JP2723347B2 - Surface treated steel sheet for welding cans - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application field] The present invention relates to a metal can for joining can bodies by electric resistance welding such as wire seam welding, and contains juice, coffee beverage, soft drink, and others. The present invention relates to a surface-treated steel sheet for welded cans having excellent weldability, high-temperature baking properties of paint, and corrosion resistance among metal can materials.

[Prior art] Canadian body welding method using wire seam welding using electric resistance has been put to practical use by Sudronic of Switzerland. Canned body can be manufactured even with tin tin with a lower weight than conventional soldering. It became. However, tin is often heated and melted to increase the luster of the tin, but this process causes alloying of tin and iron. It has been found to deteriorate. Therefore, ultra-thin tin-plated steel sheets that are tin-plated after nickel or Ni-Fe strike plating have been developed in order to suppress alloying due to heat-melting treatment even with low-weight tin and ensure good weldability,
Used as a material for welding cans.

Surface-treated steel sheets having such metallic tin on the surface layer are extremely excellent in terms of weldability and corrosion resistance, but the heat resistance of plated metal, which has recently been particularly required as a material property of surface-treated steel sheets for welding cans. Inferior in terms of.

[Problems to be Solved by the Invention] Conventionally, can coating was performed by sheet coating after cutting a surface-treated steel sheet. Switching. In coil coating, baking is performed at a high temperature because baking and curing of the paint need to be performed in a short time. However, since the tin and ultra-thin tin-plated steel sheets have metallic tin with a melting point of 232 ° C in the upper layer, a sound coating film is formed due to melting of tin in coil coating which is baked at a temperature much higher than the melting point. I can't get it. In addition, repair painting is applied to the weld inside the can,
This baking temperature is also higher than before, tinplate,
When an ultra-thin tin-plated copper plate is used, there is also a problem in the soundness of the repair coating film.

The present invention solves the unsuitability of high-temperature baking such as coil coating of pure tin-based surface-treated steel sheets by using alloy tin, and furthermore, surface-treated steel sheets having the same weldability and corrosion resistance as pure tin-based materials. The purpose is to provide.

[Means for Solving the Problems] The dissimilar metal to be alloyed with tin needs to be a metal that raises the melting point of tin by alloying and has no problem in food hygiene. As a metal that satisfies such conditions, there is nickel that has been used in beverage cans and the like. The present invention, tin and per side for a total nickel 1060 mg / m ² or more on the steel sheet surface, of 3000 mg / m ² or less of the amount
It has a Ni-Sn alloy layer and is characterized in that nickel is 10 to 30% by weight. In addition, it is characterized by having a chromate coating layer of 3 to 30 mg / m ^{2 in} terms of chromium per side on the alloy layer. In this chromate coating layer, the amount of oxide chromium is preferably 10 mg / m ² or less in terms of chromium.

The Ni-Sn alloy plated steel sheet having the above-mentioned coating layer structure has the following advantages as compared with the current surface-treated steel sheet for welding cans.

The contact resistance of Ni-Sn alloy-plated steel sheet is much lower than that of nickel-plated steel sheet, especially after heat treatment for paint baking. Is much smaller than that of nickel-plated steel sheet, so that the welding suitable current range is wide. Furthermore, since the melting point of Ni-Sn alloy is lower than that of nickel,
Easy welding is also advantageous for the weldability of the Ni-Sn alloy plated steel sheet.

In addition, in pure tin plating, tin is present on the steel sheet in the form of grains or islands, and in thin plating, exposure of the base iron is inevitable,
Further, the Sn—Fe alloy layer formed by the heat treatment is hard and has poor workability, so that cracks are easily formed. For these reasons, pure tin-plated steel sheets sometimes undergo pitting corrosion due to organic acids or phosphoric acid. However, the above-mentioned Ni-Sn alloy-plated steel sheet widely covers the steel sheet surface even at a low plating amount, thereby enhancing corrosion resistance.
In addition, since tin and nickel are alloyed, the growth of the Sn—Fe alloy is suppressed, and the occurrence of cracks that adversely affect corrosion resistance is extremely small.

Furthermore, the melting point of the Ni-Sn alloy is higher than that of tin, and there is no flow due to high temperature baking of the paint in coil coating. Further, since paint adhesion is superior to that of pure tin-plated steel sheet, phenomena such as lifting, peeling, and burning of the coating film during baking do not occur. Even a slight lift of the inner coating film cannot be neglected, since the subsequent welding repair coating causes bubbles to be generated at that position.

As described above, the Ni—Sn alloy plating film has excellent corrosion resistance and paint adhesion, but these are further improved by the chromate film. The Ni-Sn alloy layer is
Although the steel plate surface is sufficiently covered, a small amount of fine pinholes remain. The chromate coating prevents corrosion from this pinhole.

The amount of Ni-Sn alloy attached needs to be 1060 mg / m ² or more. If it is less than 1060 mg / m ² , the weldability and corrosion resistance are significantly deteriorated due to slight exposure of the base iron. If it exceeds 3000 mg / m ^2, weldability, improved performance, such as corrosion resistance was not observed, the cost benefits of a low basis weight is eliminated, 3000 mg / m
² or less.

Nickel content of Ni-Sn alloy is 10-30% by weight
It is necessary to be. If the content is less than 10% by weight, tin is excessive, and tin is partially present alone, so that a part of the tin melts at 232 ° C., and the paint high-temperature baking property is deteriorated. 30% by weight
When the value exceeds, the contact resistance due to the heat treatment is rapidly increased, so that scattering is apt to occur at the time of welding, and the appropriate welding current range is narrowed.

The amount of chromate coating is 3 to 30 mg / m on one side in terms of chromium.
Need to be ² . If it is less than 3 mg / m ² , the improvement in corrosion resistance and paint adhesion is not sufficient. If it exceeds 30 mg / m ² , the contact resistance increases remarkably, and the weldability deteriorates. Further, when the amount of oxide chromium exceeds 10 mg / m ² per one surface in terms of chromium, the weldability deteriorates.

Ni-Sn alloy plating easily forms tin with Sn ²⁺ ions such as pyrophosphate ion and chloride ion, and is obtained by electrolysis from an aqueous solution in which an anion that has the effect of bringing the deposition potential of tin closer to that of nickel coexists. Can be

[Examples] Table 1 shows examples of the present invention. All plating base plates are thick
A 0.17 mm cold-rolled steel plate was used. Each evaluation was performed as follows.

Suitable welding current range The can body is manufactured by pseudoronic welding in which copper wire is passed between the upper and lower electrode rings and the can body material, and the can body material and the copper wire are moved to perform seam welding. Was measured. The welding suitable current range was determined with the lowest welding current at which sufficient strength of the weld was obtained as the lower limit and the highest welding current at which no scattering of the molten metal due to welding was observed as the upper limit.

High-temperature baking property of paint
Baking and hardening were performed at 300 ° C. After baking, the degree of baking and peeling of the coating film was evaluated as the high-temperature baking property.

After the appropriate coating for repair painting, the repair paint was applied and baked so as to cover the painted and unpainted areas. The bubbling caused by baking was visually observed.

After painting, corrosion resistance is applied.
Extrude 3 mm with an Erichsen tester so that the intersection is at the top, and contain 50 g of 15 g / l citric acid and 15 g / l sodium chloride
Was immersed in an air-saturated aqueous solution, and evaluated by the degree of corrosion after 72 hours.

 The symbols in Table 1 represent the following contents.

◎: extremely good ○: good △: slightly poor ×: poor [Effects of the Invention] In this manner, the unsuitability of high-temperature baking of paint such as coil coating of a pure tin-based surface-treated steel sheet is advantageously solved by tin alloy, and furthermore, has the same weldability and corrosion resistance as pure tin-based materials. The present invention provides a surface-treated steel sheet and has a remarkable effect in this field.

Claims (1)

(57) [Claims] (1) at least 1060 mg / m ² per side, 3000 mg / m
is the amount of m ² or less, and nickel is 10 to 30 wt%
Lower layer consisting of Ni-Sn alloy layer and 3 per side in terms of chromium
A surface-treated steel sheet for welded cans having excellent high-temperature baking properties for paints, characterized by having an upper layer comprising a chromate coating layer of up to 30 mg / m ² .