JPS6330998B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides food cans,
The present invention relates to a method for manufacturing a surface-treated steel sheet for seam-welded cans that can improve the rust resistance of light tin coatings used in beverage cans with a tin coating amount of 1.5 g/m ² or less. Conventionally, when manufacturing food and beverage cans, tinplate bodies have been joined using solder. However, because the harmful lead contained in the solder may be leached into the contents of the can, soldering has gradually become less common in recent years, and seam welding (sudronic welding) has replaced the method. The law is becoming popular. In the Sudronik welding method, the overlap width (overlap) of the can body joint is 0.3~
Since it is 0.4 mm, the quality of the joint is greatly influenced by the surface treatment method of the steel plate. Among commercially available tinplates, the lower the amount of tin deposited, the better the weldability tends to be.
One of the reasons for this is that with tinplate that has a large amount of tin deposited, the heat generated during resistance welding is also used to melt the tin, and molten tin flows along the weld line, staining the weld area. In addition, due to the rise in tin prices, can material consumers are looking for thin tin tin, especially when used with the inner surface of the can painted, which has the lowest amount of tin adhesion (2.8 g There is a demand for materials that have a coating weight that is less than half that of so-called #25 tin, which has a coating weight of 1/m ² ). However, with such tin tin with a low amount of tin adhesion, rust may develop during the period of several months or more from the time it is manufactured to the time it is shipped and canned by the customer, making it unusable as a material for cans. . As a result of intensive research into methods for improving the rust and corrosion resistance of thin tin plating, the present inventors found that, unlike the usual method of immediately applying hot tin treatment (reflow) after tin plating, We have discovered that it is effective to apply a chromate treatment that does not cause sanitary problems to a lightly tinned surface, then perform a molten tin treatment (reflow), and then perform a normal chromate treatment after the reflow, and have developed the present invention. I've reached it. That is, if the amount of tin deposited is small, there will be many pinholes (holes where the base steel is exposed) in the tin-plated layer, and the rust resistance of the tin plate will be poor. The thiocyanate porosity test method has long been known as an indicator of the size or number of pinholes on a tin-plated surface. The thiocyanate test is a method in which a tin-plated plate of a certain area is immersed in a corrosive liquid consisting of acetic acid, hydrogen peroxide, and ammonium thiocyanate, and after a predetermined period of time, dissolved iron ions are colorimetrically determined as red iron thiocyanate. be. Figure 1 shows the relationship between the amount of tin deposited and the thiocyanate value of tin plate produced by a conventional method. By extrapolating the curve as shown by the dotted line in the figure, the amount of tin deposited is approximately
It can be seen that in tinplates of 1.5 g/m ² or less, the exposed area of the base steel is significantly large. As a sealing treatment, tin-plated steel plates usually have a pressure of about 4.5 coulombs/min after reflow.
Electrolytic chromate treatment of dm ² is carried out, but a much larger amount of chromate is required for tin-plated steel sheets with a tin adhesion of 1.5 g/dm ² or less. However, since the chromate film applied after reflow is itself an electrically insulating material, if this film is thick, it is difficult for welding current to flow, and the welding speed must be reduced. For example, when welding a steel plate with a chromate film treated with an electrical charge exceeding 10 coulombs/dm ² using a Sudronik welding machine, the welding current per nugget decreases by more than 10% compared to a case without the chromate film. Next, by applying chromate treatment to the surface of the tinned pine, that is, the surface of electrodeposited tin that has not been subjected to molten tin treatment, it is possible to improve the rust resistance of light tinting without impairing weldability. Let me explain the reason. According to the usual method of applying hot tin treatment to tin-plated steel sheets with a tin coating amount of 1.5 g/ ^m2 or less, as shown in the electron micrograph in Figure 2, a rough iron-tin alloy develops and the base steel There are many exposed parts. On the other hand, as in the present invention, a thinly coated alloy layer and its cross-sectional structure obtained by applying chromate treatment before reflow to a tin-plated steel plate with a tin coating amount of 0.05 to 1.5 g/m ² are shown in FIGS. 3 and 4, respectively. As shown in the figure. Compared to the thin tinting produced by the conventional method shown in Fig. 2, the alloy layer of the tin tin produced by the method of the present invention shown in Fig. 3 is denser, and as shown in the cross-sectional structure of Fig. 4, chromate 1 ( The iron-tin alloy layer 3 is buried in the tin layer 2 (chromium hydrated oxide) and distributed in the form of islands, thereby preventing the iron-tin alloy layer 3 from becoming coarse and reducing the exposure of the base steel 4 to the surface. The reason why the tin-plated steel sheet according to the present invention exhibits high rust resistance is that the tin-plated layer 2 has the above-described structure. That is, the chromate 1 buried in the tin layer 2 suppresses the growth of the iron-tin alloy 3 in a direction perpendicular to the steel sheet surface or in a direction close to it, and as a result, the steel sheet base 4 is formed by fine alloy crystals. This is because it is coated. The above-mentioned effect of chromate applied before reflow is noticeable when the tin coating is light, especially when the amount of tin deposited is 2.8 g/m ² or less. By the way, the method of applying chromate treatment to tin-plated steel sheets before reflow has already been reported in Japanese Patent Publication No. 48-24619 as a method for improving the sulfidation resistance of electroplating.
(hereinafter referred to as the publication). As described in the examples, the tinplate covered by this publication has a thick tint of approximately #500 (tin adhesion amount: 5.6g/m ² ), and it is said that the tinplate contained in the protein or vegetables in the contents of the can is approximately #500 (tin coating amount 5.6g/m 2 ). This material is used to prevent blackening of can walls caused by sulfur. The chromate film applied to tin-plated steel sheets with a large amount of tin coating before reflow exists as a "skin layer" on the tin-plated surface that provides a high degree of sulfidation resistance, as speculated in publications. are doing. For this reason, the iron-tin alloy layer is significantly rougher than the alloy layer formed when chromate treatment is performed before reflow on a tin-plated steel sheet with a tin coating amount of 1.5 g/ ^m2 or less, and its density is lower than that of the alloy layer formed when chromate treatment is performed before reflow. It is about the same level as the case of tinplate that is not coated (see Figure 5). Figure 5 shows that when pre-reflow chromate treatment is applied to a tin-plated steel plate with a tin coating amount exceeding 1.5 g/ ^m2 , chromate 1 is distributed only in the surface layer of the tin-plated layer 2, and the chromate 1 is distributed only on the surface layer of the tin-plated layer 2. - This shows that it is not possible to prevent the tin alloy layer 3 from becoming coarser. As is clear from the above explanation, by performing chromate treatment before reflow of a tin-plated steel plate with a small amount of tin adhesion, which is the object of the present invention, the alloy layer formed by the subsequent reflow treatment can be made denser and thinner. The objective is to improve the rust and corrosion resistance of tinplate. Furthermore, as long as the treatment is carried out to reduce the amount of tin deposited in the present invention, the chromate applied before reflow is buried in the tin layer, as seen from FIG. 4, and does not interfere with the welding current. Even in the case of thin tinting, it is essential to make the iron-tin alloy layer dense in order to improve the rust resistance and corrosion resistance of the tin. In addition to the above-mentioned requirements, tinplate as a material for welded cans, which is the object of the present invention, must be treated so as not to impede the flow of welding current. The present inventors investigated various methods to satisfy these two conditions at the same time, and found that when the amount of electrolytic chromate treated before reflow of the tin-plated steel sheet is within an appropriate range, it is possible to The present inventors have discovered that chromate is distributed in island shapes to prevent coarsening of the iron-tin alloy layer, leading to the present invention. The steel plate used in manufacturing a welded can material according to the method of the present invention may be either an ingot material or a continuous casting material. 0.15~0.33mm according to normal method
The original sheet is a steel sheet that has been cold-rolled, annealed, and temper-rolled. Normal degreasing for producing tinplate,
This original plate is pickled and then tinned. Tin plating is carried out using an acid plating bath such as a halogen bath, ferrostane bath, or borofluoride bath, or an alkaline plating bath, and the tin plating is carried out using an acid plating bath such as a halogen bath, a ferrostane bath, or a borofluoride bath, and the amount of tin is 0.05 g/m ² or more, and 1.5 g/m ² or more.
Attach the following. The reason why the amount of tin deposited in the present invention is limited in this way is to embed chromate in the form of islands in the tin layer during reflow, thereby making the iron-tin alloy fine. In other words, (1) the amount of tin attached is
If the tin coating exceeds 1.5 g/ ^m2 , only a chromate skin layer will be formed on the surface of the tin layer, and the alloy layer will not become dense.(2) If the tin coating amount is less than 0.05 g/ ^m2 , This is based on two facts: even chromate treatment cannot prevent the occurrence of pinholes. The tinned steel sheet is subsequently subjected to a chromate treatment. In the present invention, when the chromate treatment is less than 0.3 coulombs/dm ² , the chromate in the tin layer has no effect on suppressing the coarsening of the iron-tin alloy layer for tin plate with a tin coating amount of 1.5 g/m ² or less. . Furthermore, when the amount of chromate treated exceeds 10 coulombs/dm ² , the chromate in the tin layer does not become island-like, resulting in increased resistance to seam welding current. Chromate treatment is usually used as a post-treatment for tinplate.
Although this is carried out using 30 g/dichromic acid aqueous solution (40 to 60°C), the chromate treatment carried out before reflow in the present invention may be exactly the same. The electrolytic time and current density of the chromate treatment are not particularly limited in the present invention, and it is preferable that the amount of electricity as the product of both is within the above range. After tin plating with a concentration of 0.05 to 1.5 g/m ² and chromate treatment of 0.3 to 10 coulombs/dm ^{2 ,} the steel plate is subsequently subjected to a molten tin treatment (reflow). In the alloy layer formed during reflow according to the method of the present invention, due to the presence of chromate (chromium hydroxide) after tin plating, at the steel plate/tin interface,
It has a higher density than normal thin tin coating that is not subjected to chromate treatment before reflow, and therefore has a higher amount of alloyed tin. In FIG. 6, the curve shown by a solid line is for #5 tin plate which is not subjected to chromate treatment before reflow, and the curve shown by a dotted line is for #5 tin plate which is subjected to chromate treatment (5 coulombs/dm ² ) before reflow.
The relationship between the maximum reflow temperature and the alloy tin layer for tinplate is shown. From this graph, it can be seen that even if the reflow treatment is performed under the same conditions, the tin alloy treated with chromate treatment before reflow has more tin alloy. However, from the viewpoint of weldability and rust resistance, the amount of alloyed tin is preferably about 2/3 of the total amount of tin deposited.
The tin-plated steel sheet that has been reflow-treated in this way is washed with water, dried, and subjected to the usual chemical treatment for the purpose of sealing. Cathodic treatment of 4.5 coulombs/dm ² is applied. Hereinafter, the present invention will be specifically explained with reference to examples. Example 1 A degreased and pickled cold-rolled steel sheet was tinned at 0.82 g/m ² , and after washing with water, it was subjected to chromate treatment at 5 coulombs/dm ² in a 30 g/dm aqueous solution of sodium dichromate (45°C). I went. After washing and drying this tin-plated steel plate
After heating to 260℃ for 3.4 seconds and immediately cooling with water, 30℃
g/in an aqueous solution of sodium dichromate (45°C)
Cathodic treatment was performed with an electrical charge of 4.5 coulombs/dm ² . Example 2 A degreased and pickled cold-rolled steel sheet was tinned at 0.56 g/ ^m2 , and after washing with water, it was tinned in a 30 g/aqueous sodium dichromate solution (45°C) with an electric charge of 0.5 coulomb/ ^dm2 . Chromate treatment was performed. After washing and drying this plated tin-plated steel plate, it was heated to 260°C for 3.4 seconds, immediately cooled with water, and then cathodically treated in a 30g/aqueous solution of sodium dichromate (45°C) with an electric charge of 4.5 coulombs/ ^dm2. . Example 3 A degreased and pickled cold-rolled steel plate was tinned at 1.24 g/ ^m2 , and after washing with water, it was tinned with 8 coulombs/ ^dm2 of electricity in a 30 g/aqueous sodium dichromate solution (45°C). Chromate treatment was performed. After washing and drying this plated tin-plated steel plate, it was heated to 260°C for 3.4 seconds, immediately cooled with water, and then cathodically treated in a 30g/aqueous solution of sodium dichromate (45°C) with an electric charge of 4.5 coulombs/ ^dm2. . Comparative Example 1 A degreased and pickled cold-rolled steel sheet was tinned at 0.87 g/m ² , and after washing with water, it was tinned at 0.2 coulombs/dm ² in a 30 g/dm aqueous solution of sodium dichromate (45°C). Chromate treatment was performed. After washing and drying this plated tin-plated steel plate, it was heated to 260°C for 3.4 seconds, immediately cooled with water, and then cathodically treated in a 30g/aqueous solution of sodium dichromate (45°C) with an electric charge of 4.5 coulombs/ ^dm2. . Comparative Example 2 A degreased and pickled cold-rolled steel sheet was tinned at 0.92 g/m ² , and after washing with water, it was tinned in a 30 g/dm aqueous solution of sodium dichromate (45°C) with an electric charge of 12 coulombs/dm ^{2 .} Chromate treatment was performed. After washing and drying this plated tin-plated steel plate, it was heated to 260°C for 3.4 seconds, immediately cooled with water, and then cathodically treated in a 30g/aqueous solution of sodium dichromate (45°C) with an electric charge of 4.5 coulombs/ ^dm2. . Comparative Example 3 A degreased and pickled cold-rolled steel sheet was tinned at 0.85 g/m ² and heated to 260°C for 3.4 seconds after washing with water.
Immediately after cooling with water, it was cathodically treated in a 30 g sodium dichromate aqueous solution (45° C.) with an electrical charge of 4.5 coulombs/dm ² . Comparative Example 4 A degreased and pickled cold-rolled steel sheet was tinned at 2.8 g/m ² and heated to 260°C for 3.4 seconds after washing with water.
Immediately after cooling with water, it was cathodically treated in a 30 g sodium dichromate aqueous solution (45° C.) with an electrical charge of 4.5 coulombs/dm ² . This is equivalent to commercially available #25 tin. Reference example A degreased and pickled cold-rolled steel sheet is tinned at 2.16 g/ ^m2 , and after washing with water, it is chromated with an electric charge of 5 coulombs/ ^dm2 in a 30 g/aqueous sodium dichromate solution (45°C). I processed it. After washing and drying this plated tin-plated steel plate, it was heated to 260°C for 3.4 seconds, immediately cooled with water, and then cathodically treated in a 30g/aqueous solution of sodium dichromate (45°C) with an electric charge of 4.5 coulombs/ ^dm2. . A specimen measuring 50 x 80 mm was cut from the steel plate treated as described above, and the edges were sealed with adhesive tape, leaving a surface area of 40 x 70 mm. Using the sample, a wet test was performed as described below. and a salt spray test. A thiocyanate porosity test was also conducted. Furthermore, a seam weldability test was conducted using a 165.5 x 80 mm specimen. (1) Humidity test A specimen was attached to a test tank at a temperature of 50°C and a relative humidity of 93%, and after a certain period of time, the area ratio (%) of red rust on the specimen surface was visually determined. (2) Salt spray test A test was conducted based on the JIS Z 2371 method, and the red rust area ratio (%) was visually determined. (3) Thiocyanate porosity test Published by Tin Research Institute (1964 2nd edition)
Compliant with P30. (4) Seam weldability test (a) Welding machine Sudronik can manufacturing machine, built-in guide tool for 202 diameter, overlap approximately 0.4 mm (b) Welding speed 8 m/min (c) Welding current 25 to 30 A (d ) Contact force 4da.N (e) Test items (e-1) Hein test Make a V-shaped cut from the end of the cylinder that sandwiches the weld, grasp the triangular part with pliers, and pull it toward the other end. Stretch. If the welded part does not break during the process, it is considered "good". (e-2) Spatter observation Visually inspect each nugget of the weld to see if there are spatters. (e-3) Optical microscope observation of weld cross section Embed the weld cross section in resin and observe at 100x magnification. If there are no hair lines on the joint surface, it is considered "good". As is clear from Table 1 below showing the various test results for the above samples, although Examples 1 to 3 of the present invention all have a light tin weight, Comparative Examples 1 to 3
Superior in wetness tests, salt spray tests, thiocyanate values and seam weldability compared to
It can be seen that it has the same performance as the tin plate with a thick tin weight as shown in Comparative Example 4, which corresponds to commercially available #25 tin plate. That is, Comparative Example 1, in which the chromate treatment conditions were insufficient in terms of the amount of electricity, had a high thiocyanate value, poor wet test values and salt spray test values, and was inferior in rust resistance and corrosion resistance. Comparative Example 2 has an excessive amount of electricity and a significantly large amount of chromium, so the thiocyanate value is low and the rust resistance and corrosion resistance are good, but the seam weldability is poor. In Comparative Example 3, the chromate treatment was performed immediately after the tin dilution, so the thiocyanate value was high and the rust resistance and corrosion resistance deteriorated. In addition, since the reference example has a thick coating with a tin coating amount of 2.16 g/m ² , it is natural that it has good rust resistance, corrosion resistance, and seam weldability, but the purpose of the present invention is to The purpose is not achieved. In addition, the thiocyanate value of this reference example is inferior to that of the examples of the present invention, which shows that the method of the present invention is an effective method for tin thinning. As described above in detail, according to the method of manufacturing a surface-treated steel sheet for seam-welded cans of the present invention, even if the tin-plated steel sheet has a light weight (0.05 to 1.5 g/m ² ),
By performing chromate treatment at 0.3 to 10 coulombs/ ^dm2 before reflow, it has excellent rust resistance and seam weldability.
m ² ) can be obtained. 【table】

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the amount of tin deposited and the thiocyanate value of tin-plated steel sheets, Figures 2 and 3 are electron micrographs of the surface structure of the metal, and Figure 2 is a graph showing the relationship between the tin coating amount and the thiocyanate value. (Tin adhesion amount 0.85g/
Fig. ³ is a 10,000 times electron micrograph of an alloy layer with a chromate treatment (5 coulombs/dm ² ) before reflow (tin adhesion amount 0.82) ^. 10,000 times electron micrograph of an alloy layer with an alloy tin content of 0.36 g/m ^{2 )} , Figure 4 shows the amount of tin deposited.
Before reflow of 0.05~1.5g/ ^m2 tinned steel plate
Figure 5 is a cross-sectional view showing the surface structure of tin plate with a chromate treatment of 0.3 to 10 coulombs/ ^dm2 . Figure 6 is a cross-sectional view showing the surface structure of tin plate with a tin coating of 1.5 g/ ^m2 or more. is a graph showing the change in the amount of tin alloy for #5 tin with a tin adhesion amount of 0.50 to 0.65 g/m ² with and without chromate treatment before reflow. Explanation of symbols, 1...Chromate, 2...Tin layer,
3... Alloy layer, 4... Base steel.

Claims (1)

[Claims] 1 0.05 to 1.5 g per degreased and pickled cold-rolled steel plate
A seam characterized by being tin-plated with a light weight of m ² , further subjected to chromate treatment at 0.3 to 10 coulombs/dm ² in an aqueous solution of sodium dichromate, followed by hot tin treatment, and further chromate treatment. A method for manufacturing surface-treated steel sheets for welded cans.