Galvanized steel sheet silica sol composite coating and preparation process thereof

Abstract

The invention relates to the field of metal coatings, and particularly discloses a galvanized steel sheet silica sol composite coating and a preparation process thereof.The composite coating comprises a transition layer and a composite surface layer which are arranged on a galvanized steel sheet base material, and the composite surface layer is obtained by coating of coating liquid at least containing water-based acrylic emulsion, silica sol and MoS particles; the transition layer is prepared by coating a transition coating containing nano aluminum oxide, a dispersing agent, a silane coupling agent and water-borne epoxy resin; the preparation process comprises the following steps: S1, cleaning a galvanized steel sheet base material, coating the galvanized steel sheet base material with a transition coating, and primarily curing to form a transition layer; s2, mixing a water-based acrylic emulsion, silica sol and MoS particles, and stirring to prepare a coating solution; and S3, the transition layer is coated with the coating liquid and then cured again, and the composite coating is prepared. The preparation method has the characteristic that the scratch resistance and wear resistance of the coating are further improved on the basis that the prepared water-based paint realizes low VOC (volatile organic compound) emission.

Description

Technical Field

[0001] This application relates to the field of metal coatings, and more specifically, to a silica sol composite coating for galvanized steel sheets and its preparation process. Background Technology

[0002] In the field of metal surface treatment and protection, galvanized steel sheets are widely used in various industries such as construction, automobile manufacturing, and home appliance production due to their excellent corrosion resistance. Traditional galvanized steel sheet surface coatings mostly use solvent-based paints. Although these paints can provide a certain degree of protection, they have significant environmental and performance defects.

[0003] More specifically, solvent-based coatings release large amounts of volatile organic compounds (VOCs) during the coating and drying processes. These VOC emissions not only cause serious environmental pollution and affect air quality, but may also harm human health, such as causing respiratory diseases and nervous system damage. With increasing global environmental awareness and increasingly stringent environmental regulations, reducing VOC emissions has become an urgent problem for the surface treatment industry.

[0004] Secondly, traditional solvent-based coatings have relatively low hardness and poor scratch resistance. During transportation, installation, and use, the surface of galvanized steel sheets is easily scratched by friction and collision, which not only affects the appearance but may also reduce the protective effect of the coating and shorten the service life of the product.

[0005] Based on the aforementioned shortcomings of traditional solvent-based coatings, water-based coatings have gradually gained attention due to their advantages such as low VOC emissions and good environmental performance. However, water-based coatings alone still struggle to meet the demands of high-end applications in terms of hardness and abrasion resistance. Therefore, developing water-based coatings based on water-based resins for use on galvanized steel sheets to achieve low VOC emissions is crucial for improving environmental performance. Furthermore, improving the scratch resistance and abrasion resistance of the coating is of great significance for meeting high-performance requirements. Summary of the Invention

[0006] In order to obtain water-based coatings that achieve low VOC emissions and further improve the scratch resistance and wear resistance of the coating, this application provides a silica sol composite coating for galvanized steel sheets and its preparation process.

[0007] In a first aspect, this application provides a silica sol composite coating for galvanized steel sheet, which adopts the following technical solution: a silica sol composite coating for galvanized steel sheet, comprising a transition layer and a composite surface layer disposed on a galvanized steel sheet substrate, wherein the composite surface layer is obtained by coating liquid containing at least an aqueous acrylic emulsion, silica sol and MoS2 particles; The transition layer is made by coating with a transition coating containing nano-alumina, dispersant, silane coupling agent and waterborne epoxy resin.

[0008] By adopting the above technical solution, the composite surface layer in this application uses water-based acrylic emulsion as the film-forming matrix. As a water-based coating, it significantly reduces VOC emissions, meeting environmental protection requirements. Furthermore, it provides excellent water resistance, weather resistance, and flexibility. The carboxyl groups in its molecular chain form hydrogen bonds with the hydroxyl groups on the silica sol surface, enhancing their compatibility. The silica sol in the composite surface layer is formed by dispersing nano-silica particles in water. Its surface contains a large number of silanol groups, which can chemically react with zinc oxide or hydroxyl groups on the galvanized steel sheet surface to form Si-O-Zn chemical bonds. Simultaneously, the silanol groups of the silica sol can also crosslink with the carboxyl groups in the water-based acrylic emulsion, forming a dense Si-O-Si network structure, significantly improving the wear resistance and hardness of the coating. This dual chemical bonding significantly enhances the interfacial adhesion between the coating and the substrate. Furthermore, the MoS2 in the composite surface layer has a layered crystal structure with an extremely low interlayer friction coefficient, forming a lubricating film on the coating surface, enabling it to withstand repeated friction without easily breaking. Its high hardness also resists scratches from microparticles. Further improve the wear resistance and scratch resistance of the composite coating.

[0009] Furthermore, in this application, the transition layer uses waterborne epoxy resin as the film-forming base. Its epoxy groups can form certain bonds with the substrate, and it also exhibits excellent wettability for nano-alumina and silane coupling agents, thus improving the adhesion between the transition layer and the substrate. The long-chain structure of the epoxy resin can encapsulate the nano-alumina, forming a dense transition layer. Moreover, the waterborne epoxy resin has low viscosity and good permeability, allowing it to penetrate deep into the substrate to form a mechanical bond. Simultaneously, it works synergistically with the silane coupling agent to enhance the density of the transition layer. The epoxy resin has strong cohesion, high hardness after curing, and good wear resistance, enabling it to withstand better loads or friction. The high viscosity of the nano-alumina... The hardness characteristic can directly improve the scratch resistance of the coating and significantly increase its hardness. Moreover, the uniform distribution of nano-alumina particles in the transition layer coating forms a "pinning effect," which can effectively resist material peeling during friction and improve its wear resistance. One end of the silane coupling agent is bonded to the nano-alumina and the silica sol in the composite surface layer, and the other end can form a chemical bond with the metal substrate, which significantly improves the adhesion between the coating and the substrate. In addition, it can also achieve a bridging effect between nano-alumina and water-based epoxy resin, improving the interfacial bonding strength. The final composite coating has better comprehensive properties such as hardness and wear resistance.

[0010] Optionally, the transition layer comprises component A and component B in a mass ratio of 1:(1-1.2), wherein component A comprises the following parts by weight of raw materials: 65-75 parts waterborne epoxy resin, 8-15 parts nano-alumina, 2-5 parts silane coupling agent, 0.5-1 part dispersant, and 20-30 parts... Water and 8-15 parts ethanol; Component B includes a curing agent.

[0011] By adopting the above technical solution, the film-forming material of the transition layer in this application is mainly water-based epoxy resin, while acrylic emulsion has better toughness but slightly insufficient hardness and wear resistance. In this application, by distributing the film-forming materials of the transition layer and the surface layer, a gradient structure from hard to soft is formed. The hard transition layer bears the initial impact force, and the tough surface layer disperses stress through plastic deformation, avoiding local stress that causes the coating to peel off, thus improving the coating durability. Moreover, compared with a single coating that is prone to brittle peeling, the gradient structure distribution coating in this application significantly improves the scratch resistance under the same hardness.

[0012] Optionally, the transition coating is prepared by the following method: Add nano-alumina to half water, add dispersant, and ultrasonically disperse for 20-30 minutes to obtain a pre-dispersion. Mix the silane coupling agent with ethanol and the remaining water, adjust the pH to 4-5, hydrolyze for 10-15 minutes, add the pre-dispersion solution, then add the waterborne epoxy resin, stir, and obtain component A. A transition coating is prepared by mixing component A and component B.

[0013] Optionally, the composite surface layer comprises the following raw materials in parts by weight: The mixture contains 60-70 parts of water-based acrylic emulsion, 20-30 parts of silica sol, and 8-15 parts of MoS2 particles, wherein the solid content of the silica sol is 20-30%, and the particle size of the silica sol is 30-50 nm.

[0014] By adopting the above technical solution, the composite surface layer uses water-based acrylic emulsion as the film-forming material, in which silica sol is dispersed in the matrix. It can be directly anchored on the zinc plate surface by Si-O-Zn bonds, or it can form chemical bonds with the transition layer. At the same time, it crosslinks with acrylic resin through Si-OC bonds to form a three-dimensional network structure, thereby improving the performance of the composite coating.

[0015] Optionally, MoS2 particles can be added to the composite surface after modification, as detailed below: 1) Add molybdenum disulfide particles to water and ultrasonically disperse for 20-30 minutes to form a suspension; 2) Add hexadecyltrimethylammonium bromide solution to the suspension, heat to 40-50℃, stir for 1.5-2.5h, then centrifuge, wash with alcohol, and dry to obtain modified MoS2 particles.

[0016] By adopting the above technical solution, this application uses hexadecyltrimethylammonium bromide to modify molybdenum disulfide. As an amphiphilic surfactant, after dissociation in aqueous solution, its quaternary ammonium salt with integer dots is adsorbed onto the negatively charged surface of molybdenum disulfide due to edge sulfur vacancies or defect sites through electrostatic interaction, forming a physical adsorption layer on the surface of molybdenum disulfide. Its hydrophobic chains reduce the problem of molybdenum disulfide agglomeration. At the same time, since the molecular size of hexadecyltrimethylammonium bromide is smaller than the interlayer spacing of molybdenum disulfide, the above treatment will not destroy its layered structure and retain its self-lubricating properties. In this way, it ultimately helps to improve the uniform dispersion of molybdenum disulfide in aqueous acrylic emulsion, prevent agglomeration, retain the layered structure of molybdenum disulfide, form a lubricating film, reduce the coefficient of friction and directly reduce wear, and improve the wear resistance of the composite coating.

[0017] Optionally, during the MoS2 particle modification process, the mass ratio of molybdenum disulfide particles to water is 1:(6-8); the mass concentration of the hexadecyltrimethylammonium bromide solution is 2-5wt%, and the amount of hexadecyltrimethylammonium bromide added is 5-10wt% of the mass of the molybdenum disulfide particles.

[0018] By adopting the above technical solution, the thickness of the molybdenum disulfide surface coating can be controlled by controlling the amount added. This will not affect its layer structure and will prevent particle agglomeration, which will help it to be evenly dispersed in the water-based acrylic emulsion matrix and better perform its function of enhancing wear resistance.

[0019] Optionally, in the process of modifying MoS2 particles, after adding hexadecyltrimethylammonium bromide solution in step 2), the mixture is stirred at 40-50℃ for 1-2 hours, then cooled to room temperature, and then methyl vinyl ether-maleic anhydride copolymer is added, and the process is continued. The amount of methyl vinyl ether-maleic anhydride copolymer added is 3-5 wt% of the molybdenum disulfide particles.

[0020] By adopting the above technical solution, although the molybdenum disulfide particles are modified in this application, their dispersibility in aqueous acrylic emulsion is improved through electrostatic interaction and hydrophobic chain action. However, on the one hand, the high ionic strength in the aqueous emulsion leads to unstable electrostatic adsorption, resulting in desorption of both particles. On the other hand, the polarity mismatch between the long-chain alkanes and the aqueous acrylic emulsion affects their dispersion stability.

[0021] Therefore, this application also includes a methyl vinyl ether-maleic anhydride copolymer, which is adsorbed onto the surface of modified molybdenum disulfide. The electrostatic interaction between its carboxylic acid groups and the cationic quaternary ammonium salt forms an electric double layer structure, improving dispersion stability. More importantly, its hydrophilic groups combine with the polar groups of the aqueous acrylic emulsion through hydrogen bonding and other interactions, while the hydrophobic groups interact with the alkyl chains of hexadecyltrimethylammonium bromide to form a transition layer, reducing interfacial tension and enhancing the compatibility between the two. Furthermore, its maleic anhydride groups can also undergo ring-opening reactions with the sulfur vacancies on the surface of molybdenum disulfide or the amino groups in hexadecyltrimethylammonium bromide to form chemical bonds, further improving the bonding strength and ultimately further enhancing its wear resistance and scratch resistance.

[0022] Optionally, the composite surface material may also include 2-5 parts of ethylenediamine.

[0023] By adopting the above technical solution, ethylenediamine, as a diamino functional group, can form chemical bonds with functional groups such as carboxyl groups on the surface of molybdenum disulfide modified with methyl vinyl ether-maleic anhydride, and can also form certain chemical bonds with acrylic emulsion and silica sol, thereby helping to form a cross-linked network structure of the composite coating and further improving its wear resistance and other properties.

[0024] Secondly, this application provides a preparation process for a silica sol composite coating on galvanized steel sheet, employing the following technical solution: A process for preparing a silica sol composite coating on galvanized steel sheet includes the following steps: S1. After cleaning the galvanized steel sheet substrate, a transition coating is applied, and then it is initially cured to form a transition layer; S2. Mix and stir the aqueous acrylic emulsion, silica sol and MoS2 particles to obtain the coating liquid; S3. After applying the coating liquid onto the transition layer, it is cured again to form a composite surface layer, thus obtaining a composite coating.

[0025] By adopting the above technical solution, the method in this application is simple and convenient.

[0026] Optionally, the initial curing temperature in step S1 is 75-85℃, and the curing time is 20-30 min; The curing parameters in step S3 are as follows: first, cure at 60-70℃ for 30-40 minutes, then raise the temperature to 90-100℃ for 20-30 minutes, and then continue to raise the temperature to 120-130℃ for 5-10 minutes.

[0027] By adopting the above technical solution, the surface acrylic resin is cross-linked and cured through high-temperature heating treatment. The uniform dispersion of silica sol particles in the resin matrix forms a dense network structure through heating and curing, thereby improving wear resistance.

[0028] In summary, this application has the following beneficial effects: 1. In this application, waterborne acrylic emulsion and waterborne epoxy resin are used as film-forming substrates, which significantly reduces VOC emissions and is more environmentally friendly. At the same time, silica sol, as a nano-scale silica aqueous dispersion, crosslinks with the carboxyl groups in the waterborne acrylic emulsion to form a dense Si-O-Si network structure, which significantly improves the wear resistance and hardness of the coating. 2. In this application, molybdenum disulfide is modified by hexadecyltrimethylammonium bromide, which helps to improve the uniform dispersion of molybdenum disulfide in aqueous acrylic emulsions, prevents agglomeration, and retains the layered structure of molybdenum disulfide to form a lubricating film, reduce the coefficient of friction and directly reduce wear, and improve the wear resistance of the composite coating. After treatment with methyl vinyl ether-maleic anhydride copolymer, a transition bridging effect is formed, reducing interfacial tension and improving the compatibility of molybdenum disulfide with the aqueous acrylic emulsion system, without affecting its interlayer structure, improving its dispersion stability and compatibility, and improving its wear resistance. Detailed Implementation

[0029] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0030] In the following examples, the dispersant used is BYK-190, the silane coupling agent used is KH-550, and the particle size of the nano-alumina is 20-50nm. The methyl vinyl ether-maleic anhydride copolymer selected is the methyl vinyl ether-maleic anhydride copolymer from Jiangsu Runfeng Synthetic Technology Co., Ltd. The water-based acrylic emulsion selected is from Shandong Baoda New Materials Co., Ltd. The solid content of silica sol is 20-30%, and the colloidal particle size of silica sol is 30-50nm, which means that the mass ratio of silica in silica sol is 20-30%, and the remainder is water. The waterborne epoxy resin selected is Baling Petrochemical's CYDW-100 bisphenol A type waterborne epoxy resin, and the corresponding curing agent is CYDHD-280 curing agent.

[0031] The following description is based on specific embodiments.

[0032] Example 1 A process for preparing a silica sol composite coating on galvanized steel sheet includes the following steps: S1. Preparation of transition coating: Add 10 kg of nano alumina to 12 kg of water, add 0.8 kg of dispersant BYK-190, and ultrasonically disperse (ultrasonic power of 200 W) for 25 min to obtain a pre-dispersion. Mix 3 kg of silane coupling agent KH-550 with 10 kg of ethanol and 12 kg of water, adjust the pH to 4.5, hydrolyze for 12 min, add the pre-dispersion solution, then add 70 kg of waterborne epoxy resin, stir and obtain component A; Using CYDHD-280 curing agent as component B, the transition coating was prepared by mixing components A and B at a mass ratio of 1:1.1. Coating: After cleaning the galvanized steel sheet substrate, the prepared transition coating is sprayed onto the surface of the cleaned galvanized steel sheet substrate, and then cured at 80℃ for 25 minutes to form a transition layer with a thickness of 10μm. S2. Mix 65kg of aqueous acrylic emulsion, 25kg of silica sol and 10kg of MoS2 particles and stir to obtain a coating liquid. S3. After spraying the coating liquid onto the transition layer, it is cured again. The curing parameters are as follows: first, cure at 65℃ for 35 minutes, then heat to 95℃ for 25 minutes, and continue to heat to 125℃ for 8 minutes to form a 3μm composite surface layer, thus obtaining the composite coating.

[0033] Example 2 A process for preparing a silica sol composite coating on galvanized steel sheet includes the following steps: S1. Preparation of transition coating: Add 8 kg of nano alumina to 10 kg of water, add 0.5 kg of dispersant BYK-190, and ultrasonically disperse (ultrasonic power of 200W) for 20 min to obtain a pre-dispersion. Mix 2 kg of silane coupling agent KH-550 with 8 kg of ethanol and 10 kg of water, adjust the pH to 4, hydrolyze for 10 min, add the pre-dispersion liquid, then add 65 kg of waterborne epoxy resin, stir and obtain component A. Using CYDHD-280 curing agent as component B, and mixing component A and component B at a mass ratio of 1:1, a transition coating was prepared. Coating: After cleaning the galvanized steel sheet substrate, the prepared transition coating is sprayed onto the surface of the cleaned galvanized steel sheet substrate, and then cured at 75°C for 30 minutes to form a transition layer with a thickness of 8μm. S2. Mix 60 kg of aqueous acrylic emulsion, 20 kg of silica sol and 8 kg of MoS2 particles and stir to obtain a coating liquid. S3. After spraying the coating liquid onto the transition layer, it is cured again. The curing parameters are as follows: first, cure at 60℃ for 40 minutes, then heat to 90℃ for 30 minutes, and then continue to heat to 120℃ for 10 minutes to form a 2μm composite surface layer, thus obtaining the composite coating.

[0034] Example 3 A process for preparing a silica sol composite coating on galvanized steel sheet includes the following steps: S1. Preparation of transition coating: Add 15 kg of nano alumina to 15 kg of water, add 1 kg of dispersant BYK-190, and ultrasonically disperse (ultrasonic power of 200 W) for 30 min to obtain a pre-dispersion. Mix 5 kg of silane coupling agent KH-550 with 15 kg of ethanol and 15 kg of water, adjust the pH to 5, hydrolyze for 15 min, add the pre-dispersion liquid, then add 75 kg of waterborne epoxy resin, stir and obtain component A. Using CYDHD-280 curing agent as component B, the transition coating was prepared by mixing components A and B at a mass ratio of 1:1.2. Coating: After cleaning the galvanized steel sheet substrate, the prepared transition coating is sprayed onto the surface of the cleaned galvanized steel sheet substrate, and then cured at 85℃ for 20 minutes to form a transition layer with a thickness of 12μm. S2. Mix 70 kg of aqueous acrylic emulsion, 30 kg of silica sol and 15 kg of MoS2 particles and stir to obtain a coating liquid. S3. After spraying the coating liquid onto the transition layer, it is cured again. The curing parameters are as follows: first, cure at 70℃ for 30 minutes, then heat to 100℃ for 20 minutes, and continue to heat to 130℃ for 5 minutes to form a 5μm composite surface layer, thus obtaining the composite coating.

[0035] Example 4 A process for preparing a silica sol composite coating on galvanized steel sheet is carried out according to the method in Example 1, except that the MoS2 particles in the coating solution are added after modification in step S2. The specific operation is as follows: 1) Add molybdenum disulfide particles to water at a mass ratio of 7 and disperse ultrasonically (ultrasonic power of 80W) for 25 minutes to form a suspension; 2) Add a 3 wt% hexadecyltrimethylammonium bromide solution (water as solvent) to the suspension, heat to 45°C, stir for 1.5 h, cool to room temperature, add methyl vinyl ether-maleic anhydride copolymer, continue stirring for 30 min, then centrifuge, wash three times with alcohol, and dry to obtain modified MoS2 particles. The amount of hexadecyltrimethylammonium bromide added is 8 wt% of the mass of molybdenum disulfide particles, and the amount of methyl vinyl ether-maleic anhydride copolymer added is 4 wt% of the mass of molybdenum disulfide particles.

[0036] Example 5 A process for preparing a silica sol composite coating on galvanized steel sheet is carried out according to the method in Example 1, except that the MoS2 particles in the coating solution are added after modification in step S2. The specific operation is as follows: 1) Add molybdenum disulfide particles to 6 times their mass of water and ultrasonically disperse (ultrasonic power of 80W) for 20 minutes to form a suspension; 2) Add a 2 wt% hexadecyltrimethylammonium bromide solution (water as solvent) to the suspension, heat to 40°C, stir for 2 hours, cool to room temperature, add methyl vinyl ether-maleic anhydride copolymer, continue stirring for 30 minutes, centrifuge, wash three times with alcohol, and dry to obtain modified MoS2 particles. The amount of hexadecyltrimethylammonium bromide added is 5 wt% of the mass of molybdenum disulfide particles, and the amount of methyl vinyl ether-maleic anhydride copolymer added is 3 wt% of the molybdenum disulfide particles.

[0037] Example 6 A process for preparing a silica sol composite coating on galvanized steel sheet is carried out according to the method in Example 1, except that the MoS2 particles in the coating solution are added after modification in step S2. The specific operation is as follows: 1) Add molybdenum disulfide particles to water at 8 times their mass and disperse ultrasonically (ultrasonic power of 80W) for 30 minutes to form a suspension; 2) Add a 5 wt% hexadecyltrimethylammonium bromide solution (water as solvent) to the suspension, heat to 50°C, stir for 1 hour, cool to room temperature, add methyl vinyl ether-maleic anhydride copolymer, continue stirring for 30 minutes, then centrifuge, wash three times with alcohol, and dry to obtain modified MoS2 particles. The amount of hexadecyltrimethylammonium bromide added is 10 wt% of the mass of molybdenum disulfide particles, and the amount of methyl vinyl ether-maleic anhydride copolymer added is 5 wt% of the mass of molybdenum disulfide particles.

[0038] Example 7 A process for preparing a silica sol composite coating for galvanized steel sheet is carried out according to the method in Example 4, except that methyl vinyl ether-maleic anhydride copolymer is not added in step 2).

[0039] Example 8 A process for preparing a silica sol composite coating for galvanized steel sheet is carried out according to the method in Example 4, except that 4 kg of ethylenediamine is added to the coating liquid raw material in step S2.

[0040] Example 9 A process for preparing a silica sol composite coating for galvanized steel sheet is carried out according to the method in Example 4, except that 2 kg of ethylenediamine is added to the coating liquid raw material in step S2.

[0041] Example 10 A process for preparing a silica sol composite coating for galvanized steel sheet is carried out according to the method in Example 4, except that 5 kg of ethylenediamine is added to the coating liquid raw material in step S2.

[0042] Comparative Example 1 A process for preparing a silica sol composite coating for galvanized steel sheet is carried out according to the method in Example 1, except that silica sol is not added to the coating liquid raw material in step S2.

[0043] Comparative Example 2 A process for preparing a silica sol composite coating for galvanized steel sheet is carried out according to the method in Example 1, except that MoS2 particles are not added to the coating liquid raw material in step S2.

[0044] Comparative Example 3 A process for preparing a silica sol composite coating on galvanized steel sheet is carried out according to the method in Example 1, except that step S1 is not performed. Instead, the coating liquid is directly sprayed onto the galvanized steel sheet substrate to form a composite surface layer with a thickness of 13 μm.

[0045] Comparative Example 4 A process for preparing a silica sol composite coating for galvanized steel sheet is carried out according to the method in Example 1, except that in step S1, the waterborne epoxy resin in the transition coating is replaced by an equal amount of waterborne acrylic emulsion, and the transition coating only includes component A and does not contain component B.

[0046] Performance testing The composite coatings obtained in the above embodiments and comparative examples were tested for abrasion resistance, scratch resistance, and hardness. Abrasion resistance was assessed using the Taber abrasion test according to ASTM D4060. A Taber abrasion tester was used to abrade the coating surface under a specified load of 500g by rotating an abrasion wheel. The number of rotations required for the coating to reach a specific wear level (wear thickness of 10μm) was calculated; a higher number of rotations indicated better abrasion resistance. Scratch resistance was assessed using a scratch tester. The load was gradually increased on the coating surface until a visible scratch appeared. The minimum load at which a scratch appeared was recorded as the scratch strength; a higher load indicated better scratch resistance. The results are shown in Table 1 below.

[0047] Table 1: Referring to the test results in Table 1 above, the composite coating prepared in this embodiment exhibits excellent wear resistance, good scratch resistance, and good protective performance. Furthermore, as a water-based coating, it significantly reduces VOC emissions, making it more environmentally friendly. Combining the test results of Examples 1-3, the cross-linking effect of silica sol and water-based acrylic emulsion in the composite surface layer, as well as the lubricating and hardening effects of molybdenum disulfide particles, result in a high number of rotational revolutions, indicating good wear resistance and high scratch load resistance, demonstrating excellent scratch resistance. Combining the test results of Examples 1 and 4-6, when molybdenum disulfide particles are modified with hexadecyltrimethylammonium bromide and methyl vinyl-maleic anhydride copolymer, the dispersion stability and compatibility of molybdenum disulfide in aqueous acrylic emulsion are improved, further enhancing its wear resistance and scratch resistance. In Example 7, without modification with methyl vinyl ether-maleic anhydride copolymer, the compatibility of molybdenum disulfide particles is affected, resulting in a decrease in its wear resistance and scratch resistance compared to Example 4. Combining the test results of Examples 8-10, when ethylenediamine is added to the coating liquid of the composite surface, it helps to form a denser cross-linked network structure, improving wear resistance and scratch resistance.

[0048] Referring to the test results of Example 1 and Comparative Example 1, the wear resistance and scratch resistance were significantly reduced when no silica sol was added. In Comparative Example 2, the wear resistance and scratch resistance were also reduced when no molybdenum disulfide particles were added. Combining the test results of Comparative Example 3, the wear resistance and scratch resistance were also reduced when no transition layer treatment was performed. Combining the test results of Comparative Example 4, the adhesion was reduced when water-based acrylic emulsion was used instead of water-based acrylic emulsion in the transition layer, which also affected the wear resistance and scratch resistance. The distribution of film-forming substrates with different hardness in the transition layer and the surface layer in this application helps to improve both the adhesion and the wear resistance and scratch resistance.

[0049] In addition, the composite coating obtained in the embodiments of this application was tested for adhesion, hardness and corrosion resistance. The test results are shown in Table 2. The adhesion was tested according to GB / T 9286 by cross-cut test, and the corrosion resistance was tested according to ASTM B117 by neutral salt spray test.

[0050] Table 2: Performance testing Adhesion / Grade Hardness / H Corrosion resistance / h Example 1 Level 1 4 960 Example 2 Level 1 4 910 Example 3 Level 1 4 945 Example 4 Level 0 4 1050 Example 5 Level 0 4 1000 Example 6 Level 0 4 1030 Example 7 Level 0 3 980 Example 8 Level 0 4 1140 Example 9 Level 0 4 1100 Example 10 Level 0 4 1120 Comparative Example 1 Level 2 1 500 Comparative Example 2 Level 2 1 550 Comparative Example 3 Level 3 1 400 Comparative Example 4 Level 2 2 600 Referring to the test results in Table 1 above, the composite coating prepared in this embodiment has good bonding with the galvanized steel plate substrate and has excellent hardness and corrosion resistance.

[0051] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A silicasol composite coating for a zinc-coated steel sheet, characterized in that, The coating includes a transition layer and a composite surface layer, the composite surface layer is coated by a coating liquid containing water-based acrylic emulsion and silica sol and MoS2 particles; The transition layer is coated by a transition coating containing nano-alumina, dispersant and silane coupling agent and water-based epoxy resin.

2. A silicasol composite coating for a zinc-coated steel sheet according to claim 1, characterized in that: The transition layer is made of A component and B component with a mass ratio of 1: (1-1.2), wherein the A component includes the following raw materials by weight: 65-75 parts of water-based epoxy resin, 8-15 parts of nano-alumina, 2-5 parts of silane coupling agent, 0.5-1 part of dispersant, 20-30 parts of water and 8-15 parts of ethanol, and the B component includes a curing agent.

3. A silicasol composite coating for a zinc-coated steel sheet according to claim 2, characterized in that: The transition coating is made by the following method: The nano-alumina is added into half of the water, the dispersant is added, and the pre-dispersion liquid is prepared by ultrasonic dispersion for 20-30 min; The silane coupling agent is mixed with ethanol and the remaining water, the pH is adjusted to 4-5, the pre-dispersion liquid is added after hydrolysis for 10-15 min, and then the water-based epoxy resin is added, and the A component is prepared after stirring; The A component and the B component are mixed to prepare the transition coating.

4. The silicasol composite coating of a galvanized steel sheet according to claim 1, characterized in that: The composite surface layer includes the following raw materials by weight: 60-70 parts of water-based acrylic emulsion, 20-30 parts of silica sol and 8-15 parts of MoS2 particles, wherein the solid content of the silica sol is 20-30%, and the particle size of the silica sol is 30-50 nm.

5. The silicasol composite coating of a galvanized steel sheet according to claim 1, characterized in that: The MoS2 particles are added after modification in the composite surface layer, and the specific operation is as follows: 1) The molybdenum disulfide particles are added into water and ultrasonic dispersed for 20-30 min to form a suspension; 2) The cetyltrimethylammonium bromide solution is added into the suspension, heated to 40-50℃, stirred for 1.5-2.5 h, then centrifuged, alcohol washed and dried to obtain modified MoS2 particles.

6. A silicasol composite coating for a zinc-coated steel sheet according to claim 5, characterized in that: In the modification process of MoS2 particles, the mass ratio of molybdenum disulfide particles to water is 1: (6-8); the mass concentration of the cetyltrimethylammonium bromide solution is 2-5 wt%, and the addition amount of cetyltrimethylammonium bromide is 5-10 wt% of the mass of molybdenum disulfide particles.

7. A silicasol composite coating for a zinc-coated steel sheet according to claim 5, characterized in that: In the modification process of MoS2 particles, after adding the cetyltrimethylammonium bromide solution in step 2) and stirring at 40-50℃ for 1-2 h, the temperature is lowered to room temperature, then the methyl vinyl ether-maleic anhydride copolymer is added, and the stirring is continued, and the addition amount of methyl vinyl ether-maleic anhydride copolymer is 3-5 wt% of the mass of molybdenum disulfide particles.

8. The silicasol composite coating of a galvanized steel sheet according to claim 1, characterized in that: The raw materials of the composite surface layer also include 2-5 parts of ethylenediamine.

9. Process for the production of a silicasol composite coating for a zinc-coated steel sheet according to any one of claims 1 to 8, characterized in that: The method includes the following steps: S1, the galvanized steel plate substrate is cleaned and coated with a transition coating, then preliminary curing is performed to form a transition layer; S2, the water-based acrylic emulsion, silica sol and MoS2 particles are mixed and stirred to prepare a coating liquid; S3, the coating liquid is coated on the transition layer and cured again to form a composite surface layer, and a composite coating is prepared.

10. Process for the production of a silicasol composite coating for a zinc-coated steel sheet according to claim 9, characterized in that: The preliminary curing temperature in step S1 is 75-85℃, and the curing time is 20-30 min; The curing parameters in step S3 are: first curing at 60-70°C for 30-40 min, then heating to 90-100°C for 20-30 min, and further heating to 120-130°C for 5-10 min.

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