Alumina-based passivation paint, alumina-based passivation coating and application of alumina-based passivation paint

Abstract

The invention provides an aluminum oxide-based passivation coating, an aluminum oxide-based passivation coating and application of the aluminum oxide-based passivation coating and the aluminum oxide-based passivation coating, and belongs to the technical field of metal surface treatment. According to the invention, acrylic acid-polyurethane composite resin or acrylic acid-epoxy composite resin is used as water-based resin, so that an alumina-based passivation coating formed after the alumina-based passivation coating is cured can be endowed with good strength and wear resistance; the silane coupling modified nanometer aluminum oxide is adopted, the dispersity of the nanometer aluminum oxide in the aluminum oxide-based passivation coating can be improved, silanol groups contained in the silane coupling modified nanometer aluminum oxide can be subjected to hydrogen bond combination with hydroxyl on the surface of the nanometer aluminum oxide, and a silicon-oxygen chain is formed; the hydrophobic property of an aluminum oxide-based passivation coating formed after the aluminum oxide-based passivation coating is cured is enhanced, the adhesive force with stainless steel is improved, and then the surface hardness, wear resistance and corrosion resistance of the aluminum oxide-based passivation coating are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal surface treatment, and in particular to an alumina-based passivation coating, an alumina-based passivation layer and their applications. Background Art

[0002] Due to its good corrosion resistance and mechanical properties, stainless steel is widely used in many fields. However, when used under harsh conditions such as high humidity and high acidity or alkalinity, pitting, peeling and other phenomena will occur on the surface of stainless steel, reducing the service life of stainless steel. By strengthening the surface of stainless steel and forming a passivation layer on the surface of stainless steel, the surface properties such as surface hardness and corrosion resistance can be improved, and the service life can be extended.

[0003] At present, a related patent discloses an alumina epoxy protective layer. This alumina epoxy protective layer is obtained by adding alumina particles to an epoxy coating to obtain a passivation coating, spraying the passivation coating on the steel surface, and obtaining an alumina epoxy protective layer attached to the steel surface after curing, and the wear resistance of the alumina epoxy protective layer is improved by using the high hardness of the alumina particles. However, although the alumina particles have high hardness, the bonding effect between the alumina particles and the epoxy coating is poor, resulting in greater brittleness of the alumina epoxy protective layer and easy cracking, and further resulting in poor anti-corrosion performance of the alumina epoxy protective layer; moreover, the thermal expansion coefficients of the alumina particles and the steel do not match, resulting in poor interfacial bonding force between the alumina epoxy protective layer and the steel, and easy peeling in high temperature or alternating hot and cold environments.

[0004] Therefore, there is an urgent need to provide an alumina-based passivation coating that can obtain a coating with high adhesion, good wear resistance and corrosion resistance to stainless steel. Summary of the Invention

[0005] The purpose of the present invention is to provide an alumina-based passivation coating, an alumina-based passivation layer and their applications. The alumina-based passivation coating provided by the present invention can obtain a coating with high adhesion, good wear resistance and corrosion resistance to stainless steel.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides an alumina-based passivation coating, which comprises the following components in parts by weight: 8-40 parts of a water-based resin, 1-5 parts of silane-coupling modified nano-alumina, 0.01-4 parts of an anti-rust agent, 0.01-3 parts of a zirconium salt cross-linking agent, 0.1-2 parts of an auxiliary agent, and 10-20 parts of deionized water;

[0008] The water-based resin includes an acrylic-polyurethane composite resin or an acrylic-epoxy composite resin.

[0009] Preferably, the acrylic-polyurethane composite resin is obtained by mixing a polyurethane resin emulsion and an acrylic resin emulsion; the mass ratio of the polyurethane resin emulsion to the acrylic resin emulsion is 1:1;

[0010] The polyurethane resin emulsion is obtained by polymerizing a polymerization system including a polyol, an isocyanate, a catalyst, a hydrophilic chain extender, a hydrophobic chain extender, a neutralizing agent, an organic solvent, and deionized water;

[0011] The acrylic resin emulsion is obtained by polymerizing a polymerization system including an acrylic monomer, an emulsifier, an initiator, a buffer, a chain transfer agent, and deionized water.

[0012] Preferably, the polyol includes a polyether polyol or a polyester polyol.

[0013] Preferably, the isocyanate includes isophorone diisocyanate or hexamethylene diisocyanate.

[0014] Preferably, the acrylic monomer is methyl methacrylate, butyl acrylate, acrylic acid, and 2-hydroxyethyl acrylate.

[0015] Preferably, the silane-coupled modified nano-aluminum oxide is nano-α-aluminum oxide modified by a silane coupling agent; the silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and phenylaminomethyltrimethoxysilane.

[0016] Preferably, the rust inhibitor includes one or more of metaphosphate, orthophosphate, and metavanadate.

[0017] Preferably, the auxiliary agent includes a stabilizer and / or a surfactant.

[0018] The present invention also provides an alumina-based passivation coating, which is obtained by drying and curing the alumina-based passivation coating material according to the above technical solution.

[0019] The present invention also provides the application of the alumina-based passivation coating material or the alumina-based passivation coating according to the above technical solution as a stainless steel protective layer.

[0020] The present invention provides an alumina-based passivation coating, which comprises the following components by weight parts: 8-40 parts of a waterborne resin, 1-5 parts of silane-coupling modified nano-alumina, 0.01-4 parts of a rust inhibitor, 0.01-3 parts of a zirconium salt crosslinking agent, 0.1-2 parts of an auxiliary agent, and 10-20 parts of deionized water; the waterborne resin comprises an acrylic-polyurethane composite resin or an acrylic-epoxy composite resin. By using the acrylic-polyurethane composite resin or the acrylic-epoxy composite resin as the waterborne resin, the present invention can endow the alumina-based passivation coating formed after curing with good strength and wear resistance; the present invention adopts silane-coupling modified nano-alumina, which can not only improve the dispersibility of nano-alumina in the alumina-based passivation coating, and moreover, since the silanol groups contained in the silane-coupling modified nano-alumina can form hydrogen bonds with the hydroxyl groups on the surface of the nano-alumina to form a silicon-oxygen chain, the hydrophobic property of the alumina-based passivation coating formed after curing of the alumina-based passivation coating can be enhanced, the adhesion to stainless steel can be improved, and the surface hardness, wear resistance and corrosion resistance of the alumina-based passivation coating can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the test result of the electrochemical corrosion resistance test of different surfaces of the present invention;

[0022] Figure 2 It is the test result of the surface hardness of different surfaces of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention provides an alumina-based passivation coating, which comprises the following components by weight parts: 8-40 parts of a waterborne resin, 1-5 parts of silane-coupling modified nano-alumina, 0.01-4 parts of a rust inhibitor, 0.01-3 parts of a zirconium salt crosslinking agent, 0.1-2 parts of an auxiliary agent, and 10-20 parts of deionized water;

[0024] The waterborne resin comprises an acrylic-polyurethane composite resin or an acrylic-epoxy composite resin.

[0025] In the present invention, unless otherwise specified, the raw materials used in the present invention are all commercially available products well known in the art.

[0026] By weight parts, the alumina-based passivation coating provided by the present invention comprises 8-40 parts of a waterborne resin. As an embodiment of the present invention, the weight parts of the waterborne resin can be 8 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts or 40 parts. In the present invention, the waterborne resin comprises an acrylic-polyurethane composite resin or an acrylic-epoxy composite resin. By using the acrylic-polyurethane composite resin or the acrylic-epoxy composite resin as the waterborne resin, the present invention can endow the alumina-based passivation coating formed after curing with good strength and wear resistance.

[0027] In the present invention, the acrylic-polyurethane composite resin is preferably obtained by mixing a polyurethane resin emulsion and an acrylic resin emulsion.

[0028] In the present invention, the mass ratio of the polyurethane resin emulsion to the acrylic resin emulsion is preferably 1:1.

[0029] In the present invention, the polyurethane resin emulsion is preferably obtained by polymerizing a polymerization system comprising a polyol, an isocyanate, a catalyst, a hydrophilic chain extender, a hydrophobic chain extender, a neutralizing agent, an organic solvent, and deionized water.

[0030] In the present invention, the polyol preferably includes a polyether polyol or a polyester polyol. In the present invention, the polyether polyol is preferably one or more of polybutylene glycol (PTMG), polytetrahydrofuran ether diol (PTMEG), polypropylene glycol (PPG), and polyethylene glycol (PEG); the polyester polyol is preferably one or more of polybutyl acrylate (PBA), polyethylene adipate (PEA), polycaprolactone diol (PCL), and polycarbonate diol (PCD). By using the above polyols in the present invention, the polyurethane resin can have good flexibility and strength.

[0031] In the present invention, the isocyanate preferably includes isophorone diisocyanate or hexamethylene diisocyanate. By using the above isocyanate in the present invention, the mechanical properties of the polyurethane resin can be improved.

[0032] In the present invention, the catalyst is preferably dibutyltin dilaurate (DBTDL). By using a catalyst in the present invention, the efficiency of the polymerization reaction can be improved.

[0033] In the present invention, the hydrophobic chain extender is preferably a diol or a diamine, the diol is preferably 1,4-butanediol (BDO), and the diamine is preferably ethylenediamine (EDA). In the present invention, the hydrophilic chain extender is preferably dimethylolpropionic acid (DMPA) or dimethylolbutyric acid (DMBA). By adding a hydrophilic chain extender and a hydrophobic chain extender in the present invention, the molecular structure of the polyurethane resin can be regulated, and the mechanical properties and flexibility of the polyurethane resin can be improved.

[0034] In the present invention, the neutralizing agent is preferably triethylamine (TEA). In the present invention, the neutralizing agent is added to neutralize carboxylic acid.

[0035] In the present invention, the organic solvent preferably includes acetone or N-methylpyrrolidone (NMP). By adding an organic solvent in the present invention, the viscosity of the reaction system can be adjusted.

[0036] In the present invention, the deionized water is used to disperse and emulsify the polymerization system.

[0037] In the present invention, the mass ratio of the polyol, isocyanate, catalyst, hydrophilic chain extender, hydrophobic chain extender, neutralizing agent, organic solvent and deionized water is preferably (100 - 120):(40 - 50):(0.1 - 0.3):(10 - 11):(5 - 6):(7 - 8):(50 - 60):300, more preferably (110 - 120):(45 - 50):(0.2 - 0.3):(10 - 11):(5 - 6):(7 - 8):(55 - 60):300. By controlling the mass ratio of the polyol, isocyanate, catalyst, hydrophilic chain extender, hydrophobic chain extender, neutralizing agent, organic solvent and deionized water within the above range, the present invention can enable the raw materials to react fully to form a polyurethane resin emulsion.

[0038] In the present invention, the solid content of the polyurethane resin emulsion is preferably 30 - 40%, more preferably 35 - 40%.

[0039] In the present invention, the preparation method of the polyurethane resin emulsion preferably includes: mixing the polyol, isocyanate and catalyst, and carrying out a prepolymerization reaction under nitrogen protection to obtain an NCO - terminated prepolymer;

[0040] After mixing the NCO - terminated prepolymer with the organic solvent, first mix it with the hydrophilic chain extender for the first chain - extension reaction, then mix it with the hydrophobic chain extender for the second chain - extension reaction, and finally mix it with the neutralizing agent to obtain a polymer solution;

[0041] Mix the polymer solution with deionized water for emulsification to obtain a polyurethane resin emulsion.

[0042] The present invention preferably mixes the polyol, isocyanate and catalyst, and carries out a prepolymerization reaction under nitrogen protection to obtain an NCO - terminated prepolymer.

[0043] The present invention preferably dehydrates the polyol under vacuum first, and then mixes it with the isocyanate and catalyst. In the present invention, the temperature of the vacuum dehydration is preferably 65 - 85°C, more preferably 70 - 80°C; the time of the vacuum dehydration is preferably 1 - 2 h. The present invention removes the water in the polyol through vacuum dehydration.

[0044] The present invention has no special limitation on the method of mixing the polyol, isocyanate and catalyst, and it is only necessary to mix the three evenly.

[0045] In the present invention, the temperature of the prepolymerization reaction is preferably 75 - 85°C, more preferably 80 - 85°C; the time of the prepolymerization reaction is preferably 2 - 4 h, more preferably 3 - 4 h. Under the above temperature and time, and under nitrogen protection, the present invention can enable the polyol and isocyanate to react fully under the action of the catalyst to obtain an NCO - terminated prepolymer.

[0046] After obtaining the NCO-terminated prepolymer, the present invention preferably mixes the NCO-terminated prepolymer with an organic solvent, first mixes it with a hydrophilic chain extender for the first chain extension reaction, then mixes it with a hydrophobic chain extender for the second chain extension reaction, and finally mixes it with a neutralizing agent for a neutralization reaction to obtain a polymer solution.

[0047] By mixing the NCO-terminated prepolymer with an organic solvent, the present invention can adjust the viscosity of the NCO-terminated prepolymer, making the subsequent reaction more conducive to full progress.

[0048] In the present invention, the temperature of the first chain extension reaction is preferably 75-85°C, more preferably 80-85°C; the time of the first chain extension reaction is preferably 1-2 h.

[0049] In the present invention, the temperature of the second chain extension reaction is preferably 40-50°C, more preferably 45-50°C; the time of the second chain extension reaction is preferably 0.5-2 h.

[0050] In the present invention, the temperature of the neutralization reaction is preferably 25-40°C, more preferably 0.5-1 h. The present invention neutralizes the carboxylic acid in the system through the neutralization reaction.

[0051] After obtaining the polymer solution, the present invention mixes the polymer solution with deionized water for emulsification to obtain a polyurethane resin emulsion.

[0052] The present invention has no special limitation on the emulsification method, and a conventional emulsification method can be used to fully emulsify the polymer solution.

[0053] The present invention preferably distills and filters the emulsified system to obtain a polyurethane resin emulsion. The present invention has no special limitation on the distillation and filtration methods, and conventional distillation and filtration methods can be used to reduce the solvent in the emulsified system. The present invention can adjust the solid content of the polyurethane resin emulsion through distillation and filtration to make it reach 30-40%.

[0054] In the present invention, the acrylic resin emulsion is preferably obtained by polymerizing a polymerization system including acrylic monomers, emulsifiers, initiators, buffers, chain transfer agents, and deionized water.

[0055] In the present invention, the acrylic monomers are preferably methyl methacrylate (MMA), butyl acrylate (BA), acrylic acid (AA), and 2-hydroxyethyl acrylate (HEA), and the mass ratio of methyl methacrylate, butyl acrylate, acrylic acid, and 2-hydroxyethyl acrylate is preferably (30-50):(20-40):(3-10):(3-10), more preferably 40:30:5:5. By using the above acrylic monomers, the present invention is more conducive to obtaining a polyacrylic resin with good mechanical properties.

[0056] In the present invention, the emulsifier preferably includes sodium dodecyl sulfate (SDS) and / or alkylphenol polyoxyethylene ether (OP-10). By adding the emulsifier, the present invention can solubilize acrylic monomers and also enable the polyacrylic acid resin obtained from the polymerization reaction to have good dispersibility.

[0057] In the present invention, the initiator is preferably ammonium persulfate (APS). By adding the initiator, the present invention can initiate the polymerization reaction.

[0058] In the present invention, the buffer is preferably sodium bicarbonate. By adding the buffer, the present invention can improve the efficiency of the polymerization reaction.

[0059] In the present invention, the chain transfer agent is preferably dodecyl mercaptan (DDM). By adding the chain transfer agent, the present invention can regulate the molecular weight of the polypropylene resin and improve the properties of the polypropylene resin.

[0060] In the present invention, the deionized water serves as the reaction solvent.

[0061] In the present invention, the mass ratio of the acrylic monomer, emulsifier, initiator, buffer, chain transfer agent and deionized water is preferably (70 - 90):(2 - 5):(0.3 - 1.0):(0.2 - 0.5):(0.1 - 0.5):(150 - 250), more preferably 80:3:0.5:0.3:0.2:200.

[0062] In the present invention, the method for preparing the acrylic resin emulsion preferably includes: mixing deionized water, emulsifier, buffer, acrylic monomer and chain transfer agent to obtain a mixed emulsion;

[0063] Adding an initiator solution dropwise to the mixed emulsion and carrying out a polymerization reaction to obtain an acrylic resin emulsion.

[0064] The present invention has no special limitation on the method of mixing the deionized water, emulsifier, buffer, acrylic monomer and chain transfer agent, as long as the components can be mixed evenly to form a stable emulsion. In the examples of the present invention, the method of mixing the deionized water, emulsifier, buffer, acrylic monomer and chain transfer agent is preferably stirring, the rotation speed of the stirring is preferably 1000 - 1500 rpm, more preferably 1200 - 1500 rpm; the stirring time is preferably 20 - 60 min, more preferably 30 min.

[0065] After obtaining the mixed emulsion, the present invention preferably adds an initiator solution dropwise to the mixed emulsion and carries out a polymerization reaction to obtain an acrylic resin emulsion.

[0066] In the present invention, the mass concentration of the initiator solution is preferably 5-15%, more preferably 8-10%.

[0067] In the present invention, the temperature of the mixed emulsion is preferably 75-80 °C, more preferably 78-80 °C. By controlling the temperature of the mixed emulsion within the above range in the present invention, a polymerization reaction can occur as soon as the initiator solution is dropped into the mixed emulsion.

[0068] The present invention has no special limitation on the specific dropping speed, as long as the temperature of the reaction system can be maintained at 80-85 °C. By maintaining the temperature of the reaction system at 80-85 °C during dropping in the present invention, it is possible to prevent insufficient polymerization reaction caused by overly violent reaction.

[0069] In the present invention, the heat preservation temperature of the polymerization reaction is preferably 80-85 °C, more preferably 82-85 °C; the heat preservation time of the polymerization reaction is preferably 1.5-3 h, more preferably 2 h. In the present invention, the heat preservation temperature and heat preservation time of the polymerization reaction refer to the heat preservation carried out after the dropping of the initiator solution is completed. By controlling the heat preservation temperature and heat preservation time of the polymerization reaction in the present invention, it is possible to completely polymerize the acrylic monomers.

[0070] The present invention preferably filters the system obtained after the polymerization reaction to obtain an acrylic resin emulsion. The present invention has no special limitation on the filtering method, and a conventional filtering method can be used as long as the acrylic resin emulsion can be separated from deionized water. In the present invention, the solid content of the acrylic resin emulsion is preferably 30-50%, more preferably 30-45%.

[0071] In the present invention, the preparation method of the acrylic-polyurethane composite resin preferably includes mixing a polyurethane resin emulsion and an acrylic resin emulsion to obtain an acrylic-polyurethane composite resin.

[0072] In the present invention, the mass ratio of the polyurethane resin emulsion to the acrylic resin emulsion is preferably 1:1.

[0073] In the present invention, the method of mixing the polyurethane resin emulsion and the acrylic resin emulsion is preferably constant temperature oscillation, the temperature of the constant temperature oscillation is preferably 25-40 °C, more preferably 30-35 °C; the time of the constant temperature oscillation is preferably 4-8 h, more preferably 6 h.

[0074] Based on 8 to 40 parts by weight of the water-based resin, the alumina-based passivation coating provided by the present invention includes 1 to 5 parts of silane-coupling modified nano-alumina. As an embodiment of the present invention, the weight parts of the silane-coupling modified nano-alumina can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts. By adding silane-coupling modified nano-alumina, the present invention can not only improve the dispersion of nano-alumina in the alumina-based passivation coating; moreover, since the silanol groups in the silane-coupling modified nano-alumina form hydrogen bonds with the hydroxyl groups on the surface of nano-alumina to form siloxane chains, it can enhance the adhesion between the alumina-based passivation coating formed after curing of the alumina-based passivation coating and stainless steel, and improve the surface hardness, wear resistance and corrosion resistance of the alumina-based passivation coating.

[0075] In the present invention, the silane-coupling modified nano-alumina is preferably nano-α-alumina modified by a silane coupling agent; the silane coupling agent preferably includes one or more of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, phenylaminomethyltrimethoxysilane, and more preferably γ-aminopropyltriethoxysilane.

[0076] In the present invention, the preparation method of the silane-coupling agent modified nano-α-alumina preferably includes:

[0077] Mix α-alumina, ethanol and water to obtain a preliminary α-alumina dispersion;

[0078] Mix the preliminary α-alumina dispersion with a dispersant and a surfactant to obtain an α-alumina dispersion;

[0079] Mix the α-alumina dispersion and a silane coupling agent for silane modification to obtain silane-coupling agent modified nano-α-alumina.

[0080] The present invention preferably mixes α-alumina, ethanol and water to obtain a preliminary α-alumina dispersion.

[0081] In the present invention, the particle size of the α-alumina is preferably 20 to 100 nm, more preferably 30 to 50 nm.

[0082] In the present invention, the volume ratio of ethanol to water is preferably 3:1 to 1:1, more preferably 2:1 to 1.5:1.

[0083] In the present invention, the mass ratio of α-alumina to the total volume of ethanol and water is preferably (1 to 3) g:(10 to 30) mL, more preferably 2 g:20 mL.

[0084] In the present invention, the method of mixing α-aluminum oxide, ethanol, and water is preferably constant-temperature shaking. The temperature of the constant-temperature shaking is preferably 40-50 °C, more preferably 45-50 °C; the time of the constant-temperature shaking is preferably 6-8 h, more preferably 7-8 h.

[0085] After obtaining the preliminary α-aluminum oxide dispersion, the present invention preferably mixes the preliminary α-aluminum oxide dispersion with a dispersant and a surfactant to obtain an α-aluminum oxide dispersion.

[0086] In the present invention, the dispersant is preferably polyvinylpyrrolidone (PVP). The percentage of the dispersant in the total mass of the α-aluminum oxide dispersion is preferably 0.5-0.8%, more preferably 0.6-0.7%.

[0087] In the present invention, the surfactant is preferably sodium dodecylbenzenesulfonate. The percentage of the surfactant in the total mass of the α-aluminum oxide dispersion is preferably 0.2-0.5%, more preferably 0.3-0.4%.

[0088] In the present invention, the method of mixing the preliminary α-aluminum oxide dispersion with a dispersant and a surfactant is preferably constant-temperature shaking. The temperature of the constant-temperature shaking is preferably 40-50 °C, more preferably 45-50 °C; the time of the constant-temperature shaking is preferably 5-8 h, more preferably 5-7 h.

[0089] The present invention preferably filters the mixture obtained by constant-temperature shaking through a microporous filter to remove various undispersed solid impurities, thereby obtaining an α-aluminum oxide dispersion. In the present invention, the pore diameter of the microporous filter is preferably 0.2-1.0 μm, more preferably 0.45-0.8 μm.

[0090] After obtaining the α-aluminum oxide dispersion, the present invention preferably mixes the α-aluminum oxide dispersion with a silane coupling agent for silane modification to obtain silane-coupling-agent-modified nano-α-aluminum oxide.

[0091] In the present invention, the method of mixing the α-aluminum oxide dispersion with a silane coupling agent is preferably constant-temperature shaking. The temperature of the constant-temperature shaking is preferably 40-50 °C, more preferably 45-50 °C; the time of the constant-temperature shaking is preferably 10-16 h, more preferably 12 h.

[0092] The present invention preferably filters and dries the mixture obtained by constant-temperature shaking to obtain silane-coupling-agent-modified nano-aluminum oxide. The present invention has no special limitation on the methods of filtration and drying. Any conventional filtration and drying methods can be used as long as the silane-coupling-agent-modified nano-aluminum oxide can be sufficiently dried.

[0093] Based on the weight of the aqueous resin being 8 to 40 parts, the alumina-based passivation coating provided by the present invention includes 0.01 to 4 parts of a rust inhibitor. As an embodiment of the present invention, the weight of the rust inhibitor can be 0.01 part, 0.5 part, 1 part, 2 parts, 3 parts, 4 parts or 5 parts. The present invention can improve the rust prevention effect by adding a rust inhibitor.

[0094] In the present invention, the rust inhibitor preferably includes one or more of metaphosphate, orthophosphate and metavanadate, and more preferably metaphosphate. In the examples of the present invention, the metaphosphate can be sodium metaphosphate.

[0095] Based on the weight of the aqueous resin being 8 to 40 parts, the alumina-based passivation coating provided by the present invention includes 0.01 to 3 parts of a zirconium salt crosslinking agent. As an embodiment of the present invention, the weight of the zirconium salt crosslinking agent can be 0.01 part, 0.05 part, 0.5 part, 1 part, 2 parts or 3 parts. The present invention can promote the crosslinking and curing of the aqueous resin by adding a zirconium salt crosslinking agent. In the present invention, the zirconium salt crosslinking agent preferably includes ammonium zirconium carbonate or potassium zirconium carbonate.

[0096] Based on the weight of the aqueous resin being 8 to 40 parts, the alumina-based passivation coating provided by the present invention includes 0.1 to 2 parts of an additive. In the present invention, the additive preferably includes a stabilizer and / or a surfactant. In the present invention, the stabilizer preferably includes sodium citrate or sodium tetraborate; the surfactant preferably includes at least one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate and disodium hexadecylsulfophenoxybenzenesulfonate. The present invention can improve the stability and activity of the alumina-based passivation coating through the additive.

[0097] Based on the weight of the aqueous resin being 8 to 40 parts, the alumina-based passivation coating provided by the present invention includes 10 to 20 parts of deionized water. As an embodiment of the present invention, the weight of the water can be 10 parts, 12 parts, 15 parts, 18 parts or 20 parts. The present invention uses deionized water as a dispersion medium.

[0098] In the present invention, the pH value of the alumina-based passivation coating is preferably 7.5 to 9.5, and more preferably 8 to 9. The present invention controls the pH value of the alumina-based passivation coating within the above range, which is more conducive to rapid curing.

[0099] The present invention also provides a preparation method of the alumina-based passivation coating described in the above technical solution, including: mixing an aqueous resin, silane-coupled modified nano-alumina, a rust inhibitor, a zirconium salt crosslinking agent, an additive and deionized water to obtain the alumina-based passivation coating.

[0100] The present invention has no special limitation on the method of mixing the aqueous resin, silane coupling agent modified nano-aluminum oxide, rust inhibitor, zirconium salt crosslinking agent, auxiliary agent and deionized water, as long as each component can be mixed evenly to form a dispersion-stable alumina-based passivation coating. In the present invention, the method of mixing the aqueous resin, silane coupling agent modified nano-aluminum oxide, rust inhibitor, zirconium salt crosslinking agent, auxiliary agent and deionized water is preferably stirring.

[0101] The present invention also provides an alumina-based passivation coating, which is obtained by drying and curing the alumina-based passivation coating according to the above technical solution.

[0102] In the present invention, the method of drying and curing preferably includes high-temperature curing and low-temperature curing in sequence. In the present invention, the temperature of the high-temperature curing is preferably 70-100 °C, more preferably 80-90 °C; the time of the high-temperature curing is preferably 30-120 s, more preferably 40-60 s. In the present invention, the temperature of the low-temperature curing is preferably 25-60 °C, more preferably 40-50 °C; the time of the low-temperature curing is preferably 24-72 h, more preferably 48 h. By performing high-temperature curing and low-temperature curing in sequence, the present invention is more conducive to the full crosslinking and curing of the alumina-based passivation coating.

[0103] The present invention also provides the application of the alumina-based passivation coating according to the above technical solution or the alumina-based passivation coating according to the above technical solution as a stainless steel protective layer.

[0104] In the present invention, the method of applying the alumina-based passivation coating as a stainless steel protective layer is preferably as follows:

[0105] After the stainless steel is cleaned, pretreated stainless steel is obtained;

[0106] The alumina-based passivation coating is coated on the surface of the pretreated stainless steel and dried and cured.

[0107] In the present invention, the method of cleaning the stainless steel is preferably to oscillate and clean the stainless steel plate with ethanol and an alkaline degreasing agent, and then rinse and dry it with deionized water. The present invention has no special limitation on the type of the alkaline degreasing agent, and a conventional alkaline degreasing agent can be selected as long as it can fully remove the grease on the surface of the stainless steel. In the present invention, by mass percentage, the components of the alkaline degreasing agent can be: sodium hydroxide (NaOH) 1-5%, sodium carbonate (Na2CO3) 3-8%, trisodium phosphate (Na3PO4) 2-6% and the balance deionized water. In the present invention, the temperature of the oscillating cleaning is preferably 25-65 °C, more preferably 25-65 °C; the time of the oscillating cleaning is preferably 15-20 min, more preferably 18-20 min; the time of rinsing with deionized water is preferably 5-20 s, and the drying method is hot air drying.

[0108] In the present invention, the coating method is preferably a roll coating method or a dip coating method. The present invention does not have special limitations on the specific operation methods of the roll coating method or the dip coating method. Using conventional roll coating methods or dip coating methods can form a coating layer with uniform thickness on the surface of the pretreated stainless steel. In the present invention, the coating amount of the coating layer is preferably 0.5 - 3 g / m 2 , more preferably 1 - 2 g / m 2 .

[0109] By using acrylic - polyurethane composite resin or acrylic - epoxy composite resin as the water - based resin in the present invention, it can endow the alumina - based passivation coating formed after curing of the alumina - based passivation coating with good strength and wear resistance; the present invention uses silane - coupling - modified nano - alumina to improve the surface hardness, wear resistance and corrosion resistance of the alumina - based passivation coating. Therefore, using the alumina - based passivation coating provided by the present invention for the stainless steel protective layer can significantly improve the corrosion resistance and wear resistance of the stainless steel surface.

[0110] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0111] The preparation method of the acrylic - polyurethane composite resin used in the embodiments of the present invention is as follows: The polyurethane resin emulsion and the acrylic resin emulsion are mixed at a mass ratio of 1:1 and shaken at a constant temperature of 30 °C for 6 h to obtain an acrylic - polyurethane composite resin emulsion;

[0112] The preparation method of the polyurethane resin emulsion is as follows: Add 100 polyether polyol PTMG into the reaction kettle, dehydrate under vacuum at 70 °C for 1.5 h, then add 45 g of isocyanate IPDI and 0.2 g of catalyst dibutyltin dilaurate DBTDL, and react at 80 °C for 3 h under nitrogen protection to obtain an NCO - terminated prepolymer; Add 55 g of acetone to the NCO - terminated prepolymer to adjust the viscosity; Then add 10.5 g of hydrophilic chain extender DMPA and continue to react for 1.5 h, then cool down to 45 °C, add 5.5 g of hydrophobic chain extender BDO, and react until the NCO content reaches the standard (NCO standard value: 2.0% - 2.5%); Subsequently, add 7.5 g of neutralizing agent triethylamine TEA to neutralize the carboxyl group, then slowly add 300 g of deionized water, emulsify at 1200 rpm for 30 min, and finally remove acetone in the solution by vacuum distillation, filter and adjust the solid content to 35% to obtain an aqueous polyurethane emulsion.

[0113] The preparation method of the acrylic resin emulsion is as follows: Add 200 g of deionized water, emulsifiers (2 g of SDS, 1 g of OP-10), and buffer (0.3 g of sodium bicarbonate) into a 500 mL three-necked flask, and stir evenly. Mix the monomers (40 g of MMA, 30 g of BA, 5 g of AA, 5 g of HEA), add a chain transfer agent (0.2 g of DDM), stir evenly, then transfer it into the three-necked flask and stir at a high speed of 1200 rpm for 30 min to form a stable mixed emulsion. Dissolve the initiator (0.5 g of APS) in deionized water to prepare an initiator solution. Add the pre-emulsion into the three-necked flask equipped with a stirrer, thermometer and condenser, heat up to 78 °C, slowly dropwise add the initiator solution, control the dropping rate to keep the reaction temperature at 82 °C. After the initiator is completely dropped, keep the reaction at a constant temperature for 2 h. After the reaction is completed, cool it to room temperature, filter to obtain the acrylic resin emulsion with a solid content of 30%.

[0114] The preparation method of the γ-aminopropyltriethoxysilane-modified nano-α-aluminum oxide used in the examples of the present invention is as follows: Weigh 2 g of α-aluminum oxide powder (30 - 50 nm), add it into 20 mL of ethanol aqueous solution (15 mL of ethanol, 5 mL of water), use a constant temperature stirrer to continuously stir at 45 °C, then transfer it into a constant temperature shaker and oscillate at the same temperature of 45 °C for 7 h to obtain a preliminary dispersion of α-aluminum oxide; Add 0.6% of PVP dispersant and 0.3% of sodium dialkylbenzenesulfonate into the preliminary dispersion of α-aluminum oxide, continue to oscillate for 5 h, and filter it with a microporous filter to remove various undispersed solid impurities. The filtered liquid is the dispersion of α-aluminum oxide. Mix the dispersion of α-aluminum oxide with 10 mL of silane coupling agent KH550 (γ-aminopropyltriethoxysilane), and oscillate at a constant temperature for 12 h to obtain a dispersion of γ-aminopropyltriethoxysilane-modified nano-α-aluminum oxide, and obtain γ-aminopropyltriethoxysilane-modified nano-α-aluminum oxide after filtration and drying.

[0115] Example 1

[0116] An alumina-based passivation coating, by weight, the components are: 40 parts of acrylic-polyurethane composite resin, 5 parts of γ-aminopropyltriethoxysilane-modified α-nano-aluminum oxide, 0.5 part of rust inhibitor (sodium metaphosphate), 0.1 part of ammonium zirconium carbonate, 0.1 part of sodium citrate, 0.05 part of sodium dodecyl sulfate, and 20 parts of deionized water;

[0117] The preparation method of the alumina-based passivation coating is as follows: First, add the γ-aminopropyltriethoxysilane-modified nano-α-aluminum oxide into the acrylic-polyurethane composite resin, stir with a magnetic stirrer, and then sequentially add the self-healing rust inhibitor sodium metaphosphate, the zirconium salt cross-linking agent ammonium zirconium carbonate, the auxiliary agent sodium citrate and sodium dodecyl sulfate to obtain the alumina-based passivation coating.

[0118] Example 2

[0119] An alumina-based passivation coating, by weight, consists of: 30 parts of acrylic-polyurethane composite resin, 3 parts of α-nano alumina modified by γ-aminopropyltriethoxysilane, 0.4 part of rust inhibitor (sodium metaphosphate), 0.2 part of ammonium zirconium carbonate, 0.15 part of sodium citrate, 0.1 part of sodium dodecyl sulfate, and 15 parts of deionized water.

[0120] Example 3

[0121] An alumina-based passivation coating, by weight, consists of: 35 parts of acrylic-polyurethane composite resin, 4 parts of α-nano alumina modified by γ-aminopropyltriethoxysilane, 0.3 part of rust inhibitor (sodium metaphosphate), 0.3 part of ammonium zirconium carbonate, 0.2 part of sodium citrate, 0.15 part of sodium dodecyl sulfate, and 20 parts of deionized water.

[0122] Comparative Example 1

[0123] An alumina-based passivation coating, by weight, consists of: 30 parts of acrylic-polyurethane composite resin, 2 parts of α-nano alumina, 0.3 part of ammonium zirconium carbonate, 0.03 part of sodium citrate, 0.03 part of sodium dodecyl sulfate, and 15 parts of deionized water.

[0124] Comparative Example 2

[0125] An alumina-based passivation coating, by weight, consists of: 35 parts of acrylic-polyurethane composite resin, 1 part of α-nano alumina, 0.5 part of ammonium zirconium carbonate, 0.05 part of sodium citrate, 0.05 part of sodium dodecyl sulfate, and 5 parts of deionized water.

[0126] Test Example

[0127] After treating the 304 stainless steel plates of the same specification with the passivation coating according to the passivation method, performance tests were carried out: The stainless steel was oscillated and cleaned with ethanol and alkaline degreaser, and then rinsed with deionized water and dried. The temperature of the oscillating cleaning was 25 °C; the time of the oscillating cleaning was 15 min; the time of the deionized water rinsing was 20 s, and the drying method was hot air drying to obtain pretreated stainless steel;

[0128] The alumina-based passivation coating was coated on the surface of the pretreated stainless steel, and the coating amount of the coating layer was preferably 1.5 g / m 2 , and dried and cured: taken out after drying at 80 °C for 40 s and left standing for 48 h.

[0129] (1) Electrochemical corrosion resistance test: Figure 1 The test results of the electrochemical corrosion resistance test for different surfaces are shown.Figure 1 Among them, chromium-plated stainless steel represents the stainless steel blank plate, the chromium-free passivation film represents the resin passivation film formed by coating acrylic-polyurethane, and the alumina passivation film represents the alumina-based passivation coating formed after curing the alumina-based passivation coating prepared in Example 1. From Figure 1 it can be seen that from the chromium-plated stainless steel plate to the chromium-free passivation film and then to the alumina passivation film, its corrosion potential gradually increases, the self-corrosion current gradually decreases, the cathodic reaction and anodic reaction are gradually inhibited, and the corrosion resistance effect of the film layer continuously increases.

[0130] (2) Figure 2 The following are the hardness test results of different surfaces, which are tested and evaluated using a Vickers hardness tester. In Figure 2 it, the uncoated film refers to the blank stainless steel plate, the ordinary passivation film refers to the passivation film formed by only coating the water-based acrylic-polyurethane passivation solution, and the alumina passivation film refers to the alumina-based passivation coating formed after curing the alumina-based passivation coating prepared in Example 1. From Figure 2 it can be seen that the alumina-based passivation coating formed after curing the alumina-based passivation coating prepared in the present invention has a relatively high hardness.

[0131] (3) Coating stability test: The performance of the alumina-based passivation coatings formed after curing the alumina-based passivation coatings prepared in Examples 1 to 3 was tested. The stability of the alumina-based passivation coatings was measured by the sedimentation method. The lower the sedimentation volume percentage of the coating solution, the higher the stability.

[0132] (4) Surface adhesion: The test and rating standards were evaluated with reference to GB / T9286-1998 "Cross-Cutting Test for Paints and Varnishes Films", and the corrosion-resistant neutral salt spray test was evaluated with reference to the national standard GB 6458-86 "Neutral Salt Spray Test for Metal Coatings".

[0133] The performance test results are shown in the following table:

[0134] Table 1 Performance test results of the alumina-based passivation coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 2 and the alumina-based passivation coatings obtained after curing

[0135]

[0136] As can be seen from Table 1, the alumina-based passivation coatings prepared in Examples 1 to 3 have excellent stability and are not prone to sedimentation. The alumina-based passivation coatings formed after curing have excellent corrosion resistance and surface hardness, meeting the environmental protection requirements. According to the results of Comparative Examples 1 to 2, when unmodified α-alumina by silane coupling is applied to the acrylic-polyurethane coating, the agglomeration of α-alumina particles leads to an increase in the sedimentation degree of the coating; although the adhesion is good, the corrosion resistance is slightly reduced, and overall it is inferior to the alumina-based passivation coatings formed after curing in Examples 1 to 3, and the hardness reduction is relatively obvious. This is because the unmodified alumina by silane coupling itself has an agglomeration property, resulting in the non-uniform dispersion of nano-alumina in the alumina-based passivation coating, so that nano-alumina cannot be better and uniformly filled in the alumina-based passivation coating, leading to a decrease in the surface hardness of the alumina-based passivation coating; in the alumina-based passivation coating prepared with alumina modified by silane coupling, nano-alumina can have better dispersibility and is more easily uniformly filled in the pores of the alumina-based passivation coating, which can more effectively improve the surface hardness and corrosion resistance of the alumina-based passivation coating.

[0137] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An alumina-based passivation coating, comprising the following components by weight: 8 to 40 parts of a water-based resin, 1 to 5 parts of a silane-coupled modified nano-alumina, 0.01 to 4 parts of a rust inhibitor, 0.01 to 3 parts of a zirconium salt cross-linking agent, 0.1 to 2 parts of an auxiliary agent, and 10 to 20 parts of deionized water; The water-based resin includes acrylic acid-polyurethane composite resin or acrylic acid-epoxy composite resin.

2. The aluminum oxide-based passivation coating according to claim 1, characterized in that, The acrylic-polyurethane composite resin is obtained by mixing a polyurethane resin emulsion and an acrylic resin emulsion; the mass ratio of the polyurethane resin emulsion to the acrylic resin emulsion is 1:1; The polyurethane resin emulsion is obtained by polymerization of a polymerization system including polyol, isocyanate, catalyst, hydrophilic chain extender, hydrophobic chain extender, neutralizer, organic solvent and deionized water; The acrylic resin emulsion is obtained by polymerizing a polymerization system including acrylic monomers, an emulsifier, an initiator, a buffer, a chain transfer agent and deionized water.

3. The alumina-based passivation coating according to claim 2, wherein The polyol includes polyether polyol or polyester polyol.

4. The alumina-based passivation coating according to claim 2, wherein The isocyanate includes isophorone diisocyanate or hexamethylene diisocyanate.

5. The aluminum oxide-based passivation coating according to claim 2, wherein The acrylic monomers are methyl methacrylate, butyl acrylate, acrylic acid and hydroxyethyl acrylate.

6. The alumina-based passivation coating according to claim 1, wherein The silane-coupled modified nano-alumina is nano-α-alumina modified by a silane coupling agent; the silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, vinyltriethoxysilane and anilinomethyltrimethoxysilane.

7. The alumina-based passivation coating according to claim 1, wherein The rust inhibitor includes one or more of metaphosphate, orthophosphate and metavanadate.

8. The aluminum oxide-based passivation coating according to claim 1, characterized in that, The auxiliary agent includes a stabilizer and / or a surfactant.

9. An aluminum oxide-based passivation coating, which is obtained by drying and curing the aluminum oxide-based passivation coating according to any one of claims 1 to 8.

10. Use of the aluminum oxide-based passivation paint according to any one of claims 1 to 8 or the aluminum oxide-based passivation coating according to claim 9 as a stainless steel protective layer.

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