JPH07116613B2 - Surface-treated steel sheet for DI can and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a can material used for beverage cans, etc., for DI cans in which can copper is processed by a D & I (drawing & ironing) system during can making. The present invention relates to a surface-treated steel sheet.

[Prior Art] As a food can, there are used a three-piece can in which a body is upside down, and a two-piece can in which a ground and a body are integrally molded and the sky is attached to the top. There are two-piece cans with a shallow bottom made by squeezing and a so-called DI can with a deep bottom made by squeezing and ironing. The latter is often used for beverage cans. Especially when the can contents are carbonated drinks, the internal pressure becomes higher than the atmospheric pressure due to the generation of carbon dioxide gas.
There is an advantage that a thinner material than the piece can is sufficient, and that it is sanitary since it does not suck in contaminants from the outside when the can is opened.
On the other hand, the material is required to have extremely severe formability.
That is, in DI processing, a flat plate is first squeezed into a cup shape, and then ironing is applied while the die diameter is gradually narrowed in three steps. As a result, the can body after molding has a thickness of about one third of the original plate. As materials for this DI can, there are an aluminum plate and a surface-treated steel plate, and in the latter case, the surface-treatment film must fulfill the function of protecting the steel plate against corrosion in the can even after molding. After molding, the inner surface of the can is painted,
In steel cans, even if the amount of iron elution is extremely small, a so-called metallic odor is generated, and therefore the paint in the cans is subjected to a double strike.

For this reason, Sn-plated steel sheets having a large plating amount have been conventionally used as surface-treated steel sheets for DI cans. Sn is a soft metal, has good elongation for molding, and rarely causes accidents such as biting of dies, and the corrosion resistance of the steel sheet against the contents of the can is excellent, and it is harmless to the contents of the can and does not smell. There is also a track record in solder cans with a long history. However, Sn is unevenly distributed in resources, and there is a problem in using it in a large amount. Therefore, in recent years, attempts have been made to reduce the amount of Sn used. For example, JP-A-62 = 1498
In JP 97, one side of a cold-rolled steel sheet containing a small amount of Cr and others is plated with Ni or a Ni alloy, and Sn is applied to both sides of this treated steel sheet.
Disclosed is a steel sheet for containers, which is plated to give formability and corrosion resistance.

[Problems to be Solved by the Invention] However, the elution of iron from the can body may occur even after passing through the coating film when the period becomes long during storage after filling the beverage, and thus the container disclosed above. The development of a material that has a smaller elution amount of iron than steel sheets for use has become an issue.

The present invention has been made to solve this problem.
The present invention aims to provide a surface-treated steel sheet for DI cans in which the elution of iron is extremely small even when the Sn plating amount is reduced by fully utilizing the steel.

[Means for Solving the Problem] A means for achieving this object is to measure the amount of Ni on one surface of the steel sheet.
A Ni diffusion layer of 0.03 g / m ² or more and 0.6 g / m ² or less is formed, and a Ni plating layer of 0.01 g / m ² or more and 0.2 g / m ² or less and an alloy on it are formed on this diffusion layer. Not over 0.2g / m ² with Sn amount
It has a Sn plating layer of 2.8 g / m ² or less, and has a Sn plating layer of 0.5 g / m ² or more and 2.8 g / m ² or less with an unalloyed Sn amount on the other surface. Cr on the Sn plating layer
A surface treatment steel sheet for DI can having a chromate film of 1 mg / m ² or less in amount, and a method for producing the surface treatment steel sheet for DI can, which is 0.03 g / m on one side of the steel sheet before heat treatment. ² or more and 0.6 g / m ² or less Ni plating is applied, and when this Ni-plated steel sheet is heat-treated, a Ni diffusion layer is formed, and further 0.01 g / m ² or more and 0.2 g / m ² or less on this diffusion layer. Ni plating of N
After forming the i plating layer, 0.2g /
m ² or more 2.8 g / m ² subjected to the following Sn plating, the plated steel sheet was prepared by applying 0.5 g / m ² or more 2.8 g / m ² or less of Sn plating on the other side of the base steel, this plating This is a method for producing surface-treated steel sheets for DI cans in which a steel sheet is treated with a chromate solution mainly containing dichromate to form a chromate film with a Cr content of 1 mg / m ² or less. Fe alloy plating may be applied.

[Operation] As described above, the thickness of the DI can is reduced to about one third by processing. At this time, since the surface area of the plate expands as the plate thickness decreases, the plating film on the surface tends to be non-uniform. The inner surface of the molded can is subjected to chemical conversion treatment, and then the can inner surface paint is applied. This chemical conversion treatment is a pretreatment for coating, and a uniform treatment film without defects is required.

In order to obtain a uniform chemical conversion treatment film, the plating film after DI processing must be uniform, but if a Ni plating layer exists below the Sn plating layer, the Sn distribution after molding will be uniform. Figure 1 shows the effect of this Ni plating layer. Ni is plated on the Ni diffusion layer with various amounts of deposition, and Sn plating is applied on it to make a test piece. This test piece is DI processed. After that, the distribution of the amount of adhered Sn on the surface is measured by an X-ray microanalyzer. Measurement conditions are probe current 1.0 × 1
0 ^-6 A, probe diameter 2 μm, measurement area 200 μm x 200 μm
The measurement points in the visual field are 100 points x 100 points, and the collection time is 0.1 seconds for each measurement point. Since the intensity of Sn-Lα ray is high at the point with a large amount of Sn deposition, the intensity of each measurement point is averaged, and the point showing the intensity of 1/10 or less of this average value is the incomplete coating with a small amount of Sn deposition It was judged. The distribution is a uniform distribution when the number of incomplete coatings is small, and a uniform distribution when the number of incomplete coatings is large.
The vertical axis indicates the number of incomplete Sn coating portions, and the horizontal axis indicates the Ni plating amount.

The amount of incomplete Sn coating decreases with an increase in the Ni plating amount, but the reduction rate becomes abrupt when the Ni plating amount approaches 0.01 g / m ² , and then gradually decreases and gradually decreases to 0.2 g / m ^2. There is.
In addition to the effect of making the Sn distribution uniform, the Ni plating layer covers the Ni diffusion layer under the Ni plating layer to protect the base together with the Sn plating layer and prevent iron elution.

The Ni diffusion layer improves the corrosion resistance of the steel base and reduces the elution of steel into the can. This effect becomes larger as the Ni diffusion layer increases. This is shown in FIG. It is the result of measuring the amount of Fe eluted by exposing a test piece on which a certain amount of Sn was plated on the Ni diffusion layer and changing it to a corrosive environment. In the figure, the vertical axis is the amount of iron eluted, and the horizontal axis is the amount of Ni diffusion layer, which is the amount of Ni. When the amount of Ni is about 0.03 g / m ^2, the elution-reducing effect of steel appears clearly, and even if it exceeds 0.6 g / m ² , it does not change much.

The Sn plating layer is partly or wholly alloyed during DI processing, but the Ni / Sn alloy at this time is dense in crystal and has corrosion resistance.As with Sn and Ni, the base material is protected by the coating action to elute iron. prevent. Therefore, as the plating amount increases, the protective action also increases, and iron elution is prevented. This is shown in FIG. After subjecting a test piece plated with Sn on a certain amount of Ni diffusion layer with different plating amount to DI processing, degreasing and chemical conversion treatment was applied to the inner surface, the paint in the can was applied, and Fe was eluted by being exposed to the corrosive liquid. Is the result of measuring the amount of. In the figure, the vertical axis is the iron elution amount, and the horizontal axis is the Sn plating amount. Sn plating amount is 0.2g / m ²
At a certain level, the effect of suppressing iron elution becomes apparent, and 2.
It does not change much even if it is increased beyond 8g / m ² .

When Ni is plated, the coating effect of the Ni plating layer and Sn
The effect of suppressing the elution of iron is further increased in combination with the effect of making the layers uniform.

The one side described above is the side that becomes the inner surface of the can during the can making, and the other side is the outer surface of the can. In DI processing, if the coating on the outer surface is hard, it causes biting of the die and damage to the material surface. That is, the outer surface is particularly required to be easy to process. Sn
Since the plating layer is soft and rich in ductility and has good corrosion resistance and printability on the outer surface, a Sn plating layer is provided on the other surface. In this case, when the amount of the Sn plating layer is increased to about 0.5 g / m ² , surface damage during DI processing becomes almost nonexistent, and even if the amount exceeds 2.8 g / m ² , the effect does not change.

The chromate film is necessary to suppress the formation of Sn oxide, which reduces the adhesion of the paint. However, since this coating is hard and impairs workability, it is necessary to limit the amount. If the Cr content is 1 mg / m ² or less, biting and surface damage during DI processing will not occur. In order to limit the amount of this chromate film, it is sufficient to use a commonly used dipping chromate treatment liquid and not to prolong the treatment time.

The Ni plating layer applied before the heat treatment changes to the Ni diffusion layer during the heat treatment.However, when the heat treatment temperature is low, it is possible to reliably perform Ni / Fe alloy plating instead of Ni plating, such as heat treatment for overaging treatment. A diffusion layer can be obtained.

[Example] (Example 1) Ni on one surface of a cold-rolled steel sheet having a thickness of 0.28 mm was plated with Ni at 700 ° C.
After heat treatment for 0 seconds to form a Ni diffusion layer and temper rolling, Ni plating was performed on this Ni diffusion layer, then Sn plating was performed on both sides, and finally chromate treatment was performed. These treatments were performed under conditions within the scope of the present invention as examples, conditions outside the range as comparative examples, and conditions of the conventional example so that comparisons could be made. For the treated test piece,
DI processing was performed to examine the ease of processing. After that, it is degreased and subjected to chemical conversion treatment using a commonly used phosphoric acid-based treatment liquid,
Apply 50 mg / dm ² of epoxy can inner surface paint on this, 205
After baking at 10 ° C. for 10 minutes, Fe elution test was performed to evaluate the quality.

The details of these treatments or tests were as follows.

Ni _{plating: NiSO 4 · 6H 2 O 240} g / NiCl 2 · 6H 2 O 45 g / H 3 BO 3 30 g / pH 2.6 Bath temperature 50 ° C. Current density 40 A / dm ² Sn Plating: Sn ⁺⁺ 30 g / free Acid (H ₂ SO ₄ equivalent) 13 g / Brightener 5 g / Bath temperature 40 ° C Current density 30 A / dm ² Chromate treatment: Na ₂ Cr ₂ O ₇ 20 g / Bath temperature 50 ° C pH 5.5 Treatment time 1 second DI processing is First, a blank with a diameter of 123 mm is punched out, and a cup with an inner diameter of 72 mmφ and a height of 36 mm is formed by a cupping press,
Then, this cup is put into a DI machine, and redrawing and three-step ironing are performed.
A can of 52.0 mm and can height of 130 mm was formed. At this time, the punch speed is 30 mm / min, the stroke is 600 mm, and the coolant is 40 ° C.
Recycled at ~ 100 ° C. For ease of processing, 100 cans were continuously made, and the presence or absence of defective cans was evaluated.

For iron elution test, 200 ml of corrosive liquid in the test material after DI processing
Forced iron elution. The corrosive liquid is citric acid 1.5% and salt
The corrosion temperature was 38 ° C. in an aqueous solution containing 1.5%, and after 96 hours, the amount of iron eluted in this corrosion liquid was measured.

The iron elution amount was evaluated as ⊚, 1 mg / or more than 1.5 mg / less, 1.5 mg / or more 2.0 mg / or Δ, and 2.0 mg / or more ×.

Table 1 shows the test materials and the test results.

In the examples, both workability and corrosion resistance were good. On the other hand, in the comparative example, any one of the diffusion layer and the plating layer, which lacks the adhesion amount or has no chromate film, is inferior in corrosion resistance. Further, those having a small amount of Sn plating on the outer surface and those having a large amount of chromate film have a problem in workability. In the conventional example, since there is no diffusion layer or Ni plating layer, the corrosion resistance is poor when the Sn plating amount is small. Without these layers, corrosion resistance cannot be secured unless the Sn plating amount is large as in Test No. 25.

[Effects of the Invention] As described above, according to the present invention, one surface is on the Ni diffusion layer.
The Ni plating layer has a uniform thin Sn plating layer on top of it, and the other surface has a Sn plating layer in an amount that is easy to process, and the chromate layers on both sides are Sn.
Although it prevents the oxidation of, the amount has no problem in processing. Therefore, the surface-treated steel sheet for DI can of the invention has a small Sn content.
While maintaining the workability required for DI can materials, it has excellent corrosion resistance. As described above, the effect of the present invention, in which the performance suitable for each of the front and back sides and resource saving are realized, is great.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the Ni plating amount and the Sn film incomplete portion for explaining the present invention, FIG. 2 is a diagram showing the relationship between the Ni diffusion layer amount and the iron elution amount, and FIG. 3 is It is a figure which shows the relationship between Sn plating amount and iron elution amount.

Continuation of the front page (56) Reference JP 62-149897 (JP, A) JP 63-4090 (JP, A) JP 57-177991 (JP, A) JP 58-37194 (JP , A) JP 58-147589 (JP, A) JP 60-29484 (JP, A) JP 63-499 (JP, A)

Claims (3)

[Claims] 1. A 0.03 g / m ² or more of Ni amount on one surface of the steel sheet 0.6 g / m ²
Ni diffusion layer below, 0.01g / m ² or more 0.2g on this diffusion layer
/ m ² or less Ni plating layer and an unalloyed Sn amount on it has a Sn plating layer of 0.2 g / m ² or more and 2.8 g / m ² or less, and the other surface has an unalloyed Sn amount. Sn of 0.5g / m ² or more and 2.8g / m ² or less
It has a plating layer and the amount of Cr on the Sn plating layers on both sides
Characterized by having a chromate film of 1 mg / m ² or less
Surface-treated steel sheet for DI cans. 2. On one side of the steel sheet before heat treatment, 0.03 g / m ² or more and 0.6 g
/ m ² or less Ni plating is applied, and when this Ni-plated steel sheet is heat-treated, a Ni diffusion layer is generated, and a Ni diffusion layer of 0.
After forming the Ni plating layer by performing Ni plating of 01g / m ² or more and 0.2g / m ² or less, 0.2g / m ² or more and 2.8 or more on this Ni plating layer.
g / m ² subjected to the following Sn plating, and other surface is prepared plated steel sheet subjected to 0.5 g / m ² or more 2.8 g / m ² or less of Sn plating, mainly the plated steel sheet dichromate A method for producing a surface-treated steel sheet for DI cans, which comprises treating with a chromate solution to form a chromate film having a Cr content of 1 mg / m ² or less. 3. The method for producing a surface-treated steel sheet for a DI can according to claim 2, wherein Ni-Fe alloy plating is applied instead of Ni plating.