A preparation method and application of an anode applied to a passivation process of tinned plate

Abstract

This invention relates to a method for preparing an anode for tinplate passivation processes and its application, belonging to the field of electrochemistry. The method for preparing an anode for tinplate passivation processes uses a titanium plate as a substrate. First, an intermediate layer coating solution is brushed onto the surface of the titanium plate. After drying, it is subjected to constant-temperature thermal oxidation at 450–500°C for 10–15 minutes, repeated 10 times, with the final thermal oxidation time being 1 hour. The treated titanium plate is then immersed in an electroplating solution for electroplating to obtain the passivated anode material. This invention develops a passivated anode that can enhance the adhesion of tinplate surfaces. Tinplates produced using this anode exhibit good surface adhesion, and the passivation film contains less Cr(OH)3. The passivated anode produced by this invention is characterized by its hardness and density, ability to operate at high current densities, and high current efficiency.

Description

Technical Field

[0001] This invention relates to a method for preparing an anode for use in the passivation process of tin-plated plates and its application, belonging to the field of electrochemistry. Background Technology

[0002] The production process of tinplate generally includes uncoiling, welding, alkaline washing, acid washing, straightening, electroplating, reflowing, passivation, and oiling. Passivation aims to improve the corrosion resistance of the tinplate, control oxidation, inhibit the formation of sulfides during use, and enhance the adhesion of the tinplate. Therefore, the passivation process has a significant impact on various properties of the tinplate. Among these, the composition of the passivation solution and the passivation anode have the greatest impact on the adhesion of the tinplate. Currently, most steel mills use chromate solutions for electrochemical passivation of tinplate to obtain an extremely thin film composed of chromium trioxide, chromium hydroxide, or containing a small amount of free chromium; the passivation anode is generally a lead-tin alloy, low-carbon steel plate, or graphite. However, as manufacturers increase their requirements for the adhesion of tinplate, steel mills need to change the traditional passivation process. Changing the composition of the passivation solution still has significant technical limitations; therefore, it is necessary to develop a new type of anode based on the existing passivation solution, which can significantly improve the adhesion performance of the tinplate.

[0003] Tinplate requires internal coating and external printing during application. Internal coating prevents chemical reactions between the contents and the can's inner wall, and protects the contents from contamination by trace amounts of harmful substances, maintaining freshness and original flavor, and ensuring the contents retain their edible value during long-term storage, transportation, and sales. External printing primarily enhances the tinplate's corrosion resistance, aesthetics, and product diversification. External coatings not only function similarly to internal coatings but also include primers, white paints, and gloss coats, primarily using acrylic and polyester resins. This inevitably leads to adhesion issues between the tinplate surface and the organic coating. The passivation film on the tinplate surface mainly consists of Cr(OH)3 and Cr2O3, and the ratio of these two components significantly affects the adhesion of the paint film in subsequent printing processes. Current literature indicates that a higher Cr(OH)3 content in the passivation film suggests, to a certain extent, poorer paint coating performance of the tinplate, and poorer adhesion under prolonged or high-temperature conditions. Therefore, it is of great significance to enhance the adhesion of tinplate by changing the anode to reduce the Cr(OH)3 content without changing the original passivation solution.

[0004] Traditional passivation processes involve cathodic electrolytic passivation, with chromate solutions commonly used as the passivation solution. The passivation anode typically uses lead-tin alloys, low-carbon steel plates, or graphite. When low-carbon steel plates are used as passivation anodes, corrosion significantly impacts the adhesion of the tinplate. Therefore, during unit maintenance, the anode needs to be cleaned with water or a weak alkaline solution. Severely corroded areas also require sanding, severely affecting production. Meanwhile, when steel plates are used as passivation anodes, a large amount of iron ions are generated, contaminating the passivation solution and degrading the performance of tinplate. When graphite is used as the passivation anode, the tinplate produced has a low chromium content and a high content of hydrated chromium oxides in the passivation film, resulting in a thinner passivation film with poor uniformity and density, thus failing to meet the requirements of actual production. When lead-tin alloy is used as the passivation anode, the produced tinplate has poor aging properties. Furthermore, lead-tin alloy will generate lead chromate when immersed in the passivation solution for a long time. Lead chromate has poor conductivity, reducing current efficiency. In addition, the lead oxides generated when lead-tin alloy is used as the passivation anode are easy to fall off, and the fallen oxides will scratch the tinplate, degrading its performance. Therefore, none of these anodes can meet the increasingly stringent requirements of enterprises for the adhesion of tinplate. Summary of the Invention

[0005] This invention is based on the traditional passivation process, and the passivation solution still uses chromate solution. By changing the passivation anode, the adhesion performance of the tin-plated board is improved, thereby meeting the requirements of enterprises.

[0006] A method for preparing an anode for tin-plated plate passivation processes involves using a titanium plate as a substrate. First, an intermediate layer coating solution is brushed onto the surface of the titanium plate. After drying, it is subjected to constant-temperature thermal oxidation at 450–500°C for 10–15 minutes, repeated 10 times, with the final thermal oxidation lasting 1 hour. The treated titanium plate is then immersed in an electroplating solution for electroplating to obtain the passivated anode material.

[0007] The intermediate layer coating solution is prepared as follows: SnCl4-5H2O, SbCl3 and RuCl3-3H2O are dissolved in a mixed solvent consisting of isopropanol, n-butanol, ethanol and 10 ml / L HCl solution in a molar ratio of 6:1:2.

[0008] The electroplating solution is an aqueous solution composed of the following components: 150-180 g / L Pb(NO3)2, 20-30 g / L Cu(NO3)2, 0.5-1 g / L NaF, 5-8 g / L AgNO3, and 10-15 ml / L HNO3.

[0009] Preferably, the titanium plate substrate is pretreated by the following method: the titanium plate is sanded with sandpaper and washed with water; it is treated with 10% NaOH solution and heated at 90°C for 30 minutes to remove oil and washed with water; an aqueous solution of 12 ml / L HF and 40 ml / L HNO3 is prepared, the titanium plate is placed in the solution for 35 minutes, then washed with deionized water, and finally placed in alcohol for later use.

[0010] Preferably, the intermediate layer coating solution is evenly brushed onto the surface of the titanium plate and placed in a drying oven at 120-150°C for 15-20 minutes. Then, it is transferred to a muffle furnace for constant temperature thermal oxidation at 450-500°C for 10-15 minutes. After the sample is removed and slightly cooled, a second coating is applied. This process is repeated 10 times until the final thermal oxidation time is 1 hour. Afterward, the sample is allowed to cool naturally to room temperature in the furnace, and the intermediate layer preparation is complete.

[0011] Preferably, the electroplating parameters are as follows: the anode is a titanium plate, and the cathode is a copper sheet; the current density is 3-5 A / dm³. 2 Electrodeposition time: 1–1.5 h; electrode spacing: 2–3 cm; electroplating temperature: 50–60 °C

[0012] The present invention further provides an anode prepared by the above method for use in the passivation process of tin-plated plates.

[0013] An anode used in the passivation process of tinplate requires an intermediate layer to be brushed onto the titanium plate before electroplating lead dioxide. The introduction of the intermediate layer not only refines the grains of the β-PbO2 coating, but also effectively changes the conductivity of the electrode surface, reduces the tank voltage, and makes the potential distribution on the electrode surface uniform.

[0014] Another object of the present invention is to provide the application of the above-mentioned passivated anode as an anode plate in the passivation process of tin-plated plates.

[0015] A passivation process for tin-plated plates, using the anode of the process as the anode, the tin-plated plate as the cathode, and a Na2Cr2O7 solution with a concentration of 25 g / L as the passivation solution.

[0016] Preferably, the passivation process is as follows: the cathode passivation current density is 5 A / dm². 2 The passivation solution temperature was 50℃, and the passivation time was 4s.

[0017] The beneficial effects of this invention are as follows: This invention develops a passivation anode that enhances the adhesion of tin-plated sheets. Tin-plated sheets produced using this anode exhibit good surface adhesion, and the passivation film contains less Cr(OH)3. The passivation anode produced by this invention is characterized by its hardness and density, its ability to operate at high current densities, and its high current efficiency. The reagents used in this invention are relatively inexpensive, reducing production costs. The passivation anode produced by this invention has a long service life, exhibits less corrosion of the passivation solution to titanium plates, and can be reused. Compared to traditional passivation electrodes, this invention features low resistivity, stable chemical properties, less contamination of the passivation solution, and good conductivity. The passivation anode produced by this invention can reduce the flow resistance of the passivation solution, especially at high current densities, effectively preventing electrode overheating. Attached Figure Description

[0018] Figure 1 A schematic diagram of the main components of the tinplate coating;

[0019] Figure 2 This is a graph showing the adhesion levels of the tinplate coating.

[0020] Figure 3 Adhesion tests were conducted on tin-plated sheets obtained with different passivation anodes (1-lead-tin alloy; 2-low carbon steel sheet; 3-graphite; 4-lead dioxide).

[0021] Figure 4 XPS fitting images of Cr elements on the surface of tin-plated plates obtained using different passivation anodes;

[0022] Figure 5 The tin plating amount is 1.1 g / dm. 2 Adhesion test of tin-plated sheet;

[0023] Figure 6 The tin plating amount is 2.0 g / dm. 2 Adhesion test of tin-plated sheet;

[0024] Figure 7 The tin plating amount is 2.8 g / dm. 2 Adhesion test of tin-plated sheet. Detailed Implementation

[0025] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0026] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0027] A method for preparing an anode for use in the passivation process of tin-plated plates includes the following process steps:

[0028] 1. Matrix pretreatment

[0029] (1) Titanium plate is sanded with sandpaper and then washed with water;

[0030] (2) Treat with 10% NaOH solution and heat at 90℃ for 30 min to remove oil, then wash with water.

[0031] (3) Dissolve the solute in deionized water at 12 ml / L HF and 40 ml / L HNO3 to obtain a solution; place the titanium plate in the above solution for 35 min, then wash with deionized water, and finally put it in alcohol for later use.

[0032] 2. Brushing of the tin-antimony interlayer

[0033] (1) Preparation of intermediate layer solution: SnCl4-5H2O, SbCl3 and RuCl3-3H2O are mixed together in a molar ratio of 6:1:2. Then the mixture is dissolved in a 1:1:1 solution of isopropanol, n-butanol and ethanol. 10 ml / L of concentrated HCl is added and stirred thoroughly. The volume ratio of isopropanol to concentrated HCl is 1:0.01.

[0034] (2) Brushing of the intermediate layer: After uniformly brushing the solution onto the surface of the titanium plate, place it in a drying oven at 150°C for 15 min and dry it. Then, transfer it to a muffle furnace for constant temperature thermal oxidation at 500°C for 15 min. After removing the sample and slightly cooling it, perform the second coating. Repeat this process 10 times until the final thermal oxidation time is 1 h. Afterward, allow the sample to cool naturally to room temperature in the furnace. The intermediate layer preparation is complete.

[0035] 3. Electrodeposition of PbO2

[0036] (1) Electroplating solution (aqueous solution) parameters: 150g / L Pb(NO3)2, 20g / L Cu(NO3)2, 0.5g / L NaF, 5g / L AgNO3, 10ml / L HNO3.

[0037] (2) Electrodeposition of PbO2: Apparatus: water bath. Electrodeposition was performed under the stirring of a rotor to obtain titanium plates coated with lead dioxide. Electroplating parameters are shown in Table 1.

[0038] Table 1 Electroplating parameters

[0039] cathode copper sheet Current density <![CDATA[4A / dm 2 ]]> Electrodeposition time 1h Electrode spacing 2cm water bath temperature 50℃

[0040] Adhesion test charts using different passivated anodes

[0041] Substrate processing and tin plating process

[0042] The experiment used a tin-plated substrate from a steel plant, with dimensions of 90mm*60mm*0.15mm.

[0043] The tin plating process for the tin-plated substrate is as follows:

[0044] Degreasing (40g / L NaOH, 20min) → Water washing → Rust removal (10wt.% H2SO4, 9s) → Water washing → Electroplating (electroplating solution is methanesulfonic acid (MSA), electroplating time is 4s, current density is 1.4A / dm³) 2 → Wash with water → Softening (softening with a 4.0kW self-assembled softening device for 3 seconds) → Quenching in water (in deionized water at 50℃) → Place in alcohol for later use.

[0045] Passivation process and adhesion test:

[0046] 1. Take the pre-treated tinplate and cut it into a size of 90mm*60mm. Wash off the surface grease with anhydrous ethanol.

[0047] 2. Add a 25 g / L Na2Cr2O7 solution to the electrolytic cell and heat it to 50°C in a water bath.

[0048] 3. Using the titanium plate coated with lead dioxide as the anode and the pretreated tin-plated plate as the cathode, the cathode passivation current density is 5 A / dm². 2 The passivation solution temperature is 50℃, and the passivation time is 4s. The passivated tinplate is then quickly removed from the passivation solution, rinsed with deionized water, and then dried for later use.

[0049] 4. Mix epoxy resin and curing agent in a 1:1 volume ratio, apply evenly to the surface of tin-plated board using a scraper, with a coating thickness of approximately 70 μm, and then place in a drying oven to dry at 170℃ for 15 minutes.

[0050] 5. After the dried tinplate has cooled to room temperature, the resin-coated tinplate is tested using a paint film adhesion tester. The test results are as follows: Figure 3 .

[0051] Table 2 Adhesion grade test of tin-plated sheets obtained with different passivation anodes

[0052]

[0053] XPS analysis of passivation films on tin-plated substrates after different anodization passivation

[0054] Different passivation anodes were used to passivate the tin-plated sheets, and X-ray photoelectron spectroscopy analysis was performed on the resulting tin-plated sheets. The results are as follows: Figure 4 As shown in Table 3, the percentage content of different substances in the passivation film on the surface of the tin-plated plate is obtained based on the peak area.

[0055] Table 3. Percentage of Cr on the surface of tin-plated plates obtained using different passivation anodes.

[0056]

[0057]

[0058] The adhesion levels of tin-plated sheets obtained using different passivation anodes varied. The experimental results were assessed using the coating film cross-cutting test standard of GB / T1720-2020 to determine adhesion. Figure 3 It can be seen that when the passivation anode is graphite, the resin on the surface of the tinplate peels off over a large area, and the scratches at the resin peeling points are blurred, resulting in an adhesion level of three. When the passivation anode is a lead-tin alloy and a low-carbon steel plate, the adhesion level of the tinplate is level two. When lead dioxide produced in this invention is used as the passivation anode, the adhesion level of the tinplate is level one. According to X-ray photoelectron spectroscopy, using a lead dioxide anode can significantly reduce the Cr(OH)3 content. The reduction in Cr(OH)3 content can significantly improve the adhesion performance of the tinplate to a certain extent. At the same time, using a lead dioxide anode can significantly increase the Cr2O3 / Cr(OH)3 ratio. The larger the ratio, the lower the Cr(OH)3 content, and therefore the better the adhesion of the tinplate. Comprehensive analysis shows that using this type of anode can effectively reduce the content of hydrated chromium oxides in the passivation film of the tinplate and improve the adhesion of the tinplate.

[0059] Example 1

[0060] With a tin plating amount of 1.1 g / m² at a certain steel mill 2 Taking the inspection of tin-plated sheets as an example:

[0061] Test steps

[0062] 1. Cut the substrate into 90mm pieces. * A 60mm rectangular template.

[0063] 2. Immerse the substrate in a 40 g / L sodium hydroxide solution to remove oil for 20 min, then immerse it in 10 wt% H2SO4 to remove rust for 9 s.

[0064] 3. Immerse the treated tinplate in a methanesulfonic acid tin plating solution for 4 seconds at a current density of 1.4 A / dm³. 2

[0065] 4. Place the electroplated tinplate in a 4.0kW self-assembly reflow apparatus for 4 seconds. Then quench the reflowed tinplate in 50℃ deionized water, and then place it in alcohol for later use.

[0066] 5. Using the pretreated sample as the cathode and the lead dioxide-plated titanium plate as the anode, electrochemical passivation is performed. The passivation solution is a 25 g / L Na₂Cr₂O₇ solution, and the cathode passivation current density is 5 A / dm². 2 The passivation solution temperature was 50℃, and the passivation time was 4s.

[0067] 6. Mix epoxy resin and curing agent in a 1:1 volume ratio, apply evenly to the surface of tin-plated board using a scraper, with a coating thickness of approximately 70 μm, and then place in a drying oven to dry at a temperature of 170-180℃ for 12-15 minutes.

[0068] 7. After the dried tinplate has cooled to room temperature, an adhesion tester is used to test the resin-coated tinplate. The resin peeling off the tinplate is observed using an electron magnifying glass, and the adhesion grade is determined according to GB / T1720-2020 standard. The adhesion test is as follows: Figure 5 The rating is shown in Table 4.

[0069] Example 2

[0070] Taking a steel mill's tin plating amount of 2.0 g / m as an example... 2 Taking the inspection of tin-plated sheets as an example:

[0071] Test steps

[0072] 1. Cut the substrate into 90mm pieces. * A 60mm rectangular template.

[0073] 2. Immerse the substrate in a 40 g / L sodium hydroxide solution to remove oil for 20 min, then immerse it in 10 wt% H2SO4 to remove rust for 9 s.

[0074] 3. Immerse the treated tinplate in a methanesulfonic acid tin plating solution for 4 seconds at a current density of 1.4 A / dm³. 2

[0075] 4. Place the electroplated tinplate in a 4.0kW self-assembly reflow apparatus for 4 seconds. Then quench the reflowed tinplate in 50℃ deionized water, and then place it in alcohol for later use.

[0076] 5. Using the pretreated sample as the cathode and the lead dioxide-plated titanium plate as the anode, electrochemical passivation is performed. The passivation solution is a 25 g / L Na₂Cr₂O₇ solution, and the cathode passivation current density is 5 A / dm². 2 The passivation solution temperature was 50℃, and the passivation time was 4s.

[0077] 6. Mix epoxy resin and curing agent in a 1:1 volume ratio, apply evenly to the surface of tin-plated board using a scraper, with a coating thickness of approximately 70μm, and then place in a drying oven to dry at a temperature of 170-180℃ for 12-15 minutes.

[0078] 7. After the dried tinplate has cooled to room temperature, an adhesion tester is used to test the resin-coated tinplate. The resin peeling off the tinplate is observed using an electron magnifying glass, and the adhesion grade is determined according to GB / T1720-2020 standard. The adhesion test is as follows: Figure 6 The rating is shown in Table 4.

[0079] Example 3

[0080] With a tin plating amount of 2.8 g / m² at a certain steel mill 2 Taking the inspection of tin-plated sheets as an example:

[0081] Test steps

[0082] 1. Cut the substrate into 90mm pieces. * A 60mm rectangular template.

[0083] 2. Immerse the substrate in a 40 g / L sodium hydroxide solution to remove oil for 20 min, then immerse it in 10 wt% H2SO4 to remove rust for 9 s.

[0084] 3. Immerse the treated tinplate in a methanesulfonic acid tin plating solution for 4 seconds at a current density of 1.4 A / dm³. 2

[0085] 4. Place the electroplated tinplate in a 4.0kW self-assembly reflow apparatus for 4 seconds. Then quench the reflowed tinplate in 50℃ deionized water, and then place it in alcohol for later use.

[0086] 5. Using the pretreated sample as the cathode and the lead dioxide-plated titanium plate as the anode, electrochemical passivation is performed. The passivation solution is a 25 g / L Na₂Cr₂O₇ solution, and the cathode passivation current density is 5 A / dm². 2 The passivation solution temperature was 50℃, and the passivation time was 4s.

[0087] 6. Mix epoxy resin and curing agent in a 1:1 volume ratio, apply evenly to the surface of tin-plated board using a scraper, with a coating thickness of approximately 70 μm, and then place in a drying oven to dry at a temperature of 170-180℃ for 12-15 minutes.

[0088] 7. After the dried tinplate has cooled to room temperature, an adhesion tester is used to test the resin-coated tinplate. The resin peeling off the tinplate is observed using an electron magnifying glass, and the adhesion grade is determined according to GB / T1720-2020 standard. The adhesion test is as follows: Figure 7 The rating is shown in Table 4.

[0089] Table 4 Adhesion Grade Test of Tinplates with Different Tin Plating Weights

[0090]

[0091] The tinplate treated with this invention underwent adhesion testing, followed by observation under a 30x electron microscope. The resulting adhesion graph showed no large-area resin detachment from the tinplate surface, and the resin scratches were clearly visible with uniform thickness. Therefore, the adhesion level was Grade 1. This demonstrates that when the passivation anode is lead dioxide, the adhesion level of the tinplate is excellent to a certain extent, clearly meeting the current requirements of enterprises for tinplate adhesion.

Claims

1. The application of passivated anodes as anode plates in the passivation process of tin-plated plates, characterized in that: The passivated anode is prepared by the following method: using a titanium plate as a substrate, an intermediate layer coating solution is first brushed onto the surface of the titanium plate. After drying, it is subjected to constant-temperature thermal oxidation at 450~500℃ for 10~15 minutes, repeated 10 times, with the final thermal oxidation time being 1 hour. The treated titanium plate is then immersed in an electroplating solution for electroplating to obtain the passivated anode material. The intermediate layer coating solution is prepared as follows: SnCl4·5H2O, SbCl3 and RuCl3·3H2O are dissolved in a mixed solvent consisting of isopropanol, n-butanol, ethanol and 10 ml / L HCl solution in a molar ratio of 6:1:

2. The electroplating solution is an aqueous solution composed of the following components: 150~180 g / L Pb(NO3)2, 20~30 g / L Cu(NO3)2, 0.5~1 g / L NaF, 5~8 g / L AgNO3, and 10~15 ml / L HNO3.

2. The application according to claim 1, characterized in that: The titanium plate substrate is pretreated as follows: the titanium plate is sanded and washed with water; it is treated with 10% NaOH solution and heated at 90°C for 30 minutes to remove oil, and then washed with water; an aqueous solution of 12 ml / L HF and 40 ml / L HNO3 is prepared, the titanium plate is placed in the solution for 35 minutes, then washed with deionized water, and finally placed in alcohol for later use.

3. The application according to claim 1, characterized in that: The intermediate layer coating solution is evenly brushed onto the surface of the titanium plate and placed in a drying oven at 120~150℃ for 15~20 min. Then, it is transferred to a muffle furnace for constant temperature thermal oxidation at 450~500℃ for 10~15 min. After removing the sample and slightly cooling it, a second coating is applied. This process is repeated 10 times until the final thermal oxidation time is 1 hour. Afterward, the sample is allowed to cool naturally to room temperature in the furnace, and the intermediate layer preparation is complete.

4. The application according to claim 1, characterized in that: The electroplating parameters are as follows: the anode is a titanium plate, and the cathode is a copper sheet; the current density is 3~5A / dm³. 2 The electrodeposition time is 1~1.5h, the electrode spacing is 2~3cm, and the electroplating temperature is 50~60℃.

5. The application according to claim 1, characterized in that: The passivated anode was used as the anode, the tin-plated plate as the cathode, and a Na2Cr2O7 solution with a concentration of 25 g / L was used as the passivation solution.

6. The application according to claim 5, characterized in that: The passivation process is as follows: the cathode passivation current density is 5 A / dm². 2 The passivation solution temperature was 50 ℃, and the passivation time was 4 s.

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