A corrosion-resistant coating for metal surface and preparation method thereof

Abstract

The present invention relates to the technical field of coatings, and in particular to a corrosion-resistant coating for metal surfaces and a preparation method thereof. The raw materials of the coating include metal effect powder, water-based resin, dispersant, adhesion promoter, anticorrosive agent, defoamer, and curing agent. Preparation method: Mix the water-based resin with water, stir to obtain a resin solution; add metal effect powder and dispersant to the resin solution, stir, add adhesion promoter, anticorrosive agent, defoamer, stir to obtain a coating, add a curing agent to the coating, mix to obtain a finished product. Among them, the metal effect powder includes aluminum powder, copper powder, chromium powder, nickel powder, silver powder, gold powder, zinc-rich powder, and modified metal effect powder; modified metal effect powder: dissolve polyamide in a polymer solvent, add metal effect powder, stir and mix, and hot press to obtain modified metal effect powder. The present invention combines powder coating and water-based coating to explore a new anti-corrosion coating suitable for metals.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to a corrosion-resistant coating for metal surfaces and a preparation method thereof. Background Art

[0002] Metal materials are used in many fields, but they are easily corroded. Their performance and service life will be affected by corrosion. In order to reduce the loss, metal anti-corrosion coatings are usually applied on the surface of metal materials. Metal anti-corrosion coatings are usually solvent-based anti-corrosion coatings.

[0003] However, with the increasing requirements for environmental protection of coatings, the overall proportion of water-based coatings and powder coatings in the coatings industry is increasing compared to traditional coatings.

[0004] Water-based paint is a paint that uses water as a solvent or dispersion medium. Compared with traditional solvent-based paints, it has significant advantages such as environmental protection, low toxicity, and low volatility. However, the corrosion resistance of water-based paint needs to be improved.

[0005] Powder coating is a solvent-free coating in powder form. Metallic effect powder coating is a type of powder coating. Because of the reflection of light by metal particles, the coating surface of metallic effect powder coating can have a metallic glitter effect. Metallic effect powder coating has better corrosion resistance, but the metallic effect powder is easy to be unevenly dispersed in the coating.

[0006] In view of the foregoing, we tried to combine powder coatings and water-based coatings to explore a new anti-corrosion coating suitable for metals. Summary of the invention

[0007] In view of this, the present invention aims to provide a corrosion-resistant coating for metal surface and a preparation method thereof.

[0008] To achieve the above object, the technical solution of the present invention is achieved as follows: In a first aspect, a corrosion-resistant coating for metal surface includes the following raw materials: metal effect powder, water-based resin, dispersant, adhesion promoter, anticorrosive agent, defoaming agent, and curing agent.

[0009] It should be noted that the raw materials also include an appropriate amount of water.

[0010] Preferably, the metal effect powder includes at least one of aluminum powder, copper powder, chromium powder, nickel powder, silver powder, gold powder, zinc-rich powder, and modified metal effect powder.

[0011] Preferably, the water-based resin includes at least one of a water-based silicone-acrylic resin and a water-based polyurethane resin.

[0012] Preferred dispersants include at least one of polyacrylic acid and modified dispersants.

[0013] Preferably, the corrosion inhibitor includes at least one of zinc powder, molybdate and titanium dioxide.

[0014] Preferably, the adhesion promoter includes γ-aminopropyltriethoxysilane; the defoamer includes silicone oil; and the curing agent includes an isocyanate curing agent.

[0015] Preferably, by weight, the metal effect powder is 20-25 parts, the water-based resin is 40-70 parts, the dispersant is 1-3 parts, the adhesion promoter is 0.5-1 parts, the anticorrosive agent is 1-3 parts, the defoamer is 0.2-0.5 parts, and the curing agent is 10-30 parts.

[0016] Furthermore, the present invention provides a method for preparing modified metal effect powder, comprising the following steps: dissolving polyamide in a polymer solvent, then adding the metal effect powder, stirring evenly to obtain a mixture, and hot pressing the mixture at 200-300° C. to obtain the modified metal effect powder.

[0017] Furthermore, the present invention provides a method for preparing a modified dispersant, comprising the following steps: reacting a polyurethane monomer with oxalic acid in a DMSO solution to synthesize a modified dispersant.

[0018] In one embodiment of the present invention, the polyurethane monomer includes toluene diisocyanate.

[0019] In a second aspect, a method for preparing the aforementioned corrosion-resistant coating for metal surface comprises mixing a water-based resin with water, stirring at 25°C-50°C to obtain a resin solution; adding a metal effect powder and a dispersant to the resin solution, stirring, and then adding an adhesion promoter, an anti-corrosion agent, and a defoaming agent, stirring evenly to obtain a coating, adding a curing agent to the coating, mixing evenly to obtain a corrosion-resistant coating for metal surface.

[0020] Compared with the prior art, the present invention has the following advantages: 1. Improved dispersion of metal effect powder The metal effect powder in the prior art is easy to agglomerate, resulting in uneven coating surface, which affects the appearance and anti-corrosion performance of the coating. The present invention adopts a specific dispersant and preparation process to significantly improve the dispersibility of the metal effect powder, thereby solving the problem of uneven coating surface. This technical effect is verified by coating testing. In addition, the present invention also modifies the poor dispersibility of the metal effect powder (using modified metal effect powder), further improving the uniformity and stability of the coating.

[0021] 2. Enhance adhesion Traditional water-based paints have poor adhesion to metal surfaces due to their high water content and are prone to falling off, especially when exposed to harsh environments for a long time. In order to solve this problem, the present invention adds an adhesion promoter to the formula, enhances the adhesion between the paint and the metal surface through surface treatment, improves the firmness of the coating, and prevents the coating from falling off.

[0022] 3. Improve corrosion resistance The corrosion resistance of existing water-based coatings is poor, especially when exposed to harsh environments (such as high humidity and high temperature), the coating is prone to corrosion and shedding. In contrast, the present invention uses an anti-corrosion agent combined with the use of metal effect powder to significantly improve the corrosion resistance of the coating. By rationally proportioning these components, the present invention can effectively extend the service life of metal materials and maintain a good protective effect in a variety of corrosive environments.

[0023] 4. Improve weather resistance The present invention improves the weather resistance of the coating, especially the stability in high temperature and humid environment. The modification of the metal effect powder (through the preparation method of the modified metal effect powder) avoids the phenomenon of bubbles or rusting of the coating when exposed to environmental conditions, ensuring the stable performance of the coating during long-term use.

[0024] 5. Improve construction performance Due to its high specific gravity and viscosity, metal effect powder is usually difficult to disperse evenly in water-based paint, resulting in uneven spraying or sedimentation. In order to solve this problem, the present invention significantly improves the workability of the paint by optimizing the dispersibility of metal effect powder and dispersant, as well as optimizing the formula and preparation method of the paint. Users can perform spraying operations more easily without sedimentation or unevenness.

[0025] 6. Environmentally friendly and low toxicity The present invention modifies water-based paint and powder paint and then compounds them. Compared with traditional solvent-based paint, the present invention has lower volatile organic compound (VOC) emissions, meets current environmental protection requirements, and has less impact on the health of users. In particular, the paint of the present invention has significant advantages in some special environments (such as interior decoration, food industry, etc.).

[0026] 7. Formulation flexibility The present invention has great flexibility in the selection of metal effect powder, water-based resin, dispersant and other ingredients. By selecting different types of metal effect powder (such as aluminum powder, copper powder, nickel powder, etc.), the color effect, glossiness and anti-corrosion performance of the coating can be adjusted; at the same time, the diverse selection of water-based resins (such as water-based polyurethane resin, water-based silicone acrylic resin) can customize the performance requirements of the coating according to different usage scenarios.

[0027] In summary, the present invention shows significant improvements in the dispersibility, adhesion, corrosion resistance, construction performance, environmental protection, etc. of the anti-corrosion coating on metal surfaces compared to the prior art. By optimizing the formula and adopting advanced preparation technology, the composite coating of the present invention can meet the higher requirements for coating performance during metal surface coating and has broad application prospects.

[0028] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described in detail below. However, the present invention is not limited to the specific details in the following embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0030] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0031] Unless otherwise specified, the equipment and materials used in the examples can be easily obtained from commercial companies.

[0032] Technical problems to be solved in the present invention: 1. Poor dispersibility of metal effect powder: Metal effect powder is prone to agglomeration, resulting in uneven coating surface.

[0033] 2. Poor adhesion on metal surface: Due to the high water content of water-based paint, the adhesion between the paint and the metal surface is often insufficient, and the coating is easy to fall off.

[0034] 3. Poor corrosion resistance: Traditional water-based coatings have poor corrosion resistance, especially when exposed to harsh environments, the coating is prone to fall off or corrosion.

[0035] 4. Insufficient weather resistance: Since the surface of the metal effect powder may be reactive, the coating may fade or degrade if exposed to moisture or high temperature for a long time.

[0036] 5. Poor construction performance: Metal effect powder has a high specific gravity and viscosity, which makes it difficult to disperse evenly in water-based paint, which can easily lead to uneven spraying or sedimentation problems during the spraying process.

[0037] In order to solve the above technical problems, the present invention provides a formula of corrosion-resistant coating for metal surface: the raw materials are as follows by weight: 1. Metal effect powder: 20-25 parts, selected from: aluminum powder, copper powder, chromium powder, nickel powder, silver powder, gold powder, zinc-rich powder, modified metal effect powder.

[0038] 2. Water-based resin: 40-70 parts, selected from: water-based silicone acrylic resin, water-based polyurethane resin.

[0039] 3. Dispersant: 1-3 parts, selected from: polyacrylic acid (PAA), modified dispersant.

[0040] 4. Adhesion promoter: 0.5-1 part, selected from: γ-aminopropyltriethoxysilane.

[0041] 5. Anticorrosive agent: 1-3 parts, selected from: zinc powder, molybdate, titanium dioxide.

[0042] 6. Defoaming agent: 0.2-0.5 parts, selected from: silicone oil.

[0043] 7. Curing agent: 10-30 parts, selected from: isocyanate curing agent (HDI triisocyanate).

[0044] 8. Water: appropriate amount, preferably 30-40 parts.

[0045] Example 1 A method for preparing a corrosion-resistant coating for a metal surface, the specific steps are as follows: The water-based resin is mixed with water and stirred under high shear at 25°C-50°C to obtain a resin solution.

[0046] Add metal effect powder and dispersant to the resin solution, stir at high speed for 30-60 minutes, then add adhesion promoter, corrosion inhibitor and defoamer, stir evenly to obtain coating.

[0047] Before spraying, add curing agent to the paint and mix well to obtain corrosion-resistant paint for metal surface.

[0048] The curing agent and its matching solvent can also be mixed into a liquid in advance, and then added into the coating and mixed evenly.

[0049] Specific examples are given below, Examples 2 to 4 and Comparative Example 1.

[0050] The raw materials of Example 2-Example 4 and Comparative Example 1 are: 1. Metal effect powder: Aluminum powder and nickel powder are compounded, and the weight ratio of aluminum powder to nickel powder is 1:1.

[0051] Among them, aluminum powder, particle size: 10-20 µm, purity: 99.9%; Nickel powder: particle size: 5-15 µm, purity: 99.8%.

[0052] 2. Water-based resin: water-based polyurethane resin.

[0053] Among them, water-based polyurethane resin: HYDRAN HW-171, DIC.

[0054] 3. Dispersant: polyacrylic acid (PAA).

[0055] Wherein, polyacrylic acid: Sigma-Aldrich, concentration 35wt%.

[0056] 4. Adhesion promoter: γ-aminopropyltriethoxysilane.

[0057] Among them, γ-aminopropyltriethoxysilane: purity: 98% 5. Anticorrosion agent: zinc powder and titanium dioxide are compounded, and the weight ratio of zinc powder to titanium dioxide is 1:1.

[0058] Among them, zinc powder: particle size: 2-10 µm, purity: 99.5%; Titanium dioxide: Ti-Pure™ R-706, The Chemours Company.

[0059] 6. Defoaming agent: silicone oil.

[0060] Among them, silicone oil: PMX-200, Dow.

[0061] 7. Curing agent: isocyanate curing agent (HDI, i.e. HDI trimer curing agent).

[0062] Among them, HDI: Covestro, Desmodur N3300.

[0063] 8. Water Preparation: According to the above raw materials and the addition amounts in Table 1, the corrosion-resistant coating for metal surface was prepared using the method of Example 1.

[0064] Table 1

[0065] Detection: The anti-corrosion performance of the corrosion-resistant coating for metal surface of Examples 2-4 and Comparative Example 1 was tested by the following method: The corrosion-resistant coating for metal surface was sprayed on a 50mm×50mm×2mm stainless steel test piece, with a film thickness of 20-30μm. After spraying, it was cured at 180℃ for 30 minutes.

[0066] The cured stainless steel test piece is placed in a salt spray test chamber and tested according to GB / T 1771-2007 "Determination of neutral salt spray resistance of paints and varnishes" and the parameters are appropriately modified to conform to the present invention. The test temperature is increased to 50°C and the salt spray concentration is controlled to 5%. The test time is 500 hours, and the corrosion of the test piece is recorded every 100 hours.

[0067] After the test, the corrosion condition of the test piece is evaluated according to ASTM D714 to observe whether there is rust, bubbles, or shedding on the coating surface. The coating condition can also reflect the construction performance, adhesion, and weather resistance of the composite coating.

[0068] The results are as follows: Example 2: No rust, slight bubbling, medium bubble density.

[0069] Example 3: No rust, slight bubbling, bubble density is medium dense.

[0070] Example 4: No rust, slight bubbling, bubble density between very little and medium.

[0071] Comparative Example 1: Rust occurred, and the coating cracked and partially fell off.

[0072] Analysis: Compared with Example 2 and Example 3, the weight ratio of the metal effect powder and the water-based resin was adjusted while keeping the weight ratio of other components unchanged. The weight ratio of the metal effect powder and the water-based resin in Example 2 was 1:3, and the weight ratio of the metal effect powder and the water-based resin in Example 3 was 1:1.6.

[0073] Compared with Example 4, the weight ratio of the dispersant and the metal effect powder was adjusted while keeping the weight ratio of other components unchanged. The weight ratio of the dispersant and the metal effect powder in Example 2 was 1:10, and the weight ratio of the dispersant and the metal effect powder in Example 4 was about 1:6.7.

[0074] In Comparative Example 1, no metal effect powder was added.

[0075] By comparing with the water-based paint of Comparative Example 1, it can be seen that in the formula and preparation method of the present invention, the metal effect powder and the water-based paint are compounded to improve the corrosion resistance of the composite paint, and it is found that increasing the weight ratio of the water-based resin to the metal effect powder can further improve the corrosion resistance of the composite paint, and reducing the weight ratio of the metal effect powder to the dispersant can also further improve the corrosion resistance of the composite paint.

[0076] In general, in the formula and preparation method of the present invention, a new coating system is formed by combining the metal effect powder with the water-based resin. The water-based resin not only improves the structural properties and adhesion of the coating, but also forms a synergistic effect with the anti-corrosion effect of the metal effect powder. Specifically, the resin provides a stronger adhesion for the metal effect powder, so that it is evenly distributed on the metal surface; at the same time, the chemical structure of the resin and the metal effect powder work together to enhance the overall corrosion resistance of the coating, especially in high humidity and high temperature environments. This new synergistic effect significantly improves the comprehensive performance of the coating, which not only has a good metallic flash effect, but also can effectively prevent corrosion of the metal surface.

[0077] According to the test results, although Examples 2 to 4 did not rust, there are still areas for improvement. The present invention further improves the metal effect powder and the dispersant to see whether the blistering of the coating can be improved.

[0078] Example 5 Although aluminum powder and nickel powder have been compounded in Examples 2-4, an attempt is made to further enhance the synergistic effect of the compounded metal effect powders.

[0079] The modified metal effect powder is prepared in the following specific steps: Prepare the ingredients: 1. Metal effect powder: aluminum powder, nickel powder, titanium powder (1:1:1 weight parts compound); Among them, aluminum powder, particle size: 10-20 µm, purity: 99.9%; Nickel powder: particle size: 5-15 µm, purity: 99.8%.

[0080] Titanium powder: particle size: 15-25 µm, purity: 99.7%.

[0081] 2. Compounding agent: polymer resin (polyamide); Among them, polyamide: VESTAMID® L–polyamide 12, Evonik.

[0082] 3. Polymer solvent: benzene, purity 99%.

[0083] By weight, the raw materials are prepared: Mixed powder: 15 parts of aluminum powder, 15 parts of nickel powder and 15 parts of titanium powder are mixed evenly to obtain a mixed powder.

[0084] Adding a compounding agent: dissolve 5 parts of polyamide in 50 parts of benzene, add it to the mixed powder, stir evenly, and obtain a mixture.

[0085] Hot pressing: The mixture was hot pressed at 250°C for 2 hours to form composite powder particles to obtain modified metal effect powder.

[0086] It should be noted that the compounding method of the metal effect powder is changed in this embodiment. The compounding of different metal effect powders can give play to their respective advantages and form a synergistic effect that complements each other. The activity of aluminum can promote the dispersion of nickel and titanium, and the corrosion resistance of nickel and titanium can improve the stability of aluminum powder, so that the composite material has better comprehensive performance. Benzene helps the polyamide resin to form a stable solution in the liquid phase, reduces the viscosity of the resin, and enables the resin to better penetrate into the surface of the metal effect powder particles during the mixing process to form a good interface bonding. At the same time, under high temperature and hot pressing, the polyamide in the mixture melts into a fluid state, bonding each powder, so that the mutual bonding of the metal effect powder becomes tighter, and can avoid the agglomeration phenomenon between the powders, and form a stable particle structure, that is, a metal composite layer, to improve the mechanical strength and corrosion resistance of the powder.

[0087] Example 6 The modified dispersant is prepared in the following steps: Prepare the following ingredients: 1. Polymer monomer: polyurethane monomer (TDI, i.e. toluene diisocyanate); Among them, TDI: McLean, purity 98%.

[0088] 2. Organic acid: oxalic acid; Among them, oxalic acid: Sigma-Aldrich, purity 98%.

[0089] 3. Solvent: dimethyl sulfoxide (DMSO); Among them, dimethyl sulfoxide: purity 99%.

[0090] By weight, the raw materials are prepared: Four parts of polyurethane monomer and two parts of oxalic acid were reacted in five parts of DMSO solution, the reaction temperature was controlled at 50° C., and the reaction time was 4 hours to synthesize a modified dispersant.

[0091] It should be noted that when the modified dispersant synthesized by the present invention is added to the coating mixed with the metal effect powder, the modified dispersant can self-assemble in the coating. Through molecular self-assembly, a dispersion with a stable structure is formed, which can form a protective film in the coating system, reduce powder agglomeration, and improve the workability of the coating.

[0092] Example 7 Different from Example 2, the metal effect powder is the modified metal effect powder prepared in Example 5, and the rest is the same as Example 2.

[0093] Example 8 Different from Example 3, the metal effect powder is the modified metal effect powder prepared in Example 5, and the dispersant is the modified dispersant prepared in Example 6. The rest is the same as Example 3.

[0094] Example 9 Different from Example 4, the dispersant is the modified dispersant prepared in Example 6, and the rest is the same as Example 4.

[0095] The anti-corrosion performance of the corrosion-resistant coatings for metal surfaces of Examples 7-9 was tested with reference to the testing method of Examples 2-4, and the results are as follows: Example 7: No rust, slight bubbling, and very low bubble density.

[0096] Example 8: No rust, slight bubbling, bubble density between very little and medium.

[0097] Example 9: No rust, no obvious blistering or bubbles.

[0098] According to the results, the modification of the metal effect powder and the dispersant in the present invention can further reduce or avoid coating defects, improve the bonding strength between the composite coating and the substrate, improve the flatness of the coating under adverse conditions, and improve the comprehensive performance of the composite coating, such as corrosion resistance.

[0099] In detail, the present invention prepares modified metal effect powder. In the modification process, a polyamide dissolution process is introduced to perform modification treatment on the surface of the metal effect powder, which not only improves the dispersibility of the metal effect powder, but also enhances the compatibility between the powder and the water-based resin, further improves the bonding force between the metal effect powder and the coating matrix, thereby improving the service life and anti-corrosion effect of the composite coating.

[0100] The present invention prepares a modified dispersant. The water-based resin has strong hydrophilicity, while the surface of the metal effect powder itself is relatively hydrophobic and easily aggregated. In this case, on the one hand, the modified dispersant can adjust the affinity of the water-based resin to make the compatibility between the resin and the metal effect powder better, thereby forming a uniform coating. The addition of the modified dispersant enables the water-based resin to better disperse and wrap the metal effect powder, avoiding the sedimentation or stratification of the metal effect powder in the water-based coating. On the other hand, the modified dispersant interacts with the surface of the metal effect powder through its functional group, reduces the mutual attraction between the metal effect powders, thereby reducing the agglomeration phenomenon, and makes the metal effect powder better dispersed in the coating. This synergistic effect ensures the stability of the metal effect powder and improves the physical and chemical properties of the composite coating.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A corrosion-resistant coating for metal surface, characterized in that: Including the following raw materials: metal effect powder, water-based resin, dispersant, adhesion promoter, anticorrosive agent, defoamer, curing agent; Wherein, the metal effect powder includes at least one of aluminum powder, copper powder, chromium powder, nickel powder, silver powder, gold powder, zinc-rich powder, and modified metal effect powder; The preparation method of modified metal effect powder comprises the following steps: dissolving polyamide in a polymer solvent, then adding metal effect powder, stirring evenly to obtain a mixture, and hot pressing the mixture to obtain the modified metal effect powder.

2. The corrosion-resistant coating for metal surface according to claim 1, characterized in that: The dispersant includes at least one of polyacrylic acid and a modified dispersant.

3. The corrosion-resistant coating for metal surface according to claim 1, characterized in that: The preparation method of the modified dispersant comprises the following steps: reacting a polyurethane monomer with oxalic acid in a DMSO solution to synthesize the modified dispersant.

4. The corrosion-resistant coating for metal surface according to claim 1, characterized in that: The water-based resin includes at least one of a water-based silicone-acrylic resin and a water-based polyurethane resin.

5. The corrosion-resistant coating for metal surface according to claim 1, characterized in that: The anticorrosive agent includes at least one of zinc powder, molybdate and titanium dioxide.

6. The corrosion-resistant coating for metal surface according to claim 1, characterized in that: The adhesion promoter includes gamma-aminopropyltriethoxysilane; the defoaming agent includes silicone oil; and the curing agent includes an isocyanate curing agent.

7. The corrosion-resistant coating for metal surface according to claim 1, characterized in that: By weight, the metal effect powder is 20-25 parts, the water-based resin is 40-70 parts, the dispersant is 1-3 parts, the adhesion promoter is 0.5-1 parts, the anticorrosive agent is 1-3 parts, the defoaming agent is 0.2-0.5 parts, and the curing agent is 10-30 parts.

8. The corrosion-resistant coating for metal surface according to claim 1, characterized in that: In the preparation method of the modified metal effect powder, the hot pressing temperature is 200-300°C.

9. The corrosion-resistant coating for metal surface according to claim 3, characterized in that: Polyurethane monomers include toluene diisocyanate.

10. The method for preparing a corrosion-resistant coating for metal surface according to any one of claims 1 to 9, characterized in that: Mix water-based resin with water, stir at 25°C-50°C to obtain a resin solution; add metal effect powder and dispersant to the resin solution, stir, then add adhesion promoter, corrosion inhibitor, defoamer, stir evenly to obtain coating, add curing agent to the coating, mix evenly to obtain corrosion-resistant coating for metal surface.

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