Electroplating post-treatment method for cold-rolled electroplated tin steel plate

Abstract

The invention relates to an electroplating post-treatment method for a cold-rolled electroplated tin steel plate, and belongs to the technical field of post-treatment of electroplated surfaces. After tin electroplating is completed, the steps of fluxing, soft melting and four-pass passivation are carried out, specific technological parameters of fluxing, soft melting and four-pass passivation are controlled, and finally compact and multi-component film layers of metal chromium, a chromium sesquioxide passivation film, a chromium hydroxide passivation film and an oxidation film are obtained on the electroplated surface. And the adhesive force of a film layer after the cold-rolled electroplated tin steel plate is electroplated during subsequent coating can be obviously improved.

Description

Technical Field

[0001] The invention relates to a method for improving the adhesion of a film layer of a cold-rolled tin-plated steel plate after electroplating by improving the post-electroplating treatment process of the cold-rolled tin-plated steel plate, and belongs to the technical field of post-treatment of electroplated surfaces. Background Art

[0002] Cold-rolled tinplate is widely used in downstream food packaging industries that require high-temperature sterilization, such as eight-treasure porridge food cans. Eight-treasure porridge food cans require two coats of yellow paint on the inner wall, two coats of white paint on the outer wall, and more than five coats of color printing. Each of the above coats requires high-temperature baking at 165-205℃, so very strict requirements are placed on the adhesion of the film layer of the cold-rolled tinplate after electroplating, and the adhesion needs to reach level 1.

[0003] The existing post-plating treatment process of cold-rolled tin-plated steel sheets that affects the adhesion of the film layer after plating mainly involves fluxing, reflowing and passivation processes. The existing fluxing process after plating of cold-rolled tin-plated steel sheets generally uses a higher concentration of flux to improve the fluxing effect, and only imposes certain restrictions on the flux temperature and flux concentration, while the pH value, Sn 2+ There are no special restrictions on a series of core parameters such as concentration and the amount of tin mud in the flux. The surface of the tin-plated sheet obtained by the conventional fluxing process will have poor fluxing effect or excessive fluxing, which will lead to poor soft melting or excessive leveling of the tin layer in the subsequent soft melting process, which is not conducive to obtaining a uniform, dense and multi-component passivation film in the subsequent passivation step. The soft melting process often uses resistance soft melting or induction soft melting, which will result in poor soft melting or excessive soft melting, affecting the surface quality of the tin-plated sheet, and it is impossible to obtain a uniform and dense multi-component passivation film. The passivation of existing cold-rolled tin-plated steel sheets after electroplating generally uses a trough body for two-pass linkage control, and it is impossible to achieve separate control of two passes of a trough body, and the passivation film layer formed is single. Therefore, the adhesion of the film layer of the existing cold-rolled tin-plated steel sheets after electroplating reaches a maximum of level 2, which cannot meet the needs of downstream products such as food cans. Summary of the invention

[0004] The technical problem to be solved by the present invention is to improve the adhesion of the film layer of the cold-rolled tin-plated steel sheet after electroplating during subsequent painting.

[0005] The technical solution adopted by the present invention is: a method for post-plating treatment of cold-rolled electro-tinned steel sheet, comprising the following steps:

[0006] 1) Fluxing

[0007] After the electroplating of tin is completed, fluxing is performed, and alkyl sulfonic acid substances are used as fluxing agents, and the fluxing time is controlled to be 1 to 2 seconds, the fluxing temperature is 40 to 46°C, the fluxing agent concentration is 5 to 7 mL / L, the fluxing agent pH value is 1.5 to 2.5, and the Sn content in the flux is controlled to be 1.5 to 2.5.2+ Concentration < 0.5g / L and tin mud content in flux < 0.3g / L;

[0008] 2) Soft melting step: a combination of resistance soft melting and induction soft melting is used to control the soft melting temperature at 245-265°C, the soft melting time at 1-2s, the quenching temperature at 75-80°C and the iron-tin alloy layer thickness at 0.3-0.6g / m 2 ;

[0009] 3) Passivation

[0010] Sodium dichromate solution is used as the passivation solution, and the temperature of the passivation solution is controlled at 40-44°C, the concentration of the passivation solution is 30-34g / L, the pH value of the passivation solution is 3.8-4.1, and the SO4 2- <8mg / L and Fe in passivation solution 2+ <8mg / L;

[0011] Passivation is carried out in four steps, namely:

[0012] 3.1) First chemical passivation

[0013] Control current density 0A / dm 2 and passivation time 0.5~1.0s;

[0014] 3.2) Second electrolytic passivation

[0015] Control electrolysis current density 5.0~9.0A / dm 2 , passivation time 0.5 ~ 1.0s and passivation film metal chromium thickness 0.5-1.5mg / m 2 ;

[0016] 3.3) The third electrolytic passivation

[0017] Control electrolysis current density 0.5~0.9A / dm 2 and the passivation time is 0.5~1.0s;

[0018] 3.4) The fourth and third electrolytic passivation

[0019] Control electrolysis current density 0.5~0.9A / dm 2 , passivation time 0.5~1.0s, total thickness of passivation film 5.5~6.5mg / m 2 、The thickness of chromium oxide in the passivation film is 3.5~4.5mg / m 2 and oxide film thickness 0.6~0.8mc / cm 2 .

[0020] The beneficial effects of the present invention are:

[0021] 1) The present invention performs fluxing after the completion of electrotin plating, which can effectively avoid the defects of insufficient secondary leveling after the tin-plated layer melts due to too low flux concentration and excessive secondary leveling after the tin-plated layer melts due to too high flux concentration in the soft fluxing step. 2+ The concentration and the amount of tin mud in the flux can avoid the appearance of spot-like surface defects, and is also beneficial to the subsequent soft melting effect, obtaining a uniform, dense and multi-component passivation film to improve adhesion.

[0022] 2) The soft melting of the present invention allows the electroplated tin layer to be melted and then subjected to secondary leveling distribution, so that a dense iron-tin alloy layer and a thin oxide film are evenly covered on the flat surface and the pitted area of ​​the substrate, thereby improving the overall density and air oxidation resistance of the iron-tin alloy layer, thereby enhancing the adhesion of the tinplate film layer.

[0023] 3) The effects of the four pass passivation processes of the present invention are as follows: the first pass chemical passivation can quickly remove the tin oxides generated in the reflow process and activate the surface of the steel plate; the second pass electrolytic passivation uses a higher current density and can form a tin layer with a thickness of 0.5 to 1.5 mg / m on the surface of the exposed metal tin layer. 2 According to research, when a certain amount of metallic chromium is contained in the passivation film, it can significantly improve the adhesion of the cold-rolled electroplated tin steel sheet after electroplating and subsequent painting, baking and sterilization; the third pass of electrolytic passivation uses a smaller current density to continue to generate a chromium trioxide and chromium hydroxide passivation film around the metallic chromium and chromium trioxide passivation film formed in the second pass; the fourth pass of electrolytic passivation continues to maintain the small current density of the third pass, and continues to generate a uniform and dense chromium trioxide and chromium hydroxide passivation film on the basis of the previous pass, so that the total thickness of the passivation film is 5.5-6.5 mg / m 2 The thickness of the passivation film metal chromium is 0.5~1.5mg / m 2 The thickness of the passivation film chromium oxide is 3.5-4.5 mg / m 2 , the thickness of the oxide film (tin oxide) is 0.6~0.8mc / cm 2 In the four-pass passivation, by controlling the temperature of the passivation solution, the concentration of the passivation solution, the pH value of the passivation solution, the current density, the passivation time, the SO4 2- and Fe 2+ A dense and multi-component passivation film can be obtained.

[0024] After the cold-rolled tin-plated steel sheet is subjected to the post-plating treatment method of the present invention, the adhesion of the film layer of the cold-rolled tin-plated steel sheet after plating can be significantly improved during subsequent painting. DETAILED DESCRIPTION

[0025] The post-plating treatment method for cold-rolled tin-plated steel sheet of the present invention is further described below in conjunction with Examples 1 to 5.

[0026] The steps of the post-plating treatment method for cold-rolled tin-plated steel sheets in Examples 1 to 5 are the same, but the process parameter control is different, and include the following steps:

[0027] 1) Fluxing

[0028] After the electroplating of tin is completed, fluxing is performed, and alkyl sulfonic acid substances (such as hydroxybenzene sulfonic acid) are used as fluxing agents. The fluxing time, fluxing temperature, fluxing agent concentration, fluxing agent pH value, Sn content in the flux, etc. are determined. 2+ See Table 1 below for concentration and amount of tin mud in flux;

[0029] Table 1

[0030]

[0031] 2) Soft melting step: a combined soft melting of resistance soft melting and induction soft melting is used, and the soft melting temperature, soft melting time, quenching temperature and alloy layer thickness are controlled as shown in Table 2;

[0032] Table 2

[0033] Soft melting parameters Soft melting temperature (℃) Soft melting time (s) Quenching temperature(℃) <![CDATA[Alloy layer thickness (g / m 2 )]]> Example 1 245 1.3 78 0.35 Example 2 250 1.4 76 0.38 Example 3 255 1.5 78 0.45 Example 4 260 2.0 80 0.55 Example 5 265 1.8 77 0.59

[0034] 3) Passivation

[0035] Sodium dichromate solution is used as the passivation solution, and the temperature, concentration, pH value and SO4 content of the passivation solution are controlled. 2 The amount of Fe in the passivation solution 2+ See Table 3 below for the amount;

[0036] Passivation is carried out in four steps, namely:

[0037] 3.1) First chemical passivation

[0038] Control current density to 0A / dm 2 , control the passivation time see Table 3;

[0039] 3.2) Second electrolytic passivation

[0040] Controlling electrolytic current density, passivation time and metal chromium thickness see Table 3;

[0041] 3.3) The third electrolytic passivation

[0042] Control electrolysis current density and passivation time see Table 3;

[0043] 3.4) The fourth and third electrolytic passivation

[0044] See Table 3 for controlling the electrolytic current density, passivation time, total passivation film thickness, passivation film chromium oxide thickness and oxide film (tin oxide film) thickness.

[0045] Table 3

[0046]

[0047] The finished cold-rolled tin-plated steel sheets of the above-mentioned embodiments 1-5 were used as test samples, and the tests were carried out according to GB / T 2523-2008 cold-rolled metal sheet (strip) surface roughness and peak number measurement method and QB / T 2763-2006 coated tin (or chromium) thin steel sheet. The results are shown in Table 4 below.

[0048] Table 4

[0049]

[0050]

[0051] It can be seen from Table 4 that the film adhesion of the finished cold-rolled tin-plated steel sheets of Examples 1-5 treated according to the method of the present invention after electroplating all reaches Level 1.

Claims

1. A method for post-plating treatment of a cold-rolled tin-plated steel sheet, comprising the following steps: 1) Fluxing After the electroplating of tin is completed, fluxing is performed, and alkyl sulfonic acid substances are used as fluxing agents. The fluxing time is controlled to be 1 to 2 s, the fluxing temperature is 40 to 46°C, the fluxing agent concentration is 5 to 7 mL / L, the fluxing agent pH value is 1.5 to 2.5, and the Sn content in the flux is controlled to be 1.5 to 2.

5. 2+ Concentration < 0.5 g / L and tin mud content in flux < 0.3 g / L; 2) Soft melting step: a combination of resistance soft melting and induction soft melting is used to control the soft melting temperature at 245-265°C, the soft melting time at 1-2 s, the quenching temperature at 75-80°C and the iron-tin alloy layer thickness at 0.3-0.6 g / m 2 ; 3) Passivation Sodium dichromate solution was used as the passivation solution, and the temperature of the passivation solution was controlled at 40-44°C, the concentration of the passivation solution was 30-34 g / L, the pH value of the passivation solution was 3.8-4.1, and the SO4 2- <8 mg / L and Fe in passivation solution 2+ <8 mg / L; Passivation is carried out in four steps, namely: 3.1) First chemical passivation Control current density 0 A / dm 2 and passivation time 0.5~1.0 s; 3.2) Second electrolytic passivation Control electrolysis current density 5.0~9.0 A / dm 2 , passivation time 0.5 ~ 1.0 s and passivation film metal chromium thickness 0.5-1.5 mg / m 2 ; 3.3) The third electrolytic passivation Control electrolysis current density 0.5~0.9 A / dm 2 and passivation time is 0.5~1.0 s; 3.4) The fourth and third electrolytic passivation Control electrolysis current density 0.5~0.9 A / dm 2 , passivation time 0.5~1.0 s, total thickness of passivation film 5.5~6.5 mg / m 2 、The thickness of chromium oxide in the passivation film is 3.5~4.5 mg / m 2 and oxide film thickness 0.6~0.8 mc / cm 2 .

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