JP2005213580A - Production method of tin plated steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of a tin plated steel plate having excellent appearance and excellent corrosion resistance and paint adhesion by suppressing the color tone of a blue tincture of surface. <P>SOLUTION: The production method for the tin plated steel plate comprises subjecting the steel plate to a pretreatment process, tin plating process and reflow process, then performing an electrolytic treatment at 0.5 to 3.7 c/dm<SP>2</SP>with the steel plate as a cathode in 5 to 35 g/l aqueous sodium carbonate solution, thence performing the electrolytic treatment with the steel plate as a cathode in an aqueous solution of 30 to 40°C containing 10 to 60 g/l chromic anhydride, thereby forming a metal chromium layer of 5 to 20 mg/m<SP>2</SP>in the amount of chromium as a lower layer on the plating surface and forming a chromium hydration oxide layer of 10 to 30 mg/m<SP>2</SP>in terms of metal chromium as an upper layer thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a tin-plated steel sheet, and more specifically, to a method for producing a tin-plated steel sheet that is excellent in appearance by suppressing the color tone of the bluish surface and further excellent in corrosion resistance and paint adhesion.

  The tinplate (tin-plated steel sheet) is cleaned in the pre-treatment process of the continuous tin-plating facility, electroplated in the plating process, and the tin layer is melted in the reflow process. The surface of the plated steel sheet after melting the tin layer is covered with naturally occurring oxides, and properties such as paint adhesion deteriorate due to long-term storage and oxidation during paint baking. In order to prevent this, a chemical conversion process is performed following the reflow process. In the chemical conversion treatment, the plated steel sheet is electrolyzed in a chromic acid aqueous solution to remove naturally occurring tin oxide, thereby forming a chromium hydrated oxide layer.

  With the recent improvement in customer requirements, there is an increasing need for improving the corrosion resistance and paint adhesion of general tinting materials.

  It is known that in a chemical conversion treatment, corrosion resistance and paint adhesion can be improved by forming a film composed of a metal chromium layer and a chromium hydrated oxide layer (see, for example, Patent Document 1).

  As an electrolytic treatment method in a chromic acid aqueous solution, a method using a dichromic acid solution and a method using a chromic anhydride solution are known. According to the examination results of the present inventors, it is clear that when a dichromic acid solution is used, the required corrosion resistance and paint adhesion cannot be ensured in many cases, and when a chromic anhydride solution is used, this problem does not occur. Became.

The prior document information is described below.
JP 53-10331 A (first page)

  As a result of the production of products of various sizes, there are cases in which the line speed is restricted in terms of the heating / cooling capability of the reflow process, for example, in the size of thick materials. When electrolytic treatment is performed with a chromic anhydride solution, when the operation is performed at a low speed range, for example, when the line speed is 200 mpm or less, the surface of the tin-plated steel plate is discolored blue, which causes a poor appearance. It became clear that there is.

  Therefore, the present invention has an object to provide a method for producing a tin-plated steel sheet that solves the above-mentioned problems, suppresses the color tone of the surface bluish, has excellent appearance, and has excellent corrosion resistance and paint adhesion. .

The means for solving the above-mentioned problems is that the steel sheet is subjected to a pretreatment process, a tin plating process and a reflow process, and then the steel sheet is used as a cathode in a sodium carbonate aqueous solution of 5 to 35 g / l to 0.5 to 3.7 c / dm. ² followed by electrolytic treatment with 10 to 60 g / l of chromic anhydride and a steel plate as a cathode in an aqueous solution at a temperature of 30 to 40 ° C. a metal chromium layer of 20 mg / m ^2, and forming a hydrated chromium oxide layer of 10 to 30 mg / m ² reckoned as metal chromium as an upper layer, a method for producing a tin-plated steel sheet.

  According to the present invention, it is possible to manufacture a tin-plated steel sheet that is excellent in appearance, corrosion resistance, and paint adhesion, by suppressing the color tone of the bluish surface without being affected by the line speed, even at low speed operation. .

  The present inventors observed the film after chemical conversion treatment in order to investigate the cause of the blue surface. As a result, it was found that the film having a blue surface was non-uniform in shape and unevenness as compared with the other film. Therefore, various methods for uniformly depositing the film as much as possible were examined.

  First, the non-uniform deposition of the chemical conversion film is considered to be because the state of the plating surface before the electrolytic treatment with the chromic anhydride solution is unstable. Considered mitigation. As a result, in order to improve the non-uniform deposition of the chemical conversion film, the alkaline electrolysis treatment conditions should be relaxed. Specifically, a sodium carbonate solution may be used to reduce the concentration and quantity of electricity. I found it effective.

  Moreover, the presence or absence of the influence on the formation of a non-uniform chemical film was investigated. As a result, it was found that increasing the chromic anhydride concentration and lowering the solution temperature are effective in improving the non-uniform deposition of the chemical conversion film.

  And before the electrolytic treatment with the chromic anhydride solution, the electrolytic treatment was performed under specific conditions using the sodium carbonate solution, and then the electrolytic treatment was performed under the specific conditions using the anhydrous chromic acid solution. The present inventors have found that a tin-plated steel sheet having excellent corrosion resistance and paint adhesion can be obtained by solving the problem that the surface of the tin-plated steel sheet turns blue in some cases. The present invention has been made based on this finding.

In the present invention, a steel plate is subjected to a pretreatment step, a tin plating step and a reflow step, and then subjected to electrolytic treatment at 0.5 to 3.7 c / dm ² using a steel plate as a cathode in an aqueous sodium carbonate solution of 5 to 35 g / l. Next, electrolytic treatment is performed using a steel plate as a cathode in an aqueous solution containing 10 to 60 g / l chromic anhydride and having a temperature of 30 to 40 ° C., and the chromium content is 5 to 20 mg / m ² as a lower layer on the plating surface. And a chromium hydrated oxide layer of 10 to 30 mg / m ^{2 in} terms of metal chrome as an upper layer.

  The present invention will be described in detail below.

  When producing the tin-plated steel sheet of the present invention, the steel sheet (cold-rolled steel sheet) was electrolytically degreased in an alkaline aqueous solution and then subjected to a normal pretreatment step in which pickling was performed. Melt and tin tin. Next, electrolytic treatment is performed in a sodium carbonate solution, and further electrolytic treatment is performed in a chromic acid solution. An electrolytic treatment method in a sodium carbonate solution and an electrolytic treatment method in a chromic anhydride solution are described below.

(Electrolytic treatment in aqueous sodium carbonate solution)
Electrolytic treatment is performed in a sodium carbonate aqueous solution as follows using a plated steel plate as a cathode.

  The concentration of sodium carbonate is 5 to 35 g / l. When the concentration is less than 5 g / l or more than 35 g / l, the effect of reducing the instability of the plating surface state becomes insufficient, the effect of suppressing the blue color tone of the chemical conversion coating film becomes insufficient, and the appearance is improved. to degrade.

Electrolytic electrical quantity is a 0.5~3.7c / dm ^2. When the amount of electricity is less than 0.5 c / dm ² or more than 3.7 c / dm ² , the effect of reducing the instability of the plating surface state becomes insufficient, and the effect of suppressing the blue color tone of the chemical conversion coating film is insufficient. It becomes insufficient and the appearance deteriorates.

  By subjecting the plated steel plate to an electrolytic treatment under the above conditions, the instability of the plated surface state is alleviated, and uneven deposition of the chemical conversion film is alleviated when electrolytic treatment is performed with a chromic anhydride solution described later.

  From the viewpoint of alleviating the instability of the plating surface condition, the conditions other than the above are preferably in the range of pH 7.1 to 9.5, and the solution temperature is preferably in the range of 45 to 55 ° C.

(Electrolytic treatment in chromic anhydride solution)
In the present invention, the chromic acid-based treatment liquid preferably contains chromic anhydride as a main component, and further contains sulfuric acid as an auxiliary agent. By performing cathodic electrolytic treatment in these baths, a metal chromium layer and a chromium hydrated oxide layer are formed, corrosion resistance and paint adhesion are improved, and formation of tin oxide over time is suppressed.

  The chromic anhydride solution needs to contain 10 to 60 g / l of chromic anhydride. Further, the solution contains sulfuric acid as an auxiliary agent in order to improve and stabilize electrolytic efficiency by appropriately controlling pH. 1 type, or 2 or more types chosen from sodium fluoride and sodium borofluoride can be contained. When sulfuric acid is contained alone, it is desirable to contain 0.07 to 0.50 g / l of sulfuric acid. When the chromic anhydride content is less than 10 g / l or more than 60 g / l, the chemical conversion film is non-uniformly deposited, and the chemical conversion film has a bluish color tone. When the sulfuric acid content of the auxiliary agent is less than 0.07 g / l or more than 0.50 g / l, the effect of uniformly depositing the chemical conversion film is lowered, the deposition becomes unstable, and the appearance is remarkably deteriorated.

  From the viewpoint of further stabilizing the conversion coating deposition and further reducing the chemical treatment chemical cost, the chromic anhydride content is 14-16 g / l, and the sulfuric acid content of the auxiliary is 0.10-0.15 g / l. Is more preferable.

  The chromic anhydride solution temperature is 30-40 ° C. The influence of the chromic anhydride solution temperature is particularly large from the viewpoint of suppressing the non-uniformity of the chemical conversion film deposition. When the solution temperature is 40 ° C. or lower, the effect of suppressing the blue color tone of the chemical conversion film is remarkably exhibited, and particularly remarkable at 35 ° C. or lower.

Electrolytic treatment is carried out in an anhydrous chromic acid solution, and a chromium metal hydration oxide having a chromium content of 5 to 20 mg / m ² as a lower layer on the plating surface and a chromium hydrated oxide of 10 to 30 mg / m ^{2 in} terms of metal chromium as the upper layer. Form a layer.

To limit the chromium coating weight of the underlying metallic chromium layer to 5 to 20 mg / m ² is because the it is less than 5 mg / m ² reduced the corrosion resistance and paint adhesion decreases weldability at 20 mg / m ² greater is there. When the chromium adhesion amount of the metal chromium layer is limited to 8 mg / m ² or more, the corrosion resistance and paint adhesion are more excellent, and when the chromium adhesion amount of the metal chromium layer is limited to 14 mg / m ² or less, the weldability is more excellent. preferable.

To limit the deposition amount of the upper layer of hydrated chromium oxide layer in 10 to 30 mg / m ² reckoned as metal chromium is reduced paint adhesion is less than 10 mg / m ^2, weldability is 30 mg / m ² than is It is because it falls. The adhesion amount of the upper chromium hydrated oxide layer is more preferable because it is more excellent in paint adhesion when it is limited to 12 mg / m ² or more in terms of metallic chromium and more excellent when it is limited to 18 mg / m ² or less. .

  In electrolytic treatment in a chromic anhydride-containing solution, a precipitation reaction of metallic chromium and chromium hydrated oxide by electrolysis and a dissolution reaction of chromium hydrated oxide by immersion in the solution occur in parallel. The adhesion amount of the lower metal chromium layer and the upper chromium hydrated oxide layer is adjusted to a desired adhesion amount mainly by adjusting the amount of electrolysis and the concentration of chromic anhydride.

  The tin-plated steel sheet produced as described above is excellent in appearance due to the suppression of the bluish color tone of the surface, and excellent in paint adhesion, corrosion resistance, and weldability.

A cold rolled steel sheet having a thickness of 0.20 to 0.40 mm is electrolytically degreased in a 10% aqueous sodium hydroxide solution, washed with water, dipped in a 7% sulfuric acid solution, washed with water, and then washed with a known tin plating bath. Inside, tin plating of 2.8 g / m ² (per one side) was applied, and then tin was melted by reflow. The obtained plated steel sheet was subjected to cathode treatment in a sodium carbonate aqueous solution, washed with water, and then subjected to electrolytic treatment using a steel sheet as a cathode in a chromic acid solution containing sulfuric acid to form a metal chromium layer and a chromium hydrated oxide layer. . Further, it was washed with water and dried. The production conditions for the tin-plated steel sheet are shown in Table 1.

  The amount of metallic chromium and chromium hydrated oxide deposited on the tin-plated steel sheet produced above was investigated, and the surface appearance, paint adhesion, and corrosion resistance were evaluated. The methods for evaluating surface appearance, paint adhesion, and corrosion resistance are described below.

(Surface appearance)
The surface of the tin-plated steel sheet was visually observed and evaluated as follows according to the degree of blueness of the surface.
○: Blue is not conspicuous.
Δ: Slightly conspicuous blue.
X: The one where the bluish color is remarkably conspicuous.

(Paint adhesion)
A sample cut to a width of 70 mm and a length of 160 mm was air-baked at 210 ° C. for 10 minutes, and then 5 g / m ² of an epoxyphenol-based paint was applied to the surface and baked at 205 ° C. for 10 minutes. After putting a crosscut-shaped wrinkle that reaches the steel base with a cutter knife on the painted surface of this sample, the Nichiban tape (width 24 mm) is adhered to the surface, and then the adhered Nichiban tape is peeled off at once, and the coating film is peeled off. The state was observed, and “◯” indicates that there was no peeling, and “X” indicates that there was peeling.

(Corrosion resistance)
A sample cut to a width of 50 mm and a length of 150 mm is baked, painted, and baked under the same conditions as for the preparation of the sample used in the paint adhesion test. After reaching the cross-cut wrinkles that reached, Erichsen processing was performed to perform extrusion processing at a height of 5 mm, and the ends were sealed. The sample prepared above was immersed in an acid solution containing citric acid: 15 g / l and NaCl: 15 g / l for 20 hours, and Nichiban tape (width 24 mm) was adhered to the surface, and then the Nichiban tape was adhered. The film was peeled off at a stretch, and the presence or absence of rust generation at the part where the coating film was peeled was observed.

  The evaluation results are also shown in Table 1.

  The steel sheet of the invention example within the scope of the present invention has a good appearance evaluation because the color tone of the surface bluish is suppressed even at a low line speed of 200 mpm or less, and has excellent paint adhesion and corrosion resistance. On the other hand, the steel plate of the comparative example outside the scope of the present invention is inferior in at least one characteristic among appearance evaluation, paint adhesion, and corrosion resistance.

  INDUSTRIAL APPLICABILITY The present invention can be used as a method for producing a tin-plated steel sheet that suppresses the blue tone of the surface and is excellent in appearance and paint adhesion.

Claims (1)

After subjecting the steel sheet to a pretreatment step, a tin plating step and a reflow step, electrolytic treatment is performed at 0.5 to 3.7 c / dm ² using the steel plate as a cathode in a 5-35 g / l sodium carbonate aqueous solution, A metal chromium layer containing 10 to 60 g / l of chromic anhydride and electrolytically treating the steel sheet as a cathode in an aqueous solution having a temperature of 30 to 40 ° C. and having a chromium content of 5 to 20 mg / m ² as a lower layer on the plating surface And the manufacturing method of a tin-plated steel plate characterized by forming 10-30 mg / m < ² > of chromium hydrated oxide layers in conversion of metal chromium as the upper layer.