JPH0696790B2 - Surface-treated steel sheet with excellent weldability and paint adhesion - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface-treated steel sheet for welding cans suitable for various foods, beverages, and other filling and storing.

BACKGROUND ART Tin and tin-free steel sheets are generally used as materials for containers used in foods and beverages, and recently, thin tin-plated steel sheets with reduced tin plating (to ensure weldability) , Some have Ni plating on the base), and nickel-plated steel sheets are also used for the purpose of reducing material costs. In terms of cost, tin-free steel sheets are extremely superior to tin-plated steel sheets and nickel-plated steel sheets, not to mention tinplate. Also, the tin-free steel sheet is very excellent in terms of paint adhesion and corrosion resistance after painting, and the fact that these characteristics are excellent is also the reason why the demand for the tin-free steel sheet is increasing.

However, this tein-free steel plate has a very big defect that the weldability is poor, and at present, it is manufactured exclusively by a bonding method. Therefore, improving the weldability of the tin-free steel sheet has great industrial significance.

Various attempts have been made with the aim of improving the weldability of thetain-free steel sheets, and the status of these technological improvements is summarized as follows.

(1) Sn plating on the lower layer of the chrome plating layer to improve weldability is disclosed in JP-A-62-124296, JP-B-61-1518,
JP-A-56-127776, JP-A-56-44793, and (2) JP-A-62-40396 and JP-A-62-10709, which are nickel-plated under the chromium plating layer to improve weldability.
7, JP-A-61-91393, JP-A-62-205297, (3) Ingenuity of the chrome plating layer itself (in many cases, the resistance during welding is reduced by making the chrome plating projecting or discontinuous). ) Was carried out as disclosed in JP-A-62-2052.
97, JP-A-62-99497, JP-A-63-35797, JP-A-62-63
678, JP-A-61-281899, JP-A-61-213399, and many other applications have been filed.

All of these aim at improving the weldability by improving the insulating properties of the chromium plating layer and the hydrated chromium oxide layer.

Problems to be Solved by the Invention The present invention is based on the content of (1) below the chrome plating layer.
It aims to improve the weldability by Sn plating, but it is Japanese Patent Publication No. 61.
-1518, JP-A-56-127776, JP-A-56-44793, the amount of base Sn plating required to reduce the contact resistance is large, only the characteristics of thin Sn-plated steel sheet,
The characteristics of the original tein-free steel plate are sacrificed to improve weldability.

That is, although the weldability of the tin-free steel sheet is improved in all cases, the original excellent properties of the tin-free steel sheet, such as metallic luster appearance, excellent paint adhesion, and corrosion resistance after painting, are sacrificed. It cannot be said that it is an excellent surface-treated steel sheet for cans.

Further, Japanese Patent Application Laid-Open No. 62-124296 is very similar to the present invention in terms of the purpose and structure, but the state of plated Sn is normal thin Sn.
It is the same as plating, the contact resistance is lowered and the weldability is improved, but the weldability is not always satisfactory.

That is, in JP-A-62-124296, in order to secure the characteristics of the tin-free steel sheet, the exposed portion of the steel sheet is increased as much as possible, and an appropriate amount of Sn layer is secured to secure the weldability. As a result of trying to achieve these two contradictory objectives, both properties are inadequate as a result. We have
As a result of diligent study on this point, in JP-A-62-124296, by precipitating granular Sn, which is considered inappropriate, on the steel sheet, to secure the characteristics of the above-mentioned tin-free steel sheet, and weldability. We were able to achieve these two conflicting objectives of securing.

That is, the problem to be solved by the present invention is, paint adhesion, which is a characteristic of an excellent tein-free steel sheet, without impairing corrosion resistance after coating, etc., cheaper than tin plate, and easy to manufacture, weldability. It is intended to provide a surface-treated steel sheet having improved properties and capable of high-speed can making.

Means the present invention for solving the problem per side on the surface of the steel sheet, after tin plating of tin content ^{20~200mg / m 2, 30~150mg / m} 2 of metallic chromium layer, chromium to 40 mg / m ² as chromium In the steel sheet on which the hydrated oxide layer is formed, the tin in the tin plating layer is made granular and the grain size of the tin particles is
0.2-2.0μm, grain height 0.1μm or more, the number of tin grains is 1
× 10 ⁹ to 1 × 10 ¹² pieces / m ² , characterized by the presence of metallic chromium on the exposed steel plate portion where tin does not adhere, and the tin particles, and chromium hydrate oxide thereon. A surface-treated steel sheet with excellent weldability and paint adhesion.

The details will be described below.

The basis of the present invention is that the underlying tin plating has a particle size of 0.2 to 2.0 μm,
Granules with a grain height of 0.1 μm or more, and this granular tin is 1 × 10 ⁹
˜1 × 10 ¹² pieces / m ² exist. After that, the plated tin is not melted by heating, or after being melted by heating, chromium is hydrated on the exposed portion of the steel sheet and tin particles by a method for producing a normal tin-free steel sheet, and then hydrated with chromium. By forming an oxide film, the surface-treated steel sheet aimed at by the present invention can be obtained.

In particular, in the present invention, the underlying tin plating has a particle size of 0.2 to 2.0 μm,
It is very important to use granular tin with a grain height of 0.1 μm or more, and if this is uniformly thinly plated on a steel plate like normal tin plating (in the case of Sn plating, in the case of thin plating, islands in the case of thin plating are used). Plate, and does not necessarily cover a uniform surface), or during heating during melting or heating during the can manufacturing process.
/ Fe alloy is formed and does not contribute to the improvement of weldability.
The excellent metallic luster and coating properties of the TEIN FREE steel plate will be impaired.

Next, since the number of the granular tin plating is also very important, the number of the granular tin must be set to 1 × 10 ⁹ to 1 × 10 ¹² pieces / m ² . In JP-A-62-124296, the exposed portion of the steel plate is regulated, and the exposed portion of the steel plate is converted into a circle of 0.5 to 20 μm.
However, if the thickness exceeds 20 μm, the exposed portion of the steel plate becomes continuous, and most of the plated tin becomes granular with a particle size of 0.1 to 1.0 μm, and the plating adhesion is poor, which is not preferable.

Although this point is largely different from the content of the present invention, the inventors of the present invention infer that in JP-A-62-124296, the tin plating amount is 50 to 900 mg / m ² in the claims, As far as the examples are concerned, 100 to 600 mg / m ² (except for one example, 300 mg / m ²
It is considered that the adhesion of the tin-plated layer was poor, because the accuracy was relatively high in the above range.

In any case, in the present invention, in JP-A-62-124296, "continuation of exposed portion of steel sheet" which is inappropriate, is positively performed to secure the excellent characteristics of the ten-free steel sheet. And
In order to ensure weldability, tin plating should have a diameter of 0.2-2.0 μm, grain height of 0.1 μm or more, and the number of granular tin should be 1 × 1.
It was possible to reduce the contact resistance by setting it to 0 ⁹ to 1 × 10 ¹² pieces / m ² .

That is, in the steel sheet of the present invention, the amount of Sn necessary for reducing the contact resistance could be reduced by growing Sn crystals in the vertical direction on the surface of the steel sheet by granulating Sn. By reducing the required amount of Sn, it is possible to maximize the exposed part of the steel sheet and secure the excellent properties of the tin-free steel sheet.

A method for obtaining such granular tin plating is disclosed in JP-A-62-1242
As described in 96, a plating bath with an appropriate divalent tin ion concentration was obtained by removing additives (ethoxylated α-naphthol, ethoxylated α-naphthol sulfonic acid, etc.) called brighteners from ordinary tin plating baths. There must be. The tin particle size depends on the ratio of the tin ion concentration and the acid concentration and the current density, and the tin particle size increases as the acid concentration increases or the current density decreases (Japanese Patent Publication No. 57-14758). The number of grains also depends on the current density and the ratio of the tin ion concentration and the acid concentration, but the influence of the current density is large, and as the current density increases, the frequency of occurrence of electrodeposited crystal nuclei increases and The number increases.
Therefore, in Examples described later, the particle size and the number of tin particles can be controlled by the plating bath composition and the current density. Further, since the height of the tin particles greatly depends on the electrolysis time, it can be controlled by the electrolysis time in this embodiment.

In JP-A-62-124296 as well, the size of the exposed portion of the steel plate is 0.5 μ.
In the following, the surface of the steel sheet is covered with tin, and the characteristics are similar to those of the conventional ultra-thin tin-plated steel sheet, which is not preferable. In this respect, it is the same as the object of the present inventors. In order to secure the excellent metallic luster and coating characteristics of the tin-free steel sheet, it is necessary to reduce the tin coverage as much as possible. That is why the tin is made granular,
The present invention aims at maximizing the exposed portion of the steel sheet by granulating tin.
Compared with the Sn plating layer obtained in, the granular Sn obtained by growing the Sn plating layer in the direction perpendicular to the steel plate surface can have a small Sn coverage rate per unit Sn plating weight, so that the exposed steel plate part Will increase.

Furthermore, even if such granulation is performed, the Sn adhesion amount should be adjusted in order to maintain the excellent metallic luster and coating characteristics of the TEIN FREE steel plate.
It was necessary to limit it to 200 mg / m ² or less.

As described above, regarding the adhesion state of tin plating, Japanese Patent Application Laid-Open No. 62-124296
Although the contents of the present invention have been described with reference to the difference between the above and the present invention, the difference between the present invention and JP-A-62-124296 is that JP-A-62-124296 makes the exposed portion of the steel sheet discontinuous and The aim is to ensure weldability in the plated part. On the other hand, in the present invention,
Granulation of tin leaves the exposed part of the steel plate as much as possible (discontinuity) in order to secure the characteristics of the tin-free steel plate.
It is characterized by that.

The difference in these ideas and the difference in the film structure of the product also appear in the difference in the subsequent chrome plating and chromate treatment methods. That is, in JP-A-62-124296, since the tin coverage is relatively high, it is said that the chromium metal and the chromium hydrate oxide film must be deposited evenly on the tin as well as the exposed portion of the steel sheet. For this reason, it is necessary to limit the current density under the chromium plating conditions.

In the present invention, the exposed portion of the steel sheet is the majority, and if a metal chrome similar to the tin-free steel sheet and a chromium hydrated oxide film are formed on the exposed portion of the steel sheet, the characteristics of the tin-free steel sheet are secured. In particular, it is not necessary to form the same film as the exposed portion of the steel sheet on the tin grains. On the contrary, in the present invention, this granular tin protruding on the chromium plating layer aims to contribute to the reduction of the contact resistance between the steel sheets during seam welding or between the electrode and the steel sheet. It is preferable that the precipitation of metallic chromium or hydrated chromium oxide is small.

FIG. 1 shows the surface condition of the surface-treated steel sheet of the present invention with a scanning electron microscope. Clearly granular tin is formed.

First, regarding the size of tin particles, the size of tin particles is
It should be 0.2μ or more. This is because in order to improve the weldability, it is necessary to reduce the contact resistance between the steel plates during welding and between the electrode and the steel plate, and for this reason, it is necessary that the tin particles are projected on the chrome plating. is there. Metal chrome 150m
g / m ² , chromium hydrate oxide (chromium 40 mg in terms of metallic chromium)
The thickness of / m ² ) is about 0.04μ, and 0.2μ or more is required to improve the weldability by protruding on the chromium plating layer.

Next, it is set to 2.0 μ or less because tin particles having a particle size larger than this are inferior in adhesion to the steel plate surface, and 20 to 200 mg /
This is because the required number of tin particles cannot be obtained with a limited tin plating amount of m ² .

The most desirable tin grain size is 0.3 to 1.0μ, and if the tin grain size is controlled within this range, the same high-speed seam weldability as when tin plating of approximately 2.0 g / m ² or more is secured. To be done.

Next, the reason why the number of tin particles is limited to 1 × 10 ⁹ to 1 × 10 ¹² particles / m ² will be described. The lower limit is the number of tin particles that is the limit for obtaining good weldability, and the upper limit is determined within the range that does not impair the excellent metallic luster of the tin-free steel sheet and the performance such as coating properties.

That is, if it is less than 1 × 10 ⁹ pieces / m ² , the contact resistance is large and it does not have high-speed weldability. If it exceeds 1 × 10 ¹² pieces / m ² , the appearance becomes slightly white and the paint adhesion is This is because it is lower than that of the free steel plate.

Next, the reason why the tin plating amount is limited to ²⁰ to 200 mg / m ² will be described. This is a value that is naturally determined when the particle size of tin and the number of tin particles are limited as described above, but it is set to clarify the limited range of the tin plating amount. Is for the same reason that the number of tin particles is limited, the lower limit is the amount required to ensure excellent weldability, and the upper limit is the amount of tin plating limited within the range that does not impair the properties of the tin-free steel sheet. There is.

As described above, the limits of the diameter of the tin particles, the size of the tin particles, and the tin plating amount have been clarified. The above-mentioned limits are summarized as follows from the viewpoint of tin coverage. That is, taking the tin coverage as a scale, the ratio of tin grain coverage / exposed steel sheet should be about 1/19 (tin grain coverage 5%) to 2/8 (same 20%). However, the above-mentioned various conditions for tin plating are limited.

Next, the chrome plating and the chromate treatment method will be described. In the present invention, these chrome plating and chromate treatment methods are not particularly limited.
That is, according to a method for producing a normal tin-free steel plate, chromium plating and chromate treatment may be performed,
Since 80% or more of the exposed steel plate with no tin is present, if chromium plating and chromate treatment are carried out in the usual way, metallic chromium on the exposed steel plate and granular tin, and a chromium hydrate oxide layer Is formed, which means that the steel has properties equivalent to those of a normal tein-free steel plate.

The precipitation of chromium on the granular tin is less than that on the exposed portion of the steel sheet. Further, even if chromium is deposited on the granular tin, the lower soft tin has a thickness of 0.1 μ or more, which is presumed to contribute to the reduction of the contact resistance.

Therefore, in the present invention, the state of chromium deposition on tin plating is not particularly limited, and it is essential that the exposed portion of the steel plate forms the original chromium plating layer and chromium hydrate oxide layer. For this reason, the amount of chromium plating layer, chromium hydrate oxide layer of the surface-treated steel sheet of the present invention is in the range of general tein-free steel sheet, metal chromium is 30 to 150 mg / m ² , chromium hydrate oxide. The layer chromium was limited to 2-40 mg / m ² (metal chromium equivalent).

Generally, chromium in the hydrated chromium oxide is required to have a concentration of about 10 mg / m ² or more, but this is to ensure the adhesive strength in the adhesive can manufacturing method. About 2 mg / m ² is sufficient to secure the thickness of the chromium hydrated oxide layer that adversely affects the seam weldability, and it is preferable that the thickness is small. The layer) was slightly lower. Therefore, the amount of metallic chromium and the amount of hydrated chromium oxide may be appropriately selected depending on the can manufacturing method, contents and the like.

Examples Next, the content of the present invention will be specifically described based on Examples and Comparative Examples.

Example 1 A low carbon cold-rolled steel sheet having a thickness of 0.23 mm which was cold-rolled, continuously annealed, and temper-rolled by a conventional method was subjected to conventional degreasing (Na
OH 50g /, 60 ℃, current density 10A / dm ² for 1 second cathodic electrolysis treatment, pickling (sulfuric acid 50g /, 30 ℃, current density 10A / dm ² 1
Second cathodic electrolysis treatment), and then tin plating and chromium plating under the following treatment conditions to prepare Examples 1 to 5 shown in Table 1 and then Comparative Examples 1 to 5. The evaluation results are shown in Table 1.

[1] Tin plating (1) Bath conditions SnSO ₄ 10g / (Sn ⁺² 6g /) H ₂ SO ₄ 30g / bath temperature 40 ° C (2) Plating conditions Current density 3 A / dm ² Electricity 1-3 C / dm ² [2] Chromium plating (1) Bath conditions CrO ₃ 100g /, H ₂ SO ₄ 1.2g / bath temperature 50 ℃ (2) Plating conditions Current density 50 A / dm ² Electricity 50 C / dm ² [3] Evaluation (1) Adhesion of paint 3. Epoxyphenol-based paint (SJ-6256, Kansai Paint Co., Ltd.) was baked on the test material (coating amount 50 mg / dm ² ), and then 3.
After performing retort treatment at 110 ° C. for 60 minutes in a 0% NaCl solution, a scratch was put on a cross board with a knife, and a tape peeling test was performed.

(10 (good) ← → 1 (poor)) (2) Paint corrosion resistance Epoxyphenol-based paint (Kansai Paint Co., Ltd. SJ-6256) was applied on the test material after baking (coating amount 50 mg / dm ² ) and then applied. After cross-cutting the film with a knife, dip it in 1.5% NaCl, 1.5% citric acid solution (40 ° C) for 4 days, and then perform a tape peeling test on the cross-cut part to evaluate (5 (good) ← →
1 (Failure) (3) Contact resistance The test material was first heat-treated at 210 ° C for 20 minutes and then cut into 50 mm squares. The two samples were stacked and the electrode diameter was 4.5 mmφ.
It was sandwiched between the electrodes, and a pressure of 50 kgf was applied between the electrodes to measure the contact resistance. (Current flowing between electrodes is 100m
A) Passed if less than 500μΩ.

(4) Evaluation of tin-plated grains The sample material was observed with a scanning electron microscope at a magnification of 5000 to 10,000, and the size of typical tin grains was measured.

Further, the number of tin particles was counted in a field of view of 50 μ × 50 μ (actually a photograph) and converted into the number per m ² .

Effects of the Invention As described in detail above, first tin-plated in granular form,
After that, like the usual tein-free steel plate, by providing metallic chromium and chrome hydrated oxide layers, the tain-free steel plate retains its excellent appearance, paint adhesion, and corrosion resistance after painting, and at high speed. A surface-treated steel sheet having excellent seam weldability was obtained. According to the present invention, high-speed seam welding, which was conventionally possible only with tinplate, ultra-thin tin-plated steel sheets, and nickel-plated steel sheets, is now possible with surface-treated steel sheets having substantially the same characteristics as ordinary tin-free steel sheets.

[Brief description of drawings]

FIG. 1 is a drawing-substituting photograph showing the metallographic structure of the surface of the surface-treated steel sheet of the present invention taken by a scanning electron microscope.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshihiro Kaneda, Yoshihiro Kaneda, No. 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Shin-Nippon Steel Co., Ltd. Inside the Hirohata Works (56) Reference JP 62-124296 (JP, A)

Claims (1)

[Claims] 1. A steel sheet having a tin content of 20 to 200 mg / m ² per surface.
After the tin plating, the metal layer of chromium 30~150mg / m ^2, in the steel sheet to form a hydrated chromium oxide layer to 40 mg / m ² as chromium, and granulated tin of the tin plating layer, the tin grains Has a particle size of 0.2 to 2.0 μm, a particle height of 0.1 μm or more, and the number of tin particles is 1 × 10 ⁹ to 1 × 10 ¹² pieces / m ² , and the exposed steel plate portion where tin does not adhere and tin. Weldability characterized by the presence of metallic chromium on the grains and chromium hydrate oxide on it,
Surface-treated steel sheet with excellent paint adhesion.