JPS6327437B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a low-cost, surface-treated steel sheet for can manufacturing that is excellent in coating corrosion resistance, can body jointability, and particularly seam weldability as a raw material for can manufacturing. As surface-treated steel sheets for can manufacturing, electrolytic tin plated (hereinafter referred to as tinplate) and electrolytic chromic acid treated steel sheets (hereinafter referred to as TFS-CT) are generally known. Among these, tinplate is the most common and most widely used surface-treated steel sheet for can manufacturing. It is used as food cans for fish meat, soups, fruits, etc., as well as so-called beverage cans such as carbonated drink cans such as cola, fruit juice cans, etc., by taking advantage of the corrosion resistance of tin after tin is bare or painted. 18
It is also widely used for cans, pails, etc. As for can manufacturing methods, tin is used not only for so-called 3-piece cans, which employ soldering and seam welding methods other than adhesive methods, but also for manufacturing 2-piece cans, which are particularly common in beverage cans, etc. It is used because of its solid lubricity. On the other hand, TFS-CT is mainly used for beverage cans, which are relatively less corrosive, and is also used for 18 other cans, pail cans, etc., but the manufacturing method is only for 3-piece cans, and for 2-piece cans. Not used in manufacturing. This is TFS-CT
A non-metallic chromium layer mainly composed of metallic chromium and chromium hydrated oxide (hereinafter referred to as chromium oxide layer)
This is because it is hard and brittle, making it difficult to process two-piece cans, and the corrosion resistance after forming two-piece cans is greatly reduced. Even for three-piece cans, the so-called adhesive method is the main method for joining the can body, and seam welding requires polishing off the chromium layer on the surface, which is not common. In this way, conventional tinplate and TFS-CT have been used to take advantage of each other's strengths, but as the price of tin has increased in recent years, the cost of tinplate has increased significantly, and the use of TFS-CT in tinplate is progressing. The problem with converting tinplate into TFS is that depending on the contents, it may lack corrosion resistance during long-term storage, and unlike tinplate, it does not have good seam weldability, so if seam welding is used, as mentioned above, The chromium layer on the surface must be removed by polishing, and the production of two-piece cans is virtually impossible due to molding and manufacturing costs. Therefore, tin or steel plate,
In other words, in the field of TFS, there is a demand for the development of a low-cost surface-treated steel sheet that has almost the same paint corrosion resistance, seam weldability, and two-piece can formability as conventional tinplate, and the present inventors have responded to this request. We are continuing our research to create new products that fully meet these quality requirements.
This was the successful development of TFS. That is, after painting, the can is formed into a coating structure in which a Ni--Zn binary alloy coating layer is provided on both surfaces of a surface-cleaned steel sheet, and a chromium treatment layer is further provided on both surfaces of this alloy coating layer. In particular, the objective was to provide a surface-treated steel sheet for can manufacturing with excellent paint corrosion resistance and seam weldability.
The reason lies in the Zn content in the original alloy coating layer, and the limited ranges of the Zn content on the inner and outer surfaces after can manufacturing are different. Specifically, the Zn content of the alloy coating layer on the inner surface of the can after can manufacturing is 20% or less, while the Zn content on the outer surface of the can is 80% or less. The Zn content in this alloy coating layer can be freely selected within this limited range, and of course it is also possible to change the alloy composition on the front and back sides of the steel sheet. Next, the coating structure of the surface-treated steel sheet for can manufacturing of the present invention is schematically shown in FIG. 1 is a cold-rolled steel plate that is the raw material, 2 is a Ni-Zn alloy coating layer, and the coating method is direct electroplating.
Ni-Zn binary alloy plating may be performed, or Ni
It is also possible to coat two layers of Ni and Zn and then heat-treat to diffuse Ni and Zn in a solid phase to form a binary Ni-Zn alloy layer, but the former method is more common and economical. . There is a chromium treatment layer 3 on top of this Ni--Zn binary alloy coating layer, and the treatment is carried out by a commonly used electrolytic chromic acid treatment method, but the method is not particularly limited to this. The structure of the chromium treatment layer may be mainly composed of chromium hydrated oxide obtained by the tin plate chromate treatment method, and TFS-
A plating bath similar to CT, consisting of a metallic chromium layer and a non-metallic chromium layer, can be used, and can be selected appropriately depending on the application. 4 is an oil film layer that is normally formed on tinplate, TFS-CT, etc., and has the effect of preventing rust and scratches during use in can manufacturing. Here, the method for forming the Ni--Zn binary alloy coating layer, which is a feature of the present invention, will be briefly described. As mentioned above, the Zn-Ni binary alloy coating layer has different limited ranges for the inner and outer surfaces of the can, and the inner surface of the can has a
% or less, and the outer surface of the can is 80% or less. now,
A case will be described in which a Ni--Zn alloy coating layer is formed by electroplating. If the alloy composition on the surface of the steel sheet is the same, it can be obtained by plating once or several times in the same plating bath, but by changing the alloy composition on the surface of the steel sheet, for example, the Zn on the side that will become the inner surface of the can after can manufacturing can be changed.
If the Zn content is 20% or less and the Zn content on the side that becomes the outer surface of the can is different from 20 to 80%, first plate only one side with an alloy plating bath adjusted to have Zn of 20% or less. , the opposite side may be plated with an alloy plating bath adjusted to contain 20 to 80% Zn. Next, the reasons for limitations in the present invention will be explained. First, both sides of the steel plate were surface-cleaned using the usual method.
The reason why we adopted the Ni-Zn binary alloy coating is that in a single-phase Ni coating, Ni is electrochemically very noble.
Although the Ni coating itself is very stable, there are always defects in the Ni coating, and the Fe substrate is exposed in these defects. Therefore, in the corrosive environment inside the can, a galvanic action occurs between the Ni layer and the Fe substrate, and since Ni is much more noble than Fe, the galvanic current flowing due to this galvanic action dissolves the Fe substrate. flows in that direction. Moreover, since the area of exposed Fe in the Ni layer defect is very small overall, the current density becomes extremely large, and the Fe in the Ni layer defect is preferentially eluted, causing so-called Piting Corrosion.
In some cases, this may result in perforated cans, which may significantly shorten the life of the can. Therefore, the electrical potential is very noble.
If Ni is alloyed with potentially base Zn, Ni-
The potential of the Zn binary alloy layer changes in the less noble direction, and the
The galvanic effect between
Fe elution from the Ni-Zn binary alloy coating defects will decrease, and if the Zn content in the alloy layer increases,
Finally, the potential of the Ni--Zn binary alloy coating layer becomes more base than Fe, and Fe elution can be prevented by the sacrificial dissolution action of the Ni--Zn binary alloy coating. Here, after can manufacturing, the alloy coating layer on the side that becomes the inner surface of the can is
The reason why the Zn content is 20% or less is because the Zn content is 20% or less.
% or more, the dissolution of the Ni-Zn alloy coating layer under the paint film increases, and the corrosion under the paint film during can storage deteriorates. This is because there is a risk that sub-film corrosion will progress and eventually lead to peeling of the paint film, so it is limited to 20% or less. In addition, Zn in the Ni-Zn alloy coating layer
The lower limit of the content is not particularly limited, but is preferably 3% or more. If it is less than 3%, the potential is virtually the same as a single Ni layer coating, and Zn is alloyed in Ni, resulting in a galvanic effect between the Ni-Zn binary alloy coating layer and the Fe substrate in the defective areas of the coating layer and coating film. If the purpose of reducing the size of Zn is not achieved, and if the contents contain sulfides that are used for other purposes such as alloying Zn in Ni, such as fish meat or meat, the contents may be removed during retort processing for killing spores. The sulfide of Ni decomposes and reacts with the Fe base material, producing sulfide such as FeS on the inside of the can, causing the inside of the can to turn black.
- It becomes impossible to improve the so-called sulfur resistance, which is prevented by reacting with Zn in the Zn binary alloy coating layer. On the other hand, Zn in the alloy coating on the side that becomes the outer surface of the can after can manufacturing.
The reason for setting the content below 80% is that the corrosive environment on the inside of the can, that is, the side that comes into contact with the contents of the can, and the corrosive environment on the outside of the can, that is, the corrosive environment that users are exposed to while storing the can, are different from the corrosive environment on the outside of the can. Rust resistance during storage, especially if the coating film or Ni-Zn alloy coating layer is scratched, such as in the scored areas on the outer surface of the easy open end, the Zn content is high, and in some cases Ni - This is because the potential of the Zn alloy coating layer is lower than that of the base Fe, that is, the more base it is electrochemically, the better the rust resistance may be. This is because it is sufficient if the alloy composition is set as follows. A Zn content of about 70% Zn is optimal for the outer surface of the easy open end. Note that the lower limit of the Zn content in the Ni--Zn alloy coating layer is not particularly limited, but is preferably 3% or more.
This is for the same reason as in the case of the inner surface of the can described above, and when the content is less than 3%, the rust resistance is practically equivalent to that of single-layer Ni plating. The reason why we set the upper limit to 80% is that if the Zn content exceeds this level, the potential will drop too much, approaching pure Zn and becoming very active.
- This is because the Zn binary alloy layer wears out quickly, making it impossible to maintain rust resistance for a long period of time, and the white rust characteristic of Zn begins to appear, which is unfavorable for the appearance of the product. Furthermore, the coating amount of the Ni-Zn binary alloy coating layer on both the inner and outer surfaces of the can is not particularly limited, but is usually 0.05 g/m ²
~11g/ ^m2 Adhesion is sufficient, 0.05g/m2
^This is because corrosion resistance will be poor if less than 11 g/m ² is deposited, and no further improvement in corrosion resistance can be expected and it becomes uneconomical even if the amount is deposited in an amount of 11 g/m 2 or more. The reason for limiting the Zn content of the Ni--Zn binary alloy coating layer, which is a feature of the present invention, has been explained above, and now a supplementary explanation will be provided based on experimental data obtained by the present inventors. Figure 2 evaluates the corrosion resistance of can inner coating on the vertical axis.
The horizontal axis shows the evaluation values of the UCC test (undercut corrosion test) and the QC test (test that evaluates the rust resistance during can storage by repeating the Wet-Dry cycle). indicates the Zn content in the Ni-Zn binary alloy coating.
As is clear from the figure, in the UCC test, when the Zn content is 20% or more, it deteriorates rapidly, and when it is 3% or less, it is inferior. Also, in QC test, Zn content is 80%.
After peaking at
In the following, a decrease in rust resistance is seen, but the range of the evaluation mark ○, which does not pose a practical problem, is wider than the former UCC test result. Therefore, when using the coating on the inner surface of a can where corrosion resistance is important, by setting the appropriate Zn content narrowly and widening it on the outer surface of the can, it is possible to use the right material in the right place depending on the application. I found it. In addition, UCC test and QC
The test method is the same as the description of the embodiment described later. Next, another advantage of Ni-Zn binary alloy coating is that in addition to the above-mentioned paint corrosion resistance, seam welding is
This is superior to TFS-CT. The reason for the good seam weldability is that a single layer of Ni coating has a relatively high melting point (1450°C), so seam weldability cannot necessarily be said to be good, but by using a Ni-Zn binary alloy coating, the coating layer can be This is because the melting point decreases. In addition, the Ni--Zn binary alloy coating has other great effects, such as the ability to reduce manufacturing costs by alloying Ni with Zn, which is inexpensive. Next, a chromium treatment layer is further provided on both sides of the upper layer of the above-mentioned Ni--Zn alloy coating layer, and the amount of this coating is usually 1 to 50 mg/m ² in total Cr per side.
If the chromium treatment layer is less than 1mg/ ^m2 per side, the adhesion of the coating on the inner surface of the can will deteriorate, and if it is more than 50mg/ ^m2 , metal or non-metallic chromium will be removed when seam welding is used to join the can body. Seam weldability deteriorates due to the high melting point of the layer and poor electrical conductivity of the nonmetallic chromium layer. Next, specific examples of the present invention will be described. Example 1 After coating a Ni-Zn binary alloy layer (Zn content 15%) by electroplating under the conditions shown in (1), the steel plate was surface-cleaned by a conventional method and then coated with (2) and (3). A chromium-treated layer was formed by electrolytic chromic acid treatment under the conditions shown below. Further, a coating film for can manufacturing was formed under the conditions shown in (3) and then subjected to various evaluation tests. However, no coating was applied during seam weldability evaluation. (1) NiSO ₄・7H ₂ O 300g / Total basis weight 0.6g/m ² (per side) ZnSO ₄・6H ₂ O 15g / Zn content 15% H ₃ BO ₃ 35g / Bath temperature 50℃ Current density 20A / dm ² (2) Na ₂ Cr ₂ O ₇ 30g/ Total Cr amount 12mg/m ² Bath temperature 60℃ Current density 20A/dm ² (3) CrO ₃ 50g/ H ₂ SO _{4 0.4g/(SO 2-4} ^conversion ) Total Cr amount 20mg/m ² Bath temperature 50℃ Current density 40A/dm ² (4) Epoxy-phenol paint for can making 45mg/dm ² (dry weight per side) Baking at 205℃ for 10 minutes and additional baking at 180℃ for 10 minutes Example 2 After making a steel plate whose surface was cleaned by the usual method, a Ni-Zn binary alloy layer (Zn content 10%) was coated on the steel plate surface side, which will become the inner surface of the can, by electroplating under the conditions shown in (1). After can manufacturing, a Ni-Zn binary alloy layer (70% Zn content) is electroplated on the steel plate surface, which will become the outer surface of the can, under the conditions shown in (2), that is, the Zn content is different on the front and back sides of the steel plate. A Ni-Zn binary alloy coating layer was formed. Next, a chromium-treated layer was formed by electrolytic chromic acid treatment under the conditions shown in (3) and (4). After forming a coating film for can manufacturing under the conditions shown in (5), it was subjected to various evaluation tests. However, no coating was applied during seam weldability evaluation. (1) NiSO ₄・7H ₂ O 300g/ Total basis weight 0.6g/m ² ZnSO ₄・6H ₂ O 10g/ Zn content 10% H ₃ BO ₃ 30g/ Bath temperature 50℃ Current density 20A/dm ² (2 ) NiSO ₄・7H ₂ O 300g/ Total basis weight 1.0g/m ² ZnSO ₄・6H ₂ O 50g/ Zn content 70% H ₃ BO ₃ 30g/ (3) Same as (2) of Example 1 (4 ) 〃 (3) 〃 (5) 〃 (4) 〃 Next, the contents of various tests conducted with the material of the present invention will be described. (A) UCC (Undercut Film Corrosion) Test This test is one of the methods to evaluate the corrosion resistance of the paint on the inside of a can. After scratching the painted surface of the samples of Examples 1 and 2 with a knife, (mixed solution of 15 g of citric acid/15 g of salt) and kept at 50°C for 3 days while bubbling with CO ₂ gas, then the scratched area was peeled off with tape and the corrosion state around the scratch was determined. . (B) Corrosive liquid immersion test This test, like the (A) UCC test, is also one of the methods for evaluating the corrosion resistance of the paint on the inside of a can. After that, the end surface (the cut end of the sample) was completely sealed and immersed in 100% orange juice UCC solution, which is a degassed corrosive solution in a plastic container, and kept at 50℃ for 2 weeks. The amount of Fe eluted into the corrosive solution was analyzed. (C) Q/C test This test is a method for evaluating the corrosion resistance of the paint on the outside surface of the can. After scratching the paint surface of the samples of Examples 1 and 2 with a knife, an overhang of 4 mm was made using an Erx tester. It was processed and tested using a Q/C tester. A Q/C tester is a test sample that is placed in an environment that repeats wet and dry conditions, and the test conditions were wet (water temperature 20℃, air temperature
One cycle consisted of 30 minutes at 25°C and 60 minutes at dry (air at 50°C), and after repeating this cycle 960 times, the state of rust on the scratched part of the paint film was determined. (D) Seam weldability Using a seam welding machine, samples (unpainted) of Example 1 and Example 2 and Example 2 and Example 2 were separated by 0.4 mm, as in the case of actually making cans.
The seam welding was performed under the conditions of a pressing force of 50 kg/m ² and a welding current of 4.5 KA on the secondary side.The strength of the seam weld was evaluated by an impact test, and the appearance of the seam weld was evaluated visually. . The test results for each evaluation item (A) to (D) of Examples 1 and 2 are shown in Table 1. In addition, as a comparison with the present invention example, the amount of tin deposited per one side
Tinplate (hereinafter referred to as #25ET) with a chromate coating of 2.7g/m ² and a chromate coating of 15mg/m ² (metallic chromium equivalent), and a metal chromium content of 100mg/m ² and chromium oxide amount of 12mg/m ² (metallic chromium equivalent) per side. TFS-CT was used.

【table】

[Table] Good ←→ Bad Note) A) Each test was evaluated on a 4-level scale. ◎
○ △ ×
b) Both the Ni-Zn alloy coating amount and the chromium treatment layer show the coating amount on one side.
C) The upper left column of B○ corrosive liquid immersion test is A○.
The sample was immersed in UCC solution, and the lower right column was immersed in 100% orange juice.
In Example 2 of Table 1, the Ni-Zn binary alloy coating layer
The surface with 70% Zn content is used for the outer surface of the can, so
UCC Test Although no corrosive liquid immersion test was conducted, this item was tested in Comparative Example 2. First, Comparative Example 1 shows Zn in the Ni-Zn binary alloy coating layer.
This is an example of a Ni single layer coating with a content of 0%, and it is inferior in both the UCC test and corrosive liquid immersion test for can inner surface performance, and the Q/C test for can outer surface performance. Comparative Example 2 is a case in which the Zn content in the Ni-Zn binary alloy coating layer is at the upper limit value on the steel plate surface that becomes the inner surface of the can during can manufacturing, that is, 20% or more, and the Q. The C test is excellent, but the UCC test as a can internal performance,
The corrosive liquid immersion test was extremely poor and it cannot be used as the inside of a can. Next, in Comparative Example 3, the coating amount of the Ni--Zn binary alloy coating layer was below the appropriate range of the present invention, and the can inner and outer surface performances were significantly inferior. In Comparative Example 4, the coating amount of the chromium treatment layer was more than the appropriate range, and the seam weldability was significantly deteriorated. As described above, in the present invention, the Zn content of the Ni-Zn binary alloy coating layer can be freely selected to satisfy the can inner and outer surface performance, and the coating amount of the chromium treatment layer can be controlled to an appropriate value. This is a new low-cost, high-performance surface-treated steel sheet for can making that can maintain seam weldability equivalent to that of conventional tinplate. Therefore, if the new surface-treated steel sheet according to the present invention is used, it can be widely used in cans of carbonated drinks such as beer, which are the main uses of conventional TFS-CT, as well as fruit juice cans, which were used in the tinplate field. This is groundbreaking.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the coating structure of the surface-treated steel sheet for can manufacturing according to the present invention, and Figure 2 is a graph showing the relationship between the Zn content in the Zn-Ni binary alloy coating and the corrosion resistance evaluation of the inner and outer surfaces of the can. be. 1...Cold rolled steel plate, 2...Ni-Zn binary alloy coating layer, 3
...Chrome treatment layer, 4...oil film layer.

Claims (1)

[Claims] 1 A Ni-Zn binary alloy coating layer is provided on both surfaces of the surface-cleaned steel sheet, and a chromium treatment layer is further provided on both surfaces of the upper layer of the alloy coating layer.
The Zn content is 20% on the steel plate surface that becomes the inner surface of the can after can manufacturing.
A surface-treated steel sheet for can manufacturing which is subjected to can manufacturing processing after painting, with the surface that will become the outer surface of the can being 80% or less.