JPS63199895A - Tinned steel sheet for can having superior sulfide blackening resistance and production thereof - Google Patents

Abstract

PURPOSE:To obtain a tinned steel sheet for fish cans, etc., having superior sulfide blackening resistance by subjecting a steel sheet to tinning, anodizing, reflow treatment and chromating. CONSTITUTION:The surface of a steel sheet is subjected to tinning, anodizing, reflow treatment and chromating or treatment with chromic acid to form an Sn-Fe alloy layer 6, a metallic Sn layer 5, an interposed layer 1 of a mixture of metallic Sn with tin oxide, a tin oxide-base oxide layer 3 and a chromium oxide hydrate-base coating layer 2 on the steel base 10. Since the interposed layer 1 prevents cracking, a sulfide blackening phenomenon caused by the reaction of metallic Sn exposed by cracking with S in food can be suppressed.

Description

Detailed Description of the Invention "Object of the Invention" The present invention provides a tin-plated steel sheet having good resistance to sulfide blackening not only in the flat part but also in the processed part as a steel sheet for manufacturing cans of fish meat, etc. and its manufacturing method.

(Industrial Application Field) Tin-plated steel sheets with excellent sulfide blackening resistance used in cans for fish meat, etc., and their manufacturing technology.

(Prior Art) Reflow-treated tin-plated steel sheets are generally used as can materials for fish and meat, and this type of canning is usually retorted for sterilization. However, due to this retort treatment, the S (sulfur) contained in the proteins, amino acids, etc. in the contents of canned fish and meat reacts with Sn or Fe in the can stock, producing SnS or PeS. ) causes black sulfide discoloration.

Therefore, various countermeasures against this sulfide blackening have been attempted.
The formation of chromium hydrated oxide on the surface layer of tinplate is effective in suppressing the sulfide blackening reaction that mainly occurs during retort treatment, as reported in Tetsu-to-Hagane Magazine 68 (1982) No. 7, pp. 850-857. It has been published in other literature, and a Sn-plated tone plate with a chromium hydrated oxide layer formed on the surface layer of tin plate is used.

(Problems to be Solved by the Invention) However, the can body is formed using a tin-plated steel sheet that has been subjected to the romate treatment to form a chromium hydrated oxide layer as described above, and can be used for canned fish, etc. In this case, black sulfide discoloration is alleviated on the flat plate portion of the can body, but black sulfide discoloration inevitably occurs on the processed portion (the pressed portion of the can lid).

This is thought to be due to cracks appearing in the chromium hydrated oxide layer in such processed parts, exposing the tin layer. In addition, in order to obtain a dense chromium hydrated oxide layer, cathodic reduction treatment is performed in a weak alkaline solution after tin plating and before chromate treatment, or a metal chromium layer and chromium hydrated oxide are formed. An attempt was made. However, although these methods further improve the sulfide blackening on the flat plate part, the sulfide blackening on the processed can body part may worsen, so they may not be preferable.
Therefore, there is a strong demand for further measures to solve this problem.

"Structure of the invention" (Means for solving the problem) In order to solve the problem in the previous section, the inventors have carried out (1)
＠Metallic tin and A tin plated plate for cans with excellent resistance to sulfide blackening, characterized by forming an intervening layer containing mainly tin oxide.

(2) A metallic tin layer formed on the surface of the steel plate via a tin-iron alloy layer, a hydrated chromium oxide by chromate treatment or chromium 9 treatment, and a coating layer mainly composed of metallic chromium.The lower surface mainly consists of tin oxide. A tin-plated steel sheet for cans having excellent resistance to sulfide blackening, characterized in that an intervening layer containing a mixture of metallic tin and mainly tin oxide is formed between the two layers.

(3) After Sn plating on the steel plate surface, reflow treatment is performed,
Tin plating for cans with excellent resistance to sulfide blackening, characterized in that, in producing Sn-plated steel sheets by further chromate treatment or chromic acid treatment, anodic electrolysis treatment is performed after the Sn plating and before reflow treatment. Manufacturing method of steel plate.

(4) After Sn plating on the steel plate surface, reflow treatment is performed,
Furthermore, when manufacturing Sn-plated steel sheets by chromate treatment or chromic acid treatment, anodic electrolytic treatment is performed on the first surface after the Sn plating and before reflow treatment, and chromate treatment or chromic acid treatment is performed after the reflow treatment. in front,
A method for producing a tin-plated steel sheet for cans having excellent resistance to sulfide blackening, characterized in that the first surface is subjected to cathodic electrolysis treatment.

I propose this to Kura.

(Function) As described in the previous section, the feature of the present invention is that the coating layer formed on the tin-plated steel plate is based on the steel plate, and is composed of an iron pan alloy layer - a metal tin layer - metal tin and tin oxidation. A layer containing a mixture of substances, a tin oxide layer, and a hydrated chromium oxide layer (or a layer containing metallic chromium) are formed in this order, and the coating is formed in this order. Regarding the method, when used as a material for cans, resistance to sulfide blackening is important on the inner surface of the can, which is in contact with the contents, and moreover, blackening often occurs on the inner surface of the can that is subjected to mechanical processing.

Therefore, in the present invention, the structure of the coating layer on the first side (the inside side of the can, hereinafter referred to as the first side) and the second side (the outside side of the can, hereinafter referred to as the second side) is as follows. Three types were adopted: Among the above-mentioned coating layers, they can be roughly classified according to the presence or absence of an intervening layer containing a mixture of metallic tin and tin oxide, which is the most characteristic.
Type B, which clearly has an intervening layer that is approximately the same as the surface.
Type C has an intervening layer on both sides, but there are differences in the structure, shape, and composition of the intervening layer, or there are differences in the composition, structure, etc. of the chromate coating layer, and type C has an intervening layer on both sides. This type exists only on the first surface and no significant intervening layer is observed on the second surface. Incidentally, the symbol Type D is used as a comparative material in the present invention, but this is a material in which no significant intervening layer is observed on either the first or second surface. The type of product is determined by the customer's requests, such as the contents of the can and the appearance.

In addition, in the present invention, the state in which metallic chromium is contained in the hydrated chromium oxide layer may exist in the form of a layer or in the form of fine particles, but regardless of the amount or the form of existence, in either case. are also included within the scope of this invention.

A combination of mainly metallic tin and tin oxide formed between the metallic tin layer formed by tin plating and the layer mainly composed of tin oxide on the lower surface of the coating layer by chromate treatment mainly composed of hydrated chromium oxide. The mixed intervening layer prevents the occurrence of cranking during processing, such as a ring-shaped processed part applied to a can lid by pressing, due to the roughening or cushioning effect of the tin oxide mixed into the metal tin.

In this way, the intervening layer made of the mixture formed on the metal tin layer prevents the occurrence of cranks, thereby reducing the exposure of the plated metal tin in such press-formed parts. In other words, if metal tin is prevented from being exposed through the crank in such processed parts, it is possible to significantly reduce the sulfide blackening phenomenon that occurs due to the reaction of exposed metal tin with 8% in foods. Become.

The method for obtaining the above-mentioned mixture is to actively oxidize the surface layer by anodic electrolytic treatment to form a thin Sn oxide while the tin-plated surface of the iron base is rough. In this state, in the next reflow treatment, the surface layer of the pure Sn layer that thickly covers the surface of the steel plate is
When the reflow process is completed, the oxide film on the top layer has an uneven surface due to this mixing, an intervening layer containing a mixture of oxide and Sn, a pure Sn layer,
A Sn--Fe alloy layer is then formed on the steel plate. Then, chromium hydrate oxidation is performed to form a can body with the above-mentioned intervening layer by performing chromic acid treatment or chromate treatment to form a chromium hydrate oxide layer or a layer containing metallic chromium thereon. Even if the crank to the metal layer and the Sn oxide layer becomes weak (or cracks occur), the Sn oxide is mixed on the surface of the metal tin, so the exposure of Sn is reduced. There is little contact between the contents and Sn, which greatly limits the possibility of sulfide blackening.Also, cathodic electrolytic treatment on the first surface after reflow treatment and before chromate treatment or chromic acid treatment is not recommended. , has the effect of controlling the thickness of the oxide layer produced by anodizing, and has the effect of improving the adhesion of paint.

EXAMPLE To further explain the present invention as described above, the inventors of the present invention have conducted various studies and intensively investigated the problem of sulfide blackening of processed parts of can bodies as described above.
In order to improve the sulfide blackening resistance of the processed parts of the can body as described above, it is necessary to prevent the Sn layer from being exposed due to cracks entering the oxide film in the processed parts, so chromium water The present invention was achieved by confirming that it is effective to form a film in which Sn oxide and Sn oxide are mixed in a good condition.

In other words, the conventional female can plate obtained by reflow treatment and chromate treatment after tin plating is obtained by reflow treatment etc. on a metal tin layer formed on a steel base via an iron complex alloy layer. In contrast, in the present invention, a chromate layer mainly composed of hydrated chromium oxide and an oil film are formed through a layer mainly composed of tin oxide. We propose a rope board with a layered structure. In other words, the metal tin layer 5 is formed on the steel base 10 via the tin-iron alloy layer 6, and the hydrated chromium oxide is formed on the surface via the layer 3 mainly composed of tin oxide by chromate treatment. Formation of the coating layer 2 and oil film 4 mainly composed of tin oxide is the same as in the above-described conventional method, but in the present invention, the layer 3 mainly composed of tin oxide is formed.
An intervening layer M1 in which metallic tin and mainly tin oxide are mixed is formed between the metallic tin layer 5 and the metallic tin layer 5.

FIG. 2 also shows the layer structure of the coating layer of the present invention divided vertically in three dimensions, and the structure from the iron complex alloy layer to the tin oxide layer is the same as in FIG. 1, but this example The difference from FIG. 1 is that the coating formed by chromic acid treatment is a layer mainly composed of hydrated chromium oxide and metallic chromium. (Formed in Manufacturing Example 17) Fig. 3 shows a cross section of an ordinary tin-plated steel sheet, and as is clear from the drawing, there is a layer between the metallic tin layer and the layer mainly composed of tin oxide. , there is no intervening layer containing a mixture of metallic tin and tin oxide.

However, as a method for obtaining the tin-plated steel sheet for cans according to the present invention, in the ordinary tin manufacturing process, Sn is coated on the steel sheet.
After the electrodeposition, reflow treatment and electrodeposition containing hydrated chromium oxide or metallic chromium are carried out. However, in the present invention, in order to form a surface layer that is effective in improving the sulfide blackening resistance, the reflow treatment is performed before the reflow treatment. A new step of performing anodic electrolysis treatment in an appropriate treatment solution is added. As a result, more Sn oxide is generated on the surface of the Sn layer, and furthermore, after the reflow treatment, the Sn oxide is generated on the surface of the Sn layer.
The surface of the n-layer has fine irregularities, and this is because the Sn oxide suppresses the surface smoothing phenomenon caused by reflow. It has been confirmed that the tinplate shown in Figure 1 obtained through such a process has good resistance to sulfide blackening in the processed area after processing. As metal tin is exposed, sulfide blackening reactions are likely to occur in the exposed parts. , it has become possible to reduce the exposure of metal tin in the processed area.

Furthermore, it has been found that the conditions for the anodic electrolytic treatment performed before reflow are effective over a very wide range. That is, a wide range of solutions and pH values can be selected as the treatment solution for performing the anodic electrolytic treatment, such as alkaline solutions such as sodium carbonate, acidic and neutral solutions mainly containing boric acid, and the like.

Furthermore, cathodic electrolytic treatment or immersion electroless treatment may be performed in the above-mentioned treatment solution before or after anodic electrolytic treatment. Such a combination makes it possible to optimize the form and amount of surface Sn oxide produced by anodic electrolytic treatment.

The amount of electricity for anodic electrolytic treatment is 0.1 c per 1 dn+”
ou is preferably 12 or more and 30 or less coul. This is 0
．． The effect is too small if it is less than 1 couβ, while 30 couβ
If β is exceeded, Sn will be excessively oxidized, and it will be necessary to carry out strong reduction treatment in the subsequent process, which will increase power consumption, which is extremely disadvantageous, and the amount of chromium hydrated oxide and tin oxide produced will increase. This is because it becomes difficult to set appropriate amounts of both.

It has been recognized that the improvement in sulfide blackening resistance as described above is effective regardless of the amount of Sn plating, and
It has been found that similar effects can be obtained in the case of plated steel sheets plated with two or more elements including.

Practical manufacturing examples and comparative examples of the products according to the present invention as explained above will be described below.

Processing that is not specified for the first side and the second side means that the same process is performed on both sides.

Production Example 1 A 0.22 m thick tin plate was electrolytically degreased in an alkaline solution and electrolytically pickled in a sulfuric acid solution, and then plated with Sn at 2.8 g/m per side using a ferrostane tin plating solution. After that, anodic electrolysis treatment was performed for 1 second at a current density of 5 A/dmz in a 30 g/l sodium hydrogen carbonate solution.
Next, after reflowing at a maximum temperature of 250°C, cathodic electrolysis treatment was performed for 1 second at a current density of 4A/dm in a sodium dichromate solution to produce chromium hydrated oxide electrodeposited. In addition, production 11h2 was obtained by performing cathodic electrolysis treatment for 1 second at a current density of 6 A/dn+'' in a sodium dichromate solution under the same conditions as production 11m1 until reflow.

Comparative Example 1 A 0.22 m thick tin plate was electrolytically degreased in an alkaline solution and electrolytically pickled in a sulfuric acid solution, and then plated with tin at 2.8 g/rd per side using a ferrostane tin plating solution. After that, reflow was performed at a maximum temperature of 250°C, and cathodic electrolysis treatment was performed for 1 second at a current density of 2A/dm in a sodium dichromate solution to deposit chromium hydrated oxide. Also, under the same conditions as this manufacturing 11h3 and up to reflow, the temperature was 4A/dm in a sodium dichromate solution.
The product in which the cathodic electrolytic treatment was performed for 1 second at a current density of ``<6 A/dm'' was designated as Manufacturer 4, and the product in which the cathodic electrolytic treatment was performed for 1 second at the same current density of <6 A/dm was designated as Manufacturer 5.

Production Example 2 A 0.22 m thick tin plate was electrolytically degreased in an alkaline solution and electrolytically pickled in a sulfuric acid solution, and then plated with Sn at 5.6 g/rrr per side using a ferrostane tin plating solution.

3 in 20 g/l sodium dihydrogen phosphate solution.
After performing cathodic electrolysis treatment for 1 second at a current density of 5A/dn+'', anodic electrolysis treatment for 1 second at a current density of 5A/da'', then reflow at a maximum temperature of 250°C, and then dichromic acid. Manufacture 1'lh6 was obtained by cathodic electrolytic treatment for 1 second at a current density of 5 A/da'' in a sodium solution, and the same conditions were used until tin plating. After performing anodic electrolysis treatment for 1 second at a current density of 8 A/da'' in a liquid (boric acid ion 20 g/l), cathodic electrolysis treatment was performed for 1 second at a current density of 5 A/d+m'', and then at a maximum temperature of 250°C. After reflowing, a cathodic electrolytic treatment was performed in a sodium dichromate solution at a current density of 5 A/dm for 1 second to obtain a manufacturing time of 1'h7.

Comparative Example 2 A 0.22 m thick tin plate was electrolytically degreased in an alkaline solution and electrolytically pickled in a sulfuric acid solution, and then plated with Sn at 5.6 g/cd per side using a ferrostane tin plating solution. Then 3A/dm in sodium dihydrogen phosphate solution
After performing cathodic electrolytic treatment for 1 second at a current density of ``5A/dm'', and then reflowing at a maximum temperature of 250°C, cathodic electrolysis treatment was performed for 1 second at a current density of 5A/dm in a sodium dichromate solution. I got 8 things.

Comparative Example 3 A 0.22 inch thick tin plate was electrolytically degreased in an alkaline solution and electrolytically pickled in a sulfuric acid solution, and then plated with Sn at 5.6 g/rd per side using a ferrostane tin plating solution. Next, after reflowing at a maximum temperature of 250°C, cathodic electrolysis was performed in a sodium carbonate solution for 1 second at a current density of 8A/dm2, and then in a sodium dichromate solution for 1 second at a current density of 5A/dm2. A cathode electrolytic treatment was performed to obtain a product of production 11h9.

Comparative Example 4 Under the same conditions as production N19 and reflow, cathodic electrolysis treatment was performed for 1 second at a current density of IOA/dm'' in a sodium bicarbonate solution, and further at 15 A/dmz in a chromic acid solution containing ammonium fluoride. A cathodic electrolytic treatment was performed for 1 second at a current density of 100 mL to form a metal chromium layer and a chromium hydrated oxide layer, thereby obtaining a product of manufacturing grade 10.

Comparative Example 5 Manufacturing f1k19 and reflow were performed under the same conditions, and then cathodic electrolysis treatment was performed for 1 second at a current density of 2A/dm in a mixed solution of sodium dichromate and boric acid, followed by 4A/dm.
Manufacture 11 by performing cathodic electrolytic treatment for 1 second at a current density of
I got something like hllO.

Production Example 3 After electrolytically degreasing a 0.22M@thick tin plate in alkaline solution and electrolytically pickling in sulfuric acid solution, Sn was coated on one side (first side) at 2.8 g/rrf with ferrostane tin plating solution. The other side (second side) was plated at 5.4 g/nf. After that, 30g/l
6A/dm2 only on the first side in sodium hydrogen carbonate solution
After performing anodic electrolytic treatment for 1 second at a current density of 250°C, and then reflowing at a maximum temperature of 250°C, cathodic electrolysis treatment was performed for 1 second at a current density of 4 A/dm2 in a sodium dichromate solution, and chromium water was applied. Manufactured Na12 was produced by electrodepositing oxide of Na12, and 6A was deposited in a sodium dichromate solution under the same conditions as the Manufactured Na12 until reflow.
Manufactured Na13 was obtained by cathodic electrolytic treatment for 1 second at a current density of /dm''.

Production Example 4 After electrolytically degreasing a 0.22 m thick tin plate in an alkaline solution and electrolytically pickling in a sulfuric acid solution, Sn was coated on one side (both the first and second sides) using a ferrostane tin plating solution.5. 6g1
0f plated. Then, in a 20 g/l sodium dihydrogen phosphate solution, anodic electrolysis was performed on the first surface using a grid-to-grid type electrolysis method at a current density of 5 A/dm, and anodic electrolysis was performed on the second surface for 1 second at the same current density. Next, after reflowing at a maximum temperature of 245°C, cathodic electrolysis treatment was performed for 1 second at a current density of 5 A/ds+'' in a sodium dichromate solution to obtain a manufactured product 11h14, and this manufactured flh14 and tin plating. After that, the first surface was subjected to anodic electrolysis treatment at a current density of 8 A/dm in a boric acid-borax mixture solution (boric acid ion 20 g/l) using a conductor type electrolysis method. Both sides are 2A/d at the same time.
After cathodic electrolysis treatment at a current density of s+'', followed by reflow at a maximum temperature of 245° C., cathodic electrolysis was performed on the first side for 1 second at a current density of 5 A/ds+” in a sodium bicarbonate solution.

Then, cathodic electrolysis treatment was carried out in a sodium dichromate solution at a current density of 5 A/dmz for 1 second to obtain a product of production number 15.

Production Example 5 The steps up to reflow were the same as Production Example 3, and after the reflow, 1
A second cathodic electrolytic treatment was applied to the first side.

15 in a chromic acid solution containing ammonium fluoride.
Cathodic electrolysis is performed for 1 second at a current density of A/dn+'' to form metallic chromium and hydrated chromium oxide, and the manufactured Na
I got 16 of them. In addition, in production No. 16, 3A/dII+" was added in a sodium dichromate solution after reflow.
The second side was subjected to cathodic electrolysis for 1 second at a current density of 100.degree. C., and then only the first side was subjected to cathodic electrolysis treatment in an anhydrous chromic acid solution containing ammonium fluoride to obtain No. 17.

In addition, in production N116, both sides were exposed to I
It was manufactured by adding cathodic electrolytic treatment for 1 second at a current density of OA/dm'' to obtain a product of production Na1B.

A steel plate in which the composition, structure, etc. of the chromium coating layer are different between the first and second surfaces can be manufactured by processing each surface using different treatment liquid compositions and different current densities. To describe an example of equipment, after reflow, two chemical conversion treatment tanks and two washing tanks are installed, and chemical conversion treatment A (only the second side is energized) - water washing - chemical conversion treatment B (only the first side is energized) →
This equipment performs sequential washing with water. Here, the case where the treatment liquid for chemical conversion treatment A is a sodium dichromate solution and the treatment liquid for chemical conversion treatment B is a chromic acid solution containing a small amount of ammonium fluoride is manufactured! It was written as 1h17.

Note that, if the chromic acid treatment is performed at the same composition and concentration as the solution used during TFS production, metallic chromium will also precipitate along with hydrated chromium oxide.

For the tinplate produced as described above, production numbers 1 to 18,
As a sulfur blackening resistance test, epoxy phenol paint was applied, baked at 205°C for 10 minutes, pressed into a can lid shape, and then baked at 125°C in a mixture of sodium sulfide and lactic acid.
Retort treatment was carried out for 60 minutes at , and the degree of blackening of the processed part and the flat part was visually evaluated. The test was conducted on 10 samples each, and each sheet was given a score for the processed part and the flat part (the rating level was different for the processed part and the flat part). In other words, the score was given as 10 points for the fish in the best condition and 1 point for the poorest condition. Some manufacturing!
11[L3 to 5 and N118 to 11 were good in the plane part but significantly inferior in the processed part, whereas the other products according to the present invention all obtained good scores.

The following table shows the resistance to blackening due to sulfurization on the first side by type of the above-mentioned coating layer.

In addition, the one using the comparative material of the manufacturing light 5 mentioned above and the one using the manufacturing floor 1
The results of measuring the elemental distribution of micro-Auger analysis in the depth direction of the material of the present invention are shown in Section 4.5.
As shown in Fig. 6.7, in the comparative material shown in Fig. 4.5, significant oxygen was observed from the surface to a depth equivalent to about 6 minutes, indicating the presence of oxides. In the inner layer, no significant amount of oxygen is observed, that is, no distinct mixed region of metallic tin and oxides is observed. Moreover, since almost the same results are obtained in FIGS. 4 and 5, which are measured at different measurement positions, it is determined that the boundary between the metal tin layer and the oxide layer is relatively flat. This is the 8th
It is also clear from the secondary electron image taken by a scanning electron microscope of the surface of the comparative material on manufacturing floor 5 in the figure after reflow, and in this photograph, the relatively large protruding stripes extending substantially laterally are the protruding stripes of the steel plate itself. However, it is clear that the other parts form a substantially flat surface.

On the other hand, in the material according to the present invention shown in Figure 6.7, oxygen, which indicates the presence of oxides, was significantly observed from the surface to a depth corresponding to about 4 to 6 minutes, which is similar to the case of the comparative material. ing. However, in the inner layer shown in Fig. 6.7, where the measurement position was different from that shown in Fig. 4.5, there is again a portion where oxygen is significantly observed, indicating the presence of oxides.
In addition, since the positions of oxides in Figures 6 and 7, which are measured at adjacent measurement positions approximately 1 μm apart, are shifted, it is recognized that there is an intervening layer containing a mixture of metallic tin and oxides. It will be done. Furthermore, the fact that the intervening layer and the oxide on it exhibit complex irregularities as described above can also be seen from the secondary electron image taken with a scanning electron microscope of the surface of the inventive material manufactured at 11 hl in Figure 9 after reflow. It is clear - C1 Here, fine convex portions are scattered throughout. This is greatly different from FIG. 8, which is simply flat, and the presence of an intervening layer containing a mixture of metallic tin and tin oxide can be clearly understood.

"Effects of the Invention" The present invention as explained above has good sulfide blackening resistance not only on the flat surface of the can body but also on the processed parts such as the pressed part of the can lid. It is possible to provide tin-plated steel sheets, and the present invention can be applied to only one side according to the customer's request, and it is also possible to apply a different treatment to the second side, so it is industrially very effective. It is an invention.

[Brief explanation of the drawing]

The drawings show the technical content of the present invention. Figure 1 is a cross-sectional explanatory diagram showing the structural relationship of the tin-plated steel plate according to the present invention, and Figures 4.5 and 6.7 are diagrams in the depth direction. Micro Auger analysis showing the element distribution, FIG. 4.5 shows the conventional technique, and FIG. 6.7 shows the material of the present invention, with different measurement positions. FIG. 8 shows the surface of the conventional material, and FIG. 9 shows the surface of the material of the present invention after reflow, using a scanning electron microscope W1. This is a mirror photo. However, in FIG. 1, 1 is an intervening layer in which metallic tin and mainly tin oxide are mixed, 2 is a coating layer mainly composed of chromium oxide by chromate treatment, 3 is a layer mainly composed of tin oxide,
4 is an oil film, 5 is a metal tin layer, 6 is a tin-iron alloy layer, and 10 is a steel base. Fig. 2 also shows a cross-sectional view of the coating layer of the present invention, but unlike Fig. 1, the coating layer mainly composed of chromium oxide produced by chromic acid treatment becomes the coating layer 2a containing metallic chromium. FIG. 3 shows a cross section of the coating layer of a typical tin-plated steel sheet, and shows that there is no intervening layer containing a mixture of metallic tin and tin oxide. In Figures 4 to 7, a...a is tin, b...b is oxygen, C...C is chromium, d...d is iron, e...
As shown in the figure, e represents carbon, and at the beginning of sputtering (etching with argon), the carbon content appears to be relatively high due to surface deposits. Plate I 2nd Plate 5I ＼ Net: A4th X Ji←b-Mereito- $ 8 Field 9 Field

Claims (4)

[Claims] (1) Between the metallic tin layer formed on the surface of the steel sheet via the tin-iron alloy layer and the layer mainly composed of tin oxide on the lower surface of the coating layer mainly composed of hydrated chromium oxide by chromate treatment, A tin-plated steel sheet for cans having excellent resistance to sulfide blackening, characterized by forming an intervening layer containing tin and mainly tin oxide. (2) Consisting of a metallic tin layer formed on the surface of the steel plate through a tin-iron alloy layer, a coating layer mainly composed of hydrated chromium oxide and metallic chromium by chromate treatment or chromic acid treatment, and tin oxide on the lower surface. A tin-plated steel sheet for cans having excellent resistance to sulfide blackening, characterized in that an intervening layer containing a mixture of metallic tin and mainly tin oxide is formed between the two layers. (3) After Sn plating on the steel plate surface, reflow treatment is performed,
A tin-plated steel sheet for cans having excellent resistance to sulfide blackening, characterized in that, in manufacturing the Sn-plated steel sheet by further chromate treatment or chromic acid treatment, anodic electrolytic treatment is performed after the Sn plating and before reflow treatment. manufacturing method. (4) After Sn plating on the steel plate surface, reflow treatment is performed,
Furthermore, when producing a Sn-plated steel sheet by chromate treatment or chromic acid treatment, after the Sn plating and before reflow treatment, the first surface is subjected to anodic electrolysis treatment, and after reflow treatment and before chromate treatment or chromic acid treatment. A method for producing a tin-plated steel sheet for cans having excellent resistance to sulfide blackening, characterized in that the first surface is subjected to cathodic electrolytic treatment.