阅读说明：本技术 一种冷轧电镀锡钢板的铬酸钝化方法 (Chromic acid passivation method for cold-rolled electroplated tin steel plate ) 是由 许姣姣 王志登 陆永亮 穆海玲 于 2018-09-10 设计创作，主要内容包括：本发明公开了一种冷轧电镀锡钢板的铬酸钝化方法,主要解决现有技术中冷轧电镀锡钢板钝化膜总Cr含量低于10mg/m<Sup>2</Sup>的技术问题。本发明提供的一种冷轧电镀锡钢板的铬酸钝化方法,包括：对厚度为0.17～0.35mm的冷轧电镀锡钢板的基板进行电镀锡,控制冷轧电镀锡钢板的镀锡层重量为0.9～5.8g/m<Sup>2</Sup>；对冷轧电镀锡钢板进行感应加热软熔,软熔温度为260℃～280℃,软熔时间为2～3s；对冷轧电镀锡钢板进行钝化处理,所述钝化处理包括化学钝化和阴极电解钝化,钝化处理时间2.0～4.0s；对钝化后的冷轧电镀锡钢板进行冲洗。本发明生产的冷轧电镀锡钢板钝化膜总Cr含量为10～30mg/m<Sup>2</Sup>。(The invention discloses a chromic acid passivation method for a cold-rolled electrotinning steel plate, which mainly solves the problem that the total Cr content of a passive film of the cold-rolled electrotinning steel plate in the prior art is lower than 10mg/m 2 To solve the technical problem of (1). The invention provides a chromic acid passivation method of a cold-rolled electroplated tin steel plate, which comprises the following steps: electroplating tin on a substrate of a cold-rolled tin-electroplated steel plate with the thickness of 0.17-0.35 mm, and controlling the weight of a tin coating of the cold-rolled tin-electroplated steel plate to be 0.9-5.8 g/m 2 (ii) a Carrying out induction heating and reflow melting on the cold-rolled electroplated tin steel plate, wherein the reflow melting temperature is 260-280 ℃, and the reflow melting time is 2-3 s; passivating the cold-rolled electroplated tin steel plate, wherein the passivation treatment comprises chemical passivation and cathode electrolytic passivation, and the passivation treatment time is 2.0-4.0 s; to pairAnd washing the passivated cold-rolled electroplated tin steel plate. The total Cr content of the passive film of the cold-rolled electrolytic tin-plated steel plate produced by the method is 10-30 mg/m 2 。)

1. A chromic acid passivation method for a cold-rolled electroplated tin steel plate is characterized by comprising the following steps:

1) electroplating tin on a substrate of a cold-rolled tin-electroplated steel plate with the thickness of 0.17-0.35 mm, and controlling the weight of a tin coating of the cold-rolled tin-electroplated steel plate to be 0.9-5.8 g/m²；

2) Carrying out induction heating and reflow melting on the cold-rolled electroplated tin steel plate, wherein the reflow melting temperature is 260-280 ℃, and the reflow melting time is 2-3 s;

3) passivating the cold-rolled electrotinning steel plate, wherein the passivating treatment comprises chemical passivation and cathode electrolytic passivation, the passivating treatment time is 2.0-4.0 s, the cold-rolled electrotinning steel plate after being reflowed is immersed into a passivating solution, the cold-rolled electrotinning steel plate is taken as a cathode, a lead-tin alloy is taken as an anode, the cold-rolled electrotinning steel plate is subjected to cathode electrolytic passivation, the temperature of the passivating solution is 40-60 ℃, and the current density of the cathode is 4-12A/dm²(ii) a The passivation solution comprises CrO₃And H₂SO₄Wherein CrO₃Has a mass concentration of 40-80 g/L and H₂SO₄The mass concentration of the (B) is 0.4-0.8 g/L;

4) washing the passivated cold-rolled electroplated tin steel plate, wherein the washing water is desalted water, and the conductivity of the desalted water<100 mu s/cm, the temperature of flushing water is 40-70 ℃, and the flow of desalted water is 1-8 m³The washing time is 2.0-4.0 s.

2. The chromic acid passivation method of cold-rolled electrolytic tin-plated steel sheet according to claim 1, wherein the chemical passivation time is 0.5 to 1.0s, and the cathodic electrolytic passivation time is 1.5 to 3.0 s.

3. The chromic acid passivation method of cold-rolled electrolytic tin-plated steel sheet according to claim 1 or 2, wherein the total Cr content of the passive film of the cold-rolled electrolytic tin-plated steel sheet is 10 to 30mg/m²Cr in the passivation film₂O₃The mass content is more than or equal to 70 percent.

Technical Field

The invention relates to a post-treatment process of a cold-rolled electrotinning steel plate, in particular to a chromic acid passivation method of the cold-rolled electrotinning steel plate, belonging to the technical field of the post-treatment process of the cold-rolled tin plating.

Background

The cold-rolled electroplated tin steel plate refers to a steel plate or a steel strip with pure tin plated on both sides. Because the tin plate integrates the strength and formability of steel and the corrosion resistance, weldability and aesthetic property of tin, the tin plate is widely applied to industries such as food packaging, chemical coating, aerosol cans and the like. The tin plate plays a vital role in the aspect of the tin plate, and the passivation film plays a role in a barrier layer and a connecting layer at the same time, so that on one hand, the diffusion of oxygen and corrosive media such as chloride ions and sulfur ions can be blocked, and the oxidation resistance and corrosion resistance of the tin plate are improved; on the other hand, the tin plate is connected with the paint film, so that the binding force of the paint film is improved, and the performance of the passivation film is directly related to the performance of the tin plate. The post-treatment process after the reflow of the tin plate is formed by a passivation film, also called passivation treatment, and the Cr in the passivation solution is treated by adopting a cathode electrolytic passivation mode by taking 20-30 g/L sodium dichromate solution as passivation solution⁶⁺Reduction to Cr³⁺And depositing on the surface of the tinned plate after reflow, wherein the Cr content of the obtained passive film is generally 3-10 mg/m²The composition of which is mainly Cr₂O₃And Cr (OH)₃Can meet the requirements of surface painting property and corrosion resistance of most food and beverage packaging applications.

In recent years, with the development of the food industry, the improvement of the metal packaging can shape and the sterilization technology after filling puts more rigorous requirements on the bonding force between the tin plate and the paint film, and particularly, the tin plate is required to provide more excellent paint film bonding force due to the complex deformation of part of the can shape and the rolling impact in the sterilization process.

The chromium-plated plate has good painting property, the bonding force to organic paint is 3-6 times stronger than that of a tin-plated plate, and the plating layer structure comprises 70-100 mg/m²A metal Cr layer of 7-20 mg/m²Of Cr (C)₂O₃However, the gloss, coating toughness and weldability of the chromium-plated sheet are inferior to those of tin-plated sheet, and it is not feasible to completely replace the metal can with high adhesion.

Disclosure of Invention

The invention aims to provide a chromic acid passivation method for a cold-rolled electroplated tin steel plate, which mainly solves the problem of cold rolling in the prior artThe total Cr content of the passive film of the electrotinning steel plate is lower than 10mg/m²The technical problem of (2); the method effectively combines the advantages of the cold-rolled electrotinning steel plate and the chromium-plated plate, provides basic conditions for enhancing the binding capacity of the passive film and the paint film of the cold-rolled electrotinning steel plate, realizes the improvement of the painting performance of the passive film of the cold-rolled electrotinning steel plate, and meets the paint film binding force requirement of the deformation part of a complex tank shape.

The technical scheme adopted by the invention is that a chromic acid passivation method for a cold-rolled electroplated tin steel plate comprises the following steps:

1) electroplating tin on a substrate of a cold-rolled tin-electroplated steel plate with the thickness of 0.17-0.35 mm, and controlling the weight of a tin coating of the cold-rolled tin-electroplated steel plate to be 0.9-5.8 g/m²；

2) Carrying out induction heating and reflow melting on the cold-rolled electroplated tin steel plate, wherein the reflow melting temperature is 260-280 ℃, and the reflow melting time is 2-3 s;

3) passivating the cold-rolled electrotinning steel plate, wherein the passivating treatment comprises chemical passivation and cathode electrolytic passivation, the passivating treatment time is 2.0-4.0 s, the cold-rolled electrotinning steel plate after being reflowed is immersed into a passivating solution, the cold-rolled electrotinning steel plate is taken as a cathode, a lead-tin alloy is taken as an anode, the cold-rolled electrotinning steel plate is subjected to cathode electrolytic passivation, the temperature of the passivating solution is 40-60 ℃, and the current density of the cathode is 4-12A/dm²(ii) a The passivation solution comprises CrO₃And H₂SO₄Wherein CrO₃Has a mass concentration of 40-80 g/L and H₂SO₄The mass concentration of the (B) is 0.4-0.8 g/L;

4) washing the passivated cold-rolled electroplated tin steel plate, wherein the washing water is desalted water, and the conductivity of the desalted water<100 mu s/cm, the temperature of flushing water is 40-70 ℃, and the flow of desalted water is 1-8 m³And/h, the washing time is 2-4 s.

Further, the chemical passivation time is 0.5-1.0 s, and the cathode electrolytic passivation time is 1.5-3.0 s.

The total Cr content of the passive film of the cold-rolled electrolytic tin-plated steel plate produced by the method is 10-30 mg/m²Cr in the passivation film₂O₃The mass content is more than or equal to 70 percent, and the balance is Cr (OH)₃And poleA small amount of metallic Cr.

The method of the invention adopts the prior conventional tin electroplating process.

The production process adopted by the invention has the following reasons:

1. setting of reflow process

The tin plate passivation process is carried out based on the tin plate after reflow, and the surface state of the steel plate before passivation is particularly SnO and SnO₂And the existence form and proportion of Sn can influence the reaction process of subsequent chromic acid passivation, thereby influencing the Cr content of the passivation film after the passivation is finished. The oxides of Sn are mainly formed in the reflow stage, in order to avoid the formation of SnO with a higher degree of oxidation₂The method adopts a pure induction reflow mode, the reflow temperature is 260-280 ℃, and the reflow time is 2-3 s.

2. Setting of passivation Process

The main purpose of the passivation method of the invention is to generate a sufficient amount of Cr-containing film on the surface of the tin plate after reflow, wherein Cr is₂O₃Mainly comprises the balance of Cr (OH)₃Or Cr (OH)₃And a very small amount of metallic Cr. The reason is that the metal Cr layer is brittle and is easy to break when complex deformation is carried out, so that the film layer is damaged and loses the protection effect, and the excessive metal Cr is not expected to be obtained for the invention; cr (OH)₃The hydroxyl in the coating can be combined with certain functional groups in the paint film, so that the chemical adhesion between the tin plate and the paint film is improved, but the excessive hydroxyl can lose water during baking of the paint film, so that the instability of the passivation film is increased; relatively speaking, Cr₂O₃The Cr-O bond is firmer and is not easy to change under the influence of external conditions.

The reason for the components of the passivation solution is that the Cr element of the passivation film is formed of CrO₃Providing, passivating in the process Cr⁶⁺Is reduced to Cr³⁺And deposited on the surface of the steel sheet as a cathode, H₂SO₄And functions as a catalyst. CrO₃The chromic acid solution is dissolved in water, the chromic acid solution with high concentration has certain viscosity and is easy to form residue on the surface of the steel plate, and the Cr solution with low concentration³⁺The formation rate of (2) is slow and a sufficient Cr content cannot be obtained. In addition, the inventionThe human beings are found to have no H through repeated comparison tests₂SO₄Not only is beneficial to improving the cathode efficiency of passivation, but also is beneficial to improving the surface quality of the passivated tin plate. In the absence of H₂SO₄In the existing passivation solution, the obtained passivation film layer is yellow and has irregular spots, and a small amount of H is added₂SO₄The mottle on the rear panel surface disappears and the upper limit of the allowable current density is increased. The preferred CrO content of the invention is 40-80 g/L₃The passivation solution contains 0.4-0.8 g/L of H₂SO₄。

The reason for the two steps of chemical passivation and cathode electrolytic passivation is that the chemical passivation plays a role of uniformly wetting the surface of the steel plate, and the cathode electrolytic passivation is Cr⁶⁺Is reduced to Cr³⁺The above two arrangements are not allowed to be exchanged; the passivation time is mainly set according to the actual arrangement of the passivation section of the general tin plate high-speed production line. The method preferably adopts a mode of firstly chemical passivation and then cathodic electrolytic passivation, wherein the chemical passivation is carried out for 0.5-1.0 s, and the cathodic electrolytic passivation is carried out for 1.5-3.0 s.

The cathode current density is 4-12A/dm²The reason for (1) is that in CrO₃The solution has low passivation current efficiency, slow reaction process under low current density, and Cr³⁺The power of the cathode is almost all hydrogen evolution reaction, and the current density is 10A/dm especially under high current density²In the above case, the deposition of metallic Cr gradually starts, and a small amount of metallic Cr improves the corrosion resistance and stability of the passivation film, but the presence of excessive metallic Cr adversely affects the film.

The reason for the passivation temperature is that the temperature and the current density are used together, and under the condition of the current density range, the passivation solution with too low temperature has poor dispersion capability and influences Cr³⁺The current efficiency is gradually reduced when the temperature is too high, and the chromium fog evaporates to affect the environment. Considering the operability comprehensively, the passivation temperature is preferably 40-60 ℃.

3. Setting of rinsing Process

The invention adopts desalted water to wash the passivated cold-rolled electroplated tin steel plate to remove the residual steel plate surfaceFlushing the surface passivation solution for 2-4 seconds to ensure enough water flow to pass through the surface of the steel plate; especially the flow rate of 0.2-8.0m is adopted when the desalted water is washed³The best cleaning effect can be obtained by the desalted water washing, and the passivating solution with certain viscosity can be fully washed away.

Compared with the prior art, the invention has the following positive effects: 1. according to the invention, effective combination of tin plating and chromium plating processes is realized through optimization of the components of the passivation solution and the passivation process conditions, the improvement of the total Cr content of the surface of the tin plate is successfully realized, a surface structure similar to a chromium plate is obtained on the surface of the tin plate, a basic condition is provided for enhancing the combination capability of a passivation film and a paint film of a cold-rolled electroplated tin steel plate, the improvement of the painting performance of the passivation film of the cold-rolled electroplated tin steel plate is realized, and the paint film binding force requirement of a deformation part of a complex tank shape is met. 2. The passivation solution has a simple formula, the environmental protection and the economy are fully considered in the technical condition design, and the passivation solution can be realized by slightly improving the passivation section of the high-speed production line of the tin plate.

Detailed Description

The present invention will be further illustrated below with reference to specific embodiments, which are to be understood as merely illustrative and not limitative of the scope of the present invention.