KR102412968B1 - Electro Sn plated steel sheet - Google Patents

Abstract

The electrical Sn plated steel sheet of this invention is arrange|positioned on a base steel plate and a base steel plate, it has a Sn layer and an alloy layer, and is equipped with the Sn electroplating layer containing predetermined|prescribed component. Pb content of the whole electric Sn plating layer is 50 mass ppm or less. When the thickness of the Sn plating layer is t, and the area from the surface of the Sn plating layer to the (1/10) × t depth in the plate thickness direction is referred to as the surface layer area, the Pb content of the surface layer area is 5 mass ppm or more, Moreover, Pb content of a surface layer area|region is higher than Pb content of the whole electric Sn plating layer.

Description

Electro Sn plated steel sheet

The present invention relates to an electro-Sn plated steel sheet, particularly an electro-Sn-coated steel sheet having a low Pb content in the entire Sn plated layer.

This application claims priority based on Japanese Patent Application No. 2017-211788 for which it applied to Japan on November 1, 2017, and uses the content here.

In recent years, various regulations with respect to the Pb content in industrial products have been strengthened from the viewpoint of concerns about health damage and measures against environmental loads.

Sn-coated steel sheets (so-called tin cans) used in food canning are no exception. For example, in South Africa, in view of the regulation of Pb ²⁺ eluted in the can, the Pb content in the Sn plating layer needs to be 100 mass ppm or less, and introduction of the same regulation is also considered in parts of Europe and China. is becoming Moreover, there is a request similar to the above also from some consumers.

In Japan, many Sn ingots used for plating of Sn-coated steel sheets were imported from Southeast Asian countries. Since there is much Pb content contained in an ore, the Sn ingot from Southeast Asia contains 100 mass ppm or more of Pb. When the Sn ingot from Southeast Asia is used as it is, the Pb content in the Sn plating layer of the Sn coated steel sheet as a product cannot be 100 mass ppm or less. Therefore, when using the Sn ingot from Southeast Asia, the manufacturing cost increases, but by further performing electrolytic refining, the level at which the current regulation value is somehow cleared is secured. Alternatively, the transport cost increases because the transport distance is long, but the problem of the above regulation is being dealt with by purchasing a Sn ingot from South America with a small Pb content. The Pb content in the case of manufacturing a tin plate using a Sn ingot from South America is about 70 mass ppm, which is a level that somehow clears the current regulatory value.

In Patent Document 1, when an anode made of crude Sn produced from Sn ore or Sn waste material is electrolytically refined, a part of Pb contained in the anode is dissolved as Pb ²⁺ in the electrolytic solution, and this is the cause, Pb in electrolytic Sn In order to suppress mixing, an electrolytic solution of Sn composed of silicon hydrofluoric acid or a mixed acid of sulfuric acid and silicon hydrofluoric acid is withdrawn from the electrolytic tank, and alkaline earth metal carbonate is added to the electrolytic solution to precipitate Pb in the solution, and the electrolytic solution from which this precipitation has been removed The invention relates to a method for electrolytic refining of high-purity Sn, wherein the electrolytic refining of Sn is performed by returning to an electrolytic cell. However, Patent Document 1 does not describe the Pb content in the Sn plated steel sheet and the Sn plated layer.

Patent Document 2 describes a technique of removing Pb in the object by heating and melting a to-be-processed object which consists of a pure metal or an alloy, and making this molten material contact at least one of a metal halide and an oxyhalide. However, in Patent Document 2, Pb-free solder is only described as a specific to-be-processed object, and it does not describe about Pb content in the Sn plated layer of a Sn plated steel sheet.

In Patent Document 3, in order to prevent short circuit between terminals due to whisker growth, which tends to occur when Pb-free Sn plating is applied to electronic components such as semiconductor devices, the angle formed by adjacent grain boundaries in the Sn plating layer is set to 20. ° or less, the invention is described. However, Patent Document 3 does not describe a method for producing Sn plating having an extremely low Pb concentration from a plating bath containing Pb in the first place.

Japanese Patent Laid-Open No. 2003-183871 Japanese Patent Laid-Open No. 2010-111912 Japanese Patent Laid-Open No. 2009-270154

In the present invention, in consideration of the above situation and the further stringent Pb content regulation value predicted later, the Pb content of the entire electrical Sn plated layer is 50 mass ppm or less, and an electrical Sn plated steel sheet applicable to a steel sheet for a container is provided. make it a task More specifically, an object of the present invention is to provide an electro-Sn plated steel sheet having a long service life and excellent corrosion resistance, coating film adhesion and whisker resistance when applied to a steel sheet for containers.

The gist of the present invention is as follows.

[1] An electrically Sn-plated steel sheet according to one embodiment of the present invention is provided with a base steel sheet and a base steel sheet disposed on the base steel sheet, and has a Sn layer and an alloy layer, Sn: 10 to 100 mass%, Fe: 0 to 90 mass %, O: provided with an electrolytic Sn plating layer containing 0 to 0.5 mass%, the Pb content of the entire Sn electroplating layer is 50 mass ppm or less, the thickness of the Sn electroplating layer is t, and When the region from the surface to the (1/10) × t depth in the sheet thickness direction is referred to as a surface layer region, the Pb content of the surface layer region is 5 mass ppm or more, and the Pb content of the surface layer region is the entirety of the Sn plating layer. It is characterized in that it is higher than the Pb content of

[2] In the electro-Sn plated steel sheet according to [1], the Pb content/(Sn content + Pb content) of the surface layer region of the Sn plated layer is Pb content/( The value obtained by dividing by Sn content + Pb content) may be 1.1 or more.

[3] The Sn electroplated steel sheet according to [1] or [2], wherein the Sn electroplating layer comprises Ca: 0.1 to 10 mass ppm, Sr: 0.1 to 10 mass ppm, and Ba: 0.1 to 10 mass ppm You may further contain 1 type(s) or 2 or more types from a group.

[4] The electrical Sn plated steel sheet according to any one of [1] to [3], wherein the Fe-Ni layer, the Ni-Sn layer and the Fe-Ni-Sn layer are interposed between the electrical Sn plated layer and the base steel sheet. You may provide 1 type or 2 or more types further.

According to the said one aspect|mode which concerns on this invention, the Pb content of the whole Sn electroplating layer can provide the Sn electroplating steel plate applicable to the steel plate for containers whose Pb content is 50 mass ppm or less.

1 is a graph showing the change in the concentration of Pb ²⁺ in a plating bath by a crown ether method on a laboratory scale as an example of the present invention.
It is a graph which shows the GD-MS analysis result of the Sn electroplating layer of No. 16 of an Example.
It is a graph which shows the change of the thickness direction of the Sn electroplating layer of Pb/(Sn+Pb) value of No. 16 of an Example.
3A is a graph showing the GD-MS analysis result of an electrolytic Sn plating layer produced using an untreated Sn plating solution.
3B is a graph showing the GD-MS analysis result of an electrolytic Sn plating layer produced using a Sn plating solution treated by a crown ether method as an example of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described in detail. However, the present invention is not limited only to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present invention.

In the numerical limitation range described below, a lower limit and an upper limit are included in the range. Numerical values expressed as "greater than" or "less than" are not included in the numerical range.

The electro Sn plated steel sheet according to the present embodiment is disposed on the base steel sheet and the base steel sheet, has a Sn layer and an alloy layer, Sn: 10 to 100 mass%, Fe: 0 to 90 mass%, O: 0 to 0.5 mass %, Pb content of the whole said Sn electroplating layer is 50 mass ppm or less, Let the thickness of the said Sn electroplating layer be t, and the board thickness direction from the surface of the said Sn electroplating layer. When the region up to (1/10) × t depth is referred to as the surface layer region, the Pb content of the surface layer region is 5 mass ppm or more, and the Pb content of the surface layer region is higher than the Pb content of the entire Sn plating layer. characterized by high.

First, the process which led to the present inventors developing the electrolytic Sn plated steel plate which concerns on this embodiment is demonstrated.

The present inventors studied the mechanism by which Pb contained in a Sn ingot mixes in the Sn electroplating layer.

As a result of the investigation by the present inventors, with respect to the Sn electroplating layer, from observation and quantitative measurement in the depth direction, Pb is present as metal Pb in the entire Sn electroplating layer, that is, Pb is electrolytically precipitated together with Sn (vacancy). It became clear that it was not contained in the Sn plating layer by simple mixing of Sn plating solution.

The present inventors prepared a Sn plating solution (PSA plating bath) comprising p-phenolsulfonic acid, Sn(II) sulfate, and an additive, and a Pb-containing plating solution containing Pb acetate added thereto, and changed the set potential to form an electric Sn plating layer. formed As a result, there is almost no difference in the precipitation potential between Sn and Pb, and when a Sn ingot (about 50 mass ppm) with a low Pb content is used as the Sn source, the Pb content in the Sn electroplating layer is 100 mass ppm or less (about 70 mass ppm) ), but in the case of using a Sn ingot with a high Pb content (about 100 to 300 mass ppm), under the use of the Sn plating solution used in actual operation, the plating conditions such as the current density are changed and the vacancy of Pb is used. It turned out to be difficult to suppress.

The Sn plating solution used for the plating process of the Sn electroplating steel sheet supplies Sn ²⁺ in the form of a sulfuric acid bath using an insoluble anode, and the solubility of the sulfate of Sn and Pb in 20 degreeC is as follows.

SnSO ₄ : 18.9 g/100 g-H ₂ O (used)

PbSO ₄ : 0.003846g/100g-H ₂ O (slightly soluble)

In Sn plating solution in actual operation, Pb ²⁺ dissolved slightly as described above is electrically reduced together with Sn ²⁺ , and it is considered to be mixed as metal Pb in the Sn plating layer. As a result of the present inventors examining the method of removing slightly dissolved Pb ²⁺ from the Sn plating solution as mentioned above, the removal method using a crown ether was mentioned as a candidate.

Crown ethers are composed of cyclic polyether chains and can selectively interact with several heavy metal ions. Crown ethers have vacancies made of ether oxygen atoms in the molecule, and a heavy metal ion is introduced into them to bond. Therefore, a selective interaction occurs when the size of the heavy metal ion matches the size of the pore size of the crown ether. In order to selectively remove lead ions (Pb ²⁺ ) in the Sn plating solution, a crown ether whose pore size is adjusted to match the size of the lead ion may be used.

For example, in the general structural formula (-CH ₂ -CH ₂ -O-) n of the crown ether, n = 6, a crown ether with controlled pore size is used as a resin (not particularly limited, for example, silica gel , methacrylate, and polystyrene), filled in a column, and allowed to selectively remove lead ions (Pb ²⁺ ) by passing a Sn plating solution through the column.

Next, the present inventors observed the change of Pb ²⁺ in the Sn plating solution when the Sn plating solution (PSA plating bath) was treated with crown ether on a laboratory scale.

The base Sn plating solution is p-phenolsulfonic acid: 115g/L, EN-10 (Ethoxylated α-Naphthol): 5g/L, ENSA (Ethoxylated α-Naphthol Sulphonic Acid): 5g/L, _SnSO4 : 36g/L (20 g/L in terms of Sn ²⁺ ), was added to this in the form of Pb acetate so as to be 13 mg/L in terms of Pb ²⁺ (650 ppm in terms of Pb/Sn), and produced.

A total of 200 L of the Sn plating solution was passed through a column filled with crown ether, and component analysis was performed for every 20 L of the Sn plating solution passed through.

The change of the Pb ²⁺ concentration in the Sn plating solution is shown in FIG. 1 .

As shown in FIG. 1 , Pb ²⁺ in the Sn plating bath was immediately reduced to 0.05 mg/L, which was 13 mg/L, indicating that Pb ²⁺ in the Sn plating bath was removed by the crown ether. On the other hand, although not shown, the concentration of other components (Sn ²⁺ , SO ₄ ^2- , ENSA, EN) in the Sn plating solution is hardly changed, so that only Pb ²⁺ is considered to be selectively removed.

In order to ensure stable productivity, since it is common to improve the uniformity in the Sn electroplating layer, Pb content in the Sn electroplating layer is reduced uniformly in the depth direction. However, unlike the prior art, the present inventors have newly discovered that the occurrence of blackening is reduced by reducing the Pb content of the entire Sn electroplating layer, and whisker resistance is improved by concentrating Pb in the surface layer region. Moreover, the present inventors discovered newly also that coating-film adhesiveness improved by providing a gradient to Pb content in an electric Sn plating layer.

The electroplated Sn plated steel sheet according to the present embodiment is made based on the above-described knowledge. Hereinafter, the electro-Sn-coated steel sheet which concerns on this embodiment is demonstrated in detail.

[base steel plate]

The base steel sheet of the electro-Sn plated steel sheet according to the present embodiment is not particularly limited, and a steel sheet used as a base steel sheet for a general steel sheet for containers specified in JIS G 3303:2017 may be used. In this embodiment, for example, C: 0.01 to 0.06 mass %, Al: 0.001 to 0.01 mass %, Mn: 0.01 to 0.06 mass %, and the balance Fe and the base steel sheet composed of impurities can be used.

[Electric Sn plating layer]

The Sn electroplating layer according to the present embodiment is present on the surface side of the Sn electroplating layer, the Sn layer containing a lot of Sn, and the electro Sn plating layer are present on the base steel sheet side of the Sn electroplating layer, and Fe of the base steel sheet is diffused in the Sn electroplating layer. It has an alloy layer (Fe-Sn layer). The definition of an electrolytic Sn plating layer, a Sn layer, and an alloy layer is mentioned later.

In this embodiment, Pb content of the whole electric Sn plating layer is 50 mass ppm or less. When the Pb content of the whole electrolytic Sn plating layer is more than 50 mass ppm, the Pb content regulation value predicted later cannot be satisfied, and the characteristic (long life, corrosion resistance) required as a steel plate for containers cannot be acquired. As for Pb content of the whole electric Sn plating layer, 40 mass ppm or less, 30 mass ppm or less, 20 mass ppm or less, or 10 mass ppm or less are preferable. Although it is possible to make Pb content of the whole Sn electroplating layer less than 5 mass ppm, since it causes the increase of the cost in actual operation, it is good also considering the lower limit of Pb content of the whole Sn electroplating layer as 5 mass ppm.

In the Sn electroplating layer according to the present embodiment, the Pb content of the surface layer region is 5 mass ppm or more, and the Pb content of the surface layer region is higher than the Pb content of the entire Sn electroplating layer. The upper limit of the Pb content in the surface layer region may be 60 mass ppm. In this embodiment, when the thickness of the Sn electroplating layer is t, the surface layer region means a region from the surface of the Sn electroplating layer to the (1/10) × t depth in the plate thickness direction. In addition, in this embodiment, the area|region other than the surface layer area|region of an electrolytic Sn plating layer is called a deep part area|region. The deep region of the Sn plating layer is, in short, when the thickness of the Sn plating layer is t, from the surface of the Sn plating layer in the thickness direction to (1/10) × t depth to from the surface to the depth t in the thickness direction. is the area

When the Pb content of the surface layer region is equal to the Pb content of the entire Sn plating layer, or when the Pb content of the surface layer region is lower than the Pb content of the Sn plating layer as a whole, the coating film adhesion of the Sn electroplated steel sheet deteriorates.

In the Sn electroplating layer according to the present embodiment, the value obtained by dividing Pb content/(Sn content+Pb content) in the surface layer region of the Sn electroplating layer by Pb content/(Sn content+Pb content) in the deep region of the Sn electroplating layer is 1.1 or more can be done with Coating film adhesiveness of an electric Sn plated steel sheet by setting the value obtained by dividing Pb content/(Sn content + Pb content) of the surface layer region of the Sn plating layer by Pb content/(Sn content + Pb content) of the deep region of the Sn plating layer to 1.1 or more. can be further improved.

The electro-Sn plating layer which concerns on this embodiment contains Sn:10-100 mass %, Fe: 0-90 mass %, O: 0-0.5 mass % as elements other than Pb. The remainder consists of impurities. In addition, in this embodiment, an impurity means that it mixes from a Sn ingot as a raw material, a manufacturing environment, etc., and it means that it is permissible in the range which does not exert a bad influence on the electrolytic Sn plated steel sheet which concerns on this embodiment.

The Sn electroplating layer according to the present embodiment may optionally further contain one or two or more of the group consisting of Ca: 0.1 to 10 mass ppm, Sr: 0.1 to 10 mass ppm, and Ba: 0.1 to 10 mass ppm. . When the Sn electroplating layer contains one or two or more of the above groups, the Pb content of the Sn electroplating layer as a whole can be further reduced.

The electro Sn plated steel sheet according to the present embodiment is between the Sn electroplating layer and the base steel sheet, more precisely, between the alloy layer (Fe-Sn layer) and the base steel sheet, the Fe-Ni layer, the Ni-Sn layer, and the Fe-Ni layer. You may further provide 1 type(s) or 2 or more types of -Sn layer. When the Sn electroplated layer further includes one or two or more of these layers, the can life can be lengthened when the Sn electroplated steel sheet is used as a beverage can or food can, and the barrier effect is improved by the formation of a dense alloy layer. Therefore, corrosion resistance can be improved.

Next, the analysis method of the component of the Sn electroplating layer which concerns on this embodiment is demonstrated, referring FIG. 2A and FIG. 2B. The component of the Sn electroplating layer can be analyzed by GD-MS (Glow Discharge-Mass Spectrometry) analysis. GD-MS analysis is an analysis method which traces the change of the composition from the surface of a plating layer to the depth direction with progress of discharge time. Fig. 2A is a graph obtained by performing GD-MS analysis on the electro Sn-coated steel sheet of No. 16 of Example.

The graph of FIG. 2A shows the change of the content of Fe, Sn, Pb, and O from the surface side of the electrolytic Sn plating layer on the left end side of the horizontal axis toward the base steel sheet side on the right end side. Mass ppm of the ordinate is a scale on the left for Fe and Sn, and a scale on the right for Pb and O.

The graph of FIG. 2B takes out Sn content and Pb content of FIG. 2A, calculates Pb/(Sn+Pb) value, and graphs the change from the surface of the Sn electroplating layer to the depth direction.

In the present embodiment, when a sample is taken from an arbitrary position of the Sn electroplated steel sheet and the sample is subjected to GD-MS analysis in the sheet thickness direction, a region having a Sn content of 100000 ppm or more from the surface is defined as an electrolytic Sn plating layer. In addition, in FIG. 2A, although an element is not detected for several minutes after discharge, this area|region is not included in the electrolytic Sn plating layer. In addition, the area|region where Sn content is more than Fe content in the Sn electroplating layer is defined as a Sn layer, and the area|region other than the Sn layer in the Sn electroplating layer is defined as an alloy layer (Fe-Sn layer) (refer FIG. 2A). In addition, the area|region whose Fe is 10-90 mass % and Ni is 10-90 mass % is defined as an Fe-Ni layer, Ni is 10-90 mass %, and Sn is 10-90 mass %, The area|region is a Ni-Sn layer. is defined, and a region containing 10 to 80% by mass of Fe, 10 to 80% by mass of Ni, and 10 to 80% by mass of Sn is defined as an Fe-Ni-Sn layer.

Pb content of the whole electroplating layer is Pb content of the whole electroplating layer containing Sn layer and an alloy layer obtained by GD-MS analysis. The Pb content of the surface layer region is the Pb content of the region from the surface of the Sn electroplating layer to the (1/10) × t depth obtained by GD-MS analysis.

The Pb content/(Sn content + Pb content) of the surface layer region of the electrolytic Sn plating layer is obtained by dividing the Pb content (mass %) of the surface layer region by the sum of the Sn content (mass %) and Pb content (mass %) of the surface layer region . Similarly, Pb content/(Sn content + Pb content) of the deep part region of the Sn plating layer is the Pb content (mass %) of the deep part region, as the sum of the Sn content (mass %) and Pb content (mass %) of the deep part region share and get

The Ca content, Sr content, and Ba content in the Sn plating layer are obtained by dissolving the Sn plating layer using an acid containing an inhibitor, and analyzing the solution obtained by dissolving it by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). .

[Manufacturing method]

An example of the manufacturing method of the electrolytic Sn plated steel plate which concerns on this embodiment is demonstrated.

First, electroplating is performed on the base steel sheet having the above-described chemical composition. In the present embodiment, electro-Sn plating is performed using the Sn plating solution in which the Pb ²⁺ concentration is reduced by the crown ether method. Before electroplating by Sn, you may perform electrolytic degreasing. In the electro-Sn plating process of high-speed sheet-threading between a plurality of electrodes (10 passes), the current density of the 1st to 9th passes is made constant, the current density of the 10th pass (final pass) is increased, and Sn electroplating is performed. The Pb content of the surface layer area|region of an electrolytic Sn plating layer can be adjusted by adjusting the heightening width of the current density of the 10th pass. After the electro Sn plating process, flux is applied to the base steel sheet, immersed in a 10-fold dilution of Sn plating solution, roller squeezing, cold air drying, and reflow operation, energization heating and heating (80 ° C) are performed. Conduct.

By the above method, the electrolytic Sn plated steel sheet according to the present embodiment can be manufactured.

In this embodiment, you may add carbonate of alkaline-earth metal (Ca, Sr, Ba) to Sn plating liquid. Thereby, the yield of Pb ²⁺ removal by the crown ether method can be improved, and Pb content of the whole electrolytic Sn plating layer can be reduced further.

In addition, in this embodiment, you may perform Ni pre-plating or Fe-Ni pre-plating as an electroplating pre-processing of Sn. Thereby, one type or two or more types of an Fe-Ni layer, a Ni-Sn layer, or an Fe-Ni-Sn layer can be formed between a base steel plate and an electrical Sn plating layer.

Example

Examples of the present invention will be described below, but the conditions in the examples are merely examples employed to confirm the practicability and effects of the present invention, and the present invention is not limited to these condition examples. Various conditions can be employ|adopted for this invention, as long as the objective of this invention is achieved without deviating from the summary of this invention.

[Example 1]

On an actual operation scale, the effect of the fall of the Pb content in the Sn electroplating layer by the crown ether method was investigated.

The components of the Sn plating solution are Sn ²⁺ : 20 g/L, Pb ²⁺ : 5 mg/L (250 ppm in terms of Pb/Sn), EN: 5 g/L, ENSA: 5 g/L, PSA: 100 g/L, and temperature: 45 ℃ was.

A crown ether-supported resin (silica gel is used in this example) was charged in a column and passed through a Sn plating solution. This Sn plating solution is transferred to the plating cell, circulated in the plating cell, and then returned to the column. This was repeated. Although the liquid passing rate (L/hr) of the Sn plating liquid at this time depends on the resin volume (L), as a result of preliminary examination, the Sn plating liquid passing rate was set to 60 L/hr with respect to 1 L of resin.

On a laboratory scale, although a considerable effect was recognized, on an actual operation scale, it was reduced only to Pb ²⁺ :0.1 mg/L.

The present inventors guessed that the property of a crown ether fell slightly because the existing sludge (SnO2 is _a main component) exists in a large amount in an actual operation line for this cause. However, it was found that the effect was sufficiently exhibited even in an actual operation line by adjusting the flow rate and the frequency of crown ether exchange.

Furthermore, the electrolytic Sn plating layer produced with the Sn plating solution in which Pb ²⁺ was reduced by the crown ether method was analyzed.

Fig. 3b shows the result of GD-MS analysis of the Sn plating layer prepared with the Sn plating solution having Pb ²⁺ : 0.1 mg/L by the crown ether method, and the Sn plating layer prepared using the untreated Sn plating solution (comparative Example) of the GD-MS analysis result is shown in Fig. 3a.

As shown in FIG. 3A , in the electrolytic Sn plating layer prepared with the untreated Sn plating solution as a comparative example, a high concentration of Pb was detected from the vicinity of the surface along with Sn. On the other hand, in the plating layer prepared with the Sn plating solution treated with the crown ether method, as shown in Fig. 3B, only a small amount of Pb was detected.

[Example 2]

The following experiments were performed on the assumption that the electrolytic Sn plated steel sheet according to the present invention was applied to the production of tin plate as a material for a beverage can and a material for a food can.

As the base steel sheet, a steel sheet composed of C: 0.03 mass%, Al: 0.005 mass%, Mn: 0.03 mass%, and the remainder Fe and impurities was used.

The components of the Sn plating solution are Sn ²⁺ : 20 g/L, Pb ²⁺ : 5 mg/L (250 ppm in terms of Pb/Sn), EN: 5 g/L, ENSA: 5 g/L, PSA: 100 g/L, and temperature: It was 45 °C. The Pb ²⁺ concentration of this Sn plating solution was reduced by the crown ether method, and the Sn plating layer was formed sequentially at an arbitrary Pb ²⁺ concentration through an electro-Sn plating process described later. The Pb ²⁺ concentration could be reduced to 0.05 mg/L on a laboratory scale.

As a pretreatment for forming an electrolytic Sn plating layer, in the electrolytic degreasing step of the steel sheet, a current of 10 A/dm ² × 10 sec in a 10% NaOH solution at 60° C. was made to flow to the cathode side of the steel sheet. After that, immersion in 10% H ₂ SO ₄ at room temperature for 10 sec and pickling, with the aim of #25 tin plate (Sn adhesion amount on one side 2.8 g/m 2 ), using the Sn plating solution, electroplating Sn at 5A/dm ² was done.

Electro Sn plating process WHEREIN: In this Example, the electric Sn plating layer which controlled the distribution state of Pb by changing the current density of the last pass among 10 passes was formed. That is, in the case of concentrating Pb in the surface layer region, the current density of the final pass is increased, and conversely, when the Pb content of the surface layer region is reduced than the Pb content of the entire Sn electroplating layer, the current density of the final pass is lowered. In this example, the current density was 20 A/dm ² except for the last pass, and in the last pass, the current density was increased to 30 to 60 A/dm ² , and electrolytic Sn plating was performed. However, about No.11 and No.14 of Table 1, only the last pass lowered the current density, and about No.37 and No.38, the current density was made constant.

For some Sn plating solutions, carbonates of alkaline earth metals (Ca, Sr, Ba) were added.

Following the electro-Sn plating process, after flux application, immersion in a 10-fold dilution of the above-described Sn electroplating solution, roller squeezing, followed by cold-air drying, as a reflow operation, energized heating and quenching (80 ° C) are performed. did. By the above method, an electrolytic Sn plated steel sheet was obtained.

For some electro-Sn plated steel sheets, Ni pre-plating and Fe-20 mass% Ni pre-plating are performed so that the adhesion amount of Ni: 20 mg/m 2 is respectively Ni pre-plating as a pretreatment in the Sn electro-plating process, and then by reflow, An Fe-Ni layer, a Ni-Sn layer (mainly Ni ₃ Sn ₄ ), or an Fe-Ni-Sn layer was formed.

The component analysis of the electrolytic Sn plating layer was performed by the method mentioned above. In addition, for GD-MS analysis, a 30 mm x 15 mm rectangular sample was taken from the position spaced|separated by 30 mm from the edge part of the Sn electroplating steel plate, and GD-MS analysis was performed with respect to two places of the sample. Trace element analysis of alkaline earth metals (Ca, Sr, Ba) was measured by ICP-MS. Electric Sn plating layer contains Pb, Ca, Sr, and Ba shown in Table 1, Sn: 10-100 mass %, Fe: 0-90 mass %, O: Electric Sn which consists of 0-0.5 mass % and remainder impurity It was a plating layer.

"Plating layer total Pb content/mass ppm" of Table 1 is Pb content of the whole electroplating layer, "surface layer Pb content/mass ppm" is Pb content of the surface layer region of an electrolytic Sn plating layer. In the column of "Pb/(Sn+Pb) (surface layer region/deep region)" of Table 1, Pb content/(Sn content + Pb content) of the surface layer region of the Sn plating layer is a region other than the surface region (deep region region) of the Sn plating layer. ), when the value divided by the Pb content/(Sn content + Pb content) was 1.1 or more, “○” was described, and when the value was less than 1.1, “x” was described.

In Table 1, all the Examples including the invention example and the comparative example had the Sn layer and the alloy layer in the Sn electroplating layer.

The following tests were performed on the electroplated Sn plated steel sheet.

In addition, in the sulfurization resistance blackening test (retort test), a sample of a predetermined size is taken from a position 30 mm away from the end of the Sn plated steel sheet, and the sample is 25 g/L of sodium dichromate dihydrate at 50°C. In the solution, a current was passed with a target of 5A/dm ² and 10 mg/dm ² using a Pb-Sn anode (treatment #311).

ATC Test (Alloy-Tin Couple Test)

The ATC test evaluated the can life when the Sn electroplated steel sheet was applied to a beverage can or a food can. In the ATC test, an electro-Sn plated steel sheet that was de-tinned after reflow to expose the alloy layer (Fe-Sn layer) and an electro-Sn-plated steel sheet that had not been de-tinned after reflow was treated with an ATC test solution (1.5% NaCl + 1.5% citric acid solution). It was immersed in the inside, and the corrosion current flowing between the anodes was measured. The test piece was a rectangle of 130 mm x 15 mm, and this was electrolytically peeled off in a 5% NaOH solution, the test surface of 5 mm x 40 mm was left, and the other was completely sealed, and it was made to prevent electric current from leaking. The test solution was boiled for 2 minutes in a nitrogen atmosphere and cooled to room temperature. In the test tank, an electroplated Sn plated steel sheet that was detinned after reflow to expose an alloy layer (Fe-Sn layer), and an electroplated Sn plated steel sheet that had not been detinned after reflow were connected and incorporated. Stannous chloride (100 ppm in terms of Sn ²⁺ ) was put at the bottom of the test tank, and the inside of the test tank was made into nitrogen atmosphere beforehand. Transfer the ATC test solution to the test tank so that it does not come into contact with air, and after reflow, immerse the electroplated Sn plated steel sheet exposing the alloy layer (Fe-Sn layer) and the non-tin detinned electroplated steel sheet after reflow. The ATC test solution was stirred for 30 minutes to dissolve stannous chloride. After being immersed in a nitrogen atmosphere (ATC test solution) for 20 hours, the current value between the detinned electrolytic Sn plated steel sheet and the non-tin detinned electroplated Sn plated steel sheet was measured, and this was referred to as the ATC value. It shows that the can life is so favorable that an ATC value is low.

In this example, the ATC value (㎂/cm2) measured by the above method

Excellent 4 points: less than 0.1も/cm2

3 points: 0.1も/cm2 or more, less than 0.2も/cm2

2 points: 0.2も/cm2 or more, less than 0.3も/cm2

Inferior 1 point: 0.3も/cm2 or more

was rated in 4 stages. Moreover, since it was possible to use it as a steel plate for containers at 2 or more points|pieces, it determined 2 or more points|pieces as the pass.

Sulfuration resistance blackening test (retort test)

The anti-sulfurization blackening test evaluated the corrosion resistance of the Sn electroplated steel sheet. In the yellowing resistance test for yellowing, a corrosion resistance test solution obtained by mixing 0.1% sodium thiosulfate aqueous solution and 0.1N sulfuric acid in a volume ratio of 1:2 was used. An electroplated Sn plated steel sheet subjected to the #311 treatment described above was cut out to φ35 mm to be a test piece, and this test piece was placed on the mouth of a heat-resistant bottle into which the corrosion-resistance test solution was placed and fixed. Thereafter, the heat-resistant bottle was inverted so that the test piece and the corrosion-resistance test liquid were in contact. After heat treatment at 121° C. for 60 minutes, corrosion resistance was evaluated by the ratio of the corroded portion among the area in which the corrosion resistance test solution was in contact with the test piece (the area of the opening of the heat-resistant bottle).

A rating of 1 to 5 was given as the ratio of the corrosion area to the area in which the test piece was in contact with the corrosion resistance test solution. Moreover, since it was possible to use it as a steel plate for containers at 3 points|pieces or more, 3 points|pieces or more were judged as passing.

Excellent rating 5: less than 10% area

Rating 4: 10% or more, less than 25% of area

Rating 3: 25% or more, less than 40% of area

Rating 2: 40% or more, less than 55% of area

Inferiority rating 1: 55% or more of area

Coating film adhesion evaluation test

A sample was taken from an arbitrary position of the Sn electroplated steel sheet, an acrylic coating film was baked and coated on the surface of the Sn electroplating layer, cooled to room temperature, and then a tape peeling test was performed. The tape surface after the peeling test was observed, and the case where the adhesion surface of the Sn plating was less than 5% of the tape surface (the adhesive surface of the Sn plating layer and the tape) was judged to be a pass because the coating film adhesion was excellent. In the case where the adhesion surface of Sn electroplating was 5% or more of the tape surface (adhesive surface of Sn electroplating layer and a tape), it judged that the coating-film adhesiveness was inferior, and it judged that it was disqualified. Moreover, in the case where the adhesion surface of the electroplating Sn plating was less than 3% of the tape surface (the adhesive surface of the Sn electroplating layer and a tape) among the examples judged as pass, it was judged that it was especially excellent in coating-film adhesiveness. In Table 1, what was judged as passing was described as "Δ", and among the examples judged as pass, a thing especially excellent in coating film adhesiveness was described as "○", and what was judged as unacceptable was described as "x".

Whisker resistance evaluation test

A sample is taken from an arbitrary position of the Sn plated steel sheet, and the sample is left to stand for 1000 h at 40° C. and 50% RH under 5T bending, and then the outside of the bent portion is observed in a range of 10 mm × 5 mm with SEM, Three-view observation was carried out, the number of whiskers of 50 micrometers or more was counted, and the number density was obtained by dividing the number by the observation area. The case where the number of observed whiskers per mm<2> was 10 or less was judged as passing as it was excellent in whisker resistance, and the case where it exceeded 10 was judged as disqualified. In Table 1, what was judged as passing was described as "○", and what was judged as unacceptable was described as "x".

Table 1 shows the above measurement results and test results. In addition, underlined in Table 1 indicates properties that are outside the scope of the present invention or are undesirable.

No.1, No.2, and No.3 are examples in which Pb content of the whole electrolytic Sn plating layer was more than 50 mass ppm, and the rating of the ATC test and the yellowing resistance blackening test was low. Sulfuration blackening is due to the bonding of Sn and S, and discoloration is accelerated by exposure to high temperature in the retort treatment. When the Pb content of the whole electrolytic Sn plating layer was high, a region where the melting point was locally lowered occurred and the reaction point of discoloration increased.

On the other hand, in the example of the present invention, the Pb content of the entire Sn plating layer is 50 mass ppm or less, and the Pb content of the surface layer region is 5 ppm or more and higher than the Pb content of the Sn plating layer as a whole. All test results of the adhesive evaluation test and the whisker resistance evaluation test were also favorable.

In detail, corrosion resistance is more favorable when the Pb content of the whole electrolytic Sn plating layer is 30 mass ppm or less (No. 6), and in 20 mass ppm or less (No. 7, No. 8, No. 16 - No. 18), It exhibited extremely good corrosion resistance. In addition, the value obtained by dividing the Pb content/(Sn content + Pb content) in the surface layer region of the Sn plating layer by the Pb content/(Sn content + Pb content) in the deep region of the Sn plating layer is 1.1 or more, in the invention example, the coating film adhesion evaluation test In particular, good results were shown.

Nos. 19 to 23 are electroplated Sn plated steel sheets prepared by adding 0.01 to 1 g/L of calcium carbonate to a Sn plating solution corresponding to No. 10. Compared with No.10, Pb content of the whole electrolytic Sn plating layer of No.19-23 fell about 20%, and it suggested that the Pb2 ⁺ yield by the crown ether method improved.

Nos. 24 to 28 are electroplated Sn plated steel sheets prepared by adding 0.01 to 1 g/L of strontium carbonate to a Sn plating solution corresponding to No. 10. Compared with No. 10, Pb content of the whole electrolytic Sn plating layer of No. 24-28 fell about 30%, and it suggested that the Pb ²⁺ yield by the crown ether method improved.

Nos. 29 to 33 are electroplated Sn plated steel sheets prepared by adding 0.01 to 1 g/L of barium carbonate to a Sn plating solution corresponding to No. 10. Compared with No.10, Pb content of the whole electrolytic Sn plating layer of No.29-33 fell about 10%, and it suggested that the Pb2 ⁺ yield by the crown ether method improved.

No. 34 is an electrolytic Sn plated steel sheet produced by adding 0.07 g/L of calcium carbonate and 0.05 g/L of strontium carbonate to Sn plating solution corresponding to No. 10. Compared with No. 10, Pb content of the whole electrolytic Sn plating layer of No. 34 fell about 3.5%, and it suggested that the Pb ²⁺ yield by the crown ether method improved.

Nos. 35 to 38 are examples of prior Ni plating and prior Fe-20% Ni plating prior to the electro Sn plating corresponding to No. 9. In No. 35 and No. 36 which are invention examples, since 1 type or 2 types or more of a Ni-Fe layer, a Ni-Sn layer, and a Ni-Fe-Sn layer were formed, the Sn electroplating layer and the said Ni-Fe layer, Ni It turns out that the potential difference between the -Sn layer and the Ni-Fe-Sn layer became small, and the ATC value improved.

2A and 2B show the results of GD-MS analysis of the Sn electroplated layer after reflowing the Sn electroplated steel sheet produced in Example (No. 16).

The graph of FIG. 2A shows the change of the content ratio of Fe, Sn, Pb and O from the surface of the electrolytic Sn plating layer on the left short side of the abscissa toward the base steel sheet side on the right short side of the abscissa. The mass ppm of the vertical axis depends on the scale on the left for Fe and Sn, and the scale on the right for Pb and O. According to FIG. 2A, about Pb, it turns out that only about 25 mass ppm is detected from the outermost surface.

The graph of FIG. 2B takes out the Sn content and Pb content of FIG. 2A, calculates Pb/(Sn+Pb) value, and graphs the change from the surface of the Sn electroplating layer in the depth direction.

At this time, the value of Pb/(Sn+Pb) increases in the surface layer region of the Sn plating layer (the region from the surface to the (1/10) × t depth in the plate thickness direction (the region enclosed by a rectangle in FIG. 2B)), That is, it turns out that the Pb concentration phenomenon has generate|occur|produced in the vicinity of the surface.

In the example of FIG. 2B, while the average Pb/(Sn+Pb) value in the whole electrolytic Sn plating layer is about 15 mass ppm, the maximum Pb/(Sn+Pb) value in the surface layer region is about 25 mass ppm, the present condition and It was a value below the regulatory value of the Pb content predicted afterward, and there was no problem substantially.

When Pb content is the upper limit of 50 mass ppm in the whole electrolytic Sn plating layer which this invention prescribes|regulates, the upper limit of Pb content in surface layer area|region becomes 60 mass ppm.

In the present invention, in order to reduce the Pb content of the entire Sn plated layer, an electrolytic Sn plated steel sheet having a low Pb content was obtained by the method for trapping and removing the complex formation of Pb ^{2+ ions} by the crown ether. It does not exclude use other than a complex formation trap removal method.

The Sn electroplated steel sheet according to the present embodiment can provide the Sn electroplated steel sheet applicable to the steel sheet for containers in which the Pb content of the entire Sn electroplating layer is 50 mass ppm or less. Further, according to the present embodiment, it is possible to achieve a low Pb content at low cost while using a Sn ingot having a relatively high Pb content, such as a conventional Southeast Asian product, without using an expensive Sn ingot with a low Pb content. Therefore, it is an invention of great industrial significance that can be dealt with even if regulations such as Pb-freeization are strengthened in the world from now on.

Claims (5)

base steel plate,
It is disposed on the base steel sheet, has a Sn layer and an alloy layer, Sn: 10 to 100 mass%, Fe: 0 to 90 mass%, O: provided with an electric Sn plating layer containing 0 to 0.5 mass%,
The Pb content of the entire Sn plating layer is 50 mass ppm or less,
When the thickness of the Sn electroplating layer is t, and the area from the surface of the Sn electroplating layer to the (1/10) × t depth in the plate thickness direction is referred to as the surface layer region, the Pb content of the surface layer region is 5 to 60 It is mass ppm, and the Pb content of the said surface layer area|region is higher than the said Pb content of the said Sn electroplating layer as a whole, The electrolytic Sn plated steel sheet characterized by the above-mentioned. The value obtained by dividing the Pb content/(Sn content + Pb content) of the surface layer region of the Sn plating layer by the Pb content/(Sn content + Pb content) of the region other than the surface layer region of the Sn plating layer according to claim 1 Electro Sn-coated steel sheet, characterized in that 1.1 or more. The method according to claim 1 or 2, wherein the Sn plating layer,
Ca: 0.1 to 10 mass ppm,
Sr: 0.1 to 10 mass ppm and
An electrical Sn plated steel sheet characterized by further containing one or two or more types from the group consisting of Ba: 0.1 to 10 mass ppm. The method according to claim 1 or 2, further comprising one or two or more of an Fe-Ni layer, a Ni-Sn layer, and a Fe-Ni-Sn layer between the electric Sn plating layer and the base steel sheet. Electrical Sn-coated steel sheet. The electrical Sn according to claim 3, further comprising one or two or more of a Fe-Ni layer, a Ni-Sn layer, and a Fe-Ni-Sn layer between the electrical Sn plating layer and the base steel sheet. plated steel plate.

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