JPH1171699A - Steel sheet for welded can having high-speed seam weldability after high-temperature short-time coating and baking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel sheet capable of assuring metal tin sufficient for high-speed seam weldability without the progression of alloying of tin even after coating and baking at a high temp. for a short time by having granular tin plating on the steel sheet, laminar tin plating thereof and further a metal chromium layer and chromium hydroxide layer on the upper layer thereof. SOLUTION: The grain size of the granular tin plating is specified to 0.2 to 10 μm and the number thereof is regulated to 1×10<3> to 1×10<6> for each 1 mm<2> . Since the entire surface of the steel sheet is not coated by this granular tin plating alone, the granular tin plating is provided thereon with the laminar tin plating in order to eliminate the exposed parts of the steel sheet and to improve the corrosion resistance thereof. In such a case, the total tin plating quantity which is the sum of the granular and laminar tin plating quantities is regulated to 200 to 1500 mg/m<3> . Further, the upper layer of the tin plating layer is provided with the metal chromium layer and chromium hydroxide layer in order to assure a good coating material adhesion property. The coating weight of the metal chromium layer is regulated to 2 to 15 mg/m<2> and the coating weight of the chromium hydroxide layer to 2 to 20 mg/m<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate for a welding can which has sufficient tin remaining when a paint is baked at a high temperature for a short time and has good high-speed seam weldability.

[0002]

2. Description of the Related Art A metal container has a can body and a can bottom integrated with each other and has a two-piece can having an easy open end and a three-piece can having a can body, a can bottom and an easy open end. It is roughly divided into two types of cans. further,
Three-piece cans are classified into welded cans and adhesive cans according to the method of joining the can bodies. The welding can is produced by using a seam welding method as a method for joining the three-piece can bodies.

[0003] As the high-speed wire seam welding method developed by Sudronic has spread throughout the world, the production of welding cans has increased in place of conventional solder cans. It is no exaggeration to say that welding cans are currently a representative can type of three-piece cans. Conventionally, as a material for welding cans,
A nickel-plated steel sheet shown in Japanese Patent No. 69789, a thin tin-plated steel sheet shown in Japanese Patent Publication No. 62-14240, and the like have been widely used as materials capable of high-speed seam welding.

[0004]

At the beginning of development, these materials sufficiently satisfied the practical performance, but recently the use of these materials by canning companies has become more severe, so that their performance has been greatly increased. Improvements have been requested. There are two major changes in how materials are used by canning companies: the reduction of material gauges to reduce can costs and the streamlining of the coating process. Conventionally, in the painting process, coating with a cut plate has been the mainstream, but coil coating has been realized with the aim of improving productivity. 200 for cutting board painting
It is to be baked at a temperature of about ℃ for 10 to 20 minutes. On the other hand, in coil coating, the material is supplied in a coil, and after coating on a strip with a roll,
The coating is baked at a high temperature of 290 ° C. in a short time of less than 20 seconds.

[0005] As described above, since the usage of the material has changed greatly, the above-mentioned material has the following problems. First, nickel-plated steel sheets can sufficiently cope with high-temperature and short-time paint baking with coil coating, but because the contact resistance of the surface is relatively high, when the sheet thickness of the material becomes thin, it has sufficient bonding strength, In addition, the appropriate welding current range in which the generation of splash (moulded iron jumps out) is small, and the practical welding range becomes difficult. On the other hand, thin tin-plated steel sheets have a low melting point of metallic tin and are soft and have good weldability, so they can cope with gauge down to some extent. Since the process proceeds significantly more than the plate coating baking, the amount of remaining metallic tin is reduced, resulting in a decrease in weldability. In order to secure good high-speed seam weldability, it is an essential condition to secure unalloyed metal tin after paint baking. Many efforts have been made to make this metallic tin remain after baking, but a material for a welding can in which metallic tin remains even after high-temperature and short-time baking in coil coating has not yet been developed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel plate for a welding can which is excellent in high-speed weldability in which tin alloying does not progress even under conditions of high-temperature and short-time paint baking and which can secure sufficient metal tin for high-speed seam weldability. And

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the form of tin plating so that tin can sufficiently remain even at high temperature and short time baking of a paint exceeding the melting point of tin. It has been found that if the tin at the interface is granular, the alloy reaction with the base iron is unlikely to occur.Furthermore, the granular tin plating alone does not cover the entire surface of the steel sheet. It has been conceived that the plating is provided on the granular tin plating. FIG. 1 is a schematic cross-sectional view illustrating the state of lamination of plated layers of a steel plate for a welding can according to the present invention. The steel plate for a welding can of the present invention having good high-speed seam weldability after high-temperature short-time baking with coil coating has a granular tin plating 1 on a substrate 5, a layered tin plating 2 thereon, and a It has a metal chromium layer 3 and a hydrated chromium oxide layer 4 as an upper layer.

That is, the gist of the present invention is as follows. (1) High-speed seam weldability after high-temperature and short-time paint baking, characterized by having granular tin plating on a steel sheet, layered tin plating thereon, and a metal chromium layer and a hydrated chromium oxide layer thereon Excellent steel plate for welding cans. (2) The particle size of the granular tin plating is 0.2 to 10 μm, and the number thereof is 1 × 10 ³ to 1 × per 1 mm ^2.
The steel plate for a welding can according to the above (1), wherein the number is 10 ⁶ .

(3) The total tin plating amount is 200 to 1500
mg / m ² , wherein the steel sheet for a welding can according to the above (1) or (2), (4) The method according to any one of the above (1) to (3), which has a chromium metal layer of ^{2 to} 15 mg / m ^{2 and} a hydrated chromium oxide layer of ² to 20 mg / m ^{2 in} terms of chromium. Steel plate for welding cans.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. First, the steel sheet as the substrate of the present invention may be one usually used for containers, and is not particularly limited. The point of the present invention lies in the form of tin so that the tin remains sufficiently after baking at high temperature and short time. In a normal tin-plated steel sheet, when tin is baked at a high temperature for a short time, the metal tin is almost alloyed, resulting in that the metal tin essential for high-speed seam welding does not sufficiently remain.

As a result of various studies, it has been found that the tin plating should be in a granular form in order for tin to remain sufficiently even after baking at a high temperature for a short time at a temperature exceeding the melting point of tin. did. By preliminarily forming tin in a granular form, the distance from the interface between the steel sheet and the tin plating to the top of the granular tin can be increased. In this case,
Since the substantial movement distance of the atoms due to the interdiffusion between the steel sheet and the metallic tin increases, the alloying of tin is suppressed.

If the particle size of the granular tin is less than 0.2 μm, the distance from the interface between the steel sheet and the tin plating to the top of the granular tin is not sufficient, and it is difficult to leave metallic tin after baking at a high temperature. Further, if the particle size of the granular tin exceeds 10 μm, it is not preferable because the adhesion between the tin plating and the steel sheet is reduced. Also, if the number of granular tin is less than 1 × 10 ³ per 1 mm ² , the number of contacts at the time of welding decreases,
When the weldability deteriorates and the number of particles exceeds 1 × 10 ⁶ per 1 mm ² , the particle size of the granular tin becomes small, so that it becomes difficult to leave metallic tin. For the above reasons, the particle size of the granular tin is 0.2 μm to 1 μm.
0 μm and the number is 1 × 10 ³ per mm ²
Restrict to ~ 1 × 10 ⁶ .

With regard to the method of forming particulate tin, the present invention provides:
Although not particularly limited, for example, in an electrolytic bath of a general electrolytic deposition method as a tin plating method, the concentration of Sn ²⁺ is made lower than usual, without adding a brightener, and at a low current density. The electrolytic plating method is suitable for forming the granular tin. In this case, granular tin is obtained because it is in a state of “plating burnt” instead of smooth tin plating.
Since the particle size of the formed particulate tin tends to decrease as the current density increases, the control of the particle size and density of the particulate tin is relatively easy according to this method.

Since only the granular tin plating does not cover the entire surface of the steel sheet, layered tin plating is provided on the granular tin plating for the purpose of eliminating the exposed portion of the steel sheet and improving the corrosion resistance. When the total tin plating amount, which is the sum of the amount of granular tin plating and the amount of layered tin plating, is less than 200 mg / m ² , metallic tin remains after baking paint at a high temperature even when the form of tin is granular. If it exceeds 1500 mg / m ² , the effect of remaining metallic tin necessary for high-speed seam welding is saturated and is economically disadvantageous. For the above reasons, the total tin plating amount is regulated to 200 to 1500 mg / m ² .

[0015] Even if the reflow treatment is performed after the tin plating, the presence or absence of the reflow treatment is not particularly limited because the form of the granular tin is not impaired. Further, a metal chromium layer and a hydrated chromium oxide layer are provided on the tin plating layer for the purpose of ensuring good paint adhesion. It is generally said that tin-plated steel sheets have poor paint adhesion compared to electrolytic chromium steel sheets. The reason for this is that a brittle tin oxide film layer is formed during storage or baking, which causes cohesive failure. In order to prevent the growth of the tin oxide film layer, it is effective to cover the surface of metal tin with a metal chromium layer. If the amount of metallic chromium on the tin plating layer is less than 2 mg / m ² , the tin surface coating is not sufficient, and the tin oxide film layer grows during storage or baking of paint, and good paint adhesion can be secured. difficult. On the other hand, metal chrome is 15m
If it exceeds g / m ² , the effect of securing good paint adhesion is saturated. Although not as high as the hydrated chromium oxide layer, chromium metal has a high melting point and is hard, so that it does not exceed 15 mg / m ² from the viewpoint of high-speed seam weldability.

A hydrated chromium oxide layer is formed on the metal chromium layer.
Is present, which provides good adhesion at the interface with the paint.
Necessary to secure. 2mg hydrated chromium oxide layer
/ M ^TwoBelow, it is difficult to ensure good adhesion.
You. In addition, the hydrated chromium oxide layer is 20 mg / m^TwoA place to cross
The seam weldability deteriorates, and the
Disappears. For these reasons, the amount of hydrated chromium oxide is
~ 20mg / m^TwoAnd regulate.

[0017] In this manner, even with a coating method of baking a paint at a high temperature for a short time, such as a coil coating, a steel sheet for a welding can exhibiting good high-speed seam weldability can be obtained.

[0018]

Embodiments of the present invention will be described below. A 0.19 mm thick steel plate for a container was electrolytically degreased in 3% sodium hydroxide at 80 ° C. and electrolytically pickled in 10% sulfuric acid at room temperature to activate the steel plate surface. Then the bath temperature is 50 ℃
With a divalent tin ion concentration of 15 g / l, a sulfuric acid concentration of 40 g / l,
Granular tin was formed from the electrolytic bath without the brightener. The particle size and the amount of plating of the granular tin were controlled by the current density and the number of supplied coulombs during electrolysis. Thereafter, layered tin plating was performed in a tin phenolsulfonate plating bath containing a gloss additive so as to obtain a predetermined amount of metal tin. After the tin plating, a reflow treatment was immediately performed by resistance heating without applying a flux. Then, at a temperature of 50 ° C., chromic acid 100 g / l, sulfuric acid 1 g /
1 in an aqueous solution to form a metal chromium layer and a hydrated chromium oxide layer. Both the amounts of chromium metal and hydrated chromium oxide were adjusted by the current density and the number of coulombs supplied, and the amount of hydrated chromium oxide was controlled by adjusting the dissolution time from completion of electrolysis to washing with water.

Table 1 shows a comparative example produced in combination with the present invention thus produced. Here, the particle size of the granular tin was determined by observation at a magnification of 1000 to 5000 with a scanning electron microscope, and image processing was performed to determine the number per unit area. The tin amount was measured by a fluorescent X-ray method. Regarding the amount of chromium, the total amount of chromium was measured by a fluorescent X-ray method, followed by anodic electrolysis in an aqueous solution of sodium carbonate adjusted to pH 10, and the amount of residual chromium was measured by a fluorescent X-ray method to determine the amount of chromium oxide hydrate. Amount. The amount of chromium metal was determined by subtracting the amount of hydrated chromium oxide from the total amount of chromium.

The performances of these invention examples and comparative examples were evaluated by the following items. (1) Weldability The test pieces of various invention examples and comparative examples were heated to 275 ° C. in 18 seconds, and then heated at 210 ° C. for 10 minutes and at 190 ° C. for 20 minutes.
I made a minute post-baking. After that, wire speed 70
Welding was performed with a lap margin of 0.4 mm using a high-speed seam welder of m / min, and an appropriate welding current range was determined. The proper welding current range is
The welding current at which no splash was generated was taken as the upper limit, and the welding current at which sufficient joining strength was obtained in the peel test for tearing the welded portion was found as the lower limit. Table 1 shows the results of evaluating the weldability, and the evaluation criteria were based on the following criteria.

A: A level having a sufficiently wide appropriate welding current range and good weldability. ：: The appropriate welding current range is narrow, but there is no practical problem. Δ: Level where the appropriate welding current range is narrow and cannot be put to practical use. ×: Level where no appropriate welding current range exists. (2) Paint corrosion resistance 60 mg / dm ^{2 of} an epoxy phenol paint for cans was applied to test pieces of various invention examples and comparative examples, and then 275 ° C.
To 210 ° C. for 10 minutes,
After-baking was performed at 90 ° C. for 20 minutes. Then 50 × 5
It was cut to 0 mm, and the end face was sealed on the back face with lacquer. A cross-cut wound reaching the iron surface was made on the painted surface with a cutter to prepare a test piece. The prepared test piece was immersed in a mixed aqueous solution of 1.5% citric acid and 1.5% sodium chloride in 500 ml under the atmosphere and left at 50 ° C. for 96 hours.
The test piece was taken out immediately after the test, subjected to taping peeling, and the corrosion resistance after coating was evaluated. The evaluation results are shown in Table 1. The evaluation criteria were as follows.

：: No peeling of the coating film near the cross cut portion, and no point corrosion is observed in other coating portions. Δ: The coating film in the vicinity of the cross cut portion was peeled off by 0.2 to 0.5 mm, and a little point-like corrosion was also observed in other coating portions. X: The coating film in the vicinity of the cross cut portion was peeled by 0.5 mm or more, and many spot-like corrosions were also observed in other coated portions.

(3) Actual can test An epoxy phenol paint for cans was applied at 60 mg / dm ² to the test pieces of various invention examples and comparative examples, except for welded parts.
Thereafter, the temperature was raised to 275 ° C. in 18 seconds,
Post-baking was performed at 10 ° C. for 10 minutes and at 190 ° C. for 20 minutes. Thereafter, welding was performed with a lap margin of 0.4 mm using a high-speed seam welding machine with a wire speed of 70 m / min, and the weld was repaired with an organosol-based paint to produce a welded can body.

The body was double-necked and the aluminum easy open end was tightly wound, filled with coffee and orange juice as contents, and a lid made of a coated plate of electrolytic chromic acid-treated steel sheet was tightly wound. The actual can thus prepared is stored at 38 ° C. for 12 months,
The amount of iron eluted into the contents was measured. Table 1 shows the measurement results.

[0025]

[Table 1]

The amount of iron eluted is 0.1 for coffee.
5 ppm or less was determined to be good, and for orange juice, 0.8 ppm or less was determined to be good. As is clear from the comprehensive evaluation in Table 1, the steel sheet for a welding can of the present invention is suitable for baking paint at a high temperature exceeding the melting point of tin.
It has good high-speed seam weldability for practical use and good corrosion resistance after painting.

[0027]

The steel plate for a welding can of the present invention has a granular tin plating on a steel plate, a layered tin plating thereon, a metal chromium layer and a hydrated chromium oxide layer, so that the melting point of tin is exceeded. Even when the paint is baked at such a high temperature, it has practically sufficiently good high-speed seam weldability and good corrosion resistance after painting. Therefore, it can be said that the present invention is an industrially very valuable invention.

[Brief description of the drawings]

FIG. 1 is a view showing a steel plate for a welding can of the present invention.

[Explanation of symbols]

 1: Granular tin plating 2: Layered tin plating 3: Metal chromium layer 4: Hydrated chromium oxide layer 5: Substrate

Continued on the front page (72) Inventor Shigeru Hirano 1-1 Niwahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Inside Yawata Works

Claims (4)

[Claims] 1. A welding can after high-temperature and short-time paint baking, characterized in that it has granular tin plating on a steel sheet, layered tin plating thereon, and further has a metal chromium layer and a hydrated chromium oxide layer thereon. For steel plate. 2. The particle size of the granular tin plating is 0.2-1.
It is 0 .mu.m, and the number is 1 mm ² per 1 × 10
^The steel plate for a welding can according to claim 1, wherein the number is ³ to 1 x 10 < ⁶ >. 3. The total tin plating amount is 200 to 1500 mg.
/ M ^{2. The} steel sheet for a welding can according to claim 1 or 2, wherein 4. The welding according to claim 1, wherein the welding has a chromium metal layer of ^{2 to} 15 mg / m ^{2 and} a hydrated chromium oxide layer of ² to 20 mg / m ^{2 in} terms of chromium. Steel plate for cans.