JPH0448096A - Production of surface-treated steel sheet for vessel having satisfactory rust resistance at outside of can and fine appearance - Google Patents

Abstract

PURPOSE:To produce a surface-treated steel sheet for a vessel having satisfactory rust resistance at the outside of a can and fine appearance by forming a Zn plating layer of a specified thickness as a lower layer on one side of a steel sheet corresponding to the outside of a can and then forming an Sn plating layer as an upper layer under specified conditions. CONSTITUTION:A Zn plating layer of 1-10g/m<2> thickness if formed as a lower layer on at least one side of a steel sheet corresponding to the outside of a can. An Sn plating layer of 0.1-5g/m<2> thickness is then formed as an upper layer with a pyrophosphate plating bath of pH 5-12 contg. 0.01-5g/l amino acid compd. and/or 1-50g/l citrate as an Sn plating bath. The amino acid compd. may be glycine or alanine and the citrate may be sodium or potassium citrate. A plated steel sheet having satisfactory suitability to working into a can and finishing by printing after drawing and ironing (DI) and exhibiting superior rust resistance at the outside of the can is obtd.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides surface treatment for containers with excellent external rust resistance and appearance, which is used as a material for cans and can lids using drawing and ironing processing (D, I). This relates to a method of manufacturing steel sheets.

(Prior art) In recent years, there has been a remarkable development in can manufacturing methods using drawing and ironing (e.g. DI processing can manufacturing method), mainly for beverage cans, and there is a strong demand for surface-treated steel sheets for containers with higher performance than ever before. . Conventionally, tinplate with good DI formability has been used as a surface-treated steel sheet for DI cans, but there are two major problems with the outer surface of the can:

1) Rust is likely to form on the outside of the can, and especially when the can is immersed in tap water to cool it, rust will form in a short period of time at damaged areas on the bottom and wall.

2) When printing is performed after DI molding, white ink or the like does not show the original whiteness of the ink, and there is a problem with the printing finish.

Furthermore, EC Open End (hereinafter referred to as EOE),
Tin plates and electrolytic chromic acid-treated steel plates used for can lids such as ordinary ends have similar problems regarding the rust resistance of their outer surfaces.

Thus, the problem of rust resistance on the outer surface side can be explained by the potential relationship between the base iron and the plating layer. i.e. tin, T
In the case of FS, the Sn plating layer and the Cr plating layer are electrically conductive to the base steel, and there is no effect of sacrificial corrosion protection on the base steel.

In order to solve this problem, a steel plate for containers has been proposed in which a Cr-containing steel plate is plated with Sn, as can be seen in, for example, Japanese Patent Laid-Open No. 62-17199 and Japanese Patent Laid-Open No. 62-13594. The point of all of these proposals is to bring out the sacrificial anti-corrosion ability of the plating layer by adding other components (for example, chromium) to the base metal and controlling the potential of the base metal throughout. Further, although these steel sheets have a great effect of improving the rust resistance on the outer surface side, it is necessary to add about a few percent of other components in order to exhibit a sufficient effect, and there remains a problem in terms of economic efficiency.

Furthermore, the problem that the tinplate DI cans have a dark appearance after printing can be explained as follows. In other words, the Sn plating layer that has undergone severe processing such as DI molding is damaged,
This is because the underground railway is exposed. In other words, the reason why tinplate DI cans are dark is due to the low spectral reflectance of exposed iron, and in order to improve the appearance of DI cans, it is important to avoid exposing iron as much as possible after DI molding. Considering these causes, it is clear that conventional proposals cannot address the problem.

In order to solve these problems, we developed a Sn/Z film that utilizes Zn metal and has a Zn plating layer on the bottom layer and a Sn plating layer on the top layer.
Although n-double-layer plated steel sheets are effective, from a manufacturing technology perspective, the Sn plating technology applied to the upper layer is an important point. That is,
Pyrophosphoric acid-based plating baths are effective as Sn plating baths that can suppress dissolution of the underlying Zn plating layer, but the precipitation of Sn metal from pyrophosphoric acid-based plating baths deteriorates the gloss and smoothness of the plating layer. There is a big problem, and unless this problem of plating appearance is solved, the commercial value of Sn/Zn double-layer plated steel sheets will be poor and industrialization will be difficult.

(Problems to be Solved by the Invention) The present invention has been made to address these problems, and exhibits excellent rust resistance on the outer surface of the can and has good can forming processability (especially DI formability). The present invention aims to provide a method for producing a Sn/Zn double-layer plated steel sheet as a surface-treated steel sheet for containers, which has a good printing finish after DI molding and is also economical.

(Failure to solve the problem) The gist of the present invention is as follows.

(1) At least 1~
S
n As a plating bath, 0.01 to 5 g/! Apply a Sn plating layer of 0.1 to 5 g/m2 using a pyrophosphoric acid-based coating bath with a pH of 5 to 12 to which one or two types of amino acid compounds or 1 to 50 g/l of citrate are added. A method for producing a surface-treated mesh plate for containers having good rust resistance and appearance on the outer surface of the can.

(2) At least 1~
], on the upper layer of the net plate having a Zn plating layer of Og/m2,
As the Sn plating bath, a birophosphoric acid plating bath with a pH of 5 to 12 to which 0.01 to 5 g/2 of an amino acid compound or 1 to 50 g/l of citrate is added is used. 5g/rr? Apply a Sn plating layer of
A method for producing a surface-treated copper plate for a container having good rust resistance and appearance on the outer surface of the can, characterized in that a chromate film is then applied at a coating weight of 1 to 50 μ/n (in terms of chromium).

(for production) The present invention will be explained in detail below.

In the present invention, as the plated original plate, a plated original plate having a material suitable for the purpose of use as a needle plate for a container is used. The manufacturing method of the plated original plate is not particularly regulated, and it is manufactured through a normal steel billet manufacturing process such as hot rolling, pickling, cold rolling, annealing, and adjustment rolling. A Zn plating layer that exhibits stable rust resistance is applied to the lower layer of the surface corresponding to the outer surface of the can on the plated original sheet manufactured in this way, and then the upper layer is applied to improve rust resistance and provide lubrication during DI molding. A Sn plating layer with properties such as functionality is applied. There are no particular restrictions on the surface corresponding to the inner surface of the can, and it may be Sn-plated, electrolytically chromic acid-treated, or Ni-plated, and may also be coated with an organic resin thereon. Furthermore, there are no particular restrictions on their manufacturing methods.

Next, the effects of the plating layer applied to the outer surface, which is a feature of the present invention, and the manufacturing method thereof will be described.

The purpose of applying a Zn plating layer on the lower layer of the outer surface and a Sn plating layer on the upper layer is to improve the appearance of the outer surface, and to improve the appearance of the outer surface.
Formability, ■Ensuring excellent rust resistance.

First, the total amount of plating in the upper and lower layers has a large effect on improving the appearance. That is, the reason why the appearance after wide ink printing after DI molding is dark is because the plating layer is damaged during DI molding and the base metal with low spectral reflectance is exposed. In other words, in order to improve the appearance after printing, a plating layer must be applied to prevent iron from being exposed even after DI molding. Total plating amount of upper layer and lower layer, 1g per month
If it is less than /rrf, it will not be possible to prevent iron from being exposed after DI molding, and it will be difficult to ensure a good appearance.

Also, if the total plating amount exceeds 15g/rrf,
The effect of improving appearance reaches saturation and becomes economically disadvantageous.

In other words, the total plating amount for the upper and lower layers is 1.1 to 15g.
/rI'r is appropriate. Furthermore, the breakdown is as follows:
The plating amount is 1 to log/bo, and the upper Sn plating layer is 0.
It is regulated to 1-5g/ryf. The reason is that the lower layer of Zn
If the plating amount is less than Ig/rrf, good rust resistance cannot be ensured, and if it exceeds 10 g/rrf, the effect of improving rust resistance is saturated and it becomes economically disadvantageous. Furthermore, if the amount of Sn plating in the upper layer is less than 0.1 g/rrf, the amount of Sn, which has excellent lubricity, will be insufficient, resulting in deterioration of DII formability and the occurrence of defects such as "caking" during continuous molding. Therefore, it becomes impossible to ensure good moldability. In addition, if the amount of Sn plating exceeds 5 g/m2, DII
This becomes economically disadvantageous since the lubricating effect regarding formability is saturated and the amount of expensive Sn plating increases.

In other words, a double-layer plated steel sheet with a lower Zn plating layer of 1 to 10 g/rJ and an upper Sn plating layer of 0.1 to 5 g/rJ is exposed to a corrosive environment with sufficient moisture, oxygen, etc. Even if there is machining damage or pinholes in the plating layer, no rust is observed from the base metal due to the effect of the lower plating layer, and the rust resistance is good. Furthermore, the effect of the upper plating layer ensures good continuous DII formability,
Even after DI processing, the base iron is hardly exposed due to the effect of the total plating amount of the lower layer and the upper layer, and a good printing finish can be achieved.

Next, a method for manufacturing the Sn/Zn two-layer plated mesh plate described above will be described.

First, the Zn plating of the lower layer can be carried out using a sulfuric acid bath, a chloride bath, etc. that are usually used industrially, and the plating conditions are not particularly regulated, but the bath composition is 200 to 500 g/A of zinc sulfate. , 60-100 g of sodium sulfate
/l is sufficient. In addition, the current density is 10 to 100A/
dff12 and a bath temperature of 40 to 70°C are sufficient.

Next, the Sn plating of the upper layer will be described. When a Zn plating layer is provided as a lower layer and a Sn plating layer is applied on top of the Zn plating layer, it is necessary to solve the problem of dissolution of Zn metal into the Sn plating bath in terms of manufacturing technology. This is because Zn metal is extremely active because it has a base potential, and when it is immersed in a Sn plating bath, it undergoes active dissolution and is eluted into the Sn plating bath as Zn'' ions, contaminating the expensive Sn plating bath. This phenomenon is particularly noticeable when a Sn plating bath with a very low pH is used, such as a sulfuric acid-based ferrostane bath or a chloride bath, which are commonly used industrially as a Sn plating bath. Zn metal is actively dissolved in the strongly acidic and strongly alkaline PU range.The appropriate PU range for the Sn plating bath, where Zn metal is difficult to melt, is pH: 5 to 12.
It is. When the pH is less than 5, Zn metal is actively dissolved and S
plating bath becomes contaminated. In addition, if pl ( exceeds 12), it becomes too alkaline and causes active dissolution of Zn.In other words, the appropriate pH range of the Sn plating bath where active dissolution of Zn metal is difficult to occur and the Sn plating bath is not contaminated is
l+5 to 12.

As such a weak acidic to neutral to weakly alkaline Sn plating bath, a pyrophosphoric acid plating bath is suitable. The reason is that in such a pH range, Sn'' ions cannot exist alone in the plating bath, but precipitate as hydroxide.
In order to stably exist in the plating bath as a Sn" ion that can be plated, it must be present in the bath as a complex salt, and a pyrophosphate bath is suitable for this purpose.Pyrophosphate ions are stable with Sn ions. As the Sn plating bath of the present invention, a pyrophosphate-based plating bath is regulated.The concentration, plating temperature, etc. of the pyrophosphate-based Sn plating bath are not particularly regulated. .

Electrodeposition of Sn metal from a pyrophosphoric acid plating bath has major problems in terms of gloss and smoothness of the plating layer. This appears as a phenomenon in which the appearance after Sn plating takes on a gray-black color with almost no metallic luster, and the commercial value as a surface-treated mesh plate for containers is significantly impaired.

The reason for this is that the conventional pyrophosphate-based Sn plating bath
In the process of metal electrodeposition, ■ The deposition of Sn metal is a competitive reaction with the hydrogen generation reaction, and in places where a large amount of hydrogen generation has occurred, the Sn plating layer is baked, and the appearance of the plating becomes grayish-black.
Pinholes occur in the plating layer where hydrogen generation occurs locally, and the smoothness of the plating layer is lost.

■ Electrodeposition of Sn metal occurs intensively in areas where it is likely to deposit, impairing the smoothness of the plating layer.

This is because two problems arise.

The present inventors have conducted various studies in order to solve this problem, and have found that when depositing Sn metal from a pyrophosphate plating bath, one or both of amino acid compounds and citrates are added to the pyrophosphate plating bath. I discovered that it can be added to the bath.

In other words, the addition of the amino acid compound significantly increases the hydrogen overvoltage during Sn plating. The fact that this hydrogen overvoltage is high indicates that the effect of suppressing the hydrogen generation reaction is large. Thus, by adding the amino acid compound, the phenomenon of large amounts of hydrogen being generated from the pyrophosphoric acid plating bath during Sn plating is eliminated, and a Sn plating layer with metallic luster without plating burn can be obtained. Furthermore, since the local generation of a large amount of hydrogen is reduced, the number of pinholes in the Sn plating layer is reduced, and the smoothness of the plating layer is also improved.

Amino acid compounds are not particularly specified, but include compounds such as glycine, alanine, tyrosine, serine, cystine, daltamic acid, aspartic acid, lysine, histidine, etc., and gelatin and peptone, which are polymerized polymers of these amino acid compounds. , albumin, and other proteins are also included in the present invention.

Further, when Sn is precipitated in a transition state by adding citrate, it is immediately stabilized energetically, and Sn metal is precipitated uniformly over the entire cathode surface.

If citrate is not added, Sn precipitated on the cathode surface in a transition state will mechanically migrate to a more stable location and precipitate as Sn metal.

In other words, by adding citrate to the plating bath, Sn
Metal precipitation does not occur concentratedly in a specific location where metal precipitation is likely to occur, and the smoothness of the Sn plating layer is greatly improved, making it possible to obtain a Sn plating layer with a good appearance.

Citrates are not particularly regulated, and include sodium salts, potassium salts, ammonium salts, etc. of citric acid.

Next, the amounts of the amino acid compound and citrate added will be described.

First, the amount of amino acid compound added is 0.01g.
/I! If the amount is less than 5g, the effect of increasing the hydrogen overvoltage during Sn plating is small (the effect of preventing plating burn and obtaining a good Sn plating appearance with metallic luster is not recognized. If /! is exceeded, the effect of increasing the hydrogen overvoltage becomes saturated and becomes economically disadvantageous.

The amount of citrate added is 1g/! If it is less than this, the effect of energetically stabilizing Sn in a transition state is small, and good smoothness of the Sn plating layer cannot be ensured. Furthermore, if the amount added exceeds 50 g/l, the effect of ensuring smoothness is saturated and it becomes economically disadvantageous.

To summarize the above, when producing Sn/Zn double-layer plated steel sheets, in order to suppress the dissolution of the lower Zn plated layer and obtain a Sn plated layer with a good appearance, it is necessary to use 0% as the Sn plating bath.
．． 01~5 g, #! amino acid compound or 1 to 5
A pyrophosphoric acid plating bath having a pH of 5 to 12 and containing one or two types of citrate at 0 g/lfi may be used.

Furthermore, in the present invention, Sn/Z is applied to the surface equivalent to the outer surface of the can.
For the purpose of improving paint adhesion and post-painting corrosion resistance of plated steel sheets with two-layer plating layers, chromate treatment is applied as necessary. It may not be done.

When performing chromate treatment, immersion treatment in an aqueous solution of sodium salt, potassium salt, or ammonium salt of chromic acid is generally performed. This is because the chromate film produced by electrolysis has poor lubricity and deteriorates DII formability. In order to prevent discoloration of the plated layer due to air oxidation without impairing the good formability of the Sn/Zn two-layer plated layer, immersion chromate treatment may be performed. The amount of chromate deposited can be controlled by the bath concentration, but
If the amount of chromium deposited is 1 mg/m2 or more in terms of the amount of metallic chromium, discoloration due to air oxidation can be prevented.

Furthermore, in the case of DI can applications, chromate treatment or phosphoric acid treatment is performed after DI molding to improve coating performance and post-painting corrosion resistance, but in the present invention, these treatment methods and treatment conditions after DI molding are There are no particular regulations regarding this, and commonly used processing methods will apply.

In the case of DI can applications, such a small amount of chromate film is effective, but depending on the water washing conditions after DI molding in the can making process, a water washing pattern may appear on the surface.
Materials for can applications may also be manufactured without chromate treatment. Therefore, the scope of the present invention also includes cases where chromate treatment is not performed.

Further, chromate treatment for can lid applications is performed by electrolytic treatment. The chromate coating produced by electrolytic treatment prevents undercutting corrosion on the inside of the can, where the contents of the can pass through the coating and corrosion progresses under the coating.
On the outside of cans, it is very effective in improving the rust resistance against filiform corrosion, which is filamentous rust that occurs under the paint film during storage.

By forming such a romate film, the adhesion of the coating does not deteriorate over a long period of time, and good corrosion resistance and rust resistance are maintained. Further, the chromate coating has a great effect of preventing blackening of the surface of the steel plate, that is, sulfide blackening, which occurs in foods containing sulfur compounds, such as fish meat and livestock products. In this way, the chromate film has a great effect on improving performance, especially when it is used after being painted, but if too much is attached, cracks will occur in the chromate film layer in areas that have undergone severe processing such as EOE processing, and the corrosion resistance will deteriorate. may be damaged. The chromate coating mentioned here includes two types: one is a single coating of hydrated chromium oxide, that is, the original chromate coating, and the other is a coating consisting of two layers: a metallic chromium layer on the bottom layer and a hydrated chromium oxide layer on the top layer. is pointing to.

As described above, when performing chromate treatment, an appropriate ROM adhesion amount of 1 to 50 mg/m2 is selected to provide good paintability and not deteriorate the corrosion resistance of the processed area. If chromate treatment is not performed, the appropriate amount of chromium adhesion is not regulated.

In other words, when regulating the appropriate amount of chromium adhesion, it is important to remember that if the amount of chromium adhesion is less than 1/n, it will not be effective in improving paint adhesion or preventing corrosion on the paint film such as undercutting corrosion. The amount of chromium deposited should be 1 .mu./rrf or more. On the other hand, if it exceeds 50 mg/m2, the corrosion resistance of the processed parts deteriorates in the parts that have undergone severe EOE processing.

Therefore, the amount of chromium deposited should be less than 50 cm/.

The chromate treatment may be carried out by any method such as immersion treatment with an aqueous solution of various sodium salts, potassium salts, or ammonium salts of chromic acid, spray treatment, or electrolytic treatment, but cathodic electrolytic treatment is particularly excellent. In particular, cathodic electrolytic treatment in an aqueous solution in which 5042-ions, F ions (including complex ions), or a mixture thereof are added to chromic acid is most excellent. The concentration of chromic acid is not particularly limited, but a range of 20 to 200 g/l is sufficient.

The amount of anion added is 1/300 to 1/2 of Cr6”
5, preferably from 1/200 to 1150, the best chromate coating can be obtained. The amount of anion is 1/30 of Cr”
If it is less than 0, a homogeneous and uniform chromate film of good quality, which greatly affects coating performance, cannot be obtained. On the other hand, if it exceeds 1/25, the amount of anions incorporated into the formed chromate film increases, and the coating performance, especially the secondary adhesion of the paint, deteriorates. The anions to be added are added to the chromic acid bath in the form of compounds such as sulfuric acid, chromium sulfate, ammonium fluoride, and sodium fluoride.

Although the bath temperature is not particularly regulated, a range of 30 to 70°C is an acceptable temperature range from the viewpoint of workability.

A cathode electrolytic current density of 5 to 100 A/d is sufficient.The treatment time is set so that the amount of chromium deposited is 1 to 50 mg as shown above in any combination of the treatment conditions.
/m2.

In addition, the amount of the hydrated chromium oxide layer can be adjusted by adjusting the immersion time in the aqueous solution after electrolytic treatment or by dissolving it in a chromate anion treatment bath with different concentrations in a separate treatment tank. .

When used as a container material, in a corrosive environment containing aqueous organic acids such as citric acid, the corrosive aqueous solution that enters through the paint film corrodes the plating layer under the paint film, causing the precipitation of a metallic chromium layer and corrosion. The effect of suppressing the aqueous solution from reaching the plated metal surface is remarkable.

(Example) Examples of the present invention will be described below, and the results are shown in Table 1.

Through cold rolling and annealing processes, the plated original plate was adjusted to the material and thickness suitable for DI cans and 5 can lids, and was electrolytically degreased and washed with water in 5% caustic soda, and then electrolytically pickled in 10% sulfuric acid for surface activation. After that, Zn was applied to the surface corresponding to the outer surface of the can under the conditions shown in (1).
After plating, (2)-(a), (r
Sn plating was performed under the conditions shown in i) and (c). Then, those subjected to chromate treatment under the conditions shown in (3)-(a), (rJ), and (c) and those without chromate treatment were prepared. On the surface corresponding to the inside of the can,
If necessary, Sn plating, Sn plating, Ni plating, and electrolytic chromic acid treatment were performed before an organic film was attached.

(1) Zn plating conditions Plating bath composition Zinc sulfate 4oog/l! Sodium sulfate 100g/l 50°C 508 dm" (Electrolysis time is adjusted according to the amount of Zn plating) Plating bath temperature current density (2) S n Plating conditions Pyrophosphoric acid bath (a) Plating bath composition Pyrophosphoric acid Tin (0) plating bath composition (c) Plating bath composition 60 g/l Potassium pyrophosphate 250 g/l Amino acid compound 0.01 to 5 g/4 (adjust amount as necessary) Tin pyrophosphate 60 g / f Potassium birophosphate 250 g / I2 Citrate 1-50 g //! (Adjust the amount added as necessary) Tin-pyrophosphate 60 g / 1 Potassium birophosphate 250 g / ffi Amino acid compound 0.01- 5g #! (Adjust the amount added as necessary) pH of the plating bath Plating bath temperature Current density Citrate 1 to 50 g/β (Adjust the amount added as necessary) 5 to 12 (Adjust the amount as necessary) 50°C 2OA #m2 (Electrolysis time is adjusted according to the amount of Sn plating) (3) Chromate treatment conditions (a) Bath composition Na2Cr, 0724g/I.

pH 4,5 Bath temperature 45°C Treatment conditions Immersion treatment (B) Bath composition Cr (h 100g/
lSO42-1.0g/1 Bath temperature 50°C Current density 5-60A/dm2 (electrolysis time is adjusted according to the amount of chromium deposited) (c) Bath composition Cr (h 80g/
42SO42-0.05g/ 1 NazSiFh 2.5g/ fNH
4F 0.5g/1 bath temperature
45°C Current density 5-60A/4" (Electrolysis time is adjusted according to the amount of chromium deposited) (A) Appearance (gloss and smoothness) of the Sn plating layer (
After Zn plating was performed under the conditions of 1), Sn plating was applied thereon under the conditions of (2), and the appearance of the Sn plating layer was evaluated. Glossiness was determined visually, and smoothness was determined by observing the surface using an electron microscope (SEM) with a magnification of 3000 times. The criteria for determining the appearance of the Sn plating layer are as follows.

◎: The plating layer has metallic luster, and Sn metal is densely deposited over the entire surface even when observed by SEM.

○: The plating layer loses some of its luster, and SEM observation reveals areas where Sn metal is coarsely precipitated.

Δ: The plating layer becomes grayish white, and pinholes in the plating layer are observed by SEM observation.

×: The plating layer turned gray, and pinholes in the plating layer were clearly observed by SEM observation.

XX: The plating layer turned grayish-black, and pinholes were observed on the entire surface of the plating layer by SEM observation.

In addition, the above-mentioned treated material was tested for the following items (B) to (D) to evaluate its performance.

(B) DI moldability Using a water-soluble emulsion type coolant, DI cans are molded from a blank size of 136 mmφ to a can diameter of 65.91φ under molding conditions at a can manufacturing speed of 110 cans/win, and DI molding of various treated materials. The gender was evaluated. The evaluation criteria were as follows.

◎: DI moldability is extremely good.

○: Slight galling occurs on the outer surface during ironing, but DI
Good moldability.

Δ: DI molding is possible, but strong galling occurs on the outer surface during ironing, resulting in poor DI moldability.

X: The material broke during the DI molding process, making DI molding impossible.

(C) Printing finish after DI molding A DI can was created under the conditions of (B), and red, white, and yellow ink for the outside of the can was applied to a film thickness of 5I! rn, and the print finish was visually judged. The judgment criteria are as follows.

○: The appearance after printing shows the original color of the ink,
Extremely good print finish.

Δ: The appearance after printing is slightly grayish, and the print finish is slightly inferior.

×: The appearance after printing does not show the original color of the ink, and is grayish to the same extent as tinplate, and the printing finish is poor.

(D) Rust resistance on the outside surface The rust resistance on the outside surface of the DI printed cans prepared under the conditions of (B) and (C) and the evaluation materials subjected to EOE processing after painting was evaluated using the following evaluation test. . In addition, for the DI printed can, the part where the wall part was scratched and the bottom part were evaluated, and for the EOE processed material, the score part and the rivet part were evaluated.

■Tap water immersion test The evaluation materials were immersed in tap water at room temperature for 3 days, and the rusting rate of the evaluation part was measured.

■ Refrigeration cycle test evaluation After keeping the material in a freezer at -15°C for 30m1n, immediately placing it in a humidity chamber at 49°C1 relative humidity of 98% or more for 60 sins, and then leaving it indoors at room temperature for 22 hours, one cycle is 15 The cycle test was continued and the rusting rate of the relevant parts was measured.

(2) Retort test The evaluation material was subjected to steam retort at 120° C. and 90 ml of steam, and the rusting rate of the evaluation part was measured.

The evaluation criteria for rust resistance in each test are as follows.

◎: No rust was observed at all, and the rust resistance was extremely good.

○: Rust resistance is good with a rust rate of 5% or less.

Δ: Rust resistance is slightly inferior with a rust occurrence rate of 5 to 30%.

×: The rusting rate is 30% or more, and the rust resistance is inferior to that of tinplate.

XX: The rusting rate is 30% or more, and the rust resistance is inferior to that of tinplate.

(Effects of the Invention) According to the present invention, the can exhibits excellent rust resistance on the outer surface side, has good can forming processability (especially DI moldability), and has good printing finish after DI molding. It is possible to provide a surface-treated steel sheet for containers (Zn/Sn double-layer plated steel sheet) that is both economical and economical.

Claims (2)

[Claims] (1) At least 1~
On the upper layer of the steel plate with a Zn plating layer of 10g/m^2,
As the Sn plating bath, a pyrophosphate plating bath with a pH of 5 to 12 to which 0.01 to 5 g/l of an amino acid compound or 1 to 50 g/l of citrate is added is used. A method for manufacturing a surface-treated steel sheet for containers having good rust resistance and appearance on the outer surface of the can, characterized by applying a Sn plating layer of 5 g/m^2. (2) At least 1~
On the upper layer of the steel plate with a Zn plating layer of 10g/m^2,
As the Sn plating bath, a pyrophosphate plating bath with a pH of 5 to 12 to which 0.01 to 5 g/l of an amino acid compound or 1 to 50 g/l of citrate is added is used. Apply a Sn plating layer of 5g/m^2,
A method for producing a surface-treated steel sheet for containers having good rust resistance and appearance on the outer surface of the can, characterized in that a chromate film is then applied at a coating amount in terms of chromium of 1 to 50 mg/m^2.