JPH0420989B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The industrial application field of the surface-treated steel sheet for welded cans produced by the manufacturing method of the present invention is as a material for metal cans filled with food and beverages. [Prior Art] As a conventional technique for manufacturing a surface-treated steel sheet in which a steel sheet is coated with chromium and an upper layer of tin is coated, a chromium-tin two-layer plating method is known in Japanese Patent Publication No. 35136/1983. The method of this invention is to electrolessly immerse a steel plate in a chrome plating solution after electroplating with chromium, and then immerse it in a tinning bath electrolessly for less than 0.5 seconds at a current density higher than the gloss current density of tin plating. Strike plating is carried out, followed by tin plating at a bright current density. This invention relates to a tin plating method for dissolving chromium hydrated oxide remaining on chromium after chromium plating and improving the adhesion of tin. It is something to do. Some of the inventors of the present invention have previously proposed a surface-treated steel sheet with chromium on the steel sheet and tin on the upper layer.
Application No. 59-43789 was filed on March 9, 1959. The surface-treated steel sheet for welded cans of this patent application has a chromium plating layer of 30 to 300 mg/m ² per side on the steel sheet,
A tin plating layer or a tin-nickel alloy layer of 10 to 500 mg/m ² is formed on the top layer, and a chromium hydrated oxide layer of 2 to 18 mg/m ² in terms of chromium is formed on top of that. The manufacturing method is that after chrome plating, PH
2 to 50A/in an aqueous solution of 0.5 to 2 sulfuric acid, hydrochloric acid, etc.
After removing the residual chromium hydrated oxide on the chromium plating layer by treating with a cathodic current density of dm ² for 0.5-5 seconds, tin or tin-nickel alloy plating is applied, and further chromium hydrated oxide is applied. This is a method of generating. Furthermore, in order to perform tin or tin-nickel alloy plating while removing residual chromium hydrated oxide after chromium plating, a tin plating bath with a low tin ion concentration and a low PH or an alkaline bath with both tin and nickel ions are used. It is also possible to use alloy plating baths or acid alloy plating baths. [Problems to be solved by the invention] Tinplate has traditionally been widely used as a surface-treated steel sheet for welded cans filled with food and beverages, but thin tin with a reduced amount of tin plating has been developed to reduce the cost of cans. Plated steel sheets (tin plating amount less than 1.0g/ ^m2 ) and thin tin-plated steel sheets pre-plated with nickel have been developed.
It is being used experimentally. The can performance of these surface-treated steel sheets is that the amount of tin plating is 2.8 in all characteristics.
g/ ^m2 , and cans filled with highly corrosive contents such as fruits and fish cannot withstand long-term storage even if painted. It is being used on a trial basis only. The problem to be solved by the present invention is that the wire seam weldability, paint adhesion, string rust resistance, and corrosion resistance that should be provided as a surface-treated steel sheet for welded cans are insufficient with the thin tin-plated steel sheet, and the tin-plated steel sheet is insufficient. Amount 2.8
It is not comparable to tinplate of g/m ² . The present invention not only provides a low-cost surface-treated steel sheet with a tin coating of 1.0 g/m ² or less, which is comparable in performance to the performance of tin cans with a tin coating of 2.8 g/m ² which are widely used. This manufacturing method also provides a surface-treated steel sheet that has the can performance of chromium-type stain-free steel, which is often used for adhesive cans. In the surface-treated steel sheet for welded cans obtained by implementing Patent Application No. 59-43789, the tin or tin-nickel alloy plated on the chromium remains plated,
exist uniformly. It is known that thread rust progresses due to the formation of oxygen concentration batteries in areas where the paint film is scratched in a highly humid atmosphere containing chlorine or the like. As the tin layer becomes thinner, the amount of oxygen supplied to the inactive body of the thread rust increases, and the uniform presence of tin, which promotes the oxygen reduction reaction, deteriorates the thread rust resistance. The first objective of the present invention is to improve thread rust resistance. When heated during baking after painting, iron diffuses through the bores in the chromium layer, forming an iron-tin alloy, but if the tin plated on the chrome remains plated, the tin will exist uniformly. However, since the surface area is large, the amount of iron-tin alloy produced is large. A second object of the present invention is to further reduce the amount of alloy layer formed and to allow more metallic tin to remain. In foods and beverages, as-plated tin is susceptible to detinning, or sub-paint corrosion, which refers to the dissolution of tin from scratches in the paint. A third object of the present invention is to improve the detinning resistance and the corrosion resistance under the coating film. [Means for solving the problem] The inventor conducted a detailed study on the can performance of a surface-treated steel sheet obtained by tin plating while removing chromium hydrated oxide remaining on the chromium after chromium plating. As a result, they discovered that the state of the tin layer on chromium has a significant effect on can performance, leading to the present invention. That is, the tin layer as it is electrically deposited is uniform, but it lacks density, and its thread rust resistance and under-coating corrosion resistance are inferior to that of tin. By heating and melting this tin layer to 240-350° C. above the melting point of tin, tin forms an island-like and discontinuous coating on the chromium. As is well known, chromium and tin not only do not form solid solutions with each other, but also do not form intermetallic compounds. Therefore, when tin is melted on a chromium layer, a repelling phenomenon occurs, forming an island-like and discontinuous coating. The chromium layer has many pores, although there are some differences depending on the amount of chromium plating. For this reason, some iron and tin diffused from the pores during heating and melting form a very dense iron-tin alloy, so the tin layer forms an island-like and discontinuous coating and increases its adhesion on the chromium, preventing it from peeling off. I won't wake you up. Furthermore, compared to the case where the tin layer is uniform, the amount of iron-tin alloy produced by heating such as baking of paint is also smaller. FIG. 1 shows an example in which tin on a chromium layer undergoes a repelling phenomenon to form an island-like and discontinuous coating. In Figure 1, the white island-like particles are the tin layer,
The matrix corresponds to the chrome surface. The present invention solves the drawbacks of the above-mentioned thin tin-plated steel sheets and surface-treated steel sheets in which tin is uniformly plated on chromium. Chromium plating of ~150mg/ ^m2 is applied, and while removing residual chromium hydrated oxide, tin plating of 0.1~1.0g/ ^m2 is applied to the steel sheet.
This is a method for manufacturing a surface-treated steel sheet for welded cans, in which tin is melted by heating to 240 to 350°C, the tin layer is formed into an island-like and discontinuous coating, and the tin layer is further subjected to chromate treatment or electrolytic chromic acid treatment. The amount of chromium plating on the steel plate is preferably 10 to 150 mg/m ² . If the amount of chromium plating is less than 10mg/ ^m2 , the amount of exposed iron will increase, and the repelling phenomenon of tin will be insufficient in the heating and melting treatment after tin plating, and the amount of iron-tin alloy formed will increase, resulting in a decrease in metallic tin. In addition to reducing wire seam weldability, the relatively uniform presence of tin reduces thread rust resistance. The amount of chrome plating
When the concentration ^exceeds 150mg/m2, the pores in the chromium layer decrease and the exposed iron area decreases, resulting in a strong repelling phenomenon when tin is heated and melted, almost no iron-tin alloy is formed, and the adhesion of chromium and tin. is no longer sufficient. Chrome plating is performed by using a steel plate as a cathode in an aqueous solution containing chromic anhydride as the main ingredient and a small amount of sulfuric acid, sulfate, hydrofluoric acid, fluoride, silicofluoride, and borofluoride as an auxiliary agent. It can be obtained by electrolytic chromic acid treatment. It is necessary to adopt bath and electrolytic conditions that produce a small amount of chromium hydrated oxide that inevitably remains during chromium plating. In other words, it is preferable that the concentration of chromic anhydride is as high as 100 to 300 g/, and the amount of auxiliary agent is 1 to 5% by weight of the chromic anhydride.
is preferred. Bath temperature and current density are 50 to 70, respectively.
℃, 30 to 60 A/dm ² is preferable. It is also possible to use a chromium plating bath containing trivalent chromium ions, which uses chromium sulfate or chromium chloride as the main ingredient, and also includes auxiliary agents, complexing agents, and activators. In this method, the amount of chromium hydrated oxide produced is extremely small, and tin plating can be carried out in a ferrostane bath, halogen bath, etc. without removing the chromium hydrated oxide. In order to reduce as much as possible the chromium hydrated oxide remaining on the chromium after chromium plating, immersion in a chromium plating bath or a chromium plating bath whose temperature is higher than that of the chromium plating bath is effective. To remove chromium hydrated oxide remaining after chromium plating, cathodic electrolytic treatment in sulfuric acid or hydrochloric acid with a pH of 0.5 to 2 is also effective, but in this case, the chromium in the tinned layer and The adhesion force is weak. Therefore, the most effective method is to remove the remaining hydrated chromium oxide while tin plating. The amount of tin plating is preferably 0.1 to 1.0 g/m ² . 0.1
Below g/ ^m2 , most of the tin becomes an iron-tin alloy.
Not only is sufficient wire seam weldability not achieved, the appearance is equivalent to that of stain-free steel, and the tin luster is lost. At 1.0 g/m2 or ^more , the wire seam weldability becomes equal to or better than that of tin plate and reaches saturation, and at the lower limit of the amount of chromium plating, the non-uniformity of the island-like and discontinuous coating of tin decreases, resulting in thread rust resistance. deteriorates. Furthermore, as the continuity of tin increases, corrosion under the coating also increases, which increases costs and must be avoided. When applying the method of the present invention to painted cans filled with food and beverages, the amount of tin is 0.4 to 0.7.
g/m ² is more preferred. Since the tinning method performs tinning while removing residual chromium hydrated oxide, it is difficult to obtain sufficient adhesion of chromium and tin using known ferrostane baths or halogen baths. PH when tin ion concentration is 2~15g/
It is preferable to use an acidic tin plating bath with a concentration of 0.5 to 3 or an alkaline bath with a tin ion concentration of 2 to 50 g/PH and a pH of 8 to 10. In either bath, it is necessary to reduce the concentration of tin to 1/3 or less of that of conventional baths.
The alkali concentration, brightener concentration, etc. may be the same as conventional ones. As the tin concentration decreases, the current efficiency for tin deposition decreases to 3-60%, hydrogen gas is generated and residual chromium hydrated oxide is removed, the chromium surface is activated, and tin is deposited at the same time. This improves tin adhesion and uniformity. Since tin plating using only such a low-efficiency tinning bath will increase electricity costs, it is necessary to remove the remaining chromium hydrated oxide and uniformly cover the chromium surface with tin. It is necessary to use a known bath such as a ferrostan bath or a halogen bath. The heating and melting treatment of tin after tin plating is 240 to 350
°C is preferred. At temperatures below 240°C, tin partially melts, but it is not possible to form all the tin into an island-like and discontinuous coating. Although islands can be sufficiently formed at temperatures above 350°C, heating more than necessary will lead to oxidation of the tin and chromium surfaces, which will also be disadvantageous in terms of cost.
The heating and melting treatment of tin can be carried out by a resistance heating method or an induction heating method, which are often used in tin manufacturing equipment. As the tin is melted and heated to form an island-like and discontinuous coating, the surface of the treated steel sheet becomes a non-uniform structure consisting of tin and chromium. This surface-treated steel sheet is subjected to chromate treatment or electrolytic chromic acid treatment as a post-treatment. A good amount of chromate film is 2 to 20 mg/m ² in terms of chromium. 2mg/ ^m2
If it is less than 20mg/ ^m2 , the paint adhesion deteriorates over time and corrosion resistance is insufficient, and if it is more than 20mg/m2, cohesive failure of the chromate film occurs during processing, which not only reduces paint adhesion but also causes wire seam welding. Sexuality also decreases. Chromate treatment method: 20-40g/
This can be carried out by cathodic electrolysis treatment in an aqueous dichromate solution. Appropriate treatment temperatures are 40 to 70°C and cathode current densities of 2 to 10 A/dm ² . Electrolytic chromic acid treatment, which has better paint adhesion and corrosion resistance than chromate treatment, simultaneously produces metallic chromium and hydrated chromium oxide. In the present invention, 30 mg/m ² of metallic chromium and 2 to 20 mg/m ² of chromium hydrated oxide are good. If metal chromium is 3 mg/m ² or less, wire seam weldability is good, but the secondary adhesion of the coating film (paint adhesion in cans filled with food and beverages), corrosion resistance, and sulfidation resistance are insufficient. When it exceeds 30 mg/m ² , contact resistance increases due to heating such as baking after processing and painting, and wire seam weldability tends to decrease. If the chromium hydrated oxide is less than 2 mg/m ² in terms of chromium, not only the paint adhesion after aging deteriorates but also the corrosion resistance is insufficient. If it exceeds 20 mg/m ² , the chromium hydrated oxide tends to undergo cohesive failure during processing, which not only reduces paint adhesion and corrosion resistance, but also increases contact resistance and reduces wire seam weldability, which is undesirable. To simultaneously generate metallic chromium and hydrated chromium oxide, cathodic electrolysis is performed using chromic anhydride.
20~80g/add 0.3~5% by weight of sulfuric acid, sulfate, fluorine, fluoride, silica fluoride, or borofluoride or more in the bath at 40~60℃, current density 2~ It is necessary to perform this under the condition of 30A/ ^dm2 . [Operation] The surface-treated steel sheet for welded cans obtained by the manufacturing method of the present invention has tin forming an island-like and discontinuous coating on the chromium, so it is different from the conventional thin tin-plated steel sheet with high uniformity. They have very different characteristics.
Since chromium does not form alloys with tin, it acts as a barrier to the growth of iron-tin alloys, and growth of iron-tin alloys occurs only through the pores of the chromium layer. For this reason, compared to tin plating on a steel plate or tin plating preplated with nickel, which easily alloys with tin, the amount of iron-tin alloy produced by heating such as baking after painting is extremely small. . In addition, if tin plating is performed after chromium plating and the tin is not heated and melted, the tin will exist uniformly on the chromium, and since the tin layer lacks density, the tin will be melted to form an island-like and discontinuous coating. The amount of iron-tin alloy will be larger than that in the case of To suppress iron-tin alloying as much as possible, to leave as much metallic tin as possible, and to make the tin island-like and discontinuous coating,
By lowering the resistance during wire seam welding and increasing the number of contact points, it provides wire seam weldability equivalent to that of tinplate. Thread rust resistance promotes the oxygen reduction reaction, but due to the non-uniform presence of tin and the repelling phenomenon, the thickness of the tin is thicker than before melting, so oxygen diffusion is insufficient and the growth of string rust. Speed decreases. The parts where chromium is exposed have almost the same structure as stain-free steel, and like stain-free steel, it has excellent thread rust resistance. Tinplate is usually inferior in paint adhesion to flat plates, while stain-free steel is superior, but in the present invention, the chrome surface has good adhesion over the entire surface, so it is superior to tinplate. Adhesion after processing is excellent for both tinplate and stain-free steel, but thin tin-plated steel is very poor.
In the present invention, even if the amount of tin is the same, it is very superior due to the non-uniform structure. The secondary adhesion of paint deteriorates due to corrosion of exposed iron parts in food and beverages, but since the present invention has a structure in which chromium pores are filled with tin, corrosion is less likely to occur and secondary adhesion is reduced. Adhesion is excellent. Normally, the level of paint adhesion varies considerably depending on the post-treatment method, but
The present invention is characterized by being less susceptible to post-processing methods due to the non-uniform structure of chromium and tin. The food and beverage corrosion resistance of the surface-treated steel sheet of the present invention is significantly different from that of tin and stain-free steel. When a painted plate containing a scratch that reaches the iron is immersed in a degassed test solution containing citric acid or common salt, tin around the scratch is leached out and corrosion under the coating occurs, whereas with stain-free steel, the scratch is removed from the scratch. Causes pitting corrosion. In the surface-treated steel sheet of the present invention, dissolution of tin occurs in the scratched area, but due to the coexistence of passivated chromium, the corrosion rate is extremely low, and the corrosion resistance is far superior to that of tin and stain-free steel. show. If the tin on the chrome is not melted, corrosion under the paint film will occur, similar to tinplate. As described above, by forming the tin layer on chromium into an island-like and discontinuous coating, an unprecedented surface-treated steel sheet can be obtained, and the effect of the non-uniform structure has a significant feature. [Example] A difficult steel plate of 0.20 mm thickness that was cold-rolled by a conventional method, continuously annealed, and tempered was subjected to electrolytic degreasing (NaOH 70 g/, temperature 85°C, current density 5 A/d).
m ² , time 5 seconds) and pickling (H ₂ SO ₄ 70 g/,
(temperature: 20°C, time: 5 seconds), and chromium plating was performed using the following bath and conditions. Chromium plating bath composition CrO ₃ 100g / NaF 5g / Chromium plating conditions Temperature 50℃ Current density 30A/dm ² hours 0.3 to 1.8 seconds After washing the obtained chromium-plated steel plate with water, it was coated on chromium using the following bath and conditions. The first tinning was carried out while removing the remaining chromium hydrated oxide. First tinning bath composition Sn ²⁺ 5g / Phenolsulfonic acid 30g / Ethoxylated α-naphthol 5g / First tinning condition temperature 40℃ Current density 20A/dm ² hours 0.1 to 0.4 seconds Obtained tin After washing the plated steel plate with water, a second tin plating was performed in the following bath and conditions. Second tinning bath composition Sn ²⁺ 40g / Phenolsulfonic acid 30g / Ethoxylated α-naphthol 5g / Second tinning condition temperature 40℃ Current density 10A/dm ² hours 0.7-1.0 seconds Obtained chromium and a tin-plated steel plate is heated by a resistance heating method to approximately 300°C, above the melting point of tin, to melt the tin and cause a repellent phenomenon,
The coating was made into an island-like, discontinuous coating and cooled with water. After drying, post-treatment was carried out to produce metallic chromium and hydrated chromium oxide in the bath and conditions described below. Post-treatment bath composition CrO ₃ 60g / H ₂ SO ₄ 0.3g / Post-treatment conditions Temperature 45℃ Current density 10A/dm ² hours 0.4 seconds The amount of coating on the surface-treated steel sheet obtained in this way, iron-tin after heating at 210℃ for 20 minutes Alloy content, wire seam weldability (contact resistance), thread rust resistance, secondary adhesion of paint, and under-coating corrosion tests after flat plate and Eclysene processing were conducted, and the test results are shown in Figure 2 and Table 1. Indicated. [Comparative example] Using the same bath and plating conditions as in the example, a surface-treated steel sheet with a coating amount other than the claimed range and a coating amount within the claimed range, manufactured without heat-melting treatment of tin. The surface-treated steel sheet was subjected to the same post-treatment as in the example. The obtained surface-treated steel sheets were subjected to the same tests as in the examples, and the test results are shown in FIG. 2 and Table 1. In addition, tin plate and metallic chromium with a tin plating amount of 2.48 g/m ² and a chromate amount of 5.9 mg/m ² in terms of chromium.
118mg/m ² , chromium hydrated oxide converted to chromium 17
The same test as in the example was conducted using mg/m ² of protein-free steel, and the test results are shown in Table 1. Test methods for various tests in Examples and Comparative Examples will be explained. (1) Wire seam weldability test Wire seam weldability is expressed by the difference between the lower limit of current required for the mechanical strength of the weld to exceed the strength of the base metal and the upper limit of current required to generate dust from the weld. The larger the diameter, the better the wire seam weldability. This difference and two surface-treated steel plates for welding cans were stacked and inserted between two disc electrodes, and 50
After applying a load of Kg, it was rotated at a circumferential speed of 5 m/min, a DC current of 5 A was applied, and the voltage between the electrodes was measured, and there was a good inverse correlation with the contact electrical resistance value. Therefore, as an index of weldability, 210℃
It was expressed as contact resistance after heating for 20 minutes. (2) Thread rust resistance test The obtained surface-treated steel sheet was coated with 75mg/ ^dm2 of vinyl organosol, baked at 200℃ for 10 minutes,
After inserting a scratch that reaches the iron, Erichsen processing is performed for 5 mm, and after soaking in 3% saline solution for 1 hour,
Wipe off the salt water and leave it in a constant temperature bath at 45℃ and 85% relative humidity for 10 days to remove the thread rust that has occurred from the scratches.

【table】

〔Effect of the invention〕

The surface-treated steel sheet manufactured by the manufacturing method of the present invention has an island-like and discontinuous coating of tin on chromium, so as shown in Figure 2, the iron-tin alloy growth rate is low, and more metallic tin is baked into the paint. Since it remains afterwards, the wire seam weldability is equivalent to tinplate.
Because the tin is in an island-like and discontinuous coating, the thread rust resistance is equivalent to tinplate and superior to stain-free steel. The secondary adhesion of the paint is comparable to that of tinplate with very little exposed iron, and is superior to stain-free steel. Its corrosion resistance is good due to its non-uniform structure, its under-coating corrosion resistance is better than that of tinplate, and its pitting resistance is better than that of stain-free steel. Although it is more expensive than stain-free steel because it uses expensive tin, it is much cheaper than tin. From the above, the surface-treated steel sheet for welded cans manufactured by the manufacturing method of the present invention is very suitable as a material for metal cans filled with food and beverages.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph of the surface structure of a surface-treated steel sheet obtained by the manufacturing method of the present invention. The tin layer is made up of islands of white particles, and the matrix is the chromium layer. Figure 2 shows the amount of tin plating from 0.64 to
The relationship between the amount of tin in the iron-tin alloy and the amount of chromium plating produced after heating at 210℃ for 20 minutes assuming paint baking is shown for treated steel sheets with varying amounts of chromium plating at 0.68 g/ ^m2 . It is something that When tin is heated and melted, the amount of iron-tin alloy produced becomes extremely small.

Claims (1)

[Claims] 1 Metallic chromium plating of 10 to 150 mg/m ² per side is applied to a steel plate, and tin plating of 0.1 to 1.0 g/m ² is applied while removing residual chromium hydrated oxide. alms,
The steel plate is heated to 240 to 350°C to melt the tin, form an island-like and discontinuous tin layer, and further produce chromium hydrated oxide with an amount of 2 to 20 mg/m ² in terms of chromium. A method for manufacturing surface-treated steel sheets for welded cans. 2 Apply metal chromium plating of 10 to 150 mg/m ² per side on a steel plate, and apply tin plating of 0.1 to 1.0 g/m ² while removing residual chromium hydrated oxide,
The steel plate is heated to 240 to 350°C to melt the tin, forming an island-like and discontinuous tin layer, and further hydrating chromium at 3 to 30 mg/m ² of metallic chromium, or 2 to 20 mg/m ² in terms of chromium. A method for manufacturing a surface-treated steel sheet for welded cans, characterized by generating oxides.