Preparation method of varnish coating with cotton spherical cobalt oxide nanoparticles as sealing agent

Abstract

The invention discloses a preparation method of a varnish coating with cotton-ball-shaped cobalt oxide nanoparticles as a sealing agent, and the preparation method of the coating comprises the following steps: taking the cotton-ball-shaped cobalt oxide nanoparticles with bulges as the sealing agent on the surface of a metal part substrate, and then covering a layer of benzothiazole synergistic alkyd resin varnish. The coating prepared by the method has relatively high corrosion potential, relatively low corrosion current and relatively large impedance, which indicates that the coating has relatively good corrosion resistance. The coating can be applied to anticorrosion engineering of surfaces of electrical equipment such as air conditioners, electric water heaters, air conditioners and refrigerators and metal parts of mechanical equipment such as tractors and cranes.

Description

Technical Field

[0001] The invention relates to the field of anti-corrosion varnish coatings, in particular to a method for preparing a varnish coating using cotton ball-shaped cobalt oxide nanoparticles as a sealing agent. Background Art

[0002] In order to improve the corrosion resistance of metal parts, the traditional method is to use hexavalent chromium, lead tetroxide or hot water sealing method, and then cover a layer of coating. However, hexavalent chromium is toxic. In the electrical and electronic industry, the EU RoHS regulation (Restriction of Hazardous Substances) prohibits the use of hexavalent chromium compounds. Although the hot water direct sealing method is non-toxic, it has poor corrosion resistance. In practical applications, especially in harsh environments, it will encounter difficult to overcome corrosion problems. The inventor's early Chinese patents "A method for preparing an aluminum alloy organic sealing film and its film-forming solution" (patent number: CN201110315302.4) and "A method for preparing an aluminum alloy organic aminophenol composite sealing film and its film-forming solution" (patent number CN 201310075903.1) have good effects, but their effects are still limited when used in harsh environments. Therefore, it is of great significance to study a method for preparing a high-performance coating that is easy to make. Summary of the invention

[0003] The technical problem to be solved by the invention is to provide a method for preparing a varnish coating which is easy to prepare and takes cotton ball-shaped cobalt oxide nanoparticles as a sealing agent.

[0004] In order to solve the above technical problems, the present invention adopts the following technical scheme: firstly, cotton ball-shaped cobalt oxide nanoparticles are synthesized, and the surface of the metal parts is sealed with the prepared cotton ball-shaped cobalt oxide nanoparticles with protrusions, and then a layer of the prepared benzothiazole-enhanced alkyd resin varnish is covered on the surface of the sealed metal parts to obtain the result.

[0005] The method for preparing the varnish coating with cotton ball-shaped cobalt oxide nanoparticles as a sealant comprises using cotton ball-shaped cobalt oxide nanoparticles as a sealant, immersing metal parts in the sealant and ultrasonically treating the metal parts, and then covering the surface of the sealed metal parts with a layer of prepared benzothiazole-enhanced alkyd resin varnish.

[0006] The above-mentioned method for preparing a varnish coating using cotton ball-shaped cobalt oxide nanoparticles as a sealing agent comprises the following steps: <1> Synthesis of cotton-like cobalt oxide nanoparticles: 0.025 mol of cobalt nitrate hexahydrate (Co(NO3)2•6H2O), 20 ml of deionized water, and 0.001 mol of polyvinyl pyrrolidone were weighed and dissolved in 100 ml of ethanol, and 30 ml of 0.0025 g / L sodium hydroxide was slowly added and stirred vigorously for 30 minutes. The resulting solution was transferred to a reactor lined with 500 ml of polytetrafluoroethylene. ， The reaction was carried out at 200°C for 2 hours, and after cooling to room temperature, the precipitate was obtained by centrifugation, washed three times with deionized water and ethanol, and dried at 320°C for 1 hour. <2> Preparation of benzothiazole-enhanced alkyd resin varnish: 100 g of dry long oil alkyd resin, 0.5 g of cobalt naphthenate drier, and 2 g of benzothiazole are sequentially added to 50 ml of n-butanol solvent, and each chemical is mechanically stirred for 5 minutes, and finally stirred at high speed for 5 minutes to obtain the varnish; <3> Preparation of clear coat: weighing steps <1> 0.01 to 1 g of the prepared cotton ball-shaped cobalt oxide nanoparticles are added to 100 ml of a mixture of water and n-butyl in a volume ratio of 2:1, and ultrasonicated for 2 to 5 minutes. A clean metal part is immersed in the mixture to seal it, and ultrasonicated for another 2 to 5 minutes. After the metal part is taken out and dried, a layer of <2> The prepared varnish is dried naturally for 12 hours.

[0007] The experiment found that after the low-carbon steel electrode was used as the substrate and the prepared cotton-ball-shaped cobalt oxide nanoparticles were used as the sealant to seal it, a layer of prepared varnish was covered. The test was conducted on an electrochemical workstation with an exposed area of ​​1 square centimeter. The polarization curve results showed that the corrosion current of the coating covered with a layer of benzothiazole-enhanced alkyd resin varnish after the cotton-ball-shaped cobalt oxide nanoparticles were sealed was the lowest, and its corrosion potential increased by 100 mV over the unsealed alkyd resin varnish coating containing benzothiazole, and by 210 mV over the unsealed alkyd resin varnish coating without benzothiazole. The AC impedance results showed that the impedance of the coating covered with a layer of benzothiazole-enhanced alkyd resin varnish after the raised cotton-ball-shaped cobalt oxide nanoparticles were sealed exceeded the unsealed alkyd resin varnish coating containing benzothiazole by 15 kohm.cm 2 , more than 60 kohm.cm over an unsealed alkyd clearcoat without benzothiazole 2 The tinplate coated by this method was immersed in a 3.5% sodium chloride solution for 16 days and only slightly corroded. It exceeds the performance of the current alkyd resin varnish coating and is easy to make. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a scanning electron microscope image of the prepared cotton ball-shaped cobalt oxide nanoparticles.

[0009] Figure 2 The polarization curves of the coatings prepared by the method for preparing a varnish coating with cotton-ball-shaped cobalt oxide nanoparticles as a sealant in Example 1 are as follows: Curve a is an alkyd resin alcohol varnish coating without benzothiazole, Curve b is an alkyd resin alcohol varnish coating containing benzothiazole, and Curve c is an alkyd resin alcohol varnish coating after being sealed with a cotton-ball-shaped cobalt oxide nanoparticle sealant and then covered with a layer of benzothiazole-enhanced alkyd resin alcohol varnish coating.

[0010] Figure 3 This is an AC impedance diagram of a coating prepared by the method for preparing a varnish coating using cotton-ball-shaped cobalt oxide nanoparticles as a sealant in Example 1: Curve a is an alkyd resin alcohol varnish coating without benzothiazole, curve b is an alkyd resin alcohol coating containing benzothiazole, and curve c is an alkyd resin alcohol varnish coating after being sealed with a cotton-ball-shaped cobalt oxide nanoparticle sealant and then covered with a layer of benzothiazole-enhanced alkyd resin alcohol varnish coating.

[0011] Figure 4 This is a corrosion photograph of the alkyd resin varnish coating without benzothiazole in Example 1 immersed in a 3.5% sodium chloride solution for 16 days.

[0012] Figure 5 This is a corrosion photograph of the alkyd resin varnish coating containing benzothiazole in Example 1 immersed in a 3.5% sodium chloride solution for 16 days.

[0013] Figure 6 This is a corrosion photograph of the sample in Example 1 which was sealed with a cotton ball-shaped cobalt oxide nanoparticle sealant and then covered with a layer of alkyd resin varnish coating enhanced with benzothiazole and immersed in a 3.5% sodium chloride solution for 16 days. DETAILED DESCRIPTION Example

[0014] 1. Pretreatment of electrodes and tinplate sheets The electrodes (Q235 low carbon steel electrodes (1 cm in diameter) were used for electrochemical testing) and tinplate sheets (12 cm × 5 cm × 1 mm) were polished with 280-mesh and 600-mesh sandpapers, respectively. Then, they were ultrasonically cleaned in 5% hydrochloric acid for 1 min, ultrasonically cleaned in deionized water for 5 min, and finally ultrasonically cleaned in anhydrous ethanol for 5 min and dried for later use.

[0015] 2. Preparation of cotton-like cobalt oxide nanoparticles, varnish and coating film <1> Synthesis of cotton-like cobalt oxide nanoparticles: 0.025 mol of cobalt nitrate hexahydrate (Co(NO3)2•6H2O), 20 ml of deionized water, and 0.001 mol of polyvinyl pyrrolidone were weighed and dissolved in 100 ml of ethanol, and 30 ml of 0.0025 g / L sodium hydroxide was slowly added and stirred vigorously for 30 minutes. The resulting solution was transferred to a reactor lined with 500 ml of polytetrafluoroethylene. ， The reaction was carried out at 200°C for 2 hours, and after cooling to room temperature, the precipitate was obtained by centrifugation, washed three times with deionized water and ethanol, and dried at 320°C for 1 hour. <2> Preparation of benzothiazole-enhanced alkyd resin varnish: 100 g of dry long oil alkyd resin, 0.5 g of cobalt naphthenate drier, and 2 g of benzothiazole are sequentially added to 50 ml of n-butanol solvent, and each chemical is mechanically stirred for 5 minutes, and finally stirred at high speed for 5 minutes to obtain the varnish; <3> Sealing process and coating preparation: weighing steps <1> 0.05 g of the prepared cotton ball-shaped cobalt oxide nanoparticles were added to 100 ml of a mixture of water and n-butyl in a volume ratio of 2:1, and ultrasonicated for 5 minutes. The treated low carbon steel electrode or tinplate sheet was immersed in the mixture to seal, and ultrasonicated for another 5 minutes. The low carbon steel electrode or tinplate sheet was taken out and dried, and then immersed in the mixture. <2> The prepared varnish is placed in the solution for 5 minutes, and then the low carbon steel electrode or tinplate sheet is taken out and dried naturally for 12 hours to obtain a raised cotton ball-like cobalt oxide nanoparticle, which is then sealed and covered with a layer of benzothiazole-enhanced alkyd resin varnish.

[0016] <4> Preparation of coating of alkyd resin varnish without benzothiazole: First, prepare the varnish, except that no benzothiazole is added, and the preparation process steps are as follows: <2> Exactly the same, then directly immerse the treated low carbon steel electrode or tinplate sheet into the alkyd resin varnish without benzothiazole for 5 minutes, then take out the low carbon steel electrode or tinplate sheet and dry it naturally for 12 hours, thus obtaining the alkyd resin varnish coating without benzothiazole; <5> Preparation of coating of alkyd resin varnish containing benzothiazole: Immerse the treated low carbon steel electrode or tinplate sheet in step <2> The prepared alkyd resin varnish containing benzothiazole is immersed for 5 minutes, and then the low-carbon steel electrode or tinplate sheet is taken out and naturally dried for 12 hours to obtain the alkyd resin varnish coating containing benzothiazole.

[0017] 3. Anti-corrosion performance test of coating <1> The electrodes coated with the prepared alkyd resin varnish coating without benzothiazole, the alkyd resin varnish coating containing benzothiazole, and the sealed cotton-like cobalt oxide nanoparticles and then covered with a layer of benzothiazole-enhanced alkyd resin varnish coating were made so that the exposed area of ​​the coating was 1 square centimeter. Then, electrochemical polarization curves and AC impedance tests were carried out in 3.5% sodium chloride solution. The corrosion current, corrosion potential and impedance were compared. It was found that the coating sealed with raised cotton-like cobalt oxide nanoparticles and then covered with a layer of benzothiazole-enhanced alkyd resin varnish had the lowest corrosion current, and its corrosion potential increased by 100 mV more than the unsealed alkyd resin varnish coating containing benzothiazole, and 210 mV more than the unsealed alkyd resin varnish coating without benzothiazole (such as Figure 2 The impedance increase is 15 kohm.cm over the unblocked thiazole-containing alkyd resin clearcoat coating. 2 , exceeding 60kohm.cm of unsealed alkyd resin clearcoat without thiazole 2 ( like Figure 3 as shown).

[0018] <2> The prepared tinplate sheets coated with the benzothiazole-free alkyd resin varnish coating, the benzothiazole-containing alkyd resin varnish coating, the cotton-like cobalt oxide nanoparticles sealed, and covered with a layer of benzothiazole-enhanced alkyd resin varnish were immersed in a 3.5% sodium chloride solution for 16 days. It was found that the tinplate sheets coated with the benzothiazole-free alkyd resin varnish were severely corroded and had blistering (such as Figure 4 As shown); alkyd resin varnish coating containing benzothiazole, although corrosive, is slightly lighter (such as Figure 5 As shown in the figure); after the cotton-like cobalt oxide nanoparticles are sealed and covered with a layer of benzothiazole-enhanced alkyd resin varnish, there is only slight corrosion and no blistering (as shown in the figure); Figure 6 as shown).

[0019] Therefore, the coating prepared by the method for preparing a varnish coating using cotton ball-shaped cobalt oxide nanoparticles as a sealing agent has a lower corrosion current, a higher corrosion potential and a larger impedance, a strong ability to resist salt water corrosion, and better anti-corrosion performance.

Claims

1. A method for preparing a varnish coating using cotton ball-shaped cobalt oxide nanoparticles as a sealing agent, characterized in that: Cotton-ball-shaped cobalt oxide nanoparticles are used as a surface sealer for metal parts, which are then covered with a layer of benzothiazole-enhanced alkyd resin varnish. Please follow the steps below: <1> Synthesis of cotton-like cobalt oxide nanoparticles: 0.025 mol of cobalt nitrate hexahydrate (Co(NO3)2•6H2O), 20 ml of deionized water, and 0.001 mol of polyvinyl pyrrolidone were weighed and dissolved in 100 ml of ethanol, and 30 ml of sodium hydroxide with a concentration of 0.0025 g / L was slowly added and vigorously stirred for 30 minutes. The resulting solution was transferred to a reactor lined with 500 ml of polytetrafluoroethylene. ， The reaction was carried out at 200°C for 2 hours, and after cooling to room temperature, the precipitate was obtained by centrifugation, washed three times with deionized water and ethanol, and dried at 320°C for 1 hour. <2> Preparation of benzothiazole-enhanced alkyd resin varnish: 100 g of dry long oil alkyd resin, 0.5 g of cobalt naphthenate drier, and 2 g of benzothiazole are sequentially added to 50 ml of n-butanol solvent, and each chemical is mechanically stirred for 5 minutes, and finally stirred at high speed for 5 minutes to obtain the varnish; <3> Preparation of clear coat: weighing steps <1> 0.01 to 1 g of the prepared cotton ball-shaped cobalt oxide nanoparticles are added to 100 ml of a mixture of water and n-butyl in a volume ratio of 2:1, and ultrasonicated for 2 to 5 minutes. A clean metal part is immersed in the mixture to seal it, and ultrasonicated for another 2 to 5 minutes. After the metal part is taken out and dried, a layer of <2> The prepared varnish is dried naturally for 12 hours.

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