JP2737813B2 - Tin-plated steel sheet with excellent paint adhesion and seam weldability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet for food cans, beverage cans and miscellaneous cans excellent in paint adhesion, seam weldability and economy.

[0002]

2. Description of the Related Art As a material for cans, Sn-plated steel sheets generally called tinplate have been widely used. However, since Sn is an extremely expensive metal, it is intended to reduce costs. Thin Sn plating has been promoted. In recent years, a seam welding method using electric resistance welding has been widely used in place of a conventional solder joining method in a method for joining a can body, and further thinning of Sn has been advanced. When a can is made using these thin-plated steel sheets, the inner and outer surfaces of the can are painted for the purpose of improving rust resistance and corrosion resistance. In other words, the inner surface of the can is coated with a coating with excellent corrosion resistance to prevent corrosion and discoloration due to the contents, and the outer surface of the can is prevented from rusting in the atmosphere and beautifully painted to attract consumers' willingness to purchase. Is applied.

The present inventors have already disclosed a thin Sn-plated steel sheet having excellent seam weldability and corrosion resistance as disclosed in Japanese Patent Application Laid-Open No. 60-1145.
No. 96 is proposed. According to this method, the amount of Sn plating can be reduced, and the cost can be significantly reduced. Specifically, it was possible to reduce the amount of Sn plating by forming a dense Fe-Ni-Sn alloy layer after reflow treatment or baking, and by improving paint adhesion by forming a metal Cr layer.

[0004] In canning production, the production speed has been increased for the purpose of cost reduction by increasing production efficiency. Especially after the appreciation of the yen, cheap imported cans and imported empty cans appeared on the market, and production efficiency in the canning process increased rapidly. This has created a new problem.
High-speed can-making due to an increase in welding speed and high-speed packing by high-speed filling have been performed, causing a problem that cans collided in a production line and a coating film on the outer surface of the can was peeled off by impact. More recently, in order to shorten the baking time after coating, a high-temperature short-time baking treatment at a temperature equal to or higher than the melting point of Sn (232 ° C.) has been performed, and peeling of the coating film has come to occur. This is due to the melting point of Sn (232
It is considered that since high-temperature baking at a temperature of at least (° C.) or higher is performed, Sn melts and moves during baking, thereby breaking the bond with the coating film and deteriorating paint adhesion.

[0005] On the other hand, several proposals have been made so far for the purpose of improving paint adhesion of Sn-plated steel sheets. For example, there is JP-A-63-93894, which aims to improve the paint adhesion on the outer surface of the can, and reduces the amount of metal Sn remaining on the outer surface of the can after baking to less than 0.05 g / m ^2. That is, the object is achieved by depositing as much as 10 to ²⁰ mg / m ^{2 of} metallic Cr. However, since the metal Cr on the inner surface side of the can is as small as 3 to 10 mg / m ² , when high-temperature baking is performed, paint adhesion is poor and corrosion resistance is insufficient.

Japanese Patent Application Laid-Open (JP-A) No. 63-266094 aims to improve the adhesion between the outer surface of the can and the inner surface of the can. This is to improve paint adhesion by eliminating the residual metal Sn after baking on both the outer surface of the can and the inner surface of the can. However, this is because there is no residual metal Sn after baking on the inside of the can where severe corrosion resistance is required,
Since protection of Fe by sacrificial corrosion protection of Sn cannot be expected, there is a high risk of a perforated can. Japanese Patent Application Laid-Open No. 63-277794 discloses a further improvement. This is to leave a minimum necessary amount of metal Sn on the inner surface side of the can for corrosion resistance.

Since these hardly contain metal Sn after normal baking, paint adhesion after normal baking is excellent. However, before the baking, the metal Sn is sufficiently present on both the inner surface and the outer surface of the can. Therefore, at the time of high-temperature baking, Sn is melted, and the adhesion of the paint is also deteriorated. When the amount of metallic Cr was increased, the seam weldability was not sufficient.

[0008]

In the prior art, when a high temperature (above the melting point of Sn) baking treatment is performed after coating, the problem of peeling of the coating film occurs due to the melting of Sn. The present invention solves the above-mentioned problems, and is used by coating both the inner surface of the can and the outer surface of the can, and is excellent in economical efficiency without lowering seam weldability, paint adhesion, and corrosion resistance. It is an object of the present invention to provide a tin-plated steel sheet which is a material for welding cans having excellent high-speed can-making properties.

According to a first aspect of the present invention, a steel sheet for a can is provided.
Fe-Ni-Sn alloy layer on the inner surface of the can
It has a metal Sn layer, a chromate layer on the top layer, and F
An e-Ni-Sn alloy layer and a chromate layer
And the total amount of Sn on the inner surface of the can is 1.0 to 2.0 g / m ² ,
Metal Cr content is 10 to 40 mg / m ² , Cr hydrated oxide content is C
2 mg / m ² or more in terms of r , Cr water on the outer surface of the can
The amount of oxidized oxide is 2 mg / m ² or more in terms of Cr,
The total amount of metal Cr and Cr hydrated oxide on the surface is 4 in terms of Cr.
5 mg / m ² or less, paint adhesion and sea
The present invention provides a tin-plated steel sheet having excellent weldability.

According to a second aspect of the present invention, a can
Fe-Ni alloy layer on both sides of steel sheet, Fe-Ni
-Sn alloy layer, metal Sn layer on the upper layer, and the uppermost layer
It has a chromate layer and the total amount of Sn on the inner surface of the can is 1.
0 to 2.0 g / m ² , the amount of metallic Cr is 10 to 40 mg / m ² ,
The amount of hydrated oxide is 2 mg / m ² or more in terms of Cr , and the outer surface of the can
0.2 to 0.8 g / m ² , Cr hydrate acid
Is 2 mg / m ² or more in terms of Cr , and
Total amount of metallic Cr and Cr hydrated oxide is 45mg in terms of Cr
/ m ² or less, paint adhesion and seam melting
A tin-plated steel sheet having excellent contact properties is provided.

According to a third aspect of the present invention, a can
Fe-Ni alloy in order from the steel plate side to the inner surface of the steel plate can
Layer, a Fe—Ni—Sn alloy layer, a metal Sn layer on the upper layer,
Has a chromate layer on the top layer, and sequentially from the steel plate side on the outer surface of the can
Fe-Ni alloy layer, Fe-Ni-Sn alloy layer and its upper layer
Has a chromate layer, and the total amount of Sn on the inner surface of the can is
1.0 to 2.0 g / m ² , the amount of metallic Cr is 10 to 40 mg / m ² ,
Cr hydrated oxide amount is 2 mg / m ² or more in terms of Cr ,
The amount of Cr hydrated oxide on the outer surface is 2 mg / m ^{2 in} terms of Cr.
It is the above, furthermore, the metal Cr and Cr hydrated oxide on both sides
The total amount is 45 mg / m ² or less in terms of Cr.
Tinned steel sheet with excellent paint adhesion and seam weldability
Provided.

Here, the chromate on the surface to be the outer surface of the can
Preferably, the layer has at least 10 mg / m ² of metallic Cr.

Hereinafter, the present invention will be described in more detail. The present inventors considered that the cause of the peeling of the coating film during baking at a high temperature equal to or higher than the melting point of Sn is that the bond between the surface coating of the steel sheet and the coating film is cut by melting and moving the metal Sn. . Therefore, even if the temperature exceeds the melting point, the metal Sn
As a result of studying a method that does not move and repeating experiments, it has been found that it is effective to eliminate the metal Sn before the high-temperature baking or to increase the amount of the metal Cr attached. Figure 1
FIG. 3 shows the result.

"TFS" indicated by an arrow in the figure is a normal tinplate (cold rolled steel sheet of aluminum killed steel) with a metal Cr content of 10%.
The average T-peel strength level of a tin-free steel sheet having a surface coating layer of 0 mg / m ² and a Cr oxide content of 20 mg / m ² is shown.

The "conventional thin Sn-plated steel sheet" is formed by adding an Fe--Ni alloy layer or metallic Ni
A Fe—Sn—Ni alloy layer or F
The total amount of Sn of the e-Sn alloy layer and the metal Sn layer is 0.8 g / m ^2.
With 5 mg / m ² of metal Cr and 5 mg / m of Cr oxide layer on top
² shows the average T-peel strength level of the steel sheet on which the surface coating layer ² is formed.

The "conventional tinplate" is a conventional tinplate in which an Fe--Sn alloy layer and a metal Sn layer are added in a total Sn amount of 2.
The average T-peel strength level of a steel sheet having 8 g / m ² and a Cr oxide layer having a surface coating layer of 8 mg / m ^{2 on} the uppermost layer is shown.

The condition of “normal baking” is 210 ° C. × 2
0 minutes, "high-temperature baking" conditions are 260 ° C. × 30 seconds.

As shown in FIG. 1, when metal Sn is present, high-temperature baking treatment significantly deteriorates adhesion. On the other hand, when there is no metal Sn, the paint adhesion is excellent both in the case of performing normal baking and in the case of performing high-temperature baking.
Very good adhesion strength comparable to FS was obtained. FIG. 2
As shown in (1), when there is no metal Sn, high paint adhesion can be obtained even after the high-temperature baking treatment regardless of the amount of metal Cr. If the metal Sn is absent, movement due to melting of the metal Sn cannot occur, so it is considered that the paint adhesion did not deteriorate. Next, the paint adhesion after the high-temperature baking treatment in the presence of metal Sn is shown in FIG. The paint adhesion deteriorates due to the high temperature baking treatment, but the amount of metallic Cr is 1
At 0 mg / m ² or more, the same adhesive strength as that of a conventional thin Sn-plated steel sheet can be obtained. Further, it was found that when the amount of metallic Cr is 20 mg / m ² or more, even when high-temperature baking treatment is performed, very excellent paint adhesion almost equivalent to that of TFS can be obtained. When the amount of metal Cr is large, even if the metal Sn is melted, the upper metal Cr layer is suppressed, so that the movement of the metal Sn does not occur, and it is considered that the deterioration of paint adhesion is suppressed.

The properties required for the steel sheet for cans used by painting differ between the outer surface of the can and the inner surface of the can.

[0020] Corrosion resistance to the contents of the inner surface of the can is important. Specifically, it is excellent in pitting corrosion resistance, excellent in corrosion resistance under a coating film, and excellent in paint adhesion. Sn has a sacrificial anticorrosion effect on Fe, and is susceptible to pitting in the absence of metal Sn.
If n is not present, the amount of Fe exposure increases, so that corrosion under the coating film easily occurs. Therefore, it is necessary that metal Sn be present on the inner surface side of the can.

The outer surface of the can is only required to be excellent in rust resistance and coating film adhesion before coating (these two are, of course, also required on the inner surface of the can). Therefore, the performance is sufficient even without the metal Sn.

From the characteristics of the can, as a method for improving the paint adhesion after baking at a high temperature, either the method of eliminating metal Sn or the method of increasing the amount of metal Cr on the outer surface of the can may be used. The side thought that it was necessary to take a method of increasing the amount of metal Cr in the presence of metal Sn.

Therefore, the paint adhesion after the high temperature baking treatment is improved by increasing the amount of metallic Cr, but some of them have poor weldability. The present inventors conducted further tests and newly found that the weldability is affected by the amount of metallic Cr, the amount of residual metal Sn after baking treatment (see FIG. 4), and the total Cr amount of the front and back surfaces (see FIG. 5). I found out. In order to ensure good weldability, the amount of residual metal Sn after the paint baking treatment needs to be 0.1 g / m ² or more, but as shown in FIG. If the amount of residual metal Sn is small, and if the total amount of Sn is large, the amount of residual Sn after the paint baking treatment will be large. Further, as shown in FIG. 5, it was found that the weldability was also affected by the total Cr content of the front and back sides.

Based on these new findings, even when a high-temperature baking treatment at a temperature higher than the melting point of Sn is performed, the paint has excellent adhesiveness and has the corrosion resistance required for other steel plates for cans.
The inventors have invented a Sn-plated steel sheet having excellent seam weldability and high economic efficiency. The Sn-plated steel sheet of the present invention is excellent in the above performance particularly when subjected to a high-temperature baking treatment, but there is no problem if it is used as a material for performing a normal baking treatment. The present invention, which takes into account the characteristics of the inner surface of the can and the outer surface of the can and further has excellent paint adhesion, has better characteristics as a steel plate for cans than conventional materials even when ordinary baking treatment is performed.

Hereinafter, the first embodiment of the present invention will be described in more detail. The steel sheet used in the present invention is not particularly limited as long as it is a commonly used steel sheet.

The Fe—Ni—Sn alloy layers on both sides of the steel sheet are dense, have excellent continuity, and exhibit excellent corrosion resistance. When the amount of Sn plating is small in the conventional Fe-Sn alloy, the amount of exposed Fe increases, and the corrosion resistance is not sufficient.

The amount of metallic Cr on the inner surface of the can is 10 to 40 mg / m ^2.
The reason for this is that, as described above, since metal Sn is required on the inner surface side of the can from the viewpoint of corrosion resistance, deterioration of paint adhesion after high-temperature baking can be suppressed by increasing the amount of metal Cr. It is. If the amount of metallic Cr is less than 10 mg / m ² , there is no effect of suppressing deterioration of paint adhesion. On the other hand, when the amount of metallic Cr exceeds 40 mg / m ² , the amount of residual metal Sn after the paint baking treatment does not exceed 0.1 g / m ² .

The reason that the amount of Cr hydrated oxide on the inner surface side of the can is 2 mg / m ² or more is that Cr hydrated oxide is directly bonded to the coating film, so that if the amount of Cr hydrated oxide is less than 2 mg / m ^2, it is sufficient. This is because paint adhesion cannot be obtained. Further, even if the amount of the hydrated Cr oxide is too large, it is not necessary to particularly increase the amount because the effect of further improving the paint adhesion cannot be expected.

Next, the total amount of Sn on the inner surface side of the can was adjusted to 1.0 to 2.0.
The reason for g / m ² will be described. If it is less than 1.0 g / m ² , if the amount of metal Cr is 10 mg / m ² or more, 0.1 g / m ² or more of metal Sn will not remain after the baking treatment, and sufficient welding performance cannot be obtained. On the other hand, if it exceeds 2.0 g / m ² , it is out of the range of the economic efficiency aimed at by the present invention, so it was set to 2.0 g / m ² or less.

The total amount of Sn on the outer surface of the can is adjusted to 0.2 to 0.8 g / m ^2.
I will explain why. As described above, metal Sn is not particularly required on the outer surface of the can from the viewpoint of corrosion resistance. Therefore,
The amount of metal Sn may be small from the viewpoint of paint adhesion and economy. If the total amount of Sn is less than 0.2 g / m ² , sufficient corrosion resistance cannot be obtained, so the content was set to 0.2 g / m ² or more. Further, even if the amount exceeds 0.8 g / m ² , if the amount of metallic Cr is increased, the paint adhesion after the high-temperature baking treatment can be sufficiently satisfied. It was 8 g / m ² or less.

The hydrated Cr oxide on the outer surface of the can was added at 2 mg / m 2.
^The reason for setting it to ² or more is that sufficient paint adhesion cannot be obtained if the amount of Cr hydrated oxide is less than 2 mg / m ² as in the case of the inner surface of the can. Further, there is no need to particularly increase the amount of Cr hydrated oxide, since the effect of further improving paint adhesion cannot be expected even if the amount of Cr hydrated oxide is too large.

The amount of metal Cr on the outer surface of the can is not particularly limited when the amount of metal Sn on the outer surface of the can is 0.2 to 0.3 g / m ² . Is better. However, when the amount of metal Sn on the outer surface of the can exceeds 0.3 g / m ² , the amount of metal Cr needs to be 10 mg / m ² or more.

In general, the seam weldability of a steel sheet for cans is indicated by an appropriate welding current determined from the condition that a welded portion has sufficient strength and no splash is generated, and a range of 2 A or more is required. . Therefore, from the viewpoint of weldability, it is necessary that the total amount of metallic Cr and Cr hydrated oxide on both the inside and outside of the can be 45 mg / m ² or less in terms of Cr. 45mg / m
^If it exceeds ² , splash is likely to occur, so that the weldability deteriorates. More desirably, the dose is 40 mg / m ² or less (see FIG. 5).

Next, a second embodiment of the present invention will be described. When there is no metal Sn, the amount of the metal Cr on the outer surface side of the can is not particularly limited, and the paint adhesion after the high-temperature baking treatment can be sufficiently satisfied. If metal Sn is present, an appropriate amount of metal Cr may be applied accordingly.

The steel sheet according to the third aspect of the present invention is the steel sheet according to the first aspect, further provided with an Fe-Ni alloy layer between the Fe-Ni-Sn alloy layer and the steel sheet surface. This Fe-N
When an i-alloy layer is provided, the amount of Fe exposure on the steel sheet surface is further reduced, which is advantageous for corrosion resistance.

The steel sheet according to the fourth aspect of the present invention is the steel sheet according to the second aspect, further provided with an Fe—Ni alloy layer between the Fe—Ni—Sn alloy layer and the surface of the steel sheet. N
The function of the i-alloy layer is the same as in the above-described third embodiment of the present invention.

Hereinafter, an example of the method for producing a steel sheet according to the present invention will be described. Fe-Ni-Sn alloy layer and Sn plating layer on steel plate, or Fe-Ni alloy layer on steel plate,
A preferred method for forming a Fe—Ni—Sn alloy layer and a plating layer thereon is as follows.

(1) A method in which after a Ni—Sn alloy plating is applied to a steel sheet, heat treatment is performed until the base steel and the Ni—Sn alloy plating are completely alloyed, and then Sn plating is performed. (2) A method in which a steel plate is plated with Ni, further plated with Sn, and heat-treated at a temperature equal to or higher than the melting point of Sn. (3) Apply Fe-Ni alloy plating on the steel plate
A method in which n plating is performed and heat treatment is performed at a temperature equal to or higher than the melting point of Sn. (4) A method in which Ni plating is applied to a steel sheet, and heat treatment is performed in a non-oxidizing atmosphere to diffuse part or all of Ni into the steel, followed by Sn plating and heat treatment at a temperature equal to or higher than the melting point of Sn.

In particular, in the method (4), a layer (Ni diffusion layer) composed of Fe and Ni remains below the Fe—Ni—Sn alloy layer disclosed in the third embodiment, and the Fe—Ni alloy layer and the Fe—Ni alloy layer N
The i-Sn alloy layer can be formed at the same time.

For the chromate treatment, a bath in which metallic Cr is deposited may be used. H ₂ SO ₄ or NaF to chromic acid,
Auxiliaries such as Na ₂ SiF ₆ may be used added.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments.

(Example 1) The inner and outer surfaces shown in Table 1 were subjected to the following production methods, and high-temperature baking treatment was performed to produce a tin-plated steel sheet, and a characteristic test was performed. The method for measuring the composition of each layer and the method for testing properties were as follows. Table 1 shows the results.

(Preparation method A) A normal tin plate was degreased and pickled, then Ni plating was performed using a bath (a), and Sn plating was further laminated using a bath (b), and heated at a temperature equal to or higher than the melting point of Sn. Melted. After a cathodic treatment of 1 C / dm ^{2 in} a 15 g / l aqueous solution of sodium carbonate, chromate treatment was carried out using a bath (e).

(Manufacturing method B) After the ordinary tin plate after cold rolling is electrolytically degreased, (a) Ni plating is performed using a bath, and annealing is performed at 700 ° C. in a 10% H ₂ + 90% N ₂ atmosphere. Ni plating was diffused and infiltrated. After temper rolling at a reduction rate of 1.5%, the steel sheet is degreased and pickled,
(B) Sn plating was performed using a bath. Subsequently, the material was heated and melted at a temperature not lower than the melting point of Sn, subjected to a cathodic treatment of 1 C / dm ² in a 15 g / l aqueous sodium carbonate solution, and then subjected to a chromate treatment using a bath (d). / l
Was immersed in an aqueous solution of chromic acid to adjust the amount of Cr hydrated oxide.

(Preparation method C) After the usual cold rolled tin plate was electrolytically degreased, (a) Ni plating was performed using a bath, and the plate was annealed at 700 ° C. in a 10% H ₂ + 90% N ₂ atmosphere. Ni plating was diffused and infiltrated. After temper rolling at a reduction rate of 1.5%, the steel sheet is degreased and pickled,
(C) Sn plating was performed using a bath. Subsequently, the mixture was heated and melted at a temperature equal to or higher than the melting point of Sn, subjected to a cathode treatment of 1 C / dm ² in a 15 g / l aqueous sodium carbonate solution, and then subjected to a chromate treatment using a bath (e).

The compositions of the baths (a) to (e) were as follows. (A) Bath (Ni plating bath) Nickel sulfate 250 g / l Nickel chloride 45 g / l Boric acid 30 g / l (b) Bath (Sn plating bath) Stannous chloride 50 g / l Sodium fluoride 45 g / l Sodium hydrogen fluoride 13 g / l Sodium chloride 54g / l Yellow blood salt 0.8g / l Brightener qs (c) Bath (Sn plating bath) Stannous sulfate 55g / l Phenolsulfonic acid (65%) 35g / l Brightener qs ( d) Bath (chromate bath) Chromic acid 17 g / l sulfuric acid 0.12 g / l (e) Bath (chromate bath) Chromic acid 15 g / l NH ₄ F 1.5 g / l

The amount of Ni plating and the amount of Sn plating were measured using fluorescent X-rays. Sn plating amount Total Sn amount: Measured using fluorescent X-rays. Metal Sn amount: Measured using a coulometric method. The sample is placed in a furnace at an atmosphere of 260 ° C. for 30 seconds for high-temperature baking treatment .

Cr content Total Cr content: measured using fluorescent X-rays. Metal Cr content: Measured using a coulometric method. Cr hydrated oxide content: Total Cr content-Metal Cr content

T-peel strength (paint adhesion) A T-peel test was performed and evaluated. Each of the two sample surfaces was coated with an epoxy / phenolic paint at 50 mg / dm ² and baked at 260 ° C. for 30 seconds, and then the coated surfaces were hot-pressed with a 4 μm-thick nylon 12 film sandwiched therebetween and bonded. A tensile test piece was prepared. The adhesive strength of the steel plates bonded face to face was measured by a tensile tester and used as an index of paint adhesion.

Using a rust-resistant dry / wet cycle tester, the sample was exposed under conditions where a dry state at a temperature of 25 ° C. and a humidity of 50% and a wet state at a temperature of 50 ° C. and a humidity of 98% were repeated every 30 minutes. The number of rusts generated on the surface was measured and evaluated according to the following criteria.

Filiform rust resistance According to ASTM D2803. The sample surface was coated with a modified epoxy / ester type paint at 60 mg / dm ² , baked and sprayed with salt water for 4 hours. After washing, temperature 25 ℃, humidity 8
It was aged in a 5% atmosphere, taken out after 6 weeks, observed, and evaluated according to the following criteria.

An epoxyphenol-based paint was applied to the surface of the under-film corrosion sample to a thickness of 5 μm, and to this, tomato juice at 90 ° C. was added to half the volume and hot-packed. The hot pack was taken out after a lapse of 10 days at 55 ° C., and the state of corrosion was observed and evaluated according to the following criteria.

After a 5 μm-thick epoxy phenolic paint is applied to the surface of the UCC test sample, a cross cut is made. This was immersed in a solution of 1.5% salt + 1.5% citric acid, taken out after 4 days at 55 ° C., and was taken out. Corrosion of the cross cut portion, peeling width of the coating film and corrosion of the deepest portion were observed. The depth was measured.

Seam Weldability Using a copper wire having a wire diameter of 1.5 mmφ as a welding electrode, two samples were superimposed under constant pressure, and electric resistance welding was performed at a welding speed of 50 m / min while moving the welding electrode. did. At this time, the weldability was evaluated from the appropriate range of the welding current and the pressing force determined based on the condition that the welded portion had sufficient strength and no splash was generated.

[0055]

[Table 1]

[Table 2]

From the results shown in Table 1, Examples 1 to 4 of the present invention have excellent paint adhesion after high-temperature baking, have excellent corrosion resistance to contents, and have sufficient welding performance as a material for welding cans. I understood.

In particular, F between the Fe-Sn-Ni alloy and the steel sheet
Inventive Examples 3 and 4 having an e-Ni alloy layer have no rust even after two weeks and have very excellent corrosion resistance.

In Comparative Example 1, the amount of Sn on the inner surface of the can was 0.8 g / m ^2.
Therefore, sufficient weldability could not be obtained. In Comparative Example 2, rust resistance and filiform rust resistance were insufficient because the amount of Sn on the outer surface of the can was small. Comparative Example 3 was poor in weldability because the total Cr content of the Cr hydrated oxide and metal Cr on the outer and inner surfaces of the can was as large as 50 mg / m ² . Comparative Example 4 shows Sn on the inner surface side of the can.
Since the amount was as small as 0.4 g / m ² , it was found that corrosion under the coating film was apt to occur, and the corrosion was easily promoted in the width direction and the depth direction in the UCC test. In Comparative Example 5, the T-peel strength was poor because the amount of metallic Cr on the inner surface side of the can was small.

[0059]

Since the present invention is configured as described above, the tin-plated steel sheet of the present invention is excellent in rust resistance and filiform rust resistance required on the outer surface of the can, and required on the inner surface of the can. Excellent under-coating corrosion resistance and pitting corrosion resistance, as well as sufficient high-speed weldability, and has excellent paint adhesion, especially when subjected to high-temperature baking treatment at or above the melting point of Sn, and is economical. Is excellent. Therefore, the present invention greatly contributes to resource saving and energy saving, and has an extremely high economic value.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of metal Sn in a steel plate metal Sn layer before painting and baking and the T-peel strength of the steel sheet after baking treatment.

FIG. 2 is a graph showing the relationship between the amount of metal Cr in a steel sheet having no metal Sn layer and the T-peel strength of the steel sheet after baking treatment.

FIG. 3 is a graph showing the relationship between the amount of metallic Cr in a steel sheet having a metallic Sn layer and the T-peel strength of the steel sheet after baking treatment.

FIG. 4 is a graph showing the relationship between the total amount of Sn and the amount of metallic chromium and the amount of residual metal Sn after baking.

FIG. 5 is a graph showing the relationship between the total Cr content of the inner and outer surfaces of the can and the appropriate welding current range.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C25D 5/48 C25D 5/48 5/50 5/50 (72) Inventor Nobuyuki Morito 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki (56) References JP-A-64-65296 (JP, A) JP-A-63-277794 (JP, A) JP-A-63-79995 (JP, A) JP-A-63 JP-A-93894 (JP, A) JP-A-63-277787 (JP, A) JP-A-63-4090 (JP, A) JP-A-62-139899 (JP, A) JP-A-61-104088 (JP, A) )

Claims (4)

(57) [Claims] 1. A steel plate for a can which has an inner surface which is Fe-Ni-
An Sn alloy layer, a metal Sn layer on the upper layer, a chromate layer on the uppermost layer, a Fe-Ni-Sn alloy layer on the outer surface of the can and a chromate layer on the upper layer, and the total amount of Sn on the inner surface of the can is reduced. 1.0 to 2.0 g / m ² , the amount of metallic Cr is 10 to 40 mg / m ² ,
The amount of Cr hydrated oxide is 2 mg / m ² or more in terms of Cr, and the amount of Cr hydrated oxide on the outer surface of the can is 2 mg / m ^{2 in} terms of Cr.
A tin-plated steel sheet having excellent paint adhesion and seam weldability, characterized in that the total amount of metal Cr and Cr hydrated oxide on both surfaces is 45 mg / m ² or less in terms of Cr. 2. A steel sheet having an Fe—Ni alloy layer on both sides thereof, an Fe—Ni—Sn alloy layer on the upper layer, a metal Sn layer on the upper layer, and a chromate layer on the uppermost layer. Has a total Sn content of 1.0 to 2.0 g / m ² and a metallic Cr content of 10 to 2.0 g / m ² .
40 mg / m ² , the amount of Cr hydrated oxide is 2 mg / m ² or more in terms of Cr, and the total amount of Sn on the outer surface of the can is 0.2 to 0.8.
g / m ² , the amount of Cr hydrated oxide is 2 mg / m ² or more in terms of Cr, and the total amount of metal Cr and Cr hydrated oxide on both surfaces is 45 mg / m ² or less in terms of Cr. Tin-plated steel sheet with excellent paint adhesion and seam weldability. 3. A steel sheet for a can having a Fe—Ni alloy layer, an Fe—Ni—Sn alloy layer, a metal Sn layer on the upper layer, and a chromate layer on the uppermost layer in that order from the steel sheet side. Fe-Ni alloy layer, Fe-Ni-Sn on the outer surface in order from the steel plate side
It has an alloy layer and a chromate layer on the alloy layer, the total Sn content on the inner surface of the can is 1.0 to 2.0 g / m ² , and the metal Cr content is 10
４０40 mg / m ² , Cr hydrated oxide amount is 2 mg / m ^{2 in} terms of Cr
The amount of the hydrated Cr oxide on the outer surface of the can is Cr
It is 2 mg / m ² or more in conversion, and the metal Cr and C
A tin-plated steel sheet having excellent paint adhesion and seam weldability, characterized in that the total amount of r-hydrated oxides is 45 mg / m ² or less in terms of Cr. 4. The chromate layer on the outer surface of the can is 10
tin-plated steel sheet having excellent coating adhesion and seam weldability according to any one of claims 1 to 3 having mg / m ² or more metals Cr.