the coating of Example 3 is not as good as that of Example 2.

[0071] Compared with the test results of Comparative Example 1, the |Z| of Example 2 is higher. 0.01Hz The increase of four orders of magnitude indicates that the addition of Go / magnesium-cerium LDH composite material greatly enhances the physical shielding effect of the zinc-rich epoxy coating and significantly improves its corrosion resistance.

[0072] Compared with the test results of Comparative Examples 2 and 3, the corrosion resistance of zinc-rich epoxy coatings modified with only graphene oxide or magnesium-cerium LDH composite material in Example 2 was not as good as that of zinc-rich epoxy coatings modified with Go / magnesium-cerium LDH composite material. This indicates that the synergistic effect of graphene oxide and magnesium-cerium LDH composite material is necessary to achieve the corrosion resistance of zinc-rich epoxy coatings.

[0073] Compared with Comparative Examples 4-6, the solid content of zinc powder in Example 2 also affected the corrosion resistance of zinc-rich epoxy coatings. This is because if the amount of zinc powder is too low, it cannot form an effective conductive path in the coating and cannot achieve the cathodic protection effect; if the zinc powder content is too high, although it can provide cathodic protection, too much zinc powder and its subsequent corrosion products will also lead to an increase in the porosity of the coating, and the expansion of corrosion products will result in a short corrosion resistance period of the coating.

[0074] Compared to Comparative Example 7, Example 2, which added Go / magnesium-aluminum LDH composite material, exhibited only moderate corrosion resistance, at least one order of magnitude lower than Example 2. Therefore, the existing conventional combination of magnesium-aluminum LDH and graphene oxide is not effective in improving the corrosion resistance of zinc-rich epoxy coatings. In Example 2, the cerium ions in the Go / magnesium-cerium LDH composite material, with their corrosion-inhibiting properties, enhance the passivation effect on metals and the adsorption of chloride ions by the plate layer, thus demonstrating the unique corrosion-enhancing effect of the Go / magnesium-aluminum LDH composite material.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A zinc-rich epoxy coating, comprising epoxy resin, zinc powder, solvent, curing agent, and additives, characterized in that, Zinc powder accounts for 70% of the solid content of the zinc-rich epoxy coating; the additives include Go / magnesium cerium LDH composite material, which is obtained by the following method: Magnesium salt and cerium salt are dissolved in water to form a homogeneous solution. Graphene oxide slurry is dissolved in water to form a suspension. The suspension is then added to the homogeneous solution and mixed. An alkali is added to adjust the pH. After hydrothermal reaction, Go / magnesium cerium LDH composite material is obtained.

2. The zinc-rich epoxy coating according to claim 1, characterized in that, Zinc powder consists of spherical particles with a particle size of 5–10 μm.

3. The zinc-rich epoxy coating according to claim 1, characterized in that, The Go / magnesium-cerium LDH composite material accounts for 0.2% to 1.2% of the solid content of the zinc-rich epoxy coating.

4. The zinc-rich epoxy coating according to claim 1, characterized in that, The molar ratio of magnesium salt to cerium salt is 3:

1.

5. The zinc-rich epoxy coating according to claim 1, characterized in that, The mass ratio of graphene oxide to the total mass of magnesium and cerium salts is 1:1 to 2.

6. The zinc-rich epoxy coating according to claim 1, characterized in that, Cerium salts include one or more of cerium nitrate hexahydrate, cerium trichloride, and cerium sulfate.

7. The zinc-rich epoxy coating according to claim 1, characterized in that, The base is sodium hydroxide or potassium hydroxide.

8. The zinc-rich epoxy coating according to claim 1, characterized in that, The pH value is 9–10.

9. The zinc-rich epoxy coating according to claim 1, characterized in that, The hydrothermal reaction temperature is 140–160℃, and the hydrothermal reaction time is 20–28 h.

10. The method for preparing the zinc-rich epoxy coating according to any one of claims 1-9, characterized in that, Includes the following steps: Additives and epoxy resin are dissolved in a solvent, zinc powder is added and stirred to mix, and then curing agent is added and mixed evenly to finally obtain zinc-rich epoxy coating.

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