JPS6144158B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a tin-plated steel plate for welded cans, in which the tin-plated steel plate for obtaining restrained resistance welded cans is appropriately reduced in the amount of tin deposited, and furthermore, this reduction in the amount of tin deposited is treated with chromate treatment. This is supplemented by the uniform and effective formation of a thin metallic chromium film by preventing the abnormal precipitation of metallic chromium, etc. Even though it is a tin-plated steel sheet that is cheaper than conventional steel sheets, it has outstanding properties in terms of paint adhesion and post-painting corrosion resistance. The object of the present invention is to obtain a raw steel plate for cans that can stably and accurately exhibit the following properties. The steel sheet for cans conventionally used to make cans by high-speed resistance welding is a tin-plated steel sheet with a tin content of 2.8 g/m ² or more to maintain corrosion resistance on one side of the original sheet. The tin repair is tin and iron.
It is coated with a tin alloy, and a nonmetallic Cr oxide layer of several mg/m ² is formed on the surface to inhibit the growth of tin oxide. However, tin used for such coating layers is not only expensive to begin with, but also has become more expensive in recent years due to the trend of resource depletion internationally, and there is a need for cheaper materials. On the other hand, by reducing the amount of tin deposited on the raw steel sheet, it is possible to reduce the cost of the steel sheet for cans. However, when the amount of tin deposited is reduced in this way, the corrosion resistance that was conventionally maintained in the tin layer is impaired, resulting in the disadvantage that appropriate corrosion resistance cannot be ensured. Electrolytic chromate-treated steel sheets (TFS-CT), which have become particularly important in recent years as an alternative to tin-plated materials, are cheaper than tin-plated steel sheets because they do not use tin; Since it is inferior to welding in terms of welding, it is not suitable for use in welded food cans that are intended for high-speed can manufacturing as described above. The present invention was created after repeated studies in view of the above-mentioned circumstances. That is, the present inventors compensated for the reduction in the amount of tin deposited on the tin-plated steel sheet for welded cans as described above by forming a thin metal Cr film on the tin surface layer, thereby achieving a tin-plated steel sheet for welded cans that is equivalent to or higher than the conventional product as described above. We succeeded in obtaining a preferable manufacturing method for a material with corrosion resistance. In other words, the material according to the present invention is 0.55 to 1.65 per side on the steel strip.
g/ ^m2 of tin plating was electrolyzed cathodically in an aqueous sodium bicarbonate solution, and then 5 to 30 g/m2 of tin was applied.
_CrO3 and 0.5-2.0g/ _NH4F2
Further cathodic electrolysis with an aqueous solution of elemental _CrO3 results in 5 to 30 mg/ ^m2 of metallic chromium and 5 to 20 mg/m2 of chromium on the tin plating.
mg/m ² of Cr oxide. To explain the present invention more specifically, a cold-rolled and temper-rolled steel strip is used as the raw material sheet, and the clean steel strip after temper rolling is degreased and pickled on an electric tinning line. Apply tin plating. This tin plating has a tin content of 0.55 to 1.65 per side of the steel strip.
g/m ² , but if the amount of tin plating is less than 0.55 g/m ² on one side, corrosion resistance and weldability will deteriorate, so it is not suitable for use as can material. Moreover, even if the tin amount exceeds 1.65 g/ ^m2 , there is no defect in the product characteristics, it is possible to reduce the amount of tin adhesion, which is the objective of the present invention, to make the steel sheet material for cans inexpensive. This is because it would be difficult and uneconomical to provide such services. After this tinning, tin is heated and melted in a reflow process, but in the method of the present invention, the reflow process normally used in this electric tinning line can be omitted. In order to activate the tin-plated steel strip surface as described above, cathodic electrolysis is performed in an aqueous sodium bicarbonate solution. This cathodic electrolysis step is essential for the present invention, and is necessary to obtain a thin, uniform, and stable metallic Cr layer on the tin layer by electrodeposition during the subsequent electrolytic chromate treatment. This is something that should not happen. In other words, sodium bicarbonate has an excellent ability to reduce and remove the steel sheet without damaging its surface appearance, while similar products such as sodium carbonate etched the tin layer more than necessary, generating chemical stains and activating the tin layer. Subsequent chromate treatment removes partial metal
Abnormal precipitation of Cr and Cr oxides occurs, making it difficult to form a uniform thin Cr layer, and the desired performance such as corrosion resistance cannot be expected. By using sodium bicarbonate, effective reduction and removal of oxides from the surface of the tin layer can be carried out without these drawbacks. The above cathode electrolysis is 0.5 to 5 coulombs/d.
Generally, it is carried out at a temperature of 0.5 coulombs/dm ² or ^less , and it becomes difficult to deposit a uniformly stable metal Cr thin layer on the tin layer in the chromate treatment, and if it exceeds 5 coulombs/dm ² This tends to cause the surface of the tin layer of the rope to be etched more than necessary, resulting in the above-mentioned chemical stain. After completing each process as mentioned above, the rope is washed with water,
Next, _CrO3 : 5 to 30 g/,
NH ₄ F: 0.5 to 2.0 g/, F/CrO ₃ is 0.03 to 0.1, and metal Cr is actively precipitated by cathodic treatment in a low concentration CrO ₃ aqueous solution with fluorine anions added. The amount of metal Cr on the tin layer is 5 to 30 mg/m ² per side, and the amount of Cr oxide is 5 to 30 mg/m 2 per side.
Forms a chromate film of 20mg/ ^m2 . The composition and concentration of the bath are outside the above conditions, especially when NH ₄ F is 0.5
If it is less than 2.0 g/, stable Cr precipitation will not be obtained, and Cr ^ox will lack uniformity, damaging the surface appearance. On the other hand, if it is more than 2.0 g/, the precipitation efficiency of metallic Cr will decrease, At the same time, a large amount of chromium oxide precipitates, exceeding 20 mg/m ² , which impedes weldability. The bath used here can be manufactured without any modification to the existing chemical processing equipment for tin-plated steel plates, and has the advantage that the waste acid equipment can be covered by the existing equipment. The metal Cr layer formed on the tin layer improves the paint adhesion and corrosion resistance of the material, but its effect cannot be fully expected unless the amount reaches 5mg/ ^m2 as shown in the attached drawing. Not possible, and 30mg/m ²
Even if it exceeds 5 to 30 mg/m ² , no commensurate improvement in effectiveness is observed, and on the contrary, the electrical resistance during welding increases and expulsion becomes more likely to occur. The same applies to the amount of Cr oxide; if it is less than 5 mg/m ² , corrosion resistance will be poor, and if it exceeds 20 mg/m ² , the surface appearance may be damaged and welding properties may be deteriorated. Specific examples according to the present invention and comparative examples thereof are described below. Example 1 The surface of a clean steel plate after skin pass rolling with a thickness of 0.21 mm was plated with tin at 2.2 g/m ² on both sides by electroplating, and then plated with tin at 2.2 g/m 2 in an aqueous solution of sodium bicarbonate at 30 g/m ^2. Cathodic electrolysis was performed for 0.5 seconds at a current density of 1A/ ^dm2 , and after washing with water, an additional 15g/ _CrO3 , 1.5
A cathodic electrolytic treatment was carried out at 20 A/dm ² ×0.3 seconds in an aqueous solution of g/NH ₄ F to form a metal Cr film and a Cr oxide film. Example 2 The same clean steel plate surface as in Example 1 of temper rolling was plated with tin at 2.2 g/m ² on both sides by electroplating, and then the tin was melted using a combination of resistance heating and induction heating. Then, cathodic electrolysis was carried out for 5 A/dm ² × 0.5 seconds in a 30 g/aqueous sodium bicarbonate solution, and after washing with water, an additional 15 g/CrO ₃ and 1.5 g/
Cathode treatment was performed in an aqueous solution of NH ₄ F at 20 A/dm ² ×0.3 seconds to form a metal Cr film and a Cr oxide film. Example 3 The surface of the same clean steel plate after skin pass rolling as in Examples 1 and 2 was electroplated to give 1.1 g/g on both sides.
After tin-plating of ² m2, alloying of tin and iron is carried out using a combination of resistance heating and induction heating, and the entire amount of the plated tin is made into an iron-tin alloy. 8A/dm ² × 0.5 seconds of cathode electrolysis, then an additional 15g/dm after washing with water.
CrO ₃ , 20 A/dm ² × in an aqueous solution of 1.5 g/NH ₄ F
Cathode treatment was performed for 0.3 seconds to form a metal Cr film and a Cr oxide film. Comparative example 1 (#25 electric tinplate) 5.6g/m ² on both sides by normal tinplate manufacturing process
A tin-plated steel plate was manufactured and subjected to #311 treatment (cathode treatment in a dichromate bath) after reflow. Comparative example 2 (TFG-CT) Ordinary electrolytic chromate treated steel sheet (TFS-CT)
TFS-CT was manufactured by the manufacturing process. Comparative Example 3 The surface of a clean temper-rolled steel plate with a thickness of 0.21 mm was plated with tin at 2.2 g/m ² on both sides by electroplating, and then tin-plated in a 2% aqueous solution of sodium dichromate.
Cathodic electrolysis was carried out at 10 A/dm ² ×1 second to form a Cr oxide film. Comparative Example 4 The same clean steel plate as in Comparative Example 3 was plated with tin at 2.2 g/m ² on both sides by electroplating, and then subjected to tin melting treatment using a combination of resistance heating and induction heating. % sodium dichromate aqueous solution 10A/
A Cr oxide film was formed by cathodic electrolysis for dm ² ×1 second. Comparative Example 5 The same steel plate surface as Comparative Examples 3 and 4 was plated with 1.1 g/ ^m2 of tin on both sides by electroplating, and a tin-iron alloying process was performed using a combination of resistance heating and induction heating to reduce the total amount of tin. After forming a tin-iron alloy, it was subjected to cathodic electrolysis treatment at 10 A/dm ² ×1 second in a 2% sodium dichromate aqueous solution to form a Cr oxide film. Comparative tests were conducted on the performances of weldability, corrosion resistance after painting, and paint adhesion for each of the tin-plated steel sheets obtained in the above-mentioned Examples and Comparative Examples, and the results of the comprehensive evaluation are shown in the following table. It is as follows. Each test is as follows. Weldability test: Welding is performed using a Sudronik-type high-speed resistance welding machine, and the degree of "splashing" and joint strength are comprehensively evaluated. Passable, scores of 8 or above were disqualified. Undercutting test: Apply cross-cutting after baking with epoxy phenol paint.
38℃ in 1.5% NaCl−1.5% citric acid aqueous solution.
It was immersed for 96 hours and the degree of corrosion progress was comprehensively judged. Cross-cut Erichsen: After applying epoxy phenol paint and baking it, cross-cut it, extrude it to 5mm using an Erichsen tester, and then apply 1.5NaCl-
It was immersed in a 1.5% citric acid aqueous solution at 38°C for 96 hours, and the degree of corrosion progress of the machined part was comprehensively evaluated. Blister resistance test: After baking the epoxy phenol paint, retort it in 1.5% TaCl at 130℃ for 30 minutes, and then retort it in 1.5% NaCl aqueous solution at 38℃,
After soaking for one week, the degree of occurrence of blister-like corrosion was determined. Paint adhesion: After baking the epoxy phenol paint, apply a grid cross cut and apply 3% NaCl.
After retorting in an aqueous solution at 107°C for 90 minutes, washing with water and drying, paint adhesion was determined by a Scotch tape peel test.

[Table] That is, the product according to the present invention had good results in all test results, and was recognized to be preferable for use in welded cans. According to the present invention as explained above, preferable and stable corrosion resistance and paint adhesion can be obtained by uniformly and accurately forming a thin metal Cr film on the tin surface layer of a steel plate with a considerably small amount of tin plating. This invention is industrially highly effective because it enables the precise production of tin-plated steel sheets for welded cans that are durable and have appropriate high-speed resistance weldability.

[Brief explanation of the drawing]

The drawing shows the technical content of the present invention, and is a chart showing the relationship between the amount of metal Cr on the tin plating layer and paint adhesion.

Claims (1)

[Claims] 1. Tin plating of 0.55 to 1.65 g/m ² per side is applied to the rope strip, and the tin-plated rope is electrolyzed cathodically in an aqueous solution of sodium hydrogen carbonate, and then 5 to 30 g/m2 of tin plating is applied per side.
In addition to being CrO ₃ , cathode electrolysis is performed with a two-element CrO ₃ aqueous solution containing 0.5 to 2.0 g/NH ₄ F, and 5 to 30 mg/m ² of metallic chromium and 5 in terms of Cr amount are deposited on the tin plating.
A method for manufacturing a tin-plated steel sheet for welded cans, characterized by forming ~20 mg/m ² of Cr oxide.