JPH0448094A - Production of plated steel sheet for vessel having superior rust resistance at outside of can and fine appearance - Google Patents

Abstract

PURPOSE:To produce a plated steel sheet for a vessel having superior 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 is 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 ENSA and 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 exhibiting superior rust resistance at the outside of the can is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the production of plated steel sheets for containers, which are used as materials for drawn and ironed (DI) cans and can lids, and have excellent exterior rust resistance and appearance. It is about law.

[Conventional technology]

BACKGROUND ART In recent years, there has been a remarkable development in can manufacturing methods using drawing and ironing (for example, DI processing can manufacturing methods), 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 outer surface 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 parts.

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, Easy Oven End (hereinafter referred to as EOE),
Tin plates and electrolytically 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. Namely, tinplate;
In the case of TFS, the Sn plating layer and C
The r plating layer is at fault in terms of potential and has no sacrificial corrosion protection effect on the base steel.

In order to solve this problem, a container adjusting plate in which a Cr-containing steel plate is plated with Sn has been developed, as seen in, for example, Japanese Patent Laid-Open No. 62-17199 and Japanese Patent Laid-Open No. 62-13594. All of these steel plates for containers exhibit the sacrificial anticorrosion ability of the plating layer by adding other components (for example, chromium) to the base metal and controlling the potential of the base metal. Further, although these steel sheets have a great effect of improving the rust resistance on the outer surface side, in order to exhibit a sufficient effect, it is necessary to add several percent of other components, 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 tinplate DI cans are dark is due to the low spectral reflectance of the exposed iron, and to improve the appearance of 01 cans, D
It is important to avoid exposing the iron as much as possible after I-forming. Considering these causes, it is clear that conventional inventions cannot deal with them.

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.
An n-double-layer plated steel sheet is effective, but in terms of manufacturing technology, the important point is the Sn coating technique applied to the upper layer. That is,
In order to realize industrialization, the following two problems must be solved.

1) Development of a Sn plating bath that can apply a Sn plating layer to the upper layer without dissolving the lower Zn plating layer;
When performing Sn plating on the lower Zn plating layer, the lower layer Zn metal is significantly dissolved during Sn plating in the sulfuric acid bath (ferrostane bath) and chloride bath conventionally used in industry, resulting in expensive Sn plating. There is a problem in that the bath is contaminated and continuous operation is not possible.

2) Perform Sn plating without dissolving the Zn plating layer,
Development of a Sn plating bath that provides a good appearance with sufficient commercial value as a plated steel sheet for containers; Pyrophosphoric acid-based plating baths are effective as Sn plating baths that can suppress dissolution of the underlying Zn plating layer. The precipitation of Sn metal from a pyrophosphate plating bath poses a major problem in the gloss and smoothness of the plating layer, and unless this plating appearance problem can be resolved, the commercial value of Sn/Zn double-layer plated steel sheets will be poor and industrialization will be difficult. Have difficulty.

In other words, in order to enable continuous operation and realize industrialization in the production of Sn/Zn double-layer plated steel sheets, it is essential to provide a Sn plating bath that can provide a good Sn plating appearance without dissolving the underlying Zn plating layer. It is.

[Problem to be solved by the invention]

The present invention was made to address these problems, and exhibits excellent rust resistance on the outer surface of the can, has good can forming processability (particularly DI moldability), and prints after DI molding. The present invention aims to provide a method for manufacturing a Sn/Zn double-layer plated steel plate as a plated steel plate for containers that has good finishing properties and is also economically viable.

[Means for Solving the Problems] The gist of the present invention is to apply an Sn plating bath to at least the upper layer of a steel plate having a Zn coating layer of 1 to 10 g/rd on the lower layer of the surface corresponding to the outer surface of the can. As, 0.
01-5g//2 of ENSA added and 0.01
~5 g/l of amino acid compounds or 1-50 g/l
pH when one or two of the citrates of f are added
0.1 to 5 using a pyrophosphate plating bath of 5 to 12
Production of plated steel sheets for containers with excellent rust resistance and appearance on the outer surface of cans, characterized by applying a Sn coated layer of g/rtf or further applying a chromate coating of 1 to 50 μ/rd in terms of chromium deposition amount. It's in the law.

[Effect]

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 steel plate for containers is used. There are no particular restrictions on the manufacturing method of the plated original plate, and it is manufactured through a normal steel billet manufacturing process such as hot rolling, pickling, cold rolling, annealing, and temper 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 sexual function is applied. There are no particular restrictions on the surface corresponding to the inner surface of the can (it may be Sn-plated, electrolytically chromic acid treated, or Ni-plated, and even coated with organic resin. There are no particular regulations regarding 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 to the lower layer on the outer surface side and applying a Sn plating layer to the upper layer is to (1) improve the printed appearance on the outer surface side, (2) ensure good moldability, and (2) ensure 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 white 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 is 1.1g/m
If it is less than 2, it will not be possible to prevent iron from being exposed after DI molding, and it will be difficult to ensure a good appearance. Moreover, if the total amount of spacing exceeds 15 g/r+(), the effect of improving the appearance will be saturated and it will be disadvantageous from an economic point of view.

In other words, the total plating amount for the upper and lower layers is 1.1 to 15g.
/rTf is appropriate. Furthermore, the breakdown is that the amount of Zn plating on the lower layer is 1 to log/m2, and the amount of Sn plating on the upper layer is 0.
It is regulated to 1 to 5 g/m2. The reason is that the lower layer of Zn
If the plating amount is less than Ig/r4, good rust resistance cannot be ensured, and if it exceeds Log/m2, the effect of improving rust resistance is saturated and it is economically disadvantageous. Furthermore, if the amount of Sn coating in the upper layer is less than o, xg/nf, the amount of Sn, which has excellent lubricity, will be insufficient, so DI formability will deteriorate and defects such as "r" will occur during continuous molding. , it becomes impossible to ensure good formability. Also,
If the Sn plating amount exceeds 5 g/nf, the lubricating effect on DI formability will be saturated and it will be economically disadvantageous.

In other words, the lower Zn plating layer is applied at l~Log/m2,
The upper Sn plating layer is coated with a coating of 0.1 to 5 g/r+ (double-layer plated steel sheets are exposed to a corrosive environment with sufficient moisture and oxygen, and even if there is machining damage or pinholes in the coating layer) Due to the effect of the lower plating layer, no rust is observed from the base steel, and the rust resistance is good.Furthermore,
The effect of the upper coating layer ensures good continuous DI formability, and even after DI processing, the base iron is hardly exposed due to the effect of the total plating amount of the lower and upper layers, and good printing finish can be achieved.

Next, a method for manufacturing the above-mentioned Sn/Zn double-layer plated steel sheet will be described.

First, the Zn plating of the lower layer may be carried out using a sulfuric acid bath, a chloride bath, etc., which are usually used industrially, and there are no particular restrictions on the plating conditions, but the bath composition should be 200 to 500 g/j2 of zinc sulfate. , 60-100g of sodium sulfate
/n is sufficient. In addition, the current density is 10 to 100 A
/dm2 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, the following two problems must be solved as described above. Namely, 1) development of a Sn plating bath that can apply a Sn plating layer to the upper layer without dissolving the lower Zn coating layer; and 2) development of a good appearance with sufficient commercial value as a plated steel sheet for containers. This is the development of a Sn plating bath that can be used.

First, the problem of 1) dissolution of Zn metal into a Sn plating bath will be described. 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. Continuous operation becomes impossible.This phenomenon is particularly noticeable when using a Sn plating bath with a very low pH, such as a sulfuric acid-based ferrostane bath or a chloride bath, which are usually used industrially as a Sn plating bath. Zn metal is actively dissolved in the strongly acidic and strongly alkaline pn range.The appropriate pH range for the Sn plating bath, where Zn metal is unlikely to melt, is between pH 5 and 12.When the pH is less than 5. Then, Zn metal is actively dissolved and the Sn plating bath is contaminated.Also, when the pH exceeds 12, it becomes too alkaline and causes active dissolution of Zn.In other words, active dissolution of Zn metal does not occur. The appropriate pH range for the Sn plating bath without contamination is pH = 5.
~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 PTT region, Sn'' ions, which can be present alone in the plating bath, precipitate as hydroxides.
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 compatible with Sn ions. It is possible to form a stable complex salt, and as the Sn plating bath of the present invention, a pyrophosphate-based plating bath is regulated.
There are no particular restrictions on the concentration of the plating bath, the plating temperature, etc.

However, even in such a Sn plating bath with a suitable pH range, the dissolution of Zn metal is not completely suppressed, and it cannot be said to be sufficient for industrial application. In order to suppress the dissolution of Zn metal to an industrially sufficient level for continuous operation, after various studies, we decided to use Etholated α-Na as an additive.
phthol mono 5ulfonic Ac1d
(hereinafter referred to as ENSA) has been found to be suitable. This is because ENSA is a surfactant.
SA is adsorbed on the surface of Zn metal and prevents active dissolution of Zn in the Sn plating bath. Furthermore, if the amount of ENSA added is less than 0.01 g/lfi, the effect of preventing the active dissolution of Zn will be small and it will not exhibit a sufficient effect industrially. Furthermore, if the amount of ENSA added exceeds 5 g/l, the effect of preventing the dissolution of Zn metal is saturated, and this becomes economically disadvantageous. That is, an appropriate E to prevent dissolution of Zn metal.
The amount of NSA added is regulated to 0.01 to 5 g//2.

Next, 2) method of ensuring a good appearance of the Sn plating layer will be described. S from pyrophosphate plating bath
Electrodeposition of n-metal has major problems in terms of gloss and smoothness of the plating layer. This is a phenomenon in which the appearance after Sn coating is grayish-black and almost no metallic luster is observed, and the commercial value as a surface treatment plate for containers is significantly impaired. The reason for this is that in the process of electrodepositing Sn metal from the conventional pyrophosphate-based Sn plating bath,
The precipitation of Sn metal is a competitive reaction with the hydrogen generation reaction,
In places where a large amount of hydrogen has been generated, the plating of the Sn coating layer is a phenomenon that causes the plating to take on a grayish-black appearance, and in places where hydrogen generation has occurred locally, pinholes appear in the coating layer, causing the plating layer to become smooth. Gender is lost.

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

There are two points.

As a result of various studies to solve this problem, the present inventors decided to use one or two amino acid compounds or citrates in pyrophosphate plating when depositing Sn metal from a pyrophosphate plating bath. We discovered that it can be added to the bath.

In other words, it is possible to significantly increase the hydrogen overvoltage during Sn plating by adding an amino acid compound, and the fact that this hydrogen overvoltage is high indicates that the effect of suppressing the hydrogen generation reaction is large. By adding the amino acid compound, the phenomenon of large amounts of hydrogen being generated during Sn plating from a pyrophosphoric acid plating bath 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, and include compounds such as glycine, alanine, tyrosine, serine, cystine, glutamic acid, aspartic acid, lysine, and histidine, and include gelatin, peptone, and polymerized polymers of these amino acid compounds. Proteins such as albumin 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 moves to a place where it can be more energetically stabilized and precipitates as Sn metal. In other words, by adding citrate to the coating bath, the precipitation of Sn metal does not occur concentratedly in certain areas where it tends to precipitate, and the smoothness of the Sn plating layer is greatly improved, resulting in a good appearance. A Sn plating layer can be obtained.

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.
If it is less than /l, the effect of increasing hydrogen overvoltage during Sn plating is small, and the effect of preventing plating burn and obtaining a good Sn plating appearance with metallic luster is not recognized. Furthermore, if the amount added exceeds 5 g/l, the effect of increasing the hydrogen overvoltage becomes saturated and becomes economically disadvantageous.

Regarding the amount of citrate added, if it is less than 1 g/2, the effect of energetically stabilizing Sn in the transition state is small, and good smoothness of the Sn coating layer cannot be ensured. Furthermore, the amount added is 50g/I! If it exceeds this, the effect of ensuring smoothness will be saturated and it will be economically disadvantageous.

To summarize the above, when manufacturing Sn/Zn double layer steel plate,
In order to apply Sn plating on the upper layer with a good appearance without dissolving the lower Zn plating layer, the Sn plating bath should be 0.
．． Add 0.01-5g/l ENSA, 0.01-5g
/l of amino acid compound or 1 to 50 g/Q of citrate added to one or two of them (5 to 1
No. 12 pyrophosphoric acid-based Sn plating bath may be used.

Subsequently, the plated plate having the Sn/Zn two-layer plating layer on the surface corresponding to the outer surface of the can is subjected to chromate treatment as necessary for the purpose of improving paint adhesion and post-painting corrosion resistance. For 01 can applications, chromate treatment may or may not be performed.

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 I-formability. Therefore, in order to prevent discoloration of the coating layer due to air oxidation without impairing the good formability of the Sn/Zn two-layer plating layer, immersion chromate treatment may be performed. The amount of chromate deposited can be controlled by the bath concentration, but
Discoloration due to air oxidation can be prevented if the amount of chromium deposited is 1 cm/bo or more in terms of the amount of metallic chromium. Furthermore, in the case of 01 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 Dll applications, such a small amount of chromate coating is effective, but depending on the water washing conditions after DI molding in the can making process, water washing patterns may appear on the surface, so manufacturing without chromate treatment may be difficult. Sometimes it is done. Therefore,
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 filamentous rust, so-called filiform corrodigon, which 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 referred to here refers to two cases: 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. pointing.

As described above, when performing chromate treatment, the appropriate ROM adhesion amount is selected to be 1 to 50 cm/po, which has good paintability and does not deteriorate the corrosion resistance of the processed area. If chromate treatment is not performed, the appropriate amount of chromium adhesion is not regulated.

That is, when regulating the appropriate amount of chromium adhesion, if the amount of chromium adhesion is less than 1 cm/po, 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 cm/bo or more. On the other hand, if it exceeds 50 .mu./rTr, the corrosion resistance of the processed portion deteriorates in the portion that has undergone severe EOE processing. Therefore, the amount of chromium deposited should be 50 .mu./bo or less.

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 304'-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 regulated, but is 20 to 200 g/1. is sufficient.

The amount of anion added is 1/300 to 1/25 of Cr”
Preferably, the best chromate coating is obtained when the angle is 1/200 to 115 degrees. The amount of anion is 1/300 of Cr”
If it is less than that, it will not be possible to obtain a homogeneous and uniform chromate film of good quality, which will greatly affect coating performance. Moreover, if it exceeds 1/25, a large amount of anions will be incorporated into the formed chromate film, resulting in deterioration of coating performance, especially secondary paint adhesion.

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 restricted, a range of 30 to 70°C is an appropriate temperature range from the viewpoint of workability. A cathode electrolytic current density in the range of 5 to 100 A/dm is sufficient.

The treatment time is set so that the amount of chromium deposited falls within the range of 1 to 50 cm/bore as shown above under any combination of the treatment conditions.

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 metal surface is remarkable.

〔Example〕

Examples of the present invention are 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 9 DI cans and 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).
Plating is performed, and then on top of that (21 (a), (b)
Sn plating was performed under the conditions shown in (c). Moreover, as a comparative example, even under the conditions shown in (2)-'(d) and (e), Sn
Plating was done. Then, samples were prepared that were subjected to chromate treatment under the conditions shown in (3)-(a), (b) and (c), and those that were not subjected to chromate treatment. The surface corresponding to the inner surface of the can is coated with Sn plating or S as required.
After N plating, Ni plating, and electrolytic chromic acid treatment, an organic film (PET, PP) was attached.

(1) Zn plating conditions Plating bath composition Zinc sulfate 400g/l Sodium sulfate 100g/lfi Plating bath temperature 50°C Current density 50A/dm" (Electrolysis time is adjusted according to the amount of Zn plating) (2) S
n Plating conditions Pyrophosphate bath (a) Plating bath composition Tinn pyrophosphate 60g//l Potassium pyrophosphate 250gzl ENSA 0.01-5g/ρ (adjust amount as necessary) Amino acid compound 0.01-5g /l (adjust the amount added as necessary) (b) Plating bath composition Tinn pyrophosphate 60 g/l Potassium pyrophosphate 250 g/l ENSA 0.01-5 g/l (adjust the amount added as necessary) Adjustment) Citrate 1 to 50 g/l (Adjust the amount added as necessary) (c) Plating bath composition Tinn pyrophosphate 60 g/l! Potassium pyrophosphate 250 g/A ENSA 0.01-5 g/l (adjust the amount added as necessary) Amino acid compound 0.01-5 g/l (adjust the amount added as necessary) Citrate 1- 50g/l (Adjust the amount added as necessary) pH of the plating bath 5-12 (adjust the pi as necessary)
Plating bath temperature: 50°C Current density: 20A/dm" (Electrolysis time is adjusted according to the amount of Sn plating) As a comparative example, a sulfuric acid bath (ferrostane bath) and a chloride bath, which are usually used industrially, were used. Sn plating was performed.The plating conditions for each are shown in (d) and (e).

(d) Ferrostane bath Plating bath composition Tin sulfate 30-40 g/l Phenol-)l Flufonic acid 25-35 g/12E
NSA+EN 8g
/N plating bath pH 1 or less Plating bath temperature 45°C Current tooth a20A/dm2 (Electrolysis time is adjusted according to the amount of Sn plating) (e) Chloride bath Plating bath composition Stannous chloride 75g//l fluoride Sodium 25 g/l.

Potassium hydrogen fluoride 50g/l! Sodium chloride 45g/l Plating bath pH 2.7 Plating bath temperature 65℃ Current density 50A/dm" (Electrolysis time is adjusted according to the amount of Sn plating) (3) Chromate treatment conditions (a) Bath composition Na2jr'zO924g / 1p
H4,5 Bath temperature 45°C Treatment conditions Immersion treatment (b) Bath composition CrO+ 100 g/
nS0.2- 1.0 g/42 Bath temperature 5
o"C Current density 5-60A/dm" (Electrolysis time is adjusted according to the amount of chromium deposited) (c) Bath composition CrCh80g/1 504"-0.05g / f NazSiFi 1 2.58 / INHaF
0.5 g / 12 Bath temperature 45°
C Current density 5 to 60 A/dm" (Electrolysis time is adjusted according to the amount of chromium deposited) (A) Solubility of Zn plating layer After Zn plating is performed under the conditions of (1), (2)
The amount of dissolved Zn metal in the lower layer was measured when Sn plating was performed under these conditions. The method for measuring the amount of dissolved Zn plating layer is
After performing plating, the amount of Zn plating was measured by chemical analysis before and after performing Sn plating, and the difference in the amount of Zn plating was determined as the amount of dissolved Zn metal.

The amount of Zn coating in Table 1 indicates the amount of Zn plating after Sn coating, and the amount of dissolved Zn coating layer (A) in Table 1 is the amount of Zn coating obtained by the above method. It's the amount.

(B) Appearance (gloss and smoothness) of Sn plating layer (1
After performing Zn plating under the conditions of (2), Sn plating was performed thereon under the conditions of (2), and the appearance of the Sn plating layer was evaluated. Glossiness is judged visually, and smoothness is judged as 3.
The determination was made by observing the surface using an electron microscope (SEM) with a magnification of 1,000 times. The criteria for determining the appearance of the Sn plating layer are as follows.

◎: The coating layer has metallic luster, and SEM observation shows that Sn metal is densely precipitated over the entire surface.

Q: The luster of the plating layer is slightly lost, 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 coating 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 materials were tested for the following items (C) to (E) to evaluate their performance.

(C) DI moldability Using a water-soluble emulsion type coolant, DI cans are molded from a blank size of 136 holes to a can diameter of 65.9 holes at a molding speed of 110 cans/min, and subjected to various treatments. The DI formability of the material 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, 01 molding is possible, but strong galling occurs on the outer surface during ironing, and DI moldability is poor.

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

(D) Printing finish after DI molding Create a DI can under the conditions of (C), apply red, white, and yellow ink for the outside of the can at a film thickness of 5 Inn, and visually judge the printing finish. did. 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.

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

■Freezing cycle test evaluation After keeping the material in a freezer at 15°C for 30ml, placing it in a humidity chamber at 49°C and relative humidity of 98% or higher for 60ml, and 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 evaluation The material was subjected to a steam retort of 120'CX90m1n, and the rusting rate of the relevant portion was evaluated.

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.

○: Good rust resistance with a total rust occurrence rate of 5% or less.

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

×; Rust resistance is inferior to that of tinplate when the rusting rate is 30% or more.

XX: Rust resistance is inferior to tinplate with a rusting rate of 30% or more.

As is clear from the above examples, the present invention does not cause dissolution of Zn plating during Sn plating, and
The appearance of the plating layer, rust resistance, and various other properties are also consistently excellent. On the contrary, comparative examples that deviate from the present invention exhibit unstable characteristics.

(Effects of the Invention) According to the present invention, the can exhibits excellent rust resistance on the outside surface side, has good can forming processability (especially DI formability), and has good printing finish after D+ molding. It is possible to provide a Sn/Zn 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 a Sn plating bath, 0.01 to 5 g/l of ENSA is added, and one or two of 0.01 to 5 g/l of an amino acid compound or 1 to 50 g/l of citrate is added. Production of a plated steel sheet for containers with excellent rust resistance and appearance on the outer surface of the can, characterized by applying a Sn plating layer of 0.1 to 5 g/m^2 using a pyrophosphoric acid plating bath with a pH of 5 to 12. Law. (2) At least 1~
On the upper layer of the steel plate with a Zn plating layer of 10g/m^2,
As a Sn plating bath, 0.01 to 5 g/l of ENSA is added, and one or two of 0.01 to 5 g/l of an amino acid compound or 1 to 50 g/l of citrate is added. Apply a Sn plating layer of 0.1 to 5 g/m^2 using a pyrophosphoric acid plating bath with a pH of 5 to 12,
A method for producing a plated steel sheet for containers having excellent 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.